KENNEDY SPACE CENTER, FLA. -- Noted physicist Stephen Hawking (center) enjoys zero gravity during a flight aboard a modified Boeing 727 aircraft owned by Zero Gravity Corp. (Zero G). Hawking, who suffers from amyotrophic lateral sclerosis (also known as Lou Gehrig's disease) is being rotated in air by (right) Peter Diamandis, founder of the Zero G Corp., and (left) Byron Lichtenberg, former shuttle payload specialist and now president of Zero G. Kneeling below Hawking is Nicola O'Brien, a nurse practitioner who is Hawking's aide. At the celebration of his 65th birthday on January 8 this year, Hawking announced his plans for a zero-gravity flight to prepare for a sub-orbital space flight in 2009 on Virgin Galactic's space service. Photo credit: Jim Campbell, Aero-News Network KSC-07pd0958

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.