As expected, NASA today set a new, more realistic target date for launch of the next shuttle mission - between Sept. 12 and Oct. 10, 2004 - and announced a new flight that will be inserted into the launch manifest to complete tasks originally planned for the first mission.

Given post-accident requirements that sharply restrict when a shuttle can actually take off, however - launch and external tank separation in daylight and thermal constraints at the international space station - the shuttle's return to flight easily could slip into 2005 when all is said and done.

Those requirements currently translate into 26 days of launch opportunities between Sept. 16 and Oct. 11, 2004; Nov. 19-21, 2004; and Jan. 17 through 19, 2005. The next available launch window opens in March 2005.

Current estimates show photo documentation of external tank separation in daylight will not be possible until Sept. 16. But NASA managers say those estimates might change and so they added a bit of cushion to the front end of the target launch window.

Bill Readdy, NASA's associate administrator for space flight, stressed the new launch window, like the original March/April target window, remains a target only and that it may change again as planners get a better idea of how much work remains to be done.

Mission STS-114, currently assigned to the shuttle Atlantis, will include a robot arm extension and sensors to look for damage to the ship's heat-shield tiles and leading edge panels; a spacewalk to test tile and leading edge repair techniques; another spacewalk to install a new gyroscope on the space station; and supply and equipment transfers to and from the lab complex.

"We're going to be very much driven by the milestones and by the content we have to accomplish here in terms of the testing of the robotic arm, survey techniques, tile repair, modifications to the external tank, all the testing that's required," Readdy said in an evening teleconference with reporters. "So It comes down to being able to satisfactorily accomplish all of those.

"I can't tell you whether or not we're going to have more content creep in over time, whether we're going to come up on some technical hurdles. I can almost guarantee that this is going to be a long, uphill climb back to return to flight. But I also would tell you that we're getting an awful lot smarter about this and we're going to come back stronger and safer as a result."

To accommodate the tile/leading edge inspections and the repair demonstration spacewalk, NASA decided to split the original STS-114 mission into two separate flights. The new mission, known as STS-121, currently is assigned to the shuttle Discovery. It is targeted for launch Nov. 15. Again, that's a few days in advance of when a daylight tank separation because available.

Making the September launch date for the first post-Columbia mission will not be easy. Long poles include development of the robot arm extension boom and the sensors needed for in-orbit tile and leading edge inspections and development of viable techniques for repairing leading edge damage. A wild card is the impact of work to remove Atlantis' carbon composite nose cap for an extensive corrosion inspection.

But shuttle program manager Bill Parsons said it's too soon to predict how all of that might play out. As for the shuttle's sharply restricted launch windows, "I think we have some opportunities, some small opportunities in November and possibly January and some other places."

"But you know, again, we're still refining those requirements, we're still refining exactly what we need to do to meet the lit launch requirement," he said. "But I think there are some opportunities in November (2004) for us to go launch."

In perhaps the most convincing demonstration yet that NASA truly "gets it," the new chairman of the agency's mission management team today outlined major changes to improve communications among engineers and managers, to ensure dissenting views are heard and to correct the cultural shortcomings blamed in part for the Columbia disaster.

"Any arrogance I may have had went out the window on Feb. 1," said Wayne Hale, a widely respected ascent-entry flight director who brings clear credibility to the mission management team. "In my personal life, before February I thought we had it pretty much knocked. ... I would have told you we understood what we were doing and we had mature processes and good hardware. And I think all of those assumptions have been shattered."

As chairman of the revamped mission management team, Hale will oversee the conduct of all phases of flight, from the pre-launch review needed to clear a shuttle for launch to the in-flight management of its mission.

At a news conference, Hale unveiled an ambitious plan to resolve shortcomings found by the Columbia Accident Investigation Board as well as issues identified by NASA personnel in the wake of the accident. New members will be added to the MMT, outside experts will be brought in to coach the managers on decision making skills and regular mission simulations will be held to test those skills in make-believe emergencies.

Hale is even looking into what shape table to use in the MMT conference room.

"Now you laugh," he said to chuckling reporters, "but when you talk about culture and how people subconsciously deal with hierarchy and where they fit within an organization and whether they feel comfortable in bringing things up, things like the shape of the table matter.

"Being trained as an engineer, I'm wishing I'd taken more sociology classes in college. I'm learning a lot, I think we're all learning a lot in this arena and we're committed to opening lines of communication and making sure people get their dissenting opinions and minority opinions on the table so we can consider them."

Some agency veterans have criticized the new MMT plan, saying the additional voices and opinions will make it more difficult to make a final decision. But Hale disagrees.

"I am convinced that we not only should, but must, come to an understanding of why it's OK to proceed in the face of a minority opinion," he said. "My basic model is consensus. We will bring the person from the organization that's got the concern and we should be able to demonstrate in a technical, analytical, engineering sense why it's safe to proceed or we shouldn't proceed. I don't know any other way to do that.

"I will tell you I get resistance from some of the NASA alumni league who operated at a different time and a different culture who think this is not the right thing to do, who think we'll never fly again if we go down this road too far. So there is that element of folks out there. But I think we need to go down the road as far as we can to make sure that we fly safely. Because just going to fly, there's been a lot of noise in the system about launch schedules and launch dates and we've gotta go do this to make the launch schedule, you know. We have to make sure when we get ready to fly we have done everything we can to make sure it's safe."

The Columbia Accident Investigation Board was sharply critical of MMT operations during Columbia's ill-fated mission. Contrary to NASA's own rules, the MMT, under chairman Linda Ham, did not meet every day and did not seriously debate the results of a hurried analysis that mistakenly concluded Columbia was not seriously damaged by a foam debris strike during launch. Despite an almost complete lack of hard data about the possible threat posed by the strike, the MMT quashed efforts by lower-level engineers to obtain spy satellite imagery that might have revealed the extent of the damage.

Hale today vowed to learn from the mistakes of the past. And he left little doubt he believes the management culture at NASA needs to change.

"I have to say, STS-107, the Columbia flight, has been a significant emotional event in my life and I think in the life of everyone in the agency, certainly in the shuttle part of the agency," he said. "We had many of our assumptions and concerns shattered on Feb. 1.

"Those of us who lived through the events of this past spring have had our lives change in ways that are going to affect our decisions and our thought processes for years to come. We have come over the course of several months of introspection and analysis to a new understanding. In particular, the first thing we have to get out on the table is we were not good enough. We did not do what is necessary to keep the Columbia crew safe. And that is something we have to live with as a legacy that will compel us to do the right thing for future shuttle flights and for future human exploration of space."

While final details remain to be resolved, Hale said the new MMT will include:

• Seats for the directors of engineering at the Johnson Space Center in Houston and the Marshall Space Flight Center in Huntsville, Ala.;
• A seat for the director of propulsion technology at Marshall;
• Seats for the head of safety and mission assurance at NASA headquarters and for the newly formed NASA engineering safety center at the Langley Research Center in Hampton, Va.;
• A single manager (Hale) for pre-launch and in-flight operations;
• A re-emphasized rigor with permanent pre-defined agenda items covering all phases of damage assessment to make sure any possible sign of trouble is known to senior management and discussed as widely as possible;
• A dedicated group of engineers to identify possible anomalies across all disciplines;
• Participation by senior managers, not designated alternates;
• Daily meetings

An internal review of the new MMT plan will be complete by Oct. 2. By the middle of the month, all MMT members will attend a class defining the precise roles and responsibilities of panel members. By the first week in November, the MMT will participate in a so-called "warm-up" simulation, the first in a series of regularly scheduled simulations to test MMT decision-making skills.

By the first week in December, Hale hopes to stage a three-day simulation involving the shuttle and the international space station program. Another major simulation including NASA's international space station partners is planned for January with monthly management sims scheduled after that through return to flight.

Long term, outside safety and management experts will be brought in on a regular basis as part of a continuing education program. Bringing in outsiders has never been NASA's strong suit and many at JSC resented the appearance of sociologist Diane Vaughn, an expert on the decision to launch the shuttle Challenger, at a Columbia Accident Investigation Board Hearing. She now is among the experts being sought by NASA.

"I didn't know who Dr. Vaughn was when she appeared at the CAIB hearing," Hale said. "I came away a little unimpressed with it but I said I ought to go get her book and look at what she's got to say. I sat down and read ("The Challenger Launch Decision") and when I got done with it, I said wow, there is a lot of good stuff here that I never thought about. And there is valuable place for us to learn some things.

"And since then, I think I've added a number of books to my bookshelf that are decision-making related that I'm thinking about a lot more these days. And we're going to have a number of these folks come and talk to us."

NASA must develop the capability to repair damaged heat shield tiles in orbit, as well as cracks or breaches in the reinforced carbon carbon panels making up the shuttle's wing leading edges, before space shuttles return to flight, the Columbia Accident Investigation Board says.

In the board's final report, released earlier today, the CAIB made 29 recommendations, 15 of which are to be implemented before the next shuttle flight. Because of the way the report marked those recommendations, using boldface red type "RTF" tags, one five-paragraph recommendation was misinterpreted by some readers who initially thought RCC repair capability was not a requirement for return to flight.

At a news conference and later in an interview with CBS News, board chairman Harold Gehman left no doubt: NASA must be able to repair damage to both tiles and RCC panels before the next shuttle takes off.

"Recommendation 6.4.1 contains four provisions, all of which are return to flight," he said.

That is a significant requirement. While NASA is expected to have a working tile repair technique in hand within a few months, developing a reliable RCC fix is a much greater challenge because of the nature of the material and the extreme 3,000-degree temperatures it is exposed to during re-entry. Some observers believe that requirement alone will push the next shuttle flight into the summer 2004 timeframe if not later.

"We think that's probably the long pole in the tent," Gehman said in an interview. An innovative technique used by Thiokol to repair carbon composite rocket nozzles shows promise and other techniques are under study as well. But repairing breaches in RCC panels is, at present, a long way from reality.

In any case, here is the recommendation in question:

"For missions to the international space station, develop a practicable capability to inspect and effect emergency repairs to the widest possible range of damage to the Thermal Protection System, including both tile and Reinforced Carbon-Carbon, taking advantage of the additional capabilities available when near to or docked at the International Space Station.

"For non-Station missions, develop a comprehensive autonomous (independent of Station) inspection and repair capability to cover the widest possible range of damage scenarios.

"Accomplish an on-orbit Thermal Protection System inspection, using appropriate assets and capabilities, early in all missions.

"The ultimate objective should be a fully autonomous capability for all missions to address the possibility that an International Space Station mission fails to achieve the correct orbit, fails to dock successfully, or is damaged during or after undocking. [RTF]"

Editor's Note: The Columbia Accident Investigation Board, on page 77 of its final report, provided new insights into how the shuttle broke apart and the fate of the orbiter's crew. For the record, here are those observations.

At the Board's request, NASA formed a Crew Survivability Working Group within two weeks of the accident to better understand the cause of crew death and the breakup of the crew module. This group made the following observations.

Medical and Life Sciences
The Working Group found no irregularities in its extensive review of all applicable medical records and crew health data. The Armed Forces Institute of Pathology and the Federal Bureau of Investigation conducted forensic analyses on the remains of the crew of Columbia after they were recovered. It was determined that the acceleration levels the crew module experienced prior to its catastrophic failure were not lethal. The death of the crew members was due to blunt trauma and hypoxia. The exact time of death sometime after 9:00:19 a.m. Eastern Standard Time cannot be determined because of the lack of direct physical or recorded evidence.

Failure of the Crew Module
The forensic evaluation of all recovered crew module/forward fuselage components did not show any evidence of over-pressurization or explosion. This conclusion is supported by both the lack of forensic evidence and a credible source for either sort of event. The failure of the crew module resulted from the thermal degradation of structural properties, which resulted in a rapid catastrophic sequential structural breakdown rather than an instantaneous "explosive" failure.

Separation of the crew module/forward fuselage assembly from the rest of the Orbiter likely occurred immediately in front of the payload bay (between Xo576 and Xo582 bulkheads). Subsequent breakup of the assembly was a result of ballistic heating and dynamic loading. Evaluations of fractures on both primary and secondary structure elements suggest that structural failures occurred at high temperatures and in some cases at high strain rates. An extensive trajectory reconstruction established the most likely breakup sequence, shown below (see chart on page 77 of the CAIB report).

The load and heat rate calculations are shown for the crew module along its reconstructed trajectory. The band superimposed on the trajectory (starting about 9:00:58 a.m. EST) represents the window where all the evaluated debris originated. It appears that the destruction of the crew module took place over a period of 24 seconds beginning at an altitude of approximately 140,000 feet and ending at 105,000 feet. These figures are consistent with the results of independent thermal re-entry and aerodynamic models. The debris footprint proved consistent with the results of these trajectory analyses and models. Approximately 40 to 50 percent, by weight, of the crew module was recovered.

The Working Group's results significantly add to the knowledge gained from the loss of Challenger in 1986. Such knowledge is critical to efforts to improve crew survivability when designing new vehicles and identifying feasible improvements to the existing Orbiters.

Crew Worn Equipment
Videos of the crew during re-entry that have been made public demonstrate that prescribed procedures for use of equipment such as full-pressure suits, gloves, and helmets were not strictly followed. This is confirmed by the Working Group's conclusions that three crew members were not wearing gloves, and one was not wearing a helmet. However, under these circumstances, this did not affect their chances of survival.

NASA will use the Columbia Accident Investigation Board's final report as a blueprint for correcting the problems that led to the Feb. 1 shuttle disaster and returning the shuttle safely to flight, Administrator Sean O'Keefe said today.

"We have accepted the findings and will comply with the recommendations to the best of our ability," O'Keefe said in a statement. "The board has provided NASA with an important road map as we determine when we will be 'fit to fly' again.

"Due to the comprehensive, timely and open public communication displayed by the Board throughout the investigative process, we already have begun to take action on the earlier issued recommendations, and we intend to comply with the full range of recommendations released today."

Harold Gehman, chairman of the Columbia Accident Investigation Board, told CBS News this afternoon NASA has little choice. In the panel's view, he said, NASA cannot safely operate the space shuttle program without major changes in its management system.

"I think there's a little bit of denial that NASA, at least in the shuttle program, that NASA has modified its organizational structure over the years into one that no longer contains the attributes that they built their reputations on," Gehman said. "There may be some people who deny that, but the board is absolutely convinced, we think there's no room for any doubt whatsoever, the management system they have right now is not capable of safely operating the shuttle over the long term. That's the bottom line."

¾Gehman also said Congress and the White House must share blame for the Columbia disaster with NASA. Asked what he might tell President Bush about NASA and the agency's second in-flight tragedy, Gehman said he would point out that "NASA is a great organization that he and the country can have a lot of pride in. And that they are operating under and unrealistic set of rules and guidelines."

"Exploring space on a fixed cost basis is not realistic," the retired admiral said. "Launching shuttles on a calendar basis instead of an event-driven basis is not realistic. Demanding that you save money and run this thing in an efficient and effective way and that you get graded on schedule and things like that is not realistic. That the whole nation and Congress and the White House has an unrealistic view of how we do space exploration."

In addition, the board's report "clearly specifies that there is responsibility at both ends of Pennsylvania Avenue for this that are shared with NASA," Gehman said. "Now in some cases, NASA over markets what they can do. They promise more than they can deliver and they promise they can deliver it at a price that is less than it's really going to cost. But in some cases, it is demanded of them, in order to get a program approved, that they agree to unrealistic schedules and unrealistic price tags. So there's blame at both ends here."

The CAIB report focuses heavily on decisions made NASA's mission management team, the panel of senior agency leaders that oversaw the day-to-day conduct of Columbia's mission. The MMT, chaired by former flight director Linda Ham, shut down efforts to obtain spy satellite photography of Columbia's damaged wing and failed to challenge a hurried analysis that concluded the shuttle was in no danger of a catastrophic failure.

Gehman told CBS News the space agency's management system is so dysfunctional it hardly mattered who was in charge.

"We believe very, very strongly that you could substitute almost anybody in those positions and operate under the guidelines and rules and precedents that were being used in NASA and they would make the same errors," he said.

"Let me give you a specific case in point. Much has been made of the fact that the MMT didn't meet every day. NASA regulations require that they meet every day. So I had my board go back and see what were the meetings scheduled for the previous two shuttle missions? Guess what? They met every third day.

"So Linda Ham was doing her job according to the standards and precedents that were set by the establishment," he continued. "Even though the rules say you have to meet every day, you don't really have to. So that's an organizational flaw and she was performing her duties in that respect in accordance with the standards and precedents that had been previously established by her predecessors. And her predecessor's bosses had let that go on.

"So we feel very, very strongly that just moving the people around won't fix that problem. Unfortunately, we live in a town here in Washington, DC, in which they frequently demand someone pay. But we on the board were not influenced by that" and the board did not assign personal blame for any real or perceived errors in judgment.

Could a more experienced or proactive program manager or MMT chairman have made a different in Columbia's case?

"We feel there's some part of this, maybe even a lot of these problems, could have been mitigated by a stronger, a more suspicious, nervous kind of a person," Gehman said of the MMT and its chairman. "But our conclusion, our very, very strong conclusion is even if you had really brilliant people, really spectacular people, if you had the very, very best person you could get, that it would be a low probability bet that you could count on them to overcome the flaws in the organization. That is a low probability course of action."

Asked if NASA was "in denial" about serious management flaws and defects, Gehman said "in a lot of cases, they will deny that they have a basic organizational flaw which is dangerous. I think they'll deny that, some of them. Others will applaud it. It kind of depends on where you sit."

The CAIB's criticism of NASA drew an unusual response from Stephen Feldman, president of The Astronauts Memorial Foundation.

"One of the great risks of the Columbia tragedy and the subsequent report and commentary is that outstanding scientists and engineers may feel so criticized and unappreciated that they will leave NASA and the space program for higher paying and often less stressful jobs in the private sector," he said in a statement. "The outstanding safety record that NASA has compiled over the years shouldn't be forgotten because of one terrible accident on February 1, 2003." But O'Keefe's promise to full implement the CAIB recommendations drew praise from the National Space Society, a nonprofit advocacy group founded by German rocket scientist Wernher von Braun.

"The National Space Society urges NASA to embrace the recommendations of the CAIB and work diligently to fundamentally reform its decision-making processes and safety organizations so that we can safely return the Space Shuttle fleet to service," said Executive Director Brian Chase. "However, in order for NASA to fully implement the CAIB recommendations and continue the exploration of space, the agency will need appropriate funding to accomplish those tasks.

"The White House and the U.S. Congress must accept their share of responsibility for the future of our nation's space exploration efforts and provide the necessary leadership.

"Perhaps most importantly, NASA and our nation's leaders need to take this opportunity to foster development of new space transportation systems and renew a long-term commitment to human space exploration."

The Columbia Accident Investigation Board released its long-awaited report today, blaming the Feb. 1 disaster on bureaucratic inertia, slipshod internal communications and ineffective management at the top levels of NASA. The scathing, pessimistic tone of the report left little doubt the Board believes the so-called "NASA culture" is deeply flawed and in need of major modifications to prevent a repeat of the Columbia disaster in the years ahead.

"Based on NASA's history of ignoring external recommendations, or making improvements that atrophy with time, the Board has no confidence that the space shuttle can be safely operated for more than a few years based solely on renewed post-accident vigilance," the report states.

Unless NASA takes strong action to change its management culture to enhance safety margins in shuttle operations, "we have no confidence that other 'corrective actions' will improve the safety of shuttle operations. The changes we recommend will be difficult to accomplish - and they will be internally resisted."

For an agency with such a proud tradition - sending 12 men to the surface of the moon, establishing a permanent presence in low Earth orbit, exploring the solar system with unmanned robots and launching scientific sentinels to probe the depths of space and time - the criticism levied by the accident board likely will seem extreme in its harshness.

But the accident investigation board members and their investigators clearly believe the sharp tone is appropriate, in their view essential to ensuring that wide-ranging corrective actions are actually implemented. The board's investigation found that "management decisions made during Columbia's final flight reflect missed opportunities, blocked or ineffective communications channels, flawed analysis and ineffective leadership."

In the end, the report concludes, NASA managers never really understood the lessons of the 1986 Challenger disaster and "echoes of Challenger" abound in the miscues that led to Columbia's destruction.

"Connecting the parts of NASA's organizational system and drawing the parallels with Challenger demonstrate three things," the board found. "First, despite all the post-Challenger changes at NASA and the agency's notable achievements since, the causes of the institutional failure responsible for Challenger have not been fixed.

"Second, the Board strongly believes that if these persistent, systemic flaws are not resolved, the scene is set for another accident. Therefore, the recommendations for change are not only for fixing the shuttle's technical system, but also for fixing each part of the organizational system that produced Columbia's failure.

"Third, the Board's focus on the context in which decision making occurred does not mean that individuals are not responsible and accountable. To the contrary, individuals always must assume responsibility for their actions. What it does mean is that NASA's problems cannot be solved simply by retirements, resignations, or transferring personnel."

The 13-member Columbia Accident Investigation Board, under the leadership of retired Adm. Harold Gehman, spent seven months investigating the Feb. 1 Columbia disaster, reviewing more than 30,000 documents, conducting more than 200 formal interviews and collecting testimony from expert witnesses. The board also oversaw debris recovery efforts in Texas and Louisiana that involved more than 25,000 searchers. The investigation is expected to cost $19.8 million when all is said and done.

The board's 248-page report was released at 10 a.m. at the National Transportation and Safety Board in Washington. Reporters were allowed to review the report ahead of time, surrendering cell phones and wireless laptop network cards before entering a closed off "reading room" at 6 a.m. Gehman and other members of the panel plan to discuss the report during an 11 a.m. news conference. This status report will be updated as soon as possible thereafter.

In the meantime, key lawmakers vowed to take the board's recommendations to heart.

"The people of NASA have accomplished great things," Dana Rohrabacher, D-Calif., chairman of a key House space committee, told CBS News Monday. "They've put a man on the moon within a very short period of time, the people of NASA have been a source of great pride ... for the people of the United States.

"But for far too long, they've been resting on their laurels and bathing in past glories, nostalgic about the glory days," he continued. "It's time to look to the future and it's time to recapture a tough, hard-working body of people who have new challenges and are not just looking at the past but looking to the future. And that means Congress and the president have got to act on the Gehman report."

It should be noted, however, that NASA cannot develop new manned spacecraft or significantly change the general thrust of the nation's space program without approval and funding from Congress and the White House. The Bush administration has been virtually silent when it comes to the nation's manned space program and Congress has not endorsed any major changes beyond controlling the budget of the international space station.

President Bush has not yet weighed in on the report or its implications for NASA and the international space station project. He said last week he wanted a chance to review the report before commenting.

The report focuses on two broad themes: The direct cause of the disaster - falling external fuel tank foam insulation that blasted a deadly hole in the leading edge of Columbia's left wing 82 seconds after liftoff - and the management system that failed to recognize frequent foam shedding as a potentially lethal defect before Columbia even took off.

The report also focuses on how NASA's mission management team, a panel of senior agency managers responsible for the day-to-day conduct of Columbia's mission, failed to recognize the severity of the foam strike that actually occurred, virtually eliminating any chance to save the shuttle's crew, either by attempting repairs in orbit or launching a rescue mission.

The report makes 29 recommendations, 15 of which must be implemented before shuttle flights resume. Five of those were released earlier, requiring NASA to eliminate foam shedding to the maximum extent possible; to obtain better imagery from the ground and in orbit to identify any problems with the shuttle's thermal protection system; and development of tools and procedures to repair any such damage in space.

The more difficult recommendations address management changes and the establishment of an independent Technical Engineering Authority to verify launch readiness, oversee and coordinate requests for waivers and to "decide what is and is not an anomalous event." The TEA "should have no connection to or responsibility for schedule and program cost." In addition, NASA's Office of Safety and Mission Assurance should have direct authority over all shuttle safety programs and be independently funded.

"It is the Board's opinion that good leadership can direct a culture to adapt to new realities," the panel wrote. "NASA's culture must change, and the Board intends (its) recommendations to be steps toward effecting this change."

Columbia, carrying a crew of seven and scores of scientific experiments, blasted off from the Kennedy Space Center in Florida on Jan. 16. Strapped in on Columbia's upper flight deck were commander Rick Husband, making his second flight; rookie pilot William "Willie" McCool; flight engineer Kalpana Chawla, making her second flight; and rookie astronaut-flight surgeon Laurel Clark. Seated below on the shuttle's middeck were payload commander Michael Anderson, making his second flight; and two more rookies, physician-astronaut David Brown and Ilan Ramon, the first Israeli space flier.

At 81.7 seconds after liftoff from pad 39A, a suitcase-size chunk of foam broke away from the ship's external fuel tank and slammed into the left wing. The shuttle was racing skyward at more than twice the speed of sound at the time - 1,650 mph - and engineers later calculated the foam hit the left wing at some 530 mph.

The foam strike was not seen until the day after launch when engineers began reviewing tracking camera footage as they do after every launching. A film camera in Cocoa Beach that could have photographed the impact on the underside of the left wing was out of focus. A video camera at the same site was properly focused, but it lacked the resolution, or clarity, to show exactly where the foam hit or whether it caused any damage. A third camera at a different site showed the foam disappearing under the left wing and emerging as a cloud of debris after striking the underside. Again, the exact impact point could not be seen.

Stunned engineers immediately began analyzing the available film and video and ultimately determined the foam had struck heat shield tiles on the underside of the wing, perhaps near the left main landing gear door. No one ever seriously considered a direct heat on the reinforced carbon carbon panels making up the wing leading edge because no trace of foam debris was ever seen crossing the top of the wing. As the board ultimately concluded, however, the foam did, in fact, strike the leading edge on the lower side of RCC panel No. 8.

In hindsight, it's difficult to understand why the possibility of a leading edge impact didn't receive more attention. The board concluded that was due at least in part to the influential role of Calvin Schomburg, a senior engineer at the Johnson Space Center with expertise in the shuttle's heat-shield tiles.

"Shuttle program managers regarded Schomburg as an expert on the thermal protection system," the board wrote. "However, the board notes that Schomburg as not an expert on reinforced carbon carbon (RCC), which initial debris analysis indicated the foam may have struck. Because neither Schomburg nor shuttle management rigorously differentiated between tiles and RCC panels, the bounds of Schomburg's expertise were never properly qualified or questioned."

In any case, a team of Boeing engineers at the Johnson Space Center, under direction of NASA's mission management team, ultimately concluded the foam strike did not pose a safety of flight issue. Their analysis, using a computer program called CRATER, predicted areas of localized, possibly severe damage to the underside of the left wing, but no catastrophic breach. The concern, rather, was that any damage likely would require extensive repairs before Columbia could fly again.

While the damage assessment was getting under way, at least three different attempts were made to obtain spy satellite photography of the impact site to resolve the matter one way or the other. But in a series of communications miscues, the efforts ultimately were quashed by the MMT, under the direction of former flight director Linda Ham.

Ham says she was never able to find out who wanted such photographs and, without a formal requirement, had no reason to proceed. As for the debris assessment, Ham and other members of the MMT never challenged the hurried analysis or questioned the conclusion Columbia could safely return to Earth as is.

Many mid-level engineers said later they had serious misgivings about the debris assessment and heavy email traffic indicated fairly widespread concern about potentially serious problems if the foam strike had compromised Columbia's left main landing gear. Yet those concerns never percolated up the Ham, Dittemore or other members of the mission management team.

Ham and Dittemore both have said they were always open for questions or comments from lower-level engineers and that everyone on the team was encouraged, even duty bound, to bring any serious concerns to the attention of senior management.

But the CAIB disagreed.

"Communication did not flow effectively up to or down from program managers," the board wrote. "After the accident, program managers stated privately and publicly that if engineers had a safety concern, they were obligated to communicate their concerns to management. Managers did not seem to understand that as leaders they had a corresponding and perhaps greater obligation to create viable routes for the engineering community to express their views and receive information. This barrier to communications not only blocked the flow of information to managers but it also prevented the downstream flow of information from managers to engineers, leaving Debris Assessment Team members no basis for understanding the reasoning behind Mission Management Team decisions."

As for not hearing any dissent, the board wrote, "managers' claims that they didn't hear the engineers' concerns were due in part to their not asking or listening."

"Management decisions made during Columbia's final flight reflect missed opportunities, blocked or ineffective communications channels, flawed analysis and ineffective leadership," the board wrote. "Perhaps most striking is the fact that management - including Shuttle Program, Mission Management Team, Mission Evaluation Room (personnel) and flight director and mission control - displayed no interest in understanding a problem and its implications.

"Because managers failed to avail themselves of the wide range of expertise and opinion necessary to achieve the best answer to the debris strike question - 'Was this a safety-of-flight concern?' - some space shuttle program managers failed to fulfill the implicit contract to do whatever is possible to ensure the safety of the crew. In fact, their management techniques unknowingly imposed barriers that kept at bay both engineering concerns and dissenting views and ultimately helped create 'blind spots' that prevented them from seeing the danger the foam strike posed."

Shuttle program manager Dittemore and members of the mission management team "had, over the course of the space shuttle program, gradually become inured to external tank foam losses and on a fundamental level did not believe foam striking the vehicle posed a critical threat to the orbiter," the board wrote.

In the end, many NASA managers say privately, it was a moot point. Once the foam breached the leading edge of Columbia's left wing, the crew was doomed. The astronauts had no way to repair the breach - no robot arm and no tile repair equipment - and there was no realistic chance another shuttle could be readied in time for a rescue mission.

Maybe so. But NASA's flawed management system never gave the agency a chance to prove it still had the "right stuff."

It is that institutional system, or "culture," at NASA that must be changed, the board believes, to prevent another accident.

"An organization system failure calls for corrective measures that address all relevant levels of the organization, but the Board's investigation shows that for all its cutting-edge technologies, 'diving-catch' rescues and imaginative plans for the technology and the future of space exploration, NASA has shown very little understanding of the inner workings of its own organization," the report states.

"NASA's bureaucratic structure kept important information from reaching engineers and managers alike. The same NASA whose engineers showed initiative and a solid working knowledge of how to get things done fast had a managerial culture with an allegiance to bureaucracy and cost-efficiency that squelched the engineers' efforts.

"When it came to managers' own actions, however, a different set of rules prevailed. The Board found that Mission Management Team decision-making operated outside the rules even as it held its engineers to a stifling protocol. Management was not able to recognize that in unprecedented conditions, when lives are on the line, flexibility and democratic process should take priority over bureaucratic response."

The addition of a time-consuming tile inspection on the next shuttle flight, a spacewalk to test new tile repair equipment and techniques and lack of a third space station crew member to assist in equipment transfer work is forcing NASA managers to consider major changes to reduce the crew's workload.

While a variety of options is under study, it does not appear likely the STS-114 shuttle crew, commanded by Eileen Collins, will be able to accomplish its original objectives, including transfer of a fresh three-person crew and all associated equipment and supplies to the space station. NASA managers are considering the possibility of off-loading the crew transfer to a later flight, either to an additional shuttle mission or, possibly, to a Russian Soyuz flight later next year, and adding non-station crew members to the STS-114 mission to assist with logistics and equipment transfer work.

In addition, some of the mission's scientific objectives may be deferred as well because of weight limitations resulting from the expected addition of tile repair equipment and a long robot arm extension boom needed for post-launch inspection of the shuttle's thermal protection system.

Crew transfer issues depend in large part on when Atlantis can be ready for flight. A new two-person station crew is scheduled for launch aboard a Soyuz ferry craft in mid October. They will return to Earth next spring aboard Atlantis or, if the shuttle is not ready in time, aboard a Soyuz.

Most insiders, including several sources who discussed the issues last week, believe NASA will be hard pressed to get Atlantis off the ground before next summer. In that case, the October station crew likely would be replaced by two fliers launching aboard a Soyuz next April. Whether Atlantis then would take another crew up later that summer, or whether the April station crew would remain aloft until a fresh Soyuz crew arrives in Oct. 2004 - carrying either two or three station fliers - is part of the current debate about Atlantis' mission.

Any option off-loading crew rotation to the Soyuz, obviously, would require Russian concurrence. The Russians have not yet booked, or sold, a Soyuz seat for the October 2004 mission and that flight could, in theory, carry up a fresh three-person station crew. But that remains to be seen.

In the meantime, NASA managers are assessing a variety of options to alleviate the STS-114 crew timeline shortfall. The additional weight of a robot arm tile inspection camera boom, the tile repair demonstration kit and other items mean Atlantis cannot carry the originally planned complement of scientific equipment, the research gear needed to make the shuttle flight a space station "utilization" mission as originally envisioned.

"There is growing impetus, within both the shuttle and the station programs, to request (NASA) headquarters add a shuttle flight, a logistics flight, that would offload the strain of return-to-flight tasks from 114," said one NASA official familiar with the discussions.

Before Columbia's destruction Feb. 1, NASA was readying Atlantis for launch around March 1 to carry a fresh three-man crew to the space station along with supplies and research equipment stowed in a pressurized module known as an MPLM.

In addition, STS-114 features three spacewalks by astronaut Stephen Robinson and Japanese astronaut Soichi Noguchi. The objectives are to install a new control moment gyroscope, or CMG; to mount an external stowage platform, or ESP, on the outside of the station for use during upcoming solar array reconfigurations; and to mount TV camera gear and other equipment on the station's exterior.

In the wake of the Columbia tragedy, the station's three-man crew was replaced with two fliers, Yuri Malenchenko and Ed Lu. Because of limitations on fresh water, NASA and the Russian space agency will continue to staff the station with two-person crews until shuttle flights resume, leaving the STS-114 crew with a shortage of manpower in orbit to unloaded the pressurized logistics module.

The Columbia Accident Investigation Board, which will release its final report Tuesday, already has released five preliminary recommendations, including one requiring NASA to carry out extensive on-orbit tile inspections and another requiring development of an in-flight tile repair capability.

Since then, engineers have developed a lengthy tile inspection procedure expected to be carried out on the second day of the mission, in which cameras mounted on a long boom will be maneuvered about the orbiter by the shuttle's robot arm to look for signs of damage. The procedure will involve two astronauts and take up to seven hours or more to complete, throwing a wrench of sorts into normal flight-day two equipment check-out activity.

Areas of the shuttle that cannot be seen by the camera boom will be inspected by the station crew during Atlantis' final approach when Collins performs a pitch maneuver to expose the underside of the orbiter to view from the station above. She already is practicing the maneuver in flight simulators at the Johnson Space Center in Houston.

Once docked, the MPLM will have to be unloaded with one less station astronaut than usual. NASA managers are evaluating a variety of options to lighten the load, in some cases literally, by deferring some transfer items to later missions.

Agency officials hope to carry out at least two spacewalks. The CMG replacement and the tile repair demonstration. The ESP installation also is a top priority because it includes equipment that will be needed by an upcoming assembly crew. Whether it can be accommodated during Atlantis' mission is not yet clear.

The tile repair kit will be located at the back of the shuttle's cargo bay and feature a panel of deliberately damaged heat shield tiles. The spacewalkers will attempt to repair the tiles using materials and procedures currently in the development stage.

The work does not yet include any sort of repair demonstration for reinforced carbon carbon panels making up the orbiter's wing leading edges. While promising procedures are under study, it's not yet clear whether any repair techniques can be developed in time for a flight next spring.

NASA planners hope to refine the requirements of STS-114 in the next few weeks.

The co-chairman of a panel charged with assessing how well NASA meets the intent of recommendations from the Columbia Accident Investigation Board said today he's not sure the agency will have time to implement critical management changes before shuttle flights resume next year.

Richard Covey, a senior executive with Boeing who flew as pilot of the first post-Challenger mission, also said he was disappointed the safety-conscious management system implemented in the wake of the 1986 Challenger disaster broke down in Columbia's case.

"I wasn't surprised we had an accident," he told reporters after the panel's first public meeting. "Spaceflight is risky, those of us who have flown in space know there's risk and entry has always been (phase of flight) the crews have known was highly risky. So the fact that an accident happened on entry was not necessarily a surprise.

"Now, shocking? Yeah. Disappointing, particularly what I have learned of the process that maybe allowed the situation to develop where we had the accident. That was disappointing to me. It has similarities to the Challenger accident, but not perfectly."

Asked to be more specific, Covey said "the decision-making process, both pre flight and during flight, probably has some similarities to the decision-making process in the Challenger accident. If you look at the way that the known shedding of foam off the external tank was handled, you can go back and say well, all right, we knew we had some issues with the O-rings (in the flawed boosters used by) Challenger. They may not have been the same specific barriers to good decision making that occurred there, but the decision process was flawed, probably in both of those cases similarly."

Columbia was destroyed during re-entry Feb. 1 by a breach in the leading edge of the ship's left wing. The breach most likely was caused by a piece of foam insulation that fell off the shuttle's external tank during launch and struck the leading edge. The external tank project had a history of foam shedding, as Covey said, but it was not considered a safety-of-flight issue and it was not a constraint to launch. Likewise, NASA engineers knew about booster O-ring joint problems but did not ground the fleet before Challenger's final flight.

The Columbia Accident Investigation Board plans to release its report Aug. 26. To remove any doubt about NASA's willingness to follow those recommendations, NASA chartered an independent panel chaired by Covey and former Apollo astronaut Thomas Stafford to assess the agency's response to the CAIB's recommendations. The Return to Flight Task Group plans to submit its final report one month before the next shuttle flight, whenever that might be. NASA hopes to launch the shuttle Atlantis on mission STS-114 as early as March 11.

"The intent of our charter is to establish an independent assessment of NASA's responses to the Columbia Accident Investigation Board's recommendations," Covey said. "We also are asked to observe other safety and operational issues that may be pertinent relative to return to flight. It is not a broad charter, it is relatively narrow and focused. Our intent it to make sure we live up to the intent and the letter of our charter."

The task group includes numerous former NASA managers, including James Adamson, a former astronaut and aerospace executive who now runs his own consulting firm. He said the key element of the panel's charter is whether or not NASA meets the intent of the CAIB's recommendations.

"Our job, on the surface, may sound simple, but we're going to check and see if they've done that," he said. "It's not a simple yes or no question. I think everybody knows there's more than one way to skin a cat and we're going to try to look, to drill down into NASA's response to make sure they've met the intent of the recommendation."

One of the CAIB's five already released recommendations calls for improved imagery during ascent to make sure unwanted events like foam shedding do not go unnoticed. Adamson said that recommendation "is really intended to make sure that we don't re-enter with a hole in the vehicle without knowing it."

"The real intent of that is that NASA's got to take some action to be sure we don't do that again," he said. "And there are lots of ways to do that, some of them include imagery. But we're going to look at how you do that and what they're doing in response and we're going to make our assessment based on the intent."

The CAIB's final report is expected to be critical of NASA's management system and operational culture. Covey would not speculate on what the recommendations might involve, but he cautioned reporters not to expect too much too soon.

"We have already begun to try to scope the way we will address managerial, organizational type of recommendations when they come out of the CAIB," he said. "Because they may not be expected to be implemented before return to flight, then that puts us in a situation where we have to say well, what can we assess in the time period that we're chartered to do assessments? So our approach may be to look at plans, strategies or approaches that may be in place prior to the first flight and do an assessment. But it would not be a complete assessment because the real implementation may take longer."

Covey said he agreed with CAIB members who have said the shuttle should be viewed as an experimental spacecraft and not an operational vehicle.

"It goes back to my background as a test pilot and my understanding of those issues that really are important to make a vehicle operational," Covey said. "We've never been there with the space shuttle program and won't be through its life. So if indeed proper focus is the result of thinking in terms of it being experimental, I can support that. I like that."

But experimental vehicles, by their nature, face extreme risk and Covey said another failure will always be possible.

"Clearly with a fleet of three (remaining) orbiters and the demands of the space station program on our orbiter fleet ... then a safe return to fight and an ability to sustain safe flight without the loss of an orbiter is extremely important and there's no doubt about that," Covey said. "I think everybody's very sensitive to that.

"At the same time, we have to also recognize that the same demands of having safe flight and maintaining our orbiter fleet in order to support space station says we need to fly again. So there's a balance there. We'll never be absolutely sure we won't lose another orbiter. We can't do that and we should not have that expectation. We should be able, however, to find a way to make sure the things we know and the things we can learn about between now and the next flight and all those other flights" are properly implemented.

NASA will respond to the Columbia Accident Investigation Board's recommendations "almost to the letter," a senior agency official said today. But Frederick Gregory, NASA's deputy administrator, downplayed widely publicized criticism of NASA's management culture, saying "it would be difficult for me to define to you what the 'NASA culture' is."

Gregory, William Readdy, NASA's associate administrator for space flight, and Bryan O'Connor, associate administrator for safety and mission assurance - all former shuttle commanders - met with reporters at the Kennedy Space Center today after meeting with members of an independent board charged with assessing NASA's implementation of the accident board's recommendations.

Gregory was repeatedly asked about what NASA plans to do to correct problems with its management philosophy, the so called "NASA culture" that permeates agency operations. One reporter opined many believe it may prove easier to fix the shuttle's technical shortcomings than it will be to correct any major flaws in the agency's mindset before flights resume next year.

But Gregory chose not to answer the reporter's question about what NASA might be planning to address the culture issue in the weeks and months ahead.

"That's an interesting observation," he replied. "We have the five technical recommendations (already released by the CAIB), the report itself won't come out until the end of the month and perhaps some of those things you mentioned might be mentioned. But at this point, we have not received any comments officially from the accident investigation board, justifying or backing up your statements."

This reporter then asked Gregory to respond to the spirit of the first question in light of the virtual certainty the board will find fault with NASA's management procedures. Again, Gregory declined to provide any specifics.

"What we are looking at are not only are the technical issues, what we would look at is any process that might need to be modified or changed as we transition from an ops activity, an operations activity, into a return-to-flight activity," he said. "I think you will see there will be some changes, process changes, that will occur. But at this point only as we move from the operations of the standard activities that we're doing into this return to flight time."

Yet another reporter came at the question from another angle and Gregory replied that he believed most of the criticism of NASA's operating culture originated with a single CAIB member and that the board's findings would not be known until the panel's report is released Aug. 26.

"It would be difficult for me to define to you what the 'NASA culture' is," Gregory said. "As I sit here, and I have three astronauts here, I suspect if you tried to determine what the culture of the three of us is, you would find there are three different cultures here. So that's why I have said, I have to wait and see what, if anything, is being written (by the CAIB) about culture before I can respond to your question."

Readdy was somewhat more forthcoming.

"The comment that it's a 'culture thing' maybe does apply in some small area," he said. "I see a gentleman there who is wearing and Apollo shirt today. We were over in the Saturn 5 display area earlier today. There is a culture there, too, that after the Apollo 204 fire (in 1967) got us back to the moon and focused on mission. So there are different aspects of a culture.

"The real challenge will be for us to identify those things that are very positive about our culture and reinforce those and whatever the CAIB may say in terms of the negative aspects of the culture, to identify those very specifically and fix them."

How NASA plans to accomplish that before next spring was left unsaid.

NASA's current target date for the first post-Columbia mission is March 11, the opening of a window that extends through April 6. The launch window is based on a requirement to launch the next mission in daylight and to make sure its external fuel tank separates with enough lighting to ensure a good photographic assessment of its condition.

Columbia, of course, was destroyed by a breach in the ship's left wing leading edge that investigators believe was caused by a chunk of foam insulation that fell off the external tank during launch.

Most agency insiders believe the March time frame is overly optimistic and that a launching next summer is a more realistic expectation. Readdy said today the shuttle team needs a date to march toward from the standpoint of processing hardware, but he stressed that the next mission will not be launched until all parties agree it is safe to do so.

"We understand that one, we don't have the Columbia Accident Investigation Board final report in front of us so there will likely be adjustments there," he said. "Two, we also understand that perhaps March may be success oriented. But we need to have something to get the team all marching in step on and it appears the window, I think, from March 11 to April 6, honored all the constraints that we know thus far: Daylight launch, daylight external tank separation so we can do assessments there, the beta angle cutouts (for temperature control at the space station).

"Is March ambitious? Probably. But that's how you arrive at what the other, not-so-long poles are, the other things that may be potentially in the critical path and identify those so you can go off and solve them."

Gregory emphasized NASA's drive to launch would be driven by accomplishing milestones and not by any desire to meet a specific date.

""We're committed to return to flight but we are committed to doing so safely as we can," he said. "The point I want to make here is we are milestone-oriented focused, not schedule focused. If you see schedules that have a scheduled launch on it, it's only so our folks can work toward a launch date. But it does not necessarily represent the actual date that we will return to flight with the shuttle."

Earlier today, Gregory, Readdy and O'Connor met with members of the independent board charged with assessing NASA's implementation of CAIB recommendations. The panel is chaired by Apollo astronaut Thomas Stafford and shuttle veteran Richard Covey.

"Our commitment is to independently assess NASA's response and implementation of the findings and recommendations of the CAIB," Gregory said. "As you probably know, there will be no attempt whatsoever to argue or defend a recommendation from the CAIB. We will respond to each of the findings and recommendations and in fact ... we will go further than that. The Stafford-Covey task group will assess our response to the findings and recommendations and will have an opportunity, if they find some areas that they observe that have not been picked up, to make a recommendation to us."

As for when the next shuttle might get off the ground, "we will not fly until we are ready to, we have responded to the CAIB, we've had an assurance from the task group that we are headed down the right road, that we have not deviated, that we have not missed anything. Obviously, we will remain vigilant to any congressional discussions or inquiries."

Said O'Connor: "We're going to return to safe space flight by setting the bar higher than it was before."

The news conference ended with a question about whether NASA will implement every CAIB recommendation before the resumption of shuttle flights.

"I think we will be responding almost to the letter to the recommendations of the board," Gregory said. "Now again, the board has not published the report yet and I may have to back off a little bit. But what we will do is the right thing, my assumption is that we would follow to the letter the recommendations and that's why we have the Stafford-Covey task team there independently assessing our response to the board. They will tell us if we have gone down the wrong path or not."

In an emotion-charged meeting with reporters, Linda Ham, chairman of NASA's mission management team and a lightning rod for criticism of decisions made - or not made - during the shuttle Columbia's ill-fated voyage, spoke publicly for the first time today, defending NASA's management practices but agreeing major changes are needed.

Contrary to some earlier media reports, Ham said she never received any formal requests to obtain spy satellite imagery of Columbia to determine the severity of the foam strike and the issue was not discussed during any of the mission management team meetings held during Columbia's flight.

She said she accepted the results of a hurried Boeing-led analysis, carried out at the request of NASA, that concluded the foam strike was not a safety-of-flight issue. She insisted any lower-level engineers or managers who might have disagreed were free, even encouraged, to voice those concerns directly to her. But no one stepped forward and Ham had no reason to question the engineering analysis.

"It goes without saying we were all trying to do the right thing," she said. "All along, we were basing our decisions on the best information that we had at the time. Nobody wanted to do any harm to anyone. Obviously, nobody wants to hurt the crew. These people are our friends, they're our neighbors, we run with them, work out in the gym with them, you know my husband is an astronaut. I don't believe anyone is at fault for this."

But Ham, a 21-year NASA veteran, former flight director and one of the highest ranking women in the high-pressure world of human space flight operations, was removed from her post as manager of shuttle integration and chairman of the mission management team earlier this summer. She currently is in a sort of management limbo at the Johnson Space Center, where some insiders believe she is being made a scapegoat for decisions that were unanimously supported by the entire MMT.

"She did the best she could do given the information she had," said one official who asked not to be named. "She talked to people she trusted, she listened to the analysis. She doesn't deserve to be crucified for this. But she will be. She already has been. She made mistakes, but we all did."

Meeting with 10 reporters today, including the writer of this report, Ham endured occasionally pointed questions about her role in Columbia's flight, calmly fielding most with technical savvy and occasional glances at type-written notes. But when asked about criticism directed at her personally, she finally lost her composure.

"We were really doing the best we could," she said. "Our goal is to launch and of course keep the crew safe, that's the number one goal, and also bring the orbiter back safely and accomplish the mission. That's our job, our number one job. I think we all take some personal responsibility for this and I certainly feel accountable for the MMT. So it's been very difficult through this.

"I know the important thing to do right now is get the program back on (its) feet, get back to flight and get back to flight more safely than ever. My husband being an astronaut and having two kids, we've all gone through this together..."

She suddenly stopped, eyes filling with tears, and could not continue. Flight director LeRoy Cain, the man in charge of mission control during Columbia's re-entry Feb. 1, handed her a handkerchief while mission operations representative Phil Engelauf answered another question. The briefing continued. But the emotional torment on Ham's face was unmistakable. Whatever one might believe about her role in the management of Columbia's mission, there can be little doubt the disaster is never far from her mind.

"It's unconscionable to me that people can attribute to the members of the MMT or the flight control team or the rest of the folks during these missions anything other than the best of intentions," said Engelauf, himself a veteran shuttle flight director. "These are people of good conscience doing everything in their power to get the right answers. This is what we do for a living. LeRoy sits at that console and his job, and my job when I'm there, is to keep the crew safe and get them home in one piece. That is everything we do here and when we come to work that's all we're focused on.

"So in the end, yes, we lost the crew and we lost the vehicle and we can't escape that and nobody feels worse about that than every one of us who has their hands on these missions every day," Engelauf said. "But it is not because of lack of good intent or lack of effort on anybody's part. If the system fell down, we'll fix the system. But it's really difficult to me to attribute blame to any individual personalities or people. We can find mistakes in analyses and we can find places where we weren't good enough. But it's not because of malice or ill intent."

One of the enduring questions of the post-launch MMT agenda has been disposition of requests for satellite imagery of Columbia to better characterize the extent of any damage to the ship's left wing. At least two such efforts were initiated, but Ham said today the issue was never brought up to the MMT.

"That's interesting question," she said. "We have read (news) reports that the mission management team had declined a request for outside assistance and if you read through the transcripts, you'll note that the mission management team never addressed a request for outside assistance because it never came up in any of the meetings. It never came up to me personally.

"I did hear about a possible request for imagery via a phone call. When I did hear about that possible request, I began to research who was asking. What I wanted to do was find out who that person was and what exactly they wanted to look at so we could get the proper people from the ops team together with this group of people, sit down and make sure that when we made the request we really knew what we were trying to get out of it.

"So I went to our contractor, United Space Alliance, to see if they were making a request, I went to the space shuttle vehicle engineering office and I also went to the mission evaluation room where all the engineering work is done, thinking if anyone knows they will know if there's a such a request out there. I couldn't find any request so we did not pursue that."

She said she had "absolutely no reluctance to ask for outside assistance."

"We certainly would have done that if we could have gotten the right information together and the right people together and done that," she said. "Several weeks after the accident, I did find out who was asking and these folks that were asking were actually in the MMT and never brought it up. They were in the MER (mission evaluation room) meetings before the MMT and never brought it up. So for some reason, they didn't feel comfortable bringing it up in the MMT. Certainly, you would think they would have done that at those other meetings or in the hall or at any time. But it never, ever came up."

As most readers know by now, Columbia's left wing was struck by a falling piece of foam insulation that broke away from the ship's external fuel tank 81 seconds after blastoff Jan. 16. Two flights earlier, another large piece of foam had broken away from the same area of the tank and struck one of the shuttle Atlantis' solid-fuel boosters.

The Columbia debris strike was seen during analysis of launch film the day after liftoff. But the actual site of the impact was not visible and the extent of any resulting damage was unknown. A team of NASA-led contractor engineers began studying possible damage scenarios using a computer program designed to predict damage to the shuttle's heat-shield tiles. Ham said today she was content to give the team time to work before making any hasty decisions.

In the end, the engineers concluded the foam strike might lead to severe localized heat damage during re-entry but it did not pose a catastrophic "safety of flight" threat.

"We were trying to give the technical community sufficient time to do an in-depth analysis," Ham said. "They did do their analysis, they did use the Crater (program) and the other tools they had available to them, I do trust that the Mission Evaluation Room, with their mission experts, would bring forward the results of that and they did come forward on that Friday, the 24th, and said they did not believe there was a safety of flight issue and that there would be no burn through and that at most we would have a potential turn around issue, some work on the orbiter that we'd have to do post flight. I did trust that their analysis and the work they had done was correct."

No one in the MMT objected to the report. But after Columbia's catastrophic re-entry, some engineers let it be known then had deep concerns about the analysis. Ham said she never heard any such concerns. Engelauf and Cain agreed.

"We foster a culture here that very much encourages folks to talk, to communicate, the lines of communications are always open," Cain said. "That's the culture we very much encourage and foster around here. And the reason we do that, as you heard Linda mention earlier ... is because we have the safety of the crew the success of the missions at the forefront of our mind every single day we come to work.

"So in order for us to do our jobs effectively, it is crucial that we have open and clear lines of communications. It is absolutely critical and it is, frankly, expected of every single person in every organization, from the engineer all the way up to the management of the programs. Certainly for human spaceflight endeavors, that's the culture we foster. And I believe it's alive and healthy today."

Ham said lower-level engineers and managers have formal and informal avenues to approach senior management with technical concerns.

"For some reason, we didn't get it either way, which I think is also of interest," she said. "You know, whatever happened somewhere, we probably need to figure that out and see if there is a way we can improve that. But I'd also agree we have wide-open communications, our doors are always open and we're more than willing to hear what people have to say. That's the only way we can operate, that's the only way we're going to hear about these kinds of things and the only way we can continue to fly safely. So we really do need these people to feel comfortable and come forward with their issues."

Said Engelauf: "In the final analysis, every night when I go to bed, (I know) we lost STS-107, we lost the crew, we lost the vehicle. Clearly, that is not the way it is supposed to happen and that is not what we do here. So no matter how you do the arithmetic, we're getting a wrong answer and we have to fix that. We all know that. We're going to have to wait until we get some recommendations from people who look at this from a different perspective. It's very difficult to pinpoint the details. It may be something that just isn't obvious to us. I certainly don't want to leap to the easy answers and fix something that isn't' causing the problem."

Engelauf also addressed another issue that keeps popping up in the disaster investigation: The agency's long history of foam shedding and how senior managers slowly grew to accept what sociologist Diane Vaughan calls the "normalization of deviance."

"We've had incidences of foam coming off the tank throughout the history of the program and the same management processes that I think got us comfortable that that was not really a safety of flight issue have been allowed to continue, rightly or wrongly," Engelauf said. "I don't think you can point to individuals today and say that person got comfortable with it, because we've sort of inherited this from the time when Linda and I were back as front room flight controllers and there was a completely different set of people managing the program.

"But I think the intent is that our processes try to cover these sorts of things, we try to put all the checks and balances in place and we try to do all the analyses and in this particular case, I don't think the problem was that we didn't do the analysis or didn't take notice of the foam. I think we got the wrong answer on the analyses.

Cain said "at least part of the answer has to be that fundamentally, we are dealing with an incredibly complex system. It's the most complicated machine that humans have ever built. And over time, we are going to make some human errors. And that's got to be at least part of the answer. We do everything in our power, every single day in this business, to manage the systems to minimize that. And over time, with this complex of a system and the risky environment of space, that has to be at least part of the answer."

Finally, Ham, Engelauf and Cain agreed that NASA would have done everything possible to mount a rescue mission if the team had realized Columbia faced a catastrophic defect. While it is doubtful any such scenario would have succeeded, all three said NASA certainly would have made the attempt.

"Had we known that there was a catastrophic situation on orbit, we certainly would have done everything we could have, including is there anything we can do for the tile repair, we certainly would have pursued rescue. There's no doubt," Ham said.

Added Cain: "If we had known that we had a problem while we were on orbit, I certainly agree, we would have left literally no stone unturned. As to whether it would have made a difference, I think it's an impossible question to answer."

Editor's Note...
The mission management team transcripts posted by NASA today included little or no punctuation. Punctuation, based on context and content, has been added to the excerpts below to make the passages more readable.

Transcripts of meetings by senior NASA managers during the shuttle Columbia's ill-fated flight show mission management team chairman Linda Ham and other top officials, despite a dearth of technical data, simply did not believe falling insulation from the ship's external fuel tank could cause a catastrophic breach in the ship's left wing.

The transcripts, posted on a NASA web site today, include extensive discussions of relatively minor temperature control problems with Columbia's Spacehab research module and debate about the shuttle's slightly over-limit landing weight. But there is surprisingly little discussion about the foam strike investigators now believed doomed the ship 81 seconds after blastoff Jan. 16.

Instead, the management team unanimously accepted, with only a smattering of questions from Ham, the results of a hurried analysis that concluded the worst threat Columbia faced was possibly severe, but localized, tile damage that might require repairs between flights.

Ham has declined all interview requests since the shuttle tragedy and has not participated in any news briefings to this point. With the benefit of 20-20 hindsight, she has been criticized by some observers for not recognizing the severity of the foam strike and its potential for causing catastrophic damage. As chairman of the MMT, she also has been blamed for quashing efforts to obtain spy satellite photography of the shuttle to better characterize any potential damage.

But the widely reported, unsuccessful efforts to obtain spy satellite imagery were not discussed at the MMT meetings, the transcripts show, and in any case, sources say, those efforts primarily were derailed by lower level managers before reaching the MMT chairman.

Ham remains in the shuttle program office at the Johnson Space Center, but earlier this summer she was removed from her post as program integration manager and replaced by flight director John Shannon. Wayne Hale, a former flight director who now serves as deputy program manager under William Parsons, is expected to assume Ham's role in future MMT meetings.

As for Ham's role chairing the MMT meetings during Columbia's flight, the transcripts show no particularly unusual comments on her part or any obviously questionable decisions. But surprisingly, the foam strike was never a top-of-the-agenda item and it was discussed only sparingly, in summary format, and with no debate even though the strike was the most significant such impact ever observed.

When it was discussed, the team focused almost totally on possible damage to the heat shield tiles on the underside of Columbia's left wing and all but dismissed the possibility the foam strike could have damaged the reinforced carbon carbon - RCC - panels making up the wing leading edge. This was a particularly striking turn of events considering there was little or test data on how the carbon composite leading edge panels might respond to a strike by a large piece of foam and there was uncertainty about exactly where the foam had hit the wing.

During the third MMT meeting of Columbia's mission, held on Jan. 24, Don McCormack, representing NASA's mission evaluation room support team, told Ham engineers had started an assessment of potential tile damage using a program called "Crater."

While the analysis was not yet complete, McCormack said, "obviously thereÕs potential for significant tile damage here, but they do not indicate, the thermal analysis does not indicate that there is a potential for a burn through. There could be localized heating damage. Obviously, there is a lot of uncertainty in all this in terms of the size of the debris and where it hit and angle of incidence and, uh, its difficult..."

"No burn-through means no catastrophic damage and localized heating damage would mean a tile replacement?" Ham asked.

"It would mean possible impact to turnaround repairs and that sort of thing, but we do not see any kind of safety of flight issue here, yet, in anything that weÕve looked at."

"No safety of flight and no issue for this mission, nothing that weÕre going to do different, there may be a turn around (issue)?"

"Right, right, It could potentially hit the RCC and we donÕt indicate, other than possible coating damage or something, we donÕt see any issue if it hit the RCC. Although ... we could have some significant tile damage, we donÕt see a safety of flight issue."

Ham asked him to elaborate - "what do you mean by that?" - and McCormack said the foam could have scooped out a fairly large area of tile on the underside of the left wing. Even so, Calvin Schomburg, a tile expert, reassured the MMT that no burn throughs were expected and the foam strike did not represent a safety of flight issue.

In the process of discussing potential tile damage, Ham and her colleagues never revisited the RCC issue even though there was little or no data presented about how the carbon composite panels would respond to a significant impact. And the impact seen during Columbia's launching was the most significant on record.

After complaints that MMT participants listening in by phone could not hear, Ham repeated that Schomburg, who had no expertise in RCC systems, "does not believe that there is any burn throughs, so no safety of flight kind of issue. It's more of a turn around issue similar to what we have had on other flights. ThatÕs it? All right, any questions on that?"

There were no questions. And with that, any lingering concern about the health of the RCC panels was dismissed.

The foam in question broke away from the left-side "bipod ramp" area of the external tank where two large struts attach the nose of the shuttle to the top of the tank. To keep ice from forming on the struts and falling onto the shuttle, foam insulation is sprayed on the tank and then sculpted by hand to form two aerodynamic ramps, or slopes, at the base of each strut making up the bipod.

Eight-one seconds after Columbia blasted off from the Kennedy Space Center, a 1.67-pound chunk of foam from the left bipod ramp area broke free and slammed into the ship's wing at more than 500 mph. Engineers now believe it hit the leading edge on the lower side of RCC panel No. 8, punching a hole in the panel or causing enough damage to result in breach of some sort.

Recent tests at the Southwest Research Institute in San Antonio, Texas, clearly demonstrated such a breach was possible.

While the details are not known with certainty, engineers believe Columbia re-entered Earth's atmosphere Feb. 1 with a hole of some sort in the left wing leading edge. Sixteen minutes after falling into the discernible atmosphere, Columbia's flight computers lost control of the orbiter and the shuttle broke apart. Commander Rick Husband and his six crewmates were killed.

The foam strike was not discovered until engineers examined launch film the day after liftoff. The first of five mission management team meetings carried out during Columbia's flight was held earlier that day but there was no mention of the foam strike. Three days later, however, during the next MMT meeting on Jan. 21, McCormack briefed Ham and the rest of the team on the issue.

"As everyone knows, we took the hit ... somewhere on the left wing leading edge and the photo/TV guys are completed, I think, pretty much their work, although I know IÕm sure theyÕre still reviewing their stuff and they have given us, you know, approximate size for the debris and approximate area for where it came from and approximately where it hit. So we are, you know, talking about doing some sort of "parametric" type analyses and also, weÕre talking about looking at what you can do in event we really have some damage there. But..."

Ham interrupted, recalling shuttle mission STS-112 the previous October when a large piece of bipod foam fell off and struck one of the shuttle Atlantis' booster rockets. She said engineers should gather data collected in the wake of that launching, and after an earlier mission in which foam had caused damage, "and make sure that, you know, I hope we had good flight rationale then."

"Yeah, weÕll look at that," McCormack said. "You mention 87, you know we saw some fairly significant damage area between RCC panels 8 and 9 and main landing gear door down at the bottom on STS-87. We did some analyses prior to the STS-89 so, uh..."

He was not referring to actual RCC damage, rather to tile damage between the landing gear door and the leading edge just behind panels 8 and 9.

In any case, Ham interrupted again, saying "And really, I donÕt think there is much we can do, so you know itÕs not really a factor during the flight because there isnÕt much we can do about it. But what IÕm really interested in is making sure our flight rationale two flights ago was good. Maybe this is foam from a different area, IÕm not sure..."

Ham was saying, in effect, there was nothing the crew could do about tile damage in orbit. But she wanted engineers to go back and re-visit the rationale for continuing shuttle flights with a known foam shedding problem to make sure the reasoning was valid.

Toward the end of the Jan. 21 meeting, Lambert Austin, representing the shuttle integration team, made one slightly alarming observation, saying the strike that occurred later in the ascent, when the shuttle was moving faster, than what had occurred during the STS-112 launching.

"And higher machs (velocity) is going to be worse," Ham observed.

"Yes, but that, you know the debris impact locations will be different so thatÕs one of the reasons we have ... basically, like you said, give a little bit of parametric set of data to the orbiter (project) so they can decide what the worse-case scenario might be."

"OK," Ham replied.

At the next MMT meeting, on Jan. 24, McCormack reported that engineers believed there was no safety of flight issue based on the initial Crater results. Phil Engelauf, representing the mission operations directorate, told Ham flight directors had informed the crew about the foam strike and sent up a 16-second video clip "just so they are armed if they get any questions in the press conferences or that sort of thing. We made it very clear to them, no concerns."

Then, during the meeting after that - on Jan. 27 - McCormack provided an update, saying engineers still believed there was no safety of flight issue even if the foam had hit a sensitive area around the left main landing gear door.

"We looked at an area about the size of 30 inches by 7 inches, and, of course, you know, sloped, cratered out area, and our results there were similar to what we got elsewhere and that is, although local degradation of the door structure is likely if we were to have sustained a hit there, there is no predicted burn-through and no safety of flight issue."

"A turn-around issue?" Ham asked.

"Yeah, possibly."

"If it were hit there..."

"If it were hit there, itÕs a critical area there on the door, but also the Integration guys had indicated that they thought it was a low probability location but it was still one that we went off and looked at," McCormack said.

"OK," Ham replied.

"So, that completes the thermal analysis from the debris hit and with that, thatÕs all IÕve got."

The foam strike was mentioned a final time during the final MMT meeting on Jan. 30, two days before Columbia's re-entry. Ham wanted to make sure any film shot by Columbia's astronauts showing the external tank and, possibly, the area where the foam broke free, would be quickly extracted from the shuttle and returned to Houston for analysis. The foam issue would have to be addressed before the shuttle Atlantis could be cleared for launch on the next shuttle mission in March.

The astronauts aboard the shuttle Columbia, strapped into a reinforced module built to withstand extreme forces, likely survived a minute or more beyond the commander's final transmission, sources say. Engineers believe the crew died when the module, buffeted by increasingly extreme aerodynamic forces, finally broke open as it plunged steeply into the thickening atmosphere above Texas.

NASA managers and engineers have been reluctant to discuss the presumed fate of Columbia's crew out of deference to family members and because of the inherently morbid nature of such speculation. Speaking privately, NASA sources told CBS News last week the crew almost certainly survived the shuttle's initial breakup, but they spoke on background only and asked that details not be repeated. The New York Times, quoting sources with the Columbia Accident Investigation Board, reported a virtually identical scenario late Tuesday, putting the issue in the public spotlight.

Columbia was destroyed during re-entry Feb. 1 after superheated air burned its way into the ship's left wing through a deadly breach in the wing's carbon composite leading edge panels. The first sign of anything amiss was recorded on board the shuttle at 8:48:39 a.m., just four-and-a-half minutes after Columbia fell into the discernible atmosphere 400,000 feet above the Pacific Ocean northwest of Hawaii.

For the next 10 minutes, the shuttle's flight computers held the shuttle on course despite ever-worsening damage to the left wing. But finally, as the hot air burned its way into the left main landing gear wheel well, Columbia's computers displayed a tire pressure fault message on a cockpit display. The message was generated at 8:58:40 a.m. Commander Rick Husband called mission control at the Johnson Space Center in Houston seconds later, beginning "And, uh, Hou(ston)..." But his transmission was cut off.

A half minute or so later, astronaut Charles Hobaugh in mission control replied, "And Columbia, Houston, we see your tire pressure messages and we did not copy your last."

Moments later, Husband replied, "Roger, uh, buh..." and again, was cut off. He might have been saying "both" or "before," possibly referring to the tire pressure fault messages. He sounded calm, but the signal was cut off, engineers believe, by the orbiter's orientation: Radio transmissions from antennas atop the crew module were blocked by Columbia's tail fin.

In any case, nothing more was heard from the crew. At 8:59:32 a.m., all data from the shuttle suddenly stopped flowing to mission control. An on-board data recorder, however, continued operating, allowing engineers to reconstruct the shuttle's final moments after the recorder later was recovered.

A final two-second burst of downlinked telemetry was captured on the ground beginning at 9:00:02.66 a.m. At that point, the shuttle's left wing, or a large portion of it, was gone and Columbia's left orbital maneuvering system rocket pod showed signs of severe damage. The orbiter was in an "uncommanded orientation," rapidly yawing to one side. The shuttle's aft engine compartment, fuselage, right wing and crew cabin, however, were essentially intact. All three electricity producing fuel cells were operating and the life support system appeared to be functioning normally, although the ship's cooling system had shut down.

By that point, the astronauts clearly knew Columbia had suffered a catastrophic failure. But there was nothing they could do. A bit of telemetry toward the end suggested one of the pilots might have briefly moved his joystick hand controller beyond its neutral, or "detent," position. But Harold Gehman, chairman of the Columbia Accident Investigation Board, implied last week that likely was an inadvertent "stick bump" and not an attempt to take over control.

The final bit of downlinked telemetry from the shuttle timed out at 9:00:04.826 a.m. For the next 13 seconds, the shuttle's data recorder continued to function, drawing power from the fuel cells mounted beneath the floor of the payload bay. Finally, around 9:00:18 a.m., the recorder suddenly stopped as the fuselage broke apart and the electrical system failed.

The reinforced crew module, sources told CBS News, likely survived the breakup intact, much like Challenger's did when that shuttle broke up during launch in 1986. Up until the moment Columbia's fuselage failed, data from the recovered recorder indicates the crew module did not experience any fatal accelerations. How long the astronauts might have survived as the crew module plunged earthward will never be known. Sadly, they almost certainly had time to understand their fate.

The Columbia Accident Investigation Board today released a definitive scenario detailing the doomed shuttle's countdown, launch and re-entry, a scenario that merges all available telemetry from the orbiter, recorded data, debris analysis and complex computer simulations. The result is the most complete picture yet showing how a foam strike during launch punched a catastrophic hole in the shuttle's left wing that led to the ship's destruction during re-entry Feb. 1.

Board member Scott Hubbard also presented additional data from a dramatic test last Monday that lends additional credence to the updated scenario. In the test, a chunk of external tank foam insulation was fired at a wing leading edge mockup at the Southwest Research Institute in San Antonio under conditions that simulated the actual foam strike known to have occurred 82 seconds after Columbia's launching Jan. 1.

Along with blasting a 16-by-17-inch-wide hole in reinforced carbon carbon panel No. 8 - the same carbon composite panel believed to have been struck during Columbia's liftoff - the impact also broke an internal lug fitting and caused severe cracks in the surrounding material.

Hubbard said two large fragments of RCC material were blown into the breach by the impact. Dramatic high-speed camera footage shot inside a cavity behind the leading edge panels showed the fragments blowing inward with extraordinary violence. Hubbard said a similar fragment, having a surface area of 90 square inches or more, is perhaps the best explanation for a mysterious object detected by ground radar systems the day after launch that was seen slowly separating from the shuttle. The idea is a large fragment could have lodged in the breach during launch and then floated free after a day of maneuvering in orbit.

On top of that, cracking similar to that seen around the breach in the wing mockup likely led to debris shedding during re-entry. Amateur shuttle watchers on the ground filmed what appeared to be flaming debris falling away from the descending orbiter well west of Texas. Finally, the broken lug fitting observed after Monday's test would have provided a way for a so-called T-seal between RCC panels 8 and 9 to rock open and closed during entry, providing just the sort of intermittent heating needed to explain heat damage that, until now, had defied explanation.

"The board felt this testing was very, very important because it will help us, it will determine how strong a word we use to equate the foam strike, which we know happened, to the creation of some kind of damage that was pre-existing prior to the entry," CAIB chairman Harold Gehman said Friday. "This allows us now to use a word, which we haven't agreed to yet, but use a word that expresses high confidence, a very high degree of confidence that we have indeed found the cause here."

Board member James Hallock said the actual breach probably was in the six- to 10-inch-wide range. A larger hole would have let so much heat into the wing during the initial stages of re-entry that Columbia probably would not have survived all the way to Texas.

But figuring out the mechanical failure mode is only part of the CAIB's goal. The board's final report, now expected around Aug. 26, will focus just as strongly on management issues and shortcomings.

"We started off with kind of a hierarchy of factors," said Gehman. "We had the direct, mechanical thing and then below that, we had contributing factors. We've now decided that these things are equal. That's why we're being so cautious and so careful about the management sections and the safety sections and all those kinds of things. Because the way the report is going to characterize these things is we have what we're now calling the physical, or mechanical failure, and then we have the systemic failures and we're now giving them equal weight. It would be premature to go much further than that because we're writing that section."

But Gehman made it quite clear the board views the space shuttle as an experimental spacecraft as opposed to an operational vehicle. He has said that before, but today he gave a bit more background on how the board views the shuttle system.

"In the case of an operational vehicle, like a commercial airliner or something like that, the events that you use the vehicle for - takeoff and landing and transporting people and then also the turnaround in between flights - if it's an operational vehicle, you expect each one of these events will be nearly identical and repeatable," he said. "And therefore, it's easy and it's logical and it's prudent to contract that out because you essentially want repeatability, you want the thing to happen exactly the same way each time and you expect the same results each time.

"If, on the other hand, it's a developmental vehicle, your expectation is it will not be the same every time. You are always on the lookout for little, tiny little differences, your suspicious of little tiny little differences and also you demand extraordinarily accurate and intrusive instrumentation so you can detect little variances in how the thing operates.

"And you also don't have an expectation that when the thing lands that you can turn it around and get it back in the air again quickly," he said. "There is no expectation that you can do that and there's no expectation you can do that economically. To me, those are the big differences. I cannot emphasize too strongly how much the board is impressed with how deeply and how broadly the differences translate themselves into practical applications. ... We consider it to be truly significant."

Asked if NASA had to be able to repair RCC holes 16 inches across in order to resume shuttle flights, Gehman said "they have to be able to repair holes in RCC caused by debris."

"If they can't stop the debris, they've got to be able to fix the hole," he said. "If they can stop the debris to where it's tiny little pieces of debris and it causes tiny little holes, then they can have a tiny little hole fixer."

Columbia, of course, was struck with the largest piece of foam debris on record, a 1.8-pound suitcase-sized chunk that broke away from the so-called bi-pod ramp area where one of two large struts attaches the nose of the shuttle to the external fuel tank. NASA engineers now plan to launch future shuttles without any such foam insulation, using heaters instead to prevent ice buildups before launch.

"No shuttle is going to fly with a bi-pod ramp again, so you're not going to see this happen again, I don't think," Gehman said. "And I mentioned this before in press conferences and it's in our interim recommendations, that we view this as a system. NASA has to cut down on the amount of debris that comes off, they have to toughen the orbiter, they have to be able to inspect and repair the orbiter and then they've also got to give the crew a better chance to survive. All four of these contribute to safer operations and no any one of them, in my view, is a fix."

Whether NASA can address all such factors before next summer is an open question. Most insiders still believe NASA will have a hard time launching the next mission before the middle of next summer at the earliest, but agency leaders continue to hold out hope for a return to flight next spring.

While Gehman said he still believes NASA can make the necessary fixes in time for a flight six to nine months from now, he also said "the board is convinced that coming and going into orbit remains an enormously dangerous task."

"And even if you had the world's best engineers and world's best managers working on this thing, there's still a high degree of risk in what we're doing here. It's still not flying in a commercial airliner, it's not like taking a drive in your car. It's dangerous. It's very dangerous, and it will remain that way.

"So under that rubric, you could say that even if we had the best managers and best engineers in the world, you're in a business where something can still cause you to have a tragedy like this.

"On the other hand, when looking into this particular accident, we think we have found some issues, some practices, some managerial, budgetary kinds of things, which we believe could be done better even if we had not had this accident. I mean, if they had (formed) this panel to look at NASA for five months, seven days a week like we have, I suspect we would come up with probably the same set of recommendations even if the Columbia had not been lost."

While the mechanical cause of the accident seems clear, the CAIB report will not be 100 percent conclusive. Engineers simply cannot rule out a space debris impact of some sort or even impact by debris from a possibly faulty "bolt catcher" in the booster-external tank separation system.

As for management issues, Gehman declined to comment other than to toss out a few hints.

"We are not consciously saving up things for the report," he said. "But there are some parts of the report that really we have not said a whole lot about. ... The board is still wrestling with some of the words and some of the findings. That part is not very mature yet. ... And also, you haven't seen all of this written down on one piece of paper yet.

"We've talked about a thing here and a thing there, we've talked about inspections this and quality assurance that and testing of this and these things. But when you see it all written down, the tone may be something we haven't come across yet. ... There may be some news value in the tone of the report."

That might rank as one of the greater understatements of the investigation, which Gehman said likely will cost $15 million to $20 million when all is said and done.

"If you agree with me that we have not perfected, we have not learned everything we need to know yet about routinely going into space and coming back out of space, then even if you have a situation where you have a tragedy like this, your obligation to learn as much as you possibly can," Gehman said.

"And the fact that we've allowed cameras and range instrumentation and on-board instrumentation and all kinds of things like that to kind of gracefully atrophy over the years leads me to bring this issue up that there are some signs that it's been considered a routine operation or an operational vehicle rather than a test vehicle."

In a dramatic test that drew startled gasps from onlookers, engineers fired a chunk of foam insulation at a mockup of a shuttle wing leading edge today, blowing a gaping 16-inch-wide hole in the carbon composite structure and putting to rest any lingering doubts a launch-day foam strike was responsible for the Columbia disaster.

"We believe we have found the smoking gun, we believe we've established that the foam block that fell off the external tank (during Columbia's launching) was, in fact, the most probable cause, the direct cause of the Columbia accident," said Scott Hubbard, a member of the Columbia Accident Investigation Board. "I've now got a direct connection between foam shedding creating a hole that's the same order of magnitude as what must have been there when Columbia came home on Feb. 1."

Eighty one seconds after liftoff Jan. 16, a 1.67-pound chunk of foam insulation broke away from the shuttle's external fuel tank and slammed into the left wing at more than 500 mph. Enhanced video from the one camera that viewed the impact point indicated the foam struck the leading edge at or very near the lower side of reinforced carbon carbon panel No. 8, one of 22 such panels making up the leading edge of the left wing.

But the grainy video, unable to resolve anything smaller than two square feet, provided no direct evidence of actual damage. While most engineers believed the foam strike must have contributed to the breach that ultimately caused Columbia's destruction, they had no proof.

In the wake of the mishap, the Columbia Accident Investigation Board, working with NASA, decided to conduct a complex series of tests to find out whether impacts by low-density foam could, in fact, cause the kind of damage needed to bring down the shuttle. A full-scale mockup of the shuttle's wing leading edge system was built and shipped to the Southwest Research Institute in San Antonio, Texas, where a nitrogen gas cannon was available to simulate the launch-day foam strike.

Initial tests showed foam impacts could cause damage, but the results were not clear cut. Then again, the initial tests involved impacts at RCC panel No. 6, located closer to the shuttle's fuselage. RCC 6 is not as large as panel 8 and does not feature the same complex curvature. For today's test, a foam bullet was fired at the lower side of RCC panel 8, one taken from another shuttle and one with 27 previous flights to its credit.

This time around, the cannon barrel was "clocked," or tilted, 30 degrees to more accurately duplicate the predicted impact energy. The aim point was adjusted to strike the underside of RCC 8 closer to a seal between panels 8 and 9. And this time around, the results were dramatically different.

"There is a huge hole in panel 8!" one observer marveled moments after the test. "It's gone, I mean the foam didn't make it to the back (containment) curtain. You talk about an impact! Unbelievable. If you wanted a smoking gun, you've got it."

Speaking to reporters after the test, Hubbard said high-speed video showed an initial rip that "tears all the way across the panel and produces the hole. The hole is very ragged, about 16 inches by 16 inches, or about 256 square inches. There are a number of pieces that are inside the wing leading edge as well as pieces that fell outside."

One of the enduring mysteries of the investigation has been radar data indicating a piece of debris of some sort separated from Columbia the day after launch. In today's test, the foam essentially blew into the leading edge, pushing large pieces of RCC inside. Based on the size of the breach and the size of the fragments inside the leading edge cavity directly behind the RCC panels, Hubbard said the "flight day 2 object" likely was a large section of RCC 8 that worked its way free in the weightlessness of orbit.

The object seen by radar drifting away from Columbia could "very likely be part of the carbon panel itself," he said.

The foam was fired at the wing mockup at roughly 775 feet per second, or about 530 mph, at an impact angle of 22 degrees. That's higher than the impact angle during Columbia's launch. But by adjusting the impact angle, engineers were able to account for rotational energy imparted by the tumbling foam. Hubbard said the impact imparted about a ton of force to the RCC panel. All of the test parameters, taken together, represented an "average" set of conditions. The actual impact could have been somewhat worse or somewhat less violent. But the hole that was blown in RCC 8 leaves little doubt the foam strike caused the breach responsible for Columbia's destruction.

"I was surprised, I was very surprised," Hubbard said. "As a physicist conducting a test, I feel gratified that after months of work we were able to demonstrate this connection between the foam and the damage. But I know it was a source of tragedy, so that makes me feel very sad. This whole six months, we've constantly been reminded by pictures of the seven lost astronauts what this all means."

The CAIB already has released a preliminary recommendation calling for NASA to obtain spy-satellite imagery of shuttles in flight to look for possible signs of damage. The board also has recommended NASA develop techniques for repairing thermal protection system damage in orbit. Hubbard said today's test shows more data also is needed to understand how carbon composite materials age and react to impacts.

"We need to have better imagery, the shuttle program should have the capability for on-orbit inspection and repair," he said. "We need to realize this is a vehicle that needs to be looked at very carefully each flight. Aircraft, even experimental aircraft, often go through thousands of flights before they're determined to be operational. This vehicle has only 113 flights."

He said engineers are "working to try to determine whether you can do on-orbit repairs of the reinforced carbon. It is the highest temperature area of the orbiter, so finding materials that will patch that are very difficult. I don't know, personally, any way you can patch a hole this big. But that doesn't mean some expert (can't figure something out).

"The RCC has proven to be a very tough material. I think the first step is understanding RCC panels much better and understanding what kind of damage thresholds there are. Where is the dividing point? That database doesn't exist and I think that's one of the first things the shuttle program is going to have to work on."

The commander of the shuttle Columbia was informed about the foam strike most believe led to the ship's destruction in a casual email from mission control a full week after liftoff. Even though NASA's internal analysis of the foam incident was not yet complete, the email dismissed any concern about the strike as "not even worth mentioning" and said the only reason it was being brought up was to make sure the astronauts were not surprised by a question from reporters during upcoming interviews.

As it turned out, no reporters ever asked about the foam strike. But the wording of the email gave commander Rick Husband and pilot William "Willie" McCool no reason to question the conclusion that Columbia was in no danger. And indeed, the commander replied in a light-hearted manner, even making a small play on words and ending an email with a "smiley" - :) - face.

The email exchange was posted on a NASA website today. The full text follows (PAO: public affairs office; MCC/POCC: mission control center/payload operations control center; FD: flight day; chine: area of wing near the fuselage):

Rick and Willie,

You guys are doing a fantastic job staying on the timeline and accomplishing great science. Keep up the good work and let us know if there is anything that we can do better from an MCC/POCC standpoint.

There is one item that I would like to make you aware of for the upcoming PAO event on Blue FD 10 and for future PAO events later in the mission. This item is not even worth mentioning other than wanting to make sure that you are not surprised by it in a question from a reporter.

During ascent at approximately 80 seconds, photo analysis shows that some debris from the area of the -Y ET Bipod Attach Point came loose and subsequently impacted the orbiter left wing, in the area of transition from Chine to Main Wing, creating a shower of smaller particles. The impact appears to be totally on the lower surface and no particles are seen to traverse over the upper surface of the wing. Experts have reviewed the high speed photography and there is no concern for RCC or tile damage. We have seen this same phenomenon on several other flights and there is absolutely no concern for entry.

That is all for now. It's a pleasure working with you every day.

