STS-120/ISS-10A MISSION ARCHIVE (FINAL)
Updated: 11/07/07

By William Harwood
CBS News/Kennedy Space Center

The following copy originally was posted on the Current Mission space page at http://cbsnews.com/network/news/space/current.html.

Comments, suggestions and corrections welcome!

TABLE OF CONTENTS

01:10 PM, 11/7/07, Update: Melroy guides Discovery to a smooth landing (UPDATING at 3:15 p.m. with Melroy quotes; Anderson in good shape; UPDATING at 4:40 p.m. with post-landing news conference)

With commander Pam Melroy at the controls, the shuttle Discovery plunged back to Earth today, streaking across the heartland of America to a picture-perfect landing at the Kennedy Space Center to wrap up an action-packed space station assembly mission.

Banking sharply through a sweeping 195-degree right overhead turn, Melroy lined up on runway 33 and pilot George Zamka lowered the shuttle's landing gear seconds before a tire-smoking touchdown at 1:01:18 p.m. A few moments later, using a red-and-white braking parachute to slow down, Discovery rolled to a halt.

"Houston, Discovery, wheels stopped," Melroy radioed.

"Copy, wheels stopped, Discovery. Congratulations on a tremendous mission and a great landing, Pam," replied astronaut Terry Virts from mission control at the Johnson Space Center in Houston.

Unofficial mission duration was 15 days, two hours, 23 minutes even over 238 complete orbits. Total distance traveled was roughly 6.2 million miles since blastoff Oct. 23.

Melroy, Zamka, flight engineer Stephanie Wilson and spacewalkers Scott Parazynski and Doug Wheelock doffed their pressure suits for a traditional runway walk-around before returning to crew quarters for medical checks and reunions with family members.

Italian astronaut Paolo Nespoli, representing the European Space Agency aboard Discovery, and Clay Anderson, returning from a 152-day stay aboard the international space station, remained in a crew transport vehicle for routine medical checks.

"It's great to be out here on this gorgeous day," Melroy said, standing in front of Discovery on the runway. "It's great to be back in Florida, especially, the home of Discovery. We could not have done this mission without Discovery being as clean and beautiful as it was.

"Sorry that Clay and Paolo couldn't be be out here," she said. "They're doing great, they're just doing some extra medical tests so they couldn't join us right now. But I know they feel the same way, particularly Clay. He can't wait to see his wife soon, it's their 15th wedding anniversary."

Anderson, launched to the international lab complex last June aboard the shuttle Atlantis, returned to Earth resting on his back in a recumbent seat on Discovery's lower deck to ease his re-adaptation to gravity after 152 days in space. A team of flight surgeons and support personnel was standing by to assess his condition and help him off the orbiter.

While it varies from one individual to another, it typically takes returning station astronauts a month or so to largely re-adapt to gravity and up to a year to fully recover.

"Physically and mentally, I'm really ready to be home," Anderson said from orbit Tuesday. "I've worked very hard on my physical exercise since I arrived way back in June. So I think that part will be fine. The only part I don't know about is how I will react with my vestibular system and the fact that I've been off the planet with minimal gravity for five months and then I'll come thumping back to the ground - I'm sorry, Pam, smoothly come back to the ground! - and enjoy the comforts of gravity again. So it'll be interesting to find out. I'm kind of optimistic, maybe overly so.

"Regarding what I miss, I think just being able to be outside in the breezes and hear the birds and feel the sunlight and that sort of thing, you can't get that on the international space station. You can imagine it, you can look out the window and see beautiful things, but it's not the same as being outside on the ground on the beautiful planet Earth."

Along with seeing his family again, Anderson said he also plans to enjoy a steak dinner at his earliest convenience.

"I have a special, secret recipe that we like to do at home, so I'm really looking forward to that first time at home with my family," he said. "For other things, I think ice cold drinks, or things like ice cream that we don't have any opportunity to have on the international space station ... are just general cravings that I have.

"But I enjoyed my time up there immensely and it's a kind of a bitter sweet time for me to come home. But I'm ready."

Flying upside down and backward over the southern Indian Ocean, Melroy and Zamka fired Discovery's twin braking rockets at 11:58:49 a.m. for one minute and 53 seconds, slowing the ship by about 147 mph to drop out of orbit for an hourlong glide to Earth.

The original flight plan called for a southwest-to-northeast re-entry trajectory across the south Pacific Ocean, Central America and the Caribbean for a pre-dawn landing. But given the length of Discovery's extended 16-day mission, flight controllers altered the crew's schedule to bring in daylight opportunities using a so-called descending node flight path that carried Discovery across the central United States for the first time since the 2003 Columbia disaster.

"Just like driving, flying and making a landing, I think, is easier in the daylight, you have more visual cues," said Melroy, a former large aircraft test pilot and the second woman to command a space shuttle.

A half hour after the deorbit rocket firing, Discovery plunged into the discernible atmosphere 400,000 feet above the mid Pacific Ocean north of Hawaii and crossed the coast of western Canada just north of Vancouver. Moving from northwest to southeast, Discovery streaked high above Montana and central Nebraska, passing just a few miles south of Anderson's hometown of Ashland.

Flying almost directly above Topeka, Kansas, Discovery's flight computers guided the ship just south of Memphis and across the deep south to Florida. Melroy took over manual control at an altitude of 50,000 feet above north Merritt Island as the shuttle dropped below the speed of sound.

After giving Zamka a few moments of hands-on flying time, Melroy completed a sweeping 195-degree right overhead turn to line up on runway 33.

"Discovery worked perfectly, and I just want to say a big thank you to everybody at the Kennedy Space Center for everything that you do," Melroy said after landing. "Because it takes the entire team to pull it together to launch a shuttle as clean as this. And that goes for the whole agency, I think the whole agency had to pull together for this particular mission.

"We saw a lot of very unusual things happen. We did a pretty amazing (solar panel repair spacewalk) and that was very exciting. It's a thrilling day for both the space shuttle and the space station programs, vindicating both programs and their purpose and their flexibility in space. I just want say thank you, we are thrilled to be back home."

At a post-landing news conference, NASA Administrator Mike Griffin said Discovery's mission was a welcome success.

"While all of you know that I think there's no such thing as a good press conference, this one is as good as it can be because the only thing we can talk about up here is how great this mission has been from start to finish and how you've had an opportunity to see and report on NASA at its very best," he said.

Anderson was replaced aboard the space station by Dan Tani, who hitched a ride into space aboard Discovery and who remained behind with Expedition 16 commander Peggy Whitson and Yuri Malenchenko when the shuttle departed Monday.

Over the course of a dramatic assembly mission, the combined shuttle-station crews successfully attached a new pressurized module to the lab complex and moved a huge set of solar arrays to its permanent mounting point on the far left end of the lab's main solar power truss.

When the arrays were re-extended, one of them was mangled and torn by a guide wire hangup that required a mission extension and a dramatic spacewalk repair job by Parazynski and Wheelock last Saturday. But the work was successful and the array was fully extended and locked in place.

Griffin said the mission reflected a growing maturity in space operations that is difficult to appreciate.

"I think that building the space station is far more difficult, and certainly far more complex, than was executing Apollo," he said. "Apollo was an incredible leap from where we were. But it was simpler than what we are trying to do today.

"We don't have the experience base to appreciate how great it really is. Humans have been building bridges for a thousand years, more, so each new, more exciting bridge is an extension beyond what was done (before), but because it's just an extension, it's an increment, we don't see it. If somebody puts a picture of the new, highest bridge in the world in France on the internet, everybody says wow, that's great.

"Well, building the space station is like building the world's newest and highest bridge, except people can't drive across it," Griffin said. "The only way you can see it is in the photos we bring back or the TV images we send. What we are building here is larger than a football field. And we're doing it in zero gravity. ... What's happening here is extraordinary. I mean, you need to be able to appreciate it. And it's way beyond anything that has ever been done by human beings before, anywhere."

Discovery's landing kicks off a busy month in space for Whitson, Malenchenko and Tani to prepare the lab complex for the long-awaited launch of Europe's Columbus research module aboard the shuttle Atlantis on Dec. 6. Columbus was moved to launch pad 39A late Tuesday and engineers plan to haul Atlantis to the pad early Saturday.

Columbus will be attached to the Harmony module that was delivered by the Discovery astronauts and temporarily attached to the left side of the station's central Unity module.

Before Atlantis can take off, the station astronauts must detach the lab's shuttle docking port from the front of the Destiny lab module, connect it to Harmony and then move the entire assembly back to the front of the station. Three spacewalks will be required, one by Whitson and Malenchenko this Friday to finish initial preparations, and two by Whitson and Tani Nov. 20 and 24 to connect the module to the station's power and cooling systems.

"Once the shuttle leaves, we do some very complex robotic operations and maneuver the node over to its final location. ... and then I would say the big technical part of my stay on station is the EVAs that will follow, where we take fluid trays that have been stored on the station for years and we install them on the lab to provide cooling and power to the node so it can offer it to the Columbus module and the Japanese Experiment Module," Tani said before launch.

"We talk about this as a 45-day shuttle mission in terms of pace," he added. "Shuttle missions are scheduled down to 10-minute increments and generally, usually station timelines are a bit more relaxed. But we are not, we are all 'go' from the moment of launch to probably until (Atlantis) comes to get me to bring me home, we are go, go, go."

Columbus will be attached to Harmony's right-side port in December. Japanese research modules, scheduled for launch in February and April, ultimately will be attached to Harmony's left port.

Here is a schedule of upcoming events:

DATE.......TIME.......EVENT

11/09/07...06:00 AM...Whitson, Malenchenko spacewalk; Harmony outfitting
11/10/07...04:00 AM...Atlantis is moved to launch pad 39A
11/12/07...05:40 AM...Shuttle docking port moved from Destiny to Harmony
11/14/07...04:55 AM...Harmony/docking port moved to Destiny
11/14/07..............Shuttle program flight readiness review concludes
11/20/07...TBD........Whitson, Tani EVA; Harmony connected to ISS power/cooling
11/20/07..............Shuttle practice countdown
11/24/07...TBD........Whitson, Tani EVA; Harmony connected to ISS power/cooling
11/25/07..............Harmony module activated
11/26/07..............Station crew enters Harmony
11/30/07..............NASA senior management readiness review concludes
12/03/07...TBD........Start of countdown to Atlantis launch
12/06/07...04:32 PM...Launch of Atlantis and Columbus module (time approximate)
12/09/07...03:12 PM...Columbus module attached to space station
12/15/07...08:22 AM...Atlantis undocks from space station
12/17/07...12:02 PM...Atlantis lands at the Kennedy Space Center
Station flight director Holly Ridings said the lab crew will have to work through the Thanksgiving holiday to get the work done.

"They are not going to have Thanksgiving off," she said. "Even pre-flight, the crew knew that this month of November was going to be very, very challenging. And so they said right up front, if it works out that we need to work on Thanksgiving, we are more than happy to do that. And it did work out that way. So they will be working on Thanksgiving with a lot of us here working as well to support them."

Pete Hasbrook, the Expedition 16 manager at the Johnson Space Center, said NASA is mindful of falling prey to schedule pressure. But given the Bush administration's order to finish the station and retire the shuttle by 2010, pressure is inevitable.

"As far as schedule pressure, I would say yes and no," Hasbrook said. "Yes, we all know that we want to launch in December if we can. But on the other hand, we are very clear, management is very clear, our crew and medical teams are very clear, we need to give the crew an adequate rest time, we can't run them seven days a week. Some people would like to, but we know that's a bad thing to do.

"So we've put in the work-rest cycle we've talked about in a previous briefing, basically working five and a half, six-ish days a week. Toward the end of the time here before we get into flight 1E (the Columbus mission) we're going to give the crew the right amount of time off. And if that means we have to go into the December window a little bit to do that, we're going to do that. We have permission from our program management, our headquarters management to keep that on the table, protect that, protect the crew's health and also protect the ground teams' health.

"You might have (noticed) how much running the teams have been doing on the ground just to finish the 10A flight (Discovery's mission), pulling the miracle that we did at the end of that flight. There's a lot of work going into that, there are a lot of teams working extra hours, we could not have gone and done that again this week without having some delay. So we're very conscious on the pressure we might put on ourselves on schedules.

"If we find some reason we can't make December, including if something major were to break on orbit between now and then that would cost us extra days, we would have to wait until January," Hasbrook said.

That said, "launching in December is a priority for all of us, not just the U.S. side, but all of the partners."

"You might remember that after Columbia, we did a lot of replanning and our partners were very, very patient in watching us and helping us through that whole mission replanning process," Hasbrook said. "You might remember we changed the order of some of the flights. Again, the partners have been working on these modules and looking forward to their payback, to their countries, the European Space Agency, the Japanese exploration agency. They've been very patient about getting their laboratories into space, getting their science return.

"So it's important to us to recognize the support they've given us and the patience they've given us. It's not just an American mission that we're going into. It's really expanding the station to be more international than it is."

12:01 PM, 11/7/07, Update: Shuttle braking rockets fired

Flying upside down and backward over the southern Indian Ocean, commander Pam Melroy and pilot George Zamka fired Discovery's twin braking rockets at 11:58:49 a.m. for one minute and 53 seconds, slowing the ship by about 147 mph to drop out of orbit.

Discovery will follow a so-called descending node trajectory, plunging across the heartland of America for a landing around 1:01:50 p.m. on runway 33 at the Kennedy Space Center. This status report will be updated after Discovery lands or as conditions warrant.

7:00 AM, 11/7/07, Update: Astronauts prepare for landing; forecast still 'go'

With good weather expected in Florida, the Discovery astronauts are rigging the shuttle for re-entry and landing today at the Kennedy Space Center, closing out an action-packed space station assembly mission and bringing astronaut Clay Anderson back to Earth after 152 days in orbit.

Flying upside down and backward over the southern Indian Ocean, commander Pam Melroy and pilot George Zamka plan to fire Discovery's twin braking rockets at 11:59:12 a.m. for one minute and 58 seconds, slowing the ship by about 150 mph to drop out of orbit.

Discovery will follow a so-called descending node trajectory, plunging across the heartland of America for a landing at 1:01:50 p.m. on runway 33 at the Kennedy Space Center. A second landing opportunity is available one orbit later, with a deorbit rocket firing at 1:34:42 p.m. and landing at 2:36:12 p.m.

If the weather or some other problem prevents a landing today, Melroy and company will remain in orbit an extra day and try again Thursday. Depending on the forecast, entry flight director Bryan Lunney could elect to activate NASA's backup landing site at Edwards Air Force Base, Calif. But for today, Kennedy is the only active site.

Forecasters are predicting generally good weather, with scattered clouds at 4,000 feet and winds out of the north at 14 knots with gusts up to 23. For a landing on runway 33, that means a brisk 22-knot headwind but it is not expected to exceed NASA's 25-knot safety limit. The forecast for Thursday calls for a chance of broken clouds at 3,000 feet.

The original flight plan called for a southwest-to-northeast re-entry trajectory and a pre-dawn landing. But given the length of Discovery's extended 16-day mission, flight controllers altered the crew's schedule to bring in a daylight opportunity using a so-called descending node flight path that will carry Discovery across the central United States for the first time since the 2003 Columbia disaster.

"Just like driving, flying and making a landing, I think, is easier in the daylight, you have more visual cues," said Melroy, a former large aircraft test pilot and the second woman to command a space shuttle. "So I have no concerns in that area at all and I can't wait. I'm really excited."

A half hour after the deorbit rocket firing, Discovery will enter the discernible atmosphere 400,000 feet above the mid Pacific Ocean north of Hawaii and cross the coast of western Canada just north of Vancouver. Moving from northwest to southeast, Discovery will streak high above Montana and central Nebraska, passing just a few miles south of Anderson's hometown of Ashland.

Flying almost directly above Topeka, Kansas, Discovery's flight computers will guide the ship just south of Memphis and across the deep south to Florida. Melroy will take over manual control at an altitude of 50,000 feet above north Merritt Island as the shuttle drops below the speed of sound.

After giving Zamka a few moments of hands-on flying time, Melroy will take over and guide the shuttle through a sweeping 192-degree right overhead turn to line up on runway 33.

"On my first flight, we didn't do the program we have now that gives pilots the opportunity to fly a little bit," she said in an interview. "And I really experienced that on my second mission when I got that 20, 30 seconds of flying time, it was a wonderful moment. In a lot of ways, it was the best moment in the mission for me. And part of that is, everything else goes away and it's back to you and your airplane. And that's my job.

"I've been a professional pilot for my entire adult life. And so you kind of shed a lot of the worries about so many other things that are going on in the mission and you have that visceral thrill that all pilots get when they take over the vehicle. You have the feeling yeah, this is something I know how to do, I know how to fly. And it was wonderful, it was really, truly, the best moment on the mission last time. So I'm very excited about this one." Anderson, launched to the international space station last June aboard the shuttle Atlantis, will make the return to Earth resting on his back in a recumbent seat on Discovery's lower deck to ease his re-adaptation to gravity. A team of flight surgeons and support personnel will be standing by to assist.

"Physically and mentally, I'm really ready to be home," he said Tuesday. "I've worked very hard on my physical exercise since I arrived way back in June. So I think that part will be fine. The only part I don't know about is how I will react with my vestibular system and the fact that I've been off the planet with minimal gravity for five months and then I'll come thumping back to the ground - I'm sorry, Pam, smoothly come back to the ground! - and enjoy the comforts of gravity again. So it'll be interesting to find out. I'm kind of optimistic, maybe overly so."

Here is a timeline of today's re-entry events (in EST; repeating from Tuesday):

EST...........EVENT

..............1st Opportunity

07:59:12 AM...Begin deorbit timeline
08:14:12 AM...Radiator stow
08:24:12 AM...Mission specialists seat installation
08:30:12 AM...Computers set for deorbit prep
08:34:12 AM...Hydraulic system configuration
08:59:12 AM...Flash evaporator cooling system checkout
09:05:12 AM...Final payload deactivation
09:19:12 AM...Payload bay doors closed
09:29:12 AM...Mission control 'go' for OPS-3 entry software
09:39:12 AM...OPS-3 transition
10:04:12 AM...Entry switchlist verification
10:14:12 AM...Deorbit rocket firing update
10:19:12 AM...Crew entry review
10:34:12 AM...Commander/pilot don entry suits
10:51:12 AM...Navigation system alignment
10:59:12 AM...Commander/pilot strap in; MS suit don
11:16:12 AM...Shuttle steering check
11:19:12 AM...Hydraulic power unit prestart
11:26:12 AM...Toilet deactivation
11:34:12 AM...Vent doors closed for entry
11:39:12 AM...Mission control 'go' for deorbit burn
11:45:12 AM...Astronauts strap in
11:54:12 AM...Single hydraulic unit start

11:59:12 AM...Deorbit ignition on orbit 238 (dV: 147 mph; dT: 1:58)
12:01:10 PM...Deorbit burn complete (alt: 223.3 sm)

12:30:05 PM...Entry interface (alt: 75.8 sm; vel: 16,979 mph)
12:35:24 PM...1st roll command to left
12:44:14 PM...1st left to right roll reversal
12:48:00 PM...C-band radar acquisition
12:55:16 PM...Velocity less than mach 2.5 (alt: 83,700 feet)
12:57:28 PM...Velocity less than mach 1 (alt: 51,200 feet)
12:58:47 PM...Shuttle banks to line up on runway (alt: 32,200 feet; 192-degree right turn)
01:01:50 PM...Landing on runway 33

..............2nd Opportunity

01:14:42 PM...Mission control 'go' for deorbit burn
01:20:42 PM...Astronaut seat ingress
01:29:42 PM...Single APU start

01:34:42 PM...Deorbit ignition on orbit 239 (dV: 246 mph; dT: 2:00)
01:36:42 PM...Deorbit burn complete (alt: 217 sm)

02:04:13 PM...Entry interface (alt: 75.7 sm; vel: 16,979 mph)
02:09:33 PM...1st roll command to left
02:25:02 PM...1st left-to-right roll reversal
02:29:41 PM...Velocity less than mach 2.5 (alt: 83,700 feet)
02:31:54 PM...Velocity less than mach 1 (alt: 50,500 feet)
02:32:52 PM...Shuttle on the HAC (alt: 36,300 feet; 228-degree right turn)
02:36:12 PM...Landing on runway 33

5:00 PM, 11/6/07, Update: Shuttle heat shield cleared for entry

NASA managers late today cleared the shuttle Discovery for re-entry and landing Wednesday to close out a dramatic space station assembly mission, giving the ship's heat shield a clean bill of health after analyzing data from a final inspection.

Entry Flight Director Bryan Lunney, son of legendary Apollo flight director Glynn Lunney, said Discovery's entry systems were checked out earlier today and forecasters are predicting acceptable conditions with the only concern being relatively high headwinds on runway 33 at the Florida spaceport.

Given the forecast, NASA is not activating the shuttle's backup landing sites at Edwards Air Force Base, Calif., or Northrup Strip, N.M.

"We have KSC for two opportunities on Wednesday," Lunney said. "I do not have Edwards or Northrup called up at all Wednesday. If we wave off for weather or have some other problem, I'll make a determination Wednesday afternoon whether or not to call up Edwards on Thursday. So I'm not going to make that call until then."

Assuming the weather holds and no problems develop, commander Pam Melroy and pilot George Zamka plan to fire Discovery's twin braking rockets at 11:59:12 a.m. for one minute and 58 seconds, slowing the ship by about 150 mph to drop out of orbit for an hourlong glide to Earth.

Crossing the coast of North America just north of Vancouver, Discovery will follow a so-called descending node trajectory, plunging across the heartland of America for a landing at 1:01:50 p.m. A second landing opportunity is available one orbit later, with a deorbit rocket firing at 1:34:42 p.m. and landing at 2:36:12 p.m.

The Spaceflight Meteorology Group at the Johnson Space Center in Houston, which is responsible for shuttle landing forecasts, predicted scattered clouds at 3,000 feet, visibility of 7 miles and winds out of 350 degrees at 14 knots with gusts to 23. That works out to a 22-knot headwind, just 3 mph below NASA's safety limit.

"The weather right now is looking really, really good," Lunney said. "For the last few days, the forecast has been great. We've had mostly clear skies, we're forecasting scattered at 3,000 ... and the winds are going to be blowing right down the runway, peaking up to 23 (knots) with a 14-knot steady state. So real optimistic that tomorrow's landing opportunities we'll play out for us for weather."

Here is a timeline of tomorrow's deorbit opportunities (in EST; the times for deorbit ignition and landing likely will change by a few seconds based on final tracking):

EST...........EVENT

..............Rev. 238 Deorbit to KSC

07:59:12 AM...Begin deorbit timeline
08:14:12 AM...Radiator stow
08:24:12 AM...Mission specialists seat installation
08:30:12 AM...Computers set for deorbit prep
08:34:12 AM...Hydraulic system configuration
08:59:12 AM...Flash evaporator cooling system checkout
09:05:12 AM...Final payload deactivation
09:19:12 AM...Payload bay doors closed
09:29:12 AM...Mission control 'go' for OPS-3 entry software
09:39:12 AM...OPS-3 transition
10:04:12 AM...Entry switchlist verification
10:14:12 AM...Deorbit rocket firing update
10:19:12 AM...Crew entry review
10:34:12 AM...Commander/pilot don entry suits
10:51:12 AM...Navigation system alignment
10:59:12 AM...Commander/pilot strap in; MS suit don
11:16:12 AM...Shuttle steering check
11:19:12 AM...Hydraulic power unit prestart
11:26:12 AM...Toilet deactivation
11:34:12 AM...Vent doors closed for entry
11:39:12 AM...Mission control 'go' for deorbit burn
11:45:12 AM...Astronauts strap in
11:54:12 AM...Single hydraulic unit start

11:59:12 AM...Deorbit ignition (dV: 147 mph; dT: 1:58)
12:01:10 PM...Deorbit burn complete (alt: 223.3 sm)

12:30:05 PM...Entry interface (alt: 75.8 sm; vel: 16,979 mph)
12:35:24 PM...1st roll command to left
12:44:14 PM...1st left to right roll reversal
12:48:00 PM...C-band radar acquisition
12:55:16 PM...Velocity less than mach 2.5 (alt: 83,700 feet)
12:57:28 PM...Velocity less than mach 1 (alt: 51,200 feet)
12:58:47 PM...Shuttle banks to line up on runway (alt: 32,200 feet; 192-degree right turn)
01:01:50 PM...Landing on runway 33

..............Rev. 239 Deorbit to KSC

01:14:42 PM...Mission control 'go' for deorbit burn
01:20:42 PM...Astronaut seat ingress
01:29:42 PM...Single APU start

01:34:42 PM...Deorbit ignition (dV: 246 mph; dT: 2:00)
01:36:42 PM...Deorbit burn complete (alt: 217 sm)

02:04:13 PM...Entry interface (alt: 75.7 sm; vel: 16,979 mph)
02:09:33 PM...1st roll command to left
02:25:02 PM...1st left-to-right roll reversal
02:29:41 PM...Velocity less than mach 2.5 (alt: 83,700 feet)
02:31:54 PM...Velocity less than mach 1 (alt: 50,500 feet)
02:32:52 PM...Shuttle on the HAC (alt: 36,300 feet; 228-degree right turn)
02:36:12 PM...Landing on runway 33

6:00 AM, 11/6/07, Update: Astronauts test re-entry systems, pack for Wednesday landing (UPDATED at 10:30 AM with quotes from Melroy; adding flight path data)

The Discovery astronauts worked through a busy final day in space today, packing up and testing the shuttle's re-entry systems for landing Wednesday at the Kennedy Space Center.

Commander Pam Melroy, pilot George Zamka and flight engineer Stephanie Wilson fired up one of Discovery's three hydraulic power units around 5:45 a.m. as part of a flight control system checkout. Using a laptop flight simulator, Melroy and Zamka planned to practice landing procedures later in the day.

The astronauts also will set up a recumbent seat on the shuttle's lower deck for returning space station astronaut Clay Anderson. He will make the trip back to Earth resting on his back to ease his re-adaptation to gravity after 152 days in space.

In a morning message to the crew, NASA's Mission Management Team said the forecast for landing Wednesday was favorable, with generally clear skies and a brisk headwind for two back-to-back deorbit opportunities. As a result, NASA managers do not plan to activate backup landing sites in California and New Mexico.

If the weather or some other problem prevents a Florida landing Wednesday, the astronauts will remain in orbit an additional day and try again Thursday. In that case, Lunney might opt to activate Edwards Air Force Base, Calif., depending on the weather in Florida. If landing is delayed to Friday, Kennedy, Edwards and Northrup Strip, N.M., will be activated.

"The limiting orbiter consumable will be supply water with at least 7 deorbit opportunities available over 3 days," the MMT told the astronauts. "The remaining orbiter consumables will support EOM (end of mission) +3 (days) with at least 2 opportunities per day.

"The plan is to target two KSC opportunities for EOM on orbits 238 and 239. In the event of an EOM wave-off, EDW may be considered on EOM+1 pending the latest weather forecast and all three sites (KSC, EDW, NOR) will be activated on EOM+2."

Passing just off the east coast Monday, Melroy reported clear skies as cameras on the shuttle beamed down spectacular views of the entire Florida peninsula.

"Well, we could see the runway from orbit," she said. "So we're thinking the weather there is looking pretty good!"

The MMT told the crew a dry front "will pass through KSC early Wednesday morning. This front is forecast to leave behind dry, cool air and a GO forecast with a head wind of (14 knots peaking to 23) on KSC runway 33. EOM+1 has a GO forecast for EDW and NOR while KSC has a chance of precipitation and a chance of ceilings. EOM+2 has a GO forecast for KSC and NOR while EDW has a slight chance for virga (precipitation that doesn't reach the ground)."

Discovery's original flight plan called for a pre-dawn entry and a so-called ascending node approach from southwest to northeast that would carry the shuttle across Central America, the Caribbean and then into Florida.

Ascending node entries require slightly less propellant than descending node, northwest-to-southeast approaches across the heartland of America. Ascending node trajectories also avoid high-altitude, high-latitude clouds of ice crystals that can form in summer months over the Northern Hemisphere.

But Discovery's mission was extended to cope with space station problems and NASA managers ultimately decided to switch to a descending node entry, one that will carry Discovery across the central United States for the first time since the 2003 Columbia disaster.

Shuttle Program Manager Wayne Hale said Monday that noctilucent clouds don't tend to form at this time of the year and given Discovery has plenty of propellant, "we opted for a descending rev deorbit this time, which allows us to land in the daytime."

"It's a basic fact that landing in the daylight is a safer and easier task than landing in the dark," he said. "And the commander on this flight has definitely expressed a preference for daylight landing."

Asked about that today, Melroy agreed the crew preferred a daylight landing, but primarily because the change required an easier sleeping cycle shift to adapt their body clocks.

"I prefer a daylight landing, i think it's a little easier, but the real reason we asked for the switch is because the sleep shift involved, shifting later instead of earlier (is) a lot easier to do physiologically," Melroy said. "We've been doing pretty well, actually, getting to bed on time and getting good sleep. I think we've been able to maintain the pace pretty well."

In the wake of the Columbia disaster, NASA assessed the risk to the public posed by a returning shuttle that might suffer a catastrophic breakup.

"We have a standard public safety risk which is always computed and for an undamaged orbiter, this constitutes a very minimal ... risk to fly over the middle of the United States," Hale said. "The primary reason we're doing it is to allow us to have a daylight landing."

All shuttle pilots are trained to handle landing in daylight or darkness, but "I think most pilots prefer daylight landings," Hale said. "I don't think this is a really strong impetus from the commander, but it is her preference.

"More than that, we are approaching a very long mission here,' he said. "This will be the longest mission, I believe, by about 24, 26 hours, longer than any mission to the international space station and any mission other than a few we flew in the early 90s with what we called the extended duration orbiter pallet. We flew couple of very long missions with the EDO pallet.

"So this is becoming a long mission and we want to make sure we set up the commander for the very best landing conditions that we possibly can."

Melroy said she hoped people living along the shuttle's ground track "would get a chance to watch us come in. I hope they enjoy the view."

For the first landing opportunity Wednesday, the shuttle could cross the North American coast near Vancouver and then follow a track across (data provided by NASA):

For a landing on the second opportunity, the shuttle would cross the coast near Portland, Ore., and then follow a track across:

Entry flight director Bryan Lunney will provide entry details at a 2:30 p.m. briefing. In the meantime, here is an updated timeline of today's activity and a look ahead to Wednesday (in EST and mission elapsed time; includes revision R of the NASA television schedule):

DAY/EST.........DD...HH...MM...EVENT

11/06/07
Tue  02:38 AM...13...16...00...Crew wakeup
Tue  05:23 AM...13...18...45...Flight control system checkout
Tue  05:38 AM...13...19...00...Cabin stow
Tue  06:33 AM...13...19...55...Maneuvering thruster test firing
Tue  08:18 AM...13...21...40...Wing leading edge sensors deactivated
Tue  09:43 AM...13...23...05...News media interviews
Tue  10:03 AM...13...23...25...Crew meal
Tue  11:03 AM...14...00...25...Deorbit review
Tue  11:33 AM...14...00...55...Entry video setup
Tue  12:00 PM...04...01...22...Space station status briefing on NASA TV
Tue  01:48 PM...14...03...10...Ergometer stow
Tue  02:18 PM...14...03...40...Recumbent seat setup
Tue  02:30 PM...14...03...52...Mission status briefing on NASA TV
Tue  02:48 PM...14...04...10...Launch/entry suit checkout
Tue  02:54 PM...14...04...16...Orbit adjustment rocket firing
Tue  03:03 PM...14...04...25...PILOT landing practice
Tue  04:03 PM...14...05...25...KU-band antenna stow
Tue  04:03 PM...14...05...25...Laptop network teardown
Tue  06:08 PM...14...07...30...Crew sleep begins
Tue  07:00 PM...14...08...22...Daily video highlights reel on NASA TV

11/07/07
Wed  02:38 AM...14...16...00...Crew wakeup
Wed  05:43 AM...14...19...05...GIRA stow; OCAC stow
Wed  06:58 AM...14...20...20...Group B computer powerup
Wed  07:18 AM...14...20...40...IMU alignment
Wed  08:03 AM...14...21...25...Deorbit timeline begins
Wed  11:59 AM...15...01...21...1st deorbit opportunity (rev. 238)
Wed  01:01 PM...15...02...23...1st KSC landing opportunity
Wed  01:35 PM...15...02...57...2nd deorbit opportunity (rev. 239)
Wed  02:36 PM...15...03...58...2nd KSC landing opportunity

BACKUP LANDING OPPORTUNITIES (preliminary estimates)

11/08/07
Thu  10:33 AM...15...23...55...Deorbit to KSC............Orbit 253
Thu  11:33 AM...16...00...55...Landing at KSC
Thu  11:58 AM...16...01...20...Deorbit to Edwards........254
Thu  01:00 PM...16...02...22...Landing at Edwards
Thu  12:01 PM...16...01...23...Deorbit to Northrup.......254
Thu  01:03 PM...16...02...25...Landing at Northrup
Thu  12:09 PM...16...01...31...Deorbit to KSC............254
Thu  01:08 PM...16...02...30...Landing at KSC
Thu  01:34 PM...16...02...56...Deorbit to Edwards........255
Thu  02:35 PM...16...03...57...Landing at Edwards
Thu  01:37 PM...16...02...59...Deorbit to Northrup.......255
Thu  02:37 PM...16...03...59...Landing at Northrup
Thu  03:09 PM...16...04...31...Deorbit to Edwards........256
Thu  04:08 PM...16...05...30...Landing at Edwards

11/09/07
Fri  10:39 AM...17...00...01...Deorbit to KSC............269
Fri  11:39 AM...17...01...01...Landing at KSC
Fri  12:04 PM...17...01...26...Deorbit to Edwards........270
Fri  01:06 PM...17...02...28...Landing at Edwards
Fri  12:08 PM...17...01...30...Deorbit to Northrup.......270
Fri  01:09 PM...17...02...31...Landing at Northrup
Fri  12:15 PM...17...01...37...Deorbit to KSC............270
Fri  01:13 PM...17...02...35...Landing at KSC
Fri  01:40 PM...17...03...02...Deorbit to Edwards........271
Fri  02:40 PM...17...04...02...Landing at Edwards 
Fri  01:43 PM...17...03...05...Deorbit to Northrup.......271
Fri  02:42 PM...17...04...04...Landing at Northrup

7:30 AM, 11/5/07, Update: Shuttle undocking and fly around complete

The Discovery astronauts undocked from the international space station today, looped around the lab complex for a final photo run and then departed, falling back behind the outpost. Pilot George Zamka, manually guiding Discovery from the crew module's aft flight deck, had no problems despite a computer glitch that prevented him from receiving normal trajectory data.

"We're all just cheering Zambo on," Melroy told flight controllers. "I don't think people appreciate how difficult it is to do a fly around with absolutely no trajectory information. ... It's pretty challenging to do this and he's doing a fabulous job."

"We agree whole heartedly," said mission control. "We would never know he doesn't have the data. It looks great."

Astronaut Dan Tani, who hitched a ride to the station aboard Discovery and remained behind on the lab, replacing out-going Expedition 16 flight engineer Clay Anderson, passed along his own praise as a camera on the station showed the shuttle gliding through space 600 feet below.

"Discovery, Alpha on the big loop. Zambo, great job, buddy, great job flying," Tani said. "Really cool to see you out there."

"And Bo-ichi, thanks very much," Zamka replied, using the crew's nickname for Tani. "We're going to miss you, but we know you're going to have a great time up there with Peggy (Whitson) and Yuri (Malenchenko). Have a great expedition and we'll see you on the ground." "I'll do that. And the whole 'Bo crew, I miss you already," Tani said. "Fly safe, get home safe, I'll see you on the ground and thanks for not only the great ride up, but the great year and a half together. I owe you one. ... Take care and we'll see you on the ground."

"Yep, we'll see you o the ground," said Melroy.

5:40 AM, 11/5/07, Update: Shuttle Discovery undocks from space station

With pilot George Zamka at the controls, the shuttle Discovery undocked from the international space station today at 5:32 a.m. as the two spacecraft sailed 213 miles above the south Pacific Ocean. "Houston and Alpha, Discovery has physical separation," shuttle commander Pam Melroy radioed as the shuttle slowly pulled away from the lab complex.

A few moments later, station commander Peggy Whitson rang the ship's bell in the Destiny laboratory module, saying "shuttle departing."

"Discovery copies," Melroy said. "Thanks, Peggy."

"Thank you guys for the (new) module and all your help," Whitson replied.

EST........DD...HH...MM...EVENT

05:32 AM...12...18...54...UNDOCKING
05:33 AM...12...18...55...Initial orbiter separation (+10 seconds)
05:34 AM...12...18...56...ISS holds current attitude
05:37 AM...12...18...59...Range: 50 feet; reselect -X jets
05:39 AM...12...19...01...Range: 75 feet; low-Z jets
05:48 AM...12...19...10...Sunrise
05:48 AM...12...19...10...ISS: Lab forward CPA install
06:01 AM...12...19...23...Range: 400 feet; start flyaround
06:11 AM...12...19...33...Range: 600 feet
06:13 AM...12...19...35...Shuttle directly above station
06:19 AM...12...19...41...Noon
06:24 AM...12...19...46...Shuttle directly behind station
06:36 AM...12...19...58...Shuttle directly below station
06:47 AM...12...20...09...Separation burn No. 1
06:49 AM...12...20...11...Sunset
07:13 AM...12...20...35...Playback of undocking video
07:15 AM...12...20...37...Separation burn No. 2

4:39 AM, 11/5/07, Update: Astronauts set or undocking; heat shield inspection

The Discovery astronauts prepared the shuttle for undocking from the international space station today to close out a dramatic assembly mission that sets the stage for the long-awaited attachment of European and Japanese research modules over the next three shuttle flights.

With pilot George Zamka at the controls, Discovery was scheduled to disconnect from pressurized mating adapter No. 2 on the front of the Destiny laboratory module at 5:32 a.m. as the two spacecraft sailed high above the south Pacific Ocean.

The flight plan called for Zamka to guide Discovery to a point about 400 feet directly in front of the lab complex before firing thrusters to begin a photo-documentation fly around, looping up above the station then behind and below it before returning to his starting point.

The first of two separation rocket firings is planned at that point with a second burn a few minutes later to begin moving the shuttle away from the station.

"This is very similar to what we've seen in the past," said shuttle flight director Rick LaBrode. "The fly around occurs around 600 feet, all the way around. We essentially do a full lap. We try to time it such that we have good lighting for the entire fly around."

Flight controllers and engineers were looking forward to seeing the station with the newly installed Harmony module in its temporary location on the left side of the central Unity module and the redeployed P6 solar arrays extended and tracking the sun on the left end of the station's main power truss.

"The shuttle crew's continuously taking pictures of the outside of the station (during the fly around) to monitor how the external part of the station's operation," LaBrode said. "We get views during this flyaround that we don't normally get except during shuttle missions.

"Then, after the complete flyaround, we do sep 1. When we get basically right on top of it, we do sep 2. And we're off and away."

After a break for lunch, the astronauts plan to begin a final heat shield inspection using laser scanners and cameras on the end of a 50-foot-long boom attached to the shuttle's robot arm. A similar inspection was carried out the day after launch to look for any signs of ascent debris impact damage.

The goal of today's so-called late inspection is to check the shuttle's nose cap and wing leading edge panels for any damage that might have occurred since the first inspection because of impacts by space debris.

Sensors behind the leading edge panels recorded a half dozen or so readings over the coarse of the mission. Similar readings on past flights were chalked up the shuttle's aluminum structure responding to temperature changes. Today's inspection should provide the data necessary to resolve the matter.

The orbiter boom sensor system served as astronaut Scott Parazynski's work platform during a spacewalk Saturday to repair the left-side P6-4B solar array. The four sensors on the boom - two laser scanners, a video camera and a digital camera - were unpowered for about nine hours, but tests after the boom was reconnected to shuttle power showed they were "fully functional and ready to support" the late inspection, NASA's mission management team told the crew in an overnight message.

"The LCS (Laser Camera System) hardware appears nominal, and the unexpected indications from the LCS checkout are likely associated with the software and not thermally related," the MMT told the crew. "If there is time (Monday), the LCS checkout steps, which are part of the STBD survey procedures, will be performed to gather more data on the status of the LCS."

The repaired and redeployed P6 solar array and its port-side counterpart, P4, are now rotating to track the sun. Station flight director Heather Rarick said late Sunday the station is not yet tapping into the power generated by P6, pending final tests and checkout.

"We got the OK to let it rotate, so it's been tracking the sun like it's supposed to," she said. "I haven't heard any issues with it, no problems, everything seems to be working fine. So we're just waiting on a 'go' so we can start drawing the power off of it, using it to power some loads, and we're hoping that could be as early as (today). We have to have our specialists take a good, solid look, that everything's going to be OK when we go to do that."

Here is an updated timeline of today's activity (in EST and mission elapsed time; includes revision O of the NASA television schedule):

EST........DD...HH...MM...EVENT

11/05/07
01:38 AM...12...15...00...ISS crew wakeup
02:08 AM...12...15...30...STS crew wakeup
03:38 AM...12...17...00...ISS daily planning conference
04:08 AM...12...17...30...Group B computer power up
04:23 AM...12...17...45...Centerline camera installation
04:48 AM...12...18...10...Undocking operations begin
05:18 AM...12...18...40...Sunset

05:32 AM...12...18...54...UNDOCKING
05:33 AM...12...18...55...Initial orbiter separation (+10 seconds)
05:34 AM...12...18...56...ISS holds current attitude
05:37 AM...12...18...59...Range: 50 feet; reselect -X jets
05:39 AM...12...19...01...Range: 75 feet; low-Z jets
05:48 AM...12...19...10...Sunrise
05:48 AM...12...19...10...ISS: Lab forward CPA install
06:01 AM...12...19...23...Range: 400 feet; start flyaround
06:11 AM...12...19...33...Range: 600 feet
06:13 AM...12...19...35...Shuttle directly above station
06:19 AM...12...19...41...Noon
06:24 AM...12...19...46...Shuttle directly behind station
06:36 AM...12...19...58...Shuttle directly below station
06:47 AM...12...20...09...Separation burn No. 1
06:49 AM...12...20...11...Sunset
07:13 AM...12...20...35...Playback of undocking video
07:15 AM...12...20...37...Separation burn No. 2

07:19 AM...12...20...41...Sunrise
07:23 AM...12...20...45...Post undocking network reconfiguration
07:43 AM...12...21...05...Group B computer power down
08:03 AM...12...21...25...Crew meal
08:23 AM...12...21...45...ISS: CBCS target installation
09:03 AM...12...22...25...Spacesuit installation
09:13 AM...12...22...35...OBSS unberth
09:38 AM...12...23...00...Starboard wing survey
09:53 AM...12...23...15...ISS: Hatch thermal cover installation
11:18 AM...13...00...40...Nose cap survey
12:18 PM...13...01...40...Port wing survey
01:00 PM...13...02...22...Mission status briefing on NASA TV
02:03 PM...13...03...25...OBSS berthing
02:18 PM...13...03...40...ISS: Daily planning conference
02:38 PM...13...04...00...SRMS powerdown
02:43 PM...13...04...05...Laser scanner downlink
04:23 PM...13...05...45...Crew choice downlink
04:28 PM...13...05...50...ISS crew sleep begins
06:38 PM...13...08...00...STS crew sleep begins
07:00 PM...13...08...22...Daily video highlights reel on NASA TV

4:22 PM, 11/4/07, Update: Shuttle crew bids tearful farewell to station astronauts; hatches closed for undocking Monday

The Discovery astronauts bid a tearful farewell to their space station crewmates today, hugging and sharing a few final words before closing hatches and making preparations for undocking early Monday.

For Clay Anderson, who was launched to the station last June and who's flying home aboard Discovery after 152 days in space, the moment was especially emotional. Floating in the Destiny laboratory module with his shuttle and station crewmates, Anderson thanked flight controllers in the United States and Russia, stopping three times to collect himself.

"Today's my last day aboard the international space station, Alpha," he said. "Five months ago, I was lying on my back in the middeck of the orbiter Atlantis preparing to launch into orbit for the first time and wondering what the heck I'd gotten myself into. And now I'm poised to return to Earth after having served very proudly on board this magnificent complex as part of two expedition and three shuttle crews.

"And as my time draws to a close here, I'm filled with a lot of different emotions. I have a lot of blood, sweat and tears that I've left on board the international space station, it's a very wonderful place. So I want to take this time to thank each and every one of you. You've been my special family down there on the ground for quite some time and as is true for families on Earth, I sincerely believe we've all created some very fond memories.

