September 1969 The U.S. Space Task Group, headed by Vice President Spiro Agnew, recommends "development of a new space transportation capability." The program to develop a low-cost vehicle is officially born two months after the first manned lunar landing. NASA's first concepts involved a fully-recoverable, two-stage vehicle.

Jan. 5, 1972 As the Apollo program comes to a close, President Richard Nixon announces the development of a low-cost reusable space shuttle system. Cost cutting measures changed the design of the future Space Transportation System (STS) to a manned orbiter vehicle and an expendable external fuel tank.

July 1972 NASA selects North American Rockwell Corporation (later to be called Rockwell International) to design and develop the orbiter in a $2.7 billion contract. A year earlier, the Rocketdyne division of Rockwell had won the $500 million contract - later expanded to $1.3 billion - to design and develop the shuttle's main engines

August 1973 Martin Marietta wins the $153 million contract to design and develop the shuttle's immense external tank.

June 1974 Morton Thiokol wins the contract to design and develop the shuttle's solid rocket boosters.

Sept. 16, 1976 Enterprise, the first orbiter spacecraft, is rolled out from Rockwell International's plant in Palmdale, Calif. The test vehicle, called Orbiter Vehicle 101 during construction, is never flown in space.

Feb. - Oct. 1977 Enterprise, attached to the top of a modified Boeing 747, makes a series of 13 flight tests to determine the shuttle's airworthiness. The first five flights are unmanned, with the shuttle remaining coupled to the Boeing, followed by three manned but captive flights. Pilots controlled the shuttle during the final five free flights and landed it at Edwards Air Force Base in California.

January 1979 Rockwell is contracted to manufacture two additional orbiters - Discovery and Atlantis.

March 25, 1979 The Columbia orbiter is delivered to Kennedy Space Center.

April 1979 Enterprise is mated with the external tank and the solid rocket boosters for test purposes.

April 12, 1981 Space shuttle Columbia, manned by astronauts John Young and Robert Crippen, lifts off from Kennedy Space Center and is the first orbiter in space (STS-1). The duo spends more than 50 hours in space before landing the shuttle at Edwards Air Force Base in California on April 14.

Nov. 12, 1981 The second launch of Columbia with a new crew lifts off on a five-day mission. The shuttle, whose launch was delayed by more than a month, encounters the first major malfunctions when a fuel cell problem cuts the mission short by three days. Joe Engle and Dick Truly are the first to test the use of the Canadian-constructed remote manipulator system (RMS) used to retrieve satellites, service space stations and assist in spacewalks.

July 5, 1982 The Challenger orbiter is delivered to Kennedy Space Center. It is first launched on April 4, 1983, with a crew of four.

April 4, 1983 Astronauts Story Musgrave and Donald Peterson perform the first spacewalk from a space shuttle. They remain tethered to Challenger as they work in the payload bay - with its doors opened - for four hours on various tests.

July 18, 1983 Dr. Sally Ride, part of a five-person crew, becomes the first American woman in space on the STS-7 mission aboard Challenger.

Aug. 30, 1983 Challenger, with the first black American astronaut aboard, Guion Bluford, lifts off in the early morning hours to become the first night launch in the shuttle era. STS-8 also makes the first night landing just after midnight on Sept. 5 at Edwards AFB.

Nov. 9, 1983 The Discovery orbiter is delivered to Kennedy Space Center. Its first flight - the 12th shuttle mission - is Aug. 30, 1984.

Nov. 28, 1983 Columbia launches as the first flight of Spacelab, a U.S.-European joint project of scientific experiments. STS-9 becomes the longest flight with 10 days, has the first European to fly on a NASA mission and has six astronauts aboard - the most launched in one space vehicle.

Feb. 11, 1984 The shuttle lands for the first time at Kennedy Space Center. Challenger touches down at 7:15 a.m. ET after an eight-day flight, where astronauts tested the Manned Maneuvering Units (MMU) for the first time. Bruce McCandless and Robert Stewart flew the two untethered, nitrogen-propelled jetpacks around the shuttle for several minutes.

April 1984 During a seven-day mission aboard Challenger, specialists George Nelson and James van Hofton perform the first satellite repair in the shuttle's cargo bay. The five-person shuttle crew retrieves, fixes and releases the Solar Max, a satellite that studies the sun.

April 9, 1985 The Atlantis - the fourth orbiter - is delivered to Kennedy Space Center and blasts off for the first time on Oct. 3, 1985.

Nov. 26 - Dec. 3, 1985 EVAs by mission specialists Jerry Ross and Sherwood Spring test the viability of the future construction of a space station. The two assembled different structures with various sizes of struts and beams.

Jan. 28, 1986 On the shuttle program's 25th mission, Challenger explodes 73 seconds after liftoff, killing all seven people on board, including Christa McCauliffe, the first teacher to be launched into space. NASA creates a commission of inquiry to determine why the shuttle exploded.

June 9, 1986 The 14-member presidential commission, chaired by former Secretary of State William Rogers, presents its report. The cause for the Challenger disaster, it says, was the failure of an O-ring in the joint between the two lower segments of the right solid rocket booster (SRB). Freezing temperatures prior to the launch had damaged the rings, allowing ignited gases to burn into the external fuel tank, which exploded.