Husband replied to flight director Steve Stich the following day - Jan. 24 - saying "Thanks a million Steve!"

"And thanks for the great work on your part AND for the great poems!" Husband emailed. "I saw the word Chine below and thought it was "China". I guess it's believeable (sic) that you might meet someone from China by the name of Main Wing :)." Mission control uplinked a video of the foam strike Jan. 25 and Husband replied the next day, saying only "thanks for the super work! We appreciate it."

In hindsight, the emails are disturbing because of the remarkably casual manner in which the foam strike, the worst in shuttle history, was dismissed. Other emails that were released after Columbia's Feb. 1 destruction showed mid-level engineers were concerned about potentially severe re-entry damage all the way until the day before landing.

The Columbia Accident Investigation Board now believes the foam strike is the most probable cause of the Columbia disaster.

Eighty-one seconds after Columbia's launching, a suitcase-size chunk of foam insulation broke away from the shuttle's external fuel tank and slammed into the leading edge of the ship's left wing.

The foam strike was discovered during routine post-launch video analysis on Jan. 17. Mission managers promptly ordered an engineering assessment to determine whether or not Columbia's heat-shield tiles had been damaged enough to compromise safety during re-entry. An analysis carried out by Boeing concluded that while possibly severe heat damage to the underlying skin might require post-landing repairs, the impact did not pose a "safety of flight" issue.

The analysis indicated any impact on the reinforced carbon carbon leading edge panels would do little more than mar the coating. As it turned out, the analysis was deeply flawed. The engineers extrapolated from an earlier tile-impact study involving much smaller pieces of debris and had virtually no data at all regarding how such strikes might affect RCC panels. Post-accident analyses, impact tests using a nitrogen gas cannon, enhanced launch video and sensor data all indicated the 1.67-pound chunk of foam, which hit the leading edge at more than 500 mph, caused a breach that allowed super-heated air to burn its way inside during Columbia's re-entry Feb. 1. The wing ultimately failed and Columbia was destroyed.

But NASA's mission management team accepted the results of the Boeing analysis, quashed efforts to obtain spy satellite photography that might have resolved the issue one way or the other and informed the crew about the impact only in passing.

But according to a just-released transcript of internal mission control communications loops, the foam strike, or a debris impact of some sort, clearly was on the minds of flight controllers when the first signs of trouble developed during Columbia's return to Earth. Mechanical systems officer Jeffrey Kling - MMACS - was the man who first informed flight director Leroy Cain about unusual telemetry from Columbia's left wing. Kling, in turn, was backed up by other mechanical systems, or MECH, engineers, including Ken Smith and David Lechner, in a nearby support room.

"What in the world?" one of the MECH engineers wondered when the first sensor data dropped off line.

"This is not funny," Kling replied. "On the left side."

"On the left side," MECH agreed.

Seconds later, at 08:54:24 a.m., Kling informed Cain.

"FLIGHT, MMACS."

"Go ahead, MMACS."

"FYI, I've just lost four separate temperature transducers on the left side of the vehicle, hydraulic return temperatures. Two of them on system one and one in each of systems two and three. To the left outboard and left inboard elevon."

Columbia was passing over the California-Nevada state line at 22.5 times the speed of sound at an altitude of 227,400 feet. Seconds later, observers on the ground noticed a bright flash in the shuttle's plasma trail followed by the sixth known incident of debris falling away from the orbiter.

Kling's discussion with Cain has been posted previously, but the internal dialogue between Kling and the MECH officers sheds a chilling new light on the events of Feb. 1.

"OK, is there anything common to them? DSC (discrete signal conditioner) or MDM (multiplexer-demultiplexer) or anything?" Cain wondered. "I mean, you're telling me you lost them all at exactly the same time?"

"No, not exactly," Kling replied. "They were within probably four or five seconds of each other."

"OK, where are those, where is that instrumentation located?"

"All four of them are located in the aft part of the left wing, right in front of the elevons, elevon actuators. And there is no commonality."

"No commonality."

Kling then spoke to his support room, saying "OK. Keep an eye on the left side. Everything else... looks like the rest of the temperatures are good."

"Yep," MECH replied.

After answering another question from Cain about the systems involved, Kling continued his discussion with the MECH officers, struggling to figure out what might be going on. He apparently was thinking back to the foam strike on the left wing.

"Those are really spread too far apart to be pickin' up... like debris damage or anything to both of em', unless they cut a big swath... have to be two hits," Kling speculated.

"And MMACS, FLIGHT," Cain called.

"FLIGHT, MMACS," replied Kling.

"All other indications for your hydraulic system indications are good?"

"They're all good," Kling said. "We've got good quantities all the way across."

"And the other temps are normal?"

"The other temps are normal, yes sir."

"And when you say you lost these, are you saying that they went..."

"All four of them are off-scale-low," Kling replied.

"... to zero or off-scale-low?" Cain continued.

"Staggered, too," said MECH.

"And they were all staggered, they were, like I said, within several seconds of each other," Kling relayed to Cain.

"OK," the flight director said.

It was 8:58 a.m. Kling then resumed the conversation with MECH. "All the rest of the telemetry as we can see is still looking good."

"Yeah."

"Great," Kling said.

But not for long. At 8:58:48 a.m., Husband called down from Columbia, saying "And, uh, Hou(ston)," but his transmission was cut off. Seconds later, at 8:59:15 a.m., Kling called Cain with more alarming news.

"FLIGHT, MMACS."

"Go."

"We just lost tire pressure on the left outboard and left inboard, both tires."

Husband presumably was calling down to note the main landing gear tire pressure readings. Astronaut Charles Hobaugh, listening in on the flight control audio loop, promptly radioed Columbia to confirm the ground had, in fact, seen the tire data. "And Columbia, Houston, we see your tire pressure messages and we did not..."

"Is it instrumentation, MMACS? Gotta be..." Cain said.

"...copy your last."

"FLIGHT, MMACS. Those are also off, off-scale low," Kling said. Then, speaking again to MECH, he added "I am not believing this."

"No," said MECH.

Seconds later, Columbia broke apart above central Texas.

As expected, the Columbia Accident Investigation Board today released an interim recommendation requiring NASA to develop a capability to inspect the shuttle's heat shield system in orbit and to repair any significant damage that might be found.

The recommendation is the third issued by the CAIB in advance of its final report, expected around July 23, to give NASA as much time as possible to respond and to minimize the downtime before shuttle flights can resume. Two other preliminary recommendations were released April 17. One requires NASA to develop tools for evaluating the strength and integrity of heat-shield tiles and leading edge panels and the other requires NASA to obtain routine on-orbit imagery of the shuttle to look for signs of damage.

A detailed status report covering NASA's ongoing work to develop an on-orbit tile repair capability was posted on this page June 20. Here is the text of today's interim recommendation from the CAIB:

Recommendation Three:

• Before return to flight, for missions to the International Space Station (ISS,) develop a practicable capability to inspect and effect emergency repairs to the widest possible range of damage to the Thermal Protection System (TPS,) including both tile and Reinforced Carbon Carbon (RCC,) taking advantage of the additional capabilities available while in proximity to and docked at the ISS.

• Before return to flight, for non-station missions, develop a comprehensive autonomous (independent of station) inspection and repair capability to cover the widest practicable range of damage scenarios.

• An on-orbit TPS inspection should be accomplished early on all missions, using appropriate assets and capabilities.

• The ultimate objective should be a fully autonomous capability for all missions, to address the possibility that an ISS mission does not achieve the necessary orbit, fails to dock successfully, or suffers damage during or after undocking.

Facts:

• At present there is no certified on-orbit or on-station capability to inspect the orbiter TPS for damage, or to effect repairs.

• Past efforts, some predating STS-1, have not resulted in an operational capacity.

• Changes in imaging and inspection capabilities, materials technology, and the access provided by the ISS have greatly improved the prospects for deploying this capability.

Finding:

An inspection of the TPS, accomplished as soon as possible after achieving orbit/rendezvous, coupled with repair capability, would result in improved safety.

Background:

The Board is convinced of the necessity of taking all practicable steps to Òde-coupleÓ foam insulation shedding from loss of crew and vehicle, including: 1) design improvements to prevent foam shedding; 2) toughening the TPS; 3) improved TPS inspection and repair capability.

An inspection and repair capability is fundamental to improving the ability of the orbiter to experience TPS damage without catastrophic consequences.

This effort does not reduce the urgency or importance of aggressively reducing all sources of potential damage to the orbiter. Only by reducing the likelihood of damage to the orbiter, as well as developing the ability to detect and repair damage, can the maximum safety improvement be realized.

During the STS-107 flight and investigation, the lack of repair capability was cited repeatedly, and may have been a factor in decisions made during the STS-107 mission, including the decision not to seek images which might have assisted in the assessment of damage resulting from the foam strike on ascent.

A member of the Columbia Accident Investigation Board said today, for the first time, that a foam strike during the shuttle's launching is the "most probable cause" of the disaster. He also said analysis of recovered debris indicates a large portion of the ship's left wing broke off in the shuttle's final seconds at the point where the catastrophic breach occurred.

"This is probably the first time you've ever heard me say it's highly probable that the foam is the cause of the accident," said Roger Tetrault. "It's probably the first time you've heard members of the board say it with that kind of strength. We think, when you look at the analysis of all the things that are pointing to the same area in terms of the hole versus where the foam hit, that that's a fairly compelling story."

Columbia's left wing leading edge was struck by a suitcase-size chunk of foam insulation that broke off the shuttle's external fuel tank 81 seconds after liftoff Jan. 16. The foam hit the underside of the leading edge at a velocity of 500 mph or so. Investigators have long believed the foam strike played a role in the disaster, but Tetrault's comments today were the first by a board member to elevate the impact to the level of "most probable cause."

In other developments today, NASA released nearly 10 hours of videotape and still photography shot by Columbia's crew that was recovered in the ship's wreckage over the past several weeks and months. The photography provides no fresh insights into the cause of the disaster, but it no doubt provides sad comfort to family members, giving them one more glimpse of their loved ones as they cheerfully worked through their final days in orbit.

If nothing else, the video put a fresh human face on the disaster and the high stakes involved in the CAIB's efforts to make sure its final report properly addresses the "root cause" of the mishap as well as contributing factors. CAIB chairman Harold Gehman provided an impromptu preview of what that final report will include and said none of the recommendations would, by themselves, prevent NASA from resuming shuttle flights within nine months.

"I don't speculate on the date of return to flight," he told reporters at a news conference. "I would say that having read every word of the draft report and having gone over what might be possible recommendations, I don't see any recommendations which are so difficult to accomplish that they shouldn't be able to return to flight in six to nine months. Other than that, I wouldn't put any numbers on it."

Many NASA insiders believe launch likely will be delayed well into next year, but senior agency officials continue to hold out hope for a flight by the end of the year. One major wild card in all such speculation is what actions Congress might take when it begins considering the CAIB report later this fall.

In any case, Gehman said a "goodly portion of the report, perhaps half, is going to deal with the issue of management and management techniques at NASA."

"We will not tell NASA how to organize, we will not draw a wiring diagram for them," he said. "But we will tell them what we believe are the characteristics of what we believe to be essentially a flight development program that would help ensure safe operations. We won't tell them how to do it, but we will tell them what needs to be done."

By including the phrase "flight development program," Gehman was serving notice that the board views shuttle operations as more of a series of on-going test flights than as any sort of routine, operational program. He said the CAIB report will force NASA to address the issue of foam shedding, debris impacts and on-orbit inspection and repair of possible post-launch damage.

"I believe the report is going to suggest that you have to take action in each of four areas," he said. "First, you have to take action to either minimize or prevent as best you can foam loss and certainly you have to prevent the egregious foam loss, the big pieces.

"But we're also going to suggest you have to toughen the orbiter's ability to take debris hits because the orbiter is going to continue to take debris hits. It was designed not to, but that's now proven to be not the case. So you have to increase the orbiter's ability to take hits.

"You also - number 3 - you also have to improve your ability to recover from a hit," Gehman said. "That means you have to be able to inspect the orbiter after it's launched and if you find something wrong, you have to be able to make emergency, temporary, one-mission repairs in case the first two steps don't accomplish it."

The fourth item on his list was crew escape. While the board will not make any specific recommendations in that area, Gehman said "we're going to comment on how we got to the present status. But whether or not improvements need to be made, we're leaving that to NASA."

An interim recommendation that will require NASA to develop an in-flight ability to repair damage to heat shield tiles and reinforced carbon carbon leading edge panels is nearing completion. Its release has been held up while the board struggles to fine-tune the wording. "We're trying to state what we want to happen, not how to do it," Gehman said.

A detailed overview of NASA's efforts to develop just such a tile repair capability is available in the June 20 CBS News status report posted below.

Tetrault provided a fresh look at Columbia's final moments today, outlining how the shuttle's left wing broke apart in the ship's final seconds. He reviewed earlier evidence pointing toward a breach at or near reinforced carbon carbon panel No. 8, the largest of 22 such panels that make up the left wing's leading edge. The panel is located at the point where the wing's sweep angle changes and as such features a complex, curved shape.

Tetrault briefly reviewed recorded sensor data and the timing of sensor failures as a plume of super-heated air burned its way through wire bundles inside the left wing, both of which indicate a breach at or near RCC 8.

He reminded reporters that very little debris has been recovered from the area of RCC panels 8 through 10. No attachment fittings, known as spanner beams and spar fittings, have been found. No portions of the lower halves of the RCC panels themselves have been recovered. So-called knife-edge erosion, indicative of extreme heating, is present in the few fragments of RCC 8 and 9 that have been found, suggesting the breach occurred at or near the lower half of panel 8.

"The fact that there's such a significant amount of missing material from this particular area is very telling and it certainly in my mind points to a problem between panels 8 to 10," Tetrault said. "And it also points to the fact that we are likely to have burned up much of this material, particularly in the spanner beams and spar fittings from these areas."

He showed a map pinpointing where every piece of recovered wing debris had been found. Interestingly, the tiles found farthest to the west, indicating they fell away early in the shuttle's breakup, were located directly behind RCC panels 8 and 9.

"What that indicates is there was probably a breach somewhere in the 8 to 9 area, the hot gas flowed into that breach, it heated up the inside of that wing, the RTV (adhesive) which holds the tiles to the outside skin of the wing heated up and basically lost its adhesion capability at approximately 400 degrees Fahrenheit and fell off to the west," Tetrault said.

"One of the other important parts are in this area, we have a number of tiles which have a light brown deposit on them. And we've taken some preliminary chemical analysis of that light brown deposit. And what we find out from that preliminary analysis is that deposit is high in iron and it's also high in nickel.

"You may recall the spanner beams which hold the RCC, which appear to be missing, are, in fact, high in nickel," he said. "And the spar fittings, which hold the panels to the spar itself, are stainless steel, so they would be high in iron. What you can surmise from that, in fact, is the hole was somewhere in the 8 and 9 area and as the airflow was flowing in, some of this molten material from the spar fittings and from the spanner beams was in fact being deposited on the lower side of the wing. And that's what we're seeing when we do the chemical analysis."

He reminded reporters that so-called "knife-edge" erosion patterns were found on what few pieces of RCC 8 and 9 material that were recovered, indicating the flow of extreme heat from 8 toward 9. He said unusual slag deposits found on the interior surface of fragments from the upper half of RCC 8 showed high concentrations of nickel, "again indicating one of the first things to melt inside the wing leading edge after the breach occurred were the spanner beams."

The spherical slag deposits indicate molten material was splattered back on the inner surface of the panel from a breach on the lower side of RCC 8.

Showing a plot of recovered wing debris, Tetrault said debris from RCC panels 8 through 22 were found farther west than any other fragments from the left wing leading edge. Next came fragments of RCC 1 through 7, then debris from the shuttle's vertical stabilizer and finally, wreckage from the right wing.

"What this suggests is that at breakup, what we first saw was the left wing or a portion of the left wing left the aircraft, fell to the ground, followed by the tail, followed by the right wing," Tetrault said. "What's really important in all of this, when you look at the left wing it's a very long (debris) stream.

"What we believe happened is somewhere in this area a portion of the left wing came off," he said. "A portion of the left wing continued to ride with the aircraft downstream and that would have contained panels 1 through 7. And at some point later on, panels 1 through 7 began to come off the aircraft, we believe it probably ablated (melted) as much as fell off, that the pieces were just open to the airstream.

Interestingly, fragments of panel 8 were found in widely separated areas.

"That begins to indicate to us that, in fact, the breach, not only the breach but also the wing, broke apart at panel number 8 region," Tetrault said. "Otherwise, you wouldn't have those pieces strewn over that lengthy piece of territory. So those are the indicators that we have from the debris.

"I think when you look at it you could probably conclude from the debris alone that the most likely breach that we had in the wing occurred at panel No. 8 or in the vicinity of panel number 8. ... I would also include the T-seals on either side of it. So we feel fairly certain on where the breach was."

As for exactly how the left wing came apart, Tetrault said investigators don't yet known whether "half the wing that came off at area 8 or just the leading edge of half the wing."

"I think the prevailing theory right now is it was more than likely the leading edge of wing (that came off) and heavy spars held for some period later. But if you lost the leading edge, you would lose the RCC panels from 8 through 22."

Looking at all the data and how they fit together, Tetrault said, "they certainly are pointing us to the area of RCC panel 8 as being an indicator of where the breach occurred in the wing. Not only that, but as you well know we have the photographic analysis and evidence that indicates the foam struck on panels 6 through 9. And when you put all of those pieces of Swiss cheese together, it's a pretty compelling story that, in fact, the foam is the most probable cause of the shuttle accident."

Gehman said the full board has yet to decide on what terminology will be used in the panel's final report. But a final round of tests at the Southwest Research Institute in San Antonio, Texas, could go a long way toward determining how strongly the board links the foam strike to Columbia's destruction.

Using a powerful nitrogen gas cannon, researchers have been firing foam debris at a wing leading edge mockup to determine whether a strike like the one observed during Columbia's launching could actually break one of the carbon composite panels or an associated T-seal. A test shot at RCC panel No. 6, taken from the shuttle Discovery, resulted in multiple cracks and showed the impact forces were transmitted to adjacent panels and T-seals. Just as important as showing cracks were possible, the impacts showed the leading edge components responded to the impact as an integrated system.

But panel 6 is smaller than 8 and does not have the same complex curvature. As a result, CAIB member Scott Hubbard has decided to shoot at RCC panel 8 from the shuttle Atlantis. Adjacent panels and mounting hardware also will be flight articles.

"The thing that I'm trying to do with these tests, and I think the board is looking at this information as a piece of that most probable cause, is to connect that dot, from foam to breach," Hubbard said today. "So that's where I stand. I think the panel 6 tests that we did showed that we've got a plausible failure scenario, we created a substantial crack, five inches long, but we haven't created yet a breach that is like what has been described by the debris.

"Maybe I'm one step behind Roger in coming to a conclusion, but as Admiral Gehman said, that's part of our discussion here."

Gehman said the board will have to decide "what words we want to use when we describe the degree of certainty we use to say the foam caused damage to the leading edge of the left wing. Do we want to say we 'think' it did, we're 'sure' it did, it 'might have,' we think 'most likely' it did, the board is 'confident that?' I have 13 different opinions on that and at some time I'm going to have to lock everybody in a room and come out with one set of words."

Shuttle engineers believe the tools and techniques needed for spacewalking repair crews to access and patch areas of potentially catastrophic damage to an orbiter's heat-shield tiles will be in place by the end of the year.

Major challenges include development of reliable techniques for inspecting a shuttle for damage, gaining access to all possible damage sites and perfecting the tools and materials needed to actually patch over cracked, eroded or missing tiles. But so far, engineers have not identified any show-stoppers, sources say, at least for shuttle missions bound for the international space station where access is less of an issue.

But techniques for repairing damage to a shuttle's wing leading edge panels pose a much more difficult challenge and likely will take longer to develop. A breach in the leading edge of the shuttle Columbia's left wing led to the ship's destruction during re-entry Feb. 1, allowing a plume of super-heated air to burn its way into the wing's interior.

NASA has studied in-flight tile repair options in the past and is drawing on that background now to develop a workable repair technique for future flights. But no previous efforts were undertaken for the shuttle's carbon composite nose cap and wing leading edge panels, which are made of different material, feature complex curved surfaces and experience the most extreme temperatures during re-entry.

The panels play a critical role in the creation of a so-called boundary layer as the shuttle plows through the region of maximum heating. The boundary layer provides a natural insulating effect, limiting entry temperatures to "just" 3,000 degrees or so. Any repair option would have to not just plug a breach but also ensure the smooth airflow needed to set up an insulating boundary layer.

Analysis of a dozen or so possible RCC repair options and materials is underway, sources say, but testing is in its early stages and a final solution is far from clear.

Even in the case of tile repair options, engineers have not yet settled on what sort of caulk-like patch material is best suited for repairing broad areas of tile damage. Issues include the viscosity of the material, which astronauts must be able to apply and then spread or mold to some degree, and the time needed for any such material to cure, or "set up." Engineers currently are testing a silicon-based compound similar to one developed in the late 1970s as part of a tile repair technique that was never implemented.

Tests also will be required to ensure any such material can stand-up to worst-case re-entry temperatures and conditions.

The Columbia Accident Investigation Board is expected to recommend that NASA develop capabilities for on-orbit repair of tile and reinforced carbon carbon (RCC) leading edge panels. The board's final report is expected around the end of July. But NASA is not waiting for the final report or even any interim recommendations to begin developing a repair capability. A "tiger team" under the leadership of space station flight director Paul Hill at the Johnson Space Center in Houston has been in place for months.

A request for an interview with Hill was turned down by Michael Kostelnik, deputy associate administrator for the shuttle and space station programs at NASA headquarters, on the grounds that any such discussion is "pre-decisional" and that no final decisions have been made. The real issue, however, appears to be a general reluctance on NASA's part to publicly address any topic the CAIB might discuss in its final report or any interim recommendations that might be released between now and then.

Even so, a broad outline of NASA's on-orbit repair strategy has emerged in recent weeks that focuses on four general areas:

• Defining the critical damage size, i.e., the damage threshold that would trigger some sort of spacewalk inspection and/or repair attempt
  
• Techniques for inspecting a shuttle for damage
  
• The materials and tools needed to repair damage
  
• The spacewalk access required to implement any such repairs
  

For the purposes of this discussion, it is assumed any inspections and repairs would be staged at the international space station. Only one non-station flight is currently on the books - a mission to service the Hubble Space Telescope - and it's not yet clear how inspections or repairs could be carried out in the absence of the space station's robot arm, multiple EVA anchor points and numerous external cameras. The Hubble flight, however, is several launchings down the road and engineers will have more time to develop viable "stand alone" repair techniques.

In the near term, shuttle missions to the space station will be launched in daylight to give engineers a better chance of spotting debris impacts that might damage an orbiter's thermal protection system (TPS). In addition, mission managers likely will require external fuel tank separation in daylight as well, to improve the odds of spotting any areas of foam shedding in orbit. Given those two requirements alone, and the orbital mechanics required to rendezvous with the space station, the number of possible launch days in a given month will be sharply reduced.

In any case, the TPS damage threshold is believed to be roughly a quarter of an inch for an RCC wing leading edge panel, a half-inch or so for the RCC nose cap and 1 inch around critical seals in the thermal protection system. It's not known what powerful spy satellites might be able to detect, but approaching shuttles will perform a pirouette 400 to 600 feet below the station to give lab crews a chance to photograph the orbiter's underside.

Tests indicate pre- and post-docking photography, by the crew and by cameras on the shuttle's robot arm and the mobile Canadarm2 spacecrane attached to the space station, should provide the coverage needed to spot any significant damage. But determining the depth of any tile damage - a critical factor - might not be possible without a spacewalk inspection or the development of some sort of laser scanner.

The materials and tools need to carry out a TPS repair in orbit are based on an existing "cure-in-place" ablator compound that would be applied by a spacewalking astronaut using a sort of high-tech caulk gun. Tests are planned later this summer during flights aboard a NASA aircraft that provides brief periods of weightlessness. Sources say other tests are planned to determine vacuum cure times and temperature limits.

Different materials and application techniques are being developed for RCC damage but details are not yet available.

The most significant challenge, perhaps, is figuring out how to anchor a spacewalker in the weightlessness of orbit to apply the patch material and, depending on the situation, smooth it out or shape it.

One possibility under consideration is using the shuttle's robot arm to lock onto a grapple fixture on the space station and then, after docking latches are released, to properly position the orbiter. Spacewalkers then would ride the station's robot arm to the actual repair site.

An engineering analysis indicates the shuttle's robot arm is strong enough to move the 120-ton space shuttle, but a telescoping boom of some sort may be needed to extend the reach of the Canadarm2 to all possible damage sites. A similar boom is being considered for use by the shuttle arm during non-station missions.

Engineers initially considered the possibility of astronauts using small jetpacks, known as SAFERs, to reach possible damage sites for repair work, but that no longer appears feasible. The backpacks could, however, be used under certain conditions for initial inspections to determine the severity of any damage.

NASA is considering five options for redesigning the so-called "bi-pod" ramp on the shuttle's external fuel tank, the area where a chunk of foam insulation broke away during Columbia's launch, hit the left wing and possibly caused a catastrophic breach. The currently favored option calls for eliminating the use of foam in the area in favor of an exposed fitting equipped with heaters to prevent pre-launch ice buildups.

Senior NASA and contractor managers and engineers met Tuesday and today in Michoud, La., where Lockheed Martin Space Systems Co. builds the external tanks, to review the bi-pod redesign options in preparation for making a final selection in the next few weeks. While most observers believe NASA will not be able to resume shuttle flights until well into 2004 at the earliest, senior agency managers say they believe launchings could resume as early as mid-to-late December. In any case, engineers plan to have the bi-pod fix in place as soon as possible, eliminating what many believe was the initiating event in the Columbia disaster.

"Clearly, there's been a lot of focus on the foam, the bi-pod foam in particular, and our redesign efforts have been ongoing in that particular activity for a couple of months already," Michael Kostelnik, NASA's deputy associate administrator for shuttle and space station, told reporters today. "We will solve the shedding problem of foam in that particular area and our technical plan for that allows us a return to flight window in December."

The external fuel tank forms the structural backbone of the shuttle "stack" for the climb to space. Solid-fuel boosters are attached on each side with massive explosive bolts while the shuttle is attached by fittings under its nose and engine compartment. The aft end of the shuttle is attached with massive fittings where 17-inch propellant lines from the external tank feed into the ship's aft engine compartment. The nose is attached by a so-called bi-pod, two cylindrical struts that meet at a single attachment plate just behind the nose landing gear doors. The struts attach to a pair of fittings on the external tank, forming a triangular bi-pod assembly.

At launch, the tank is loaded with a half-million gallons of supercold liquid oxygen and liquid hydrogen rocket fuel. From the beginning, the bi-pod strut attachment fittings have been buried in hand-sprayed foam insulation to prevent ice from forming around the aluminum fittings. Any such ice likely would break away when subjected to the vibration of launch, posing an impact hazard to the underside of the shuttle. The foam covering the bi-pod fittings is hand carved to form an aerodynamically benign ramp allowing the smooth flow of air over the protrusions.

As it turns out, the bi-pod ramp prevented ice buildups but created another impact hazard: The foam itself.

A suitcase-size chunk of foam from Columbia's left bi-pod ramp area pulled free during launch Jan. 16 and struck the left wing's leading edge at some 500 mph. The foam strike presumably caused the breach that led to the ship's destruction during re-entry Feb. 1. Another large piece of foam broke away from the same area during an October shuttle flight and hit a booster. All told, investigators have identified at least six missions, and possibly seven, in which large pieces of foam debris fell off the bi-pod ramps of the external tanks.

It is not yet clear what causes the foam to break away. Many engineers believe some form of "cryopumping" may be involved, in which trapped air in the foam liquifies after the tank is chilled during fueling. In this scenario, heating during ascent causes the trapped liquid to warm and expand, weakening the foam in that area. But recent tests by the Columbia Accident Investigation Board indicate cryopumping alone is not the answer and that some combination of factors may be responsible.

In any case, there is little doubt the CAIB's final report, expected in late July, will include a recommendation to redesign the bi-pod attachment system to preclude foam shedding in the future. In the meantime, NASA is pressing ahead with work to do just that.

Of the five options currently on the table, the favored solution, known as option 2a, is one in which the aerodynamically shaped foam ramp is eliminated entirely in favor of an exposed fitting equipped with one or more heaters to eliminate the possibility of pre-launch ice buildups. Aluminum end covers and caps would be replaced with tougher Inconel covers. Other changes include the addition of wiring for the heaters and additional electrical power from ground-support equipment prior to liftoff.

Other options include:

• Option 1: Reduced volume ramp with a minimum 50 percent reduction in the amount of foam required; aluminum end covers replaced by super lightweight ablator material; new heater elements and wiring.

• Option 2: Partially exposed fitting with an 80 percent reduction in foam ramp volume; Inconel end covers and caps; new heater and wiring.

• Option 3: Inconel fairing over the entire bi-pod fitting, eliminating need for a foam ramp. Strip heaters would be attached to the interior of the welded fairing. This option was an early favorite.

• Option 3A: Small Inconel fairing, equipped with strip heaters, that covers the central shaft of the bi-pod fitting. No ramp foam is required.

Agency managers, with input from the Columbia Accident Investigation Board, hope to settle on a redesign option in the next few weeks.

Accident investigators have stumbled on a potentially catastrophic shortcoming in the explosive bolt attachment system used to latch a space shuttle's boosters to its external fuel tank. While there is no evidence Columbia was struck by falling debris from a faulty "bolt catcher" during its launching Jan. 16, corrective actions almost certainly will be required before shuttle flights resume.

Members of the Columbia Accident Investigation Board said today a foam strike during launch remains the most plausible explanation for the breach in the shuttle's left wing leading edge that ultimately doomed the orbiter and its crew during re-entry Feb. 1. One of the more intriguing aspects of the failure scenario is the rapidity with which a plume of super-heated air managed to eat its way inside during the first moments of Columbia's descent into the discernible atmosphere.

The accident board today released dramatic video of a test using an 8,000-degree arc jet that vividly illustrates just how fast a small breach can deteriorate into a gaping hole. Engineers fired the jet of super-heated air at a circular one-inch-wide hole in a strip of aluminum representing a wing spar, the metal structure directly behind the carbon composite panels making up the leading edge. Like a match flame burning through tissue paper from below, a one-inch hole in the plate grew to six inches across in just 20 seconds. The plume also burned through a thick wire bundle in less than one minute, in generally good agreement with the way the plume that burned into Columbia's wing quickly ate through sensor wiring once inside.

"It's really very impressive. You cannot imagine the destructive power of the gases that would flow in through that hole," said Douglas Osheroff, a Nobel laureate in low-temperature physics and a member of the accident board. "It's really pretty scary to see."

During a normal shuttle entry, the maximum temperatures experienced by the wing leading edges and the ship's carbon composite nose cap is 3,000 degrees. The temperature is moderated by the way air smoothly flows across the skin of the shuttle, setting up what is known as a boundary layer that acts as an insulator of sorts. But in a breach, no such protection exists and temperatures can soar much higher, "so hot that in fact the oxygen molecules are split into individual atoms," Osheroff said. "That makes them much more highly reactive."

"It was just very impressive to see how quickly that kind of an atmosphere, simulating as best they could the conditions on re-entry, would slice through aluminum in particular," he said. "It was just absolutely amazing."

Osheroff is the second Nobel prize winner to sit on a shuttle accident board. Richard Feynman served in that capacity for the 1986 Challenger disaster, performing a memorably simple experiment during an early hearing that showed how booster O-ring seals are affected by cold weather. He dipped a small O-ring into a glass of ice water, held it up and showed how it had stiffened, a characteristic that would have reduced a real O-ring's ability to work properly during cold weather. Challenger, of course, was destroyed by an O-ring seal failure during launch in cold weather.

Today, Osheroff discussed a modest experiment of his own, carried out in his kitchen with about $100 in equipment, that suggests NASA has never understood the mechanism responsible for external tank foam shedding. It also suggests, to borrow a phrase from Apple Computer, that Nobel prize winners "think different."

"I became rather rapidly interested in the properties of this foam," said Osheroff, a Mac user. "It's really fascinating stuff. It's highly anisotropic, that is to say it's mechanical properties depend upon which direction you squeeze it, for instance. So I decided to do some experiments on the foam."

Osheroff, with the help of a graduate student, had a metal plate machined to serve as a stand-in for the skin of the external tank. He then glued a cube of BX-250 to the plate, a sample of the same type of foam that came off Columbia's tank. A small hole in the plate allowed him to apply pressure at the interface between the foam and the metal.

"The idea was to try to understand, as I increased the pressure, how ultimately this resulted in some sort of a fault that propagated through to the surface," Osheroff said. "This is important because for many years, people at NASA assumed, in fact, that one of the main mechanisms for foam shedding from the external tank was that liquid nitrogen (from trapped air) would somehow condense in a void or something inside the foam near the metal surface. And as you started getting aero heating (during launch), this liquid nitrogen would warm up, pressure would build up and it would throw foam off of the external tank.

"What I found was that, in fact, the mechanism by which the liquid expands is not consistent in any way with ejection of foam from the surface. What it does, it tends to make a two dimensional, rather flat crack or fault, which propagates up to the surface and it meets the surface normal to the surface in almost every case. This has to do with anisotropic properties of the foam."

Translation: Expanding gas in a pocket, or void, near the ultra-cold skin of an external tank produces linear surface cracks in the foam, it doesn't blow out the overlying material. In addition, calculations show heating due to atmospheric friction would not have had time to turn any pockets of liquified air into a gas by 81 seconds into flight.P> "That's less than 30 seconds into aero heating," Osheroff said. "Is it possible for the heat to propagate through the foam and actually boil off the liquid nitrogen that might have condensed in that brief period of time? ... The thermal relaxation times are much too long for that."

"So the conclusion I have reached, and that independently the people at Marshall Space Flight Center have reached, is that the process by which foam is ejected is undoubtedly a very complex one involving more than just cryo condensation and ejection.

"I dare say, in fact, that these sorts of experiments which I have done, which were actually done in my kitchen at home for about a hundred dollars, are the sorts of things I think we need to see more of done. Specifically, experiments to try to understand the physical mechanisms (behind) why the foam behaves the way it does."

In a revelation that generated quite a bit of media interest, board member John Barry revealed investigators are looking into apparent problems with the system used to capture and restrain pieces of the exploding bolts used to hold a shuttle's boosters to its external tank during launch.

The boosters separate two minutes and five seconds or so into flight when explosive charges cut the massive 80-pound bolts in half. The upper half of a bolt is blown upward and captured in the dome of a fully enclosed "bolt catcher" assembly on the tank. The bottom half is captured by a bolt catcher on the booster.

The bolt catchers are designed to prevent any debris from a blown bolt from getting into the airstream and possibly impacting the shuttle.

"The problem we found was the original certification was done without the real flight hardware in 1979," Barry said. "The other thing we found out, this bolt that was used in STS-107 (Columbia) was done with a new vendor and the NDE, the non-destructive evaluation, wasn't done as well as it should have been.

"They did some bolt static tests that resulted in this dome fracturing at a lower pressure than was anticipated," he said. "In fact, it was below a 1.4 safety margin. So this dome is made of aluminum and covered with ablative. If that comes loose, with or without that half of the bolt in it, it still can cause some serious risk to the orbiter. So this is a possible return to flight issue that we're examining."

Complicating the picture, radar data from Columbia's launching shows unidentified debris separating from the shuttle 126 seconds into flight, right about the time of booster separation. Debris has been seen on radar during past missions, presumed chunks of ice, for example, and there is no evidence the debris seen during Columbia's flight involved the bolt catcher. Certainly there's no recorded data or telemetry from Columbia suggesting any kind of an impact 126 seconds into flight.

But engineers cannot rule out the possibility debris may have been released into the airstream.

"What we have here is a possibility that we have found another source of debris," said CAIB chairman Harold Gehman. "We don't have any evidence that it was a source of debris except the radar tracking of the Columbia indicated that at the time of SRB separation, 126 seconds, at a time when there's not supposed to be any debris, it noticed a piece of debris. We don't know what that was."

He said engineers are trying to determine if a bolt catcher failure could "create any debris which might fall back on the wing?"

"We're just at the front end of this and we're not ready to make any statements about how this affects the process. The question, then, is we have a potential piece of debris here now. Or in a future flight. But in this particular case, STS-107, it's a potential that we've got a piece of debris.

"Then we go back to the radar of the launch. ... And lo and behold, at 126 seconds after launch, at the time of SRB separation, something is seen on the radar which indicates that there's a piece of debris ejected from the separation. It could be the bolt catcher. We can't prove that. But in an effort to positively close out the fault tree - and you multiply this times a thousand - you can see why this investigation has taken five months. So here's one we can't close out."

But he and other board members downplayed the possibility that a 40-pound bolt fragment could have hit Columbia without being detected by the shuttle's myriad sensors. The real issue is fixing the problem before flights resume.

"There's no indication, in either the (recorded) OEX data that we know about or any of the telemetry, that something hit the wing past 120 seconds," Barry said.

"What we're trying to couch here is it's very important that we understand all potential debris. We're not changing our working scenario, it's still pretty evident foam came off and hit the wing. But we also have to take into consideration any other future debris elements that could be potentially catastrophic to the orbiter."

Engineers studying the effects of a foam impact test today that cracked a shuttle wing leading edge panel found a second crack late this afternoon. The initially observed crack, in reinforced carbon carbon panel No. 6, measured about three inches long. The second crack was found in a so-called T-seal between RCC panels 6 and 7. The dimensions of the second crack were not immediately available.

The 6:45 p.m. status report below has been updated to reflect the presence of the second crack.

The final report of the Columbia Accident Investigation Board will go far beyond identifying the most probable cause of the Feb. 1 shuttle disaster. According to a draft outline of the 10-chapter report, the board will provide a contextual history of the shuttle program, a review of the engineering tradeoffs and budget issues that resulted in the shuttle's current design and operation as well as a critical evaluation of the NASA management practices.

A source close to the investigation said today the draft outline, currently in revision 6, is a "work in progress" and that additional revisions are expected. But in its current form, the outline provides the following breakdown:

• Chapter 1: Evolution of the Space Shuttle Program. A comprehensive overview of the early history of the shuttle, design tradeoffs, the Challenger disaster and how NASA operated the shuttle system in the post-Challenger environment.
  

• Chapter 2: Columbia's Final Flight. An overview of pre-launch and launch preparations and events, a discussion of the mission objectives and a review of "notable pre-launch conditions" such as the causes of launch delays, the amount of time Columbia spent on the launch pad and security issues related to the presence of Israeli crew member Ilan Ramon. Chapter 2 also will discuss on-orbit events such as the separation of a mystery object on flight day 2, re-entry events including the shuttle's destruction, NASA's response to the crises, the establishment of the CAIB and debris recovery.
  

• Chapter 3: The Proximate Causes of the Accident Sequence. Beginning with a review of the proximate cause of the disaster - presumably a foam strike on the left wing's leading edge - Chapter 3 will review the CAIB's impact analysis, issues involving external tank foam application and in-flight shedding as well as a discussion of the performance of the shuttle's leading edge systems. The chapter also will deal with the re-entry sequence, walking through a detailed timeline based on telemetry, recorded data and debris analysis that leads to a most probable failure scenario.
  

• Chapter 4: Beyond the Proximate Cause. As board chairman Harold Gehman has repeatedly promised, the final report will go far beyond identifying the most probable cause of the accident. In Chapter 4, the board will lay out NASA's organization policy and budget factors, including the influence of Congress, the White House and past NASA administrators "on the ability of the space shuttle team to manage the shuttle program," the source said. The analysis will include a review of the Challenger disaster and policy changes in the aftermath, an overview of NASA's efforts over the years to privatize the program or at least turn over segments of it to private industry and an evaluation of NASA's safety and mission assurance program. Other issues include the effects of moving shuttle program management from the Johnson Space Center back to NASA headquarters in Washington.
  

• Chapter 5: Factors that Contributed to the Loss. This chapter focuses on a discussion of contributing factors, everything from vulnerability in the original shuttle design to eroding safety margins and what sociologist Diane Vaughan calls the "normalization of deviance," the slow acceptance of problems, like foam shedding, as normal events after repeated flights with no major difficulties. The chapter will deal with the "signals that were coming from the orbiter and what actions NASA took to detect those signals," the source said. This chapter also will focus on the performance of NASA's mission management team and will outline the results of a study on whether the wing damage could have been repaired in orbit or whether NASA could have mounted a rescue mission of some sort.
  

• Chapter 6: The Accident's Underlying Causes. An evaluation of NASA's organizational culture and performance. This chapter will review literature outlining how other high reliability organizations - like off-shore oil rigs, aircraft carrier flight decks, nuclear submarines and reactors - deal with safety and look at how NASA's safety organization works.
  

• Chapter 7: A Look Ahead. The implications of the accident on the future of the shuttle program and U.S. space policy in general. The chapter includes sections on the conditions necessary for a return to flight. The board won't designate "what kind of bolt needs to be used or that sort of thing," the source said, rather it will focus on goals and safety issues in general. The source said it will identify issues that need to be resolved, like the effects of shuttle aging, operational costs and long-term upgrades or modifications that might be required.
  

• Chapter 8: Other Significant Observations. Issues not directly related to the accident, but potential problems that need to be addressed. Lapses in flight controller certification, for example, fall into this category.
  

• Chapter 9: Findings and Recommendations. The draft outline does not yet include any actual recommendations beyond those already announced by the CAIB. But the final report will include a requirement for a detailed follow up to make sure the recommendations are implemented. NASA has already set up an independent panel under former astronaut Thomas Stafford to do just that.
  

• Chapter 10: The CAIB Investigation. The final chapter will provide documentation on how the board was established, expanded and operated.

"The board is looking at this as a pretty thorough look at what happened, and not just the immediate technical issues," the source said. "Nothing in the report is secret. (The outline) is a pre-decisional document and it's not the final version. (But) I think the report is consistent with the admiral's public statements."

The report will be released in late July in Washington, in book form and on CD-ROM. The CD will include a variety of graphic presentations and video clips to support the board's conclusions.

In a potentially significant breakthrough, engineers fired a 1.7-pound chunk of foam insulation at shuttle wing mockup today, visibly cracking a leading edge panel in a test that strongly supports the widely held hypothesis that a foam strike during Columbia's launch doomed the orbiter and its crew.

With a throng of reporters, engineers and a member of the Columbia Accident Investigation Board looking on, a powerful nitrogen gas cannon at the Southwest Research Institute in San Antonio, Texas, fired the box-shaped foam "bullet" at a mockup of a shuttle wing leading edge at a blistering 523.7 mph (768 feet per second). The foam hit a reinforced carbon carbon - RCC - panel taken from the shuttle Discovery. The foam instantly disintegrated in a shower of debris reminiscent of the powdery debris that fell away from Columbia.

From a viewing site 50 yards away, no cracks or other obvious signs of damage were evident. But a close-up inspection revealed a three-inch long crack in the panel through an interior rib. The crack penetrated the panel and high-speed cameras mounted inside the leading edge cavity showed foam fragments blasting into the interior. The force of the impact jammed the inboard side of the panel up against a T-seal between RCC panel 6 and a Fiberglass panel in the inboard No. 5 position and widened the gap between the outboard side of RCC 6 and the T-seal between panel 6 and 7.

Late this afternoon, engineers discovered a second crack in the T-seal itself, near the location of the RCC crack. no dimensions were immediately available.

While today's test doesn't prove the foam lost during Columbia's launch was the initiating event of the disaster, it's the best evidence yet a foam strike could have been, in fact, the root cause.

"This is the first evidence that we've had that a piece of foam that approximates what was observed in the accident can, in fact, crack and damage a piece of flight reinforced carbon panel," said CAIB member Scott Hubbard.

But Hubbard would not speculate on whether damage similar to what was seen today could have led to Columbia's destruction.

"The obvious question one asks is what does this mean in terms of the thermal and structural characteristics and at this point, it's simply too early to draw a conclusion," he said. We've got a couple of the world's experts in RCC and structures over here and they're scratching their heads and trying to figure out what this might mean. As you saw, the response of this is quite different than the response of the Fiberglass."

He was referring to a test last week in which foam was fired at a Fiberglass leading edge panel taken from the prototype shuttle Enterprise. In that test, the impact caused visible shock waves to ripple across the structure, pushing the outboard T-seal out of place and leaving a large gap between the seal and the edge of the target panel.

"Given that the response of the Fiberglass was so dramatic, I think many of us felt there was going to be something perhaps equally dramatic (today)," Hubbard said. "But as I've said, this is why you do the experiment. Drama, of course, wasn't the point of the test, although reporters made friendly wagers on its outcome. As Hubbard pointed out later, the Fiberglass shot, while dramatic, did not cause any cracks or other major damage.

"We didn't show any damage at all on the Fiberglass," Hubbard said. "We had a lot of movement and a lot of high stresses, but here we demonstrated for the first time that foam at the speed of the accident can actually break RCC.

"To me, that's a step forward, maybe a significant step forward in our knowledge."

Eighty one point seven seconds after the shuttle Columbia's liftoff Jan. 16, a suitcase-size piece of foam insulation broke away from the ship's external tank. Columbia was traveling at better than twice the speed of sound at the time - 1,568 mph - and the foam underwent a sharp deceleration when it fell into the airstream. Even so, engineers believe it slammed into the lower side of the left wing's leading edge at some 775 feet per second, or 528 mph while tumbling at 18 revolutions per second.

Columbia was destroyed during re-entry by a breach in the lead edge of its left wing. Analysis of sensor data and evaluation of recovered debris indicates the breach occurred on the lower side of reinforced carbon carbon panel No. 8, one of 22 U-shaped heat-resistant panels making up the leading edge of the wing.

Detailed analysis of launch day footage indicates the external tank foam hit at or very near RCC panel 8. But in the absence of any hard data, investigators have been unable to make a direct connection between the foam strike and the failure.

To find out if foam is at least capable of causing enough leading edge damage to result in a catastrophic breach, the Columbia Accident Investigation Board and NASA, working with the Southwest Research Institute, decided to fire foam bullets at a leading edge mockup in an attempt to duplicate the failure mode. While such tests cannot prove the hypothesis, they can at least show whether it is possible and thus help confirm or rule out various scenarios.

The nitrogen cannon normally is used to fire gel-filled "chicken simulators" at aircraft components to study the effects of bird strikes. For the shuttle tests, a heavily instrumented leading edge mockup was built at the Johnson Space Center and shipped to San Antonio. The mockup includes RCC panels 5 through 10 as well as the T-seals between each panel that effectively lock them in place.

The tests were designed before engineers pinpointed the general location of the breach. As a result, RCC panels 6 and 9 were taken from Enterprise to "bracket" all possible breach locations. For today's test, the foam was fired at RCC panel 6. Upcoming tests will aim at panel 9, both a Fiberglass stand in and the real thing.

For today's experiment, all of the leading edge panels but one - RCC-6 - and all of the T-seals except the one between panels 6 and 7 were made of Fiberglass. Real T-seals and RCC panels, valued at some $800,000 each, are considered too valuable to be risked in any but the most significant of tests. Only one complete "ship set" of spare RCC panels is available, along with the panels already in use by the shuttle's Discovery, Atlantis and Endeavour.

As a result, the first test last week involved firing foam at a Fiberglass panel in the No. 6 position. At least four such firings were planned, but the first test provided dramatic results: The foam lifted and permanently deformed the T-seal between panels 6 and 7, leaving a visible quarter inch gap in the leading edge. Stain gauges measured impact forces up to seven times higher than predicted by computer analysis.

"What we saw was a system response," Hubbard said in a teleconference Wednesday. "We expected to observe an impact and measure that on panel 6, of course. What we found was that we had ... created a response that involved at least three of the panels, maybe more. It was clear the force went from panel 6 to the T-seal to panel 7 and even some measurements in panel 8. So in the accident, then, we have to think of not just the impact point but also the response of the entire wing leading edge."

Worried additional test firings could damage RCC support hardware and make it more difficult to ensure accurate results, Hubbard decided to forego any additional Fiberglass firings and to press ahead with the real RCC panel. To make the test as accurate as possible, a panel was taken from Discovery that has flown in space 30 times, making it comparable to the panels on Columbia's wings.

The foam fired last week and today measured 22.5 by 5.5 by 11.5 inches and weighed 1.67 pounds. The mass, impact angle and velocity were chosen to duplicate the actual impact conditions that occurred during Columbia's launching. Because the nitrogen cannon could not impart the kind of rotational energy seen in the real foam strike, the impact angle was increased, from the actual 15 degrees to 20 degrees, to achieve the same level of kinetic energy.

An initial attempt to fire the cannon failed when an electrical component malfunctioned. Engineers fixed the problem and successfully fired the gun at 3:19 p.m. The blast could be felt by reporters, who were clustered behind a rope watching the test through binoculars.

Speaking to reporters later, Hubbard said "the first significant finding is that we cracked a rib on the structure. Let me emphasize this is the first finding. We will do a complete set of evaluations on this panel, including some specialized non-destructive evaluation, perhaps later today or tomorrow, and we'll be looking at the sensor readings."

The crack, while relatively small, "is not anything you would fly with," Hubbard said. "This would be a piece of hardware that would be rejected. Whether or not this was sufficient to cause structural damage to the whole leading edge or whether it represents a thermal problem is yet to be determined."

Over the next week or so, engineers will prepare the gun to shoot at RCC panel 9.

"We have about a week break here while we reposition the gun and we'll be taking shots at first Fiberglass panel nine and then a shot against the RCC panel nine as well," Hubbard said. "Between then and now we're going to closely evaluate (RCC panel 6), we're going to look at the internal structure and integrity, we're going to look at the sensor readings and see where the forces were and we'll be thinking very carefully about where we want the aim point on panel 9 to be. Nobody has ever characterized this material in this way to see where the point of maximum flexure or maximum strength is."

Stormy weather in Texas forced the Columbia Accident Investigation Board to delay a critical test designed to find out whether foam debris could have caused the kind of wing leading edge damage that doomed the shuttle and its crew during re-entry.

The test, a potentially critical milestone in the ongoing shuttle investigation, had been planned for this afternoon at the Southwest Research Institute in San Antonio. But heavy rains grounded CAIB investigators in Houston and delayed work to prepare a wing leading edge mockup for the test. As a result, the test was delayed to Friday, between noon and 5 p.m., weather permitting.

"I know everybody there is disappointed, we're disappointed as well," said CAIB member Scott Hubbard, who is overseeing the test. "But in the interest of doing a really correct test and doing it in the manner in which we'd been planning to do, we felt this was the best decision."

Hubbard, other members of the CAIB and key NASA personnel were grounded in Houston by heavy rains. Hubbard spoke to reporters gathered at the Southwest Research Institute by telephone.

"This is like a launch delay," he said. "We had several other things I wanted to do at the test site, particularly I wanted to personally discuss and inspect a few features of the test plan. We don't have a signed test plan yet and just like in a space launch where there are go/no-go criteria, one of our go/no-go criteria is a signed test plan and I needed to put my personal eyes on a few areas and discuss them with the crew there to be sure we are all ready to go.

"This is a complex test with hundreds of sensors and a lot of other features, so seeing we were unable to get there and we had another delay at both ends it seemed like the right thing to do to not rush it and to be sure we had everything exactly correct."

Columbia was destroyed during re-entry Feb. 1 by a breach in the leading edge of its left wing. Sixteen days earlier, a piece of foam insulation broke off the shuttle's external tank during launch and hit the left wing at or very near the point where the breach occurred. While many observers believe the foam strike was the "root cause" of the breach, there is no actual data to prove that one way or the other.

To find out if external tank foam is even capable of causing that kind of damage, engineers at the Southwest Research Institute have rigged a nitrogen gas cannon to fire a similar-size chunk of foam at a mockup of a shuttle wing, duplicating the conditions known to exist during Columbia's launching. The cannon, normally used to fire gel-filled "chicken simulators" at aircraft components to simulate bird strikes, will fire the foam at 530 mph while a bank of high-speed cameras and hundreds of sensors record the results.

See the June 4 status report below for additional details.

Computer analysis and the results of a dramatic test last week indicate a critical experiment on tap Thursday may help investigators determine, to the satisfaction of most, that a foam strike during the shuttle Columbia's launching was the initiating event that led to the ship's destruction. While the root cause will never be known with 100 percent certainty, engineers believe Thursday's experiment could go a long way toward eliminating any lingering doubt about what damaged the leading edge of the shuttle's left wing, creating the breach that ultimately doomed the ship and its crew.

"From my perspective, and I'm not speaking for the board now, I think it moves us a lot closer toward a very likely initiating event," said Scott Hubbard, a member of the Columbia Accident Investigation Board overseeing the tests. "I think it establishes foam can break (wing leading edge panels) in a realistic environment and for my own sake, I think it moves us a significant step toward establishing that is an initiating event. There could have been other initiating events, but I think this moves us a lot closer to saying the foam can do this kind of damage."

Columbia was destroyed Feb. 1 by a breach in the leading edge of the ship's left wing that allowed super-heated air to burn its way into the interior. At issue is what caused the breach in the first place. During launch Jan. 16, a large piece of foam insulation broke off Columbia's external fuel tank and slammed into the underside of the left wing's leading edge at some 530 mph. A NASA analysis during the mission concluded the foam might damage heat-shield tiles, but that it wouldn't cause any safety of flight concerns. The analysis all but dismissed any possibility of significant leading edge damage.

Since the accident, engineers have been trying to pin down exactly what sort of damage might actually have been caused such an impact. They have refined their initial estimates of the mass of the foam, based on enhanced photography and computer analysis, and they now believe it struck the leading edge, while rapidly rotating, at an angle of 15 degrees.

During the test last week at the Southwest Research Institute in San Antonio, Texas, a 1.7-pound piece of external fuel tank foam insulation was fired at a mockup of a shuttle wing leading edge by a nitrogen gas canon. The foam, traveling at some 531 mph, stuck a Fiberglass leading edge panel, taken from the prototype shuttle Enterprise, at an angle of 20 degrees. The higher angle was chosen to account for rotational energy in the actual impact that cannot be simulated. The Fiberglass panel, mounted in position No. 6, served as a stand in for the reinforced carbon carbon panels actually used on the space shuttle.

Fiberglass is 2.5 times tougher than RCC carbon composite material and engineers were surprised by the results. The impact lifted and deformed a so-called T-seal between panels 6 and 7 while generating up to seven times the force computer models had predicted. Nothing broke and there was no direct gas path into the interior of the structure, but the higher-than-expected impact force caught investigators off guard.

"I was standing there and I heard all these assertions about well, this only weighs a pound and a half and (the leading edge) is tough stuff," Hubbard said today. "When the gun fires, there's a blast wave that comes out and you can feel it and then I saw the streak and clearly, something happened. I thought to myself, this is more than I had expected. ... I thought oh my God, this is something! This isn't just a light bounce.

"People's intuitive sense of physics is sometimes way off. You don't feel this can do anything. But you fire this at 500 mph and there you saw it, I really did think oh my God, this is really an impact, this is a significant effect. Then when we actually looked at it and saw things spread apart and all that, that's when it really came home to me what one-half MV squared really means."

He was referring to the formula for computing kinetic energy. While the mass of the foam is low, the velocity is very high and that is the term in the equation that is squared. The impact force delivered by the foam is roughly equivalent to catching a basketball moving at 500 mph.

Hubbard and his team originally planned four foam shots at Fiberglass panel No. 6 before shooting at a real RCC panel taken from the shuttle Discovery that is similar in age to the panels making up Columbia's leading edge. But given the higher-than-expected forces observed during last week's test, engineers have decided to forego any additional shots at panel 6 to make sure they don't inadvertently damage any critical support hardware. Instead, they plan to shoot at Discovery's RCC panel Thursday.

"Because the observed effects, the fact that the peak loads were higher than expected in panel 7, the fact that we deformed permanently the T-seal, the fact that the loads in panel 6 were in some cases a factor of seven higher than anticipated, all led us to believe we probably had learned as much as we needed to and that we should proceed to the RCC," Hubbard said.

Thursday's test will use an identical piece of foam as the one fired last week. The foam will hit at the same velocity and impact angle. Computer models, adjusted with a correction factor to account for the different strengths of Fiberglass and RCC carbon composite material, indicate Thursday's impact will deliver more than enough energy to break the RCC panel.

"Those predictions would say that we have by maybe 70 percent more force than we need to break the RCC," Hubbard said. "Now, whether it actually turns out that way or not, that's why we do the experiment. But the analysts are saying it looks like it'll break it."

If it does, or if it causes any remotely significant damage, investigators will have solid evidence the launch day foam strike could have been the root cause of the Columbia disaster. Not absolute proof, but solid evidence.

Engineers for the first time today fired a large chunk of foam insulation at a Fiberglass wing leading edge panel, knocking a so-called T-seal out of place and leaving a long gap between two panels. Such a gap on a real shuttle wing leading edge would provide an entry point for deadly super-heated gas during the descent from orbit. Today's test results, assuming no problems are found, mark the first concrete evidence supporting the widely held theory that a foam impact during the shuttle Columbia's launch doomed the orbiter and its seven-person crew by creating a breach in the left wing's leading edge.

"Investigators are always a little cautious and there were no raised eyebrows, but it certainly is an interesting initial result," said a spokesman for the Columbia Accident Investigation Board.

The tests are being conducted at the Southwest Research Institute in San Antonio, Texas, using a nitrogen gas canon capable of firing large pieces of foam insulation at velocities of more than 500 mph. Earlier test runs focused on firing foam chunks at panels of heat-shield tiles like those on the belly of the shuttle. Today's test was the first using a large mockup of a wing leading edge.

The goal was to collect engineering data to ensure the validity of future tests. Investigators eventually plan to fire foam at an actual shuttle reinforced carbon carbon panel taken from the shuttle Discovery that has a flight history similar to panels that were aboard Columbia.

For today's test, a 1.67-pound chunk of foam with a volume of 1,200 cubic inches was fired at a Fiberglass panel in RCC position No. 6. The foam was fired at a velocity of 779 feet per second, or 531 mph, striking the Fiberglass panel at an angle of 20 degrees. The actual angle of impact in the Columbia foam strike is believed to have been less than that.

The leading edge panels are attached to the wing spar with so-called T-seals. Each edge of an RCC panel fits into a T-seal that is bolted to the front of the spar. The result is an alternating pattern of RCC panel, T-seal, RCC panel, T-seal and so on.

In today's test, the the foam strike caused the T-seal between RCC panels 6 and 7 to lift and pull away toward the outboard panel 7, the CAIB spokesman said, leaving an opening approximately 22 inches long. The width of the resulting gap varied from the thickness of a dime to more than a quarter inch.

A suitcase-size chunk of foam insulation broke away from Columbia's external fuel tank 81 seconds after launch, slamming into the left wing around RCC panels 7 and 8 at more than 500 mph. Engineers have long suspected the impact caused damage that left the shuttle with an open breach when the crew began re-entry Feb. 1. Today's test is the first to provide concrete evidence such an impact could actually displace a T-seal.

But the CAIB spokesman pointed out that Fiberglass is 2.5 times more resilient to impacts than the carbon composite material making up a real RCC panel. And the angle of impact was different, imparting more energy than a lower angle-of-incidence impact. How those variables are balanced in upcoming tests aiming at an actual RCC panel will go a long way toward determining whether or not a foam strike could have doomed Columbia.

Interestingly, the day after launch a piece of debris drifted away from Columbia that was detected by Air Force radar systems. Subsequent tests show the debris could have been a T-seal or, perhaps, a large section of an RCC panel. It is possible, some investigators believe, that the foam strike weakened a T-seal or cracked an RCC panel and that a piece of the damaged component finally broke free the day after launch. The Southwest Research Institute tests may provide the hard data needed to support, if not prove, that theory or some variation. Computer modeling software developed and refined in the wake of the Columbia accident predicted damage similear to what was observed after today's test. Engineers plan to begin shooting foam at an actual RCC panel around June 10. More information on today's test will be provided as it becomes available.

The chairman of the Columbia Accident Investigation Board said today he has no plans to require NASA to recertify shuttle systems before flights resume or to mount a test flight of some sort to validate recommended design changes or to collect more data.

But Harold Gehman said recertification is being assessed as a potentially useful long-range project in light of NASA's stated goal of flying its remaining three orbiters for another 15 years or more.

"The board is considering but has not yet ruled on whether or not a recertification or a requalification of either part or all of the STS system should be necessary for another 20 years of flight," he said during the board's final Houston news conference.

"My own personal opinion is that would not be a return to flight issue. The recertification or requalification issue is related to the announced intention of NASA to fly these things for another 20 years. It's not our charter to address that issue, but we may comment upon it."

Asked if the board might recommend a shuttle test flight before resumption of space station assembly missions, Gehman said "it's a matter under consideration." But after the news conference, when asked to clarify his thoughts on the need for a test flight, the retired admiral said he did not think the board would make any such recommendation.

The board hopes to have its final report finished before the end of July, when Congress adjourns for its summer recess. But that is strictly a target and "we'd rather get it right than get it in a hurry," Gehman said. While the board is still developing and refining its conclusions, Gehman gave reporters a hint of what to expect when the printing presses finally start rolling.

"I can tell you it is going to be a very, very thick report and that it will be in narrative form, that is, it's going to start off 'once upon a time,' you know, at the beginning and it's going to be a multi-layered report," he said.

"That is, you'll be able to have a beginning where it has a very high level cursory discussion of something and then you just keep going and it gets down to the next layer and you keep going and it gets down to a very, very detailed engineering layer. And I also know you're going to kind of have to read the report to pull the recommendations out. It's not going to be a comic book kind of a report."

To the relief of reporters ultimately faced with the challenge of digesting the report on deadline, Gehman said later a list of all the panel's recommendations will be available in an appendix. He said three professional writers have been hired to combine and edit reports from individual board members to give the final document a consistent "layered narrative" style.

"We're going to try and make it easy to read in the sense that each chapter will be kind of a stand-alone chapter," he said. "You're not going to have to be flipping back and forth to appendixes and things like that to find things. Whatever charts and graphs and pictures we refer to will be right there in the text. But it'll be a thick report. It'll be voluminous."

And it won't necessarily blame Columbia's destruction on the impact of foam debris on the ship's left wing 82 seconds after liftoff. While the foam clearly hit the left wing's leading edge at or near where investigators believe a breach occurred during re-entry, it might not be possible to prove a direct connection.

"We may or may not be able to state with unequivocal, complete certainty that the foam strike, which obviously did happen, knocked a hole in the leading edge of the orbiter," Gehman said. "There's no question the foam hit the orbiter, but we may not be able to prove it actually caused some kind of a breach or not. Therefore, because we're working so hard on determining exactly what caused this shuttle not to return safely to Earth and (because) we're looking at so many engineering and physical and mechanical processes, chemical processes, that took place, it has caused us to look broader, much more broadly at the material condition and the operation of the shuttle program."

He said the final report will probe NASA's shuttle operation "probably more broadly than any review in the past. This probably is a blessing in disguise, particularly if you're thinking about operating the shuttle for another 20 years."

"Therefore our findings and our recommendations are going to be based on this very, very broad review and not based on a single, solitary initiating event like the foam hitting the orbiter," he said. "We're not going to rule it out, I mean the foam hitting the orbiter may have caused a breach and that may have been what allowed the heat to get into the wing. But since we can't prove that, and we can't disprove, for example, orbital debris or micrometeorite (impacts), we're left with the position of having the report stand on its own weight.

"And all of these other things that we're looking into, like safety and management and risk assessment and work force issues and the stature of the (safety and mission assurance) organization, all these other things are going to have to stand on their own. Our conclusions and findings will have to stand on the merits of our work and we cannot refer back to the foam hitting the orbiter as proof of everything.

While the board may end up concluding the foam strike was the most likely initiating event, "we can't prove it," Gehman said. "We have to allow for the possibility that something else initiated this event and our report will have to take that into account."

One reporter, using a murder mystery analogy, said enough circumstantial evidence was available for most people to indict the foam. But Gehman disagreed.

"We do indeed have witnesses that saw someone shoot a gun," he said. "But the problem is we don't have a hole. We have a patient who died but we don't know why he died. There's where the analogy breaks down. ... If I had a picture of a hole or if we came back and somebody found a piece of RCC (reinforced carbon carbon) on the ground some place that had a (hole in it), I might change my mind. But as you well know, in this area where we're projecting the breach occurred, we have no RCC. It's all burned away."

Management issues will be a major focus of the final report and the perception that agency managers somehow lost sight of the post-Challenger emphasis on proving it's safe to launch a shuttle rather than proving it's not.

"A considerable part of our report is going to be addressing this underlying and hard-to-pin-down attitude or climate," Gehman said. "Some people have characterized it as a change in posture from one in which you had to prove that it was safe to fly to one in which you had to prove it was unsafe to fly," Gehman said. "In other words, the people who had doubts about anything were essentially outside the circle and had to work their way in rather than the doubters being inside the circle.

"Of course, there are a lot of reasons for this, this is not criminal activity or anything. You have 112 successful flights, you've got to assume you're doing something right. You've got thousands and thousands of dedicated people being very careful about what they do, catching many, many flaws before you launch. So they've got lots and lots of successes to prove they're doing a lot of things right. But there are a number of underlying issues we're going to attempt to address in this report. And we want to be sure that we've got them addressed in a responsible way."

Along those lines, the board will look into what other outside panels determined about the foam threat in years past because "NASA is being reviewed by somebody all the time. Well, what do all these other panels say about this? ... We are actually conducting a review of the literature to see where all these other wise people were on the subject of foam and whether or not if we had been called in before the space shuttle Columbia took off, whether or not we would have raised alarm bells about this foam business ourselves.

"In hindsight, it's really easy to find these flaws," Gehman said. "So if these flaws are out there laying around and everybody should have seen them, OK, well tell me what the next one is if you're so smart. Tell me the next one. If we as a board can't answer that question, we are very slow to sling spears at other people who also failed to answer that question."

But he said "if there's a flaw in the system or a better way to do that, we are going to document that and be very straight-forward in pointing that out."

The CAIB is in the process of wrapping up its operations in Houston before relocating in Washington. Gehman said the board's "hot lines" for public comments and suggestions will be taken down at the end of the month. Since Feb. 1, the board has received 3,150 unsolicited public comments, half of them "what I would call serious inputs," Gehman said.

"A goodly number of them were just letters which said 'I know where a piece of debris is' or something like that. But about half of them were serious analytical suggestions."

He said 778 of the 3,150 unsolicited comments and observations were actually checked out by board investigators.

"About 25 percent of the inputs we got were serious, were valuable, were things we actually followed up on to see if they were actually right or not," he said. "I consider that to be a pretty successful enterprise."

If NASA managers had realized early on that Columbia had suffered a catastrophic breach in its left wing during launch - either by obtaining satellite imagery or, more likely, by having the astronauts stage an inspection spacewalk - they might have had time to mount a repair spacewalk or even an emergency rescue mission with the shuttle Atlantis, the chairman of the Columbia Accident Investigation Board said today.

But both scenarios, while emotionally dramatic, had virtually no chance of being executed in reality because of two assumptions the CAIB made that restricted the NASA study to technical feasibility alone. The first assumption was that NASA managers had conclusive proof of a catastrophic breach by the third or fourth day of Columbia's mission. They had no such evidence. The second assumption was that agency managers would commit another orbiter to flight without knowing whether it might fall victim to the same problem. Given NASA's past history, that's extremely unlikely.

"This whole question that we asked, and NASA's whole response, is based on a set of assumptions ... which set conditions which were not present in January of 2003," CAIB Chairman Harold Gehman told reporters today in a teleconference. "In other words, we set a scenario here that was not the scenario of the Columbia. Nobody told us on day 4 that we had a hole in the leading edge of the left wing. So these are two different sets of conditions."

But the bottom line, he said, "is that it's all feasible. There are no show stoppers. But it all turns out to be extraordinarily (difficult)."

Investigators believe Columbia re-entered the atmosphere Feb. 1 with a sizeable breach in the leading edge of its left wing, a breach presumably related to the impact of external tank foam insulation that broke away and hit the orbiter 82 seconds after liftoff Jan. 16.

Engineers first saw the foam strike the day after launch while reviewing long-range tracking camera footage. NASA managers ordered an engineering analysis to determine the severity of the problem and ultimately concluded the impact had not caused any catastrophic damage. Initial requests for spy satellite imagery to examine the impact site in detail were halted.

The day of the accident, shuttle program manager Ronald Dittemore said shuttle managers didn't ask for imagery because past experience indicated it would not have helped all that much and because there was nothing the crew could have done even if a major problem had been spotted.

"Recall a year or two ago, we lost the drag chute door (from a shuttle)," Dittemore said. "Right at liftoff, it fell off. And we actually tried to take some pictures of the back end of the vehicle to see what was really there so that we can understand our thermal heating in that case, and those pictures that we received were not very useful to us. So that was part of our background.

"Combine that - our feeling that we didn't believe the pictures would be very useful to us - with the fact that there was not much, there was zero that we could do about it, and in this case, we elected not even to take the pictures.

"We believed that our technical analysis was sufficient. We couldn't do anything about it anyway. We were in the best possible position, and so we elected not to take any pictures from any other sources, and that's the way it played out."

Gehman said today the CAIB commissioned the repair/rescue mission study in part because board members were disturbed by repeated comments from NASA and contractor engineers and managers that nothing could have been done to save Columbia's crew even if they had known about the breach.

"To us, the area that we thought becomes more problematic when you deal with a question like this is the implications of the decisions made regarding the photography and the foam strike analysis and whether or not you should get on-orbit photography changes from being kind of a bureaucratic, administrative, fumbling, bumbling, to a much more serious life and death kind of a decision process," he said.

"Because it turns out a lot of people were saying, well it doesn't make any difference if you take photography or not because there's nothing we can do, it doesn't make any difference if the foam strike analysis was good, bad or indifferent because there was nothing that you could have done anyway.

"Now, those kinds of benign administrative decisions which were taken now look more ominous because now it looks like maybe there was something you could do. That's the area we were concerned about."

Ever since the shuttle's loss, reporters, politicians and the public have wondered whether anything could have been done to save Columbia and its seven astronauts if NASA had realized the severity of the problem. An internal NASA study concluded the astronauts would not have been able to survive entry on board Columbia, even if they managed to dump 15 tons of equipment overboard to minimize entry heating.

But in a subsequent study commissioned by the CAIB and discussed today for the first time by Gehman, agency engineers concluded the crew might have been able to patch the breach during an emergency spacewalk. Whether the makeshift patch would have protected the wing long enough for Columbia to make it through the region of peak heating is unknown. A better option, although only marginally so, would have been to rush the shuttle Atlantis to the launch pad for an emergency rescue mission.

Columbia had enough food, water and power to remain in orbit more than a month. The limiting consumable was lithium hydroxide, a chemical used to scrub carbon dioxide form the shuttle's air supply. Normally, NASA does not allow the partial pressure of CO2 to rise above 2 percent. But by relaxing those restrictions and accepting levels of up to 3.5 percent or so, the shuttle's air supply would have supported the crew for 30 days, until the evening of Feb. 15.

To make it that long, the crew would have had to power down the orbiter and do everything possible to minimize physical activity and their consumption of oxygen. Staging more than one spacewalk likely would have eliminated the Atlantis rescue option because of air lost overboard when the airlock was cycled.

But the spacewalk repair option is interesting if for no other reason than NASA managers initially ruled out any chance for an on-orbit fix.

"They inventoried everything that was on board the Columbia," Gehman said. "There are two EVA suits. They devised a successful way to get out to the area of the damage without further damage to the TPS (thermal protection system). They devised a way that they thought they could work out there and they ... came up with a patch that they would jam stuff in the hole."

After plugging the breach, the spacewalkers would position a plastic water bag over the opening.

"Then, after a day or two of maneuvering the orbiter so that section of the wing was in the shade all the time, the water would freeze solid and then that holds the stuff in place," Gehman said. "They would then put something over the top of the hole, some Teflon tape or something like that, and then they would attempt to re-enter.

"No studies have been done on the thermal characteristics of this patch," he said. "Whether it would hold for 30 seconds, 60 seconds, 90 seconds or three minutes we have no clue. Those studies will be done, but we've got no clue, we can't put a number, a probability, that this patch would have worked. It kind of comes under the category of 'at least we would have done something.'"

The Atlantis rescue scenario is a bit more believable, but only just. At the time of Columbia's launching, Atlantis was being prepared for a flight to the international space station in March. It's tank and boosters were mated in early January and Atlantis was scheduled to be moved from its hangar to the Vehicle Assembly Building Jan. 29 for attachment and subsequent roll out to the pad.

Assuming an inspection spacewalk by flight day 5 - Jan. 20 - and a decision that day to begin around-the-clock processing of Atlantis, the NASA study concluded the shuttle could, in theory, be ready for a launch by Feb. 10 or 11. That corresponds to flight day 26/27 for Columbia's crew. The launch schedule assumes the elimination of non-essential countdown "holds," the elimination of non-essential pre-launch tests and simulations, no mechanical problems or processing snags and good weather.

"The study indicates if you have five or six 'ifs' that line up and you get an affirmative answer to each of the five or six 'ifs,' the launch of the second shuttle and the rescue was conceivable," Gehman said. "It isn't easy, it's not even highly likely. But it is conceivable.

"By the six ifs, I'm saying if you could have reduced the processing time satisfactorily and if you could go through the launch countdown and prelaunch preparations without a mechanical problem and if the weather was suitable and if the rendezvous was successful and the two orbiters could maintain station on each other and if the multitude of EVAs worked all right, you could have done this. It is possible."

Atlantis would carry four veteran astronauts and would launch at night, rendezvousing with Columbia within 24 hours. The shuttle's flight computers would use a software "load" developed for the March shuttle mission, patched to take into account altitude changes and other factors relating to an immediate rendezvous.

Columbia would be oriented with its payload bay facing Earth and its tail in the direction of travel. Atlantis would approach from below in a manner similar to past linkups with the Russian Mir space station. Picturing Columbia moving upside down and tail first to the left, Atlantis would approach from directly below with its left wing facing the direction of travel and its open payload bay facing Columbia. The long axis of Atlantis would thus be turned 90 degrees with respect to the long axis of Columbia.

Once on station at a distance of 50 to 60 feet, spacewalkers from Atlantis would carry two spacesuits and additional lithium hydroxide to Columbia, staying in contact with safety tethers at all times. The final two astronauts to leave Columbia would configure cockpit switches and on-board software to permit flight controllers to remotely deorbit Columbia.

"Columbia would be lost," Gehman said. "There was no way to recover Columbia. The last two astronauts who left the Columbia would flip certain switches in certain positions so Columbia could be deorbited on command from Houston. And then the Columbia would be lost, ditched in the ocean."

All 11 astronauts - four of them sitting on the floor of Atlantis's lower deck - then would return to Earth. "Based on the verbal report the board got, it indicated the launch of the Atlantis was the less risky and the more probable (of the two options studied)," Gehman said. "The on-orbit repair was very, very unknown as to whether or not it would have worked or not. But obviously, it's inconceivable that we would have done nothing if we had known."

He said the decision to launch a rescue mission ultimately would have depended "solely on how good the knowledge of the damage to the orbiter was."

"In other words, if somebody came and said we've got a little tiny hole in the leading edge and we think the orbiter can re enter safely but it might not, then probably the decision to launch another orbiter would be very hard to come by," he said. "If on the other hand an inspection said 'holy mackerel, we've got a great big hole and the orbiter is doomed, the crew has no chance whatsoever,' then the probability they would have launched a rescue mission probably would have gone up."

He summed up the rescue scenario by saying "it's technically possible, very, very risky and a whole bunch of ifs have to line up. ... But I have no idea if it would have been successful or not."

Based on chemical analysis of slag found on the back side of a wing leading edge fragment, investigators now believe the breach that destroyed the shuttle Columbia occurred at or very near the lower inboard corner of reinforced carbon carbon panel No. 8, very close to where a so-called T-seal was mounted between RCC panels 7 and 8.

But a member of the Columbia Accident Investigation Board said today it's unlikely Columbia began its Feb. 1 re-entry with a large hole in RCC panel No. 8. It's more likely the disaster began with a smaller breach, possibly a gap caused by a missing T-seal, or part of the T-seal between RCC panels 7 and 8.

"If it is, for example, a T-seal, you're talking about a narrow slit which eventually is going to have to start growing in size," said James Hallock, one of the CAIB members trying to pin down the exact failure scenario. "And how does it grow? Maybe it grows by having the bottom part of panel 8 break off and that's when you're now talking about a large amount of this hot gas getting in there and things happening rather quickly after that.

"With this very small hole, things would slowly transpire and take place over a period of time. And the timing is very critical. The comment we constantly keep saying to each other is gee, this craft made it (all the way) to eastern Texas. If we had an eight-inch hole (in RCC panel 8) out over the Pacific, I'm not sure we're going to make it to Texas.

"So we have to have something that has to evolve with time," he said. "So that's the part where I'm saying, I don't think we had a big eight-inch hole there initially, I think we had something that then grew with time."

The day after Columbia's launch, military radars detected an object separating from the space shuttle. More than two dozen shuttle components have now been tested at Wright Patterson Air Force Base to compare their radar "signatures" with the flight day two mystery object. Only two components match: Part of a T-seal with support hardware attached and a large section of an RCC panel.

While the bottom half of RCC panel 8 is missing, portions of the upper section of the U-shaped panel have been recovered. Investigators have found small globules of slag-like material on the inner surface of the recovered fragments. Those globules apparently were blown there by a plume of super-heated air rushing into a breach, melting insulation and support hardware and splattering molten material back onto the inner surface of the panel.

"By taking X-rays of this thing, they've been able to find a lot of very small globular shapes, spherical shapes," Hallock said. "And when they analyze them, they all turn out to be inconel (or a related material). Why is that important? These globular shapes we're finding only behind Number 8, which is quite interesting. We're looking at doing both a chemical analysis as well as trying to understand the pattern of the deposition of all this slag. It's very interesting.

"If you look at just the chemical analysis and just the slag itself, particularly behind panel 8, it's very much talking about perhaps a breach right down in the lower part of panel 8, right near 7. Why do I say that? When you look at the layers of all the material, the molten layers that have formed, the slag itself, the lowest layer of this thing contains inconel. Now inconel is stuff that comes from the spanner beam, and foil insulation and the fittings.

"So it's beginning to tell us that indeed, when this so-called breach happened, that it was the fittings that were hit," Hallock said. "The reason we're saying it's more toward (panel 7) is that over on (the outboard) side we have a lot of other mounting hardware and it's all stainless steel and we did not find any stainless steel in the slag in behind panel No. 8. So that's sort of telling us a little bit about direction."

Inconel melts at about 3,200 degrees Fahrenheit.

"When you look at all of that, particularly around panel 8, it really does line up very nicely with a breach in the lower left hand corner of it," Hallock said. "The part of it that we're still trying to decide is that THE event or is that something that came along later? Because it's fairly clear from what we've seen, the bottom pieces of all these RCC panels in this neighborhood all came off. So was this before or after the initial event?

"For the most part, I'd say maybe 90 percent of us think that probably was the place where it came in but I can't really put it down as saying absolutely it is at this point. I hope to, but I don't know if I'll get to that stage or not."

CAIB Chairman Harold Gehman said the board plans to begin relocating in the Washington, DC, area beginning the week of June 2 and to hold a public hearing there on June 12. In the near term, investigators are gearing up to begin critical tests with a mockup of Columbia's left wing leading edge in an attempt to find out whether the impact of external tank foam insulation could have broken a T-seal or cracked an RCC panel during Columbia's launching.

A suitcase-size piece of debris broke away from Columbia's external tank 81 seconds after liftoff Jan. 16 and slammed into the left wing leading edge at more than 500 mph. Hallock said today an accelerometer on board the shuttle actually detected the impact. But investigators have not yet been able to prove whether the foam strike caused the breach that doomed the shuttle during re-entry.

"The issue that's the hard part in all of this thing is the cause and effect," Hallock said. "There's no question I can prove foam hit the shuttle and I think we can prove it hit underneath the left wing. ... Not only do we have a lot of movies that show that, we even have an accelerometer that was bouncing around, like plus or minus 1 G, and then suddenly went to 2 Gs at precisely the same time it looks like it hit. That I can do.

"Now, did it do damage? That is the hard part. How do you show whether it did damage then or not? If you didn't, and I don't know this, then where do I turn? So all of these things play together in a very complex type of thing. Right now, what we're trying to do, because we're looking at the calendar ... we're going to have to make some calls here."

The leading edge simulator was shipped to the Southwest Research Institute in San Antonio, Texas, Monday. A Fiberglass panel substitutes for RCC panel No. 5 while RCC-6, taken from the shuttle Discovery, has flown 30 times and is considered a close match to the panels in place aboard Columbia. Using a nitrogen gas canon, SRI engineers plan to fire foam debris at the Fiberglass panel starting May 28 to collect critical engineering data.

If all goes well, foam will be fired at the flight article - RCC panel 6 - starting June 7. Whether the foam impacts actually break anything remains to be seen. But Gehman said in the end, it doesn't matter.

"The board's report is not going to be scenario dependent," he said today. "By that I mean, unlike the Rogers report on the Challenger, in which they had a specific event with a specific cause that was directly related to the accident and then they went right at how to fix that, we are conducting a much broader review of NASA here.

"Not only are we going to address the foam shedding issue, but we're going to address a dozen other issues that we're concerned about. We're going to tell them to fix the foam shedding, absolutely. But we're actually looking more broadly than that. Maybe the fact that we can't prove that the foam actually broke a hole in the orbiter, it may actually be a good thing in the long run because it really is causing us to look much, much broader at contributing factors in this accident, down to and including climate and atmosphere and leadership and management and safety programs and things like that which I believe will give a much, much deeper and broader report in the end.

"So it may be the fact we don't have a cause and effect that hits us in the head like a 2-by-4 may actually be a blessing in disguise. Obviously, we find that the process of rationalizing away the impact of foam hitting the orbiter over a period of all these years is not one that we're going to be able to live with."

Gehman said it "doesn't bother me in the least" if the CAIB fails to define a root cause of the Columbia disaster. And he pointed out the current best-fit scenario could quickly change.

"You heard Jim Hallock just now talking about T-seals and lower halves of RCC panels," he said. "I would point out that the entire lower half of RCC panel No. 9 is missing. One of the reasons we're not talking about the slag on RCC panel No. 9 is because there isn't any RCC panel No. 9. Suppose tomorrow we wake up and farmer Brown finds all of panel No. (9) out on his field? Well, there goes that theory. We can't write a report that's that scenario dependent because somebody will find the offending piece.

