On-board orbit calculation and tracking system of the S band inter-satellite communication equipment (SIC) for Japan's Engineering Test Satellite-VI (ETT-VI) to be launched in 1992, is presented. The SIC provides a multibeam phased array antenna with 54 phase shifters for beam pointing. The beams are directed to any desired user satellites automatically by controlling 54 phase shifters according to results of on-board orbit calculations by an on-board microprocessor. As accurate on-board beam pointing is required in inter-satellite communications, this paper describes a method of on-board orbit calculation and estimations of beam pointing errors caused by using the system considering perturbations.
