A history of gamma-ray satellites

Long before they could detect gamma rays, scientists suspected this type of radiation was produced throughout the universe. To identify these emissions, Earth-bound detectors would have to be placed outside our atmosphere, which typically absorbs gamma rays. In 1961, the Explorer XI satellite carried the first gamma-ray telescope into Earth orbit, which gathered fewer than 100 cosmic gamma-ray photons.

While astronomers use Earth-based observatories to identify gamma ray bursts, they still utilize orbiting telescopes for studying gamma rays. These satellites have made significant contributions to gamma-ray astronomy in their five-decade history.

Listed below are gamma-ray satellites that have helped us develop a better understanding of these high-energy photons.

Explorer XI
Launch Year: 1961
Agency: NASA

Carrying a telescope built by Massachusetts Institute of Technology (MIT) scientists William L. Kraushaar and George W. Clark, Explorer XI was the first satellite dedicated to gamma-ray astronomy. Placed in an eccentric orbit around Earth, the satellite searched for the signs of cosmic-ray interaction with interstellar material. Because Explorer could not be actively directed, the spacecraft rotated end over end, providing a rough scan of the celestial sphere. The satellite detected 22 cosmic gamma-ray events before its power source deteriorated.