"On the other hand, I do believe we can do NASA and the shuttle program a world of good if we take a very broad and complex view of this and go after multiple causes and multiple flaws and shore them all up. I'm quite confident with that approach. It's harder and it may be a little bit of a challenge for us o write the report in ways people understand the point we're trying to make here. But I believe it actually (will be) a better report."

Gehman said the board hopes to have its final report finished before Congress takes its summer recess in August.

The Columbia Accident Investigation Board today released the clearest video yet showing a tumbling piece of foam insulation slamming into the shuttle's left wing during launch Jan. 16. Investigators say the enhanced video, along with ongoing mathematical modeling, indicates the foam struck the wing at some 529 mph, imparting up to a ton of force across an area of the leading edge measuring roughly six by 12 inches.

Investigators believe the foam impact likely cracked or breached one of the reinforced carbon carbon panels making up the leading edge of the left wing or damaged a so-called T-seal between two adjacent panels. Whatever the exact mechanism, investigators believe Columbia began its re-entry Feb. 1 with a breach at or near RCC panel 8 or perhaps near the T-seal between panels 8 and 9. Super-heated air burned its way into the wing through this presumed breach, leading to the shuttle's eventual destruction.

CAIB and NASA investigators are gearing up for a crucial series of tests at the Southwest Research Institute in San Antonio, Texas, early next month to help pin down whether the foam impact was, in fact, a "root cause" of the disaster.

Five initial test runs already have been carried out shooting foam "bullets" at heat shield tiles on a landing gear door taken from the prototype shuttle Enterprise. The tests were set up early on in the investigation, before engineers knew the impact had actually occurred at the leading edge.

In a teleconference with reporters today, CAIB member Scott Hubbard said only minimal tile damage resulted from the initial impact tests using foam bullets, weighing between 1.2 and 2.5 pounds, impacting at angles between 5 and 13 degrees. But the tests have helped verify the predictions of two computer models and confirm the actual impact happened at or very near the leading edge.

Early next month, engineers will begin firing foam at a high-fidelity mockup of a shuttle leading edge, complete with RCC panels taken from the shuttle Discovery that have flown more than two dozen times. The leading edge simulator will be heavily instrumented with more than 100 channels of data charting the stresses and strains imparted by the impacts.

The foam will be fired from a 30-foot-long nitrogen-gas canon with a rectangular bore measuring 5.5 inches by 11.5 inches. Foam bullets similar in size to the actual debris that hit Columbia will be fired at the simulator at velocities of up to 775 feet per second, or 528.5 mph. Six high-speed cameras, some capable of recording 7,000 frames per second, will photograph the impacts in exquisite ultra slow-motion detail, permitting precise determination of impact velocities and angles.

"All the experts looking at all the data have begun to home in on a sweet spot," Hubbard said of work to determine the size of the foam debris that struck Columbia. "The current best guess, and this may change a little bit over the next week or so, is an impact projectile of about 1,240 cubic inches traveling at about 775 feet per second."

One wild card is the contribution of the foam's rotational velocity. Up until now, engineers have calculated the force imparted by the impact based on the foam's straight-line velocity. But Hubbard said the debris was tumbling wildly and that regardless of the direction of the tumble, the rotational velocity must be factored in.

"A major element has been to include the rotational velocity," he said. "This is something that had personally been gnawing at me in looking at the video, of how this piece was rotating. It seemed to me to be a source of additional energy. ... Some preliminary calculations show that we may need to either adjust the velocity or the angle to compensate for this."

Some outside observers worried the initial test results, showing only minimal damage to the landing gear door tiles, might indicate the foam would have little effect on the RCC panels, leaving NASA without a clear-cut root cause for the disaster.

But Hubbard said today there is little or no data on how RCC panels respond to impacts. And unlike the tiles, which are supported across their full length and width, RCC panels are only supported at their edges, by the T-seal. The central, unsupported area is just a third of an inch thick.

"The difficulty is in modeling this curved surface," he said of the U-shaped RCC panels. "There was some initial ... analysis that was done on an impact of a piece of foam of the 2-pound variety traveling at 700 feet per second against a flat plate (of carbon composite material). What that seems to indicate - and I really underscore 'seems' - is that it should break the panel.

"But I don't want to go any further than that because that's a flat panel and not a curved surface. As we've learned from doing this first set of tests, getting the tumbling, the angle and all of that just right is a tricky business. So I don't think at this point we know exactly what we might find. That's why we're doing the tests."

The impact angle chosen for the tests is especially critical. That angle is measured relative to the flat bottom of the wing, not relative to the tangent of the curve at the point of impact as common sense might dictate. Relative to the belly of the orbiter, impact angles for debris striking the lower side of the leading edge RCC panels could range from 10 to 20 degrees or so.

Velocity also is critical. As every high school physics student learns, an object's kinetic energy is one half its mass multiplied by the square of its velocity. While the mass is low in this case, the velocity is high and that is the term being squared.

"Very light things, when you accelerate them to very high velocities, carry an enormous amount of force and the types of forces we're dealing with here, with the foam size and velocities we're talking about, even at these relatively shallow angles, are something close to a ton of total force, upwards of 2,000 pounds of total force delivered in relatively small area of about 5 or 6 inches by a foot," Hubbard said.

Trying to extrapolate the results of the initial tile impacts to the RCC panels is not possible because "it's a little bit apples and oranges," Hubbard said. While engineers understand how tiles respond to impacts, no such database exists for carbon composites.

"The tiles have a certain crush force that we now understand fairly well based on all the earlier tests," Hubbard said. "We don't have that same level of information yet for aged RCC. One case (tile), you have a glass-like material that is very sensitive to the angle of the impact and that angle, I feel almost certain, has something to do with how the edge of the foam digs into it. If the leading edge were at 20 degrees or so and made out of tiles, I think we would see a substantial amount of damage. The fact is, that angle that we saw, the angle that exists on the bottom of the orbiter, is only 5 or 10 degrees. That's one story.

"A completely different story is the RCC panel, which is only supported on the ends and is maybe a third of an inch thick or so and has quite different material properties. It will probably show some angular dependence. The smallest angle of intersection that we've measured is about 10 degrees and it goes up to well over 20 degrees.

"At that range of angles, you transfer a lot of force and that amount of force could be, we think, enough to break it. But we won't know for sure until we do the tests."

Investigators have not yet decided exactly where they will aim their foam bullets at the high-fidelity leading edge simulator. Because each strike will affect the simulator in some fashion, causing an unknown amount of damage, only a limited number of firings will be possible.

The current schedule calls for shooting at panels 5 through 7 beginning the week of June 2. Panels 8 through 10 will be hit starting the week of June 23rd.

"At this point I'm fairly well convinced we're going to hit panel 6 pretty much in the middle of the panel," Hubbard said. "I'm looking at two or three options for the panel 8-9 tests. One is down at the bottom of the panel. The other though is ... the T-seal area (between panels 8 and 9). And I haven't made, nor have we agreed with NASA yet, exactly the best place to put that impact and that's one of the things we're going to be looking at in the next two weeks or so."

NASA today named William Parsons, director of the agency's Stennis Space Center, as the new manager of the space shuttle program, replacing Ronald Dittemore who announced his retirement late last month. Parsons, who began his NASA career at the Kennedy Space Center in 1990, will take over from Dittemore sometime this summer, after an on-the-job training transition period.

"This is not a job that just anybody could do and this is not a time for other than the very best candidate," said Michael Kostelnik, deputy associate administrator for shuttle and space station. "We were fortunate all these things came together.

"We looked far and wide, both within NASA and exterior to NASA, looked at a lot of great candidates with a lot of great skills. We were concerned with leadership, we were concerned with management acumen, we were concerned with professional characteristics and obviously wanted somebody experienced in the program."

Parsons is widely respected by agency insiders, bringing a wide range of experience to a difficult job, a man "who's spent time at a variety of (NASA facilities) and has learned what works and doesn't work," said one senior manager. "Personally, I believe he brings a level of leadership not often found."

Parsons began his space career readying military cargos for launch on the space shuttle and ultimately joined NASA's shuttle workforce at the Kennedy Space Center, integrating payloads for launch and eventually serving as a flow director in charge of the shuttle Discovery's ground processing.

He then moved to the Stennis Space Center where he ran space shuttle main engine testing before moving on to the Johnson Space Center in Houston, serving as manager of center operations and then as deputy center director. A native of Mississippi, he returned to Stennis in 2001 and was named center director in 2002.

The job of center director is one of the highest management positions in NASA. In some respects, one could look at Parsons' decision to take over management of the shuttle program as a step down, even though the shuttle program has a much larger budget and a much larger workforce.

"I don't look at things that way," Parsons said today. "I'm proud to be a member of this agency, I'm proud to be able to serve this agency, I look forward to being asked to do this and I look forward to being given this challenge and to have an opportunity to help this program get back to flying."

Said Kostelnik: "Looking both exterior to NASA and interior to NASA, we could not have found a better qualified candidate. A natural leader, trained in leadership early on in his Marine Corps days, a very astute manager, technical degrees and solid technical experience in these programs. ... He has great people skills, he is well respected in our industry."

Parsons said he plans to work closely with Dittemore over the next two months or so to learn the intricacies of an inherently complex program before taking over later this summer.

"I think I can learn some good things from Ron," Parsons said. "I think Ron has been an outstanding program manager. ... I think his approach to running the shuttle program has been very solid, I think he has good processes in place, I think we'll use those processes to maximize the efficiencies and effectiveness of what we do from this point forward.

"I think Ron also showed us a strong character when we had our tragedy. I hope I don't have to deal with a situation like that, but I think I learned a lot from Ron on how he approached that event."

Asked what he considered his greatest challenge, Parsons said "to take the findings of the Columbia Accident Investigation Board and work with the entire community to then lay out a plan on how we're going to return to flight."

"It's probably not the easiest time to come in and take over the shuttle program," he said. "But then again, I look forward to the challenge, I think I have a great team in place right now that will help work through those issues and as we get the findings from the board, then we'll start working hard on trying to do the right things so we can get back to flying safely."

He took issue with comments by Rep. Joe Barton, R-Texas, who said Thursday the space shuttle "is an unsafe system and it is technically impossible to make it safe enough, in my opinion."

"I find it troublesome, maybe, that there are thoughts like that out there," Parsons said today. "But we have to work our way through that. I think we can fly this shuttle safely and so we look forward to doing that in the future."

Even so, he took the job with "quite a bit of trepidation. I mean, this is a big challenge for me and I had to think my way through it. But again, the shuttle program is extremely important to this agency and to have the opportunity to work with the contractors and the program folks to get this shuttle flying again so we can complete the international space station is something I look forward to."

Dittemore, a former flight controller, flight director and chief of shuttle engineering, was named shuttle program manager in 1999. He won widespread respect in the aftermath of the Feb. 1 Columbia disaster for holding daily news briefings to keep the public informed about the progress of NASA's ongoing investigation.

In late April, Dittemore told reporters he had made plans to retire before Columbia's launch and that he initially put those plans on hold following Columbia's loss. But he said it was important for NASA to select a replacement as soon as possible, before return-to-flight activities mature, so the new program manager can have time to absorb the intricacies of the job.

Kostelnik agreed today, saying Parsons will need to work closely with Dittemore in the weeks ahead to get up to speed on shuttle operations from the perspective of program manager.

"The shuttle is an incredibly complex piece of machinery," Kostelnik said. "It has an annual budget of about $3.5 billion or so, there are not only operational issues there are acquisition aspects, it'a a very complex management job and it does take some time to have a transition.

"Bill's a great leader and a solid manager, but has not been involved intimately with some of the moving parts of the shuttle and this will give them a reasonable time to do a graceful transition."

Parsons graduated from the University of Mississippi with a bachelor's degree in engineering. He also holds a master's degree in engineering management from the University of Central Florida. No specific date has been set for his replacement of Dittemore.

Reliable sources say NASA plans to name a new space shuttle program manager Friday to replace Ronald Dittemore, the widely-respected man in charge during the Columbia disaster who announced his retirement late last month. The identity of Dittemore's replacement is not yet known and a NASA headquarters spokesman reached at home late Wednesday said he had no knowledge of any such announcement. But sources said a successor has, in fact, been selected and that an announcement is planned for Friday in Washington.

In other developments, researchers have begun initial test runs firing external fuel tank foam insulation at a shuttle landing gear door in a bid to calibrate damage prediction software and to assess how much damage high-speed impacts might actually do to a shuttle's heat-shield tiles. Engineers ultimately plan to fire foam debris at a mockup of the shuttle's wing leading edge system, the location of the breach that doomed Columbia.

In the initial runs, firing foam from a nitrogen gas canon at the Southwest Research Institute in San Antonio, Texas, only minor damage was observed in the landing gear door tiles, sources said.

Columbia's left wing was struck by falling external tank insulation 82 seconds after launch Jan. 16. Investigators suspect the impact damaged the leading edge of the wing in some fashion, directly causing, or at least contributing to, the creation of a breach that destroyed the ship during re-entry on Feb. 1.

The Columbia Accident Investigation Board is overseeing a complex series of tests at the Southwest Research Institute that will culminate early next month with firings aimed at a highly-instrumented mockup of a wing leading edge.

In three of four initial runs this past week, tiles on a landing gear door taken from the prototype shuttle Enterprise withstood foam impacts at angles of 5 degrees with little or no damage, sources said. The foam samples were not as large as the piece of debris that hit Columbia, but engineers can achieve the desired results by properly varying mass and velocity to achieve the range of kinetic energy imparted in the actual launch impact.

The fourth run in the series, in which the canon fired a foam sample at an 8-degree impact angle and a slightly higher-than-planned velocity, caused visible but relatively minor gouging. The foam that hit Columbia's wing was moving between 416 and 573 mph, engineers believe.

CAIB members have stressed that the landing gear door target was selected early on, before engineers knew the breach occurred in the leading edge, and that these results are not directly applicable to the board's current failure scenario. The real test will come next month, when investigators begin firing foam at the leading edge mockup.

Dittemore, a former flight controller, flight director and chief of shuttle engineering, was named shuttle program manager in 1999. He won widespread respect in the aftermath of the Feb. 1 Columbia disaster for holding daily news briefings to keep the public informed about the progress of NASA's ongoing investigation.

CBS News reported Dittemore's plans to retire April 19. The following week, he told reporters he had made plans to retire before Columbia's launch and that he initially put those plans on hold following Columbia's loss. But he said it was important for NASA to select a replacement as soon as possible, before return-to-flight activities mature, so the new program manager can have time to absorb the intricacies of the job.

"It would be very important to have new leadership in place, to have that foundation established," he said. "And as you move forward over the coming months, building on that foundation from a new leader perspective, you're going to be that much more prepared, both from a leadership point of view and a team responding to that leadership, to move right into return to flight and then, picking up the flight rate again.

"I believe personally this transition time frame would be extremely beneficial to allow this new leader time to prepare, the time to respond to recommendations, the time to implement recommendations, to have a strong foundation, to have a strong springboard to jump forward into the coming years."

For the first time, the Columbia Accident Investigation Board has endorsed a detailed failure scenario developed by NASA and contractor engineers that traces the shuttle's destruction to a breach in the ship's left wing at or near leading edge panels 8 and 9. That scenario, first reported by CBS News on April 20, assumes Columbia began its ill-fated Feb. 1 descent to Earth with a breach in the leading edge and that hot gas ate its way into the interior of the wing less than eight minutes after the orbiter fell into the discernible atmosphere 76 miles above the Pacific Ocean.

How large the initial breach might have been is not yet known. But the day after Columbia's launching, military radars tracked an object separating from the orbiter. Investigators believe the "flight day 2 mystery object" left an opening of some sort that provided a direct path for hot air to enter a cavity behind the U-shaped reinforced carbon carbon panels making up the leading edge of the left wing. More than two dozen shuttle components have been tested to find the best match with the radar data and today, experts testified before the CAIB that only two candidates are still on the table (a third has yet to be tested).

One is a large section of an RCC panel measuring up to 120 square inches. The other is a T-seal, one of 22 such fasteners used to lock the RCC panels together. Under the scenario developed by NASA and the CAIB, the mystery object could be either the T-seal between RCC panels 8 and 9 or a large section of the lower portions of the RCC panels themselves.

"From all the testing and analysis we've done, we feel RCC T-seals as a class cannot be excluded and RCC, what we call acreage, or pieces of the panel, cannot be excluded," said Steve Rickman, chief of the thermal design branch at the Johnson Space Center. "But there is another point to be made there, that the panel acreage itself would have to be on the order of 0.33 inches thick for it to have the correct ballistics. ... It turns out that on the lower panel acreage in the panel 8-to-9 region you do have RCC panel acreage that is of this thickness."

The loss of a T-seal would have left a slot-like gap between panels 8 and 9 just a few inches across as opposed to the much larger hole represented by the loss of a section of RCC panel measuring between 90 and 120 square inches. Engineers currently are trying to determine how big the actual breach must have been to permit the entrance of enough heat to explain the timing of sensor readings and dozens of subsequent sensor failures.

"My understanding is that NASA is, in fact, doing specific analyses for those different shapes, sort of two-dimensional analysis," said board member Sheila Widnall. "My understanding is the hole sizes they've been using to date are quite a bit smaller than the RCC panel that was suggested in the Wright Patterson radar tests. So I think more analysis is clearly required."

Board chairman Harold Gehman said "this is one of the key areas we're going to continue to focus on."

"The way I like to describe it is that the breach that was there at the time of entry has to be big enough to cause the heat scenario that we saw but it also has to be small enough to permit the orbiter to get all the way to Texas. Keeping in mind that we've got some bounds in there and we've got a very, very rich timeline, I believe we've got a good chance of achieving the analysis it's going to take to be more specific about this. We're talking about weeks of work here. It's just plain hard work."

But it is critical work and it will play a major role in how NASA and CAIB investigators design upcoming tests at the Southwest Research Institute in San Antonia, Texas, to fire external tank foam insulation into leading edge components in a bid to simulate what went wrong in the first place.

As is well known by now, just 82 seconds after liftoff Jan. 16, a large piece of foam broke away from Columbia's external fuel tank. The debris originated at or near the left bipod ramp, an aerodynamically shaped area of foam just in front of a strut that helps hold the nose of the shuttle to the tank. At least three distinct pieces can be seen falling away from the bipod area in enhanced footage from ground cameras. But only one - the largest - actually hit the left wing. Experts testified today the large piece measured 24 inches by 15 inches with an uncertainty of 3 inches. The thickness of the debris has not been determined but it is believed to be relatively thin. The impact velocity was somewhere between 610 feet per second and 840 feet per second, or between 416 mph and 573 mph.

The debris hit the left wing in a "footprint" centered on the lower side of RCC panels 6 through 9. It's possible the impact damaged the T-seal between panels 8 and 9 - or cracked one of the RCC panels - and that the damaged component finally shook free the day after launch, leaving an opening into the cavity behind the leading edge. Investigators have not yet come up with a credible mechanism to explain how the damaged component was able to remain in place for a full day and then separated on flight day two.

But for their part, Gehman said the board has deliberately excluded the foam impact as a direct cause of the disaster in its working hypothesis of what went wrong.

"We were careful not to say the foam knocked a hole in the leading edge of the orbiter because we can't prove it," he said. "Now that's not to say we don't believe that's what happened, but we were careful here to base our working scenario on agreed facts and right now, we aren't willing to make that kind of a statement."

Whatever caused the breach in the leading edge, the pathway for hot air was large enough to trigger a remarkably rapid series of events. The shuttle entered the atmosphere at 8:44:09 a.m. Less than eight minutes later, at 8:52:05 a.m., the shuttle began responding to unusual aerodynamic forces. At some point between that moment and 8:52:16 a.m. - 11 seconds later - the hot air had burned its way through the wing spar and into the wing's interior. One minute later, by 8:53:10 a.m., 120 sensors had dropped off line as the super-heated air burned through wiring inside the wing just behind the spar.

That data was recorded on board and not transmitted to the ground. The first realtime indication of a possible problem in the left wing came at just about that same moment - 8:53:10 a.m. - showing up on a computer display monitored by the mechanical systems officer in mission control. By that point, the wing was in severe distress and complete failure was just seven minutes away.

The upcoming tests at the Southwest Research Institute, scheduled to begin in early June, "will demonstrate to us whether or not we have a plausible scenario," Gehman said. "But it doesn't seem to me that it will prove anything one way or the other."

Gehman said the board hopes to begin writing its report later this month. No more hearings are currently scheduled for Houston but the board plans to relocate in Washington next month and one or more hearings may be held there to flesh out questions about NASA's management and operating philosophy. Gehman said it will not matter in the long run whether investigators ever conclusively link the foam impact with the leading edge breach.

"We can make fairly good case of what we think the return-to-flight criteria should be with or without any positive knowledge or positive proof that the foam caused the accident," he said. "Because we're going to make return-to-flight recommendations that are designed to enhance the safety of the orbiter in every way we find that it needs to be enhanced.

"Just fixing the foam alone won't do it. So I'm not the least bit concerned that our inability to make a positive statement with proof that the foam knocked a hole in the leading edge of the orbiter in any way slows us up or in any way restricts what we need to do in order to come up with a criteria for return to flight. Most of our work on return-to-flight issues has to do with the fact that the safety margins have been changed over the years and we're going to try to restore those safety margins back to at least as far as we're comfortable with."

Lest there be any doubt Gehman is serious about addressing a wide-range of issues in the board's final report, he stressed again today that "we're looking at this program and these shuttles in a very, very broad way. We have to, because we don't have a single point failure like the O-rings (that caused the Challenger disaster). And therefore we're going to come up with a broad range of recommendations, which taken together, we believe, will make the program safer. The fact that we don't have a single causal event doesn't bother me in the least. ... It may not be quite so easy to explain, but practice wise and function wise, it doesn't bother me in the least."

He also said the board plans to address the overall risk of flying the shuttle to stimulate public debate.

"The board is going to attempt to characterize the true risk in our own words," Gehman said. "Whether or not we put a number on that, the board hasn't decided. But we are going to attempt to describe for our constituents - the Congress, the administration, the astronauts and the people of the United States - what the risk is in this enterprise. It's not zero, it's not anywhere near zero.

"I don't know that the board would be interested in putting a number on it. ... Whether or not we pass judgment on any number that NASA uses remains to be seen. But we will attempt to characterize the risk in our own terms and if it differs from NASA's, so be it. But that will be one of our goals, to restate the risks in terms that there can be a good public policy debate on whether or not we should be doing this or not."

Readers are encouraged to review the April 20 CBS News status report below for details about NASA's failure scenario. Here is the text of a CAIB news release today summarizing the board's conclusions to date:

Columbia Accident Investigation Board Releases Working Scenario

Houston, Texas Ğ The Columbia Accident Investigation Board (CAIB) today released their working scenario.

After three months of intense investigation including thorough reviews of hardware forensic analysis, orbiter telemetry, Modular Auxiliary Data System (MADS) recorder measurements, general public still and video photography, hypersonic wind tunnel testing, and aerodynamic and thermal analysis, the Columbia Accident Investigation Board, with the assistance of the NASA Accident Investigation Team (NAIT), has reached the following preliminary conclusions.

Launch:
Approximately 81 seconds after a 10:39 EST launch on January 16, 2003, post launch photographic analysis determined that foam from the External Tank (ET) left bipod ramp area impacted Columbia in the vicinity of the lower left wing RCC panels 5-9.

Orbit:
While Columbia was on orbit for 16 days, there was no indication of damage based on orbiter telemetry, crew downlinked video, still photography or crew reports.

An Air Force Space Command post flight evaluation of radar tracking data indicated an object in the vicinity of the orbiter on flight day two, remained on orbit for approximately two and a half days, then reentered the atmosphere. Radar testing and ballistics analysis of various thermal protection system items and thermal blankets, along with careful inspection of downlinked orbiter payload bay video, has been used in an attempt to identify that object. Testing and analysis to date have eliminated from consideration all but a piece of an RCC T-seal or RCC panel with a rib. However, there is no conclusive evidence that either of these items was the object that departed the orbiter.

Entry:
The de-orbit burn and entry targeting were accomplished using well-established Mission Control Center procedures. There were no problems identified with this process.

On the morning of February 1, Columbia entered with unknown damage to an RCC panel or T-seal in the left wing RCC panel 5-9 area. Hardware forensic analysis and a review of MADS temperature and strain measurements on the left wing leading edge structure point to the RCC panel 8/9 area as the most likely area of damage. The forensic evidence indicated the RCC panel 8/9 area was subjected to extreme entry heating over a long period of time, leading to RCC rib erosion, severely slumped carrier panel tiles, and substantial metallic slag deposition on the RCC panels nearest the damaged area.

MADS data indicated the RCC cavity temperature and the temperature behind the wing leading edge spar began to rise at approximately 8:49:00 EST. This indicates that hot gas flowed into the RCC cavity between entry interface 8:44:09 EST and 8:49:00 EST. Three minutes later, at 8:52:00 EST, temperature and strain measurements indicated that hot gas penetrated the internal part of the wing via a breach in the wing leading edge spar. Immediately, the hot gas inside the wing began to heat wire bundles containing real-time telemetry and MADS data. A MADS upper left wing pressure measurement was the first to fail at approximately 8:52:16 EST. Over the next four minutes, 164 other measurements fail, with the last failure at approximately 8:56:24 EST. Most measurements failed very quickly, within the first two minutes of the breach.

ColumbiaÕs flight control system began to sense increased drag on the left wing due to the damage at 8:52:05 EST. The vehicle easily compensated for the initial aerodynamic disturbance. A significant change in the vehicle aerodynamics was observed at 8:54:20 EST, indicating a change in the damage to the left wing. At the same time several very bright debris events were seen in ground-based videos.

Soon after the hot gas entered the left wing multiple debris events were captured on video by observers on the ground. These video images begin at 8:53:46 EST (20 seconds after California coastal crossing) and end with ColumbiaÕs final break-up. The exact source of the debris may never be fully understood. However, upper wing skin and Thermal Protection System (TPS) parts are possible candidates. Damage to the internal aluminum wing structure was most probable during this timeframe as well. These debris events appeared to affect orbiter communication. There were 13 unexplained communication dropouts in this timeframe.

By 8:56:16 EST hot gas had penetrated the wheel well wall as indicated by an off-nominal rise in hydraulic line temperatures. Another significant change in ColumbiaÕs aerodynamics occurred at 8:58:09 EST, accompanied by several more debris events. The vehicle responded to this event with a sharp change in its aileron trim. Additionally, by 8:58:56 EST all left main gear tire pressure and temperature measurements were lost, indicating a rapid progression of damage inside the wheel well. A continual progression of left wing damage caused another abrupt change in the vehicleÕs aerodynamics at 8:59:29 EST. Columbia attempted to compensate by firing all four right yaw jets. By 8:59:32 EST the Mission Control Center had lost all telemetry data. MADS recorder data was lost at 9:00:14 EST. Based on video imagery, main vehicle aerodynamic break-up occurred at 9:00:23 EST.

Analysis and Testing Underway to Support the Working Scenario:
Although there is an abundance of existing evidence supporting the Working Scenario described above, the CAIB and NAIT have the following analyses and testing underway to refine the details of the scenario:

1. Completion of RCC and tile impact testing at Southwest Research Institute.

2. Aerothermal analyses to correlate off nominal heating trends in left fuselage sidewall and left Orbiter Maneuvering System (OMS) pod heating that were observed in the MADS data.

3. Instrumentation wire burn-through arc jet tests and thermal analyses to support the timing of observed instrumentation failures.

4. Instrumentation circuit analyses or testing to confirm the failure signatures observed in the data.

5. Hypersonic wind tunnel testing and aerodynamic analyses to explain aerodynamic roll and yaw moments observed in flight data.

6. Thermal analysis of RCC panel 9 clevis and spar temperature sensor responses to support or refute flight data.

7. Gas flow and heat transfer calculations internal to the wing to support the MADS sensor readings in and around the wheel well.

8. Arc jet testing and/or analysis of previous arc jet testing to determine feasibility of RCC erosion observed in several key pieces of RCC panel 8/9 debris.

9. Continued forensic testing and analysis of significant recovered debris.

10. ET dissection and cryopumping tests.

The CAIB has not reached any final conclusions and has not determined the cause of the loss of the shuttle and crew. The board's final report will be issued later this summer.

"By building a working hypothesis, it really enables us to focus the testing, it enables us to much more narrowly direct the analysis, it really produces a very synergistic effect on different disciplines," Gehman said.

"The real value of this is that it tells us what to do now and where to go next," he said. "The foam impact testing is very important to us, we have to continue the very, very hard work on the aerothermal analyses to correlate some of these events that we have really good data on but yet we can't quite fully understand everything that's happening, like how long does it take to burn through Kapton wiring, how long does it take to create a knife edge (burn pattern) in a piece of RCC that's a third of an inch thick, how long does it take to burn through aluminum skin and those kinds of things."

As NASA and independent investigators close in on the root cause of the Columbia disaster, one question lingers in the minds of many armchair analysts: What, if anything, could have been done to save the crew if engineers had known early on that the orbiter had a non-survivable breach in the leading edge of its left wing?

The answer, according to a detailed NASA analysis obtained by CBS News, is that Columbia was doomed from the moment the wing was damaged, most likely during ascent, and that nothing could have been done to reduce the stress of re-entry enough to save the ship and its seven astronauts.

Not that NASA wouldn't have tried. But given the severity of the leading edge breach investigators now know was present at the start of Columbia's descent, there simply were no Apollo 13-class engineering rabbits to pull out of the hat.

"I have wracked my brains over this," LeRoy Cain, the entry flight director for mission STS-107, said in an interview. "There just was no way we were getting that vehicle back. If we'd gone and taken some pictures and done whatever else anybody could think of, it wouldn't have changed the outcome for Columbia."

NASA's oldest space shuttle was launched Jan. 16 on a planned 16-day science mission. Eighty one seconds after liftoff, a large piece of foam insulation broke away from the ship's external fuel tank and hit the left wing's leading edge at some 450 mph.

While an independent investigation into the disaster is not yet complete, many engineers believe the foam impact, possibly in combination with other factors, damaged one of the wing's reinforced carbon carbon composite panels, providing a path for super-heated air to enter the wing during re-entry Feb. 1.

In the wake of the resulting catastrophe, Cain was charged with carrying out an "entry options" review to determine what might have been possible to reduce re-entry temperature extremes, or loads. The study will be presented to shuttle program management next week.

As it turned out, the only viable options involved lowering the shuttle's orbit before beginning the descent and drastically reducing the ship's weight by as much as 15 tons.

Diverting Columbia to the international space station was never an option because the two spacecraft were in different orbital planes and the shuttle did not carry nearly enough fuel to make such a rendezvous. Cain's review did not address the possibility of launching an emergency shuttle rescue mission. But engineers say they do not believe it would have been possible to get the next shuttle in the launch sequence - Atlantis - into orbit before Columbia's crew ran out of carbon dioxide-scrubbing lithium hydroxide.

That said, three options were evaluated in Cain's review but the best results were achieved in the third, most extreme scenario, one that assumed the astronauts dumped everything possible overboard to reduce the shuttle's weight to an absolute minimum while keeping barely enough fuel and other supplies on board to ensure a survivable landing.

It is not a scenario flight controllers would ever actually implement in its entirety. It is fraught with extreme risk and major unknowns, risks that might well outweigh the threat posed by a damaged thermal protection system. But the goal of the entry options review was to assess what might be possible, in theory, regardless of likely operational constraints.

Scenario 3 assumed the astronauts, staging at least two emergency spacewalks, could dump 31,321 pounds of equipment and supplies overboard, including Columbia's pressurized Spacehab research module (18,071 pounds), a pallet of experiments in the cargo bay known as Freestar (4,428 pounds) and unneeded crew equipment (4,663 pounds). Another 4,159 pounds of consumables - propellants, hydrogen, oxygen, water, hydraulic power system fuel - also would have to be dumped or used up.

The scenario requires numerous flight rule violations and would leave the shuttle at "absolute minimums in critical systems" with no deorbit waveoff opportunities and only a minimal ability to cope with additional failures. But it did reduce the maximum temperatures associated with re-entry.

"When we messed around enough with the weight, we started to see some reductions, getting some thermal relief in a generic sense, which makes sense," Cain said. "If we bring the altitude down before we deorbit, we're reducing the energy, if we get a bunch of weight off then we're reducing the energy. All that weight translates into energy dissipation we have to do during entry.

"So we did that. And really, what we did here is we tried to bound the problem and that's important to understand. We did it not because we said this is realistically things we can go do, this is throwing everything in the kitty, pulling out all the stops, doing things we really wouldn't really be able to accomplish all of and adding it all up and seeing what it does for you."

The study examined heating at three representative points on the orbiter leading edge and under belly. In an important caveat, all the scenarios assumed there was no damage to the shuttle's thermal protection system (TPS) because there are no computer models capable of accurately predicting how even minor damage might affect heating.

"One of the major, significant caveats to the whole thing is we did this for a nominal TPS," Cain said. "If I have exposed structure, then even getting rid of 32,000 pounds isn't going to save the day for me. It's just not, whether it's exposed structure on the lower surface or its on the wing leading edge.

"We don't know what we had (on STS-107), but we had somewhere from some amount of damage to exposed structure. We don't have a model to put in some amount of damage and then understand the resulting thermal protection."

That said, the scenario 3 results show:

• A 7 percent reduction in the wing leading edge maximum temperature near reinforced carbon carbon panel No. 9;

• A 24 percent reduction in heat load and a 34 percent reduction in heat rate for tiles just in front of the main landing gear doors;

• A 29 percent reduction in heat load and a 56 percent reduction in heat rate for tiles aft of the main landing gear doors.

Heat rate is the maximum temperature a component might experience during entry while the heat load is a measure of the amount of time the heat is applied to the orbiter's structure. To see how this works, consider a shuttle making a shallower descent than normal. While that would reduce the maximum temperatures experienced by the orbiter, it would increase the peak load because heating would be stretched out over a longer period of time.

"The thermal tradeoff line that we have today is a balancing act of those two things for the various surfaces," Cain said. "It's a delicate balance and the shuttle TPS is so complex. It just boggles my mind. It's even more complex than I thought it was before STS-107, just in terms of the different kinds of TPS we have and everything."

In Columbia's case, of course, it was the leading edge that mattered. Cain said a 7 percent reduction in leading edge temperature would not have been enough to prevent disaster. Even if the crew oriented the shuttle so that the belly of the craft was in shadow for more than two full days prior to entry, "cold soaking" the thermal protection system and lowering its temperature by 65 degrees, the outcome would have been the same.

"On STS-107, wing temps may have increased as much as 700 degrees in 400 seconds post EI (entry interface)," the entry options review stated. "A 65-degree decrease in EI wing temp would have resulted in (about a) 37-second delay in onset of same max temps and heat load."

Cain said the temperature improvement, however minor, possibly could be useful "if you had something that wasn't totally nominal in terms of TPS but it was maybe minor damage."

"Let's say on the wing leading edge you had a crack, you didn't have a breach yet but somehow you'd compromised the integrity of that part of the structure," he said. "Then that 6 or 7 percent, it might be significant for that case. I don't know enough to say today one way or the other. I do know that with respect to the 107 case it definitely wasn't significant."

During Columbia's flight, engineers concluded the foam impact during launch was not a "safety of flight" issue. As such, NASA managers did not request any spy satellite imagery to provide additional insight. Whether that was a good decision or not, the management team had no conclusive evidence that Columbia faced a serious threat.

But to have accomplished the extreme measures listed in scenario 3, planning would have had to begin almost immediately, meaning NASA managers would have needed convincing proof a safety of flight issue did, in fact, exist, within a day or two of launch.

"Excessive risks associated with any of the three options (scenario 1, 2 or 3 or any other combination) would require that significant and convincing data exist proving that the orbiter could not survive entry," the entry options review noted.

The scenarios all assumed "certified" re-entry profiles, meaning "our models match what we really see in flight," Cain said. "'Uncertified' means we don't know, we haven't done it for sure in flight, we haven't analyzed it and we haven't simulated it."

He said he could not imagine a real-world scenario that would lead the flight control team to order an uncertified entry requiring, for example, a higher- or lower-than-normal angle of attack to reduce heating on a specific area.

"There are certainly things that I can dream up where if you had some situation in flight that really put us in a bad situation, we're going to brainstorm and think of anything we can and at some point you've got to pick an option and go with it because you're running out of time," Cain said. "But for this case, I can't really imagine (that scenario)."

Ongoing analysis of recovered debris from the shuttle Columbia indicates the deadly breach in the ship's left wing may have been centered on a broken leading edge panel and not slightly outboard at a so-called "T-seal" as investigators were thinking last week, the Columbia Accident Investigation Board said today.

While a T-seal failure has not yet been ruled out, several lines of evidence now point to a failure at or very near the lower half of leading edge panel No. 8. That's where NASA investigators assumed the breach was located in their own failure scenario, which was briefed to the CAIB last week (see the April 20 status report below for complete details).

"I wouldn't say that T-seal No. 8 is totally out of the picture," said board member Roger Tetrault. "I've found that every time you think you have an answer ... something shows up that takes the wind out of your sails. But I'd say it was getting more probable that the breach is a little bit farther to the inboard side of the wing than where T-seal No. 8 is."

Columbia was destroyed Feb. 1 during re-entry when a breach in the leading edge of its left wing allowed a plume of super-heated air to eat its way inside, ultimately triggering a catastrophic structural failure. The damage is believed to have been caused, at least in part, by the impact of foam insulation that broke away from the shuttle's external fuel tank 81 seconds after liftoff Jan. 16. The foam slammed into the leading edge of the left wing at more than 450 mph.

The leading edge is made up of 22 U-shaped reinforced carbon carbon panels that handle the aerodynamic loads and extreme temperatures of re-entry. The panels are held in place at each end by U-shaped T-seals bolted to the front spar of the wing.

The day after Columbia's launching, military radar systems detected an object moving away from the shuttle. That mystery object, first reported by CBS News, is now believed to have separated from the breach area. CAIB investigators said last week a T-seal, or a substantial piece of a T-seal, was consistent with the "radar signature" and area-to-mass ratio of the mystery object.

That is still true. But today, Tetrault said additional evidence raises questions about the T-seal hypothesis. First of all, there is now some uncertainty as to whether recovered T-seal fragments came from the inboard side of RCC panel 9 or from father outboard on the wing. More telling, perhaps, X-ray analysis of slag-like deposits found on the inner surface of fragments from RCC panel 8 are consistent with a breach in the lower part of that panel. NASA has recovered three pieces that once made up the upper section of RCC panel 8 but nothing from the lower half.

"What you see on the X-ray you do not see visually," Tetrault said. "What you begin to see (are) deposits of heavy metals in certain patterns that we don't see when we look at it visually. ... There are small nodules of metal which are being deposited in a very uniform pattern.

"If you stood behind the RCC panel and took a paint brush and sprayed it at the back of the RCC panel, you would get deposits that look very similar to this. They are very uniform and very straight up and down. It begins to indicate that we're not getting a lot of side flow from, say, a T-seal position or even a panel further back."

Translation: Assume a hole in the lower half of RCC panel 8 and visualize the shuttle oriented in a 40-degree nose-up entry attitude. Hot air would enter such a breach at an angle, impinge on and ultimately burn through insulation on the front of the spar and eventually through the spar itself. Molten droplets of metal would have been blown backwards as this process proceeded, onto the inside surface of the upper part of RCC panel 8. The slag pattern seen in the X-rays Tetrault referred to is not consistent with the sort of "side flow" one would expect if the breach was located at the outboard T-seal or farther out the leading edge.

When the plume finally burned its way into the wing's interior, it hit the upper surface of the outboard side of the left main landing gear wheel well and burned through cable bundles mounted there in a top-to-bottom sequence.

Based on analysis of the known locations of sensor wires just behind the spar; the timing of sensor failures as the plume burned through various wire bundles; the observed heat damage to recovered debris from RCC panel 8; and heat damage seen in debris from areas adjacent to panel 8, it now appears the breach may have, in fact, occurred on the lower side of panel 8 as NASA investigators assumed when they developed their own "best fit" failure scenario.

The plume "probably hit the (insulation) material before it hit the spar and that was the first deposits that were made to the back of the RCC panels," Tetrault said today. "With regard to the cutting of the wires along the wheel well, actually by moving a little bit father inboard, you actually close the distance between those wires that were cut along the spar versus the wires that were probably cut along the wheel well and that makes it even more possible this sequence works properly."

Starting next week, investigators using a nitrogen gas canon at the Southwest Research Institute in San Antonio, Texas, will begin firing large pieces of foam insulation at selected wing targets to determine what sorts of damage might result from high-speed impacts.

Foam will be fired first at large areas of heat-shield tiles representative of the surface of the underside of Columbia's left wing. By early June, investigators hope to begin firing foam at a test rig that will simulate the left wing leading edge system between RCC panels 6 through 9.

"The testing starts this week," said board chairman Harold Gehman. "But the testing is limited by the target, not by the bullets. We have plenty of foam. But when we decided to do foam testing 30 days ago, we were talking about (landing gear) wheel well breaches and so the first test rig that we built was a wheel well. That's what we're ready to shoot at. Now we're talking about the leading edge system and it'll take us a couple of weeks to build a representative of the leading edge."

To make the test as accurate as possible, high-flight-time leading edge panels from other shuttles, as well as pristine panels from the prototype shuttle Enterprise, will be mounted on the test rig using T-seals.

"We're building up a leading edge section that's going to be essentially from panel No. 6 to panel No. 9 so that we can shoot at anything we want," Gehman said. "By the time we get ready to actually shoot at it, we'll know more about what angles we cover. We may want to shoot it at an angle that covers two T-seals and one panel or two panels and one T-seal. And we may shoot a couple of times."

He said the tests are being designed to indicate "whether or not a foam strike of the size and the velocity we saw in this particular event has the capacity to damage the leading edge system with sufficient damage to cause a hole that would initiate this event."

"Even if we do create damage on the test article that is of sufficient magnitude to initiate this event, that doesn't prove it did it," Gehman said. "It just proves it could have done it. And oh by the way, we have oversimplified to some degree what we're talking about here. I can pound on this table with a sledge hammer and not do any damage to the table, but (I might still) break a leg. The same thing could be true of the leading edge system. We could hit the outside of the leading edge system and not do any damage to it, but we could break the support structure, break a bolt, break a pin, in which case we would have something flapping in the breeze that might come off later.

"So we're going to carefully instrument the inside of this target so that we can, through analysis, better characterize all the ways that it could fail, not just a fracture through the RCC."

The NASA Accident Investigation Team today presented results of the agency's on-going analysis of the Columbia disaster to the independent board charged with finding the root cause of the disaster. That presentation is believed to have included one or more possible "best-fit" scenarios based on telemetry, recorded data and debris recovered to date.

One such scenario, which assumes a breach in Columbia's left wing at or near leading edge panel No. 8, was outlined on this page last weekend. Major elements of that scenario presumably were briefed to the CAIB today. Ten members of the board were either present for the briefing or listening in via telecon. Between 30 and 40 NASA and contractor personnel participated.

But in a short news release, the board said "in order to finalize a primary working scenario, more work is required in four areas of analysis.

"Those four areas are: aerothermal analysis, foam impact testing, testing of flown reinforced carbon carbon panels, and metallurgical analysis from debris," the statement said. "The NAIT provided an overview of the latest data recorder information and the CAIB issued its guidance based on that data and board investigatorsÕ continuing analysis of the latest orbiter debris."

The release concluded that "the CAIB has not reached any final conclusions and has not determined the cause of the loss of the shuttle and crew."

A source close to the board said CAIB investigators were in "violent agreement" on the basics of the accident scenario, i.e., a breach in the left wing led to the disaster. But there is not yet agreement on the finer details of how the plume of super-heated air entering the breach propagated through the wing and ultimately led to its failure.

"It has to do with the level of detail of the (NASA) scenario," the source said. "At a very high level, there's a whole series of facts that I believe we're getting very good agreement on. When you go and penetrate down to detailed timelines, to detailed interpretations, that is where we need to do more work.

"And that's part of what's laid out (in the CAIB press release) in terms of aerothermal analysis, how did the heat that got into the left wing propagate and can you really demonstrate that this sensor going up here is consistent with that or did it come from a different direction? You have to get down to that next level or two of detail. They called it multiple scenarios, I'd say multiple interpretations of the facts."

In case there were any doubts, the chairman of the Columbia Accident Investigation Board said Wednesday that finding the root cause of the shuttle disaster is only part of the panel's charter and that lawmakers in Washington have made it clear they expect broad changes in NASA's organizational structure.

And that's exactly what they're going to get.

"You can see the depth and the details that we are exploring (in) these issues of risk, risk management," Harold Gehman told reporters after the board's fifth public hearing. "We're going to interview many, many more experts on this subject and we're going to approach this issue probably more broadly than the Challenger report did. But we're also going to approach it with great care because of the 'law of unintended consequences.' We are not experts in this area, but clearly this area can stand some scrutiny."

"I'm just probably a little bit dense," a reporter said, "but it finally sunk in to me today, listening to some of your questions, that the management system-slash-culture, and I'm not sure how you separate those two, really is going to come under your microscope and you really are going to change it, aren't you?"

"That's correct," Gehman replied. "This is a result of my direct liaison with all of the (congressional) oversight committees, both the chairmen and minority members, who want a broader report than just what happened. And that's what they're going to get."

In earlier testimony before the board, a sociologist who spent years researching the organizational flaws that led to the 1986 Challenger disaster said that she, like former astronaut and CAIB member Sally Ride, hears "echoes of Challenger" in the way NASA managers came to accept as normal serious problems in a critical system.

In the case of Challenger, that critical system involved the O-ring seals in the joints of the shuttle's solid-fuel boosters. Flame from the interior of the rocket was never supposed to reach the O-rings, but heat damage was seen so frequently it came to be accepted as a normal occurrence and not a "safety of flight" issue. Challenger was destroyed by an O-ring burn-through.

In the case of Columbia, the critical system was the shuttle's thermal protection system. Foam insulation on the external fuel tank is not supposed to come off in flight. Yet dozens of protective heat-shield tiles on the shuttle's belly are damaged in virtually every flight by bits of foam debris breaking away during ascent. A large foam impact is believed by many to have played a role in the Columbia disaster.

In testimony at an earlier hearing, external tank engineers told the board that a top level requirement calling for no foam shedding at all remains on the books and that project engineers were well aware that a large enough piece of foam debris could pose a catastrophic threat to the shuttle.

A large piece broke off during a flight in October, hitting one of the shuttle's boosters. But foam shedding was not considered a safety of flight issue and while the impact was discussed at a flight readiness review before the next launch, it was not discussed in any detail during Columbia's FRR.

Eighty-one seconds after Columbia took off on Jan. 16, a suitcase-size piece of foam broke off the tank. One second later, it slammed into the leading edge of the shuttle's left wing at 450 mph, disintegrating in a shower of debris. A hurried analysis during the mission concluded the wing might have been damaged, but not to any catastrophic extent. It was not, in other words, a safety of flight issue and requests for close-up satellite imagery to inspect the area were turned down.

"I want to start from the point of view of Sally Ride's now famous statement, (that) she hears echoes of Challenger in Columbia," Diane Vaughan, author of "The Challenger Launch Decision," told the Columbia Accident Investigation Board Wednesday. "The question is what do these echoes mean? When you have problems that persist over time in spite of the change in personnel, it means that something systematic is going on in the organizations where these people work.

"Challenger was not just an O-ring failure, but it was a failure of the organizational system," she said. "What the echoes mean is that the problems that existed at the time of Challenger have not been fixed, despite all the resources and all the insights the presidential commission found, that these problems have still remained.

"And so one of the things that we need to think about is when an organizational system creates problems, the (corrective) strategies to make, the changes have to, in fact, address the causes in the system. If you don't do that, then the problems repeat and I believe that's what happened with Columbia."

Vaughan, a professor at Boston College, described the process in which well-intentioned NASA managers came to accept O-ring damage - or external tank foam shedding - as normal an "incremental descent into poor judgment" based on the "normalization of deviance."

"This was (a) design from which there were predicted to be no problems with the O-rings, no damage," she said. "An anomaly occurred early in flights of the shuttle and they accepted that anomaly. And then they continued to have anomalies and accepted more and more. This was not just blind acceptance, but they analyzed them thoroughly and on the basis of their engineering analysis and their tests they concluded that it was not a threat to flight safety.

"It's important to understand that this history was the background on which they made decisions on the eve of launch and that was one more step in which they, again, gradually had expanded the bounds of acceptable risk."

So how did this normalization of deviance, this eventual acceptance of damage in a system that was not supposed to experience regular damage, become standard operating procedure?

"It's important to know they were making decisions against a backdrop where problems were expected," Vaughan said. "Because the shuttle was designed to be reusable, they knew it was going to come back from outer space with damage and so there was damage on every mission. Put simply, in an environment like that, to have a problem is itself normal.

"So what to us in hindsight seemed to be clear signals of danger that should have been heeded, that is, the number of flaws in O-ring erosion that had happened prior to Challenger, looked different to them. What we saw as signals of danger they saw as mixed signals.

"They would have a problem flight, it would be followed by a flight in which there was no problem. They would have weak signals, something that in retrospect seemed to us to be a flight stopper to them was interpreted differently at the time. For example, cold, which was a problem with the Challenger flight, was not a clear problem and not a clear cause on an earlier launch.

"Finally, what we saw as signals of danger came to be routine," Vaughan said. "In the year before Challenger, they were having O-ring erosion on seven out of nine flights. At this time, it became a routine signal, not a warning sign."

By implication, NASA's acceptance of foam shedding as a routine event resulted in a mindset that played a role in the agency's post-launch decision-making process. The Boeing analysis of the foam impact was accepted even though it was based on limited test data based on impacts by much smaller pieces of debris. The analysis concluded there was no safety of flight issue. Requests for satellite imagery were never made, officials have said, because there was no safety of flight issue.

"What was obvious with Challenger was that on the eve of the launch that the concerns of the engineers were not prioritized," Vaughan said. "It also seems to be the case in the requests for the imagery from Columbia that concerned engineers discovering the foam strike at this point described it as large, there was nothing in their experience like this. It was the size of a Coke cooler. This was unique.

They wanted better imagery, she said, to help determine how extensive the damage might be.

"But somebody up the hierarchy canceled the request," Vaughan said. "The request did not go through proper channels, which points to me the significance of rules and hierarchies over deference to technical expertise."

In both Challenger and Columbia, she said, "following the normal rules and procedures seemed to take precedence. And we know that, in fact, in conditions of uncertainty, people do follow habits and routines.

"However, under these circumstances, where you have something without precedent, it would seem that this would be a time not for hierarchical decision making, but for a more collective, collaborative, what does everybody think, let's open the floodgates and not pull on the usual people but especially, what are the concerns of our engineers?

"And also to let up on the idea that you have to have hard data. Engineering hunches and intuitions are not what you want to launch a mission with. But when you have a problem that occurs that's a crisis and you don't have adequate information ... engineering hunches and intuition ought to be enough to cause concerns."

Vaughan also cited external pressures on the system - policy directives from Washington, budget shortfalls and unrealistic expectations - as factors affecting the way decisions are made. But the focus of her testimony was lessons learned from Challenger and how NASA might develop a better way to track problems and to identify those that pose potential risks before those risks are manifested.

"When you're working in a situation where problems are expected, you have problems every day and people are busy with daily engineering decisions, it becomes very difficult to identify and stay in touch with the big picture," she said. "How do you identify the trend so that people are aware when they're gradually increasing the bounds of acceptable risk? It is certainly true based on what we know about organizations and accidents that this is a risky system. And what we know is the greater the complexity of the organization, the greater the possibility of failure."

In a series of questions, Gehman displayed a strong interest in figuring out how to improve the system without falling victim to what he called the "law of unintended consequences."

"I'm still trying to understand the principles here," he said to Vaughan. "It seems to me that in a very, very large, complex organization like NASA is, with a very, very risky mission, some decisions have to be taken at middle management levels. Not every decision and not every problem can be raised up to the top. And there must be a process by which the level 3 and level 4 (managers), the decisions are taken, minority views are listened to, competent engineers weigh these things and then they take a deep breath and say OK, we've heard you now we're going to move on. Then they report up that they've done their due diligence, you might say.

"I'm struggling to find a model, an organization model in my head, when you've got literally thousands and thousands of these decisions to make that you can keep bumping them up higher in the organization with the expectation that people up higher in the organization are better positioned to make engineering decisions than the engineers. You said yourself hindsight is perfect. We've got to be really careful about hindsight.

"I'm trying to figure out what principles to apply," Gehman repeated. "We as a board are certainly skittish about making organizational changes to a very complex organization for fear of invoking the law of unintended consequences. So I need to understand the principles, I'm trying to figure out a way I can apply your very useful analysis here and apply it to find a way to figure out what the principles are we ought to apply to this case. So the part I'm hung up on right now is how else can you resolve literally thousands of engineering issues except in a hierarchical manner in which some manager, he has 125 of these and he's sorted through them and he reports to his boss that his 125 are under control. I don't know how to do that."

Vaughan offered two observations.

"Somehow or other in the shuttle program there is a process by which when a design doesn't predict an anomaly it can be accepted," she said. "That seems to me to be a critical point, that if this is not supposed to be happening, why are we getting hundreds of debris hits if it wasn't supposed to happen at all?

"It's certainly true that in a program where technical problems are normal, you have to set priorities. But if there is no design flaw predicted, then having a problem should itself be a warning sign, not something that is taken for granted. The idea is to spot little mistakes so that they don't turn into big catastrophes, which means spotting them early on.

"Two things, both of them NASA may be very aware of, is that engineers' concerns need to be dealt with. I can understand the requirement for hard data. But what about the more intuitive kinds of arguments? People feel disempowered because they've got a hunch or intuition and let somebody else handle it because they feel like they're going to be chastised for arguing on the basis of what at NASA is considered subjective information and they're not going to speak up. So there need to be channels to assure that, even giving engineers special powers if that's what's necessary. The other is the idea of giving more clout to the safety people to surface problems."

In the end, she said, "What we find out from this comparison between Columbia and Challenger is that NASA as an organization did not learn from its previous mistakes and it did not properly address all the factors the presidential commission identified.

"They need to reach out and get more information and look at other models as well. Thinking about how you might restructure the post-launch decision making process so that what appears to have happened in Columbia doesn't happen again. How can that be made more efficient? Maybe it needs to look more like the pre-launch decision process. But is there any evidence that NASA has really played with alternative models? My point about organizational structure is as organizations grow and change, you have to change the structures. But don't do it without thinking about what the consequences might be on the ground."

For its part, NASA has expressed no interest in Vaughan's conclusions or expertise. In a particularly insightful - and funny - exchange, board member John Logsdon asked Vaughan if anyone at NASA had ever called her for organizational advice, pointing out that her book is required reading in the Navy's nuclear training program.

"The book did get quite a lot of publicity," she replied. "I heard from many organizations that were concerned with reducing risk and reducing errors and mistakes. The U.S. Forest Service called and I spoke to hot shots and smoke jumpers, I went to a conference the physicians held looking at errors in hospitals, I was called by people working in nuclear regulatory operations, (by) regular businesses where it wasn't risky in the sense that human lives were at cost. Everybody called. My high school boyfriend called. But NASA never called."

Shuttle program manager Ronald Dittemore, the straight-talking "voice of NASA" credited with boosting the agency's image in the immediate aftermath of the Columbia disaster, will leave NASA after an independent accident investigation board completes its work, he told reporters today.

In an interview following a teleconference in Washington, Dittemore told CBS News he was not at all concerned about anyone getting the impression he had been sacked in the wake of the disaster.

"I made this personal decision some time ago in the fall," he said by telephone, waiting for a flight back to Houston. "Of course the timing was terrible right after (Columbia). So I just delayed it and (now) feel the timing is right. No, I'm not worried about the perceptions. It's one of those things where you make a personal decision and you feel that it's right and you just go with it."

The Orlando Sentinel and CBS News reported Saturday that Dittemore had planned to retire and take a job in private industry after the successful completion of Columbia's mission and that he stayed on in the wake of the disaster to oversee return-to-flight activities and to support the Columbia Accident Investigation Board.

Varous sources, however, said Dittemore planned to take a job with a particular shuttle contractor. But he told CBS News today that "I've made no agreements with anybody on any particular opportunities."

"Those opportunities in my opinion are wide open for me to discuss and think about and to entertain and whether it's in the human spaceflight business or some other business, I think they're all going to be something I'll look at. But at this stage, that's not my first priority and I'll work on that as time is available."

As a senior NASA manager, Dittemore would need a waiver from agency Administrator Sean O'Keefe before taking any job in which he would be representing a shuttle contractor in any future negotiations with the government. Without such a waiver - and they are rare - senior managers must wait a year before taking on such jobs.

During a teleconference from NASA headquarters earlier today, Dittemore said he began discussing his retirement with senior management last year and that now, as the accident probe begins transitioning from investigation to recommendations for corrective actions, was a good time to make his own personal transition.

"When you first come into a job like this, program manager for space shuttle, you recognize you have a tremendous opportunity," he said. "You get to work with some of the most capable and creative people ever gathered together in one place for one common cause. But you also recognize you cannot do it forever.

"Last summer, my wife and I and our family discussed the possibilities for the future and felt ... it was time for us to consider other opportunities. That's when the dialogue began with (senior management) about the possibilities and potential of leaving early in the spring of 2003.

"As the events unfolded in February, certainly all personal plans had to take a back seat," Dittemore said. "As the last two months have unfolded and now I see we're starting to move into a different realm of our investigation ... it seemed to me it was appropriate to talk with (management) again and pick this time to make a transition in leadership."

Dittemore, a former flight controller, flight director and chief of shuttle engineering, was named shuttle program manager in 1999. He said today it is important to begin the process of searching for his replacement now, before return-to-flight activities mature, so the new program manager can have time to absorb the intricacies of the job.

"It would be very important to have new leadership in place, to have that foundation established," he said. "And as you move forward over the coming months, building on that foundation from a new leader perspective, you're going to be that much more prepared, both from a leadership point of view and a team responding to that leadership, to move right into return to flight and then, picking up the flight rate again.

"I believe personally this transition time frame would be extremely beneficial to allow this new leader time to prepare, the time to respond to recommendations, the time to implement recommendations, to have a strong foundation, to have a strong springboard to jump forward into the coming years."

Michael Kostelnik, who oversees the shuttle and station programs for Bill Readdy, NASA's associate administrator for spaceflight, said he and Dittemore first discussed the program manager's departure last fall. And then the Columbia tragedy occurrred.

"Ron put aside his plans and his thoughts for pursuing opportunities because there clearly was a tough job to be done and I think you all were as much as anybody a beneficiary of his expertise because early on, when there were a lot of questions, Ron Dittemore was the voice of the program for the things that were happening, trying to put in context what we had experienced," Kostelnik said.

"I think most of you will agree that Ron during that time period did an outstanding job relaying some very complex, very technical thoughts in a way the media could deal with. And I think a lot of the credit NASA received early on for being open and being forthcoming with as much information as we had at the time, a lot of that we owe to Ron. In his role as the program manager, he did an outstanding job.

He said it will be difficult to find a suitable replacement for Dittemore because "it takes a certain kind of individual to step up to the challenge, not only a big program management job but one that has human life on the line."

"It's not very often we ask people in this country to do this," Kostelnik said. "It is a unique role and although we're sad to see Ron choose to go at this time, we know it's the right kind of thing for him if his chooses to do that. We wish him well as he pursues other opportunities downstream. We're all grateful for his 26 years of service."

Dittemore would not discuss the ongoing accident investigation, saying he did not want to comment on any potential findings before the Columbia Accident Investigation Board releases its final report this summer.

He did say NASA would need to do a better job tracking potentially dangerous trends across all the components of the vehicle to spot and recognize the potential severity of problems like foam insulation falling from the external fuel tank during launch. Foam shedding was a well-known known problem in the program and a foam impact on Columbia's left wing 82 seconds after launch probably played a role in the disaster. But foam shedding was never considered a "safety of flight" issue.

"Tracking trends is in the eye of the beholder and it's a difficult job," Dittemore said. "We have six or seven hardware elements in different locations. They have different databases of anomalies that may have happened either in manufacturing, or production or even in processing. We link those databases together today, but perhaps that linkage is not as optimized as it could be. And we're going to have to take a look at that, to do a better job of trending."

During shuttle mission STS-112 late last year, a large piece of foam insulation broke free and struck one of the shuttle's boosters. In the wake of the Columbia accident - and with the benefit of hindsight - many observers have questioned the wisdom of continuing to launch missions without first correcting the foam shedding problem.

Dittemore today defended the agency's response, saying every senior manager in the program was briefed on the matter.

"As a result of the foam strike on STS-112, there were actions that were given to the appropriate individuals and elements to discuss that strike, to understand its impact," he said. "There were actions to discuss that both at our change board within the program and at the level one flight readiness review. So that scenario and repercussions of that scenario were briefed across the program and to senior agency management in the flight readiness review and it was a healthy discussion.

"And so I consider that an appropriate response to an event," he said. "Now whether or not we nailed everything down and pounded it flat, I think hindsight might call that into question. But at the time, we followed our processes and we investigated it as thoroughly as we thought we should at the time and we'll develop lessons learned from that activity."

Dittemore also was asked about decisions made during Columbia's mission not to request spy satellite imagery of the shuttle to look for signs of damaged after engineers realized a large piece of foam insulation had struck the shuttle's left wing. Dittemore declined to comment.

"The thing to concentrate on is that over the last two months we have learned a lot about our system, about capabilities," he said. "And I believe we will find some lessons learned out of all these activities that we can correct. ... So my focus is not on what coulda, shoulda happened or what I might have said, my focus is on what (are the) lessons learned and how are we going to implement corrections and how are we going to be better in the future?"

As for his personal plans, Dittemore said he hopes to end up in aerospace when he moves into the private sector.

"The last thing on my priority list is my personal opportunities," he said. "I have invested most of my professional career in the human spaceflight business. I feel passionately about it, I think it's the right thing for us as a nation to do, I think it offers many side benefits to our society. And I think it's our destiny to do these types of things. I would hope that as I consider opportunities that those opportunities would remain in human space flight. That's where I feel emotionally attached."

Dittemore joined NASA in 1977 as a shuttle propulsion systems engineer, became a flight controller and ultimately a shuttle flight director. In 1992, he was named deputy assistant director of the space station program before transitioning to shuttle program management the following year.

In 1995, Dittemore became manager of space shuttle integration and served as chairman of NASA's mission management team, which oversees the day-to-day conduct of a shuttle mission. He was serving as manager of the shuttle engineering office when he was named to replace Tommy Holloway as overall manager of the shuttle program in 1999.

Investigators probing the Columbia disaster are developing an increasingly detailed scenario that explains the sequence of events that led to Columbia's destruction, a scenario that matches up with telemetry and recorded data as well as the damage seen in recovered debris. Only two out of 10 initial scenarios are still being actively developed by NASA investigators, officials say, but one of them, which assumes a breach in the left wing at or near leading edge panel No. 8, has emerged as the leading contender.

This scenario, No. 2 on the original list of 10 being assessed by agency managers and engineers, matches the telemetry downlinked from the shuttle before its breakup as well as data recorded on board by Columbia's payload experiment support recorder, or OEX, which was recovered near Hemphill, Texas, March 19. It also explains unusual communications dropouts and unexplained flashes seen in the wake of the shuttle as it descended across the southwest United States.

The scenario matches up well with the known point of impact where foam debris from Columbia's external fuel tank slammed into the left wing at 450 mph just 82 seconds after liftoff. In fact, OEX data from thermocouple V07T9895, located on the left wing spar just aft of reinforced carbon carbon panel No. 9, shows a slight temperature increase after the strike that may be indicative - this is not yet confirmed - of leading edge damage.

OEX data recorded during re-entry also is consistent with the severe heat damage seen in recovered debris, which strongly suggests a breach at or very near the underside of RCC panel 8, one of 22 such carbon composite panels making up the leading edge of the left wing.

The U-shaped panels, held in place by so-called T-seals that are bolted to the front face of the wing spar with inconel fittings, are designed to protect the wing from 3,000-degree re-entry temperatures and to handle aerodynamic loads as the shuttle falls into the thickening atmosphere.

"Independent teams examining the recovered debris are finding that the most likely location of (the) initial breach into the vehicle was into the left hand wing RCC panel 8/9 area," according to a summary of the scenario. Scott Hubbard, a member of the Columbia Accident Investigation Board, said much the same thing during a news conference last Tuesday.

The only other scenario still under active consideration by NASA engineers involves a breach in RCC panels closer to the shuttle's fuselage. But it does not fit the facts as closely as scenario No. 2.

NASA's development of failure scenarios is in support of the Columbia Accident Investigation Board, which is responsible for determining the root cause of the disaster. All such scenarios must be confirmed by the accident board and readers are cautioned that the scenario presented below is preliminary and subject to change. That said, here is how scenario No. 2 currently plays out.

Columbia fell into the discernible atmosphere 400,000 feet above the Pacific Ocean northwest of Hawaii - entry interface, or EI - at 8:44:09 a.m. on Feb. 1. Scenario No. 2 assumes the shuttle began its descent with significant damage to the underside of RCC panel No. 8. The scenario assumes spar insulation behind the RCC panels was directly exposed to re-entry heating.

During a news conference Tuesday, members of the Columbia Accident Investigation Board said investigators were focusing on the possibility a lost "T-seal" between RCC panels 8 and 9 might have left a gap an inch wide or greater between the adjacent panels, providing a direct path into the leading edge.

What caused the damage has not yet been pinned down, although most investigators believe it likely was caused by a piece of foam insulation that broke off Columbia's external fuel tank 81 seconds after liftoff and slammed into the left wing's leading edge one second later at some 450 mph. That impact may have cracked or penetrated an RCC panel or damaged a T-seal enough to result in failure.

The day after launch, military radars detected debris floating away from Columbia after a routine maneuver. The debris has not yet been identified, but radar tests are underway at Wright Patterson Air Force Base to determine whether a T-seal or a piece of an RCC panel could explain the sightings.

Regardless of the exact location of the breach - RCC panel 8 or an adjacent T-seal - it did not take long for hot gas to penetrate Columbia's left wing during re-entry. At 8:48:39 a.m., 270 seconds after entry interface, a strain gauge (V12G9921) in the leading edge near RCC panel 9 first showed an unusual increase.

"Thermal stresses build due to the breach in the wing and hot gas impingement on the spar," the scenario reads. "Pressure also starts to build in the RCC wing cavity adding to the load on the spar. The damaged wing causes a change in the load path that increases the wing spar strain. All these loads combine and put an off nominal strain on the spar."

Twenty seconds later, at 8:48:59 a.m., heat entering the RCC cavity through the presumed breach in panel 8 is first registered by a temperature sensor on a fitting between RCC panels 9 and 10 (V09T9910). Almost simultaneously, insulation on the forward face of the spar was compromised, allowing super-heated air to begin eroding the spar structure itself.

As the leading edge heating continued, temperature sensors on Columbia's left-side orbital maneuvering system rocket pod began sensing cooler temperatures than usual. This trend began developing at 8:49:49 a.m., or 340 seconds after entry interface. Computational fluid dynamics calculations indicate this was due to leading edge RCC panel damage affecting the flow of air over the wing.

At 8:50:00 a.m., the first in a series of brief communications drop outs were observed. Engineers now believe these interruptions were caused by the release of molten metals from the eroding wing spar and spar insulators into the hot air surrounding the space shuttle. The effect was similar to that of "chaff" released from military aircraft to foil weapons sensors.

At 8:50:09 a.m., the disrupted airflow over the leading edge of the left wing resulted in a cooling trend on the left side of Columbia's fuselage. Ten seconds later, at 8:50:19 a.m., increasing damage to the leading edge caused a thermocouple on the lower side of the wing near RCC panel 9 to begin sensing an off-nominal increase.

The inside surface of the left wing spar then began showing an unusual temperature rise (sensor V09T9895) at 8:51:14 a.m. This reading, following the RCC interface temperature increase noted at 8:48:59 a.m., confirms hot gas penetrated the cavity behind the RCC panels before entering the interior of the wing itself.

At 8:52:05 a.m., telemetry from the shuttle showed the start of an unusual yawing motion pulling the nose of the orbiter to the left. This was due to the growing damage to the leading edge affecting the aerodynamic behavior of the spacecraft. Computational fluid dynamics confirms this unbalanced force would continue to increase as the damage worsened.

Just four seconds later, at 8:52:09 a.m., the plume of super heated air in the RCC cavity finally burned through the wing spar itself, allowing hot gas to flow into the wing's interior. The plume of hot air impinged on the main landing gear wheel well box, about halfway down its outboard side, and began burning through cable bundles, cutting off data from scores of left wing sensors.

Based on the order of the cable bundle burn throughs, it is possible the hot gas plume impacted the upper skin of the wing and then was deflected along the skin to the wire bundles running along the upper part of the wheel well box. The top two cable bundles were damaged first, followed 30 seconds later by a third bundle lower down the side of the wheel well.

Analysis of the timing of the cable burn throughs appears to confirm the general location of where the burn throughs are believed to have occured and they are consistent with a breach at RCC panels 8/9.

The hot gas quickly spread throughout the interior of the unpressurized wing, triggering a sharp rise in the temperature being recorded by sensor V09T9895 - the same interior sensor that first detected higher spar temperatures a minute earlier - at 8:52:10 a.m. Seven seconds later, hot gas in the wing was first registered by a brake line sensor in the left main landing gear wheel well.

"As heat enters wing, thermal stresses are created and structural failures start to occur," reads a scenario entry for 8:52:19 a.m. "Hot gas continues to flow into wing, with pressure and temperatures building in the wheel well cavity." At 8:52:41 a.m., a second wheel well temperature sensor begins indicating an unusual increase.

In the meantime, the leading edge continued to deteriorate, affecting the flow of air over the wing. At 8:53:29 a.m., OEX data indicated the left fuselage began heating up as a vortex of disturbed air began moving forward along the side of the orbiter. The movement of this shock wave occurred at the same time as a sudden increase in yaw motion, which appears to confirm increasing leading edge damage.

It was at roughly this point, beginning at 8:53:44 a.m., that observers along Columbia's ground track began noticing debris falling away from the shuttle. At 8:54:20 a.m., the shuttle's "roll moment" changed sign, going from negative to positive. One explanation is an unexplained increase in lift on the left wing, presumably due to increasing structural damage. Another explanation, however, is damage to the upper surface of the wing.

"Hot gas continues to progress down the RCC and may burn through top of wing shedding skin and creating a hole," the scenario reads. "Damage pushes shock wave/vortex onto vertical tail leading to large increase in rolling moment."

Ground controllers at the Johnson space Center in Houston did not notice anything unusual until 8:54:24 a.m. when mechanical systems officer Jeff Kling informed flight director Leroy Cain "I've just lost four separate temperature transducers on the left side of the vehicle, hydraulic return temperatures. Two of them on system one and one in each of systems two and three."

Nine seconds later, at 8:54:33 a.m., a bright flash was noted by ground observers. This is now believed to be the result of maneuvering jet firings and interactions with debris falling away from the shuttle.

Then, at 8:56:16 a.m., the super-heated air entering the wing from the breach in the leading edge finally burned through the outboard wall of the left landing gear wheel well, triggering dramatic temperature increases in sensors located inside the wheel well. The plume is believed to have impinged directly on the left main landing gear strut. One such strut has been recovered and while engineers have not yet determined whether it was from the right or left landing gear, it shows severe melting consistent with a direct plume impingement.

Forty-four seconds after the wheel well was breached - at 8:57:00 a.m. - the plume burned through the forward inboard corner of the main landing gear door, providing an exit path for the hot gas in the wing. As a point of reference, the famous Kirtland Air Force Base telephoto view of Columbia, a photograph showing obvious signs of distress at the leading edge, was taken at 8:57:14 a.m.

At 8:58:03 a.m., a sharp aileron trim change was noted, an indication large pieces of the wing's overheated skin were blowing off and falling away. At the same time, the wheel well continued to heat up. All tire pressure and temperature data were lost during a 20-second period beginning at 8:58:38 a.m.

Ten seconds later, commander Rick Husband radioed, "And, uh, Hou(ston)..." The transmission was garbled. Thirty seconds later, Kling told Cain "We just lost tire pressure on the left outboard and left inboard, both tires."

"And Columbia, Houston, we see your tire pressure messages and we did not copy your last," astronaut Charles Hobaugh called form mission control.

"Roger, uh, buh..." Husband replied at 8:59:32 a.m., interrupted again by a comm drop out. It was the final transmission from the crew.

"The aerodynamic forces and the aero heating become more intense leading to further structural degradation of the vehicle," the scenario concludes. Columbia ultimately became aerodynamically unstable and broke up around 9:00:21 a.m.

Evidence supporting scenario No. 2 includes:

• Heavy slag-like deposits on the interior of RCC panel 8 fragments. The slag presumably is the result of molten aluminum spraying away from the point where hot gas impinged the wing spar.
• Severe heat damage on a tile carrier panel located between the lower edge of RCC panel 9 and the heat shield tiles permanently bonded to the lower side of the wing; erosion and slumping of the heat-resistant tiles indicate prolonged exposure to extreme temperatures.
• Severe heat damage to a tile carrier panel located just behind the upper edge of RCC panel 8.
• "Knife-edge" erosion of pieces from RCC panels 8 and 9; RCC erosion requires temperatures in excess of 3,000 degrees Fahrenheit; the knife-edge pattern, only seen on debris from panels 8 and 9, is indicative of such extreme heating.
• Recovery of an upper wing tile farther west than any other confirmed shuttle debris; the tile, originally mounted on the upper surface behind RCC panel 9, presumably fell off earlier than others because of the disturbed airflow and heating caused by the breach.

"Data is emerging that shows very significant and unusual damage at the interface between (RCC) panels 8 and 9," Hubbard said Tuesday. "For example, the splattered metal on panel 8 is much heavier than elsewhere and there is erosion of the reinforced carbon carbon elements, the ribs, what's called the lug where the attachment occurs.

"What we see is something that's not seen thus far anywhere else on the wing leading edge or indeed in the orbiter debris, which is pieces of a very tough material, this reinforced carbon carbon, eroded to knife edges. Where a normal piece is a half an inch (thick), it's been eroded to about the thickness of a dime. This kind of heating event indicates long duration, very extreme heating.

"We don't know quite what to make of this yet, other than what I said, a very severe heating event in the intersection between panels 8 and 9," Hubbard said. "The carrier panel, that is, the piece of material that goes between the reinforced carbon carbon and all the tiles on the bottom of the orbiter, that carrier panel also shows severe heating. It's slumped, like you overheated Styrofoam. That's another indication of some very severe heating events."

Shuttle program manager Ronald Dittemore, the clean-cut, straight-talking engineer whose daily briefings in the wake of the Columbia disaster won widespread respect, plans to leave NASA in the near future, sources say, presumably to take a job in private industry. Calls to Dittemore's home Friday evening and Saturday were not successful and NASA officials were not immediately available for comment.

Reliable NASA and contractor sources, however, said Dittemore made plans to leave the space agency before Columbia's ill-fated mission and that he had planned to step down once the flight was complete. Those plans changed in the wake of the Feb. 1 disaster and he remained on the job to help coordinate NASA's investigation of the tragedy.

Dittemore's daily briefings lasted just a week before the independent Columbia Accident Investigation Board took over the public conduct of the accident probe. But Dittemore's willingness to share initial flight data and to answer questions in a public forum was in stark contrast to NASA's no-comment response to the 1986 Challenger disaster 17 years earlier. While some NASA insiders privately groused about Dittemore's openness, many more praised his performance, crediting him with convincing skeptics that NASA had the right stuff to deal with the disaster.

"Let me say it is with some relief that I welcome (the accident board) here," Dittemore said Feb. 6, in his final news briefing. "We need their expertise, we need their independent look at what we have been doing and we will work closely with (board chairman Harold Gehman) and his board.

"These five days have been exhausting to the team. They have been difficult emotionally and physically. But we're going to carry on and we're going to continue our determination to find the root cause and do so as quickly and reasonably as we can."

As a senior NASA manager, Dittemore would need a waiver from agency Administrator Sean O'Keefe before taking any job in which he would be representing a shuttle contractor in any future negotiations with the government. Without such a waiver - and they are rare - senior managers must wait a year before taking on such jobs.

The specifics in this case are not yet known, but the loss of Dittemore's firm hand at the helm of the shuttle program will be keenly felt.

"He did a good job, Ron is a solid manager," said one senior aerospace manager. "One of his traits was he was not unwilling to make hard decisions. He made decisions that weren't always popular, but they were the right thing to do."

Dittemore joined NASA in 1977 as a shuttle propulsion systems engineer, became a flight controller and ultimately a shuttle flight director. In 1992, he was named deputy assistant director of the space station program before transitioning to shuttle program management the following year.

In 1995, Dittemore became manager of space shuttle integration and served as chairman of NASA's mission management team, which oversees the day-to-day conduct of a shuttle mission. He was serving as manager of the shuttle engineering office when he was named to replace Tommy Holloway as overall manager of the shuttle program in 1999.

"The space shuttle is more reliable, more capable and more efficient today than ever before," Dittemore said in a statement when he took on the program management job. "At the same time, with assembly of the station, the shuttle has a bigger job ahead of it than ever before. As we do that job, above all, my goal is to fly the shuttle safely and continue the tradition of excellence that has been instilled in this program.

"The shuttle has a lot of life ahead with the capability to continue to fly for decades to come, and we plan to continue to make it as safe and efficient as possible as we build the station and prepare for the future."

As expected, the Columbia Accident Investigation Board today released its first two interim recommendations to NASA, calling for routine spy satellite imagery of shuttles in orbit and detailed pre-flight inspections of the protective panels on the leading edges of the shuttle's wings. A breach in a reinforced carbon carbon (RCC) panel on Columbia's left wing is believed to have triggered the shuttle's breakup during re-entry Feb. 1.

An agreement to make classified on-orbit imagery a routine requirement during shuttle flights is already in work by NASA and the National Imagery and Mapping Agency, or NIMA. But what might be required to implement the board's other recommendation - extensive pre-flight tests of the shuttle's leading edge panels - and how long such tests might take to complete is not yet clear.

"This recommendation was issued because of the board's finding that current inspection techniques are not adequate to assess structural integrity of RCC, supporting structure, and attaching hardware," the board said.

During Columbia's launching Jan. 16, a chunk of external tank foam insulation broke off 81 seconds after liftoff and slammed into the left wing leading edge, at 450 mph, one second later. NASA managers decided not to request satellite imagery of the shuttle's wing after concluding the orbiter could safely land as is. That decision has faced criticism and second guessing in the aftermath of the disaster and the accident investigation board has concluded such imagery should be routine for future flights.

"Prior to return to flight, NASA should modify its Memorandum of Agreement with National Imagery and Mapping Agency (NIMA) to make on-orbit imaging for each Shuttle flight a standard requirement," the board stated today.

The interim recommendation included three supporting facts: A) The U.S. government has the capability to image the shuttle on orbit; B) a Memorandum of Agreement exists between NASA and NIMA regarding on-orbit imaging of the shuttle; and C) "during the flight of STS-107, there were no on-orbit images taken of sufficient resolution to assess the orbiter's condition."

But the board's primary recommendation was for NASA to implement non-destructive evaluation, or NDE, to determine the heath of the RCC leading edge panels before shuttles are cleared for launch.

"Prior to return to flight, NASA should develop and implement a comprehensive inspection plan to determine the structural integrity of all Reinforce Carbon-Carbon (RCC) system components," the board wrote. "This inspection plan should take advantage of advanced non-destructive inspection technology."

The board noted that the RCC panels are a non-redundant, "crit 1" system, meaning a failure results in the loss of the vehicle and its crew. During initial manufacturing, the carbon-carbon composite is tested at various stages in the assembly process "by physical tap, ultrasonic, radiographic, eddy current, weight gain, and visual tests."

"In addition, a flat plate control panel made in parallel with the production piece is destructively tested at various points in the production process," the board wrote. The projected lifetime of the panels assumes the material and its support hardware are free of any internal defects.

Going into Columbia's mission, "visual external inspections and tactile checks" were the only tests required to assure the RCC panels were safe to fly unless visually obvious problems results in replacement.

But in the wake of the Columbia disaster, "non-destructive testing of some post-flight RCC components has shown indications of RCC material defects not previously identified by visual inspection methods currently employed," the board wrote, recommending the implementation of routine NDE of the leading edge.

A major question mark, however, is what technology is needed to implement such tests and inspections and how long it might take to thoroughly examine the 44 RCC panels on each orbiter. And the board did not specifically state whether such inspections are required before return to flight or before every flight.

Ongoing analysis of sensor data and recovered debris indicate the deadly breach in the shuttle Columbia's left wing was located slightly outboard of the best previous guess, possibly at or near the intersection of leading edge panels 8 and 9, investigators said today. Recovered debris from that area shows damage consistent with extreme, prolonged heating and matches up well with telemetry and recorded data showing unusual temperature increases in the early phases of the shuttle's catastrophic re-entry.

The Columbia Accident Investigation Board also revealed today that investigators are now focusing on a so-called T-seal, part of the leading edge system, as a possible candidate to explain a mystery object seen floating away from the shuttle on the second day of its mission. Board members initially believed the object might have been a carrier panel that somehow shook loose following impact by a piece of foam debris during launch.

But testing at Wright Patterson Air Force Base to determine the radar signature of various potential debris candidates does not match up with a carrier panel. In addition, search crews have now recovered fragments from all of the carrier panels originally located behind leading edge panels 5 through 10. Engineers now plan to test a variety of components, including a T-seal, a large fragment of a reinforced carbon carbon - RCC - leading edge panel and other leading edge components to find a better match with the radar data.

"Given that we have found pieces of all of the carrier panels in this region, it's looking less likely that was a drift away object, although it could have been an impact zone," said board member Scott Hubbard.

He said ongoing analysis of launch video shows a large piece of external tank foam insulation struck Columbia's wing between RCC panels 7 through 9. Recovered fragments of these RCC panels show slag-like deposits on their inner surfaces, presumably the result of a plume of super-heated air melting underlying components and splashing molten material on nearby components.

"Data is emerging that shows very significant and unusual damage at the interface between (RCC) panels 8 and 9," Hubbard said. "For example, the splattered metal on panel 8 is much heavier than elsewhere and there is erosion of the reinforced carbon carbon elements, the ribs, what's called the lug where the attachment occurs.

"What we see is something that's not seen thus far anywhere else on the wing leading edge or indeed in the orbiter debris, which is pieces of a very tough material, this reinforced carbon carbon, eroded to knife edges. Where a normal piece is a half an inch (thick), it's been eroded to about the thickness of a dime. This kind of heating event indicates long duration, very extreme heating.

