Autonomous attitude determination and control system for the Ørsted satellite

The Ørsted satellite mission imposes comparatively high requirements on autonomy of the attitude control system. Cost requirements, on the other hand, impose simple hardware and cheap actuators in form of magnetorquer coils. These conflicting requirements are fulfilled through development of novel attitude and control algorithms and wide on-board autonomy. The entire control and attitude determination system has the ability to reconfigure in real time, based on mission phase and contingency operation requirements. Attitude determination embraces three different strategies, dependent on the availability of attitude sensors. Possible sensor faults are detected and a control system supervisor autonomously reconfigures attitude determination. Estimated satellite attitude and angular velocity are used in the attitude controller. Control tasks vary with the mission phase. Initially, after release from the launch vehicle, the angular velocity is controlled. In subsequent mission phases, the satellite is three-axis stabilized. The main contributions are development of novel algorithms for attitude control applying magnetic torquing, attitude determination schemes based on the geomagnetic field measurements, and integration into a supervisory control architecture. The salient feature of this system is fault tolerant autonomous operation with a minimum of hardware redundancy