NERVA.
The Nuclear Engine for Rocket Vehicle Application (NERVA) was a rocket engine development program intended to establish a technology base for nuclear thermal rocket systems for space missions, as this promised to be more efficient than chemical rockets. NERVA was a joint effort of the Atomic Energy Commission and NASA, and was managed by the Space Nuclear Propulsion Office (SNPO). NERVA was considered a successful program in that it met or exceeded its program goals and demonstrated that nuclear thermal rocket engines were a feasible and reliable tool for space exploration. At the end of 1968 the SNPO deemed that the latest NERVA engine, the XE (pictured), met the requirements for a human mission to Mars. It had strong political support but was canceled by President Richard Nixon in 1973. Although NERVA engines were built and tested largely with flight-certified components and were deemed ready for integration into spacecraft, they never flew in space.
