Trajectory optimization and maintenance for ascending from the surface of Phobos

The ascending trajectory from the surface of Phobos to a resonant quasi-satellite orbit around Phobos is investigated with a newly proposed dynamical model based on the Elliptic Restricted Three-Body Problem. The proposed model incorporates the non-spherical gravity field and physical libration of Phobos as well. The trajectories from the surface of Phobos are classified into three types according to their z-componentsas short-, middle-, and long-term ascending trajectories. The total ΔV of the two-impulse ascending trajectories is optimized with the particle swarm optimization method. The total ΔV and time of flight of the optimized ascending trajectories are analyzed, and the Pareto Front is refined from the optimized solutions. A multi-impulse maintenance strategy based on the target point method is constructed to ensure that the ascender can insert into the target orbit accurately along the nominal trajectory in the real environment. The robustness of the maintenance strategy is validated by Monte-Carlo simulations in a high-fidelity model, i.e., the N-body problem with the ephemeris, Phobos’ physical libration, non-spherical gravity field of Phobos, and a Gaussian uncertain perturbation. The number of the correction impulses needed is highly positively correlated with the time of flight of the trajectory. Based on the results, middle-term ascending trajectories with less time of flight on the Pareto Front are recommended.