CAPE CANAVERAL, Fla. -- At NASA's Kennedy Space Center in Florida, space shuttle Discovery backs out of its processing bay, Orbiter Processing Facility-2, or OPF-2, to begin the move to the Vehicle Assembly Building, or VAB. Discovery will be stored inside the VAB for approximately one month while shuttle Atlantis undergoes processing in OPF-2 following its final mission, STS-135. Discovery flew its 39th and final mission, STS-133, in February and March 2011, and currently is being prepared for public display at the Smithsonian's National Air and Space Museum Steven F. Udvar-Hazy Center in Virginia. For more information about Discovery's Transition and Retirement, visit www.nasa.gov/mission_pages/shuttle/launch/discovery_rss_collection_archive_1.html. Photo credit: NASA/Jim Grossmann KSC-2011-5527

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.