Optimized Trajectories to the Nearest Stars Using Lightweight High-Velocity Photon Sails
René Heller et al 2017 AJ 154 115
Photogravitational assists may be more effective when the star is used as a bumper (i.e., the light sail passes “in front of” the star) rather than as a catapult (i.e., the sail passes “behind” or “around” the star).