Two nuclear reactors are bound for the moon’s south pole. Neither is coming home.
The Outer Space Treaty forbids owning the moon by claim, by use or by occupation. It says nothing about a ring of ground no one may enter, or about how long such a ring may last. The United States wants its reactor running by 2030; Russia promises one for China by 2036.
Chess makes a distinction the Outer Space Treaty does not. A piece stands on one square and commands others. Games are decided by squares no piece ever occupies, and a player who sees only where the pieces stand will lose to one who sees where they reach.
In late August 2026, NASA asked contractors to prepare a nuclear reactor that could survive the voyage to the moon and run without maintenance near its south pole, the New York Times reported in October. The agency wants it ready to launch by December 2030. Russia, under a partnership with China, has set 2036 for a reactor of its own. The machines are modest. NASA’s would produce about 20 kilowatts, roughly what 16 American homes draw, and Russia’s up to half that. The ground is modest too. NASA named 13 candidate landing regions for its first crewed return in 2022 and narrowed them to nine in 2024, all on a handful of ridges and crater rims near the pole, where the sunlight is nearly constant and the shadowed craters beside them are thought to hold ice. That is the whole prize: a few named places on a body whose surface is larger than Africa.
A reactor at power cannot be approached safely without shielding. On Earth it sits inside a containment building. On the moon, the Times reports, it would more likely sit inside a no-go zone, a ring that neither astronauts nor machines may safely enter. The treaty that governs the moon, signed in 1967, forbids “national appropriation by claim of sovereignty, by means of use or occupation, or by any other means.” Sovereignty, use and occupation are three ways of standing somewhere. The text says nothing about denial. So a handful of the only usable sites on the moon can be made unenterable by acts that break no rule. The one instrument that provides for ending such a zone is not a treaty but a political declaration, signed by one of the two builders and not the other.
And neither reactor is coming home. When a reactor on Earth reaches the end of its life, decommissioning takes years. On the moon, according to Selam Gebrekidan’s reporting in the Times, both NASA and the Russian agencies say they would simply leave the radioactive material behind. The zone will not end when the machine does. In chess, remove a piece and every square it commanded is free at once. The moon is being offered a piece that keeps its squares.
I
Twenty Kilowatts
The reactor NASA wants is small, and nobody has calculated the load. The Times reports that for the first years both programmes need only enough power to keep equipment warm and charge rovers, that solar and radioisotope systems would serve, and that how much electricity a base would need is open to speculation. Two powers are racing to install a power source for a base that does not exist, against a demand nobody has measured. NASA’s machine, as the Times describes it, must work for five years with no intervention; the Russian design, called Selena, for a decade. Neither is a power station. Each is built to carry a base through the dark, and at the pole the dark comes in gaps of a day or two rather than weeks, under a sun that never climbs far above the horizon. That is why both programmes say a reactor must come.
The place is small too. Of the moon’s 37.9 million square kilometres, the parts that matter for a base are the ones where two things meet: ridges high enough to catch sunlight for most of the lunar day, and craters deep enough that sunlight has never reached their floors. The first supply power and bearable temperatures. The second, NASA says, “can preserve resources, including water,” from which oxygen and hydrogen can be extracted for life support and fuel. Such places are few, and they cluster at the south pole. In 2022 NASA named 13 candidate regions for its first crewed landing there, and in October 2024 narrowed them to nine, a short list of massifs, rims and plains whose names will become familiar. Those are landing regions, not reactor sites, which no one has announced. But they are the published evidence of which ground is worth having, and the Chinese-led International Lunar Research Station is aimed at the same pole.
A reactor set on that ground does not command a clean circle. In open space a radiation radius is a sphere. On a crater rim it is cast like a shadow across whatever lies in reach. Set behind a ridge, its reach falls on one slope and not the other. Set near a crater, where the approaches are few, it can cover them. Its zone will be shaped by the terrain it sits in, and so will the question of what the zone denies.
Nobody wanted this yet. A fission reactor is a later need, brought forward. NASA moved its date up because Russia is building one. Russia is building one because China, in the one core task it appears to have delegated, asked it to. Nothing in the record says Moscow set its clock by Washington’s. So only one player is in zugzwang, the position in which the obligation to move is itself the harm, and it is the one bound by the Accords. Every move it has — an earlier launch, a bigger reactor, a looser rule — takes something from the position both sides depend on: a moon that no one owns. The treaty that guarantees it was written for players who stand on squares. The next move puts down a piece that reaches.
II
By Any Other Means
The treaty’s second article is one sentence long. Outer space, including the moon, “is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means.” Appropriation is the term of art, and it means taking a thing as one’s own. Sovereignty, use and occupation are three ways of doing it: declaring, working, staying. Of the three, use is the widest, and it was put there to catch exploitation that stops short of a flag. A reactor is a use, and a specialist’s first answer will be that a reactor whose radius denies ground is appropriation by means of use. But a radius takes nothing. It makes ground nobody’s rather than somebody’s. The treaty forbids turning the commons into property. It says nothing about turning it into waste. Denial is not acquisition. No claim to any part of the moon has ever been recognized by any state, and no clause of the article mentions keeping others from a part of it.