"You all kept me safe, you've shown me unwavering patience and professionalism... And you've all overlooked my shortcomings and it's my hope that maybe you've even had a few laughs along the way... What I'd like to say is what we are doing here is very important for all of human kind. It's worth the risk, it's worth the cost and you folks on the ground are the people who make it happen. So I want you to take pride in your work and constantly look toward the heavens, for it is there you will see your future.

"For all the flight control, training and engineering teams in Houston, Huntsville and Moscow... I say thank you," Anderson concluded. "You are indeed the best and the brightest that our world has to offer."

"Hey Clay, we appreciate the words," astronaut Kevin Ford said from mission control as flight controllers applauded. "Great work on your expedition and we're looking forward to having you back here."

Ford then put lead station flight director Derek Hassmann on the line.

"It's really, really great to see everybody together there in the lab," he said. "I just wanted to echo Kevin's comments, it was an honor and a privilege to watch you guys do your work. What an unbelievably successful mission. ... Great job, guys. Thanks."

Discovery carried Anderson's replacement, Dan Tani, into orbit and shuttle commander Pam Melroy teared up herself as she welcomed Anderson and said farewell to Tani and his new crewmates, station commander Peggy Whitson and cosmonaut Yuri Malenchenko.

"I guess this is the time when Discovery officially welcomes Clay with open arms to our crew," Melroy said. "We can't wait to bring you home to your family and we're very happy to have you. It's not even a question of fitting in, because our crews have matched so well. There's been a lot of laughter and a lot of fun and a lot of really hard work over the last few docked days.

"And it's also our time to say farewell to Dan... he told me not to do this (cry)... Dan has brought us so many wonderful memories and so many wonderful moments. We're going to miss you terribly. We promise we'll send somebody to come pick you up and bring you home. And to Peggy, thank you, it's just been an honor and a privilege to share command of this mission with you. Our personal relationship has just made it all that much better. And Yuri, thank you so much for all the help you gave to us as well."

Saying "we're family now," Melroy embraced Whitson and the two crews shared a few final smiles and hugs before the shuttle astronauts floated back aboard Discovery for good.

If all goes well, Discovery will undock from the space station at 5:32 a.m. Monday. Landing is scheduled for 1:02 p.m. Wednesday, Anderson's 15th wedding anniversary.

5:30 AM, 11/4/07, Update: Astronauts pack for hatch closure, Monday undocking

The Discovery astronauts packed up today, moving equipment back to the shuttle in preparation for closing hatches between the orbiter and the international space station this afternoon. If all goes well, Discovery will undock from the lab complex early Monday, setting the stage for landing Wednesday to close out a dramatic space station assembly mission.

In overnight messages to the crew, flight controllers offered congratulations for Saturday's successful spacewalk by Scott Parazynski and Doug Wheelock to repair a damaged space station solar blanket, an improvised fix that was needed to keep station assembly on track.

"Congratulations!!! Yesterday "Too Tall" finally found his niche in the cosmos!!!" controllers said, referring to Parazynski.

"Wow!!! Yesterday was an absolutely awesome day! But now you have done it," they said. "This flight has drained our bucket of superlative adjectives absolutely dry. Therefore, it is time for you to think about coming home!"

NASA's mission management team chimed in as well, saying "the entire team was awed by the outstanding work that you performed to make EVA 4 a great success."

"The extended team, both on-orbit and on the ground, deserves congratulations and it is a good day to be a part of the extended NASA family," the team said in the crew's morning "execute package" of instructions and timeline revisions. "The MMT briefly reviewed the status and health of the orbiter, which continues to perform very well. The remaining timeline was discussed at a high level, and the MMT is beginning to turn its attention to undocking, late inspection, and end-of-mission."

Parazynski now ranks fifth in the world for cumulative spacewalk time with 47 hours and five minutes over seven EVAs. Spacewalk planners in mission control found a few superlatives of their own.

"What an AWESOME, history-making EVA!" they said in the execute package. "This one will go down as one of our biggest successes in EVA history. Words can not express how proud you made everyone with the execution by the entire team. Scott, what a way to add to an already impressive EVA career! The summit of Everest will have a hard time competing with the view from the boom."

The astronauts will enjoy a bit of off-duty time this morning before gathering in the space station's Destiny laboratory module for a brief farewell ceremony at 1:28 p.m., about 20 minutes before hatches will be closed between the orbiter and the lab complex.

Astronaut Dan Tani, who hitched a ride to the station aboard Discovery, will remain on the station with Expedition 16 commander Peggy Whitson and Yuri Malenchenko. The man Tani replaced - astronaut Clay Anderson - will return to Earth aboard Discovery, along with Parazynski, Wheelock, commander Pam Melroy, pilot George Zamka, flight engineer Stephanie Wilson and Italian astronaut Paolo Nespoli.

Undocking is planned for 5:32 a.m. Monday, followed by a final inspection of the shuttle's nose cap and wing leading edge panels. A laser scanner and cameras on the end of Discovery's heat shield inspection boom, used in the solar array repair work Saturday, will be used to look for any signs of impact damage from space debris or micrometeoroids.

During the solar array repair spacewalk, the boom's instruments were unpowered for about nine hours. Overnight tests showed the laser scanner remains fully functional and tests are planned later today to check out the camera system.

Here is an updated timeline of today's activity (in EST and mission elapsed time; includes revision N of the NASA television schedule):

EST........DD...HH...MM...EVENT

11/04/07
02:08 AM...11...14...30...STS/ISS crew wakeup
03:08 AM...11...16...30...ISS daily planning conference
03:38 AM...11...17...00...Logistics transfers
03:53 AM...11...17...15...Oxygen system teardown
04:08 AM...11...17...30...Spacesuits prepped for move to shuttle
04:23 AM...11...17...45...Shuttle docking port (PMA-2) ground strap
04:58 AM...11...18...20...Logistics transfers
05:03 AM...11...18...25...Italian media event
05:23 AM...11...18...45...Heat shield boom (OBSS) sensor checkout
06:08 AM...11...19...30...Spacesuits moved to shuttle
07:53 AM...11...21...15...Lab forward CPA installation
08:08 AM...11...21...30...Crew meal
09:08 AM...11...22...30...Shuttle crew off duty
09:13 AM...11...22...35...ISS: CBCS target installation
09:43 AM...11...23...05...ISS: Lab hatch thermal cover installation
11:30 AM...12...00...52...Mission status briefing on NASA TV
12:58 PM...12...02...20...PMA-2 berthing mechanism bolts
01:28 PM...12...02...50...Farewell ceremony
01:43 PM...12...03...05...Hatch closed
01:43 PM...12...03...05...Rendezvous tools checkout
02:23 PM...12...03...45...Orbiter docking system leak check
04:43 PM...12...06...05...Crew choice downlink
05:08 PM...12...06...30...ISS crew sleep begins
06:08 PM...12...07...30...STS crew sleep begins
07:00 PM...12...08...22...Daily video highlights reel on NASA TV
10:00 PM...12...11...22...Flight director update on NASA TV

01:30 PM, 11/3/07, Update: Solar array redeployed after dramatic repair; NASA managers say panel now fully operational (UPDATED at 5:35 p.m. with news conference)

Physician-astronaut Scott Parazynski, working on the end of a boom carried by the space station's robot arm, successfully repaired a mangled solar array today, cutting away a snarled guidewire, installing five suture-like braces and then standing by while his crewmates extended the array its full 110-foot length.

Working with deliberate care, astronaut Dan Tani, sending commands from a computer inside the shuttle-station complex, extended the array's central mast a half bay at a time, stopping and letting Parazynski assess the health of the repairs as tension slowly built up on the just-installed braces.

There were no problems and as the last bay of the array's mast extended and locked into place, sensors indicated full extension and Tani exclaimed, "Oh, we've got deploy discretes, two deploy discretes!"

"Yay, all right!" someone yelled.

"Beautiful."

"Great news," Parazynski said. "What an accomplishment."

"Nice teamwork," congratulated station commander Peggy Whitson.

"Phenomenal," Parazynski agreed.

"Excellent work, guys, excellent," Whitson said. "But it's not over yet," Discovery commander Pam Melroy said. "We've still got to get you inside."

"That would be nice," Parazynski said.

"Those are the minor details, but thank you guys very much," astronaut Steve Swanson radioed from Houston.

A successful repair was critical to NASA's plans for continuing space station assembly. At the Kennedy Space Center in Florida on Saturday, engineers moved the shuttle Atlantis from its hangar to the Vehicle Assembly Building for attachment to a set of boosters and an external tank. Launch on the next space station assembly mission, a high-profile flight to deliver Europe's Columbus research module, is targeted for Dec. 6.

Because of problems with the station's right-side solar array rotary joint, NASA needed to get the P6 array repaired and fully extended to provide the power necessary to support the attachment of Columbus next month as well as Japanese research modules scheduled for launch early next year.

With today's successful repair job, the December flight should remain on track.

"There is quite a bit of work that has to be done from this point to the point of launch," Suffredini said of Atlantis and the Columbus module. "We are currently asking the shuttle program to hold the sixth of December as a launch date. My guess is we may not quite make the sixth, but we're going to give it a good go. ... We have a good chance of having several (launch) attempts before the (launch window closes) on Dec. 13. And that's outstanding news."

But the schedule is tight and it will be up to station commander Peggy Whitson, Tani and flight engineer Yuri Malenchenko to complete a long list of chores to clear the way for Atlantis' long-awaited mission.

First, Whitson and Malenchenko plan a spacewalk Nov. 9 to finish rigging the newly delivered Harmony module for its move to the front of the space station. Harmony was temporarily attached to the Unity module's left port. On Nov. 12, the crew will use the station's robot arm to move the shuttle docking port from the front of the Destiny lab module to Harmony. Two days later, the Harmony/docking port assembly will be moved to the front of Destiny and bolted in place.

Whitson and Tani plan two more spacewalks, on Nov. 20 and 24, to connect Harmony to the space station's main power and cooling systems. That will set the stage for the Columbus module's attachment to Harmony's right-side port in December. Japanese modules will be attached to Harmony's upper and left-side ports in February and April.

Here is a schedule of major upcoming events (in EST):

DATE.......TIME.......EVENT

11/05/07...05:32 AM...Discovery undocks from space station
11/07/07...01:02 PM...Discovery lands at the Kennedy Space Center
11/09/07...06:00 AM...Whitson, Malenchenko spacewalk; Harmony outfitting
11/10/07...04:00 AM...Atlantis is moved to launch pad 39A
11/12/07...05:40 AM...Shuttle docking port moved from Destiny to Harmony
11/14/07...04:55 AM...Harmony/docking port moved to Destiny
11/14/07..............Shuttle program flight readiness review concludes
11/20/07...TBD........Whitson, Tani EVA; Harmony connected to ISS power/cooling
11/20/07..............Shuttle practice countdown; headquarters review concludes
11/24/07...TBD........Whitson, Tani EVA; Harmony connected to ISS power/cooling
12/03/07...TBD........Start of countdown to Atlantis launch
12/06/07...04:32 PM...Launch of Atlantis and Columbus module (time approximate)
12/09/07...03:12 PM...Columbus module attached to space station
12/15/07...08:22 AM...Atlantis undocks from space station
12/17/07...12:02 PM...Atlantis lands at the Kennedy Space Center
"We're in great shape," Suffredini said today. The repaired P6 solar array "doesn't quite look like we'd expected, but you know it's just like anybody, you have your baby, your baby's beautiful to you, and our baby is still beautiful to us. Best of all, we're ready to get on with the work to get us to the launch of the Columbus."

Parazynski and Wheelock ended today's spacewalk at 1:22 p.m., seven hours and 19 minutes after they switched their spacesuits to battery power to officially kick off the fourth and final spacewalk of Discovery's mission. Duration of all four EVAs was 27 hours and 14 minutes, moving Parazynski to fifth in the world in cumulative spacewalk time with 47 hours and five minutes over seven EVAs.

"I tell you what, I'm not sure I believe it when I look at this video of what we just did," Melroy said later, narrating footage shot by the astronauts from Discovery's flight deck.

Working at the end of the shuttle's heat shield inspection boom, Parazynski installed a suture-like strap to help stabilize the damaged blanket and cut away a snarled guide wire that hung up during deployment Tuesday. After installing four more so-called cufflinks to hold the damaged blanket together, the array was successfully extended.

"The spacewalk to repair the 4B solar array was just a complete success," said Derek Hassmann, lead space station flight director. "We installed the cufflinks, we completed the deploy of the 4B solar array and we put it in what we call high-tension mode, which puts it in a completely nominal configuration. ... Just a fabulous day, a fabulous shift and one of the greatest things that I personally have ever been involved in in my career here at NASA.

"How smooth today's spacewalk went is a tribute to all the people on the engineering and operations teams who've been working 24/7 since we first tried the 4B deploy and saw the tear in the solar array.

The 17-ton P6 solar array truss segment was launched in 2000 to provide power during the initial stages of assembly. The lab's main power truss is now built and equipped with huge sets of solar panels on each end: starboard 4 (S4) on the right side and port 4 (P4) on the left. The outermost right side S6 arrays, scheduled for launch next fall, will be attached to a short spacer segment known as S5.

During two recent shuttle flights, astronauts retracted the two wings of the P6 array and disconnected it from the station's power system. Spacewalkers had problems retracting the 4B panel, however, encountering a frayed guidewire that repeatedly hung up on grommets during the retraction process.

On Tuesday, P6 was unbolted from its initial mounting point and moved to the far left end of the power truss and bolted to the P5 spacer segment. The first of its two solar array wings, known as P6-2B, extended a full 110 feet as required, but the crew aborted deployment of the 4B wing when one section of hinged blanket slats hung up due to a guide wire snag. Two seams between adjacent slats pulled open, resulting in separate tears, and the edges of several nearby slats were crumpled. The largest rip measured some two-and-a-half feet long.

Eighty percent deployed, the P6-4B array was able to generate more than 95 percent percent of the electricity of a fully extended wing. But without being fully extended, the array did not have the structural stability required for sun tracking. As a result, the station's left-side solar alpha rotary joint, or SARJ, was locked in place until the damage could be fixed.

With today's repair, the left side arrays can once again be turned to track the sun. While a few solar cells in the 4B wing apparently were damaged in the initial hang up Tuesday, Suffredini said the panel would provide all the power the station needs.

"This was just a fabulous effort," he said. "The idea of this was to regain the functionality of the solar array, it wasn't about looking good when it was over with, it just had to provide the power. And in fact, we're under high tension and so we've got full structural capability back.

"When I left the mission evaluation room, they told me the array was providing about 217 amps," he said. "That's about 3 amps from what we normally expect to get from an array, which is much, much higher than what we need to provide the required power to the space station as a whole. That would indicate that perhaps we had some damage, minor damage, to some of the cells. But we're certainly getting more than enough power out of the array, as much as the design requires.

"From a functionality standpoint, we've recovered the array, we can go on to normal operations and expect to get the normal amount of power we had planned for in the ISS program for the life of the program."

With P6 and P4 rotating normally to track the sun, NASA will have a bit of breathing room to troubleshoot a problem with the right-side solar alpha rotary joint, or SARJ. Two massive rotary joints, one on each side of the station's main power truss, slowly turn the port and starboard solar arrays to track the sun as the lab complex circles the globe.

During a spacewalk last Sunday, Tani discovered metallic contamination inside the right-side SARJ, indicating a potentially serious bearing or alignment problem. A planned heat-shield repair demonstration spacewalk originally planned for Thursday was called off to permit a more thorough inspection of the starboard SARJ. Then on Tuesday, the P6 array was damaged during deployment and NASA managers ultimately scrapped the SARJ inspection to make way for today's repair work.

Suffredini said the SARJ issue will be addressed during a future flight, but no decisions have been made about where it might fit into the station assembly sequence. As of today, he said, engineers believe the station will have enough power for normal operations through February, when NASA plans to launch the first of two Japanese modules.

But it's not yet clear whether the starboard SARJ must be operational by the time Japan's large Kibo research lab is launched in April.

10:36 AM, 11/3/07, Update: Snarled wire cut away; Parazynski installs 'cufflink' stabilizers to repair solar blanket; deployment on tap

Performing emergency surgery 213 miles up, astronaut-physician Scott Parazynski cut away snarled guidewire hanging up a mangled space station solar array and installed five long suture-like straps to prevent two rips in the fragile panel from pulling open. The dramatic repair work, conducted high above the far left end of the station's main solar power truss, took a bit longer than expected, but the MacGyver-style fix using homemade brackets, seemed to work as well as engineers had hoped.

After installing a single suspender strap to add support to the torn solar blanket, Parazynski used wire cutters to snip a wire leading to a snag. He used an L-shaped, insulated tool dubbed the hockey still to keep the panels from rebounding into him.

"The big thing here, I think, you are possibly going to release some tension," commander Pam Melroy radioed before Parazynski made the first cut. "So you are going to want to have that hockey stick right close to hand, that's your best friend."

"Here is comes," Parazynski said. "OK, it is cut. And it's really slick. The grommet is retaining the hinge wire. The panel did fold back as we anticipated. no contact with me, there's about eight inches remaining outside the hinge doubler. And it's pointed up towards me so I have easy access with my vice grips."

Next, he cut the guidewire below the damaged section of solar blanket to release the tension mangling the array. Astronaut Doug Wheelock, stationed at the base of the P6-4B array, used needle-nose pliers to slowly guide the wire into a take-up reel.

"Houston, do we have a go to cut the guide wire?" Melroy asked mission control.

"Discovery, you have a go to cut the guide wire," astronaut Steve Swanson replied from Houston.

"Copy that," Melroy said. "OK, Scott, just let Wheels know when you've got it."

"It's a bit of a reach here," said Parazynski, nicknamed "Longbo" by his crewmates.

"That's what those monkey arms are for," Melroy joked.

"They're getting tested today!" Parazynski laughed.

"Not too many people in the office could do what you're doing right now, Scott," Melroy said.

"I hope they don't have to!"

A few moments later, he cut the wire.

"Three, two one, snip," he radioed as the cable wound down into the take-up reel. "OK, it's retracting, beautiful, good braking."

Before installing four more cufflink-clasp suspenders, Parazynski used his cutters to snip a fray toward to top of the array to ensure the cable wouldn't snag on any grommets later as the array was extended.

"Got it... it's free," he radioed. "I'm doing a lay back. It was a nice, clean cut. It looks like everything above is traveling through the grommets very nicely."

At that point, he turned his attention to installing the remaining suspender braces, working from the inner edge of the blanket to the outside. He had no problems and television shots showed the white straps in place like giant stitches, preventing the rips from opening further when the panel was fully deployed and subjected to some 70 pounds of tension.

Around 11 a.m., robot arm operator Stephanie Wilson began backing Parazynsky away from the array, setting the stage for a dramatic attempt to complete the panel's extension.

9:20 AM, 11/3/07, Update: Hinge-stabilizing 'cufflink' installed; Parazynski describes complex wire tangle; debates options for cutting snarl away

Video from spacewalker Scott Parazynski's helmet camera revealed a complex wire snarl hanging up damaged solar array slats on the P6-4B array. The snarl will require Parazynski to cut the cables to clear the snag, but the crew and controllers are discussing the best possible approach.

"I see two major areas of fraying," Parazynski reported. "One at the small damage site, lower to the grommet that was probably, formerly, at the small damage site. And the fray is in excess of one-inch long, which is hard to do with this kind of wire. And then there's another grommet under tension emanating from the large damage site and there are several strands of wire all grouped together there."

"We've got an excellent view of your closeup of the snarl," Melroy said.

"Isn't that amazing?"

"Oh, that's just ugly," Melroy said.

"Yeah," Parazynski said.

A few minutes later, Melroy asked: "Do you see a lot of loose hinge wire kind of curling around there?"

"I think that's not hinge wire, I think that's the guidewire has become unfrayed," Parazynski said. "It's almost like it's been stripped."

"Oh wow," Melroy said. "Oh, that's really frayed!"

The astronauts and flight controllers then debated how best to deal with the wire tangle.

9:00 AM, 11/3/07, Update: Parazynski provides first detailed description of solar array damage

Anchored to the end of a boom on the space station's robot arm, astronaut Scott Parazynski gave flight controllers their first detailed description of damage to a ripped solar array, reporting a complex tangle of guide wires, hinge pins and grommets around an area that was mangled during deployment Tuesday.

"The damage is as anticipated," he reported, examining the damage from a few feet away. "There is a hairball (tangle) with the guidewire, the hinge between (blanket slats) 35 and 36 and a grommet, not sure of the origin of it, but probably at the 35-36 location. That's almost certainly where it came from. There is separation of the doubler, the physical hinge off of the inboard, lower side of panel, let me get this right here, 36. Looks to be about 8 to 10 inches in length, it's ripped clean from the edge of the panel. You can see that the cells are still intact on the back side, it just came off from the edge.

"The hinge wire itself still courses through the doubler and goes out to the edge of the wing. You can see it touching almost the FCC (flat cable connector) at the level of the small damage there. There appear to be numerous sharp edges, I don't see any sparking or anything of that nature at this point. It doesn't look like the damage itself pulled the hinge wire inboard, which is, I think, good news. I reported earlier, I'm not sure if you copied me, but I reported that it looked like the outboard side of the 35-36 hinge line there was intact, there was no separation. And that's consistent with my observation here, that the damage did not pull the whole hinge wire inboard."

"Houston copies all and concurs. Thanks a bunch for that description," replied astronaut Steve Swanson in mission control.

"You're very welcome. Looking at the FCC, it looks like it has held structural integrity the full length. I am looking at a couple of areas on the inboard side of panel 35, it looksõ like some of the Kapton has separated from the wire bundle coming from the panel. But I don't see any separation of wiring, it looks like the wire from that panel has held going into the FCC.

"The most badly damaged panel, which is 36, the wire bundle coming from the panel going to the FCC does appear to be bent, but I don't see it severed. It probably still is generating power, is my guess. Those are the only two areas of real concern that I see FCC wise."

Looking closely, he several hinges between adjacent slats near the main damage area appeared to have pulled apart slightly.

"So there's been a zippering effect at one, two, three, four levels," he said. "Between 36 and 37, though, it appears intact."

Shuttle commander Pam Melroy then summed it up, "So both hinge wires from the large and the small damage sites, the guidewire and one or more grommets are all knotted together?"

"That appears to be what happened, yes," Parazynski replied.

He also reported seeing a few cracked solar cells before beginning work to install a so-called cufflink-like strap between blanket slats well above and below the damage site to prevent any additional separation and keep the two rips from getting worse before addressing the guide wire tangle. Five cufflink straps will be installed in all to carry the tension needed for the array's final extension.

Video from Parazynski's helmet cam showed him threading the homemade 66-inch-long cufflink strap through a reinforced hole in a slat above the damage. Threading the other end into a hole well below the damage, the strap should provide the support needed during the rest of the repair.

"That was a beautiful thing, to see that cufflink go into the hole," Melroy radioed.

"Yes, it was. I just want to apply a little force to get it fully engaged there," Parazynski said, giving the strap a light pull. "That's how you do it."

"Yeah, that tug test looks good," Melroy said.

"Peggy and Zambo, nice handiwork," Parazynski said, complimenting station commander Peggy Whitson and shuttle pilot George Zamka.

"Yeah, that was a really nice job," Melroy said. "It took them all day and now they'll be out there forever, which is kind of fun."

"Yes it is."

"Got big smiles in here," mission control said.

7:45 AM, 11/3/07, Update: Parazynski, on robot arm, begins 45-minute ride to damaged solar array

Spacewalker Scott Parazynski, his feet anchored to the end of a boom on the space station's robot arm, began a slow-motion, 45-minute ride from the lab's main power truss to a damaged solar array on the far left side of the lab complex at 7:27 a.m.

"This is gonna be a great ride," Parazynski said earlier, attaching a foot restraint to the end of the robot arm boom. When the arm began moving him he told fellow spacewalker Doug Wheelock: "Let's get her done."

During the ride over to the P6-4B solar array, Italian astronaut Paolo Nespoli read the spacewalkers a long list of warnings, some of them common to all spacewalks and some due to concern about working around the electrically active solar arrays.

"We have a bunch of warnings related to shock hazard," Nespoli radioed. "Here's one about EMU contact with ... solar array panels. EV crew will only contact energized surfaces with approved tools that have been insulated with Kapton tape to prevent molten metal and shock. ... The last box is minimize contact between metal array components and exposed damaged solar cells on active side. Note some sparking may be expected. Avoid contact with solar panels except with insulated tools. Sharp edges likely present at damage locations."

A few minutes later, as the shuttle-station complex sailed up the East Coast of the United States, Parazynski asked, "Can you guys see my wireless video? This is just beyond description!"

"It's fantastic, but it's ratty right now," mission control replied.

"Oh, what a shame."

"Scott, I assure you, from window 1 the view is just as spectacular," shuttle commander Pam Melroy reassured him.

"Oh, man!" Parazynski marveled at the world spread out below him. "Words can't do this justice. No way, at least not mine."

6:40 AM, 11/3/07, Update: Melroy reports solar array wires appear tangled; wires may have to be cut

Shuttle commander Pam Melroy, using binoculars to take a close-up look at a damaged solar array on the left side of the international space station, told spacewalker Scott Parazynski not to expect an easy repair today.

"Hey Scott, this is Pambo, I've got a great view out window 1 of the damage site, I got out the binoculars and took a really close look," she radioed Parazynski as he was making his way to the station's robot arm for transport to the damaged array.

"What do you think?" he asked.

"Well, it looks to me like the hinge wire at the large tear has been busted at about the point, oh let's see, let me make sure I've got the, I'm trying to think of the name of the vertical tape that has the holes in them, it's about halfway from the inboard edge and that tape. So some hinge wire is still left down there, kind of hanging out in the middle of that most inboard section. And then the rest of it has snarled through the (garble) wire and it also looks like... hang on a second... OK, then the upper hinge wire, the small tear, that hinge wire is also snarled. So it looks to me like both hinge wires, the guide wire and a grommet are all snarled up. In fact, I had kind of a back shadow of it on the panel and I could actually see the little fur ball outlined in shadow."

"Well, that sounds like we have to do the whole enchilada for the repair, huh?" Parazynski said, referring to a repair scenario that would have him cut the tangled wires.

"Concur," Melroy said. "It doesn't look like an easy, just rattle-it-and-shake-loose-the-grommet kind of situation."

6:05 AM, 11/3/07, Update: Spacewalk begins

Running about a half-hour ahead of schedule, astronauts Scott Parazynski and Doug Wheelock switched their spacesuits to internal battery power at 6:03 a.m., officially kicking off a dramatic solar array repair spacewalk.

"Go out there and fix that thing for us," space station commander Peggy Whitson radioed as the astronauts prepared to leave the airlock.

"We will," Parazynski promised.

Here is an updated timeline based on the actual start time of today's spacewalk (in EDT and spacewalk elapsed time; subject to change):

EDT........DD...HH...MM...EVENT

06:08 AM...00...00......Airlock egress

06:38 AM...00...30......Heat shield boom (OBSS) setup
........................1. Move to P1 truss/bay 12; perform tether swap
........................2. Install work site interface extension
........................3. Install foot restraint on WIF extension
........................4. Astronaut gets In foot restraint

07:08 AM...01...00......SSRMS maneuver to P6-4B solar array wing
........................1. Check OBSS stability prior to P1 departure
........................2. Station arm moves astronaut to P6-4B array wing

08:08 AM...02...00......4B SAW troubleshooting
........................1. Assess/report guide wire configuration
........................2. Clear guide wires; cut if necessary
........................3. Install hinge stabilization cufflinks

10:38 AM...04...30......OBSS maneuver to egress point
........................1. SSRMS moves OBSS back to P1 bay 12 for egress

11:08 AM...05...00......Foot restraint egress and OBSS cleanup
........................1. Egress foot restraint; remove/stow OBSS hardware

11:38 AM...05...30......EVA-4 cleanup
........................1. Stow WIF extender on ESP-2; stow tools
........................2. Return to airlock

12:08 PM...06...00......Airlock ingress
12:38 PM...06...30......Airlock repressurization

4:00 AM, 11/3/07, Update: Astronauts set for solar blanket repair spacewalk

Astronauts Scott Parazynski and Doug Wheelock are suiting up in the space station's Quest airlock module this morning for a high-stakes spacewalk to repair a mangled solar array. If the orbital surgery is successful, the partially deployed solar wing will be fully extended and NASA will be clear to press ahead with plans to launch a European research module in December. If the fix falls short, more repair work could be needed and the next shuttle flight likely would slip into next year.

But NASA managers are optimistic Parazynski, a physician trained in emergency medicine and one of the agency's most experienced spacewalkers, will be able to clear a snarled guidewire and install cufflink-like suspenders around two rips in the blanket to strengthen it enough for full extension.

Lead flight director Derek Hassmann said Friday he felt "really good about where we are, about the robotics pieces of the procedures, about the spacewalking techniques, about the hardware, about our understanding of the area of damage, about our approaches to fixing that damage and also about the ground choreography and how the timeline's going to play out in mission control."

Parazynski and Wheelock are scheduled to begin the dramatic spacewalk around 6:30 a.m., but they got off to a fast start today and they could begin the excursion up to a half hour early. This will be the 96th spacewalk devoted to station assembly and maintenance since construction began in 1998, the 19th so far this year and the fourth for the Discovery astronauts. Parazynski, Wheelock and station astronaut Dan Tani have logged 19 hours and 55 minutes of spacewalk time so far during Discovery's flight.

After leaving the Quest airlock on the right side of the station's central Unity module, Parazynski and Wheelock will make their way up onto the lab's main solar power truss, which runs right angle to the long axis formed by the station's pressurized modules. Parazynski will attach a foot restraint to a 50-foot boom carried by the station's robot arm and then lock his boots in place for a spectacular 45-minute ride to the damaged array.

Wheelock, meanwhile, will make his way to the base of the P6-4B solar array on the far left end of the main power truss and provide verbal guidance cues for arm operators Stephanie Wilson and Tani, working inside the Destiny laboratory module.

The P6-4B solar array is half a football field from the space station's pressurized modules. The robot arm alone cannot reach the damage site, even when positioned at a work site on the end of the power truss. But using the shuttle's heat shield inspection boom as an extension, the space crane can just barely get Parazynski into position.

After reaching the damage site, Parazynski first will inspect the mangled section of the 4B solar blanket to determine what might be needed to release an apparently snarled guidewire believed to have ripped open two blanket panel hinges during deployment Tuesday.

Because the solar array is generating electricity, Parazynski's tools and the exposed metal on his spacesuit were covered in non-conducting tape to minimize the risk of a shock. NASA managers said that risk was minimal, but the spacewalkers were cautioned not to touch any exposed wires or conducting surfaces.

Before addressing the presumed snarl, Parazynski will attach a homemade clip, dubbed a cufflink, threading clasps on each end through reinforced holes above and below the rips in the blanket. That way, if the tension on the blanket changes because of work to free the snarl, it will not widen the tears that are already there. Five such cufflinks will be installed across the 15-foot width of the blanket before any attempt is made to complete its extension.

If NASA is lucky, Parazynski will be able to simply move the guidewire to one side, freeing the snarl. If the tangle cannot be freed, he will cut the wire and Wheelock will use pliers at the base of the array to control its winding back onto a take-up reel.

"He'll assess the damage, that's his first job, to figure out what is really wrong up there," station flight director Heather Rarick said late Friday. "He'll call down that assessment, then he'll probably be given a go to install the cufflinks, which will provide some stabilization for the solar array. And he'll do that in the middle of the solar array and that'll help prevent any further tears as he's working.

"His next job is then to try to make sure the guide wire is released from its location. We think that's what's caught in the damaged area. So he'll either move it away if he can do it without requiring any cutting, otherwise he'll need to do some cutting. There's also a hinge pin that's sticking out that he'll need to cut and then he'll need to install four additional cufflinks to provide the final amounts of stabilization for the wing."

The spacewalk is timelined to last up to six hours and 30 minutes. But Hassmann said if Parazynski doesn't run into any major problems, the actual repair work could be completed in as little as a half hour. The astronauts inside the space station will attempt to redeploy the repair panel as soon as Parazynski can be moved out of the way.

Here is an updated timeline of today's activity (in EDT and mission elapsed time; includes revision M of the NASA television schedule, updated spacewalk timeline):

EDT........DD...HH...MM...EVENT

11/03/07
01:38 AM...10...14...00...STS/ISS crew wakeup
02:13 AM...10...14...35...EVA-4: Airlock repress; hygiene break
03:23 AM...10...15...45...EVA-4: Airlock campout resumes
04:53 AM...10...17...15...EVA-4: Spacesuit purge
05:08 AM...10...17...30...EVA-4: Oxygen pre-breathe
05:13 AM...10...17...35...Shuttle boom (OBSS) handoff to station arm (SSRMS)
05:58 AM...10...18...20...EVA-4: Airlock depress
06:28 AM...10...18...50...EVA-4: Spacesuits to battery power
06:33 AM...10...18...55...EVA-4: Airlock egress
07:03 AM..................SSRMS/OBSS setup
..........................1. Move to P1 truss/bay 12; perform tether swap
..........................2. Install work site interface extension
..........................3. Install foot restraint on WIF extension
..........................4. Astronaut gets In foot restraint
07:33 AM..................SSRMS maneuver to P6-4B solar array wing
..........................1. Check OBSS stability prior to P1 departure
..........................2. Station arm moves astronaut to P6-4B SAW
08:33 AM..................Solar array troubleshooting
..........................1. Assess/report guide wire configuration
..........................2. Clear guide wires; cut if necessary
..........................3. Install hinge stabilization cufflinks
11:03 AM..................OBSS maneuver to egress point
..........................1. SSRMS moves OBSS back to P1 bay 12 for egress
11:33 AM..................Astronaut egress and OBSS cleanup
..........................1. Egress foot restraint; remove/stow OBSS hardware
12:03 PM..................EVA cleanup
..........................1. Stow WIF extender on ESP-2; stow tools
..........................2. Return to airlock
12:33 PM...11...00...55...EVA-4: Cleanup and airlock ingress
01:08 PM...11...01...30...EVA-4: Airlock repressurization
01:13 PM...11...01...35...SSRMS/OBSS handoff maneuver
01:18 PM...11...01...40...Spacesuit servicing
01:58 PM...11...02...20...SRMS grapples OBSS
02:13 PM...11...02...35...SSRMS releases OBSS
02:58 PM...11...03...20...SRMS maneuver
03:00 PM...11...03...22...Mission status briefing on NASA TV
03:38 PM...11...04...00...Crew choice downlink
05:38 PM...11...06...00...ISS crew sleep begins
06:08 PM...11...06...30...STS crew sleep begins
07:00 PM...11...07...22...Daily video highlights reel on NASA TV
10:00 PM...11...10...22...Flight director update on NASA TV
The 17-ton P6 solar array truss segment was launched in 2000 to provide power during the initial stages of assembly. The lab's main power truss is now built and equipped with huge sets of solar panels on each end: starboard 4 (S4) on the right side and port 4 (P4) on the left. The outermost right side S6 arrays, scheduled for launch next fall, will be attached to a short spacer segment known as S5.

On Tuesday, P6 was unbolted from its initial mounting point and moved to the far left end of the power truss and bolted to the P5 spacer segment. The first of its two solar array wings, known as P6-2B, extended a full 110 feet as required, but the crew aborted deployment of the 4B wing when one section of hinged blanket slats hung up, presumably due to a guide wire snag. Two seams between adjacent slats pulled open, resulting in separate tears, and the edges of several nearby slats were crumpled. The largest rip measured some two-and-a-half feet long.

Eighty percent deployed, the P6-4B array can generate 97 percent of the electricity of a fully extended wing. But with a partially deployed panel, none of the arrays on the left side of the main power truss can be rotated as required to track the sun without risking additional damage. As a result, the station's left-side solar alpha rotary joint, or SARJ, is locked in place until the damage is fixed.

6:45 PM, 11/2/07, Update: NASA says additional risk to spacewalker minimal; optimistic about successful repair

The Discovery astronauts today reviewed plans for a dramatic solar array repair spacewalk early Saturday and appeared confident they have a good shot at fixing the mangled panel to keep space station assembly on track. Lead flight director Derek Hassmann said concern that spacewalker Scott Parazynski could get zapped by an unexpected electrical discharge while working near the charged array was misplaced and that the additional risk was minimal.

"As I left the control center today, I felt really, really good about where we are, about the robotics pieces of the procedures, about the spacewalking techniques, about the hardware, about our understanding of the area of damage, about our approaches to fixing that damage and also about the ground choreography and how the timeline's going to play out in mission control," he said. "I walked away from my shift today very, very impressed with the incredible amount of progress that's occurred over the last 24 hours."

Said lead spacewalk officer Dina Contella: "Having the extra day to prepare for this spacewalk has really been a good thing for the EVA team, we've really hammered flat a lot of the details. ... It's really been a huge, coordinated effort. The big picture really hasn't changed. it's just a matter of the details, really, getting (figured) out in the extra day that we had."

A successful repair is critical to NASA's plans for continuing space station assembly. At the Kennedy Space Center in Florida on Saturday, engineers are scheduled to move the shuttle Atlantis from its hangar to the Vehicle Assembly Building for attachment to a set of boosters and an external tank. Launch on the next space station assembly mission, a high-profile flight to deliver Europe's Columbus research module, is targeted for Dec. 6.

Because of problems with the station's right-side solar array rotary joint, NASA needs to get the P6 array repaired and fully extended to provide the power necessary to support the attachment of Columbus next month as well as Japanese research modules scheduled for launch early next year.

"At this point, we've got problems on both ends of the truss, unfortunately," Hassmann said. "We've got the issues with the starboard truss, with the starboard solar array rotary joint, and now we've got this issue on the port side of the truss with the 4B solar array. ... We need to address one of these two problems before we proceed.

"Based on the discussions I've been involved in, we need to get the solar array addressed and fixed, fully deployed, structurally stable, available for power before we would proceed with 1E (the Columbus mission)."

Parazynski and astronaut Doug Wheelock plan to begin the dramatic spacewalk around 6:30 a.m., floating out of the station's Quest airlock module and making their way up onto the lab's main solar power truss. Parazynski will attach a foot restraint to a 50-foot boom carried by the station's robot arm and then lock his boots in place for a slow but spectacular 45-minute ride to the damaged array.

Wheelock, meanwhile, will make his way to the base of the P6-4B solar array on the far left end of the main power truss and provide verbal guidance cues for arm operators Stephanie Wilson and Dan Tani, working inside the Destiny laboratory module.

The P6-4B solar array is mounted on the far left end of the space station's main power truss, half a football field from the space station's pressurized modules. The robot arm alone cannot reach the damage site, even when positioned at a work site on the end of the power truss. But using the shuttle's heat shield inspection boom as an extension, the space crane can just barely get Parazynski into position.

On Thursday, mission managers said it would take Parazynski more than 30 minutes to reach the safety of the station's airlock in the event of a major spacesuit malfunction, primarily because of time needed to maneuver the robot arm. All NASA suits are equipped with a 30-minute supply of emergency oxygen and NASA has never before planned a station spacewalk that could put an astronaut in a position where he or she couldn't reach the airlock in a half hour.

But Contella said Friday engineers had refined their plans and that she believed Parazynski could get back to the Quest module before running out of air in any credible failure scenario.

After reaching the damage site, Parazynski, one of NASA's most experienced spacewalkers, first will inspect the mangled section of the 4B solar blanket to determine what might be needed to release an apparently snarled guidewire believed to have ripped open two blanket panel hinges during deployment Tuesday.

Before addressing the presumed snarl, the spacewalker will attach a homemade clip dubbed a cufflink, threading clasps on each end through reinforced holes above and below the rips in the blanket. That way, if the tension on the blanket changes because of work to free the snarl, it will not worsen the tears that are already there. Five such cufflinks will be installed across the 15-foot width of the blanket before any attempt is made to complete its extension.

If NASA is lucky, Parazynski will be able to simply move the guidewire to one side, freeing the snarl. If the tangle cannot be freed, he will cut the wire and Wheelock will use pliers at the base of the array to control its winding back onto a take-up reel.

"The problem would come is if we get there and we realize the snag either can't be cleared or maybe the snag has altered the guidewire, for example, in some way that we don't really want to do the deploy with the guide wire in that particular state, we don't think it's a good idea to have the damage as is for a deploy," Contella said.

"So if we get in either of those two cases, then we will cut the guidewire. So the idea is, Wheels would get ready at the bottom of the array. Remember, there's the take-up reel mechanism at the bottom and Wheels will have needle-nose pliers at the base and he'll get ready and basically grip the bottom part of the wire. And this is because we want to have a controlled intake as opposed to something that would accelerate and potentially end up with a big snarl at the base."

The spacewalk is timelined to last up to six hours and 30 minutes. But Hassmann and Contella said if Parazynski doesn't run into any major problems, the actual repair work could be completed in as little as a half hour. The astronauts inside the space station will attempt to redeploy the repair panel as soon as Parazynski can be moved out of the way.

NASA expects to have good video coverage of the repair work, using cameras mounted on the space station and in the helmets of both spacewalkers. But Hassmann said video was not required. It will be up to Parazynski, the man on the scene, to determine the best course of action.

"We don't have fantastic photography of this area, we just don't have the capability to see exactly what's happening," Contella said. "So at that point, Scott's going to have to use his best judgment on what he thinks we're going to do."

In the end, she said, "it's a snag clear; it's not rocket science. So you want him to probably tell you what he thinks would be the best thing and then we'll just discuss it on the groundÊand make sure everybody sort of agrees that yeah, the solar array's not going to have some sort of adverse dynamics because of the way he wants to clear it, something like that."

During a news briefing Thursday, astronaut Dave Wolf downplayed the threat of a shock hazard, but told reporters it was possible, in theory, for an astronaut to get electrocuted in a worst-case short. Today, Hassmann downplayed those concerns saying "a number of things have to happen all at once for there even to be a small risk of any kind of electrical problem or shock hazard while Scott's out there doing his work."

"The thing to remember," he said, "is a pristine solar array, an undamaged solar array is completely isolated. The suit itself, obviously, is completely isolated. ... A spacewalking astronaut could put his hand on that solar array and there would be no risk of any kind of shock of any kind.

"What we do is, we think about the worse case scenarios and any possible way a shock hazard, any kind of electricity incident, could occur. And really what you have to do in your mind to make that happen is to find a metal piece on the suit, which in general is the rings around the gloves, the ring around the waist, the ring around the boots, and you'd have to take one of those metal rings and apply that to a hot part of the solar array. And in order to find a hot part of the solar array, you'd have to find a damaged portion.

"So if you could find that hot wire, a crew could put a metal portion of his suit, which is very limited, on the hot part and then he'd have to complete the circuit. So he'd have to find another part of his suit, the boot ring, for example, or the waist ring, and he'd have to apply that to another part of the solar array in order to complete that circuit in order to come anywhere close to any kind of shock hazard."

Each of the slats making up the folding solar blanket generates about 300 watts of power. The electricity cascades down a strip that runs from top to bottom along the left inboard edge of the panel near where the two rips are present. Control systems at the base of the array send a regulated 160 volts of direct current electricity into the station's power system. That output is converted to 124 volts for use by lab systems.

Playing it safe, Parazynski's tools were wrapped in non-conducting tape, as were the glove, boot and waist rings on his spacesuit.

The 17-ton P6 solar array truss segment was launched in 2000 to provide power during the initial stages of assembly. The lab's main power truss is now built and equipped with huge sets of solar panels on each end: starboard 4 (S4) on the right side and port 4 (P4) on the left. The outermost right side S6 arrays, scheduled for launch next fall, will be attached to a short spacer segment known as S5.

During two recent shuttle flights, astronauts retracted the two wings of the P6 array and disconnected it from the station's power system. Spacewalkers had problems retracting the 4B panel, however, encountering a frayed guidewire that repeatedly hung up on grommets during the retraction process.

On Tuesday, P6 was unbolted from its initial mounting point and moved to the far left end of the power truss and bolted to the P5 spacer segment. The first of its two solar array wings, known as P6-2B, extended a full 110 feet as required, but the crew aborted deployment of the 4B wing when one section of hinged blanket slats hung up, presumably due to a guide wire snag. Two seams between adjacent slats pulled open, resulting in separate tears, and the edges of several nearby slats were crumpled. The largest rip measured some two-and-a-half feet long.

Eighty percent deployed, the P6-4B array can generate 97 percent of the electricity of a fully extended wing. The station is not yet using power from the torn array, but engineers say tests confirm no major damage to its internal wiring.

The immediate concern is figuring out a way to fully extend the P6-4B wing to provide the necessary structural rigidity. With a partially deployed panel, none of the arrays on the left side of the main power truss can be rotated as required to track the sun without risking additional damage. As a result, the station's left-side solar alpha rotary joint, or SARJ, is locked in place until the damage is fixed.

