Nuclear Thermal

Nuclear thermal engines use the heat of a nuclear reactor to heat a propellant. Although early Russian designs used ammonia or alcohol as propellant, the ideal working fluid for space applications is the liquid form of the lightest element, hydrogen. Nuclear engines would have twice the performance of conventional chemical rocket engines. Although successfully ground-tested in both Russia and America, they have never been flown due primarily to environmental and safety concerns. For operations in the atmosphere, some aircraft and missile designs of the 1950's would use the heat of the reactor to directly warm ambient air, resulting in an unlimited source of fuel and virtually unlimited range for the aircraft.