"We don't know quite what to make of this yet, other than what I said, a very severe heating event in the intersection between panels 8 and 9," Hubbard said. "The carrier panel, that is, the piece of material that goes between the reinforced carbon carbon and all the tiles on the bottom of the orbiter, that carrier panel also shows severe heating. It's slumped, like you overheated Styrofoam. That's another indication of some very severe heating events."

Temperature data from the OEX recorder recovered March 19 shows severe heating in the cavity just behind RCC panel 9 and "we have the debris speaking to us and saying something severe happened in the interface between panels 8 and 9," Hubbard said. Even so, he emphasized other explanations might be possible and "this story of exactly what happened and where it happened, while we're closing in on it, is going to continue to evolve."

In the meantime, engineers are gearing up for a critical series of tests at Southwest Research Institute in San Antonio to validate or disprove the leading suspicion about what caused the disaster: The impact of foam debris 82 seconds after liftoff.

Using a nitrogen gas canon, engineers plan to begin firing foam at representative heat-shield tiles by the end of the month. By mid May, a leading edge mock-up, including RCC panels 6 through 10, will be ready for impact tests. Panels from the prototype shuttle Enterprise will be used on the mockup, along with flight panels from the shuttle Discovery that closely match Columbia's panels in terms of age and flight experience.

The idea is to fire foam closely matching the debris from Columbia's external tank at leading edge components at some 500 mph to determine what sort of damage might result. Of special interest are the T-seals bolted to the front of the wing spar that form the interlocking framework holding the RCC panels in place. The T-seals, in turn, are held in place by two bolts at each end and it's possible to lose or break a T-seal without breaking an adjacent RCC panel.

"The space between panels 8 and 9 happens to line up with where the T-seal is," Hubbard said. "So that has become a suspicious region. And in the preliminary planning for the impact tests, we're putting strong consideration on hitting not the middle of a panel, but that intersection where the T-seal is and seeing what happens, what kind of damage would be caused."

Board chairman Harold Gehman said a lost T-seal would leave a slot-like gap between adjacent RCC panels. That gap could be an inch or more in width, providing a direct path into the leading edge. If a T-seal was damaged during launch and somehow separated from Columbia on the second day of the mission, the left wing would have been vulnerable to hot gas intrusion during re-entry on Feb. 1. Engineers now are running complex calculations to determine if a slot-like initial breach can explain the entry data and observed debris damage.

"The jury is still out on how much of a breach you would have to have in order to create the effects you see, in particular the understanding or the feeling, from the visual data that we may not be dealing with a round hole, but instead something that created a long narrow slit," Hubbard said. "So the thermal dynamics people have gone back to the drawing board to figure out what a long, narrow slit would do as distinguished from a hole."

The search for Columbia's wreckage is now drawing to a close. Underwater searches are virtually complete, grid searches on land have covered 78 percent of the primary debris field and aircraft searches are 80 percent complete. More than 70,000 pieces of shuttle debris have been recovered, representing about 78,000 pounds or roughly 36 percent of Columbia's dry weight. In early May, NASA plans to shut down its Disaster Field Office in Lufkin, Texas, and to consolidate remaining recovery efforts at a Columbia Recovery Office at the Johnson Space Center in Houston. In addition, four Incident Command Posts managed by the U.S. and Texas Forest Services will be closed by the end of the month.

Shuttle program manager Ronald Dittemore, in the first issue of a new internal newsletter aimed at keeping the shuttle workforce informed about the progress of the Columbia investigation, said "we have turned the corner" and "we have reason to be optimistic." He also said Linda Ham, manager of NASA's mission management team during Columbia's flight, will represent the shuttle program office in return-to-flight planning.

"I recently received a letter in the mail expressing support for the human space flight program and reaffirming their belief in our team that we would "find it, fix it and fly," Dittemore wrote in a section titled "Program Manager's Comments." "I wholeheartedly agree with this simple statement. It summarizes our efforts and our unceasing dedication to return to flight.

"We have made great progress since February 1st. I believe we have turned the corner and are beginning to see the light at the end of the tunnel. Fault trees are beginning to be closed. Special testing is being planned and completed. Important clues that will lead to the root cause are being identified and assessed.

"We have reason to be optimistic. Our teams are continuing to work very hard and have been fortunate in recovering important elements of Columbia that will help us determine the root cause of the accident. A special return to flight planning team, led by Col. Jim Halsell, has been established and we are embarking on the path that will lead us back to flight. Ms. Linda Ham will represent the Space Shuttle Program on this planning team."

The newsletter, dated April 4, also said the Columbia Accident Investigation Board has indicated "their belief that major activities will wrap up in 6-8 weeks. CAIB findings and recommendations will be identified to NASA as soon as the findings are agreed upon by the CAIB."

In addition, the newsletter said the leading candidate for replacement of foam insulation in front of the struts holding the nose of the orbiter to the external fuel tank is "a simple metal cover that could be installed at KSC on the delivered tanks. A final down select for the design will be completed prior to the end of April."

Foam debris falling from the so-called bipod strut area hit Columbia's left wing during launch.

Harold Gehman, chairman of the Columbia Accident Investigation Board, said today two interim recommendations will be released late this week or early next and that the panel likely will write its final report in June. Gehman also said "privileged," or confidential testimony from senior shuttle managers, engineers and technicians, will never be made public, either in a public hearing or in final report transcripts.

"If a witness under privilege tells us that a board meeting was a sham and people weren't free to speak up or something like that, then we will corroborate that, which will see the light of day," Gehman said in a brief interview following a news conference. "But as far as the public hearings are concerned, the public hearings are essentially board meetings in public. That's what we do all day long. We interview, we talk to people like that and it's simply an opportunity for the public to see how we work and go along with us. I mean, you're learning at the same time we're learning. It's not a press event, it's not a news event, it's just an opportunity to do some of our business in public. And that's the intent of it."

The CAIB is interviewing senior shuttle managers and engineers under conditions of confidentiality. By granting such privileged status, the board guarantees witnesses their testimony will never been made public and that criticisms of systems, procedures or other individuals will not be traceable. The idea is to encourage a more open, more honest dialogue with board members and investigators.

Under this policy, the public will never hear directly from Linda Ham, for example, chairman of NASA's mission management team during Columbia's flight, or any other managers responsible for deciding what to do about the foam impact during launch that is now believed to have played a major role in the disaster.

Asked if conducting such interviews in secret might represent a disservice to the public, Gehman said "we consider this to be a strength, not a weakness."

"We are going to be able to get at the intricacies of that process in a way that you could never, the Rogers Commission (that investigated the Challenger disaster) could never, for example, get," Gehman said. "By granting people privilege, we're going to find things out that they wouldn't say in public. And so we believe we'll actually be able to go deep and get a richer and more fundamental understanding of these processes than you can in public.

"Now in order for it to get into our report, we're going to have to corroborate what they say. Just because somebody's mad at his boss or somebody doesn't listen to his opinion, he can say that in privilege. That doesn't mean it's going to make it into our report."

Gehman said the board is finalizing two interim recommendations, one formally asking NASA to routinely obtain in-flight imagery of shuttles to look for signs of damage - already in work by NASA - and the other aimed at implementation of non-destructive evaluation or testing - NDE - to check the health of various systems like the panels making up the leading edge of the shuttle's wing. Gehman said those interim recommendations are undergoing final technical review and could be released as early as Friday.

As for the board's future activities, Gehman said "I think the months of April and May, I suspect we're still going to be receiving data."

"But I suspect in May, the rate of receiving things is going to start to taper off," he said. "We're still interviewing witnesses, still picking up debris, we've got the OEX (data) recorder, which hasn't been analyzed yet. So we're clearly going to be on the receiving end through at least the rest of April.

"I think around May it's going to shift to where we're going to start doing more deliberations and more output-oriented things, issuing more interim recommendations and then start to shrink the staff down. In June, the board's going to have to roll its sleeves up and start writing."

Asked if the final recommendations might include any directives to redesign or strengthen the leading edge systems, Gehman said "I can't give you any sense of that at all." But he said the CAIB is "very concerned about the characterization of an aging vehicle."

One such age-related issue is the health of the carbon composite leading edge panels that protect the shuttle's wings from the fierce heat of re-entry. At present, engineers do little more than visually inspect the panels between flights for signs of damage that might need repair. They do not subject the panels to more sophisticated types of NDE that might reveal hidden problems.

"If NASA doesn't know the condition of its vehicles, we would be leery of recommending that they fly," Gehman said. "Some of these things might be pretty simple, you know, a CAT scan of the leading edge, you can do it in place, you don't have to remove it, if it passes you're good to go. But there are other areas, too.

"I'll tell you one of the things that's really hanging out in my mind is, I find it to be an intellectual weakness to take the O-ring story and the foam story and keep beating NASA over the head with it unless you could point to exhibit C, D and E."

He was referring to the O-ring seal failure that doomed Challenger in 1986 and the foam debris impact to Columbia's left wing during launch that is believed to have led to the wing's failure during re-entry. In both cases, NASA continued to launch shuttles even though engineers knew the systems in question - booster O-ring seals and external tank foam insulation - were not operating properly. But Gehman said two such instances do not necessarily make a trend.

"What are the other three things that are continuously sending you signals? I'd like to find what those other three things are," he said. "I'd like to find some more things that are kind of strange looking, kind of funny looking and NASA says we're going to live with them. ... I find it to be not very intellectually honest to just beat (NASA) about the hindsight thing. I'd like to find other funny looking numbers they've also decided to live with and then be able to make a judgment about that."

Editor's Note...
The following status report recaps highlights from two days of hearings before the Columbia Accident Investigation Board. A separate status report will be filed later covering a CAIB news conference Tuesday.

The shedding of foam insulation from space shuttle external tanks was never considered a safety-of-flight issue, experts told the Columbia Accident Investigation Board this week. But tank engineers have worried for more than 20 years about potentially catastrophic impacts and a top level program requirement held that any shedding of large, potentially dangerous pieces of debris was forbidden.

Even so, despite years of work to eliminate foam shedding, the fleetwide average for foam impact damage resulting in tile blemishes more than one-inch across runs about 30 per mission. So instead of meeting the still existing design goal of no shedding, shuttle program managers somehow came to accept a certain level of impact-related tile damage as a normal occurrence.

In hindsight, the reasoning that allowed NASA to continue launching space shuttles even after a large piece of foam debris broke away from the shuttle Atlantis last October is even more difficult to understand given the critical nature of the shuttle's fragile heat-shield tiles and other insulation. The thermal protection system, or TPS, is one of three systems that have no backup and are not considered fail safe.

"The shuttle was designed with the philosophy that you should not have a system in which you suffer a failure and you lose your vehicle or your crew," said James Halsell, a senior shuttle commander and former launch integration manager at the Kennedy Space Center. "It needs to be fail safe. Furthermore, there was a high operational desire to be fail operational, that is, suffer a failure and still complete the mission.

"The basic requirements are the vehicle and all of its subsystems will be fail safe. From the very beginning, there were three systems which it was acknowledged we could not achieve that desired goal. The thermal protection system was one, it was recognized as being criticality 1, that is, if it doesn't work you're going to lose the vehicle and/or the crew. And we don't have a backup system to it."

Columbia's left wing was struck by a large piece of external tank foam debris 82 seconds after launch Jan. 16. The debris broke away from an aerodynamic ramp in front of the left bipod attachment strut, one of two struts that hold the nose of the orbiter to the tank. The impact is believed to have damaged the wing's leading edge enough to permit a catastrophic plume of super-heated air to burn its way into the wing during re-entry Feb. 1, triggering the shuttle's destruction.

Investigators now believe the fatal breach occurred just outboard of leading edge panel No. 6 - the panel in the center of the foam debris impact "footprint" - somewhere at or near panels 7 through 9. Ongoing wind tunnel testing shows unusual temperature increases seen on Columbia's aft left rocket pod can be explained, for example, by a breach at or near panel 9. Whether the breach occurred because of damaged leading edge panel or because of damage to a so-called carrier panel is not yet clear.

In any case, during a flight by Atlantis late last year - mission STS-112 - a large piece of foam broke away from the bipod ramp area and hit one of the shuttle's solid-fuel boosters. That impact did not cause any major damage, but NASA managers ordered engineers to explore redesign options to minimize or eliminate such bipod ramp foam shedding. But they did not declare the shedding an "in-flight anomaly," or IFA, with a constraint to flight. In other words, the shuttle program could continue flying while the redesign was implemented.

The reasoning behind that decision was that foam shedding did not represent a "safety of flight" concern. It was viewed as a maintenance issue only, i.e., the impact could cause re-entry heating damage requiring tile repairs after a flight that could delay processing for a shuttle's next mission.

How that conclusion might have evolved into a mindset is the subject of intense scrutiny by the Columbia Accident Investigation Board. For board member Sally Ride, the first American woman in space and a member of the presidential commission that investigated the 1986 Challenger disaster, the nature of that evolution is of more than passing interest.

"We're actually trying to understand that," she said Tuesday at a post-hearing news conference. "There is the guiding principle that nothing should hit the orbiter. And it's written in the documentation. The other thing that's written in the documentation is that the TPS (thermal protection system) is criticality 1. That's on the one side and on the other side is that through the history of the hundred flights or so, there's been debris impacting the orbiter on virtually every flight.

"I can tell you, tile damage was a very big concern in the early stages of the shuttle program, a huge concern," she said. "Everyone was worried about the main engines on ascent and the tile on re-entry. Those were the two leading issues in the early days of the program. The early flights came back with some tile damage, but in almost every case it was a turn-around issue.

"As time went on, people, I think. got used to tile damage from debris off the external tank, got used to repairing that between flights, got used to thinking of it as a turnaround issue and I think we saw that in the way that problems were handled after STS-87, STS-112 and during 107. And that is just the sort of thing that we're trying to get at.

"Of course, during the Rogers Commission, one of the things that came out early on was that the (solid-fuel booster) O-rings (blamed for the mishap) were not a problem for the first time on that flight, on 51L (Challenger). They'd been a problem on not just one, not just two, not just three, but several shuttle flights before the Challenger accident. It was almost the case that if you, you know, the famous discussion of Richard Feynman, that you survived it the first time so suddenly it becomes more normal. And it happened enough and now it's a normal occurrence. I think that we're trying to understand whether that same thinking crept in with the foam off the tank."

Richard Blomberg, president of Dunlap and Associates Inc. and former chairman of NASA's independent Aeropace Safety and Advisory Panel, said in the end, the Columbia disaster will be blamed on human error or oversight. But he said NASA could not be faulted for not trying as hard as humanly possible to prevent such oversights from happening.

"I'm a human factors person and I'm the first one to tell you humans are perhaps the mosty fallable part of any system," he told the CAIB. "We design the systems, we operate the systems, we make the decisions to go. So somewhere in whatever you're going to find for Columbia, humans failed. But the question I would want asked is did we fail through malice, did we fail through neglect or did we fail through ignorance? If we failed through ignorance, let's learn from it, let's increase our vigilence and make the system better and keep that closed loop going. That's all we can do with any vehicle.

"I am sure that whatever caused the accident escaped a process at some point," he added. "It had to have, because it flew. So at some point in the process, somebody missed it and it may have been my panel. We may have been staring it in the face and missed it. But it wasn't for lack of trying, I'm convinced, on the part of all concerned because as I said in my opening remarks, I just have never seen a system more safety conscious and people more dedicated to safety. That's not a hundred percent assurance, it just says their heart is in the right place."

For their part, tank experts have known foam shedding was a potentially serious problem for years. And they have been aware all along that the tank isn't supposed to shed any foam in the first place. But they, like everyone else, grew to accept the reality of foam impacts as an unavoidable aspect of flight.

"The program level requirement is that we shall release no debris that is harmful to the orbiter," said Lee Foster, a senior engineer at the Marshall Space Flight Center with extensive experience in external tank issues. "So it's a very subjective thing and while we have been working hand and glove with the system over the years, you know, we've worked with them on debris teams and all that, again, everything was judged as a maintenance item and not a safety of flight issue. I'm not going to say that was right or wrong in the past, but that's the way it happened."

In a hearing Monday, Air Force Maj. Gen. Kenneth Hess asked Foster and Scott Sparks, a senior tank engineer at Marshall, "did you ever think that it was possible to pop a big enough piece of foam of this external tank to severely damage the shuttle itself?"

"The answer is yes," Foster said. "We have large areas where we have closeout materials that we know are hard to spray. So yeah, we are always worried there's going to be a big piece that comes out that would throw us over that maintenance item line."

Said Sparks: "I agree with Lee, we watch (ascent) very closely. Because we know that material could come off and cause some damage. We understand that's a potential and we understand it does require a lot of focus on that material to make it not do that."

So why, in the wake of mission STS-112, didn't NASA managers view the bipod ramp foam shedding as a safety of flight issue?

"It looks to me like something hitting the thermal protection system or damaging the thermal protection system, it's a crit 1 system and therefore damaging, anything that hits the TPS ought to be an IFA, looks to me like," said CAIB chairman Harold Gehman. ""How in the world ... does the system determine there's no safety of flight issue?"

Halsell, who until recently oversaw launch processing and provided the final "go" for flight for the agency's mission management team, said engineers and managers believed the STS-107 foam shedding event was a random occurrence and not evidence of a generic problem.

"The nature of the rationale that was presented in that forum was that the external tank (project) had gone back, even at that point in time, before they had responded to the follow on action, and they had vigorously tried to understand did we do something different with the tank where we had this problem as compared to all the other tanks that had flown successfully?

"And what came out of that was they felt comfortable there was no generic new issue that they could identify ... that they had no generic issue that indicted follow on future tanks that we were going to go fly. ... There was no elevated level of concern that anything liberated from that location would have impacted the orbiter. And what all this added up to was the conclusion that we had not moved up and to the right on the risk matrix with respect to the previously accepted hazard."

Sparks and Foster testified that despite more than two decades of work to eliminate foam shedding, the shuttle's external tank continues to release enough debris during every ascent to cause an average of 30 or so "hits" on the shuttle's belly that cause blemishes larger than one inch across. In at least five cases, foam broke away from the bipod ramp area.

The majority of these shedding events occur in the intertank region of the external fuel tank, the section that separates the ET's liquid oxygen and hydrogen tanks. The intertank features ribbed structural members, or stringers, and other components used to attach the solid-fuel boosters and the bipod assembly struts that hold the nose of the orbiter in place.

The ribbing, bolts in the flange area where the top of the hydrogen tank connects to the intertank, the bipod components and other components must be insulated by hand with sprayed-on foam. How that foam is applied and how it bonds with the complex geometry of the underlying structure is believed to play a role in debris shedding. Air inside voids in the foam, for example, can liquefy once the tank is loaded with supercold propellants. During launch, such liquid air can warm up and explosively evaporate, blowing off pieces of insulation.

"You've got a foam that has to be applied over a certain type of underlying structure and making that so that it is free from shedding seems to be, over the last 20 years, a tough thing to do," observed board member Scott Hubbard.

"Yes sir. And generally, you've really got to go back to the beginning as far as the design of the tank," said Sparks. "I'm not so sure the TPS (thermal protection system) processors were in the same room when they designed the tank.

"Because it was designed structurally to be optimized. It's not designed for the TPS to be processed on there. If you were to redesign completely a tank, you would make the exterior a bit smoother, you know, you'd have those people in the same room."

In the meantime, despite ongoing work to eliminate shedding, the current impact average evolved into a baseline of sorts that is accepted as a routine occurance.

"This is a very impressive list of all the things that have been done over the past 22 years to address the shedding of external tank debris," Hubbard said. "Nevertheless ... the line is pretty much a flat line there, whether it's 10 or 15 or 20 or whatever. So do you see any way to drive that line down to zero or near zero?"

"We're always trying to improve the product," Sparks said. "But we don't want to change the product unless we're justifiably sure that's going to improve the product. ... There have been several improvements that I think the program has been proactive in pursuing. But indeed, there's still a level (of debris) and generally they're coming from those closeouts in that intertank region that seem to be problematic. So we try to improve our processing to the extent possible but thus far, it's staying in that (average) range."

Hubbard followed up, saying "I guess if I had a problem that in over 20 years, the average stayed essentially constant, it seems to me that that might argue something about the basic chemistry, or basic properties of the thing you're dealing with, the foam itself. Do you see the foam as being difficult to control in a very precise manner?"

"No, I don't, Mr. Hubbard," Sparks replied. "Really, what I'm seeing ... is that it's an issue of trying to process that material the best you can. If I had to take a guesstimate as far as the location where we're shedding the most debris, it would be in that hydrogen-intertank-flange area. That's just a hard area to close out, there's a lot of bolts there and when you're spraying that material a lot of potential for shadowing of that foam and possibly having some voids behind that. We've always attributed that to the reason why we're losing some of that material from that area."

As for STS-112, Sparks said "the position was that it was a random occurrence of faulty processing and that nothing had changed in this system to indicate that was a systemic issue as far as processing or material, they had gone and done their homework as far as that goes."

In earlier testimony, Halsell strongly defended NASA's post-Challenger management practices, saying problems are thoroughly discussed before each flight and that engineers are encouraged to weigh in with contrary opinions or to challenge assumptions.

"I know that after Challenger it was recognized that these processes were not as disciplined and rigorous as they should be and what I hope to tell you today, what I hope comes out, is that following the Challenger disaster we went back and did rigorously enforce that discipline," he said. "And the degree to which we fell short in the Columbia accident, that's why we're here today and that's what we want to find out."

Halsell defended NASA's waiver process, whereby components can be cleared for flight even if they don't meet specifications. A study was conducted in 2000, he said, to find out "how many are out there, are they all still valid, how often do we review this situation so that we're not guilty of unknowingly accumulating waivers, to what degree are we confident that we have good rationale for retaining waivers in place? And what we found out from that review is that we do have a good process in place. There's an annual review of the waivers to make sure it's still appropriate, it's still applicable, it's still necessary."

Halsell also defended NASA's flight readiness approval process. Board member Steven Wallace pointed out that by the time a mission's flight readiness review is held a few weeks before launch, most major issues already have been addressed by lower-level engineers and managers.

"This is sort of a recurring message, the work is kind of done before these meetings," Wallace said. "I'm curious, is it fair to say these meetings then don't get scheduled until the work is done, or is it unusual that things get stopped at these meetings because you know, does the meeting become sort of a sign off formality?"

Halsell said when he first moved into management, "I perceived some of the same flavor that you're talking about, that is, the important work was being done and being done exceptionally well, so well in fact that when we got to some of these milestone reviews, it appeared to me that all of the hard issues had been discussed, all of the hard decisions and tradeoffs had been made. So I questioned the value to our senior management of these level of reviews.

"But after being in the job for a longer period of time and having discussed the situation with a number of my project managers, they had a different point of view. They didn't disagree with the fact that the way we do business is such that most of these problems - not always - but most of them had been flattened out by the time of the formal review.

But it's because of the presence of these formal reviews and the fact that you know that senior NASA management, the people you answer to and the people who are ultimately responsible for the safety of the upcoming mission, because you know they're going to be there to hear that story, it drives all that outstanding work that happens before. So from the point of view of the projects and elements, they did not want to change or consider any dramatic changes to the form or to the agenda of any of these reviews because from their perspective, they were driving the kind of reaction within the system that was healthy and needed."

Halsell also went to great lengths to defend the analysis following the foam impact during the launch of Atlantis on mission STS-112.

"It's well known that we did liberate a piece of foam on STS-112," he said. "The process by which we went through understanding what had happened, how that related to our previously accepted hazards ... and what was the appropriate course of action from that point on, all followed the processes we had in place to try to ensure the right decision and right tradeoffs and risks got made.

"For example, the in flight anomaly situation for STS-112, that did come to a program requirements change board, it was decided there that an in-flight anomaly designation was not required for this particular item because the previously accepted and documented hazards, and if I remember correctly there were two integrated hazards which were violated, or which were called into question by this particular instance, two of them dealing with the external tank liberating foam and creating a hazard to some other vehicle component, there was nothing about that particular instance which invalidated the rationale for the previously accepted risk.

"In other words, we didn't move up into the right on the risk matrix according to what we knew at that point in time," Halsell said. "So the action that was levied at that program requirements change board was to the external tank project, to go back and fully understand what had happened, why it had happened and what we were going to do to keep it from happening in the future. Also another action was levied to bring that item forward at the flight readiness review to make sure it was discussed fully prior to STS-113. So using that as my example, I would say that that's an example of how the process worked properly and the item was brought forward to the flight readiness review and it was discussed at some considerable length there."

Asked who had the ultimate responsibility for accepting or rejecting such analyses, Halsell said "the short answer is that it's the space shuttle program manager's job to organize the appropriate response to any and all issues when it comes to making the final determination if we can recommend to the associate administrator that we're ready to go fly safely. So if Ron Dittemore was sitting here in front of me, he would say it's my in box because he's the one who controls the resources and the application of those resources."

Revision I of the CBS News-compiled STS-107 integrated entry timeline has been posted. This revision includes initial OEX recorder data - OEX start time, seven data points (from four sensors), PCM/FDM data stop times - and a few other relatively minor updates. As always, suggestions, corrections and comments are appreciated.

The radar signature of an object floating away from the shuttle Columbia on the second day of its mission matches up well with a wing leading edge carrier panel, members of the Columbia Accident Investigation Board revealed today. The tile-covered carrier panels form a smooth surface between the edges of U-shaped reinforced carbon carbon - RCC - panels making up the wing leading edge and heat-shield tiles permanently bonded to the wing's lower surface. If Columbia began its ill-fated re-entry with a missing carrier panel, enough heat could have entered the left wing to trigger the catastrophic chain of events that led to the shuttle's destruction.

But board member Roger Tetrault said other explanations are possible and that it's still not certain a carrier panel is what was separating from the orbiter on flight day two. Asked if one could conclude a missing carrier panel was the root cause of the disaster based on all the data to date, Tetrault said "your logic could lead to someone's death."

Even though photo analysis shows foam debris from Columbia's external fuel tank hit Columbia's left wing leading edge around RCC panel 6 - and that it could have hit the carrier panel immediately behind RCC panel 6 or an adjacent panel - that doesn't mean the breach that doomed Columbia began at that location.

At least not until engineers rule out other scenarios that are still on the table.

"You can't rule out all of these (other scenarios) and make this leap of faith that something you know happened between (RCC) panels 6 and 12 actually happened in this particular area," Tetrault said. "You just can't make that leap of faith."

But he agreed that the loss of a single carrier panel almost certainly would have allowed enough heat to enter the wing behind the leading edge to trigger the temperature increases seen early on. And "early on" is clearly the operative expression when it coms to Columbia's catastrophic descent.

Ongoing analysis of data recovered from a salvaged telemetry recorder shows the onset of heating in Columbia's left wing began 270 seconds after the shuttle entered the discernible atmosphere. That's three minutes and 26 seconds earlier than the previously known first indication of anything unusual - an unexpected yawing motion - and three minutes and 38 seconds before the previous first indication of elevated temperatures in a brake line in the left main landing gear wheel well.

As it turns out, that earlier brake line reading, a 1.5-degree Fahrenheit increase detected at 8:52:17 a.m., may have been normal. Tetrault said NASA investigators have identified at least 13 previous shuttle flights with so-called 1.5-degree "bit flips" in the first eight minutes and 20 seconds after atmospheric entry, or EI+500 seconds. In 11 of those missions, bit flips occurred earlier than the one seen aboard Columbia.

"We are finding brake line temperature D (sensor), which established the first sensor previously, is probably not off nominal at the time that's on the timeline," Tetrault said. "It's probably later than that. That's an important point because sensor D goes off first and it is in the aft of the wheel well and it is high in the wheel well, which tends to indicate heat is coming from the aft part of the wheel well moving forward.

"If you really look at it, it is much more likely that the heat is coming from the forward side of the wheel well going aft," he said. "Temperature D is probably nominal for a much longer period of time."

In any case, more than a hundred engineers working over the weekend have managed to extract key data from the recovered payload experiments recorder, or OEX recorder, that was found by search crews near Hemphill, Texas, on March 19. Tetrault briefed reporters today on the performance of four specific sensors in the left wing.

Columbia fell into the discernible atmosphere - entry interface, or EI - 400,000 feet above the Pacific Ocean northwest of Hawaii at 8:44:09 a.m. Sensor G9921, a strain gauge located in the interior of the shuttle's left wing roughly in line with RCC panel 9, began to show signs of unusual stress at 8:48:39 a.m., or EI+270 seconds. That was 206 seconds earlier than the first signs of unusual yaw moments at EI+476 seconds.

Twenty seconds after sensor G9921 went "off nominal," a temperature sensor mounted on a support brace on the outboard side of RCC panel 9 began sensing unusual temperatures. This sensor was located under insulation in a cavity behind the U-shaped RCC panels just in front of the wing spar. It began sensing high heat at 8:48:59 a.m. and then failed at 8:52:19 a.m., after reading 50 degrees, presumably because the hot air rushing into the wing cut through its wiring.

The next sensor to show unusual readings was located on the front side of Columbia's left orbital maneuvering system rocket pod. At 8:49:53 a.m., sensor 9220 started seeing unusually low temperatures. Nine minutes later, the sensor showed a rapid increase in heating, climbing as high as 1,200 degrees Fahrenheit. The normal reading is 600 degrees.

"First, we think there is a change in the mass flow, which moves the mass flow probably below the OMS pod, and then there is something else that happens that brings the temperature rapidly up, which may be burning or burning aluminum or a number of other effects we have to go look at," Tetrault said.

At 8:51:14 a.m., or EI+425 seconds, sensor 9895, located directly behind RCC panel 9 on the inner side of the wing spar, began recording an unusual temperature rise. One minute and 35 seconds later, the sensor failed after reaching 450 degrees.

Analysis of the OEX data is continuing and the investigation board plans to wrap that information into NASA's existing re-entry timeline, which currently stands at revision 15.

The OEX tape contains two types of data. One set ends at 9:00:13.4 a.m. and the other stops at 9:00:19.4 a.m. The latter is 15 seconds beyond the point where telemetry that was downlinked in realtime came to a sudden stop on Feb. 1. During a final two-second burst of downlinked telemetry, the shuttle was seen to be yawing rapidly to one side. Main vehicle breakup, based on video analysis, began around 9:00:21 a.m.

The OEX data likely will help engineers pinpoint how Columbia began breaking apart and what major components tore off first. In addition, the OEX data will shed light on what was going on during a 25-second dropout in the downlinked telemetry that occurred between 8:59:37 a.m. and 9:00:02 a.m.

At the front end of the timeline, the OEX data "will show us that when we start looking at where the electrical lines were cut - a lot of them cut 540 seconds after EI - that it will begin to help us to localize where in the front edge the problem is," Tetrault said. "Up until now, if I took collectively all the data we had, I could in my mind locate this event somewhere between RCC panel no. 5 and no. 12. I think this will help shrink that down to some much narrower (focus).

"When you begin to put that where the photos have shown where the foam hit, I think you can start making some assessments of what are the probabilities of that being an initiating event, if you will. I wouldn't say necessarily the cause, but there may be an initiating event that leads to a whole series of other things that winds up at the accident."

One possible initiating event is the loss of a carrier panel on flight day two. NASA sent 29 leading edge components and tiles to Wright Patterson Air Force Base for testing to match up their radar signatures with the debris seen leaving Columbia. As of today, a carrier panel is the only item that has not been ruled out.

"With 3,100-plus observations of Columbia by the DOD, we've got a lot of radar cross section feedback," said board member Maj. Gen. John Barry. "There have been 29 various materials examined at Wright Patterson Air Force Base and we've concluded that right now, that only the carrier panel remains a viable candidate for the day two object. ... We think with the (attachment hardware) and the carrier panel, it gives us one of the best candidates we've had so far after reviewing all the testing. But we still have some more testing to do."

The carrier panels are mounted in place by bolts at each end. The bolts run through the heat-shield tiles on their outer surface and the bolt holes are filled with ceramic plugs. The bolt holes are relative weak spots and tests are planned to determine what sort of damage might have been caused by an impact on one of those tiles during launch.

Tetrault said video of Columbia's launch and the subsequent foam impact had been enhanced by the National Imagery and Mapping Agency, or NIMA, and that investigators now believe the shuttle was stuck just once, by a piece of foam measuring 24 inches by 15 inches by 5 inches, with an uncertainty of a few inches in any dimension. The debris, thought to have weighed about two pounds, slammed into the left wing at 640 feet per second, or 436 mph.

The foam hit the left wing in a two-foot-wide footprint centered on the lower surface of RCC panel 6. The footprint includes parts of two carrier panels.

Tests are on tap at the Southwest Research Institute in San Antonio, Texas, to fire foam debris into leading edge panels, carrier panels and other hardware to determine damage scenarios. Those tests originally were scheduled to begin early next week, but they will be delayed a week or so to give engineers more time to develop procedures incorporating foam samples closer to the size the new NIMA analysis indicates.

On another front, Barry said engineers have cut into the insulating foam of an external tank similar to Columbia's and found numerous voids where the material is bonded to the tank structure. The area in question is the so-called bipod ramp, an aerodynamic slope in the insulation that protects struts holding the nose of the shuttle to the tank from aerodynamic stress.

Engineers looking under the foam in the bipod ramp area of tank 120 found 14 voids, or open spaces, under bipod ramp foam on the right side of the tank and 18 on the left. Such voids are potential trouble spots because extreme low temperatures in the tank during launch can cause air to liquefy in the voids and then explosively evaporate during ascent, blowing foam off in the process. That mechanism is one possible explanation for the foam that came off during Columbia's launch.

To double-check their findings to date, engineers plan to cut into the foam of a tank that is virtually identical to Columbia's - tank 94 - to find out if similar voids are present.

On yet another front, investigators are looking into the formation of pinhole defects in the RCC panels themselves. Barry said today any given RCC panel has between 20 and 40 such age-related pinholes. Any such defects greater than 0.04 inches across are repaired or refurbished. Virtually all of Columbia's leading edge panels had experienced such repairs or refurbishment and investigators are looking into how that process is carried out.

As it turns out, the pinholes may be caused by material from launch pad primer that causes oxidation on the RCC panels. But that remains to be seen.

Finally, Tetrault said the OEX data showed no clear evidence any kind of response from the foam impact on the left wing. But sources familiar with the OEX analysis say a pressure sensor located on the lower surface of the wing, roughly in line with RCC panel 9, shows a small "spike" at 84 seconds that could be the result of post-impact cloud of foam debris sweeping past the detector. No other sensors detected anything unusual.

NASA late Monday posted nearly 30 megabytes of internal email traffic and attachments regarding the potential threat of foam debris striking the shuttle Columbia's left wing; concerns about corrosion that could interfere with proper operation of the ship's body flap during entry; and discussions regarding Columbia's heavier-than-usual landing weight. NASA also posted charts and data used to clear Columbia for flight during a formal flight readiness review before launch.

The sheer volume of the posted material precludes a quick analysis, but a cursory review turned up no significant departures from the tone and general context of concern found in emails released by NASA last month. Quite a few engineers were seriously concerned about the potential threat posed by the debris impact, saying it was the most significant such impact to date and one that was well outside NASA's previous experience. But most ultimately deferred to an analysis carried out by Boeing that concluded whatever damage might be present was a turnaround/repair issue and not a "safety of flight" concern.

One draft memo posted separately, however, did show a previously unseen level of concern about senior management's decision not to request spy satellite photography of Columbia's left wing to better characterize the potential damage. The memo was in draft form and never sent via email to 14 listed recipients. Instead, according to a hand-written note, the contents of the memo - drafted around Jan. 22, six days after Columbia's launch - were discussed verbally with an unknown number of engineers and managers.

"In my humble technical opinion, this is the wrong (and bordering on irresponsible) answer from the SSP [Editor's note: space shuttle program] and Orbiter not to request additional imaging help from any outside source," wrote Rodney Rocha, a chief engineer in the structural engineering division at the Johnson Space Center.

"I must emphasize (again) that severe enough damage (3 or 4 multiple tiles knocked out down to the densification layer) combined with the heating and resulting damage to the underlying structure at the most critical location (viz, MLG Door/wheels/tires/hydraulics or the X1191 spar cap) could present potentially grave hazards. The engineering team will admit it might not achieve definitive high confidence answers even with additional images, but, without action to request help (to) clarify the damage visually, we will guarantee it will not.

"Can we talk to Frank Benz before Friday's MMT [Editor's note: mission management team]? Remember the NASA safety posters everywhere around site stating 'if it's not safe, say so?' Yes, it's that serious."

A more detailed review of the newly posted emails and supporting documents will be posted here later this week as warranted.

Ongoing analysis of a "treasure trove" of data from a recorder recovered in the wreckage of the shuttle Columbia shows a deadly plume of super-heated air first began eating its way into the ship's left wing just five minutes after the orbiter fell into the discernible atmosphere. The sudden temperature increase, in a cavity behind the U-shaped panels making up the leading edge of the left wing, came a full three minutes earlier than previous telemetry indicated the start of unusual heating.

Entry interface occurred at 8:44:09 a.m. and a sensor mounted on a brace behind leading edge panel No. 9 began responding to a very sharp temperature increase at 8:49:09 a.m., nearly two minutes before the shuttle entered the region of maximum heating (this is earlier than officials reported Sunday evening based on quick-look data analysis of the OEX data). In any case, exactly three minutes after that initial temperature rise, the sensor failed and dropped off line after detecting a temperature of 450 degrees Fahrenheit. Eight seconds later, at 8:52:17 a.m., a sensor mounted on a brake line in the left main landing gear wheel well recorded the start of an unusual temperature rise.

Harold Gehman, chairman of the Columbia Accident Investigation Board, said today the timing of these events suggests Columbia began its re-entry with a fatal flaw that allowed hot gas to first enter the cavity behind the leading edge panels and then to burn its way into the interior of the wing. The hot gas presumably entered the wheel well through a vent on its forward face, triggering the brake line temperature increase.

A few seconds later, beginning at 8:52:49 a.m., a sensor mounted on the forward interior edge of the wing, just behind the failed sensor in the leading edge cavity, began registering a rapid increase as hot gas shot through the interior. Seven seconds after that, data from sensors mounted toward the back of the wing began dropping off line as the plume burned its way through a wire bundle routed around the outside of the landing gear wheel well.

"Now interestingly enough, the first temperature rise we see inside the wheel well occurs at 52:17," Gehman said. "Just about the time the sensor outside the wing spar fails, the temperature inside the wing spar starts to go up. So this is interesting to us."

The sensor mounted on the inner surface of the wing spar roughly behind leading edge panel No. 9 "starts to rise 520 seconds after EI, which is something like eight minutes and 40 seconds, which would make it something like 52:49," Gehman said. "The temperature sensor inside the wing starts to rise almost coincidentally with the time the temperature sensor outside the spar goes off line, which leads you to believe there was a whole lot of heat outside the spar which finally ate its way into the wing.

"Remembering the melting temperature of aluminum is something like 900 degrees, it got really hot outside the spar, ate its way through and the temperature sensor outside the spar goes off line," he said. "It probably got destroyed."

Enhanced video of Columbia's launching shows a suitcase-size piece of foam debris from the shuttle's external fuel tank pulled away and slammed into the left wing about 82 seconds after liftoff. The two-foot-wide impact footprint is centered on reinforced carbon carbon - RCC - leading edge panel No. 6. The impact could have affected two adjacent RCC panels as well as protective tiles atop so-called "carrier panels" marking the interface between the lower edge of the RCC panels and permanent heat-shield tiles on the lower surface of the wing.

Gehman said the temperature data recovered from Columbia's orbiter payload experiments recorder, or OEX recorder, does not rule out or confirm an initial breach at or near RCC panel 6. He said engineers will be making calculations over the next few days to determine what sort of breach would be required near RCC 6 to produce a temperature increase like the one seen on the sensor behind RCC 9. At the shuttle's extreme altitude, the dynamic pressure was low and there was not much air to transmit heat. Whether the aluminum structure of the wing spar could have conducted that much heat, or whether a breach occurred outboard of RCC 6, is not yet known.

But it now seems all but certain Columbia began its entry with a fatal flaw already in place, an entry point for the super-heated air that ultimately led to its destruction.

"At the altitude and the speed the orbiter was going at the time the new temperature rise was seen, the aerodynamic pressures are extraordinarily low," Gehman said. "So you could conclude the orbiter began it's entry with a pre-existing fault. In other words, it wasn't air pressure that knocked this thing off, it wasn't some kind of a weakness in which some part of the orbiter was ripped off when it entered the atmosphere, this looks to us like it probably had a pre-existing condition."

But Gehman urged reporters not to jump to any conclusions about the possible location of the initial breach.

"Where the temperature sensor is does not suggest where the breach is," he said. "We are still pulling all the data together to attempt to indicate where the breach is. But this certainly leads us away from things like tile and landing gear doors and things like that."

The OEX recorder is capable of recording data from some 721 sensors scattered across the shuttle. About 150 sensors were not operational during Columbia's entry because of past problems or wiring issues. Gehman said engineers hope to recover data from about 570 sensors when all is said and done.

"It's a treasure trove of data," Gehman said.

Along with showing when the first signs of heating occurred in the left wing, the OEX data shows unusual heating effects on the left orbital maneuvering system rocket pod just to the left of the shuttle's vertical stabilizer.

"Temperature sensors on the skin of the orbiter high up in the vicinity of the OMS pod, the maneuvering engine covers high up on the port side, they start to do all kinds of strange things," Gehman said. "Some of them go up, some are going down. Some go down and then rise later. Some rise and then cool off. We don't know what to make of that except the heating pattern and the flow pattern over the top of the left wing, which then spreads over the side of the fuselage, is obviously disturbed in some way."

Prior to the discovery of the OEX recorder, realtime telemetry from the shuttle showed an initial loss of contact at 8:59:32 a.m. Thirty seconds later, a final two-second burst of telemetry was received that showed Columbia was in the process of yawing out of control to the left. Gehman said today the OEX recorder ran for an additional eight seconds. That data has not yet been recovered, but it should shed additional light on how much of the ship was still intact at that point and when final breakup began.

At the other end of the scale, investigators are working to extract data about the forces acting on Columbia during launch. Gehman said engineers are especially interested in seeing what sorts of forces were acting on the orbiter around the time the external tank debris hit the left wing. Columbia encountered high wind shear during launch, prompting more extreme booster steering movements than normal. Whether those forces contibuted to stresses that, when aggravated by the debris strike, could have led to an RCC failure or a carrier panel problem is not yet known. But Gehman said OEX data from ascent will be factored into upcoming tests in which foam will be fired at leading edge components to determine what sort of damage they might have suffered.

Gehman said engineers will add the OEX data to NASA's current entry timeline (revision 15) and issue updates as warranted. Whenever those updates are made available, they will be added to the CBS News integrated timeline, currently in revision H.

A data recorder recovered in the wreckage of the shuttle Columbia shows hot gas entered the leading edge of the spacecraft's left wing within 16 seconds of the point when the orbiter entered the region of maximum aerodynamic heating during re-entry Feb. 1. Temperature sensors located behind two leading edge panels, both just outboard of the point where engineers believe a deadly breach occurred, showed a sudden rapid spike, or increase, before the sensors failed and dropped off line. The readings, which occurred a minute and eight seconds earlier than previous signs of trouble - suggest Columbia almost certainly began its descent with a pre-existing problem and that it might have suddenly worsened as the ship plunged back into the atmosphere.

"They go way up and then they go to zero," said a representative of the Columbia Accident Investigation Board. Along with showing unusual heating effects earlier than previous telemetry that was downlinked in realtime, "I think what it also indicates is the mechanism of failure was already in place."

Columbia was destroyed by a breach in the ship's left wing. Up until now, NASA engineers relied on telemetry that was downlinked from the orbiter in realtime to reconstruct what might have gone wrong. That data indicated the shuttle began responding to unusual aerodynamic forces around 8:52 a.m., more than a minute after the orbiter entered the region of maximum heating at 8:50:53 a.m. The downlinked telemetry shows the first signs of unusual heating occurred at 08:52:17 a.m. when a brake line in the left main landing gear wheel well began showing an unusual rise.

From that point on, a series of sensors failed as a plume of super heated air burned its way into the left wing, eating through sensor cables and causing temperatures to climb throughout the wheel well. The presumed entry point of the plume - at or near the underside of leading edge panel No. 6 - is believed to have worsened as entry proceeded, causing increasing aerodynamic drag. The shuttle eventually yawed out of control and broke up over Texas about 20 seconds after 9 a.m.

But re-entry readings from hundreds of other temperature, vibration and pressure sensors were stored on a data recorder and not downlinked to the ground. The recorder was recovered by search crews March 19 and after work to clean and stabilized the tape, engineers began work this weekend to examine what data might be present.

The board representative said the tape holds valid data and shows unusual heating in the left wing, behind leading edge panels 9 and 10. One of those sensors is located on the front surface of the wing spar, underneath insulation, while the other is behind it, on the other side of the spar.

The sudden temperature spikes, which began at 8:51:09 a.m. - 16 seconds after the shuttle entered the region of maximum heating off the coast of California - would be consistent with the entry of hot air through a pre-existing breach in the leading edge. The hot air would have shot down a cavity in the U-shaped leading edge panels, trigging the observed temperature spikes in the two outboard sensors, before working its way into the wing's interior.

The timing of how the leading edge sensors responded to the increased temperature is unclear. One of them failed and went off line 20 seconds or so after its counterpart. But they showed sharp temperature increases that were clearly above what the sensors would detect during a normal entry, the board's representative said.

While it is too soon to draw any concrete conclusions, the OEX recorder promises to provide a gold mine of new aerodynamic and thermal data to engineers trying to re-construct the devastating chain of events that led to Columbia's destruction.

"The board is very, very happy that the data could be retrieved," the board representative said. "They're anxious to see what more we can learn about how the heating was moving along the left wing."

Engineers plan to meet Monday to discuss the status of the OEX data reconstruction. Over the next several days, they will begin the process of weaving the new information into NASA's entry timeline. They also plan to continue work to recover OEX data recorded during Columbia's ascent to determine if any readings might be indicative of external tank foam striking the left wing 82 seconds or so after liftoff.

A preliminary look at the ascent data shows a potentially interesting signature, but officials say it may well be the result of a wiring defect. Additional analysis should resolve the matter one way or the other in the days ahead.

The National Imagery and Mapping Agency, one of the government organizations that sets targets for spy satellites, has agreed to routinely inspect space shuttles in orbit for signs of possible damage.

In a March 25 letter to NIMA Director James Clapper, NASA Administrator Sean O'Keefe wrote that he appreciated NIMA's "willingness to add our requirements to your routine operations."

"Thank you very much for the briefing that you and your staff presented to us at NASA on March 13, 2003," O'Keefe wrote. "We appreciate your offer of close cooperation regarding the use of NIMA assets relative to future space shuttle operations.

"As agreed during that session, we deeply appreciate your intention to make available the products of NIMA assets on a routine basis, without specific tasking from NASA. This will be very helpful as we continually assess the condition of the shuttle during on-orbit operations. Significantly, your willingness to employ NIMA assets during targets of opportunity without specific tasking will be another useful source of information to help us assess the potential for on-orbit anomalies."

The issue of shuttle imagery was discussed in the days following Columbia's launch because of concern about possible damage to the ship's left wing following impact by foam debris during launch. But senior NASA managers ultimately decided not to request any spy satellite or ground-based imagery of the spacecraft based on an analysis that concluded the shuttle was not in any danger.

That decision has been the subject of second-guessing and criticism in the wake of the disaster. In the days after the mishap, shuttle program manager Ronald Dittemore said no request for satellite imagery was made because the resolution of the imagery, based on past NASA experience, would not be high enough to reveal damage to individual tiles and because the damage assessment, carried out by Boeing, had concluded Columbia could land safely.

During Columbia's mission, however, Wayne Hale, a senior flight director now serving as launch integration manager at the Kennedy Space Center, made inquiries about the possibility of Air Force help inspecting Columbia. Those initial efforts later were terminated by senior management.

As it turned out, NASA didn't even have to ask for help. An unidentified agency - presumably NIMA - offered to inspect Columbia if NASA made a request for emergency assistance. But William Readdy, associate administrator for spaceflight, declined to make such a request because NASA engineers did not believe the imagery would help all that much and because "there was no safety of flight issue. For those reasons," Readdy wrote in a letter to the Columbia Accident Investigation Board, "there was no rationale for requesting emergency or high priority support."

Prior to today, this page included every CBS News shuttle status report filed since Feb. 1, the day the shuttle Columbia was destroyed. Even though these status reports are essentially unformatted text files and as such, fairly compact, the sheer volume of copy - more than 50,000 words - has made the Current Mission page increasingly slow to download for readers with dial-up modems.

As a result, all previous status reports have now been added to the CBS News STS-107 Mission Archive. In a departure from past practice, however, the archive now ranks status reports in reverse order, with the latest copy at the top of the file and the oldest at the bottom. Consistent with past practice, status reports will remain posted on the Current Mission page for a day or so before being transferred into the Mission Archive.

Editor's Note...
Due to other commitments, I was unable to immediately file the following update on the status of Columbia's OEX recorder. I apologize for the inconvenience.

Time-code information at the end of a tape in a recovered data recorder designed to store critical flight information shows the device apparently operated until 9:00:18 a.m. on Feb. 1, stopping less than 10 seconds before the shuttle Columbia's fuselage broke apart during re-entry.

Assuming the entire tape proves to hold valid data, engineers attempting to reconstruct Columbia's final minutes stand to gain crucial insights into the aerodynamic forces acting on the spacecraft as it plunged back into the atmosphere. Investigators may even be able to pinpoint the location of a breach in Columbia's left wing by using data from dozens of OEX temperature sensors - including two in close proximity to the presumed breach location - to plot the path of a deadly plume of super-heated air as it burned its way into the wing's interior.

The OEX recorder can hold about two hours of data on a one-inch-wide 28-track tape that is recorded at 15 inches per second. The recorder only operates during launch and re-entry. For launch, the recorder is activated 15 minutes before liftoff and shut down six minutes after main engine cutoff. Total runtime is about 15 minutes. For entry, it begins running 10 minutes prior to the moment the shuttle falls into the discernible atmosphere at an altitude of 400,000 feet - entry interface - and continues through landing. For Columbia's entry, that translates into a start time of around 8:34 a.m. on Feb. 1. Landing originally was scheduled for 9:16 a.m., but the recorder failed in the final seconds before vehicle breakup, which began around 9:00:21 a.m.

Engineers believe 721 sensors feeding the OEX recorder were operational during Columbia's mission. Here is a breakdown of the number of sensors providing specific types of data:

• Main engine vibration data: 29 FDM (frequency division multiplexer data)
• Thermal aerodynamic pressure: 182 PCM (pulse code modulation data)
• Thermal aerodynamic temperature: 38 PCM
• Thermal protection system temperature: 15 PCM
• Structural loads: 24 FDM
• Wing box stress and strain: 246 PCM
• Elevon stress and strain: 52 PCM
• Vertical tail fin stress and strain: 38 PCM and 6 FDM
• Rudder and speed brake strains: 12 FDM
• Mid fuselage loads: 40 PCM and 9 FDM
• Fuselage aft head shield and tail cone: 18 FDM
• Timing data: 2 FDM
  
  
• TOTAL: 721

Engineers plan to examine the OEX data in exhaustive detail to map out the flow of hot air through the left wing and to gain a more precise knowledge about how the craft was being buffeted by disturbed airflow over the damaged wing and how the shuttle's flight control system responded to keep the ship on course.

They also plan to examine the launch phase to look for any evidence - elevon flutter, strain gauge readings, etc. - that might indicate the force imparted by external tank foam debris that slammed into the left wing leading edge around 82 seconds after liftoff. That debris impact may have caused the initial damage that led to Columbia's destruction during re-entry. OEX data, in theory, could give engineers a more precise idea about the actual force imparted to the shuttle.

But the foam impact occurred when the shuttle was still experiencing high aerodynamic pressure and the impact likely was "drowned out" (low signal-to-noise ratio) by the strength of normal readings during this phase of flight. But engineers nonetheless are going to look for an impact signature.

Engineers hope to begin analyzing data this weekend from a recovered tape recorder that stored readings from some 721 sensors throughout the shuttle Columbia during its final 45 minutes of flight. Analysts hope the data will help them precisely map out the flow of hot gas through the doomed ship's left wing to confirm and refine - or possibly modify - current theories about where the initial breach occurred and how the deadly plume then worked its way through the interior of the wing.

The orbiter payload experiments, or OEX, recorder was found during a grid search March 19 near Hemphill, Texas. The device was remarkably intact with one edge buried about three inches in soft soil. Over the weekend, engineers with Imation Corp. in Minnesota cleaned and stabilized the 1-inch-wide, 28-track tape and sent it on to the Kennedy Space Center for duplication. Engineers at the Johnson Space Center in Houston hope to begin analyzing whatever data was recorded this weekend.

"In a perfect world, we will have 721 measurements, sensor outputs," said Scott Hubbard, a member of the Columbia Accident Investigation Board. "This covers the wings, the fuselage and the vertical tail surfaces. Of particular interest are going to be 182 pressure measurements, 53 temperature measurements and 447 loads, dynamics and stress measurements.

"Among these will include a series of measurements - if we get all the data back - on the left wing: strains, stresses and strains, temperature and pressures.

"Now we have to note, this has been through a very severe environment," he cautioned. "We don't know if the tape has been demagnetized, we don't know yet the quality of the data in there."

But if the tape is, in fact, readable, "this would be a gold mine of information that could lead us to a much, much better understanding of what happened throughout the vehicle and particularly on the left wing."

During a news conference following a public hearing by the CAIB, Hubbard said additional study of enhanced photography of foam debris slamming into Columbia's left wing shows the material hit the underside of the ship's leading edge in a roughly two-square-foot region centered on a specific panel of protective carbon composite material just forward of the left main landing gear wheel well.

Ongoing analysis of recovered debris, meanwhile, shows the concentration of metallic slag splattered on the inner surface of the leading edge panels increases as one approaches the region where the foam impact occurred.

The two independent lines of evidence are consistent with a breach at or near reinforced carbon carbon - RCC - panel No. 6, or an adjacent closeout panel, that allowed a deadly plume of superheated air to burn its way into the wing, triggering a catastrophic chain of events that led to Columbia's destruction 200,000 feet above Texas.

At today's hearing, two CAIB investigators revealed yet another piece of evidence that supports a burn through near the suspected foam impact point at RCC-6: A partially melted RCC support strut from just behind RCC panel 11, located outboard of RCC-6, that shows hot gas in a cavity enclosed by the wing's RCC panels was moving outboard, as one would expect from a breach located closer inboard to the fuselage.

"There's actually an open space inside the leading edge," said Gregory Kovacs, a professor at Stanford University. "So it's possible if there was a breach, something could have flowed down that open space and then eroded the components in there. So on that score, I think we are thinking about flows down there, where they're concentrated maybe closer to the breach. That's the kind of thinking we're going through."

As it turns out, two temperature sensors monitored by the OEX recorder were mounted underneath insulation on the wing spar behind RCC panels 9 and 10. If a breach really did occur inboard of there, near RCC-6, for example, those sensors may have recorded the initial intrusion of hot gas before it ate its way into the interior of the wing.

"It's expected that if this was a normal mission, (the OEX recorder) would have about 30 minutes of data from ascent and in a nominal mission, an hour of entry data," Hubbard said.

But Columbia's re-entry ended 45 minutes after it began. In addition, the wiring from many sensors in the left wing was routed around the left main landing gear wheel well. Many of those wires may have been severed by the super-heated plume that ultimately burned its way into the wheel well. Even so, that would not affect data from other sensors expected to shed light on the thermal environment and the aerodynamic forces acting on the ship in its final moments.

To put all of that in perspective, here is a brief recap of what investigators believe may have happened to Columbia. Readers are cautioned that details almost certainly will change and the timing of some events is uncertain. The board has not yet presented any theory as a "leading candidate" and some of what follows is an interpretation of what the CAIB has revealed to date:

• A large piece of foam insulation weighing about one pound and measuring three inches thick, 12 inches wide and 24 inches long pulled away from the external tank bipod ramp area 81 seconds after launch. The bipod ramp is just that, an aerodynamic ramp of shaped foam just in front of one of the two struts that held Columbia's nose to the tank.
  
  
• The foam, moving at roughly 500 mph in the slipstream between the orbiter and tank, hit the lower side of the left wing leading edge in a two-foot-wide footprint centered on RCC panel 6. It may have damaged parts of RCC panels 5, 6 and 7 or, more likely some believe, one or two so-called carrier panels that form a flush surface between the RCC panels and heat-shield tiles permanently bonded to the lower surface of the wing.
  
  
• The day after launch, military radars tracked an object leaving the space shuttle. It is not yet known what that object might have been, but sources close to NASA's investigation believe it may have been part of an RCC panel or one of the carrier panels in question. Tests to determine precise radar signatures of various types of possible debris are not yet complete.
  
  
• During re-entry, hot gas breached the leading edge from the presumed foam impact damage site. The gas presumably first moved through the cavity behind the RCC panels, damaging various support structures, before entering the wing itself. At about this same time - before any realtime sensors detected anything unusual - the shuttle's flight control system began responding to unusual aerodynamic forces. Whatever was wrong with the front of the wing presumably was disrupting the airflow over the wing's upper and lower surfaces enough to prompt a response from Columbia's digital autopilot.
  
  
• The plume began melting leading edge support components and the forward wing spar, splattering molten metal back across the inner surface of the RCC panels. The timing of such splattering is uncertain, but the slag can be seen on recovered debris, concentrated near the region of the presumed breach.
  
  
• At the same time, pieces of the leading edge, support structure or adjacent tiles began falling off. Some components may have fallen into the worsening breach. "If you think about the static pressure loads, certainly at the beginning, there's a lot of force," said Kovacs. "So if a piece is sort of flapping around and it's on the underside, if you think about the (40-degree) angle of attack, it's easy to believe a piece could be folded and broken off and end up wedged inside there. It would be driven back as things are melting and if it's RCC (material), it may well survive that and end up stuck there."
  
  
• A brake line temperature sensor in the left main landing gear wheel well recorded a slight but unusual increase as hot gas swirling into the wing entered the wheel well through a vent on its forward face.
  
  
• The breach worsened as Columbia's descent continued until a plume of super-heated air impacting the side or forward face of the wheel well burned through wiring from sensors located toward the rear of the wing. Lost data from those sensors were among the first indications in mission control that anything was amiss.
  
  
• The plume eventually burned through the outboard wall of the wheel well, or perhaps through its forward face depending on the actual breach location, dramatically raising temperatures in the well. A titanium pin used to mount the left landing gear door to the outboard side of the wheel well is partially melted, indicated it was subjected to temperatures as high as 3,400 degrees. Other debris from an area just inboard of the forward corner of the door shows signs of hot gas outflow. Engineers believe the plume of hot gas entering the wheel well likely exited around the corners of the heat-softened landing gear door.
  
  
• Columbia's flight control system struggled to keep the shuttle on course, counteracting increasing aerodynamic drag by adjusting the ship's roll trim and, when that wasn't enough, firing four right-side yaw thrusters. Eventually even that was not enough, and the spacecraft yawed out of control, breaking up at Mach 18.
  
  

The OEX data could prove crucial to confirming and refining the above scenario or, possibly, sending investigators down another path.

"We have focused a lot of our attention on the left wing and particularly the left wing leading edge," Hubbard said. "If the sensors that are there were active and working and got recorded, that information would be extremely valuable. If for some reason those sensors dropped out, the orientation of the vehicle, from some of the other sensors that also help us determine the attitude of the vehicle, might give us a better sense of what was going on."

Starting around April 6, engineers at the Southwest Research Institute in San Antonio, Texas, plan to being firing large pieces of foam insulation at RCC panels and carrier panels at various angles of incidence to determine what sort of damage might have occurred during launch. The foam will be fired from a nitrogen gas canon at impact velocities of around 500 mph.

An RCC panel and upper and lower carrier panels taken from the prototype shuttle Enterprise will be heavily instrumented to determine impact stresses. An RCC panel taken from the shuttle Discovery, which has flown 30 times and closely matches the original-equipment panels that were on Columbia for its 28th flight, also will be subjected to foam impact for a more realistic assessment of what might have happened to Columbia. In addition, foam will be fired at so-called acreage tile, that is, normal heat-shield tiles located in the presumed foam debris footprint just behind the lower carrier panels.

In the meantime, NASA and CAIB investigators are continuing detailed chemical and metallurgical analysis of recovered debris to decipher complex damage patterns in hopes of pinning down the breach location and plume propagation path.

Mark Tanner, an expert in failure and forensic analysis with Mechanical and Materials Engineering, said "what we're trying to do is get an idea from the flow patterns, the splatter patterns and the deposits, where was the breach, where was the origin this whole thing started from. Or origins."

Complicating the picture is the ever present problem of determining when the observed damage occurred.

"A key question when we're looking at these pieces is with the damage we see, was it caused by something that happened on ascent, on descent, breakup or ground impact," Kovacs asked. "A lot of these pieces, you look at them and there's pine needles embedded in them. So clearly that did not happen in space and we're taking great care to understand the relationships of those issues."

All in all, he said, "there's a lot of jigsaw puzzling going on out there. It is like putting together a multi-thousand piece 3D jigsaw puzzle on a 2D surface."

So far, some 54,000 pounds of shuttle wreckage have been recovered, or about 24 percent of Columbia's 223,000-pound dry weight. That total represents 45,762 different parts or pieces of debris, of which just 1,406 have been laid out on a grid mapping the shuttle's lower surface. Dozens of RCC fragments have been found, but most have not yet been precisely identified as to their original location. Almost nothing from the RCC panel 6 location has been recovered, but sections of adjacent panels, along with RCC support hardware, are under analysis.

Engineers believe between 35 percent and 50 percent of the shuttle actually made it to the ground. The rest presumably burned up in the atmosphere following breakup, including virtually all of the aluminum skin structure of the wings.

"A lot of the parts have come through an aluminum molten rain cloud if you will, where they have aluminum splatter over much of the debris," NASA test director Steve Altemus said of the wreckage recovered to date. "We see that molten aluminum on almost everything we have back. It may also speak to why we don't have upper wing surface on the left wing in that that's very thin aluminum. So yes, we expect a great deal of the aluminum not to have made it to the ground."

Asked if anything unusual leaps out under casual inspection, Altemus said "what did strike me as odd, first of all, is the size of the pieces, how small they actually are, and also there's very little left wing lower surface structure and very little left wing upper surface structure. When you walk the grid, hat's what you notice, what is not present as opposed to what is there."

In any case, with spring blooming fast approaching, NASA expects to conclude its massive ground search in the next four to six weeks.

"As the spring comes on, the undergrowth begins to leaf out and the canopy begins to cover," said Michael Rudolphi, deputy director of NASA's Stennis Space Center. "Obviously, the first area you'll lose search capability will be from the helicopter. And then on the ground, as the brambles and the briars begin to leaf out, it's going to damage our ability to see and to identify any material on the ground.

"The forest service thinks we've got another four to six weeks before that becomes real serious," he said. "But ... it is already starting to green up. And It will impair our ability to find as much as we would like to find. There is a time element to do the thoroughness we would like to do. Obviously, we can keep walking around in the woods after it's greened up and we can keep looking, we just won't be as successful."

Shuttle debris fell in a 4- to 5-mile-wide footprint stretching some 250 miles across central Texas and western Louisiana. The debris field impacts some 169 counties in Texas and 39 in Louisiana. Of that total, 143 Texas counties have been searched, 10 counties are in the process of being searched and 26 remain to be searched. Thirty one Louisiana counties have been cleared with eight left to go.

While some 1,800 potential targets have been found on lake bottoms in the debris field using sonar, no major pieces of wreckage have yet been recovered by divers. And no debris has been found west of Texas.

Two flatbed truckloads of debris, each one carrying about 4,000 pounds of wreckage, arrive at the Kennedy Space Center each week. It is then examined, identified and bar coded and analyzed. A two-dimensional reconstruction of the shuttle's lower surface is being laid out on a grid in a 40,000-square-foot hangar near the shuttle landing facility.

Analysts are in the process of developing a computerized three-dimensional virtual reconstruction that will show recovered debris modeled on an imaginary orbiter much like aircraft wreckage is sometimes reassembled to aid visualization and to map out the actual locations of various pieces of debris.

"There are a couple of hundred small pieces of RCC panels," Tanner said. "This would be like putting together a solid gray puzzle. What complicates this is in some cases the fractures that would mate normally really well have been eroded away. So it is going to be a time consuming process of putting this together."

Just how long it might take is anyone's guess at this point.

"We're doing our very best. But this is the first time in human history anyone's had to analyze a hypersonic space re-entry disintegration of a craft," Kovacs said. "And so there's no one to ask how long will it take. And there's nothing out there on the floor I look at and go, well, it's going to be another month and we're out of here."

Even so, he said, "I'm very optimistic. I think we're going to be able to figure it out. We feel pretty confident."

An independent aerospace expert told the Columbia Accident Investigation Board today NASA managers somehow missed the obvious when it came to the potential threat of foam debris falling off the space shuttle's external fuel tank. Aloysius Casey, a retired Air Force lieutenant general with decades of experience managing intercontinental ballistic missile programs and heavy-lift launchers, implied that NASA managers allowed themselves to be lulled into a false sense of security by their own past successes.

"I'm not going to act like I'm some expert in this particular failure because I am not," he told the board during a hearing in Port Canaveral, Fla. "But I would make these observations: High-speed impacts of material on the shuttle wings are beyond the qualification envelope of the orbiter. ... Regardless of the specific sequence and the details of the failure events, it seems to me the remedy is to preclude debris from impacting critical systems during ascent or any time. I believe this was doubtless an original design requirement for the whole system, that you do not have debris impact some vehicle systems. However, I think this is a design requirement that was not achieved. Demonstrably not achieved."

Board chairman Harold Gehman could be seen nodding in agreement during Casey's opening comments.

The shuttle Columbia was destroyed Feb. 1 when a plume of superheated air burned its way into the ship's left wing, at or near the leading edge just in front of the left landing gear wheel well. The deadly breach disrupted the airflow around the orbiter during the hottest part of its re-entry and severely weakened the wing itself, setting up a catastrophic chain of events that ultimately led to the orbiter's breakup 200,000 feet above Texas.

What might have caused the breach remains under investigation, but a major suspect is impact damage from external tank foam that ripped away 81 seconds after launch and slammed into the left wing on the lower surface of the leading edge. High-speed tracking cameras show a suitcase-size piece of foam fell away from the left bipod ramp area, where the nose of the shuttle attaches to the tank.

The accident board has been looking into past flights in which foam debris fell away from the tank and examining the decision-making process that allowed the shuttle fleet to keep flying despite a known problem that was, in hindsight, clearly beyond the shuttle's design criteria.

Casey said the key issue is retaining built-in safety margins and not exceeding them. Shuttle systems are certified, based on testing and analysis, to be able to withstand a certain, specified level of stress that is above and beyond what the system might actually see in flight. But Casey said the shuttle's wings were not designed to be struck by 500 mph-foam and that the foam wasn't supposed to come off in the first place.

Shuttle program manager Ronald Dittemore has not hesitated to ground the fleet in the past to correct seemingly minor problems. But the foam shedding problem was never viewed as a safety of flight issue. CAIB members have made no secret of their concern that NASA was lulled into a sense of false security in this case and Casey seemed to agree.

"It's absolutely critical that we retain margins," Casey said. "A concerted effort needs to be made to operate within design margins, and again, I'm talking about margins that are verified and qual tested for each and every one of the subsystems. A series of successful flights does not verify margin. You may be skating on the very edge and you come up to that flight where either the environment or the hardware causes you to go negative.

"Special efforts should be made to preclude waivers or deviations in production and assembly or pre-flight checkout or any other kind of method that's used for accepting the things you've been talking about here today, that they do not, in fact, reduce the margin. And that's very difficult to decide, it requires expert system engineering judgment to look at that particular point, how we buy this thing off does not in fact reduce our margins.

"Aging and repeated use may also erode the margin unbeknownst to the operators of the system," he said. "I believe it is absolutely essential that comprehensive system engineering effort is made to not only know what the margins are, but to be sure that we protect them in all the ensuing operations."

Casey's comments clearly struck a chord with Gehman.

"Your comments are very helpful because in some of the readings we've all done as part of our review of some of these programs, that subject, of successful flights don't re-establish margins, has come back again and again," Gehman said.

He said successful flights prior to Challenger's destruction were no indication that flawed O-ring seals were safe to fly and "they should not be used to indicate everything is OK here."

"When you use the term 'qualify the system,' if you take the case of the ET for example, the external tank, we would agree in its present situation, the ET is an unqualified system because it's shedding foam continuously," Gehman said. "It wasn't designed to shed foam, we didn't design this thing to have the shuttle orbiter to be impacted by foam, therefore it's currently not qualified in the sense we're using in this room."

"Exactly. That's right," Casey said. "There's no way in my mind that you can say I'm operating within margin if I have an unknown mass impacting an aerodynamic surface."

Gehman then brought up Challenger again, at least obliquely, by questioning the very decision-making philosophy NASA uses to clear shuttles for flight, echoing discussions in hearings 17 years ago that were focused on Challenger and its O-rings.

"What we should do is we should change the operative question on the table here," he said. "The present question is that you've got to prove to me that something is unsafe before I'll change it. What we need to do is, we should require the system to prove it is safe, particularly if we have something that appears to be exhibiting anomalies. The impetus should be to prove it's safe, the burden shouldn't be on me to prove it's not safe. The burden should be on the system to prove it is safe."

"Yes I would agree with that," Casey said. "Obviously, we have to give a lot of credence to any indicators we get. But I am equally as worried about those things that, in fact, are so subtle you haven't seen them yet but in fact, the margin isn't there and you can lose it."

Of course, such a discussion benefits from 20-20 hindsight. Roy Bridges, director of the Kennedy Space Center and one of the managers who signs off on the certificate of flight readiness, or COFR, said he never had any idea the foam represented a safety of flight issue. "To be honest, I did not think the bipod foam coming off had caused any significant damage in the program to date," he told the board today. "I believe it came off about four times before that we know of. I personally looked at every shuttle that's come back during my tenure here and I've seen no significant damage from any of the foam coming off.

"It's certainly been a maintenance concern, it's a lot of work to go out and have to repair all of those things and we don't take that lightly," he said. "We want to get to the root cause of those things and get them fixed. I personally was not aware there was any safety of flight concern with the ramp foam coming off prior to this flight. Had I been aware of that, I certainly would have put my hand up at the FRR (flight readiness review) that we would stop flying. I think this is certainly a surprise to all of us."

In answer to a question by board member John Logsdon, a space policy analyst at George Washington University, Bridges said the launch team was not influenced by any undue pressure to continue space station assembly flights. Schedule pressure was cited as a contributing factor to the Challenger disaster.

"Certainly it was something that I was aware of, trying to make sure we did not lapse back into that mode," Bridges said. "I was an active astronaut before Challenger and I was watching the flight rate go up to one a month about the time I was flying and was aware of intense schedule pressure at that time frame. So I'd say I was pretty highly tuned to trying make sure we didn't fall back into that situation."

He agreed that NASA was driving to meet the space station's initial completion date, saying "we were on a roll and we would have liked to finish it in February of '04. It would have been a brilliant achievement if we could have done that.

"But we were not going to let things like (propellant line) cracks or any other items like that that popped up be, you might say, squashed in order to meet that schedule milestone," he said. "I never felt any concern that if we brought this up to (NASA spaceflight chief) Bill Readdy or the administrator, Sean O'Keefe, that they would do anything except applaud us for letting them know we had a serious problem, we need to take a time out to fix it."

Bridges is a commander of the Air Force Flight Test Center at Edwards Air Force Base, Calif. As such, he had broad experience dealing with test programs, the problems that routinely come up and the decision making needed to work through them.

Discussing problems during flight tests of F-15 fighter jets, Bridges provided a bit of insight into how he views such issues and what it takes to consider grounding a vehicle.

"Certainly, we're interested inn anything that falls off test aircraft and anything that could cause a problem," he said. "I will tell you that the desert floor around Edwards is littered with so-called F-15 tail feathers, little flaps around the engine nozzles, and other things like that that did not work out too well on aircraft but were not thought to cause damage.

"And while we really didn't like dropping things on the desert out there, in order to get the test program moving forward we did not ground the fleet every time we had some minor thing like that happen. So it really depends on what the potential for damage was. If it was a safety issue, certainly I would engage and recommend that we stop flying until we fixed it. If it's not a safety issue, we certainly tried to come up with some kind of fix."

The problem, of course, is being able to recognize a safety issue in the first place. And that's not always easy in a system as complex as the space shuttle.

"Our challenge is to receive those (warning) messages and do something about them," Gehman said later to Casey. "That's the tricky part. I agree with you completely, your presentation made some of those things crystal clear. I would say there really are two cases. There's one where you have the indicators and you have to act on them. And the other one is where in fact, you're losing your margin and you don't have indicators. And those are the really tough ones."

Casey concluded his presentation by arguing shuttle flights will remain relatively risky events regardless of any post-Columbia changes that are implemented and that as a result, NASA should consider limiting the shuttle's crew size to the bare minimum necessary to support a given mission. He also said NASA should not launch shuttles if a mission can be conducted using unmanned rockets and/or robotic systems.

After the hearing, Gehman said the board likely will not address the issue of shuttle crew size or how the vehicle is used.

"Our recommendations, our report, will attempt to quantify the costs and the risks and the benefits," he said. "It will be up to someone else to determine what you're going to charge and how we're going to pay for those things. I doubt we will specify a crew size."

Magnetic tape inside a data recorder recovered last week in Texas appears to be in remarkably good shape, despite the stresses it experienced during the shuttle Columbia's catastrophic breakup Feb. 1 and the recorder's long fall back to Earth. Engineers are increasingly optimistic about recovering potentially valuable data from the salvaged tape that could shed additional light on the aerodynamic forces and temperatures the shuttle experienced during its final minutes.

"They're taking a great deal of care with it," said Bradley Allen, a spokesman for Imation Corp., a Minnesota company that specializes in data storage and recovery. "My understanding is at least visually, it came in in fairly good condition considering what the device went through."

The so-called OEX recorder was located last week by search crews walking a grid near Hemphill, Texas. It was found slightly embedded in soft ground and while the case showed signs of damage, it appeared to be surprisingly intact.

The recorder was shipped to Imation Friday for initial inspection. Imation engineers opened the OEX recorder over the weekend and first removed unrecorded tape from the supply reel to gain experience handling the material. They then removed the recorded tape on the takeup reel and began cleaning it by hand.

The tape will be shipped to the Kennedy Space Center Tuesday, where it will be copied. Only then will engineers begin the process of playing back whatever data might be present.

Unlike the reel-to-reel recorders familiar to audiophiles, those with side-by-side takeup and supply reels, the OEX recorder features two large reels stacked on top of each other. The lower supply reel plays out tape when the machine is activated and after data is encoded, the tape is wound onto the upper takeup reel.

The OEX tape was broken between the supply and takeup reels, but engineers say the amount of tape seen on the takeup reel indicates the recorder began operating as planned roughly 15 minutes before Columbia's descent began.

Columbia was the only shuttle equipped with an OEX recorder. Columbia was NASA's first space shuttle and as such, it was more heavily instrumented than subsequent orbiters to provide essential test flight data.

While NASA already has telemetry from Columbia that was beamed back to Earth in realtime during the shuttle's descent, the OEX recorder was designed to store data from hundreds of other sensors, providing direct measurements of temperature, vibration, dynamic pressure and other forces during launch and re-entry.

Assuming the tape holds readable data, NASA investigators hope to gain potentially crucial new insights about Columbia's final minutes. At the very least, officials say, the OEX data should help investigators validate, or confirm, the realtime telemetry already in hand, which in some cases was garbled during transmission.

The OEX recorder carried 9,400 feet of 1-inch-wide 28-track magnetic tape. The device operates at 15 inches per second - 75 feet per minute - and can hold two hours worth of data. NASA officials say the recorder was activated 15 minutes before Columbia's re-entry began, or around 8 a.m. on Feb. 1. The recorder presumably ran until vehicle breakup a few seconds past 9 a.m.

But at least some of the tape near the point where it separated between the takeup and supply reels is too damaged for any data recovery. That lost data presumably covered the very final seconds of entry just prior to breakup.

NASA today announced a revamped management team to oversee the agency's internal investigation of the Columbia disaster in accordance with a request made late last month by the independent Columbia Accident Investigation Board.

The concern by the board was that senior NASA managers overseeing the disaster investigation - managers who played a role in clearing Columbia for launch and then managing its mission - would at some point face questioning by the CAIB about the decisions they made leading up to launch and during the conduct of the flight.

"It has become apparent that some of the chief managers of the investigation which NASA and this board share are also members of these boards that we're going to be looking at," Harold Gehman, CAIB chairman, said March 4. "We are then put into the place of having the investigators investigate themselves.

"That's not exactly true because NASA is not investigating management issues. Only we are investigating management issues," he said. "But ... I can't possibly have key investigatory managers also be the people whose performance we're looking at in other areas."

NASA today announced the formation of a new team - the NASA Accident Investigation Team, or NAIT - that will take over the role of the original Mishap Response Team that was formed immediately after Columbia's destruction Feb. 1. The MRT was chaired by Linda Ham, a former flight director who served as chairman of the agency's mission management team.

The MMT, a panel of senior shuttle managers formed in the wake of the 1986 Challenger disaster, was responsible for clearing Columbia for launch and for the top-level day-to-day decisions during the mission that defined the flight.

The MMT, for example, declined to request spy satellite imagery during Columbia's mission to inspect the shuttle's left wing for signs of damage after external tank debris fell off and hit the wing 81 seconds after blastoff. Instead, the MMT accepted a Boeing analysis indicating the shuttle could safely land despite potentially significant wing damage.

Late last month, Gehman asked NASA Administrator Sean O'Keefe to remove senior shuttle managers who played a role in the conduct of Columbia's mission from duties supporting the ongoing accident investigation.

O'Keefe initially balked at making any immediate changes, but he later agreed to assign NASA personnel not directly involved in the conduct of shuttle missions to key teams supporting the board's investigation.

And so Randy Stone, a widely respected former flight director who now serves as deputy director of the Johnson Space center, will take over as chairman of the newly formed NASA Accident Investigation Team.

The new team will be made up of three subdivisions matching similar elements of the CAIB's structure. Stone, along with chairing the NAIT, will manage a subdivision focusing on flight operations, mission control, flight planning and crew training.

Frank Benz, director of engineering at the Johnson Space Center, will oversee engineering and technology issues, including debris analysis, imagery and fault tree analysis. He will replace Ralph Roe, director of the shuttle vehicle engineering office at JSC. Jim Kennedy, deputy director of the Kennedy Space Center, will manage a review of maintenance, program management and internal processes.

"The Mishap Response Team met for the first time within two hours of the Columbia accident, and its demanding work has been highly efficient, methodical and productive," Stone said in a statement. "They have done a tremendous job under extremely difficult circumstances. Now, many of the initial mishap response activities are nearing their close, and it is time for NASA's accident support structure to transition to an organization designed to provide long term investigation support."

The statement says that over the next four to six weeks, search teams hope to wrap up search and recovery efforts in east Texas.

"Most of the organized search effort should be completed around May 1, 2003, weather permitting," the statement said. "Other activities coming to a close include NASA's Emergency Operations Center, which assisted in fielding thousands of calls about the accident and received almost 7,000 images from sources external to NASA."

The NAIT will meet for the first time Monday.

Search crews walking a grid near Hemphills, Texas, have found the shuttle Columbia's orbiter experiments recorder, or OEX, a tape recorder that stored key data about the shuttle's performance during re-entry. The recorder was found essentially intact, according to a spokeswoman for the Columbia Accident Investigation Board, but the device may have suffered heat damage and in any case, the condition of the data tape inside is not yet known.

But if data on the tape can be recovered, NASA investigators could find a gold mine of information shedding more light on the aerodynamic forces acting on the spacecraft as its flight control system struggled to keep the doomed ship on course.

"We have no way of knowing whether the data's in a condition where it can be recovered or not," said Laura Brown, a spokeswoman for the CAIB. "They suspect there may be heat damage. We just don't know what condition it might be in."

The OEX recorder was found essentially intact on the ground. Seventeen years ago, divers recovered tapes from the submerged wreckage of the shuttle Challenger and managed to extract data despite extensive damage. Engineers are hopeful they can recover data from Columbia's recorders as well.

"They're taking it to JSC (Johnson Space Center) for analysis," Brown said. "They'll clean it and they're developing a testing plan for it. They want to be as careful as they can with it so they don't lose any data."

The recorder stores data on aerodynamic pressure, temperature, vibration and other variables. Only Columbia, NASA's original space shuttle, is equipped with an OEX recorder as part of a complex system used to collect data during the ship's initial test flights. The OEX recorder should not be confused with the shuttle's operational recorders, which store additional flight data as well as voice traffic from the crew's intercom. The OPS recorders have not yet been located.

Here is a bit of background on the OEX recorders from NASA's shuttle reference book:

The support system for the orbiter experiments was developed to record data obtained and to provide time correlation for the recorded data. The information obtained through the sensors of the OEX instruments must be recorded during the orbiter mission because there is no real-time or delayed downlink of OEX data. In addition, the analog data produced by certain instruments must be digitized for recording.

The support system for OEX comprises three subsystems: the OEX recorder, the system control module and the pulse code modulation system. The SCM is the primary interface between the OEX recorder and the experiment instruments and between the recorder and the orbiter systems. It transmits operating commands to the experiments. After such commands are transmitted, it controls the operation of the recorder to correspond to the experiment operation. The SCM is a microprocessor-based, solid-state control unit that provides a flexible means of commanding the OEX tape recorder and the OEX and modular auxiliary data system.

The PCM system accepts both digital and analog data from the experiments. It digitizes the analog data and molds it and the digital data received directly from the experiments into a single digital data stream that is recorded on the OEX recorder. The PCM also receives time information from the orbiter timing buffer and injects it into the digital data stream to provide the required time correlation for the OEX data.

The SCM selects any of 32 inputs and routes them to any of 28 recorder tracks or four-line driver outputs to the T-0 umbilical; executes real-time commands; controls experiments and data system components; and provides manual, semiautomatic and automatic control.

The recorder carries 9,400 feet of magnetic tape that permits up to two hours of recording time at a tape speed of 15 inches per second. After the return of the orbiter, the data tape is played back for recording on a ground system. The tape is not usually removed from the recorder.

Editor's Note...
Due to other commitments, I was unable to immediately file a status report covering the March 18 hearing by the Columbia Accident Investigation Board. My apologies for the delay.

As investigators increasingly focus on a breach at or just behind the leading edge of the shuttle Columbia's left wing as the root cause of the Feb. 1 disaster, engineers poring over telemetry from the doomed ship are zeroing in on exactly where the breach must have occurred - and how it must have propagated - to explain the orbiter's response to the resulting aerodynamic forces that ultimately ripped the ship apart.

