Reinforcement Learning for Low-Thrust Trajectory Design of Interplanetary Missions
This work addresses robust trajectory design for interplanetary missions, which is a domain-specific problem, and appears incremental as it applies an existing reinforcement learning method to this context.
This paper tackles the problem of designing robust low-thrust interplanetary trajectories under severe disturbances by using reinforcement learning, resulting in a Guidance and Control Network that provides both a robust nominal trajectory and closed-loop guidance law, with validation through comparison to optimal indirect methods and Monte Carlo simulations for an Earth-Mars mission.
This paper investigates the use of Reinforcement Learning for the robust design of low-thrust interplanetary trajectories in presence of severe disturbances, modeled alternatively as Gaussian additive process noise, observation noise, control actuation errors on thrust magnitude and direction, and possibly multiple missed thrust events. The optimal control problem is recast as a time-discrete Markov Decision Process to comply with the standard formulation of reinforcement learning. An open-source implementation of the state-of-the-art algorithm Proximal Policy Optimization is adopted to carry out the training process of a deep neural network, used to map the spacecraft (observed) states to the optimal control policy. The resulting Guidance and Control Network provides both a robust nominal trajectory and the associated closed-loop guidance law. Numerical results are presented for a typical Earth-Mars mission. First, in order to validate the proposed approach, the solution found in a (deterministic) unperturbed scenario is compared with the optimal one provided by an indirect technique. Then, the robustness and optimality of the obtained closed-loop guidance laws is assessed by means of Monte Carlo campaigns performed in the considered uncertain scenarios. These preliminary results open up new horizons for the use of reinforcement learning in the robust design of interplanetary missions.