High-Accuracy Attitude Determination for the X-Ray Satellite ROSAT

Kurzfassung

The ROSAT Mission requires highly accurate attitude data. Therefore, an attitude determination procedure has been established at the German Space Operations Center (GSOC) using star camera measurements and gyro data. The latter replaces the model in a modified Kalman filter. A quaternion representation of the attitude is used. A fiducial light star system monitors the relative motion between telescope axis and star cameras. The reference is a star catalog for the epoch 2000.0. Results of first flight data demonstrate the capability of the post facto altitude determination system to obtain attitude accuracies of a few arcseconds. The first year of the ROSAT mission has shown that the results presented in this paper are representative for the performance of the two operational spacecraft modes "scan" and "pointing" that are described here.