Adding to NASA's problems, the station's right-side arrays also are locked in place because of unexpected metallic contamination inside the starboard SARJ. Parazynski and Doug Wheelock were in the process of gearing up Wednesday for a spacewalk to inspect the starboard SARJ Thursday when NASA managers decided to focus instead on fixing the P6-4B solar blanket.

Engineers initially held out hope for a repair spacewalk Friday, but NASA managers decided early Thursday to wait until Saturday, giving engineers more time to fine-tune the plan.

5:00 AM, 11/2/07, Update: Astronauts prepare for repair spacewalk

The Discovery astronauts prepared equipment today for a dramatic solar array repair spacewalk Saturday while engineers in Houston put the finishing touches on the procedures needed to sew up gashes in the mangled blanket.

Originally planned for today, the excursion was delayed to Saturday to give the ground team more time to work out the details. Early today, in the daily "execute package" of notes and instructions to the crew, the astronauts were told the spacewalk was still on track for Saturday.

"Good Morning Discovery!!! Just in case you are wondering, EVA 4 is still scheduled for tomorrow and the content is still to repair the solar array," flight controllers wrote. "All procedures should be on board before lunch. Undocking is still currently planned for Monday and landing is planned for Wednesday. Have a great day today, preparing for tomorrow!!!"

The repair plan calls for spacewalker Scott Parazynski, anchored to the end of the shuttle's heat shield inspection boom, to be carried to the left-most P6-4B solar array by the space station's robot arm. Astronaut Doug Wheelock, at the base of the array, will provide guidance cues to arm operators Stephanie Wilson and Dan Tani. Once in position, Parazynski will inspect two rips in the fragile blanket and give flight controllers an up-close assessment of what it might take to untangle or cut snarled guidewires.

After the guidewires have been straightened out (or removed), Parazynski plans to install homemade cufflink-like straps to carry the tension that otherwise would tend to pull the rips open as the array is fully extended.

"We've had people in almost around the clock supporting the extra efforts of the console teams so that we could focus on keeping the systems running and performing the plans that we have built," station flight director Heather Rarick said late Thursday. "So we've had at least three or four extra teams running throughout the shifts and they've done a remarkable job to try to pull this all together. It's been a fantastic effort that's gone into what we're hopefully going to be executing on Saturday."

One problem for NASA is the need to minimize the time the shuttle's heat shield inspection boom, called the OBSS, is disconnected from keep-alive power. A laser scanner and camera mounted on one end of the boom are needed to carry out a final inspection of the shuttle's nose cap and wing leading edge panels after the ship undocks from the station. If the boom is unpowered too long, the instruments might not work properly.

Today's flight plan called for the space station's robot arm, mounted atop a tram-like mobile transporter, to be moved some 80 feet, from work site 8 on the far left end of the station's main power truss to work site 3 near the center of the beam.

Once in place, the arm will be used to pluck the OBSS from its perch in Discovery's cargo bay. It then will be handed off to the shuttle's robot arm, which is equipped to provide power to the boom. The station arm then will be hauled back to work site 8, the closest it can get to the left-side solar panels.

The OBSS will remain on the shuttle arm overnight and handed back to the station arm, known as the SSRMS, Saturday, just before the spacewalk. NASA's Mission Management Team reviewed the plan Thursday, including the possibility of damage to the sensors on the end of the boom.

"At the time of the MMT, it was estimated that the OBSS would remain unpowered for a total of 12 hours," flight controllers wrote in the morning execute package. "The first 4 hours pertain to the timeframe where the (station arm) has grappled the OBSS and is translating from WS 3 to WS 8. The remaining 8 hours pertain to the timeframe associated with EVA 4. Post-MMT, the operations team further refined the plan. OBSS will now be handed off to (the shuttle arm) prior to (the move) to WS 8, and then handed back to SSRMS on the morning of the EVA. This will minimize the unpowered time to only that required to support EVA 4 (about 8 hours)."

Here is an updated timeline of today's activity (in EDT and mission elapsed time; includes revision K of the NASA television schedule):

EDT........DD...HH...MM...EVENT

11/02/07
01:08 AM...09...13...30...STS/ISS crew wakeup
03:08 AM...09...15...30...ISS daily planning conference
03:43 AM...09...16...05...Shuttle arm (SRMS) powerup
03:58 AM...09...16...20...SRMS moves to shuttle boom (OBSS) grapple position
04:08 AM...09...16...30...Logistics transfers resume
04:08 AM...09...16...30...Mobile transporter moves from WS-8 to WS-3
05:08 AM...09...17...30...OBSS unlatched
06:13 AM...09...18...35...Station arm (SSRMS) moves to pre-grapple position
06:58 AM...09...19...20...SSRMS grapples/unberths OBSS
07:38 AM...09...20...00...EVA-4: Procedures review
07:38 AM...09...20...00...Crew meals
07:58 AM...09...20...20...SRMS grapples OBSS
08:08 AM...09...20...30...EVA-4: On-board conference
08:13 AM...09...20...35...OBSS handoff to SRMS
09:08 AM...09...21...30...Mobile transporter moves from WS-3 to WS-8
09:38 AM...09...22...00...EVA-4: Tools configured
11:08 AM...09...23...30...SSRMS to pre-grapple position at WS-8
11:38 AM...10...00...00...EVA-4: Robotics conference
01:08 PM...10...01...30...EVA-4: EVA/robotics conference with MCC
01:38 PM...10...02...00...EVA-4: Procedures review resumes
02:00 PM...10...02...22...Mission status briefing on NASA TV
03:18 PM...10...03...40...Crew choice downlink
03:53 PM...10...04...15...EVA-4: Airlock campout begins
05:08 PM...10...05...30...ISS crew sleep begins
05:38 PM...10...06...00...STS crew sleep begins
06:00 PM...10...06...22...Daily video highlights reel on NASA TV
10:00 PM...10...10...22...Flight director update on NASA TV

06:00 PM, 11/1/07, Update: Solar array repair plan comes together; officials optimistic dramatic spacewalk will salvage mangled array

Working around the clock, flight controllers, astronauts and engineers are fine tuning a daring plan to put an astronaut on the end of a long boom attached to the space station's robot arm - farther from the safety of the lab's airlock than any spacewalker before him - to perform emergency surgery on a mangled solar array.

Using insulated tools to minimize the risk of shock from the damaged-but-electrically-active solar panel, Scott Parazynski, a former emergency room physician and one of NASA's most experienced spacewalkers, plans to cut snagged guidewires if necessary to release tension before installing cufflink-like clips to strengthen the torn blanket enough to permit its full extension.

The P6-4B solar array is mounted on the far left end of the space station's main power truss, half a football field from the space station's pressurized modules. To reach the site of the damage, Parazynsky, perched on the end of the shuttle's heat-shield inspection boom and carried by the space station's robot arm, will be positioned eight to nine stories from the end of the lab's main power truss.

To put that in perspective, picture the space station's pressurized modules running across a football field at the 50-yard line. Looking down from the press box, Parazynski will be anchored to a boom high above the left end zone goal posts.

"We're faced with a difficult situation," said astronaut Dave Wolf, a Mir veteran who oversees NASA's spacewalk office at the Johnson Space Center in Houston. "It's a real test of the adaptability of this team, the baseline knowledge, how to work in space. We're pulling that all together, we have a time limit, of course, on this mission, we're working around the clock. And I think we're onto a solution that should work, get us pretty close to a permanently acceptable situation. We'll see how it goes Saturday."

Said lead spacewalk planner Dina Contella: "We have just a huge number of people that are right now trying to help the EVA (spacewalk) team how to go and both clear what snagged on the array and help understand how to fix the structural loading issue we might have with the array. It's been an incredible effort to pull it all together."

The Discovery astronauts successfully moved the 17-ton P6 solar array truss segment Tuesday, bolting it to the far left end of the space station's main power truss. The first of its two solar array wings, known as P6-2B, extended a full 110 feet as required, but the crew aborted deployment of the second P6-4B wing when one section of hinged blanket slats hung up, possibly due to a guide wire snag. Two seams between adjacent slats pulled open, resulting in separate tears, and the edges of several nearby slats were crumpled. The largest rip measured some two-and-a-half feet long.

Eighty percent deployed, the P6-4B array can generate 97 percent of the electricity of a fully extended wing. The station is not yet using power from the torn array, but engineers say tests confirm no major damage to its internal wiring.

The immediate concern is figuring out a way to fully extend the P6-4B wing to provide the necessary structural rigidity. With a partially deployed panel, none of the arrays on the left side of the main power truss can be rotated as required to track the sun without risking additional damage. As a result, the station's left-side solar alpha rotary joint, or SARJ, is locked in place until the damage is fixed.

Adding to NASA's problems, the station's right-side arrays also are locked in place because of unexpected metallic contamination inside the starboard SARJ. Parazynski and Doug Wheelock were in the process of gearing up Wednesday for a spacewalk to inspect the starboard SARJ Thursday when NASA managers decided to focus instead on fixing the P6-4B solar blanket.

Engineers initially held out hope for a repair spacewalk Friday, but NASA managers decided early Thursday to wait until Saturday, giving engineers more time to fine-tune the plan.

"We made a decision last night that we weren't going to get there, that we weren't going to be ready for a Friday spacewalk," station flight director Derek Hassmann said today. "We knew it would be a full court press to get there on Friday. I'm disappointed we didn't get there, but I'm satisfied we made a good call."

On Friday, the station's robot arm will be moved 80 feet, from work site 8 on the left end of the main power truss back to work site 3 near the center of the lab complex. Once in place, it will reach into the shuttle's cargo bay and pull out a 50-foot-long heat shield inspection boom, grappling an attachment fitting in the center.

Pulling the orbiter boom sensor system, or OBSS, clear of Discovery, the station arm will hand it off to the shuttle's own robot arm to provide keep-alive power for heaters and other systems in the boom that support a laser scanner and camera mounted on one end. The instruments will be used after undocking from the station to look for signs of impact damage on the shuttle's nose cap and wing leading edge panels.

With the shuttle arm holding the OBSS, the station arm will be moved back out to work site 8, the closest the Canadian-built crane can get to the P6-4B solar arrays. Early Saturday, the station arm will re-grapple the OBSS and position it just to the left of the central section of the power truss to await Parazynski and Wheelock.

The spacewalk is scheduled to begin around 6:30 a.m. Saturday. After attaching a foot restraint and an extension fitting to one end of the OBSS, Parazynski will lock his boots in place and the arm will slowly maneuver him outboard to the P6-4B array. Wheelock, meanwhile, will make his way to the base of the outermost solar array to provide visual cues to arm operators Stephanie Wilson and Dan Tani.

At that point, Parazynski will be farther from the safety of the station's airlock than any astronaut has ever been. NASA's spacesuits are equipped with an emergency oxygen supply good for 30 minutes in case of a major problem that might cut off an astronaut's air supply. Spacewalks typically are designed so an astronaut is never more than a half hour away from the airlock.

But not in this case. Wheelock will be roughly the same physical distance from the airlock as Parazynski, but it would take Parazynski longer to get there in an emergency because of the slow movement of the robot arm.

"There are some things in this spacewalk that are a little higher risk than usual," Wolf said. "One is being very close to a damaged electrical power generating system and perhaps with some free parts as we cut pieces away. We've taken measures with the (tools) and various insulating materials ... Another is when Scott is out in that remote position, it will take longer than usual should he have a suit failure to come back in. We try to make that 30 minutes normally. He won't be within 30 minutes. We're making it as short as we can. But there comes a time when station needs repair, one time events, where we, with good mitigation and knowledge, accept higher risks in some areas. And that's one of them."

Here is a preliminary timeline of major events planned for Saturday's spacewalk (in EDT and elapsed time; subject to change):

                       
EDT........HH...MM...EVENT

06:28 AM...00...00...Spacewalk begins
06:58 AM...00...30...Heat shield boom (OBSS) setup
.....................1. Move to P1 truss/bay 12; perform tether swap
.....................2. Install work site interface extension on station arm
.....................3. Install foot restraint on WIF extension
.....................4. Astronaut gets In foot restraint

07:43 AM...01...15...SSRMS maneuver to P6-4B solar array wing
.....................1. Check OBSS stability prior to P1 departure
.....................2. Station arm moves astronaut to P6-4B solar array wing

08:50 AM...02...22...P6-4B SAW troubleshooting
.....................1. Assess/report guide wire configuration
.....................2. Clear guide wires; cut if necessary
.....................3. Install hinge stabilization cufflinks

11:28 AM...05...00...OBSS maneuver back to egress point
.....................1. SSRMS moves OBSS back to P1 bay 12 for egress

12:08 PM...05...40...Foot restraint egress and OBSS cleanup
.....................1. Egress OBSS; remove/stow OBSS hardware
.....................2. Return to airlock

12:38 PM...06...10...EVA-4 cleanup
.....................1. Stow WIF extender on ESP-2; stow tools
.....................2. Return to airlock

12:58 PM...06...30...Airlock ingress
01:08 PM...06...40...Airlock repressurization
Once in position near the rips in the solar arrays, Parazynski will give engineers their first detailed description of the damage.

"To be honest, we don't have a really great feel for the exact configuration for that snarl," Contella said. "We know there's a snag there, but we're not sure if it's something that's really easy, that you'd be able to clear, or if it's something that's going to be a little bit more complicated."

One major concern is the guidewire that presumably caused the damage when it hung up during deploy.

"If we have any kind of issue where we suspect that we'd have a problem with the guidewire then we'd have to cut the guidewire," Contella said. "And so, currently the idea is you have a pretty big snarl here, you cut at the bottom, you cut at the top and then take the offending part out. It sounds pretty easy, but pulling from the bottom is a guidewire tension mechanism that's pulling with about a pound of force, which is not very much force at all. But when we cut it, we're expecting it to maybe automatically retract down into the lower containment box of the array.

"So it would just pull straight through the grommets and be wound at the bottom," she said. "At this point, we're trying to determine what is the best way to allow that to occur. It might be it doesn't retract at all. ... potentially you couldÊhave it such that it comes down and it doesn't retract enough and you might need to assist it in some way or if it gets caught up, you might need to cut the whole thing off and wrap that up and put it in a trash bag."

Fixing the rips in the blanket is another challenge, but engineers devised a clever solution. The idea is for Parazynski to insert pre-made tabs that work like cufflinks through holes in the blanket slats that were used to secure the panels during launch. Fold-out latches, like the wings of a cufflink, would prevent a tab from pulling back out of a hole. The other end would be inserted through the corresponding alignment hole in an adjacent slat.

The cufflinks should enable the blanket to carry the 70 pounds or so of tension it will experience when the array is fully extended without pulling the ripped seams apart. It is that tension that provides the necessary structural stability and, in this context, the force that could pull the ripped slats apart if nothing was done to strengthen the area.

Throughout the work, Parazynski will take care not to touch the electrically active solar array or allow any of his tools to come in contact with the structure. The tools will be triple wrapped in non-conducting tape. While the risk of a potentially deadly shock is not zero, Wolf said, training, preparation and common sense reduced the likelihood of injury to an acceptable level.

"You can come up with scenarios that would do anything," Wolf said when asked if electrocution was possible. "We have upwards of over a hundred volts DC power on that array. ... It's not the kind of thing that would burn you, but we could get conduction through the heart, let's say, or mild shocks. This is not going to happen, we have very good techniques to insulate and control the array."

2:30 AM, 11/1/07, Update: Solar array repair spacewalk delayed to Saturday

NASA managers today decided to delay a daring solar array repair spacewalk from Friday to Saturday to give engineers more time to develop the tools and procedures needed to fix a rip in one of the outermost solar blankets on the international space station.

The dramatic repair job, carried out by astronauts Scott Parazynski and Doug Wheelock, calls for attaching cufflink-like clips across the 15-foot width of the torn P6-4B solar array blanket to provide the strength needed to permit its full extension. Parazynski, anchored to the end of a boom carried by the space station's robot arm, will install the clips while Wheelock provides guidance for arm operators inside the station.

"As you can probably imagine, there are some technical challenges associated with this and we want to make sure we have a good plan for you," astronaut Chris Ferguson radioed the crew early today from mission control at the Johnson Space Center in Houston. "So what we've elected to do is bypass the EVA opportunity for tomorrow and instead get to a plan later on today that you can review through the evening and into tomorrow for an EVA on flight day 12 (Saturday).

"So that said, I know earlier we had given you some words about conducting some robotic operations today. We have a little more flexibility there given that we will not be going EVA tomorrow. So we may or may not actually conduct those ops today. We'll put a plan together for you with regard to that and we'll get that up to you a little later on.

"So what that'll leave you with is a little bit of white space in your schedule today," Ferguson told shuttle commander Pam Melroy. "Our plan is to fill that up with some transfer activity and some additional time off, so you can look forward to that. Right now, the station planning conference is going on over on (station commander Peggy Whitson's) side and she's hearing pretty much these same words with regard to the slide of the EVA for one day.

"And what that'll leave you with long term, provided the EVA goes well on flight day 12, is a nominal undocking on flight day 14. So that's all we have for you right now. I know it's probably a little bit of a disappointment given that Scott and Wheels were eager to get out the door tomorrow. But we want to get a good plan up to you and as the day goes on, we'll have pieces of that plan sent up your way."

"OK, Fergie, we copy all," Melroy said. "And we absolutely concur that the right thing to do is to move forward with a plan that has a little shelf life and maturity and that you've thought about it and you feel confident in it. We do appreciate you sending stuff up to us as soon as you think it's got some at least moderate level of maturity so that we can stay in synch with you all the way through the day. And yeah, I think it's a disappointment we will get to not go out. We were getting ready to do it, but we'll just have a little more time to prepare. So I don't think that's a problem at all. We sure appreciate the update."

"OK, thanks for your flexibility today, Pam," Ferguson replied. "As you can tell, it's going to be a little bit of a dynamic flight plan. We'll get things up to you as they come and in the meantime, we'll try to leave you alone and you can go enjoy the rest of your post-sleep time."

5:30 PM, 10/31/07, Update: Suffredini says mangled array now top priority; engineers refine repair options (UPDATED at 9:15 p.m. to fix typo; robot arm move planned for Thursday, not Sunday)

Repairing a mangled space station solar array is now NASA's top priority because of concern the ripped, partially deployed blanket could pull apart under the stresses and strains of normal operations, possibly forcing a future crew to dump the panels overboard, NASA officials said today.

After studying the issue overnight, "it became clear to me this needed to be our priority as a program," Mike Suffredini, manager of the space station program at the Johnson Space Center in Houston, told reporters today. "I need this array. This array is in a position where the potential exists for further damage if we leave it in this condition. It's very hard to analyze this specific damage in terms of understanding structurally how much force, how much load it can take.

"Given the fact we could potentially damage this array if we leave it in this configuration, and if we damage this array enough, we could potentially not have it available for the life of the program, this then becomes our priority."

Earlier today, NASA managers called off plans for a spacewalk Thursday by Scott Parazynski and Doug Wheelock to inspect a contaminated solar array rotary joint on the right side of the station's main power truss. Instead, Wheelock and Parazynski, a former emergency room physician, will attempt a daring bit of space surgery to effectively sew up the two rips in the P6-4B solar blanket on the far right side of the power truss and possibly cut away a fouled guidewire.

While engineers have not yet finalized the repair plan, the general idea is to put Parazynski on the end of a shuttle heat shield inspection boom attached to the space station's 50-foot-long robot arm. With the space crane based at a work site at the far left end of the power truss, Parazynski could be maneuvered into position near the damage site on the P6-4B array.

Wheelock, meanwhile, likely would be anchored at the base of the damaged array to provide verbal guidance cues to arm operators back inside the Destiny laboratory module.

Engineers are still debating the details of the surgery, but one option would be for Parazynski to insert pre-made tabs that work like cufflinks through holes in the blanket slats that were used to secure the panels during launch. Fold-out latches, like the wings of a cufflink, would prevent a tab from pulling back out of a hole. The other end would be inserted through the corresponding alignment hole in an adjacent slat.

The idea is for the connected cufflinks, or something like them, to carry the 70 pounds or so of tension the blanket experiences when the array is fully extended. It is that tension that provides the necessary structural stability and, in this context, the force that could pull the ripped slats apart if nothing was done to strengthen the area.

"There is a lot of work ahead of us on this," Suffredini said. "The team has worked extremely hard. We've got a lot of great ideas. ... We feel pretty good about our chances of getting out for an EVA-4 on Friday. But we haven't actually made a determination that's what we're going to do. We've asked the team to go work this. Later on, late tonight, we're going to look where we're at. If we have the procedures in place and we're comfortable we have a plan that we can implement then we will formally ask the crew to implement that on EVA-4 on Friday."

Covering all the bases, Suffredini said "what I'd like to have if at all possible is another opportunity to go outside if we need it."

"First, we do EVA-4 on Friday and we get as much work as we can get done," he said. "If we're successful, we can call it a mission and let the crew stand down, we'll get the shuttle all configured for return (and) we'll let the shuttle go home. ... If, on the other hand, we don't quite get all our work done (on EVA-4) - and that's a distinct possibility - then we'd like to have the option to pursue an EVA-5 on Sunday."

In that case, Discovery's mission - already extended one day because of now-canceled plans to carry out a rotary joint inspection - would have to be extended an additional day.

"So where we are as a program is, the team is off trying to come up with way to approach the array, to clear the snag and then perhaps install some load-bearing straps, if you will, to take on the load so we can redeploy the array," Suffredini said. "If we can't get all our work done on Friday, we'll sit down with the shuttle team and the ops team and look at whether or not we can gain ourselves a second EVA on Sunday and have the shuttle leave one day later."

Parazynski and Wheelock will carry out the proposed Friday spacewalk, with Parazynski, one of NASA's most experienced spacewalkers, on the end of the 50-foot-long orbiter boom sensor system.

In normal operations, the shuttle's robot arm latches onto a grapple fixture at one end of the boom. The other end carries a laser scanner and camera for use in heat shield inspections, along with a fitting that can accommodate an astronaut foot restraint. The station's arm is not compatible with shuttle grapple fixtures and instead will have to pick it up using a station fixture mounted at the center of the boom. That will extend the station arm's reach by about 25 feet instead of the full 50.

The station arm currently is parked atop the space station's mobile transporter at work site 8 on the far left end of the main solar power boom. If the repair plan is approved, the arm will be moved back to a central worksite Thursday to pick up the OBSS, currently mounted in Discovery's cargo bay. The transporter then would take the station crane and the OBSS back to work site 8 to await Parazynski and Wheelock on Friday.

It is not yet clear who would carry out a second spacewalk Sunday should one be required. But Suffredini made it clear NASA needs to fix the torn blanket and a second spacewalk opportunity would provide time to complete any unfinished work or perhaps correct any additional problems.

"The snag is providing a sort of ripping function on the blanket," Suffredini said. "Right now, we're supposed to be able to distribute 70 pounds of load across a 15-foot hinge and we're missing about three feet of that hinge. Not only are we trying to distribute that load across the remainder of the hinge, but you also have a high stress area right where you see the rip beginning.

"Given that configuration, the fact that we have sort of a forcing function the way it's being ripped up, we believe we're in a condition where we could, over time, tear the blanket further. And if we do enough damage to the blanket we could potentially get in a configuration where we couldn't stabilize the array and if we can't stabilize the array, we'll have to figure out what to do about that and we don't have a lot of options. The most likely option is we'd have to jettison it. So before we get to that position ... we've made it a priority to go repair it. It's stable right now, we've got time to go work this problem."

In yet another major change for mission planners - and the Discovery astronauts - the Mission Management Team today approved a revised landing strategy that would move re-entry next week from before dawn to the afternoon. The change will require the astronauts to adjust their sleep cycles and fly a trajectory that will carry them over the heartland of America, a northwest-to-southeast flight path NASA has avoided since the 2003 Columbia disaster. The change will permit additional landing opportunities.

11:17 AM, 10/31/07, Update: NASA confirms spacewalk Friday for solar array repair work

NASA managers today told the Discovery astronauts to forego a planned Thursday spacewalk to inspect a contaminated solar array rotary joint and instead to focus on a spacewalk Friday to attempt repairs of a torn space station solar array blanket. Confirming earlier unofficial accounts of morning discussions to assess repair scenarios, astronaut Tony Antonelli passed the news up to shuttle commander Pam Melroy a few minutes before a spacewalk planning conference.

"For the EVA conference, thought you might be wanting to listen in to at least part of that," he said. "We're going to change the plan for the next couple of days. EVA-4 will not be executed on flight day 10 (Thursday). We're going to shoot for flight day 11 (Friday) ... the contents of which will be solar array wing stuff.

"You'll hear more about that in the conference," he said. "We'll leave flight day 11 as a placeholder for now and if we don't get ready, then we'll try flight day 12 (Saturday). If you've got any questions on the big picture stuff, just let me know."

"OK, Houston, thank you," Melroy replied from inside the Destiny laboratory module. Peggy (station commander Peggy Whitson) and I copy all. We understand we are not going EVA tomorrow and we will talk more about it in the EVA conference, which I will be attending."

Despite the serious nature of the work, outgoing station astronaut Clay Anderson reminded viewers on Earth that Halloween is not limited to Earth's surface, wearing a long black cape as he floated about the station.

Astronauts Scott Parazynski and Doug Wheelock had planned to stage a spacewalk Thursday, the fourth of Discovery's mission, to inspect a contaminated solar alpha rotary joint on the right side of the main power truss that currently is locked in place. It normally turns outboard solar arrays to track the sun, but the source of contamination discovered during a spacewalk Sunday must be determined, and possibly corrected, before it can resume normal operation.

Changing the content of the spacewalk indicates the high priority NASA is placing on repairing the ripped solar array blanket on the P6-4B array on the left side of the station's power truss. In its current partially deployed state, the array does not have the structural rigidity for normal sun-tracking rotation.

Delaying the initial repair attempt until Friday at the earliest will give engineers more time to come up with workable solutions. But it also means delaying a planned spacewalk Saturday by Whitson and station flight engineer Yuri Malenchenko to prepare the newly installed Harmony module for its move to the front of the station after Discovery undocks.

With a solar array repair spacewalk on tap Friday or, if preparations take more time, Saturday, Whitson's spacewalk will be delayed until after the shuttle's departure, adding one more major task to the station crew's plate as they prepare for delivery of a European laboratory module in December.

Whitson and crewmate Dan Tani already planned two spacewalks to connect Harmony to the station's power and cooling systems.

See the 10:30 a.m. status report for additional details and background. This story will be updated after a 2 p.m. news conference with mission managers.

5:10 AM, 10/31/07, Update: Crew news conference; spacewalk planning continues (UPDATED at 10:30 a.m. with crew quotes; Sources say NASA expected to delay fourth spacewalk; attempt solar array repair Friday

NASA and contractor engineers worked through the night assessing a variety of options for possible repairs to fix a ripped solar blanket on a partially extended space station array. Station program managers recommended early today, sources said, that NASA delay a fourth spacewalk from Thursday to Friday and devote the excursion to solar array repair work.

Under that scenario, the astronauts would forego any immediate inspection of a contaminated solar array rotary joint, deferring that work to a later mission, and delay a spacewalk by station commander Peggy Whitson and flight engineer Yuri Malenchenko until after the shuttle Discovery departs.

Flight controllers asked Whitson and shuttle commander Pam Melroy to join them for a discussion of the crew's options earlier this morning, but the conversation was "privatized" and not broadcast on NASA's satellite television downlink. Sources said the decision to pursue a solar array repair was now the top priority, but there was no immediate official confirmation from NASA.

At a news conference earlier today, lead spacewalker Scott Parazynski said he and fellow spacewalker Doug Wheelock were ready for whatever NASA managers decided to do.

"I certainly don't have all the data on board yet," he said. "We've taken hundreds of photographs from our windows and from the station assets and folks in Houston are poring over the data trying to figure out exactly what might have happened. My initial take on it was maybe a guidewire that had been frayed earlier might have been the culprit. However, it looks to our eye via binoculars and photos that that guidewire may be intact.

"It really depends on what the root cause is. We have trained quite a bit (in Houston) and there are numerous contingencies we could effect on the solar array wing. Not sure if they're applicable to this situation, however. One of those might be (to) clip the guidewire, if that might be of help. But we'll see what (the ground team concludes)."

Asked how he and Wheelock might gain access to the damage site, which is well away from any point the station's robot arm can easily reach, Parazynski said the array could be retracted far enough to give the repair team access.

Italian astronaut Paolo Nespoli "suggested we just climb up the mast and give it a good shake!," Parazynski joked this morning. "But that might be a little bit too aggressive."

"We actually have pretty good work site access from the bottom," he said. "We have (equipment) that allows us to basically place our foot restraint a little bit higher above the P6 structure. So we can reach about eight to 10 feet, I think, and get up above the level of the blanket box and make some repairs fairly low in. So if there were a need to effect a repair out where the damage occurred, we'd have to retract that array and do the repair close into the lower blanket box."

The Discovery astronauts successfully moved the 17-ton P6 solar array truss segment Tuesday, bolting it to the far left end of the power truss. The first of its two solar array wings, known as P6-2B, extended a full 110 feet as required, but the crew aborted deployment of the second P6-4B wing when one section of hinged blanket slats hung up, possibly due to a guide wire snag. Two seams between adjacent slats pulled open, resulting in separate tears, and the edges of several nearby slats were crumpled. The largest rip measured some two-and-a-half feet long.

"It was a tough situation because with the beta angle that we're at, which is the angle of the sun, the sun was shining directly into our camera views," Melroy said today. "In fact at one point, we actually did stop (the deploy) because we were concerned we had lost our big picture.

"Of course, we're always going to second guess ourselves and there might have been some other things we could have done. But I think we certainly aborted as soon as we saw something that wasn't right. And at the place we had stopped earlier, everything looked nominal so it was only a few more bays. So I think it happened fairly quickly and probably at a moment there was sun in our eyes. As soon as the sun was gone, we were able to stop. I think we did as well as we could under the environmental circumstances."

Eighty percent deployed, the P6-4B array can generate 97 percent of the electricity of a fully extended wing. The station is not yet using power from the torn array, but engineers say tests confirm no major damage to its internal wiring.

The immediate concern is figuring out a way to fully extend the P6-4B wing to provide the necessary structural rigidity. With a partially deployed panel, none of the arrays on the left side of the main power truss can be rotated as required to track the sun without risking additional damage. As a result, the station's left-side solar alpha rotary joint, or SARJ, is locked in place while engineers assess their options.

Adding to NASA's problems, the station's right-side arrays also are locked in place because of unexpected metallic contamination inside the starboard SARJ. Astronauts Scott Parazynski and Doug Wheelock worked earlier today to prepare their spacesuits and tools for a planned spacewalk Thursday to carry out a more detailed inspection of the right-side SARJ to look for the source of the contamination.

The SARJ mechanism features two 10-foot-wide bull gears and two redundant drive motors called drive lock assemblies, or DLAs. Only one DLA is used at a time to drive the outboard bull gear. The mechanism relies on 12 so-called trundle bearings, pressing against the outboard gear race with 1,000 pounds of force, to rotate smoothly.

During a spacewalk Sunday, astronaut Dan Tani removed one of 22 thermal blankets to look inside for any sign of whatever might be causing unusual vibration and power usage. He was surprised to find large amounts of metallic shavings in the joint, a clear sign of some sort of misalignment or other potentially serious problem.

Parazynski and Wheelock originally planned to test a new heat shield repair technique during the mission's fourth spacewalk but that work was deferred to a future mission to clear the way for a more thorough SARJ inspection. It is that work that would be delayed if NASA presses ahead with a solar array repair spacewalk Friday.

As of this writing, no official decisions have been announced. Space station flight director Heather Rarick said late Tuesday engineers needed additional photographs to help assess the solar panel's condition.

"We have some pictures that we've processed and they're not giving us the best insight into what it is at this point," she said late Tuesday. "I think we're asking (for) the crew to take some more pictures (Wednesday)."

Positioned on the far left end of the main power truss, the P6 solar array wings extend beyond the reach of the space station's robot arm. Engineers are studying the possibility of using the shuttle's 50-foot-long heat shield inspection boom to give the station arm additional reach and it may be possible to retract the damaged wing far enough for an astronaut to reach the damaged section.

"What to do next? Not really a clear answer yet," Rarick said late Tuesday. "They're putting ideas on the table. One of the key factors we have to figure out is how we access it, how we get a crew member up there if we do need to do some work, physically at the site as opposed to being able to do it by commands, wither by deploying or retracting. So that's being looked at, that'll take probably a fair amount of time to figure out and put that plan in place.

"Until we know what we think the cause is, maybe until we get some better pictures, I don't think we really have any solid leads on how to fix it yet," she said.

Here is an updated timeline of today's activity (in EDT and mission elapsed time; includes revision G of the NASA television schedule):

EDT........DD...HH...MM...EVENT

10/31/07
12:38 AM...07...13...00...STS/ISS crew wakeup
03:28 AM...07...15...50...Spacesuit resizing
04:13 AM...07...16...35...ESA/Italian Space Agency VIP event
04:28 AM...07...16...50...EVA-4: Tools configured
05:30 AM...07...17...52...ESA/ASI PAO event replay with translation
05:53 AM...07...18...15...EVA-4: Procedures review
06:48 AM...07...19...10...Joint crew meal
07:48 AM...07...20...10...Crew news conference
08:28 AM...07...20...50...Joint crew photo
08:43 AM...07...21...05...EVA-4: Airlock preps
09:00 AM...07...21...22...Crew news conference replay with translation
10:13 AM...07...22...35...EVA-4: Preparation review
11:08 AM...07...23...30...EVA-4: Conference
12:08 PM...08...00...30...EVA-4: Procedure review
01:53 PM...08...02...15...Crew choice video downlink
02:00 PM...08...02...22...Mission status briefing on NASA TV
02:28 PM...08...02...50...EVA-4: Airlock campout/tools configured
03:38 PM...08...04...00...ISS crew sleep begins
04:08 PM...08...04...30...STS crew sleep begins
05:00 PM...08...05...22...Daily video highlight reel on NASA TV
09:30 PM...08...09...52...Flight director update on NASA TV
Station problems aside, the shuttle Discovery is operating smoothly with no major problems. Earlier in the mission, NASA's Mission Management Team concluded the ship's heat shield came through launch in good condition with no major problems. The only open items as of this writing are a half-dozen readings from wing leading edge sensors in place to measure possible strikes by ascent debris micrometeoroids. Similar readings on past flights were attributed to the effects of temperature changes on the shuttle's aluminum structure. In keeping with post-Columbia practice, the wing leading edge indications will be checked out during an inspection after the shuttle undocks from the space station.

6:00 PM, 10/30/07, Update: Engineers assess options for fixing torn solar array; Suffredini says array stable in near term, but fix needed for normal operations

Engineers are scrambling to recover from a solar array hang up that ripped a two-and-a-half-foot tear in one fragile panel as the hinged blanket was pulled from its storage box today. The disheartening, hard-to-reach hang up occurred as the Discovery astronauts were "95 percent of the way to a perfect day," as one NASA official put it, moving the 17-ton P6 solar array truss segment to its permanent mounting point on the far left end of the lab's main power truss.

"In the configuration we are in today, right this moment, we're basically providing all the power we need from this array," said Mike Suffredini, space station program manager at the Johnson Space Center in Houston. "When I left (mission control), we were about 3 percent shy of the amount of power being provided by the other array. And that's indicative of the fact that we're not fully deployed.

"What that means is we haven't damaged the (power) feed wires," he said. "So that's great news. ... Structurally the array's in fine shape, so we have plenty of time to go sort out this problem."

But until the problem is resolved, the P6-4B array cannot be fully extended and locked in position with the 75 pounds of tension on the blankets that is required to provide structural stability. And until that issue is resolved, the left-side arrays - P6 and P4 - cannot be rotated continuously to track the sun, which limits their ability to generate power.

Given that the station's right-side arrays are now locked in place because of concern about unusual contamination inside a rotary joint, the blanket tear on the outermost right-side array was an especially disheartening setback. NASA hopes to launch a long-awaited European research lab aboard the shuttle Atlantis on Dec. 6 but Suffredini said he would not be comfortable pressing ahead until this latest problem is dealt with.

"We have a lot to talk about," Suffredini said. "We will talk about options, about EVA-4, about EVA-5, when we need to plan to do these EVAs, what we need to accomplish, what the priorities are, what we know today, what we'll know tomorrow, can we come up with reasonable plans to implement? So all this is forward work. We haven't had a lot of time to sort it out.

The combined station-shuttle crew currently plan two more spacewalks: One Thursday to inspect the contaminated rotary joint on the right side of the main power truss; and a final outing Saturday by station commander Peggy Whitson and Yuri Malenchenko to prepare the newly installed Harmony module for its move to the front of the space station after Discovery departs.

Harmony will serve as the attachment point for Europe's Columbus research lab in December and Japan's Kibo lab modules, scheduled for delivery in February and April. Every day added to Discovery's mission will trigger a corresponding delay for work required to prepare Harmony for Columbus and Suffredini said he wants to preserve the Whitson/Malenchenko spacewalk if at all possible.

But he said the content of either spacewalk could change depending on what engineers come up with for addressing the P6-4B problem. And he would not rule out an additional mission extension if necessary.

"We have a lot of options," he said. "We're in a good configuration to sit here and work through this problem. So from our perspective, if you have to deal with this sort of thing, this is the way we'd like to be, we like to be in a nice, stable config while we think through our options. So that's what we'll do over the next few days."

The blanket problem developed at the end of an otherwise successful day, one in which spacewalkers Scott Parazynski and Doug Wheelock, working with robot arm operators Stephanie Wilson and Dan Tani, successfully attached the 35,000-pound P6 solar array truss segment to the left end of the station's main power truss.

The station design incorporates four huge sets of solar arrays, two on each end of a truss that will span the length of a football field when fully assembled. Each array segment - P4 and P6 on the left, or port, side and S4 and S6 on the right side - features two 110-foot-long, 15-foot-wide "wings" made up of two folding blankets supported by central self-assembling masts that extend outward on opposite sides.

Two blankets making up the 2B side of the newly installed P6 solar arrays were successfully re-extended today after the truss was connected to the power truss. But the astronauts aborted extension of a second set of panels after noticing an apparent guidewire hangup and a jagged tear in one of the two remaining blankets.

The second set of blankets was more than three quarters extended at that point. In television views from the station, it appeared as if several slats making up the blanket might have gotten hung up on a guidewire, increasing tension in that area and ripping a two-and-a-half-foot tear in a seam. But it was not immediately clear what might have gone wrong.

Astronauts had major problems retracting the P6 arrays during previous shuttle visits in preparation for this week's 145-foot move from a central mounting point to its permanent position on the left end of the power truss. Grommets on the sides of the blankets hung up on frayed guide wires during the retraction process, requiring spacewalking astronauts to provide a manual assist. Eventually, the blankets were coaxed back into their storage boxes.

Whitson said the ripped seam between two slats apparently occurred in the same area where a frayed guidewire was noticed during the earlier retraction.

"And Houston, Alpha on one, just some further information," she called. "When we were deploying it, we noticed there were more dynamics around the bay 11 point where we were expecting there might be that problem with the frayed line. And at that point, we still thought we were OK. But it appears that maybe that was the extra motion we saw.

"We didn't abort because we didn't see the tear. Unfortunately, the sun angle was such that it was in a place that we just didn't see it. You know, we paused it later, but by that point in time the problem area was behind the (robot) arm in one view and the sun angle in out other view was such that it covered it up. So, it was a combination of really bad sun angles, but I think we did see it, you know, we saw the extra motion when it probably happened and it probably happened as we were pulling it out of the blanket box."

"Hey, no worries Peggy, we had good video, too, and we were keeping our eye on it, so that's just the way it goes," astronaut Kevin Ford replied from Houston. "We appreciate you doing the abort when you did, that was awesome. And we'll just keep working this."

To ease tension on the torn blanket, commands were sent to retract the mast a few feet while engineers debated their options and the astronauts took additional photographs to document the array's condition.

"There was a point late in the shift where I thought the entire thing was going to go off with(out) a hitch," said lead flight director Derek Hassmann. "Before we start talking about the surprises and the things that didn't go quite as well as expected, I'd just like to emphasize that the spacewalk itself was just unbelievably successful. We were able to accomplish all the planned objectives, including the P6 attach to P5, which we knew was going to be a tough and challenging activity. ... All of the P6 attach went by the book, extremely well."

But the P6-4B hangup cast a shadow on the day's activity.

"That was a little bit of a disappointment at the end of an extremely successful day, but we've got folks already having meetings, talking about our go-forward plan from here," Hassmann said. "So I expect that tomorrow we'll have a much better handle on our approach to that solar array."

A major problem for NASA is that P6 is so far out on the power truss that the station's robot arm cannot reach far enough to get an astronaut to the area where the damage occurred. To either fix the tear or release the snag, the astronauts likely will have to retract the P6-4B array far enough to provide access. If engineers can figure out a way for the station arm to pick up the shuttle's 50-foot-long heat shield inspection boom, known as the orbiter boom sensor system, it may be possible to get a spacewalker farther up the mast to the damage site.

"We're going to have to get this area where we can get to it," Suffredini said. "There has been a discussion about the OBSS. Unfortunately, the grapple fixture on the end of the OBSS is not a station grapple fixture, it's the shuttle arm grapple fixture. It's a little different than the space station grapple fixture and in fact, the guys are going off to find out if they can grapple it with the SSRMS (station arm). All of this is forward work. My guess is you'll hear us talk about trying to retract the arrays a little bit to try to get them within reach."

Until the problem is resolved, the P6-4B array cannot be fully extended and its blanket subjected to the normal 75 pounds of tension need to provide structural stability because of concern the force could pull the blanket apart at the tear. Without that structural stability, the arrays cannot be rotated to track the sun. And if the arrays cannot rotate, they cannot generate the power required for the upcoming addition of the European and Japanese research modules.

That's in part because of contamination found in the solar alpha rotary joint, or SARJ, that is used to turn the station's right side arrays. Metallic contamination was discovered in the massive joint during a spacewalk Sunday and as a result, mission managers extended Discovery's flight by one day, deferred a heat shield repair demonstration and devoted an entire spacewalk Thursday to a more thorough inspection.

During today's spacewalk, Parazynski inspected the left-side SARJ to provide a point of reference and found no visible contamination. Suffredini said the problem with the right-side SARJ could involve one of 12 so-called trundle bearings, which press against a bearing race with 1,000 pounds of force, or the two drive motors that engage a 10-foot-diameter bull gear to turn the outboard arrays.

There are no spare drive motors in orbit, but two spare trundle bearings are available if it turns one one of the 12 in the right-side SARJ is the source of the contamination. But it was unclear whether a replacement operation would be attempted during Discovery's mission even if the problem is clearly identified Thursday.

While Suffredini held open the option of adding solar array repair work to Thursday's spacewalk, engineers appeared to favor sticking with the SARJ inspection and using the additional time to come up with a plan to address the array tear.

"We need power out of P6 in order to go ahead and live with the SARJ problem," Suffredini said. "This is an additional challenge for us. Station is a robust vehicle and we have many, many options of how to deal with the problem. And so it's not a situation where anybody's particularly panicked. But if, on the other hand, what we want to do is get this fixed to a point where we can continue assembly the way we had planned, this is a significant challenge for us to deal with.

"But we will deal with it. If we get the array down and we cut the snag and we figure out how to reinforce it, we'll deploy the array. It's giving all the power we need, that's all we need out of that array, is power. It doesn't have to look good, it just has to get us power. It's not about style points at this point with this array. We need it out and we need about as much power as it provides today. Any one of the fixes we have considered ... will be plenty of power for us as a program."

In the meantime, he said, "I don't want to do any more damage to the array than has already been done."

"We need to first figure out what the condition is, how we're snagged, whether that snag is putting us at risk of ripping further or worse in my mind, ripping the power cables," Suffredini said. "Before the shuttle leaves during this docked mission, we will know what we're dealing with and we'll have assessed what to do on the next shuttle flight by then. ... But right this instant, I wouldn't want to plan (the Columbus mission) until I know better what's going on with this array."

12:45 PM, 10/30/07, Update: P6 solar array extension halted; engineers assess damage to one blanket (UPDATED at 1:30 p.m. with additional details; quotes from Whitson)

Two blankets making up one side of the newly installed P6 solar arrays were successfully re-extended today after the 17-ton truss segment was bolted to the far left end of the space station's main power truss. But the astronauts aborted extension of a second set of panels after noticing an apparent guidewire hangup and a jagged tear in one of the two remaining blankets.

