Stabilization of rigid spacecraft with uncertainties and input saturation in a central gravitational field

The problem of stabilization of rigid spacecraft subject to a gravity-gradient disturbance is considered. Two control laws are derived, either in the case of absence or in presence of saturation on the inputs. It is assumed that the system parameters are constant but unknown, while the distance between the Earth and the spacecraft is an unknown parameter, slowly varying and hence practically constant. Moreover, the entire state of the system is supposed available for implementing the control. Simulations show the performances of the controls