CAPE CANAVERAL, Fla. - In Orbiter Processing Facility bay 3 at NASA's Kennedy Space Center in Florida, space shuttle main engine No. 3 has been installed in space shuttle Discovery. Each engine is 14 feet long, weighs about 6,700 pounds, and is 7.5 feet in diameter at the end of the nozzle. Discovery is being processed for its next mission, STS-119, targeted for launch on Feb. 12, 2009. Discovery and its crew will deliver integrated truss structure 6 (S6) and solar arrays to the International Space Station. Photo credit: NASA/Dimitri Gerondidakis KSC-08pd2938

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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