The second set of blankets was more than halfway extended at that point, but it was not clear how flight controllers might opt to proceed given the obvious tear between two slats in one of the flexible blankets. In television views from the station, it appeared as if several slats might have gotten hung up on a guidewire, increasing tension in that area and ripping a seam. But engineers did not immediately offer an assessment of what might have gone wrong. Or what, if anything, can be done to fix it.

Astronauts had major problems retracting the P6 arrays during previous shuttle visits in preparation for this week's move from a central mounting point to the truss segment's permanent position on the far left end of the power truss. Grommets on the sides of the blankets hung up on frayed guide wires during the retraction process, requiring spacewalking astronauts to provide a manual assist. Eventually, the blankets were coaxed back into their storage boxes.

Station commander Peggy Whitson said the ripped seam between to slats apparently occurred in the same area where a frayed guidewire was noticed during retraction.

"And Houston, Alpha on one, just some further information," she called. "When we were deploying it, we noticed there were more dynamics around the bay 11 point where we were expecting there might be that problem with the frayed line. And at that point, we still thought we were OK. But it appears that maybe that was the extra motion we saw.

"We didn't abort because we didn't see the tear. Unfortunately, the sun angle was such that it was in a place that we just didn't see it. You know, we paused it later, but by that point in time the problem area was behind the (robot) arm in one view and the sun angle in out other view was such that it covered it up. So, it was a combination of really bad sun angles, but I think we did see it, you know, we saw the extra motion when it probably happened and it probably happened as we were pulling it out of the blanket box."

"Hey, no worries Peggy, we had good video, too, and we were keeping our eye on it, so that's just the way it goes," astronaut Kevin Ford replied from Houston. "We appreciate you doing the abort when you did, that was awesome. And we'll just keep working this."

To ease tension on the torn blanket, commands were sent to retract the mast a few feet while engineers debated their options and the astronauts took additional photographs to document the array's condition.

Given the design of the arrays, NASA managers said they did not expect any problems with the re-deployment and the first set of panels - P6-2B - extended smoothly.

"It looks like they're getting the array all the way out," astronaut Clay Anderson radioed spacewalkers Doug Wheelock and Scott Parazynski from inside the shuttle-station complex as the first of the two arrays slowly extended to its full length.

"Wow, that's great," Wheelock replied.

"Thanks for the update, Clay," Parazynski said. "That's a good day's work right there."

Wheelock and Parazynski were in the process of wrapping up a successful seven-hour eight-minute spacewalk when the P6-2B array was pulled from its storage box by an ingenious motor-driven self-assembling mast. The deployment was carried out in stages, first just a few inches, then one mast bay and finally all the way out.

Parazynski reported seeing small bits of debris floating out of the blanket boxes during the initial stages of extension.

"I can actually see quite a bit of sparkling material glinting in the sun, I guess, probably mylar fragments or something coming out the blanket box," he observed. "Both of the blanket boxes, actually. I don't know if you can see thatÊout of the aft flight deck. But lots of little sparkles there."

"We copy, EV-1, and that is expected," someone replied.

With the P6-2B array fully extended, the astronauts sent commands to deploy the 4B array at 12:08 p.m. as the space station sailed high above the south Pacific Ocean.

"Three, two, one, mark," shuttle commander Pam Melroy radioed as the the second array began extending. About halfway through the deployment, Melroy halted the procedure to improve the crew's camera views. A few minutes later, the drive motor was restarted and the 4B arrays resumed extension. Then, Melroy ordered another abort when the tear became apparent.

"Aborting," she called. "Houston, Alpha, on the big loop. We detected some what appears to be a wrap around or some damage and we're zoomed in on it on camera 24 right now."

"OK, Pambo, we see it," Ford replied from mission control. "Thanks for the view."

"And of course, we aborted," Melroy continued. "And sorry it took us a little while to be sure that we weren't being fooled by the lighting."

"Hey, no problem, Pambo, it was a good call on the abort," Ford said. "And we're having a look. ... We'll take anything you have for us to send down what you guys saw or anything while we're talking about it as well. Don't be shy."

"On camera 22, the sun angle was such that we couldn't actually see it and so we didn't see it until we were zooming out on camera 24," Whitson said. "We didn't really notice any significant perturbations as it was deploying. But we just saw the tear and stopped."

Because of the array's location on the far end of the power truss, the astronauts cannot reach the area of the tear. One option might be to retract the arrays, resolve the hangup and redeploy, but NASA managers and engineers will need to complete a thorough assessment before deciding on any course of action.

Today's spacewalk began at 4:45 a.m. and ended at 11:53 a.m., pushing the crew's total EVA time to 19 hours and 55 minutes over three of five planned excursions. Overall, this was the 95th spacewalk devoted to station assembly and maintenance since assembly began in 1998 and the 18th so far this year, pushing the cumulative total to 587 hours and 54 minutes (note: NASA recently added an hour to its total, which is not reflected here; I am researching the discrepancy).

Italian astronaut Paolo Nespoli, assisting Parazynski and Wheelock as they doffed their suits and stowed tools, reported the crew was missing a digital camera and flash.

"It's probably outside on the tool box on the airlock," he reported.

No word yet on whether that camera was used to snap pictures of the left-side solar array rotary joint inspected by Parazynski earlier in the spacewalk. The camera presumably can be retrieved during a spacewalk Thursday to inspect the right-side joint. During a spacewalk Sunday, contamination was discovered in that joint that may indicate a serious problem.

9:45 AM, 10/30/07, Update: Port rotary joint appears in good condition; no internal contamination

Spacewalker Scott Parazynski opened up a second solar array rotary joint today, peered inside and told ground controllers he saw no signs of any internal contamination like the metal shavings fellow spacewalker Dan Tani discovered in the space station's right-side rotary joint during a spacewalk Sunday.

"it's like Easter. You open up an egg for a surprise," Italian astronaut Paolo Nespoli said as Parazynski was removing a thermal cover on the left-side solar alpha rotary joint, or SARJ.

"Yes, well again, I don't want to jump to conclusions, but I have a happy story, at least so far, that I don't see filings or debris," Parazynski said. "The races look nice and clean. Let's see what else is underneath here... "

He then stowed the thermal cover and took a closer look.

"See if you see anything out of the ordinary, anything (like) Dan described," Nespoli asked.

"The race rings themselves look like they're brand new machined, no wear on any of the teeth," Parazynski said of the 10-foot-wide motor-driven gear and the race rings used by big bearings in the joint. "Looking at the race rings themselves, very, very smooth and no particulate matter there, no galling."

After Parazynski had looked about a bit, Nespoli asked him for additional confirmation.

"And Scott, from what you are describing, what I see on your wireless (helmet camera), I don't see absolutely any sign of any damage, anything."

Parazynski examined the underside of the thermal blanket he removed earlier to make sure aluminum insulation was still in place.

"The other side is pristine, right out of the shop," he reported. "No debris whatsoever."

And with that, he repositioned the thermal blanket and closed out the area while fellow spacewalker Doug Wheelock worked to move a 525-pound electrical switching unit from Discovery to an external storage platform near the station's main airlock.

Two massive SARJ joints, one on each side of the power truss, are in place to rotate outboard solar arrays to keep them face on to the sun as the station orbits the Earth. Engineers began noticing higher-than-normal vibration and power usage in the starboard SARJ just under two months ago and Tani was asked to carry out a quick inspection during the crew's second spacewalk Sunday.

After removing a thermal blanket, he was surprised to discover large amounts of metallic contamination inside the joint. NASA managers asked Parazynski to look inside the port SARJ today to serve as a baseline for comparison. The port SARJ has operated flawlessly, with no signs of vibration or abnormal power use.

Based on Parazynski's observations today, internal contamination is not at all normal and the shavings Tani discovered are a clear sign something is amiss in the starboard SARJ. A more-thorough inspection of the now-parked starboard SARJ will be carried out during a spacewalk Thursday.

9:00 AM, 10/30/07, Update: P6 truss in place; radiator deployed; SARJ inspection on tap

Spacewalkers Scott Parazynski and Doug Wheelock successfully attached the 17-ton P6 solar array truss segment to the far left end of the space station's main power truss today, connected ground straps and electrical cables, removed thermal covers and monitored deployment of the segment's folding ammonia radiator panels.

Ground controllers plan to deploy the segment's folding solar blankets later this morning. Wheelock, meanwhile, is pressing ahead with work to move a spare power switching unit from the shuttle Discovery to a stowage platform on the space station while Parazynski prepares to inspect the left-side solar alpha rotary joint.

Two massive SARJ joints, one on each side of the power truss, are in place to rotate outboard solar arrays to keep them face on to the sun as the station orbits the Earth. With engineers concerned about high vibration and power usage in the starboard SARJ, astronaut Dan Tani carried out an inspection Sunday and discovered large amounts of metallic contamination inside the mechanism.

To help engineers understand what might be going on in the joint, Parazynski is going to look into the port-side SARJ, which is operating normally, to get a baseline for comparison. A more thorough inspection of the starboard SARJ is planned for the crew's fourth spacewalk Thursday.

The astronauts are running ahead of schedule and have encountered no major problems.

"Robeau, if you could pass it on to the transfer guys that P6 transfer is complete," Parazynski joked to robot arm operator Stephanie Wilson.

"Hey guys, just for 15 seconds here, fantastic job out there guiding us in," Tani radioed from inside the shuttle-station complex. "And of course, we all know we couldn't have done this without (our trainers). We couldn't have done it without you guys, fantastic success to all of you."

"Here, here," Parazynski agreed. "I second that."

A few minutes later, as both astronauts wrapped up their work on the far end of the power truss, Wheelock marveled: "What a tremendous view!"

"End of the road out here, Wheels," Parazynski said. Looking at the scene a few minutes later, he added: "ISS is one of the modern marvels of the world. Look at all this amazing technology. Beautiful."

7:15 AM, 10/30/07, Update: P6 solar array successfully mounted on left end of power truss

With verbal cues from spacewalkers Scott Parazynski and Doug Wheelock, robot arm operator Stephanie "Robeau" Wilson and Dan Tani carefully inched a 35,000-pound solar array segment into position on the far left end of the space station's main power truss today, wrapping up a two-day 145-foot move in a major milestone in the station's assembly.

With the massive array precisely positioned and all four corner bolts lined up with guidance cones, Wheelock used a power tool at 6:17 a.m. to engage a central capture claw on the P5 spacer segment, pulling P6 into position for bolting. The spacewalkers then began tightening the four corner bolts to complete the long-awaited attachment.

"Hey Wheels. Don't put your fingers right here, OK?" Parazynski joked just before Wilson moved the huge truss in for capture.

Television shots from spacesuit helmet cameras showed the base of the P6 segment precisely lined up with the P5 spacer segment as it moved slowly into position for capture, maneuvered with remarkable precision by Wilson and Tani. While Parazynski and Wheelock provided verbal cues for guidance, Wilson appeared to have no problem driving the big segment into place.

"Fifty seven foot pounds on corner one," Parazynski reported as he and Wheelock torqued the attachment bolts as required. Dwarfed by the big solar array segments, the astronauts also had to connect electrical grounding straps between P5 and P6 and four power umbilicals that will route telemetry to and from P6 once it is re-activated, along with electricity from its solar arrays.

Around 7:10 a.m., Wilson was cleared to detach the robot arm from the P6 segment and reposition it to provide camera views of solar array re-deployment later this morning.

"I love this job," one of the spacewalkers said earlier as the shuttle-station complex flew 210 miles above India. "Beautiful view."

4:50 AM, 10/30/07, Update: Spacewalk begins

Running about 45 minutes ahead of schedule, astronauts Scott Parazynski and Doug Wheelock, floating in the space station's Quest airlock module, switched their spacesuits to battery power at 4:45 a.m. to officially begin a planned six-and-a-half-hour spacewalk. The goals of the excursion are to re-attach a 35,000-pound solar array truss segment; install a spare power switching unit; and inspect a second solar panel rotary joint to help engineers figure out what might be causing contamination in a similar joint on the other side of the station.

This is the 95th spacewalk devoted to station assembly and maintenance since construction began in 1998, the 18th so far this year and the third of five planned for Discovery's mission. See the 3:30 a.m. CBS News status report for details about today's activities.

3:30 AM, 10/30/07, Update: Astronauts gear up for dramatic spacewalk to re-attach P6 solar array truss

Astronauts Scott Parazynski and Doug Wheelock are gearing up for a dramatic spacewalk today to re-attach the 35,000-pound P6 solar array truss after a two-day, 145-foot move, bolting it to the far left end of the space station's main power truss where it will remain for the life of the lab complex. Parazynski also plans to carry out a brief inspection of a second solar array rotary joint to provide more insight into what might be causing contamination in a joint inspected Sunday.

P6 was the first set of U.S. solar arrays launched to the station, attached to a central truss in 2000 to provide the power needed during the early stages of construction. The lab's main power truss is now built, with solar arrays - port 4 (P4) and starboard 4 (S4) - now in place on both sides, clearing the way to move P6 to its permanent mounting point on the left end of the power truss. A fourth set of arrays, S6, will be mounted on the right end of the truss next year.

Getting the P6 arrays re-extended on the end of the port power truss is critical for continuing station assembly. Because of contamination in the right-side solar array rotary joint, the S4 solar array panels on the starboard side of the station are locked in place and are not turning to track the sun, reducing the amount of power available to the station's systems.

To support the upcoming addition of European and Japanese research modules, NASA needs to get the P6 arrays re-extended and rotating alongside the P4 arrays to generate as much power as possible while engineers figure out how to resolve the contamination issue in the right-side rotary joint.

The P6 truss, its two huge solar panels stowed and its electrical systems shut down, was detached during a spacewalk by Parazynski and Dan Tani on Sunday. The station's robot arm handed the segment off to the shuttle's arm on Monday, moved 80 feet to a work site at the left end of the power truss and re-grappled P6 for today's installation. The arm will be operated by Stephanie Wilson and Tani from inside the Destiny laboratory module.

To install P6, the 50-foot-long station arm will be fully extended from its position at work site No. 8 on the power truss, moving the massive segment outboard of the P4 arrays and a short spacer segment known as P5. Parazynski and Wheelock will be positioned near P5 to provide guidance cues for Wilson and Tani. Once the base of the segment is close enough to P5, Wheelock will activate a capture claw to pull the two components together before bolts at all four corners are engaged to complete the job.

"On flight day 8 I'll be going out again with Doug Wheelock, on what I think will be our most spectacular spacewalk," Parazynski said in a NASA interview. "We'll be at the very tip of the space station, as far as you can possibly get from the comforts of the airlock, a (greater) distance then we've ever had the opportunity to go. We'll have Dan and Stephanie at the controls of the space station robotic arm. We'll be giving them verbal feedback on the precise alignment of the P6 truss relative to the P5 truss.

"Once we see everything is perfectly aligned, then they'll be issuing a command to bring the P6 into opposition with the mating interface there. Hopefully, we've given them the best insight possible, everything is perfectly aligned and we'll drive those four RTAS bolts around the corners of the truss, and then it'll be hard mated, where P6 will live for the duration of the international space station."

Parazynski will connect four power cables and both spacewalkers will remove thermal covers that were placed over critical electrical components called sequential shunt units before P6 was detached. Parazynski then plans to release restraints holding P6's ammonia radiator panels in place so the astronauts inside the station can deploy them. Wheelock will make his way back to the shuttle to move a spare 525-pound power switching unit to an external stowage platform near the station's airlock.

"Doug and I will mate several connectors, power and data, to and from the P6 truss," Parazynski said. "We'll then travel out to the very tip of P6 and remove those blankets that we installed on EVA-1 over the sequential shunt unit boxes. Doug will then depart and head back toward the center part of the space station, for the lab. He'll set up the shuttle arm with a foot restraint. And he'll get in work to transfer the MBSU, or the Main Bus Switching Unit Ð we have that on a side wall carrier in the payload bay Ð he'll bring that up to space station.

"Later in the spacewalk I'll help him attach that to a kind of a maintenance and logistics depot that we call ESP-2, or External Stowage Platform number 2. It's very close to the airlock. While he's off working with the robotic arm, Stephanie and George Zamka on the flight deck of the shuttle will be controlling that portion of the flight. I'll stay out at the tip of P6 and I'll deploy or enable deployment of the aft radiator. There's several cinches and other interfaces that I'll have to work with, to enable that. Once that's complete, I'll get out of the way and then the ground controllers are really off to the races."

Deployment of the P6 solar panels is scheduled to begin toward the end of the spacewalk and should be complete about an hour after it is over, stretching 240 feet from tip to tip.

"There's actually three separate teams in mission control working on the power systems of P6," Parazynski said. "Very complex choreography and sequenced events such that we can hopefully get both solar arrays deployed on flight day 8. That's our goal. So as I clear the P6 worksite, the radiator will come out and hopefully fairly soon thereafter we'll start deploying the solar array wings. Pam and Dan Tani inside will be on a PCS, a laptop display and looking at various cameras and working in close concert with folks on the ground to deploy those radiators."

In the original flight plan, Parazynski planned to leave P6 after releasing the radiator restraints and move to the P1 truss segment to activate the deployment mechanism on two large radiators, part of the station's main cooling system. But the plan was changed in the wake of Sunday's spacewalk when Tani, inspecting the starboard solar array rotary joint - used to turn outboard arrays to keep them face on to the sun - discovered metallic shavings contaminating the interior of the mechanism.

NASA managers decided to have Parazynski inspect the port-side solar alpha rotary joint, or SARJ, during today's spacewalk to provide a comparison and document the condition of a joint known to be operating smoothly. NASA's Mission Management Team decided Monday to extend Discovery's flight one day and to revise the crew's fourth spacewalk Thursday to include a more thorough inspection of the right-side SARJ. A fifth and final spacewalk is now planned for Saturday, by station commander Peggy Whitson and flight engineer Yuri Malenchenko, to continue outfitting the newly installed Harmony module.

Here is a timeline of today's activity. Readers are advised that as of 3 a.m., the spacewalkers were running well ahead of schedule (in EDT and mission elapsed time; include revision E of the NASA television schedule):

EDT........DD...HH...MM...EVENT

12:38 AM...06...13...00...STS/ISS crew wakeup
01:13 AM...06...13...35...EVA-3: Airlock repress to 14.7 psi; hygiene break
02:23 AM...06...14...45...EVA-3; Campout EVA preps
03:53 AM...06...16...15...EVA-3: Spacesuit purge
04:08 AM...06...16...30...EVA-3: Spacesuit oxygen pre-breathe
05:08 AM...06...17...30...EVA-3: Airlock depressurization
05:28 AM...06...17...50...EVA-3: Spacesuits to battery power
05:33 AM...06...17...55...EVA-3: Airlock egress
06:03 AM...06...18...25...EVA-3: Parazynski: Attach P6 to P5
06:18 AM...06...18...40...EVA-3: Wheelock: Attach P6 to P5
08:13 AM...06...20...35...Station arm (SSRMS): P6 ungrapple
08:13 AM...06...20...35...EVA-3: Parazynski: P5/P6 umbilical connections
08:48 AM...06...21...10...EVA-3: Wheelock: P5/P6 umbilical connections
08:53 AM...06...21...15...EVA-3: Parazynski: SSU shroud removal
09:03 AM...06...21...25...EVA-3: Wheelock: SSU shroud removal
09:28 AM...06...21...50...EVA-3: Parazynski: Radiator cinch release
10:03 AM...06...22...25...EVA-3: Wheelock: MBSU transfer
10:28 AM...06...22...50...EVA-3: Parazynski: Port SARJ inspection
10:33 AM...06...22...55...P6 radiator deployment
11:08 AM...06...23...30...EVA-3: Parazynski: Radiator squib firing unit (if time available)
11:18 AM...06...23...40...EVA-3: Parazynski: MBSU transfer
11:58 AM...07...00...20...P6 solar array deployment begins
12:03 PM...07...00...25...EVA-3: Parazynski: Airlock ingress
12:18 PM...07...00...40...EVA-3: Wheelock: Airlock ingress
12:38 PM...07...01...00...EVA-3: Airlock repressurization
12:38 PM...07...01...00...2B array 100 percent deployed
01:28 PM...07...01...50...4B array 100 percent deployed
01:48 PM...07...02...10...SSRMS powerdown
02:30 PM...07...02...52...Mission status briefing on NASA TV
04:08 PM...07...04...30...ISS crew sleep begins
04:38 PM...07...05...00...STS crew sleep begins
05:00 PM...07...05...22...Daily video highlights reel on NASA TV
10:30 PM...07...10...52...Flight director update on NASA TV
Deployment of the P6 solar arrays will be carefully monitored, in part because of problems experienced retracting the huge panels during a previous shuttle mission when frayed guidewires hung up on grommets and the arrays did not fold properly along panel hinge lines. NASA managers are confident the arrays will deploy smoothly today because like a road map, it is easier to pull the folding panels open than it is to fold them neatly into compact storage boxes.

"The mechanics of the retraction versus the deploy are very different," said flight director Derek Hassmann. "When we deploy the array, there's significantly more force, or load, on the array. So I would not expect that type of grommet sticking to be a problem. Another problem we saw in multiple places on the 2B and 4B arrays during the retraction was the folding issue where the hinges of the array did not fold in the proper direction. ... We don't expect that to be a problem on the deploy, either, because again, you're applying a consistent load across each of the solar array wings.

"So there's a fair amount of confidence and a fair amount of optimism that the deploy's going to go well. We've looked at all the failure mechanisms that we think are possible or conceivable and it's very different from a retraction. I have quite a bit of confidence this will go well. If it doesn't, we have time built into the timeline and the crew is trained to go outside and do a spacewalk and help us out if we need that kind of help."

But there is not a lot spacewalking astronauts can do if the deployment runs into problems. Because of P6's location at the far left end of the power truss, the station's robot arm does not have enough reach to position a spacewalker beyond the base of the arrays. The astronauts could manually extend the panels using power tools if necessary, but they will be unable to reach more than the lowest sections of the two array masts.

"With P6 on Z1 (in its original position), we were able to put an EVA crew member on the station robotic arm and essentially maneuver him to any place on the array where we thought we had a problem," Hassmann said. "Basically, they would identify an area of interest or perhaps a grommet snag or any other problem they might have seen, then we could maneuver them to the area of interest.

"With P6 on P5, the (station arm) simply cannot reach. We can use it for viewing, but with the mobile transporter at work site 8 and the station robotic arm extended as far as it can practically get, we can't use it to support an EVA crew member on the arm. If we do need to support any kind of contingency operations, we'll have the EVA crew basically in an extending device attached to the structure of P6 and their access will only be to the first couple of panels, essentially, and then to the blanket box. So that's one limitation we're going to have to deal with."

5:21 PM, 10/29/07, Update: Landing time update

Flight controllers have adjusted the shuttle Discovery's revised landing time. The latest projections show a deorbit rocket firing at 4:09 a.m. EST on Nov. 7 with landing expected around 5:11 a.m. An updated flight plan and television schedule will be posted as soon as they are available.

4:21 PM, 10/29/07, Update: Shuttle flight extended one day; spacewalk Thursday devoted to SARJ inspection; heat shield repair demonstration deferred

As expected, NASA's Mission Management Team today agreed with a recommendation from space station officials to extend the shuttle Discovery's flight one day to permit a more thorough inspection of a contaminated solar array rotary joint during a spacewalk Thursday.

The original content of that excursion - a heat shield repair demonstration - will be deferred to a future mission and a fifth and final spacewalk, originally planned for Friday, will slip one day to Saturday.

Under the revised schedule, Discovery would undock from the space station early Nov. 5 for a landing back at the Kennedy Space Center around 3:38 a.m. on Wednesday, Nov. 7.

See the 2:44 p.m. status report below for details and background on the rotary joint issue.

2:44 PM, 10/29/07, Update: Station managers recommend mission extension, spacewalk to inspect contaminated solar array joint

Space station managers today recommended extending the shuttle Discovery's mission by one day to permit a dedicated spacewalk devoted to inspecting an apparently contaminated solar array rotary joint. NASA managers want to track down the source of metallic shavings found inside the joint during a brief inspection Sunday to help figure out what might be needed to fix it.

"We have a lot of ideas. My personal opinion is we're probably still dealing with something that's rubbing that's not supposed to," said Mike Suffredini, space station program manager at the Johnson Space Center in Houston. "I don't think we're in any situation we can't recover from, it's just a matter of time."

The Discovery astronauts have conducted two of five planned spacewalks, helping install a new multi-hatch module Friday and detaching a 35,000-pound solar array truss segment during an excursion Sunday so it can be mounted on the far left end of the station's main power truss Tuesday.

The port-6, or P6 segment was "parked" overnight on the end of the station's robot arm. Early today, arm operators Dan Tani and Clay Anderson "handed" the massive segment to the shuttle's robot arm, operated by Stephanie Wilson and pilot George Zamka.

While the shuttle arm held onto P6, the station arm, mounted atop a tram on the front of the lab's main solar power beam, was moved about 80 feet to a work site on the far left end. From there, the arm re-grappled P6 and the shuttle arm let go, completing the second handoff of the day.

Early Tuesday, astronauts Scott Parazynski and Doug Wheelock plan to stage a six-and-a-half-hour spacewalk to attach P6 to the far left end of the power truss and to monitor the re-deployment of its huge solar wings. After releasing a stowed radiator panel, Parazynski plans to remove one of 22 insulation blankets from the left-side solar alpha rotary joint, or SARJ. The idea is to look for any signs of contamination like the metallic shavings discovered by Tani during an inspection of the right-side SARJ on Sunday.

The massive SARJ joints, one on each side, use a motor-driven 10-foot-wide gear to slowly turn the outboard solar arrays to keep them face on to the sun and ensure maximum power generation. The inspection of the starboard SARJ Sunday was ordered after engineers noticed higher-than-expected vibration levels and power over the past two months or so.

Tani used adhesive tape to collect samples of the contamination and station commander Peggy Whitson used a magnet today to show the material is metallic and not made up of mylar insulation as engineers speculated Sunday.

"The significance of it being ferrous is an indication that it's not aluminized mylar and it's not from the (thermal) covers," Suffredini said. "The covers are aluminum, the aluminized mylar obviously has aluminum in it as well. So that would tell you perhaps it's some of the steel from the bearings or the race or some other area."

To gather additional data, flight controllers decided overnight to have Parazynski carry out a brief inspection of the left-side SARJ during the spacewalk Tuesday. The port SARJ is operating normally and engineers want to get a better idea of how it might differ from the starboard SARJ.

"What we thought we'd do is go look on the (port) side and see what it looks like," Suffredini said today. "And that will give us some indication of what is nominal. You can glean a lot of information from this. It won't necessarily tell you what's good and what's not, but it certainly will tell you more about what the design produces as opposed to (what) we're dealing with on the starboard side."

The shuttle flight plan originally called for a fourth spacewalk Thursday to test a new heat shield repair technique and a final excursion Friday, this one by Whitson and flight engineer Yuri Malenchenko, to continue outfitting the newly installed Harmony module. Staging the spacewalks back to back out of the station's Quest airlock module limited the duration of the tile repair exercise to provide enough turnaround time for Whitson and Malenchenko.

Suffredini said the station project wanted to turn the fourth spacewalk into a dedicated full-duration inspection of the starboard SARJ. That plan would require extending Discovery's mission one day to give Whitson and Malenchenko enough time to prepare for their spacewalk.

"Right now, the team is leaning toward inspecting under every (thermal) panel during EVA-4," Suffredini said. "The plan right now, assuming our shuttle friends agree at the MMT (is) to do a full length EVA-4. That requires us to have a day off between EVAs 4 and 5 so don't be surprised at the end of the MMT today if we formally announce that we'll extend the flight one additional day in order to allow EVA-4 to be its full length."

Suffredini said engineers debated whether the astronauts could carry out an abbreviated tile repair demonstration, but "we are going to recommend that we use the entire full-length EVA to do this inspection. We need the entire EVA to remove every cover and inspect under each cover. We also plan to take samples in any areas where the data might look different."

Until the issue is resolved, the starboard SARJ will remain locked in one position except on the few occasions when it needs to be reoriented due to thruster firings or other operations. With only the port arrays rotating to track the sun, the station's power production will suffer. But Suffredini said today a new analysis shows the lab complex will have enough power to operate normally through the end of the year and into early 2008 and that it should not affect plans to launch Europe's Columbus research module in early December.

But both SARJs eventually must be operational to support a full slate of science operations inside Columbia, the U.S. Destiny lab module and two pressurized Japanese labs scheduled for delivery in February and April.

In a worst-case scenario, Suffredini said, spacewalkers could reposition two drive motors and 12 trundle bearings to use an inboard drive gear in the starboard joint. Assuming the astronauts could clean up the contamination to prevent additional wear and tear, the SARJ would be in a near-new state. But the work is complicated, it would require multiple spacewalks and it would disrupt station assembly.

Engineers are hopeful the inspection of the port SARJ by Parazynski on Tuesday, and a more thorough look at the starboard SARJ later in the week, will give them the insight they need to determine the best course of action.

As of this writing, NASA managers have not yet finalized plans for the fourth and fifth spacewalks or officially approved the mission extension. In the meantime, here is an updated timeline of Tuesday's spacewalk - EVA-3 - including Parazynski's inspection of the left-side SARJ (in EDT and mission elapsed time).

EDT........DD...HH...MM...EVENT

12:38 AM...06...13...00...STS/ISS crew wakeup
01:13 AM...06...13...35...EVA-3: Airlock repressurized to 14.7 psi; hygiene break
02:23 AM...06...14...45...EVA-3; Spacewalk preps
03:53 AM...06...16...15...EVA-3: Spacesuit purge
04:08 AM...06...16...30...EVA-3: Spacesuit oxygen pre-breathe
05:08 AM...06...17...30...EVA-3: Airlock depressurization
05:33 AM...06...17...55...EVA-3: Airlock egress
06:03 AM...06...18...25...EVA-3: Parazynski: Attach P6 to P5
06:18 AM...06...18...40...EVA-3: Wheelock: Attach P6 to P5
08:13 AM...06...20...35...Shuttle robot arm (SSRMS): P6 ungrapple
08:13 AM...06...20...35...EVA-3: Parazynski: P5/P6 umbilical connections
08:48 AM...06...21...10...EVA-3: Wheelock: P5/P6 umbilical connections
08:53 AM...06...21...15...EVA-3: Parazynski: Electronic box shroud removal
09:03 AM...06...21...25...EVA-3: Wheelock: Shroud removal
09:28 AM...06...21...50...EVA-3: Parazynski: Radiator cinch release
10:03 AM...06...22...25...EVA-3: Wheelock: Spare power switching unit transfer to ISS
10:28 AM...06...22...50...EVA-3: Parazynski: Port SARJ inspection
11:08 AM...06...23...30...EVA-3: Parazynski: Radiator squib firing unit activation
11:18 AM...06...23...40...EVA-3: Parazynski: Switching unit transfer
11:58 AM...07...00...20...P6 solar mast 1 deploy operations begin
12:03 PM...07...00...25...EVA-3: Parazynski: Airlock ingress
12:18 PM...07...00...40...EVA-3: Wheelock: Airlock ingress
12:38 PM...07...01...00...EVA-3: Airlock repressurization
12:38 PM...07...01...00...2B array 100 percent deployed
01:28 PM...07...01...50...4B array 100 percent deployed
01:48 PM...07...02...10...Shuttle robot arm (SRMS) powerdown
04:08 PM...07...04...30...ISS crew sleep begins
04:38 PM...07...05...00...STS crew sleep begins

4:14 AM, 10/29/07, Update: olar array handoff in work; port SARJ inspection added to Tuesday spacewalk

The space station's robot arm handed a 35,000-pound solar array truss segment to the shuttle's arm today as part of a carefully choreographed, step-by-step procedure to move the stowed arrays to the far left end of the station's main power truss.

Detached from its central mounting point during a spacewalk Sunday, the P6 array will be held by the shuttle arm until a transporter on the front face of the power truss can carry the station arm 80 feet or so to an outboard work site. Once in place, the station arm will take the array truss back and hold it in place until a spacewalk Tuesday to bolt P6 to the P5 spacer truss on the outboard side of an identical set of arrays known as P4.

At that point, the stowed solar panels will be re-extended, a radiator will be deployed and the left side of the station's power truss will be complete. A final set of arrays for the right side of the truss, S6, will be attached next fall.

Earlier today, flight controllers sent commands to deploy two folding radiator panels on the S1 truss segment as part of an ongoing procedure to fully activate the station's power and cooling systems. Additional radiators on the port side of the power truss will be deployed later.

The astronauts will enjoy four hours of off-duty time this morning, winding up with a joint crew meal at 8:08 a.m. After lunch, the station arm will lock onto the P6 solar array to complete the handoff procedure.

The entire crew plans to participate in a spacewalk review session this afternoon to go over the flight plan for Tuesday's excursion by Scott Parazynski and Doug Wheelock to bolt P6 to the station's main power truss.

In an overnight message to the astronauts, flight controllers said the timeline for Tuesday's spacewalk had been amended to let Parazynski carry out a brief inspection of the station's left-side solar alpha rotary joint to collect data for comparison to the right-side SARJ. The two SARJ joints turn the station's solar arrays to keep them face-on to the sun.

During an inspection of the starboard SARJ Sunday, spacewalker Dan Tani reported seeing what appeared to be metal shavings or filings on the joint's 10-foot wide outboard drive gear and bearing race. He also reported an apparent discoloration, or mottling, of the bearing race ring. Engineers asked for the inspection because of recently observed vibration and higher-than-normal power consumption, both signs of unwanted friction in the mechanism.

The source of the debris is not clear and engineers at the Johnson Space Center are evaluation a variety of options for additional inspections on an upcoming spacewalk. For Tuesday's outing, the only additional task is an inspection of the port SARJ, which is operating normally, to see if any similar debris and discoloration might be present.

"Anytime we run into these unknowns we end up with a lot of options on the table at once initially and we have to sort through them," station flight director Heather Rarick said late Sunday. "One of the things we've talked about is sending someone during the next EVA to the port side and see the SARJ, or the rotational ring out there, and find out what it looks like nominally because we haven't experienced any issues out there. That's one of the things we're considering doing."

The revised flight plan for Tuesday now includes a 40-minute block of time for Parazynski, starting just over five hours into the EVA, to remove one of 22 thermal blankets and inspect the interior of the port SARJ.

"Big picture for EVA 3: On the way back from deploying the P6 radiator, Scott will be stopping by the port SARJ, removing cover 12, and performing an inspection, picture snapping (with flash!) and sample-taking similar to EVA 2," flight controllers said in the overnight message to the crew. "This will give us a baseline to use for comparison in the (starboard) SARJ troubleshooting activities."

Here is an updated timeline of today's activity (in EDT and mission elapsed time; includes revision E of the NASA TV schedule):

EDT........DD...HH...MM...EVENT

01:23 AM...05...13...45...S1 radiator deploy
12:38 AM...05...13...00...STS/ISS crew wakeup
02:38 AM...05...15...00...Spacesuit resizing
03:08 AM...05...15...30...Shuttle arm (SRMS): P6 grapple
03:38 AM...05...16...00...Station arm (SSRMS): P6 ungrapple
03:53 AM...05...16...15...Mobile transporter moves SSRMS to work site 8
04:08 AM...05...16...30...Spacesuit swap
04:18 AM...05...16...40...Nespoli ham radio opportunity
04:38 AM...05...17...00...Shuttle crew off duty
05:38 AM...05...18...00...Station crew off duty
08:08 AM...05...20...30...Joint crew meal
09:08 AM...05...21...30...SSRMS: P6 grapple
09:28 AM...05...21...50...Equipment lock preps
09:38 AM...05...22...00...Harmony module avionics rack outfitting
09:53 AM...05...22...15...SRMS: P6 ungrapple
10:13 AM...05...22...35...EVA-3 tools configured
10:30 AM...05...22...52...Mission status briefing on NASA TV
12:38 PM...06...01...00...EVA-3: Procedures review
01:43 PM...06...02...05...ABC, NBC, CNN crew interviews on NASA TV
02:38 PM...06...03...00...Crew choice downlink
02:53 PM...06...03...15...EVA-3: prebreathe and tools configured
04:08 PM...06...04...30...ISS crew sleep begins
04:38 PM...06...05...00...STS crew sleep begins
05:00 PM...06...05...22...Daily video highlights reel
10:30 PM...06...10...52...Flight director update on NASA TV
Designed as the sixth and final segment of the port, or left, side of the station's main power truss, P6 was mounted at the center of the station in December 2000 to provide power to the U.S. segment during the initial stages of assembly.

Now, with identical solar panels in place on the left and right sides of the main power truss, NASA is moving P6 to its permanent position on the far left end of the beam. The segment's huge arrays, stretching 240 feet from tip to tip, were stowed during shuttle missions last December and June. Power and cooling lines were disconnected during an August flight, setting the stage for the massive truss's detachment, relocation and re-extension during Discovery's mission.

4:50 PM, 10/28/07, Update: SARJ debris may prompt additional spacewalk inspection; engineers mull options

Space station engineers are scrambling to determine the source of unexpected debris in a critical solar array rotary joint and considering whether to order an additional, more thorough spacewalk inspection to figure out what sort of downstream repair work might be necessary.

The international space station's right-side solar alpha rotary joint, or SARJ - a 10-foot-wide, 2,500-pound motorized gear used to turn outboard arrays to keep them face on to the sun - needs to work normally to generate the electricity required by the growing space station's myriad systems.

The Discovery astronauts attached a new module to the station Friday that will serve as the attachment point for European and Japanese research labs scheduled for launch in December, February and April.

Mike Suffredini, manager of the space station program at the Johnson Space Center in Houston, said the starboard SARJ can be locked in place in the near term while engineers study the contamination problem and its possible solution. He said even with the starboard S4 solar arrays locked in place, they would generate enough power, in concert with two set of arrays on the left side of the station's main truss, to permit launch of the European Space Agency's Columbus module Dec. 6 as planned.

But at some point over the next few months, the problem must be resolved or the station might not be able to provide the required power when two Japanese research modules are attached in February and April.

"We have lots of time to work through this problem, it's not an immediate issue," Suffredini said. "The system is robust in terms of providing the power we need. We know how to operate around it so we can get all the power that we require. So we can pamper, if you will, the joint while we sort through the anomaly and make sure we fully understand it before we go back to nominal operation."

The space station ultimately will be equipped with four sets of huge solar arrays, two on each end of a beam the length of a football field. A SARJ on each side of the truss rotates the outboard solar arrays like giant paddle wheels as the station circles the Earth to maximize electrical generation.

The station currently is equipped with one set of arrays on each side of the power truss: S4, or starboard 4, on the right and P4 on the left. A third set of arrays, P6, initially was mounted at the center of the station to provide power during the initial stages of construction. That 35,000-pound segment, with its arrays stowed, was detached today and will be installed on the far left end of the power truss during a spacewalk Tuesday. The fourth and final set of arrays, S6, is scheduled for launch next Fall.

The port SARJ has operated normally since its installation last year and the starboard joint, installed last June, showed no immediate problems. But just under two months ago, engineers began noticing higher vibration levels and power usage. While the port SARJ motor operates at an average of 0.1 amps, its counterpart on the right side has been averaging 0.2 to 0.3 amps with peaks up to 0.9 amps.

Believing an insulation panel might be rubbing against something in the mechanism, NASA managers added an inspection to today's spacewalk. Astronaut Dan Tani took a look around the perimeter of the joint and saw nothing out of the ordinary. But when he removed one of 22 insulation blankets to look inside, he was surprised to see what appeared to be metal shavings on the main bearing race and drive gear.

"We have been watching a slight increase in currents on the starboard SARJ joint," Suffredini said. "The currents indicated to us some friction increase in the joint, so that's why we asked the ops team if they would take a look. We did find what seems to be an indication of some particulate that we would not expect in the joint.

"In addition to that ... the flat surface right below the gear is the race the bearing runs on, it looks kind of mottled and it we would expect it to look shiny. There's about 1,000 pound force on that surface, so any little bit of particulate on that surface could potentially cause additional drag."

Each SARJ features two huge drive gears, one inboard and one outboard, and two drive lock assemblies, or motors, and associated electronics. Both DLAs can be positioned to engage the drive gear by remote control and both are on the outboard side of the starboard joint. Only one DLA is used at a time.

"This is a very low current motor that's driving these joints, very high precision joints," Suffredini said. "So any little bit of particulate, of course, can have an effect on the ability of the DLA's to overcome the friction in the joint. Of course, if the friction gets high enough, then we can't drive the joint. Now we're not at that point today, but it was important for us to start looking at it because we have had some peaks as high as .8 and .9 amps."

Tani described the debris in the joint as metallic shavings. Suffredini said engineers on the ground believe it may be aluminized mylar insulation, a tinfoil-like material on the interior of the 22 thermal blankets mounted around the joint. The blankets are anchored on the outboard side of the joint and extend across the drive gears like diving boards with about a half-inch of clearance. They rotate around the SARJ as the outboard truss rotates.

Suffredini said if any of the foil under one or more thermal blankets was rubbing against the outboard bearing race or gear, it would be damaged and that could explain the debris seen today. Finding the source of the debris may require removing all 22 thermal shields. How to clean up the debris that's already there could be a more difficult problem.

"We'll spend quite a bit of time trying to figure out what we should do next relative to this investigation," Suffredini said. "In the meantime, our plan is to limit use of the SARJ in what we call the auto-track function, simply the function that allows it to follow the sun as we go around the Earth. We have completed our assessment of the remainder of this mission and believe for the most part, we can keep it parked. We'll have to reposition it every so often in order to deal with a couple of thruster firings and, I believe, for undocking. But repositioning is not a big impact.

"In the meantime, the team is off assessing the ability to park the SARJ for the (period between Discovery's mission and the December launch of Columbus) and for the docked timeframe for 1E (the Columbus mission). My belief, and don't take this to the bank because the guys haven't finished their analysis, but I believe ... we'll have the power we need to limit the movement of the SARJ to the greatest extent possible and still be able to accomplish the objectives of our future missions.

"So, we have time to go work through this anomaly," he said. "We'll talk a lot about whether or not we want to modify one of the EVAs during (Discovery's) flight in order to look some more. I think the prevailing thought is the team would like to go ahead and take off the remainder of the covers. There's 22 in all, so we've looked under one, perhaps look under the other 21 and perhaps find an area where perhaps some portion of the mechanism is rubbing on one of the panels. If not, to get a complete assessment of the entire mechanism to decide what our future plan is. So the team is off working that right now."

The Discovery astronauts currently plan spacewalks Tuesday, Thursday and Friday. Tuesday's excursion is required to attach the P6 solar array to the far left end of the main power truss, a critical operation, and it would appear unlikely NASA would opt to add additional SARJ inspections to the crew's already busy timeline.

The mission's fourth spacewalk is a relatively short excursion to test a heat shield repair technique. The day after that, station commander Peggy Whitson and cosmonaut Yuri Malenchenko plan to stage a spacewalk to get the newly installed Harmony module ready for its eventual move to the front of the lab complex after Discovery departs.

Mission managers could opt to defer the tile repair demonstration and instead have spacewalkers Scott Parazynski and Doug Wheelock conduct an additional SARJ inspection in its place. To have more time for planning, managers also could opt to replace the tile repair spacewalk with Whitson's, extend the mission a day and stage a revised fifth spacewalk to look into the SARJ. No decisions have been made one way or the other.

"We would like very much to get (the Columbus) mission accomplished before the Christmas holidays," Suffredini said. "So It would be our intention to try to do whatever we can during this docked mission. If we don't figure out a way to recover nominal operations with the SARJ, we would figure out how to use it in a limited capacity to get us through the next stage and the next flight and then look at perhaps a subsequent EVA" during a future mission."

In a worst-case scenario, spacewalking astronauts could remove the drive motors and the 12 trundle bearings that press on the outboard bearing race and reposition the components on the inboard gear of the joint, effectively replacing the entire assembly. But that would require multiple spacewalks and is strictly last resort."

"If we decide this damage is great enough we don't want to live with it long term, we could choose to totally reconfigure that joint," Suffredini said. "I suspect that would be at the very end of our list of things to talk about. If we can figure out the source of the problem and reduce the contamination, if we can operate the joint without the vibrations that we're getting - and it's really not the current, it's the vibrations that are the long-term concern for us - then we'd probably try to live as is."

Vibration is more of a long-term concern, he said, because it could lead to life-limiting metal fatigue.

12:15 PM, 10/28/07, Update: Spacewalk ends

Astronauts Scott Parazynski and Dan Tani began repressurizing the space station's Quest airlock module today at 12:05 p.m. to officially end a six-hour 33-minute spacewalk, the second of five planned for the shuttle Discovery's mission.

The astronauts disconnected the 35,000-pound P6 solar array truss segment, installed handrails on the newly installed Harmony module and confirmed a potentially serious problem with the drive mechanism of a massive rotary joint used to slowly turn the station's right-side solar panels to keep them face-on to the sun.

