Nuclear Rocket Engine

a rocket engine in which thrust is produced by the energy released in radioactive decay or a nuclear reaction. Depending on the type of nuclear reaction used in the engine, a distinction is made between radioisotope rocket engines, thermonuclear rocket engines, and nuclear rocket engines proper (nuclear-fission rocket engines).

A nuclear-fission rocket engine consists of a reactor, nozzle, turbopump unit for feeding the working fluid to the reactor from the tank of the propulsion unit (where it is stored as a liquid), control units, and other elements. In the nuclear reactor the working fluid is converted to a high-temperature gas that creates thrust as it escapes. The gas for driving the turbopump unit can be produced by heating the main working fluid in the reactor. The nozzle of the turbopump unit and many other units of a nuclear-fission rocket engine are similar to the corresponding units of liquid-propellant rocket engines. The fundamental difference lies in the use of a nuclear reactor instead of a combustion chamber. The advantage of the nuclear-fission rocket engine is the high specific impulse derived from the high exhaust velocity of the working fluid, which reaches 50 km/sec or more. The resulting specific impulse is much higher than in chemical rocket engines, in which the exhaust velocity of the working fluid does not exceed 4.5 km/sec. The US experimental rocket engine Nerva-1, in the developmental stage in 1977, weighs 11 tons and develops a thrust of more than 300 kilonewtons with a specific impulse of 8.1 km/sec. Experimental models of radioisotope rocket engines with thrust ratings with a specific impulse up to several newtons had been developed by 1978. All types of nuclear rocket engines are intended for operation only in outer space.