Calculation of the Spin-Axis Orientation of the TELSTAR Satellites from Optical Data

A novel method was devised to determine the orientation in space of the Telstar satellites. The method used grew out of limitations on weight, power, and telemetry facilities, and consists of three highly reflective mirrors and six solar aspect cells attached to the outside of the satellites. The mirrors reflect sunlight to a ground observation station,* and the solar aspect cells measure the direction of the sun with respect to reference coordinates in the satellite. The method has proved successful in determining the orientation of the Telstar satellites with sufficient accuracy both to deduce the residual magnetic moments of the satellites and to correct their precession by means of an equatorial torque coil. The remainder of the discussion concerns the details of the attitude determination scheme. See Ref. 1 for a description of the photoelectric equipment used. We will restrict the discussion to a spin-stabilized * T h e use of mirrors for this purpose was first suggested by D. Gibble of Bell Laboratories. 2943