Autonomous Angles-Only Navigation for Spacecraft Swarms around Planetary Bodies

摘要

This paper presents and demonstrates an algorithmic framework for autonomous navigation of spacecraft swarms around planetary bodies, using angles-only measurements from onboard cameras. Angles-only methods are compelling as they reduce reliance on external measurement sources. However, prior demonstrations have faced limitations, including 1) inability to treat more than one observer and target in a swarm, 2) lack of autonomy and reliance on external state information, and 3) treatment of only Earth-orbit scenarios. The new Absolute and Relative Trajectory Measurement System (ARTMS) overcomes these challenges and consists of three core modules leveraging novel algorithms: Image Processing, which tracks and identifies targets in images and computes their bearing angles; Batch Orbit Determination, which computes a swarm state initialization from angles-only measurements; and Sequential Orbit Determination, which uses an unscented Kalman filter to refine the swarm state estimate, seamlessly fusing measurements from multiple observers to achieve the autonomy, robustness and distribution needed for deep space navigation. Theoretical performance of ARTMS is investigated through a quantitative observability analysis of multi-observer angles-only navigation in Mars orbit. For swarms of at least 3 spacecraft and at least 2 observers, the complete swarm state is observable. After two orbits, the absolute orbit is estimated to within 1 km, target ranges are estimated to within 0.5%, and other relative state components are estimated to 0.02% of target range. Clock offsets are estimated to within 0.05s. These accuracies are validated with camera-in-the-loop simulations of a four-spacecraft swarm taking distributed measurements in an eccentric Mars orbit. ARTMS displays robust navigation across a variety of formations and under challenging conditions, and achieves the necessary performance to support the proposed objectives.