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ROSAT Information
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ROSAT – short for Röntgensatellit – is a German X-Ray Satellite Observatory. Launched on June 1, 1990, ROSAT had a 18-month planned mission but continued to operate until February 12, 1999. The satellite’s mission enabled scientists to perform an all-sky survey of X-Ray Sources with an imaging observatory for the first time. X-Rays are often associated with high energy processes that are involved in the formation of Black Holes and Neutron Stars. ROSAT was planned to gain knowledge on these elements of the universe and shed some light on many questions that were unanswered at the time.
The Spacecraft
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The ROSAT satellite has a total mass of 2,426kg, 1,555kg of which are accounted for its payload suite. In its launch configuration it was 2,38m x 2,13m x 4,50m, in flight, the satellite’s dimensions are 2,30m x 4,70m x 8,90m. Three-axis stabilization allowed pointed observations and slews from target to target. Reaction wheels where used to point the spacecraft. The X-Ray Telecope is enclosed by the square central body which also serves as optical bench between the mirror assembly and focal plane instrumentation elements. Located at the front end are two star trackers and the gyro package. Those units were essential for spacecraft navigation and attitude control. Two compartments on both sides of the spacecraft house almost all instruments and avionics of the satellite making access and integration fairly easy. Power for the electronics and instruments was generated by one centrally fixed solar panel and two deployable solar arrays providing a 12m² surface area in total. 1,000W of power were available to the satellite with a maximum power consumption of 609 Watts during day passes. Command and data handling electronics are mounted and enclosed in the telescope aft. Communications were handled via an S-Band Antenna Assembly which is located at the end of a deployable boom. All moving elements were deployed after the vehicle had separated from the launcher. Problems with any deployable parts have not been noted. Thermal requirements are met by the use of multilayer insulation on the exterior of the spacecraft as well as passive and active thermal regulation.
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 Photo: DLR Artist's illustration of ROSAT in Orbit
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Payloads/Instruments
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The instrument suite of ROSAT is comprised of two
imaging telescopes - XRT and WFC.
XRT – X-Ray Telescope
PSPC
HRI
WFC – Wide Field Camera
Other XRT Components
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 Image: DLR XRT Mirror Assembly
 image: DLR Rosat during construction and testing
 Image: DLR PSPC prior to Spacecraft Integration
 Image: MPE Anode Grid
 Image: MPE Focal Instrument Package (Yellow Spheres: Detector Gas Tanks)
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The Mission
ROSAT was proposed in Germany back in 1975, approval by government institutions came in 1983. Operational agreements with NASA and the British Science and Engineering Research Council (SERC) followed.
The satellite was developed through a cooperative program involving Germany, the United Kingdom and the United States. Germany was in charge of satellite design and operation. The US launched the spacecraft. Dornier was the prime contractor in charge of developing the satellite's structure, manufacturing the satellite, integrating its payloads and performing extensive testing of the spacecraft. The German Max-Planck-Institute for Extraterrestrical Physics developed the focal plane instrumentation of the X-Ray Telescope. MPE was also the science data center that analyzed and interpreted all data acquired by the satellite. NASA contributed the High Resolution Imager that was developed by the Smithsonian Astrophysical Observatory. SERC provided the Wide Field Camera, a second imaging instrument with its own mirrors and focal instruments.
The manufacturing process began in 1983. Integration of the spacecraft was completed in late 1985 followed by extensive system and electrical tests. A solar array simulation was also performed. After Challenger, it became clear that ROSAT would have to wait until 1994 to have a ride on the Shuttle. A search for alternatives began and in 1987, the decision was made to launch aboard a Delta II Vehicle. Necessary changes to payload interface adapters were made and a sequencer was implemented to automatically initiate essential systems after spacecraft separation. In 1988, the Delta II launch version of ROSAT was ready for another round of testing that included a vibration test, an accustic noise test, a thermal balance and thermal vacuum test as well as electrical and functional tests. Before launch, the X-Ray telescope was calibrated for two months to ensure accurate readings.
The satellite was developed through a cooperative program involving Germany, the United Kingdom and the United States. Germany was in charge of satellite design and operation. The US launched the spacecraft. Dornier was the prime contractor in charge of developing the satellite's structure, manufacturing the satellite, integrating its payloads and performing extensive testing of the spacecraft. The German Max-Planck-Institute for Extraterrestrical Physics developed the focal plane instrumentation of the X-Ray Telescope. MPE was also the science data center that analyzed and interpreted all data acquired by the satellite. NASA contributed the High Resolution Imager that was developed by the Smithsonian Astrophysical Observatory. SERC provided the Wide Field Camera, a second imaging instrument with its own mirrors and focal instruments.
