KENNEDY SPACE CENTER, FLA. -- Seated in the cockpit of the shuttle training aircraft, or STA, STS-120 Commander Pamela Melroy is eager to begin landing practice on NASA's Shuttle Landing Facility runway. A modified Grumman American Aviation-built Gulf Stream II jet, the STA simulates an orbiter's cockpit, motion and visual cues and handling qualities. In flight, the STA duplicates the orbiter's atmospheric descent trajectory from approximately 35,000 feet altitude to landing on a runway. Melroy and other crew members are at Kennedy Space Center to take part in the terminal countdown demonstration test, which also includes a simulated launch countdown. Mission STS-120 is targeted for Oct. 23. Photo credit: NASA/Kim Shiflett KSC-07pd2691

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.