Editing ROSAT (section)

== Overview ==
The Roentgensatellit (ROSAT) was a joint German, U.S. and British X-ray astrophysics project.<ref name="NASA, ROSAT" >{{cite web|title=Overview of ROSAT|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1990-049A|publisher=[[NASA]]}}</ref> ROSAT carried a German-built imaging X-ray Telescope (XRT) with three focal plane instruments: two German Position Sensitive [[Proportional counter|Proportional Counter]]s (PSPC) and the US-supplied High Resolution Imager (HRI). The X-ray mirror assembly was a [[angle of incidence (optics)|grazing incidence]] four-fold nested [[Wolter telescope|Wolter I telescope]] with an 84-cm diameter aperture and 240-cm focal length. The angular resolution was less than 5&nbsp;[[Minute of arc|arcsecond]] at half energy width (the "angle within which half of the electromagnetic radiation"<ref>[http://sci2.esa.int/glossary/glossary_h.html ESA Science Glossary]</ref> is focused). The XRT assembly was sensitive to X-rays between 0.1 and 2&nbsp;keV (one thousand [[Electronvolt]]).

In addition, a British-supplied extreme ultraviolet (XUV) telescope, the Wide Field Camera (WFC), was coaligned with the XRT and covered the energy band from 0.042 to 0.21&nbsp;keV (30 to 6&nbsp;[[nanometre|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 stabilisation|three-axis stabilized]] satellite which can be used for pointed observations, for [[Slew (spacecraft)|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&nbsp;deg. in ~15&nbsp;min.) which makes it possible to observe two targets on opposite hemispheres during each orbit. The pointing accuracy was 1&nbsp;arcminute with stability less than 5&nbsp;arcsec per sec and jitter radius of ~10&nbsp;arcsec. 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&nbsp;arcsec.

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.

{{See also|X-ray astronomy}}