Precision landing on large and small planetary bodies is a technology of utmost importance for future human and robotic exploration of the solar system. In this context, the Zero-Effort-Miss/Zero-Effort-Velocity (ZEM/ZEV) feedback guidance algorithm has been studied extensively and is still a field of active research. The algorithm, although powerful in terms of accuracy and ease of implementation, has some limitations. Therefore with this paper we present an adaptive guidance algorithm based on classical ZEM/ZEV in which machine learning is used to overcome its limitations and create a closed loop guidance algorithm that is sufficiently lightweight to be implemented on board spacecraft and flexible enough to be able to adapt to the given constraint scenario. The adopted methodology is an actor-critic reinforcement learning algorithm that learns the parameters of the above-mentioned guidance architecture according to the given problem constraints.
Future missions to the Moon and Mars will require advanced guidance navigation and control algorithms for the powered descent phase. These algorithm should be capable of reconstructing the state of the spacecraft using the inputs from an array of sensors and apply the required command to ensure pinpoint landing accuracy, possibly in an optimal way. This has historically been solved using off-line architectures that rely on the computation of the optimal trajectory beforehand which is then used to drive the controller. The advent of machine learning and artificial intelligence has opened new possibilities for closed-loop optimal guidance. Specifically, the use of reinforcement learning can lead to intelligent systems that learn from a simulated environment how to perform optimally a certain task. In this paper we present an adaptive landing algorithm that learns from experience how to derive the optimal thrust in a lunar pinpoint landing problem using images and altimeter data as input.
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