In October of 1963 the US Air Force launched the first in a series of satellites inspired by a recently signed nuclear test ban treaty. Signatories of this treaty agreed not to test nuclear devices in the atmosphere or in space. These "Vela" (from the Spanish verb velar, to watch) satellites were part of an unclassified program whose goal was to develop the technology to monitor nuclear tests from space. A Vela satellite is pictured above in an artist's conception, keeping watch over the Earth. The high energy radiation sensors onboard the Velas did not detect any clandestine nuclear explosions. Instead, in the most surprising discovery in the history of space based astronomy, they found bursts of gamma rays coming from deep space! The mysterious origin of these brief, intense flashes of gamma rays is one of the most hotly debated topics in modern astrophysics.