Growing activity in the lunar environment and cislunar space is turning power and mobility into strategic determinants of both capability and visibility. Nuclear systems offer continuous energy, compact propulsion and greater operational freedom, opening the door to expanded exploration and, equally, to new uncertainties around stealth and competition.
Interest in space nuclear systems has grown in recent years, after earlier efforts stalled following the cancellation of Project Prometheus, Dr. Roger M. Myers, independent consultant at R Myers Consulting and retired executive director at Aerojet Rocketdyne, told Constellations. Advances in high assay low enriched uranium about 15 years ago prompted renewed studies into the economics and practicality of nuclear power and propulsion, and that the new fuel opened the door to a broader range of government and commercial projects in the field, he said.
The biggest barrier to past programs has not been technology but the lack of mission demand, Myers said. “If the customers don’t really have to have it, then at the first sign of a big challenge in a development program, they pull the money,” he said, noting that this dynamic contributed to the end of both Project Prometheus and the more recent DRACO propulsion effort.
NASA now has a stronger mission need as it pursues its Space Reactor 1 system, which shares common technology with the planned Lunar Reactor 1.
The lunar base will ultimately need a highly reliable, autonomous reactor and power conversion system capable of continuous multiyear operation without maintenance, Myers said. “We’ve got to develop robust, long-life systems that are autonomous,” he said. The base will also require a lunar microgrid that can manage fluctuating power demands from rovers, instruments and future activities such as propellant production or mining, Myers said.
Operations and Engineering Realities
With this in mind, nuclear systems could become central to sustaining long duration activity on the Moon, especially given the roughly two-week lunar night and the fact that many critical resources like ice lie in permanently shadowed regions with no sunlight, Koroush Shirvan, professor at MIT’s Department of Nuclear Science and Engineering, told Constellations.
Nuclear systems could become central to sustaining long duration activity on the Moon.
Fission offers a major advantage in these environments because its energy density is “about 70,000 times denser per kg than natural gas or 35,000 times denser per kg than hydrogen,” making mass — the primary cost driver in spaceflight — dramatically more efficient, Shirvan said.
Reactors can support both power and propulsion, meaning they can “move assets of interest at command, [making] it harder for foreign powers to confiscate,” Shirvan said. “We are still not great at tracking objects in cislunar space, so nuclear added fuel lifetime could provide that advantage,” Shirvan said.
Space radiation remains one of the most significant obstacles to reliable sensor and electronics performance on long duration missions, Dr. Igor Jovanovic, professor at University of California Berkeley’s Nuclear Engineering Department, told Constellations. He noted that researchers are working to design electronic systems that can better withstand ionizing radiation, explaining that efforts include “developing device architectures that are less affected by ionizing radiation” and, in some cases, using software or circuit design to help systems recover from damage, Jovanovic said. A parallel line of research focuses on new semiconductor materials that are inherently more radiation resistant, Jovanovic said.
Radiation generated by space-based nuclear power systems adds another challenge, he said. Because shielding mass is limited, electronics placed near a reactor must be arranged to minimize radiation exposure while staying within weight constraints, Jovanovic said.
Advances in imaging could support early detection of reactor issues in orbit by adapting techniques used in terrestrial nuclear facilities, Jovanovic said. For example, leakage of small amounts of fission products such as noble gases can provide early evidence of fuel damage, he said. Ultrasonic methods used to detect cracking in structural materials on Earth could also be relevant in space, he said.
The greater challenge may come after a problem is identified. “If such anomalies are detected in space, what kind of action is available to us in those situations?” Jovanovic said.
Security, Proliferation and Governance
From a security standpoint, cyberattacks are an obvious risk and one that is already extensively studied for terrestrial systems, said Jovanovic. The industry also needs to think about how it would respond to such threats when the nuclear systems are deployed far from Earth. The long communication delays involved in operating nuclear technologies on distant space missions add significant challenges, because these systems travel so far from us, he said.
