KENNEDY SPACE CENTER, FLA. -- At NASA's Kennedy Space Center, the STS-120 crew exits the crew transport vehicle after their successful landing aboard space shuttle Discovery. Leading the way is Commander Pamela Melroy, followed by Pilot George Zamka and mission specialists Scott Parazynski, Stephanie Wilson and Doug Wheelock. Discovery completed the 15-day mission STS-120, with an on-time landing at 1:01:16 p.m. Wheel stop was at 1:02:07 p.m. Mission elapsed time was 15 days, 2 hours, 24 minutes and 2 seconds. Mission STS-120 continued the construction of the station with the installation of the Harmony Node 2 module and the relocation of the P6 truss. Photo credit: NASA//Kim Shiflett KSC-07pd3175

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.