As part of Operation Dominic, the United States launched a Thor rocket carrying a 1.4-megaton warhead that detonated in space above Johnston Atoll. The explosion, known as Starfish Prime, produced an electromagnetic pulse that damaged electrical systems nearly 900 miles away in Hawaii and generated radiation belts that disabled several satellites, including one of the world's first commercial communications satellites, Telstar, months later.
At the height of Cold War anxiety over ballistic missile defense, American scientists wanted to know what a nuclear explosion in space would actually do — to missiles, to satellites, to the ionosphere itself. On July 9, 1962, a Thor rocket lifted off from Johnston Atoll and carried its 1.4-megaton warhead to an altitude of about 250 miles before detonating.
The result stunned observers as far away as Hawaii, nearly 900 miles distant, where the night sky turned brilliant green and red for several minutes, and streetlights across Honolulu blinked out as the electromagnetic pulse fried surge arrestors and circuit breakers. Ham radio operators around the Pacific reported disruptions for hours.
More lastingly, the blast injected high-energy electrons into the Earth's magnetic field, creating an artificial radiation belt that persisted for years and gradually crippled satellites never designed to survive it, including Telstar 1, the pioneering communications satellite, which failed within months. Starfish Prime became the textbook case for the danger of electromagnetic pulse, a threat that still shapes military planning around hardening electronics against a nuclear detonation in space.