The first shuttle, Enterprise, was built for the Approach and Landing Tests and had no orbital capability. Four fully operational orbiters were initially built: Columbia, Challenger, Discovery, and Atlantis. Of these, Challenger and Columbia were destroyed in mission accidents in 1986 and 2003 respectively, in which a total of fourteen astronauts were killed. A fifth operational orbiter, Endeavour, was built in 1991 to replace Challenger.
The shuttles made 135 flights during the Space Shuttle Program. To find out more information about each flight, use the web-object on the right.