Fine Sun Tracker for Advanced Orbiting Solar Observatory

The analysis and design of a fine sun tracker for the Advanced Orbiting Solar Observatory are discussed. The tracker provides accurate pointing information in pitch and yaw, permitting precise static and dynamic orientation of the observatory with respect to the sun's apparent disc, in accordance with ground commands. The tracker uses a servo driven optical slab in each axis to offset the optical null by the required amount. The error signal thus developed in a pair of matched silicon photo-voltaic cells is fed to the observatory control system, to produce the desired orientation in that axis. The essential features of the tracker design are incorporated in a breadboard model. The performance of this model verifies the inherent capability of the design to achieve a 2 are-second r.m.s. pointing accuracy.