On June 1, 1990 the German X-ray observatory ROSAT started its mission to open a new era in X-ray astronomy. Doubtless, this is the most ambitious project realized up to now in the short history of this young astronomical discipline. Equipped with the largest imaging X-ray telescope ever inserted into an earth orbit ROSAT has provided a tremendous amount of new scientific data and insights.

ROSAT was proposed by MPE in 1975 and after extensive advance developments and studies approved by the Bundesministerium für Forschung und Technologie (BMFT), now Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF), in 1983. Accordingly cooperational agreements have been concluded with the American National Aeronautics and Space Administration (NASA) and with the British Science and Engineering Research Council (SERC).

On behalf of the BMFT the German Aerospace Center and later the Deutsche Agentur für Raumfahrtangelegenheiten GmbH (DARA) is acting as customer while Dornier represents the industrial prime contractor responsible for the development, manifacturing, integration, and test of the spacecraft.

The scientific management and the responsibility for developing the focal plane instrumentation of the X-ray telescope are with the Max-Plank-Institute for Extraterrestrical Physics (MPE). Here was established also the science data center for analysis and interpretation of all scientific data gained.

NASA has contributed with the launch on the Delta-II rocket and with the high resolution imager (HRI), an X-ray detector built by the Smithsonian Astrophysical Observatory (SAO). A similar instrument has already been flown on the American Einstein mission.

SERC has provided the wide fiels camera (WFC) a second imaging telescope. The WFC has been built by a consortium of English institutes under the leadership of Leicester University.

Mission operations has been performed just after the seperation from the second stage of the rocket by the German Space Operation Center (GSOC). Any telecommunication with the spacecraft uses the GSOC ground station in Weilheim/Germany.