June 1, 1990 · The ROSAT Mission · February 12, 1999

The German-US-UK X-ray observatory ROSAT (Röntgen Satellite) was launched into a 550 km circular orbit on June 1, 1990. It carried two imaging telescopes operating in the soft X-ray (0.1-2.4 keV) and EUV (0.06-0.2 keV) ranges. The X-ray telescope consisted of four nested Wolter type I-mirrors. The manufacturing of the X-ray mirrors - the largest and most accurate ones at that time - pioneered the use of Zerodur (a ceramics with zero thermal expansion) and an extremely low surface roughness (0.25 nm rms). In its focus were two position sensitive proportional counters (PSPC, 20 arc sec) and one high resolution imager (HRI, 5 arc sec). The EUV telescope consisted of three nested Wolter-Schwarzschild mirrors and two channel plate detectors (3 arc min). The satellite and the X-ray telescope was designed, built and operated by Germany. NASA provided the Delta launch and the high resolution imager while the UK built and operated the EUV telescope. The prime ROSAT data centers were and are at the Max-Planck-Institute for Extraterrestrial Physics in Garching (X-rays) and at the University of Leicester (EUV) with mirror sites at the Goddard Space Flight Center and other scientific institutions.

ROSAT performed the first all sky surveys with imaging telescopes leading to the discovery of 125,000 X-ray and 479 EUV sources. In addition the diffuse galactic X-ray emission was mapped with unprecedented angular resolution (< 1 arcmin). Most of the mission time was devoted to pointed observations at selected targets. In total 4580 PSPC and 4482 HRI fields were covered with observation times between ~ 2,000 sec and ~ 1 Million sec. 700 Scientists (Principal Investigators) from 24 countries were involved in these pointed observations. The total number of ROSAT based publications is 4787, with 54,9 % in referred journals (status August 2001). All ROSAT data are calibrated and available via an on-line archive. ROSAT was switched off in February 1999 after 8 1/2 years of successful operation.

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 Wirtschaft und Technologie (BMWI), in 1983. Accordingly cooperational agreements were 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) was acting as customer while Dornier represented 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 were with the Max-Plank-Institute for Extraterrestrical Physics (MPE). Here also the science data center for analysis and interpretation of all scientific data gained was established.

NASA had 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 was already flown on the American Einstein mission.

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

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