Nuclear Pulse Propulsion
In 1947, an agency of the Department of Defense, DARPA (Defense Advanced Research Projects Agency), proposed a theoretical spacecraft propulsion system using the explosions of atomic bombs to thrust the craft into space. To prevent heat damage of engine components, the atomic explosions would be sited two hundred feet behind the craft, and directed against a large steel pusher plate, to pump liquid fuel through a nuclear reactor, expanding the fuel and producing thrust.
Because of practical limitations to the control of heat damage, as well as security issues, the idea languished. During the late 1950s, General Atomics envisioned a large, single-stage ship capable of traveling to Mars and back in four weeks. (Practical rocket technology of 2016 can deliver a crew to Mars in six months, for a one-year round trip.) Unfortunately, few people in authority had particular interest in going to Mars in the 1950s.
Russia’s almost completely unanticipated 1957 launch of the Sputnik satellite made Americans feel inadequate and anxious. Partly because the USA felt a need to prove its technological prowess, a Moon-focused American space program got under way after 1960. Although emphasis was given to traditional rocket fuels and engines, atomic-pulse engines and other alternate technologies remained in the official “Maybe” file. The Air Force got a first look at all space agency programs, and the Air Force looked for military applications. Atomic- pulse engines might conceivably push a weapons platform into space, but the platforms would be vulnerable to Soviet missiles. So, to the Air Force, the propulsion idea had little merit. Further, the Partial Nuclear Test Ban Treaty of 1963 blocked atomic explosions in space.
Because the political and military landscapes are plastic and unpredictable, the U.S. Atomic Energy Commission (AEC; later called the Department of Energy) revived the nuclear-pulse idea in the late 1960s. The AEC sponsored a project called NERVA (Nuclear Engine for Rocket Fuel Application), which came close to a flight prototype before cancellation in 1972.
More than forty years later, nuclear-pulse propulsion remains theoretical.
Conjecture about a future, practical system using electromagnetic energy created by induced nuclear fission suggests maximum attainable speeds of 5 percent of the speed of light, or just under fifteen million miles per second. At that rate of travel, a spacecraft would travel from Earth to Proxima Centauri in about eighty- five years—fewer than three generations, and thus conceivable and (reasonably) practical.