A new ISL-aided method for improving real-time kinematic orbit and clock estimation robustness of LEO satellites with degraded onboard observations

Abstract

Onboard global navigation satellite system (GNSS) receivers have become the most convenient means to realize autonomous orbit determination and clock estimation for low Earth orbit (LEO) satellites. However, signal outages and blockages in complex space environments cause GNSS observation degradation, which restricts the accuracy and robustness of orbit and clock offset estimation. Inter-satellite links (ISL) with ranging capability can provide an additional enhancement approach to address this problem. This study proposes a method to incorporate ISL measurements as constraints into LEO satellite real-time kinematic orbit and clock offset processing to improve its robustness against degraded GNSS observation. Experiments are carried out on GRACE-C and GRACE-D satellites under GNSS interruption and occlusion scenarios, with both single-satellite and dual-satellite ISL constraint modes investigated. Taking solutions from normal GNSS observations as references, the results show that: (1) the single-satellite mode exhibits superior performance over the dual-satellite mode; (2) the orbit in the along-track gains the largest improvement for accuracy and robustness; (3) in the interruption scenario, single-satellite ISL constraints reduce the 3D orbital error by approximately 59.9%, from 149.9 cm to 61.5 cm, and the clock offset STD by 40.6%, from 2.44 ns to 1.45 ns; (4) in the occlusion scenario, dual-satellite ISL constraints reduce the 3D orbital error by approximately 39.2%, from 62.1 cm to 37.9 cm, and the clock offset STD by 37.4%, from 0.92 ns to 0.58 ns. Overall, this method is well-suited for real-time high-precision orbit determination of LEO satellites in complex observational environments.