Our push into space will have applications on earth.
Companies and government agencies propose nuclear reactors for space
In 2018 at the Nevada National Security Site, scientists finished tests of the first new US nuclear reactor design in about 40 years. That new device wasn’t a typical reactor. Called Kilopower, it was meant not for use on Earth but for use in space. For a total of 28 hours, the reactor core sustained a controlled chain reaction involving uranium-235. That fission generated approximately 3 to 4 kilowatts of thermal energy, which flowed through heat pipes and into an electricity-producing Stirling engine.
Someday, such a system could power and propel spacecraft or keep the lights on in lunar or Martian habitats. That sort of nuclear electricity source would be a major advance; no one has launched a fission reactor since 1965. A series of federal policy declarations has helped revive research on those devices, and the possibility has caught the eye of the US Space Force (USSF).
Eric Felt, space vehicles director at the Air Force Research Laboratory (which supports both the air and space forces), spoke to Physics Today on behalf of the space force’s interests. The branch, he says, is monitoring developments in space-based nuclear reactors but not yet funding them. The recently established branch has no immediate plans to use off-Earth nuclear reactors and hasn’t determined if or how space fission fits into its portfolio. Felt says both the technological and policy barriers have shrunk; the obstacle that remains is to find a goal that needs nuclear fission.
One place where nuclear technology could fit is cislunar space—the expanse between Earth and the Moon. The region is set to grow more populated in the coming decades. “When there was nothing up there, we were not as concerned about it,” says Felt. But as new satellites, spacecraft, and space debris occupy the region, the space force wants to keep track of it all, deter and respond to threats, and deal with emergencies that may arise, such as astronaut rescue scenarios. “For example, if the SpaceX Starship propulsion were to fail during a return journey from the Moon to the Earth, and Japanese billionaire Yusaku Maezawa needed to be rescued, the USSF would use whatever capabilities we have to assist,” Felt says.