A 1.45 megaton nuclear explosion occurred in space 399 km. (248 miles) above Johnston Island in the Pacific Ocean on July 9, 1962. The 755 kg. (1665 pound) warhead was launched by the US Air Force using a Thor Missile. Codenamed Starfish Prime, the explosion was more than 100 times more powerful than the Hiroshima blast and formed its own artificial aurora. The height of the detonation is equivalent to the orbital altitude of the present-day Space Shuttle.

Starfish Prime was part of a series of 36 atmospheric nuclear tests known as Operation Dominic that took place on Johnston Island or nearby Christmas Island in 1962. Operation Dominic was initiated by the United States following a series of Soviet atmospheric tests late the previous year. Starfish Prime was intended to test the effectiveness of missile-launched nuclear weapons in destroying enemy satellites or ballistic missiles re-entering the atmosphere. The test had some unintended consequences, including the momentary creation of an artificial aurora as radioactive particles interacted with the Earth’s magnetic field. The explosion also knocked out electronic systems on the island of Oahu in Hawaii 1200 km. (800 miles) away – this was a new discovery known as the Electro-Magnetic Pulse (EMP). Atmospheric nuclear explosions were banned by treaty in 1963.