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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
- 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
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
- 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
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.
Copyright © 1998 Max-Planck-Institut für extraterrestrische Physik,
85740 Garching, Germany.
The ROSAT project is run by the German Aerospace Center (DLR) (former DARA),
Bonn, by order of the Bundesministerium für Bildung, Wissenschaft, Forschung
und Technologie (BMBF). All rights reserved.