Optimal solar sail transfers between Halo orbits of different Sun-planet systems

This paper investigates time-optimal solar sail trajectories between Libration Point Orbits (LPOs) of different circular restricted Sun-planet three-body systems. Key in the investigations is the search for transfers that require little steering effort to enable the transfers with low-control authority solar sail-like devices such as SpaceChips. Two transfers are considered: (1) from a Sun-Earth L2-Halo orbit to a Sun-Mars L1-Halo orbit and (2) from a Sun-Earth L1-Halo orbit to a Sun-Mercury L2-Halo orbit. The optimal control problem to find these time-optimal transfers is derived, including a constraint to mimic limited steering capabilities, and is solved with a direct pseudospectral method for which novel first guess solutions are developed. For a near-term sail performance comparable to that of NASA's Sunjammer sail, the results show transfers that indeed require very little steering effort: the sail acceleration vector can be bounded to a cone around the Sun-sail line with a half-angle of 7.5 deg. These transfers can serve a range of novel solar sail applications covering the entire spectrum of sail length-scales: micro-sized SpaceChips could establish a continuous Earth-Mars communication link, a traditional-sized sail provides opportunities for in-situ observations of Mercury and a future kilometer-sized sail could create an Earth-Mars cargo transport gateway for human exploration of Mars.