On-Orbit Performance and Lessons Learned for Autonomous Angles-Only Navigation of a Satellite Swarm

This paper presents flight results and lessons learned from optical angles-only navigation of a satellite swarm, conducted during the Starling Formation-Flying Optical Experiment (Star FOX). Star FOX is a core payload of the NASA Starling mission, which consists of four propulsive CubeSats launched in July 2023. Prior angles-only flight demonstrations have been limited to a single observer and single target, and have relied upon a-priori target orbit knowledge for initialization, translational maneuvers to resolve target range, and external absolute orbit updates to maintain convergence. Star-FOX removes these limitations by applying a new angles-only architecture called the Absolute and Relative Trajectory Measurement System (ARTMS), which integrates novel algorithms for image processing, batch orbit determination and sequential orbit determination. During StarFOX experiments from December 2023 to May 2024, images from on-board star trackers were used to perform multi-target and multi-observer relative navigation; to autonomously track and initialize navigation for unknown targets; and to perform simultaneous absolute and relative orbit determination without GPS. Relative positioning uncertainties (1σ ) of 1.3 % of target range are achieved for a single observer, reduced to 0.6 % with multiple observers (without orbit control maneuvers). However, in-flight conditions proved more challenging than anticipated with respect to swarm visibility, image signal-to-noise ratios, image time-tag synchronization, and overall measurement reliability. The impact of these conditions on performance is studied by comparing in-flight telemetry to telemetry produced by an ARTMS digital twin running on the ground, using both in-flight measurement data and synthetic measurement data from pre-launch simulations. Usage of the digital twin facilitated efficient troubleshooting and mitigation via in-flight software updates. Upcoming StarFOX+ experiments in 2025 will extend ARTMS with additional capabilities, such as opportunistic detection and identification of passing resident space objects, which are preliminarily demonstrated via proof-of-concept simulations using StarFOX flight data.