Earth oriented satellite and process for controlling the position, nutation and spin

Process for controlling attitude, nutation and momentum of a satellite orbiting in a low earth orbit, with a medium inclination in an earth oriented alignment, said satellite being of the type having an earth sensor for measuring in two axes;

• a spin wheel having an axis of rotation oriented in parallel to a pitch axis of the satellite and two magnet coils for generating control moments, a first one of the two magnet coils being aligned substantially in parallel to a roll axis of the satellite and a second one of the two magnet coils being aligned substantially in parallel to a yaw axis of the satellite, said process comprising at least one of the steps of:
• controlling attitude and nutation of said satellite by activating said magnet coils based on a linear control algorithm which in the case of attitude control is a function of a roll angle measured by the earth sensor and of a yaw angle estimated by means of an observer or measured by an additional sensor on said satellite and, in the case of nutation control, a function of a roll angle chance determined by earth sensor measurements and a yaw angle chance estimated by the observer or measured by an additional sensor;
• and
• controlling wheel spin by activation of at least said first magnet coil, as a function of a deviation from a desired value for spin, and of a yaw component of th earth's magnetic field based on PI feedback control;
• wherein said linear control algorithm for attitude control is given by ##EQU31## m.sub.x.sup.(h), m.sup.(h) being the magnetic moments to be generated by the roll and yaw axis magnet coils;
• h.sub.0x, h.sub.0z being the roll and yaw components of the satellite spin vector, respectively, related to the yaw and roll angles, .phi. and .PHI. respectively, by the equations h.sub.0x =.phi.h.sub.w and h.sub.0z =-.phi.h.sub.w, h.sub.w being the magnitude of the wheel spin vector;
• and K.sub.ij.sup.(h) being amplification parameters.