ROSAT

The Roentgensatellit (ROSAT) was a joint German, U.S. and British X-ray astrophysics project.{{cite web|title=Overview of ROSAT|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1990-049A|publisher=NASA}} ROSAT carried a German-built imaging X-ray Telescope (XRT) with three focal plane instruments: two German Position Sensitive Proportional Counters (PSPC) and the US-supplied High Resolution Imager (HRI). The X-ray mirror assembly was a grazing incidence four-fold nested Wolter I telescope with an 84-cm diameter aperture and 240-cm focal length. The angular resolution was less than 5 arcsecond at half energy width (the "angle within which half of the electromagnetic radiation"[http://sci2.esa.int/glossary/glossary_h.html ESA Science Glossary] is focused). The XRT assembly was sensitive to X-rays between 0.1 and 2 keV (one thousand Electronvolt).

In addition, a British-supplied extreme ultraviolet (XUV) telescope, the Wide Field Camera (WFC), was coaligned with the XRT and covered the energy band from 0.042 to 0.21 keV (30 to 6 nm).

ROSAT's unique strengths were high spatial resolution, low-background, soft X-ray imaging for the study of the structure of low surface brightness features, and for low-resolution spectroscopy.

The ROSAT spacecraft was a three-axis stabilized satellite which can be used for pointed observations, for slewing between targets, and for performing scanning observations on great circles perpendicular to the plane of the ecliptic. ROSAT was capable of fast slews (180 deg. in ~15 min.) which makes it possible to observe two targets on opposite hemispheres during each orbit. The pointing accuracy was 1 arcminute with stability less than 5 arcsec per sec and jitter radius of ~10 arcsec. Two CCD star sensors were used for optical position sensing of guide stars and attitude determination of the spacecraft. The post facto attitude determination accuracy was 6 arcsec.

The ROSAT mission was divided into two phases:

1. After a two-month on-orbit calibration and verification period, an all-sky survey was performed for six months using the PSPC in the focus of XRT, and in two XUV bands using the WFC. The survey was carried out in the scan mode.
2. The second phase consists of the remainder of the mission and was devoted to pointed observations of selected astrophysical sources. In ROSAT's pointed phase, observing time was allocated to Guest Investigators from all three participating countries through peer review of submitted proposals. ROSAT had a design life of 18 months, but was expected to operate beyond its nominal lifetime.

{{See also|X-ray astronomy}}

The main assembly was a German-built imaging X-ray Telescope (XRT) with three focal plane instruments: two German Position Sensitive Proportional Counters (PSPC) and the US-supplied High Resolution Imager (HRI). The X-ray mirror assembly was a grazing incidence four-fold nested Wolter I telescope with an {{Convert|84|cm|in|0|abbr=on|adj=on}} diameter aperture and {{Convert|240|cm|in|0|abbr=on|adj=on}} focal length. The angular resolution was less than 5 arcsec at half energy width. The XRT assembly was sensitive to X-rays between 0.1 and 2 keV.

{{Expand section|date=September 2011}}

There are two Position Sensitive Proportional Counters (PSPC), PSPC-B and PSPC-C, mounted on a carousel within the focal plane turret of ROSAT. PSPC-C was intended to be the primary detector for the mission and was used for the bulk of the All-Sky Survey until it was destroyed during the AMCS glitch on 25 January 1991. After the glitch, PSPC-B was used for all further observations. Two more PSPCs(PSPC-A and PSPC-D) were mounted on ROSAT for ground calibration.{{Cite web |date=June 22, 2001 |title=The ROSAT PSPC |url=https://heasarc.gsfc.nasa.gov/docs/rosat/pspc.html}}

Each PSPC is a thin-window gas counter. Each incoming X-ray photon produces an electron cloud whose position and charge are detected using two wire grids. The photon position is determined with an accuracy of about 120 micrometers. The electron cloud's charge corresponds to the photon energy,{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1990-049A-02|title=Position Sensitive Proportional Counter}} with a nominal spectral bandpass 0.1-2.4 keV.

{{Expand section|date=September 2011}}

The US-supplied High Resolution Imager used a crossed grid detector with a position accuracy to 25 micrometers.{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/experiment/display.action?id=1990-049A-01|title=High Resolution Imager (HRI)}} The instrument was damaged by solar exposure on 20 September 1998.

{{Expand section|date=September 2011}}

The Wide Field Camera (WFC) was a UK-supplied extreme ultraviolet (XUV) telescope co-aligned with the XRT and covered the wave band between 300 and 60 angstroms (0.042 to 0.21 keV).

