Project Orion was the first engineering design study of a spacecraft powered by nuclear pulse propulsion, an idea proposed first by Stanisław Ulam during 1947. The project, initiated in 1958, envisioned the explosion of atomic bombs behind the craft and was led by Ted Taylor at General Atomics and physicist Freeman Dyson, who at Taylor's request took a year away from the Princeton Institute for Advanced Study to work on the project.
By using energetic nuclear power, Orion offered both great thrust and great specific impulse — the optimum combination for spacecraft propulsion. It offered performance greater than the most advanced conventional or nuclear rocket engines now being studied. Cheap interplanetary travel was the goal of the Orion Project. Its supporters felt that it had potential for space travel, but it lost political approval because of concerns with fallout from its propulsion. This concern could be addressed partially by building it in orbit. The Partial Test Ban Treaty of 1963 is generally acknowledged to have ended the project.