Boresight stabilization of an Earth-pointing satellite using magnetorquers

This paper proposes a boresight stabilization law for an Earth-pointing satellite using only magnetorquers as torque actuators. The proposed law is able to align the boresight axis of an instrument with the nadir direction with no spinning about the boresight axis to avoid blurred measurements. The law is of the Proportional Derivative (PD) type and employs measurements of the geomagnetic field, of the angular velocity with respect to the orbital frame, and of the nadir direction which can be obtained by using appropriate sensors (e.g. horizon sensors). The presented algorithm does not require accurate knowledge of the satellite inertia parameters. The paper proposes a method to select the PD gains based on stability properties of periodic state representations. A numerical study validates the proposed law both in nominal and perturbed scenarios.