Attitude Determination of the Ariel III Satellite

Abstract

ARIEL III, the third UK/US satellite, was successfully placed into orbit on May 5, 1967, with apogee and perigee approximately 600 km and 500 km, respectively, and inclination 80°. It had been suggested some time before launch that the spin axis direction required for the interpretation of data from some of the experiments could be monitored by observing fluctuations in the telemetry AGC recordings as the satellite rotated; this method had been adopted for the Ariel II satellite1, but the analysis proved difficult and because the telemetry polar diagrams for Ariel III were found to be nearly circular this technique was regarded as unpromising. An alternative method was therefore proposed similar to that used on Telstar2—namely, observing the glints of solar reflexions from the solar cell panels and from special mirrors placed on the spacecraft. Solar aspect sensors already included in the payload would determine the angle between the spin axis of the satellite and the direction of the Sun, thus defining a conical surface containing the spin axis. To position the spin axis on this cone another frame of reference would be required and the mirror glints would define this. The method was adopted successfully for Ariel III, and spin axis direction to better than ±2° has been calculated together with coning angle and spin rate.