Solar-sail control laws for perturbed Earth-bound trajectories

Solar sailing is a spacecraft propulsion method relying solely on solar radiation pressure to provide thrust and is therefore propellantless by nature. Although it represents a practical and promising propulsion system particularly suited for heliocentric flight regimes, near-term sailcraft missions will remain Earth-bound due to the current technology readiness level. This paper aims to show the suitability of solar sailing for planetocentric applications for future Earth-bound solar-sail missions. In Earth orbit, the sailcraft is subjected to perturbations absent or negligible in heliocentric flight, including the effect of eclipses, non-spherical gravity and aerodynamic drag. The magnitude of these perturbations can be comparable to, or even exceed that of solar radiation pressure and their effect on the solarsail dynamics should be investigated to ensure the sailcraft’s transfer capabilities and controllability. This paper does so by including the gravitational and aerodynamic perturbations in the optimal control problem. From this formulation, steering laws can be derived to optimally change individual orbital elements. These newly derived steering laws form an extension to the laws found by McInnes for unperturbed solar-sail Earth-bound motion. By accounting for the perturbations in the derivation of the steering laws, their effect can be exploited by the sailcraft to achieve orbits otherwise unreachable. The improved maneuverability will be quantified based on the established increase of the targeted orbital element. A range of different starting orbits will be considered to characterize how the perturbations affect the solar-sail maneuvering capabilities in different orbital regimes. As demonstration of the real need for this investigation, NASA’s Advanced Composite Solar Sail System (ACS3) mission will be considered as real-case scenario. This mission is scheduled for launch in mid-2022 and may benefit from the steering laws derived in this paper to proof the maneuverability of solar sails in Earth orbit.