Reviving the 70-year-old space race, the US and Russia – the latter collaborating with China – are set on building the first substantial nuclear reactor on the moon. Both projects seek to power new demand systems, with fears around ‘keep-out’ zones and future mineral dominance spurring the need to win.
However, the timescales are ambitious; US Secretary of Transportation and Acting NASA Administrator Sean Duffy announced in August that the US would put a 100 kW nuclear reactor on the moon by 2030, five years ahead of Russia and China’s plans to do the same.
The US’ planned reactor will power the Artemis base camp, but there is some industry scepticism around the plausibility of overcoming mountainous engineering hurdles in the time frame outlined. Russia and China will face the same hurdles, although on a somewhat less pressured timescale, to realise their plan to power the joint International Lunar Research Station.
The history of powering the moon
The use of nuclear power on the moon is not new. Radioisotope thermoelectric generators (RTGs) have been part of lunar operations since the Apollo 12 mission in 1969, when RTGs containing plutonium 238 were used to power scientific instruments left on the moon’s surface. The heat from radioactive decay is converted into electricity by exploiting the thermoelectric effect and such systems are simple, light and reliable.
Since then, RTGs have been the go-to power source for many space missions, powering more than 25 US space vehicles. RTGs powered Pioneer 10 and Pioneer 11, the first crafts to fly past Jupiter and Saturn, respectively, and the Ulysses orbiter, which was the first to pass by the poles of the Sun in 1994. RTGs also power rovers including Perseverance and Curiosity on Mars, and the Voyager probes, now the most distant human-made objects ever launched.
However, RTGs are difficult to scale. Mohammed Ziauddin, analyst at NEi parent company, GlobalData, explains: “RTGs can only produce a small amount of electrical power for their weight – typically only around 2–3 W per kilogram. This is fine for spacecraft instruments, but not enough for the kilowatt or megawatt levels needed for a lunar base or propulsion system.” Plutonium 238 – the most common power source – is also rare and expensive.
Aside from RTGs, there have been two other answers to powering lunar exploration: solar and fuel cells. The former hits an immediate snag: the US, Russia and China have their sights set on the southern polar region of the moon where its significant water ice could be used to develop lunar infrastructure for crews and to manufacture future commodities and resources. However, at these latitudes the sun barely creeps over the horizon.
Alternatively, fuel cells have been fundamental in powering space exploration, used on the Gemini and Apollo missions, and more recently on the Space Shuttle. With the advantage of water as a byproduct, the technology is also lightweight and offers high energy density, making it scalable. Such a system requires regular replenishment of fuel though, and a delivery hiccup could result in a loss of power at the base. Fuel cells also degrade over time.
With these options off the table, nuclear fission has emerged as the most viable, durable solution.
The vision for fission: transporting a nuclear reactor
Putting nuclear power on the moon is feasible but not straightforward. A spokesperson from the US Department of Energy (DoE) explains: “a lunar reactor will be transported fully constructed via rocket to the moon, which will create size and weight limitations. Landing, activating and operating a reactor on the lunar surface will be a novel challenge given the unique environment”.
In June 2022, the DoE’s Idaho National Laboratory awarded initial design contracts to X-Energy, Westinghouse and Lockheed Martin to develop designs for a 40 kW reactor that could weigh up to six tonnes. However, the final design will be 100 kW and must fit on a human delivery-class lander, which can accommodate up to 15 tonnes.
Efficiency is therefore the name of the game. Nasa has specified that its design will use a Brayton cycle system, including one or more loops, each of which would contain a turbine generator, compressor and heat exchanger. It may also include pumps and valves, but fewer mechanical parts mean fewer opportunities for mechanical breakdown, while the added mass and drain on the power source could impact the nuclear system’s efficiency.
Once the working fluid has expanded through the turbine, it must be cooled and compressed to restart the cycle; waste heat will likely be rejected through radiative cooling, in which the exiting gas will pass through a large radiator, dissipating waste heat into space.
Most nuclear reactors have an efficiency of around 36% (although some, such as helium-cooled reactors, can reach more than 40%). Waste heat is therefore significant, unavoidable and tricky to reject, thanks to the absence of air – and therefore convection – in space. It is a significant engineering hurdle, says senior manager of business development at Lockheed Martin Space Kerry Timmons, and a key focus.
