Analytical evaluation of effective solar sail attitude control using metasurfaces for deep space exploration
We examine the theoretical implications of incorporating metasurfaces on solar sails, and the effect they can have on the forces and torques applied to the sail. This would enable a significant enhancement over state-of-the- art attitude control by demonstrating a novel, propellant-free and low mass approach to induce a roll torque on the sail, which is a current limitation in present state-of-the-art technology. We do so by utilizing anomalous optical reflections from the metasurfaces to generate a net in-plane lateral force. This can lead to a net torque along the roll axis of the sail, in addition to the other spatial movements exhibited by the sail from solar radiation pressure. We characterize this net lateral force as a function of incidence angle. In addition, the influence of the phase gradients and anomalous conversion efficiency characteristics of the metasurfaces are independently considered. The optimum incidence angle that corresponded with the maximum net lateral-to-normal force ratio was found to be -30° for a metasurface exhibiting 75% anomalous conversion efficiency with a phase gradient of 0.71k0. Upon comparison with the force and torque plots from current reflection control devices such as those that were utilized on IKAROS, the anomalously reflecting metasurfaces offer a considerable increase in torque along the roll axis. This is important because up until this point, roll control has been a particularly difficult aspect of solar sail attitude control to manipulate without the use of reaction wheels or propellant. The torque along the roll axis can reach values of torque as high as 358 μN m under ideal conditions.