Within 600 seconds of the shuttle's plunge back into the discernible atmosphere 400,000 feet above the Pacific Ocean, a deadly plume of super heated gas managed to work itself into the ship's left wing, burning through a thick bundle of wires carrying data from various wing sensors and then into the left main landing gear wheel well. Once inside the wheel well, the plume apparently burned its way through the heat-softened corners of the left landing gear door, spewing out in jets at right angles to the flow of hot air rushing across the belly of the ship.

During the second day of a hearing by the Columbia Accident Investigation Board, NASA specialists outlined a wide-ranging, multi-center effort using wind tunnels, computational fluid dynamics and other sophisticated tools to develop scenarios that best explain the telemetry from the stricken spacecraft.

While the work is far from complete, they are zeroing in on a breach at or very near the leading edge of the left wing. And they are beginning to rule out scenarios that received attention earlier in the investigation, including a breach at or near the left main landing gear door and the earlier-than-normal onset of turbulence and high heating that might have resulted from any inherent "roughness" in the surface of the left wing or from unusually high atmospheric density.

Instead, investigators are assuming a small breach near the leading edge of the left wing allowed hot gas to begin entering the structure 488 seconds after entry interface, the moment Columbia began encountering the discernible atmosphere. The breach probably was there before the shuttle dropped out of orbit, but for the purposes of developing credible scenarios, investigators are assuming it opened up 488 seconds past "EI" because that's when the first signs of a temperature increase inside the wing showed up in telemetry from the shuttle.

"We're looking at about the first 600 seconds of entry, what happened from entry interface to the point where we believe there's a breach in the wheel well and the temperatures start rising," Stephen Labbe, chief of NASA's applied aeroscience and computational fluid dynamics branch, told the CAIB. "So if we can get that solved, we feel we'll have made a significant contribution to the investigation."

Entry interface occurred at 8:44:09 a.m. on Feb. 1. At 8:52:05 a.m., telemetry shows Columbia's autopilot starting to adjust the shuttle's wing flaps, or elevons, to counteract subtle but unusual aerodynamic forces acting on the left wing. Twelve seconds later, a landing gear brake line temperature sensor registered a "one bit flip" change, indicating an increase of about 1.5 degrees. The sensor was located in the left main landing gear wheel well.

At 8:52:59 a.m., data from a temperature sensor at the back of the wing suddenly went "off-scale low," indicating a complete failure. Other sensors at the back of the wing soon followed suit. The wiring for those sensors was routed forward, along the left side of the landing gear wheel well and then across the well's forward face just a foot or so from the area of the left wing's leading edge where engineers believe the breach occurred.

At 8:54:10 a.m., temperatures began rising dramatically across the wheel well and 10 seconds after that, telemetry indicates an unusual trend acting to pull the shuttle's nose to the left somehow reversed, as if the left wing suddenly gained more lift.

Labbe painted an intriguing picture of how the data might fit together. The brake line temperature increase, he said, "suggests a breach, a first initial breach into the wing."

"There must have been ingestion of hot gas in order to create that change in the wheel well," he said. "The second one is a burn through of the wire bundle that holds all of those instruments so that whatever was being ingested had to be able to burn through that wire bundle. When we get to the wheel well breach, we see a significant rate of change. Instead of just drifting up, now we see a large increase in the rate of change and that corresponds to a change in the aerodynamic trend where (the shuttle's rolling moment) was drifting negative and now it's starting to go back positive."

In the shuttle coordinate system, yaw and roll are considered positive when the shuttle is moving to the right and negative when moving to the left. During normal re-entries, the shuttle's flight control system keeps both centered around zero. But in Columbia's case, both roll and yaw went negative very early on, indicating aerodynamic forces were acting to pull the ship's nose to the left while at the same time trying to roll the ship slightly in the same direction.

Around 8:53:46, the first known piece of debris fell away from Columbia as documented in amateur video shot during the shuttle's descent across California. At 8:54:07 a.m., the fifth such "debris shedding" event was noted. The unusual change in the shuttle's rolling moment - from negative to positive - occurred at 8:54:20 a.m., just 10 seconds after the onset of a rapid climb in wheel well temperature.

At 8:54:22 a.m., a sensor mounted on the sidewall of Columbia's fuselage, well above the left wing, recorded an unusual temperature rise. Eleven seconds after that, a bright flash was seen by ground observers, followed seconds later by what appears to be a relatively large piece of debris falling away, the sixth such event and one of the two most significant.

"Somewhere between debris 5 and 6 is when we see this event where the rolling moment was drifting negative, the change in rolling moment, and it changes direction and starts this positive trend," Labbe said. "And we think this is a very key point for us in trying to understand what happened. Something changed about the configuration, some damage, and since we know we were shedding debris, something significant happened there that changed the trend on rolling moment."

Board chairman Harold Gehman then asked what sort of change in the aerodynamics of the spacecraft could cause it to suddenly start rolling back to the right.

"You've asked the $64,000 question there, I believe, and that's what our work is going to be," Labbe replied. "What it suggests early on is that I was losing lift on the left wing. And then something changed to start creating lift on the left wing, or pushing up on the left wing. ... The damage is so significant, it's creating locally a very high pressure that's on the lower surface of the wing and starting to push up on the wing."

An opening on the underside of the wing could provide that sort of lift, but engineers believe the left main landing gear door remained in place until vehicle breakup or just before. But jets of hot air spewing out around the corners of the door probably could provide sufficient pressure to reverse the rolling moment.

"I think if you have a jet, if it's coming out with a strong enough rate that you create a jet or create enough flow out of there, it will set up a shock in front of that, which will create a high pressure, which would be on the lower surface, which would push up on the wing and probably create more lift," Labbe said.

It's also possible disturbed air flow caused by a worsening breach near the leading edge could have had the same result. John Bertin, a professor of aeronautics at the U.S. Air Force Academy, told the board the loss of two or three reinforced carbon carbon panels from the leading edge could create a shock zone of higher pressure.

"That could have caused the pressure to be higher and giving you an asymmetric force," he said.

NASA's integrated aerodynamics, aerothermodynamics and thermal analysis review is attempting to figure out, using wind tunnel tests, complex computational fluid dynamics and other tools just what sort of breach must have occurred to explain what happened to Columbia.

"So what kind of hole or damage can be created in from entry interface to 488 seconds that could produce that initial change in the instrumentation?" Labbe asked, referring to the initial brake line temperature rise. "Then we go on to the next step. Step B is we burn through that wire (bundle) in another 42 seconds. So if we pick a location and we have a burn through, can it then also burn through the wire 42 seconds later?

"Then we have the breach into the wheel well at 600 seconds where we see the rate of change and of course, that has to be consistent with the initial breach and the burning through the wire. So you can see how we're trying to piece all these together. And then finally, we see this change in the fuselage wall temperatures and whatever is producing that, is the damage consistent?"

Contact with Columbia was lost a few seconds after 9 a.m. when the vehicle, yawing sharply to the left, broke up high above Texas. Because of the shuttle's high altitude - more than 200,000 feet - the dynamic pressure acting on the shuttle was roughly equivalent to what one would feel at sea level in a 150 mph wind. One maneuvering thruster, or just a degree or so of aileron trim can keep the ship properly oriented.

Toward the end of Columbia's flight, however, the shuttle was experiencing some 160,000 foot pounds of force acting to the left.

"That requires all four (right-firing yaw) jets, three or four degrees of aileron, sideslip, everything the vehicle had to try to counteract that moment, it was using," he said.

"Hold your arm outside of a car, you can feel (the wind) trying to pull your arm back," he explained. "That's a moment of what you're feeling about your shoulder and you're talking maybe, you know, 10 pounds, 20 foot pounds of moment. Not very much at all. And we're talking about over a hundred thousand food pounds of moment."

Even with all the damage that must have occurred because of the initial, quickly worsening breach, "the flight control system still was commanding the vehicle to do exactly what it guidance was telling it to do," Labbe said. The unusual change in sign indicating a positive roll due to increase lift on the left wing was "almost like the damage has returned the vehicle back to its original flight characteristics," Labbe said. "But then, of course, we see a rapid increase and then essentially going off the cliff there at the end."

Damage patterns in recovered debris and ongoing analysis of telemetry indicates the initial breach probably occurred at or near RCC panels 6 and 9 on the left leading edge. Or just behind them. So-called carrier panels, covered with heat-shield tiles, are bolted in place just behind the RCC panels to provide a flush surface between the carbon-carbon composite material and the tiles permanently bonded to the wing's underside.

Some investigators believe it is likely a damaged carrier panel or a broken/missing tile on a carrier panel just behind the RCC panels in question could have provided the entry point for the plume of hot air that ultimately destroyed the left wing. The day after launch, ground radars detected an object separating from Columbia that was roughly the same size as a carrier panel.

Whether a carrier panel came off before or during entry, "it would be very easy to have damage occur and such that the RCC panels themselves would come off," said board member James Hallock. "They're only held on by, I believe, two bolts. Get this thing out, get some heat in there in the right place on those inconel bolts and they could come loose and that's what could be happening, all this stuff is starting to open up into a larger area."

Engineers are conducting wind tunnel tests and carrying out complex computational analyses to determine how such a breach might worsen.

"We're going to be looking at multiple panels in this thing and other panels missing and that's really where our future work is focused, is to first do a survey of the wing leading edge and then start looking at other damage scenarios that try to produce that," Labbe said. "And then eventually, get our higher fidelity CFD (computational fluid dynamics) analysis to get to the actual flight conditions."

One issue that remains to be resolved is whether the initial breach was present before re-entry began, which most observers believe, or whether it opened up during the descent, which Labbe's scenario suggests. In recent weeks, much has been made of NASA's decision not to request high-resolution spy satellite photography of Columbia in the days after launch to look for signs of damage.

Whether the breach was the result of some weakened component failing during descent or whether a visible defect was present prior to entry is significant.

"It bears on a lot of things because if the fault just manifests itself right here (during entry), even though aerodynamic pressures are practically nothing but maybe enough to remove something or cause something that was weakened (to fail), then all this stuff about on-orbit photography becomes irrelevant," Gehman said. "It's important to know whether or not the orbiter had a pre-existing condition, which then didn't manifest itself heat wise until you got enough heat."

Regardless of when it actually opened up, the presumed breach between RCC panels 6 and 9 was in a particularly bad area. As it turns out, RCC panel 9 is precisely where two hypersonic shock fronts interact during shuttle descents.

"For the shuttle, without damage, the sweep angle (of the wing) is such that the interaction effects are relatively benign," Bertin said. "So that while there's a shock-shock interaction, the highly swept leading edge prevents you from having strong interactions."

But if multiple RCC panels were missing, providing what amounts to an unswept wing leading edge, "you'd have strong interactions and very large heating going on," Bertin said.

A blurry photograph of Columbia taken by off-duty personnel at Kirtland Air Force Base in New Mexico shows the shuttle within a minute or so of its destruction. The photo has been enhanced now and it clearly shows signs of significant damage to the left leading edge area. Bertin believes the imagery is actually showing the high-density shock zone that formed just in front of the damaged area.

"So if you were missing, maybe not one panel but maybe two panels and maybe it's downstream from the initial problem that you had and stuff like that, then you've got a little like two teeth missing from the leading edge and you've got a little notch in there," he said. "Now the flow can go in that notch and create a shock pattern that in my mind kind of looks like what the Kirtland photograph might be telling you."

He said the initial breach might have started out small, but it would have quickly worsened.

"I'm assuming RCCs possibly were lost in time and a very early one, maybe one would be missing, maybe more," Bertin said. "But then because the under structure is exposed, that some additional damage occurred and other ones would have come off in some fashion. With just one missing, you could get the damage that maybe was observed eventually. But from seeing the Kirtland (photo), I'd think you'd have a pretty good piece missing."

Once the plume from the breach got into the wing, it quickly made its way into the left landing gear wheel well. The exact mechanism is not yet known but investigators have recovered debris from the landing gear door attachment system that indicates some areas in the well were subjected to temperatures high enough to melt titanium, nearly 3,000 degrees. Interestingly, sensors in other areas of the well did not record anything out of the ordinary.

"When this plume entered, it can bounce around," Hallock said. "This is a very rarified atmosphere still and so we could be having 3,000 degrees at one end, which is melting titanium, and at the other end we'll have a sensor that doesn't even know much is happening. You've got to have enough molecules in there, atoms in there, to be able to convey the temperature itself.

"Temperature is a quantity that depends on having something for it to register on," he explained. "You've seen in these reports where they say astronomers have found a place where the temperature is 10 million degrees and this is a place in space itself. Why? There's two or three molecules moving around with such energy that yes indeed, if you had a thing that those things could hit against, they would register a temperature that high.

"So don't think of it as being like heating up the air in this room. It's very different because there are so few molecules there that you can get a great gradation right across the entire area."

Gehman said the board was particularly interested in the sort of chemical reactions that can occur when aluminum is subjected to extreme temperatures.

"What we're leading to, of course, is a scenario in which a new path into the wheel well could be developed in seconds," he said. "We're trying to establish just how rapidly other kinds of processes can rearrange the inside of the wheel well and then match up with these temperatures. Right now, we're still in the exploratory stage of that."

In other developments, Gehman said the board is close to releasing "interim recommendations" to NASA. He would not discuss what those recommendations might require, but after the news conference he told reporters one of them will focus on how NASA and the operators of military imaging systems like spy satellites should work together in the future.

"The business of NASA and the various intelligence gathering agencies of United States getting their act together so at they don't talk past each other - we're talking about on-orbit photography and things like that - NASA doesn't need to wait, they can go ahead and get that sorted out right now," Gehman said. "I'm not going to comment on exactly what could be done, but one of the earliest recommendations we think is coming up for board consideration is guidance to NASA to get their act together."

He said NASA personnel were not at all up to date on the capabilities of modern military imaging assets and that no interface existed to bridge that gap. Agency managers decided early on not to request spy satellite imagery of Columbia's left wing because they did not believe the systems had enough resolution to see presumably small signs of damage on the leading edge or in the heat-shield tiles.

While Gehman did not discuss the capabilities of modern imaging systems, Ted Molczan, a respected satellite observer, has calculated that Columbia could have been imaged on multiple occasions by classified optical imaging satellites. Resolution would have varied from six to 16 centimeters, or 2.3 to about six inches.

"We think both sides of the house bear equal blame," Gehman said. "Improvements in on-orbit photography that have come along, nobody from that part of the house has come down here (to NASA), knocked on their door and said, you know, things have changed since we made this agreement. And NASA doesn't have the right people cleared to receive the data. ... They made decisions without having the right information. The point is, this is a system that broke."

Editor's Note...
Due to other commitments, I was unable to immediately file a status report covering the March 17 hearing by the Columbia Accident Investigation Board. My apologies for the delay.

A NASA flight director told the Columbia Accident Investigation Board Monday he was amazed the doomed spacecraft was able to continue flying in relatively normal fashion for nearly 10 minutes while shedding multiple pieces of flaming debris as a plume of superheated air burned its way into the stricken ship's left wing.

The shuttle's flight computers faced an impossible task. But in silent testimonial to the foresight and cleverness of their programmers, the computers methodically adjusted the positions of wing flaps, or elevons, to offset steadily increasing levels of aerodynamic drag acting to pull the ship's nose to one side.

At 8:52:05 a.m. on Feb. 1, one minute and 12 seconds after Columbia entered the region of peak heating off the coast of California, analysis of telemetry from the doomed craft shows the first indications of the computer system reacting to counteract an unusual yaw to one side by adjusting the shuttle's aileron trim. Fifty-six seconds later, the computers began counteracting an additional rolling motion, or moment.

The space shuttle is not equipped with ailerons like a typical airplane. Instead, each wing has two large flaps, or elevons, one inboard and one outboard, that can be positioned independently to produce the same effect as ailerons.

"The aileron is a theoretical difference between the elevon position on one side of the vehicle and the elevon position on the other side of the vehicle," said Robert "Doug" White, director of operational requirements for United Space Alliance, the shuttle prime contractor. "By adjusting the elevons ... you can create an aileron effect. So that aileron effect was keeping the vehicle flying the way we wanted it to. So as the forces began to change on the vehicle, the trim changed and we saw that in the data."

At 8:58:03 a.m., the telemetry shows a sharp increase in the movement of the shuttle's elevons to keep the ship pointed in the right direction.

"The vehicle was in control and was responding to commands up to that point and after that point something changed, apparently," White told the CAIB. "It still continued to be in control and still continued to respond to commands, but the rates and the amount of muscle it needed to continue flying the vehicle the way it should be flown was continuing to increase. Something definitely happened at that point, again we don't know what, but something definitely happened at that point to cause the flight control system to need more muscle and start having to fight harder to control the vehicle."

Board member Sheila Widnall, an aerodynamicist, observed: "That really coincides with a rather sharp increase in the rate of rise of dynamic pressure."

"Yes," said White, "it does."

What might have happened at that moment is not yet known. But Columbia was in distress almost from the moment it began experiencing the effects of atmospheric heating high above the Pacific Ocean approaching the California coast. Video shot by amateurs, several of them technically accomplished amateur astronomers, show multiple pieces of debris falling away from Columbia beginning at 8:53:44 a.m., roughly three minutes after entering the region of peak heating. It is likely debris was shed even earlier than that, out of view of the cameras.

Investigators believe a breach at or near the leading edge of the left wing allowed a jet of super-heated air to burn its way into the unpressurized structure. The latest thinking, NASA sources say, is that the plume entered the wing around the position of reinforced carbon carbon panel No. 6, one of 22 such protective carbon composite panels making up the leading edge of the wing. This region of the wing was hit by debris falling off the shuttle's external tank 81 seconds after liftoff. The RCC panel or its mounting hardware may have been damaged enough by the debris strike to cause a breach during entry. It's also possible damage to a carrier panel just behind the lower edge of the panel provided an entry point for hot air as Columbia descended.

NASA is having tests conducted at Wright Patterson Air Force Base in part to determine if debris seen floating away from Columbia the day after launch could have come from this area. While engineers are still working to pin down the exact breach location, the above scenario provides the best match yet with telemetry and the known aerodynamic forces acting on Columbia as it returned to Earth.

Once inside the wing, the plume of super-heated air appears to have burned through electrical cables routed along the outside of the left main landing gear wheel well just a foot or so behind the RCC panel, ultimately eating its way into the well itself where it triggered additional sensor failures and elevated temperatures. The plume may have jetted out of the wing through gaps near the corners of the heat-softened aluminum landing gear door.

Whatever the exact sequence of events, the left wing ultimately failed as the shuttle yawed out of control around 9 a.m.

Flight director Paul Hill, who has been coordinating NASA's efforts to integrate amateur video into the agency's second-by-second entry timeline, said imagery of Columbia's catastrophic plunge across the southwest holds no clues as to exactly what was falling away from Columbia or even how large the pieces, whatever they were, might have been. Only relative sizes can be inferred. "I am confident that many, if not all, of the things we label as 'debris shedding events' are, in fact, some object coming off of the orbiter," Hill said. "Can I tell you is it golf ball sized, or is it the size of this sheet of paper? I can't.

"It very well could be something as small as a marble in most of those videos and the ones we think are so significant and have gotten us so excited, those things could be golf ball sized. We really don't know. We know relative sizes, we know relative motions, but we don't know specifically what they are.

"But we are very confident, based on the way they behave after they separate from the orbiter, that they are, in fact, separate ballistic objects or objects that have mass in almost all cases. In the case of some of these flares, they could be something different like combustion products."

A major flaring event occurred around 8:54:33 a.m., just prior to the separation of an object known as debris 6. Other flares were observed later in the sequence.

"It is possible it is something that burned and came off the vehicle," Hill said of debris 6 and its associated flare. "It is what you would expect to see if we were to, say, vent a fluid or if we were to burn something and as we gave off combustion products - significant combustion products, not something on the order of, say, one of our reaction control jets - but if we were actually burning something substantial and as we put that out in the plasma wake, you would expect, because that would have relatively no mass, certainly when compared to an object, that those combustion products would immediately go essentially static compared to the orbiter or compared to what we consider normal ballistic behavior for an object that has significant mass.

"So it is reasonable to assume that something came off that was very light or that was some kind of combustion product, like potentially aluminum slag that also was burning as it came off the orbiter and then went stationary there in the wake and looked more persistent."

Of 16 documented debris shedding events, debris 6 and 14 were by far the brightest. Debris 14 was the brightest of all. "Debris 6 you can see persists, depending on the video you look at, for between 6 and 12 seconds," Hill said. "Debris 14 we see persist for four-and-a-half to seven-and-a-half seconds. But debris 14 also is much, much brighter than any other object, including debris 6. How do you interpret that? We're not sure.

"We do think that relative brightness is an indicator of something that's larger and more massive," he said. "We think the amount of time that individual flares or the light around the debris persists is also indicative of the larger ballistic numbers, which tells you you're dealing with something that's probably larger and heavier. But that's as much as we know."

While the video does not yet shed light on the nature of the debris, it clearly documents a surprising number of events. Hill said engineers "continue to be shocked that we had debris coming off the orbiter as we crossed the California coast."

"We clearly had an external breach in the vehicle and had hot gas somewhere in the left wing for that significant period of time and the vehicle flew perfectly, no indication of what was going on in flight control and virtually no indication of what was going on in telemetry on the ground, other than we saw a few temperature, pressure indications that didn't make sense to us," he said. "But aside from that, the vehicle flew like a champ until right up until the breakup. So that did surprise us."

But Hill said he was not surprised search teams combing eastern Texas for debris have not recovered more wreckage.

"Are we surprised that we only have 15 to 20 percent by weight of the orbiter? I don't think so," he said. "I would think when you first see the debris count and you see how many individual pieces of debris (have been recovered), our first reaction was one of surprise, how could we have gotten that much of the orbiter down from 200,000 feet intact?

"I think you've all seen at KSC, what they have is a whole lot of little tiny pieces of what used to be an orbiter. And if you go look at it laying on the ground there in the high bay at KSC, you don't have a spacecraft laying there, you've got a whole lot of nothing. And I think that fits in with what our conventional wisdom was prior to this."

At Monday's hearing, the second held by the Columbia Accident Investigation Board, an expert in re-entry breakups said the shuttle's destruction was in keeping with the mechanisms known to be at work during more mundane satellite entries.

"The heating is like, in a sense, cooking an onion," said William Ailor, director of the Aerospace Corp.'s Center for Orbital and Reentry Debris Studies. "You basically start from the outside and then as you heat the pieces up to a point where the materials will fail, that'll expose some new materials, they'll go through the same process and the object can be broken apart."

Interestingly, Columbia's breakup, in general, mirrored the way much smaller, fragile satellites and rocket stages break apart when falling through the atmosphere.

"Basically, a typical way for things to break up when they re-enter is they will come down through the atmosphere for a certain amount of time, they look absolutely fine, we've seen videos of these things where they just look like spacecraft coming down. All of the sudden, they come apart and when they come apart, they just disintegrate.

"That altitude typically is around 42 nautical miles plus or minus a few nautical miles," he said. "But that's a pretty good guess. Just as a rule of thumb, it seems like a critical point for spacecraft re-entry and breakup is around 42 miles."

Unlike re-entering satellites, Columbia had a thermal protection system and wings to provide some amount of lift. Even so, the orbiter only made it to an altitude of around 38 miles before suddenly, and catastrophically, breaking up.

Ailor said the recovery of debris shed early in Columbia's descent likely will prove critical to determining the root cause of the disaster.

"The orbiter was controlled for a good period of the time and if evidence is found that could have occurred during that period and it indicates a particular flow pattern or something like that, I think that could be very useful," Ailor said. "I think the early debris would be very critical to an analysis like that."

Such debris will be difficult to find. As of now, nearly seven weeks after the disaster, no wreckage has been found west of Texas. But Hill's team has been able to determine the probable trajectories of several pieces of debris that fell off early. Using that data, researchers have found ground radar traces matching at least four debris shedding events, three of them in the debris 6 "footprint." Investigators are just now beginning to look for radar traces in the presumed debris 14 footprint.

"We think the brighter objects are more massive, are more significant, potentially higher ballistic numbers," Hill reiterated. "Certainly the (brightening associated with) the individual pieces of debris persists longer. We expect that those objects are more massive, higher ballistic number, because we think that the reason they persist longer is they are moving faster so they stay lit, they have their own plasma wake longer than, say, some lighter things, say an individual tile comes off versus some other heavier object.

"But I'll also say we cannot just look at these videos and determine what is it that's coming off the vehicle. Are we losing a tile here, are we losing some section of ... thermal blanket that's on part of the external surface of the vehicle? We can't tell that. And until this day, with the good data we have on the ballistic analysis and the footprints, we still cannot say exactly what it is we see coming off. We are making some judgments on which of them are more significant or more massive than the others (such as) debris 6 and debris 14."

Said Ailor: "The work that's going on relative to finding the debris is really an important part and that really has to be emphasized. That's going to be a key to solving this puzzle, I believe."

Revision H of the CBS News-compiled STS-107 integrated entry timeline has been posted. This revision includes significant updates from NASA's latest STS-107 Master Timeline (rev. 15), including the location and start/stop times of video shot during Columbia's descent, unexpected S-band communications drop outs and other details about the shuttle's post loss-of-signal trajectory. As always, suggestions, corrections and comments are appreciated.

William Readdy, associate administrator for spaceflight and a former shuttle commander, told the Columbia Accident Investigation Board he did not consider asking for a spy satellite inspection of Columbia's left wing during the doomed ship's mission because the agency had already concluded the shuttle could land safely.

But in a letter to the CAIB, the Senate and House Intelligence committees and the NASA Inspector General, Readdy said he agreed that NASA could accept an offer from an unnamed government agency - presumably the National Imagery and Mapping Agency - to perform such an inspection on a "not-to-interfere basis."

But no such inspection was ever formally requested by NASA and no such remote inspection ever took place.

"If we had thought for a moment there was a problem, we would have asked," Readdy told reporters today in Washington.

During Columbia's launching Jan. 16, three pieces of debris broke away from the shuttle's external fuel tank about 81 seconds into flight. One piece, roughly the size of a suitcase, slammed into the underside leading edge area of the orbiter's left wing.

When the impact was discovered during routine post-launch analysis of ascent film and video, NASA managers ordered Boeing to carry out an analysis to determine what sort of damage such an impact might have caused. The Boeing team ultimately concluded the tank debris could have caused enough damage to the shuttle's fragile heat-shield tiles to produce localized, potentially severe damage. But the engineers concluded the potential damage did not pose a safety-of-flight concern and that Columbia could safely land.

NASA's mission management team, chaired by Linda Ham, a former ascent/entry flight director, accepted that analysis and the space agency never requested help from NIMA or other agencies operating the nation's most sophisticated imaging satellites and ground-based satellite-tracking telescopes.

That decision has been the subject of second-guessing and criticism in the wake of the disaster. In the days after the mishap, shuttle program manager Ronald Dittemore said no request for satellite imagery was made because the resolution of the imagery, based on past NASA experience, would not be high enough to reveal damage to individual tiles and because the Boeing analysis had concluded Columbia could land safely.

During Columbia's mission, however, Wayne Hale, a senior flight director now serving as launch integration manager at the Kennedy Space Center, made inquiries about the possibility of Air Force help inspecting Columbia. But those initial efforts were terminated by senior management.

"The SSP (space shuttle program) did not want any data and in fact there was never a formal MOD (mission operations directorate) request made from the FDOs (flight dynamics officers) or the Flight Director," Steve Stich, a flight director himself, wrote in an email to a colleague.

In a February interview, Hale declined comment on the matter, saying "I probably ought to wait until I tell the board my story. That's coming up."

Readdy's letter to the CAIB, obtained by CBS News today, shows more senior managers also discussed the issue.

"A NASA individual visited me in my office," Readdy's letter to the CAIB begins. "That person and another individual from another agency had been discussing the external tank debris issue during STS-107 ascent. He wanted to discuss an 'offer of support' from the other agency with respect to observing the space shuttle Columbia on orbit. He explained that NASA would have to request that support on an emergency or high priority basis.

"I explained that the ET debris and possible implications to the left wing thermal protection system had been analyzed and reported to the Mission Management Team and documented in MER (mission evaluation report) daily report FD (flight day) 12 dated 1/28/03 1245 GMT.

"My understanding was that the space shuttle program was well aware of those capabilities that could be provided by the other agency and it had concluded that the offer would not contribute to the analysis. I related that as well as the conclusion reached by the MMT that there was no 'safety of flight' issue, and for those reasons there was no rationale for requesting emergency or high priority support.

"He reiterated that the other agency desired to support on a 'not-to- interfere' basis. I acknowledged this information, told him again that this was not viewed as a 'safety of flight' issue, but told him to accept the offer of support on a 'not-to-interfere' basis."

Ted Molczan, a respected satellite observer, has calculated that Columbia could have been imaged on multiple occasions by classified optical imaging satellites. Resolution would have varied from six to 16 centimeters, or 2.3 to about six inches.

"As of this writing, the precise cause of the Columbia accident is unknown, so it is impossible to know whether or not high-resolution imagery would have been useful," Molczan writes on a web page devoted to the topic. "There may not have been any outwardly visible signs. Even if there was something portentous to be seen, the outcome might have been the same. At this point in the investigation, having clear imagery of the left wing probably would be valuable, but that is easy to say in hindsight."

In other developments, Readdy sent a letter Wednesday to Michael Kostelnik, deputy associate administrator for the space shuttle and the international space station programs, asking him to "begin to identify those critical actions now that we believe need to be completed before a safe return to flight can be assumed. We will adjust this preliminary planning as necessary as we receive recommendations from the CAlB."

"The Deputy Associate Administrator for International Space Station and Space Shuttle Programs will establish a formal "Return to Flight" team, and provide direction for the team to address these actions and other actions determined necessary to comply with the formal recommendations of the CAIB," Readdy wrote.

The team "will plan for a safe return to flight as soon as practicable. As a goal, the SSP shall plan for corrective actions and reviews which support a launch opportunity as early as the Fall of 2003. The team will work closely with the leadership of the International Space Station (ISS) program to ensure that return to flight plans support an optimal return to the tasks of ISS assembly and continued logistics support."

Readdy said the team should consider:

• A thorough review of key shuttle systems, including the insulation currently used on the external tank;
• Development of in-flight tile inspection and repair kits;
• A review of radar and photographic coverage policies for launch and entry;
• A review of failure modes and effects analyses, critical items lists, waivers and hazards; Operational concepts for on-orbit inspection and repair of TPS;
• How in-flight safety issues are resolved, "including the appropriate level of management visibility and decision in that process."

"I am asking you to initiate these Return to Flight activities as soon as possible, establish this team, and provide a preliminary action plan no later than 1 April 2003," Readdy concluded. "You will be responsible for providing the team charter and day-to-day direction."

Readdy plans to establish and chair a Spaceflight Leadership Council to oversee return-to-flight activities. Michael Greenfield, associate deputy administrator for technical programs, will co-chair the panel.

"Much needs to be done as we move forward to fly again," Readdy concluded. "I anticipate that our processes will be strengthened and that the safety of flight enhanced as we return to flight."

Readers should keep in mind that setting this Fall as a goal for return to flight is little more than motivational talk at this point. Until the CAIB completes its report and NASA assesses what corrective actions might be necessary, talk of launch dates seems more than a bit premature.

Investigators have recovered debris from the shuttle Columbia that appears to support the increasingly held belief that the doomed ship's left landing gear door remained in place as a plume of super-heated air entering through a breach near the leading edge of the left wing wreaked havoc inside the wheel well. The heat-weakened door may have deformed enough to permit jets of hot air to spew out around the corners as the wing literally burned up from the inside, its skin buckling and shedding tiles along the way.

On another front, examination of contrast-enhanced video shot during Columbia's Jan. 16 launching indicates the possibility foam debris from the ship's external tank may have struck at least two different areas on the orbiter's left side, one well in front of the left wing, according to sources close to the accident investigation.

Running a video clip on a laptop computer, one of the sources, who spoke on condition of anonymity, showed how a suitcase-size piece of debris falling away from the external tank slammed into the lower leading edge of Columbia's left wing. That much was already known. But playing the clip over and over again in a loop, he pointed out a subtle brightening as the debris fell past the left side of Columbia's fuselage near the extreme forward part of the wing known as the "chine" area.

"It tumbles and then I want to point out a subtlety to you," he said. "Watch the contrast against this black line (in the chine area) and you'll see what appears to be an apparent contact way up here. We're not sure if it actually contacts it or not. It may just be the light foam against the dark background. ... But you can see it against the dark."

(Editor's note: For readers with access to the time-stamped video, look for a subtle brightening in the black chine area at 15:40:21.847 GMT. The leading edge impact occurs at 15:40:21.882 GMT.)

One of the earliest signs of anything amiss aboard Columbia during re-entry was an unusual temperature increase in a water dump nozzle located on the left side of the fuselage just behind the crew cabin hatch. No one has yet been able to explain that telemetry, but the nozzle is located near the chine area in question.

Regardless of whether the chine area suffered an actual debris impact - the brightening may simply be the result of lighting effects as the debris tumbled toward the wing - the sources said investigators are increasingly convinced a major breach occurred at or near the site where that same piece of debris crashed into the bottom side of the leading edge of the shuttle's left wing near where it joins the fuselage. And they are increasingly convinced a plume of super-heated air entering the breach worked its way into the left main landing gear wheel well and that the landing gear door remained in place as the disaster unfolded.

Heat-damaged debris indicates the plume of rarified but extremely hot air shooting into the well heated the aluminum structure of the left landing gear door enough to cause it to deform slightly, possibly forming gaps at the corners that allowed jets of hot air to spew out.

The sources stressed that no conclusions have been drawn and that scenarios like the one outlined above may be incorrect. "Think of what kind of disaster we'd have if we jump to a conclusion that fits all the facts and come up with the answer and it's the wrong answer," one of the investigators said. "So we have to be prepared to really look at multiple answers and not jump to a conclusion."

But so far, a leading edge scenario, or one very much like it, provides the best fit with telemetry from the shuttle and damage patterns seen in recovered debris.

"This event started to evolve almost immediately after EI (entry interface), it's fairly clear that the mechanism of failure had to be in place before the re-entry," one of the sources said. "So we're looking for mechanisms which lead to a very rapid problem occurrence after Ei.

"There was a lot of concern about the (landing gear) door because as everybody knows, that's a very weak area. And the initial photographs appeared to indicate the foam may have hit the door area or adjacent to it. Where we're at now has been really moved. In my opinion, it is low probability that we're looking at a strike on the door or a door issue or acreage issue around it. That it's much more likely that we have a problem or a breach that occurred up in the RCC area or the carrier panels adjacent to that."

He was referring to the 22 reinforced carbon carbon composite panels making up the leading edge of the left wing and narrow, removable panels equipped with protective tiles on one side that form a flush interface between the RCC panels and heat-shield tiles permanently bonded to the underside of the wing. The carrier panels are bolted in place with screws that go through the tiles on each end making such tiles inherently weaker than those without such holes. The screws are covered by a ceramic plug.

Three pieces of debris appeared to separate from Columbia's external fuel tank 81 seconds after launch. In the contrast-enhanced video released Tuesday, a chunk measuring 25 by 15 inches can be seen slamming into the left leading edge around RCC panels 6, 7 and 8. This same piece may have glanced off the chine area as well. "It may be more complicated than we have assumed it to be because it's possible - not probable, but possible - that there may be multiple breaches," one of the sources said. "We know there were three pieces that came down, if three pieces come down you have to think in terms of there potentially having been multiple breaches. As we look at this, we may be seeing sprays coming from different directions, which will be confusing to us as we go through this."

Whether the known foam impact occurred directly on one of the RCC panels or a carrier panel or both is not yet known. But the sources interviewed for this story said relatively minor problems with either component likely would grow in the fierce heat of re-entry, quickly leading to a re-entry disaster like the one that claimed Columbia and its crew.

For example, if one of the so-called T-seals used to hold an RCC panels in place was damaged or missing, enough of a gap probably would exist to let super-heated air into the void behind the leading edge. Likewise, a missing carrier panel tile would leave an exposed surface susceptible to burn through. While the gas in this case is not ionized enough to meet the textbook definition of a plasma, it is more than hot enough to melt the wing's aluminum sub-structure.

"You've got a gas there that is at 10,000 degrees," one of the investigators said. "Because it's so rarified, the transfer of the heat from that creates a temperature in (the wing) of about 2,500, 2,800 degrees. The transfer mechanism in here is what they're struggling with. It's not strictly convection, it's not strictly radiation. You're dealing with a hundred thousand times lower pressure than you have on the surface."

The resulting plume may well have moved about as Columbia rolled through normal entry maneuvers and as the breach itself worsened, subjecting different areas to extreme heat.

"If you think of a fire hose that you're not holding and it's moving all around, we may find that's more what we're dealing with," one of the investigators said. "As it hits a hole that has different surfaces, the surfaces are going to be directing it in different directions. I think when (Columbia is) in the right bank, it may very well be forcing some of this air ... laterally down the spar and then when you go into the left bank, it actually moves up. It goes from one side to the other and you might find this thing changing over periods of time depending on the hole size as it eats away, what's in its way and those kind of things. So it may be much more complicated than just trying to point a finger and say it came in this hole and it went right through the wing here."

Despite those extreme temperatures and the mercurial nature of such a plume, investigators say it would be very difficult to trigger a disaster without having a fairly sizeable area of damage. Whatever happened to Columbia, it may have started out small and rapidly worsened.

"One RCC doesn't do it and a couple of tiles won't do it," one of the sources said. "So we have to look for things that may increase in size over periods of time. One of the things we're looking at is if one panel comes off, it's likely others will come off because you've got hot air ... melting pieces and you would have a cascading kind of event. People have talked about unzippering of tiles. We're talking about unzippering of RCCs."

Alternatively, a small but growing breach in the leading edge area could cause surrounding RCC panels to partially melt and collapse inward. So far, recovered RCC panel fragments and support hardware don't provide definitive clues as to which scenario may be more accurate.

But it now seems likely a plume of hot gas entered the wing just forward of the landing gear wheel well, burning through the forward skin of the wing, spraying aluminum slag back on the inner surfaces of nearby RCC panels and ultimately working its way into the main landing gear wheel well.

Damage found in recovered debris increasingly indicates the left landing gear door remained in place until the wing itself began breaking up late in Columbia's re-entry and that a plume of super-heated air entering the wing from the breach near the leading edge worked its way into the wheel well and then out through seals around the landing gear door.

Burn damage on recovered debris just inboard of the door indicates a plume of hot gas spewed out of the well's forward inboard corner in the direction of the shuttle's centerline. Recently recovered debris indicates the possibility of a similar jet from the outboard forward corner of the door."

"There is a similar one, but much smaller in nature, on the other side," one source said. "We have a piece on the outboard side that has a very small indication of the same effect. You can't have that effect if the door is gone. You have to have something that's holding the pressure in and allowing the vent hole to occur. Again, we're coming back to the theory that if the door is lost, the door is lost very, very late in the event.

"We also have another debris item," he added, "a door hook roller uplock. It's not the hook itself, it's the pin, uplock pin, the door latches to. And it appears to be eaten away on one corner, which may be a key to us for the direction of flow.

"We believe you're getting heat coming into the well, heat and air coming into the well, building up temperature on the inside and pressure on the inside. What's happening is then that temperature and pressure is allowing the aluminum corners to get a little bit soft and the pressure pushes up the corners a little bit and that's where the events are coming from. That also indicates, again, that the door is still on."

Adding credence to that picture, search crews in Texas have recovered numerous tiles that came off the door. Had a major breach occurred in the door area, investigators believe, fewer tiles would have been recovered. And in the initial video showing the debris impact, there are no obvious signs of tile damage. Admittedly, the resolution is low, but one would expect to see a lighter color on the belly of the orbiter if the black surface layer of many tiles was removed in an impact event. No obvious brightening, however, can be detected.

"No item would you rest a case on individually," the source said. "But when you put all these together, it appears to give you a story that we're really dealing with something which is farther up from the wheel well and all these things about the wheel well and tile fractures is probably not the story."

In the next few weeks, investigators at the Southwest Research Institute plan to begin a series of tests that could shed light on just what happened when the foam impact occurred. Pieces of foam insulation roughly the same size as the chunks seen falling away from Columbia's external tank will be fired into various wing components with a powerful "chicken gun" normally used to shoot debris into jet engines.

One RCC panel and support hardware taken from the shuttle Discovery will serve as a target, as will two RCC panels removed from Enterprise, a non-space worthy shuttle prototype. In addition, foam will be fired at a landing gear door removed from Enterprise and "acreage" tile to determine the effects of impacts with broad areas of tile on the underside of the wing.

Unlike earlier tests carried out at Southwest Research Institute in 1999, the upcoming runs will use large pieces of foam and include impacts on tile edges and other areas. The tests will not be exhaustive, but "they will, I think, provide a piece of information that's going to be critical to determining what kind of damage you can do, what kind of damage you can't do."

"This isn't going to just be a piece of carbon carbon on plywood," he said. "They're actually taking the structure and instrumenting it with accelerometers and strain gauges to figure out how much of a lateral push it gets, how much compression it gets and then do the before and after."

Said the other source: "I don't see where foam is going to hit an RCC and break the (RCC). I can see more likely where it might break some of the support structure underneath it, a T-seal potentially, or shear a bolt or something. But inherently, this is a very weak area."

NASA managers meeting 90 minutes after the Columbia disaster Feb. 1 discussed a re-analysis of the potential damage caused by foam debris slamming into the shuttle's left wing during launch. But senior managers decided the public would be told, during an initial press conference, that the debris hit "on the left wing was reviewed and not determined to be safety of flight issue."

That is certainly true. During Columbia's mission, an analysis carried out by Boeing determined Columbia could safely land despite potentially significant damage to its left wing from the foam debris hit. NASA's mission management team accepted that analysis and the issue was formally closed out.

But it is interesting to note that in the minutes of the first meeting of NASA's Mishap Response Team, which convened at 10:30 a.m. - roughly 90 minutes after Columbia's breakup over Texas - a re-analysis of the Boeing assessment had already been ordered.

"Mr. Ralph Roe of the Space Shuttle Vehicle Engineering Office reported that the Mission Evaluation Room (MER) had invoked their emergency plan and were generating narratives of observations and producing engineering timelines," the minutes read. "A meeting is scheduled later this afternoon to status timeline development. The ascent ET foam debris data is being re-analyzed."

Shuttle program manager Ron Dittemore, the minutes say, "stated that information on the left wing and all data, especially debris, associated with it is very important and noted the importance of an immediate daylight search."

A few sentences later, the minutes show NASA Administrator Sean O'Keefe and William Readdy, NASA's associate administrator for space flight, planned to hold a news conference "to summarize the facts including: 1) loss of contact at 9:00 am EST, 2) that a contingency had been officially declared at 9:16 a.m. EST, 3) receipt of a video from a TV station southeast of Dallas, 4) all mission data was being impounded, 5) the reported ascent foam debris hit on the left wing was reviewed and not determined to be safety of flight issue, and 6) there was no indication of foul play."

NASA managers have said throughout that Boeing's analysis was accepted as valid and that no one expected any problems during Columbia's re-entry. But the loss of data from the left wing prior to the shuttle's breakup prompted a very speedy decision to re-assess the analysis. It is not yet known where that re-analysis stands or what it might show.

The Columbia Accident Investigation Board today showed video of Columbia's launching that indicates foam debris falling away from the ship's external fuel tank slammed into the lower leading edge of the orbiter's left wing within a few feet of where it merged with the fuselage.

The board also revealed that 20 seconds before the foam fell away from the so-called "bipod ramp" area of the tank just under the shuttle's nose, Columbia rocketed through unusually high wind shear. The steering system in the shuttle's left-side solid fuel booster swiveled the rocket's nozzle slightly to counteract the effects of the shear, putting some additional stress on the left side of the vehicle.

This event occurred three seconds or so after Columbia endured "max Q," or maximum dynamic pressure. This number varies from flight to flight, but for Columbia, it was around 741 pounds per square foot. Whether that had anything to do with any subsequent damage to the wing is not yet known, but investigators are looking into the matter.

"At 62 seconds on launch, we saw one of the larger transients we've seen on the solid rocket motor," said Maj. Gen. John Barry. "It was well within parameters, but interestingly enough, the two largest ones we've seen on ascent both happen to be Columbia, both happen to be going on 39-degree inclinations (trajectories), both have lightweight tanks. So we're trying to identify if there's any commonality there as an additional stress load on the left-hand side of the orbiter, because it was with the left solid rocket motor that had this input."

Investigators also are looking into pre-launch repair work in the bipod area of the external tank where foam insulation can be seen breaking away 81 seconds after launch. The shuttle's nose is attached to the forward part of the tank by a two-strut bipod. Just in front of each strut, where they attach to the tank, is an incline made of shaved foam that serves to reduce stress and minimize turbulence as air flows over the area during ascent.

Because of schedule changes prompted by the grounding of the shuttle fleet last year due to engine propellant line cracks, Columbia's tank was detached from its booster rockets for a booster swapout. It was then reattached to the new booster set. Engineers wrote up a "problem report" on damage seen near the left bipod ramp area, but the matter was closed out after a visual inspection. The nature of the damage, and what role, if any, it might have played in the subsequent separation of foam from that area is not yet known.

Regardless of what factor or combination of factors led to the initial damage in Columbia's left wing, investigators increasingly believe a breach at or near the leading edge of the wing, near where it joined the fuselage, led to Columbia's destruction. A jet of super heated plasma appears to have burned its way into the interior of the wing and ultimately into the left landing gear wheel well.

The effects of such a plume are extreme. Board member Sheila Widnall, an aerodynamicist at the Massachusetts Institute of Technology, said she discussed such heating with colleagues at MIT over the weekend and "one of the issues we got into was to talk about the thermal environment seen by the vehicle and by its structure and the properties of aluminum at very high temperatures."

"Without it's oxide coating, aluminum is a very reactive material," she said. "And when it's exposed to very high temperatures and high-speed gas flow, the possibility exists of vaporization of aluminium, which could be followed then by a very rapid burning of aluminum vapor. That's obviously a a scenario that we'll want to follow up."

In any case, damage seen in recovered debris suggests the plume exited the wheel well through seals around the landing gear door. At the same time, a vortex of hot air probably formed along the upper surface of the wing, ripping insulation tiles and blankets away as the disaster unfolded.

Increasing aerodynamic drag on the left wing prompted Columbia's flight control system to compensate, first by adjusting the ship's roll trim and ultimately by firing right-side yaw jets in a futile bid to keep the ship's nose pointed in the right direction. Columbia eventually yawed out of control in a sort of tilted flat spin before breaking up high above Texas.

The leading edge of a shuttle's wing is protected from intense re-entry heating by 22 panels of reinforced carbon carbon composite. The panels are numbered from 1 to 22, beginning near the fuselage. Based on an examination of enhanced video shot during Columbia's launch, the foam debris in question slammed into the left wing at or near RCC panels 6, 7 and 8.

"That piece of debris appears to hit on the leading edge, but on the lower half of the RCC," said board Chairman Harold Gehman. "In other words, the debris doesn't appear to go over the top and under the wing. All the debris appears to go under the wing. So it appears to hit the leading edge, but kind of on the underside of the leading edge and then all the debris follows the wind pattern. It appears to hit somewhere (at or near) RCC panel 6, 7 or 8, no closer than 6, no more than 8.

That section of the wing could not be seen by Columbia's astronauts in orbit. It would have been invisible behind the ship's left-side payload bay door.

"As you see after the debris goes by (during ascent), there's no missing tile," Gehman said. "Nothing's missing, so once again we have these tantalizing little pieces of evidence that don't fit together."

A wind tunnel analysis shows the loss of a single leading edge panel of reinforced carbon carbon is not nearly enough to explain the unusual and rapidly intensifying aerodynamic forces acting on the vehicle during re-entry. Three to four panels would have had to be missing to explain the re-entry data and no such damage can be seen in the launch footage.

A single blurry image taken by Air Force researchers in New Mexico using a small telescope just a minute or so before Columbia's breakup is undergoing analysis by photo enhancement experts to find out what additional data might be gleaned. The photo appears to show major damage to the left leading edge area, but the details are literally unclear.

"Those photo experts are just now beginning their work in liaison with aerodynamics experts and plasma experts to try to see what the picture will really yield," said Maj. Gen. Kenneth Hess, a member of the CAIB. "But the important part right now is to enhance the photo as much as can be done without adjusting the facts behind the photo."

Another factor that has been discussed in recent weeks is a phenomenon known as asymmetric boundary layer transition - the sudden onset of turbulence during hypersonic flight that could have affected Columbia's left wing more than its right.

Widnall said today calculations show an asymmetric boundary layer transition, acting in the absence of any other problems, would have been too small by a factor of four to explain the unbalanced forces that led to Columbia's destruction.

Based on a detailed timeline of Columbia's re-entry, engineers now know problems began long before the shuttle's breakup. Gehman said the question that is most interesting to him is what came first, "in other words, did a thermal event cause loss of tiles and thereby these aerodynamic forces or did we lose an aerodynamic surface first which then allowed the heat to start unzippering this aircraft?"

"Every time I think I've got it figured out, I get a piece of data that changes my mind," he said. "If the aerodynamic surface were disturbed long before re-entry, that then leads you to believe there was some physical misarrangement of the wing that had nothing to do with entry. On the other hand, all of our photographic evidence indicates if there was a physical misarrangement on the wing it was so tiny it's not visible to anybody else, which would lead you (to believe) that it was some kind of a thermal event which was the triggering event which then started the unzippering process.

"And so, the fact that the orbiter was fighting an aerodynamic misarrangement earlier than we previously had thought makes my riddle very intriguing."

For her part, Widnall sees "a heating event followed by a very rapidly developing aerodynamic event."

"The aerodynamic event, when it occurs, is pretty dramatic and I mulled over that for a while and I looked at the flight profile and I realized that the aerodynamic event occurs at the time when the dynamic pressure is undergoing a rapid increase of roughly 30 percent," she said. "Now that makes sense to me, that the vehicle was kind of coasting along with heat damage and then there was a sudden increase in dynamic pressure that came from the (normal flight profile) and that was the onset of the aerodynamic event. That makes sense."

While she declined to speculate on what caused the thermal event, she said "there is a point in time when the guidance and control analysis indicates the onset of a rapidly increasing, I hate to use the word - yaw moment - because it's so technical, but it's the twisting moment on the vehicle."

Said Gehman: "As the vehicle re-enters the Earth's atmosphere, there is a time when the aero forces start going up more rapidly than a straight line. And lo and behold, at that point the orbiter starts to exhibit non-aerodynamic tendencies, remarkably more."

Investigators and board members plan to visit a Lockheed Martin facility next week to learn more about how RCC panels are repaired, serviced and mounted on the shuttle. Investigators are particularly interested in how pockets, or voids, form in the layers making up the composite material due to oxidation. If Columbia had any RCC panels with similar voids, and if the panels were then hit by falling foam impacting at high speeds, a failure could result.

Putting it all together - bipod foam repairs, wind shear, debris impacts, thermal and aerodynamic events - is a complex job. But it may well be a combination of factors doomed Columbia, not any one specific failure.

"What we're really looking at is a complex failure of a complex system," Gehman said. "It's possible, one of the scenarios we're looking at, it's possible the foam striking a healthy orbiter would not have done enough damage to cause the loss of this orbiter.

"But it's possible foam striking an unhealthy orbiter that had problems in it either due to stresses on launch - we talked about the wind shear, too much heating in transition of years before, aging of the orbiter, like the RCC faults we see, or a whole number of other complex issues - it's possible you could do some damage to this orbiter that ... she could have survived, maybe, at age 10, maybe she couldn't survive it at age 21."

At the Kennedy Space Center, meanwhile, 28,286 pieces of shuttle debris have been catalogued, amounting to about 39,300 pounds of the orbiter's dry weight. Of that total, 25,404 pieces of debris have been positively identified. More than 4,000 men and women continue to search for debris on a daily basis, assisted by a dozen aircraft and Navy dive teams. Sonar scans have located more than 200 submerged targets in two Texas lakes.

Bob Daugherty, a senior engineer at NASA's Langley Research Center, said today his widely publicized emails outlining various dire scenarios for the shuttle Columbia's re-entry Feb. 1 were misinterpreted by the media. While he was "uneasy" after watching video replays of foam debris slamming into Columbia's left wing during launch, he had no inkling a catastrophe was about to unfold as he drove to work Feb. 1 to watch the shuttle's return to Earth.

"By all accounts, there was some ambiguity to this whole thing," Daugherty told reporters today during a teleconference. "We'd all seen the video, I'd seen the video, and even though we were absolutely doing 'what iffing' during the week, that was in my mind.

"So of course, there was some natural uneasiness on my part. But again, nothing that I believed (would lead to a catastrophe). I certainly believed everything was going to be perfectly fine and again, I expected to see pictures taken of the damaged area (of the wing) after they (the astronauts) were walking around the vehicle on the runway."

In the wake of Columbia's launching, concern about wing damage from foam debris that fell away from the shuttle's external tank 81 seconds after liftoff prompted an engineering analysis by Boeing engineers. NASA's mission management team ultimately accepted the company's conclusion, that while the wing might suffer significant damage due to battered tiles and aerodynamic heating, the shuttle could safely return to Earth.

But Daugherty was contacted to assess what the impact of possibly higher-than-normal heating to the underside of the orbiter might mean for Columbia's left-side main landing gear. And so began a series of emails that continued all the way through Jan. 31, the day before the shuttle's catastrophic re-entry.

The emails generated widespread publicity because they seemed to indicate growing concern among mid-level engineers that Columbia might somehow be at risk. The discussion was not passed on to senior NASA managers - or to Columbia's astronauts - prompting some observers to question NASA's management system.

In an earlier teleconference, two Johnson Space Center participants in the email exchanges said no one believed Columbia faced a serious problem and that all of the post-analysis discussion was simply a matter of "what iffing," part of a normal engineering dialogue aimed at making sure flight controllers in Houston were prepared for any landing gear issue that might crop up.

"Honestly I was very surprised by the attention my writing received," Daugherty said today. "I view my involvement as a small sideline focused on landing issues. I've been in somewhat of a quandary. I really do believe the best thing I can do for the investigation is to talk to the (Columbia Accident Investigation Board) first. On the other hand, it's frustrating that my work is being misinterpreted. My quandary has now been relieved since the board has said they don't mind if I speak up. So I want to clear the air as much as possible."

Daugherty's boss, Mark Shuart, director of the materials and structures branch at Langley, said NASA Administrator Sean O'Keefe visited the Virginia facility in the wake of Columbia's destruction and "I'm the guy who told him this was not an engineer waving a red flag and nobody paying attention. ... That was far from the facts."

In one of the emails, Shuart wrote: "I am advised that the fact that this incident occurred is not being widely discussed."

Worried more about the impact of re-entry heating on Columbia's left main landing gear tires than he was about a high-altitude catastrophe, Daugherty emailed Shuart later that "we can't imagine why getting information is being treated like the Plague. Apparently, the thermal folks have used words like they think things are 'survivable,' but 'marginal.' I imagine this will be the last we hear of this."

Daugherty said today this email was widely misunderstood. It was written in response to problems getting simulator time scheduled to determine the consequences of landing with flat tires.

"The comment about getting information like the plague, first of all it was work between friends and I tend to be a little more colorful when I'm with my friends," he told reporters. "Again, it was frustration in a sense because there were simulations already going on and approved that were in a sense very similar to what we were after, but different enough that we couldn't just jump in in the middle of the astronaut training that was going on. And again, I always want to get the information I'm after immediately so there was some frustration there about getting that information. And that comment was truly very specific, just to the issue of trying to get these simulation runs."

Asked if the emails in general should have been passed on to more senior managers, Daugherty said "I don't think it should have. My email was technical issues that I intended to have technical people discuss and that's exactly what happened."

"There really wasn't a level of concern," he said. "I know you can get that from the emails. But these were emails between two long time colleagues and we spent a lot of time talking in the emails like we might talk in person. There was not concern from my standpoint in the emails. I had no clue whatsoever that the (Boeing) analysis might or might not be right, we were simply looking into well, let's be conservative, what if the analysis weren't right, let's think of the things you might want to plan for and have a game plan in your back pocket."

Asked if the astronauts should have been informed, Daugherty said "absolutely not, because they weren't really concerns, they certainly weren't warnings. They were simply, be ready for anything, just like there are a myriad of other things (flight controllers) have plan Bs in their console books. And this is nothing more than some more extensive plan Bs in this slightly unusual situation. They absolutely met my expectations and absolutely handled it at the level I intended."

But it was, in fact, an unusual situation. Shuart said he could not recall a similar discussion between Langley and Johnson Space Center engineers about potentially serious problems during a shuttle mission.

Revision G of the CBS News-compiled STS-107 integrated entry timeline has been posted. This revision includes significant updates from NASA's STS-107 Master Timeline (rev. 14), including details gleaned from a final two-second burst of telemetry that was captured on the ground seconds before Columbia's breakup Feb. 1. As always, suggestions, corrections and comments are appreciated.

Ongoing analysis of the final two seconds of telemetry from the shuttle Columbia during re-entry Feb. 1 shows the doomed ship's fuselage, crew module, right wing and right-side rocket pod were essentially intact 32 seconds after the commander's final transmission and that the orbiter's digital autopilot was still flying the spacecraft. A computer alarm generated in that final two seconds of data suggests one of the pilots' joystick hand controllers may have been briefly engaged, but the autopilot was never deactivated before contact was lost.

By that point, however, there was nothing the crew could have done to stop the quickening disaster. The telemetry shows Columbia's left wing and left-side orbital maneuvering system rocket pod were either gone or severely damaged, the ship's hydraulic system was empty, its flash evaporator cooling system was in shut down and multiple computer alarms were being generated because of lost data from the orbiter's left side orbital maneuvering system rocket pod.

Guidance and navigation data show the shuttle was in an "uncommanded" orientation, yawing rapidly to one side, presumably toward Earth, in what may have been the start of a banking tumble. The yaw rate - a measure of how fast Columbia's nose was swinging to one side - was at least 20 degrees per second, the maximum value the sensors are designed to measure. The actual yaw rate may have been higher.

That same two seconds of "ratty" telemetry shows one of the cockpit's two rotational hand controllers, or joysticks, may have been briefly engaged as early as 9:00:01.7 a.m. That was nearly 30 seconds after commander Rick Husband's final interrupted transmission to Houston at 8:59:32 a.m. But the timing is uncertain because of the duration of software-driven data sampling rates. The final bit of telemetry, however, shows Columbia digital autopilot was still in control when the flow of data finally ceased and that the hand controller was in its normal "centered" position. As such, it is not known whether the RHC was bumped inadvertently by the commander or pilot or whether one of them intentionally gripped the stick with thoughts of taking over manual control.

It is also possible both scenarios are false. Data from this final two-second period was corrupted by transmission errors and as such, it is subject to error or misinterpretation. But it was included as part of revision 14 to NASA's STS-107 Mishap Investigation Master Timeline, a revision that was never released, sources say, because an updated version is in the final stages of preparation. At least some of the data in revision 14 may have been corrected, eliminated or expanded in the latest revision. This status report will be updated as warranted when the new revision is released.

In any case, engineers now believe the main body of the spacecraft did not begin breaking up until nearly 20 seconds after the final two-second burst of telemetry. Vehicle breakup was preceded by the separation of at least three major pieces of debris beginning around 9:00:02 a.m., at almost the same instant the final two seconds of telemetry began flowing back to Earth after a 25-second data dropout.

The timeline also includes more than a dozen "debris shedding" events recorded by observers on the ground as Columbia crossed above California and the southwestern United States. The first such confirmed instance of debris falling away from the shuttle occurred around 8:53:44 a.m., 18 seconds after the spacecraft passed above the California coast just north of San Francisco.

But it is the orbiter's final minutes that grip the imagination as the data plays out with a sort of slow-motion inevitability.

At 8:59:32 a.m., Husband called Houston, presumably to report or confirm a computer fault message showing lost pressure from both left-side main landing gear tires.

"Roger, uh, buh..." he radioed, but he was cut off. The "buh" may have been the beginning of the word "both" or possibly "before." There is no way to know, but engineers now say that final transmission was interrupted not because of the mounting problems on board the shuttle, but because the line of sight between a forward antenna cluster and the NASA communications satellite then in use was blocked by Columbia's vertical stabilizer and aft engine compartment.

In any case, raw data continued to flow for another five seconds before it, too, was interrupted by antenna blockage. A master alarm sounded in the cockpit during those five seconds, computer messages were generated that noted problems with the shuttle's flight control system and an electrical system powered down.

Toward the end of that five seconds, the aerodynamic "sideslip" being experienced by Columbia began reinforcing the aerodynamic drag already pulling the ship to the left because of problems with the left wing. At 8:59:36 a.m., the digital autopilot, struggling to keep the shuttle properly oriented, was forced to drop the left wing to compensate for the increasing aerodynamic forces acting on the craft.

Less than a second later, the autopilot commanded a right-pointing yaw thruster to fire to help counteract the growing yaw motion. Two other jets already were firing and a fourth was commanded on less than a second after the third.

And then, at 8:59:37.396 a.m., telemetry was cut off. For the next 25 seconds, no telemetry was received due to antenna blockage. A final two-second burst came down beginning at 9:00:02.660 a.m. The data were garbled and some of the readings are not clear cut. But engineers were able to recover computer message stored in "buffers" that provide at least some insight into what was going on during that preceding 25 seconds.

The shuttle's primary flight computers generated a "roll reference" fault message around 8:59:46 a.m. Six seconds later the first in a series of left OMS rocket pod alarms was generated by the shuttle's flight computers. In the final two seconds of telemetry, additional OMS pod alarms were generated, along with an alarm indicating an apparent short circut.

In the final two seconds of telemetry, it appears Columbia's hydraulic power units were operating relatively normally, the shuttle's water spray boilers were cooling the hydraulic system lubrication oil, the main propulsion system and aft engine compartment were intact and the shuttle's three electricity generating fuel cells were operating.

In addition, Columbia's communications equipment and navigation systems were still functioning and temperature readings were still being received from the ship's vertical stabilizer, body flap, main engine compartment and the right wing.

But all three hydraulic systems were operating at zero pressure with empty hydraulic fluid reservoirs, presumably because of severe left wing damage that ruptured the triply redundant hydraulic lines. Temperature readings from the left wing elevon actuators were absent, the shuttle's flash evaporator cooling system had apparently shut down and the majority of the sensors in the left orbital maneuvering system rocket pod were either disabled or showing abnormal readings. Major electrical problems were beginning to develop and elevated temperatures were noted on the belly of the shuttle and along its left side.

Guidance and navigation data suggests vehicle was in an uncommanded attitude and was exhibiting "uncontrolled rates," the timeline states. "Yaw rate was at the sensor maximum of 20 degrees per second. The flight control mode was in AUTO. Based on the nominal and off-nominal system performance described above, it appears that the fwd/mid/aft fuselage, right wing and right pod were still intact."

The final bit of telemetry from Columbia showed a computer fault message regarding the rotational hand controller. While the "digital autopilot roll stick function" was initialized, "available vehicle data indicates the RHC was in detent (in the normal centered position) and (the) digital autopilot was in AUTO."

Working through a process of elimination, NASA engineers are focusing on 10 major failure scenarios - and combinations thereof - to explain what went wrong during the shuttle Columbia's catastrophic re-entry Feb. 1, sources say. Several of those scenarios, outlined in general in the March 7 status report below, assume a breach at or near the leading edge area of Columbia's left wing and a resulting plume of super heated air that burned its way into the wing's interior. Heat damage in recovered wreckage and telemetry from the doomed ship indicate the deadly plasma may have worked its way into the left landing gear wheel well and then burned through seals around the left landing gear door.

Many NASA investigators believe such a scenario, or a variation of that chain of events, best explain the sensor failures and temperature readings downlinked during Columbia's final minutes as well as burn damage on wreckage recovered to date. But other failure scenarios are possible as well and NASA has assigned teams to work through each one in exhaustive detail to determine which ones best fit the existing data and debris damage patterns, agency sources say. The analysis is being carried out as part of NASA's support of the independent Columbia Accident Investigation Board, which has the final say in determining what happened to Columbia and, more important, why it happened.

While the leading edge of the left wing is clearly an area of prime focus, engineers have not yet ruled out a burn through from the bottom of the wing, either in an area of presumably widespread tile damage or because of damaged tiles and seals at or near the landing gear door itself. But nearly all of the scenarios under discussion involve presumed breaches toward the front, inboard section of the wing, from the landing gear door forward. And again, NASA sources and others close to the accident investigation board say a breach in the leading edge area is among the most plausible failure scenarios to emerge so far.

In other developments, sources told CBS News late last week that Randy Stone, a respected former flight director and now deputy director of the Johnson Space Center, will take over at least some of Linda Ham's duties supporting the independent Columbia Accident Investigation Board.

Ham, chairman of NASA's mission management team, played a key role in the decision, during Columbia's mission, to accept an analysis indicating the shuttle could safely land despite potentially significant wing damage from the apparent impact of foam debris from the shuttle's external tank during launch. Ham also oversees NASA's Mishap Response Team

Late last month, board Chairman Harold Gehman asked NASA Administrator Sean O'Keefe to remove senior shuttle managers who played a role in the conduct of Columbia's mission from duties supporting the ongoing accident investigation. The stated goal was to eliminate any appearance of a conflict of interest.

Gehman's letter to O'Keefe did not list any names. But sources said the board wanted senior managers like Ham, who ultimately will face the accident board as part its investigation into how NASA managed Columbia's mission, removed from direct roles in the ongoing investigation.

"It has become apparent that some of the chief managers of the investigation which NASA and this board share are also members of these boards that we're going to be looking at," Gehman said March 4. "We are then put into the place of having the investigators investigate themselves."

"That's not exactly true because NASA is not investigating management issues. Only we are investigating management issues. But ... I can't possibly have key investigatory managers also be the people whose performance we're looking at in other areas."

O'Keefe initially balked at making any immediate changes, but he later agreed to assign NASA personnel not directly involved in the conduct of shuttle missions to key teams supporting the board's investigation.

NASA engineers struggling to match up telemetry from the shuttle Columbia's left wing and hot gas flow patterns found in wing debris increasingly suspect a plume of hot gas may have entered the wing from a breach at or near the leading edge area, close to the ship's fuselage, and worked its way into the left main landing gear wheel well. NASA sources say wreckage from the underbelly of the shuttle just adjacent to the left landing gear door indicates hot gas from inside the wheel well may have spewed out around the inboard edge of the door as the catastrophe unfolded.

A source close to the independent Columbia Accident Investigation Board outlined a similar scenario today, but he said other explanations are possible and that board members have not yet drawn any conclusions about where the breach occurred or what might have caused it in the first place.

But the source said several lines of evidence point to the possibility of a breach toward the front of the wing that burned its way deeper inside toward the wheel well as Columbia crossed above California and the southwest. Investigators are trying to determine the location of the breach and the behavior of the presumed internal plume of plasma by making various assumptions and then determining which scenarios best fit the pattern of sensor failures and elevated temperatures that were recorded during the shuttle's final minutes.

Such scenarios also predict certain types of heat-related damage that can then be checked against actual wreckage as it is recovered. That work is far from complete. But the source familiar with the accident board's investigation outlined one such scenario to provide a sense of how engineers are working through the problem.

Assume the shuttle began shedding debris, possibly one or more of the reinforced carbon carbon panels making up the leading of the left wing, early on as Columbia re-entered the atmosphere. As the shuttle plunged into the atmosphere and began heating up, the initially small problem area would worsen. Perhaps additional RCC panels, or nearby heat-shield tiles loosened and fell away as the disaster unfolded. Multiple "debris shedding" events were photographed and videotaped by ground observers as Columbia raced across the west-southwestern United States.

Under this scenario, at some point the forward edge of the wing just behind the RCC panels was breached, allowing hot plasma to burn its way into the unpressurized wing volume in front of the left main landing gear wheel well box. As the shuttle soared through a steep right bank to bleed off energy, the internal plume initially impinged on the lower part of the forward face of the wheel well box near where it merges with the aluminum skin of the lower wing. Then, as the shuttle banked to the left, the plume direction may have changed, possibly allowing the hot gas to burn through electrical cables routed around the upper front face of the wheel well.

Eventually, the plume entered the wheel well itself, possibly impinging on one or both tires and bouncing off to another part of the well. The board source said a plasma jet in the thin air where the shuttle was flying at the time can do that. Then at some point after that, hot air inside the wheel well may have worked its way out, through seals around the main landing gear door.

"My reading when I look at the tile around the door, that one piece we've been talking about, it looks to me that the plume is coming out," the source said. "What's happening is it's burned through the seals and it's coming out, not going in."

NASA sources said a similar analysis was presented at a Mishap Response Team meeting today at the Johnson Space Center in Houston.

But another board source stressed other explanations are possible and said some investigators have not yet ruled out a breach in the door seal area.

"I don't think anything right now is THE leading scenario because we're looking at a group of scenarios that, based on the evidence, are probably more likely than other scenarios," the source said, adding that initial scenarios in aircraft disasters frequently get discarded as an investigation proceeds.

Complicating the picture in Columbia's case, engineers have not yet conclusively determined whether the damage seen in many pieces of debris occurred before the breakup or later, as the result of atmospheric heating.

Assuming, however, a left wing leading edge burn through, the smooth flow of air over the wing would have been disrupted, possibly generating a hot vortex that then spun back along the left side of the shuttle's fuselage, above the left wing. Upper surface tiles and blankets may have been ripped away, showing up as debris shedding events to observers below. And such a vortex would explain elevated temperatures detected by sensors well above the wing on the side of the fuselage.

"There's a lot of stuff coming off that thing and nobody's saying anything," the board source said of Columbia's crew and flight controllers in Houston. "Why is that happening?"

A blurry picture of Columbia shot through a small Air Force telescope in New Mexico roughly a minute before the shuttle's breakup over Texas shows what appears to be major damage along the front of the left wing. The picture is very blurry, but whatever is going on in that region of the wing appears at or near the leading edge close to the fuselage.

"It looks like a large number of RCC panels are missing," the board source said.

The forward edge of the left wing is protected by 22 U-shaped RCC panels that protect the wing spar from extreme heating during entry while at the same time directing a smooth flow of air back over the upper and lower surface of the wing. RCC panel No. 1, located where the leading edge merges with the chine area of the fuselage, has been recovered. Sources say it is heavily damaged with a large area missing where it would have butted up against panel No. 2. That panel - No. 2 - has not been found. A panel that could be No. 3 or No. 4 has been found, with deposits of aluminum and steel slag on its inner surface. Panel No. 5 and others located farther outboard along the wing also have been recovered, as has a large portion of the wing tip area. Surprisingly, that piece of wreckage shows few signs of extreme heating or stress.

But the board source said if the breach occurred at or near RCC panel No. 2, the plasma would have impinged the forward face of the wing spar, possibly blowing molten metal back toward the front as it burned its way inside. As the breach worsened, the aerodynamic characteristics of the wing would have been affected, producing increasing drag. Columbia's flight computers initially counteracted this drag by adjusting roll trim with the ship's elevons and later, by firing four right-firing maneuvering jets.

Commander Rick Husband made a final call to mission control at 8:59:32 a.m., radioing "Roger, uh, buh..." He may have been about to say the word "both" or "before" in reference to a landing gear tire pressure alarm. The transmission was cut off when the antenna being used to reach a NASA communications satellite over the Indian Ocean was blocked by Columbia's vertical stabilizer. Another five seconds of telemetry made it through, showing the shuttle was still on course and under control up to that moment.

Then, even the telemetry stream was blocked. Twenty-five seconds later, a final two seconds of telemetry was received. The data showed the shuttle's fuselage was still intact and that it's major systems were operating normally. But there was no data from the left wing and the shuttle's hydraulic system was out of fluid, indicating the triply redundant hydraulic lines in the wing were ruptured.

In addition, the telemetry showed multiple computer alarms indicating severe problems with Columbia's left-side orbital maneuvering system rocket pod. The craft was in an "uncommanded" attitude, or orientation, and yawing quickly to one side. Eventually, the craft yawed out of control and broke up.

But the initiating cause of the disaster is still unknown.

Shuttle program manager Ronald Dittemore, testifying before the Columbia Accident Investigation Board, said safety is the agency's "lifeblood" and that his door is always open to any lower-level engineer who might be worried a safety issue is not being properly addressed.

Making his first public appearance since a round of high-profile news conferences immediately after the Columbia disaster, Dittemore said the system currently in place ensures critical information and safety concerns make their way up to senior managers and that this culture of safety is firmly in place across the manned space program.

"All I can say is we cultivate that culture," Dittemore said. "Anybody can come and walk in my office and say they've got a problem. Anybody can walk into any of our senior (managers') offices, say they have a problem and we will listen to then. I would be very disappointed if I found it to be otherwise."

But Harry McDonald, former director of NASA's Ames Research Center and chairman of a 1999 independent review of shuttle systems and maintenance practices, said the system can only work if it's based on the correct assumptions about what constitutes risk and if a system is in place to help managers access technical data.

"I have no concern at all that people like Ron Dittemore, presented with the facts, will make the right decision," McDonald said today. "No concern at all on that issue. The concern is presenting him with the facts and many of them are buried deep."

Many of the major recommendations made by McDonald's panel - the Space Shuttle Independent Assessment Team - were implemented by NASA. But others were not. McDonald said the agency continues to rely on archaic database technology that makes it difficult to quickly search for relevant test results across the program's history.

Case in point is concern about potential damage to the shuttle's protective heat shield tiles from impacts by foam insulation ripping free of the ship's external fuel tank during launch. A large piece of debris fell off Columbia's tank 81 seconds after liftoff Jan. 16 and struck the underside of orbiter's left wing.

Columbia was destroyed Feb. 1 when a breach in the left wing, possibly caused by the foam impact, allowed super-heated air to burn its way inside, ultimately triggering the shuttle's aerodynamic breakup 207,000 feet above Texas. All seven crew members were killed.

During the flight, engineers carried out an analysis based on earlier tests and extrapolated from that data to conclude that while Columbia's wing might suffer significant damage, there was no safety of flight issue.

But McDonald said problems with foam pulling off the tank were well known before launch and he questioned the process used to clear Columbia and other shuttles for flight in the first place. He questioned whether managers have ready access to data from flights, possibly years earlier, that could have a bearing on the current mission.

"What was the resolution of the foam issue on (flight) STS-87, what was the flight clearance process on STS-88, when the problem reoccurred on 88, how was it resolved for 90 and then 91? I mean, when someone like Dittemore goes and tries to make an assessment of what his risk is for the FRR, flight readiness review, the instant access to all that past history would have been valuable, incredibly valuable, I think. But we had not given that, in my view, sufficiently high priority."

After the hearing, he said the availability of more information to "people like Dittemore would result in a change in the culture, automatically. I think an engineer looking at that would say, you know this really isn't a very good extrapolation, from a square inch to a square foot."

A reporter said "but they did know that."

"Did Dittemore or people like that who were making the decision about flight readiness?" McDonald asked. "I mean, what had been communicated up to the flight readiness review team?"

McDonald praised the NASA workforce, telling the accident board his original team was "continually impressed with the skill, dedication, commitment and concern for astronaut safety by the entire shuttle workforce. And I see no reason to qualify either of these remarks today."

But he said any safety program is only as good as the assumptions that go into it.

"I think there's a basic flaw in the reasoning of many well-intentioned people and that is the concept that if you have a 1-in-100 risk of an event occuring, the event can occur on the first or the last, it's equal probability of when the event will occur. There seems to be the perception in the agency that if I've flown 20 times then the risk is less than if I've just flown once.

"And we were continually attempting to inform them that unless you've changed the risk positively, they still have the same issue even after 50 flights or 60 flights."

Several members of the Columbia Accident Investigation Board nodded in agreement.

"Now how do you address that issue?" McDonald went on. "Clearly, clearly, everybody in the agency has this desire and sense of importance, of the critical importance of safety. There's no issue about that. The question is how do you translate that into a safe and effective program? And that is very, very difficult given the complexity of the issue."

For his part, Dittemore articulately told the accident board he was confident the proper safeguards are, in fact, in place to ensure problems are properly dealt with, that managers have the data necessary to make the right decision and that individuals are encouraged to raise safety issues if they believe an issue is being overlooked.

"I think you have to cultivate a culture that allows everyone the opportunity to raise their hand and say they have a concern, to have the workforce feel no matter what position they are in in their organization that they can bring to management's attention an issue that they feel is significant, that management ought to address from a safety of flight point of view. The culture and the process have to be there. And I believe that is true today in our culture and our process."

"However, I must also state that we also cultivate a culture of second guessing, challenge, checks and balances and healthy tension," he said, speaking in the clear, direct manner that won praise during the initial post disaster news briefings. "We want our system, we want the people in our system, to challenge the assumptions. We want them to challenge the results of technical analysis or tests. And we do not feel threatened at all by that challenge. In fact, we believe it is healthy for us.

"And so when I hear about people in the system that are challenging and talking about particular analysis, that's what I want them to do. I want that to be part of our culture. But I also want them, if they believe that they have an issue, I want them to raise their hand and bring it forward to management.

"If they don't, given that I believe the culture is there and established for them to do so, then I must conclude that they do not believe strongly enough to bring it to management's attention, that it is something that they're in this challenging stage and they're doing a what-if type of discussion, which we also want them to do, to cover any event."

Speaking earlier, Jefferson Howell, director of the Johnson Space Center, told the accident board "everybody is totally intent on making this a safe activity at all levels, all the way to the end."

"I probably can't say it sufficiently how important safety is to every person who works at that center," he said. "It's a way of life. You can say it's number one. If we were fish, it's the ocean we swim in there. It's an attitude and so any time anybody raises that flag at any level, it gets people's attention very quickly. And people are going to take care of it."

While he said he was satisfied the system works properly at present, he said an ongoing concern for the future is the upcoming retirement of many senior civil servants with skills that will be hard to replace.

"I have a concern because a very large number of our civil servants are at the age where they may retire in the next several years," he said. "So I have that challenge in the future ahead of me. But as we speak right now, I'm very confident in the capabilities and skill levels of our people and our ability to support the shuttle program."

As for McDonald's concerns, Howell said the mission management team that oversees missions in progress and handles problems as they come up is a "very robust organization. This is really serious business and we commit a very robust engineering and operations team anytime we have a mission ongoing."

And he said pressure to continue building the international space station - the kind of schedule pressure another panel concluded played a role in the 1986 Challenger disaster - was not a factor in Columbia's demise or in the decision to launch any other mission.

"I've been accused of being too success oriented," he said. "That's sort of the nature of the beast at our center. One thing we have going for us, we have an administrator who is just beating upon us how important safety is and that should be our first primary consideration in everything we do. And he starts every meeting saying that and he ends every meeting saying that.

"We are very eager and excited about getting this station assembled," he said. "I'm excited about that and we're eager to get on with it and get that done. However, we understand the stakes and we are not going to do anything and press anybody to put aside any kind of quality assurance or safety issues."

Dittemore told the board NASA's morale "is generally pretty good considering the conditions we're operating under."

"It's been six weeks since we had an event that changed all our lives," he said. "And every day that goes by gets better as far as the workforce is concerned. As I mentioned to some folks earlier, the best therapy that we can do is be extremely engaged in solving this particular problem and everybody wants to be engaged in this effort. Without exception.

"Morale is good in that sense. There is an even more increased determination and a greater commitment to look very closely at the system and they are determined to identify if there is any weakness. It's broader than just what may be determined as the root cause. They're going to look to see if there's something else in the system that may have existed for many years, but now they will come back and make a recommendation to me that they'd like to make some improvements. Even though it may have nothing to do with the root cause."

The next public hearing is scheduled for March 17 and 18 in Houston.

"The role of the public hearings is to read things into the public record, to start at the beginning and we will then build upon that to get to the substantive issues," board Chairman Harold Gehman told reporters after today's hearing. "And then also to hear from experts that are not NASA people and kind of open our aperture a little bit.

"We thought all the witnesses were very forthcoming, they all answered our questions fully, nobody was defensive and so we were quite happy with the witnesses."

The Columbia Accident Investigation Board, reporting solid progress in its ongoing probe of the Columbia disaster, has not yet pinned down the location of catastrophic breach that allowed superheated air to enter the doomed ship's left wing during re-entry Feb. 1. But intriguing deposits of aluminum-and-steel slag behind panels making up the leading edge of Columbia's left wing near where it joins the fuselage suggest the breach may have occurred toward the front of the wing, close to the shuttle's fuselage, allowing hot plasma to work its way through the wing's interior with deadly results.

But investigators have not yet ruled out a breach in the left main landing gear wheel well, despite sensor data that fails to show the sort of blowtorch-like heating one might expect from a direct plasma intrusion. In the absence, however, of any wreckage from the left landing gear door - and because of unusual heat damage seen in pieces of the forward inboard landing gear door frame - investigators say a wheel well breach remains a possibility, albeit one that is difficult to explain at present.

"Our job is just beginning," said board member Roger Tetrault. "What we will be doing is trying to follow the heat. And I'm going to say that again. What we have to do is follow the heat. We will be doing this in order to back into the location of the original breach in the wing. We're going to be using all the tools at our command, including aerodynamic and thermodynamic computer models, we'll be using wind tunnel testing to do that and of course, we'll also use a sizeable amount of the telemetry that's available to us."

As of today, 22,563 pieces of shuttle debris have been recovered, including all six of Columbia's nose and main landing gear tires and 25 of the ship's 35 internal propellant and storage tanks. Of that total, 16,063 pieces of debris have been identified. Wreckage recovered to date totals 32,100 pounds, or about 13.7 percent of the shuttle's intact weight.

During a news conference today, Tetrault revealed that investigators have discovered a "thin black deposit" on heat shield tiles recovered from Columbia's left and right wings. The deposits show a high concentration of aluminum, which makes up the underlying structure of a space shuttle.

"If you look at the debris from the right side, you can see that there is significant damage to the right side from re-entry," he said. "We see the black deposits on the right side, not to the extent we see it on the left side, but it's on the right side as well, which means you had molten aluminum being sprayed or deposited onto those tiles on the right side where the event was not occurring. That's a very hot re-entry."

Both left-side main landing gear tires have now been recovered and both show signs of "extreme trauma," Tetrault said, in contrast to a tire from the right side that shows less extensive damage. The left-side tires may have overpressurized and exploded due to extreme heating as the shuttle broke apart 207,000 feet above Texas. But investigators do not believe tire detonation played a significant role in the disaster.

"We've recovered both of the tires from the left wheel well and we've been able to identify their exact position inside the wheel well by the amount of patches that there were inside the tire," Tetrault said. "The tires on the left side obviously have a significant difference in appearance from the ones that are on the right side."

