Strong Solar Radiation Forces from Anomalously Reflecting Metasurfaces for Solar Sail Attitude Control.

We examine the theoretical implications of incorporating metasurfaces on solar sails, and the effect they can have on the forces 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, which 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 efficiencies 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.