Optimal counter-intuitive solar sail escape trajectories

Minimum-time escape trajectories using a solar sail for propulsion are presented. Results are obtained from a direct collocation with nonlinear programming optimization algorithm which indicate that previous assumptions of the near-optimality for minimum time escape by maximizing the instantaneous rate of increase in total orbital energy may not always be correct. Under some circumstances, reduced escape times can be achieved by temporarily decreasing orbital energy at opportune points along the escape trajectory. These unanticipated results have motivated the development of a feasible trajectory generator using a search technique known as a rapidly-exploring random tree that is capable of negotiating multi-modal search spaces to find counter-intuitive escape trajectories - i.e., trajectories that move inward towards the central body before escaping. These feasible trajectories can then be used as initial guesses for gradient-based optimization techniques.