Abstract: Low-latency, high-precision satellite orbits are critical for large-scale applications of low-Earth orbit (LEO) satellites, such as navigation augmentation and massive internet constellations. Therefore, researching real-time orbit determination for LEO satellites based on Galileo High Accuracy Service (HAS) holds significant importance for their widespread deployment. This paper evaluates the accuracy of broadcast ephemeris and HAS products for GPS and Galileo, and investigates and validates real-time orbit determination performance using onboard GNSS observations from a Chinese LEO satellite platform. First, using GPS LNAV, Galileo INAV broadcast ephemeris, and concurrent Galileo HAS correction data as the foundation, the availability and accuracy of HAS products are systematically evaluated. Analysis revealed that Galileo satellite availability reached 95.0%, while GPS only achieved 85.9%. Both GPS and Galileo orbital HAS products achieved accuracy better than 10cm, with clock offset standard deviations better than 0.3ns, representing significant improvements over broadcast ephemeris in orbit and clock offset precision. This study further employed HAS products to evaluate real-time high-precision orbit determination performance for low-Earth orbit satellites using onboard GPS and Galileo observations from Chinese satellite platforms. The real-time orbit determination accuracy for along-track, cross-track, radial, and three-dimensional components based on onboard GPS observations is 8.9cm, 4.1cm, 4.2cm, and 10.7cm, respectively, while the real-time orbit determination accuracy in all directions based on Galileo observations is 7.4cm, 3.7cm, 4.4cm, and 9.5cm, respectively, representing improvements of 58.5% and 30.1% over real-time orbit determination using broadcast ephemeris alone, demonstrating significant accuracy gains. After accounting for signal in space ranging error parameter compensation, real-time orbit determination accuracy based on GPS and Galileo broadcast ephemeris improved by 42.9% and 24.4%, respectively. In contrast, the improvement based on HAS ephemeris was limited, achieving only 4.5% and 10.4% enhancements. The study demonstrates that real-time precise orbit determination for LEO satellites based on Galileo HAS precise ephemeris achieves 10cm-level accuracy. This enables autonomous real-time orbit updates with high precision for LEO satellites, providing orbital position data support for real-time high-precision applications of LEO satellites.

Key words: low Earth orbit satellite, real-time precise orbit determination, onboard GNSS, broadcast ephemeris, Galileo HAS