Model-Based Reinforcement Learning and Neural-Network-Based Policy Compression for Spacecraft Rendezvous on Resource-Constrained Embedded Systems

Autonomous spacecraft rendezvous is very challenging in increasingly complex space missions. In this article, we present our approach model-based reinforcement learning for spacecraft rendezvous guidance (MBRL4SRG). We build a Markov decision process model based on the Clohessy-Wiltshire equation of spacecraft dynamics and use dynamic programming to solve it and generate the decision table as the optimal agent policy. Since the onboard computing system of spacecraft is resource constrained in terms of both memory size and processing speed, we train a neural network (NN) as a compact and efficient function approximation to the tabular representation of the decision table. The NN outputs are formally verified using the verification tool ReluVal, and the verification results show that the robustness of the NN is maintained. Experimental results indicate that MBRL4SRG achieves lower computational overhead than the conventional proportional-integral-derivative algorithm and has higher trustworthiness and better computational efficiency during training than the model-free reinforcement learning algorithms.