SPIN DECAY OF A CLASS OF SATELLITES CAUSED BY SOLAR RADIATION

A study is presented of the interaction with the solar radiation field of a spinning satellite having long flexible rods. The dynamics of thermal bending of the rods is analyzed, including the effect of vehicle rotation, and the shape, amplitude and phase are calculated. The radiation pressure on the periodically bent rods produces a net average despin torque that depends critically on the phase lag of the thermal bending. The theory is compared with flight data from the Alouette I and S48 satellites, and the agreement indicates that the mechanism studied is the primary cause of despin of these vehicles. A means of preventing despin is proposed. It consists of polished plates mounted on the tips of the rods. The torque produced by the solar pressure acting on them is opposite to that on the rods. The plate area required for complete cancellation of the despin torque is of order 1/4 to 1/2 of the projected rod area. (Author)