“There will need to be a local system that will need to respond to the cyber threat autonomously.” –Dr. Igor Jovanovic, UC Berkeley
“There will need to be a local system that will need to respond to the cyber threat autonomously,” said Jovanovic. “Because of the speed with which it will have to respond with addressing any kind of cyber threat from Earth, this is an important new development that will need to be considered for these future systems.”
Beyond cyber risks, there are also concerns about handling nuclear material in space, Jovanovic noted. Strict barriers already exist to prevent nuclear material from being repurposed into weapons, so proliferation risks are always a consideration, he said. On Earth, we rely on extensive institutions and safeguards to control activities like uranium enrichment. If we place nuclear assets in space, we will need new technologies capable of verifying how much material is present at a given location, how it is managed, and whether it could be accessed and potentially redirected for weapons-related purposes, Jovanovic said.
This is yet another area where the necessary technology simply doesn’t exist yet. In addition, current treaties restrict the placement of nuclear weapons – particularly in space. “And so I will always be concerned about kind of using this kind of nuclear system as a way to actually deploy some kind of weapons system that would be a violation of the Outer Space Treaty,” Jovanovic said.
Managing a nuclear power system in space requires ensuring it can operate safely on its own in abnormal situations.
“We need to be able to autonomously operate it for its own safety,” said Jovanovic. In those cases, the system has to function remotely and without a human in the loop, he said. That likely means relying on robotics and redesigning reactors so they can run independently and withstand malfunctions, he said.
Monitoring nuclear material, particularly plutonium, also raises concerns about proliferation, Jovanovic said. Tracking this material depends on verifying reactor power and confirming that its operation aligns with declared activities, Jovanovic said. “There’s basically a balance of nuclear material that needs to be understood,” he said. Safeguards must ensure that material is not reprocessed for nuclear weapons rather than used for propulsion or other legitimate purposes, even if reactors are placed on the moon and other planets, he said.
On Earth, inspections conducted by organizations such as the International Atomic Energy Agency help verify that reactors are operating as declared. “There is no such thing that we can easily do in space,” he said. New technical solutions will be necessary to monitor space-based systems, including sensors that cannot be manipulated or deceived, he said. “We need new ideas on how the sensors cannot be fooled,” Jovanovic said.
Governments remain the only actors with the resources to respond effectively to concerning nuclear-related activities, Jovanovic said. He explained that detection would rely heavily on existing institutions, noting that “our current institutions are very effective” and can continue to evolve.
Maintaining a clear understanding of how these emerging systems are developed will help intelligence efforts stay ahead of potential risks, Jovanovic said. “Staying on top of understanding what these processes will be … is going to help us simply through intelligence gathering,” he said. He added that 3D printing is one powerful technology already being evaluated for monitoring on Earth and could serve as an example of what may also need attention in future space related oversight.
Dual Use Risks and Strategic Posture
One technology that could prove key for a sustained human presence beyond LEO but also carries risks is lunar mass drivers, Andre Sonntag, independent space power and policy analyst, said in the recently published American Foreign Policy Council (AFPC) report “Strategic Implications of Lunar Mass Drivers as a Dual-Use Technology.”
Lunar mass drivers are launch systems that use electrical power to accelerate payloads to high velocity, relying on electromechanical or electromagnetic acceleration instead of chemical propellants or explosives, Sonntag noted in the report.
“While mass drivers can bootstrap an off-world economy, they carry an equally potent and unsettling military capability: the ability to operate as an unassailable, undetectable first-strike platform,” Sonntag said. “A mass driver that can send a 1-ton payload of propellant from the lunar surface on its way to LEO can likewise fire a 1-ton warhead at anything in orbit or on the surface of the Earth. Survivability being a primary consideration in any strategic weapon system, the Moon offers mass drivers an inherent advantage in this regard.
The Space Force’s creation of a Lunar Coordination Office reflects a recognition that U.S. strategic and economic interests are expected to expand to the moon, Dr. Peter Garretson, senior fellow in defense studies at the AFPC, writer on space policy and strategy and retired Lt. Col. for the U.S. Air Force, told Constellations.
