Reinforcement learning in spacecraft control applications: Advances, prospects, and challenges

This paper presents and analyzes Reinforcement Learning (RL) based approaches to solve spacecraft control problems. Different application fields are considered, e.g., guidance, navigation and control systems for spacecraft landing on celestial bodies, constellation orbital control, and maneuver planning in orbit transfers. It is discussed how RL solutions can address the emerging needs of designing spacecraft with highly autonomous on-board capabilities and implementing controllers (i.e., RL agents) robust to system uncertainties and adaptive to changing environments. For each application field, the RL framework core elements (e.g., the reward function, the RL algorithm and the environment model used for the RL agent training) are discussed with the aim of providing some guidelines in the formulation of spacecraft control problems via a RL framework. At the same time, the adoption of RL in real space projects is also analyzed. Different open points are identified and discussed, e.g., the availability of high-fidelity simulators for the RL agent training and the verification of RL-based solutions. This way, recommendations for future work are proposed with the aim of reducing the technological gap between the solutions proposed by the academic community and the needs/requirements of the space industry.