Based on the observed damage and failure patterns, "we believe it is possible - and I'll say that again, it is possible - that the tires on the left side blew very late in this event," he said. "This would have been a late event because we have data that indicates that the orbiter was flying under control until the last few minutes before breakup. The blowing of these tires would likely have been a very catastrophic event so it couldn't have occurred until late in the event."

Said board chairman Harold Gehman: "We have telemetry from the wheel well up until the time of loss of signal that indicates those tires were intact, they had the right air pressure and they had the right temperature. So whatever happened, happened after the loss of signal."

In addition to both left-side main landing gear tires, recovery teams have found an actuator used to move Columbia's left inboard elevon, or wing flap. The actuator has a hole in it, apparently the result of a burn through during or just after vehicle breakup, measuring two inches by four inches. Interestingly, traces of hydraulic fluid from the actuator show no signs of heat-related distress.

Data in the final two seconds of telemetry from Columbia - a final burst that followed a 25-second loss of data - showed Columbia was still on course with its fuselage intact and its major systems still functioning. But that two seconds of data contained no telemetry from any systems in the left wing and showed the shuttle's hydraulic reservoirs were empty. By that point, Gehman said after today's briefing, the left wing was either gone or so severely damaged the triply redundant hydraulic lines running into the wing had been severed.

That much had been surmised before. The most intriguing bit of news from today's briefing involved deposits of aluminum and steel slag on the inner surface of U-shaped reinforced carbon carbon - RCC - panels that made up the leading edge of the left wing.

"We have identified at least one piece from sixteen of the 22 leading edge systems," Tetrault said. "These are either pieces of the reinforced carbon carbon, the RCC, or the structural components that attach them to the wing spare and those are made of stainless steel. In some cases, we have pieces of both. We ran some tests this weekend on RCC panel No. 9, or at least a portion of it, and there was slag on the inside of that RCC panel which we tested and it shows deposits of aluminum and stainless steel."

Many observers have speculated the failure of an RCC panel, damage to one of the "T-seals" that hold them in place or problems with the tiles that mark the boundary between the leading edge and the rest of the wing provide the best explanation for where the breach occurred. In this scenario, hot gas entered at or near the leading edge and then worked its way back to the wheel well, burning through sensor wiring and raising temperatures in brake lines and other systems as seen in the downlinked telemetry.

But Tetrault said engineers have not yet explained "how does (molten material) blow forward and how do you get stainless steel and aluminum up onto the back edge, if you will, of an RCC when in fact that stainless steel is behind the area?"

Rear Admiral Stephen A. Turcotte, another board member who spoke today, said analysts are studying how convection from a plasma burn through could affect interior wing components, possibly causing the kind of back-flow seen in the RCC slag deposits. While the board has not reached any conclusions, it is interesting to note that "the closer you get to the chine, or panel No. 9 where it (nears the fuselage), you see more molten (deposits). As you get farther away down the left edge of the wing, you see less molten spray," Turcotte said.

When asked whether investigators favor a leading edge failure or a wheel well burn through as the most likely cause of Columbia's loss, Tetrault said "I think those are both equally alive. Everybody has their own theory, I'm sure each of you have your own theory, everybody on the board has their own theory. I'm going to be patient and not express my theory at this time."

But when asked about telemetry from the wheel well, which showed a more gradual increase in temperature than one might expect from a direct burn through, Tetrault said "I'm having difficulty with some of the off-nominal timings."

"One of the reasons I'm having trouble is it's very simple, very simple physics," he said. "There was a temperature A brake line (sensor), hydraulic fluid temperature A, that went up very early in the event, it was either the second or the third one that went off nominal. Temperature B, which sits about two inches away from it, did not rise until about a minute and a half later whereas temperature C, which is probably six feet away, and temperature D, which is four feet away, are all rising off nominal.

"It doesn't make a lot of physical sense to me," he said. "What we found as we looked at these temperatures is that it appears to be a straight line up and at some point, NASA has called it off nominal. And there may be some variability on where that call is on where it is off nominal. So what I'm trying to tell you is if you're trying to put together a timeline, I think you can be fairly certain when (a sensor) went off line. But when it says it's off nominal, I think you're going to have to take that with a little bit of a grain of salt."

Asked about the relationship between Columbia's attitude, or orientation, and telemetry indicating elevated temperatures, Tetrault said "it's interesting to note that all of them were going up off nominal but then they went up in a very, very sharp fashion as soon as it rolled into the left wing down attitude. I won't say anything more, but it's interesting to note that that occurred that way."

Columbia had completed a right bank, or roll reversal, and was banking to the left when the ship broke apart.

Adding yet another piece to the puzzle, Gehman said a closer analysis of the telemetry from Columbia shows the ship's flight computers began working to counteract atmospheric drag on the left wing earlier than investigators originally thought and that they applied quite a bit of muscle in the final seconds to keep the ship on course.

"Even at the time of the final two seconds (of telemetry), the vehicle's attitude and position were correct," he said. "We do believe that the vehicle was fighting forces more strongly, the fight was getting a little more vigorous at that point and we also believe that the beginning of this, of some of the control measures that the vehicle was taking to maintain its attitude, started earlier than we previously thought."

In the meantime, he said, the board's computer modeling is getting more accurate and sophisticated.

"We are still trying to do what we call a backfit," he said. "We're trying to find a scenario which fits the temperature readings. And we are inducing (virtual) holes and we are inducing heat flow into the vehicle in various places and we are more sophisticatedly modeling how the heat flows in through all the little openings and cubby holes and things like that. So we don't have anything to tell you that's on the conclusion side, all I can say is the analysis is getting more sophisticated and we're doing more of it."

At the beginning of today's briefing he said the board "remains completely determined and energized to finding the answer to this problem. We are still working seven days a week, our energy and our seriousness have not flagged, we still have confidence that we're going to find the cause, the direct cause, and determine the contributing causes. We're dedicated to that end and we have no slacking off and we're not getting discouraged just because we haven't found it so far."

Said Tetrault: "I think it would be fair to say we have more questions than answers right now. But we're getting smarter fast and I believe there's a very good chance that we will, in fact, be able to localize the breach that occurred in the left wing. And we certainly need to do this in order to determine the cause of the accident. Until we have determined that location of the breach, every postulated cause of the accident is really just a theory."

In other developments, Gehman said today NASA Administrator Sean O'Keefe has agreed to reassign unnamed senior shuttle managers currently active in the disaster investigation to avoid any possible conflicts of interest. O'Keefe initially balked at Gehman's request. While no names have been officially mentioned, several sources have said the board was concerned about the ongoing involvement of several high-ranking shuttle managers, including Linda Ham, a former flight director who served as chairman of NASA's mission management team for Columbia's flight.

"It has become apparent that some of the chief managers of the investigation which NASA and this board share are also members of these boards that we're going to be looking at," Gehman said today. "We are then put into the place of having the investigators investigate themselves."

"That's not exactly true because NASA is not investigating management issues. Only we are investigating management issues. But ... I can't possibly have key investigatory managers also be the people whose performance we're looking at in other areas."

He said he was satisfied with O'Keefe's response.

Revision F of the CBS News-compiled STS-107 integrated entry timeline has been posted. This revision includes a transcript of crew cabin intercom voice traffic beginning two minutes prior to entry interface and continuing until the tape ends. The ICOM audio was recovered on a 13-minute videotape shot by the astronauts on Columbia's flight deck. The tape ends five minutes before any indications of problems in the shuttle's left wing and 12-and-a-half minutes before vehicle breakup.

Due to the quality of the audio on the tape transcribed for this revision, minor errors may be present in a few instances. Any comments, suggestions or corrections will be appreciated!

Contrary to published reports, the Columbia Accident Investigation Board did not ask NASA Administrator Sean O'Keefe to remove shuttle program manager Ronald Dittemore from an active role in the agency's ongoing probe of the Columbia disaster, sources say. The New York Times reported today that board Chairman Harold Gehman requested the reassignment of Dittemore and other unnamed senior managers because of concerns about conflicts of interest.

Sources close to the investigation told CBS News today that Dittemore, who inspected wreckage at the Kennedy Space Center today, was not among the names submitted to O'Keefe. Two sources said the list included Linda Ham, a former flight director and the head of NASA's mission management team, and Ralph Roe, a former launch director and manager of the shuttle program's vehicle engineering office at the Johnson Space Center in Houston. It is not yet known if the board requested any additional reassignments.

A source said the request for reassignments was not meant as a reflection on anyone's personal integrity, it was simply in keeping with a desire to ensure the independence of the ongoing investigation.

As chairman of the MMT, Ham ultimately accepted the results of a Boeing analysis of the potential damage to Columbia's left wing from the impact of foam debris from the ship's external tank 81 seconds after launch. The analysis concluded Columbia's wing might suffer significant damage during re-entry, but that even so, the vehicle could safely land.

Ham presumably played a role in a decision not to request a detailed photo survey of Columbia's underside using powerful Air Force telescopes. Wayne Hale, a senior flight director now serving as launch integration manager at the Kennedy Space Center, made inquiries about the possibility of Air Force help inspecting Columbia, but those initial efforts were terminated by senior management.

"The SSP (space shuttle program) did not want any data and in fact there was never a formal MOD (mission operations directorate) request made from the FDOs (flight dynamics officers) or the Flight Director," Steve Stich, a flight director himself, wrote in an email to a colleague.

In an interview today to discuss various aspects of hypersonic flight, Hale declined comment on the matter, saying "I probably ought to wait until I tell the board my story. That's coming up."

In the days following the disaster, Dittemore said the program did not request Air Force assistance inspecting Columbia because engineers did not believe the optical systems, as powerful as they might be, could show enough detail to resolve the kind of damage expected from the foam impact.

But as the investigation wears on, critics of that decision argue (with 20-20 hindsight) that a photographic inspection of Columbia in orbit might have revealed enough detail to at least point investigators toward the area of the wing where the failure originated.

Thirteen minutes before the shuttle Columbia broke apart 207,000 feet above Texas, commander Rick Husband and his crewmates marveled at the hot gas surrounding the spaceplane as it plunged deeper and deeper into the atmosphere.

"This is amazing, it's really getting, uh, fairly bright out there," shuttle pilot William "Willie" McCool commented in a cockpit videotape recovered by salvage crews.

"Yep. Yeah, you definitely don't want to be outside now," Husband replied at 8:46:51 a.m. as Columbia approached the coast of California.

"What, like we did before?" joked flight engineer Kalpana Chawla, drawing a round of laughter from her crewmates.

A few minutes earlier, enjoying the light show outside the cockpit windows as hot plasma built up around the spacecraft - the same hot plasma that ultimately would trigger the shuttle's destruction - Husband told his rookie pilot: "Wait until you start seeing the swirl patterns out your left and right windows."

"Wow," McCool exclaimed.

"Looks like a blast furnace," Husband replied.

The light-hearted banter was captured in a dramatic 13-minute section of heavily damaged videotape recovered in shuttle wreckage that fell to Earth near Palestine, Texas, following the orbiter's destruction at 9 a.m. on Feb. 1. The tape was shot by a hand-held camera on the flight deck where Husband, McCool, Chawla and physician-astronaut Laurel Clark were preparing for landing.

Crewmates Michael Anderson, David Brown and Israeli Ilan Ramon were seated out of sight on Columbia's lower deck.

The video begins nine minutes before the shuttle fell into the discernible atmosphere over the Pacific Ocean northwest of Hawaii. It ends four minutes after "entry interface" and three minutes before the first sign of telemetry showing unusual temperature increases in the left wing's landing gear wheel well. The tape ends abruptly, apparently the result of heat damage after the shuttle broke up.

As such, the video offers no insights into what went wrong that day other than to show the astronauts were at ease and looking forward to a landing at the Kennedy Space Center to close out a successful 16-day science mission.

Earlier in the flight, the astronauts were told that debris from the shuttle's external tank had hit the left wing 81 seconds after launch. But a formal analysis concluded Columbia could safely land despite potential damage to the underside of the wing.

NASA officials said later the astronauts accepted the results of the analysis and did not discuss it again. They certainly showed no outward signs of any concerns in the videotape released today.

Columbia's re-entry began over the Indian Ocean at 8:15:30 a.m. on Feb. 1 with a two-minute 38-second rocket firing that slowed the shuttle by just 176 mph. That was enough to lower the far side of the shuttle's orbit deep into the atmosphere over the Kennedy Space Center.

For the next 29 minutes, Columbia fell toward the discernible atmosphere and began feeling its effects at 8:44:09 a.m. - entry interface - at an altitude of 400,000 feet above the Pacific northwest of Hawaii.

Nine minutes earlier - at 8:35 a.m. - as Columbia sailed 500,000 feet above the south central Pacific, the cockpit camera was turned on. The camera was mounted on the forward instrument panel just in front of McCool. He later handed the camera back to Clark, sitting directly behind him.

Chawla, seated to Clark's left, kept the crew on track following a detailed entry checklist of standard procedures. As the minutes ticked by, flashes from rocket firings can be seen out the cockpit windows and eventually, the buildup of a pinkish plasma around the vehicle.

Here are the crew's comments toward the end of the tape. The time stamps assume the tape began at exactly 8:35:00 a.m.

08:45:32 a.m. - McCool: "It's starting to glow a little bit more now, Laurel."

Clark: "Ok."

08:45:52 a.m. - McCool: "Do see it over my shoulder now, Laurel?"

Clark: "I was filming, it doesn't show up nearly as much as the back." She was referring to the spectacular plasma sheath streaming away from Columbia's vertical stabilizer as viewed through an overhead window.

08:45:58 a.m. - McCool: "It's going pretty good, now. Ilan, it's really neat, just a bright orange yellow out over the nose, all around the nose."

08:46:10 a.m. - Husband: "Wait until you start seeing the swirl patterns out your left and right windows."

McCool: "Wow."

Husband: "Looks like a blast furnace."

08:46:31 a.m. - Husband: "Let's see here... look at that."

McCool: "Yep, we're getting some Gs." He was referring to the onset of gravity.

Husband: "Yeah."

McCool: "I let go of a card, and it falls."

08:46:39 a.m. - McCool: "I got a bit flip here on the accel now."

Husband: "Yep. Alright, we're at, uh, hundredth of a G."

08:46:51 a.m. - McCool: "This is amazing, it's really getting, uh, fairly bright out there."

> 08:46:56 a.m. - Husband: "Yep. Yeah, you definitely don't want to be outside now."

08:47:01 a.m. - Chawla: "What, like we did before?" (laughter) Husband: "Good point."

The tape abruptly ends one minute later as Columbia was descending over the Pacific Ocean southwest of Hawaii. The first telemetry indicating anything amiss with the shuttle came at 8:52:17 a.m. when a sensor in the shuttle's left main landing gear wheel well showed an "off nominal" temperature rise."

At 8:59:32 a.m., Husband made a final transmission to mission control, beginning "Roger, uh, buh..." The transmission was cut off and 32 seconds later, Columbia broke apart.

The New York Times reports in Friday's edition that the Columbia Accident Investigation Board has asked NASA Administrator Sean O'Keefe to remove several NASA managers, including shuttle program manager Ronald Dittemore, from the ongoing accident investigation. The Times reports that CAIB chairman Harold Gehman made the request because of concerns about conflicts of interest. An unnamed congressional aide told the Times the board "didn't want to have the leaders of the internal NASA investigation be the very same people who would be the subject of the investigation."

The Columbia Accident Investigation Board released a photograph this evening showing a heavily damaged, almost melted looking segment of left wing debris from an area near the ship's left main landing gear door.

The heat shield tiles on the outer surface of the wing debris appear almost lava like in appearance, certainly melted looking, indicating exposure to extreme heating.

The left-wing landing gear wheel well is an area of intense interest because telemetry showed abnormal temperature increases and sensor failures in the well in the minutes before Columbia's destruction Feb. 1. Engineers theorize a breach in the left wing allowed hot gas to circulate in or around the wheel well as the shuttle encountered the region of maximum atmospheric heating. The breach presumably worsened until a structural failure occurred.

Whether or not the debris shown in the photograph released this evening shows signs of such a breach is not yet known. But the tile damage is unusual in appearance, indicating exposure to extreme temperatures. Interestingly, the underside of the debris, sources say, shows no signs of such heating.

Speaking on Capitol Hill, NASA Administrator Sean O'Keefe said today the space station's international partners have agreed to keep the lab complex manned with rotating two-person crews launched aboard Russian Soyuz ferry craft until space shuttles return to flight.

The first such crew, taking a fresh Soyuz lifeboat to the station, is scheduled to take off in late April or early May. The station's current crew - Expedition 6 commander Kenneth Bowersox, flight engineer Nikolai Budarin and science officer Donald Pettit - will return to Earth four to six days later aboard the lab's current Soyuz lifeboat.

The launch date is somewhat uncertain due to ongoing discussions of lighting requirements for landing of the ISS-6 crew.

In any case, the Soyuz lifeboats must be replaced every six months and the station partners now plan to use those so-called taxi flights to rotate two-man crews as well.

"As of yesterday, we were able to reach a very specific set of solutions on that approach," O'Keefe told the House Science Committee today. "The deliberations have been very constructive and all the partners are acting like partners in the development of a partnership solution."

He said the partners "agreed to use the Russian Soyuz emergency egress spacecraft that are rotated twice a year to international space station to rotate the crews, the expedition crews, aboard the station for this interim period."

O'Keefe said the new Expedition 7 crew will be made up of a Russian Soyuz commander and a NASA astronaut trained to operate U.S. systems. Both are already in training at Star City in Russia, but O'Keefe did not identify them. NASA officials later said four men - cosmonauts Yuri Malenchenko and Alexander Kaleri, along with NASA astronauts Edward Lu and Michael Foale, are in training and that two of them, one Russian and one American, will be named next month to serve as the ISS-7 crew.

U.S. and Russian sources have said that Malenchenko and Lu will make up the ISS-7 crew while Kaleri and Foale will replace them in the fall as the ISS-8 crew. NASA officials would not confirm that breakdown, however.

Malenchenko, Lu and Kaleri already were in training to replace Bowersox and company in March. The ISS-7 crew planned to ride the shuttle Atlantis into orbit, but loss of the shuttle Columbia Feb. 1 grounded the shuttle fleet and prompted a reassessment of how to operate the station in the meantime.

Instead, the revised ISS-7 crew will ride a Soyuz to the station and dock at an Earth-facing port on the Zarya module. The current Soyuz, the one the ISS-6 crew will come home in, is docked to the Pirs airlock module.

The primary source of fresh water for station crews is the shuttle, which produces water as a byproduct of generating electricity in its hydrogen-oxygen fuel cells. Without regular shuttle visits, the station cannot support a three-person long-duration crew, forcing the partners to explore options for two-person caretaker crews.

The plan at present, O'Keefe said today, is to launch fresh two-person crews to the station every six months until the shuttle can resume flights. The ISS-8 crew will ride another Soyuz to the station in October if the shuttle fleet is still grounded at that point.

At the same time, he said, the international partners have agreed to accelerate the production of unmanned Progress spacecraft to deliver the supplies necessary to keep even two-person crews in space. Without additional Progress capsules, the station cannot remain manned much past the end of the year.

"So the partnership has agreed to that," O'Keefe said. "We are all in agreement on the approach on how we will proceed in order to maintain that capacity and to assure that we can operationally continue this important laboratory condition."

But he provided no details about how the Russians would finance the accelerated development of Progress supply ships or how they would be compensated for losing income from the European Space Agency. ESA astronauts had been scheduled to visit the station twice, in May and October, as members of Soyuz rotation flights. Russia charges between $20 million and $30 million for such flights and in the short term, at least one of the ESA flights will have to be deferred, depriving the Russian space program of much-needed cash.

An ESA astronaut is expected to be aboard in October when the next Soyuz is launched, but he will return to Earth with the two-man ISS-7 crew.

Under the Iran Non-Proliferation Act of 2000, NASA is barred from directly financing Russian launchings or helping pay for development of additional Progress supply ships. Russian space officials already have approached their ESA counterparts to discuss the option of European financial support of Progress development in exchange for seats on future long-duration crews.

Nick Lampson (D-Texas) said today he planned to introduce legislation to amend the Iran Non-Proliferation Act to permit possible U.S. financial assistance.

"I believe we need to ensure the space station remains operational while the shuttle fleet is grounded," he said. "Therefore, I plan to introduce legislation today that amends the Iran Non-Proliferation Act of 2000 to allow NASA to purchase additional Soyuz and Progress vehicles if the president notifies Congress they are needed to ensure the safety of the crew aboard the international space station and to maintain its operational viability while the space shuttle fleet is grounded."

In response to a question from Science Committee Chairman Sherwood Boehlert (R-N.Y.), O'Keefe said the partners would not hesitate to bring a crew home and to leave the lab complex unmanned if safety is ever compromised.

"What is it that would motivate us to decrew or abandon the space station? Any safety consideration would immediately motivate us to direct the crew to get into the Soyuz vehicle and return home and dim the lights," he said.

"Because we do not want to compromise the safety of those human beings one moment. Our attempt here is to assure we can continue to support their activity, to maintain some science and research objectives aboard, not nearly as optimum as we can now, but to maintain this so we can get to the point of returning to shuttle flight."

Answering another question, he said the station could be safely operated in an unmanned mode for just six months to a year, and that assumes no major problems crop up that would require astronaut repair work.

"Assuming all that stayed exactly right and we could move the orbit of the international space station to avoid debris, to keep its altitude at the appropriate orbit levels, we could probably do that for six months to a year, assuming no other unforeseen circumstances," he said.

Any major problems, in the absence of a crew, "could compromise its continued operations."

Mechanical systems officer Jeff Kling, the flight controller who first noticed problems in the shuttle Columbia's left wing during re-entry Feb. 1, said today he had no idea a disaster was about to unfold and that "what-if" discussions he had by email the day before were just that and not an indication of any real concern on his part.

In a teleconference this evening with a small group of reporters, Kling said he fully expected a normal re-entry and landing when he showed up for work that morning, despite knowing a piece of debris from the shuttle's external tank had hit the ship's left wing during launch.

Kling said the flight control team was satisfied with the conclusion of a Boeing analysis of the impact, which concluded Columbia could land safely.

"From our console standpoint, there was not a huge concern out there," he said. "We had proper teams looking at thermal analyses and what we thought was a good result. I had no reason to doubt the thermal analysis that said there was not going to be any burn through on the vehicle.

"The emails we had were what-if kind of scenarios where we talked about, like we do in our normal jobs, we bat things around and say, you know, what if, and work through the whole thing. Because I had confidence in the thermal analysis I was not at all concerned with the health of the vehicle on entry day.

"However, when events started unfolding, there was a little bit of disbelief right at first when we got the first indications and we just kind of went down that path of, you know, I can't believe this is happening and what did I miss, what did we miss as a team? But we certainly never anticipated this and it was not a concern at all from our console prior to the deorbit burn."

Following the Boeing analysis and its formal disposition on Jan. 28, an engineer at NASA's Langley Research Center in Virginia raised questions within the landing gear and flight control communities about what excessive heating on the left wing might do to the left main landing gear. Emails between the various participants in the discussion were released by NASA today and last week.

The emails show a spirited discussion about what to do if Columbia's landing gear really was damaged. But Robert Doremus, head of the mechanical systems group at the Johnson Space Center, said the discussion was little more than a routine exercise that serves to keep the team sharp.

"We discuss cases sometimes that we don't necessarily expect to happen," he said. "But in doing so, we expand our own knowledge and kind of challenge ourselves to think outside the box and be ready for things."

The discussions were not passed onto senior managers because "again, it was more of an exercise within our group."

"There weren't any new data that came to us originally that said the tile problem might be worse than the analysis said," he explained. "Had there been data in that email that we got, yeah, there would have been quite a bit of concern raised and we would have definitely started looking at what do we need to change as far as entry is concerned.

"But what we got was well, if the analysis is not correct, this is what it might look like and we were joining in on that discussion. But it was not an alarm because it did not contain additional information that would have told us we have a concern."

Kling said the reality of what was happening to Columbia on Feb. 1 did not fully sink in until he saw video showing flaming wreckage streaking across the Texas sky.

"On entry day when we lost the first set of sensors, there was a little bit of disbelief and some concern but we've been trained to do that sort of stuff before," he said. "The fact it was on the left side, it kind of raised your eyebrows a little bit with the first set of sensors.

"When the second set came along, you start playing back some of the things that you went through, and wondering. It didn't actually sink in for me probably until I actually saw some of the taped video footage of the vehicle itself. The rest of the time, I was going through my job, talking to the escape officer, looking for evidence of the crew bailing out or whatever."

But even if the flight control team had understood the severity of the problem well before Columbia's re-entry, Doremus said there was nothing NASA could have done to save the shuttle or even to maneuver it to a point where the crew could bail out.

"We already minimize as best we can the entry profile to make the orbiter have the safest possible entry that it can have," he said. "I don't think, aside from a few tweaks, we could have gotten there with our particular scenario."

See the 5:45 p.m. status report immediately below for a detailed look at the emails and "what-if" scenarios in question.

Despite NASA's oft-stated position that no one was overly worried about potentially catastrophic damage to the shuttle Columbia's left wing after launch, engineers and even some flight controllers continued to debate worst-case "what if" scenarios as late as the afternoon before the orbiter's destruction, according to internal emails released today.

One scenario outlined by a Johnson Space Center engineer on Jan. 31, the day before the disaster, is a virtual blueprint for what actually happened as Columbia plunged back into the atmosphere above the Pacific Ocean and streaked across the southwestern United States.

The emails also show an initial request, presumably from Wayne Hale, a veteran flight director, to have powerful Air Force telescopes and other assets inspect Columbia for possible signs of tile damage before re-entry was shut down by senior management.

"The SSP (space shuttle program) did not want any data and in fact there was never a formal MOD (mission operations directorate) request made from the FDOs (flight dynamics officers) or the Flight Director," wrote one flight director, Steve Stich, to another, John Shannon.

While Columbia's crew could not have been saved even if NASA managers had known the full extent of the presumed damage to the ship's left wing, a photographic survey might have provided enough data to help accident investigators reconstruct what ultimately went wrong.

But shuttle program manager Ronald Dittemore said earlier that no such request was made because even big military telescopes probably would not have been able to resolve a relatively small area of damage. And because of a Boeing analysis that concluded Columbia could safely return despite significant tile damage.

Perhaps the most intriguing email in the latest batch released by NASA is one from Kevin McCluney, an engineer at the Johnson Space Center, who outlined a disaster scenario the day before entry that is almost photo realistic in its predictions.

"Let's surmise just what sort of signature we'd see if a limited stream of hot plasma did get into the (left wing landing gear wheel) well," he wrote in an email to a team of other controllers and engineers. He assumed a hot gas intrusion in Columbia's left wing from around the moment the shuttle first hit the discernible atmosphere 400,000 feet above the Pacific Ocean until the craft fell to a point roughly 200,000 feet up. For Columbia's entry, that would mark a point above central Texas.

"First would be a temperature rise for the tires, brakes, strut actuator and the uplock actuator return," he emailed. "The pressure ... would rise given enough time, and assuming the tire(s) doesn't get holed. Then the data would start dropping out as the electrical wiring is severed, both to the transducers and the wiring to the valves, etc. ... Data loss would include that for tire pressures and temperatures, brake pressures and temperatures, prox box indications and valve indications."

Here's what actually happened:

The orbiter entered the discernible atmosphere about 400,000 feet above the Pacific at 8:44:09 a.m. on Feb. 1. This is known as "entry interface," or EI. The shuttle entered the region of peak atmospheric heating at 8:50:53 a.m.

Engineers believe a breach in Columbia's left wing, possibly caused by impact with space debris in orbit or by foam or ice from the ship's external tank that fell off and hit the wing 81 seconds after liftoff Jan. 16, allowed a jet of superheated gas eat its way inside.

Telemetry radioed back to Earth from Columbia showed a series of left wing sensor failures and rising temperatures in the left main landing gear wheel well area. Engineers believe the breach was close to the wheel well and that plasma burned through nearby sensor cabling and elevated temperatures in the well itself.

The first telemetry indicating abnormal heating timed out at 8:52:17 a.m., just one minute and 24 seconds after Columbia entered the region of peak heating. Over the next eight minutes, sensor after sensor either failed or detected higher than normal temperatures in the left wing.

Jeff Kling, the mechanical systems officer - MMACS - in mission control that day, called entry flight director Leroy Cain at 8:54:24 a.m. to report the first sensor failures.

KLING: "FLIGHT, MMACS."

CAIN: "Go ahead, MMACS."

KLING: "FYI, I've just lost four separate temperature transducers on the left side of the vehicle, hydraulic return temperatures. Two of them on system one and one in each of systems two and three."

CAIN: "Four hyd return temps?"

KLING: "To the left outboard and left inboard elevon."

CAIN: "OK, is there anything common to them? DSC (discrete signal conditioner) or MDM (multiplexer-demultiplexer) or anything? I mean, you're telling me you lost them all at exactly the same time?"

KLING: "No, not exactly. They were within probably four or five seconds of each other."

CAIN: "OK, where are those, where is that instrumentation located?"

KLING: "All four of them are located in the aft part of the left wing, right in front of the elevons, elevon actuators. And there is no commonality."

While this discussion is going on, Columbia descended across California, Arizona and New Mexico, approaching northwest Texas as it streaked toward a landing in Florida. Throughout this period, telemetry beamed back to Houston showed multiple sensor failures or signs of heating in the wheel well area. But many of these readings were not displayed in realtime on consoles in mission control.

Then, at 8:59:15 a.m. - just 17 seconds before the last voice transmission from the shuttle's commander - Kling reported additional sensor anomalies.

KLING: "FLIGHT, MMACS."

CAIN: "Go."

KLING: "We just lost tire pressure on the left outboard and left inboard, both tires."

CAIN: "Copy. Is it instrumentation, MMACS? Gotta be..."

KLING: "FLIGHT, MMACS, those are also off-scale low."

Moments later, Columbia broke apart 207,000 feet above Texas just west of the Dallas-Fort Worth area. Still not realizing what was happening to Columbia and its crew, additional sensor failures were discussed in mission control.

CAIN: "MACCS, FLIGHT."

KLING: "FLIGHT, MMACS."

CAIN: "And there's no commonality between all these tire pressure instrumentations and the hydraulic return instrumentations?"

KLING: MCC-MMACS: "No sir, there's not. We've also lost the nose gear down talkback and the right main gear down talkback."

CAIN: "Nose gear and right main gear down talkbacks?"

KLING: "Yes sir."

McCluney's eerily prescient scenario, written the day before Columbia's re-entry, is the latest in a series of internal emails charting concern about Columbia's health and what might happen as a result of presumed wing damage.

During a teleconference in the days following the disaster, Cain and senior flight director Milt Heflin said such discussions among engineers and flight controllers are normal examples of "what-ifing" that are a routine part of the engineering world.

What makes them interesting, however, is they continued in depth even after NASA's mission management team collectively dismissed concerns about post-launch tile damage following an assessment by Boeing engineers that while the wing might be damaged during entry, it would not fail. The quality and thoroughness of that analysis has since been called into question and the Columbia Accident Investigation Board has promised a re-analysis to verify or overturn those initial results.

The Boeing assessment was approved on Jan. 28. That same day, Robert Daugherty, a landing gear expert at NASA's Langley Research Center in Virginia, wrote in an email: "Any more activity today on the tile damage or are people just relegated to crossing their fingers and hoping for the best?" While management appears to have dismissed the issue, the engineering community continued discussions showing at least some level of concern about the potential for serious tile damage.

Responding to emailed concern about possible landing gear damage and what options should be exercised to safely land the heavy shuttle, Kling said "if there was hot plasma sneaking into the wheel wells, we would see increases in our landing gear temperatures and likely our tire pressures."

"If we actually saw our instrumentation in the wheel wells disappear during entry then I suspect that the gear will not deploy anyway because the wires that control the pyros and all the hydraulic valves would burn up too.

"Ultimately, our (MMACS) recommendation in that case is going to be to set up for a bailout (assuming the wing doesn't burn off before we can get the crew out).* The rest of the cases are great big what-ifs. We can manage the drag and from early gear deploy if it happens before Mach 1. Any burn-through damage would be discovered well before that." (* Editor's note: Kling's parentheses.)

Another engineer, William Anderson, however, downplayed concerns about a breach in the landing gear wheel well. While agreeing with Kling's assessment, he said he did not believe Columbia was in any danger.

"Why are we talking about this on the day before landing, and not the day after launch?" he wrote to Kling and others. "...if there were evidence on this flight that we were missing tiles/RCC (reinforced carbon carbon panels), I might be worried."

A fragment of videotape shot by one of the astronauts on Columbia's flight deck during the early stages of re-entry Feb. 1 has been recovered by NASA. But sources say the heat-damaged tape ends before the onset of problems in the left wing that ultimately led to the orbiter's destruction and the deaths of the ship's crew. As such, the tape provides no insight into the mishap.

But sources familiar with the tape say the astronauts showed no signs of any concern as they prepared for return to Earth after a 16-day science mission. The tape has been shown to astronaut family members, the sources say, and will be shown to lawmakers in Washington on Wednesday before its eventual release to the media and public.

The digital video tape, presumably shot by astronaut Laurel Clark, begins around 8:35 a.m., some nine minutes before Columbia fell into the discernible atmosphere 400,000 feet above the Pacific Ocean northwest of Hawaii.

The tape continues for four minutes past "entry interface" and then abruptly ends around 8:48 a.m., four minutes before the first telemetry was received indicating problems in the shuttle's left wing. Sources say no other tape remained on the heavily damaged cassette.

Commander Rick Husband, pilot William "Willie" McCool, flight engineer Kalpana Chawla and Clark were seated on Columbia's flight deck for entry. Crewmates Michael Anderson, David Brown and Israeli astronaut Ilan Ramon were seated out of sight on the shuttle's lower deck.

Unlike the pilots and the flight engineer, Clark had no specific re-entry duties and presumably shot the video recovered by NASA. But that is not yet known.

At a weekly news conference by members of the Columbia Accident Investigation Board, board member Scott Hubbard said the final two seconds of telemetry from Columbia showed all of the orbiter's major systems were running and that its fuselage was still intact.

As CBS News reported here late last week, the final two seconds of data, which followed a 25-second period in which no data were received, also showed Columbia's triply redundant hydraulic system had lost all pressure and that its reservoirs of hydraulic fluid were empty.

"The conclusion seems to be that somewhere in that 25 seconds of unrecovered data there was some sort of failure that affected all three hydraulic units," Hubbard said.

Board chairman Hal Gehman provided a bit of additional insight by adding later that no data from the left wing showed up in the final two seconds of telemetry. This is consistent with severe wing damage - or even its complete removal just prior to the final burst of telemetry - that severed all of the hydraulic lines leading to the wing's elevons and landing gear wheel well.

Gehman said engineers studying debris from the shuttle still do not know what caused the catastrophe. But without being specific, he said the ongoing recovery of debris is beginning to pay off.

"Debris continues to be important to us," he said. "We are now beginning to learn some things - that's probably too strong - but we're beginning to see some interesting trends and evidence in the debris."

He then showed pictures of a heat shield tile frrom Columbia's left wing that was found near the town of Powell, Texas. The tile shows severe damage from heating effects, "probably by hot gasses."

"I am told this is not typical of a re-entry tile," he said. "This is very unusual. One of the riddles we have to sort out is whether or not this damage was done while the tile was still attached to the orbiter or whether this damage was done after the breakup and that's what it looks like when you try to re-enter the atmosphere in a non-aerodynamic state."

Another fragment of tile found farther west, near Littlefield, Texas, appears to have come from the upper surface of the left wing near the so-called "glove" area where the wing joined the fuselage."

Most investigators believe the catastrophe began with a breach in the left wing that allowed superheated gas, or plasma, to work its way inside. The hot gas then burned through sensor wiring and caused temperatures in the left landing gear wheel well to climb.

The breach may have been the result of damage from external tank debris that hit the wing during launch, impact by space debris during the mission or some other factor. Exactly where the breach occurred - at or near the left main landing gear wheel well or closer to the leading edge of the wing - is not yet known.

Earlier today, NASA has posted images of Columbia while it was still in orbit that were shot by a powerful Air Force telescope in Hawaii. But Columbia's open cargo bay is facing the camera in all of the images and no details of the underside of the ship can be seen.

In any case, engineers have not yet ruled out any "root cause" of the Columbia disaster. Investigators are running computer models to create "virtual" breaches at various points on the wing to come up with locations that at least explain the series of sensor failures and rising temperatures that were radioed to Earth before Columbia broke up.

But Hubbard cautioned that a simple answer might not be forthcoming.

"It's well known that accidents in complex systems often involve a chain of events," he said. "It's not often one single thing caused the whole accident. So this complex series of events needs to be evaluated together. For example, eventually we would like to see if you can couple the external tank shedding event with TPS sensitivities with the calculations that are being done by the aerodynamics folks.

"So what we're doing right now is trying to bound the events in the orbiter, we're trying to go from the town to the ballpark to the seat."

He then provided three examples to illustrate the difficulty of "bounding the event."

"We did a hypothetical study of a 20-square-inch breach in the wing, 4 by 5 (inches), near the main landing gear door or the seal, that seems to account for the temperature rise," he said. "But this is a first cut with an initial set of assumptions. Figuring out what might happen to a plume going inside a wing is a very complex task. It's a good first step, but we don't have an answer there yet.

"Secondly, the sensor data that we've all looked at, the rise in temperature, the sensors going off line, seems to be consistent with wires going through the wheel well being severed. But there is a sensor near the front of the spacecraft that also had an anomaly. How do you account for that? Again, it's a little early to conclude we have a complete story.

"And finally, some initial aerodynamic analysis seems to indicate there was some disturbance going on in the vicinity of the left main landing gear wheel well, but eight different calculations all gave somewhat different answers.

"So the story I'm trying to communicate to you is it's early yet to draw conclusions that we have boxed this story in, that we really have bounded the event. We're making good progress, we need to validate the data interpretations with analysis of debris, experimental tests and in selected cases with independent calculations and perhaps independent tests. We need to look at the system."

As of today, Gehman said, 8,110 pieces of confirmed shuttle debris have been found, representing a bit more than 10 percent of the orbiter by weight.

In a final bit of news from today's briefing, it was reported that investigators studying Air Force radar tracking tapes made during Columbia's mission clearly show a small object measuring about .3 by .4 meters separated from the shuttle on the second day of the flight. The object later re-entered the atmosphere on its own. CBS News reported this "event" on Feb. 7, but it is still not known what it might have been or whether it played any role in the ensuing catastrophe.

A post-launch analysis by Boeing engineers shows three pieces of debris falling off the shuttle Columbia's external fuel tank one minute and 22 seconds after launch Jan. 16 slammed into the orbiter's left wing. While the Boeing team concluded Columbia could safely land despite potential damage to the shuttle's fragile heat-shield tiles, internal agency emails released today raised potentially troubling questions about how the damage was assessed within NASA and how widespread discussion of its possible impact really was.

"I am advised that the fact that this incident occurred is not being widely discussed," Mark Shuart, an engineer at NASA's Langley Research Center in Virginia, wrote in an email to two colleagues.

Worried more about the impact of re-entry heating on Columbia's left main landing gear tires than he was about a high-altitude catastrophe, Robert Daugherty emailed Shuart later that "we can't imagine why getting information is being treated like the Plague. Apparently, the thermal folks have used words like they think things are 'survivable,' but 'marginal.' I imagine this will be the last we hear of this."

In another email, Daniel Mazanek with Langley's Spacecraft and Systems Branch, questioned the Boeing team's assumption the debris was made up of low-density foam insulation falling from Columbia's external tank. Mazanek wrote a colleague the debris could have been ice or even hardware from somewhere else on the orbiter or tank.

"The debris may have been made of ice or some other material(s) and could be much more massive than the calculated 1.211 kg (2.67 lb)," he wrote. "If the photogrammetric measurements accurately measured the debris to be (20 X 16 X 6 inches), and it was made of solid ice, the mass could be approximately 28.7 kg (63.4 lb). The energy released from this impact could be almost 25 times greater than estimated. Other dense materials, such as aluminum, would make this impact even more damaging."

Mazanek suggested a re-analysis of the launch video to more accurately determine what the debris was and where it came from.

"As a reference, if the debris was 1.211 kg and assuming a conservative relative impact velocity of 457.2 m/s, the kinetic energy would have equivalent to a 500 lb safe impacting at 75 mph," he emailed. "If the debris was 28.7 kg, that would be the equivalent of a 500 lb safe hitting the wing at 365 mph."

Within days of Columbia's launching, a team of Boeing engineers began assessing the debris impact, using software to model various damage scenarios. While many observers, including this reporter, saw two pieces of debris while replaying launch videos in the days after Columbia's destruction, the report released today is the first citing three such pieces.

"At about 82 seconds into the flight, multiple pieces of debris were seen emanating from the ET (external tank) bipod area and later seen impacting the Orbiter lower surface," the Jan. 24 report states.

"Film analysis results indicate impact at about 1/3 of the wing from the vehicle centerline."

Three pieces of debris were observed, the report continued, with a maximum size estimated at 20 inches.

The report is one in a series of studies done in the wake of Columbia's launching to determine what sort of damage the debris might have caused. In two widely reported studies released earlier, the engineers said the loss of a single tile could cause serious damage, but would not result in a loss of the shuttle.

But those studies did not include analysis of damage that might remove or seriously erode multiple heat-shield tiles. They simply said that pending the completion of that analysis, the team believed Columbia could safely land.

The charts released today did not shed any light on that issue, although they do show the expected impact angles and velocities of the debris. For the worst-case scenario, one in which it was assumed a 20-by-16-by-6-inch piece of foam hit the left wing, the impact velocities averaged 643 feet per second, or 438 mph. Impact angles averaged 15.3 degrees for impacts on the leading edge of the wing and 9.3 degrees for the tiles just behind the edge.

But the charts released today do not explain what conclusions the engineers reached from that data or what those conclusions were based on.

"Three sets of charts, from Jan. 21, Jan. 23, and Jan. 24, were part of an analysis conducted during the STS-107 mission of the impact of external tank foam debris striking Columbia during ascent," NASA said in a brief statement accompanying today's release.

"The analysis was presented to the STS-107 Mission Management Team on Jan. 27 with the conclusion that the effects of the debris did not pose a safety of flight concern for Columbia. Mission managers concurred with that conclusion.

"These charts do not represent a comprehensive look at the analysis, which included extensive verbal communication, and took place over more than a week while Columbia was in orbit. All open work shown on these charts was completed and reported to space shuttle management."

The Columbia Accident Investigation Board has concluded an intrusion of superheated plasma from a breach in the left wing led to Columbia's destruction. But it is not yet known where the breach occurred or what caused it. Engineers are focusing on the leading edge area and the left main landing gear door and associated seals.

Wiring from sensors located at the back of the wing was routed to immediate left and then in front of the main landing gear wheel well. Those sensors dropped off line early in Columbia's descent, indicating plasma ate through the wiring. That's consistent with a breach in the leading edge area ahead of the wheel well. But a breach in the wheel well itself has not yet been ruled out, even though the temperature increases seen there were far below the temperature of the presumed plasma.

Regardless of the details, the post-launch engineering analysis of the debris impact - the assumptions made, how the conclusions were reached and how they were reported to senior management - will no doubt continue to receive attention. The charts released today shed little light on those matters.

But the email traffic that has surfaced in the wake of the disaster shows many engineers in the shuttle entry systems community were worried about the possible consequences of the presumed tile damage.

Dennis Bushnell, a Langley manager who participated in the shuttle's original flight certification back in 1980 and 1981, emailed a colleague on Feb. 5 that boundary layer turbulence, magnified by tile damage, could be a lethal combination.

"If the flow is turbulent at peak heating the heat shield would/could burn through the wheel well doors [even with undamaged tiles]," he wrote.

"More extensive tile damage, whether from external tank insulation or ice impingement would obviously add insult to injury and compromise TPS (thermal protection system) integrity AS WELL AS ACT AS A BOUNDARY LAYER TRIP. If the gouges (caused by debris impacts) were extensive enough then free shear layers form which have VERY LOW TRANSITION REYNOLDS NUMBERS [below a hundred thousand] AND large impingement HEATING PEAKS."

NASA, he said, "should have done more analysis of this whole situation/taken it more seriously."

That was an after-the-fact observation. Before Columbia returned to Earth, it's not clear whether anyone believed a catastrophe was imminent.

Shuart ended a Jan. 30 email by writing, "It will be interesting to see the extent of the damage after landing on Saturday."

Revision E of the CBS News-compiled STS-107 integrated entry timeline has been posted. This revision includes "debris shedding" and "flash" events along Columbia's ground track as identified by NASA analysts using amateur video of the shuttle's flight across California and the southwest. Additional telemetry included as well.

The shuttle Columbia's fuselage remained essentially intact for at least a half minute after the commander's final transmission, according to sources familiar with an ongoing analysis of the last 32 seconds of telemetry from the doomed spacecraft. The astronauts almost certainly had some awareness of the unfolding disaster, but there is no insight at this point to indicate what they might have known, or when.

The telemetry data, radioed back to Earth 30 to 32 seconds after normal communications with Columbia were interrupted 207,000 feet above Texas, indicate the shuttle's left wing was either gone or so severely damaged by a catastrophic "burn through" that hydraulic lines leading to the wing's elevons and landing gear had been severed or ruptured.

That final burst of telemetry shows the orbiter's hydraulic power units, or APUs, were still functioning, as were the ship's flight computers, navigation systems and its electrical generators. But the data show no pressure in the triply redundant hydraulic power system lines running to the left wing. The hydraulic fluid presumably was being pumped overboard following a structural failure of some sort in the left wing.

Whatever happened to Columbia began while the ship was descending over the Pacific Ocean off the west coast of California. Engineers believe hot plasma ate its way into the left wing because of a breach in the shuttle's thermal protection system. The exact location of the breach is not yet known, but engineers are focusing on two areas: The leading edge of the left wing and the left main landing gear door area.

In any case, as Columbia's descent continued the plasma burned through wiring, routed around the wheel well, that led to sensors mounted near the rear of the wing. The plasma intrusion also caused temperatures to rise dramatically in the left landing gear wheel well, triggering additional sensor failures. Video and still photography shot by amateurs as far west as California show debris falling away from Columbias as it streaked eastward across the southwestern United States.

A team of NASA engineers studying FAA radar tapes has identified at least two possible debris tracks, which are expected to greatly narrow the search area for tiles or other material that might have fallen away from Columbia well before its eventual breakup. Any such debris could prove critical for pinpointing where the plasma breach occurred (see the 7:45 p.m., 2/20/03, update below for additional details).

Wherever it began, the breach ultimately caused unusual aerodynamic drag to develop on the left side of the spacecraft, forcing Columbia's flight computers to adjust the shuttle's roll trim with the elevons, or wing flaps, on each wing. Eventually, two right-firing rocket thrusters were ignited to provide additional muscle. But it was a losing battle.

Shuttle commander Rick Husband, replying to a call from mission control about the loss of tire pressure data from Columbia's left main landing gear, radioed Houston for the last time at 8:59:32 a.m., saying "Roger, uh, (garble)." The transmission was cut off, but Husband's voice did not indicate any apparent alarm.

Shuttle program manager Ronald Dittemore said in the days following the mishap that engineers were attempting to extract data from up to 32 seconds of telemetry received on the ground after Husband's final call. The telemetry likely was transmitted continuously during that 32-second period, but line-of-sight communications through NASA's tracking and data relay satellite were sporadic, possibly because of the shuttle's changing orientation.

Analysis of the telemetry that was received is not complete. But officials say valid data continued flowing down for about five seconds after Husband's interrupted transmission. During that five-second period, two more right-firing thrusters ignited on command of Columbia's flight computers, joining the two already in operation to counteract an increasing aerodynamic drag on the left side of the vehicle.

Following that initial five seconds of data, there are 25 seconds with no data at all. Then, in a final burst of telemetry between 9:00:02 a.m. and 9:00:04 a.m., data showed Columbia's hydraulic power units were still running. The APUS are located in the aft engine compartment and the fuel cells are under the floor of the cargo bay, showing the fuselage - from the aft compartment to the crew module - was still essentially intact at that point.

Analysis shows a "roll reference message" was generated by the ship's flight computers at one point to alert the crew to problems maintaining the shuttle's orientation. Whether that message ever reached a cockpit display is not yet known.

Video showing Columbia's track across the Texas sky indicates the orbiter began breaking up as or just after the last bits of telemetry were transmitted. Within 26 seconds of the final telemetry, time-stamped video from Apache helicopters flying near Fort Hood, Texas, showed multiple contrails indicating the catastrophic breakup of America's first space shuttle, presumably due to aerodynamic effects following the failure of the left wing.

In January 1980, NASA announced a contract to develop a kit for astronauts to repair damaged heat shield tiles on the space shuttle. No such kit has been flown on a shuttle in recent memory, but the release makes for interesting reading in light of the shuttle Columbia's catastrophic breakup during re-entry Feb. 1. Here is the text of the Jan. 22, 1980, news release:

RELEASE NO: 80-004
For Release Upon Receipt

MARTIN RECEIVES TPS REPAIR CONTRACT

NASA has signed a letter contract with Martin Marietta Aerospace, Denver Division, for the development and production of a Space Shuttle on-orbit thermal tile repair kit. The kit is designed for use by Shuttle crews to repair possible damage to any of the thousands of ceramic-based tiles which cover the Orbiter and protect it from intense heat during entry into the Earth's atmosphere.

The kit will not be flown on the first test flight but will be held in reserve for possible use on later flights where the launch environment approaches design conditions. The letter contract with Martin Marietta is preliminary to an official contract award and authorizes the aerospace firm to proceed with immediate design and development of the tile repair kit. Estimated value of the contract is $2.1 million.

The contract follows studies conducted by four aerospace firms for the NASA Johnson Space Center, Houston. Proposals for the production contract were received from General Electric Company, Philadelphia, Pennsylvania, and Martin Marietta Aerospace.

The contract calls for Martin to design and fabricate three repair kits for delivery to NASA. Two of the units are for flight use and the third is for astronaut training. The kit weighs about 300 pounds and will be stored atop the Auxiliary Equipment Storage Assembly in the Orbiter cargo bay.

There are two separate types of repair material: blocks of precured ablative material to fill in large holes and ablative paste which will be used as an adhesive for the replacement blocks as well as a cure-in-place filler to repair areas smaller than tile size. Each kit will contain 160 replacement blocks. Each block will be approximately six-by-six inches in size with varying thicknesses of 3/4-inch to 1.5-inch.

The blocks are principally made of silicone rubber which will ablate when subjected to the heat of reentry. The actual Orbiter tiles do not ablate during the heat of entry. The cure-in-place ablator is a paste-like substance with a silicone-rubber base. It will be applied with an applicator which resembles a conventional caulking gun. Eight applicator guns are included in the repair kit.

If necessary to perform repairs, a spacesuited astronaut would don a backpack maneuvering unit in the Shuttle cargo bay, inspect the outside of the Orbiter, and if necessary, use the kit to apply the ablative materials.

The backpack referred to above was the Manned Maneuvering Unit, or MMU, a large jet backpack developed and tested before the 1986 Challenger disaster. It has not been used since. A smaller jetpack known as SAFER (Simplified Aid for EVA Rescue) is currently available to space station construction crews as an emergency device for getting back to the station or a shuttle in the event a spacewalker somehow became untethered.

Whether a repair kit like the one described above is an option for future shuttle flights is not yet known. And still unresolved is how a spacewalking astronaut could make repairs on the belly of the shuttle where there are no anchor points or handholds.

The Columbia Accident Investigation Board is making "significant progress" analyzing video, still photographs, radar data and other sources of civilian and government data to more precisely determine where debris shed early in the shuttle Columbia's re-entry might have fallen, the board reported today.

Late this evening, NASA's mishap response team, which reports to the CAIB, issued a news release saying investigators are searching the Caliente, Nev., area for debris believed to have been tracked by air traffic control radar during Columbia's descent over California and Nevada.

"Video imagery of Columbia's entry provided to NASA was analyzed by imagery, trajectory and ballistics experts," the release said. "The results of that analysis were then provided to National Transportation Safety Board officials who reviewed air traffic control radar imagery in that area during the time of Columbia's descent.

"The review resulted in what is believed to be a significant radar track of a piece of debris as it fell to Earth. As a result, a search of the Caliente area near the Nevada-Utah border is under way using Civil Air Patrol assets. A search using additional means also may be forthcoming."

The statement said about 25,000 pounds of shuttle debris has been transported to the Kennedy Space Center, about 11 percent of Columbia's re-entry weight.

Meanwhile, a group of experts known as the Advanced Sightings Team is coordinating and analyzing data from NASA, the public, the Department of Defense, the Department of Energy, the National Oceanic and Atmospheric Administration, the United States Geologic Survey and "all other sources of valuable information that become available."

A press release said collaboration by all federal agencies "has been outstanding" and "the team is piecing together the information from these sources to learn as much as possible about anomalous conditions during the entry of Columbia."

The release said information under analysis includes:

• On-orbit photography and analysis by the DOD (presumably entry footage shot at a military installation in Hawaii)
• Military radar searches
• Sonic boom analysis
• Military radar coverage of the possible separation of debris while Columbia was in orbit
• Military analysis of launch footage
• Military identification of debris shedding events
• Analysis of a photograph taken at Kirtland Air Force Base, N.M.

To get a sense of the wide range of assets available to the board, consider the sonic boom analysis. An infrasound array in Lajitas, Texas - about 500 miles south of Dallas - recorded the sound of multiple detonations as Columbia broke up.

"The signal was recorded at about 14:30 GMT," according to a Southern Methodist University web site. "It shows a gradual ramp up of signal followed by a series of sharp events that appear to be explosions, somewhere between 7 and 12 separate events, with one widely spaced small event near the end. It took the sound wave about 30 minutes to arrive at the infrasound array in Lajitas, Texas."

Another SMU Department of Geology web page shows a fascinating animation of radar data from the National Weather Service showing the path of falling debris across Texas.

Shuttle engineers attempting to reconstruct the accident are especially interested in any debris that might have fallen away earlier in Columbia's descent to pinpoint exactly where the failure began. Telemetry indicates hot plasma worked its way into Columbia's left wing and ultimately triggered a catastrophic structural failure. But it's not yet known where the burn through occurred. Recovery of any debris shed early in the descent likely would shed light on the origin of the failure.

Gene Blevins, a freelance photographer who works with the Los Angeles Daily News, was photographing Columbia's re-entry from a radio telescope facility in California. He was among the first to see the sort of debris shedding that interests the Accident Board.

"Once we got our cameras set up, sure enough, around 5:52, 5:53 (a.m. Pacific Time), sure enough, here comes this big white dot out over the mountains coming right at us," Blevins said in a telephone interview. "Once it got a little more north of us, this thing was coming in at incredible speed. That's why I set my cameras up in advance."

After triggering his cameras, "I was looking straight north and I could see little red, like lava chunks, falling off from it ... flaking off from it and then getting sucked back into the plasma trail," Blevins said.

Blevins' re-entry photograph, especially when magnified with image processing software, clearly shows two flaring events in the plasma trail toward the left of the image.

He didn't immediately think anything of it. But as the shuttle moved away and his cameras stopped shooting, "I saw this big red flare come from underneath the shuttle and being forced downward. I was like, 'whoa!'" He turned to another photographer, Bill Hartenstein, and said "Bill, did you see that? Something came off the shuttle!"

The Advanced Sightings Team of the Columbia Accident Investigation Board "is analyzing video footage turned in by space flight enthusiasts and other sources of information to document exactly when these events occurred," today's board statement said. "The earliest shedding of shuttle hardware may well have been documented by videos taken near the California coast. The team identifies anomalous events from the video data and correlates them to the entry timeline.

"Analysts calculate the exact time and angles of the observation by determining exactly where the videos were taken from and by identifying planets or star fields in the background. The team calculates trajectories to predict probabilities of where the debris may have fallen to Earth by estimating properties of possible debris from the video and incorporating known atmospheric and wind data. Radar data is then retrieved and investigated to search for specific signatures. This process serves to drastically reduce the area that must be searched.

"The Advanced Sightings Team is making significant progress in accurately characterizing possible debris events. They are in the process of making the subsequent calculations and taking the next steps. The most western find is still not far from Fort Worth, Texas. Using this process and other possible means, we hope debris discovered farther west would help to unravel the mystery of why this tragedy occurred."

The commander of the international space station said today if the shuttle remains grounded for a prolonged period, and if the Russians cannot produce more Progress supply ships, the orbiting laboratory may not be able to support even two-person "caretaker" crews for any extended period.

It is a complex situation under daily, heated discussion by NASA, the Russians and their international partners as the agencies struggle to reconcile conflicting requirements in the wake of the Columbia disaster and the indefinite grounding of the shuttle fleet.

A European wire service reported today that Yuri Koptev, head of the Russian space agency, had appealed to the European Space Agency to help fund development of additional Progress supply ships in exchange for permanent slots aboard the space station for European astronauts.

"We have made a proposal to our European colleagues: we are looking to make it possible for their astronauts to participate in permanent missions aboard the ISS, on condition that they agree to take on a certain financial contribution," Koptev said in Moscow.

Asked if the U.S. manned space program might be facing a more serious crisis than many now suspect, station commander Kenneth Bowersox said today "I get the sense it's a very serious situation and that we will be more crystallized in our will as a country after we work through it, we'll know for sure what we want to do in space."

"I know that's the way it is for me as an individual, I mean you don't step on a rocket, don't take on a long space mission without knowing exactly why you're doing it," he told CBS News. "And we're doing it because we want to explore space, we want to lay the bricks on the road to leave our planet. And I think as we work through the process, our international team will know better why we're doing this mission."

On a more personal note, Bowersox also said he and his Expedition 6 crewmates - flight engineer Nikolai Budarin and science officer Donald Pettit - took advantage of regularly scheduled medical sessions with doctors on the ground to receive grief counseling after the Columbia disaster.

"As a matter of fact, there are planned sessions for us with our psychological support on the ground on a regular basis and we pretty much continued those," he said. "We received some good advice from them on how to deal with the situation. But for the most part, they prepared us before we ever launched for such an occurrence and I think our psychological team did a great job there."

Asked for an example of what the doctors provided in the wake of the Feb. 1 loss of Columbia, Bowersox said "for one thing, we've talked a little bit about standard grief responses and the type of emotions you might feel. We also talked a little bit about the best way to work through that grief response and we talked about one of the best ways to receive support on board is to try to support the folks on the ground right now."

Bowersox, Budarin and Pettit, launched Nov. 23 and working through their 89th day in space today, originally planned to return to Earth aboard the shuttle Atlantis in March. That mission was to have ferried up a fresh crew, but the shuttle program is now grounded. While no final decisions have been made, it is all but certain the Expedition 6 crew will land in May aboard the lab's Russian Soyuz lifeboat.

The Soyuz lifeboats must be replaced every six months and the next craft is scheduled for launch April 26. That so-called "taxi" flight originally included commander Gennady Padalka and European Space Agency astronaut Pedro Duque. After a weeklong stay aboard the station, Padalka and Duque had planned to return to Earth aboard the older Soyuz, leaving the fresh lifeboat behind at the station.

All of those plans are now up in the air. NASA, the Russians and their international partners are in intense discussions about launching a so-called "caretaker" crew to replace Bowersox and company. The caretaker crew - made up of just two crew members because of the station's limited on-board water supplies - would remain in orbit until at least October when another fresh Soyuz is scheduled for delivery.

One member of any caretaker crew must be a Russian Soyuz commander. NASA says the other member of the crew must be an American with the comprehensive training necessary to maintain systems in the station's U.S. modules. Several names have been bandied about in recent days, but no final decisions have been made.

This is a complex issue for the station's international partners. The Russians were counting on income from launching two European Space Agency astronauts this year on Soyuz taxi flights. If Duque is bumped from the April mission, which appears all but certain at this point, it's not clear how the Russians would make up for the funding shortfall.

This is potentially significant down the road because NASA is barred by law from buying Soyuz or unmanned Progress supply flights directly from the Russians. If the shuttle fleet remains grounded for more than a year, the Russians would have to increase the Progress flight rate to deliver the supplies and fuel necessary to periodically boost the station's altitude and to keep even a two-man crew in orbit.

"If we were to keep the same number of Progresses we have per year in the current plan, it would be difficult to maintain the station as we currently are running it," Bowersox said today.

"We'd probably have to back off a lot from what we're doing, maybe even go to less than two people on board. But if we increase the number of Progresses, we should be able to maintain operations, at least from all the data we've seen from the ground. And of course, that's still being studied."

The next unmanned Progress launch is targeted for June 8. Another follows on Sept. 18 and the one after that on Jan. 30. If that schedule holds up, it's not clear whether enough supplies will be available - in the continuing absence of the space shuttle - to keep the station manned a full year.

"We must be ready for the worst-case scenario," Koptev said in the AFP wire story. "If we don't take the decision today on the construction of the necessary number of vessels and don't ensure the financing, there will be no vessels in 2004 as currently scheduled. Next year risks being critical in terms of serving the station with fuel and water."

For their part, Bowersox, Budarin and Pettit say they would happily remain in orbit a year or more if necessary.

"We came up here thinking we might be the shortest mission ever," he said today. "We were happy to get to come to the station at all, but we were hoping we would get to stay a little bit longer. We were mentally prepared for a year because you don't want to be disappointed thinking you're going to come home in six months and then not get to do it.

"So mentally, you just have to be ready for up to a year and we weren't joking about that, we really are," he said. "Nikolai's been on a space station for seven months before and he says he's definitely ready to stay at least that long and knows that it's not a problem. So we would be happy to stay longer aboard space station, that would be a good thing for our crew."

As for landing in a Soyuz whenever they do come home, Bowersox said his crew will be properly trained and ready.

"We went through the full course of training that's required for entry on the Soyuz, our friends in Star City insisted on that so that if we would need to use it, we'd be safe and we completed that course successfully," he said.

"The second thing is we do have trainers and information handbooks up here that we can study to help us prepare. Of course, the best training device we have is the Soyuz itself, we can go in there and work with the switches and panels and prepare ourselves for entry. But if it is decided we'll come down in the Soyuz, we'll have dedicated training sessions with specialists on the ground to make sure our skills are peaked up a little bit better than they are now before we come home."

Revision D of the STS-107 integrated entry timeline has been posted. This revision corrects three acronym explanations (TSU and DSC (two instances)).

Engineers dissecting telemetry from the shuttle Columbia and videotape of its fiery re-entry now believe eyewitness accounts of debris falling away from the spacecraft as it passed above California, well before its ultimate breakup high above Texas. At the same time, investigators believe the breach that let hot gas eat its way into the shuttle's left wing probably was located at or near the leading edge of the wing or perhaps at or near a seal in the left main landing gear door.

While no options have been ruled out, many NASA insiders favor the leading edge theory as the best explanation of the telemetry released to date. Wherever the breach occurred, a member of the independent Columbia Accident Investigation Board said today it must have been fairly large to explain the resulting catastrophe.

"When you're flying in this superheated air area, what's forming around the spacecraft itself is actually called a shock front," said board member James Hallock. "It's creating a boundary layer so it's not that you have a little tiny pinhole, you need something bigger than just a pinhole for something to actually be able to penetrate within that area.

"But once it gets in there, then it starts off as being a very small thing and then it would propagate. And it becomes much like, I guess, an arc welder's torch."

While the media will no doubt focus on that description, Hallock agreed later that calling a plasma intrusion a 'jet' or "torch" was misleading. An aerodynamicist with expertise in re-entry physics said in an email "there is no such thing as 'plasma jet' inside the wing or inside the landing gear well."

"Once the plasma in the shock layer of the external flow enters into the wing structure passages, the electrons and ions recombine at very high rate due to the high pressure (larger than 1 pound per square foot), and to the catalytic effect of the walls," he wrote. "The air inside is just at low pressure and very hot."

Hot enough to eat through sensor wiring, raise temperatures in the shuttle's left main landing gear wheel well and, ultimately, to affect the aerodynamic characteristics and structural integrity of the left wing itself. Hallock said the accident board has not ruled out anything in its search for what caused the fatal breach. Among the more likely suspects are impact by high-velocity space debris; impact by a micrometeoroid; damage caused by foam insulation from Columbia's external tank that fell off during launch and struck the underside of the left wing; or some combination of these and other factors.

On another front, engineers are slowly but surely coaxing additional data from the telemetry beamed down from Columbia just before it broke apart.

In the days following the disaster, shuttle program manager Ronald Dittemore said ground systems recorded sporadic telemetry from Columbia for up to 32 seconds after commander Rick Husband's final transmission at 8:59:32 a.m. Additional analysis has now extended the time Columbia was known to be intact by five seconds or so beyond Husband's final call, showing two more right-firing rocket thrusters were commanded to fire in a futile bid to prevent aerodynamic drag on the left wing from pulling the spacecraft into a fatal "sideslip" orientation.

In addition, sources say a "roll reference message" generated by Columbia's flight computers at some point midway through that 32-second period also was seen in the telemetry. The message got as far as a computer buffer but it never reached the crew's cockpit displays. By that point, the astronauts undoubtedly knew something was amiss.

While he did not confirm the roll reference message, Hallock said "we continue to dig data out of that 32-second period of time."

Columbia was in a left bank at the time, descending at Mach 18 over northwest Texas at an altitude of more than 200,000 feet. While the exact timing is still unclear, time-stamped video from an Apache helicopter flying near Fort Hood, Texas, shows multiple contrails by 9:00:30 a.m., indicating Columbia broke completely apart less than a minute after the last valid data frame was downlinked.

Already released telemetry from the shuttle shows whatever went wrong went wrong early in the descent, with unusual temperature increases beginning just a minute and 24 seconds after the shuttle reached the region of maximum heating while approaching the coast of California.

While this page has generally avoided the "competitive speculation" fueling many media accounts of the tragedy, a fair number of agency insiders now suspect that a breach at or near the leading edge of the left wing in front of the wheel well is a reasonable explanation for the telemetry released to date.

Telemetry shows the first clear signs of elevated temperatures in the left main landing gear wheel well while Columbia was still off the coast of California. As the shuttle's descent proceeded, additional wheel well sensors either failed or recorded high temperatures while other skin temperature and hydraulic sensors positioned near the back of the wing simply failed. Wiring from those sensors was routed around the left side of the landing gear wheel well and then directly in front of it before entering Columbia's fuselage. A plasma intrusion near the wheel well could have affected the rear-wing sensor wiring as well as the sensors in the unpressurized wheel well.

"When you look at how the wires are set up within the craft itself, it leads you directly towards the wheel well, there's no question," Hallock said. "The wires that lead to those sensors that we're talking about go right in front of the wheel well. Then when you look where the temperature sensors are and you get a sense of how they're reading, you can almost triangulate (to where the problem is). That's what we're trying to do."

NASA engineers familiar with the shuttle's constru?tion say a plasma intrusion directly into the wheel well, perhaps from a breach in a landing gear door seal, would have wreaked more immediate havoc than the relatively modest temperature increases seen in Columbia's telemetry. But a wheel well breach has not yet been ruled out.

Video shot by amateurs along Columbia's path shows what appear to be pieces of debris breaking away from the shuttle well before Husband's final transmission. The accident investigation team has asked the public for help locating any such debris, which could include reinforced carbon carbon leading edge panels or heat shield tiles. Investigators also are seeking FAA and military radar tapes and checking into widespread reports of sonic booms over California and Nevada. Such booms would be consistent with the passage of high-velocity debris.

Outside experts have been asked to evaluate the trajectory of any debris that might have broken free of Columbia over California and the southwest to help search teams narrow the potential debris "footprint." So far, no such debris has been located.

But there is little doubt that Columbia was shedding some sort of debris well before its breakup. Numerous witnesses reported seeing what appeared to be debris falling away from the orbiter or hearing muffled rumbling that may have been caused by torn-off shuttle components falling along the spacecraft's ground track.

"We have been poring over the films," said Hallock. "From the timing I've seen right now, it does look like things were beginning to come from the shuttle as it approached, right about California. So it's not something that was close in, it began way out in that area.

"People are looking at the pieces (on film), we're trying to get a sense by looking at them where we have these films and trying to extract from them what we think the mass would be and then how it's moving. Some people here at (the Johnson Space Center) are trying to extrapolate that to the point of where it might land so we can pick some places and try to find it. Obviously, it would be very important to understand what those pieces are, particularly those that started falling off at the very beginning."

Near town of Twain Hart, Calif., 4,000 feet above sea level in the foothills of the Sierra Mountains, Glen Caldwell and his daughter got up early to watch Columbia fly overhead. A veteran of two previous shuttle re-entries, Caldwell knew what to expect and told his grown daughter the view would be worth the early morning effort.

The weather was excellent and "it's right on time, coming out of the west, and when it gets pretty darn high in the sky for us, we see a little, like a fireball, like a Roman candle or a fire come off this thing," Caldwell, an insurance broker, said today in a telephone interview. "Then a second later or so, we see it again. I commented at that time to my daughter, 'it looks like that thing is falling apart.'" Walking back to his house, Caldwell watched the remainder of Columbia's entry on NASA's satellite television channel, which he was recording. All too soon, the projected ground track of the shuttle, visible on a projection TV screen in mission control, stopped updating over Texas.

"I see the ground track stop and I'm getting a little bit concerned and starting to put two and two together," Caldwell said. He later calculated that Columbia's ground track must have passed about 15 miles north of his location, giving him a good, high-elevation view of the ship's fiery path across the sky. For scale, he said imagine holding an almond at arm's length.

Relative to that almond, "what we saw come off the side of this thing were two pieces the size of a BB," he said. "The orbiter is very, very bright, very iridescent when it comes in and these two pieces when they came off were the same color and intensity. They were very, very bright, very easily discernible and very clearly separate from the orbiter. From our perspective, they disappeared very quickly into the (shuttle's plasma) trail and disappeared."

Unlike video of Columbia's debris falling over Texas, in which different pieces of wreckage fell together, "what I saw was kind of the opposite," Caldwell said. "They peeled off and the orbiter raced away from them."

Mike Dambacher, who was taking a morning walk Feb. 1 and saw the shuttle pass over by accident, did not see any signs of debris falling away. But he heard a rumbling that might have been sonic booms triggered by the passage of unseen debris.

"I'm watching this ball of flame going over," he said in a telephone interview. "I'm watching for probably 15 seconds. My first thought was, I'm watching a falling star, except it's not falling."

A few moments later, he heard a boom and "I'm thinking is that a sonic boom? We hear sonic booms occasionally because they do test flights over here. This was a very muffled sound. There as such a delay, I couldn't tie that to what I saw fly over."

Watching news reports in his home a few minutes later, Dambacher realized he had just seen the shuttle fly over. Comparing notes later with other witnesses, he said some people heard two booms, others heard one.

"The sonic boom is not heard when something goes subsonic!" the re-entry expert said in another email. "Every time a supersonic body flies over an ear at ground level, its bow shock will excite the ear with what we call a 'sonic boom.' The sonic boom is influenced by atmospheric effects, body size, rigidity, acceleration, etc. They all contribute to what we call the 'signature of the sonic boom.'"

Large craft like the space shuttle and the Concorde produce double sonic booms caused by bow shock and wake shock.

"A cluster of supersonic bodies will produce a very complicated sonic boom. Anything can happen, but it will sound more like a long thunder, like a rumble, as the cluster of bodies continues to break down. The shock waves coalesce and form a complicated acoustic pulse."

Small bodies a few inches across - including shuttle tiles - would not produce sonic booms," he said. And while higher Mach numbers yield stronger booms, higher altitudes tend to weaken the boom.

"You will not hear a sonic boom from one tile," he said. "You may from a cluster of tiles (about 20) if they go off simultaneously. But you will hear an alteration of the vehicle's 'nominal' signature if a non-structural member starts to flutter."

For example, one of the insulation blankets on the side of the shuttle.

"The human ear is very good at signature analysis of broad band noise," the physicist continued. "The abnormal noise people heard could have been related to the shedding off of (an insulation blanket)."

Revision C of the STS-107 integrated entry timeline has been posted. Changes include corrections for transcription errors and typos, abbreviation explanations and personnel updates.

An updated STS-107 timeline (revision B) charting the shuttle Columbia's re-entry and breakup is now available from CBS News. The new timeline includes a time-stamped transcript of the NASA commentator and mission control flight director audio loops as well as the latest telemetry released by the Columbia Accident Investigation Board. The telemetry entries include all the data presented in the CAIB's release last week.

Updates will be posted as new information becomes available. The very latest telemetry - the firing of two additional right-thrusting jets just after the last voice contact with Columbia's crew - is not yet included because timing data has been released.

In other developments, search teams found one of Columbia's main engine turbopumps buried in 14 feet of soft soil near Fort Polk, Louisiana. One of the ship's five general purpose computers also has been identified, but a battery was missing and there is little hope of extracting data from the machine, which is not equipped with a hard drive or other storage device. Several crew cabin lockers also have been found, sources said. NASA has not yet announced whether any major portions of the crew module have been located but search teams are combing a large debris "footprint" in eastern Texas.

CAIB Chairman Adm. Hal Gehman added another new member today: Sheila Widnall, former Secretary of the Air Force and a member of the faculty of the Massachusetts Institute of Technology. The board will hold its second formal news conference at 3 p.m. EST Tuesday at the Johnson Space Center in Houston.

For entry flight director Leroy Cain, struggling to make sense of unexpected telemetry from the shuttle Columbia and still hoping to regain radio contact, it was a moment of reluctant, dawning realization that a day he'd hoped would never come was finally there.

Mission operations representative Phil Engelauf, sitting directly behind Cain in mission control, had just heard that television views of Columbia high above Texas showed multiple contrails, the result of the orbiter's apparent catastrophic destruction.

Clearly stunned, Engelauf turned to astronaut Ellen Ochoa on his right and told her the hard news. Ochoa gasped, looked up at the ceiling and muttered to herself as if saying "oh my God" or "oh, no." Engelauf then leaned across his console to Cain and passed on the same grim report. Cain's back was to the camera but he appeared to sag slightly. He lightly slapped the console a few times with pent-up, controlled emotion, straightened and turned back to face his flight control team.

"GC, Flight," he called.

"Flight, GC," the controller replied.

"Lock the doors," Cain ordered, initiating contingency procedures in mission control for the first time since the Challenger disaster 17 years before.

It is a few minutes past 9 a.m. EST on Feb 1, 2003. Columbia and its seven-member crew had just flown into history, leaving Cain and his controllers in a haze of emotion-tinged duty as the enormity of the moment sank in.

NASA released dramatic mission control video today showing Cain and the flight control team during Columbia's re-entry, a gripping view of men and women at a moment of great crisis. At one point, Cain can be seen with tears on his face, but he somehow kept his emotions in check as he guided the team through emergency procedures.

"What I was doing right at that moment in time, I was saying a prayer and then after I did that, I knew it was time to go and take the next step," he said today. "My prayer was for the crew and for the families.

"You have to remember that even at that point, we didn't know the details of the breakup, we didn't know the details of the situation as it was. All we knew was that we had a significant event that was probably catastrophic. But in my mind, I still didn't know perhaps part of the crew module could have remained intact for some period of time, so I began to think about things like ground forces and getting people mobilized and looking for chutes and things of that nature."

A few minutes later, it became clear Columbia had suffered a non-survivable breakup.

Cain said today there was nothing the mission control team could have done to save Columbia and its crew. Even if engineers had know the shuttle's left wing had suffered fatal damage prior to entry, the ship's descent through the atmosphere could not have been modified enough to make a difference.

"Because the trajectory that we designed and the trajectory that we flew is one that by definition, from a thermal heat load, heat rate standpoint, is optimized," he said. "So we do not think that for a given, knowledge of a given hole or a breach or something of that nature, everything we know today says we're doing the best we can with the trajectory we flew."

He praised his flight controllers and Columbia's crew, saying "it was just pure joy being around them and working with them."

"Our hearts and our thoughts and our prayers go out to the crew and their families and that will continue to be with us for a very long time," he said at the beginning of today's briefing.

"I will tell you that this team, the NASA team, has great resolve. We will get through this and we will do it with the help of each other and the help of the community, our families and the rest of the agency. The public has shown us just a tremendous amount of support. ... We very much look forward to better days in the future where we will fly again and move forward."

Just one minute and 24 seconds after reaching the region of maximum aerodynamic heating off the coast of California, telemetry from the shuttle Columbia shows the first sign of unusual heating in the ship's left wing main landing gear wheel well, according to a dramatic new accident timeline released today by NASA.

The timeline plots Columbia's course from a point 400,000 feet above the Pacific Ocean west of Hawaii to the point over Texas where the last data from the stricken ship was transmitted. Overlayed on the map and the shuttle's ground track are boxes showing all of the unusual telemetry beamed back from the shuttle as it streaked eastward toward destruction.

The new timeline includes the latitude and longitude of the orbiter at each point where telemetry was transmitted, the altitude and velocity of the spacecraft at that time and additional details about what each bit of telemetry actually indicated.

As the chart shows, re-entry began in earnest at 8:44:09 a.m. as the shuttle fell into the discernible atmosphere 395,010 feet above the Pacific Ocean northwest of Hawaii. At 8:50:53 a.m., Columbia began encountering the region of peak heating at an altitude of 243,048 feet and a velocity of 24.1 times the speed of sound.

One minute and 24 seconds later, at 8:52:17 a.m., telemetry indicated the start of an unusual rise in temperature from a sensor on the left main landing gear brake line on the inboard sidewall of the main landing gear wheel well. The shuttle's altitude at that moment was 236,791 feet and its velocity was Mach 23.58. The shuttle was well off the coast of California west of San Francisco at a 38.9 degrees north latitude and 129.2 degrees west longitude.

Twenty-four seconds later, a temperature sensor on a strut in the wheel well that faces the main landing gear door began registering an unusual temperature increase. Starting at 8:52:59 a.m. and continuing for another 12 seconds, four temperature sensors near the back of Columbia's left wing suddenly dropped off line. Wire bundles leading to the sensors were routed along the left, or outboard, side of the main landing gear wheel well before crossing in front of the well and into the shuttle's fuselage.

Moments later, in mission control at the Johnson Space Center in Houston, mechanical systems officer Jeff Kling noticed at least some of the unsettling telemetry.

"FYI, I've just lost four separate temperature transducers on the left side of the vehicle, hydraulic return temperatures," he told entry flight director Leroy Cain. "Two of them on system one and one in each of systems two and three."

Cain: "Four hyd return temps?"

Kling: "To the left outboard and left inboard elevon."

Cain: "OK, is there anything common to them? DSC or MDM or anything? I mean, you're telling me you lost them all at exactly the same time?"

Kling: "No, not exactly. They were within probably four or five seconds of each other."

Cain: "OK, where are those, where is that instrumentation located?

Kling: "All four of them are located in the aft part of the left wing, right in front of the elevons, elevon actuators. And there is no commonality."

Cain: "No commonality."

NASA officials said today the most likely explanation for the temperature rise ultimately seen in the wheel well was hot plasma circulating inside the wing from a breach, or penetration, elsewhere. Such a breach could have damaged the hydraulic sensor wiring, explaining the loss of data from systems at the back of the wing, while at the same time explaining the rising temperatures in the wheel well.

That much is informed speculation. That a breach occurred at some point well before breakup now seems all but certain.

"Preliminary analysis by a NASA working group this week indicates that the temperature indications seen in Columbia's left wheel well during entry would require the presence of plasma (super heated gas surrounding the orbiter during re-entry)," NASA said in a statement.

"Heat transfer through the structure as from a missing tile would not be sufficient to cause the temperature indications seen in the last minutes of flight. Additional analysis is underway, looking at various scenarios in which a breach of some type, allowing plasma into the wheel well area or elsewhere in the wing, could occur."

In any case, the next unusual telemetry was transmitted at 8:53:31 a.m. as Columbia was passing 231,304 feet above Sonoma County, Calif., at 23 times the speed of sound. Another rear elevon hydraulic line temperature sensor failed "off-scale low."

More ominously, at 8:53:46 a.m., as the shuttle passed above Interstate 505 west of Sacramento, Calif., a sensor on the left main gear brake line, mounted on a strut facing the landing gear door, began registering an unusual, steady increase, jumping from 1.4 degrees Fahrenheit per minute to 5.5 degrees per minute. The temperature recorded by brake line temperature sensor A continued increasing until loss of signal.

Twenty-four seconds later, at 8:54:10 a.m., brake line temperature sensor B began showing an unusual increase as Columbia passed above the Toiyabe National Forest. Ten seconds after that, telemetry shows the shuttle's wing flaps, or elevons, began moving in response to the ship's flight control system to counteract increasing aerodynamic drag on the left side of the shuttle.

Just two seconds later, at 8:54:22 a.m., as Columbia neared the border of Nevada, two temperature sensors mounted on the left side of the shuttle's fuselage above the left wing began experiencing an unusual temperature rise. One went from the normal 1-degree per minute increase to 7.6 degrees per minute while the other, located slightly aft, showed a rise to 5.5 degrees per minute.

After two more anomalous temperature readings while Columbia was streaking across Nevada, telemetry indicates increasing aerodynamic drag at 8:55:21 a.m. By this point, the shuttle had fallen to an altitude of 224,002 feet but its velocity was still a blistering 21.9 times the speed of sound.

The end was just five minutes away.

Streaking across Arizona, a flurry of readings painted an ever-worsening picture of problems in the shuttle's left wing. Additional landing gear sensors recorded fast jumps in temperature, a sensor on the underside of the left wing dropped off line followed a few seconds later by a sensor on the upper side of the wing, both presumably due to wiring damage elsewhere.

At 8:56:30 a.m., as Columbia descended through 219,820 feet, the flight control system began the first of four planned "roll reversals," or banks, to bleed off energy, routine maneuvers to help a returning shuttle shed velocity. The first roll reversal was completed at 8:56:55 a.m.

Just northwest of Albuquerque, telemetry registered a "bit flip," or an anomalous reading, at 8:57:19 a.m. from a left hand outboard landing gear tire pressure sensor. Five seconds later, a second left outboard tire pressure sensor exhibited unusual readings.

Additional elevon trim motions were recorded at 8:57:35 a.m. as the shuttle crossed 216,062 feet above Interstate 40 at Mach 20.21. After additional telemetry hits, the data shows the start of "sharp" elevon trim motions around 8:58:03 a.m. The timing is approximate, but the flight control system is obviously struggling to maintain the shuttle in the proper orientation.

At 8:58:32 a.m., left main landing gear tire pressures and temperatures began dropping off line followed 14 seconds later by a decrease in the left inboard wheel temperature. At 8:58:39 a.m., Columbia's backup flight system computer issued an alarm calling the crew's attention to the loss of tire pressure telemetry. "And, uh, Hou..." shuttle commander Rick Husband radioed. His transmission, however, was cutoff, presumably because the shuttle's antennas did not have a clean line of sight to NASA's communications satellite.

