Mechanism-free control method of solar/thermal radiation pressure for application to attitude control

Solar radiation pressure (SRP) impinging on spacecraft is usually regarded as a disturbance for attitude motion, but it can be harnessed to solve the very problem it creates. Active SRP control is possible with solar radiation powered thin-film devices such as reflectivity control devices or liquid crystal devices with reflective microstructure. Thermal radiation pressure (TRP) can likewise be used to solve flight attitude problems caused by SRP, TRP, or other factors. TRP on solar cells can be controlled by switching regulators under the control of them, resulting in temperature change. These SRP/TRP controls are free from mechanisms, such as reaction wheels, and thus they do not produce internal disturbances. In addition, the magnitude of SRP/TRP torques is generally much smaller than internal disturbance torques produced by reaction wheels, which creates a potential for precision far beyond that achieved with mechanical controls. This paper summarizes how SRP/TRP can be used by means of numerical simulations of typical control methods. The usefulness of this mechanism-free attitude control is verified for future use on both Earth orbiting satellites and interplanetary spacecraft including solar sails.