He pointed to the administration’s executive order, which states that U.S. “vital economic interests will expand outward and include the moon,” and that those interests will need protection, Garretson said.
Assessing another nation’s nuclear activities in space remains challenging and often depends on voluntary disclosure, Garretson said. “The primary way we assess is by what they choose to tell us or advertise,” he said. Certain spacecraft characteristics, such as power system signatures, would indicate whether a satellite is using nuclear rather than solar power, he said.
Large nuclear powered space missions are unlikely to be concealed because of cost and scale, Garretson said. “These are large, expensive programs,” he said, adding that nations would be unlikely to conduct such activities on orbit without announcing them in advance.
Nuclear detonation in space would be catastrophic for satellites in low Earth orbit, but a space-based nuclear weapon is more likely to be used for strategic coercion or to threaten the destruction of critical systems.
Nuclear detonation in space would be catastrophic for satellites in low Earth orbit, but a space-based nuclear weapon is more likely to be used for strategic coercion or to threaten the destruction of critical systems, Garretson said. “Nuclear weapons in space – the primary function is probably blackmail and coercion,” he said.
Safety, Timelines and Deployment Path
MIT’s Shirvan emphasized that the current systems under consideration “are not nuclear bombs” and cannot detonate like one due to fundamental physics. Even in a maximum hypothetical accident, the potential radiation exposure from a sub megawatt surface reactor would be minimal – roughly one fifth the annual allowable dose for a radiation worker after a month of continuous proximity – a level considered safe, he said.
Launching a reactor may be safer than launching radioisotope systems because reactors are sent up inactive, but commercial nuclear launches would still face significant regulatory hurdles.
Launching a reactor may be safer than launching radioisotope systems because reactors are sent up inactive, but commercial nuclear launches would still face significant regulatory hurdles, Garretson said. Once such launches occur safely a few times, they may become routine, and other nations may promote their own preferred standards, he added.
Only a few clear regulatory signals exist today: combined Chinese Russian plans for lunar power, China’s interest in megawatt-class space reactors, U.S. demand through Artemis for mission services and new commercial efforts focused on nuclear propulsion, said Garretson. Recent administrations have worked to streamline launch rules, but the United States has not flown a space reactor in decades, leaving much of the process untested, he said.
NASA’s target of deploying a lunar reactor by 2030 and China’s plan to build a lunar plant by 2035 are likely to rely on fission technologies, Jovanovic said. The more significant differences will come from how each country transports and deploys a reactor on the lunar surface, including how such systems are launched safely, he said.
Some decay-based systems already reach lifetimes of about 100 years, including radioisotope power generators that rely solely on radioactive decay, Jovanovic said. “There is significant interest in developing nuclear batteries,” he said, noting that their main challenges stem from auxiliary components such as semiconductor energy conversion systems that must withstand radiation over decades.
Reactor based systems are already proven to operate for decades in submarines and aircraft carriers but pushing them further raises concerns about long term material performance, Jovanovic said. Future designs might need alternative refueling concepts, including systems that regenerate (breed) fuel while operating. In such cases, material durability may become the limiting factor, he said.
A mobile reactor may ultimately offer the best long-term utility on the lunar surface, but a staged approach is the most realistic path forward, according to Shirvan. “The lower nuclear power with limited mobility will allow for a more near-term deployment. If we try to do too much then the U.S. program will be delayed. Russia and China have already announced their intentions so U.S. could risk falling behind,” he said. Demonstrating a surface power system on Earth would be sufficient, while even a low orbit propulsion test would put the United States on par with Russia’s historically faster nuclear space program, he said.
“To me it comes down to reliability and months of proven operation on earth at the intended power scale with all its power equipment,” Shirvan said. “Too many companies right now are toying around with concepts that we don’t even know they will operate for 24 hours without interruption. The lunar environment, will only make it harder.”
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