STS-1 was the first orbital flight of NASA's Space Shuttle program. The first orbiter, Space Shuttle Columbia, launched on 12 April 1981 and returned to Earth on 14 April, having orbited the Earth 37 times during its 54.5-hour mission. Columbia carried a crew of two – mission commander John W. Young and pilot Robert L. Crippen. It was the first American manned space flight since the Apollo-Soyuz Test Project on 15 July 1975. STS-1 was also the only US manned maiden test flight of a new spacecraft system, although it was the culmination of atmospheric testing of the Space Shuttle orbiter.