The U.S. Space Shuttle program started with the awarding of the contract to Rockwell International's Space Transportation Systems Division. There were 6 shuttles built, Enterprise OV-101 (Orbital Vehicle) for testing, Columbia OV-102, Challenger OV-099, Discovery OV-103, Atlantis OV-104 and Endeavour OV-105. The first of 135 Space Shuttle missions took place April 12, 1981 and lasted 2 days 6 hours when STS-1 (Space Transportation System) was launched using Space Shuttle Columbia. Of the 135 mission launches there were 2 tragedies when Columbia and Challenger plus their crews were lost.
