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ROSAT Status Report #175: ROSAT NEWS No.67

Date: Tue, 3 Nov 1998 14:23:33 +0100
Subject: ROSAT NEWS No.67

=                                                                       =
=              ROSAT NEWS No. 67     ---     3-Nov-1998                 =
=                                                                       =
=                 ROSAT Scientific Data Center at the                   =
=       Max-Planck-Institut fuer Extraterrestrische Physik (MPE)        =
=               Postfach 1603, D-85740 Garching, Germany                =
=  e-mail address:   rosat_svc@mpe.mpg.de                               =
=  ROSAT Service Area (including ROSAT Data Archive):                   =
=   www address:  http://wave.xray.mpe.mpg.de/rosat                     =
=   ftp rosat_svc.mpe-garching.mpg.de      user: anonymous              =
=   interactive account (including ROSAT Result Archive):               =
=     telnet xray.mpe-garching.mpg.de  user: xray  no password          =
=  XUV Center: GXUVDC@AIT.PHYSIK.UNI-TUEBINGEN.DE                       =
=   WFC Archive access via telnet/ftp ait.physik.uni-tuebingen.de       =
=                                user: xuv  (password: xuv_archive)     =
=   www address:  http://astro.uni-tuebingen.de/rosat.html              =



After eight years of successful operations it was agreed among the ROSAT
institutions in Germany, the USA, and the UK to officially terminate the
guest observer programme of the observatory. The reason for this 
decision is the irreversible damage of the High Resolution Imager (HRI)
due to an accident on 20 September 1998. The HRI was the only focal 
plane instrument available for X-ray observations since September 1994, 
when the gas supply of the Position Sensitive Proportional Counters 
(PSPC) effectively became exhausted. ROSAT had an extraordinary long life
compared with astronomy satellites in a near earth orbit, longer than 
any other X-ray astronomy satellite. 
The recent problems started on 28 April 1998 when the star tracker 
attached to the X-ray telescope used for navigating the satellite failed.
The remedy was to bring the star tracker of the Wide Field Camera (WFC) 
into the loop of the attitude control system (AMCS). This activity was 
initiated immediately and the DASA engineers were supported by experts 
from the ground station (GSOC/DLR), MPE and Leicester University/RAL. 
The task soon turned out to be more difficult than anticipated; one of 
the problems was the fine tuning between the software of the AMCS and 
that of the star tracker, the latter never designed to be incorporated 
into an active attitude control system. As a result the satellite 
suffered from many safe mode triggers over the summer, and only a few 
scientific observations could be performed during this period. At the 
end of August the situation had improved significantly by fine tuning the
parameters of the AMCS software, and almost normal scientific operations 
were resumed. Shortly before a revised version of the AMCS software was 
uplinked an 'accident' happened on 20th September: during a slew the 
pointing direction of the satellite came close to the sun; as a result 
the HRI was irreversibly damaged. 

ROSAT was initiated by MPE in 1975 and became a collaborative project 
between Germany, the United States and the United Kingdom in 1983. 
Germany built and operated the spacecraft, and also provided the X-ray 
telescope including two X-ray cameras, i.e. the Position Sensitive 
Proportional Counters. The United States provided the launch with a 
Delta rocket and the High Resolution Imager as the third X-ray camera 
aboard, while the United Kingdom contributed the Wide Field Camera 
operating in the extreme ultraviolet range. The data analysis, archiving,
and distribution has been done as a joint effort of the ROSAT data 
centers: in Germany these are the Max-Planck-Institut fuer 
extraterrestrische Physik (MPE) and the Institut fuer Astronomie und 
Astrophysik at the University Tuebingen (IAAT), in the US the Goddard 
Space Flight Center (GSFC) and the Smithonian Astrophysical Observatory 
(SAO), and in the UK the University of Leicester (UL) and the Rutherford 
Appleton Laboratory (RAL).

After the launch on 1 June 1990 ROSAT carried out the first All Sky 
Survey with imaging X-ray and EUV telescopes. This half year operation 
led to the discovery of some 80 000 X-ray and 500 EUV sources. In the 
following 7 1/2 years about 9 000 fields in the sky were observed in a 
guest observer programme involving 650 principal investigators from 26 
countries. Numerous discoveries have been made and more than 3 000 
scientific publications with more than 4 000 scientists as co-authors 
have been published until now. The ROSAT discoveries concern almost all 
fields of astrophysics from the closest objects - moon and comets - to 
the most distant ones - high redshift quasars -, from the smallest 
- single neutron stars - to the largest objects in the universe 
- clusters of galaxies. 

ROSAT will continue to have a strong impact on astrophysics. At present,
the utilization of the ROSAT archives is very high, and currently more 
than one ROSAT based publication appears every day in the scientific 

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