ROSAT Attitude Operations after Gyro Failures.

Abstract

The X-ray astronomie satellite ROSAT is a cooperative project between Germany, USA and the UK. It is carrying the largest X-ray telescope in space in a 580 Km orbit with 53 inclination. Main contractor for the spacecraft was Dornier/DASA, the attitude subsystem was built by MBB (now also DASA). All operational aspects are covered by the German Space Operations Center (GSOC), Oberpfaffenhofen. The spacecraft is controlled via the GSOC ground station at Weilheim. This leads to a contact pattern of 5-6 consecutive contacts of max. 10 minutes duration, followed by an invisibility period of 15-17 hours. In case of contingencies there are more contacts via DSN-stations possible. The spacecraft is operated in 2 nominal modes, scan and pointing. In scan mode ROSAT is rotating with a constant rate about the axis satellite-sun with 1 revolution per orbit. After half a year the whole celestial sphere is scanned with the 2 field of view of the telescope by a 1 overlap. In pointing mode the satellite is directed to selected targets and slewing between them. The pointing mode is the nominal operational mode after scan until the end of the mission. In case of anomalies a safe mode is implemented which disables the scientific instruments and points the spacecraft to the sun.