Sliding mode control for attitude maneuvers of Helianthus solar sail

The recent successes of demonstration missions based on solar sail technology have paved the way for designing new mission scenarios with propellantless propulsion systems. In this context, the Italian Space Agency has been supporting a preliminary study of Helianthus, an innovative concept of deep-space mission, which is designed to use a solar sail to generate an artificial equilibrium point in the Sun–Earth gravitational field. Exploiting such a vantage point, located along the Sun–Earth line, Helianthus will be able to perform scientific observations of the solar corona and send to Earth an early warning information in case of solar flares. The attitude control system required to maintain the spacecraft at the unstable artificial equilibrium point is actuated by electrochromic devices, which change their optical properties in response to an electric input, thus generating suitable control torques. The aim of this work is to illustrate a possible control strategy that guarantees the spacecraft station keeping with feasible attitude maneuvers. A nonlinear sliding mode controller is used for the robustness properties it guarantees, and its performance is illustrated in some test maneuvers.