Parazynski and Tani were unable to complete all of their planned objectives, however, running out of time to install a replacement circuit breaker in the station's electrical system and complete power connections with a newly installed robot arm grapple fixture on Harmony.

"We had a little of everything today," Tani commented before repressurizing the airlock.

"Good day today. Great job," Parazynski said.

This was the 94th spacewalk devoted to station assembly and maintenance since construction began in 1998 and the 17th so far this year. Spacewalk time for station assembly now stands at 580 hours and 46 minutes overall and 12 hours 47 minutes for Discovery's crew.

Wrapping up today's excursion, Tani took a moment to enjoy the view of Chicago and the midwest from 213 miles up.

"Break, break, for just one, 30 seconds, I'm looking at my home town!" he exclaimed.

"Really?" Parazynski asked.

"Yeah, let me see if I can find Lombard, (Ill.)."

"Oh, look at that!" someone said.

"That's an awesome view."

"I see O'Hare, the airport, so I can make out my home town Lombard," Tani said.

"Too bad about those Cubbies, though," Parazynski quipped.

"Yeah, well, there's always next century," Tani said.

9:40 AM, 10/28/07, Update: SARJ background

Here is background on the space station solar alpha rotary joint used to turn outboard solar arrays to track the sun. The port side SARJ on the international space station is operating normally, but the starboard unit has experienced high vibration and power usage in recent weeks. During an inspection today, spacewalker Dan Tani reporter numerous metal shavings in the SARJ mechanism.

Each SARJ is a 10-foot-wide rotary joint weighing about 2,500 pounds. The port SARJ is part of the P3 truss segment while the starboard unit is part of the S3 truss. The joints can turn in tandem or one at a time and both typically drive outboard solar arrays through a full 360-degrees like giant paddle wheels, once per orbit, as the station circles the Earth. They were built by Lockheed Martin in Sunnyvale, Calif.

To help readers understand the operation of the SARJ mechanism, here is background from a recent NASA press kit:

Source: NASA

Race Rings
The SARJ includes an inboard and an outboard race ring, which provide the structural connection between the P3 and P4 elements. Along the circumference of each race ring are gear teeth that mesh with the drive lock assembly (DLA) pinion gear to rotate the SARJ. The outboard race ring is used by the DLA for rotating the SARJ.

Trundle Bearings
The 12 equally-spaced trundle bearings hold the SARJ inboard and outboard race rings together. Each trundle bearing is fixed to the inboard race ring and is clamped onto the outboard race ring with a roller interface to allow for SARJ rotation. There are three rollers on the trundle bearing that interface with the outboard race ring; the inner and outer upper rollers and the center roller. Each roller consists of two bearings: the primary and journal bearings. The primary bearing rotates. If the primary bearing seizes up, the journal bearings will begin rotating. The journal bearing is designed to operate for about 30 days. There are micro-switches in the trundle bearing that allow the ground to know if the journal bearing is rotating.

Drive Lock Assembly
Two Drive Lock Assemblies (DLAs) are responsible for rotating and locking the SARJ. Each DLA includes the engage-disengage mechanism (EDM) motor, drive motor, pinion gear, lock rack and two follower arms. The EDM motor is a stepper motor that pivots the lock rack and pinion gear about the lock/engage pivot point to the desired position. The DLA positions are locked, engaged and neutral. For the locked position, the lock rack is in contact with the race ring gear teeth to prevent the SARJ from rotating. For the engaged position, the DLA pinion gear is meshed with the race ring gear to rotate the SARJ with the drive motor. In the neutral position, neither the lock rack nor pinion gear is engaged to the race ring gear. The follower arms, which are of the same design as the trundle bearings, are used to secure the DLA to the race ring.

Rotary Joint Motor Controller
The two rotary joint motor controllers (RJMCs) are mounted on the structural ribs of the inboard race ring and control the operation of the DLA motors via commands from the 3 multiplexers/demultiplexers (MDMs). Each RJMC has two heaters and a resistive thermal device sensor monitored by the P3 MDMs. The RJMC supplies and receives voltage signals from the resolvers on the Utility Transfer Assembly to determine the position f the SARJ (resolver A is connected to RJMC 1, resolver B is connected to RJMC 2). For SARJ outboard operations, one RJMC is moved to the outboard race ring.

SARJ Structural Support
At launch, the SARJ is secured with 16 launch locks and 10 launch restraints. All the launch locks and the six outboard launch restraints will be removed on orbit before the SARJ is rotated, first in a short test, then in its operational configuration. On the longerons for two sides of the SARJ, there are stub rail segments that bridge over the interface that enables the SARJ to rotate. The launch restraints on the inboard and outboard side hold the stub rail segments in place. When the SARJ is operating in the inboard mode, the outboard launch restraints are removed and the inboard launch restraints are left in place so that the stubs rails are canilevered over the rotating SARJ interface. The SARJ inboard bulkhead is structurally attached to P3 at the P3 longerons and four SARJ braces. The braces are stowed on the diagonals and not connected to the inboard bulkhead for launch so that the SARJ loads path is suported entirely by the launch restraints.

9:00 AM, 10/28/07, Update: Metal shavings seen in solar array rotary joint

Spacewalker Dan Tani, inspecting a massive solar array rotary joint that has been experiencing high vibration and power usage, reported a large number of metal shavings inside the mechanism after removing a thermal cover and to get a glimpse at the joint's inner workings.

"Great Discovery, Dan," spacewalker Scott Parazynski radioed. "I didn't think you'd be able to see anything, but..."

"It's quite clear," Tani said. "There's metal-to-metal scraping, or something, and it's widespread."

"Wow."

Engineers had speculated a thermal blanket or perhaps a misaligned bolt was causing unusual friction in the rotating mechanism of the right-side solar alpha rotary joint, or SARJ. The space station is equipped with two SARJ units, one on each side of the main power truss, to turn outboard solar arrays and keep them face-on to the sun. The port, or left-side, SARJ is operating normally and while the starboard unit still functions, engineers have been monitoring high vibration and current use in recent weeks.

It was not immediately clear what might be producing the metal shavings Tani reported. He did not immediately see what might be causing the problem.

Tani initially simply floated around the perimeter of the joint and inspected its outward appearance, checking each of 22 thermal blankets and making sure no bolts were out of position.

"I see you've done everything from 1 to 22," Italian astronaut Paolo Nespoli said. "You don't see any missing bolts, the gap looks more or less constant everywhere. "All the swing arms are locked, the gap looks very constant, yes," Tani reported. "And nothing obvious, no scratching. The only thing I could see maybe is these big SLR, the outboard, the SLR parts that rotate, the corner braces at the corners? They might rub up against the MLI (multi-layer insulation), but I don't see any marks on the MLI. So I don't know if that's happened. And it looks like it's designed for the MLI to stay out of there."

"OK, Paolo, is there anything you or the ground want me to do while I'm out here? I guess, unfortunately, I have nothing to report in terms of anomalous conditions."

Tani then was asked to peel back one of the insulation blankets to look inside the joint. That's when he saw the shavings.

"There are lots of very fine metal shavings, and I can see that because the motor that is the, what is that, that's a trunnion bearing, has a lot of those iron shavings. It's like the (result) that you get with the metal, iron filings and you put a magnet under it and they stand straight up."

Footage from Tani's helmet camera showed the large gear inside the starboard solar alpha rotary joint, but the filings he reported were not obvious.

The shavings, he said, could be seen "on this big motor, it looks like a big magnet that is this upper roller, I don't know why there'd be a magnet here but there's a magnet. I see microswitches, there's two microswitches on it and a metal squarish 2- by 2-inch by 2-inch cube that I believe holds the roller and it looksÊlike it's magnetic because it looks like there are these iron filings, or shavings, on it.

"There's quite a bit and then the outer race, the flat part, is discolored, if you can see that, from the teeth, the angled portion that are between the teeth and the thin part of the race is all sort of discolored. I would almost say corroded in some way. And there are even some filings... I'm going to look up, there's a connector here that says J-15 outboard, looks like there are some filings there. There must be something magnetic to hold those on."

In a worst-case scenario, the starboard SARJ could be locked in a position to maximize solar energy production while engineers assess various options for future troubleshooting. Lead station flight director Derek Hassmann said Friday the station could operate with one stationary set of solar arrays without any major problems.

"One of the concerns we have about the way the SARJ is behaving is the potential it might stall in a position that's not optimal for power," he said. "So one of the things we have been talking about ... is to find a current (power) value at which we're going to stop rotating the SARJ and put it in a position that's good for power consumption. We've basically got constraints to find that will allow us to park the SARJ in a good power producing attitude before it would stall.

"As long as we can get it into an attitude that's reasonably good for power generation, combined with what the other SARJ can produce, we wouldn't have any significant power impacts that we couldn't deal with."

Tani was asked to collect samples of the shavings to help engineers troubleshoot the problem. His camera, meanwhile, malfunction and prevented him from immediately completing the desired photo documentation.

7:25 AM, 10/28/07, Update: P6 truss segment detached from space station

Astronauts Scott Parazynski and Dan Tani disconnected electrical grounding straps, used power tools to unscrew four bolts and then released a final capture latch holding the 35,000-pound P6 solar array truss segment in place atop the international space station.

Stephanie Wilson and Doug Wheelock, operating the space station's Canadian-built robot arm from inside the station's Destiny laboratory module, then carefully pulled the massive solar array segment away, the first step in a complex, two-day procedure to move P6 to the far left end of the station's main power truss.

The first bolt was unscrewed at 6:40 a.m. and about 15 minutes later, the capture claw was released.

"Just a quick observation, P6 is separated from Z1 by about an inch, already," Parazynski radioed at 6:57 a.m.

"Copy," Italian astronaut Paolo Nespoli radioed from inside the space shuttle. "It cannot wait to go."

"Yeah, it's just excited to get off the ISS," Parazynski joked.

After verifying no straps or wires remained connected to P6, Nespoli called Wilson and Wheelock: "Alpha, Discovery, for robotics. Doug, you have a go to take the baby away."

"Copy, go to demate P6," Wheelock replied. "And we also copied that (Parazynski and Tani) are in position to monitor separation."

"Verified, Wheels," Parazynski confirmed.

"Verified," Tani said.

Moments later, the arm began pulling P6 up and away from the Z1 truss extending up from the central Unity module.

"Good motion!" Parazynski said when the truss began pulling away. The spacewalkers monitored the slow separation procedure for a few minutes before moving back down the Z1 truss to stow tools in the station's airlock before pressing ahead with the rest of the day's work.

The P6 truss segment will remain "parked" on the end of the station arm overnight. It will be handed off to the shuttle's robot arm Monday and then, after the station arm is moved to an outboard work site, P6 will be handed back for installation and redeployment on the far left end of the power truss during a third spacewalk Tuesday.

With P6 successfully "demated," Parazynski is pressing ahead with work to continue outfitting the newly installed Harmony module, attached to the space station Friday. Tani, meanwhile, moved to equipment carts attached to a mobile transporter that creeps along the front of the solar array truss to move the station arm to various work sites. Engineers have noticed a discoloration on handrails on the carts and Tani took pictures to help engineers determine if there are any sharp edges or any other defects that could pose problems.

Tani also plans to inspect a massive rotary joint on the right side of the power truss to look for signs of anything that might be interfering with the joint's motion.

Higher-than-normal vibration and power usage have been noticed in recent weeks, prompting concern an insulation blanket or some other debris is causing friction in the mechanism. The station is equipped with two solar alpha rotary joints that slowly turn outboard solar arrays to keep them face on to the sun. Tani is not expected to attempt any repairs today, he is simply going to visually inspect the joint and take photographs to document the joint's current condition.

Tani and Parazynski also plan to attach a grapple fixture to Harmony later in the spacewalk that will be used by the station arm later, after Discovery departs, to move the module from its current, temporary attachment point to its permanent location on the front of the space station.

"Wow, beautiful terminator," Tani marveled earlier, watching sunrise approach high above the south Pacific Ocean. "The blue, red color around the Earth's terminator. Fantastic."

"You lucky dog, you get to see that for another..."

"...couple of months, yeah," Tani said.

5:45 AM, 10/28/07, Update: Spacewalk begins

Floating inside the space station's Quest airlock module, astronauts Scott Parazynski and Dan Tani switched their spacesuits to battery power at 5:32 a.m. to officially kick off a six-and-a-half-hour spacewalk, the second of five planned during the shuttle Discovery's visit.

The astronauts were ahead of schedule most of the morning and began the excursion about a half hour early. As it turned out, they needed a few minutes to restart Parazynski's spacesuit electronics when it hung up after the switch to battery power. The restart worked and the astronauts pressed on with the timeline.

The first item on today's agenda is disconnection of the port 6, or P6, solar array truss segment. After Parazynski and Tani disconnect final umbilicals, the station's robot arm, already locked onto P6, will pull it away from its mounting point on the central Z1 truss around 8:15 a.m.

4:21 AM, 10/28/07, Update: Spacewalk expected to start around 5 a.m.

Spacewalkers Scott Parazynski and Dan Tani are expected to start today's spacewalk about an hour ahead of schedule. Here is a timeline of today's activity (in EDT and mission elapsed time) that assumes an early start; the actual start time may vary:

EDT........DD...HH...MM...EVENT

10/28/07
05:03 AM...04...17...25...EVA-2: Airlock egress
05:18 AM...04...17...40...EVA-2: Disconnect Z1/P6 umbilical
05:43 AM...04...18...05...EVA-2: Parazynski: Detach P6 solar array truss segment
05:58 AM...04...18...20...EVA-2: EV3: Detach P6 solar array truss segment
07:03 AM...04...19...25...EVA-2: EV3: Airlock ops
07:13 AM...04...19...35...EVA-2: Parazynski: Harmony outfitting
07:13 AM...04...19...35...Station arm (SSRMS): P6 disconnection
07:43 AM...04...20...05...EVA-2: EV3: Rotary joint inspection
08:43 AM...04...21...05...EVA-2: EV3: S1 SFU
09:03 AM...04...21...25...EVA-1: EV3: Power switching unit installation
09:13 AM...04...21...35...EVA-2: EV3: Circuit breaker replacement
09:43 AM...04...22...05...EVA-2: Node 2 grapple fixture installation
10:58 AM...04...23...20...EVA-2: Parazynski: Harmony outfitting
11:18 AM...04...23...40...EVA-2: Airlock ingress
11:38 AM...05...00...00...EVA-2: Airlock repressurization

04:02 AM, 10/28/07, Update: Astronauts gear up for dramatic spacewalk

Running an hour ahead of schedule, astronauts Scott Parazynski and Dan Tani suited up and made final preparations for a dramatic six-and-a-half-hour spacewalk today to disconnect a 35,000-pound solar array segment for a two-day move to the far left end of the space station's main power truss.

The port 6, or P6, truss segment will remain on the end of the space station's robot arm overnight before being handed off to the shuttle's arm on Monday. The station arm then will ride a transporter to the far end of the power truss and re-grapple P6. If all goes well, the arm will maneuver the truss into position for attachment to the P5 segment Tuesday during the crew's third spacewalk.

With the arm fully extended, operator Stephanie Wilson will have little or no visibility of the attachment interface. Instead, she will rely on guidance from spacewalkers Parazynski and astronaut Doug Wheelock. Once the truss segment is bolted in place, it's two huge solar panels will be re-extended to accomplish one of the primary goals of Discovery's mission.

"It's a big truss," lead flight director Rick LaBrode said Saturday. "Putting it outboard of P5 is pretty tricky. The robotic ops involved are complex, the arm is pretty nearly reached out and you're working essentially at the very end of its capability. And then the visuals are non existent. So for the most part, we're relying on the (spacewalkers to guide) it into place. So you have this big truss, the arm's fully extended and you're trying to thread a needle without really good visuals. So it is extremely complex, but ... I have every bit of confidence we're bgoing to pull this off."

Said Wheelock in an interview with CBS News: "Our confidence level is very high. We're very excited, we've trained and trained for this task and we are ready. We're even ready for any contingencies we might see. We're very excited about our spacewalk (Sunday) with Scott and Dan going out the door. (Stephanie Wilson) and I will be backing them up on robotics and we're just real, real excited."

For today's excursion, Parazynski and Tani, after disconnecting P6, will focus on outfitting the newly installed Harmony module. Tani also will spend an hour or so inspecting a massive rotary joint on the right side of the power truss to look for any signs of whatever might be causing excessive friction in the mechanism that turns outboard solar panels to track the sun.

"We're seeing some increased currents, which are indicative of some increased friction on that joint," said Kirk Shireman, deputy manager of the space station program. "We've collected most of the data we can collect with the sensors that we have in place and what we need to do is get some visual inspection of that joint. So ... we made a decisoin to send one of the crew members out to that interface during EVA-2 and actually go 360 degrees around that joint and look at specific bolts and thermal blankets and make sure they're all in configuration."

For today's spacewalk, Parazynski (call sign EV-1) will be wearing a spacesuit with red stripes around the legs. Tani's suit has broken red stripes. His call sign is EV-3.

This is the 94th spacewalk devoted to station assembly and maintenance since assembly began in 1998, the 17th so far this year and the second of five planned for Discovery's mission. Going into today's excursion, 73 astronauts and cosmonauts representing the United States, Russia, Canada, Japan, Germany, France and Sweden had logged 574 hours and 13 minutes of EVA time building and maintaining the space station.

Here is an updated timeline of today's activity (in EDT and mission elapsed time; includes revision D of the NASA television schedule). This timeline assumes the spacewalk begins one hour early; the actual time may vary:

EDT........DD...HH...MM...EVENT

10/28/07
05:03 AM...04...17...25...EVA-2: Airlock egress
05:18 AM...04...17...40...EVA-2: Disconnect Z1/P6 umbilical
05:43 AM...04...18...05...EVA-2: Parazynski: Detach P6 solar array
05:58 AM...04...18...20...EVA-2: EV3: Detach P6 solar array
07:03 AM...04...19...25...EVA-2: EV3: Airlock ops
07:13 AM...04...19...35...EVA-2: Parazynski: Node 2 outfitting
07:13 AM...04...19...35...SSRMS: P6 demate
07:43 AM...04...20...05...EVA-2: EV3: SARJ inspection
08:43 AM...04...21...05...EVA-2: EV3: S1 SFU
09:03 AM...04...21...25...EVA-1: EV3: MBSU installation
09:13 AM...04...21...35...EVA-2: EV3: RPCM replacement
09:43 AM...04...22...05...EVA-2: Node 2 PDGF installation
10:58 AM...04...23...20...EVA-2: Parazynski: Node 2 outfitting
11:18 AM...05...23...40...EVA-2: Airlock ingress
11:38 AM...05...00...00...EVA-2: Airlock repressurization
02:30 PM...05...02...52...Mission status briefing on NASA TV
04:08 PM...05...04...30...ISS crew sleep begins
04:38 PM...05...05...00...STS crew sleep begins
05:00 PM...05...05...22...Video highlights reel on NASA TV
10:30 PM...05...10...52...Flight director update on NASA TV
Designed as the sixth and final segment of the port, or left, side of the station's main power truss, P6 was mounted at the center of the station in December 2000 to provide power to the U.S. segment during the initial stages of assembly.

Now, with identical solar panels in place on the left and right sides of the main power truss, NASA needs to move P6 to its permanent position on the far left end of the beam. The segment's huge arrays, stretching 240 feet from tip to tip, were stowed during shuttle missions last December and June. Power and cooling lines were disconnected during an August flight, setting the stage for the massive truss's detachment, relocation and re-extension during Discovery's mission.

Complicating the work, the station's robot arm cannot reach far enough on its own to make the move. So the station arm, after handing P6 off to the shuttle's space crane, will be moved by the station's mobile transporter to the far end of the power truss. At that point, the shuttle arm will hand the truss segment back to the station arm and Parazynski and Wheelock, making their third spacewalk by that point, will oversee its attachment to the P5 truss segment.

"Moving the P6 solar array will be a major activity," shuttle commander Pam Melroy said in a NASA interview. "On our second spacewalk - our first spacewalk is all about node 2 - we'll be using the robotic arm in one location to actually reach around and pull P6 off ... with the assistance of our spacewalkers.

"Once the P6 has been detached from the space station, then the robotic arm will move it around to the port side of the shuttle, at which point it will be handed off to the shuttle arm. The shuttle robotic arm will take control of the P6 truss while the space station robotic arm is reconfigured and rolled out on the mobile transporter, the mobile platform, all the way to the far end of the port truss. And then, we'll use the station arm to take it back and install it in its final location.

"This is pretty nearly the design-limiting case for the robotic arm of the space station, so it's out at its full extension, trying to get that truss out there," Melroy said. "We'll have the help of the spacewalkers on the third spacewalk to do that. So, all these activities will actually span three days, three full days, two spacewalks with robotics in the middle."

Last December, attempts to stow the folding blankets making up one side of the P6 array ran into problems when several of the slats making up the blankets folded the wrong way along their creases. The astronauts ultimately were successful and engineers don't anticipate major problems re-extending the arrays.

They'd better be right. The station's robot arm will be fully extended just to attach P6 to P5. It will not have the reach necessary to position a spacewalker beyond the lowest few feet of the huge arrays if any major problems are encountered.

"One of perhaps the most audacious things we've ever done in space is this P6 solar array truss relocation," said Parazynski, an emergency room physician and veteran spacewalker making his fifth shuttle flight. "We're powering down this major element, something that we've never done before, basically shutting off the lights, shutting off the computers, turning off the cooling, unbolting it, disconnecting all the fluid and electrical and data lines and then via a process of EVA and very complex robotics we're going to take it to the very tip of the space station and then reverse the process: bolt it together, hook up connectors, deploy solar arrays, deploy a radiator.

"One of the things I love about NASA is we plan for success but we prepare for failure. And so we are very well prepared. A lot of people, a lot of smart rocket scientists around the Johnson Space Center ... have spent a lot of time figuring out what could go wrong and what we might do to address those things. We have a very long list of procedures we can run if things don't go exactly to plan."

A fourth and final set of solar arrays - S6 - will be mounted on the starboard, or right, side of the main truss during a shuttle flight next year.

9:00 AM, 10/27/07, Update: Astronauts enter Harmony (UPDATING earlier report)

Space station commander Peggy Whitson and Italian astronaut Paolo Nespoli opened the hatch to the newly installed Italian-built Harmony module at 8:24 a.m. today and floated into the roomy, brightly lighted room that will serve as the gateway to European and Japanese research modules scheduled for launch late this year and early next.

"We just wanted to welcome the Harmony module on board the international space station," Whitson said. "It's not in its final location, but we opened the hatch to enter and we wanted to acknowledge the process and christen the Harmony module itself. We think Harmony is a very good name for this module because it represents the culmination of a lot of international partner work and will allow additional international partner modules to be added on."

"Harmony" was submitted by students in six different schools who entered a nationwide competition to name the station's newest module. Nespoli, representing Italy and the European Space Agency, called Harmony "this very beautiful piece of hardware."

"It was built in Europe, in Italy, through an agreement with the European Space Agency and the Italian Space Agency and built by Italian industry," said Nespoli, the fifth Italian to fly in space. "I'd like to thank everybody who worked hard making this possible."

Harmony was built by Thales Alenia Space in Torino, Italy. Boeing, NASA's prime contractor for the station project, installed a variety of subsystems, "including lights, fans, power switches and converters, racks, air diffusers, smoke detectors, hatches and Common Berthing Mechanisms," according to a NASA press kit.

Also known as node 2, Harmony weighs 31,500 pounds and measures 23.6 feet long and 14.5 feet wide, adding 2,600 cubic feet of pressurized volume to the international lab complex. It was attached to the left side of the central Unity module (node 1) Friday and robotically locked in place with 16 motorized berthing mechanism bolts.

"The crew will remove a cover and some hardware that was used to help mate it to the station and we'll also have them connect the power and the data cables," station flight director Heather Rarick said late Friday. "And then we'll open the hatch and go inside for the first time. We'll also have to put a temporary air duct into the node 2 so it can start circulating the air through the space station filters. After the air gets turned over a couple of times, the crew will go back in there and do some more work."

One of the major items on the agenda is to start removing hundreds of bolts, or launch locks, that were needed to provide rigidity during climb to orbit.

"Like any spacecraft, anything that launches from the ground has to withstand the huge forces of launch, the vibrations and the accelerations, of launch," newly arrived station astronaut Dan Tani said in a NASA interview. "So even though weÕre going to end up in a zero-g environment where the loads are very small, everything has to be designed to withstand those launch loads and vibrations.

"There are over (700) screws and bolts that are installed on the node 2 just to hold things down, to survive the launch phase, that we will not need on orbit. So we will go in and we have a very detailed procedure to remove all (700) and something of those bolts and washers that are required so that the Harmony can withstand the launch loads but that are not needed once theyÕre in orbit.

"So thatÕs the majority of the work inside the node 2, initially," he said. "There are other activation things: there are fire extinguishers and masks that we store as emergency equipment inside the Node 2, that are not made to launch in their final configuration, so we install those. ThereÕs some computer outfitting, electrical outfitting, those kinds of things. But weÕre getting it ready to, taking it out of its launch mode into its on orbit mode and activating it."

After Discovery departs, the station crew will use the lab's robot arm to disconnect the shuttle docking port, known as pressurized mating adapter No. 2, on the front of the Destiny lab module and attach it to Harmony. The new module then will be moved to the front of Destiny, its permanent location, and connected to the station's power and cooling systems in preparation for arrival of the European Space Agency's Columbus research module in December. Columbus will be attached to Harmony's right-side port and Japan's Kibo laboratory will be attached to the left-side hatch early next year.

Along with initial node 2 outfitting today, the astronauts also plan to review procedures and set up tools for a spacewalk Sunday by Tani and Scott Parazynski to detach the 35,000-pound P6 solar array truss segment so it can be moved to the left end of the station's main power truss on Tuesday during the mission's third spacewalk.

P6 was mounted on a short truss extending up from the Unity module in 2000 to provide the station's interim power during the initial stages of construction. Now that the lab's main solar power truss is in place, P6 must be moved to its permanent position. Its huge solar arrays were stowed during to previous shuttle visits and its power and cooling systems disconnected.

Tani also will take a moment Sunday to inspect a massive joint on the right side of the truss that rotates the outboard solar arrays to track the sun. Engineers have noticed higher-than-normal vibrations and power usage in the joint and they suspect some sort of interference in the mechanism. Tani will visually inspect the joint to look for signs of anything unusual.

Tani and Parazynski will spend the night in the station's Quest airlock module at a reduced air pressure to purge nitrogen from their bloodstreams in preparation for working in NASA's low-pressure spacesuits. The so-called "camp-out" procedure is needed to help prevent the bends.

Here is an updated timeline of today's activity (in EDT and mission elapsed time; includes revision C of the NASA television schedule):

EDT........DD...HH...MM...EVENT

01:38 AM...03...14...00...STS crew wakeup
02:08 AM...03...14...30...ISS crew wakeup
04:38 AM...03...17...00...Heat shield inspection boom (OBSS) in handoff position
05:08 AM...03...17...30...Spacesuit swap
05:38 AM...03...18...00...Station arm (SSRMS) grapples OBSS
05:53 AM...03...18...15...Shuttle arm (SRMS) ungrapples OBSS
06:33 AM...03...18...55...Harmony/Node 2 vestibule outfitting
06:48 AM...03...19...10...OBSS reberthed in shuttle cargo bay
07:33 AM...03...19...55...SSRMS locks onto power and data grapple fixture No. 3
07:43 AM...03...20...05...Crew meals begin
08:58 AM...03...21...20...Harmony/Node 2 ingress and setup (actual: 8:24 a.m.)
10:13 AM...03...22...35...Spacesuit resizing
10:53 AM...03...23...15...EVA-2: Airlock preps
11:30 AM...03...23...52...Mission status briefing on NASA TV
11:38 AM...04...00...00...EVA-2: Tools configured
01:03 PM...04...01...25...EVA-2: Procedures review
02:03 PM...04...02...25...CBS News, Fox News, WHAM TV interviews
03:23 PM...04...03...45...EVA-2: Mask pre-breathe/campout operations
04:38 PM...04...05...00...ISS crew sleep begins
05:08 PM...04...05...30...STS crew sleep begins
06:00 PM...04...06...22...Daily video highlights reel on NASA TV
10:30 PM...04...10...52...Flight director update on NASA TV

4:40 PM, 10/26/07, Update: SARJ inspection added to Sunday spacewalk

NASA managers said today's installation of the new Harmony module on the international space station, and work by two spacewalking astronauts to prepare the stowed P6 solar array truss segment for its long-awaited detachment during a second spacewalk Sunday, went "extremely well." There were no problems of any significance and all of the crew's major objectives were accomplished.

While the spacewalk was going on, NASA managers decided to add a task to Sunday's excursion, a visual inspection of the massive rotary joint on the right side of the station's main power truss that turns the lab's starboard solar arrays to keep them face-on to the sun.

The station is equipped with two such solar alpha rotary joints, or SARJ units, to turn the left and right solar arrays like giant paddle wheels. The port SARJ is operating normally, but engineers recently noticed increased electrical demands and vibration in the right-side SARJ that indicate unwanted friction somewhere in the system. An alert flight controller also noticed the vibration while watching zoomed-in television views from a camera on the truss. At first, controllers thought the camera mounting might be loose. But they quickly realized the vibration was correlated with the current spikes.

"We're seeing some increased currents, which are indicative of some increased friction on that joint," said Kirk Shireman, deputy space station program manager at the Johnson Space Center in Houston. "We've collected most of the data we can collect with the sensors that we have in place and what we need to do is get some visual inspection of that joint. So ... we made a decision to send one of the crew members out to that interface during EVA-2 and actually go 360 degrees around that joint and look at specific bolts and thermal blankets and make sure they're all in (proper) configuration."

The SARJ features 22 multi-layer insulation thermal blankets that are "cantilevered over the joint," Shireman said. "So they rotate around and there's another surface that's right below it, so these blankets could be dragging on that surface and that would cause an increased drag. There's also some bolts that come out and actually were holding these blankets from the rotating side. When you undo those bolts, which we did (when the SARJ was installed), they swing out of the way. But if one of those bolts didn't swing out of the way, it could be there, it could be dragging.

"So there are a number of things we believe visually we could see just from doing this inspection. Internally, where the actual bearings and the gears and the drive lock assemblies (motors) are, there could be foreign object debris inside there, there could be a misconfiguration of not only the drive lock assemblies, there could be a misconfiguration of even some of the structure that's underneath there."

If the visual inspection Sunday doesn't turn up anything obvious, Shireman said, "it's likely we'll do additional troubleshooting in the future."

Shireman said the SARJ is equipped with redundant drive motors and redundant electronic controllers, which are equipped with circuitry that would prevent the motors from drawing too much power. The current spikes have been seen regardless of which motor was driving the joint and even when the joint was rotated in the opposite direction.

Derek Hassmann, lead space station flight director, said the SARJ issue poses no immediate threat to the station. Shuttles can dock and undock as needed and if worse comes to worse, the starboard arrays can be locked in a favorable orientation for power generation while troubleshooting continues.

"One of the concerns we have about the way the SARJ is behaving is the potential it might stall in a position that's not optimal for power," Hassmann said. "So one of the things we have been talking about ... is to find a current value at which we're going to stop rotating the SARJ and put it in a position that's good for power consumption. We've basically got constraints to find that will allow us to park the SARJ in a good power producing attitude before it would stall. As long as we can get it into an attitude that's reasonably good for power generation, combined with what the other SARJ can produce, we wouldn't have any significant power impacts that we couldn't deal with."

During a six-hour and 14-minute spacewalk today, astronauts Scott Parazynski and Doug Wheelock retrieved an S-band antenna assembly for return to Earth; prepared the Harmony module for installation; and unplugged ammonia coolant lines leading to the P6 truss segment in preparation for moving the 35,000-pound segment to the far left end of the station's main power truss. They also installed thermal blankets to protect sensitive electronic components from temperature extremes after the truss is detached.

While that work was going on, the astronauts inside the shuttle-station complex robotically locked Harmony in place on the left side hatch of the central Unity module. If all goes well, the crew will enter the new module Saturday and begin removing more than 700 bolts that added rigidity during launch. After Discovery departs, the station crew will move Harmony to its permanent mounting point on the front end of the Destiny laboratory module.

"I would ... classify this as a hugely successful day," said Dina Contella, the mission's lead spacewalk officer. "The EVA team is really happy to have conducted such a successful EVA. Scott and Wheels did a fantastic job. This was Wheels' first EVA and he did it like a real pro. So we're hugely thrilled with how the day went."

During disconnection of four ammonia umbilicals, Parazynski reported seeing a few flakes of ammonia ice spew out into space.

"There is a history with those (quick-disconnect fittings) and we have quite a bit of crew training that goes into what we would do in case there's a little bit of ammonia that comes out," Contella said. "Of course, our big worry is that we have a lot of ammonia come out, and that was not the case today. Really, he jiggled the connector and a few flakes came off and that's about all we saw. But just to be on the safe side, we went ahead at the time and had Wheels come over and look at Scott and make sure he didn't have any visible ammonia on him and ran through a calculator to make sure we were outside long enough to make sure the ammonia would bake off the suit had there been any on there. And then when we came back in the airlock at the end of the EVA, we did do some testing to verify we were not going to bring any ammonia into the cabin. It was all pretty conservative, but necessary."

During Sunday's spacewalk by Parazynski and station astronaut Dan Tani, the P6 truss segment will be disconnected from its central mounting point atop Unity. It is scheduled for installation and redeployment on the far left end of the main power truss during a third spacewalk Tuesday.

12:30 PM, 10/26/07, Update: Harmony attached to the international space station

Astronauts Scott Parazynski and Doug Wheelock, after waiting out a routine ammonia decontamination procedure, repressurized the space station's airlock today to officially close out a successful six-hour 14-minute spacewalk. A half hour earlier, at 11:38 a.m., the new 31,500-pound Harmony module was attached to its temporary home on the left side of the central Unity module to accomplish one of the major objectives of the shuttle Discovery's mission.

"Good job on the (Harmony installation), it's awesome," one of the spacewalkers called from the airlock.

"Yeah, I sat around and made lunch for everybody and watched them just totally do a fantastic job," commander Pam Melroy said.

"It was so cool. We saw it hanging out there. ... Pambo, bringing harmony!" he said, referring to Melroy's mission nickname.

"Well, I don't know that anybody's ever told our crew that we bring harmony with us, but we sure bring fun," Melroy said.

"Agreed."

Today's spacewalk, the first of five planned for Discovery's mission, began at 6:02 a.m. and ended at 12:16 p.m., about 15 minutes ahead of schedule. The astronauts entered the airlock early to allow time for any trace amounts of ammonia ice crystals on either of their spacesuits to outgas and dissipate. The procedure, carried out as a precaution, was ordered after Parazynski disconnected four ammonia coolant lines leading to the stowed P6 solar array truss segment and reported seeing a few ice crystals.

There were no visible signs of contamination on his suit, but the decontamination procedure is mandatory in such cases. While they waited, station astronaut Dan Tani, who worked with shuttle flight engineer Stephanie Wilson to install Harmony with the lab's robot arm, provided an update.

"Just to let you know, we just completed the ungrapple procedure," Tani said. "It's been a long robotics day and we're greatly indebted to our fantastic team of robotics trainers and console operators ... and all the folks who got us here and helped us and made this a success."

"Well, everybody appreciates your work, Dan, and thank you guys," astronaut Kevin Ford said from space station control in Houston. "Looking at where you're at in the timeline, you guys ended up about an hour and a half ahead or so. We appreciate you working right through lunch and getting it all done."

11:00 AM, 10/26/07, Update: Harmony module pulled from cargo bay

Astronauts Stephanie Wilson and Dan Tani, operating the space station's robot arm, carefully pulled the 31,500-pound Harmony module from the shuttle Discovery's cargo bay today for attachment to the international lab complex. Spectacular video beamed down from the shuttle showed the massive module being slowly maneuvered above the spaceplane over toward the left side of the outpost where it will be installed on the central Unity module.

Spacewalkers Scott Parazynski and Doug Wheelock, meanwhile, worked at the top of the central Z1 truss to prepare a huge set of stowed solar arrays for relocation to the far left side of the station's main solar power truss later in the mission. Parazynski's main goal was to disconnect four ammonia coolant lines between the P6 solar array to the Z1 truss and to remate them to dummy connectors on Z1. He also had to cap the open lines on the P6 side of the interface and secure the quick-disconnect fittings.

Before launch, Parazynski said he worried about ammonia leakage and potential contamination. The valves in question have "been open now for almost seven years," he said. "I would envision we will take a little bit of ammonia contamination, hopefully not a lot. We are well trained to handle anything that might happen along those lines. But they are very difficult to handle, I don't have a perfect work site for it, so that'll be one of the things that will be very challenging on the flight."

As it turned out, only a few ammonia ice crystals were reported as the umbilicals were disconnected and remated. But that was enough to trigger a contamination inspection. The concern was the potential for carrying unseen ammonia ice crystals back into the space station.

"If I took any hits it was mostly at the chest level, I believe," Parazynski said. "And Wheels, they looked like just little tiny pieces of ice or almost hail."

But Wheelock did not see any signs of contamination on Parazynski's suit.

"The sun's coming up. But again, I don't see anything, Scott, I don't see any discoloration or anything that looks waxy or a different texture. Can you see that, Paolo? I don't see anything."

"Roger, copy," Italian astronaut Paolo Nespoli replied from inside the shuttle. "And Houston, I guess you followed along. I'm not sure if you have wireless (television) or not. But it looks like EV-2 (Wheelock) is not seeing any contamination on EV-1 (Parazynski)."

The spacewalkers then focused on attaching thermal shrouds to protect a stowed radiator on P6 and two electronics boxes toward the top of the array truss.

Wilson and Tani, meanwhile, carefully positioned Harmony to line it up for attachment to the Unity module using motor-driven bolts in a so-called common berthing mechanism, or CBM. The attachment does not require the spacewalkers and will be carried out robotically.

"And Scott and Wheels, do you have a minute? Nespoli asked as the shuttle-station complex sailed high above the Gulf of Mexico.

"Sure."

"If you look down, starboard side, you're about the pass right over Houston. Say hello to MCC (mission control center)."

"Starboard side, huh?" Parazynski asked.

"That's affirm, you see the coastline there," Nespoli said.

"Ooohhhh, look at that!"

"Oh, that's beautiful."

"Hello, Houston!" Parazynski said.

A few minutes later, Parazynski caught site of Harmony nearing its attachment point on the Unity module.

"Hey Wheels, look down, ISS nadir, you'll see that they've got the node about two meters out," he said.

"Oh, my goodness!"

"Isn't that great?"

"Hey, what do you think? Robeau and all the gang here have been working hard," Nespoli said, referring to Wilson by her mission nickname.

"Yes, they have," Parazynski agreed.

"All right, let's get going here," Nespoli said. "We have one hour and 10 minutes to go."

9:15 AM, 10/26/07, Update: Astronauts remove S-band antenna; prepare Harmony for attachment to station

Astronaut Doug Wheelock, anchored to the end of the space station's robot arm, manually carried a large S-band antenna assembly down to a stowage location in the shuttle Discovery's cargo bay for return to Earth. Wheelock and Scott Parazynski then tethered a robot arm grapple fixture to the new Harmony module and prepared it for attachment to the international space station.

"Steph and Dan, that's good flying," Wheelock said as Stephanie Wilson and Dan Tani, operating the robot arm from inside the Destiny laboratory module maneuvered him to the shuttle. "Man, I'm just staring off into deep space, I don't have anything to reference. It's awesome. What an awesome view."

"We've got eyeballs on you, though, you're looking great," shuttle pilot George Zamka reassured him.

"It's beautiful," Wheelock said. Television from the space station showed Wheelock on the end of the arm silhouetted against the black of space and the thin blue limb of Earth.

Parazynski joined him in the shuttle's cargo bay to anchor the S-band antenna support assembly to a side wall. After a bit of trouble getting bolts to engage, the astronauts completed the task, tightening six fasteners to hold the antenna securely.

"I'll bet Mr. Suffredini's happy," Parazynski said, referring to space station Program Manager Mike Suffredini.

"I think so," Wheelock agreed.

"He's got a SASA."

Parazynski and Wheelock then unbolted a power and data grapple fixture from the cargo bay and tethered it to the front of the Harmony module. The grapple fixture, which can be used in the future to anchor the station's robot arm, will be firmly mounted to the module during a spacewalk by Parazynski and Tani on Sunday.

With the PDGF in place, the spacewalkers removed eight contamination covers from the new module, along with a cable that provided shuttle power to internal heaters. That cleared the way for Wilson and Tani to lock the robot arm onto Harmony and begin pulling it from the shuttle's cargo bay. Attachment to the left hatch of the Unity module will be done robotically.

While that work was going on, Parazynski and Wheelock made their way back to the Quest airlock module to drop off equipment and to recharge Wheelock's oxygen supply. They plan to move up to the Z1 truss extending up from the central Unity module where the stowed P6 solar array is mounted to prepare the 35,000-pound truss segment for its move to the far end of the station's main power truss later in the mission.

6:05 AM, 10/26/07, Update: Spacewalk begins

Floating in the space station's Quest airlock module, astronauts Scott Parazynski and Doug Wheelock switched their spacesuits to battery power at 6:02 a.m. to officially kick off a planned six-and-a-half-hour spacewalk. The spacewalk began about a half hour ahead of schedule. The goals of today's excursion are to help prepare a new multi-hatch module for installation on the space station and to disconnect ammonia coolant lines from a solar array truss segment that will be moved later in the mission.

The spacewalk began as the space station was passing 213 miles above the Andes of central Chile.

"You're not going to believe this," Parazynski, making his fourth spacewalk, told Wheelock. A few minutes later, passing over the Amazon rain forest, Wheelock marveled, "What a gorgeous view. Wow."

04:15 AM, 10/26/07, Update: Spacewalk, Harmony installation on tap

Astronauts Scott Parazynski and Doug Wheelock are gearing up for a six-and-a-half hour spacewalk today to help install the new Harmony module on the international space station. They also plan to retrieve an S-band antenna assembly for return to Earth and prepare a solar array truss segment for relocation later in the mission.

The astronauts spent the night in the space station's Quest airlock module at a reduced pressure of 10.2 pounds per square inch to help purge their bloodstreams of nitrogen in preparation for work in NASA's low-pressure spacesuits. The excursion was scheduled to begin around 6:30 a.m., but the crew was running a half hour ahead of schedule earlier today and the spacewalk could begin early.

This will be the 93rd spacewalk devoted to station assembly and maintenance since construction began in 1998, the 16th so far this year and the first of five planned for Discovery's mission. Going into today's EVA, 72 astronauts and cosmonauts from the United States, Russia, Canada, Japan, Germany, France and Sweden had logged 567 hours 59 minutes of spacewalk time building the international lab complex.

For identification, Parazynski (call sign EV-1) will be wearing a spacesuit with red stripes around the legs. He is a veteran of three previous spacewalks. Wheelock (EV-2), making his first EVA, will be in an all-white suit. The space station's robot arm, or SSRMS, will be used to move the Harmony module from Discovery's cargo bay to a temporary attachment point on the left side of the central Unity module. The SSRMS will be operated by Discovery flight engineer Stephanie Wilson and newly arrived space station flight engineer Dan Tani.

"Doug Wheelock and I will go out the hatch together," Parazynski said in a NASA interview. "It will be Doug's first spacewalk. I'm looking forward to seeing him have that experience. Our first activity right off the bat will be to transfer an S-band antenna that will be returned to the ground for servicing and then flown back up, on a future flight as a spare. The reason we have to do it so early in the flight - it's not our highest priority activity - it's just that's the only time the robotic arm is available and in position to support this activity. So we'll pluck this off of the Z1 truss through a handoff, we call it a leap frog maneuver. Doug will hand the SASA antenna to me; it's about 10 feet, 8 to 10 feet in length. I'll hold on to it, then he'll jump into the space station robotic arm, I'll hand it back to him, then he'll take a beautiful ride down to the payload bay, while I translate hand over hand, to support him in installing that on the side wall of the orbiter for return to Earth.

"Then we really get into the meat of our assembly activities. We'll activate the Node 2 or Harmony module in the payload bay," Parazynski said. "First we'll be translating a payload and grapple fixture that's on a side wall in the payload bay, and we'll temporarily stow it on the front end of the node. And I'll get a free ride to its installation location. So we'll just tether it in place up on the front of the node and then we'll go to the back of the payload bay and we'll move some protective covers on the seals that we'll mate to the Unity module. We'll also work with some power connectors, the launch activation cable on the front of the module and some other cables on the back of the node."

