Optimal Trajectory Design for Solar Sails under Piecewise Constant Control Laws

This work addresses the problem of solar sails trajectory optimization, aiming to minimize the flight time for various mission scenarios. In particular, a new control law is proposed: the sail attitude is piecewise constant with respect to an interial observer. This control strategy results more realistic if compared to the one based on piecewise constant cone angle, since it allows to reduce the effort required by the attitude control system. After an introduction about solar sailing concept and its technological evolution, SRP physical principles are analyzed, considering both optical and ideal thrust models. Bidimensional equations of motion are formulated in polar coordinates and different applications are considered: Neptune flyby, Mars and Venus rendezvous, and orbital phasing. The Smart Dust concept is also introduced highlighting the possibility to perform in-orbit diagnostic through on-off control maneuvers. The optimization is performed starting with a genetic algorithm followed by gradient-based methods. Finally, the continuous optimal control problem is discussed and solved thorugh Pontryagin principle. This case is used as a reference to validate the results obtained with the piecewise constant control law.