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 Columbia disaster orbiter prevented safe reentry. The shuttle's main fuel tank is covered in thermal insulation foam intended to prevent ice from forming when the tank is full of liquid hydrogen and oxygen. Such ice could damage the shuttle if shed during lift-off. Mission STS-107 was the 113th Space Shuttle launch. Planned to begin on January 11, 2001, the mission was delayed 18 times and eventually launched on January 16, 2003, following STS-113. (The Columbia Accident Investigation Board determined that this delay had nothing to do with the catastrophic failure.) 81.7 seconds after launch from Kennedy Space Center's LC-39-A, a suitcase-sized piece