Harmony, providing an additional 1,230 cubic feet of habitable volume, will be temporarily attached to the left side of the station's central Unity module, which connects the U.S. and Russian segments of the complex. After Discovery departs, Whitson, Tani and Expedition 16 flight engineer Yuri Malenchenko will use the station's robot arm to detach the lab's main shuttle docking port so it can be bolted onto Harmony. Then Harmony will be detached and permanently mounted on the front end of the U.S. Destiny laboratory module. European and Japanese research modules will be attached to Harmony's left and right ports in December and early next year.

While Wilson and Tani begin pulling Harmony from the cargo bay with the station's robot arm, Parazynski and Wheelock will float up to the central Z1 truss and begin work to prepare the P6 solar array truss for relocation later in the mission.

"While we're outside, preparing the P6 for its move, inside Stephanie and Dan will be working, very, very hard with the robotic arm," Wheelock said. "(Pilot) George Zamka will be operating our common berthing mechanism, the actual physical mechanism that connects the two modules together. So they're very busy inside and out, during EVA 1."

Designed as the sixth and final segment of the port, or left, side of the station's main power truss, P6 was mounted at the center of the station in December 2000 to provide power to the U.S. segment during the initial stages of assembly. Now, with identical solar panels in place on the left and right sides of the main power truss, NASA needs to move P6 to its permanent position on the far left end of the beam. The 35,000-pound segment's huge arrays, stretching 240 feet from tip to tip, were stowed during shuttle missions last December and June.

"Once we're completed with all our work in the payload bay, we'll translate back up to the airlock and drop off some gear, and then we'll head up to the P6 truss," Parazynski said. "Again, these are all independent, closely choreographed, tasks. I'll begin demating the (ammonia) cooling umbilicals that have been connected between P6 and the Z1 truss for almost seven years now. So I'll have to close those valves very carefully and stow them back on the Z1 truss. We're hoping for no leaks, but since the valves have been operational for so long, that's one area of concern that we don't want to get any contamination.

"While I'm doing that, Doug will be up on the P6 truss about 10 or 15 feet higher than me, and he'll be deploying a blanket over the radiator there. I will join him for the final activities associated with that radiator blanket. And then we'll go to the top of the world, the top of the P6 truss, and we'll be installing two protective thermal blankets on sequential shunt units. They're basically large power boxes, associated with each of the large P6 solar arrays. So we'll put those blankets on, probably take a few pictures, I imagine, because that vantage point up there is just spectacular. And that will be the completion of our first spacewalk."

Here is a timeline of today's activity (in EDT and mission elapsed time; includes revision B of the NASA TV schedule):

EDT........DD...HH...MM...EVENT

01:38 AM...02...14...00...STS/ISS crew wakeup
02:13 AM...02...14...35...EVA-1: 14.7 psi repress/hygiene break
03:23 AM...02...15...45...EVA-1: Campout EVA preps
04:43 AM...02...17...05...ISS: Tani pressure suit leak checks and drying
04:53 AM...02...17...15...EVA-1: Spacesuit purge
05:08 AM...02...17...30...EVA-1: Spacesuit prebreathe
05:58 AM...02...18...20...EVA-1: Crew lock depressurization
06:33 AM...02...18...55...EVA-1: Airlock egress
06:53 AM...02...19...15...EVA-1: S-band antenna retrieval
07:33 AM...02...19...55...EVA-2: Wheelock-: S-band antenna stow
07:43 AM...02...20...05...EVA-1: EV-1: Node prepped for unberthing
08:08 AM...02...20...30...EVA-1: EV-1: S-band antenna stow
08:43 AM...02...21...05...EVA-1: EV-1: Node prepped for unberthing
08:48 AM...02...21...10...EVA-1: EV-2: Node prepped for unberthing
10:23 AM...02...22...45...Station arm (SSRMS) grapples Harmony (node 2)
10:23 AM...02...22...45...EVA-1: EV-1: Disconnect Z1/P6 fluid lines
10:43 AM...02...23...05...SSRMS unberths Harmony
10:53 AM...02...23...15...EVA-1: EV-2: P6 aft radiator shroud
11:38 AM...03...00...00...EVA-1: EV-1: P6 shroud
11:53 AM...03...00...15...EVA-1: Sequential shunt unit shroud
12:28 PM...03...00...50...EVA-1: Airlock ingress
12:33 PM...03...00...55...Harmony attached to Unity leftside port
01:08 PM...03...01...30...EVA-1: Airlock repressurization
01:18 PM...03...01...40...Spacesuit servicing
01:28 PM...03...01...50...SSRMS ungrapples Harmony
02:23 PM...03...02...45...Harmony/Unity leak checks
03:00 PM...03...03...22...Mission status briefing on NASA TV
05:00 PM...03...05...22...Post-MMT briefing on NASA TV
05:38 PM...03...06...00...STS/ISS crew sleep begins
06:00 PM...03...06...22...Daily video highlights reel on NASA TV
10:30 PM...03...10...52...Flight director update on NASA TV
"EVA is the ultimate astronaut experience, I think," Parazynski said. "But to be perfectly honest, celebrating a job well done, mission success, I think one of our perpetual fears is not doing the job well, to not get the job done. So I'm very focused when I'm outside doing a spacewalk, I'm in the zone. But every once in a while you can take a look up and take it all in and enjoy the experience."

5:30 PM, 10/25/07, Update: Shuttle heat shield appears in good shape; no additional inspection planned before undocking

The shuttle Discovery appears to have come through its launch and climb to space in good shape with no major heat shield problems and no need for any additional, "focused" inspections before undocking, NASA managers said today.

"I've got some good news and that is the Orbiter Project is going to recommend to the Mission Management Team tomorrow that focused inspection is not required," astronaut Tony Antonelli radioed from mission control shortly before the crew went to bed.

"Oh man, that is fantastic news!" shuttle commander Pam Melroy replied.

"Just to be clear, that is an initial report, they've still got a few things to look at so you'll get more in the MMT summaries (overnight), but just wanted to pass that along."

"We sure appreciate it," Melroy said. "Obviously, it's been a question, it's very much on our minds. So we're pretty excited to hear about that because it will give us more time with Node 2, which is just great. We can't wait to get inside."

Node 2, a multi-hatch module recently named Harmony, will be pulled out of Discovery's cargo bay Friday, during the first of five planned spacewalks, and temporarily mounted on the left side of the central Unity module. Harmony's installation is a major milestone for the space station project because it will serve as the connecting point for long-awaited European and Japanese research modules scheduled for launches in December, February and April.

The crew's flight plan included time for an additional heat shield inspection Saturday, if necessary, a time-consuming procedure using a 50-foot-long boom attached to the shuttle's robot arm. While analysis is not yet complete, laser scans of the shuttle's critical wing leading edge panels show no signs of trouble and close-up photography of heat shield tiles on the shuttle's belly, taken today during final approach to the space station, show only minimal damage.

"It's a pretty clean vehicle," said John Shannon, chairman of NASA's Mission Management Team. "Overall, we are not working ay issues. The imagery team is taking a close look at all the data but they have not seen anything that would cause them any concern at this time. So we'll go ahead and go through that process and report out on it just like we have for every mission."

Before launch, some engineers raised questions about degraded coating on three of the 44 reinforced carbon carbon - RCC - panels on the front of each wing. The engineers said recent analyses indicated the cause of the degradation was not as well understood as previously believed. Without a solid "root cause," they argued, it was impossible to predict how the degradation might evolve over time. As such, the engineers recommended delaying launch to replace the panels in question.

Mission managers opted to launch on schedule based on the past history of the panels - the degradation has been relatively stable over the past two mission - and the crew's post-Columbia ability to detect and repair minor heat shield damage.

"We haven't seen anything on the three panels that were brought up by the NESC (NASA Engineering and Safety Center)," Shannon said.

In an overnight message to the astronauts, the MMT mentioned a piece of ice that formed before launch and shook off during main engine ignition. The ice fell, lightly grazing one of the propellant feedline doors on the belly of the shuttle as the ship began its ascent. Shannon said today the umbilical doors appeared to be in excellent condition and that the ice did not fall far enough or hit at a steep enough angle to cause any damage.

Footage from cameras mounted on Discovery's solid-fuel boosters will be examined this weekend, but based on live views from a camera mounted on the external tank, engineers do not expect any major surprises.

All in all, Shannon said, "we are extremely lucky that we have a vehicle that is in such incredible shape. If I had to pick a mission where the vehicle would give us no problems and we'd just be able to concentrate on the mission and the assembly sequence, this would be the one. So we've really gotten lucky."

Discovery's mission is considered by many to be the most complex station assembly flight yet attempted. After getting Harmony attached to the station, the astronauts will stage two spacewalks and use two robot arms on the shuttle and the station to move a 35,000-pound solar array segment to the far left end of the lab's main power truss. Another spacewalk is planned to test a new heat shield repair technique and a fifth is on tap to complete preparations to move Harmony to the front of the space station as required after Discovery undocks.

For the space station's crew - commander Peggy Whitson, flight engineer Yuri Malenchenko and just-arrived astronaut Dan Tani - Discovery's departure will kick off a busy month of work to prepare Harmony and the station for delivery of Europe's Columbus research lab in December. Whitson and Tani plan two spacewalks in mid November to connect Harmony to the station's main power and cooling systems.

Given the complexity of all that work, Shannon said NASA does not want to extend Discovery's mission unless problems require additional time to resolve.

"If we can get all of our work done and leave (on time) that would be really good for the ISS team," he said. "They have a very highly thought-out timeline that gets them on track for STS-122 and the Columbus module, launching on Dec. 6, and really, if we extended this mission a day or two like we've done in the past, that would impact that timeline. So there is a premium on getting our work done on this flight and getting undocked from the space station and letting them carry on with their stage work. Even though we have a lot of (power), I would expect that unless we run into some significant problems we would not be talking about extending this mission. But of course, we have to see how that goes."

One open item that may affect one of the crew's spacewalks is an unusual vibration in one of the rotary joints that turns the station's right-side solar arrays to keep them face on to the sun. Shannon said a quick inspection of the starboard solar alpha rotary joint, or SARJ, might be requested if it can be worked into the spacewalk timeline.

"There's some vibration," he said. "I don't think they really have a good idea yet exactly what's causing it. There was some discussion today (about) is there anything they want to go look at on one of the EVAs to maybe go narrow down what the issue might be? From a shuttle standpoint, (the issue is) no impact to us at all. We can undock, we can do all of our activities and it's no impact. ... But I don't think they have a real good handle on exactly what the problem is. I wouldn't be surprised if they came in and asked on EVA 2 to go look at something and we'll have the EVA team go and assess that and make sure it's something we can safely do."

Asked about the critical nature of Discovery's mission, Shannon said "I told my team before we started this mission, this is the kind of mission we all came to NASA for. This is why we're here. ... We've got the infrastructure built, now we're kind of putting the living space on. And it's extremely exciting, it's very gratifying. Especially after the hiatus we went through after Columbia. You know, we all kind of thought jeez, can we get this done? To see the team step up to improve the vehicle and improve our operations and pick up where we left off is just a wonderful thing to see."

8:50 AM, 10/25/07, Update: Discovery docks with space station (UPDATED at 12:30 p.m. with hatch opening; Tani joins station crew)

Commander Pam Melroy deftly guided the shuttle Discovery to a "picture-perfect" docking with the international space station today, setting the stage for the first of five spacewalks Friday to install a new module, move a huge solar array truss and test a potentially valuable heat shield repair technique.

Streaking through space at 5 miles per second 212 miles above the south Pacific Ocean, the 248,000-pound shuttle's docking system gently engaged its counterpart on the front of the half-million-pound space station at 8:40 a.m. after a precisely choreographed rendezvous.

"Houston, Discovery and Alpha, capture confirmed," an astronaut radioed as the vehicles came together.

"And ISS is in free drift," station commander Peggy Whitson confirmed. Following naval tradition, Whitson then rang the ship's bell in the Destiny laboratory module, saying "Discovery, arriving."

Astronaut Chris Ferguson in mission control congratulated the shuttle crew on the flawless docking, asking lead spacewalker Scott Parazynski to "pass on to Pam and the rest of the crew, super job on the rendezvous today."

"Thank you so much," Parazynski replied. "Everyone here is just ecstatic, we're so fired up to be here and looking forward to the next several days shared with the station crew."

Two hours later, after firmly locking the two spacecraft together and completing leak checks, the crews opened a final hatch between Discovery and the space station and the shuttle crew was welcomed aboard at 10:39 a.m. by Whitson, flight engineer Yuri Malenchenko and outgoing flight engineer Clay Anderson.

"She did great," flight director Rick LaBrode said of Melroy's piloting skills. "It was amazing, there were a lot of activities going on. Yesterday, I said we had all our network problems solved. And boy, was I wrong. We had nothing but network problems throughout the day yesterday. ... As soon as the crew got up this morning and started bringing up the computers they use, it started causing network problems again. So, we had to deal with troubleshooting those network problems while we were trying to do a rendezvous and that was challenging. But the crew did an exceptional job. All the targeting went extremely well, the burns were right on and the prox ops piloting was phenomenal. Pam did a great job."

Melroy is only the second female shuttle commander while Whitson is the first woman to command a space station crew. Both flew together in 2002, when Melroy served as a shuttle pilot and Whitson was a space station flight engineer, and they clearly enjoyed greeting each other again in orbit, smiling and laughing as they embraced in the lab module.

A few moments later, Whitson welcomed the rest of the shuttle crew aboard - pilot George Zamka, flight engineer Stephanie Wilson, Doug Wheelock, Italian astronaut Paolo Nespoli, Parazynski and Dan Tani, who launched aboard Discovery as Anderson's replacement.

After the brief "meet and greet" in the lab module, all 10 shuttle-station crew members floated back to the Russian Zvezda command module for a quick safety briefing before pressing on with a full day of work.

"Obviously, I'm delighted to be flying in space with Peggy again," Melroy said before launch. "She was on Expedition 5 when I was on STS-112 and we worked together in space and had a wonderful time and developed a great friendship. So this is a really special event for us. I think it is just indicative that there are enough women in the program that coincidentally this can happen. And that is a wonderful thing. It says a lot about the first 50 years of spaceflight that this is where we're at. I look forward to the next 50 and many future women commanders, including one going to the moon, I hope."

Following the safety briefing, Tani moved his custom Soyuz seat-liner from the shuttle to the station and officially replaced Anderson as Expedition 16 flight engineer No. 2. The seat liner will permit

"Houston, Alpha, on the big loop from the new FE-2, just to let you know, IELK (seat-liner) is installed and I have to send out my 'I have moved' card," Tani radioed from the Destiny module, starting his first day as a station crew member.

"And Houston copies, Dan, welcome aboard as Expedition 16 FE-2."

"Thanks very much, feels great and glad to be part of the crew here."

"And Houston on the big loop, he's behind already one month in rent," joked Anderson, now a shuttle crew member. Anderson was launched to the outpost aboard the shuttle Atlantis last June and as of today has logged 139 days in space.

Anderson and Wilson were in the process of using the station's robot arm to latch onto the shuttle's 50-foot-long heat shield inspection boom. After pulling it from the cargo bay, the station arm will hand the boom off to the shuttle arm for use Friday and later in the mission.

"Big ticket items still remaining on the crew's day today, now that the vehicles are mated we'll power up the system we use to transfer power from the station to the shuttle," LaBrode said. "We'll activate that and do a checkout of that system. We also need to grapple the orbiter boom sensor system, and they'll do that with the station arm because the shuttle arm can't reach it any longer after the mating. We'll grab it with the station arm and then we'll hand it off to the shuttle arm. We have to do that in preparation for tomorrow's activities, where the Harmony module is unberthed and installed on ... the international space station. There are clearance issues with the boom in its stowed location."

The primary goals of Discovery's mission are to install Harmony, a multi-hatch module that will serve as the gateway for European and Japanese research modules, and to move a 35,000-pound solar array truss segment to the far left end of the station's main power beam. Five spacewalks are planned, including one to test a promising heat shield repair technique.

Parazynski and Wheelock plan to stage the first excursion early Friday to help temporarily mount Harmony on the left port of the central Unity module. Both astronauts plan to spend the night in the station's airlock at a reduced pressure of 10.2 pounds per square inch to help purge nitrogen from their bloodstreams. The so-called "campout" procedure is part of a process that helps prevent the bends after working in NASA's low-pressure spacesuits.

Friday's spacewalk is scheduled to begin at 6:28 a.m. and end a few minutes after 1 p.m.

After Discovery departs, the station crew will detach the shuttle docking port from the front of the Destiny module, attach it to Harmony and then move the mated Harmony/docking port back to the front of Destiny. Whitson and Tani plan two spacewalks in November to connect Harmony to the station's main power and cooling systems, setting the stage for delivery of the European Columbus research lab in December.

06:00 AM, 10/25/07, Update: Discovery closes in on space station

Trailing the international space station by about 9.2 miles, shuttle commander Pam Melroy and pilot George Zamka fired Discovery's maneuvering rockets today at 5:55 a.m. to kick off the final stages of a two-day rendezvous procedure that began with launch Tuesday. If all goes well, Melroy will guide Discovery to a docking with pressurized mating adapter No. 2 on the front of the lab complex around 8:33 a.m.

"The rendezvous is a very exciting time for us, for a lot of different reasons," Melroy, the second woman to command a space shuttle, said in a NASA interview. "First of all, for the pilot and commander, we're test pilots. So any opportunity to fly the vehicle is what really gets us excited, and we focus a lot on it during training. But I also find, on a personal level, it's very exciting because when you approach the space station, it's an extraordinary sight. Everybody can go to Florida, if they want to, and watch a space shuttle launch. But only astronauts get to see the space station. And it actually inspires that same sense of awe and wonder as you approach. So it's a very exciting moment, to see it there. You just can't believe how huge it is, and it's absolutely gorgeous!"

The astronauts have been wrestling with computer network glitches involving laptop computers used for a variety of tasks, but engineers came up with a way to work around the problem in the near term and it's not expected to have any impact on today's rendezvous and docking. On the station, engineers have been monitoring higher-than-expected vibration and electricity use by a massive rotating joint that is used to slowly turn the lab's right-side solar arrays to keep them face on to the sun. This issue has been under study for the past few weeks and the plan today is simply to lock the joint in place during Discovery's final approach.

Following a standard approach profile, Discovery will reach a point 600 feet directly below the lab complex around 7:25 a.m. A few minutes later, Melroy will guide the shuttle through a slow back flip to expose the orbiter's belly to the station. Using digital cameras with 400-mm and 800-mm lenses, the station crew will photograph the heat shield tiles on the shuttle's belly to look for signs of damage.

Based on preliminary analysis of camera views during and after launch, along with laser scans carried out by the astronauts Wednesday, mission managers believe Discovery's heat shield is in good shape. But the rendezvous pitch maneuver provides the best close-up views of the shuttle's belly.

"We do that as part of the heat shield inspection procedures that are in place now," Zamka said in a NASA interview. "About 600 feet below the space station on the R-bar, (the imaginary line) between the space station and the surface of the Earth, Pam Melroy will initiate a three-quarter-of-a-degree per second flip. ItÕs nose going over the tail. And as sheÕs going over, we expose the underside of the shuttle, all the heat shield tiles to the space station. Onboard the space station we have crew members (who will be) systematically taking pictures of the tiles on the space shuttle."

Once the rendezvous pitch maneuver is complete, Melroy will position the shuttle directly in front of the space station with its tail pointing toward Earth and its open payload bay toward the station. From there, she will slowly guide the orbiter in for a docking at PMA-2. After leak checks to make sure the docking mechanisms are fully engaged, hatches between the shuttle and the station will be opened and the station crew will welcome their shuttle colleagues aboard around 10:33 a.m.

One of the first items on the agenda is to transfer a Soyuz seat-liner from the shuttle to the station so astronaut Dan Tani can replace astronaut Clay Anderson aboard the lab complex. Anderson, launched to the station last June, will return to Earth aboard Discovery while Tani remains behind with Expedition 16 commander Peggy Whitson and flight engineer Yuri Malenchenko.

Here is an updated timeline of today's events (including rev. B of the NASA television schedule; in EDT and mission elapsed time):

01:08 AM...01...13...30...ISS crew wakeup
01:38 AM...01...14...00...STS crew wakeup
02:43 AM...01...15...05...Group B computer powerup
02:58 AM...01...15...20...Begin rendezvous timeline
04:24 AM...01...16...46...NC-4 rendezvous rocket firing
05:45 AM...01...18...07...ISS in attitude for docking
05:55 AM...01...18...17...Terminal phase initiation (TI) burn
06:31 AM...01...18...53...Sunset
06:31 AM...01...18...53...ISS in rendezvous mode
06:45 AM...01...19...07...US solar arrays feathered
06:54 AM...01...19...16...Range: 10,000 feet
07:01 AM...01...19...23...Sunrise
07:02 AM...01...19...24...Range: 5,000 feet
07:08 AM...01...19...30...Range: 3,000 feet
07:12 AM...01...19...34...MC-4 rendezvous burn
07:16 AM...01...19...38...Range: 1,500 feet
07:17 AM...01...19...39...Rendezvous pitch start window open
07:21 AM...01...19...43...Range: 1,000 feet
07:24 AM...01...19...46...KU antenna to low power
07:25 AM...01...19...47...+R bar arrival; Discovery is directly below ISS
07:30 AM...01...19...52...Range: 600 feet
07:32 AM...01...19...54...Start pitch maneuver
07:32 AM...01...19...54...Noon
07:39 AM...01...20...01...RPM full photo window close
07:40 AM...01...20...02...End pitch maneuver
07:43 AM...01...20...05...Initiate pitch up maneuver
07:47 AM...01...20...09...RPM start window close
07:47 AM...01...20...09...Russian solar arrays feathered
07:54 AM...01...20...16...+V bar arrival; Discovery is directly in front of ISS
07:55 AM...01...20...17...Range: 300 feet
07:59 AM...01...20...21...Range: 250 feet
08:03 AM...01...20...25...Sunset
08:03 AM...01...20...25...Range: 200 feet
08:06 AM...01...20...28...Range: 170 feet
08:08 AM...01...20...30...Range: 150 feet
08:12 AM...01...20...34...Range: 100 feet
08:15 AM...01...20...37...Range: 75 feet
08:19 AM...01...20...41...Range: 50 feet
08:22 AM...01...20...44...Range: 30 feet; start station keeping
08:27 AM...01...20...49...End station keeping; push to dock
08:33 AM...01...20...55...Sunrise

08:33 AM...01...20...55...DOCKING

08:58 AM...01...21...20...Leak checks
08:58 AM...01...21...20...Post-rendezvous laptop reconfig
09:18 AM...01...21...40...Group B computer powerdown
09:28 AM...01...21...50...Airlock prepped for ingress
09:48 AM...01...22...10...Hatch opening
09:53 AM...01...22...15...Video playback of docking
10:33 AM...01...22...55...Welcome aboard!
10:38 AM...01...23...00...Safety briefing
11:00 AM...01...23...22...Mission status briefing on NASA TV
11:03 AM...01...23...25...Station robot arm grapples/unberths heat shield inspection boom
11:03 AM...01...23...25...Spacewalk tools transferred to ISS
11:23 AM...01...23...45...Inspection boom handoff to shuttle robot arm
11:33 AM...01...23...55...Soyuz seatliner transfer
12:03 PM...02...00...25...Airlock preps
01:58 PM...02...02...20...EVA-1: Procedures review
03:53 PM...02...04...15...EVA-1: Mask pre-breathe
05:08 PM...02...05...30...ISS crew sleep begins
05:38 PM...02...06...00...STS crew sleep begin
06:00 PM...02...06...22...Post-MMT briefring on NASA TV
07:00 PM...02...07...22...Daily video highlights reel
10:30 PM...02...10...52...Flight director update on NASA TV

08:30 PM, 10/24/07, Update: Shuttle tank performed well, Shannon says; no surprises and no apparent damage to shuttle heat shield

The shuttle Discovery's foam-covered external fuel tank performed well during launch Tuesday, NASA officials said today, shedding only a half-dozen pieces of insulation - all well after the period when such debris can pose an impact hazard - with no signs of damage to the orbiter's heat shield.

John Shannon, chairman of NASA's Mission Management Team, said a preliminary assessment of launch imagery, television shots from the shuttle during the climb to space and imagery shot by the astronauts as Discovery separated from the tank in space showed no major problems.

"We have not seen anything that would cause us any concern at all," he told reporters after an unusually short MMT meeting Wednesday. "We'll continue to look, we'll look at the solid rocket booster videos on Friday to make sure that's true, but there was nothing of any mass at all that was released during that (aerodynamically critical) time. Even the material that was released later on, we don't think it was anything that could have caused damage."

Today, the Discovery astronauts inspected the shuttle's reinforced carbon carbon - RCC - nose cap and wing leading edge panels using a laser scanner and a high-resolution digital camera. While the analysis is not yet complete, engineers have not seen any obvious signs of trouble with any of the critical panels, including three that raised concern before launch because of degradation in a protective coating.

"The performance of the tank was outstanding," Shannon said. "The tank really performed well. The RCC imagery, it was the same thing, no one has seen anything that was of any concern to them. They do a much more detailed analysis as the evening goes on, we'll continue to look at it, but there was really nothing. ... Right now we have no TPS (thermal protection system) issues at all."

External tank No. 120 was jokingly referred to as "Frankentank" by NASA insiders because of extensive foam dissection and modification work carried out in the wake of earlier problems. ET-120 was replaced for the first post-Columbia mission because of problems with hydrogen tank fuel sensors. The tank was sent back to Lockheed Martin's Michoud Assembly Facility in New Orleans to serve as a test article in the wake of a major foam loss during the first post-Columbia flight. It later was returned to flight status and assigned to Discovery.

Shannon said ET-120's performance during Discovery's launch was not a surprise, saying "I'm extremely confident in the tanks we're flying now, but we're just making them better."

Of the half-dozen pieces of foam that fell from the tank after solid rocket booster separation, one was an 8-by-6-inch chunk near one of the forward bipod struts used to anchor the shuttle's nose to the tank. Shannon said this is the third flight in a row where foam has separated from that area, apparently due to a phenomenon known as "cryo-pumping."

When air gets under the foam, either due to a crack or some other avenue, it liquifies because of the tank's ultra-low temperature. During launch, when the tank heats up due to atmospheric friction, the liquid can turn back into a gas with enough force to blow off small chunks of overlying foam. Shannon said engineers are unsure about what's going on in the area near the bipod strut. But given the timing of the releases, it does not pose an impact threat to the shuttle.

"We didn't see anything new on this tank that surprised us at all," he said. "The performance was just better. We'll go look at that one little area and see if there's some collateral damage potentially that is causing that same area to pop off on three flights in a row. It's not a concern to us because of when it comes off but you'd like to understand what's going on so we'll go look at that. But overall, the tank performed extremely well."

The Discovery astronauts plan to dock with the international space station early Thursday to kick off one of the most challenging orbital construction missions yet attempted. Here is a timeline of the final stages of the rendezvous (in EDT and mission elapsed time):

DATE/EDT...DD...HH...MM...EVENT

10/25/07
01:08 AM...01...13...30...ISS crew wakeup
01:38 AM...01...14...00...STS crew wakeup
02:53 AM...01...15...15...Group B computer powerup
02:58 AM...01...15...25...Begin rendezvous timeline
05:45 AM...01...18...07...ISS in attitude for docking
05:55 AM...01...18...17...TI burn
06:31 AM...01...18...53...Sunset
06:31 AM...01...18...53...Zvezda module lights on
06:31 AM...01...18...53...ISS in rendezvous mode
06:45 AM...01...19...07...US arrays feathered
06:54 AM...01...19...16...Range: 10,000 feet
07:01 AM...01...19...23...Sunrise
07:02 AM...01...19...24...Range: 5,000 feet
07:08 AM...01...19...30...Range: 3,000 feet
07:12 AM...01...19...34...MC-4 rendezvous burn
07:16 AM...01...19...38...Range: 1,500 feet
07:17 AM...01...19...39...Rendezvous pitch start window open
07:21 AM...01...19...43...Range: 1,000 feet
07:24 AM...01...19...46...KU antenna to low power
07:25 AM...01...19...47...+R bar arrival; Discovery is directl y below ISS
07:30 AM...01...19...52...Range: 600 feet
07:32 AM...01...19...54...Start pitch maneuver
07:32 AM...01...19...54...Noon
07:39 AM...01...20...01...RPM full photo window close
07:40 AM...01...20...02...End pitch maneuver
07:43 AM...01...20...05...Initiate pitch up maneuver
07:47 AM...01...20...09...RPM start window close
07:47 AM...01...20...09...Russian arrays feathered
07:54 AM...01...20...16...+V bar arrival; Discovery is directly in front of ISS
07:55 AM...01...20...17...Range: 300 feet
07:59 AM...01...20...21...Range: 250 feet
08:03 AM...01...20...25...Sunset
08:03 AM...01...20...25...Range: 200 feet
08:06 AM...01...20...28...Range: 170 feet
08:08 AM...01...20...30...Range: 150 feet
08:12 AM...01...20...34...Range: 100 feet
08:15 AM...01...20...37...Range: 75 feet
08:19 AM...01...20...41...Range: 50 feet
08:22 AM...01...20...44...Range: 30 feet; start station keeping
08:27 AM...01...20...49...End station keeping; push to dock
08:32 AM...01...20...54...Range: 10 feet
08:33 AM...01...20...55...Sunrise
08:33 AM...01...20...55...DOCKING

12:05 PM, 10/24/07, Update: Wing scans complete; no obvious problems seen

The shuttle Discovery's crew used a laser scanner and a high-resolution digital camera on the end of a long boom today to inspect the ship's reinforced carbon carbon nose cap and wing leading edge panels in a now-standard exercise for post-Columbia crews.

Today's scan took on a bit of added significance because of pre-launch concern over subtle degradation in a protective coating on three of the 44 wing leading edge panels, which experience some of the most extreme heating during re-entry. While it will take another few days to complete analysis of the inspection data, nothing obvious could be seen in video downlinked from the shuttle.

"This briefing ought to be pretty short and sweet," lead flight director Rick LaBrode told reporters in a later morning status report. I'm happy to report that things are going extremely well. When the crew woke up this morning, they got started with their day, they were in outstanding spirits, it's really a pleasure to see them on the video downlink and see how happy they are and ready to get going. The vehicle is operating perfectly, we're not tracking any major issues."

Asked about the wing leading edge inspections, LaBrode said "we completed the starboard wing scan, the nose cap and the port scan was in progress, near the very end, when I left the console. And all of that was going very well."

While he did not watch the entire downlink, "I personally did not see anything of significance. The report that I heard from some of the folks in the hall was that nobody's seen anything of any significance."

He also said there was not yet any detailed update on the performance of Discovery's external tank during the climb to orbit. NASA managers said Tuesday a quick look at ascent imagery showed what appeared to be a half dozen small pieces of foam insulation falling from the tank after the shuttle's solid-fuel boosters separated two minutes into flight. By that point, the shuttle is out of the dense lower atmosphere and debris is not as much of a concern.

"As far as the foam liberation, I don't have any additional data," LaBrode said. "What I had heard was that they had seen a couple of indications and they were after SRB sep, so that they really weren't in what is considered the timeframe of concern. But I don't have any additional data on that."

A briefing by Mission Management Team Chairman John Shannon is scheduled for 6 p.m.

5:25 AM, 10/24/07, Update: Astronauts prepare for heat shield inspection

The Discovery astronauts are working through a busy day in space today, carrying out a critical heat shield inspection and preparing the shuttle for docking Thursday with the international space station.

Commander Pam Melroy, pilot George Zamka, flight engineer Stephanie Wilson, Italian astronaut Paolo Nespoli, spacewalkers Scott Parazynski, Doug Wheelock and new space station crew member Dan Tani were awakened at 1:39 a.m. for their first full day in orbit. Today's wakeup music beamed up from mission control was a recording of "Lord of the Dance" performed by John Langstaff.

"Good morning Discovery, and a special good morning to you today, Pam," astronaut Shannon Lucid radioed. "Welcome to your first full space day."

"Thanks, Shannon," replied Melroy, who lists jazz and tap dancing among her hobbies. "That was one of my favorite songs. Thanks to my husband Doug. I love you."

"And we all really enjoyed the music, too, Pam."

The major item on the crew's agenda today is a detailed inspection of Discovery's reinforced carbon carbon nose cap and RCC wing leading edge panels using a laser scanner and a high-resolution camera.

The scanner and camera, mounted on the end of a 50 foot boom known as the orbiter boom sensor system, or OBSS, will be moved along the front of both wings and the nose cap by Discovery's robot arm to look for any signs of launch-related impact damage. The inspection was scheduled to begin around 6 a.m.

In a slight change in procedure from past flights, one of the multiple passes along the wing leading edge panels will be carried out at a slower speed than usual to improve the view of any abnormalities in a protective coating. Three of the 44 wing leading edge panels on Discovery - RCC panels 9 right, 13 right and 12 left - have known areas of coating degradation and engineers want to make sure those areas do not get worse.

"We are slowing down just one of the scans, one pass on each one of the wings, just to give us an opportunity to get a little bit better, higher-fidelity imagery with our laser scans," said LeRoy Cain, launch integration manager at the Kennedy Space Center.

Before launch, an independent NASA engineering group recommended delaying Discovery's flight to replace the panels after concluding the root cause of the degradation was not as well understood as previously believed. Without a known root cause, they argued, it is not possible to make accurate predictions about how such degradation might evolve over time.

NASA managers, however, cleared Discovery for launch as is based on past experience with the panels - the degradation has been fairly stable over two previous missions - and because any major change for the worse would be spotted by the crew during their normal heat shield inspections and if necessary, repairs could be made.

But in a bid to gather more details about the issue and how the degradation changes over time, a slower scan of the areas in question will be carried out today.

"Our big ticket item for flight day two is scanning the wing leading edges and the nose cap," shuttle flight director Rick LaBrode said at a pre-launch briefing. "They start with the starboard wing, and you can see it looks like they do it multiple times and really, they do because they're coming at it from different angles. They come from the bottom for the first pass and then they go around to the top. They do the nose cap and move over to the port wing.

"Some of the other significant activities we do on flight day two are getting ready for the rendezvous the next day. We install the centerline camera, we deploy the orbiter docking system ring, check out the (rendezvous) tools, the handheld laser and those. And the crew also will be doing (spacesuit) checkout for the two suits that Scott Parazynski and Doug Wheelock will be using for the first EVA. They'll do a quick checkout and get those ready for transfer as soon as we get docked."

A mission status briefing is scheduled for 11:30 a.m. A second briefing, following today's Mission Management Team meeting, is planned for 6 p.m. Here is an updated timeline of today's activities (in EDT and mission elapsed time; includes revision A of the NASA TV schedule):

EDT........DD...HH...MM...EVENT

10/24/07
01:38 AM...00...14...00...Crew wakeup
04:38 AM...00...17...00...Ergometer setup
04:53 AM...00...17...15...NC-2 rendezvous rocket firing
04:53 AM...00...17...15...OBSS unberth
05:53 AM...00...18...15...OBSS starboard wing survey
07:38 AM...00...20...00...Spacesuit checkout preps
07:38 AM...00...20...00...SAFER emergency jetpack checkout
07:48 AM...00...20...10...OBSS nose cap survey
08:08 AM...00...20...30...Crew meals begin
09:08 AM...00...21...30...Spacesuit checkout
09:48 AM...00...22...10...OBSS port wing survey
10:23 AM...00...22...45...Spacesuit transfer preps
11:30 AM...00...23...52...Mission status briefing on NTV
11:48 AM...01...00...10...OBSS berthing
11:58 AM...01...00...20...Laser scanner downlink
12:23 PM...01...00...45...Centerline camera installation
12:53 PM...01...01...15...Orbiter docking system ring extension
01:23 PM...01...01...45...OMS rocket pod survey
01:58 PM...01...02...20...Rendezvous tools checkout
03:29 PM...01...03...51...NC-3 rendezvous rocket firing
05:38 PM...01...06...00...Crew sleep begins
06:00 PM...01...06...22...Post-MMT briefing on NTV
07:00 PM...01...07...22...Daily video highlights reel on NTV

02:30 PM, 10/23/07, Update: Shuttle Discovery launched (UPDATED at 3 p.m. with post-launch news conference; quotes and details; correcting time of docking)

The shuttle Discovery, carrying seven astronauts and a critical connecting module for the international space station, roared to life and rocketed into orbit today, kicking off a high-stakes five-spacewalk mission considered by many the most complex orbital construction work ever attempted.

"I don't think there's ever been an astronaut who doesn't consider their flight the most dramatic, exciting, complex mission ever," lead spacewalker Scott Parazynski said before launch. "But ours is!"

With its three hydrogen-fueled main engines roaring at full throttle, Discovery's twin solid-fuel boosters ignited with a rush of fire and thunder at 11:38:19 a.m., instantly pushing the huge spacecraft away from pad 39A.

Seconds later, Discovery's flight computers sent commands to the booster steering system, rolling the spacecraft about its vertical axis to put the crew in a heads down orientation as the spaceplane arced out over the Atlantic Ocean on a trajectory paralleling the East Coast of the United States.

NASA managers were worried early today about an ice buildup on an umbilical on the lower section of the shuttle's external fuel tank and by threatening weather. But as the morning wore on, the anticipated cloud development held off, engineers decided the ice would most likely shake off at launch and Discovery was cleared for launch.

"OK, Pambo, on behalf of your KSC family, I'd like to wish you good luck, Godspeed, have a little fun up there," Launch Director Mike Leinbach radioed the crew a few minutes before launch.

"Copy that, Mike," replied Melroy, the second woman to command a space shuttle. "We feel a tremendous amount of pride in the 10A and Discovery team and a lot of gratitude for the hard work to get us here. And we're ready to take Harmony to her new home."

Joining Melroy on Discovery's flight deck were Marine Corps pilot George Zamka, flight engineer Stephanie Wilson and Doug Wheelock, an Army helicopter pilot. Strapped in on the orbiter's lower deck were physician-astronaut Parazynski, Italian astronaut Paolo Nespoli and Dan Tani, a space station crew member hitching a ride to the lab complex aboard Discovery. Tani will replace station engineer Clay Anderson, who will return to Earth aboard the shuttle.

Television views from a camera mounted on Discovery's external fuel tank provided spectacular views of the Florida spaceport dropping away and then the limb of the Earth as the ship headed for orbit. Bill Gerstenmaier, chief of space flight operations for NASA, said a quick look at the video indicated about a half-dozen small pieces of foam insulation fell away from the shuttle's external tank during the climb to space.

But in all cases, Gerstenmaier said, the debris separated after Discovery's solid-fuel boosters were jettisoned and well beyond the regime in which the denser lower atmosphere can slow lightweight foam enough to cause impact damage when the shuttle can run into it at a high relative velocity.

"We took a quick look at the video and we saw probably six instances of foam loss off the tank and they were all after solid rocket booster separation," Gerstenmaier said. "So in that sense, they're not a concern from a damage-to-the-orbiter standpoint. ... We'll see when we get some good pictures of the external tank here later today or tomorrow."

While Gerstenmaier was addressing reporters at a post-launch news conference, astronaut Terry Virts in mission control at the Johnson Space Center in Houston, radioed Melroy with a debris update.

"Pam, there were several events noted during ascent," he said. "They occurred after the critical transport mach number. We will continue to look at it. This is just preliminary only, but it did look like a clean ascent. Also there was some ice on the aft LH2 (liquid hydrogen) lines on the tank, we saw that pre launch and it cleared right at T-0 as expected."

The astronauts photographed the tank shortly after it separated from the shuttle in orbit and Parazynski reported "no visible, at least to the naked eye, loss of big pieces of foam."

The crew will carry out a detailed inspection of the shuttle's nose cap and wing leading edge panels using a laser scanner and high-resolution camera on Wednesday while engineers on the ground continue analysis of long-range tracking camera and launch pad footage. In the meantime, NASA managers were thrilled with today 's launching.

"This is a great start to a very challenging mission in front of us," Gerstenmaier said. "If I look at this mission and what's coming up for us, we're combining, effectively, activities we've done on at least four other missions, all into one mission. So this is a pretty exciting mission. We're going to do a solar array deploy, a radiator deploy, a pressurized module addition, just a tremendous series of challenges in front of us.

"I think the teams are ready, really prepared for any eventualilty. ... I can't think of a better start to this mission than what we got today. So again, hats off to the KSC folks and the orbiter folks who gave us a great vehicle and a great ride to start a great mission."

Discovery took off at roughly the moment Earth's rotation carried the launch pad into the plane of the space station's orbit. If all goes well, Melroy will manually guide the shuttle to a linkup with the station around 8:35 a.m. Thursday.

Discovery's docking and the usual welcome aboard ceremony will have an unusual flavor this time around as Expedition 16 commander Peggy Whitson, the station's first female commander, welcomes Melroy, probably the final woman to command a shuttle before the program is retired in 2010. Both women flew together in 2002 when Whitson served as flight engineer of the fifth station expedition and Melroy visited as pilot of the shuttle Atlantis during mission STS-112.

"One of the moments I'm looking forward to the most is when the hatch opens and I see Peggy's face on the other side and we reach through for the traditional handshake," Melroy said in an interview. "That will be a really special moment for me."

Whitson said the timing of their flights was a coincidence, "but I do think it is special, not only special just for Pam and I because, you know, we have flown in space before, but the experience of having two women up there at the same time will hopefully be an inspiration to somebody."

"I was inspired when I was young by the Apollo era astronauts and in particular, I was motivated to become an astronaut when they selected the first female astronauts," she said. "I would hope that we could be a role model like that."

The day after docking, the astronauts will use the station's robot arm to pull the 31,500-pound Harmony module from Discovery's cargo bay as part of the first of the mission's five spacewalks.

Harmony will be temporarily mounted on the left side of the station's central Unity module. After the shuttle departs, Whitson, flight engineer Yuri Malenchenko and Tani will detach the station's main shuttle docking port, known as pressurized mating adapter No. 2, mount it on Harmony and then use the station's robot arm to move both components on the front end of the Destiny laboratory module.

Whitson and Tani plan to stage two spacewalks in November to connect Harmony to the station's cooling system and power grid to clear the way for launch of the European Space Agency's Columbus research lab aboard the shuttle Atlantis in December. Columbus will be attached to Harmony's right-side port while Japan's Kibo lab module will be connected to Harmony's left hatch next year.

"Harmony has six different ports that we can add modules onto to build the station," said Whitson. "So it's, it's our next big connecting piece in our puzzle of putting this huge station together on orbit."

Attaching a new pressurized module would have been the highlight of many past assembly missions. But for Discovery's crew, it is just the beginning. The second major objective of the flight is the disconnection and relocation of a huge set of solar arrays known as P6. Designed as the sixth and final segment of the port, or left, side of the station's main power truss, P6 was mounted at the center of the station in December 2000 to provide power to the U.S. segment during the initial stages of assembly.

Now, with identical solar panels in place on the left and right sides of the main power truss, NASA needs to move P6 to its permanent position on the far left end of the beam. The 35,000-pound segment's huge arrays, stretching 240 feet from tip to tip, were stowed during shuttle missions last December and June. Power and cooling lines were disconnected during an August flight, setting the stage for the massive truss's detachment, relocation and re-extension during Discovery's mission.

The station's robot arm cannot reach far enough on its own to make the move. So the station arm, after handing P6 off to the shuttle's space crane, will be moved by the station's mobile transporter to the far end of the power truss. At that point, the shuttle arm will hand the truss segment back to the station arm and Parazynski and Wheelock, making their third spacewalk by that point, will oversee its attachment to the P5 truss segment.

"Moving the P6 solar array will be a major activity," Melroy said in a NASA interview. "On our second spacewalk - our first spacewalk is all about (Harmony) - we'll be using the robotic arm in one location to actually reach around and pull P6 off ... with the assistance of our spacewalkers.

"Once the P6 has been detached from the space station, then the robotic arm will move it around to the port side of the shuttle, at which point it will be handed off to the shuttle arm. The shuttle robotic arm will take control of the P6 truss while the space station robotic arm is reconfigured and rolled out on the mobile transporter, the mobile platform, all the way to the far end of the port truss. And then, we'll use the station arm to take it back and install it in its final location.

"This is pretty nearly the design-limiting case for the robotic arm of the space station, so it's out at its full extension, trying to get that truss out there," Melroy said. "We'll have the help of the spacewalkers on the third spacewalk to do that. So, all these activities will actually span three days, three full days, two spacewalks with robotics in the middle."

Discovery is scheduled to land back at the Kennedy Space Center on Nov. 6.

