Nuclear propulsion

Abstract

The idea that nuclear energy could be used for rocket propulsion dates back almost to the beginning of the twentieth century. While Konstantin Tsiolkovsky was writing about the exploration of space, and Robert Goddard was preparing for his first experiments, the aeronautics pioneer Robert Esnault-Pelterie was giving a paper at the French Physics Society in which he identified the release of ‘infra-atomic energy’ as the only solution to long interplanetary voyages. Typical of those times, he was an engineer who had already developed and built the first all-metal monoplane. Goddard had indeed anticipated this idea in 1906/7, but only in a private journal. This was before the structure of the atom had been fully elucidated; and before Einstein’s equation of energy to mass, published in 1905, was well known. The only known process was radioactivity, in substances like radium. Thus, the idea of nuclear energy for space applications grew up alongside the practical development of the chemical rocket. Once a practical demonstration of nuclear energy release had been achieved, in 1942, it was not long before designs of nuclear rockets began to appear. All during the late 1940s and the 1950s, nuclear rocket studies proceeded alongside the studies of large chemical rockets. The early (post Sputnik) ideas for the United States manned lunar programme included the use of nuclear upper stages on the NOVA rocket. In the event, it was the all-chemical Saturn V that gave the United States its unique place in the history of space exploration. Among the reasons for this were the very high thrust and power output needed to escape from Earth’s gravity. Nuclear fuel has a very high specific energy (joules per kilogramme), but power levels equivalent, say, to the Saturn V first stage F-l engines, were not achievable with a nuclear rocket, whilst being held within reasonable mass and size limits. In any case, international treaties would soon ban the use of nuclear rockets in the Earth’s atmosphere.