ROSAT

Reentry 23 October 2011

ROSAT ( X-ray satellite) was a is laid out as X-ray observatory satellite. With 2426 kg, he was the heaviest German satellite, costing 560 million DM ( with U.S. and British participation), from 1990 until 1999 and was destroyed in the Earth's atmosphere on October 23, 2011 during re-entry.

Active Time

ROSAT should be transported back to Earth with a space shuttle into space and back originally. After the crash of the Challenger the schedule was modified in favor of a conventional rocket. ROSAT was launched on a Delta II on 1 June 1990 in the orbit at 580 km altitude with an inclination of 53 °, was until February 12, 1999, thereby exceeding the threshold operation and the originally planned mission duration of five years significantly. In addition to a fourfold nested Wolter telescope (his mirror were long according to the Guinness Book of Records as the smoothest in the world) in the soft and medium-hard X-ray range was ROSAT still with a triple nested Wolter telescope for the extreme ultraviolet range ( EUV range ) equipped. The instruments included various particle counter, a high-resolution detector for X-ray and UV radiation (High Resolution Imager, HRI ) and a Wide Angle Camera ( Wide Field Camera, WFC). The satellite was controlled by the DLR in Oberpfaffenhofen, near Munich. The scientific leadership was at the Max Planck Institute for Extraterrestrial Physics under the direction of Professor Joachim Trümper. ROSAT was built under the leadership system of the Dornier System GmbH in Friedrichshafen involving national (Carl Zeiss ), American (NASA) and UK companies.

With ROSAT, the entire sky in X-rays was screened. There were thereby discovered 125,000 new X-ray sources and 479 EUV sources. The scientific results are set out in more than 7000 worldwide publications that have been cited about 100,000 times.

Among the most important discoveries include the dissolution of the cosmic X-ray background in the emission of quasars and other active galaxies, the discovery of neutron stars, which radiate heat alone, the X-ray radiation of the comet Hyakutake in 1996, as well as dozens of new supernova remnants. Also, an X-ray source at the position of the supernova 1987A in the Large Magellanic Cloud could be found. Also in view of the very successful space observatory were clusters of galaxies, X-ray binaries and black holes. ROSATs temporal resolution allowed even the temporal separation of the Crab pulsar ( flashing time 0.033 s ). ROSAT also discovered that the moon reflects X-rays of the sun.

1998 ROSAT suffered several defects that significantly affected its usability. On 25 April 1998 the primary star sensor of the X-ray telescope fell out; the resulting misalignment lead to overheating by the solar radiation. On the 20th of September, by saturation of a momentum wheel again to a misalignment that the HRI directly exposed to the sun and heavily damaged. After the fuel for the position control was also almost depleted, ROSAT was shut down on 12 February 1999. The satellite was from this point in a slowly descending orbit.

Re-entry in 2011

The calculations of the DLR and other bodies had revealed that the satellite will not completely burn up on re-entry into the atmosphere due to its large mass and the compact components made of heat-resistant materials. Since ROSAT had no engine, there was no way to bring him to crash deliberately.

In the 1980s, as ROSAT was designed and manufactured, no special precautions were taken for a complete burn up during re-entry of satellites usually. It was not until the late 1990s it was possible to calculate the breaking and burning up of satellite during re-entry, for example with the software SCARAB ( Spacecraft Atmospheric Re-entry and aero -thermal break-up ), which was in 1995 commissioned by ESA contract. Here SCARAB also determined the impact area and the resulting risk of damage. In the case of ROSAT needed for these calculations out the heat resistance of the glass ceramic Zerodur and other materials in the laboratory are determined to simulate the behavior of the satellite in the atmosphere.

From the DLR were time and location of re-entry into Earth's atmosphere with October 23, 2011, 01:30 UTC ( 3:50 CEST clock ) indicated above the Bay of Bengal. From space- track.org the reentry coordinates 7 ° 0 ( the Nicobar Islands Indian Ocean west ) were 'N, 90 ° 0' O790 specified. As crash time here 01:50 UTC / is - called 7 min. Confirmed reports about reaching the Earth's surface or damage by debris are not available.