Starfish Prime was a high-altitude nuclear test conducted by the United States on July 9, 1962. It was intended to test the effects of a nuclear explosion on Earth's magnetosphere. A 13-kiloton nuclear warhead was detonated over Johnson Atoll in the North Pacific Ocean. This warhead was 100 times stronger than the nuclear detonation in Hiroshima.
The Starfish Prime test caused an electromagnetic pulse that knocked out electrical and telephone systems 1,300 miles away in Hawaii. It temporarily disrupted the Van Allen radiation belt by creating its own artificial radiation belt, which led to visible auroras across the South Pacific Ocean. Numerous satellites in low orbit were destroyed by the blast. By some estimates, as many as one-third of Earth's current satellites were damaged or entirely destroyed by Starfish Prime. The artificial radiation belt persisted longer than anticipated, with electrons from the test detected by satellites five years later.
The United States performed the test in response to the Soviet Union's Tsar Bomb test. Tsar Bomb was a 1961 weapons test that resulted in the largest nuclear detonation in history. It began an escalating series of nuclear tests on both sides. These tests led to the Cuban Missile Crisis in 1962.