by Boudour Mefteh (Policy Intern at CELI)
Nuclear power in the realm of our solar system, aside from our Earth, has been the dual result of innovation as well as the recipient of continuous concerns. Since the early 1960s, reactors as well as Radioisotope Thermoelectric Generators have been employed in the pursuit of essential missions in space, where the availability of sunlight is insufficient for the implementation of solar energy.[1] Nonetheless, these achievements have led to the reality of our ability to explore outer space with the hope of establishing settlement stations on the Moon and Mars. But simultaneously, there also exists the history of nuclear power in space, and this cannot be separated from the fear related to the Cold War, as incidents like the uncontrolled re-entry of the Soviet satellite, Cosmos 954, in 1978, which dropped plutonium over northern Canada, also made space nuclear power a source of environmental and political risk.[2]
In the 1960s, both the United States and the Soviet Union tested nuclear-powered satellites and reactors, which quickly raised a number of concerns about outer space becoming a testing ground for hazardous nuclear technologies and underscoring the need for international legal constraints.[3] These directly influenced the development of the Outer Space Treaty (OST) (1967) and associated legal instruments,[4] which prohibited placing nuclear weapons in space and other harmful contamination, proclaimed outer space for peaceful use, and benefited all countries. Although the Outer Space Treaty explicitly prohibits nuclear weapons and any other weapons of mass destruction in outer space, it does not forbid their use for peaceful purposes. It subjects such activities to the general obligations of state responsibility, international liability for damage, and due regard for the interests of other states in an attempt to mitigate environmental harm as well as strategic risks.
Notably, nuclear power in space is a contentious issue even today. Major spacefaring countries are currently pursuing the operation of nuclear reactors on the lunar surface for application in habitats, scientific bases, and ISRU due to the appeal offered by very significant benefits: steady power during the two-week-long lunar night and greatly improved capability for long-duration exploration. At the same time, such developments raise difficult issues relating to legal and safety matters: launch failure, operational malfunction, or uncontrolled re-entry may lead to radioactive contamination in space or on Earth; further, the dual-use potential of nuclear technologies places under intense light the underlying tension between peaceful applications and strategic capacity under international space law, whereby treaty obligations shall go hand in hand with appropriate risk management frameworks.
I. Key International Space Law Instruments
- Space law treaties
The Outer Space Treaty[5] is the cornerstone of space law and directly frames nuclear activities. It declares that space “shall be free for exploration and use by all States” for “the benefit and interests of all countries”.[6] Space and celestial bodies, which are the Moon, planets, etc., “shall be used exclusively for peaceful purposes”.[7] OST Article IV explicitly prohibits placing nuclear weapons or other Weapons of Mass Destruction (WMDs) in orbit or on celestial bodies[8], but it does not ban peaceful nuclear reactors or RTGs. In fact, the Treaty’s emphasis is on non-appropriation, which means that states cannot claim sovereignty over any part of space or the Moon.[9] The OST does require that states be responsible for all their space activities (Article VI) and liable for any damage caused by their space objects (Article VII).[10] Crucially, Article IX mandates that states must avoid “harmful contamination” of space and celestial bodies, and must conduct activities with “due regard to the corresponding interests of all other States”. As Professor Michelle L.D. Hanlonsummarizes, “That statement means if one country places a nuclear reactor on the Moon, others must navigate around it, legally and physically. In effect, it draws a line on the lunar map. If the reactor anchors a larger, long-term facility, it could quietly shape what countries do and how their moves are interpreted legally, on the Moon and beyond”.[11]
Beyond the OST, other related treaties are relevant to the use of nuclear power sources in outer space.[12] Briefly we can mention, the Liability Convention (1972)[13] establishes that a launching State bears absolute liability for damage caused by its space objects on the surface of the Earth or to aircraft in flight, meaning that a nuclear powered spacecraft is treated no differently from any other space object in the event of an accident. By contrast, damage occurring in outer space, such as collisions, triggers fault-based liability under Article III of the Convention, a standard that remains particularly uncertain in the context of nuclear power sources, as fault may depend on whether operators complied with vaguely defined “internationally agreed safety principles.”[14] When it comes to the Rescue and Return Agreement (1968)[15], while primarily focused on astronauts and space objects, also requires States to notify the launching authority and provide assistance when space objects, including those containing radioactive material, are found on their territory; an obligation of particular relevance in the event of an unexpected re-entry of a nuclear powered satellite. Finally, the Registration Convention (1975)[16] obliges States to register all space objects they launch, thereby enhancing transparency with respect to nuclear-capable payloads; however, the Convention remains largely administrative in nature and does not impose substantive requirements relating to safety, environmental protection, or radioactive contamination.[17]
- International law’s instruments
There are other international laws that come into play in the development of nuclear power in space that supplement the Outer Space Treaty framework. This could be because the international environment principles now encoded in the Outer Space Treaty Article IX that exclude harmful contaminations are rooted in the no-harm principle of environmental law as adopted in the 1972 Declaration of Stockholm. In view of the precautionary principle of the present international law, States must choose the safer option in situations where there are long-term risks that are uncertain, as in nuclear missions.
