Method of determining and controlling the attitude of a spin-stabilized

Abstract

The attitude of a satellite carrying terrestrial and solar sensors and spin-stabilized about an axis V--V is determined and controlled prior to its transfer from an elliptical transfer orbit to a circular geostationary orbit by means of an apogee motor firing. The attitude is defined relative to an inertial X-Y-Z frame of reference the Z axis of which is directed towards geographical North, by a declination .alpha. between the axis V--V and the X-Y plane and by a right ascension .beta. between the projection of the axis V--V onto the X-Y plane and the X axis. After injection of the satellite by a launch vehicle into the transfer orbit at its perigee, with an initial attitude approximating the predetermined final attitude for the apogee motor firing, the right ascension .beta. of the satellite is modified to confer on it an intermediate attitude such that the earth is in the field of view of the terrestrial sensors for a position of the satellite in the transfer orbit offset at least 10.degree. from the apogee. The declination .alpha. of the rotation axis of the satellite is measured and then adjusted to the value required for the apogee motor firing. Maintaining this declination constant, the right ascension is adjusted on the basis of the solar sensor measurements so as to bring the satellite into its final attitude, and the apogee motor firing is then commanded.