Improving LEO Real-Time Precise Orbit Determination Using the Combination of Onboard GNSS and Intersatellite Link Observations

Abstract

The rapid development of real-time remote sensing applications and low Earth orbit (LEO) augmented navigation creates an unprecedented demand for accurate real-time position information of LEO satellites. Traditional real-time precise orbit determination (POD) relies on onboard GNSS techniques. For purposes such as data communication and precise ranging, the spacecraft from several geodetic missions and large LEO constellations also carry intersatellite link (ISL) payloads, which hold potential benefits for real-time POD. In this study, we propose a reduced-dynamic real-time POD model combining the onboard GNSS and ISL observations. The contribution of GNSS+ISL fusion to the real-time POD is demonstrated by a comprehensive analysis based on the GRACE-FO mission and a simulated LEO constellation. The experiment based on three-month GPS and K-band ranging (KBR) data of the GRACE-FO mission is first conducted. The results show that the additional observation information offered by the KBR measurements enables better decoupling of the orbit state parameters and phase ambiguities, yielding a higher ambiguity-fixing rate for GRACE-FO satellites. Compared to the GNSS-only solution, orbit errors of the GNSS+ISL solution can be reduced by 11.0 % for GRACE-C and 26.7 % for GRACE-D. Meanwhile, the inclusion of KBR observations allows the GNSS+ISL solution to converge more rapidly to centimeter-level accuracy, with a maximum convergence time reduction of 13.0 % relative to the GNSS-only solution. In addition, the integration of GPS and KBR observations increases observation redundancy, significantly enhancing the robustness of the orbit solution under limited GNSS tracking conditions. A simulation analysis based on an LEO constellation further confirms that intraorbit and interorbit ISL observations can substantially improve the performance of real-time POD for an LEO network, in particular balancing orbit accuracy in the horizontal components.