The Nuclear Accident Conventions (1986)[18] and the International Atomic Energy Agency (IAEA) Early Notification and Assistance Conventions, which were designed in response to the lessons learned from the Chernobyl disaster, epitomize the need for information-sharing and mutual assistance following any transboundary release of radioactivity, although the Conventions were primarily designed for events in the terrestrial environment, they might theoretically apply to a reactor re-entering another State’s territory from a lunar or satellite mission, thus mandating the concerned Statenotify all possible impacted nations through the IAEA.[19] Last, the Nuclear Safety and Physical Protection Conventions (1980, 1994)[20] have created international standards for the safety and security of nuclear materials on Earth.[21] Even if the Conventions do not apply specifically to space reactors, they clearly emphasize the importance of having high standards for safety and protection against the risk of nuclear materials misuse; a matter immediately relevant to the assembly, launch, and operation of any space-based nuclear reactors.
- Soft-Law Guidance: Nuclear Power Sources (NPS) Principles and Safety Framework
Over decades the UN space community has developed non-binding guidance for nuclear space power. In 1992, COPUOS adopted the “Principles Relevant to the Use of Nuclear Power Sources in Outer Space,”[22] Was later endorsed by the UN General Assembly. These principles are soft law (not legally binding) but carry weight. They essentially say: nuclear sources should be used only when absolutely necessary (when no other power option is practical) and should be kept to a minimum number. They emphasize strict safety at every stage: safe design, launch, operation, and especially re-entry.[23] The principles require prior notice to other states of any launch or Earth-return of NPS-bearing spacecraft, and call for mutual assistance in emergencies, clear responsibility for accidents, and peaceful resolution of disputes. As one commentary notes, the 1992 Principles “established essential safety guidelines” even though non-binding.
Building on earlier guidance, in 2009 the United Nations, through COPUOS and in cooperation with the IAEA, issued a more detailed Safety Framework for Nuclear Power Sources (NPS) Applications in Outer Space.[24] While still advisory, the Framework provides comprehensive best practices covering all stages of a nuclear space mission: from national management responsibilities and independent safety reviews to technical design standards, launch evaluation, operational monitoring, and emergency procedures. It emphasizes the importance of international communication channels, including prompt accident notifications, and sets measures to minimize any potential radioactive release to the Earth or to mission crews. Essentially, the Framework extends the principles of terrestrial nuclear safety culture to the unique operational and environmental challenges of space missions.
II. Current Developments:
- The New Space Race for Nuclear Power
Interest in space nuclear power has surged. China, Russia and the U.S. have all announced plans to deploy reactors or power plants on the Moon by the 2030s. In April 2025 China unveiled a lunar nuclear plant project for 2035; the U.S. followed in August 2025 when Acting NASA Administrator Sean Duffy accelerated a plan for a U.S. lunar reactor by 2030.[25] Duffy framed it bluntly: “We’re in a race with China to the moon…we want to get there first and claim that for America”.[26] Nuclear News reports that NASA’s new directive envisions large reactor systems landed by 2030, surpassing earlier efforts.