“The heat rejection and the thermal management of the system is one of the core technologies that Lockheed Martin has been focusing on, because nuclear systems do get very hot. We are converting that heat into electric energy, but we also have to reject some of it,” she says.
Aerospace and nuclear engineer Ugur Guven suggests the use of a helium-cooled nuclear reactor, “because helium is an inert gas and behaves well, hence it is easy to use as a coolant. The right nuclear fuel would also have to be used or, to generate a lot of power, a gaseous core reactor with uranium hexafluoride could be used.”
The moon’s environment for nuclear power
Efficiency aside, the moon’s environment presents a set of practical challenges including reduced gravity, cosmic radiation, micrometeors, and the lack of atmosphere.
Guven explains that “gravity on the moon is approximately a sixth of the Earth’s, so engineers must make the reactor work in a stable manner in a reduced gravity environment. Plus, it must be shielded properly, because the moon lacks the protection of the atmosphere, which protects against small meteorites.”
Beyond these already significant threats, the reactor must also withstand the moon’s extreme thermal cycles and abrasive dust, without regular maintenance.
Protecting the reactor will likely involve in-situ regolith shielding, which will avoid increasing the launch weight. Nasa reports that this may involve digging a hole and
partially burying the reactor or building barriers known as berms but notes that a shielded area will eventually face complications during the decommissioning and disposal process with potentially larger volumes of contaminated material.
The reactor will need to endure difficult conditions from its deployment. The DoE spokesperson says that “astronauts in space suits are not going to be able to do the same kind of maintenance, nor as frequently. Components, particularly electronic components like sensors and controls, will therefore need to be designed to last many years without the need to be replaced.”
The race is on: which country is poised to win?
Both the US’ 2030 ambition and Russia and China’s 2035 plan are striving to reach the same end goal: to power a base on the moon. Aside from the need for electricity and heating to sustain human life, nuclear power will also be used to recharge lunar terrain vehicles for exploration, resource utilisation and infrastructure maintenance and development.
“2030 is an ambitious but achievable goal,” says the DoE spokesperson. “A nuclear reactor on the moon will enable discovery and economic opportunities by
providing robust power for research and industrial operations in a harsh environment. DoE is excited to continue working with federal partners, advanced reactor developers and the burgeoning commercial US space industry to enable US scientific, exploration and national security objectives.”
The race against Russia and China adds a particular emphasis to the US’ national security objectives, but with advancements by internationally leading companies including aerospace company SpaceX, the US could maintain its edge.
Guven points out that the components and manufacturing techniques of the 1960s Apollo missions – “the more classical, proven method of going to the moon” – no longer exist. Instead, SpaceX’s Starship rocket system (due to be used as the Human Landing System in Nasa’s Artemis III) is vastly more complex, requiring several refuelling ships.
However, “if they can make it happen, it is far beyond the Russian or Chinese technology right now, in terms of manned missions,” he says.
This optimism could be misplaced though, he warns, because it requires continued financial backing. While the DoE and Lockheed Martin have both expressed optimism about the US’ lead in the race, Guven warns that “if the current spending and political backing of Nasa projects doesn’t change, there is a good chance that China is going to outpace the US in putting a nuclear reactor on the moon”.
Indeed, there have already been delays to Artemis III, which was due to put two astronauts on the moon by 2026 but now expects to do so in 2027, following issues with the Orion capsule’s heat shield.
In comparison, China has seen success in its Chang’e missions, and Russia maintains much of its old-school technology, which hit many milestones in the early space race including the first person in space (Yuri Gagarin, 1961), the first woman in space (Valentina Tereshkova, 1963) and the first spacewalk (Alexei Leonov, 1965).
Ziauddin notes that: “Russia contributes TOPAZ legacy expertise, and the project will involve global nuclear power giants from both countries such as Rosatom, OKBM Afrikantov, CNSA and CNNC,” with the Chang’e seven and eight missions set to provide precursor tests in 2026–2028.
China also has the advantage of a complete Atlas of the moon, offering insight into the minerals and resources available. “They have mapped all the resources for helium 3, which is a very important material if you want to create nuclear fusion energy for Earth,” says Guven.
He summarises: “Russia uses older but reliable technology, while China uses newer but untested technology; I think this combination can be successful, but the US can still outpace them with the right attitude and, more importantly, with the right budget.”