August 1987 NASA awards Rockwell International a $1.3 billion contract to build a new, improved shuttle, later named Endeavour.

Sept. 29, 1988 Discovery lifts off, marking return to flight status of shuttle program. In the previous two years more than 400 changes are made to the shuttle and all components to make the program safer.

April 24, 1990 Discovery blasts off to deliver the Hubble Space Telescope into earth orbit. The shuttle reaches a record orbiter altitude of more than 300 miles from earth.

May 7, 1991 Space shuttle Endeavour - the fifth and currently youngest orbiter - is delivered to Kennedy Space Center and makes its first flight exactly one year later.

June 27, 1995 Atlantis launches for an historic linkup with Russian space station Mir. The flight is the first in a series of U.S.-Russo missions to the orbiting outpost with American astronauts living aboard the station.

Oct. 29, 1998 Sen. John Glenn becomes the oldest person to travel into space. The former Mercury astronaut and first American to orbit space in 1962 is 77 when he flies aboard Discovery.

Dec. 4, 1998 For the first time a shuttle carries a part of the International Space Station into orbit. Endeavour, on the programs' 93rd shuttle flight, carries the Unity module docking station in its bay and links it to the Russian Zarya module.

Oct. 11, 2000 Space shuttle Discovery blasts off to begin the program's 100th flight. It docks with the International Space Station and the crew adds more elements to the ISS.

Feb. 1, 2003 Space shuttle Columbia breaks apart in flames about 203,000 feet over Texas, 16 minutes before it was supposed to touch down in Florida. All seven aboard are killed: William McCool, Rick Husband, Michael Anderson, Kalpana Chawla, David Brown, Laurel Clark and Ilan Ramon, who was Israel's first astronaut.

Aug. 27, 2003 An independent investigation board releases a stinging 248-page report on the Columbia disaster, finding that foam insulation that broke off during launch tore a hole in the shuttle's left wing, resulting in the accident. It warns that that without sweeping changes at the space agency, "the scene is set for another accident."

Jan. 14, 2004 In outlining a new plan for American space exploration, President Bush proposes retiring the shuttle fleet by the end of the decade.

July 26, 2005 The U.S. launches its first manned spaceflight since the Columbia disaster when shuttle Discovery lifts off from Cape Canaveral into clear skies and under intense scrutiny. The mission to the International Space Station is the first to implement new procedures and technology to make the shuttle safer, including the use of more than 100 cameras to record any possible damage to the spacecraft.

July 27, 2005 Following an incident during Discovery's liftoff in which a large chunk of foam broke off the external fuel tank, NASA grounds all future shuttle flights. NASA says a piece of the foam hit the shuttle wing, but Discovery, still on its mission and successfully docked with the International Space Station, is described as a "clean bird" by a NASA administrator.

March 14, 2006 NASA announces it is pushing back the launch of space shuttle Discovery from May until at least July because of a faulty fuel tank sensor. A similar problem briefly delayed the July launch of Discovery. NASA said it needs the time to open up the spacecraft's hydrogen fuel tank and replace the sensor, which gave an electrical current reading that was slightly off. The space agency plans to replace the three other sensors in the tank, too, to be safe.

June 17, 2006 NASA managers select July 1 to launch the first space shuttle flight in almost a year, despite recommendations against a liftoff attempt by the space agency's chief engineer and several of its safety officers. The decision to launch the shuttle Discovery on a trip to the international space station was made after two days of meetings by NASA's leading managers and engineers at the Kennedy Space Center.

July 4, 2006 After two attempts to launch Discovery were scrubbed due to the weather, the shuttle finally lifts off to begin a 13-day mission in space.

July 17, 2006 Discovery and its crew of six returned to Earth, ending a successful mission that put NASA back in the space station construction business. Discovery glided down through an overcast sky onto the Kennedy Space Center runway, allowing NASA to declare total victory for the first time since before the 2003 Columbia disaster.

Sept. 9, 2006 After a two-week delay, Atlantis and its six-person crew lift off on an 11-day mission -- the first dedicated to assembly of the international space station in almost four years. During three spacewalks, crew members will install new solar energy arrays on a 17 1/2-ton addition and perform a series of construction tasks.

Sept. 19, 2006 NASA postpones Atlantis' scheduled Sept. 20 landing over concerns of floating debris outside the shuttle.

Sept. 21, 2006 Atlantis and its six astronauts glided to a safe landing in pre-dawn darkness, ending a 12-day mission whose smooth success was briefly upstaged by the high drama caused by mysterious floating debris that prompted NASA to order up extra inspections of the spacecraft's delicate skin to make sure it was safe to come home.

Dec. 9, 2006 The shuttle Discovery lights up the sky in the first nighttime space shuttle launch in four years — the latest step in NASA's ambitious schedule to complete the international space station. During their 12-day mission, Discovery's crew will rewire the space station, deliver an $11 million addition to the space lab and bring home one of the space station's three crew members, German astronaut Thomas Reiter of the European Space Agency. American astronaut Sunita "Suni" Williams will replace him, and stay for six months.