Onboard Orbit Determination With Inter-Satellite Range Measurements

Abstract

Current orbit determination methods for satellites in low Earth orbit (LEO) largely depend on ground-based observations or positioning, navigation, and timing (PNT) services. For satellite constellations, in particular, the unavailability of these services may jeopardize constellation operations. To improve resilience, this study proposes an onboard orbit determination framework for a Local Satellite in a constellation using only inter-satellite link (ISL) range measurements from four neighboring Remote Satellites. An observability assessment based on the Fisher information matrix (FIM) is performed to evaluate the measurement geometry. In the proposed framework, the Local Satellite receives ISL range measurements and ephemerides from the Remote Satellites. An extended Kalman filter (EKF), whose statistical consistency was assessed using a chi-square test, was implemented with both a reduced-fidelity numerical propagator and Keplerian propagator to estimate the orbital state. While the numerical-propagator implementation achieves an approximately 24 cm three-dimensional root-mean-square (3D RMS) position error and an approximately 4 mm/s velocity error, the 3D RMS position error exceeds 160 cm with the Keplerian propagator. Although the Keplerian propagator yields larger velocity errors, it reduces the maximum and mean runtimes by approximately 50% and 90%, respectively. Depending on mission requirements and available onboard computational resources, the proposed framework can provide an onboard orbit determination capability while reducing reliance on ground observations and PNT services and enabling autonomous orbit determination.