The manufacturing process began in 1983. Integration of the spacecraft was completed in late 1985 followed by extensive system and electrical tests. A solar array simulation was also performed. After Challenger, it became clear that ROSAT would have to wait until 1994 to have a ride on the Shuttle. A search for alternatives began and in 1987, the decision was made to launch aboard a Delta II Vehicle. Necessary changes to payload interface adapters were made and a sequencer was implemented to automatically initiate essential systems after spacecraft separation. In 1988, the Delta II launch version of ROSAT was ready for another round of testing that included a vibration test, an accustic noise test, a thermal balance and thermal vacuum test as well as electrical and functional tests. Before launch, the X-Ray telescope was calibrated for two months to ensure accurate readings.
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ROSAT was launched aboard a Delta II Rocket from Cape Canaveral, Florida on June 1, 1990 at 5:48 local time. Originally, the satellite was supposed to launch aboard the Space Shuttle, but the Challenger accident caused is to be fitted for the Delta Platform to finally launch on that Vehicle. The Spacecraft was inserted into a circular orbit at an altitude of 580km (360mi) and an inclination of 53°. Mission Control was located at the German Aerospace Center’s (DLR) Space Operation Center (GSOC), Oberpfaffenhofen. Mission Control conducted mission operations such as data processing and display, spacecraft instruments performance analysis, orbit and altitude determination and control, command generation and uplink. A communication link to the satellite was established via the 15-meter dish at the DLR/GSOC Ground Station Weilheim. ROSAT had six short communication windows with the ground as it passed Earth every 96 minutes. Contacts came on 6 consecutive orbits and were 6 to 8 minutes in duration. This sort of satellite operation required a lot of automated procedures that were performed by onboard computers as well as extensive on-board data storage to accommodate short downlink windows.
After being launched, ROSAT went through a 2-month activation and commissioning phase before starting the first portion of the mission. During the initial six months of science operations, ROSAT was operated in a scan mode to perform an All-Sky Survey in X-Ray and Extreme Ultraviolet wavelengths. ROSAT was planned to operate for 18 months, but its mission was extended based on spacecraft performance. Its last observation was performed before being turned off on February 12, 1999. |
 Photo: NASA/DLR ROSAT launches aboard a Delta II in 1990
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 Image: MPE First Light! To celebrate the first science calibration reading of ROSAT, the Mission Team at MPE and GSOC signed a copy of the first Data that was downlinked when the Intrumets surveyed the Large Magellanic Cloud.
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In 1994, the Gas supply for PSPC Measurements ran out which was planned to occur at that time into the misson. X-Ray Observations were made with the HRI only for the remainder of the spacecraft’s lifetime. A small amount of Gas was saved to re-perform portions of the all-sky survey that were blocked due to technical reasons. It turned out that the amount of gas inside the tanks was sufficient for more observations in the pointed mode so that a few full data collection phases were conducted in 1998 and early 1999.
Initial Failures began to occur in April of 1998 when the primary star tracker of the vehicle stopped to function. Without a star tracker, attitude control became an issue. Pointing errors that led to solar overheating were observed. Another Star Tracker was attached to the Wide Field Camera and technicians developed a contingency procedure to switch to this healthy tracker. ROSAT became operational again, but still experienced some problems associated with navigation and control. On September 20, 1998, the satellite sustained major damage when a reaction wheel in the AMCS (Attitude Measuring and Control System) began rotating at its maximum speed. Consequently, the telescope axis was pointed near the sun and the High Resolution Imager was severly damaged due to exposure to the sun. It was determined that the damage was irreversible and the satellite was no longer of scientific use. On February 12, 1999, more than 8.5 years after launch, the ROSAT Spacecraft was shut down. ROSAT has been uncontrolled ever since. Its orbital altitude started to decrease and the satellite has been on a path leading to an uncontrolled re-entry since it was shut down. There are no capabilites of controlling the spacecraft or making contact with it. Re-Entry will occur in late 2011. For detailed information on ROSAT’s Re-Entry and the latest Updates&Predictions, visit the ROSAT Re-Entry Information Page. |
Science Objectives and Results
The ROSAT Mission was conceived for two particular tasks: the first all-sky survey with an imaging X-Ray and Extreme Ultraviolet Observatory.
The project’s aim was to improve understanding of the origin, structure and evolution of the universe.
For the first six months after being launched and commissioned, the satellite performed the all-sky survey, imaging the entire sky with its Position Sensitive Proportional Counter (PSPC) detector to complete the first survey of this kind. About 80,000 X-Ray sources were detected and catalogued. 6,000 sources in the extreme Ultraviolet regime were recorded by the British Wide Field Camera. The all-sky survey was performed to build the basis for statistical investigations concerning overall X-Ray sources in the universe. In addition to that, a virtually unlimited field of view was provided that enabled the observation of objects of interest such as supernovae or black holes. Being able to evaluate all X-Ray sources gave scientists the opportunity to pick objects of special interest for more detailed surveys and examinations. ROSAT data is still of value today as many X-Ray sources are variable over time and this mission provided an early look at those objects. Scientists can use ROSAT data to further understand X-Ray variations over time and the processes behind those phenomena. This first mission phase was completed in February 1991. During the all sky survey, ROSAT provided readings on objects whose intensity is a hundred times weaker than the weakest sources in earlier X-Ray studies.
