Autonomous Navigation of a Satellite Swarm Using Inter-Satellite Bearing Angles

This paper presents flight results for optical angles-only navigation of a satellite swarm, conducted during the Starling Formation-Flying Optical Experiment (StarFOX). StarFOX is a payload of the NASA Starling mission, which consists of four propulsive CubeSats launched in 2023. Angles-only methods apply inter-satellite bearing angles obtained by onboard cameras for navigation. StarFOX flight data provides the first in-flight demonstrations of 1) multi-target and multi-observer angles-only navigation, 2) autonomous onboard initialization of relative navigation for an unknown target, 3) long-term maneuver-free convergence of angles-only orbit estimates, and 4) simultaneous absolute and relative orbit determination using angles-only measurements. StarFOX applies the Absolute and Relative Trajectory Measurement System (ARTMS), which integrates three algorithms. Image processing detects and tracks multiple targets in images, using hypothesis methods and kinematic modeling, and computes target bearing angles. Batch orbit determination computes initial swarm orbit estimates from bearing angle batches via iterative batch least squares and sampling of weakly observable target range. Sequential orbit determination leverages an adaptive, efficient unscented Kalman filter with nonlinear models to refine swarm state estimates over time. Multi-observer measurements shared over an intersatellite link are seamlessly fused to enable robust absolute and relative orbit determination. Relative positioning uncertainties of 1.3% of the target range (Formula: see text) are achieved for a single observer under challenging conditions, reduced to 0.6% (Formula: see text) with multiple observers. Results demonstrate promising performance, robustness, flexibility, and autonomy with regard to enabling future distributed missions.