Originally published 2021-11-25.
NASA is working with the US Department of Energy to put a small nuclear fission reactor on the Moon. In late 2021 the two agencies asked industry for designs for a "Fission Surface Power" system of about 40 kilowatts, enough to run a lunar outpost through the long, freezing lunar night. Three design teams were chosen in 2022, and in August 2025 NASA raised the goal to a reactor of at least 100 kilowatts, ready to launch by the end of the decade. No reactor has reached the Moon yet.
This guide covers why NASA wants nuclear power on the Moon, how a lunar reactor would work, who is building it, how the timeline has shifted, and the safety and political questions it raises.
Why the Moon needs nuclear power
Solar panels work well in space, but the Moon has a serious drawback: in most places, night lasts about 14 Earth days. A base relying only on sunlight would need enormous batteries to survive two weeks of darkness, with surface temperatures falling far below freezing. Even near the lunar south pole, where some high ground gets sunlight most of the time, deep craters stay in permanent shadow and some areas still face weeks-long dark periods.
A fission reactor solves this by producing steady power day and night, regardless of sunlight, dust or location. That matters for the things a long-term human presence would need:
- keeping habitats warm and pressurised;
- running life-support systems and scientific instruments;
- charging rovers and other vehicles;
- extracting water from ice in shadowed craters and splitting it into oxygen and hydrogen for breathing air and rocket fuel.
NASA has described a 40-kilowatt system as roughly enough to power about 30 average US households continuously for ten years, which gives a sense of scale: small by power-station standards, but a lot for a lunar outpost.
How a small lunar reactor works
A space reactor is nothing like the giant cooling towers people picture. It is a compact unit, small enough to fit on a lunar lander, in which uranium fuel undergoes controlled fission and produces heat. That heat is carried away and converted into electricity, while radiators shed the leftover heat into space.
NASA tested the basic idea on Earth with its Kilopower project. From November 2017 to March 2018 the KRUSTY experiment at the Nevada National Security Site ran a prototype with a uranium-235 core. On 20 March 2018 it operated for 28 hours at full power, reaching about 850 °C and producing around 5.5 kilowatts of fission power. Passive sodium heat pipes moved the heat to Stirling engines, which turned it into electricity without the pumps and moving coolant loops of a conventional plant.
The Fission Surface Power project builds on that work. NASA's targets for the system include:
- about 40 kilowatts of electric power for at least 10 years;
- a mass under 6,000 kg, so it can be carried on a lander;
- radiation of less than 5 rem per year at a distance of one kilometre;
- initial designs based on low-enriched uranium, which is easier to handle safely than the high-enriched fuel used in KRUSTY.
NASA's Glenn Research Center manages the project, working with the Department of Energy's Idaho National Laboratory.
From proposals to design contracts
When the agencies invited proposals in 2021, Sebastian Corbisiero, the Fission Surface Power project lead at Idaho National Laboratory, struck an optimistic note, telling ScienceAlert: "Providing a reliable, high-power system on the Moon is a vital next step in human space exploration, and achieving it is within our grasp."
On 21 June 2022, NASA and the Idaho National Laboratory selected three teams for 12-month design contracts worth about $5 million each:
- Lockheed Martin, with BWXT and Creare;
- Westinghouse, with Aerojet Rocketdyne;
- IX, a joint venture of Intuitive Machines and X-Energy, with Maxar and Boeing.
The stated goal at that point was to demonstrate a 40-kilowatt reactor on the Moon by the end of the decade. INL director John Wagner called the contracts "a very achievable first step toward the United States establishing nuclear power on the moon."
The timeline: how plans have shifted
The original 2021 reporting tied the reactor to NASA's plan to return astronauts to the Moon in 2024, which would have been the first crewed landing since Apollo 17 in December 1972. That date slipped, as most spaceflight schedules do. Artemis II, the first crewed flight of NASA's new Moon programme, launched on 1 April 2026 and sent four astronauts around the Moon and back without landing, splashing down on 11 April.
The reactor plan has changed too. On 5 August 2025, then-acting NASA administrator Sean Duffy issued a directive, first reported by Politico, calling for a reactor of at least 100 kilowatts, ready for launch by late 2029 and on the lunar surface by around 2030, according to Scientific American. In March 2026, NASA said its Lunar Reactor-1 design would draw on Space Reactor-1 Freedom, a fission-powered spacecraft planned to launch to Mars in December 2028.
These are targets, not guarantees. Designing, testing, licensing and launching a nuclear reactor are separate milestones, and each one can be delayed.
Safety and the politics of the lunar south pole
Launching nuclear material raises obvious questions. Reactors of this kind are typically launched "cold": the fuel is only mildly radioactive until the reactor is switched on at its destination, which limits the risk if a launch fails. Low-enriched uranium fuel also reduces security concerns. Once operating, the reactor would be placed at a distance from habitats, sometimes with natural shielding such as lunar soil, to protect crews.
There is also a geopolitical side. China and Russia have announced plans for a joint research station near the lunar south pole, possibly powered by nuclear energy, by the mid-2030s, and the 2025 NASA directive explicitly cited that competition. It also mentioned a "keep-out zone" around a reactor. Under the 1967 Outer Space Treaty no country can claim ownership of the Moon, but nations must show "due regard" for others' activities, so a reactor could in practice give its operator influence over a valuable area.
Common misconceptions
"NASA is building a nuclear power plant on the Moon"
The planned systems are tiny compared with Earth's power stations, which produce hundreds of thousands of kilowatts or more. A lunar reactor is closer in scale to a backup generator for a small community.
"Nuclear power in space is new"
Spacecraft have used radioisotope power sources, which produce electricity from the natural decay of plutonium, for decades, including the Voyager probes and Mars rovers. A fission reactor is different and far more powerful, but nuclear energy in space has a long track record.
"The reactor is already on its way"
As of now, the project is in design and development. No lunar fission reactor has been launched.
If the plan succeeds, a compact reactor could make the difference between short visits to the Moon and a permanent base where people live and work through the lunar night.
Sources: Idaho National Laboratory, 21 June 2022; Wikipedia: Fission Surface Power; Wikipedia: Kilopower; Scientific American, August 2025; Wikipedia: Artemis II; originally reported by ScienceAlert.
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