On-orbit control system performance of the ROSAT spacecraft☆

The on-orbit performance of the attitude control system of the ROSAT spacecraft is described. It is performing both precise pointing observations and scanning over the sky. The control system consists of high precision star trackers and gyros for attitude reference and reaction wheels for maneuvers. Since launch on 1 June 1990 first the checkout and calibration phase was performed, indicating that pointing accuracies <1 arc min, slew maneuver accuracies <4 arc min, and scan accuracies <13 arc min are achieved. These are, like all other performance values, well inside the specifications. Since 30 July, the sky survey is in progress without problems. The magnitude calibration of the star trackers and one type of anomaly detected during the survey are discussed additionally.