The fine sun sensor

The fine sun sensor of the IRAS satellite consists of two mutually perpendicular identical sensor parts for measuring the x- and y-components of the angle made between the sun and the z-axis. Each of the two sensors is subdivided into a coarse and fine part. The problem of the phase difference between the coarse and fine detector is analyzed. In the coarse sensor the combination of photocells is so arranged as to give the tangent of the angle of incidence of the light coming through the slot in Gray code. In the fine sensor part, the cell current, as function of the angle of incidence, is nearly a perfect sine wave. Four such waves are generated, which are used in the final computation of the required components.