Russian achievements with satellites caused a rapid change in United States policy on space; from a second-priority scientific investigation, space became a major national effort. During the 1950s, missile development and research and development projects on hydrogen provided the basis for substantially increasing U.S. launch vehicle capability. The Air Force project on a hydrogen-fueled airplane, started in 1956, did not reach fruition; but its managers, technology, liquefiers, transport dewars, and other equipment transferred directly to the development of an upper stage for Atlas-Centaur-which became the first hydrogen-fueled rocket that flew.
Research sponsored by the Air Force on the feasibility of large rocket engines, beginning in 1955, provided the basis for moving quickly during 1958 to start the development of a large rocket engine of 6.7 meganewtons-ten times larger than the largest current engine.. Concepts pushed by the Advanced Research Projects Agency led to the authorization of the first large launch vehicle, using a cluster of existing ICBM engines in the first stage.
Competition between the Air Force, Army, ARPA, and the National Aeronautics and Space Administration for planning and developing large launch vehicles led to decisions for a single large launch vehicle, Saturn 1, with NASA as the responsible agency. Disagreement over the upper stage configuration of the vehicle, and particularly whether to use conventional fuel or liquid hydrogen, led to a bold decision at the end of 1959 to use hydrogen. This decision was one of the keys to the success of the Apollo moon landing missions of the 1960s and 1970s.