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ROentgen SATellite

Phase: Past

Launch Date: June 01, 1990

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ROSAT, the ROentgen SATellite, was an X-ray observatory developed through a cooperative program between the Germany, the United States, and the United Kingdom. The satellite was designed and operated by Germany, and was launched by the United States on June 1, 1990. The ROSAT mission began with a six-month, all-sky PSPC survey, after which the satellite began a series of pointed observations. It was turned off on February 12, 1999. ROSAT deorbited on October 23, 2011.

The ROSAT mission was divided into two phases: (1) After a two-month on-orbit calibration and verification period, an all-sky survey was performed for six months using the PSPC in the focus of XRT, and in two XUV bands using the WFC. The survey was carried out in the scan mode. (2) The second phase consists of the remainder of the mission and was devoted to pointed observations of selected astrophysical sources. In ROSAT's pointed phase, observing time was allocated to Guest Investigators from all three participating countries through peer review of submitted proposals. ROSAT had a design life of 18 months, but was expected to operate beyond its nominal lifetime.

On September 11, 1994, after four years of successful operation, the PSPC was shut down to conserve the remaining detector gas. This remaining gas was thought to have been used up during 1997 in a series of pointings to complete the all-sky survey coverage, but several other PSPC observations were carried out in 1998 and early 1999.

Science Highlights

After nearly nine years of science observations, ROSAT left a significant scientific legacy in more than 8500 publications. ROSAT discovered that almost all astronomical objects emit X-ray radiation, including some objects where this had not been expected. The observed objects included the Moon, comets, stars, X-ray binary stars, neutron stars, supernovae and supernova remnants, the interstellar medium, galaxies, active galactic nuclei, black holes, nebulae and the cosmic X-ray background. Some other results include:

  • the first ever full-sky survey with an imaging X-ray telescope producing a catalog containing more than 100,000 X-ray sources
  • the surprising discovery that comets emit X-ray radiation
  • the detection of isolated neutron stars

Last updated: April 24, 2015

Related Links
  • German ROSAT web page -