Mission Overview

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.

Lifetime: 1 June 1990 - 12 February 1999
Energy Range: X-ray 0.1 - 2.5 keV , EUV 62-206 eV
Special Feature: All sky-survey in the soft X-ray band

Launch Information
Launch Date: 1990-06-01 at 21:48:00 UTC
Launch Vehicle: Delta II
Launch Site: Cape Canaveral, United States
Decay Date: 2011-10-23

Trajectory Details
Type: Orbiter
Central Body: Earth
Epoch start: 1990-06-01 00:00:00 UTC

Orbital Parameters
Periapsis 580.0 km
Apoapsis 580.0 km
Period 96.0 minutes
Inclination 53.0°

Eccentricity 0.0
Regions Traversed
Trapped particle belts

• An X-ray telescope used in conjunction with one of the following instruments (0.1-2.5 keV)
    o Position Sensitive Proportional Counter
    (PSPC) 2 units : detector B, used for the pointed phase, & detector C ,used for the survey
    FOV 2 ° diameter eff area 240 cm2 at 1 keV
    energy resolution of deltaE/E=0.43 (E/0.93)-0.5
    o High Resolution Imager (HRI)
    FOV 38 ' square ; eff area 80 cm2 at 1 keV
    ~ 2 arcsec spatial resolution (FWHM)
• A Wide Field Camera with its own mirror system
(62-206 eV) FOV 5 ° diameter


• X-ray all-sky survey catalog, more than 150000 objects
• Source catalogs from the pointed phase (PSPC and HRI) containing ~ 100000 serendipitous sources
• Detailed morphology of supernova remnants and clusters of galaxies.
• Detection of shadowing of diffuse X-ray emission by molecular clouds.
• Detection (Finally!) of pulsations from Geminga.
• Detection of isolated neutron stars.
• Discovery of X-ray emission from comets.
• Observation of X-ray emission from the collision of Comet Shoemaker-Levy with Jupiter.