File:Moon in x-rays.gif

File:Vela_SNR_-_RASS.jpg, imaged by ROSAT]]

• X-ray all-sky survey catalog, more than 150,000 objects
• XUV all-sky survey catalog (479 objects)
• Source catalogs from the pointed phase (PSPC and HRI) containing ~ 100,000 serendipitous sources
• Detailed morphology of supernova remnants and clusters of galaxies.
• Detection of shadowing of diffuse X-ray emission by molecular clouds.
• Detection of pulsations from Geminga.
• Detection of isolated neutron stars.
• Discovery of X-ray emission from comets.
• Observation of X-ray emission from the collision of Comet Shoemaker-Levy with Jupiter.

• 1RXS – an acronym which is the prefix used for the First ROSAT X-ray Survey (1st ROSAT X-ray Survey), a catalogue of astronomical objects visible for ROSAT in the X-ray spectrum.

• :Category:ROSAT objects

ROSAT was originally planned to be launched on the Space Shuttle but the Challenger disaster caused it to be moved to the Delta platform. This move made it impossible to recapture ROSAT with a Shuttle and bring it back to Earth.{{citation needed|date=November 2012}}

Originally designed for a five-year mission, ROSAT continued in its extended mission for a further four years before equipment failure forced an end to the mission. For some months after this, ROSAT completed its very last observations before being finally switched off on 12 February 1999.{{cite web|title=ROSAT completes almost a decade of discovery|url=http://www.ledas.ac.uk/rosat-goc/rosat_pr.html|date=18 February 1999|publisher=UK ROSAT Guest Observer Centre}}

On 25 April 1998, failure of the primary star tracker on the X-ray Telescope led to pointing errors that in turn had caused solar overheating.{{cite journal|title=ROSAT/LEDAS electronic newsletter|issue=12|date=5 June 1998|url=http://ledas-www.star.le.ac.uk/rosat-goc/rosnews12|publisher=UK ROSAT Guest Observer Centre|journal=ROSAT News |url-status=dead|archive-url=https://web.archive.org/web/20151228232103/http://ledas-www.star.le.ac.uk/rosat-goc/rosnews12|archive-date=28 December 2015}} A contingency plan and the necessary software had already been developed to utilise an alternative star tracker attached to the Wide Field Camera.

ROSAT was soon operational again, but with some restrictions to the effectiveness of its tracking and thus its control.{{cite web|title=Severe Damage to ROSAT High Resolution Imager|url=http://ledas-www.star.le.ac.uk/rosat-goc/mpenews66|work=star.le.ac.uk|date=15 October 1998|access-date=23 October 2011|archive-date=10 December 2000|archive-url=https://web.archive.org/web/20001210175800/http://ledas-www.star.le.ac.uk/rosat-goc/mpenews66|url-status=dead}} It was severely damaged on 20 September 1998 when a reaction wheel in the spacecraft's Attitude Measuring and Control System reached its maximum rotational speed,A reaction wheel operates by changing its rotational velocity, conservation of angular momentum then causing the more massive satellite to rotate in opposition. Their maximum speed is limited by design, which in turn means they are limited in the rotational velocity they can impart to a satellite.{{clarify|date=September 2011}} "Reaching maximum speed" means merely that it cannot impart any more velocity change, not that it's approaching mechanical damage to itself. losing control of a slew, damaging the High Resolution Imager by exposure to the sun. This failure was initially attributed to the difficulties of controlling the satellite under these difficult circumstances outside its initial design parameters.

In 2008, NASA investigators were reported to have found that the ROSAT failure was linked to a cyber-intrusion at Goddard Space Flight Center.{{cite web

|title=Network Security Breaches Plague NASA

|url=http://www.businessweek.com/print/magazine/content/08_48/b4110072404167.htm

|archive-url=https://archive.today/20120414223803/http://www.businessweek.com/print/magazine/content/08_48/b4110072404167.htm

|url-status=dead

|archive-date=14 April 2012

|date=20 November 2008

|publisher=Business Week

|quote=Without warning one day, the ROSAT satellite turned, seemingly inexplicably, toward the sun. The move damaged a critical optical sensor, rendering the satellite useless in its mission of making X-ray and ultraviolet images of deep space.}} The root of this allegation is a 1999 advisory report by Thomas Talleur, senior investigator for cyber-security at NASA. This advisory{{cite book

|title=Russian Domain Attacks Against NASA Network Systems|last=Talleur|first=Thomas J.|date=18 January 1999|publisher=Inspector General's office, NASA|pages=26 |no-pp=y|location=Not publicly published. Classified as "For Official Use Only—No Foreign Dissemination"}} is reported to describe a series of attacks from Russia that reached computers in the X-ray Astrophysics Section (i.e. ROSAT's) at Goddard, and took control of computers used for the control of satellites, not just a passive "snooping" attack. The advisory stated:

"Hostile activities compromised [NASA] computer systems that directly and indirectly deal with the design, testing, and transferring of satellite package command-and-control codes."

