Starfish Prime was the largest nuclear detonation conducted in outer space, revealing unexpected electromagnetic and radiation effects at high altitude.
Key Facts
- Detonation Altitude
- 250 miles (400 km)
- Warhead Yield
- 1.4 megatons Mt
- Launch Site
- Johnston Atoll, Pacific Ocean
- Distance from Hawaii
- ~900 miles (1,450 km)
- Rocket Used
- Thor rocket with W49 thermonuclear warhead
- Test Date
- July 9, 1962, 11 PM Hawaii time
By the Numbers
Location
Cause → Event → Consequence
During the Cold War, the United States and Soviet Union conducted extensive nuclear testing programs. The U.S. Atomic Energy Commission and Defense Atomic Support Agency sought to understand the effects of high-altitude nuclear detonations on military communications, electronics, and space systems, prompting a series of exoatmospheric nuclear tests.
On July 9, 1962, a Thor rocket carrying a W49 thermonuclear warhead was launched from Johnston Atoll. The warhead detonated at an altitude of 250 miles above the Pacific Ocean, yielding 1.4 megatons. It became the largest nuclear explosion ever conducted in outer space, one of five such tests performed by the United States.
The detonation produced a powerful electromagnetic pulse and created an artificial radiation belt that damaged or disabled several satellites in low Earth orbit. The visible effects, including a vivid aurora visible from Hawaii, revealed that high-altitude nuclear explosions had far broader and longer-lasting electromagnetic and radiological consequences than previously anticipated.