NERVA

is an acronym for Nuclear Engine for Rocket Vehicle Applications; the engine was actually developed and tested in Nevada, with a similar version developed at the Los Alamos Labs in New Mexico. It was ready, or close to ready, for flight testing when Project Rover was abandoned in 1973.

The engine did not use nuclear-electric propulsion by ejecting ions (presumably the preferred method that would be used today), but used a nuclear reactor to heat liquid hydrogen from near absolute zero to more than 2000 degrees C. As the gas expands it forces its way out of a nozzle at high velocity, which provides the driving force by the recoil principle.

In practice things were somewhat more complicated. Expansion of the gas by itself would be insufficient for both the required exit velocity and for cooling the reactor, so a turbine driven by the warm hydrogen gas at a shaft power of 5 MW drove the hydrogen through the reactor's fuel assembly at a rate of some 3 tons a minute, raising its pressure by about 97 atmospheres. Control was achieved by regulating the flow of hydrogen, which acted as both the (neutron absorbing) moderator and coolant, through a tube bypassing the turbine. As in other reactors, operation was stable and self-regulating: a spurious change in power is self-defeating.

There is no danger of a hydrogen explosion inside the fuel tank, since no oxygen is present; the hot hydrogen does burn the atmosphere, but only after leaving the nozzle and combining with atmo- spheric oxygen in a reaction that is not part of the propulsion system a marked difference from the chemical fuel that exploded in the launch of the Challenger.

However, this should not be misinterpreted to mean "If only nuclear rocketry had not been abandoned, the space shuffle tragedy could have beer, avoided." The NERVA engine was meant for small probes into outer space and the planets. Although by this time it would almost certainly have been developed and its problems ironed out, it could not have taken the payload of the Challenger into orbit. Sympathy for a maligned and artificially suppressed technology should not cloud ones judgement: emotional and propagandistic hot air can be reliably left to Tom Wicker and Madame Fonda.

[More: For current space information I again recommend a subscription to from Brosz's Commercial Space Report (see editorial). For NASA's policy toward private space enterprise, see P. Cox, "Space Entrepreneurs," Reason, Jan. 1985. Literature on nuclear propulsion is not easy to come by: my main sources were Nuclear Propulsion for Space by W.R. Corliss and F.C. Schwenk (US AEC Div. Tech. Info., 1968/1971), Thrust into Space by M.W. Hunter (Holt, Rinehart & Winston, 1966), and some other space literature of the mid-60s to early 70s that can still be found in engineering libraries; also interviews with Los Alamos engineers who had worked on Project Rover (and whose help is gratefully acknowledged). The comeback of nuclear power for internal electric power supplies is reported in current electrical and aeronautical periodicals.]