The ninth article is where the radius enters, and it enters as a duty rather than a loophole. States must conduct their activities “with due regard to the corresponding interests of all other States Parties,” must avoid harmful contamination of celestial bodies, and, where an activity “would cause potentially harmful interference with activities of other States Parties,” must undertake “appropriate international consultations before proceeding.” The duty falls on the state that acts. The builder of a reactor owes due regard to everyone else’s interests, which on a straight reading is a constraint on where it may put the thing. The builder’s answer is that the zone is the due regard: a ring that keeps everyone else safe from what it has built. So one clause both demands the zone and forbids what the zone does, and nothing in the text says which reading governs. The two articles close on each other: obeying the ninth produces the condition the second forbids.
Eight years earlier the Antarctic Treaty had frozen the sector claims that seven nations had drawn across the map of a continent, and the two texts share four prohibitions almost word for word. Antarctica “shall be used for peaceful purposes only,” the earlier treaty says, and forbids “military bases and fortifications,” “military maneuvers” and “the testing of any types of weapons.” The moon treaty repeats all four. But the Antarctic text has a fifth article that the space text does not: “Any nuclear explosions in Antarctica and the disposal there of radioactive waste material shall be prohibited.” An American reactor, SNAP-10A, had already flown, in April 1965, two years before the space treaty was signed, and the treaty says nothing about a reactor stopping.
The law of the sea, drafted fifteen years later, shows what such a rule looks like. Article 60 is not a legal parallel. Its zones sit in waters where the coastal state already has sovereign rights, not in a commons. It is a drafting model, and it shows the two devices the moon’s treaty lacks: a zone with a stated maximum, 500 metres from the structure’s outer edge, and a duty to remove what is finished — installations “which are abandoned or disused shall be removed.” The ice treaty banned leaving the waste. The sea treaty bounded the zone and required removal. The moon’s treaty did neither, no instrument since has set a maximum for a lunar safety zone, and neither programme has published the radius it intends.
III
The Case for the Zone
The case for the reactor begins with the dark. Away from the poles a lunar night lasts about fourteen days, and the pole is not exempt so much as different. The best-lit ground there, by NASA’s own measurement, is lit up to 90 percent of the time, and nowhere on the moon is lit always. A 2010 NASA study found a site near Shackleton crater sunlit about 240 days a year, with its longest stretch of darkness about a day and a half. The sun never rises far above the horizon, so solar panels must stand on edge and are shadowed by the very terrain that makes the site worth having. The radioisotope generators that have powered spacecraft since the 1960s make watts, not kilowatts. An expanded base, the Times reports, would need far more power than those systems can give. On this reading the reactor is not an instrument of policy. It is the answer to a place that is lethally short of energy.
The safety case is nearly as strong. Both NASA and Russia say their reactors will be launched cold, never having been switched on, and the Times reports that nuclear engineers regard cold uranium fuel as posing little radioactive threat even if it tumbles to Earth. The fuel NASA specifies sits below weapons-usable enrichment. On the safety case as its advocates put it, a cold launch materially reduces the risk, and the reactor becomes dangerous only once it is running, on the moon, where no one lives.
The third pillar is the law itself. The Artemis Accords, the political declaration that 59 nations have signed, provide for “safety zones” around lunar operations. The Accords say a safety zone “should be the area in which nominal operations of a relevant activity or an anomalous event could reasonably cause harmful interference,” that signatories “commit to respect the principle of free access to all areas of celestial bodies,” and, at Section 11, paragraph 7(c), that “safety zones will ultimately be temporary, ending when the relevant operation ceases.” The defence writes itself. Nobody is appropriating anything. The zone is a coordination device, published in advance, bounded by function, and gone the day the plug is pulled.
Each pillar holds. The moon is dark, the launch is clean, and the Accords do bind their signatories to free access and to zones that end. Then come the two facts the defence does not survive.
The first is that only one of the two builders has signed the promise. The Accords have no force beyond their signatories, and Russia and China are not among the 59. They are building the International Lunar Research Station outside that framework. The guarantee that a lunar safety zone will be temporary binds the United States and does not touch the other reactor at all. The symmetry of the race is false at the point where it matters: one builder has also signed something the other has not. One has accepted a constraint it may be about to breach by leaving its reactor where it stands. The other has accepted nothing. And the promise itself was drafted with an escape in it. A drafter who meant zones end when operations end does not write ultimately. The adverb lets a zone persist for a very long time while still being called temporary, and it sits in the only sentence in any instrument that says a zone will end.