This “Infrastructure Race” has geopolitical and legal dimensions. While peaceful nuclear power is not banned – as one space lawyer observes, “nothing in international law prohibits the peaceful use of nuclear power on the Moon”[27] ,how it’s deployed is critical. A lunar reactor could, practically speaking, establish a high-power base at a prime site, enabling sustained operations there. But that raises questions under space law: OST forbids national appropriation, so any exclusive control must be justified on safety or logistics grounds, not sovereignty. Indeed, the U.S. led Artemis Accords (which China and Russia have not joined) allow short-lived “safety zones” around missions, but reaffirm OST’s free-access and due-regard principles.[28] NASA itself cautioned that “the first country to get a reactor on the moon could potentially declare a keep-out zone”, a capability that alarms rivals.[29] In short, nuclear deployment may be allowed, but it must be done with transparency and international consultation to respect the OST.
- Legal Analysis: Nuclear reactor on the Moon, Good or Bad?
From a legal standpoint, is putting a reactor on the Moon good or bad? It depends on compliance and coordination. Legally, peaceful nuclear power is permitted (no treaty forbids it), so NASA is not running afoul of the OST by planning a Moon reactor. Indeed, the OST’s general promise is to use “outer space for the benefit of all countries” something a reactor could help achieve via shared science. But space law also demands that activities do not unreasonably harm others’ interests. OST’s due-regard clause (Art. IX) means the U.S. must consult and design the project so as not to block other missions. A unilateral reactor with no transparency would be legally suspect.
On the environmental front, outer space itself is subject to contamination rules. If a reactor crash also sent debris toward Earth, the launching state would be absolutely liable for damages (Earth’s environment or property) under the Liability Convention. The Soviet reimbursement to Canada after Cosmos 954 shows how liability works: without international consensus on safety, the launch state must make good on accidents. This risk incentivizes extra caution and robust safety design (as the 2009 Safety Framework prescribes).
In practice, then, a lunar reactor could be acceptable if and only if it observes all applicable norms. That means strict adherence to the NPS safety frameworks and full cooperation with other spacefaring nations. If NASA shares data and involves partners (perhaps even inviting inspections) to ensure “due regard”, the project could proceed. On the other hand, moving too fast without consensus may prompt legal friction. The Artemis Accords already embody an international agreement to keep lunar activities open and consultative; violating those principles would raise diplomatic and legal issues.
Conclusion
Nuclear power in space holds enormous promise – from powering astronauts on Mars to enabling robotic explorers far from the Sun. But its past history of accidents and secrecy also demands humility. The current surge (with NASA racing China and others) is a test for the space legal regime. The treaties of the 1960s–70s provide a broad framework: peaceful use is allowed, but states are responsible for safety and must avoid contamination. The soft-law principles and frameworks of 1992 and 2009 fill in many safety gaps, but without binding force.
Going forward, the international community should build on these foundations. COPUOS is already working on a new implementation plan (2024–28) specifically to update the Safety Framework and gather best practices.[30] Major space powers, and even private companies, ought to converge on common standards for nuclear space missions. For example, harmonized launch safety reviews, joint accident response exercises, and real-time data-sharing could turn a national reactor project into a model of international cooperation. Only by combining legal restraint with technological excellence can nuclear space power remain an asset, not a hazard. deploying nuclear reactors in space is not inherently illegal or unethical, but it must be managed transparently, it could be looked for as a “A call for governance, not alarm”[31]. Used well, space nuclear power can light the way to distant worlds. Used recklessly, it could spark new conflicts or environmental threats. The coming years will show whether humanity can balance these pros and cons under the rule of law.
