The Compton Gamma-Ray Observatory (CGRO) The Compton Gamma-Ray Observatory was launched April 7, 1991. It is the version of the Hubble Space Telescope that detects gamma-ray emissions. Its mission is to study gamma-ray emissions in not only our galaxy, but other galaxies beyond ours, and to investigate how neutron stars and black holes change over time. The Compton Observatory is expected to ...