Space Nuclear Propulsion Systems

The idea of using nuclear energy to power a spacecraft emerged shortly after the discovery of radioactivity: it was conceived by a Frenchman, Robert Esnault-Pelterie, the father of the French aeronautics industry. In 1912, he gave a lecture to the French Physics Society.  where he showed that, for reasons of energy density, the only solution for interplanetary travel was to use "subatomic" energy. He used the example of the energy content of one kilogram of radium, which, during its lifetime, releases nearly a million times more energy through spontaneous radioactive decay than the combustion of one kilogram of hydrogen-oxygen mixture. He also expressed a reservation: it was still necessary to find a way to release this "infra-atomic" energy much more quickly than through spontaneous radioactive decay, and in a controlled manner, so that it could be used for space propulsion (since this requires not only sufficiently high energy density but also high power density). This means, the creation of a self-sustaining and controlled nuclear fission chain reaction, was demonstrated in 1942 in the Chicago Pile-1. The first studies of "nuclear rocket engines" began immediately after the end of World War II, in parallel with those on high-power chemical rocket engines; both were motivated by defense needs (intercontinental ballistic missiles). They were initially part of the broad Nuclear Energy for the Propulsion of Aircraft program before becoming, in 1955, the subject of a large-scale project with dual civil and military purposes: Project Rover. Within this program, the NERVA program for the technological and engineering development of "nuclear engines for rocket vehicle applications" began in 1961. The significant developments made in this context until 1972, as well as in the Soviet Union until the mid-1980s, demonstrated that nuclear thermal propulsion systems met all the requirements for a transport system to the Moon and for manned missions to Mars. With the fall of the Soviet Union and the refocusing of manned space exploration on Earth orbit and the International Space Station, such systems were no longer necessary.

Today, the technologies used for space propulsion—chemical (thermal) and solar electric—are approaching their physical limits, beyond which any improvement in performance is impossible. This explains why the dawn of a new era of human space exploration, notably with the Artemis program aiming to return astronauts...