Here is an abbreviated NASA television schedule of major mission milestones (in EDT/EST and mission elapsed time):

ORB.EVENT..................................DD/HH:MM...EDT........GMT

TUESDAY, OCTOBER 23 - Flight Day 1
....LAUNCH.................................00/00:00...11:38 AM...15:38
1...POST LAUNCH NEWS CONFERENCE............00/01:07...12:45 PM...16:45
2...PAYLOAD BAY DOOR OPENING...............00/01:27...01:05 PM...17:05
3...RMS CHECKOUT...........................00/03:45...03:23 PM...19:23
3...PLAYBACK OF ET SEP VIDEO...............00/04:20...03:58 PM...19:58
5...DISCOVERY CREW SLEEP BEGINS............00/06:00...05:38 PM...21:38
5...LAUNCH ENGINEERING REPLAYS FROM KSC....00/06:22...06:00 PM...22:00
6...FLIGHT DAY 1 HIGHLIGHTS................00/07:22...07:00 PM...23:00

WEDNESDAY, OCTOBER 24 - FD 2
10...DISCOVERY CREW WAKE UP (FD 2).........00/14:00...01:38 AM...05:38
12...RMS GRAPPLE & UNBERTH OF OBSS.........00/17:15...04:53 AM...08:53
13...HEAT SHIELD SURVEY BEGINS.............00/18:15...05:53 AM...09:53
20...DISCOVERY CREW SLEEP BEGINS...........01/06:00...05:38 PM...21:38
21...POST-MMT BRIEFING.....................01/06:22...06:00 PM...22:00
21...FLIGHT DAY 2 HIGHLIGHTS...............01/07:22...07:00 PM...23:00

THURSDAY, OCTOBER 25 - FD 3
26...DISCOVERY CREW WAKE UP (FD 3).........01/14:00...01:38 AM...05:38
30...DISCOVERY/ISS DOCKING.................01/20:57...08:35 AM...12:35
32...DISCOVERY/ISS CREW HATCH OPENING......01/22:55...10:33 AM...14:33
32...MISSION STATUS BRIEFING...............01/23:22...11:00 AM...15:00
36...DISCOVERY CREW SLEEP BEGINS...........02/06:00...05:38 PM...21:38
36...POST-MMT BRIEFING.....................02/06:22...06:00 PM...22:00
37...FLIGHT DAY 3 HIGHLIGHTS...............02/07:22...07:00 PM...23:00

FRIDAY, OCTOBER 26 - FD 4
42...DISCOVERY/ISS CREW WAKE UP (FD 4).....02/14:00...01:38 AM...05:38
45...EVA #1 BEGINS FROM ISS QUEST AIRLOCK..02/18:50...06:28 AM...10:28
47...SSRMS GRAPPLE & UNBERTH NODE 2........02/22:45...10:23 AM...14:23
49...SSRMS INSTALLS NODE 2 ONTO NODE 1.....03/00:55...12:33 PM...16:33
49...EVA #1 ENDS...........................03/01:30...01:08 PM...17:08
50...NODE 1 - NODE 2 LEAK CHECKS...........03/02:45...02:23 PM...18:23
50...MISSION STATUS BRIEFING...............03/03:22...03:00 PM...19:00
52...POST-MMT BRIEFING.....................03/05:22...05:00 PM...21:00
52...DISCOVERY/ISS CREW SLEEP BEGINS.......03/06:00...05:38 PM...21:38
52...FLIGHT DAY 4 HIGHLIGHTS...............03/06:22...06:00 PM...22:00

SATURDAY, OCTOBER 27 - FD 5
57...ISS FLIGHT DIRECTOR UPDATE REPLAY.....03/13:22...01:00 AM...05:00
57...DISCOVERY CREW WAKE UP (FD 5).........03/14:00...01:38 AM...05:38
58...ISS CREW WAKE UP......................03/14:30...02:08 AM...06:08
62...NODE 2 HATCH OPEN AND INGRESS.........03/21:25...09:03 AM...13:03
64...MISSION STATUS BRIEFING...............03/23:52...11:30 AM...15:30
65...U.S. PAO EVENT........................04/02:25...02:03 PM...18:03
67...POST-MMT BRIEFING.....................04/05:22...05:00 PM...21:00
67...DISCOVERY CREW SLEEP BEGINS...........04/05:30...05:08 PM...21:08
68...FLIGHT DAY 5 HIGHLIGHTS...............04/06:22...06:00 PM...22:00

SUNDAY, OCTOBER 28 - FD 6/FD - 7
73....DISCOVERY/ISS CREW WAKE UP (FD 6)....04/13:30...01:08 AM...05:08
75...SSRMS GRAPPLES P6 TRUSS...............04/17:15...04:53 AM...08:53
76...EVA #2 BEGINS.........................04/18:20...05:58 AM...09:58
77...P6 DETACHMENT FROM Z1.................04/20:35...08:13 AM...12:13
80...EVA #2 ENDS...........................05/01:00...12:38 PM...16:38
81...MISSION STATUS BRIEFING...............05/02:52...02:30 PM...18:30
83...DISCOVERY CREW SLEEP BEGINS...........05/05:00...04:38 PM...20:38
83...FLIGHT DAY 6 HIGHLIGHTS...............05/05:22...05:00 PM...21:00

MONDAY, OCTOBER 29 - FD 7/FD 8
88...DISCOVERY/ ISS CREW WAKE UP (FD 7)....05/13:00...12:38 AM...04:38
90...SSRMS HANDOFF P6 TO SRMS..............05/15:30...03:08 AM...07:08
91...MT MOVES FROM WORKSITE 4 TO 8.........05/17:45...05:23 AM...09:23
94...SRMS HANDOFF P6 BACK TO SSRMS.........05/21:30...09:08 AM...13:08
95...MISSION STATUS BRIEFING...............05/22:52...10:30 AM...14:30
97...U.S. PAO EVENT........................06/02:05...01:43 PM...17:43
99...DISCOVERY CREW SLEEP BEGINS...........06/05:00...04:38 PM...20:38
99...FLIGHT DAY 7 HIGHLIGHTS...............06/05:22...05:00 PM...21:00

TUESDAY, OCTOBER 30 - FD 8/FD 9
104...DISCOVERY/ISS CREW WAKE UP (FD 8)....06/13:00...12:38 AM...04:38
107...EVA #3 BEGINS........................06/17:50...05:28 AM...09:28
108...SSRMS INSTALLS P6 ONTO P5 TRUSS......06/18:25...06:03 AM...10:03
112...EVA #3 ENDS..........................07/01:00...12:38 PM...16:38
112...P6 4B ARRAY REDEPLOYMENT BEGINS......07/01:50...01:28 PM...17:28
113...MISSION STATUS BRIEFING..............07/02:52...02:30 PM...18:30
115...DISCOVERY CREW SLEEP BEGINS..........07/05:00...04:38 PM...20:38
115...FLIGHT DAY 8 HIGHLIGHTS..............07/05:22...05:00 PM...21:00

WEDNESDAY, OCTOBER 31 - FD 9/FD 10
120...DISCOVERY/ISS CREW WAKE UP (FD 9)....07/13:00...12:38 AM...04:38
124...JOINT CREW NEWS CONFERENCE...........07/20:10...07:48 AM...11:48
130...DISCOVERY CREW SLEEP BEGINS..........08/04:00...03:38 PM...19:38
130...FLIGHT DAY 9 HIGHLIGHTS..............08/04:22...04:00 PM...20:00
135...DISCOVERY/ISS CREW WAKE UP (FD 10)...08/12:00...11:38 PM...03:38

THURSDAY, NOVEMBER 1 - FD 10/FD 11
138...EVA #4 BEGINS........................08/16:50...04:28 AM...08:28
141...EVA #4 ENDS..........................08/21:35...09:13 AM...13:13
143...MISSION STATUS BRIEFING..............08/23:52...11:30 AM...15:30
145...DISCOVERY CREW SLEEP BEGINS..........09/03:30...03:08 PM...19:08
146...FLIGHT DAY 10 HIGHLIGHTS.............09/04:22...04:00 PM...20:00
150...DISCOVERY/ISS CREW WAKE UP (FD 11)...09/11:30...11:08 PM...03:08

FRIDAY, NOVEMBER 2 - FD 11/FD 12
154...EVA #5 BEGINS........................09/16:20...03:58 AM...07:58
158...EVA #5 ENDS..........................09/23:00...10:38 AM...14:38
159...MISSION STATUS BRIEFING..............10/00:52...12:30 PM...16:30
161...DISCOVERY CREW SLEEP BEGINS..........10/03:00...02:38 PM...18:38
161...FLIGHT DAY 11 HIGHLIGHTS.............10/03:22...03:00 PM...19:00
166...DISCOVERY/ISS CREW WAKE UP (FD 12)...10/11:00...10:38 PM...02:38

SATURDAY, NOVEMBER 3 - FD 12/FD 13
168...DISCOVERY/ISS FINAL TRANSFERS RESUME.10/14:50...02:28 AM...06:28
170...DISCOVERY/ISS FINAL HATCH CLOSURE....10/17:15...04:53 AM...08:53
172...MISSION STATUS BRIEFING..............10/20:22...08:00 AM...12:00
176...DISCOVERY CREW SLEEP BEGINS..........11/02:00...01:38 PM...17:38
176...FLIGHT DAY 12 HIGHLIGHTS.............11/02:22...02:00 PM...18:00
181...DISCOVERY/ISS CREW WAKE UP (FD 13)...11/10:00...09:38 PM...01:38

SUNDAY, NOVEMBER 4 - FD 13/FD 14
183...DISCOVERY/ISS UNDOCKING..............11/13:56...01:34 AM...05:34

ORB.EVENT..................................DD/HH:MM...EST........GMT

184...FINAL SEPARATION FROM ISS............11/15:39...02:17 AM...07:17
186...HEAT SHIELD LATE INSPECTION..........11/18:10...04:48 AM...09:48
188...MISSION STATUS BRIEFING..............11/20:22...07:00 AM...11:13
191...DISCOVERY CREW SLEEP BEGINS..........12/02:00...12:38 PM...17:38
192...FLIGHT DAY 13 HIGHLIGHTS.............12/02:22...01:00 PM...18:00
197...DISCOVERY CREW WAKE UP (FD 14).......12/10:00...08:38 PM...01:38

MONDAY, NOVEMBER 5 - FD 14/FD 15
199...FCS CHECKOUT.........................12/13:35...12:13 AM...05:13
200...RCS HOT FIRE.........................12/14:45...01:23 AM...06:23
202...U.S. PAO EVENT.......................12/17:35...04:13 AM...09:13
203...MISSION STATUS BRIEFING..............12/20:22...07:00 AM...12:00
207...DISCOVERY CREW SLEEP BEGINS..........13/02:00...12:38 PM...17:38
207...FLIGHT DAY 14 HIGHLIGHTS.............13/02:22...01:00 PM...18:00
209...POST-MMT BRIEFING....................13/05:22...04:00 PM...21:00
212...DISCOVERY CREW WAKE UP (FD 15).......13/10:00...08:38 PM...01:38
214...DEORBIT PREPARATIONS BEGIN...........13/13:10...11:48 PM...04:48

TUESDAY, NOVEMBER 6 - FD 15
215...PMA-2 RELOCATION TO HARMONY BEGINS...13/14:17...12:55 AM...05:55
215...PAYLOAD BAY DOOR CLOSING.............13/14:29...01:07 AM...06:07
217...DEORBIT BURN.........................13/17:09...03:47 AM...08:47
218...KSC LANDING..........................13/18:12...04:50 AM...09:50

10:33 AM, 10/23/07, Update: Weather, ice buildup assessed

The Discovery astronauts strapped in for launch today at 11:38:19 a.m. to kick off an ambitious space station assembly mission. There are no technical problems at pad 39A, but NASA managers are assessing the potential impact of an ice buildup around an umbilical near the base of the shuttle's external fuel tank while forecasters monitor the weather. Conditions were observed to be "go" most of the morning, but clouds were expected to build up as launch time approached.

This status report will be updated after Discovery takes off or as conditions warrant.

5:20 AM, 10/23/07, Update: Shuttle fueled for launch

The shuttle Discovery's external tank has been loaded with a half-million gallons of liquid oxygen and hydrogen rocket fuel in preparation for launch today at 11:38:22 a.m. on a space station assembly mission.

The three-hour fueling procedure began on time at 2:13 a.m. and ended at 5:12 a.m. There are no technical problems of any significance at pad 39A and the only concern remains the weather, with forecasters calling for a 60 percent chance of clouds and rain that could cause a delay.

NASA television coverage begins at 6:30 a.m. Here is a timeline of the rest of today's countdown (in EDT):

EDT...........EVENT

05:13 AM......Begin 2-hour 30-minute built-in hold (T-minus 3 hours)
05:13 AM......Closeout crew to white room
05:13 AM......External tank in stable replenish mode
05:43 AM......Astronaut support personnel comm checks
06:00 AM......Crew breakfast/photo op
06:18 AM......Pre-ingress switch reconfig
06:30 AM......NASA Television coverage begins (replay of crew photo op)
07:08 AM......Final crew weather briefing
07:18 AM......Crew dons pressure suits

07:43 AM......Countdown resumes (T-minus 3 hours)
07:48 AM......Crew departs O&C building
08:18 AM......Crew ingress
09:08 AM......Astronaut comm checks
09:23 AM......Hatch closure
10:18 AM......White room closeout

10:23 AM......Begin 10-minute built-in hold (T-minus 20m)
10:33 AM......NASA test director (NTD) countdown briefing

10:33 AM......Resume countdown (T-minus 20m)
10:34 AM......Backup flight computer to OPS 1
10:38 AM......KSC area clear to launch

10:44 AM......Begin final built-in hold (T-minus 9m)
11:14 AM......NTD launch status verification

11:29:22 AM...Countdown resumes (T-minus 9m)
11:30:52 AM...Orbiter access arm retraction
11:33:22 AM...Launch window opens
11:33:22 AM...Hydraulic power system (APU) start
11:33:27 AM...Terminate LO2 replenish
11:34:22 AM...Purge sequence 4 hydraulic test
11:34:22 AM...Inertial measurement units to inertial
11:34:27 AM...Aerosurface profile
11:34:52 AM...Main engine steering test
11:35:27 AM...LO2 tank pressurization
11:35:47 AM...Fuel cells to internal reactants
11:35:52 AM...Clear caution-and-warning memory
11:36:22 AM...Crew closes visors
11:36:25 AM...LH2 tank pressurization
11:37:32 AM...Solid rocket booster (SRB) joint heater deactivation
11:37:51 AM...Shuttle flight computers take control of countdown
11:38:01 AM...SRB steering test
11:38:15 AM...Main engine start (T-6.6 seconds)
11:38:22 AM...SRB ignition
11:46:46 AM...Main engine shutdown command
12:15 PM......OMS-2 orbit circularization rocket firing
12:28 PM......Post orbit insertion timeline begins
12:45 PM......Post-launch news conference
02:08 PM......Laptop computer network setup
02:30 PM......NC-1 rendezvous rocket firing
02:48 PM......Group B computer powerdown
03:08 PM......Shuttle robot arm (SRMS) powerup
03:08 PM......Wing leading edge sensor system setup
03:23 PM......Robot arm checkout
03:28 PM......External tank handheld photography downlink
03:38 PM......Umbilical well camera downlink
03:58 PM......ET video downlink
04:08 PM......Robot arm powerdown
05:38 PM......Crew sleep begins
06:00 PM......Launch engineering replays
07:00 PM......Daily video highlights reel on NASA TV

01:00 PM, 10/22/07, Update: Shuttle countdown on track; weather now 60 percent 'no go'

The shuttle Discovery's countdown is ticking smoothly toward launch Tuesday on a space station assembly mission, but forecasters say the weather has taken a turn for the worse and the odds are now 60 percent "no go" because of expected clouds and isolated showers in the Kennedy Space Center area.

Hoping for the best, engineers plan to begin loading Discovery's external tank with a half million gallons of liquid oxygen and hydrogen rocket fuel starting at 2:13 a.m. Tuesday for a launch attempt at 11:38:22 a.m.

"At this point in the count, we're on schedule," said NASA Test Director Steve Payne. "Our systems are all good, we're in great shape and there are no issues we're tracking."

The shuttle must launch within about five minutes of the moment Earth's rotation carries the launch pad into the plane of the space station's orbit. To improve performance and abort options, NASA typically targets the middle of the 10-minute launch window - in this case, 11:38:22 a.m. - giving the crew just five minutes to get off the pad.

For Discovery's mission, the close of the window can be extended slightly, from 11:43:22 a.m. to 11:46:33 a.m., but a launch during that additional three-minute 11-second period would force a one-day delay for docking with the space station. In that case, Discovery's flight would be extended one day.

NASA normally foregoes so-called "flight-day four" dockings because it compresses the time available to accomplish mission objectives. But Discovery is equipped with a new power system that enables the shuttle to tap into the space station's solar power grid. That, in turn, allows a mission extension without using up the shuttle's own power supplies.

But even with a flight-day four rendezvous, Discovery's launch window Tuesday will only be open for eight minutes and 11 seconds. Shuttle weather officer Kathy Winters said today she expects a 60 percent chance for showers and low clouds at launch time that would force a delay.

"We are concerned about the weather tomorrow for launch, mainly due to the fact that the launch time is right around the time our sea breeze will start developing," she said. "We're in a southeasterly flow pattern so usually what happens is the sea breeze develops and then pushes inland. The time of the launch is the same time that sea breeze will be forming and so with that, and the moisture in the atmosphere, we're expecting some cumulus cloud development. Also, we should see some coastal showers in the area and we also could have concern for (a low cloud) ceiling in the area right around that time. So with that, we do have a 60 percent chance of KSC weather prohibiting launch."

Conditions in Florida are expected to improve to 60 percent "go" on Wednesday and Thursday, but forecasters are predicting out-of-limits winds and rain showers at all three of NASA's emergency runways in Spain and France both days. At least one European runway must be acceptable for a launch to proceed.

02:00 PM, 10/21/07, Update: MMT clears Discovery for flight; forecast marginally favorable; Cain defends RCC decision (mission preview)

Nine years after the United States and Russia began building the international space station, NASA is poised for what many agency insiders consider the most difficult assembly mission attempted to date, one that will test the limits of orbital construction.

The space shuttle Discovery, carrying an international crew of seven and an Italian-built multi-port station module, is scheduled for liftoff from launch complex 39A at the Kennedy Space Center at 11:38:20 a.m. Tuesday. In a strange coincidence, the launch time and day of week are identical to those of Challenger's final flight.

At the controls aboard Discovery will be Pam Melroy, the second woman to command a space shuttle, and rookie pilot George Zamka, a colonel in the Marine Corps. Their crewmates are flight engineer Stephanie Wilson, Italian astronaut Paolo Nespoli and spacewalkers Scott Parazynski, a physician, Doug Wheelock, a veteran Army helicopter pilot, and Dan Tani, who is hitching a ride to the lab complex to join the Expedition 16 crew.

Forecasters are predicting a 60 percent chance of acceptable weather Tuesday and Wednesday, improving to 70 percent "go" by Thursday. But depending on when an expected frontal system moves through the area, the outlook could change dramatically, with low clouds, rain and thunderstorms. Complicating the issue, the weather at two of NASA's three emergency runways in Spain and France are predicted to be "no go" Tuesday and all three are expected to be out of limits Wednesday and Thursday. At least one overseas landing site must be available for launch.

Hoping for the best, NASA's Mission Management Team met Sunday and Chairman LeRoy Cain said there were no technical issues of any significance. He also vigorously defended an earlier decision to press ahead with launch despite mixed interpretation of subtle test data indicating possible problems with the coating that protects the ship's critical wing leading edge panels.

While there are no data indicating any imminent failure with three panels aboard Discovery that have areas of degraded coating, engineers do not understand what causes the coating to break down. As such, they cannot predict how degraded areas might change from flight to flight. NASA managers decided last week to clear Discovery for flight based on the crew's ability to detect and repair coating damage in orbit, along with past flight history that indicates the areas of concern are relatively stable.

"We believe, to the best of our ability to know today, this risk is certainly lower than some of the more significant risks that we take becauseÊof the inherent nature of this vehicle," Cain said. "We feel very confident we have a vehicle that's safe to go fly. We would not launch if we didn't think that was true."

The primary goal of the 120th shuttle mission is delivery of node 2, or Harmony, a roomy 31,500-pound module measuring 23.6 feet long and 14.5 feet wide that will serve as the gateway to European and Japanese research modules that will form the scientific heart of the space station and permit the crew's eventual expansion from three to six.

"Harmony has six different ports that we can add modules onto to build the station," said Expedition 16 commander Peggy Whitson, the first woman to command the station. "So it's, it's our next big connecting piece in our puzzle of putting this huge station together on orbit.

"Node 2 is required to power and provide the thermal heat rejection for the science laboratory modules that'll be coming up, the one built by the European Space Agency and the one built by the Japanese space agency. So it's a pretty key module for us, for the continued development of the station. It's an important step."

Harmony, providing an additional 1,230 cubic feet of habitable volume, will be temporarily attached to the left side of the station's central Unity module, which connects the U.S. and Russian segments of the complex. After Discovery departs, Whitson, Tani and Expedition 16 flight engineer Yuri Malenchenko will use the station's robot arm to detach the lab's main shuttle docking port so it can be bolted onto Harmony. Then Harmony will be detached and permanently mounted on the front end of the U.S. Destiny laboratory module.

Attaching a new pressurized module would have been the highlight of many past assembly missions. But for Discovery's crew, it is just the beginning. The second major objective of the flight is the long-awaited disconnection and relocation of a huge set of solar arrays known as P6. Designed as the sixth and final segment of the port, or left, side of the station's main power truss, P6 was mounted at the center of the station in December 2000 to provide power to the U.S. segment during the initial stages of assembly.

Now, with identical solar panels in place on the left and right sides of the main power truss, NASA needs to move P6 to its permanent position on the far left end of the beam. The 35,000-pound segment's huge arrays, stretching 240 feet from tip to tip, were stowed during shuttle missions last December and June. Power and cooling lines were disconnected during an August flight, setting the stage for the massive truss's detachment, relocation and re-extension during Discovery's mission.

Complicating the work, the station's robot arm cannot reach far enough on its own to make the move. So the station arm, after handing P6 off to the shuttle's space crane, will be moved by the station's mobile transporter to the far end of the power truss. At that point, the shuttle arm will hand the truss segment back to the station arm and Parazynski and Wheelock, making their third spacewalk by that point, will oversee its attachment to the P5 truss segment.

"Moving the P6 solar array will be a major activity," Melroy said in a NASA interview. "On our second spacewalk - our first spacewalk is all about node 2 - we'll be using the robotic arm in one location to actually reach around and pull P6 off ... with the assistance of our spacewalkers.

"Once the P6 has been detached from the space station, then the robotic arm will move it around to the port side of the shuttle, at which point it will be handed off to the shuttle arm. The shuttle robotic arm will take control of the P6 truss while the space station robotic arm is reconfigured and rolled out on the mobile transporter, the mobile platform, all the way to the far end of the port truss. And then, we'll use the station arm to take it back and install it in its final location.

"This is pretty nearly the design-limiting case for the robotic arm of the space station, so it's out at its full extension, trying to get that truss out there," Melroy said. "We'll have the help of the spacewalkers on the third spacewalk to do that. So, all these activities will actually span three days, three full days, two spacewalks with robotics in the middle."

Last December, attempts to stow the folding blankets making up one side of the P6 array ran into problems when several of the slats making up the blankets folded the wrong way along their creases. The astronauts ultimately were successful and engineers don't anticipate major problems re-extending the arrays.

They'd better be right. The station's robot arm will be fully extended just to attach P6 to P5. It will not have the reach necessary to position a spacewalker beyond the lowest few feet of the huge arrays if any major problems are encountered.

"One of perhaps the most audacious things we've ever done in space is this P6 solar array truss relocation," said Parazynski, an emergency room physician and veteran spacewalker making his fifth shuttle flight. "We're powering down this major element, something that we've never done before, basically shutting off the lights, shutting off the computers, turning off the cooling, unbolting it, disconnecting all the fluid and electrical and data lines and then via a process of EVA and very complex robotics we're going to take it to the very tip of the space station and then reverse the process: bolt it together, hook up connectors, deploy solar arrays, deploy a radiator.

"One of the things I love about NASA is we plan for success but we prepare for failure. And so we are very well prepared. A lot of people, a lot of smart rocket scientists around the Johnson Space Center ... have spent a lot of time figuring out what could go wrong and what we might do to address those things. We have a very long list of procedures we can run if things don't go exactly to plan."

A fourth and final set of solar arrays - S6 - will be mounted on the starboard, or right, side of the main truss during a shuttle flight next year.

Five spacewalks are planned during Discovery's mission: One to temporarily install the Harmony module on Unity's left port; two to move and redeploy P6 and continue Harmony outfitting; and one by Whitson and Malenchenko to continue HarmonyÕs activation and outfitting.

In September, NASA managers decided to add a fifth spacewalk to the mission that will be sandwiched between the P6 redeployment work and the Harmony outfitting by Whitson and Malenchenko: An excursion by Parazynski and Wheelock to test a heat shield repair technique that could prove useful in the event of damage like that seen during a shuttle flight in August.

The idea is to use a device similar to a pressurized caulk gun to first mix two components and then squirt out the resulting concoction, a thick reddish material known as Shuttle Tile Ablator 54, or STA-54, to fill in small holes or cracks in shuttle heat shield tiles. NASA originally planned to test the so-called "T-RAD" gun ("tile repair ablator dispenser") during a flight next year, but moved the demonstration up to Discovery's mission after experiencing tile damage during the August shuttle flight.

In that case, engineers ultimately concluded the shuttle could safely re-enter without repairs. But the incident prompted extensive discussions about how much confidence to place in an untested repair technique. One concern is the formation of bubbles in the material as the mixture sets up that could degrade its ability to perform.

"We've done all the testing we can do on the ground," said shuttle Program Manager Wayne Hale. "It looks very good on the ground, we've used it in the vacuum glove boxes and it looks very good there. But until we actually do a demonstration in orbit with several simulated damaged tiles and bring those back and see how well it filled, what size the bubbles were, how well it adhered, all those kinds of questions, we don't know for sure.

"So this test is actually a confidence builder. We think the tile repair capability will work as we have it today, but we'd like to be able to go forward in the future with a higher degree of confidence than perhaps we have had to date. And that's why we ordered these tests."

Assuming an on-time liftoff, Melroy will guide Discovery to a linkup with the space station on Oct. 25. Waiting to welcome the shuttle crew aboard will be Whitson, Malenchenko and NASA astronaut Clay Anderson, who was launched to the station last June aboard the shuttle Atlantis.

At that time, Anderson replaced Sunita Williams, joining Expedition 15 commander Fyodor Yurchikhin and flight engineer Oleg Kotov, who were launched to the outpost aboard a Russian Soyuz spacecraft last April. Yurchikhin and Kotov were replaced by Whitson and Malenchenko, who were launched to the station aboard a Soyuz on Oct. 10 along with Malaysian guest cosmonaut Sheikh Muszaphar Shukor.

Yurchikhin, Kotov and Shukor returned to Earth early Oct. 21 aboard the Soyuz TMA-10 capsule. The day Discovery docks, Tani will replace Anderson as an Expedition 16 crew member and Anderson will return to Earth in his place aboard the shuttle.

Discovery's docking and the usual welcome aboard ceremony will have an unusual flavor this time around as the station's first female commander welcomes Melroy, probably the final woman to command a shuttle before the program is retired in 2010. Both women flew together in 2002 when Whitson served as flight engineer of the fifth station expedition and Melroy visited as pilot of the shuttle Atlantis during mission STS-112.

"It is coincidental that it is happening," Whitson told CBS News. "But I do think it is special, not only special just for Pam and I because, you know, we have flown in space before, but the experience of having two women up there at the same time will hopefully be an inspiration to somebody. I was inspired when I was young by the Apollo era astronauts and in particular, I was motivated to become an astronaut when they selected the first female astronauts. I would hope that we could be a role model like that."

Melroy agreed, saying "I remember (astronaut) Sally Ride coming to speak in college and it was just amazing inspiration. I think the part about this that makes me the happiest is that it happened by accident. I really like that. In no way could this be misinterpreted as some major effort on the part of someone to set a special milestone or do something like that. it just happened to be those of our turns."

Coincidence or not, both women looked forward to working together in space on one of the most complex and critical space station assembly missions yet attempted.

"There are things that you feel and see and hear in space that you don't experience anywhere else," Melroy said. "And so it creates this incredible bond between the crew members. And one of the moments I'm looking forward to the most is when the hatch opens and I see Peggy's face on the other side and we reach through for the traditional handshake. That will be a really special moment for me."

For Whitson, Malenchenko and Tani, Discovery's flight kicks off a critical period in the station's assembly. The day the shuttle lands - Nov. 6 - the station crew will detach the station's main shuttle docking port, pressurized mating adapter No. 2, from the Destiny module and bolt it to Harmony. The next day, Whitson and company will use the lab's robot arm to move Harmony and PMA-2 to the front of Destiny, the most critical piece of robotic assembly yet attempted in the absence of a shuttle crew.

"After shuttle undocks, pulling off PMA-2 from the front of the lab, moving it over to the node and then re-installing the node on the front of the lab, that's huge," said Paul Hill, deputy director of mission operations at the Johnson Space Center in Houston. "Because first, there's no shuttle there so there's only three crew members to get all that done with very limited views outside. And, from the time we pull the PMA off until the whole thing is complete, there's not a shuttle docking port. So that'll be sporty."

With Harmony safely in place on the front end of Destiny, Whitson and Tani will stage two spacewalks Nov. 14 and 18 to route power, data and ammonia coolant lines from the main power truss to the new module.

"We bring up the Harmony, this node 2, and the complexity of the shuttle mission is astounding," Tani said in an interview with CBS News. "Even a few years ago, any one of the major things we're doing, any one of them would have been a full shuttle's worth of activities. Bringing the node up, attaching it to the station in a temporary location, starting the outfitting - that's a huge task - moving the P6 from its temporary initial location out to the side location, huge, that's a big robotic operation, a big EVA.

Throwing in a tile repair demonstration spacewalk, "the significance of this particular mission is big, we're doing many, many complex things and again, allowing the international partners to then bring their hardware up and join the station. ... Once the shuttle leaves, we do some very complex robotic operations and maneuver the node over to its final location. ... and then I would say the big technical part of my stay on station is the EVAs that will follow, where we take fluid trays that have been stored on the station for years and we install them on the lab to provide cooling and power to the node so it can offer it to the Columbus module and the Japanese Experiment Module.

"We talk about this as a 45-day shuttle mission in terms of pace," Tani said. "Shuttle missions are scheduled down to 10-minute increments and generally, usually station timelines are a bit more relaxed. But we are not, we are all 'go' from the moment of launch to probably until (Atlantis) comes to get me to bring me home, we are go, go, go."

The shuttle Atlantis - Tani's ride home - is scheduled for launch Dec. 6 to carry the European Space Agency's Columbus research module into orbit. Columbus will be attached to Harmony's right-side port and European Space Agency astronaut Leopold Eyharts, a French air force general, will replace Tani as an Expedition 16 crew member.

Whitson, Malenchenko and Eyharts then will accept delivery of the first of two Japanese research modules next February, which will be temporarily attached to Harmony's upward-facing zenith port. The huge Japanese Experiment Module, known as Kibo, will be attached to Harmony's left-side port next April. The pressurized experiment module launched in February later will be moved from Harmony's zenith port to an upward-facing port on the far end of Kibo.

"Every phase of exploration involves some stepping-stones," Whitson said in a NASA interview. "I think ISS is a key stepping-stone, not only for the development of an international relationship that allows us to extend as a world beyond our planet, which I think is a key thing, but also just the nuts and the bolts of figuring out what types of hardware fail on orbit, what do we need to do in the next phase to engineer something that will be better, what things did work, what didn't work, what surprised us.

"There have been a lot of surprises we've seen in constructing such a big facility on orbit, and those are some important lessons that have to be learned that we wouldn't have learned otherwise. It's a key, I think, a stepping-stone to allowing us to go beyond Earth, hopefully minimizing some of the risks of doing that. Obviously there is always risk associated with exploration, which is what makes it so exciting."

02:05 PM, 10/20/07, Update: Shuttle countdown begins

NASA started the shuttle Discovery's countdown today at 2 p.m., setting the stage for launch on a space station assembly mission at 11:38 a.m. Tuesday. Here is a countdown timeline (in EDT):

DATE/EDT......EVENT

Sat  10/20/07
	
01:30 PM......Call to stations
02:00 PM......Countdown begins
05:00 PM......Shuttle crew sleep begins

Sun  10/21/07

12:00 AM......Fuel cell reactant load preps
12:05 PM......Soyuz TMA-10 hatch closure
01:00 AM......Shuttle crew wakeup
02:00 AM......Launch Complex-39A periphery walkdown
03:14 AM......Soyuz TMA-10 undocking from space station
05:47 AM......Soyuz TMA-10 deorbit burn
06:00 AM......Clear crew module

06:00 AM......Begin 4-hour built-in hold
06:37 AM......Soyuz TMA-10 landing in Kazakhstan
06:55 AM......Orbiter pyro-initiator controller (PIC) test
07:05 AM......SRB PIC test
07:55 AM......Master events controller pre-flight BITE test

10:00 AM......Countdown resumes
11:30 AM......Fuel cell oxygen loading begins
02:00 PM......Fuel cell oxygen load complete
02:00 PM......Fuel cell hydrogen loading begins
04:30 PM......Fuel cell hydrogen loading complete
04:30 PM......Crew sleep begins
05:30 PM......Pad open; ingress white room

06:00 PM......Begin 4-hour built-in hold
06:00 PM......Crew module clean and vacuum
06:00 PM......Auxilliary power unit, engine covers off
06:30 PM......Fuel cell loading boom demate
08:00 PM......Mobile launch platform interior secured

10:00 PM......Countdown resumes
10:00 PM......Main engine preps
10:00 PM......Master events controllers 1 and 2 on
11:30 PM......Remove OMS engine covers, throat plugs

Mon  10/22/07

12:00 AM......Deflate rotating service structure dock seals
12:30 AM......Tile inspection
12:30 AM......Crew wakeup
05:00 AM......Tail service mast prepped for fueling

06:00 AM......Begin 13-hour 13-minute hold
06:00 AM......OIS communications check
08:00 AM......Crew weather briefing
08:20 AM......JSC flight control team on station
08:20 AM......Astronaut support personnel crew module cable inspection
09:30 AM......Comm activation
10:00 AM......Crew module voice checks
10:30 AM......Launch pad debris inspection
11:10 AM......Flight crew equipment late stow
03:00 PM......Rotating service structure moved to park position
03:30 PM......Ascent switch list
04:00 PM......Final tile, debris inspection
04:30 PM......Crew sleep begins

07:13 PM......Countdown resumes
07:13 PM......Terminate pad tours
07:33 PM......Auxilliary power unit bite test
07:33 PM......Pad clear of non-essential personnel
08:23 PM......Fuel cell activation
09:13 PM......Booster joint heater activation
09:50 PM......Master events controller pre-flight bite test
09:58 PM......Tanking weather update
10:13 PM......Final fueling preps; launch area clear
11:13 PM......Red crew assembled
11:58 PM......Fuel cell integrity checks complete

Tue  10/23/07

12:13 AM......Begin 2-hour built-in hold (T-minus 6 hours)
12:23 AM......Safe-and-arm PIC test
01:28 AM......Mission management team tanking meeting
01:30 AM......Crew wakeup
01:43 AM......Test team ready for ET loading

02:13 AM......Countdown resumes (T-minus 6 hours)
02:13 AM......LO2, LH2 transfer line chilldown
02:23 AM......Main propulsion system chill down
02:23 AM......LH2 slow fill
02:53 AM......LO2 slow fill
03:03 AM......Hydrogen ECO sensors go wet
03:03 AM......LO2 fast fill
03:13 AM......LH2 fast fill
05:08 AM......LH2 topping
05:13 AM......LH2 replenish
05:13 AM......LO2 replenish

05:13 AM......Begin 2-hour 30-minute built-in hold (T-minus 3 hours)
05:13 AM......Closeout crew to white room
05:13 AM......External tank in stable replenish mode
05:43 AM......Astronaut support personnel comm checks
06:00 AM......Crew breakfast/photo op
06:18 AM......Pre-ingress switch reconfig
06:30 AM......NASA Television coverage begins
07:08 AM......Final crew weather briefing
07:18 AM......Crew dons pressure suits

07:43 AM......Countdown resumes (T-minus 3 hours)
07:48 AM......Crew departs O&C building
08:18 AM......Crew ingress
09:08 AM......Astronaut comm checks
09:23 AM......Hatch closure
10:18 AM......White room closeout

10:23 AM......Begin 10-minute built-in hold (T-minus 20m)
10:33 AM......NASA test director countdown briefing

10:33 AM......Resume countdown (T-minus 20m)
10:34 AM......Backup flight computer to OPS 1
10:38 AM......KSC area clear to launch

10:44 AM......Begin final built-in hold (T-minus 9m)
11:14 AM......NTD launch status verification

11:29:20 AM...Countdown resumes (T-minus 9m)
11:30:50 AM...Orbiter access arm retraction
11:33:20 AM...Launch window opens
11:33:20 AM...Hydraulic power system (APU) start
11:33:25 AM...Terminate LO2 replenish
11:34:20 AM...Purge sequence 4 hydraulic test
11:34:20 AM...Inertial measurement units to inertial
11:34:25 AM...Aerosurface profile
11:34:50 AM...Main engine steering test
11:35:25 AM...LO2 tank pressurization
11:35:45 AM...Fuel cells to internal reactants
11:35:50 AM...Clear caution-and-warning memory
11:36:20 AM...Crew closes visors
11:36:23 AM...LH2 tank pressurization
11:37:30 AM...Solid rocket booster (SRB) joint heater deactivation
11:37:49 AM...Shuttle flight computers take control of countdown
11:37:59 AM...SRB steering test
11:38:13 AM...Main engine start (T-6.6 seconds)
11:38:20 AM...SRB ignition

11:21 AM, 10/20/07, Update: Shuttle countdown on tap; weather 60 percent 'go'

NASA's shuttle launch team geared up to start Discovery's countdown today for a launch attempt Tuesday on what many consider the most challenging space station assembly mission yet attempted. Forecasters are predicting a 60 percent chance of good weather.

The countdown was scheduled to begin at 2 p.m. and NASA Test Director Charlie Blackwell-Thompson said there were no technical issues of any significance at launch pad 39A.

"In summary, all of our systems are in good shape, our countdown is on schedule, I have no issues to report," she said. "Our team is ready. Discovery is ready and we're looking forward to Tuesday's launch and to a safe and successful mission."

The goal of Discovery's flight is to deliver a new multi-hatch module that will serve as the gateway to European and Japanese research labs scheduled for launch in December, February and April. The shuttle crew also plans to move a set of solar arrays to its permanent mounting point on the end of the station's main power truss.

Aboard the station today, outgoing Expedition 15 commander Fyodor Yurchikhin, flight engineer Oleg Kotov and Malaysian guest cosmonaut Sheikh Muszaphar Shukor made final preparations for return to Earth on Sunday aboard the Soyuz TMA-10 spacecraft. Undocking is expected around 3:14 a.m. EDT Sunday with touchdown in Kazakhstan on tap around 6:37 a.m.

Shukor rode into orbit Oct. 10 aboard the Soyuz TMA-11 capsule with Expedition 16 commander Peggy Whitson, the first female to command the space station, and veteran Russian cosmonaut Yuri Malenchenko. Whitson, Malenchenko and NASA astronaut Clay Anderson, launched to the lab complex aboard the shuttle Atlantis last June, will prepare the station for Discovery's arrival late next week.

On Sunday, a few hours after the Soyuz TMA-10 landing, shuttle engineers plan to load liquid hydrogen and oxygen into Discovery to power the ship's electrical generators.

"We will have enough on-board commodities in our power generation system to get four launch attempts in five days," said Blackwell-Thompson. "In summary, all of our systems are in good shape, our countdown is on schedule, I have no issues to report. Our team is ready, Discovery is ready and we're looking forward to Tuesday's launch and to a safe and successful mission."

But shuttle weather officer Kathy Winters said she expects only a 60 percent chance of acceptable weather Tuesday, Wednesday and Thursday because of an approaching frontal system that could bring low clouds and rain into the area.

"We are concerned about some showers in the area on the day of launch and also due to the fact that the sea breeze will be developing right around the launch time," she said. "We're concerned we could also get some cumulus cloud development within 10 nautical miles of the launch pad and also a (low broken) ceilingÊcould develop in the area as well. So we have several concerns for launch day."

Backup landing sites in New Mexico and California are expected to be "go" next week, but high winds and rain threaten two of the shuttle's three European landing sites Tuesday and Wednesday. All three runways - two in Spain and one in France - are expected to be no-go on Thursday.

Asked about the long-range outlook, Winters said "there's a front that will be threatening the area right around the 48-hour point, sometime in there. So if it doesn't affect us that day it may be an issue for us in the following days."

"Climatologically, if they push through then we start getting crosswind concerns," she said. "But right now, it mainly looks like the front's going to be affecting us sometime around that Thursday time period, or just after that, and then we'd have to start just watching all that moisture coming up with the front. And fronts tend to stall this time of year instead of pushing on through real cleanly so that can leave a lot of ceilings and moisture in the area.

"So right now it doesn't look great, but having many days without (a launch) attempt is not usually typical. Usually we get a good day in there somewhere."

2:28 PM, 10/19/07, Update: Astronauts arrive for launch; Melroy says crew confident wing leading edge panels

The shuttle Discovery's crew flew to Florida Friday for launch Tuesday on what many observers consider the most challenging and complex space station assembly flight yet attempted. Commander Pam Melroy, speaking to reporters at the Kennedy Space Center's shuttle runway, said the crew agreed with the decision earlier this week to press ahead with launch despite a recommendation from an independent engineering group to replace three wing leading edge panels that have areas of degraded coating.

NASA engineers have been studying how a protective silicon carbide coating on the wing leading edge panels can degrade over time. They thought they understood the process, but recent analysis indicates the root cause may not, in fact, be understood. Because of that, the engineering group said, it's not possible to predict how degradation might evolve or what sort of risk it might pose.

Three of the 44 reinforced carbon carbon - RCC - wing leading edge panels on Discovery have areas of known degradation. NASA managers decided after a lengthy flight readiness review Tuesday it was safe to proceed with flight while engineers continue to study the issue. There is no evidence the mechanism responsible for coating degradation will suddenly get worse and even if it somehow did, program managers concluded, the crew would see it during normal heat shield inspections and would be able to make repairs if necessary. The managers decided the odds of a sudden coating failure in the few days between the final heat shield inspection and re-entry were too low to warrant a two-month or longer launch delay.

"Of course, we watched the flight readiness review with great interest on Tuesday," Melroy said today. "Tuesday was a busy day for us, it was the day we went into quarantine, we had an integrated entry simulation that took up most of the morning and other activities in the afternoon. We finally settled into crew quarters at Johnson Space Center and I found myself wondering why I hadn't heard yet what was going on."

She said Ellen Ochoa, director of flight crew operations at JSC, told her that agency managers had spent 12 hours reviewing Discovery's readiness to launch, including a lengthy discussion about whether the leading edge panels should be replaced.

"The issues were discussed in tremendous detail and I think for me, the biggest thing that I got out of that is that with a 12-hour discussion, I feel very confident that everybody's voice was heard," Melroy said. "Everybody discussed every element of the vehicle that needed to be discussed. And I think that is what makes me so confident that the process that we have in place now allows everybody's voice to be heard.

"We were also allowed to review the data ourselves and have all our technical questions answered. And as a result of that, I'm proud to say that the STS-120 crew is totally confident that the RCC on Discovery is ready to protect us on our ride home."

Discovery's countdown is scheduled to begin at 2 p.m. Saturday for a launch attempt at 11:38:20 a.m. Tuesday. Forecasters are predicting a 40 percent chance of showers and cloud cover that would prevent takeoff.

Joining Melroy for the year's third shuttle mission are pilot George Zamka, flight engineer Stephanie Wilson, Italian astronaut Paolo Nespoli and spacewalkers Scott Parazynski, flight Doug Wheelock and space station crew member Dan Tani.

The goal of the flight is to deliver a new multi-hatch module to the space station that will serve as the connecting point for European and Japanese research modules scheduled for launch in December, February and April. The astronauts also plan to move a huge set of stowed solar arrays from an interim mounting point to its permanent location on the left end of the lab's main power truss.

Five spacewalks are planned, including one devoted to testing a promising heat shield repair technique.

"We're like a bunch of kids on Christmas Eve here, full of anticipation, both personal and professional," said lead spacewalker Parazynski. "I think by almost any measure this is one of the most challenging and audacious missions in the shuttle-ISS era. And we're all very proud to serve and be part of this flight."

