Solar sail attitude control through in-plane moving masses

A three-axis solar sail attitude control system for interplanetary missions is proposed: required steering is achieved by means of a small control mass in the solar sail plane, whereas roll-axis control is achieved through the rotation of ballast with two masses at the extremities. The satellite is fixed at the sail geometrical centre: this solution avoids the difficulties arising from the employment of an out-of-plane control boom with the satellite at the end, i.e. pointing problems for optical payloads and communication antennas. A circular sailcraft of 220 kg with characteristic acceleration a_c = 0.5 mm/s² is considered, and the control system performances are presented in terms of pointing accuracy for a rendezvous mission to Mercury. The dynamical model takes into account the perturbation torque because of an offset between the centre of pressure and the geometrical sail centre, as well as the Sun gravity-gradient effect and a perturbation torque on the roll axis.