The X-ray small satellite ABRIXAS - Mission analysis and attitude control

The trajectory design and control aspects of ABRIXAS, an astronomical mission to scan the sky for hard X-ray sources, is the central topic of this paper. A mission and control concept is developed to meet the scientific requirements within the framework of a small satellite mission, characterized by limited resources on-board and severe cost constraints. Trade-offs between inclined and equatorial orbits of different altitudes have been performed, on the basis of parameter variations using modem computer-algebra tools, in order to optimize ground contact, eclipse durations and scientific observation periods. With respect to a low-cost layout, a recommendation for an orbit with a 53 degrees inclination resulted. The attitude control subsystem has to perform a continuous scan movement of one rotation per orbit in order to guarantee a complete scan of the sky without gaps, and to provide a high post factum attitude measurement accuracy. Simulation analyses lead to the recommendation of a sensor package, consisting of magnetometers, a gyro and a sun sensor for coarse attitude determination, as well as one very precise star sensor and one sun sensor for high accuracy attitude determination. As actuators three magnetic coils and one reaction wheel are proposed. (C) 1997 Elsevier Science Ltd.