Solar sail H-reversal trajectory: a review of its advances and applications

The set of the orbital angular-momentum reversal, or H-reversal, sailcraft trajectory was born as a type of unconventional precursor interstellar mission trajectory by using highperformance solar sails. Starting from an outline of the H-reversal sail trajectory, this paper mainly focuses on the 2D reversal-mode solution to the general solar-photon sail motion equations. The feasible region for H-reversal trajectories in fixed sail attitude angles is illustrated. Some interesting applications of the H-reversal trajectory are presented in detail to show its advantages. As a special case, a precursor interstellar probe can be delivered with a constant sail orientation in the H-reversal trajectory to be compared with the direct-motion sail flyby of the Sun. Of importance are the heliocentric periodic orbits in double H-reversal modes, obtained via both fixed and time-varying sail attitude angles. Two more applications involving H-reversal trajectories are discussed in terms of asteroid deflection and transfer trajectory to rectilinear orbits. Finally, some items of the mathematics behind the 3D motion-reversal trajectories are summarized.