Nuclear Physicist Wants To Catch Hidden Space Nukes by Using Earth’s Radiation Belts

A proposed CubeSat inspector could verify a treaty that space powers mostly take on trust.

Somewhere above Earth, natural radiation may be doing what spies cannot: probing satellites for hidden nuclear weapons.

Although the 1967 Outer Space Treaty bans nuclear weapons in space, there’s currently no way to verify that satellites aren’t carrying them — and there are very good reasons to believe some nations have secretly deployed such weapons in Earth’s orbit.

In a study, Areg Danagoulian, a nuclear scientist at MIT, proposes a novel way to detect nukes in space using radiation. His idea is not to shoot radiation at a suspect spacecraft, but to let Earth’s own radiation belts do the work. High-energy protons trapped around the planet would strike uranium in a nuclear device and knock loose neutrons — a signal that a nearby “inspector” satellite could, in theory, detect.

A Treaty Without a Geiger Counter

For decades, the treaty’s weakness mattered less because orbit was sparse and geopolitical risks were low after the end of the Cold War. Both are no longer true. Near-Earth space has become critical infrastructure. It carries military communications, missile-warning systems, weather data, navigation signals, broadband internet and the daily machinery of modern life.

The orbit is much more crowded. The European Space Agency estimates that about 15,900 functioning satellites are now in orbit, while roughly 45,700 tracked objects circle Earth overall. Starlink alone has around 10,000 satellites, and Amazon’s Leo network is approaching 400 as it builds out a planned 3,200-satellite constellation, according to Reuters.

That is why a nuclear weapon in orbit would be so dangerous. It would not need to strike satellites one by one. In 1962, the United States detonated Starfish Prime about 400 kilometers above the Pacific. It was basically a nuclear weapon test in space. The blast flooded Earth’s magnetic field with energetic particles, creating an artificial radiation belt that damaged satellite electronics and helped disable several early spacecraft. A similar explosion today could threaten thousands of satellites at once, especially those not hardened for intense radiation.

“The reason this is under pressure is that the U.S. heavily depends on space capabilities for military power, and Russia, in particular, is exploring how to take those space capabilities away,” Jeffrey Lewis, a nuclear nonproliferation expert, told Scientific American.

“They seem to be considering mass kill [of satellites] in orbit, and if you think about it, what’s the easiest way to get rid of all those Starlink satellites? It would be to detonate a small number of nuclear weapons,” Lewis said.

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U.S. officials have accused Russia of developing a satellite meant to carry a nuclear weapon in orbit. In 2024, Vipin Narang, then a senior Pentagon space policy official, said Russia was developing “a new satellite designed to carry a nuclear weapon on orbit” that, if detonated, “could potentially wipe out an entire orbit of assets.” Russia has denied the allegation.

Turning Space Radiation Into a Detector

Danagoulian’s proposal rests on the activity of the inner Van Allen belt, a harsh region where Earth’s magnetic field traps high-energy protons and electrons.

In February 2022, Russia launched Kosmos 2553 into an unusual orbit about 2,000 kilometers above Earth. Moscow has said the satellite belongs to its Neitron radar system and is used for surveillance and remote sensing. U.S. officials have described it differently: as a possible test platform for a nuclear anti-satellite weapon. Kosmos 2553 is smack in the middle of the inner Van Allen belt.

If a spacecraft carried a thermonuclear device with a uranium radiation case, protons would slam into heavy atomic nuclei and trigger a process called spallation. In plain language, the collision would chip neutrons out of the material.

“If you detect those neutrons, that itself can be a telltale sign that there is an unusual amount of uranium on the satellite, and it’s most likely to be a nuclear weapon,” Danagoulian said.

The proposed inspector would be small: roughly the size of a 9U CubeSat. In the proposed model, it carries two square detector panels, each 30 centimeters across, built from pixel-like sensors. Diamond layers would help reject charged particles such as electrons and protons, while plastic scintillators would register neutrons.

The diamonds are “very good at detecting charged particles, such as electrons and protons, but are essentially transparent to neutrons,” Danagoulian told Scientific American. “If a neutron comes in, it’s not going to interact with the diamond, but it will interact with an internal neutron detector.”

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Sensitivity is key to this task as the orbit is noisy. Neutrons also bounce up from Earth’s atmosphere. The system would need to tell whether a neutron came from the suspect satellite above or from somewhere else. Danagoulian’s model borrows from neutron scatter cameras, using two detector planes to reconstruct the incoming direction.

The Hard Part Is Getting Close

This is not a device that could scan all of orbit for secret weapons. It would work only after another source — intelligence, tracking data or suspicious behavior — had already identified a satellite worth inspecting. You’d need one of these nuke sniffer satellites for every suspect object operated by a hostile nation.

In Danagoulian’s model, one CubeSat could identify a hypothetical thermonuclear weapon from about four kilometers away after roughly one week of observation. A group of 10 inspectors could reduce that time to about 15 hours. At one kilometer, the job might take about an hour — essentially one flyby.

That is scientifically intriguing but more politically fraught. Shadowing another nation’s satellite at close range could itself look hostile and cause all sort of incidents. Recent years have already seen several close approaches among U.S., Russian and Chinese satellites, but routine nuclear inspections in orbit could result in unwanted escalation.

Danagoulian is careful not to oversell the idea. “I say in the paper this isn’t a completely proven system,” he told MIT News. “The purpose of the paper is to show the scientific community that it’s scientifically possible to do this. But there are many more practical considerations to be made to actually build these detectors.”

There are technical caveats, too. Shielding could weaken the neutron signal. Some heavy non-nuclear materials, such as lead or tungsten, might also produce neutrons. The model assumes a particular weapon design and an unshielded uranium mass; real weapons are classified and variable.

Still, the proposal gives the Outer Space Treaty something it has never really had: a physics-based path toward verification. A treaty with no means of verifying if the parties adhere to its clauses is not worth the paper it was written on.

The findings were reported in the journal Nature.