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The Roentgensatellit (ROSAT) was a joint German, US and British X-ray astrophysics project. ROSAT carried a German-built imaging X-ray Telescope (XRT) with three focal plane instruments: two German Position Sensitive Proportional Counters (PSPC) and the US-supplied High Resolution Imager (HRI). The X-ray mirror assembly was a grazing incidence four-fold nested Wolter I telescope with an 84-cm diameter aperture and 240-cm focal length. The angular resolution was <5 arc-s at half energy width. The XRT assembly was sensitive to X-rays between 0.1-2 keV (10-0.6 nm). In addition, the British-supplied extreme ultraviolet (XUV) telescope, the Wide Field Camera (WFC), was coaligned with the XRT and covered the energy band from 0.042-0.21 keV (30-6 nm).

ROSAT's unique strengths were high spatial resolution, low-background, soft X-ray imaging for the study of the structure of low surface brightness features, and for low-resolution spectroscopy.

The ROSAT spacecraft was a three-axis stablized satellite which could be used for pointed observations, for slewing between targets, and for performing scanning observations on great circles perpendicular to the plane of the ecliptic. ROSAT was capable of fast slews (180 degrees in ~15 min.) which made it possible to observe two targets on opposite hemispheres during each orbit. The pointing accuracy was 1 arc-minute with stability <5 arc-s/s and jitter radius of ~10 arc-s. Two CCD star sensors were used for optical position sensing of guide stars and attitude determination of the spacecraft. The post facto attitude determination accuracy was 6 arc-s.

The ROSAT mission was divided into two phases. 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. 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.

Alternate Names

  • 20638
  • German X-Ray Satellite
  • Roentgen Satellite

Facts in Brief

Launch Date: 1990-06-01
Launch Vehicle: Delta II
Launch Site: Cape Canaveral, United States
Mass: 2421.1 kg
Nominal Power: 905 W

Funding Agencies

  • Bundesministerium fuer Forschung und Tecnnologie (Federal Republic of Germany)
  • NASA-Office of Space Science Applications (United States)


  • Astronomy

Additional Information

Questions and comments about this spacecraft can be directed to: Coordinated Request and User Support Office



NameRoleOriginal AffiliationE-mail
Dr. M. OtterbeinProgram ManagerBundesministerium fuer Forschung und Technologie
Dr. Stephen S. HoltProject ScientistNASA Goddard Space Flight
Prof. Joachim TruemperProject ScientistMax-Planck-Institut fur Extraterrestrische
Mr. Karl H. PfeifferProject ManagerDeutsche Zentrum fuer Luft- und Raumfahrt (DLR)
Dr. Guenter R. ReiglerProgram ManagerNASA
Mr. Jerre B. HartmanProject ManagerNASA Goddard Space Flight
Dr. Robert PetreProject ScientistNASA Goddard Space Flight
Dr. Alan N. BunnerProgram ScientistNASA Headquarters

Selected References

  • Ayres, T. S., et al., Digging in the coronal graveyard: A ROSAT observation of the red giant Arcturus, Astrophys. J., 376, No. 2, L45-L48, doi:10.1086/186099, Aug. 1991.
  • ROSAT mission description, ROSAT Scientific Data Center and Max-Plank-Institut fur Extraterrestriche Physik, NRA 91-OSSA-3, Appendix F, Jan. 1991.

US Active Archive for ROSAT Information/Data

The ROSAT Archive at HEASARC

Other Sources of ROSAT Information/Data

SAO ROSAT Science Data Center
ROSAT Home Page at MPE
The UK ROSAT Public Data Archive at Leicester

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