Payload

The scientific payload of ROSAT consists of two imaging telescopes. The main payload is the large X-ray telescope (XRT), the most powerful one ever built, designed for measurement of soft X-rays in the energy range of 0.1 keV - 2 keV, corresponding to wavwlengths of 100 Å - 6 Å. The wide field camera (WFC), as the secondary payload, extends the measuring range to the extreme ultraviolet region with energies 0f 0.04 keV - 0.2 keV (300 Å - 60 Å).

X-ray Mirror Integration

The X-ray telescope consists of the following groups:

• The telescope door mechanism keeps the door closed during the launch and opens the door by spring forces on command from ground.
   
• The thermal baffle limits the heat loss via the telescope aperture and serves as straylight shield.
   
• The Wolter I-type mirror assembly focusses the incoming X-rays by means of four nested confocal parabolic-hyperbolic mirror pairs, made of the glass ceramic material Zerodur.
   
• The magnetic electron deflector identifies and reduces the electron backgound count rate of the detector by a factor of about 100.
   
• The fiducial light system identifies and measures misalignment due to thermal distorsion of the telescope and X-ray detector displacements after detector changes.
   
• The focal plane instrumentation houses the complete scientific equipment. As X-ray detectors serve two position sensitive proportional counters (PSPC) and one high resolution imager (HRI), which are mounted on a turret for alternate positioning in the focus. Also installed on the turrt are the preamplifiers for the detectors and a gas supply system to provide a continuous flow of detector gas (60% Ar, 20% Xe, 20% CH₄) to the PSPCs. The experiment data acquisition and control electronics is arranged on a fixed platform around the turret housing.
   
• The XRT structure supports and connects all the above mentioned groups and has to guarantee the structural and thermal alignment requirements.
   
• The XRT thermal control provides the thermal environment according to very stringend requirements especially from the mirror assembly and the telescope structure, by means of both active and passive thermal control measures.

X-ray Telescope - Cross Section

Attached to the telescope front tube are the two star trackers and the gyro package, the most inportant attitude measurement units.

The wide field camera (WFC) uses three nested aluminium mirrors to focus the extreme ultraviolet (XUV) radiation on a microchannel plate (MCP) X-ray detector. A focal plane turret assembly is used to select one of two identical detector assemblies. Each MCP detector is mounted integrally with its high voltage power supply and pre-amplifiers.

A forward closure door is used to protect the mirror aperture and is opend for in-orbit operation.

A baffle assembly mounted in front of the mirrors excludes scattered solar radiation from the mirror aperture and provides thermal decoupling between mirrors and space.

Background electrons reflected by the mirrors into the telescope are deflected out of the detector aperture by a magnetic diverter system.

Attitude data is obtained from a star tracker unit, coaligned with the optical axis of the mirrors and mounted externally to the telescope, together with the star tracker electronics.

The power supply unit is also attached to the telescope outside.

A command and data handling electronics package is mounted to the telescope aft end and enclosed by hemispherical cover.

The external surfaces of the WFC are covered by multilayer thermal insulation.