KENNEDY SPACE CENTER, FLA. - The Pegasus barge is towed toward the turn basin dock in the Launch Complex 39 Area at NASA's Kennedy Space Center. Onboard the barge is the external tank No. 123, designated to launch Space Shuttle Discovery on mission STS-116 in December. The tank, which was shipped from NASA's Michoud Assembly Facility in New Orleans, has undergone major safety changes, including removal of the protuberance air load ramps. Mission STS-116 will deliver the P5 truss segment, a SPACEHAB module and other key components to the International Space Station. Launch is currently scheduled no earlier than Dec. 14. Photo credit: NASA/George Shelton KSC-06pd2172

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.