No-guess indirect optimization of asteroid mission using electric propulsion

This paper researches the optimal opportunities and trajectories for an asteroid-Earth return mission and compares different options in terms of time length and reentry velocity. High specific impulse and steering capabilities of solar electric propulsion are exploited to perform deep space maneuvers. An indirect method based on the theory of optimal control is applied to find the trajectory that maximizes the final mass. The boundary value problem that arises from the application of the optimal control theory is solved by means of a shooting procedure based on Newton's method. In particular, the best opportunities to reach the Earth are first analyzed by searching a time-free transfer that intercepts the Earth's orbit at the most favorable point; suitable launch windows are then determined. This technique shows significant benefit to define the initial solution that is required to start the optimization process so that no initial guess of adjoints is required for the optimization. Mission opportunities returning from asteroid Bennu (101955) are presented.