The project’s aim was to improve understanding of the origin, structure and evolution of the universe.
For the first six months after being launched and commissioned, the satellite performed the all-sky survey, imaging the entire sky with its Position Sensitive Proportional Counter (PSPC) detector to complete the first survey of this kind. About 80,000 X-Ray sources were detected and catalogued. 6,000 sources in the extreme Ultraviolet regime were recorded by the British Wide Field Camera. The all-sky survey was performed to build the basis for statistical investigations concerning overall X-Ray sources in the universe. In addition to that, a virtually unlimited field of view was provided that enabled the observation of objects of interest such as supernovae or black holes. Being able to evaluate all X-Ray sources gave scientists the opportunity to pick objects of special interest for more detailed surveys and examinations. ROSAT data is still of value today as many X-Ray sources are variable over time and this mission provided an early look at those objects. Scientists can use ROSAT data to further understand X-Ray variations over time and the processes behind those phenomena. This first mission phase was completed in February 1991. During the all sky survey, ROSAT provided readings on objects whose intensity is a hundred times weaker than the weakest sources in earlier X-Ray studies.
Image: DLR/MPE
All Sky X-Ray Survey
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During the second part of the mission that lasted until 1998, pointed observations were carried out by the space observatory. Scientists were able to file applications for objects they were interested in. The MPE led the Guest Observer Programme. 4,000 scientists from 26 countries participated in the programme and gathered data on various X-Ray sources. More than 9,000 pointed observations were conducted varying from a few hours to two weeks in duration. Almost all kinds of astronomical objects were observed with ROSAT’s instrument package. The sensitivity provided in the pointed mode was at least two times bigger than that of previous missions. ROSAT brought about more than 8,100 publications involving results of its observations. The ROSAT catalogue contains the position and count rates of more than 100,000 X-Ray Objects.
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 Image: DLR/MPE Galaxy A 3528 was studied as part of pointed operations
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Key Scientific Discoveries/Observations by ROSAT
Photos: MPE unless noted
Mission Personnel and Institutions
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Project ROSAT was an initiative from the MPE - Max Planck Institute for Extraterrestrial Physics located in Garching, Germany. MPE was the scientific project leader and developed&contributed two models of the PSPC, the X-Ray Detector in use for ROSAT. The pricipal investigator for ROSAT was Joachim Trümper (MPE). Project Management was provided by DLR – the German Aerospace Center. Satellite development, construction and testing was conducted by Dornier, now EADS Astrium, in Friedrichshafen, Germany. Numerous optical instruments were built by Carl Zeiss. NASA was responisble for provision of the Delta II Rocket and the launch. The US Space Agency was in charge of all launch operations at Cape Canaveral. In addition to that, NASA provided the High Resolution Imager that was developed in Cambridge, Massachusetts. The Universtiy of Leicester, UK led the development of the third instrument of ROSAT, the Wide Field Camera. Mission operations were based at the German Space Operation Center (GSOC), DLR Oberpfaffenhofen. From there, downlinked data was forwarded to the partners at MPE (Germany), NASA Goddard (USA) and Leicester (UK). Archiving and cataloguing of ROSAT data was performed at the Astrophysical Institute of Potsdam. The Guest Observer Programme was led by MPE and involved 4,000 scientists from 26 countries.
The Program Scientist, based at NASA HQ was Dr. Alan N. Bunner. German Project Scientists/Managers were Dr. M. Otterbein, German Federal Ministry of Research and Technology, and PI Joachim Trümper. On the US side, Project Scientists Dr. Stephen Holt and Dr. Robert Petre of the Goddard Space Flight Center were providing operational support. Program and Project management was provided by Jerre Hartman (Goddard), Dr. Guenter Reigler (NASA HQ) and Karl Pfeiffer (DLR). |
 Image: DLR The ROSAT Project Team
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Image Credits:
DLR: Deutsches Zentrum für Luft- und Raumfahrt - http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10425/615_read-826/
MPE: Max-Planck-Institut für extraterrestrische Physik - http://www.mpe.mpg.de/xray/wave/rosat/gallery/index.php?lang=en
DLR: Deutsches Zentrum für Luft- und Raumfahrt - http://www.dlr.de/dlr/en/desktopdefault.aspx/tabid-10425/615_read-826/
MPE: Max-Planck-Institut für extraterrestrische Physik - http://www.mpe.mpg.de/xray/wave/rosat/gallery/index.php?lang=en