Distributed autonomous orbit determination for LEO constellations using HAS and inter-satellite links

Low Earth orbit (LEO) satellites have shown great potential for enhancing global navigation satellite system (GNSS)-based positioning, navigation, and timing (PNT) services because of their high orbital velocity and strong signal power. Autonomous orbit determination (AOD) is a promising technique for large LEO constellations, as it enables real-time onboard orbit estimation while reducing dependence on ground infrastructure. However, conventional AOD mainly relies on onboard GNSS observations and broadcast ephemerides, whose limited accuracy restricts orbit determination performance. The Galileo High Accuracy Service (HAS) provides precise orbit and clock corrections through broadcast signals, offering new opportunities to improve AOD without ground support. Meanwhile, inter-satellite links (ISLs) can provide direct ranging measurements between LEO satellites, thereby enhancing constellation geometry and improving solution robustness. Considering the limited onboard computational capacity and inter-satellite communication bandwidth in large LEO constellations, this study investigates a distributed AOD method that integrates Galileo HAS corrections and ISL measurements. A Walker (120/12/0) LEO constellation is simulated to assess the performance of the proposed method under different ISL accuracies and link establishment strategies (Nearest-neighbor-based and Visibility-based). The results show that, under the Visibility-based strategy with an ISL accuracy of 0.03 m, the 3D orbit error of the combined GPS and Galileo solution can reach 0.044 m. In addition, experiments under various data interruption scenarios demonstrate that the combined use of HAS corrections and ISL effectively improves the robustness and reliability of AOD for LEO constellations.