After additional readings from other sensors recording anomalous data, the backup flight system issues a final tire pressure alarm at 8:58:56 a.m. Ten seconds later, telemetry from a "downlock" sensor indicates Columbia's left main landing gear had deployed. A nearby "uplock" sensor, however, showed no change and flight controllers believe the gear remain stowed through loss of signal.

"Flight data including gear position indicators and drag information does not support the scenario of an early deployment of the left gear," NASA said in a statement.

By this point in the timeline, the aerodynamic drag was increasing at a rapid rate because of the deterioration of the left wing.

Kling suddenly tells Cain: "We just lost tire pressure on the left outboard and left inboard, both tires."

"And Columbia, Houston, we see your tire pressure messages and we did not copy your last," astronaut Charles Hobaugh radioes the crew from Houston.

Cain: "Is it instrumentation, MMACS?"

Kling: "Those are also off-scale low."

Husband then makes what turns out to be his final attempt to contact Houston around 8:59:28 a.m.:

"Roger, uh, buh..." Husband began around 8:59:28 a.m. But this last transmission from the shuttle was cut off. Seconds later, at 8:59:30 a.m., two of Columbia's right-firing yaw jets ignite to assist the elevons in keeping the shuttle on course. One second after that, data shows the elevons sweeping through their largest deflections yet. The left elevon moved up 8.11 degrees.

One second after that, all data was lost. At that point, the shuttle was roughly 200,767 feet up and traveling at Mach 18.16 northeast of Abilene, Texas.

Just a minute or so after this loss of signal, time-stamped video shot by the crew of an Apache helicopter showed the tracks of multiple pieces of flaming debris arcing across the Texas sky.

"Columbia out of communications at present with mission control as it continues its course toward Florida," NASA commentator James Hartsfield said at 9:01 a.m. Two minutes later he said, "Fourteen minutes to touchdown for Columbia at the Kennedy Space Center. Flight controllers are continuing to stand by to regain communications with the spacecraft..."

"Columbia, Houston, comm check," Hobaugh radioed at 9:03 a.m. And again seconds later, "Columbia, Houston, UHF comm check."

There was no reply.

In a teleconference today, a NASA spokesman said telemetry from the shuttle Columbia indicating the deployment of its left main landing gear 26 seconds before the orbiter broke up was the result of a bad data and not because the gear actually deployed.

Had that occurred, NASA spokesman James Hartsfield said, the crew would have felt a noticeable increase in turbulence and other sensors would have confirmed the event as well. As it is, those other sensors, showing the landing gear firmly stowed, remained unchanged through vehicle breakup.

The left landing gear wheel well has been the subject of intense scrutiny because of sensor data during Columbia's final eight minutes that showed an unusual increase in temperature. Up until this point, investigators had not ruled out radiative heating as a possible explanation. They now believe a jet of hot plasma must have gotten into the wing from a breach somewhere else.

"The temperature trends that were seen by the various instrumentation inside the left wheel well ... was unlikely to have been caused by radiational heating alone, radiational heating meaning that it would unlikely be caused by the aluminum skin of the wheel well getting hot and warming the inside of the wheel well," Hartsfield said today. "That kind of radiational heating alone would not have caused the temperature trend.

"You would likely have to have a breach of skin somewhere and have plasma flow inside the orbiter skin somewhere in order to cause that temperature trend. Now, they do not and have not ... pinpointed any general location as to where that plasma flow would have to originate. The wheel well is not a pressurized area, it's not sealed off by walls completely from the rest of the inside of the fuselage, it has venting in it and that kind of thing.

"So, you have a breach in the skin, which is in the leading edge of the wing or the fuselage or the skin of the wing or the wheel well door seals, any of those could be potential causes for the temperature trends we saw."

During a news conference last week, shuttle program manager Ronald Dittemore said the landing gear doors must have remained intact because the temperature rise - a 30- to 40-degree rise over five minutes - would have been much greater if plasma was flowing directly into the wheel well.

NASA managers say an engineer's email discussing a worst-case scenario based on the assumption a foam debris impact during the shuttle Columbia's launch did, in fact, seriously damage the ship's heat-shield tiles is an example of normal "what-iffing" and not an expression of real concern that somehow failed to reach upper management.

In an occasionally heated teleconference with reporters late Wednesday, Milt Heflin, chief of NASA's flight director corps, and Leroy Cain, the flight director on duty during Columbia's descent, insisted the emails in question were simply examples of the kind of routine engineering dialogue that goes on all the time in the flight control community.

"I would not expect those kinds of things to get elevated to me or for me to then take something like that and elevate it to the management team unless there was something that came out of those discussions that resulted in a recommended change to our procedures or mission rules or something that we were going to do different in realtime related to it," Cain said.

"And the answer to those questions from the MMACS (mechanical systems) folks was, no."

It is worth remembering that if the shuttle's thermal protection system was, in fact, seriously compromised at launch - i.e., the root cause of the disaster was the impact of external tank foam insulation on Columbia's left wing - post-launch discussions about the possible severity of the damage were moot.

If that scenario is what actually happened, there was nothing management could have done to prevent a re-entry catastrophe. The crew had no way to repair or even inspect the underside of the wing and there was no way to alter the ship's re-entry profile to significantly reduce the heating and aerodynamic stress the orbiter would experience returning to Earth.

But the way NASA's management system operates is certainly of interest in any post-disaster investigation and reporters have focused in recent days on how safety concerns at the engineering level filter up to NASA management.

As is now well known, a large section of foam insulation broke away from Columbia's external tank about 81 seconds after launch Jan. 16. In long-range tracking camera footage, the foam can be seen disappearing under the shuttle's left wing and then emerging in a shower of fine particles. The foam clearly hit the underside of the wing, but the precise area of impact is not known.

In the days following launch, engineers carried out an analysis to determine what the foam impact might have done to the shuttle's protective heat-shield tiles.

The relative air velocity between the shuttle and the tank at the time the debris came off was about 750 feet per second, or just over 500 mph. The debris hit the tile at a shallow angle and engineers were concerned it could have broken through the black surface layer across a broad area, eroding and reducing the thickness of numerous tiles.

Three different reports apparently were generated, but only two have been seen by reporters. In those, the effects of a single lost or seriously damaged tile were evaluated. "Contingent on multiple tile loss thermal analysis showing no violation of M/OD criteria, safe return indicated even with significant tile damage," one report concluded.

But the analysis of the effects of a multiple tile loss scenario have not yet surfaced. All that is known at present is that on Jan. 28, a status report was forwarded to mission management that concluded:

"The impact analysis indicates the potential for a large damage area to the tile. Damage to the RCC (reinforced carbon carbon leading edge insulation) should be limited to coating only and have no mission impact.

"Additionally, thermal analyses were performed for different locations and damage conditions. The damage conditions included one tile missing down to the densified layer of the tile and multiple tiles missing over an area of about 7 in by 30 in. These thermal analyses indicate possible localized structural damage but no burn-through, and no safety of flight issue."

That report was issued on Jan. 28. Shortly thereafter, mechanical systems engineers at the Johnson Space Center contacted support personnel at NASA's Langley Research Center and asked for an assessment of what might happen if the left-side main landing gear doors were breached during entry.

Even though a formal analysis concluded the debris impact was not a safety of flight issue, the engineers apparently wanted to discuss scenarios in which the debris damaged a landing gear door enough to allow significant heating in the wheel well.

An engineer at Langley emailed back that "before I begin, I would offer that I am admittedly erring way on the side of absolute worst-case scenarios and I don't really believe things are as bad as what I'm getting ready to make them out. But I certainly believe that to not be ready for a gut-wrenching decision after seeing instrumentation in the wheel well not be there after entry is irresponsible. One of my personal theories is that you should seriously consider the possibility of the gear not deploying at all if there is a substantial breach of the wheel well."

If damage in the wheel well was severe enough, he continued, "something could get screwed up enough to prevent deployment and then you are in a world of hurt." He then went through a list of possible landing issues, all focused on problems with the main landing gear at touchdown.

An engineer at the Johnson Space Center in Houston emailed back: "Your input is beneficial. Like everyone, we hope that the debris impact analysis is correct and all this discussion is mute (sic)."

The status of the left main landing gear wheel well has been the subject of much concern throughout the accident investigation because numerous sensors in the well either failed in Columbia's final moments or recorded higher-than-normal temperatures.

In NASA's latest telemetry timeline (revision 12.1), at least one sensor recorded landing gear deployment at 8:59:06 a.m., a full 26 seconds before contact with Columbia was lost. Reliable sources close to the investigation said today the telemetry is believed to be the result of a sensor failure, or "bit flip," and not any indication of an actual deployment.

Deployment of a main landing gear at a velocity of 12,500 mph would generate significant turbulence and additional telemetry. But other sensors in the landing gear deployment system did not show any change prior to loss of signal.

During Wednesday's teleconference, Heflin and Cain went to great lengths to convince reporters NASA's management and problem reporting system worked as designed, even though senior managers were never informed about the Langley landing gear scenarios.

"I was aware of these 'what-iffing' discussions," Heflin said. "I think it was Monday the 3rd. What's interesting is that it didn't surprise me, I didn't think of it as something 'oh my goodness' because I'm used that kind of stuff going on all the time that we don't necessarily hear about unless they believe it's something they need to bring to the flight director and the flight control team to deal with."

Asked if the matter received enough attention, Heflin said "if it comes to the flight director, it's a different story. It did not because they had concluded they didn't need to bring it to the flight director because they believed, with the analysis that was done, and they decided there wasn't anything they needed to do."

He said "the process is a good one. Again, we don't know what happened here yet. When we know what happens, then there'll be other questions we'll be asking ourselves."

But not all the reporters were convinced. One jumped in a few moments later and asked: "Sorry, who said 'there is no reason to rethink the process,' who was that?"

"That was Milt Heflin," replied NASA spokesman James Hartsfield.

"Now, now read that back to me what you just said," Heflin interjected.

"'There is no reason to rethink the process,'" the reporter replied.

"Well now, be careful," Heflin responded with some emotion. "At this point, the process that we used and that we went through is a good process. I stand by that. What I'm saying, at this point, you don't want to rethink the process because you do not know what happened to you yet. We may have to rethink the process later, I don't know, we'll find out. Did you get it this time?"

"I heard you both times."

The teleconference ended in confusion after a reporter repeatedly asked why no one at NASA made a connection about the possibility of serious damage to the landing gear doors based on the original tile impact analysis and the subsequent concerns from Langley.

But the landing gear discussion was prompted by the original impact analysis and it's not clear what the reporter was implying. For their part, Cain and Heflin never seemed to understand the thrust of the reporter's question and the teleconference ended on a sour note.

Earlier in the briefing, however, Heflin said subsequent discussion of the landing gear issue was a routine example of engineers working through "what if" scenarios following an analysis like the one that concluded the foam impact was not a safety-of-flight issue.

"That was the conclusion," he said. "A lot of people were involved in that discussion. Yes, (the engineer at Langley) is an expert, but there are experts in other places, too. This was dealt with by a lot of very smart people reaching the conclusion it was not a safety-of-flight issue.

"And again, let's be careful here, let's don't start taking this and assuming we know what happened here, because we don't yet. But in their particular discussion of the foam and potential contact and damage or whatever, it was concluded it was not a safety-of-flight issue. I'm repeating myself, but again, we train our flight controllers to even go beyond that at times and just continually think of what, maybe, did we miss anything, is there anything we need to be concerned about?

"And in their discussions after that time, they came to the conclusion that what we've got on the books as far as flight rules and procedures and so forth are good, there's nothing else to do and so therefore they did not bring this to the flight director or beyond. They did not, because they did not feel the need to do that. They had reached a conclusion."

Post-launch analysis and debate aside, Cain provided the first glimpse into what the flight control team was thinking as the first signs of trouble appeared during Columbia's descent. Upon hearing a flight controller inform him that four temperature sensors had dropped off line in the left wing, Cain immediately thought of the debris impact.

"I was intimately aware of the debris on ascent and the subsequent analysis and the disposition of all that through our normal process during the mission," Cain said. "I was very aware of that as was everyone else. And when the MMACS (mechanical systems officer) in realtime during entry called me and told me he had these four measurements on the left wing, that's the first thing that entered my mind. But it was momentary."

Maintaining a strictly business approach, Cain and the entry flight control team simply worked through their normal procedures as the descent continued. But as more telemetry failures were noticed and Houston lost contact with Columbia, it began to sink in that something was terribly wrong.

"At one point, I and other people in the room, obviously, knew that we were in a very dire situation," Cain said. "But rather than dwell on that, our training kicked in and we immediately went into action and did the things that we needed (to do).

"Backing up from that, there were several minutes of time after we lost the signal and before we had any kind of confirmation the vehicle had broken up where we marched through our normal procedures for trying to regain communications. We went through and did the things we would normally do as a team. I was not convinced it was anything more than a short-duration loss of comm, which is not uncommon for entry. We were coming up on the time period where I was expecting us to have a short outage, because we changed satellite antenna selections. We didn't expect it to be that long.

"I had brief moments in that timeframe of concern," Cain said. "But like I said, we didn't dwell on those moments. In the training, you go on and do the next step, whatever it might be, what time it is on the clock and how close I am to where touchdown is and whether or not I should have C-band tracking and where the UHF site is. And so we went through our normal procedures because we, in fact, didn't have the information to verify the vehicle was no longer with us. We did eventually, and we activated contingency procedures."

Cain said it was not until he went home late that night that the full impact sank in.

"This was a crew I was particularly close to and it was a crew that was very easy to fall in love with in my opinion," he said. "And that was my experience. We were very close, our children go to school together, it's a very intimate situation. But we are professionals and the Columbia crew, I believe they would be proud of our behavior in the last several days."

The chairman of the independent Columbia Accident Investigation Board - AIB - said today the root cause of the Feb. 1 shuttle disaster may never be known, but he vowed to leave no stone unturned in a herculean effort to nail down exactly what triggered NASA's second shuttle disaster.

Speaking at the board's first news conference, retired Navy Adm. Harold Gehman said his panel, including some of the nation's leading accident investigation experts, will conduct a fully independent probe beyond any possible influence from NASA.

It is an "extraordinarily rich and deep board in accident investigations and aircraft matters," Gehman said of his colleagues. "Among them they have been either the chief investigator or an investigator on essentially every major aircraft mishap in the United States probably for the last couple of years. Each of them is qualified to be the chairman of this board.

"They are probably the most senior and the most talented aviation mishap individuals in the United States of America. They got that way because of years and years of hard work, independence and integrity and I can assure you nobody is going to put that reputation on the line and allow themselves to be influenced by any outside influences."

In the end, he said, "there is only one investigation going on. And it is our investigation."

He said the AIB will continue NASA's policy of openness, saying raw data, debris reports, imagery and other bits of evidence and data pertinent to the investigation will be released as it is collected and reviewed. At the same time, data and other impounded items will be released to the public as soon as the board determines nothing will be lost to the investigation.

In one of the board's first acts along those lines, the mission control audio tape recorded the morning of Columbia's re-entry was released today, providing a compelling glimpse into how the flight control team struggled to make sense of the sensor failures and unexpected readings that preceded the shuttle's breakup.

Gehman also said the AIB is establishing its own data and analysis review committee to double check any technical conclusions reached by NASA to independently verify their accuracy.

"It's not that we don't believe the NASA data, it's just that in order that the report be truly independent and that the conclusions be based on good solid analytical work, both inside NASA and outside NASA, this team will advise us on when we come across one of those junctures in the road," Gehman said. "They will also write the statement of work, they will also liaison with whatever laboratory or university that's doing the independent analysis."

The board's charter gives the team 60 days to reach a conclusion. But Gehman said that is more of a guideline than a firm deadline.

"We are driven by two imperatives," he said. "The first imperative is to get it right for a number of reasons, including the safety of follow-on shuttle crews, not to mention the continuation of the program. That imperative drives us to take our time and be very meticulous.

"We have another imperative, which is the welfare of the three astronauts who are on orbit right now who depend on the shuttle system, at least for their transportation if not for their supplies. In that sense, we have an imperative to move along as rapidly as we can."

Gehman said that as of today, no confirmed shuttle debris has been found west of Fort Worth. But numerous witnesses reported seeing what looked like debris falling away from Columbia as it streaked across California and Nevada on its way toward Texas.

"We have reason to believe, we don't have proof, but we have reason to believe we should keep looking west of Fort Worth," Gehman said. "The difficulty is as we reconstruct this accident in greater detail, the more data, the more pictures we get, the more videos we get, the more we examine the engineering data, the more we realize when this incident started. If there are credible possibilities west of Fort Worth, we're going to energetically pursue them because it's possible there's something out there."

But, he added, "there's a lot of empty space west of Fort Worth."

"And what NASA has been attempting to do since day one is to be more predictive as to where we should look for the debris," Gehman said. "We're trying to find radar tapes from Nellis Air Force Base, we're looking every place to see whether or not any unusual radar returns (are available). We're calling in many outside NASA and we have outside people now to look at the predictive analysis of where the debris might have landed."

So far, Gehman said, more than 1,600 pieces of shuttle debris have been identified. The first truckload of debris is now en route to the Kennedy Space Center where technicians will partially reconstruct the spacecraft in a large hangar near the shuttle runway. Gehman said part of the ship's left wing has been identified, but reports yesterday that one of Columbia's five general purpose computers had been located were incorrect. Instead, searchers found the electronics box used by the shuttle's KU-band television antenna system.

While vowing to conduct an open, independent investigation, Gehman said the goal was simply to find out what went wrong and that his team has no interest in placing blame.

"We aren't out to find any guilty people or any negligence or culpability," he said. "But if you have a secretary and a potted plant outside your office, then you're fair game."

Asked if he is confident about finding a single root cause of the Columbia disaster, Gehman deferred to two of his board members.

Maj. Gen. Kenneth W. Hess, Air Force chief of safety and commander of the Air Force Safety Center at Kirtland Air Force Base, N.M.,. said in many cases accident investigators can only point out "what we most likely think may have happened. But you can never prove it with all certainty."

"And so we'll likely get ourselves into probable causes in any number of areas here in this particular mishap," he said. "Our charter is to try to find the cause and to the extent we can drill down and ask enough questions of why, we're going to attempt to do that. But it is a probable outcome that we may not find the exact cause of this mishap. But we will have to let the information speak for itself in the course of the investigation."

Rear Adm. Stephen A. Turcotte, commander of the Naval Safety Center in Norfolk, Va., said "if we do get to the point where we have not exactly found the mishap, we will have covered everything else, we will have looked at those positives, was it this, was it that ... so we'll have narrowed the focus.

"Looking at the complexity of this, it is huge," he said. "It is one of the biggest debris fields I think any of us have ever seen. The complexity of the science and technology that goes into it, it is huge. We're going to look at everything and we're going to narrow it down to the most probable cause, if not the cause."

The AIB members spent the morning flying re-entries in NASA's shuttle simulators at the Johnson Space Center. They are flying to the Kennedy Space Center Wednesday for two days of familiarization and tours before heading on to the Marshall Space Flight Center in Huntsville, Ala. They plan to return to Houston next week.

Meanwhile, a joint congressional hearing is planned Wednesday beginning at 9:30 a.m. in the Russell Caucus Room of the Russell Senate Office Building. NASA Administrator Sean O'Keefe and William Readdy, associate administrator of space flight, are scheduled to testify.

The joint hearing, chaired by Sen. John McCain and Rep. Sherwood Boehlert, will be carried live on NASA television.

On Saturday morning, Feb. 1, the three-man crew of the international space station was working through its 70th day in orbit, preparing for a daily planning session with flight controllers in Houston and Moscow. There were no technical problems of any great significance and the crew expected a routine update on the shuttle Columbia's re-entry and landing at the Kennedy Space Center to close out a 16-day science mission.

It was not the update they expected. Instead of having a routine chat with the astronaut "CAPCOM" in mission control, Johnson Space Center Director Jefferson Howell, a retired Marine Corps general, came on the line.

"We were scheduled for a normal planning meeting on Saturday," Expedition 6 commander Kenneth Bowersox said today. "And Gen. Howell, the director of the Johnson Space Center, came in and told us we lost the vehicle on entry.

"My first reaction was sheer shock, I was numb and it was hard to believe that what we were experiencing was really happening. And then as the reality wore on, we were able to feel some sadness. It's the classic grieving responses our psychologists had warned us about, you feel sad, you feel angry, all those things. And now, as time goes on, we're able to put those aside and focus a lot better on our work."

Said science officer Donald Pettit: "When I first heard, at that point it was not known what the condition the crew were in and so we were hoping that there were going to be survivors. And then as it unwound, we learned there were no survivors and that's when the magnitude of that really hit me."

Thinking about it later, he said, the disaster re-emphasized the risks of spaceflight.

"For myself, I had always imagined the launch phase to be the dangerous part with the pucker power to it," he said. "And now it's maybe (remember) that all that energy that those big boosters put into you on launch has to be taken out by the atmosphere when you re-enter. And that's a lot of energy, as we are so patently aware of now. It just made these things a little clearer in my mind in terms of where the risks really are."

Bowersox, Pettit and Russian cosmonaut Nikolai Budarin, the station's flight engineer, were launched Nov. 23, 2002. Today is their 80th day in space, their 78th aboard the station.

"The folks on the ground have been real good about reducing our schedule and we've had time to grieve our friends," Bowersox said of Columbia's fallen crew. "And that was very important. When you're up here this long, you can't just bottle up your emotions and focus all the time.

"It's important for us to acknowledge that the people on STS-107 were our friends, that we had a connection with them and that we feel their loss. And each of us had a chance to shed some tears. But now, it's time to move forward and we're doing that slowly. This press conference today is a huge step towards helping us move along toward our normal objectives and fulfilling our mission here."

Pettit said grieving "is sort of a personal thing and myself, I like the privacy to grieve in the quiet surroundings we have here on space station."

Three days after Columbia broke apart in the sky above Texas, President Bush attended a memorial service at the Johnson Space Center. Bowersox, Pettit and Budarin listened in via radio, sharing the moment with friends, family and co-workers on the ground.

"At the conclusion of that memorial service, after the bells had wrung on the ground and the T-38s had flown by and it was very quiet on board, we rang our ship bell seven times," Bowersox reflected. "And at that point, it was very, very quiet on board the international space station. We spent 15, 20 minutes in silence and then we moved on, we had work to do, we had to unload our Progress (supply ship). At that point, we started thinking about good things, we pulled out the fresh fruit, the oranges, the mail we got from home and it gave us quite a lift after the memorial service."

Bowersox and his two crewmates are the sixth full-time crew to live aboard the international space station. As of today, the outpost has been continuously manned for 832 days.

The Expedition 6 crew originally planned to return to Earth aboard the shuttle Atlantis in March, but with the shuttle fleet grounded indefinitely, it now appears they will return in May aboard the station's Soyuz lifeboat.

A three-seat Soyuz is always attached to the station to provide a way home for the lab's permanent crew in case of an emergency. The lifeboats are certified for six months in space and so-called "taxi" crews periodically ferry up fresh spacecraft and ride the old ones back to Earth. The next taxi flight is scheduled for launch April 26.

Sources say Bowersox and company will almost certainly return to Earth aboard the lab's current Soyuz. Current plans call for the taxi crew to remain aboard the station as a sort of caretaker crew until shuttle flights resume or until the next taxi mission in October.

While a Soyuz can launch with three crew members, only two are expected to launch in April. That's because the station's water supplies - normally topped off during shuttle visits - cannot support three people for a long-duration stay.

For their part, Bowersox, Budarin and Pettit have told U.S. and Russian station managers that they would be happy to stay aloft an additional six months or even longer.

"We are enjoying our mission up here, we enjoy the environment on the space station and we're going to enjoy the next two and a half, three months here," Bowersox said. "So the extra stay is not something that we consider a negative.

"In fact, for us it's positive. We actually volunteered to stay longer. We told our management if they needed us to stay a year, that's fine, they've got blanket approval for that. If they want us to go longer than a year, please give us a couple of months notice. So we like living on space station. And we feel comfortable that we have a way home, we have complete confidence in our Soyuz vehicle and the ability of our Russian partners to operate that vehicle and get us home safely."

He said the crew trained in Soyuz systems before launch, but "because it's been a few months since we've been in a simulator, we'll do additional training here on board if it should be required for us to come home in the Soyuz."

As for what a two-person crew could do aboard the station, Pettit said they would be "real busy just maintaining the systems on space station.

"However, there would be time to do some level of research and by virtue of having people here, you're always doing research on your body itself, looking at the effects of long duration weightlessness on human physiology. So it's important to keep people on station."

But for Bowersox, there's another, equally compelling reason to keep the complex staffed.

"The reason I came here to space is because I believe exploring is important, that we're laying a foundation for our children and their children to leave the planet someday," he said. "Part of that legacy we're going to leave them is a continuous human presence here (in space) that started back in the Mir program. And we would like to see that.

"But that's as much emotional as logical. If we were to have to de-man the station, it would not be a huge setback for our program, the station will keep flying and we'll be able to send people back here if we need to. But on an emotional level, I really want to see people stay."

But it won't be easy. Bowersox said a two-person crew would have a different social dynamic than the current three-person teams.

"Having two people on station would change things quite a bit, it would change the dynamic of how you support each other emotionally," he said. "It's really nice where if two people are getting a little bit irritated, one of them can go and talk to the third or the third can act as a referee. It's sort of like with our international partnership. The more people, the more partners you have, the more work is required to maintain that partnership but the stronger you are because you have more bodies, more hands to get things done."

The April Soyuz mission will include a Russian commander. European Space Agency astronaut Pedro Duque is currently assigned to the flight, but he is expected to be replaced by an American astronaut who has the training necessary to maintain U.S. systems. Sources say NASA already has a short list of candidates for the mission, but discussions with all of the station's international partners are not yet concluded and details remain to be worked out.

In the meantime, the ISS-6 crew will conserve their supplies while they wait for an official decision. Bowersox amused reporters with a discussion of what he's doing to help.

"One of the easiest things to conserve is clothing," he said. "Up here, we've got the perfect air temperature all the time and a good humidity level, so we really don't get our clothing sweaty. The only articles of clothing that do get that way are the ones we use on the exercise equipment.

"One of my personal sacrifices is I've been wearing the same pair of shorts for the past two-and-a-half months. They're very special shorts, I wore them up on the space shuttle, we call them our 'Dittemore shorts' because (shuttle program manager) Ron Dittemore is credited for getting us a bunch of those in the space shuttle program. And I like them so well, I just can't give them up and now they're sort of my lucky shorts. I'm going to try to keep them going until they've got holes in the bottom."

NASA engineers confirmed the recovery of debris from the shuttle Columbia's left wing today amid reports one of the orbiter's four general purpose flight computers - or some sort of avionics box - might have been located.

NASA Administrator Sean O'Keefe said some 12,000 pieces of shuttle debris have now been recovered and that the first trucks carrying the spacecraft's remains should begin arriving at the Kennedy Space Center this Wednesday for reconstruction by accident investigators.

In the meantime, O'Keefe said, "there is no favorite theory" about what triggered Columbia's catastrophic breakup Feb. 1 as it flew across Texas on the way to a landing at the Kennedy Space Center.

"There is no preferred or optimal or more probable consequence or cause that we see," he said. "Everything is on the table."

The independent Columbia Accident Investigation Board, chaired by retired Navy Adm. Harold W. Gehman Jr., will hold its first news conference at 3 p.m. Tuesday. O'Keefe said the AIB will now take over day-to-day operation of the investigation as NASA assumes a support role.

"It's become a very methodical, very structured process to assure we aren't defaulting in the direction of one favored approach or one favored theory or one more today's vox populi theory versus another so that we're not then in turn seeing a trail that could have been pursued then start to grow a little cold as we work through it," O'Keefe said.

Michael Kostelnik, who oversees shuttle and space station operations at NASA headquarters in Washington, said search teams had confirmed recovery of a portion of Columbia's left wing, but it was not found just west of Fort Worth as originally stated. Instead, it was found about halfway between Fort Worth and Lufkin, Texas.

"They have at least one piece of the left wing," Kostelnik said. "Clearly, you have to understand when you go out in the field and look at this material, our own experts are having a difficult time determining what some of these objects are. We're not just finding them, we're cataloging them and bagging them to get them back to the reconstruction site (at Kennedy) just as quickly as we can."

So far, he said, no confirmed shuttle debris has been found west of Fort Worth.

Late today, NASA officials said search crews might have located one of the shuttle's four general purpose flight computers. Later still, however, they said they were not sure what had been recovered. Engineers are eager to recover any debris that might include intact computer memory, drives or tape, which might hold data that could shed light on what went wrong during Columbia's re-entry.

On another front, Kostelnik said photo analysts are attempting to enhance long-range imagery of the shuttle in hopes of more clearly showing what sort of damage the left wing might have suffered during re-entry. A low-resolution image of the shuttle released Friday clearly showed something amiss near the leading edge of the left wing, but NASA officials have said they do not yet have a sharper image in hand. Media reports today indicated such imagery does, in fact, exist.

"We have a couple of photo images that we're putting into small study groups to get the right kind of people looking to see what these things could be," Kostelnik said.

In addition, Air Force personnel are reviewing radar data indicating something might have broken away from the shuttle the day after launch. The object was discovered after radar operators, acting on a multi-agency request from NASA, reviewed stored data.

"This was a request to go back and run the tapes and see if any anomalies were observed," Kostelnik said. "In this instance, this piece of space debris, a characterization which has been accurately reported in the media, was found on the tape by the Air Force.

"They are continuing in the process now of trying to confirm their calculations that based on where it was when they found it, (where) based on orbital mechanics it would have backed up to be on the second day of the orbiter's mission in the general vicinity of the orbiter, so much that it could have been something associated with the orbiter. The Air Force is going back to reconfirm their calculations."

At the same time, NASA and Boeing engineers are reviewing telemetry from the shuttle "to take a look at everything we knew about that, was there anything that the crew noticed, were their any measurements on the shuttle that would have detected some impact or some movement. We're going into an incredible amount of detail with everything we know about that time period to have some sense of what it could be."

The radar data indicates an object suddenly moving away from Columbia at about 11 mph, raising the prospect of impact by high-velocity space debris that might have knocked off a piece of the shuttle. At this point, however, it's not known what might explain the observation.

Mike Mott, Boeing vice president and general manager for NASA systems, said more than 1,000 company employees are working on the shuttle recovery operation with clearance from senior management "to bring in whatever expertise we need."

"We've brought in some folks from commercial aircraft early who are experts in accident investigations and they understand about debris recovery and reconstruction of debris," he said in an interview. "I think they've been really key players in helping NASA.

"We've brought in some thermal experts, we've brought in some photo enhancement expertise and all sorts of things in aerodynamic modeling. We've got folks out in the field helping in debris recovery and obviously continuing all our normal, technical and engineering and analytical work here just trying to help in any way we can."

A timeline of events that occurred between the shuttle Columbia's atmospheric entry Feb. 1 and the ship's destruction above Texas is now available, merging telemetry from the shuttle with commentary on NASA-Select television. This is a strictly preliminary timeline and it does not yet contain the flight director's audio loop. In addition, the telemetry timing is preliminary and subject to some uncertainty, according to shuttle program manager Ronald Dittemore. The STS-107 entry timeline (rev. A) will be updated as more accurate information becomes available.

A military radar system shows indications that an object might have separated from the shuttle Columbia in orbit, prompting a review of telemetry by NASA flight controllers to look for signs of anything - including impact by high-velocity space debris - that might have contributed to the shuttle's breakup Feb. 1 during re-entry.

NASA sources said the radar data apparently shows a small object suddenly separating from the shuttle at about five meters per second, or roughly 11.2 mph, on Jan. 17, about 24 hours after Columbia's launch from the Kennedy Space Center.

NASA officials late Saturday confirmed shuttle engineers are reviewing telemetry from the ship to determine if any sort of propulsive or other event might have happened that could explain such radar observations.

Shuttle crews routinely dump waste water overboard, which instantly turns into a rapidly expanding cloud of ice crystals. It's not yet known whether a routine water dump could have resulted in the observed radar "signature."

Occasionally, large plugs of ice develop on the water dump nozzles. Whether such an ice plug might have been blown off during an otherwise routine water dump - showing up on radar as an object moving away from the orbiter - is not yet known.

It's also possible some piece of non-critical hardware was somehow released or ejected from the shuttle without the crew's knowledge, something that would not have played a role in Columbia's re-entry breakup Feb. 1 over Texas.

Columbia was destroyed 16 minutes from landing when it veered out of control. Telemetry from the shuttle shows elevated temperatures in a landing gear wheel well and along the left side of the fuselage during the final eight minutes of flight.

Telemetry also shows an unusual aerodynamic drag on the left wing, which tended to force the ship to pull to the left. Columbia's flight control system attempt to correct for this drag by adjusting the craft's trim. Moments later, contact was lost.

What might have caused problems for the left wing is not yet known.

During launch Jan. 16, foam debris from the shuttle's external tank hit the underside of the wing and outside analysts have speculated that impact might have weakened the shuttle's thermal protection system tiles enough to trigger the catastrophe during re-entry.

But it's also possible impact by space debris could have damaged the heat shield tile or the carbon-carbon panels protecting the leading edge of the wing by knocking a piece off the shuttle. While a tile would be visible to a powerful radar, NASA engineers have not yet confirmed such an impact took place. Agency officials stress they are investigating those possibilities and many others.

In east Texas, meanwhile, large section of the shuttle Columbia's lower fuselage - possibly part of its rear body flap or a piece of a landing gear door - was recovered today near Nacogdoches. But NASA engineers have not yet determined whether debris found earlier near Fort Worth is part of the ship's left or right wing.

The debris found near Nacogdoches appears to have curved hinge components on each side, indicating it was moveable hardware. Heavily damaged black heat shield tiles on the debris show it came from the bottom of the spacecraft.

The only large hinged panels on the shuttle's fuselage are the nose and main landing gear doors, the external tank umbilical attachment covers and a large "body flap" at the rear of the shuttle that shields the main engines from heat during re-entry.

The debris found today appeared to be part of the body flap, but television views were not conclusive. While its shape was roughly correct, it was smaller than a complete body flap, indicating a large piece is still missing.

NASA officials, meanwhile, said work continues to establish a reliable timeline showing when various sensors failed during re-entry or detected higher-than-normal temperatures on the left side of the shuttle. The timeline is not yet complete, but officials hope to finalize the details over the next few days.

NASA officials also dismissed media reports earlier today that raised the possibility precautions could have been taken before Columbia's return to Earth that might have helped minimize left-wing heating during re-entry.

During a flight in 2000, engineers studying launch video were concerned a six-inch piece of ice falling away from the ship's external fuel tank might have hit and damaged protective tiles on one of the wings. Playing it safe, flight controllers re-oriented the shuttle just before re-entry, "shadowing" the area in question to help lower its temperature. The idea was to slow the onset of entry heating.

In Columbia's case, officials said today, the shuttle's orientation, or attitude, during the mission resulted in lower-than-normal temperatures across the lower fuselage. As a result, Columbia was re-oriented to warm the belly slightly, part of a routine procedure to properly control main landing gear tire pressure.

NASA spokesman Kyle Herring said the re-entry flight profile was normal and dismissed speculation flight controllers could have re-oriented the shuttle during its descent through the atmosphere to ease the effects of heating.

"There is no protected, secret attitude we can fly," he said. "We already fly the most benign entry possible."

Flight director Ron Dittemore said much the same thing last week, point out that any attempt to favor one wing would subject the other wing to extreme, inherently hazardous conditions.

The families of NASA's astronaut corps at the Johnson Space Center in Houston released an open letter to the nation Saturday, thanking supporters for their sympathy and encouragement in the wake of the Columbia disaster one week ago today.

"We, the spouses and children of the NASA astronaut corps, would like to thank the people of the world from the bottom of our hearts for the incredible outpouring of support and love that you have shown us in our time of deep grief.

"NASA centers have been overwhelmed with cards, letters, emails, and phone calls from you expressing your concern and support. We have also received hundreds of personal calls, emails, flowers, food, and cards at our homes. The makeshift shrine in front of the Johnson Space Center is overflowing with flowers, signs, and balloons from well wishers from all over the world. Memorial services throughout the world have honored our dear friends. You, our brothers and sisters of the world community, have been a tremendous source of comfort and love to us and we are so grateful. We are deeply mourning our dear friends Rick, Willie, Mike, Kalpana, Ilan, Laurel, and Dave and we ask that you continue to keep their parents, wives, husbands, and children in your thoughts and prayers.

"We would also like the world community to know that as terrible and as difficult as this journey has been and will continue to be for all of our families, we cannot stress enough how blessed and honored we feel to be counted as members of the NASA family. We proudly support the noble goals and objectives of NASA and we will continue to support NASA in its finest and its darkest hours. It is our deepest hope that you also will continue to share in our belief and support of NASA's dreams. We believe NASA is a beacon of hope and light to all nations, for NASA has proven beyond the shadow of a doubt, that peoples from all races, genders, cultures, religions, and political backgrounds can transcend those differences and become the closest of friends. And these friends will continue to pursue space exploration and scientific discovery for the single purpose of helping and furthering all of mankind. Thank you for your love and support."

The letter was signed by "The husbands, wives, and children of the NASA Astronaut Corps."

After a day of media speculation about Air Force imagery reportedly showing clear evidence of structural damage at or near the leading edge of the shuttle Columbia's left wing, NASA released a single blurry frame late today that raised more questions than it answered.

While the picture appears to show a subtle asymmetry in the shape of the left wing's leading edge, along with a plume of some sort trailing behind the orbiter, it did not provide any clear evidence of exactly what type of damage the wing suffered during the shuttle's final minutes.

It is possible that specialists can glean valuable insights by enhancing or manipulating the image in some fashion, but nothing obvious jumped out at reporters attending shuttle program manager Ronald Dittemore's final daily news conference. In fact, it was a bit anticlimactic.

"We continue to look at photographic evidence," Dittemore said. "It is challenging and difficult and proceeding slowly. We did receive a photo from the Air Force Optical Range at Kirtland Air Force Base in New Mexico. I'm aware there may be some of you who are saying this photo is revealing. We have looked at it, we had it during the week, and it's not tremendously revealing to us yet. I'm not an expert at looking at these types of photos and so we're asking experts to do an evaluation of the photo ... to help us understand if there's anything wrong with the left wing.

"It looks a little more distorted on this large screen than it is in the actual photograph. But the nature of the photograph, because of its resolution, has a little choppiness to the wing leading edge. Some people are looking at this area in the bottom area of the photograph, which would be the wing leading edge, and they're trying to draw some conclusions from that area. It's not clear to me there's something there yet."

Dittemore did not say if additional Air Force imagery is in hand or whether any other high resolution pictures showing Columbia's left wing are currently in NASA's possession. Aviation Week & Space Technology, a respected aerospace magazine, reported such imagery was, in fact, under study by NASA. But there was no way to know whether the photo shown today was the one referred to in Aviation Week or whether it was a representative frame from a series of images or whether it was something else entirely.

In any case, Dittemore said search crews have now identified wing debris near Fort Worth, but it's not yet known which wing the debris came from. Engineers hope to recover fragments from the left wing, which might hold clues about exactly what happened during the shuttle's final minutes. Dittemore said he hoped to have a positive identification in the next few days.

He also presented a detailed series of charts showing sensors in the shuttle's left wing that either failed during Columbia's final eight minutes of flight or recorded abnormal pressure or temperature readings.

He did not interpret the data, but from the still-uncertain timing of the failures and the progression of abnormal readings, one could make a case that some sort of destructive event must have occurred near the left-side main landing gear wheel well. Wiring to failing sensors mounted in the rear section of the wing ran near the wheel well and because the sensors they ran to dropped off line first, it's possible whatever was going on in the wing occurred at or near the cable harnesses and not inside the wheel well itself.

But sensors in the wheel well also dropped off line or recorded unusually high temperatures as the minutes raced by, indicating heat from whatever first affected the cable harnesses was making itself felt in the surrounding structure. But that's pure speculation at this point and it doesn't explain high temperature readings from a sensor mounted on the side of Columbia's left fuselage above the wing.

Dittemore said today's briefing was his final regularly planned appearance before the media. The independent Columbia Accident Investigation Board - AIB - is taking over the mantle of authority for probing the shuttle disaster and Dittemore and his team will assume more of a support role in the days and weeks ahead.

The AIB, in turn, is expected to control the flow of information about the progress of the investigation and to hold its own news briefings as events might warrant. Officials say one to two briefings a week might eventually be staged, but details remain to be worked out.

There will be no briefings over the weekend. A NASA headquarters update will be carried on NASA television Monday morning, followed by a news conference with the international space station's three man crew Tuesday. Later in the day, the AIB will hold its first formal news conference at the Johnson Space Center in Houston.

One can only hope the AIB will be as forthcoming and straight-forward with the public as Dittemore, whose reputation and credibility survived an enormously difficult week wholly intact.

A large section of one of the shuttle Columbia's wings has been found near Fort Worth, a NASA official said today, but it's not yet clear whether it's the right wing of the left, the one that suffered a catastrophic structural problem during the ship's re-entry Saturday.

Michael Kostelnik, a senior NASA administrator in Washington, said the debris marked a "significant recovery," describing it as a "piece of the leading edge of the reinforced carbon carbon composite."

The leading edge of the left wing is the subject of an article in Aviation Week & Space Technology's Feb. 10 issue. The story quotes sources saying Air Force tracking cameras were able to detect major structural problems with the leading edge of Columbia's left wing one minute before the ship broke up. The appearance of the carbon carbon panels making up the left wing's leading edge was described as "jagged."

Any degradation at the protective leading edge panels, designed to reject the fierce heat of re-entry, likely would set up a fatal chain of events, leading to further structural damage and increasing aerodynamic drag.

Telemetry from the shuttle is consistent with this scenario, reflecting temperature-related sensor failures in the left wing's main landing gear wheel well, elevated temperatures along the left side of the fuselage above the wing and increasing aerodynamic drag that pulled the shuttle's nose to the left. It appears that drag ultimately exceeded the flight control system's ability to counteract, leading to the structural breakup of the vehicle.

"We do have a large piece of one of the wings," said Kostelnik. "It is not clear which wing this is, but obviously given the anomalies we have on the descent coming through the left wing, obviously this structure is very important."

As for the Air Force imagery, Kostelnik said "it is a long range optical photo taken by an Air Force laboratory and this optical photo, which is very poor resolution, you could draw a lot of (conclusions), but this photo was taken during the descent in between the start of these anomalies on the California coast and before the termination.

"So I can't really make a judgment on what the image actually shows. ... Clearly, this is the type of information the (independent investigation) board will make these judgments on and what it means. But it is during the time period when we're getting these anomalies on the ground. So whatever is happening, it's probably consistent with what that photo shows."

Kostelnik said he was not aware of any high-resolution military imagery of Columbia's left wing.

The Air Force told CBS News imagery from Kirtland Air Force Base in New Mexico was turned over to NASA for analysis. Kirtland operates powerful telescopes in Hawaii and the continental United States, including the Starfire Optical Range in New Mexico that would have been well-positioned to follow Columbia's fiery plunge through the atmosphere.

The Starfire facility includes several sophisticated telescopes, including a 1.5-meter instrument and a large 3.5-meter telescope. Whether one of these instruments produced the high-resolution imagery noted by Aviation Week is not yet known.

Otherwise, Kostelnik said debris recovery is continuing at full throttle as NASA's internal investigation makes the transition from leading the probe to serving the independent Columbia Accident Investigation Board in a support capacity.

As of this writing, no confirmed shuttle debris has been found west of Fort Worth. Debris recovered in California may or may not be shuttle related and is currently under analysis.

Kostelnik said nearly 1,500 men and women from a wide variety of agencies are participating in the search. About 220 NASA personnel are involved, some 800 National Guard troops in Texas and Louisiana, about 400 state troopers, 25 horse-mounted officers, dive teams, dog teams and 36 game wardens.

The Air Force confirms that pictures of the shuttle Columbia during its fiery plunge to Earth last Saturday, presumably shot through powerful military telescopes, has been turned over to NASA for use in the agency's on-going accident investiagation.

Air Force officials contacted by CBS News would not discuss the content of imagery except to say it was collected by operators at Kirtland Air Force Base, N.M. Kirtland operates powerful telescopes in Hawaii and New Mexico.

Aviation Week & Space Technology magazine reports in its Feb. 10 edition that a high-resolution military telescope in the southwestern United States took pictures of Columbia roughly one minute before contact was lost.

According to the magazine, the pictures show significant damage to the leading edge of Columbia's left wing. See the 1 a.m. update below for complete details.

Former astronaut Robert Crippen, pilot of the shuttle Columbia for its maiden voyage in 1981, remembered NASA's oldest orbiter today in a moving tribute before a throng of workers gathered on the broad shuttle runway at the Kennedy Space Center.

It was at that same runway that technicians, engineers, family members and journalists gathered last Saturday to welcome Columbia and its seven-member crew back to Earth after a successful 16-day science mission. But they waited in vain. Columbia was destroyed just 16 minutes before its anticipated arrival when it veered out of control in the thin air 200,000 feet above Texas.

Crippen, who helped oversee NASA's initial response to the 1986 Challenger disaster, first flew in space aboard Columbia on April 12, 1981, when he and commander John Young rocketed away from pad 39A. More than two decades later, he delivered Columbia's eulogy, struggling to keep his emotions in check as he remembered the shuttle and its fallen crew.

"We're gathered here this morning to honor and salute the Columbia crew and mission STS-107," he said. "The grief in the hearts of the crew's families and the entire NASA family, which includes all of our contractor community which supports the agency, is very heavy. Still, this crew lived lives that deserve our celebration. Yes, they were cut short. But these brave men and women lived their lives to the fullest doing much more in their time here on Earth than many can imagine.

"Words at a time like this seem weak. They don't fully communicate the depth of our feelings. The NASA family speaks much clearer with actions. The action that is being taken to find the cause of the accident, correct it and continue the crew's journey of discovery in space is the grandest tribute that we can pay to them. I'm certain that is what they would have wanted.

"It is fitting we are gathered here on the shuttle runway for this event," Crippen said. "It was here last Saturday that family and friends waited anxiously to celebrate with the crew their successful mission and safe return to Earth. It never happened. I'm sure that Columbia, which had traveled millions of miles and made that fiery re-entry 27 times before, struggled mightily in those last moments to bring her crew home safely once again. She wasn't successful.

"Columbia was a fine ship. She was named after Robert Gray's exploration ship, which sailed out of Boston Harbor in the 18th century. Columbia and the other orbiters were all named after great explorer ships, because that is their mission, to explore the unknown.

"Columbia was hardly a thing of beauty, except to those of us who loved and cared for her," Crippen said. "She was often bad mouthed for being a little heavy in the rear end. But many of us can relate to that. Many said she was old and past her prime. Still, she had only lived barely a quarter of her design life; in years, she was only 22. Columbia had a great many missions ahead of her. She along with the crew had her life snuffed out in her prime.

"I was here at the shuttle runway in March of 1978 when Columbia first arrived at the Kennedy Space Center. She came in on the back of a 747 escorted by Deke Slayton in a T-38. She certainly wasn't very pretty at that time. A large number of her tiles had not been installed and many that had were not adhering very well. KSC management made a fairly unpopular statement at the time, that it was going to take several years to get her ready to fly. They were right.

"Readied for launch by the loving care of the Kennedy team, the same care they've given to all 28 of her flights, she was finally ready to fly in April 1981. John Young and I were privileged to take her on that maiden flight. She performed magnificently, the world's greatest electric flying machine was what John described her as. Because she was a little heavy, she didn't get some of the more glamorous missions. But she was our leader in doing science on orbit. Just as she was doing with this crew in Spacehab on mission STS-107, microgravity scientific exploration was her bag. She carried Spacelab numerous times, studying materials processing, life sciences, all of which were focused on giving us a better life here on Earth.

"Columbia also helped us better understand about the heavens and understand the origins of the universe with several missions, including Astro, also deploying the most advanced X-ray observatory every built, the Chandra X-ray Telescope, and by her very recent Hubble Space Telescope servicing mission. Just as the crew has, Columbia has left us quite a legacy.

"There's heavy grief in our hearts, which will diminish in time, but it will never go away and we will never forget," Crippen said. "Hail Rick, Willie, KC, Mike, Laurel, Dave and Ilan. Hail Columbia."

Aviation Week & Space Technology magazine reports in its Feb. 10 edition that an Air Force tracking camera in the southwestern United States captured images of the shuttle Columbia one minute before it broke apart, clearly showing major structural damage to the leading edge of its left wing.

The imagery, if confirmed, could explain telemetry from the shuttle indicating high temperatures in the left wing's main landing gear wheel well and along the left side of the vehicle's fuselage above the wing.

Telemetry also shows that in the last minute of flight, just before Columbia broke apart Saturday more than 200,000 feet above Texas, the spacecraft suffered from aerodynamic drag on its left side that tended to pull the ship's nose to the left.

Columbia's flight control system tried to counteract that drag by adjusting roll trim with the shuttle's elevons. The drag eventually became strong enough for the flight computers to fire rocket thrusters to assist the elevons. Moments later, however, contact was lost as Columbia presumably slipped too far off track and began breaking up under excessive aerodynamic loads.

That much was already known. What might have caused the aerodynamic drag and the elevated temperatures has been a matter of speculation up to this point.

"According to sources close to the investigation, the images, under analysis at the Johnson Space Center in Houston, show a jagged edge on the left inboard wing structure near where the wing begins to intersect the fuselage," Aviation Week reports in its Feb. 10 edition.

"They also show the orbiter's right aft yaw thrusters firing, trying to correct the vehicle's attitude that was being adversely affected by the left wing damage. Columbia's fuselage and right wing appear normal. Unlike the damaged and jagged left wing section, the right wing appears smooth along its entire length. The imagery is consistent with telemetry.

"The ragged edge on the left leading edge indicates that either a small structural breach - such as a crack - occurred, allowing the 2,500F reentry heating to erode additional structure there, or that a small portion of the leading edge fell off at that location," Aviation Week reported.

"Either way, the damage affected the vehicle's flying qualities as well as allowed hot gases to flow into critical wing structure - a fatal combination."

A NASA spokesman reached at home early this morning said the agency had no immediate comment on any imagery under analysis as part of the Columbia accident investigation. He did not confirm or deny any such imagery is currently under analysis.

What might have caused the "jagged" appearance of the left-side leading edge is not yet known. Presumably a small breach in one of the 22 reusable carbon-carbon - RCC - panels on the front of the left wing allowed hot gas to reach the interior, setting up a fatal sequence of events. Several reporters and outside analysts have speculated that leading edge damage was the best explanation of the telemetry revealed to date.

The gray-colored U-shaped RCC panels are bolted to the front of each wing to protect the underlying structure from extreme atmospheric heating. The highest temperatures experienced during entry affect the shuttle's leading edges and the RCC nose cap.

It is possible foam debris that fell away from Columbia's external fuel tank 81 seconds after blastoff Jan. 16 weakened one of the RCC panels bolted to the left wing.

It is also possible a bit of space debris caused the damage, puncturing an RCC panel or other structure earlier in the mission. Other explanations are possible as well.

But in any case, a hot gas jet into the wing from a breach in the leading edge would explain the telemetry received before Columbia broke apart, raising temperatures in the left wheel well and along the upper fuselage depending on the location and severity of the breach.

Amid congressional concern about NASA's objectivity in the wake of the Columbia disaster Saturday, the quasi-independent Accident Investigation Board, beefed up with non-NASA staff and board members, will assume the mantle of sole authority in determining what caused the crash that claimed the lives of seven astronauts.

AIB board chairman Harold W. Gehman, Jr., a retired Navy admiral, flew to Houston Wednesday to set up a base of operations at the Johnson Space Center. NASA Administrator Sean O'Keefe said today language in the charter that set up the AIB will be modified immediately to guarantee the panel's complete independence from NASA.

"We want the facts and the evidence to speak to the conclusions, ultimately inform the conclusions in terms of what caused this horrific event," O'Keefe said. "And in doing so, we do not want to rule out any theory, any approach, any possible set of factors that could be, when combined, lead to some other judgment. That is a determination that the Columbia Accident Investigation Board will render.

"As a consequence there ... we have been advised by the board that certain clarifications of the charter to assure the board's independence be modified. Those modifications we have immediately agreed to. ... This is to absolutely guarantee that we've eliminated any ambiguity as to the independence of this board."

In the days following the accident, NASA own internal investigation has proceeded around the clock. Daily briefings by shuttle program manager Ronald Dittemore served to inform the press and public about the progress of the probe. In stark contrast to NASA's policy after the 1986 Challenger disaster, Dittemore provided details about telemetry from the shuttle and how the spacecraft behaved in its final minutes.

And therein was a potential problem.

On Sunday, Dittemore told reporters telemetry indicated elevated temperatures and sensor failures in the left wing of the orbiter followed by the development of unusual aerodynamic drag along the left side of the fuselage. The spacecraft eventually veered out of control and broke up, presumably due to aerodynamic stress. At issue is the root cause of the failure, i.e., what caused the observed temperature increases and the aerodynamic drag.

Launch video shows debris from the external tank striking the underside of the shuttle's left wing 81 seconds after liftoff Jan. 16. On Monday, Dittemore told reporters one team of engineers was assuming the debris was the root cause. This is standard practice in a fault-tree investigation.

"We have a team of engineers and managers and technicians that are ... making the assumption from the start that the external tank was the root cause of the problem that lost Columbia," he said at the time. "That's our starting point when we look at the tank. And based on that assumption, what is the fault tree that would substantiate that particular assumption? And so we're attacking that. And that's a fairly drastic assumption and it's sobering."

Other teams of engineers were considering other branches of the fault tree, assuming different types of failures in a bid to rule out false trails and to zero in on the actual problem. Again, all standard procedure. But many in the media reported that the debris impact on the tank was the leading suspect in the shuttle disaster. That is not what Dittemore meant, this writer believes, but that was the impression.

On Wednesday, after a memorial service Tuesday to honor Columbia's crew, Dittemore responded to the media accounts by saying he personally did not believe the tank foam could have caused enough damage to result in a loss of the vehicle. And he said, rather emphatically, that he did not believe ice on the tank was a contributing factor. The media then reported NASA had "backed off" the foam theory.

The back-and-forth coverage of the investigation may have ruffled feathers in Washington. In any case, it likely added to concern among lawmakers demanding a fully independent panel of investigators in the mold of the Rogers Commission that investigated the Challenger disaster.

"We would respectfully ask that the charter of the AIB be re-drafted to reflect a broad mandate encompassing contributory causes, management issues, and pressures on the system," Rep. Ralph M. Hall (D-TX), Rep. Bart Gordon (D-TN) and others wrote President Bush on Thursday. "In addition, we would recommend that, to ensure its complete independence, the AIB should report directly to you and to the Congress and that the support staff for the Board should come from agencies other than NASA."

O'Keefe said late this afternoon that Gehman and his panel would have complete independence. Apparently reflecting outside concern that a possible failure mode - debris from the tank - had been eliminated from consideration, O'Keefe said "we really want to be sure there is no ambiguity whatsoever and that we are not eliminating any set of possibilities of what could have contributed to this accident."

"The intention here very clearly is they (the AIB) will reach conclusions and the conclusions will come from them and only them," the administrator said. "We will not have competing positions on this. ... The board findings are what we will be guided by."

Dittemore then held his afternoon briefing as usual and said from a personal standpoint, "I'm very pleased to have Adm. Gehman here with his team and we offer our full support. Anything that Adm. Gehman needs, we will provide to him. And we pledge to him that we will continue to support him as we have done in the past. As we have prepared investigation plans and procedures, we will transition our thoughts and our plans over to the board and we'll follow his leadership."

Dittemore said so far, more than 1,000 pieces of shuttle debris have been recovered. But no confirmed shuttle debris has so far been identified west of Forth Worth, Texas. He said engineers are continuing to study telemetry from the shuttle and are continuing to develop the fault tree of possible causes.

"Let me emphasize again, we have not ruled out any possible cause," Dittemore said today. "And even though we scratch our heads from time to time and wonder if we're going down a right path, it's important to understand that the first step in any investigation is to develop a fault tree.

"And in the fault tree, you examine and identify every possible cause no matter how remote or no matter what you think about the possibility of that cause. And once you develop that tree, then you establish a process where you systematically close out each branch of the tree. So in the end, you have left no stone (unturned). You have looked at each branch, each possible block, each possible cause and satisfied yourself that you have done a thorough and complete job, independent of what you might think of the probabilities or possibilities.

"As I talked to you yesterday, I mentioned to you that we believe in some instances that it's hard for us to understand how a piece of foam that has flown off the tank could have been the root cause. But that is not stopping us from continuing to investigate that particular event as being a potential root cause. We are planning testing of foam impact on tiles. We're performing analyses. That's just an example, that even though we scratch our heads and don't quite understand how this could be a contributor, it still exists in the fault tree and we're going to pursue that branch of the fault tree until we close it as a possibility.

"We're still looking for that elusive missing link," he said. "And we're hopeful that as we examine our fault trees across the program and perform our testing and look at and examine the debris we have gathered that we will find the missing link. That may take some time to do. You can imagine if you look at the fault tree, it's going to have thousands of blocks to pursue, many different branches to follow. So systematically, the large team that we have gathered will go through each one of those branches and this activity again will be led by the accident investigation board and we will support that activity to the best of our abilities.

"Again, let me say it is with some relief that I welcome Adm. Gehman here," Dittemore said. "We need their expertise, we need their independent look at what we have been doing and we will work closely with him and his board."

Dittemore did not provide any new details today, but he said he hopes to present graphics Friday that will overlay Columbia's ground track across the southwestern United States with time-coded telemetry readings showing when data from the shuttle indicated problems.

He was asked today about amateur video shot in Reno and north of Flagstaff that show what appears to be debris breaking off the orbiter well before the shuttle's breakup over Texas.

"I have seen some of the video," Dittemore said. "It's interesting, but we haven't yet determined what's happening, obviously. As far as any possible pieces of the orbiter or tile falling off, it doesn't appear to show up on any of our data as affecting our flight control until later on in the time frame that we have discussed.

"In that (early) time frame as we look at the data, unless you had some pictures indicating an event was happening, you wouldn't be able to tell by looking at the system's performance or even the flight control handling qualities, it looks normal to us. And that's part of the mystery. If there is something that's shedding from the orbiter, we'll have to determine that to be the case because it doesn't show up in the data."

Asked about the morale of the NASA team in the wake of the disaster, Dittemore said "certainly, there has been trauma in our system. ... But I think the healing process has begun."

"I'm seeing a very professional manner in all of our teams, a resolve to get to the bottom of this, a determination to find a root cause and I know that to a person we will not rest until we have solved this problem, until we have put all the pieces together, until we find that missing link.

"And we will support the leadership of our investigation board to make sure this happen. These five days have been exhausting to the team. They have been difficult emotionally and physically. But we're going to carry on and we're going to continue our determination to find the root cause and do so as quickly and reasonably as we can."

A group of lawmakers has asked President Bush to name an independent board to investigate the Columbia disaster. An internal NASA investigation currently is underway, along with a parallel investigation by a board made up of non-NASA personnel invited to participiate by agency Administrator Sean O'Keefe. That panel is known as the Columbia Accident Investigation Board, or AIB.

Rep. Ralph M. Hall (D-TX), Rep. Bart Gordon (D-TN) and other lawmakers questioned the objectivity of the accident probe and in a letter to the president today, asked that a presidential commission be established because "all of the support personnel initially provided to the AIB are senior NASA officials."

"While we commend the openness with which NASA has shared information on the Columbia accident with the public and the Congress, we are concerned that the AIB has the appearance of a non-independent board controlled by NASA," Hall and Gordon wrote. "This is in contrast to President Reagan's establishment of the Rogers Commission, which provided for a truly independent, broad-ranging panel (to investigate the Challenger disaster).

"We would respectfully ask that the charter of the AIB be re-drafted to reflect a broad mandate encompassing contributory causes, management issues, and pressures on the system. In addition, we would recommend that, to ensure its complete independence, the AIB should report directly to you and to the Congress and that the support staff for the Board should come from agencies other than NASA.

"This is not meant in any way to demean the dedication and excellence of NASA's workforce, but to ensure, as President Reagan did 17 years ago, that the AIB would proceed in as unfettered and open a manner as possible. Finally we would suggest that the membership of the AIB be expanded in a manner similar to that of the Rogers Commission, and that Administrator O'Keefe solicit suggestions for new members from key Members of Congress. Mr. O'Keefe has already indicated a willingness to consider Congressional nominations."

International space station planners are debating the possibility of launching a two- or three-man caretaker crew in late April or early May aboard a Russian Soyuz spacecraft to replace the lab's current crew and to keep the outpost occupied until space shuttle flights resume.

The current station crew - Expedition 6 commander Kenneth Bowersox, flight engineer Nikolai Budarin and science officer Donald Pettit - originally planned to come home in March aboard the shuttle Atlantis after a 114-day stay in space.

But that was before the shuttle Columbia disintegrated in the sky above Texas last Saturday, indefinitely grounding the shuttle fleet.

The Russians already planned to launch a Soyuz "taxi" mission on April 26 to deliver a fresh lifeboat to the station. Soyuz capsules are delivered every six months by so-called taxi crews who then return to Earth in the lab's older Soyuz. The spacecraft are certified for six months in orbit and must be regularly replaced.

Russian commander Gennady Padalka and European Space Agency astronaut Pedro Duque - one of John Glenn's crew members on shuttle mission STS-95 - make up the currently assigned taxi crew. The third seat in the Soyuz is unoccupied.

The current Expedition 6 crew has enough on-board supplies to remain aloft until late June in a worst-case scenario.

But U.S. and Russian planners are studying a variety of options to keep the station manned with so-called "caretaker" crews until space shuttles can resume flights.

One leading option is to launch a replacement crew aboard the April taxi flight. Under that scenario, the ISS-6 crew would return to Earth in the lab's current Soyuz.

But several questions remain to be resolved. The ISS-6 astronauts trained on Soyuz systems before flight, but they never planned on returning to Earth aboard one. Additional training may be required.

Because of concern about how much drinking water will be available on the station - the shuttle is a primary source of fresh water - the size of the proposed caretaker crew could be limited to two. The commander must be a Russian cosmonaut familiar with Soyuz systems and an American astronaut presumably would be needed to operate and maintain systems in NASA's modules.

But if the station can support a three-member caretaker crew, the European Space Agency could see its first long-duration representative in orbit for an extended flight.

NASA originally planned to replace Bowersox and company with Expedition 7 commander Yuri Malenchenko, flight engineer Alexander Kaleri and science officer Edward Lu, a NASA astronaut.

But the ISS-7 crew is specially trained to carry out research operations and station assembly work. NASA does not want to waste that involved training on an expedition that is unlikely to see any additional construction.

Launch of Padalka and whoever might accompany him is targeted for April 26, but the flight could slip to as late as May 10 depending on crew training requirements. The next taxi mission after that is scheduled for October.

Shuttle program manager Ronald Dittemore told reporters today they were, in effect, mistaken if they assumed from previous briefings the Columbia disaster investigation was focused primarily on the possibility foam debris from the ship's external tank triggered the orbiter's destruction during entry Saturday.

While it's true at least one team of engineers was told to assume the debris was, in fact, responsible - by hitting fragile tile on the bottom of Columbia's left wing 81 seconds after launch - that scenario does not appear to be an especially plausible explanation.

Revisiting an engineering analysis that occurred during Columbia's flight, after film analysis prompted concern about the debris strike, Dittemore said engineers assumed A) the debris measured 16 by 20 by 6 inches; B) that it weighed 2.67 pounds; and C) that the air velocity between the shuttle and the tank was about 1,500 feet per second, or 1,023 mph.

In reality, he said, the relative air speed was about 750 feet per second, or about 511 mph. The assumed dimensions and weight were conservative estimates and the data was processed by modeling software that over-predicts tile impact damage. The result was a conclusion that the debris impact, while a possible source for wing damage due to entry heating loads, would not have led to a loss of the vehicle.

"So it's difficult for us to believe, as engineers, as management and as a team, that this particular piece of foam debris shedding from the tank represented a safety of flight issue," Dittemore said. "So we're looking somewhere else. Was there another event that escaped detection?

"As I mentioned before, we're trying to find the missing link and as you focus your attention on the debris, we're focusing our attention on what we didn't see. We believe there's something else. And that's why we're doing a fault tree analysis and that's why we're investigating every area. Right now, it just doesn't make sense to us that a piece of (foam) debris could be the root cause of the loss of Columbia and its crew. It's got to be another reason."

Because of recent media attention on the foam issue, Dittemore came to today's briefing with a large chunk of tank insulation. Contrary to recent speculation, he said, the foam is virtually waterproof. He said ice team inspections the day of launch found no signs of any ice buildups on the tank and that in his opinion, the foam did not end up with ice imbedded in it.

"It is very lightweight," Dittemore said. "So it's designed to be resilient and be an insulating material to keep the tank cold. It's designed to be on the tank also to keep the structure from getting too hot and it's also designed to make sure we reduce the aerodynamic loads and the flow stream around the tank.

"It's fragile, it's easy to break and it's easy to break up into particles. It's very lightweight. ... I don't think there is an embedded ice question here, I don't think this came off as a chunk of foam and solidified with ice. When it hits the wing, this piece of foam disintegrates. Although we're going to look, we did not have icing conditions that day. We didn't have the ice, it's impervious to water. So it's something else. It's something else."

It's not altogether clear whether he meant the foam could not have played a role in the disaster or that it could not have played a role without some other contributing factor.

In any case, enhanced frames from a tracking camera also were presented today, showing the underside of the left wing before and after the debris strike. While the resolution of the video is poor, there are no obvious signs of damage on the wing.

"As you can see it's not very good for any detailed analysis," Dittemore said. "But it does show, as you look at it both before and after impact, there really are no gross large areas of damage. We are attempting to try to improve the resolution of the launch video to see if we can get any better information. But from a gross sense, we didn't see anything that would cause us a concern."

In the meantime, the investigation is leaving no stone unturned in attempting to pin down what might have gone wrong.

The first telemetry from Columbia showing signs of trouble came roughly eight minutes before the craft broke apart high above Texas. The data show temperature build ups in the left landing gear wheel well and along the left side of the fuselage. An unusual aerodynamic drag developed on the left side of the spacecraft, forcing the ship's flight control system to send commands to elevons and thrusters to keep the nose pointed in the right direction. Eventually, the drag became too much to overcome and the vehicle slipped out of control at a velocity of 12,500 mph.

While it's not clear what caused the problem - tile failures, impact by space debris or a micrometeoroid, problems with the carbon-carbon panels on the leading edge of the wing - the result was increased temperatures on the left side of the vehicle and some sort of structural issue that led to an unusual - and steadily increasing - aerodynamic drag.

Engineering teams are using the telemetry to "reverse engineer" the problem, trying to figure out what sorts of failures could produce the observed high temperatures, elevon deflections, thruster firings and sensor failures observed in the final eight minutes of telemetry from Columbia. "I talked to you previously about the temperature rise and the loss of sensors along the left-hand wing," Dittemore said. "We are continuing to review that information and are backing out where we believe the heat source would need to be in order for us to have those indications present. So we are performing some reverse engineering, some reverse analysis to try to understand what would be the cause of such temperature rises in the wing.

"On the flight control side, we are doing a very similar reverse engineering task and we're modeling the aerosurface positions, we're backing out the drag and the loads that would be required to cause the aerosurfaces to react and the jets to fire. We are continuing to build a fault tree and we have many areas to investigate. We have not narrowed it down to any one particular conclusion or any one favorite topic. We have many areas to investigate."

Engineers plan to test external tank foam impacts and tile strength to get a better understanding of the mechanics of such impacts. Others are attempting to coax better imagery from the tracking camera footage. But recovery of debris on the ground could prove the most crucial to the ongoing investigation, especially any debris that fell away from the vehicle early on in the descent. Recovery of any such debris could help engineers determine exactly where the problem, whatever it was, began.

"The evidence that we find on the ground, and evaluating it and testing it, will help us point in the right direction, whether it was something that happened ... during the on-orbit phase, was it something that happened during the entry phase or was it something that happened during ascent and we didn't see it," Dittemore said. "Those are all possibilities.

"I know a lot of you have focused on the ET shedding of the debris, but we have not. We're looking at all these other areas because they are also possible and we just don't have any evidence to point us in one direction or the other and we are struggling to find that indicator or pointer to help us find that missing link."

Engineers studying data from the shuttle Columbia before it broke apart Saturday say temperature readings in the ship's left-side landing gear wheel well may be indicating a catastrophic "burn through" in a different part of the wing, not the wheel well itself.

It is still not known what might have caused such a penetration through the heat-shield tiles protecting the shuttle's underbelly from the fierce heat of re-entry. But program manager Ronald Dittemore said today engineers have been asked to re-assess whether a large piece of insulation that peeled off Columbia's external tank 81 seconds after launch and crashed into the underside of the wing could have compromised the integrity of the thermal protection system.

"Certainly this debris is one of our primary areas of emphasis," Dittemore said. "We're completely redoing the analysis from scratch. We want to know if we made any erroneous assumptions. We want to know if we weren't conservative enough. We want to know if we made any mistakes, and so we're redoing the complete analysis.

"Secondarily, we have a team of engineers and managers and technicians that are ... making the assumption from the start that the external tank was the root cause of the problem that lost Columbia. That's our starting point when we look at the tank. And based on that assumption, what is the fault tree that would substantiate that particular assumption? And so we're attacking that. And that's a fairly drastic assumption and it's sobering."

Columbia was destroyed Saturday when it suffered a catastrophic failure around 9 a.m. EST while en route to the Kennedy Space Center to close out a 16-day science mission. All seven crew members perished.

But the problem first manifested itself in telemetry beamed back to mission control as the spacecraft approached and crossed over the coast of California. Dittemore provided more details today on just what that telemetry indicated (all times converted to EST).

1. 08:52 a.m. - Three left main gear brake line temperature sensors show an unusual increase. "This was the first event, the first occurance of a significant thermal event in the wheel well on the left-hand side," Dittemore said.

2. 08:53 a.m. - A fourth left brake line strut actuator and uplock actuator (the mechanism that holds the landing gear stowed in the wheel well) temperature measurements rise 30 to 40 degrees over a five-minute period.

3. 08:55 a.m. - A fifth main gear brake line temperature sensor shows an unusual temperature rise.

4. 08:57 a.m. - Now passing over Arizona and New Mexico, upper and lower left wing skin temperature sensors fail off-scale low, indicating sensor failures.

5. 08:59 a.m. - The shuttle responds to increasing left-side aerodynamic drag that is attempting to yaw the orbiter to the left. Columbia's flight control system sent commands to the wing elevons to counteract the drag and to move the ship back to the right. Data also indicates two of four right-firing rocket thrusters fired as well to assist.

"Although I said yesterday it was well within our capability to maintain attitude, it was well within the flight control system's capability to handle the excursion, as we have continued to pour over the data, it's not the absolute value of the attitude change that is interesting," Dittemore said. "What is becoming interesting to us now is the rate of change.

"The aerosurfaces were doing what they needed to do to counteract the drag on the left side of the vehicle, the right yaw jets had to kick in to help the aerosurfaces and it appears we were losing ground as far as the rate of attitude excursion. It was not long after that point we lost all data and communications with the crew."

Dittemore said the temperature spikes recorded by the wheel well sensors and others were not enough to indicate a catastrophic burn through of the landing gear doors.

"The outside temperature is above 2,000 degrees," he said.l "Seeing an increase in the wheel well of 30 to 40 degrees seems to indicate that that's not the point of any large thermal excursion. That's reflecting something else."

In short, it now seems more likely the readings from the wheel well and the fuselage just above it were "reflecting an overall increase in temperature but were not the exact point of the penetration."

"I'm speculating a little bit here because I have no data or evidence to say that's really what happened," Dittemore said. "But I'm trying to think in my own mind how would the temperature increase in the wheel well and on the side of the fuselage and still end up with an event that lost the vehicle.

"It does not seem logical that the wheel well is the source of the problem because the temperature does not reflect it. We've had now five different temperature sensors all showing a 40- to 50-degree increase over five minutes, the side of the fuselage showing an increase. There's some other event, some other missing link that we don't have yet that's contributing to this temperature increase. And we've got to go find that."

Still in question is what might have caused the penetration, wherever it occurred.

While Columbia was still in orbit, engineers analyzed long-range tracking camera footage of the external tank debris striking the left wing of the shuttle. Running software designed to predict the effects of such impacts, they assumed the debris measured 20 by 16 by 6 inches and weighed 2.67 pounds. The ran the program using various impact angles to determine worst-case damage scenarios.

As CBS News reported early Monday, the engineers studied two such scenarios. In one, most of a single tile was assumed to be missing and in the other, it was assumed several tiles in a region measuring roughly 7 by 30 inches. In both cases, the engineers concluded, "possible localized structural damage" could have occurred, "but no burn-through and no safety of flight issue."

"For the loss of a single tile at the main landing gear door and for the other case where you have more acreage damaged, in both those cases the analysis predicted that even though you might have structural damage - and what I mean by structural damage is localized heating where you may have some effect on the basic structure in that area - even though you might have localized structural damage, you would not have damage sufficient to cause the catastrophic event nor impact the flying qualities of the vehicle," Dittemore said.

But engineers don't like coincidences and Dittemore has ordered a second debris review to determine if the original analysis stands up.

A NASA analysis of potential tile damage resulting from the impact of external tank foam insulation during the shuttle Columbia's launch concluded no significant damage would have resulted during re-entry even if multiple tiles were missing.

During Columbia's launching Jan. 16, long-range tracking cameras showed a relatively large piece of foam debris falling away from the shuttle's external tank and striking the underside of the orbiter's left wing. The debris is believed to have measured about 20 inches in its longest dimension.

The actual impact occurs out of view under the wing, but a cloud, or spray, of fine white material erupts from the area and quickly streams away in the shuttle's exhaust plume. The video, obtained earlier by CBS News and other organizations, was released by NASA today.

Columbia was destroyed during re-entry Saturday, breaking apart 200,000 feet above Texas while streaking toward the Kennedy Space Center at more than 18 times the speed of sound.

Telemetry from the shuttle indicates a sudden temperature rise in the left landing gear wheel well and above the wing along the left side fuselage. It is not known what caused the thermal distress, but it actually began seven minutes or so before the shuttle broke up.

The impact of the foam debris on the underside of the wing near in the general area of the left main landing gear door has prompted speculation about possible tile damage that could have worsened during entry.

An analysis by NASA engineers while Columbia was still in orbit, however, concludes that while the impact and resulting heat stress could have caused structural damage in the immediate area, it would not have led to a loss of the vehicle. The analysis, or at least this summarization of it, was dated Jan. 28 - the 17th anniversary of the 1986 Challenger disaster.

The engineers assumed the debris was foam insulation and studied possible damage scenarios based on the visible trajectory of the foam.

Damage to the reinforced carbon-carbon composite insulation on the leading edge of the wing would have been limited to "coating only and have no mission impact," the update said.

But impact on the black thermal protection tiles on the belly of the orbiter had the potential "for a large damage area to the tile."

A thermal analysis was performed to determine the implications of such damage assuming various levels of damage, including multiple tiles missing over an area measuring roughly 7 by 30 inches.

"These thermal analyses indicate possible localized structural damage but no burn-through and no safety of flight issue," the status report concluded.

Shuttle program manager Ronald Dittemore said much the same thing during a news briefing Sunday. While he did not provide test data, he said engineers still believed the impact was insignificant.

NASA plans two news briefings today, one from Washington at 11:30 a.m. EST and another from the Johnson Space Center at 4:30 p.m. This status report will be updated after each briefing or as conditions warrant.

NASA engineers are studying telemetry from the shuttle that indicates a sudden increase in temperature inside the left wing's main landing gear wheel well in the moments before the shuttle's destruction. What might have caused the temperature spikes, along with sensor malfunctions in the same area, is not yet known. But these could be indicators that whatever destroyed the shuttle started in this area.

"I'm going to be honest and open with you and tell you exactly what we know and hope you understand that from day to day, it will change," said shuttle program manager Ronald Dittemore. He then provided a detailed blow-by-blow account as follows (all times converted to EST):

At 8:53 a.m. EST, he said, as Columbia was sailing high above California on its way to landing at the Kennedy Space Center, "four left-hand elevon (wing flap) hydraulic return line temperature measurements dropped off scale. The left brake line, (landing gear) strut actuator and uplock actuator temperature measurements rose significantly, 20 to 30 degrees in five minutes. This is significant in that these measurements were located in the left wheel well. This was the first occurance of a significant thermal event.

"It's also important to us that we understand and have found out that the elevon temperature measurements that I talked about (Saturday) that dropped off scale low are routed adjacent to the wheel well area.

"At 8:54, we were over eastern California and western Nevada. At this time, the mid fuselage left bondline temperature sensor showed an unusual temperature rise," Dittemore said. "We're talking about a temperature on the left side of the vehicle above the wing. The temperature rose 60 degrees over five minutes whereas on the right-hand side of the vehicle, in the same location but opposite on the right-hand side, showed a nominal 15-degree rise over five minutes.

"Another interesting piece of information, that even though the mid fuselage bondline temp showed a 60-degree rise in five minutes, just inside that wall, in the payload bay, our cryo tanks were nominal. So it didn't look like there was any increase in temperature in the payload bay as far as we are able to discern today.

"At 8:58 a.m. over New Mexico, the roll trim in the elevons started to increase, indicating we had an increase in drag on the left side of the vehicle," Dittemore said. "Does this mean something to us? We're not sure. It could be indicative of rough tile, it could be indicative perhaps of missing tile. We're not sure. We do know it's indicative there was an increase in drag on the left side of the vehicle.

"At this time, we also lost the left main landing gear tire pressure and wheel temperature measurements. We're fairly confident that this loss of information was measurement related and not loss of the tires themselves because the measurements were staggered in their loss. If we'd have lost a tire, we believe we would have lost all the measurements at the same time. That didn't occur.

"At 8:59 a.m. we were over west Texas. Again we see an increase in the roll trim as indicated by elevon motion, indicating the vehicle was reacting to an increased drag on the left-hand side. The flight control system was countering that drag by trying to command the vehicle to roll to the right-hand side. ... Soon after, we had loss of signal."

Engineers believe there's another 32 seconds of data available in the telemetry stream that was not downlinked because of increasing amounts of data corruption in the shuttle's electronic nervous system. Some of that data may be recoverable.

"In addition, Dittemore said images taken by an observer in California that appears to show an early trail of debris behind the shuttle will be examined and compared with the actual telemetry.

"We're going to overlay his report with what the data shows to us and hopefully the two of them will help us piece together a path that might help lead us to the cause," Dittemore said. "Again, we're very early in our analysis and we're still poring over a lot of data. So bear with us as we go through this effort and bear with us as we report to you because it's going to be fluid, it's going to change, and it's certainly possible we'll contradict ourselves from day to day. That's just the nature of what we have to go through right now."

The big question is what might have caused the anomalies seen in the left wing. About 80 seconds after Columbia blasted off Jan. 16, long-range tracking cameras show what appears to be a sizeable piece of insulation from the shuttle's external fuel tank breaking away and hitting the underside of the left wing. Engineers today said the piece measured 20 inches across in its largest dimension.

Dittemore said engineers studied the issue in detail in the days following Columbia's launch and concluded the foam posed no danger to the ship or crew. He reiterated that viewpoint today. But he did not rule out the possibility the debris played a role in the mishap.

Here's one purely speculative scenario that could link the two events. If the debris happened to hit and damage protective heat-shield tiles around the left-wing's main landing gear door, the thermal stress of re-entry, when temperatures reach 3,000 degrees on the belly of the shuttle, could have magnified whatever damage was initially present.

"We certainly know the wheel well area is one of our sensitive areas thermally," Dittemore said. "We've analyzed that area intensively in the past and the loss of any one single tile we believe would not be a cause for loss of a vehicle. In fact, we believe we can lose a tile in different locations and all by themselves we don't believe that would represent loss of vehicle. It may represent some structural damage, but not loss of a vehicle."

But Dittemore did not mention the possibility of a debris impact that could have compromised the tile in the area of the landing gear door. But he said engineers at the Kennedy Space Center likely will be asked to inspect the shuttle Discovery "to help us understand what (Columbia) looked like to see if there were any thermal breeches, would that also affect the wheel well and the wiring?"

Astronaut Robert Cabana, meanwhile, told reporters NASA would not discuss the recovery of crew remains out of deference to family members.

"Yesterday was probably the hardest day of my life, to have to sit down with the families of close friends and tell them that their husbands and wives and moms and dads aren't going to be coming home," he said with uncharacteristic emotion. "And if you've never had to do that, I hope you never have to."

In response to a question later, Cabana said identifiable remains from all seven shuttle fliers had been recovered. He later said he misspoke and crew recovery operations continue.

NASA sources say a sizeable section of what may be the shuttle Columbia's forward fuselage has been found near the Lufkin-Nocogdoches area southeast of Dallas near the Louisiana border. Recovery teams continue to search for remains of Columbia's astronauts and while sources say remains have, in fact, been found, no details about the astronauts have been released out of deference to family members

Veteran shuttle commander James Wetherbee is coordinating NASA's initial recovery efforts from Barksdale Air Force Base near Shreveport, La. Jerry Ross, veteran of seven shuttle missions, is coordinating recovery of Columbia's crew. Any remains found, sources said, will be transferred to Barksdale and then flown to Dover Air Force Base in Delaware for examination.

NASA and contractor engineers, meanwhile, continue studying telemetry from Columbia to precisely characterize how the shuttle's myriad systems were operating during the final moments of re-entry. The hope is that data in that telemetry stream will help pinpoint what might have triggered the shuttle's catastrophic break up. In the meantime, debris recovery continues.

A news conference with shuttle program manager Ronald Dittemore and Robert Cabana, director of flight crew operations at the Johnson Space Center, is scheduled to begin at 4:30 p.m. A detailed update will be posted after the briefing is over.

Looking ahead, NASA now plans to hold two news briefings each day, the first from NASA headquarters in Washington at 11:30 a.m. EST and the second, from the Johnson Space Center in Houston, at 4:30 p.m.

NASA Administrator Sean O'Keefe today named the members of the Space Shuttle Mishap Interagency Investigation Board, charged with conducting an independent review of the Columbia re-entry disaster. The board will hold its first meeting Monday at Barksdale Air Force Base, Louisiana.

The panel is chaired by retired U.S. Navy Adm. Harold W. Gehman, Jr., who served as co-chairman of an independent panel that investigated the USS Cole attack in Yemen in October 2000.

"While the NASA family and the entire world mourn the loss of our colleagues, we have a responsibility to quickly move forward with an external assessment to determine exactly what happened and why," O'Keefe said in a statement. "We're honored to have such a distinguished panel of experts, led by Admiral Gehman."

