Space nuclear systems: an introduction

Because they offer exceptional energy density, nuclear systems for power generation in space and for space propulsion began to be developed as early as the late 1950s. Thermoelectric radioisotope generators and radioisotope heaters have been used in space since the early 1960s, making possible a number of emblematic space exploration missions and enabling humankind to make considerable progress in its knowledge of the solar system. Space fission electronuclear generators of a few kWe were widely used by the Soviet Union until the late 1980s to power military observation satellites in Earth orbit. Major developments in the USA and the Soviet Union in the 1960s-1970s demonstrated that nuclear thermal propulsion systems met all the requirements for a transport system to the Moon, as well as for manned missions to Mars. The opening of a new era in human space exploration, with the Artemis program targeting first the Moon and then Mars, and the sharp rise in geopolitical tensions, which have also had an impact on the military use of space, have led to a strong revival in programs to develop new nuclear space power and propulsion systems, mainly in the USA, Russia and China. Some of these programs are aimed at first demonstrations in space, some before the end of the 2020s.

This article is intended as an introduction to the field of space nuclear systems, giving an overview of their principles, merits and potential areas of application.

The first part of this article is dedicated to space nuclear systems for power generation in space. It begins by discussing the fields of application and merits of nuclear power as a means of generating electricity in space, in comparison with solar photovoltaics. This is followed by a presentation of low-power, radioisotope-based systems: principles and design, performance, history and limits of use; then fission electronuclear generators: description, state of the art, specific features compared with terrestrial electronuclear microreactors and implications for the technologies to be implemented.

The second part of the article deals with space nuclear propulsion systems. They are first placed in the context of the general problem of propulsion in space, to identify the applications for which they offer potential advantages over existing technologies and their future progress: chemical propulsion and solar electric propulsion. Nuclear thermal propulsion and nuclear electric propulsion systems are then discussed in turn: principle, design, state of the art and technological challenges.

The last part of the article deals with safety control of space nuclear systems.

This article is by no means exhaustive. The aim is to provide engineers, in particular, with technical...