Also the given name for U.S. Space Transportation System Orbiter OV-105 (Space Shuttle). Endeavour was not one of the original planned build of four orbiters; rather, she was built afterwards. Her construction offset the loss of orbiter OV-101 Challenger on mission STS-51L. Although the 'line' for the Space Shuttle orbiters had been mothballed, there were a large percentage of the parts required for another orbiter already built, nearly the complete 'long lead time' list. They had been produced in the expectation of using them as spares, and in the hope of getting the budget for another orbiter. As a result, the construction of OV-105 did not require the massive investment of rebuilding a construction line and complete supply chain for one vehicle.