The second fact is the harder one. Radioactivity decays. A reactor that is switched off stops fissioning at once, but its core stays hot with the decay of its fission products, intensely at first and then less so for a very long time. A spent reactor becomes approachable, by degrees, over decades and centuries. So the zone is not permanent, only long, and a reader who knows this will conclude that the radius has an end after all, and that the end is a matter of physics rather than law.
The answer is not an argument but a place.
IV
Rules for the Wrong Place
There is a body of law for reactors in space. It was written for the sky, and it is written in the grammar of the sky. The Principles Relevant to the Use of Nuclear Power Sources in Outer Space were adopted by the General Assembly on December 14, 1992, as resolution 47/68, fourteen years after a Soviet reactor came down over Canada. Their operative paragraphs on reactors permit three things: operation “on interplanetary missions,” operation “in sufficiently high orbits,” and operation in low orbit on condition that the reactor is afterwards “stored in sufficiently high orbits.” A sufficiently high orbit is one “in which the orbital lifetime is long enough to allow for a sufficient decay of the fission products to approximately the activity of the actinides.” That is the Principles’ entire doctrine of disposal, and it is a doctrine of altitude and time. Put the thing where nothing lives, and wait.
A reactor at the lunar pole satisfies the first half of that rule and inverts the second. It will rest where nothing lives yet, and it will rest there for as long as the orbital rule contemplates. But the orbit the Principles had in mind is a trajectory nobody walks, and the pole is the one piece of ground that both programmes have named as the place they intend to go. The disposal rule for the sky, applied to the surface, produces the radius. The law’s idea of success and the pole’s idea of denial are the same object at a different address.
The Principles are also out of date about the fuel, and out of date in the direction that matters. Principle 3 instructs that “nuclear reactors shall use only highly enriched uranium 235 as fuel,” which in 1992 was the engineer’s choice, because it is lighter and cheaper to launch. Representative Bill Foster, a physicist, told the Times what highly enriched uranium is on the ground: a machine shop and a little high explosive away from a credible weapon. NASA’s documents now specify high-assay low-enriched uranium, which sits below weapons-usable enrichment, and which Russia produces in greater quantity than anyone, and which the United States has banned from Russian sources since 2024. The only rule the United Nations has ever written about the fuel of a space reactor commands the leading builder to do the opposite of what it is doing, and the alliance that has not disclosed its fuel is the one whose older reactors used the fuel the rule prescribes. None of this binds anyone. A General Assembly resolution is a recommendation, and the United Nations working group that Leopold Summerer leads exists to encourage states to follow such rules, not to enforce them.
The Principles are at their most exact on the one moment everyone agrees is dangerous. The United States and Russia say their reactors will be unirradiated until they arrive, and the Times reports that nuclear engineers regard cold fuel as a small radiological threat even if it falls back to Earth. The Principles take the same view and set down what a cold reactor must survive without going critical: “rocket explosion, re-entry, impact on ground or water, submersion in water or water intruding into the core.” A reactor had come down over Canada before the clause was written. Water moderates neutrons; a core that is safely subcritical in air can be critical in the sea; most launch pads stand beside water. “This is the moment when there is a lot of risk,” Summerer told the Times. In October 2019 a State Department official told the General Assembly’s First Committee that a Russian missile which had lain on the bed of the White Sea since a failed test had, when it was recovered that August, produced “the result of a nuclear reaction.” At least five workers died, the Times reports. Russia said the missile was not powered by a reactor. Nuclear experts told the Times that a reactor going critical in water is probably what happened: the event the clause was written to prevent, in the country with more space reactors behind it than any other.
And the law has been tested once on the ground, in the only way it knows. On January 24, 1978, Kosmos 954 re-entered over the Northwest Territories and scattered radioactive debris across a search area of more than 124,000 square kilometres. The cleanup was called Operation Morning Light; it ran through October, and almost none of the fuel was ever found. Canada billed the Soviet Union just over six million Canadian dollars under the 1972 Liability Convention, and the Soviet Union paid about three million. That is the only time international law has been asked what to do when a reactor comes to rest where it should not, and its answer was to price the damage and send an invoice. On Earth a reactor’s resting place is a misfortune and not an asset. On the moon the asset is the resting place. The Convention knows who pays. It has no idea who is owed. Denial of ground in a commons injures nobody in particular, and nobody in particular has a claim.
The law of the space reactor is a law of the moving piece. It knows what the piece must survive on the way, what fuel it may carry and how high it must be parked when its work is done. It has no sentence for a piece that has stopped on the one square everybody wanted, because in the sky the stopping was the solution.
