Ephemeris Error Correction for Tracking Non-Cooperative LEO Satellites with Pseudorange Measurements

Correcting the ephemeris of a poorly known "non-cooperative" low Earth orbit (LEO) satellite, by utilizing pseudorange measurements by a ground-based receiver is considered. First, the satellite’s ephemeris error is analyzed, leading to a model parametrizing the error dynamics of the satellite’s argument of latitude. This model is then exploited in an initial tracking stage to reduce the satellite’s large initial along-track errors, after which the position and velocity states of the satellite are estimated. Next, an extended Kalman filter (EKF) is formulated to estimate the satellite’s dynamic states (position, velocity, and clock errors) using pseudorange measurements. Simulation studies comprising varying age-of-ephemeris scenarios are conducted to evaluate the tracking performance of the proposed framework for four different LEO satellite constellations: Starlink, OneWeb, Orbcomm, and Iridium, showing significant reduction in the satellite tracking error via the proposed framework. Experimental results are presented where the proposed framework was used to track 4 Starlink, 2 OneWeb, and 1 Orbcomm LEO satellites using carrier phase measurements. The corrected ephemerides are used to localize a ground receiver. Starting with an initial error of about 2.83 km, using the corrected ephemerides, the final three-dimensional (3-D) localization error was 63.04 m. In contrast, employing the open-loop SGP4-propagated ephemerides resulted in a localization error of about 2.21 km.