CAPE CANAVERAL, Fla. -- The crew of space shuttle Discovery's STS-124 mission arrive at NASA Kennedy Space Center's Shuttle Landing Facility to take part in the Terminal Countdown Demonstration Test, or TCDT. Here, Commander Mark Kelly is greeted by Shuttle Launch Director Mike Leinbach. Behind Leinbach is Mission Specialist Greg Chamitoff. TCDT is a rehearsal for launch that includes practicing emergency procedures, handling on-orbit equipment, and simulating a launch countdown. On the STS-124 mission, the crew will deliver and install the Japanese Experiment Module – Pressurized Module and Japanese Remote Manipulator System. Discovery's launch is targeted for May 31. Photo credit: NASA/Kim Shiflett KSC-08pd1149

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.