The advisory is further reported as claiming that the ROSAT incident was "coincident with the intrusion" and that, "Operational characteristics and commanding of the ROSAT were sufficiently similar to other space assets to provide intruders with valuable information about how such platforms are commanded,". Without public access to the advisory, it is obviously impossible to comment in detail. Even if it did describe a real intrusion, there is a plausible "no attack" explanation for ROSAT's failure, and the report is claimed to link the two incidents as no more than "coincident."{{or|date=April 2024}} However, NASA officials in charge of the day-to-day operations of the ROSAT mission at Goddard, including GSFC Rosat Project Scientist Rob Petre, say definitively that no such incident occurred. Talleur's information appears to have come from one of his interns who exaggerated a hacking incident on an office computer not related to flight operations.{{cite interview | last = Petre | first = Rob | interviewer = Jonathan McDowell |title = ROSAT hacking claim |url= https://planet4589.org/space/jsr/back/news.649.txt | year = 2011}}

IT security remains a significant issue for NASA. Other systems including the Earth Observing System have also been attacked.

{{cite web|url= http://oig.nasa.gov/NASA2007ManagementChallenges.pdf |title=NASA's Most Serious Management and Performance Challenges }} {{small|(73 KB)}} 13 November 2007, p.3

File:ROSAT one of the last images before reentry.jpg

In 1990, the satellite was put in an orbit at an altitude of {{convert|580|km|mi|0|abbr=on}} and inclination of 53°.{{Cite web |title=ROSAT - Launch and Operations |url=http://www.mpe.mpg.de/xray/wave/rosat/mission/rosat/launch.php |url-status=dead |archive-url=https://web.archive.org/web/20111006030341/http://www.mpe.mpg.de/xray/wave/rosat/mission/rosat/launch.php |archive-date=6 October 2011 |access-date=26 September 2011 |publisher=Max-Planck-Institut für extraterrestrische Physik}} Due to atmospheric drag, the satellite slowly lost height until, in September 2011, the satellite was orbiting approximately {{convert|270|km|mi|0|abbr=on}} above the Earth. On 23 October 2011 ROSAT re-entered the Earth's atmosphere sometime between 1:45 UTC and 2:15 UTC over the Bay of Bengal, east of India. There was no confirmation if pieces of debris had reached the Earth's surface.{{cite web|url=http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10424|title=ROSAT – latest news|date=25 October 2011|work=DLR Portal|access-date=25 October 2011}}{{cite web|title=ROSAT Information|publisher=Heavens-Above|url=http://www.heavens-above.com/satinfo.aspx?SatID=20638|access-date=1 April 2009}}{{cite web|url=https://www.newscientist.com/article/dn20955-second-big-satellite-set-to-resist-reentry-burnup.html |title=Second big satellite set to resist re-entry burn-up – space – 23 September 2011 |publisher=New Scientist |access-date=2012-01-30}}

eROSITA launched on board the Russian-German Spektr-RG space observatory in 2019.{{cite web |date=13 July 2019 |title=Spektr-RG observatory has been put into orbit |url=http://en.roscosmos.ru/20814/ |website=ROSCOSMOS |access-date=16 July 2019}} It will provide an updated all-sky survey of the X-ray sky, extending the energy range to 10keV, increase the sensitivity by a factor of 25 and improve the spatial and spectral resolution.

{{Reflist|group=note}}

{{Reflist}}

{{Portal|Spaceflight}}

• List of X-ray space telescopes

{{Commons category|ROSAT}}

• {{cite web |title=ROSAT |url=http://www.dlr.de/en/rosat |publisher=German Aerospace Center DLR}}
• {{cite web|title=The ROSAT Mission|url=http://www.mpe.mpg.de/ROSAT|publisher=Max-Planck-Institut für extraterrestrische Physik}}
• {{cite web |title=UK ROSAT Guest Observer Centre |url=http://ledas-www.star.le.ac.uk/rosat-goc/ |publisher=University of Leicester, Department of Physics & Astronomy |ref=ROSAT UK GOC |access-date=24 November 2008 |archive-date=17 August 2000 |archive-url=https://web.archive.org/web/20000817172142/http://ledas-www.star.le.ac.uk/rosat-goc/ |url-status=dead }}
• {{cite web |url=https://twitter.com/ROSAT_Reentry |title=ROSAT reentry Twitter feed}}
• [http://www.xray.mpe.mpg.de/rosat/survey/rass-bsc/ 1RXS Catalog site] {{Webarchive|url=https://web.archive.org/web/20100113095354/http://www.xray.mpe.mpg.de/rosat/survey/rass-bsc/ |date=13 January 2010 }}
• [https://projects.mpe.mpg.de/heg/rosat/mission/rosat/development.html MPE – ROSAT Development]

{{Space observatories}}

{{Orbital launches in 1990}}

{{DEFAULTSORT:Rosat}}

Category:Spacecraft which reentered in 2011

Category:Space telescopes

Category:X-ray telescopes

Category:Satellites of Germany

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Category:Spacecraft launched in 1990