Aboard the international space station today, outgoing Expedition 15 commander Fyodor Yurchikhin formally turned over control of the lab complex to Expedition 16 commander Peggy Whitson, the first woman to be put in charge of the outpost. Whitson, flight engineer Yuri Malenchenko and Malaysian guest cosmonaut Sheikh Muszaphar Shukor were launched Oct. 10 aboard the Russian Soyuz TMA-11 spacecraft.

Yurchikhin, flight engineer Oleg Kotov and Shukor plan to return to Earth early Sunday aboard the Soyuz TMA-10 capsule. Astronaut Clay Anderson, launched to the station aboard the shuttle Atlantis last June, will remain aboard the complex with Whitson and Malenchenko until his replacement - Tani - arrives. Anderson will fly home aboard Discovery.

"On a personal note, there's something special, always very special about showing up in Florida," said Melroy, the second woman to command a shuttle. "I'm just really excited to come out and actually get going. There's a time when you need to talk and the flight readiness review was the time to talk. And then there's a time to go do it. And I'm happy to say we're really here and ready to go do it."

Here is a timeline of upcoming events from NASA's initial television schedule. The complete TV schedule, along with an updated flight plan, countdown timeline and other useful data, are available on the CBS News STS-120 Quick-Look page:

http://www.cbsnews.com/network/news/space/currentglance.html

DATE/EVENT........................................EDT........GMT

SATURDAY, OCTOBER 20
COUNTDOWN STATUS BRIEFING.........................10:00 AM...14:00
EXPEDITION 15 FAREWELL AND HATCH CLOSURE..........11:45 PM...03:45

SUNDAY, OCTOBER 21
EXPEDITION 15 UNDOCKING FROM ISS COVERAGE.........02:45 AM...06:45
EXPEDITION 15 DEORBIT BURN & LANDING..............05:15 AM...09:15
EXPEDITION 15 LANDING VIDEO FILE..................09:30 AM...13:30
COUNTDOWN STATUS BRIEFING.........................10:00 AM...14:00
LAUNCH READINESS NEWS CONFERENCE..................01:00 PM...17:00

MONDAY, OCTOBER 22
COUNTDOWN STATUS BRIEFING.........................10:00 AM...14:00
EXPEDITION 16 ISS COMMENTARY......................11:00 AM...15:00
EXPEDITION 16 PAO EDUCATIONAL EVENT...............12:10 PM...16:10
VIDEO FILE........................................12:30 PM...16:30
EXPLORATION SYSTEMS BRIEFING......................01:00 PM...17:00

TUESDAY, OCTOBER 23
DISCOVERY LAUNCH COVERAGE BEGINS..................06:30 AM...10:30
LAUNCH............................................11:38 AM...15:38

11:45 PM, 10/16/07, Update: Discovery cleared for launch Oct. 23; Hale confident suspect wing panels safe

Senior NASA managers today cleared the shuttle Discovery for launch Oct. 23 on a critical space station assembly mission, concluding concern about the integrity of a protective coating on three of 44 wing leading edge panels did not warrant a lengthy delay. While there were no official dissenting opinions, NASA's chief engineer opted to write down his concerns about the decision to proceed with flight and a NASA engineering panel stuck to an earlier recommendation to replace the panels in question.

In a worst-case failure, one in which some unknown mechanism caused the protective coating to somehow come off after the crew's normal heat-shield inspections in orbit and before peak heating during re-entry, the shuttle could suffer a catastrophic leading edge burn through. Replacing the panels in question would eliminate the threat but the work would delay launch for two months or more.

NASA is attempting to complete the international space station and retire the shuttle by the end of fiscal 2010. At a news conference late Tuesday, Hale did not address how the prospect of a long delay might have played into the launch decision. But he made it clear he believes it is safe to proceed with Discovery's flight while testing continues, saying there is no engineering data to support the worst-case scenario.

"We certainly explored it in a great deal of depth," Hale said. "Everybody got to ask questions, everybody got to give their understanding of it down to the working-troop level. And at the end of the day, the flight readiness review board decided we were in an acceptable risk posture to go fly. Which is not to say we completely and perfectly understand the problem that's been laid out. We're going to continue to work very hard on it as the data comes in. We will continually re-evaluate our position from flight to flight and if the risk grows to an unacceptable level, we will take action, whether that's to change some hardware or to delay some flights while we do testing or what have you.

"I really think this was a credit to the lessons that we learned since Challenger and Columbia to be able to listen to all the opinions, to think very clearly about what they mean, apply some critical thought processes and, I trust, come to a good decision that provides us with an acceptable reason to go fly. We have a very important mission ahead of us and the crew is going to have a very intense time on orbit. We need to focus on what they are getting ready to do ... because it's absolutely critical to the next stage of building the international space station which is, after all, the reason for which we're flying the space shuttle."

Discovery's crew - commander Pam Melroy, pilot George Zamka, Scott Parazynski, flight engineer Stephanie Wilson, Doug Wheelock, Italian astronaut Paolo Nespoli and space station crew member Dan Tani - is scheduled to fly to the Kennedy Space Center Friday for the start of the shuttle's countdown Saturday afternoon. Launch is targeted for 11:38 a.m. Tuesday.

Bill Gerstenmaier, NASA's chief of space flight operations, said the crew, represented by the astronaut office at the Johnson Space Center in Houston, agreed with the decision to press ahead with launch.

The primary goal of Discovery's mission is to deliver a new multi-hatch module called Harmony that will serve as the connecting point for European and Japanese research modules scheduled for launch in December and early next year. The astronauts also plan to move a stowed set of solar arrays to its permanent mounting point on the far left end of the station's main power truss and stage a recently added spacewalk to test heat shield repair techniques.

Discovery's flight is the first to use a new management approval process, splitting up the traditional flight readiness review into separate program- and headquarters-level meetings. The idea behind the change was to make it easier for mid-level managers and engineers to express their views and opinions, part of NASA's on-going drive to improve communications between engineers and managers.

The program-level review was held Oct. 10 and during that meeting, shuttle project and wing leading edge subsystem engineers recommended launching Discovery on time despite concern raised by the NASA Engineering and Safety Center - NESC - that the coating on three reinforced carbon carbon (RCC) wing leading edge panels might be susceptible to failure.

The issue involves a protective silicon-carbide coating on the shuttle's RCC nose cap and wing leading edge panels. The nose cap and 44 RCC leading edge panels - 22 on each wing - protect the shuttle from the most extreme heating during re-entry when temperatures exceed 3,000 degrees Fahrenheit. A breach in Columbia's left wing leading edge, caused by the impact of foam debris from the ship's external tank, led to the shuttle's destruction in 2003.

Since then, NASA and contractor engineers have paid close attention to the RCC panels and nose cap, devising sophisticated non-destructive tests to assess the health of the critical carbon composite material before each flight. One of those new techniques is called thermography, which measures how heat dissipates in the carbon composite material. The technique can show areas where the protective coating on the panels might be degrading.

"Before Columbia there were two instances where we landed and some of this coating, visibly little amounts ... was off the vehicle when it landed," Hale said. "Nothing bad had happened, the vehicle survived. There was a theory as to why this happened, we developed a screening technique that we thought would detect the problem before it became critical, before it became a safety-of-flight issue."

After the first post-Columbia mission, however, thermography revealed an area of concern on an RCC panel from the shuttle's right wing. The panel - 8R - was removed and returned to the vendor, Lockheed Martin, for refurbishment. In the course of post-flight inspections, Hale said, engineers discovered "there was more sub-surface damage than we would have expected on that panel."

"That kicked off this whole concern and starting in about May, we have been trying to understand do we really have a flight safety concern?" Hale said. "Because we don't know that we do. There are some hypothesized, proposed failure modes that would say you potentially could have a safety-of-flight issue. So we're working through that engineering data.

"Now that's not a simple sound bite," he said. "There is disagreement over the interpretation of results from this panel, which we have now taken and cut little slices of and looked at under a microscope and compared that back with what the thermography readings were before. What does all this mean to us? It's a very complicated problem, it's a very complicated system and we absolutely need to make sure it works right and I can tell you right now, today, there is some question whether or not all these panels will work right. And the question is, do we stop and wait until we completely understand this problem, do we remove three or four or five of these panels and try to replace them with newer and potentially better panels? What do we do? That's what we've been grappling with, that's the issue."

The area of concern is near the apex of the curved RCC panels where they join together with so-called T-seals. Three panels on Discovery - RCC panels 9 right, 13 right and 12 left - were known to have small areas of degraded coating.

Until recently, the leading theory for the cause of such coating degradation was a slow process of oxidation, one that would not be expected to lead to a sudden loss of protection. The areas of concern on the three panels aboard Discovery had not shown any signs of worsening after three flights.

But the NASA Engineering and Safety Center, an independent review group set up after the 2003 Columbia disaster, concluded ongoing analysis of test data did not support the presumed root cause of the coating degradation and that as a result, engineers could not predict how the damage might evolve over time or accurately assess the danger it might pose. The NESC recommended replacing all three panels.

But Hale said there is no actual test or flight data that would suggest a sudden coating failure is a credible scenario. If any such loss did occur during launch or the crew's orbital operations, it would be detected by now-standard post-Columbia heat shield inspections. If any such damage was detected, it could be repaired, in theory at least, by spacewalking astronauts. For severe damage, the crew could take refuge aboard the space station and await rescue by another shuttle.

But if something caused a coating loss after the crew's normal inspections, the shuttle could re-enter with an undetected, potentially catastrophic heat shield defect. The problem for NASA is the recent conclusion that the previously held oxidation explanation may not be valid and as such, engineers do not understand the underlying causes of coating degradation or how that degradation might change over time.

"I would love to be in the position of saying we understand all our problems completely and we have resolved them all and there is nothing that's worrying anybody," Hale said. "The fact of the matter is this is a very complicated vehicle, it's an old vehicle and there are a lot of loose ends out there. We fly every time without having solved every one of our problems, found a root cause of every one of our issues.

"This is an absolutely critical subsystem for the safety of flight and the potential is a catastrophic loss of vehicle. So therefore, we have to pay particularly close attention to it. And we are committed to (finding) a root cause. ... The question you have to ask yourself is do we have sufficient understanding and sufficient mitigation - and in this case, mitigation is things like inspection and repair - to go proceed to fly while we're proceeding to work root cause?"

Gerstenmaier said the question comes down to "where is that line, when is the right time to ... take some remedial action or when is it not a problem? And frankly, we don't know and that's what the teams are struggling with."

"Without an underlying cause mechanism, you can go in one direction that says you ought to (replace the panels) at this value, another direction at a different value. When we thought we had oxidation as a root cause it was clear then we had margin to go fly for an extended period of time. Now, because we don't know what that failure mode is, depending on which failure mode we hypothesize, we may not have as much margin as we like. Then we have to go look at other mitigating circumstances."

Asked how NASA could proceed with flight with major unknowns about a potentially critical failure mode, Hale said "I don't know what else to say other than what we've told you."

"We have a new technique to inspect these panels," he said. "It's showing us some interesting things, we're trying to understand what that means. In the process of understanding, some folks that I highly respect, who are good engineers, have hypothesized this could lead to a very bad situation. We haven't demonstrated that, we have a test program to go out and understand all of that.

"So you ask yourself, should we quit flying? Should we do some minor repairs on these piece parts? What should we do? You look at the mitigations. If it happens during the launch phase, we can detect it on orbit and repair it. And we think if it happens late in entry it won't be a problem. If it happens early in entry, we've done an awfulÊlot of work and calculations and it probably, to a fairly high degree, won't be a problem although it could be. That's the kind of logic we go through."

Said Gerstenmaier: "We would have to lose the coating sometime prior to peak heating to have this potential problem during entry based on our conservative entry tools. So when you factor all those things together, even though you have all these unknowns, even if you extrapolate those unknowns to the worst case, we have enough rationale that says we're OK to continue to fly while we continue to aggressively investigate this."

02:00 PM, 10/10/07, Update: Practice countdown; wing leading edge issue assessed (UPDATED at 7:45 p.m. with meeting results)

The shuttle Discovery's crew strapped in for a dress-rehearsal countdown today to clear the way for launch Oct. 23 on a critical space station assembly mission. NASA managers, meanwhile, met for a program-level flight readiness review but were unable to reach a consensus on whether to replace three suspect wing leading edge panels or to launch Discovery as is.

Replacing the panels would require moving Discovery off the launch pad and back to its hangar for repairs, work that likely would delay launch for weeks if not longer. A decision on how to proceed is expected next week, after a headquarters-level flight readiness review Tuesday.

The issue involves a protective silicon-carbide coating on the shuttle's reinforced carbon carbon nose cap and wing leading edge panels. The nose cap and 44 RCC leading edge panels - 22 on each wing - protect the shuttle from the most extreme heating during re-entry when temperatures exceed 3,000 degrees Fahrenheit. A breach in Columbia's left wing leading edge led to the shuttle's destruction in 2003.

Since then, NASA and contractor engineers have paid close attention to the RCC panels and nose cap, devising sophisticated non-destructive tests to assess the health of the critical carbon composite material before each flight. In this case, engineers already knew about three RCC panels - 9 right, 13 right and 12 left - that had small areas of coating degradation.

Going into Discovery's launch campaign, the leading theory for the cause of the degradation was a slow process of oxidation. Using a technique known as thermography, engineers showed that the areas of concern were stable and had not worsened over the two most recent flights. Based on that, along with past experience with the panels and other test data, the orbiter project and wing leading edge subsystem engineers concluded in August that Discovery could safely be launched as is. The groups repeated that recommendation today.

In the meantime, the NASA Engineering and Safety Center, an independent review group set up after the 2003 Columbia disaster, concluded ongoing analysis of test data did not support the presumed root cause of the coating degradation and that as a result, engineers cannot predict how the damage might evolve over time or accurately assess the danger it might pose.

The NESC today recommended replacing RCC panels 9 right, 13 right and 12 left, work that, if ordered, would cause a significant launch delay because the panels cannot be changed out at the launch pad.

Shuttle program manager Wayne Hale chaired today's program-level review, but no final decisions were made. Discovery's flight is the first to use a new approval process, splitting up the traditional flight readiness review into separate program- and headquarters-level meetings. A NASA spokesman said the RCC issue, along with a handful of other open items, will be reviewed at next Tuesday's senior-level readiness review.

Discovery's crew, meanwhile, donned pressure suits and strapped in aboard the shuttle today for a dress-rehearsal countdown, a milestone training exercise for the entire launch team. Half a world away at the Baikonur Cosmodrome in Kazakhstan, the space station's next full-time crew was successfully launched as preparations for the next shuttle visit move into high gear.

The primary goal of Discovery's mission is to deliver a new multi-hatch module that will serve as the connecting point for European and Japanese research modules scheduled for launch in December and early next year. The astronauts also plan to move a stowed set of solar arrays to its permanent mounting point on the far left end of the station's main power truss.

NASA is attempting to complete the station and retire the space shuttle by the end of fiscal 2010. The agency began the year with a three-month launch delay caused by hail damage to a shuttle's external fuel tank and another major delay now would raise new questions about the agency's ability to complete the lab complex on schedule.

Briefing reporters last month, Hale said he was optimistic about meeting the schedule even if unexpected problems crop up.

"We have a lot of schedule margin to complete the space station by 2010," he said. "As you know, we had a little bit of unfortunate weather early this spring that cost us about three months on the schedule. People frequently ask me, can e complete the international space station by the time the president and Congress have directed us to retire the space shuttle? And my answer is yes, we have plenty of margin.

"We have been exploring a number of options that would allow us to fly flights more rapidly should we encounter some other unforeseen difficulty, say a weather situation like a hurricane or a hail storm or some technical problem. Right now, we think it will take us most of the time to 2010 to complete space station but we have a number of options to ease that schedule, potentially by using more bays of the VAB (Vehicle Assembly Building), potentially by flying Atlantis more often, a number of different options that we could execute that would allow us to take up any slack or any problems that we might encounter.

"So I'm very optimistic we will be able to complete the international space station well ahead of the goal date to retire the shuttle and indeed to service the Hubble Space Telescope about this time next year."

01:30 PM, 9/30/07, Update: Shuttle Discovery moved to launch pad

A powerful Apollo-era crawler-transporter slowly carried the shuttle Discovery from the Vehicle Assembly Building to launch complex 39A today for work to ready the ship for blastoff Oct. 23 on a complex space station assembly mission.

The 3.2-mile trip began around 6:47 a.m. and the orbiter's mobile launch platform was expected to be "hard down" at the pad by 2 p.m.

Shuttle Discovery, atop a crawler-transporter, moves to launch pad 39A early today
(photo by William Harwood)

NASA had hoped to move the ship to the pad last week, but the trip was delayed after engineers discovered a hydraulic leak in the shuttle's right main landing gear strut. Four seals in the strut mechanism were replaced, clearing the way for rollout Saturday - sooner than expected - but another delay was ordered because of threatening weather.

Even with the slips, Discovery processing manager Stephanie Stilson told reporters today engineers still have two full days of contingency time to handle unexpected problems between now and Oct. 23, thanks in large part to changes intended to streamline the loading of rocket fuel for the ship's maneuvering thrusters.

"As usual, you hit stumbling blocks along the way, scheduling issues, weather and so forth, but overall the vehicle looks real good, everything we have scheduled is laid out well," Stilson said. "We'd like to have more contingency (time), we'd always like to have more. That way, you just have that much more assurance you're going to make your launch date. But we feel comfortable with two (days) and when we're ready to go, we'll go. If we can't make it on the 23rd, we'll do it as soon as we can. But right now, the 23rd is looking like a good day for us."

The goal of Discovery's mission is to deliver the multi-hatch Harmony module to the international space station, a pressurized compartment that ultimately will be attached to the front of the Destiny laboratory module to serve as the anchor point for European and Japanese research modules.

The Discovery astronauts plan to stage five spacewalks to attach and outfit Harmony, to move a set of stowed solar arrays to the far left end of the station's main power truss and to test shuttle heat shield repair techniques.

"I don't think there's ever been an astronaut who doesn't consider their flight the most dramatic, exciting, complex mission ever. But ours is!" lead spacewalker Scott Parazynski joked in a recent interview with CBS News.

"A couple of years ago, I looked at the assembly sequence and looked at all the tasks that are out there and I thought the P6 (solar array) relocation flight, that was the most audacious thing we've ever done and I would love to be on that flight. ... It really is an operational challenge."

Parazynski and his crewmates - commander Pam Melroy, pilot George Zamka, flight engineer Stephanie Wilson, Doug Wheelock, Italian astronaut Paolo Nespoli and space station astronaut Dan Tani - plan to strap in aboard Discovery on Oct. 10 for a dress rehearsal countdown.

That same day, the space station's next commander and flight engineer - NASA astronaut Peggy Whitson and Russian cosmonaut Yuri Malenchenko - are scheduled for launch aboard a Soyuz spacecraft from the Baikonur Cosmodrome in Kazakhstan. They will be joined by Malaysian physician Sheikh Muszaphar Shukor.

Shukor, a guest cosmonaut flying under an arrangement with the Russian government, will return to Earth on Oct. 21 with outgoing Expedition 15 commander Fyodor Yurchikhin and flight engineer Oleg Kotov. NASA astronaut Clay Anderson, launched to the station aboard Atlantis in June, will remain aboard the lab complex with Whitson and Malenchenko until Tani arrives to replace him. Anderson will return to Earth aboard Discovery.

Harmony will be temporarily attached to the left port of the Unity module, which connects the U.S. and Russian segments of the station. Initial outfitting will be carried out during spacewalks by Parazynski, Wheelock, Whitson and Tani. After Discovery departs, the shuttle docking port on the front end of Destiny will be disconnected and attached to Harmony. The new module then will be moved to its permanent home on the front of Destiny.

Whitson and Tani plan to stage two more spacewalks Nov. 13 and 17 to hook up power and data cables and ammonia coolant lines leading back to radiators on the station's main truss. At that point, the stage will be set for launch of the European Space Agency's Columbus research module in early December.

View from the CBS News/Kennedy Space Center bureau
(Photo by William Harwood)

"The significance of this particular mission is big, we're doing many, many complex things and again, allowing the international partners to then bring their hardware up and join the station," Tani said in an interview. "Once the shuttle leaves, we do some very complex robotic operations and maneuver (Harmony) over to its final location.

"And then I would say the big technical part of my stay on station is the EVAs that will follow, where we take fluid trays that have been stored on the station for years and we install them on the lab to provide cooling and power to the node so it can offer it to the Columbus module and the JEM (Japanese Experiment Module).

"We talk about this as a 45-day shuttle mission in terms of pace," Tani said. "Shuttle missions are scheduled down to 10-minute increments and generally, station timelines are a bit more relaxed. But we are not. We are all 'go' from the moment of launch to probably until (shuttle Atlantis) comes to get me to bring me home, we are go, go, go."

1:06 PM, 9/20/07, Update: Landing gear repair going well; no expected impact on 10/23 launch

Work to replace suspect hydraulic seals in the shuttle Discovery's right main landing gear is going smoothly and barring additional problems, NASA managers said today, the shuttle should be ready for blastoff Oct. 23 as originally planned.

Engineers now plan to roll Discovery from its processing hangar to the Vehicle Assembly Building for attachment to an external fuel tank and two solid-fuel boosters early Sunday. If all goes well, the orbiter will be moved to launch pad 39A on Sept. 30, three day later than originally planned.

The initial repair schedule was typically conservative, predicting up to a week and a half of work to replace and retest suspect hydraulic seals in the right main landing gear strut that absorbs the shock of touchdown. Even though only one of four seals was thought to be leaking, managers decided to replace them all to be on the safe side. That work went faster than expected and testing should be complete by Saturday.

NASA had several days of contingency time built into the processing schedule before the hydraulic leak was discovered last week. As it now stands, engineers hope to still have one day of contingency time left in the on-pad flow to handle any unexpected problems that might crop up.

The goal of Discovery's five-spacewalk mission is to reposition a set of solar arrays and install a new multi-hatch module that will serve as the attachment point for European and Japanese research modules. NASA hopes to close out the year by launching the European Space Agency's Columbus module aboard the shuttle Atlantis on Dec. 6.

Ongoing work to fix corrosion and other problems with the huge doors of the Apollo-era Vehicle Assembly Building had limited NASA to a single high bay for shuttle processing. But work on the doors of a second high bay is wrapping up ahead of schedule and officials say the delay getting Discovery to the pad will have no impact on the December mission.

6:15 PM, 9/17/07, Update: NASA opts to replace leaky hydraulic seals

NASA managers today opted to replace suspect seals in the hydraulic system of the shuttle Discovery's right main landing gear strut, work that could delay launch on a space station assembly mission by two to three days.

In an unrelated development, agency managers today also officially approved the addition of a fifth spacewalk for Discovery's mission to test a heat-shield repair tool that could prove useful in the event of damage like the tile gouge experienced during the last shuttle mission.

The additional spacewalk makes Discovery's mission one of the most ambitious space station assembly flights yet attempted. Along with delivering a new multi-hatch 31,300-pound module to the lab complex, the astronauts also will detach a set of stowed solar arrays, move it to the far end of the station's main power truss and then re-extend the huge panels.

Discovery's mission sets the stage for delivery of European and Japanese research modules scheduled for launch late this year and early next. Those modules will be attached to Harmony and as such, Discovery's mission is a long-awaited milestone for NASA's international partners.

But the schedule for launching the European Space Agency's Columbus module in early December was already tight and with the unexpected landing gear work, NASA will not have much, if any, contingency time left to handle additional problems with either mission.

The right main landing gear hydraulic leak was discovered during routine testing in preparation for the shuttle's rollover from its processing hangar to the Vehicle Assembly Building this week for attachment to an external fuel tank and solid-fuel boosters.

The allowable leak rate for the seals in question is one drop of hydraulic fluid per hour. When jacks holding Discovery off the hangar floor were lowered and the full weight of the orbiter was put on the landing gear, engineers initially noted a "weight-on-wheels" leak rate of 285 drops per hour.

After cycling the landing gear multiple times, the calculated leak rate decreased to just 23 drops per hour. But that was still far beyond specification and after reviewing the issue today, LeRoy Cain, manager of shuttle integration at the Kennedy Space Center, ordered both seals replaced.

The work will require engineers to remove the right-side tires and brakes and disconnect the hydraulic system and instrumentation before replacing the seals.

"The vendor (Goodrich) arrives tomorrow, the replacement seals arrive Wednesday," said a NASA spokesman. "Between now and then they'll have the vehicle prepped and ready to change those out."

Rollover to the Vehicle Assembly Building had been planned for Wednesday with rollout to pad 39A on tap Sept. 27 and launch Oct. 23.

The landing gear work now is expected to delay rollover a week or so, to around Sept. 25 or 26. The launch team had five days of contingency time built into the processing schedule. Taking that time into account, the seal replacement could delay launch by two to three days.

But officials said today it's too early to predict what impact the work will actually have. Initial NASA and contractor schedule estimates in cases like this tend to be conservative and engineers frequently do better than initially expected. But that remains to be seen.

1:13 PM, 9/16/07, Update: Engineers troubleshoot shuttle main landing gear hydraulic leak

Engineers are assessing an apparent hydraulic leak in the shuttle Discovery's right-side main landing gear strut. If internal seals have to be replaced, launch on a space station assembly mission could slip a few days, officials said today, but they cautioned that it's not yet clear how long such repairs might actually take.

The leak was discovered during routine testing in preparation for the shuttle's rollover from its processing hangar to the Vehicle Assembly Building for attachment to an external fuel tank and solid-fuel boosters. As of Friday, rollout to launch pad 39A was targeted for Sept. 27, setting the stage for launch Oct. 23.

But work to replace the hydraulic seals, if required, would delay rollover and rollout. Even with several days of contingency time in the schedule, launch could be delayed a few days if repairs are ordered. What impact, if any, such work might have on plans to launch the shuttle Atlantis around Dec. 6 is not yet known.

NASA and contractor managers plan to meet Monday to discuss the issue and make a decision on how to proceed.

10:49 AM, 9/10/07, Update: NASA managers expected to add fifth spacewalk to shuttle mission

NASA managers are expected to add a fifth spacewalk to the shuttle Discovery's upcoming space station assembly mission, officials say. The additional EVA will be devoted to testing a heat-shield repair tool that could prove useful in the event of damage like the tile gouge experienced during the last shuttle mission.

While the putty-like STA-54 repair material and an applicator gun were on board Endeavour last month, NASA managers decided against making repairs after ground testing and computer analysis showed Endeavour could safely land as is.

But the repair tool, a caulk gun-like device called the TPS repair ablator dispenser, or T-RAD, has never been tested in space. NASA had planned to test it on a mission next year, but after the Endeavour incident, managers started discussions aimed at moving it up to Discovery's mission.

Discovery is scheduled for launch Oct. 23 and adding a spacewalk this late in the flow is unusual. While official approval has not yet been granted, the astronauts are officials say, approval is expected.

Assuming an on-time launch, Discovery will dock with the space station on Oct. 25. The next day, the crew's flight-day four, astronauts Scott Parazynski and Doug Wheelock will stage a six-and-a-half-hour spacewalk to hook up the multi-hatch Harmony module carried up aboard Discovery.

Two days later, on flight day six, Parazynski and newly arrived station astronaut Dan Tani will carry out a second spacewalk to prepare the stowed P6 solar array for relocation on the far left end of the station's main power truss. Parazynski and Wheelock will venture outside on flight day eight to assist with the actual P6 relocation.

The original flight plan called for station commander Peggy Whitson and flight engineer Yuri Malenchenko to stage a fourth spacewalk to make preparations for Harmony's eventual move to the front of the Destiny lab module.

Instead, the mission's fourth spacewalk, carried out by Parazynski and Wheelock, would be devoted to testing the T-RAD repair technique. Deliberately damaged tiles will be carried up inside the shuttle's crew cabin. The spacewalkers will take them to Discovery's cargo bay and use the T-RAD applicator to make simulated repairs. The tiles will e left on a mount in the cargo bay for return to Earth.

The spacewalk is expected to last about three-and-a-half hours.

The next day, flight day 11, Whitson and Malenchenko will stage the fifth spacewalk to make preparations for Harmony's move.

A revised mission flight plan reflecting the additional spacewalk will be posted here shortly.

09:15 AM, 8/30/07, Update: PMA-3 successfully moved in critical relocation

The crew of the international space station ran into unexpected problems today detaching a docking port on the left side of the multi-hatch Unity module. After considerable troubleshooting on the ground, flight controllers cleared the crew to press ahead and pressurized mating adapter No. 3 was successfully moved to Unity's downward-facing port as planned.

The move was required to make way for attachment of a new module during a visit by the shuttle Discovery in late October.

With the station's robot arm locked onto a grapple fixture on PMA-3, the lab crew sent commands to back out the first of four motorized bolts in the common berthing mechanism early today and received fault messages indicating possible problems. The crew pressed ahead and received similar, though intermittent, messages on the next two bolts they tried.

"Flight controllers continuing to troubleshoot some fault indicators seen in attempts to undock PMA-3 from the port side of the Unity node in preparation to its mate to the nadir docking port on Unity 90 degrees away," mission control commentator John Ira Petty said around 7:45 a.m. "Grapple of PMA-3 by Canadarm 2 proceeded normally. The undock procedure seemed to be going normally as well until a little before (6:20 a.m.) there was a fault indicator that occurred on one of the bolts. That indicator appeared after the bolt had reached an indicated load of zero.

"Troubleshooting was unable to identify an instrumentation problem. A decision was made to continue with the undocking procedure and subsequent fault indicators were seen on additional bolts. These indications were intermittent. So flight controllers and engineers on the ground asked for another hold, asked the crew to stand down in their procedures to undock PMA-3 while they scratch their heads over this."

After additional discussion on the ground, flight controllers decided it was safe to proceed with the undocking procedure, concluding the fault messages did not indicate any sort of problem that might cause damage to the common berthing mechanism.

The fourth bolt was backed out without incident. PMA-3 was detached from Unity's left-side port around 8:20 a.m. and was firmly bolted to the nadir port by 9:07 a.m.

But the fault indicators must be explained to resolve any lingering concern about whether the bolts will work as required to lock the Harmony module to Unity's left-side hatch in October.

"Through all these discussions, it was of paramount importance that nothing be done to compromise the docking of the Harmony node to be brought to the international space station ... by Discovery," Petty said.

With Harmony mated to Unity's left port, the station crew will detach a shuttle docking port - PMA-2 - from the front of the Destiny lab module and attach it to Harmony. Then Harmony/PMA-2 will be detached from Unity and moved to the front end of Destiny.

Harmony will serve as the connecting point for European and Japanese research modules scheduled for launch late this year and early next. But before any of that work can begin, Harmony must be successfully mated to Unity and that key step requires a healthy common berthing mechanism.

6:00 PM, 8/24/07, Update: Hale says external tank fix not expected to delay next shuttle flight

Shuttle program managers have ordered repairs to downstream external fuel tanks to remove underlying insulation around propellant feedline support brackets because of cracks found in the wake of a foam-shedding incident that damaged the shuttle Endeavour's heat shield earlier this month. The work is not expected to delay the next shuttle flight, targeted for launch around Oct. 23, but the schedule is extremely tight for the flight after that in December.

"We think this work will take about nine days, give or take, in the Vehicle Assembly Building," shuttle Program Manager Wayne Hale told reporters today. "We have looked at the launch schedule and that will still allow us, with a number of days of reserve, to launch the next shuttle mission on October the 23rd. We're looking at downstream schedules, but at first review of those schedules it appears that we can still launch the subsequent mission by the end of the December launch window ... with very little to no contingency time."

But Hale stressed that properly fixing the external tanks - not the pre-existing launch schedule - is NASA's top priority.

"The point is, we will take the amount of time that we need to to get this repair done properly," he said. "We will not rush and if we happen to fall a day or two after the 23rd, that is not a huge impact to our schedule. The schedules for the following flights obviously are more fluid and we'll be reviewing those as the work goes forward."

The shuttle Discovery is scheduled for blastoff Oct. 23 on a flight to deliver a new multi-hatch connecting module to the international space station. That module, after the station crew attaches it to the front of the Destiny laboratory module, will serve as the mounting point for the European Space Agency's Columbus research lab, scheduled for launch in early December, and the Japanese Kibo laboratory complex, which will be carried aloft early next year.

Getting the international partner modules launched is NASA's major near-term priority after years of delays caused in large part by the 2003 Columbia disaster.

Columbia was brought down by a large hole in its left wing leading edge that was caused by the impact of foam debris during launch. Redesigning the tank's insulation in the wake of the accident to minimize foam shedding has been a major challenge for the engineering community.

That point was brought home during the flight of shuttle Endeavour earlier this month when a half-ounce piece of debris popped off a liquid oxygen feedline support bracket, hit a downstream attach strut and ricocheted into the belly of the orbiter. The impact gouged a hole almost all the way through two tiles.

After around-the-clock tests and analyses, NASA managers concluded Endeavour could safely re-enter as is. After the ship's uneventful touchdown Tuesday, engineers found little additional damage and Endeavour should be repaired in short order.

But the incident raised new questions about the insulation on the feedline brackets. NASA already had decided to make a change, ordering titanium brackets for future tanks that will minimize the need for insulation in that area. But the new brackets won't be ready until four flights from now, prompting hurried analysis to determine what, if anything, to do about the next three tanks in the sequence.

"Part of the review of the video (from Endeavour's flight) indicates we potentially lost an underlying thermal protection agent called super-lightweight ablative, SLA as it's commonly called, which was added to this fitting on the tank when we thought we were going to fly different trajectories which have a higher heating during ascent," Hale said.

"We now know, and have known for some time, that the super-lightweight ablative is not really required. The damage that we saw on STS-118, given the trajectory, the size and speed of the debris, could not have been caused, we don't believe, by the lightweight foam alone, but must have had a heavier weight component, either this SLA underlying that foam or potentially ice on the foam."

Hale said engineers this week X-rayed the five oxygen feedline brackets on external tank No. 120, scheduled for use by Discovery in October, and found several small cracks in the underlying SLA material. Other downstream tanks also had cracks in the bracket insulation.

"The exact origin of those cracks is still under investigation," Hale said. "We think it's associated with the manufacturing process, but clearly this could lead to a shedding of foam debris along with this heavier weight SLA, which we now know could have a debris transport path to the underside of the orbiter. Therefore we've decided this is an unacceptable situation."

At the Kennedy Space Center this weekend, engineers from Lockheed Martin's Michoud Assembly Facility in New Orleans, where the huge tanks are built, will begin removing the outer BX foam and underlying SLA from at least the top four feedline brackets on ET-120.

"We will replace that with only the lightweight foam, which will provide us the ice growth inhibiting function and certainly is acceptable for all ascent phases," Hale said. "We still have about five contingency days remaining in our schedule for Oct. 23."

Hale said the super-lightweight ablator is intended to protect the brackets from heating as the shuttle accelerates out of the atmosphere. The foam on the outside is primarily intended to prevent ice from forming on the brackets before launch when the tank is loaded with supercold propellants.

Wind tunnel testing and computer analysis show the trajectories the shuttle currently uses to reach orbit for space station assembly flights do not subject the brackets to the level of heating originally expected and Hale said the SLA can be safely replaced with low-density BX foam instead.

While engineers are hopeful they can keep Discovery on track for launch on or close to its Oct. 23 target date, the picture is less clear for the flight after that. The launch window for Atlantis and the Columbus module, defined in part by temperature constraints imposed by the station's orbit, opens Dec. 6 and closes just one week later.

The problem for NASA is that work to refurbish aging systems in the Vehicle Assembly Building where shuttles, tanks and boosters are assembled has created a bottleneck of sorts, preventing the sort of parallel processing that might otherwise be possible.

As it now stands, Hale said Atlantis can still make the end of its December launch window. But just barely. The launch window will reopen at the end of December but NASA wants to avoid flying over the New Year break if at all possible.

For readers interested in looking ahead to October, an updated launch windows chart is available on the CBS News STS-120 Quick-Look page, along with links to crew bios, mission assignments, flight personnel and a preliminary flight plan.

12:45 PM, 8/21/07, Update: Shuttle Endeavour glides to smooth Florida landing (UPDATED at 1:40 p.m. with video of tile damage; UPDATED at 2:15 p.m. with crew departure; Morgan not seen; UPDATED at 4:30 p.m. with Griffin news conference; Morgan woozy after landing; UPDATED at 5:45 with crew news conference)

Falling back to Earth, the shuttle Endeavour streaked across Central America and high above Cuba today before gliding up the length of the Florida peninsula to a sunny landing at the Kennedy Space Center to close out a dramatic two-week space station assembly mission. The ship's gouged heat shield appeared to come through re-entry in good shape with only slightly more damage than it started with, vindicating an earlier decision to forego a spacewalk repair job.

"Houston, Endeavour, wheels stopped," commander Scott Kelly radioed as the shuttle rolled to a halt on the centerline of runway 15.

"Roger wheels stopped, Endeavour," astronaut Chris Ferguson replied from mission control in Houston. "Congratulations, welcome home. You've given a new meaning to 'higher' education."

He was referring to teacher-turned-astronaut Barbara Morgan, strapped into a seat on the flight deck just behind the two pilots. Christa McAuliffe's backup in the original Teacher-in-Space program, Morgan waited 21 years to fulfill the legacy of the fallen Challenger astronauts. While she did not teach any lessons from space as McAuliffe once planned, she chatted with school kids during two modest educational events and plans a busy schedule of post-flight appearances to promote science and math education.

Touchdown at 12:32:16 p.m. wrapped up a 5.2-million-mile voyage spanning 12 days 17 hours 55 minutes and 34 second over 201 complete orbits since blastoff Aug. 8 from nearby launch complex 39A. Endeavour's flight now sets the stage for a complex sequence of missions to attach a new docking module to the station in October, followed by the European Space Agency's Columbus laboratory module in December and two flights early next year to attach Japanese modules.

Endeavour made its fiery return to Earth with a small-but-deep gouge in two heat shield tiles on the belly of the ship behind its right main landing gear door. The gouge was caused by a half-ounce piece of foam insulation that fell off an external tank propellant feedline bracket 58 seconds after launch.

NASA managers spent more than half of Endeavour's mission studying the gouge to determine whether it posed any re-entry threat to the shuttle or its crew. Late last week, based on super-computer analysis and tests of a mockup in a furnace that can simulate re-entry heating, NASA's Mission Management Team concluded the damage would have little or no impact and cleared the shuttle for return to Earth as is.

"We agree absolutely 100 percent with the decision to not repair the damage," Kelly said during an in-flight news conference. "We've had shuttles land with worse damage than this. We gave this a very thorough look and I am very, very comfortable and there will be no extra concern in my mind (during re-entry) due to this damage."

Based on close-up video from the runway, the heat of re-entry did no apparent damage to surrounding tiles. The extent of the damage appeared roughly the same, although a gash at the deepest part of the pit looked a bit larger. But there were no other obvious signs of damage and it clearly had no impact on landing.

"There's maybe slightly a little bit more erosion on the, kind of the forward edge, but not too dramatic," said Bill Gerstenmaier, associate administrator for space flight at NASA headquarters. "It didn't get extremely hot and (the underlying material) didn't char. But again, I caution you with this quick analysis we're doing here, the teams will pop these tiles off, we'll take a look to make sure there's no damage, there's nothing going on."

Kelly, pilot Charles Hobaugh, flight engineer Rick Mastracchio, Tracy Caldwell, Al Drew and Canadian astronaut Dave Williams doffed their heavy pressure suits and gathered on the runway for a brief inspection of the shuttle an hour or so after landing. Morgan, feeling a bit woozy as she readjusted to gravity, did not join her crewmates, staying inside NASA's astronaut transporter for post-landing medical checks. All seven astronauts plan to spend the night in Florida before flying back to the Johnson Space Center in Houston on Wednesday.

"The flight was absolutely wonderful," Morgan, 55, told reporters five hours after landing. "I'm really proud of our whole team and the team on the ground. ... it all worked out really, really well I thought. How did I do? It took me a little while at first to get used to microgravity, it took a couple of days, and the first day - and I think this was the biggest surprise of all - I felt I was upside down the entire first day. It wasn't a bad feeling, it was just an unusual feeling."

Asked how she felt after landing, Morgan said: "The room still spins a little bit, but that's OK."

"What I really want to do is take what this experience was and figure out how we can do a better job to help serve our students and our teachers in a way they want that will be more helpful to them," Morgan said. "And I would love to figure out how we can make more and more of these opportunities available for more and more of our teachers."

With Endeavour back on the ground, NASA managers and engineers will carry out a detailed inspection to precisely determine the extent of damage related to the foam strike while debating a half-dozen potential near-term fixes to prevent insulation from falling off the liquid oxygen feedline brackets during upcoming launches.

A bracket redesign already was in work, scheduled to debut on a tank four missions from now. The question facing NASA is what to do about the next three flights, currently scheduled for launchings Oct. 23, Dec. 6 and Feb. 14.

Shuttle Program Manager Wayne Hale said Monday it's too soon to say what impact work to recover from Endeavour's unexpected foam debris incident might have on the upcoming schedule. But Gerstenmaier said today that at this point, major delays do not appear to be in the cards.

"We're still pointed toward Oct. 23," Gerstenmaier said. "We have a meeting today going on to have a look at the tank to see if there's anything we want to do in terms of modifying the tank ... or we leave it the way it is and head for Oct. 23. But I think we're still clearly focused on the next mission and we're ready to move forward."

From the local processing perspective, "it really and truly depends on how long we need to do the analysis for the repair if it turns out to be necessary or not," said Launch Director Mike Leinbach. "We were going to mate the external tank (and boosters) yesterday for the next mission, so we're in kind of a holding pattern here. We've got several days to work with, so we're in no immediate danger of delaying the next mission at all, that's certainly not in the cards. We have some time in the schedule to make up as we go along. So it's going to depend on the results of the study, whether we need to do a fix or not, how long we take to do that fix and then what that would translate into for (processing)."

Hale said engineers are working on "five different options to improve the situation on the next tank. We will expect there will be some readjustment to our schedule as we work through those options. However, I believe that based on the discussions we've had, that our impacts to the next flight in terms of the actual launch date of Oct. 23 will be small, we think we have plenty of time to evaluate some changes and in fact implement them if we feel that they are well justified."

At NASA's traditional post-landing news conference, NASA Administrator Mike Griffin showed off spectacular post-undocking pictures of the international space station, calling the unfinished lab complex "one of the great accomplishments of mankind."

"We're building a space station here, one flight at a time, and while I appreciated the media's attention on the ding in the tile, actually the orbiter overall was really pretty clean," he said. "We had one kind of ugly ding and we paid appropriate attention to it. I would have liked to have seen some media attention on what a magnificent accomplishment we're undertaking here. I think we're doing pretty well with it."

Endeavour docked with the space station Aug. 10 and the next day, the astronauts installed a short spacer segment on the right end of the station's main solar power truss. Two days later, Mastracchio and Williams replaced a faulty stabilizing gyroscope on the station amid work to transfer 5,000 pounds of equipment and supplies to and from the lab complex. The astronauts used robot arms on the shuttle and space station to attach a 7,000-pound equipment storage platform to the solar array truss and staged a third spacewalk Aug. 15 to complete a variety of station assembly get-ahead tasks.

Endeavour is the first shuttle equipped with a new station-to-shuttle power transfer system that enabled the orbiter to plug into the space station's solar power grid. As a result, NASA managers extended the flight three days and added a fourth spacewalk. Originally scheduled for last Friday, the excursion was delayed one day while NASA managers debated whether to turn the excursion into a tile repair spacewalk.

In the end, a repair was deemed unnecessary and Williams and space station flight engineer Clay Anderson were cleared to carry out the originally planned EVA on Saturday. But the threat of Hurricane Dean raised the possibility flight controllers at the Johnson Space Center might have to evacuate. As a result, NASA managers shortened Saturday's spacewalk and moved undocking from Monday to Sunday to get Endeavour back on the ground today.

As it turned out, Dean never threatened the Texas coast but by that point NASA was committed and the crew returned to Earth today.

Flying backward over the Indian Ocean at a velocity of 5 miles per second, Kelly and Hobaugh fired Endeavour's twin braking rockets at 11:25 a.m. for three minutes and 33 seconds, slowing the ship by 246 mph and lowering the far side of its orbit into the atmosphere. A half-hour later, the shuttle fell into the discernible atmosphere at an altitude of 76 miles. At that point, Endeavour was 5,020 miles from touchdown.

The shuttle's ground track carried it high above Central America just west of the Panama Canal on a course carrying it across central Cuba and up the Florida peninsula to the Kennedy Space Center.