Space Shuttle program March 25, 1979, and was first launched on April 12, 1981—the 20th anniversary of Yuri Gagarin's space flight—with a crew of two. "Challenger" (OV-099) was delivered to KSC in July 1982, "Discovery" (OV-103) in November 1983, "Atlantis" (OV-104) in April 1985 and "Endeavour" in May 1991. "Challenger" was originally built and used as a Structural Test Article (STA-099), but was converted to a complete orbiter when this was found to be less expensive than converting "Enterprise" from its Approach and Landing Test configuration into a spaceworthy vehicle. On April 24, 1990, "Discovery" carried the Hubble Space Telescope into space during
Space Shuttle of Defense's assistance and refused the request for the spacewalk, and thus the feasibility of scenarios for astronaut repair or rescue by "Atlantis" were not considered by NASA management at the time. NASA retired the Space Shuttle in 2011, after 30 years of service. The Shuttle was originally conceived of and presented to the public as a "Space Truck", which would, among other things, be used to build a United States space station in low earth orbit in the early 1990s. When the U.S. space station evolved into the International Space Station project, which suffered from long delays and design