Minimum switching control for spacecraft precision pointing with on/off actuators

Maintaining the spacecraft attitude precisely aligned to a given orientation, while rejecting a persistent disturbance, using on/off actuators, is crucial for missions involving electric propulsion spacecraft. The objective is to enforce an oscillating attitude motion about the setpoint, so as to simultaneously minimize both the propellant consumption and the switching frequency of the control system. This paper evaluates the feasibility of a recently proposed feedback control law for this problem. This techniques is able to track both the period and the phase of periodic oscillations along the rotational axes, which is instrumental to minimize the switching frequency in the presence of input coupling. Two simulation case studies of a low Earth orbit missions are considered, showing that the proposed approach can effectively deal with both constant and time-varying disturbance torques.