A constellation of cubesats fitted with special detectors could sniff out nuclear weapons hidden on satellites launched by adversary nations, according to a new study.
In 2024, rumors began to swirl in military circles that Russia might be developing a space-borne nuclear weapon. At that time, two years into the war in Ukraine, Russia was well aware of how big a lifeline SpaceX's Starlink broadband constellation had been for the Ukrainians. Starlink has not only provided connectivity to ravaged cities and frontline troops but also helped Ukrainians counter-attack the Russian invaders more effectively.
Drones fitted with Starlink terminals could reach much more distant targets than those controlled via conventional radio links. As the Starlink signal is almost impossible to disrupt by jamming, the idea that Russia might consider wiping the megaconstellation out by brute force didn't seem impossible.
Researchers know that a nuclear detonation in orbit would flood the space around Earth with fast, energetic electrons. These particles would destroy most unhardened satellites within range, which would extend to orbits even hundreds of miles away from the explosion.
"It would make the low Earth orbit and very low Earth orbit — where the Starlink satellites are, where many reconnaissance and communications satellites are, and where the International Space Station is — uninhabitable for a long period of time," Areg Danagoulian, an associate professor of nuclear science and engineering at the Massachusetts Institute of Technology and the author of the new paper describing the proposed detection method, told Space.com.
"We would essentially not only lose the satellites in those orbits, we would lose those orbits for a few years," he added.
Humankind has already seen the effects of a nuclear explosion in space. In 1962, the U.S. detonated a 1.4-megaton hydrogen bomb at an altitude of 240 miles (400 kilometers) above the Pacific Ocean. Radiation from the explosion, known as the Starfish Prime test, destroyed one-third of all satellites in orbit at that time. Admittedly, there weren't that many up there — fewer than 100 — but the impact was far-reaching.
Today, a nuclear detonation in space would be a catastrophe. It would knock out internet-beaming constellations such as Starlink and Amazon Leo, as well as hundreds of Earth-observing satellites that keep an eye on the activity of adversary nations, the changing climate and areas struck by natural disasters.
No reliable way currently exists to detect and defuse a nuclear bomb in space. Danagoulian proposes a constellation of small "9U" cubesats, each one about the size of a large shoebox and each carrying a special detector capable of sensing radiation emitted by unexploded nulear bombs.
He explores a scenario in which Russia launches a suspected space nuke into an orbit with an altitude of 1,200 miles (2,000 km). That number is not random. In 2022, Russia's Kosmos 2553 satellite, orbiting at that exact altitude, triggered suspicions it might be testing components for a future orbital nuclear weapon.
Russia claims the satellite just observes Earth. At that altitude, the satellite passes through the Van Allen belt, a region of intense cosmic radiation trapped by Earth's magnetic field. Most of the belt stretches between altitudes of around 600 miles (1,000 km) to tens of thousands of miles, but in some areas the radiation can reach much closer to Earth's surface.
The interaction between the fissile material inside the nuke and the energetic particles from the radiation belt would create distinct signatures, Danagoulian said, which could help confirm whether a suspicious satellite carries a nuke or not.
"The thermonuclear weapon would contain a significant amount of uranium," Danagoulian said. "The high-energy protons [in the uranium] would break up when another proton is coming in and shred the nuclei. That would knock out a large number of neutrons. This interaction turns that device into a very intense neutron source that otherwise would not be there."
The process is known as proton-induced neutron spallation, which essentially means the ejection of fragments from material triggered by impacts of protons.
The detector satellite Danagoulian proposes would have to be able to get quite close to the suspect spacecraft — a few kilometers. The inspector spacecraft would carry a sensor combining two types of detectors. At the heart of the device is a neutron scintillator, which detects all incoming neutrons and protons. Around it is a "cage of diamond" detector that detects only neutrons — not protons. Such a set-up helps filter out the particles present in the environment naturally, said Danagoulian. In addition, by using two "planes of neutron detectors," the sensor can determine the direction from which the neutrons arrived.
"If the external diamond detector triggers and gives a signal, you can ignore the particle, because it's most likely a proton and not a neutron," said Danagoulian. "Once you identify those neutrons, by having those two detections, you can back project and find out where the neutron came from."
Danagoulian says such a nuke sniffer would have to be launched into an orbit aligned with that of the suspicious satellite and creep up as close as 2.5 miles (4 km) from it. It would then take about a week to gather enough measurements to confirm whether the object is hiding a nuke or not. A constellation of 10 such satellites could reduce the process to mere hours, Danagoulian said.
If a nuke were detected, the military could then try to jam the satellite's communications link from the ground, making it impossible for the adversary to remotely detonate the bomb. There is currently no technology available to safely defuse a nuclear weapon in space.
The United Nations Outer Space Treaty, which provides the legal foundation for humankind's use of outer space, bans the use of nuclear weapons in orbit. However, the treaty has no means to ensure compliance.
Other approaches to nuke detection in space have been explored, including maneuverable X-ray satellites, but those would be quite a bit more complex and expensive.
Danagoulian also suggests that high-grade radiation hardening could improve satellites' chances of surviving a nuclear winter in space.
The paper was published online in the journal Nature today (July 8).
