The Vela Incident: A Double Flash and a Hidden Nuclear Test

On September 22, 1979, the US satellite Vela 6911 recorded a double flash over the ocean between the South Atlantic and the Indian Ocean. This is the kind of signal Vela was built to find: the light of an atmospheric nuclear explosion.

Vela was not a weather satellite. The 1963 Partial Test Ban Treaty banned nuclear tests on land, underwater, and in the atmosphere. After that treaty, the United States put Vela in orbit to look for secret atmospheric tests. The light sensor on Vela was called a bhangmeter.