Safety-Aware Optimal Attitude Pointing for Low-Thrust Satellites

• Main Authors: Helen Henninger, James Biggs, Karl von Ellenrieder
• Format: Article
• Language: English
• Published: MDPI AG 2021-03-01
• Series: Applied Sciences
• Subjects: attitude control; satellites; geometric control; reinforcement learning; constrained motion planning
• Online Access: https://www.mdpi.com/2076-3417/11/7/3002

In geostationary orbit, long eclipses and the seasonal variations in the direction and intensity of the solar input can cause damage to sensitive equipment during attitude maneuvers, which may inadvertently point the equipment towards the Sun. The requirement that transmitting and receiving antennae remain pointed towards the Earth creates further restrictions to pointing directions. The aim of the study is to construct a novel geometric and reinforcement-learning-based method to determine attitude guidance maneuvers that maintain the equipment in safe and operational orientations throughout an attitude maneuver. The attitude trajectory is computed numerically using the geometric framing of Pontryagin’s maximum principle applied to the vehicle kinematics using the global matrix Lie group representation on <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>S</mi><mi>O</mi><mo>(</mo><mn>3</mn><mo>)</mo></mrow></semantics></math></inline-formula>, and the angular velocities are shaped using free parameters. The values of these free parameters are determined by a reinforcement learning algorithm to avoid the forbidden areas while maintaining the pointing in operational areas (modeled as subsets of the two-sphere of all possible pointing directions of a particular axis). The method is applied to a model geosynchronous satellite and demonstrated in a simulation.