One nuclear blast 500 km up could knock out 99% of Earth's satellites within two weeks, study finds

A single nuclear weapon detonated at the right altitude could disable virtually every satellite circling Earth within a month — not through the force of the explosion itself, but through an invisible, lingering radiation trap that satellites would fly through again and again until they failed. That is the central finding of a new simulation by researchers at the University of Wisconsin–Madison and Princeton University, published as a preprint and not yet peer-reviewed.

To conduct the simulation, the team chose a 1-megaton nuclear detonation at an altitude of 500 kilometers above the South Atlantic, positioned near the South Atlantic Anomaly — a broad zone where Earth's magnetic field is notably weaker than elsewhere. Using a starting figure of 13,300 active low-Earth orbit satellites as of January this year, they traced the aftermath hour by hour and then day by day.

The initial blast would disable only a small fraction of satellites directly. The far larger threat comes afterward: electrons released by radioactive fission-product decay become trapped in Earth's magnetic field, forming an artificial radiation belt. Every satellite in low-Earth orbit keeps passing through that belt on each orbit, accumulating damage until it fails.

Electrons from radioactive fission-product decay became trapped in Earth's magnetic field, creating an artificial radiation belt that damaged satellites. Unlike the prompt burst, a trapped belt repeatedly exposes spacecraft as they pass through it. A comparable event today would occur in a much more densely populated orbital environment.— Zach Petersen, lead author and UW astronomy-physics student

The timeline in the simulation is steep. Within one day, 25 percent of the entire satellite fleet would be disabled. By day three, 78 percent. After one week, 98 percent. By day 15, 99.4 percent of all satellites in low-Earth orbit would be gone, according to the study.

Even satellites built with significantly stronger radiation shielding would not escape: in a scenario where spacecraft were given tripled radiation protection, 99.3 percent would still be disabled within 30 days, the researchers found. A smaller, 100-kiloton warhead would slow the process but not stop it — neutralizing 99 percent of satellites within a year.

The consequences would extend well beyond the initial wave of failures. As satellites lose the ability to maneuver, the risk of collisions rises sharply. The researchers estimate approximately 20 collisions within the first two years, generating around 3,900 new fragments of space debris over a decade. The team warns that "continued collisions among long-lived objects are expected to sustain debris production beyond the simulated decade, with the possibility of a slow buildup and eventual runaway growth on century timescales."

Rebuilding would not simply mean launching replacement satellites. Any new spacecraft sent up would have to survive both the residual radiation belt and the debris field left behind — a compounding problem the researchers say could leave orbital services disrupted for years.

Restoring orbital services would require more than replacing the lost spacecraft: new satellites would need to survive the remaining radiation and debris. The prospect of rapid infrastructure loss followed by years of disruption reinforces the need to prevent the deployment and use of nuclear weapons in space.— study authors

The scenario is not purely theoretical. Eighteen high-altitude nuclear explosions were carried out by the US and USSR during the Cold War. Among them was Starfish Prime, in which a 1.4-megaton warhead was detonated over the Pacific Ocean at 400 kilometers altitude in 1962. That test disabled several satellites of the era and produced precisely the type of trapped radiation belt that the new study models. One year later, the US and Soviet Union agreed to halt above-ground nuclear testing by signing the Partial Nuclear Test Ban Treaty.

A separate 2025 RAND report, sponsored by the Cybersecurity and Infrastructure Security Agency and covering publicly available literature on high-altitude nuclear explosions, examined prompt and delayed radiation effects in illustrative cases at different altitudes and yields. RAND's authors note that outcomes depend heavily on assumptions about detonation location, weapon yield, and how well satellites are hardened against radiation. The new preprint represents a specific worst-case scenario rather than a universal prediction.

What has changed since 1962 is the scale of what is at stake. Low-Earth orbit now holds more than 13,000 active satellites that underpin weather forecasting, telephone and data communications, satellite internet services, navigation, and remote sensing. The researchers' conclusion is blunt: the density of today's orbital environment makes a comparable detonation categorically more destructive than anything the Cold War produced.

Why it matters — More than 13,000 satellites underpin the weather forecasts, communications, navigation, and internet services that modern economies and militaries depend on daily — and this study suggests all of it could be erased within two weeks by a single weapon.

Sources differ on Proportion of LEO satellites immediately disabled by a high-altitude nuclear detonation: ~99% within 15 days (1-megaton at 500 km over South Atlantic Anomaly) (arxiv.org / sciencealert.com) vs ~20% from prompt effects (different yield and altitude scenarios) (rand.org)

Reported by arxiv.org, sciencealert.com, heise.de, rand.org