Solar Sailing Attitude Control of Large Geostationary Satellite

Abstract

On geostationary satellite, the main source of attitude disturbance during normal mode Is the solar pressure effect on the body, the antennas and the solar arrays. In presence of these disturbances it is necessary, in a momentum biased control system, to maintain the momentum direction perpendicular to the orbit plane (roll/yaw control); as it has been demonstrated in orbit on OTS2, the solar pressure can be used to maintain this orientation. The originality of the proposed design consists in the use of two fixed sails mounted on the solar arrays to improve the control efficiency. The disturbing torques can be estimated on ground and compensated by command on the solar arrays pointing angle. The residual part of the disturbances as well as the nutation motion are controlled in closed loop. The control torques are achieved by low depolnting oi the solar arrays. These depointing angles are on-board computed by a microprocessor using a simplified model of the solar pressure effect on the sails. The total required depointing of the solar arrays limits their efficiency loss to 1%. After a brief description of the geostationary spacecraft environment, the solar pressure effect on the sails as also the solar sailing control laws arc precisely described in the paper. A summary of the performances is presented including the pointing accuracy. As a conclusion, the improvement due to the proposed solar sailing design is recalled and growth capacity is briefly indicated.