Robust solar sail attitude control via ballast mass displacement

Solar sails enable continuous, propellant-free acceleration by harnessing solar radiation pressure, offering a promising solution for long-duration interplanetary missions. This work presents an attitude control strategy based on the displacement of internal ballast masses to modulate the spacecraft’s center of mass, thereby controlling the offset relative to the optical center of pressure. The goal is to accurately track a prescribed attitude profile, defined by constant cone and clock angles in the radial-transverse-normal reference frame. To achieve this, a nonlinear sliding mode controller is designed to ensure robust performance in the presence of system uncertainties and external disturbances. The simulation framework incorporates the effects of membrane deformations (specifically, wrinkling and billowing), which change the distribution of forces from solar radiation pressure. Numerical results show that the proposed controller achieves high-precision attitude tracking and maintains robustness under realistic perturbations, confirming that ballast-based actuation is an effective strategy for future solar sail missions.