Astronomical performance of the engineering model Ørsted Advanced Stellar Compass

The Danish geomagnetic microsatellite, Orsted, is an autonomous sciencecraft which is scheduled for a May 1997 launch into polar orbit. It is produced by a consortium of universities, industry and government and is Denmark's first national spacecraft. NASA support includes JPL real sky evaluation of its star tracker, the Advanced Stellar Compass (ASC). The ASC features low cost, low mass, low power, low magnetic disturbance, autonomous operation, a high level of functionality and the high precision. These features are enabled by the use of advanced optical and electronic design which permit the direct integration of the ASC and the science payload. The ASC provides the required attitude information for its associated vector magnetometer and the sciencecraft. It consists of two units, a CCD based camera head and a data processing unit with a powerful microcomputer. The microcomputer contains two large star data bases which enable the computer to recognize star patterns in the field-of-view, to quickly solve the lost-in-space acquisition problem and to derive the attitude of the ASC camera head. The flight model of the camera head has a mass and a power consumption of 127 grams (without baffle) and 0.5 W, respectively. Typical, beginning-of-life, relative measurement precisions in pitch and yaw are in the order of two arcseconds (1 c3.) or better have been achieved in the tests and are substantiated.