Active Momentum Control Coatings for Solar Sails

The development of thin-film coatings with an actively tunable solar reflectance is proposed for momentum control on solar sails. As currently conceived, maneuvering and attitude control on solar sail spacecraft is achieved by mechanically adjusting the angle of one or more solar sails or panels with respect to the solar flux to create torque. The maneuvering and propulsion force is obtained from the solar radiation pressure with the realizable force depending on the spectral reflectance and absorption of the sail and its angle with respect to the flux. The proposed coatings offer a non-mechanical, low weight alternative to currently anticipated methods of maneuvering and attitude control. The coatings are applied to a limited area of the solar sail in a location that maximizes the torque on the spacecraft. In Phase I, the materials and design for the coating will be developed with emphasis on performance and stability on thin, flexible polymer sheet suitable for solar sail construction. Functioning, small-area (25 cm2) samples will be fabricated to demonstrate performance. In Phase II, the coatings will be optimized, scaled to larger areas, and integrated into a prototype solar sail and subjected to extensive testing for space environment stability.