On this day: 26 May 1983, ESA’s X-ray observatory, Exosat, was launched by a Thor-Delta rocket from Vandenberg Air Force Base, USA. Designed to observe and detect high-energy sources, Exosat was the first ESA mission to study the Universe at X-ray wavelengths, and one of the first unmanned satellites to feature an onboard computer. The spacecraft was operational from May 1983 to April 1986 and during that time made 1780 observations of a wide variety of objects. Natural decay of the orbit caused the satellite to enter the atmosphere on 6 May 1986.