CAPE CANAVERAL, Fla. - STS-125 commander Scott Altman speaks to the media at the Shuttle Landing Facility at NASA’s Kennedy Space Center in Florida. Altman arrived in a T-38 jet for Terminal Countdown Demonstration Test, or TCDT, activities. During TCDT, space shuttle Atlantis’ STS-125 crew members will participate in a simulated launch countdown, practice emergency egress procedures at the launch pad and continue to familiarize themselves with the mission payload and hardware. STS-125 is the fifth and final shuttle Hubble Space Telescope servicing mission. Launch is targeted for Oct. 10. Photo credit: NASA/Kim Shiflett KSC-08pd2753

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.