An international research team from the National Time Service Center(NTSC) of the Chinese Academy of Sciences (CAS) and Curtin University in Australia has proposed a novel method to enhance the accuracy and integrity of low Earth orbit (LEO) satellite orbit predictions.

The study was published in NAVIGATION on July 23.

Thanks to the lower orbital altitudes, faster speeds, and stronger signals, low Earth orbit (LEO) satellites are increasingly seen as valuable complements to traditional Global Navigation Satellite Systems (GNSS). Their integration into real-time Positioning, Navigation, and Timing (PNT) systems is expected to significantly improve performance. However, the reliability of these systems hinges on the availability of highly accurate, real-time orbital products, which are themselves dependent on precise orbit determination (POD).

In real-world engineering scenarios, onboard GNSS observations of LEO satellites could experience significant interruptions due to factors such as data downlinking strategies, receiver tracking performance, and the scheduling of other tasks. These interruptions can severely degrade the accuracy of near-real-time POD, which in turn affects the quality of the predicted orbits and ultimately compromises the accuracy and integrity of the real-time orbital products delivered to users.

To address the challenges posed by imperfect GNSS observation status and large observation gaps for LEO satellites, the

the joint research team systematically investigated the impact of varying observation gap durations and lengths of post-gap orbital segments. They optimized and combined different LEO POD strategies to improve near-real-time orbit determination under conditions of large data gaps. Their approach significantly enhanced short- to mid-term orbit prediction accuracy and provided new insights into integrity performance under imperfect GNSS data scenarios.

"This method improves POD strategies for LEO satellites when facing significant GNSS observation interruptions," said Prof. WANG Kan Wang, head of the LEO satellite precise orbit and clock determination at NTSC. "It improves the accuracy and integrity of LEO orbit predictions, ensuring that future users of LEO-augmented PNT services can access precise and reliable real-time LEO satellite orbital products, even under non-ideal data conditions."

This should help enhance the precision and integrity of the future LEO-augmented BeiDou/GNSS positioning and timing.

The researchers validated their approach using the Sentinel-6A satellite, which orbits at approximately 1,300 kilometers. By combining dynamic modeling strategies tailored to both continuous (RP) and gap-interrupted (CP) observation periods, they demonstrated improved POD robustness. Their detailed analysis of orbit prediction accuracy and integrity under various gap scenarios illustrated the real-world applicability of their method.

This study presents a valuable investigation into LEO orbit determination considering practical data gap scenarios, extending beyond idealized simulations.

This work was supported by the International Partnership Program of CAS.

Near-real-time along-track LEO satellite orbital accuracy applying different orbit determination strategies (top) and the adjusted strategy (bottom) under large GNSS observation gap(Image by Chen et al.)