MIT researcher proposes neutron sensor to detect nuclear weapons aboard satellites

Specifically, the proposed sensor would search for neutrons released when a high-energy proton strikes an element with a high atomic number, such as uranium or plutonium. Each individual proton would release around 40 neutrons, he explains. When you detonate a nuclear weapon in space, essentially the entire explosive device is ionized and nearly every electron in the weapon is released.

Two scintillator detector panels, embedded between artificial diamond crystals, are intended to produce flashes of light when struck by radioactive radiation or neutrons. This would allow the direction of the neutrons to be determined and to distinguish whether they originate from a suspect satellite or from the cosmic background radiation. From a maximum distance of 1,000 meters, the required observation time would drop to as little as one hour; from approximately 4,000 meters away, the satellite would need to be monitored for roughly a week from a maximum distance of 4,000 meters to determine with 99 percent certainty whether it carries a nuclear bomb.

Legal situation and lack of control

The study is set against concerns that the stationing of nuclear weapons in space is prohibited under the Outer Space Treaty, but that this prohibition may be being violated. The states parties to the treaty undertake not to place in orbit around the Earth any objects carrying nuclear weapons or other weapons of mass destruction, not to install such weapons on celestial bodies, and not to station such weapons in outer space in any other manner. A total of 118 states have signed the treaty, including the United States, China, and Russia (then the Soviet Union). To date, there are no publicly known methods for verifying compliance with this rule.

In early 2024, the US government informed Congress and European allies about Russian advances in developing a nuclear weapon for use in space. However, Russia blocked any tightening of these rules in 2024 with a veto in the UN Security Council. Russia states that the Kosmos 2553 satellite launched in 2022 carries out reconnaissance from space; its orbit is, however, considered by researchers to be unsuitable for conventional reconnaissance and to be particularly radiation-intensive.

Potential consequences of a detonation in orbit

Danagoulian argues that precisely this orbit would be particularly suited to detonating a nuclear weapon capable of destroying US reconnaissance satellites and international communications networks such as Starlink. By detonating a nuclear weapon in orbit, numerous satellites could be destroyed in a single blow. This could not only severely damage the network of Starlink satellites, but communications and reconnaissance satellites could also be taken out of service in this way. GPS, telecommunications, and space-based internet would all be under threat.

The consequences would be severe: such an attack would simultaneously render parts of orbit unusable, with catastrophic fallout. Today, the explosion of a nuclear bomb in orbit could disable many satellites for months at a time. The detonation of a nuclear bomb in Earth orbit could have catastrophic consequences for humanity. As early as 1962, the United States detonated a 1.4-megaton nuclear bomb at an altitude of 400 km over the Pacific (Starfish Prime), after which many of the satellites deployed at the time were damaged or failed.

Verification as leverage

Danagoulian sees verification as the real lever: "Wenn wir irgendwann einen Verifikations-Mechanismus für den Weltraumvertrag haben, wird das Druck auf die Staaten ausüben, diesen auch einzuhalten oder offenzulegen, was sie im All tun. Sie wissen dann, dass wir es herausfinden werden". He sums it up with the sentence: "Man kann Geheimdienstberichte fälschen, aber nicht die Physik." He says his proposal is a signal to the community of nations that violations would in future be technically detectable.

However, the work is so far only a feasibility study. The concept still needs to be tested, Danagoulian says. He is calling on government laboratories to develop prototypes so that political decision-makers recognize the relevance of the technology for security. It is likely to take years before operational scanners are flying in orbit. The geopolitical debate over anti-satellite weapons and the future of the 1967 Outer Space Treaty, which originated at the initiative of the United Nations, is, however, already being fed with a new technical argument.

This article was written by Stefan Parsch and appeared in Tagesspiegel Plus. It traces how a physical idea at MIT became a politically highly relevant proposal that could close the decades-old gap in verifying the Outer Space Treaty.