Abstract: The apparatus has n non aligned antennas, where n is at least for receiving radio signals from a plurality of OPS satellites. Radio frequency signals received by the various antennas are processed for measuring their phase differences, and for computing attitude on the basis of said phase differences. The measurement and computing system is repeatedly calibrated on the basis of measurements performed by a star sensor during periods when it provides usable data.

Abstract: For controlling the attitude of the body of an earth satellite placed on a low orbit, values of components of the geomagnetic field of the earth are measured along three axes of a frame of reference bound to the body. The values are derivated with respect to time, and multiplied by a gain. Currents responsive to the multiplicated derivatives are passed through magnetic torquers located along the three axes of the body to create magnetic torques that bias the body to a fixed angular position relative to the field lines of the geomagnetic field. Such steps are continuously carried out during eclipse periods. Out of eclipse periods, the pitch of the body is controlled by modifying an internal momentum in response to a signal provided by a solar sensor, so as to maintain solar generators carried by the body of the satellite oriented towards the Sun.