Exosat was an ESA (European Space Agency) satellite for X-ray astronomy that carried out observations of variable X-ray sources in the energy range 0.05–20 kiloelectronvolts (keV) (corresponding to wavelengths of 0.025–1.24 nanometers). On board were three instruments: an imaging telescope, a proportional counter, and a gas scintillation proportional counter array.


Exosat made 1,780 observations of a wide variety of objects, including active galactic nuclei, stellar coronae, cataclysmic variables, white dwarfs, X-ray binaries, clusters of galaxies, and supernova remnants. It stopped operating after three years, on April 9, 1986.


launch date May 26, 1983
launch vehicle Delta 3914
launch site Vandenberg Air Force Base
orbit 340 × 191,878 km × 72.5°
mass 510 kg