The German-US-UK X-ray observatory ROSAT
(Röntgen Satellite) was launched into an 550 km
circular orbit in June 1990. It carried two imaging telescopes operating
in the soft X-ray (0.1-2.4 keV) and EUV (006-0.2 keV) ranges.
The X-ray telescope consisted of four nested Wolter type I-mirrors.
The manufacturing of the X-ray mirrors - the largest and most accurate ones
at that time - pioneered the use of Zerodur (a ceramics with zero
thermal expansion) and an extremely low surface roughness (0.25 nm rms).
In its focus were two position sensitive proportional counters
(PSPC, 20 arc sec) and one high resolution imager (HRI, 5 arc sec).
The EUV telescope consisted of three nested Wolter-Schwarzschild mirrors
and two channel plate detectors (3 arc min). The satellite and the X-ray
telescope was designed, built and operated by Germany.
NASA provided the Delta launch and the high resolution imager while the
UK built and operated the EUV telescope. The prime ROSAT data centers were
and are at the Max-Planck-Institute for Extraterrestrial Physics in Garching
(X-rays) and at the University of Leicester (EUV) with mirror sites at the
Goddard Space Flight Center and other scientific institutions.
ROSAT performed the first all sky surveys with imaging telescopes leading
to the discovery of 125,000 X-ray and 479 EUV sources. In addition the
diffuse galactic X-ray emission was mapped with unprecedented angular
resolution (< 1 arcmin). Most of the mission time was devoted
to pointed observations at selected targets. In total 4580 PSPC and 4482 HRI
fields were covered with observation times between ~ 2,000 sec
and ~ 1 Million sec. 700 Scientists
from 24 countries were involved in these pointed observations. The total
number of ROSAT based publications is 4787, with 54,9 % in referred journals
(status August 2001). All ROSAT data are calibrated, archived and are
ROSAT was switched off in February 1999 after 8 1/2 years of successful