High-altitude nuclear burst. - the Wikipedia description
"...The only nations to detonate nuclear weapons in outer space are the United States and the Soviet Union. The U.S. program began in 1958 with the Hardtack Teak and Hardtack Orange shots, both 3.8 megatons. These warheads were initially carried on Redstone rockets. Later tests were delivered by Thor missiles for Operation Dominic I tests, and modified Lockheed X-17 missiles for the Argus tests. The purpose of the shots was to determine both feasibility of nuclear weapons as an anti-ballistic missile defense, as well as a means to defeat satellites and manned orbiting vehicles in space. High-altitude nuclear blasts produce significantly different effects. In the lower reaches of vacuous space, the resulting fireball grows much larger and faster than it does near the ground, and the radiation it emits travels much farther...."
Reference: wikipedia.org .