V
What Stays
Chess has one premise so basic that it is never written down: a piece can be lifted. Every rule of the game assumes it. Capture, retreat, resignation, the pieces back in the box; the squares a piece commanded are free the moment the hand closes on it. The reactor is the first piece offered to the moon that the premise does not cover. It will be set down on a named ridge by a lander nobody has yet built, it will run for five years without a hand touching it, and then, by the stated intention of both builders, it will stay. The question is no longer what a piece commands. It is what a piece that cannot be lifted commands, and for how long.
The Earth has answered that question once. On May 2, 1986, six days after the fourth reactor at Chernobyl burned, a Soviet government commission drew a circle of thirty kilometres around it and ordered the whole of it cleared. The circle was drawn by a state that no longer exists. It is administered today by an agency of a state that was not then sovereign, the State Agency of Ukraine on Exclusion Zone Management, and it covers about 2,600 square kilometres, having been enlarged in 1997 to take in ground the wind had reached. The physics of the place has followed the curve the safety case rests on: the short-lived isotopes are long gone and much of the zone is less dangerous than it was. The line has not followed the curve. Forty years on, it is a border with checkpoints, closed to visitors since the invasion of 2022, and the building at its centre is a war target. On February 14, 2025, a Russian drone struck the New Safe Confinement, the arch completed in 2019 to hold the ruined reactor for at least a hundred years; it opened a hole in the cladding and damaged the crane system inside, and the European Bank for Reconstruction and Development puts the repair at a minimum of €500 million, to be finished by 2030. The zone is not permanent. It is only long, and this is what long has meant in practice: a radius that outlived its author, acquired a bureaucracy, became a frontier, and drew fire from a third party in a war its drafters could not have imagined, all because of what stayed at the centre.
Fourteen years before the fire, two Soviet novelists had described something with the same shape. In Roadside Picnic, published in 1972, Arkady and Boris Strugatsky imagined Zones left behind by visitors who stopped on Earth briefly, left their litter, and moved on, and the people who crept in after them were called stalkers. By way of Tarkovsky’s 1979 film Stalker and a 2007 video game, the book’s word became the word for those who enter the real zone without permission. The novel’s title is its argument. The visitors meant nothing by what they left. The zone was not a claim and not an attack. It was the residue of someone else’s convenience, and it governed the lives of everyone who lived at its edge for as long as it lasted.
That is the shape of the thing the moon is being offered. The radius has an end, and the end is a matter of physics, and zones on Earth have in fact contracted as the physics changed. Japan has lifted its Fukushima evacuation orders in stages as dose rates fell, and in August 2022 the order came off part of Futaba, one of the two towns that host the plant. But zones shrink from the outside in, and they have never reached the middle. Fukushima has given back town after town and the plant site remains closed; at Chernobyl the centre is what is under a €500 million repair. What was returned was contaminated ground around a reactor. What was never returned was the reactor.
The lunar zone is a centre with no periphery. There is no dispersed fallout to clean and no farmland anyone wants back; the ring is the asset, the ridge and the approaches and the ice, so the one mechanism by which terrestrial zones have ever contracted has nothing to work on. The lunar zone will be drawn by its builder, under a declaration that promises it will “ultimately” end, or by a builder that has promised nothing, and no instrument names who may draw the second line, the one that says the first has expired. The Outer Space Treaty forbids the flag. It has nothing to say about the circle, and the circle is what stays.
The first reactor is scheduled to stop in the middle of the 2030s, when the second is scheduled to start. Somebody may be standing at the pole then, under one declaration or none, looking at a ring on a ridge that nobody owns and nobody may enter. Whether they call it a precaution or a border is the smaller question. The larger one is whether a place no one can enter is owned, or only lost, and nothing yet written says who gets to decide.
❧
Sources: the reactor programmes, dates, power levels, fuel, launch safety, the White Sea and Kosmos 954 as reported by Selam Gebrekidan, “Superpowers Race to Put Nuclear Reactors on the Moon,” The New York Times, October 4, 2026. Treaty texts read at source: the Outer Space Treaty (1967), Articles II and IX; the Antarctic Treaty (1959), Articles I and V; the UN Convention on the Law of the Sea (1982), Article 60; General Assembly resolution 47/68 (1992), Principles Relevant to the Use of Nuclear Power Sources in Outer Space, Principle 3; the Artemis Accords (2020), Section 11. NASA on Artemis III candidate regions (2022, 2024), on polar illumination (Mazarico et al., 2010; LROC, 2019) and on the moon’s radius. The 2019 State Department statement from Arms Control Today and RFE/RL. Operation Morning Light from The Canadian Encyclopedia. The Chernobyl zone’s establishment, area, administration and closure from secondary reporting, matched across at least two accounts; the New Safe Confinement from the European Bank for Reconstruction and Development at source. Fukushima evacuation orders from Japan’s Ministry of the Environment.
Header and interior images generated with Gemini for this essay. Drafted with Claude Fable 5.1 and Claude Opus 5.5; literary editing by Claude Opus 5; copy editing by Gemini.