KENNEDY SPACE CENTER, FLA. -- (From top) STS-123 Mission Specialists Mike Foreman, Takao Doi and Garrett Reisman are in their seats in space shuttle Endeavour to participate in a simulated launch countdown. The countdown is the culmination of the terminal countdown demonstration test, or TCDT. The TCDT provides astronauts and ground crews with an opportunity to participate in various countdown activities, including equipment familiarization and emergency egress training. Endeavour is targeted to launch at 2:28 a.m. EDT March 11 on the 16-day STS-123 mission to the International Space Station. Endeavour and its crew will deliver the first section of the Japan Aerospace Exploration Agency's Kibo laboratory and the Canadian Space Agency's two-armed robotic system, Dextre. Photo credit: NASA/Kim Shiflett KSC-08pd0579

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.