The other members of the independent review are:

• Rear Admiral Stephen Turcotte, Commander, U.S. Naval Safety Center, Norfolk, Va.

• Major General John L. Barry, Director, Plans and Programs, Headquarters Air Force Materiel Command, Wright-Patterson Air Force Base, Ohio

• Major General Kenneth W. Hess, Commander, U.S. Air Force Chief of Safety, Kirtland Air Force Base, N.M.

• Dr. James N. Hallock, Aviation Safety Division Chief, U.S. Department of Transportation, Cambridge, Mass.

• Steven B. Wallace, Director of Accident Investigation, Federal Aviation Administration, Washington

• Brigadier General Duane Deal, Commander 21st Space Wing, Peterson Air Foce Base, Colo.

The panel also will include Scott Hubbard, director of NASA's Ames Research Center. Bryan O'Connor, a former shuttle commander and senior NASA managers, will serve as an ex-officio member while NASA's chief engineer, Theron Bradley, will serve as executive secretary.

"We need to be responsible, accountable, and extremely thorough in this investigation," O'Keefe said in the statement. "This panel is charged with a most difficult task, but I am confident in their ability, their integrity, and their dedication to doing what's right. Their findings will help push America's space program successfully into the future."

An internal NASA review also is underway, "drawing on the extensive expertise throughout the agency," O'Keefe said. "Public officials for NASA, the Federal Emergency Management Agency, and other federal, state, and local entities are coordinating talents to help find the cause of this tragedy."

Editor's Note...
Due to broadcast commitments in the wake of the shuttle tragedy Saturday, I was unable to post a story in a timely fashion. Our apologies for the inconvenience.

The shuttle Columbia suffered a catastrophic failure returning to Earth Saturday, breaking apart 207,135 feet above Texas en route to a landing at the Kennedy Space Center to close out a 16-day science mission. The shuttle's seven-member crew - two women and five men, including the first Israeli space flier - perished in the disaster, the first loss of life on the high frontier since the 1986 Challenger disaster.

The initial phases of the descent went normally and Columbia crossed above the coast of California just north of San Francisco around 5:51 a.m. local time, or 8:51 a.m. EST, on track for a landing on runway 33 at the Kennedy Space Center just 25 minutes later at 9:16 a.m.

The first sign of anything unusual came at 8:53 a.m., when the shuttle was flying high above the heartland of America.

Telemetry showed a sudden loss of hydraulic system data from the inboard and outboard wing flaps, or elevons, on Columbia's left wing. Three minutes later, sensors in the brake lines and tires of the shuttle's left-side main landing gear suddenly stopped providing data.

The shuttle continued to fly in a normal manner with no hint that a catastrophic failure was imminent.

Then at 8:58 a.m., sensors that monitor temperatures where the shuttle's protective thermal tiles are glued or bonded to the airframe suddenly dropped out followed one minute later by loss of data from landing gear pressure sensors on the left side tires. Columbia's flight computers alerted the astronauts to the pressure indication and one of the crew members acknowledged the alert in a brief call to mission control.

That was the final transmission from the space shuttle. Moments later, all data was lost and the vehicle broke up while traveling 18.3 times the speed of sound. Mission duration to that point was 15 days 22 hours 20 minutes and 22 seconds, translating to 8:59:22 a.m. EST. Wreckage was soon found strewn over a debris "footprint" stretching across eastern Texas and into Louisiana. There was no immediate word on where Columbia's reinforced crew module might have crashed to Earth.

In a brief address to the nation, President Bush said "this day has brought terrible news and great sadness to our country. ... Columbia is lost. There are no survivors."

"The same creator who names the stars also knows the names of the seven souls we mourn today," he said. "The crew of the shuttle Columbia did not return safely to Earth. Yet we can pray they are all safely home."

Said NASA Administrator Sean O'Keefe: "The loss of this valiant crew is something we will never be able to get over."

Family members were standing by at the shuttle runway to welcome their loved ones back to Earth. William Readdy, NASA's associate administrator for space flight and a veteran shuttle commander, praised the astronauts' families for showing an "incredible amount of dignity considering their loss."

"They knew the crew was absolutely dedicated to the mission they were performing," he said, barely able to control his emotions. "They believed in what they were doing and in the conversations with the families, they said we must find what happened, fix it and move on. We can't let their sacrifice be in vain.

"Today was a very stark reminder this is a very risky endevour, pushing back the frontiers in outer space. Unfortunately, people have a tendency to look at it as something that is more or less routine. I can assure you, it is not.

"I have to say as the one responsible for shuttle and (space) station within NASA, I know the people in NASA did everything possible preparing for this flight to make it as perfect as possible," Readdy said. "My promise to the crew and the crew families is the investigation we just launched will find the cause. We'll fix it. And then we'll move on."

The goal of mission STS-107 was to carry out space station-class research in a variety of disciplines, ranging from biology to medicine, from materials science to pure physics and technology development, research that cannot yet be accommodated on the still-unfinished international space station.

More than 80 experiments were on board, most of them in a Spacehab research module in Columbia's cargo bay. To collect as much data as possible, the astronauts worked around the clock in two 12-hour shifts. By all accounts, the crew accomplished all of their major objectives.

At an afternoon news conference, shuttle program Ronald Dittemore and senior flight director Milt Heflin reviewed the telemetry from the shuttle and answered as many questions as possible. NASA's openness during the immediate aftermath of a devastating day was in stark contrast to the strict "no comment" policy implemented in the wake of the 1986 Challenger disaster that frustrated the public and tarnished the agency's reputation for openness.

"We're devastated because of the events that unfolded this morning," Dittemore said. "There's a certain amount of shock in our system because we have suffered the loss of seven family members. And we're learning to deal with that. Certainly, a somber mood in our teams as we continue to try to understand the events that occurred, but our thoughts and our prayers go out to the families.

"As difficult as this is for us, we wanted to meet with you and be as fair and open with you (as possible), given the facts as we understand them today," he said. "We will certainly be learning more as we go through the coming hours, days and weeks. We'll tell you as much as we know, we'll be as honest as we can with you and certainly we'll try to fill in the blanks over the coming days and weeks."

An internal NASA team of senior managers was named to handle the initial investigation into the disaster. An independent team of experts also was named to ensure objectivity. All flight control data and shuttle telemetry was impounded and "tiger teams" were formed to begin the painful tasks of sifting the data and coordinating the recovery of debris.

Dittemore said the shuttle fleet will remain grounded until engineers pinpoint what went wrong with Columbia and determine what corrections might be necessary.

Columbia's flight was one of only two remaining on NASA's long term launch schedule that does not involve the international space station. NASA had planned to launch the shuttle Atlantis around March 6 to ferry a fresh crew to the station and to bring the lab's current occupants back to Earth after 114 days in space.

Around 9:30 a.m. Saturday, flight controllers informed Expedition 6 commander Kenneth Bowersox, flight engineer Nikolai Budarin and science officer Donald Pettit that Columbia had been lost during re-entry.

Bowersox and his crewmates have enough on-board supplies to remain aloft aboard the station through June. In fact, an unmanned Russian Progress supply ship is scheduled for launch Sunday from the Baikonur Cosmodrome in Kazakstan. That launch will proceed as planned, officials said.

If the shuttle fleet remains grounded through June, the station crew could be forced to abandon the station and return to Earth aboard a Russian Soyuz lifeboat. Fresh lifeboats are delivered to the station every six months to ensure the crew has a way to bail out in case of problems with the shuttle fleet or some other in-flight emergency.

With enough supplies on board to last Bowersox and his crewmates until late June, "there's some time for us to work through this," Dittemore said. "Right now, certainly there is a hold on future flights until we get ourselves established and understand the root cause of this disaster."

Dittemore provided a sense of the loss felt by NASA and its contractors when he said "it's an emotional event, when we work together, we work together as family member and we treat each other that way. ... It's a sad loss for us.

"We understand the risks that are involved in human spaceflight and we know these risks are manageable and we also know they're serious and can have deadly consequences," he said. "So we are bound together with the threat of disaster all the time. ... We all rely on each other to make each spaceflight successful. So when we have an event like today, when we lose seven family members, it's just devastating to us."

Columbia blasted off on the 113th shuttle mission Jan. 16. The climb to space appeared uneventful, but about one minute and 20 seconds after liftoff, long-range tracking cameras showed a piece of foam insulation from the shuttle's external tank breaking away and hitting Columbia's left wing. The foam came from near the area where a forward bipod assembly attaches the nose of the shuttle to the tank. The debris hit the left wing near its leading edge.

Entry flight director Leroy Cain said Friday a detailed analysis of the debris impact led engineers to believe there was no serious damage. Columbia was not equipped with a robot arm for this Spacehab research mission and the impact area was not visible from the shuttle's crew cabin.

Whether the debris caused enough damage to compromise the integrity of the wing's thermal protection system is not yet known. But when the failure occurred, the shuttle was experiencing maximum heat loads of nearly 3,000 degrees Fahrenheit.

"If we did have a structural problem or a thermal problem, you would expect to get it at the peak heating," he said. "The most extreme thermal environment was right at mach 18 and that's where we lost the vehicle."

The shuttle Challenger was lost 17 years ago by the failure of an O-ring seal in one of the ship's two solid-fuel boosters. All seven crew members perished, including New Hampshire social studies teacher Christa McAuliffe. McAuliffe's backup, Idaho teacher Barbara Morgan, witnessed the disaster from the NASA press site 4.2 miles from Challenger's launch pad.

In a painful footnote to Saturday tragedy, Morgan was once again at the Kennedy Space Center, this time as a full-time astronaut awaiting launch in November on Columbia's next mission. Morgan is the first member of a new class of educator astronauts, part of a program initiated by O'Keefe to help generate more student interest in science and technology.

Since the educator-astronaut program was announced last month, more than 1,000 teachers have expressed interest or been nominated as potential candidates by students, family members or friends. The status of that program, and the impact of Columbia's loss on Morgan's flight, is not yet known.

But as President Bush promised family members and the nation Saturday, "the cause for which they died will continue. ... Our journey into space will go on."

Commander Rick Husband and pilot William "Willie" McCool fired the shuttle Columbia's twin braking rockets at 8:15 a.m., slowing the ship's by 176 mph to begin an hourlong glide to landing at the Kennedy Space Center. The rocket firing went well and touchdown is expected around 9:15:50 a.m. to close out a 16-day microgravity research mission.

This status report will be updated after Columbia lands or as conditions warrant.

The Columbia astronauts closed the shuttle's payload bay doors around 5:45 a.m., preparing the ship for re-entry and landing back at the Kennedy Space Center to close out a 16-day science mission. Forecasters are keeping close tabs on area fog and lower-than-expected clouds, but conditions are expected to improve as the morning wears on and flight controllers are optimistic about an on-time landing.

"We've just been watching the weather at the Cape," astronaut Charles Hobaugh radioed from mission control. "This morning when we got in it looked pretty gruesome. There was some fog and low layers. The T-38 has already done its first weather (observation run) and the weather has improved greatly. ... We're expecting those patches of thin layers to clear up as the sun comes up."

Flying upside down and backward over the Indian Ocean, commander Rick Husband and William "Willie" McCool plan to fire Columbia's twin orbital maneuvering system braking rockets at 8:15:18 a.m. to begin the hourlong descent to Earth. The rocket firing will last for two minutes and 38 seconds, slowing the shuttle by 176 mph and dropping the far side of its orbit deep into the atmosphere.

Following that new trajectory, Columbia will fall for 35 minutes and 47 seconds before entering the discernible atmosphere over the Pacific Ocean around 8:45 a.m. Range to touchdown at that point will be 5,113 miles.

Columbia's flight path will carry it over the coast of California near San Francisco at 8:55 a.m. EST (5:55 a.m. PST), an hour before sunrise. Weather permitting, early risers may be treated to a spectacular sky show as the space shuttle streaks across the predawn sky.

Husband will take over manual control of the spacecraft 50,000 feet above the Kennedy Space Center, guiding the ship through a sweeping 213-degree right-overhead turn to line up on runway 33. At touchdown, Columbia's seven-member crew will have completed 255 full orbits and traveled 6.6 million miles since blastoff Jan. 16 from nearby pad 39A.

Husband, McCool, flight engineer Kalpana Chawla, payload commander Michael Anderson, David Brown, Laurel Clark and Israeli payload specialist Ilan Ramon plan to spend the night in Florida before flying back to the Johnson Space Center in Houston on Sunday.

Anderson, Clark, Brown and Ramon will be carried off the shuttle on stretchers as part of ongoing medical research to chart their adaptation to weightlessness and re-adaptation to gravity.

"Post flight, we have data collection for approximately a month," Clark said during a crew news conference earlier this week. "For several days we'll be very busy and then we have data collections every couple of days and that goes out for about a month or 45 days afterward."

Columbia has two landing opportunities today on successive orbits. The shuttle has enough supplies to remain in orbit until Wednesday in a worst-case scenario, but no one expects any significant delays.

Here is a detailed timeline of today's entry activities (in EST):

Orbit.........255
dT............02:38 (deorbit burn duration)
dV............176 mph (change in velocity)
Freefall......35:47 (time to discernible atmosphere)
Range to KSC..5,113 sm
Crossrange....Left-14 sm (distance from normal ground track)
Turn..........Right-213 degrees
Runway........33

TIME..........EVENT

05:45:00 AM...Mission control 'go' for OPS-3 entry software load
05:55:00 AM...OPS-3 transition
06:20:00 AM...Entry switchlist verification
06:30:00 AM...Deorbit maneuver update
06:35:00 AM...Crew entry review
06:50:00 AM...Commander/pilot don entry suits
07:07:00 AM...Navigation system (IMU) alignment
07:15:00 AM...Commander/pilot strap in; others don suits
07:32:00 AM...Shuttle steering check
07:35:00 AM...APU hydraulic power system prestart
07:42:00 AM...Toilet deactivation
07:50:00 AM...Payload bay vent doors closed for entry
07:55:00 AM...Mission control 'go' for deorbit burn
08:01:00 AM...Astronaut seat ingress
08:10:00 AM...Single APU start
08:12:34 AM...TDRS-West comsat acquisition of signal
08:15:18 AM...Deorbit ignition
08:17:56 AM...Deorbit burn complete
08:43:53 AM...Shuttle hits discernible atmosphere
08:49:26 AM...23-degree right roll command
08:56:15 AM...63-degree roll reversal
09:09:29 AM...Velocity less than mach 2.5
09:11:38 AM...Velocity less than mach 1
09:12:39 AM...Shuttle turns to line up on runway
09:15:50 AM...Landing on runway 33

Orbit.........256
dT............02:38
dV............176 mph
Crossrange....Left-815 sm
Range.........5,020 sm
Turn..........Right-240 degrees
Runway........33

09:29:00 AM...MCC 'go' for deorbit burn
09:35:00 AM...MS seat ingress
09:44:00 AM...Single APU start
09:48:07 AM...AOS TDRS-West
09:49:36 AM...Deorbit ignition
09:52:14 AM...Deorbit ignition complete
10:18:34 AM...Entry interface
10:24:04 AM...21-degree right roll command
10:39:20 AM...51-degree roll reversal
10:44:10 AM...Velocity less than mach 2.5
10:46:21 AM...Velocity less than mach 1
10:47:04 AM...Shuttle on the HAC
10:50:29 AM...Landing on runway 33

Entry flight director Leroy Cain says the shuttle Columbia sailed through morning entry tests with flying colors and that with good weather expected, the crew should have no problems returning to the Kennedy Space Center early Saturday.

"This has been a very successful mission," Cain said. "Fair to say it's far exceeded folks' expectations from a science standpoint. So we're very pleased.

"The vehicle Columbia and the crew are doing very well today," he continued. "It's been a quiet day with respect to science as we start to ramp down on most of those experiments and put them away. We spent most of our day today getting set up for entry.

"We did our normal flight control systems checkout. ... All the systems we use for entry, we had no problems, the vehicle performed flawlessly today as it has the entire mission."

The only issue - and Cain said it was not significant - is a bit of possible tile damage on Columbia's left wing. Video of launch shows what appears to be a piece of foam insulation from the shuttle's external tank falling away during ascent and hitting the left wing near its leading edge.

But Cain said engineers "took a very thorough look at the situation with the tile on the left wing and we have no concerns whatsoever. We haven't changed anything with respect to our trajectory design. It will be a nominal, standard trajectory."

Commander Rick Husband and pilot William McCool plan to fire Columbia's twin braking rockets at 8:15 a.m. Saturday to begin the hourlong glide to Earth. Touchdown on runway 33 at the Kennedy Space Center is expected at 9:16 a.m.

For early risers in the San Francisco area, Columbia should put on quite a show as it streaks across the sky in pre-dawn darkness. Assuming an on-time deorbit "burn," Columbia will make landfall around 5:55 a.m. PST.

"This will be a very good visual sighting for folks on the West Coast as well as mid Arizona, the New Mexico area," Cain said. "It should be a pretty spectacular event for folks (in the San Francisco area) who have never seen a shuttle sighting at night. It's a sight to see and this one should be a very good one."

Following touchdown, four of Columbia's seven crew members - Laurel Clark, Michael Anderson, David Brown and Ilan Ramon, the first Israeli in space, will be carried off the shuttle on stretchers as part of ongoing medical research charting the body's adaptation to weightlessness and re-adaptation to gravity.

"Post flight, we have data collection for approximately a month," Clark said during a crew news conference earlier this week. "For several days we'll be very busy and then we have data collections every couple of days and that goes out for about a month or 45 days afterward."

Cain said Columbia has enough on-board supplies to remain in orbit until Wednesday in a worst-case scenario. But no such problems are expected and the forecast for Florida calls for good weather Saturday with scattered clouds and light winds.

Columbia commander Rick Husband, pilot William McCool and flight engineer Kalpana Chawla tested the shuttle's re-entry systems today, setting the stage for landing Saturday to close out a 16-day science mission. Touchdown on runway 33 at the Kennedy Space Center currently is targeted for 9:15:50 a.m.

Good weather is expected, with scattered clouds at 3,500 feet and 25,000 feet, winds out of 300 degrees at 10 knots gusting to 15 and visibility of seven miles. There are no predicted flight rule violations.

NASA does not plan to staff the shuttle's backup landing site at Edwards Air Force Base, Calif., for Saturday's landing attempt. Instead, Husband and company will have two opportunities on back-to-back orbits - 255 and 256 - to land in Florida. If they can't make it for any reason, they will remain in orbit an extra day and try again Sunday.

The crew's science operations are virtually complete. The MEIDEX multispectral camera is making a few final runs today, but the crew's primary focus today is packing up and readying the shuttle for re-entry.

Here is a detailed timeline of entry-day activities for both of Saturday's landing opportunities:

Orbit.........255
dT............02:38 (deorbit burn duration)
dV............176 mph (change in velocity)
Freefall......35:47 (time to discernible atmosphere)
Range to KSC..5,113 sm
Crossrange....Left-14 sm (distance from normal ground track)
Turn..........Right-213 degrees
Runway........33

TIME..........EVENT

04:15:00 AM...Begin deorbit timeline
04:30:00 AM...Radiator stow
04:40:00 AM...Mission specialists seat installation
04:46:00 AM...Computers set for deorbit prep
04:50:00 AM...Hydraulic system configuration
05:15:00 AM...Flash evaporator cooling system checkout
05:21:00 AM...Final payload deactivation
05:35:00 AM...Payload bay doors closed
05:45:00 AM...Mission control 'go' for OPS-3 entry software load
05:55:00 AM...OPS-3 transition
06:20:00 AM...Entry switchlist verification
06:30:00 AM...Deorbit maneuver update
06:35:00 AM...Crew entry review
06:50:00 AM...Commander/pilot don entry suits
07:07:00 AM...Navigation system (IMU) alignment
07:15:00 AM...Commander/pilot strap in; others don suits
07:32:00 AM...Shuttle steering check
07:35:00 AM...APU hydraulic power system prestart
07:42:00 AM...Toilet deactivation
07:50:00 AM...Payload bay vent doors closed for entry
07:55:00 AM...Mission control 'go' for deorbit burn
08:01:00 AM...Astronaut seat ingress
08:10:00 AM...Single APU start
08:12:34 AM...TDRS-West comsat acquisition of signal
08:15:18 AM...Deorbit ignition
08:17:56 AM...Deorbit burn complete
08:43:53 AM...Shuttle hits discernible atmosphere
08:49:26 AM...23-degree right roll command
08:56:15 AM...63-degree roll reversal
09:09:29 AM...Velocity less than mach 2.5
09:11:38 AM...Velocity less than mach 1
09:12:39 AM...Shuttle turns to line up on runway
09:15:50 AM...Landing on runway 33

Orbit.........256
dT............02:38
dV............176 mph
Crossrange....Left-815 sm
Range.........5,020 sm
Turn..........Right-240 degrees
Runway........33

09:29:00 AM...MCC 'go' for deorbit burn
09:35:00 AM...MS seat ingress
09:44:00 AM...Single APU start
09:48:07 AM...AOS TDRS-West
09:49:36 AM...Deorbit ignition
09:52:14 AM...Deorbit ignition complete
10:18:34 AM...Entry interface
10:24:04 AM...21-degree right roll command
10:39:20 AM...51-degree roll reversal
10:44:10 AM...Velocity less than mach 2.5
10:46:21 AM...Velocity less than mach 1
10:47:04 AM...Shuttle on the HAC
10:50:29 AM...Landing on runway 33

Additional entry details will be posteed here after a status briefing later today with entry flight director Leroy Cain.

Shuttle Columbia's astronauts are working through their final full day of research today before packing up and checking out the ship's re-entry systems Friday for a planned Saturday morning landing at the Kennedy Space Center. The forecast for Saturday is generally favorable with a slight chance of fog.

For readers interested in a quick look ahead, here are the latest deorbit and landing numbers from the Johnson Space Center:

   DATE.......ORBIT...SITE....TIG...........LANDING

   Saturday...255.....KSC.....08:15 a.m.....09:16 a.m.
   ...........256.....KSC.....09:50 a.m.....10:50 a.m.

   Sunday.....270.....KSC.....06:40 a.m.....07:38 a.m.
   ...........271.....KSC.....08:15 a.m.....09:12 a.m.
   ...........272.....EDW.....09:41 a.m.....10:38 a.m.
   ...........273.....EDW.....11:15 a.m.....12:12 p.m.

   Monday.....286.....KSC.....06:37 a.m.....07:34 a.m.
   ...........287.....KSC.....08:11 a.m.....09:09 a.m.
   ...........288.....EDW.....09:37 a.m.....10:35 a.m.

A detailed entry timeline will be posted here Friday, along with an updated forecast.

The Columbia astronauts, in the home stretch of a grueling dual-shift 16-day science mission, told reporters today their research is proceeding in fine fashion and that scores of scientists on the ground should be pleased with their results.

"A lot of what we're doing now is really in preparation for future flights aboard the space station," said payload commander Michael Anderson. "A lot of experiments that we have are really just being demonstrated and developed and once they're fully developed, they'll reside aboard the space station and the scientists will have years to conduct the experiments we're trying to do here in a relatively short period of time.

"Science wise, this flight has been absolutely fantastic. I think a lot of our experiments have exceeded our expectations by a hundred percent. We've seen things we never expected to see on board this flight. ... Overall, this flight's been absolutely fantastic, the science has been spectacular and we just can't wait to bring it all home so the scientists can really take a close look at what we've done."

To collect as much data as possible from the more than 80 experiments on board, the astronauts are working around the clock in two 12-hour shifts, sharing bunks on the shuttle's lower deck. Shuttle commander Rick Husband said despite all the hustle and bustle of orbital operations, "we've been sleeping pretty well."

"We've got sleep stations in the middeck and they've got sound suppression padding in there an it's extremely dark," he said. "Some of us wear earplugs as well and so when you get to that level of sensory protection, it's actually pretty quiet and dark in those sleep stations."

Along with seven astronauts, Columbia is carrying a small menagerie of animals and insects, including ants, bees, silkworms and moths, fish, rats and spiders, many of them on board as test subjects for student experiments.

"They're all doing well," Anderson said. "The spiders, the ants, the moths, the rats, they're all doing just great ... and I think we're getting good science from it. Most of those experiments are educational experiments and we're beaming down video to students at schools all around the world. I'm sure they're really excited about what they're seeing and I'm sure they're excited for us to bring their specimens back so they can get a closer look at them."

Ilan Ramon, the first Israeli to fly in space, said he's been struck by the view of Earth from orbit, saying "the world looks marvelous from up here, so peaceful, so wonderful and so fragile."

"The atmosphere is so clean and fragile and I think that everybody, all of us, have to keep it clean and good," he said. "For the people of Israel, I wish we will have a peaceful land to live in very soon."

Ramon is on board in part to operate an experiment known as MEIDEX. Mounted in the shuttle's cargo bay, MEIDEX consists of a multi-spectral camera designed to characterize how dust particles from desert storms affect weather patterns.

"In the first seven days, I believe, we didn't have any dust up in the atmosphere," Ramon said. "But it looks like ... we had a big dust storm over the Atlantic (recently) that lasted for two or three days and I think the scientists were very, very successful with their experiment. Other than that, we had another quite big experiment with MEIDEX, which is called Sprite, which is actually lightning going up from the top of the clouds through the atmosphere and we have a lot of lightning storms recorded."

Columbia is scheduled to land Saturday at the Kennedy Space Center. Touchdown is expected around 9:15 a.m. to close out a 16-day, 6.6-million-mile mission.

As Columbia's marathon science mission enters its final week, the shuttle continues to operate in near flawless condition while the astronauts methodically work their way through a long list of more than 80 microgravity research projects.

"We had a really good weekend," said Phil Engelauf, representing NASA's mission operations directorate. "For those of you that have been following along and have been aware of the thermal issues we wrestled with last week, we have overcome most of that problem, we're over the hump, and with some of the larger heat-generating experiments having completed their operations, the cabin temperatures have fallen back to a pretty comfortable level, both the crew module temperatures in the orbiter and the temperatures back in the Spacehab are running around the mid 70s. We don't foresee any more problems through the rest of the mission.

"The crew is in great spirits, they're working through the timeline doing a great job keeping up with everything," Engelauf said. "I think we've done just an absolutely superb job executing all the tasks on the list for the crew. The science community is very happy with the progress we've made to date."

To collect as much data as possible, Columbia's crew is working around the clock in two 12-hour shifts roughly corresponding to day and night in the United States. Earlier today, the astronauts on the day shift spent a few moments chatting with the international space station's three-man crew, Expedition 6 commander Kenneth Bowersox, flight engineer Nikolai Budarin and science officer Donald Pettit.

The Columbia astronauts are pressing ahead with a full-slate of orbital research today, adjusting the shuttle's air conditioner to make up for a loss of cooling in their Spacehab research module. NASA managers describe the problem as an "annoyance," saying it will have no impact on the crew's science agenda.

"The orbiter and the crew are all doing very, very well," said Phil Engelauf, a senior flight director representing NASA's mission operations directorate. "They're all in good spirits, everybody seems to be doing very well. The orbiter also is doing great, we have no significant anomalies to report on the orbiter.

"The only thing that we have of any significance to talk about is at this point, an annoyance and we think we're going to be around the corner on that (soon). We have had a cooling problem with the Spacehab cooling system. It's technically actually a problem with separating out condensed water. The cooling system is cooling OK, but in order to avoid getting a lot of condensed water under the floorboards back there, we've had to back off on some of the cooling. We're in the process of a workaround."

Columbia has its own cooling system, which is working normally. The Spacehab research module in the shuttle's cargo bay has a cooling system as well, which utilizes a device called a "rotary separator" to remove excess water, or humidity, from the air as it is cooled. Two rotary separators are available for redundancy.

On Saturday, rotary separator No. 1 shut down after becoming flooded with excess water. The astronauts turned on the backup and used towels to soak up about two quarts of water from the engineering spaces under the floor of the module. The backup worked fine until Sunday, when it shorted out and blew a circuit breaker. Both separators have been off since then.

Engineers told the crew to turn down the shuttle's thermostat to send more cold air back to the Spacehab module. In addition, the astronauts have been adjusting valves in the Spacehab module to modify how cooling water circulates between various experiment packages and subsystems.

"We're in the process of trying to implement a quick fix by adjusting the amount of cooling water that flows to different parts of the Spacehab to provide more cooling to some of the equipment racks in order to keep all the experiments operating," Engelauf said. "Even though the air temperatures are a little bit warmer in the hab than they would normally be, it's really not a factor for the crew, it's really not outside their comfort level. ... We think we have the temperature problem essentially under control."

He said the normal temperature in the shuttle is 72 degrees. After the Spacehab cooling system problem, the temperature climbed as high as 84 degrees or so before dropping back down to around 76 degrees. One experiment missed a data run today because of the problems, but Engelauf said the astronauts will make that up later with no loss of science.

Otherwise, NASA mission scientist John Charles said today the crew's research agenda is on track. The astronauts are carrying out more than 80 government, university, commercial and student experiments during the course of Columbia's 16-day mission, working around the clock in two 12-hour shifts to maximize the science return.

The day shift - commander Rick Husband, Kalpana Chawla, Laurel Clark and Israeli payload specialist Ilan Ramon took a break today to chat with Israeli Prime Minister Ariel Sharon in Jerusalem.

"Our congratulations and our blessings from Jerusalem, the capitol of the Jewish people for 3,000 years and for eternity," Sharon radioed. He thanked President Bush and former President Bill Clinton "who decided to send one of our astronauts to space."

"I would like to thank NASA as well and to all those who have exerted effort to bring us to this achievement," Sharon said. "And I hope it is just one amongst all our flights into space."

Ramon at one point held up a small scroll given to him by a Holocaust survivor who is now a professor at Tel Aviv University and a member of the Israeli shuttle research team. The Torah scroll was given to the professor, then a boy, by a rabbi who died in the same concentration camp.

"This represents more than anything the ability of the Jewish people to survive despite everything from horrible periods, black days, to reach periods of hope and belief in the future," Ramon said, floating on the shuttle's flight deck.

Sharon invited Ramon and his shuttle crewmates to visit Israel after the flight.

Two days into one of the most ambitious shuttle science missions in years, the commander of the shuttle Columbia said his dual-shift team has encountered remarkably few problems and that "things are going really well."

"Columbia is in great shape and working absolutely perfectly and the experiments are working very well also," commander Rick Husband told CBS News in an interview from orbit. "So I'd say we're batting at least a thousand for starters."

Laurel Clark, a Navy physician making her first flight, said working in Columbia's roomy Spacehab module is a breeze.

"I would call it anything but cramped," she said. "In fact, I'm still getting my space legs, but I use them even more when I have to go back to Spacehab because there's so much room back there. Which is an advantage because when many of us are working there's room to get around and do the things we need to do.

"The experiments are going wonderfully," she added. "We've been busier than I even imagined, since things really do take longer up here. But we've already activated most of the experiments and they're doing very well, the ground teams are getting excellent data and we're very happy."

Columbia is loaded with more than 80 experiments in a variety of disciplines, ranging from medicine and biology to materials science, basic physics and student research involving bees, spiders, silkworms, ants and fish.

Other experiments mounted in the shuttle's cargo bay are part of investigations to characterize the ozone layer, the sun's energy output and the transport of dust particles over the Mediterranean basin. Ilan Ramon, the first Israeli in space, is on board in part to operate the multispectral MEIDEX dust camera.

So far, the weather hasn't cooperated, but Ramon said he's been busy nonetheless. So busy, in fact, "I didn't even have a chance to think about the Sabbath."

"I'm secular and I didn't get any special permission (to work on the Sabbath)," he said. "I'm here with special teammates, crewmates, and I'm working every day. The only thing I did have is a kiddush cup, but I even missed that yesterday, for Friday. I hope I'll do it next Friday."

Asked about the significance of Israel becoming the 30th nation to put a representative in space, Ramon had remarkably little to say.

"I sure thought about it before getting to space, but the last two or three day we were real busy getting our (space) legs on and I didn't have a chance to think about it up here," he said. "I'm sure I will have the chance later on."

As for voting in Israel's national elections Jan. 28: "I haven't voted and I will not vote. I will send my father back (from the U.S.) to vote on behalf of me."

Columbia's crew features four first-time fliers: Ramon, Clark, pilot William McCool and David Brown. Clark said the biggest surprise for her so far was "how much the ascent felt just like the simulation."

"I guess the second one that I noticed immediately was, obviously everything floats, the zippers and all the belts that have D-rings that we hold things down with are always floating and hitting each other and jingling and its makes this beautiful tinkling music in the background all the time," Clark said. "It just caught me off guard and it was beautiful."

At an afternoon status briefing, flight director Robert Castle, representing NASA's mission operations directorate, said Columbia is operating with "virtually no anomalies" and that the crew's power margins remain positive for a full-duration 16-day mission.

NASA mission scientist John Charles said the first human life sciences data takes were made today, including multiple blood draws and the collection of urine and saliva samples to support metabolic studies, including research to learn more about why astronauts lose bone mass in weightlessness."

"Our experiment is looking at what we call calcium kinetics, which is the movement of calcium through the body," said investigator Scott Smith. "The way we do that is we use tracers, we give a special form of calcium to the astronauts, they take one of these orally, one is infused intravenously, and we then collect samples and trace the movement of calcium through the body.

"Bone changes, as we all know, are very important during spaceflight, that is, the loss of bone is a significant health concern for astronauts. The amount of bone that's lost in a short-duration flight, in a few weeks, really is not that significant. It's actually very hard to measure. So what we look at is the change in calcium and we look at the change in markers of biochemistry, things that we can measure in the blood and in the urine that tell us what the bones are doing."

As it turns out, bone loss in people who have been recently paralyzed is similar to what astronauts experience during long-duration space flights. Somehow, in both cases, the body "understands" bone mass is no longer needed and metabolic changes are the result. Exactly what triggers those changes, and how they might be nullified or even reversed, is not yet known.

But barring implementation of technology that simulates gravity in space, resolving this issue is critical before humans can begin the long-duration flights needed to someday explore the solar system.

"Ultimately, our goal is to help mitigate or reduce if not eliminate the bone loss during spaceflight," Smith said. "What we're doing on this flight will help us understand the early changes during spaceflight, what happens during the first days and weeks of weightlessness and how the body adapts to that.

"We have done some preliminary studies on Mir," he said. "We're looking forward, hopefully, to be able to do these studies on the (international) space station to look at the time course of changes in calcium metabolism over time."

Later today, the Columbia's crew will begin work with an experiment to light small fires in a high-tech combustion module to learn more about how flames develop and propagate in the absence of gravity.

While it's not unusual these days to turn on the TV and watch construction projects going on in outer space, it is a bit out of the ordinary when ants - not astronauts - are the ones doing the building.

Fifteen ants are on board the shuttle Columbia as part of a student experiment to study the effects of weightlessness on behavior. Judging by video of the ant colony beamed down to mission control this afternoon, the absence of gravity doesn't seem to be bothering the workers all that much as they busily dig tunnels in a special gel.

The astronauts, of course, are busy with higher-priority payloads and experiments, working around the clock in two shifts to maximize the data that will be collected during this 16-day mission. More than 80 experiments are on board and mission managers are pleased with the initial progress of the flight.

"It's great to finally be in orbit," said Phil Engelauf, a senior flight director at the Johnson Space Center. "Spaceflight is a team sport and there's a huge number of people involved in getting a mission off the ground and executing it. And that's especially true of STS-107.

"We had a beautiful launch (Thursday), the vehicle is performing exceptionally well, we're very, very clean, with only one or two extremely minor issues to work on at this point. The crew is doing well on the timeline, most of the payload activations are complete - all of them scheduled up to this point are completed - with only a few remaining to be performed as scheduled later in the mission.

"So we're doing really, really well. ... Everyone is extremely pleased with what we've accomplished in the first 24 hours of the flight."

The only problems so far are minor. A backup intercom channel is not working properly, one of two heaters in a fuel cell tank did not turn on this morning and ground controllers are working to straighten out a data processing issue. But Engelauf said none of these issues would have an impact on the flight.

Mission scientist John Charles said "all in all, things are going as scheduled and we're looking forward to, I can't believe it, over two weeks of detailed and highly intensive data collection from a lot of experiments that have been waiting a long time for this chance to fly in space."

Because Columbia's KU-band antenna system is being used to transmit realtime science data to the ground, television showing the crew will be in extremely short supply during this flight. Every day or so, however, the astronauts will beam down 10 minutes or so of "crew choice video" showing whatever they think might be interesting to the public. The first such session is planned for 6:09 p.m. this evening.

The Columbia astronauts are plowing through a busy day of science today, getting into the meat of their research agenda after activating experiments in the shuttle's Spacehab research module and outside in the ship's cargo bay.

A mission status briefing is scheduled for 2 p.m., but so far there are no technical problems of any significance. Revision B of the NASA television schedule is posted below, along with a minor revision to the crew's flight plan to reflect a four-minute change to the projected landing time.

An updated status report will be posted here after today's mission status briefing at the Johnson Space Center in Houston.

After years of delay and post-9/11 concerns about security, the successful launch of the shuttle Columbia today brought a collective sigh of relief from NASA and Israeli officials on hand at the Kennedy Space Center to cheer on countryman Ilan Ramon.

Israeli Ambassador Daniel Ayalon described the launching as "really awesome, it was a very special moment with great excitement and ultimately, pride."

"In Israel, unfortunately, for the last two-and-a-half years we have been subjected to the most total campaign of terror," he said. "Terror has been striking all over, but in Israel especially. So anything that can take the mind off (such problems), even momentarily, for great and beautiful things is very much appreciated."

Ayalon said the security precautions taken by NASA, the Air Force and other U.S. government agencies "was very appropriate and we are grateful for NASA and the American authorities, Florida authorities, for this great security."

"Unfortunately, after 9/11 it's quite evident we have to watch, that this is an element that has to be factored in to almost any mission," he said.

Air Force fighters patrolled an FAA-mandated no-fly zone extending 30 miles in all directions from Columbia's launch pad, powerful radars monitored the launch area and the Coast Guard patrolled off shore.

But officials said no one entered the security zone without permission.

Security aside, Ramon's flight "is a testament to Israeli achievements in science and technology and we're very happy and proud to share and pull together with our best friend and ally the United States," Ayalon said. "Cooperation is great, it's another dimension that we've taken into space and it's a great beginning of many more opportunities to come."

Linda Ham, chairman of NASA's mission management team and the person who gave the final "go" for takeoff, called Columbia's ascent "an outstanding, picture-perfect launch."

"This is the first mission in a while that's completely dedicated to science," she said. "It was just an outstanding launch, a beautiful day, great weather, the launch countdown went exceptionally well."

Said launch director Michael Leinbach: "From my perspective, it was very easy, which is nice to say, and it was very pretty looking out the window of the firing room. It's going to be a fantastic mission."

The astronauts, as one might expect, were also pleased. Columbia completed its ascent with no problems of any significance, the ship's cargo bay doors were opened without incident and the crew is gearing up to activate the Spacehab research module.

"To have a sensitive moment, we hope your wait for space was worth it," radioed astronaut Charles Hobaugh in mission control. "We saw a flawless ascent and insertion for your now-veteran crew of astronauts and especially a big welcome to Ilan, as you join the international community of human spaceflight."

"Thank you very much, Houston," replied commander Rick Husband. "We made sure we welcomed everybody to space and they're all doing great. Thanks a million."

With Columbia's launch, Israel became the 30th country to send an astronaut or cosmonaut into space.

With fighter planes and radars scanning the sky for intruders, the shuttle Columbia thundered away on a marathon 16-day science mission today, carrying a crew of seven - including the first Israeli astronaut - scores of experiments and a menagerie of animal and insect research subjects.

Running two years behind schedule, Columbia finally roared to life at 10:39 a.m. and rocketed away from pad 39A to kick off the 113th shuttle mission, one of the last missions on NASA's manifest that doesn't involve the international space station.

The goal of the flight is to carry out space station-class research in a variety of disciplines, ranging from biology to medicine, from materials science to pure physics and technology development, research that cannot yet be accommodated on the still-unfinished international space station.

"We're all familiar with the overhead required for continuing station operations, especially with a crew size of three," said U.S. mission scientist John Charles. "Missions like STS-107 were inserted in the manifest to do science as if they were on the space station.

"This is simulated space station science, although the science itself stands on its own right, with the goal of keeping the scientists who are involved in this kind of activity engaged and productive and moving forward until the space station can assume the leading role in research."

At the controls were commander Rick Husband, pilot William "Willie" McCool and flight engineer Kalpana Chawla. Their crewmates are physicians David Brown and Laurel Clark, payload commander Michael Anderson and Israeli air force Col. Ilan Ramon, at least the seventh Jew to fly in space but the first from Israel.

Also on board are 13 rats, eight garden orb weaver spiders, five silkworms and three cocoons, four Medaka fish eggs that will develop in space, three carpenter bees, 15 harvester ants and an assortment of fish.

The animals and insects are subjects of experiments, many of them designed by students, to learn more about how weightlessness affects growth and behavior.

"This mission is fairly unique compared to the shuttle flights we've flown recently in that it is a dedicated science mission," said lead flight director Kelly Beck. "It will span multiple disciplines, such as the life sciences, physical sciences, Earth and space sciences as well as the educational arena. This flight involves multiple NASA centers, the international community and universities and schools throughout the world."

To maximize their research time, the astronauts will work around the clock in two 12-hour shifts. Husband, Chawla, Clark and Ramon will make up the "red shift," working what amounts to a day shift in the United States, while McCool, Brown and Anderson will work the overnight "blue shift."

Ramon's presence on Columbia's crew generated more interest than usual in security precautions. But NASA managers insisted the policy implemented last year in the wake of the Sept. 11 terrorist attacks in New York and Washington was essentially unchanged.

Fighter jets were patrolling an FAA-mandated no-fly zone extending 30 miles in all directions from pad 39A, powerful military radar systems and reconnaissance planes were on station, scanning the skies for intruders, and the Coast Guard was patrolling off shore.

Truck-mounted missile batteries presumably were in place at the nearby Cape Canaveral Air Force Station, but Air Force officials do not discuss what ground assets are actually in place for a given launch.

But all of that is pretty much standard procedure in the post-Sept. 11 climate. NASA security chief David Saleeba, a former Secret Service agent, said his team has been "tweaking and re-tweaking" security precautions in recent weeks, but no major changes have been implemented.

"You're not going to see that much difference in the area of security for this launch than you did for the last several launches," he told reporters last week. "We're trying to still maintain an openness within the agency while still maintaining an appropriate level of security."

More armed guards than usual were visible at the Kennedy Space Center this morning, but security seemed more or less normal in the post-Sept. 11 climate. In any case, no incidents were immediately reported.

Columbia's mission is one of the most complex shuttle flights attempted in recent years, a mix of more than 80 government, university and commercial experiments from researchers in the United States, Canada, Japan, the European Space Agency and Israel.

But it is a mission that had a harder time than most getting off the ground.

The flight first showed up on the NASA manifest in September 1999 when launch was scheduled for Nov. 30, 2000. But the mission was delayed six times before a crew could even be named because of shuttle refurbishment and payload changes, including the addition - and subsequent deletion - of former Vice President Al Gore's Triana Earth-watching satellite.

Chawla, Anderson, Brown, Clark and Ramon were named to the flight in September 2000. At that point, launch was targeted for June 2001. By the time Husband and McCool were added to the crew in December 2000, launch had slipped to August 2001. It eventually slipped another year, to July 19, 2002, primarily because of technical problems with the orbiter and delays in space station missions.

Then, a month and a half before launch last summer, the shuttle fleet was grounded because of small but potentially dangerous cracks in fuel line baffles. When all was said and done, Columbia's flight slipped to this month, behind two higher-priority space station missions, STS-112 and STS-113.

"Initially there might be a bit of letdown or disappointment," Husband said of the most recent delay. "But then we realized we've been given a gift of more time to prepare. We were able to take some time off, so that was good for us and our families morale-wise, and we were also able to keep our level of proficiency with our training up. ... We feel like we're as well trained as we can possibly be."

Columbia's flight is a throwback to pre-station science missions using NASA's now-retired European-built Spacelab modules.

But in this modern incarnation, the bulk of the crew's research will be carried out in a commercially built Spacehab research double module made up of two smaller modules bolted together to make a single two-room laboratory connected to the shuttle's crew cabin by a long tunnel.

Mounted just behind the Spacehab module is a pallet of six more multi-investigation experiment packages that do not require hands-on operation.

"In the areas of biology and physiology, we'll be conducting several studies to study the effects of weightlessness on crystal growth, plant growth and also the cardiovascular and musculo-skeletal systems," Beck said. "The information we gain from these studies will help develop better drugs, with particular interest in the areas of cancer and osteoporosis research.

"We also have studies of weightless on the human body, which will lead a better understanding of the effects of spaceflight and help us develop better techniques to combat those effects and increase our durations in space," Beck said. "There are studies of combustion and fire suppression processes that will help us potentially lead to cleaner burning techniques here on the ground as well as improved fire suppresion and prevention techniques.

"We have experiments investigating compression of wet sand, which could lead to improved construction techniques, we also will be studying dust storms to gain a better understanding of those effects on weather patterns and to improve our forecasting capabilities.

"We also have experiments to refine the solar constant and the study the Earth's ozone layer. We also have several experiments to demonstrate new technologies, such as water recycling, thermal control, communications and navigation. So that just kind of gives you a flavor of the wide variety of things we'll be doing on this mission."

The research double module, or RDM, is 20 feet long, 14 feet wide and 11 feet high, provides 2,200 cubic feet of pressurized volume and is capable of accommodating up to 9,000 pounds of cargo and experiment hardware. For Columbia's flight, the module is loaded with about 7,500 pounds of experiment gear and supplies. Another 800 pounds of research equipment and samples are mounted in the shuttle middeck area.

Spacehab Inc. builds and outfits such modules for NASA on a commercial basis, primarily for use ferrying hardware and supplies to and from the international space station.

The company's modules have been used for research in the past, but the Spacehab double research module aboard Columbia is the first to be equipped with the support systems needed for space station-class science. Eighteen percent of the research space aboard the RDM aboard Columbia was sold by Spacehab to commercial users around the world while NASA booked the remaining 82 percent.

The shuttle Columbia's countdown resumed after a planned 10-minute hold at 10:09 a.m. at the T-minus 20-minute mark. The shuttle's seven-member crew is strapped in, there are no technical problems of any significance and the weather is ideal for the year's first shuttle launching at 10:39 a.m. This status report will be updated after Columbia takes off or as conditions warrant.

The shuttle Columbia's external fuel tank is loaded with liquid oxygen and hydrogen rocket fuel, setting the stage for blastoff this morning on a 16-day science mission. There are no technical problems at pad 39A and the weather appears ideal for liftoff at 10:39 a.m., the opening of a 2.5-hour launch window.

Columbia's seven-member crew is believed to be suiting up at this hour after a traditional breakfast photo op at crew quarters. Based on a standard shuttle countdown, the astronauts are expected to head for the launch pad around 7:20 a.m. to strap in for launch. That's merely a guesstimate, however, because NASA no longer publicizes crew schedules as part of the agency's post Sept. 11 security policy.

Speaking of security - Columbia's crew includes Ilan Ramon, the first Israeli astronaut - no obvious signs of anything too unusual were evident this morning, at least to this reporter. Long lines of traffic were backed up at guard gates leading into the Kennedy Space Center as security personnel "hand touched" each ID badge under the watchful eyes of officers holding automatic weapons at the ready.

But the guns are fairly routine in the post-Sept. 11 environment and the traffic appeared to be the result of the hands-on badge checks and the normal rush of workers driving in at shift-change time. Still, it's safe to assume security is on high alert at the spaceport as Columbia's launch time approaches.

Unlike space station launch countdowns, which typically feature five-minute launch windows, Columbia's crew will have a full two-and-a-half hours to get off the ground starting at 10:39 a.m. The window in this case is limited only by NASA's allowable "crew on back time," giving the launch team plenty of time to handle any problems that might crop up.

Engineers ran into minor problems this morning that delayed the start of fueling, but the tank is now loaded and all systems appear "go" for launch.

NASA's mission management team met today and formally - finally - resolved lingering questions about shuttle fuel line bearings, officially clearing the shuttle Columbia for launch Thursday on a 16-day microgravity research mission. There are no other technical issues under discussion and the forecast remains 95 percent "go" during Columbia's 2.5-hour launch window Thursday. Liftoff is targeted for 10:39 a.m.

NASA's initial television schedule and the STS-107 flight plan, updated to reflect the actual launch time, are posted below.

NASA unveiled the shuttle Columbia's exact launch time today - 10:39:00 a.m. Thursday. Unlike recent space station missions that have had just five minutes or so to get off the ground, Columbia's crew will enjoy a full 2.5-hour launch window limited only by the time NASA allows a crew to stay on their backs at the pad. There are no technical problems at pad 39A and forecasters continue to predict a 95 percent chance of good weather during Columbia's launch window.

"Our launch countdown is proceeding very well," said NASA test director Jeff Spaulding. "We've really had no significant issues since the countdown began."

Technicians have finished loading Columbia's Spacehab research module with experiment samples and equipment and are working today to complete stowage of time-critical experiment materials on the shuttle's lower deck.

NASA's mission management team began meeting at 9 a.m. for a final review of work to clear up an issue with bearings in the shuttle's propellant lines. They also will discuss the potential impact of contamination found on a spacesuit valve during refurbishment at the factory. But as of this writing, neither issue is expected to delay Columbia's launch.

The shuttle Columbia is poised for blastoff Thursday on a marathon 16-day microgravity research mission, carrying scores of experiments and a menagerie of animal, plant, insect and human research subjects, including the first Israeli astronaut.

Under a now-familiar blanket of heightened post-Sept. 11 security, engineers are readying Columbia for blastoff on the 113th shuttle mission - STS-107 - at 10:39 a.m. Thursday at the opening of a 2.5-hour launch window. Ideal weather is expected.

The goal of the flight is to carry out space station-class research in a variety of disciplines, ranging from biology to medicine, from materials science to pure physics and technology development, research that cannot yet be accommodated on the still-unfinished international space station.

"We're all familiar with the overhead required for continuing station operations, especially with a crew size of three," said U.S. mission scientist John Charles. "Missions like STS-107 were inserted in the manifest to do science as if they were on the space station.

"This is simulated space station science, although the science itself stands on its own right, with the goal of keeping the scientists who are involved in this kind of activity engaged and productive and moving forward until the space station can assume the leading role in research." On board will be commander Rick Husband, pilot William "Willie" McCool, Indian-born flight engineer Kalpana Chawla, physicians David Brown and Laurel Clark, payload commander Michael Anderson and Israeli air force Col. Ilan Ramon.

Joining them will be 13 rats, eight garden orb weaver spiders, five silkworms and three cocoons, four Medaka fish eggs that will develop in space, three carpenter bees, 15 harvester ants and an assortment of fish.

The animals and insects are subjects of experiments, many of them designed by students, to learn more about how weightlessness affects growth and behavior.

To maximize their time in orbit, the astronauts will work around the clock in two 12-hour shifts. Husband, Chawla, Clark and Ramon will make up the "red shift," working what amounts to a day shift in the United States, while McCool, Brown and Anderson will work the overnight "blue shift." "STS-107 is a dual-shift, 16-day dedicated science mission," said lead flight director Kelly Beck. "This flight's going to provide multiple NASA centers, the international community as well as universities and schools throughout the world a very unique opportunity to perform a lot of science and a lot of research and technology demonstrations. So we're really looking forward to this flight." Ramon's presence on the crew has generated more interest than usual in security precautions. But NASA managers insist the policy implemented last year in the wake of the Sept. 11 terrorist attacks in New York and Washington is essentially unchanged.

Fighter jets will be patrolling an FAA-mandated no-fly zone extending 30 miles in all directions from pad 39A, powerful military radar systems and reconnaissance planes will be scanning the skies and the Coast Guard will be patrolling off shore.

But all of that is pretty much standard procedure in the post-Sept. 11 climate. NASA security chief David Saleeba, a former Secret Service agent, said his team has been "tweaking and re-tweaking" security precautions in recent weeks, but no major changes have been implemented.

"You're not going to see that much difference in the area of security for this launch than you did for the last several launches," Saleeba said. "We're trying to still maintain an openness within the agency while still maintaining an appropriate level of security." Even so, based on the world climate today, "I would be foolish to try to make you believe that the presence of an Israeli astronaut on this flight would not make it a higher profile flight," Saleeba said.

"It's unfortunate that that is true, it shouldn't be," he said. "He's first and foremost and astronaut and a scientist. And on a secondary note, he's Israeli. But we fly international people, people from all over the world on many of our flights. But because of the fact that he is Israeli, and what's going on in the world today, it's a natural assumption that this may be a higher profile flight." But Saleeba said there have been no credible threats against the space shuttle since Sept. 11, including Columbia's mission.

"We always have concerns about these missions because the shuttle is a fairly prominent symbol of American technology," he said. "But no, we don't have any threats right now that we're overly concerned about." In a departure from past missions, local law enforcement personnel are on watch and extra security personnel and barricades are in place at a Cocoa Beach hotel where Israeli dignitaries, researchers and family members are staying. A spokeswoman for the Brevard County Sheriff's Department described the precautions as unprecedented.

"I really think the NASA security people are taking care of all the security issues very good, I have all the confidence they're doing their job for the best of all of us and we really feel, all the crew, including me, we feel that we are being treated as properly as we could," Ramon said in an interview with CBS News.

"I believe the post-Sept. 11 (aftermath) put the world in an unusual and new situation," he said. "Everybody is more focused on the risks wherever they could be. It's obvious the media is trying to concentrate on this risk. But again, I think the NASA security people are doing their job."

A COMPLEX MISSION

Columbia's mission is one of the most complex shuttle flights attempted in recent years, a mix of more than 80 government, university and commercial experiments from researchers in the United States, Canada, Japan, the European Space Agency and Israel.

"We do have a lot of experiments on this flight ... and we're really covering all the major scientific disciplines," said payload commander Anderson. "And each experiment really does have a good application back here on Earth." But it is a mission that's had a harder time than most getting off the ground.

The flight first showed up on the NASA manifest in September 1999 when launch was scheduled for Nov. 30, 2000. But the mission was delayed six times before a crew could even be named because of shuttle refurbishment and payload changes, including the addition - and subsequent deletion - of former Vice President Al Gore's Triana Earth-watching satellite.

Chawla, Anderson, Brown, Clark and Ramon were named to the flight in September 2000. At that point, launch was targeted for June 2001. By the time Husband and McCool were added to the crew in December 2000, launch had slipped to August 2001. It eventually slipped another year, to July 19, 2002, primarily because of technical problems with the orbiter and delays in space station missions.

Then, a month and a half before launch last summer, the shuttle fleet was grounded because of small but potentially dangerous cracks in fuel line baffles. When all was said and done, Columbia's flight slipped to this month, behind two higher-priority space station missions, STS-112 and STS-113.

"We've made very good use of our time," Husband said of the most recent delay. "Whenever we have these types of launch delays, I would say probably initially there might be a bit of letdown or disappointment, but then we realized we've been given a gift of more time to prepare.

"So we've made really good use of our time. We were able to take some time off, so that was good for us and our families morale-wise, and we were also able to keep our level of proficiency with our training up. So we're doing great now and really looking forward to going to launch. We feel like we're as well trained as we can possibly be." Columbia's flight is a throwback to pre-station science missions using NASA's now-retired European-built Spacelab modules.

But in this modern incarnation, the bulk of the crew's research will be carried out in a commercially built Spacehab research double module made up of two smaller modules bolted together to make a single two-room laboratory connected to the shuttle's crew cabin by a long tunnel.

Mounted just behind the Spacehab module is a pallet of six more multi-investigation experiment packages that do not require hands-on operation. Still more experiments are mounted on top of the Spacehab module and in the shuttle's crew cabin.

"This mission is fairly unique compared to the shuttle flights we've flown recently in that it is a dedicated science mission," Beck said. "It will span multiple disciplines, such as the life sciences, physical sciences, Earth and space sciences as well as the educational arena. This flight involves multiple NASA centers, the international community and universities and schools throughout the world.

"In the areas of biology and physiology, we'll be conducting several studies to study the effects of weightlessness on crystal growth, plant growth and also the cardiovascular and musculo-skeletal systems. The information we gain from these studies will help develop better drugs, with particular interest in the areas of cancer and osteoporosis research.

"We also have studies of weightless on the human body, which will lead a better understanding of the effects of spaceflight and help us develop better techniques to combat those effects and increase our durations in space," Beck said. "There are studies of combustion and fire suppression processes that will help us potentially lead to cleaner burning techniques here on the ground as well as improved fire suppresion and prevention techniques.

"We have experiments investigating compression of wet sand, which could lead to improved construction techniques, we also will be studying dust storms to gain a better understanding of those effects on weather patterns and to improve our forecasting capabilities.

"We also have experiments to refine the solar constant and the study the Earth's ozone layer. We also have several experiments to demonstrate new technologies, such as water recycling, thermal control, communications and navigation. So that just kind of gives you a flavor of the wide variety of things we'll be doing on this mission." The research double module, or RDM, is 20 feet long, 14 feet wide and 11 feet high, provides 2,200 cubic feet of pressurized volume and is capable of accommodating up to 9,000 pounds of cargo and experiment hardware. For Columbia's flight, the module is loaded with about 7,500 pounds of experiment gear and supplies. Another 800 pounds of research equipment and samples are mounted in the shuttle middeck area.

Spacehab Inc. builds and outfits such modules for NASA on a commercial basis, primarily for use ferrying hardware and supplies to and from the international space station.

The company's modules have been used for research in the past, but the Spacehab double research module aboard Columbia is the first to be equipped with the support systems needed for space station-class science. Eighteen percent of the research space aboard the RDM aboard Columbia was sold by Spacehab to commercial users around the world while NASA booked the remaining 82 percent.

The NASA experiments require up to 60 percent or more of the mass available in the Spacehab module, 58 percent of the volume and 71 percent of the crew time "largely because of the medical experiments we're undertaking," Charles said.

The module is loaded with nine commercial payloads supporting 21 investigations into bone loss, protein crystal growth, the effects of weightlessness on human physiology and technology demonstrations in space navigation, satellite communications and thermal control systems.

Another four payloads provided by the European Space Agency will support 14 other investigations. And NASA is responsible for a space station risk mitigation experiment, along with 18 payloads sponsored by the office of Biological and Physical Research for 23 investigations.

"I'm really excited," said Clark. "We're doing a huge number of different science experiments in different disciplines. I'm especially excited about the wide range of medical experiments we're doing that will benefit people I know and patients here on Earth."

ASTRONAUTS LOOK FORWARD TO EARTHLY BENEFITS FROM RESEARCH

One of the payloads, known as the Advanced Respiratory Monitoring System, or ARMS, will be used to study how weightlessness affects the heart, lungs and metabolism.

"We'll be doing a complicated set of breathing maneuvers," Clark said. "There are eight different experiments with dozens of investigators, primarily from Europe, and they're looking at the changes in the oxygen exchange in your lungs as the blood flow changes with different body positions.

"They're looking specifically at the changes in respiratory or lung function when patients have to be on their backs for extended periods of time. In fact, there's some good evidence that patients in intensive care units would be better off on their stomachs as opposed to their backs.

"This entails a huge amount of overhead to take care of them that way but certainly if there's much better oxygen exchange and lung function, then it's worth that overhead," Clark said. "They've been studying us in different positions, on our stomachs and on our backs, studying the air exchange." For Brown, bone loss experiments could provide insights into problems affecting millions on Earth.

"That's something that's a problem for everybody when we get older, particularly women," he said. "It turns out astronauts, when we go to space and no longer have the stress of gravity on our skeletons, we lose calcium and so we're going to be studied for that.

"We're actually a very good model, a very accelerated model, for what happens to people over many, many, many years. So it's useful to study us to learn more about how to slow or prevent osteoporosis here on Earth. ... We also have quite a few locker experiments that have bone cells in them, again, to study the same metabolism and why bone cells either gain or lose calcium." Chawla highlighted a zeolite crystal growth experiment that could help pave the way for efficient fuel cells.

"We carry precursor solutions in tubes that we mix on orbit," she said. "And once the solutions are mixed, we put these tubes in a furnace and let the crystals grow. Zeolites are materials that have lots of holes in them much like a sponge, but they attract materials of unique capacities towards them, unique characteristics.

"The applications are very wide ranging and very interesting," she said. "One of them is to come up with dyes that hold better to the paper. Another one is these days we are talking about coming up with alternate fuels like hydrogen as opposed to gasoline combustion. And it's hard to store hydrogen at room temperatures. You have to basically compress it and then it becomes a hazardous thing to deal with.

"One of the experiments that a (researcher) is doing on this flight is to come up with a material that can have hydrogen embedded in the zeolite material so you can store it at room temperatures." Another suite of six experiments was provided by students in six countries as part of an education program managed by Space Media, a Spacehab subsidiary.

In one, students in Australia will study how weightlessness affects the webs of garden orb weaver spiders. A Chinese experiment study how the lack of gravity affects the development of silkworms and a Japanese project will do the same with Medaka fish. A school in Liechtenstein is studying the tunneling behavior of carpenter bees and students at a high school in New York will study how weightlessness affects a small colony of ants.

Three technology demonstration experiments are mounted on the roof of the RDM, exposed to the space environment. Another six experiment packages, known collectively by the acronym FREESTAR, are mounted on a truss just behind the RDM in Columbia's cargo bay.

One FREESTAR experiment is devoted to studying the behavior of xenon at low temperatures, another will characterize Earth's ozone layer and a third will measure the amount of solar radiation reaching Earth, part of an ongoing study to chart the value of the solar constant.

"One of the experiments I'm working on is called SOLSE, shuttle-ozone limb sounding experiment, and it's to evaluate a new algorithm to measure the ozone levels in an altitude-type profile instead of looking straight down," McCool said. "I think the world as a whole is interested in global warming and the preservation of our ozone layer and this will certainly help in understanding the ozone and its depletion." The FREESTAR suite also includes a package of 10 student experiments in the Space Experiment Module; an experimental space radio; and the Mediterranean Israeli Dust Experiment, or MEIDEX, featuring a multi-spectral camera designed to measure the distribution and properties of desert dust suspended in the atmosphere over the Mediterranean basin.

MEIDEX also will be used to study strange "transient luminous events," or sprites, that shoot upward toward space from thunderstorm clouds.

Ramon, who will help operate the instrument, said the Israeli experiment marked "a door opening for scientists from both countries to have mutual research and collaboration." "This is ongoing, actually. A few months ago, there was talk between scientists here in the United States and they were talking about a continuous Meidex experiment, a Meidex 2. The idea was to put a Meidex camera on the station." A flood of data from the experiments aboard Columbia will be beamed back to Earth in realtime using the shuttle's Ku-band antenna, all but eliminating live television from the orbiter. Only a handful of media interviews, a crew news conference and occasional 10-minute crew-choice video downlinks are currently planned.

Assuming an on-time liftoff, Columbia will return to Earth around 8:49 a.m. on Feb. 1.

Launch of an Air Force Titan 4B rocket carrying a Milstar military communications satellite, originally scheduled for Jan. 21, has been delayed indefinitely because of software-related problems. The slip means the shuttle Columbia can take advantage of additional launch slots if its liftoff on a 16-day microgravity research mission is delayed past Friday.

NASA can only make two back-to-back attempts to launch Columbia before standing down for four days to refurbish on-board experiments and to top off fuel supplies for its electricity generating fuel cells. As long as the Titan/Milstar launch was set for Jan. 21, a shuttle launch slip past Friday would have meant standing down until around Jan. 25, after two launch attempts for the Titan and after two days to reconfigure Air Force tracking systems.

With the Titan launch now on hold, Columbia's crew can make launch attempts Thursday, Friday and then make two more attempts starting four days later.

Shuttle program manager Ronald Dittemore has decided to give engineers an additional day to resolve questions about the health of bearings inside the shuttle Columbia's fuel lines. While engineers believe there is no problem launching Columbia Thursday as planned, Dittemore said late today the team looking into the issue (see below for details) wanted additional time to make sure nothing had been overlooked in the rush of the countdown.

"I'm satisfied that we are on the right path that will resolve all these technical issues within the next 24 hours," Dittemore said. "We had sufficient discussion to convince the engineering and operations teams, along with management, that the resolution is acceptable to fly.

"The team did ask for a 24-hour time period for them to make sure they did not overlook anything," he added. "We graciously allowed them the 24-hours. So we agreed to hold an L-1 day review tomorrow just to make sure we didn't overlook anything in our process."

Otherwise, there are no technical problems of any significance at pad 39A and forecasters continue to predict a 95 percent chance of good weather during Thursday's launch window.

Technicians at the Kennedy Space Center are spending the day loading experiment samples, subjects and hardware into a Spacehab module in the shuttle Columbia's cargo bay in preparation for launch Thursday on a 16-day microgravity research mission. With no technical problems at pad 39A, forecasters continue to predict a 95 percent chance of good weather during Columbia's launch window. The odds drop to 40 percent "go" on Friday.

NASA managers, meanwhile, plan to meet this afternoon for a standard launch-minus-two-day review of Columbia's processing and readiness for flight. The only open issue on the table is the results of an investigation into the health of large bearings in the shuttle's propellant lines that allow the pipes to flex slightly under launch vibrations.

A crack was found in one of the shuttle Discovery's 16 bearings last month and while no other cracks have been found to date, Columbia's bearings cannot be inspected at the pad. Engineers have been studying the issue to determine whether a bearing failure in flight could produce debris that, in turn, could get sucked into a main engine with possibly catastrophic results.

This issue was all but put to bed during an engineering teleconference Sunday. Barring some unexpected result from a few final tests, NASA's mission management team is expected to formally resolve the matter today and clear Columbia for takeoff.

Overnight, engineers successfully filled on-board tanks with liquid oxygen and hydrogen to power Columbia's three electricity producing fuel cells for the duration of the 16-day mission.

At pad 39A today, technicians are working to install last-minute experiment samples and subjects, including high-tech cages for 13 rats, into Columbia's Spacehab research module. Because the shuttle is vertical at the pad, a technician must be lowered down a tunnel between the shuttle's crew cabin and the Spacehab module to make the necessary installations.

"All told, it's about 20 hours of very demanding work," said Jack Keifenheim, a payloads manager at the Kennedy Space Center. "It's critical that we stay on schedule because following that, we get into our middeck late stowage and everything has to go like clockwork."

He was referring to installation Wednesday of final experiments, samples and critters in lockers on the shuttle's lower deck. Despite the tricky, last-minute nature of the work, no problems are expected.

"In summary, the launch countdown is continuing right on track for Thursday, the flight and the ground hardware and systems are in great shape," said NASA test conductor Pete Nickolenko. "The launch team and the many mission support teams around the world are focused and ready to support launch on Thursday."

Liftoff is targeted for sometime between 10 a.m. and 2 p.m. The exact launch time will be announced Wednesday.

Countdown clocks began ticking late Sunday for launch of the shuttle Columbia Thursday on a 16-day microgravity research mission featuring dozens of high-tech experiments and a seven-member crew that includes the first Israeli astronaut. There are no technical problems at pad 39A and forecasters are predicting a 95 percent chance of good weather during the shuttle's morning launch period. The odds drop to 40 percent "go" Friday when rain and high winds are expected.

"The STS-107 launch countdown has begun and things are proceeding well," said NASA test director Jeff Spaulding. "The shuttle Columbia is in excellent shape and we're continuing our preparations for Thursday's launch of the Spacehab research double module."

Liftoff is targeted for sometime between 10 a.m. and 2 p.m. Under NASA's post Sept. 11 security policy, the exact time will not be announced until the day before launch.

The only wild card in all of this is ongoing work to determine the health of large bearings in the shuttle's propellant feed lines after a crack was found last month in a bearing aboard the shuttle Discovery.

Each shuttle is equipped with 16 such bearings, each the size of a cue ball, which anchor flexible bellows assemblies that allow the propellant lines to bend slightly when subjected to the vibrations of launch. The concern is that a bearing might crack and break apart during flight, allowing metal debris to get sucked into a main engine with possibly catastrophic results.

Only one such crack has been found - aboard Discovery - but Columbia's bearings cannot be inspected at the launch pad. Engineers have been reviewing data and subjecting similar bearings to various stresses to develop a rationale for launching Columbia as is.

During a teleconference Sunday, NASA managers gave the launch team clearance to begin Columbia's countdown while a final few tests are carried out. Senior NASA managers will review the analysis Tuesday and, barring some unexpected development, they are expected to clear Columbia for launch Thursday.

"That analysis thus far has gone very well and has given us enough confidence to begin the launch countdown," Spaulding said. "We do expect to have final flight rationale presented tomorrow afternoon."

Columbia is carrying scores of experiments into orbit, many of them commercially funded, for 16 days of around-the-clock research. Because many of the experiment subjects and samples have a short shelf life, Columbia's seven-member crew will have just two days to get off the ground before standing down for four days to refurbish the science hardware and reload fuel for the shuttle's electrical generators.

In this case, however, four days beyond Friday would put the shuttle flight in conflict with launch of an Air Force Titan 4B rocket carrying a high priority Milstar communications satellite. The Titan is scheduled for liftoff from the Cape Canaveral Air Force Station on Jan. 21 and the Air Force will get at least two days to get the rocket off the ground. Engineers then would need two more days to reconfigure radar tracking systems to support the shuttle. As a result, if Columbia is not off the ground by Friday, launch likely will slip to Jan. 25. And that assumes a small NASA satellite already scheduled for launch Jan. 25 on an air-launched Pegasus rocket slips a few days to make room.

Columbia originally was scheduled for liftoff last July, but the shuttle fleet was grounded by work to repair small cracks in fuel line baffles. Columbia ended up slipping behind two space station assembly missions, pushing the flight to this month.

"It has been a long road for us," flight engineer Kalpana Chawla said after flying to Florida Sunday evening. "I'm very, very happy to be here. I think we're going to go."

NASA managers have scheduled a teleconference Sunday, hours before the start of the shuttle Columbia's countdown to blastoff Thursday on a microgravity research mission, to assess the health of critical bearings in the ship's fuel lines. While a flight readiness review has tentatively cleared Columbia for blastoff, formal approval to proceed will not be issued until the bearing issue is put to rest.

"It is all coming together, except that we just weren't able to pull all the data and finish all of the testing in time to support this readiness review, which we had scheduled for today," said shuttle program manager Ronald Dittemore. "We're optimistic. That's why we targeted our launch date (for Jan. 16 as planned) and that's why we are putting the crew in (medical) quarantine. We don't have any real indications that look like this is going to be a show stopper."

Regardless of the outcome of the teleconference Sunday, NASA managers likely will not formally put the matter to rest until holding their standard launch-minus-two-days mission management team meeting Tuesday.

There are no known problems with any of the 16 cue-ball-size bearings in Columbia's fuel lines. But a crack found in a bearing in the shuttle Discovery last month - and recent tests to determine what might happen should a bearing crack and fragment during engine operation - have raised safety questions that must be resolved. At issue is debris getting sucked into one of the shuttle's three main engines, possibly with catastrophic results.

Bearings in NASA's other shuttles have been inspected and found to be free of any visible defects. No such inspections have been made with Columbia, however. Standing vertically at the launch pad, attached to an external fuel tank with three engines installed, only a handful of the 16 bearings are accessible for boroscope inspection.

The 2.25-inch-wide bearings are part of a system that allows propellant line bellows inside the shuttle's engine compartment to flex slightly while maintaining their structural integrity. Eight such bearings are present in the liquid oxygen lines and eight more in the ship's liquid hydrogen feed system.

Inside a given bellows section, two sets of struts forming interlocking three-legged pyramids are hooked together under compression. The bearing in question serves as a common apex of sorts for the interlocking struts. Should a bearing crack apart in flight, when propellant is rushing by at high velocity, debris could get sucked into an engine.

During recent tests, engineers were able to roughly duplicate the crack found in Discovery's bearing, but the nature of the "foreign object debris," or FOD, was not what they expected. Engineers currently are reviewing data and continuing their analysis to build a rationale for flight even though Columbia's bearings cannot all be inspected at the pad.

This issue is complex because there is no easy way to make repairs, should any be needed. The bearings are spread out in the engine compartment's maze of plumbing. To replace one, the propellant line in question would pretty much have to be disassembled, a job that would cause lengthy processing delays.

In the meantime, engineers at the Kennedy Space Center are continuing to ready Columbia for launch Thursday on the year's first shuttle flight, one of the last missions on NASA's manifest that does not involve the international space station. The ship's crew, including Israeli astronaut Illan Ramon, is expected to arrive Sunday.

Liftoff is targeted for sometime between 10 a.m. and 2 p.m. Thursday. The exact launch time will be revealed 24 hours before launch as part of NASA's post Sept. 11 security policy. Once in orbit, the crew will work in two shifts, around the clock, to carry out dozens of microgravity experiments. Assuming an on-time launch, Columbia will return to Earth Feb. 1.

Engineers are studying the potential impact of a crack found in a cue ball-sized bearing inside a liquid oxygen feed line aboard the shuttle Discovery. The crack was discovered during routine inspections as part of on-going maintenance and modifications every orbiter periodically goes through. At issue is what caused the crack, whether it represents a safety threat and whether or not it poses any sort of fleet-wide issue.

As of this writing, engineers are optimistic it's not a generic problem. But shuttle program manager Ronald Dittemore has ordered a team of engineers to investigate the matter and to examine a similar bearing in the shuttle Atlantis' oxygen feed line to see if any problems are present.

NASA currently has its collective sights set on launching the shuttle Columbia Jan. 16 on a Spacehab microgravity research mission featuring the first Israeli astronaut. There are no plans at present to attempt any sort of inspection of the bearing aboard Columbia, which sources say would be difficult with the orbiter in the vertical orientation at launch pad 39A. But that could change depending on how the investigation plays out.

The 2.25-inch-wide bearing in question is part of a system that allows a big 17-inch-wide feed line bellows inside the shuttle's engine compartment to flex slightly while maintaining its structural integrity. Inside the propellant line, two sets of struts forming interlocking three-legged pyramids are hooked together under compression. The bearing in question, located upstream of the point where the main oxygen line branches apart to serve each main engine, serves as a common apex of sorts for the interlocking struts.

During an inspection of this bearing in the liquid oxygen feed line aboard Discovery, engineers noticed a "discernible crack," one official said. One concern is the possibility that a piece of metal could break off and get sucked into one of the shuttle's three main engines during ascent.

As of this writing, any speculation about the potential impact of this issue is just that - speculation - but NASA managers are hopeful the upcoming inspections will show the bearing problem is isolated to Discovery.

Last summer, during routine post-flight inspections of Atlantis, engineers discovered a small crack in a liner inside the 12-inch-wide liquid hydrogen feed line leading to main engine No. 1. Two more cracks in the same flow liner were found the next day.

Similar cracks then were found aboard Discovery, Columbia and Endeavour, prompting Dittemore to ground the fleet until corrective action could be taken. Shuttle flights resumed in October after a three-month hiatus.

Engineers say the current issue is unrelated to the earlier flow liner cracks and may be of no consequence when all is said and done. Then again, that's what some engineers thought after the flow liner issue first surfaced. Stay tuned.

The shuttle Columbia was hauled to launch pad 39A at the Kennedy Space Center today, setting the stage for liftoff Jan. 16 on a Spacehab microgravity research mission featuring the first Israeli astronaut. In keeping with NASA's post Sept. 11 security plan, the exact launch time will not be revealed until the day before launch.

The goal of the 16-day flight - one of the last missions left on NASA's manifest that does not involve the international space station - is to conduct a smorgasbord of experiments in a wide variety of scientific disciplines. To maximize science results, the shuttle's KU-band antenna, normally used to downlink television through NASA's fleet of TDRS communications satellites, will be used almost exclusively to downlink data during Columbia's flight, miminizing live television from the orbiter.

In addition, the ship's crew - commander Rick Husband, pilot William "Willie" McCool, flight engineer Kalpana Chawla, Michael Anderson, David Brown, Laurel Clark and Ilan Ramon, a colonel in the Israeli air force, will work around the clouk in two 12-hour shifts throughout the flight. Husband, Chawla and Anderson are veterans of one shuttle flight each while the rest are space rookies.

Rollout pictures are available in the KSC multimedia gallery. For readers interested in a quick overview of the 113th shuttle flight, here is an edited version of NASA's mission overview:

Source: NASA/USA STS-107 Press Kit

Space shuttle mission STS-107, the 28th flight of the space shuttle Columbia and the 112th shuttle mission to date, will give more than 70 international scientists access to both the microgravity environment of space and a set of seven human researchers for 16 uninterrupted days.

Columbia's 16-day mission is dedicated to a mixed complement of competitively selected and commercially sponsored research in the space, life and physical sciences. An international crew of seven, including the first Israeli astronaut, will work 24 hours a day in two alternating shifts to carry out experiments in the areas of astronaut health and safety; advanced technology development; and Earth and space sciences.

When Columbia is launched from Kennedy Space Center's Launch Pad 39A it will carry a SPACEHAB Research Double Module (RDM) in its payload bay. The RDM is a pressurized environment that is accessible to the crew while in orbit via a tunnel from the shuttle's middeck. Together, the RDM and the middeck will accommodate the majority of the mission's payloads/experiments. STS-107 marks the first flight of the RDM, though SPACEHAB Modules and Cargo Carriers have flown on 17 previous space shuttle missions.

Astronaut Rick Husband (Colonel, USAF) will command STS-107 and will be joined on Columbia's flight deck by pilot William "Willie" McCool (Commander, USN). Columbia will be crewed by Mission Specialist 2 (Flight Engineer) Kalpana Chawla (Ph.D.), Mission Specialist 3 (Payload Commander) Michael Anderson (Lieutenant Colonel, USAF), Mission Specialist 1 David Brown (Captain, USN), Mission Specialist 4 Laurel Clark (Commander, USN) and Payload Specialist 1 Ilan Ramon (Colonel, Israeli Air Force), the first Israeli astronaut.

The seven crewmembers will work in two shifts throughout their 16 days in space. The Red Shift will include Husband, Chawla, Clark and Ramon, while the Blue Shift will include McCool, Brown and Anderson. The seven astronauts will work round-the-clock to complete a multidisciplinary research program involving 32 payloads with 59 separate investigations.

Under an agreement with NASA, SPACEHAB, Inc. has marketed 18 percent of the module?s capacity of 9,000 pounds to international and industry commercial users from around the world. NASA research will utilize the remaining 82 percent of the payload capacity.

Experiments in the SPACEHAB RDM include nine commercial payloads involving 21 separate investigations, four payloads for the European Space Agency with 14 investigations, one payload/investigation for ISS Risk Mitigation and 18 payloads supporting 23 investigations for NASA's Office of Biological and Physical Research (OBPR).

In the physical sciences, three studies inside a large, rugged chamber will examine the physics of combustion, soot production and fire quenching processes in microgravity. These experiments will provide new insights into combustion and firesuppression that cannot be gained on Earth. An experiment that compresses granular materials, in the absence of gravity, will further our understanding of construction techniques. This information can help engineers provide stronger foundations for structures in areas where earthquakes, floods and landslides are common. Another experiment will evaluate the formation of zeolite crystals, which can speed the chemical reactions that are the basis for chemical processes used in refining, biomedical and other areas. Yet another experiment will use pressurized liquid xenon to mimic the behaviors of more complex fluids such as blood flowing through capillaries.

In the area of biological applications, two separate OBPR experiments will allow different types of cell cultures to grow together in weightlessness to enhance their development of enhanced genetic characteristics - one will be used to combat prostate cancer, the other to improve crop yield. Another experiment will evaluate the commercial usefulness of plant products grown in space. A facility for forming protein crystals more purely and with fewer flaws than is possible on Earth may lead to a drug designed for specific diseases with fewer side effects.

A commercially sponsored facility will house two experiments to grow protein crystals to study possible therapies against the factors that cause cancers to spread and bone cancer to cause intense pain to its sufferers. A third experiment will look at developing a new technique of encapsulating anti-cancer drugs to improve their efficiency. Other studies will focus on changes, due to spaceflight, in the cardiovascular and musculoskeletal systems; in the systems which sense and respond to gravity; and in the capability of organisms to respond to stress and maintain normal function. NASA is also testing a new technology to recycle water prior to installing a device to recycle water permanently aboard the International Space Station.

The European Space Agency (ESA), through a contract with SPACEHAB, is flying an important payload focused on astronaut health, biological function and basic physical phenomena in space. These experiments will address different aspects of many of the same phenomena that NASA is interested in, providing a more thorough description of the effects of spaceflight, often in the same subjects or specimens. ESA will perform seven in-flight experiments, and one ground-based, on the cardiopulmonary changes that occur in astronauts.

Additional ESA biological investigations will examine bone formation and maintenance; immune system functioning; connective tissue growth and repair; and bacterial and yeast cell responses to the stresses of spaceflight. A special facility will grow large, well-ordered protein and virus crystals that are expected to lead to improved drug designs. Another will study the physical characteristics of bubbles and droplets in the absence of the effects of Earth's gravity.

SPACEHAB is also making it possible for universities, companies and other government agencies to do important research in space without having to provide their own spacecraft. The Canadian Space Agency is sponsoring three bone-growth experiments, and is collaborating with ESA on two others. The German Space Agency will measure the development of the gravity-sensing organs of fish in the absence of gravity. A university is growing ultra-pure protein crystals for drug research. Another university is testing a navigation system for future satellites. The U.S. Air Force is conducting a communications experiment. Students from six schools in Australia, China, Israel, Japan, Liechtenstein and the United States are probing the effects of spaceflight on spiders, silkworms, inorganic crystals, fish, bees and ants, respectively.

There are also experiments in Columbia's payload bay, including three attached to the top of the RDM: the Combined Two-Phase Loop Experiment (COM2PLEX), Miniature Satellite Threat Reporting System (MSTRS) and Star Navigation (STARNAV).

There are six payloads/experiments on the Hitchhiker pallet - the Fast Reaction Experiments Enabling Science, Technology, Applications and Research (FREESTAR), which is mounted on a bridge-like structure spanning the width of the payload bay. These six investigations look outward to the Sun, downward at Earth's atmosphere and inward into the physics of fluid phenomena, as well as testing technology for space communications. FREESTAR will hold the Critical Viscosity of Xenon-2 (CVX-2), Low Power Transceiver (LPT), Mediterranean Israeli Dust Experiment (MEIDEX), Space Experiment Module (SEM-14), Solar Constant Experiment-3 (SOLCON-3) and Shuttle Ozone Limb Sounding Experiment (SOLSE-2).

The SEM is made up of separate student experiments from schools across the U.S. and is the 14th flight of a SEM on the space shuttle.

Additional secondary payloads are the Shuttle Ionospheric Modification with Pulsed Local Exhaust Experiment (SIMPLEX) and Ram Burn Observation (RAMBO).