Simultaneous control of orbit and attitude maneuvers for the GRO satellite

This paper addresses the problem of minimum time transfer of the GRO satellite, where it is required to raise the satellite to a higher orbit after reaching the minimum allowed altitude. The required force is provided by four pairs of thrusters that can provide low level of thrusts. During the boosting process, the attitude and attitude rates, as a result of thrusters misalignment, have to be within a prespecified limit. The resulting optimal control problem with control and state constraints is solved using a direct method. The optimal solution results in a thrusters firing time percentage of 90%, a 60% increase over the firing time percentage used by NASA.