Solar Torque Control By Using Thin -Film Directionally Sensitive Surfaces

This pa per presents a novel technique for passively compensating spacecraft sol ar pressure disturbance torques caused by large deployed appendages by use of thin -film materials with directionally sensitive thermophsyical properties . Directionally sensitive surfaces are engineered to have varying optical properties (absorptivity, refl ectivity, and emmisivity) as a function of sun incidence angle. The basic concept uses a directionally absorptive/reflective surface, mounted on the sun -side of the appendage, to passively compensate solar pressure disturbance torques by shifting the surf ace effective CP as a function of sun incidence angle. The surface optical properties and geometrical characteristics are design parameters which depend upon the spacecraft configuration. The paper first presents an introduction to motivate the need for t his innovative invention, the analytical models for calculating the solar pressure torques produced by a thin -film directionally sensitive surface, followed by a numerical example which illustrates the solar disturbance torque reduction achievable for a ty pical science spacecraft configuration. Finally, conclusions and recommendations for further research work are presented. The concepts presented in this pap er have been patented by Northrop Grumman Corporation .