The scientific payload of ROSAT

The ROentgen SATellite (ROSAT) is equipped with two telescopes that have ceased to function. The satellite carried the large X-ray telescope (XRT) as the primary instrument, and a Wide Field Camera (WFC) that measured radiation from celestial bodies in the extreme ultraviolet regime of the spectrum.

The large X-ray telescope gathered and focussed the X-ray radiation received using a Wolter optical system. Since the X-ray radiation would simply be absorbed by a conventional lens or mirror, the German physicist Hans Wolter developed this special-purpose optical system in 1951, based on the principle that X-ray radiation can be only be reflected at grazing angles. The Wolter mirror has an extremely smooth and specially shaped surface made of a glass-ceramic material, known as Zerodur, coated with a thin layer of gold. The X-ray telescope on board the ROSAT satellite consisted of four nested Wolter mirrors of different sizes that focussed X-ray light by means of two grazing reflections.

Two different types of detectors recorded radiation, and these were deployed alternatively in the path of the incoming X-ray beam: the Position Sensitive Proportional Counter (PSPC) and the High Resolution Imager (HRI).

The two PSPC detectors were developed at the Max-Planck Institute for Extraterrestrial Physics in Garching, near Munich. Their advantage was a wide field of view as well as energy resolution characteristics that enabled them to distinguish between four 'colours'. The HRI detector was provided by NASA, and was manufactured at the Smithsonian Astrophysical Observatory (SAO). The PSPC detector took X-ray 'colour pictures' whereas the HRI detector delivered sharper monochrome images. Both types of detector were therefore complementary.

The wide field camera (WFC) from the University of Leicester, in the UK, recorded radiation in the extreme ultraviolet end of the spectrum. The instrument had three nested, gold-coated, Wolter-Schwarzschild Type aluminium mirrors, with a microchannel plate detector at their common focus.

Last modified: 30/06/2011 11:38:25

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The ROSAT mirror system

Das Spiegelsystem von Rosat

The ROSAT system of mirrors comprises four nesting Wolter mirrors with a focal length of 2.4 metres. Each of the ring-shaped mirrors measures 50 centimetres in length, and the largest has a diameter of 84 centimetres. The mirrors, manufactured by Carl Zeiss, possess the smoothest mirror surfaces ever produced. This photograph depicts the mirror system from the 'viewpoint' of inbound X-ray radiation.

The PSPC detector on board ROSAT

Der PSPC%2dDetektor an Bord von Rosat

Rosat is equipped with three detectors. Two of these are identical four-wire proportional counters known as Position Sensitive Proportional Counters detectors (PSPC), developed by the Max Planck Institute of Extraterrestrial Physics (MPE) in Garching, near Munich. The PSPC detector provides a wide field of view and a level of energy resolution that enables it to distinguish four colours.

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  • Max-Planck Institute for Extraterrestrial Physics (MPE)