Attitude Determination and Prediction of Spin-Stabilized Satellites

To maintain a defined attitude in space, the Telstar I and II satellites were spin stabilized. By this method of passive attitude control, a satellite is rotated about an axis of symmetry and consequently exhibits the characteristics of a gyroscope. In the absence of disturbing torques, the satellite's spin axis maintains its spatial orientation fixed with respect to an inertial reference frame throughout its orbit. For the Telstar I and II satellites, this is desirable because of certain required attitude constraints. First of all, the satellite communication antenna is not omnidirectional. More energy is radiated along the equator of the satellite than along its spin poles, as shown by the antenna pattern of Fig. 1. This fact dictates an attitude for which the line of sight from Fig. 1 -- Antenna p a t t e r n at 4170 inc.