CAPE CANAVERAL, Fla. -- During a simulated launch countdown on Launch Pad 39A at NASA's Kennedy Space Center in Florida, STS-133 Mission Specialists Nicole Stott, left, and Michael Barratt are strapped into their seats on space shuttle Discovery. Next, they will practice escaping the shuttle, in preparation for an unlikely emergency at the pad on launch day. The simulated launch countdown and emergency exit training are part of a week-long Terminal Countdown Demonstration Test (TCDT). Discovery and its STS-133 crew will deliver the Permanent Multipurpose Module, packed with supplies and critical spare parts, as well as Robonaut 2, the dexterous humanoid astronaut helper, to the International Space Station. Launch is targeted for Nov. 1 at 4:40 p.m. For more information on the STS-133 mission, visit www.nasa.gov/mission_pages/shuttle/shuttlemissions/sts133/. Photo credit: NASA/Kim Shiflett KSC-2010-5204

The Space Shuttle program was the United States government's manned launch vehicle program from 1981 to 2011, administered by NASA and officially beginning in 1972. The Space Shuttle system—composed of an orbiter launched with two reusable solid rocket boosters and a disposable external fuel tank— carried up to eight astronauts and up to 50,000 lb (23,000 kg) of payload into low Earth orbit (LEO). When its mission was complete, the orbiter would re-enter the Earth's atmosphere and lands as a glider. Although the concept had been explored since the late 1960s, the program formally commenced in 1972 and was the focus of NASA's manned operations after the final Apollo and Skylab flights in the mid-1970s. It started with the launch of the first shuttle Columbia on April 12, 1981, on STS-1. and finished with its last mission, STS-135 flown by Atlantis, in July 2011.

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