[1] U.S. Department of Energy, “The History of Nuclear Power in Space,” Energy.gov, June 9, 2015, https://www.energy.gov/articles/history-nuclear-power-space
[2] Committee to Bridge the Gap, “Banning Orbiting Nukes,” Committee to Bridge the Gap, accessed January 15, 2026, https://www.committeetobridgethegap.org/banning-orbiting-nukes
[3] Ibid.
[4] See Kuan Yang and Manzoor Hassan, “International Regulation for the Use of Nuclear Power Sources in Outer Space: Status Quo, Shortcomings and Possible Ways Out,” Acta Astronautica (August 2025): 128–137, https://www.sciencedirect.com/science/article/pii/S0094576525002218
[5] Kuan Yang and Manzoor Hassan, “International Regulation for the Use of Nuclear Power Sources in Outer Space: Status Quo, Shortcomings and Possible Ways Out,” Ibid.
[6] United Nations Office for Outer Space Affairs, “Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, including the Moon and Other Celestial Bodies,” UNOOSA, https://www.unoosa.org/oosa/en/ourwork/spacelaw/treaties/introouterspacetreaty.html
[7] Ibid.
[8] Ibid.
[9] Ibid.
[10] Ibid.
[11] Michelle L.D. Hanlon, “A Nuclear Reactors on the Moon?” FlaglerLive, August 10, 2025,
[12] Kuan Yang and Manzoor Hassan, “International Regulation for the Use of Nuclear Power Sources in Outer Space: Status Quo, Shortcomings and Possible Ways Out,” Ibid.
[13] United Nations, Convention on International Liability for Damage Caused by Space Objects, opened for signature March 29, 1972, entered into force September 1, 1972, United Nations Treaty Series, vol. 961, p. 187.
[14] Ibid.
[15] United Nations, Agreement on the Rescue of Astronauts, the Return of Astronauts and the Return of Objects Launched into Outer Space, opened for signature April 22, 1968, entered into force December 3, 1968, United Nations Treaty Series, vol. 672, p. 119.
[16] United Nations, Convention on Registration of Objects Launched into Outer Space, opened for signature January 14, 1975, entered into force September 15, 1976, United Nations Treaty Series, vol. 1027, p. 15.
[17] Ibid.
[18] International Atomic Energy Agency, Convention on Early Notification of a Nuclear Accident, adopted September 26, 1986, entered into force October 27, 1986, United Nations Treaty Series, vol. 1439, p. 24404.
[19] Kuan Yang and Manzoor Hassan, Ibid.
[20] Convention on Nuclear Safety, International Atomic Energy Agency, Oct. 24, 1996.
[21] Kuan Yang and Manzoor Hassan, Ibid.
[22] United nations treaties and principles on outer space, UN office for outer space affairs, UN doc A/AC.105/722/Add.1 and A/AC.105/572/Rev.3.
[23] Kuan Yang and Manzoor Hassan, Ibid.
[24] United Nations Office for Outer Space Affairs, “Working Group on the Use of Nuclear Power Sources in Outer Space,” UNOOSA, https://www.unoosa.org/oosa/en/ourwork/copuos/stsc/nps/index.html
[25] Jennifer M. Dooren, “NASA, Department of Energy to Develop Lunar Surface Reactor by 2030,” NASA, https://www.nasa.gov/news-release/nasa-department-of-energy-to-develop-lunar-surface-reactor-by-2030/
[26] American Nuclear Society, “Nuclear Power on the Moon: What We’re Watching,” Nuclear Newswire, September 2, 2025, https://www.ans.org/news/2025-09-02/article-7336/nuclear-power-on-the-moon-what-were-watching/
[27] Michelle L.D. Hanlon, “A Nuclear Reactors on the Moon?” Ibid.
[28] American Nuclear Society, “Nuclear Power on the Moon: What We’re Watching,” Ibid.
[29] Ibid.
[30] United Nations Office for Outer Space Affairs, “Working Group on the Use of Nuclear Power Sources in Outer Space,” Ibid.
[31] Michelle L.D. Hanlon, “A Nuclear Reactors on the Moon?” Ibid.
