Integrated kinematic precise orbit determination and clock estimation for low Earth orbit satellites with onboard and regional ground observations

Many low Earth orbit (LEO) satellite constellations have been designed in recent years to provide global broadband Internet services. These constellations provide opportunities for LEO satellites to serve as navigation satellites by launching navigation signals while also being equipped with an onboard global navigation satellite system (GNSS) receiver. We propose a kinematic precise orbit determination (KPOD) and precise clock estimation (PCE) approach for LEO satellites by integrating regional ground observations and onboard observations of LEO satellites. By taking into account the LEO satellite clock bias, this approach can demonstrate the contributions of the ground and onboard observations of LEO satellites to the orbit and clock results, respectively. A composite LEO satellite constellation consisting of 168 satellites and observations from regional ground stations and LEO satellite onboard receivers are simulated considering the LEO satellite clock bias to verify the proposed approach. The results indicate that the convergence time of LEO satellite orbit determination can reach 9.38 min with the integrated KPOD (IKPOD) method, which is a reduction of 24.0% compared with the traditional KPOD method. However, the additional improvement in the LEO satellite orbit accuracy after convergence is very limited. The average root mean square (RMS) and standard deviation (STD) values of all LEO satellite clocks using the integrated PCE (IPCE) method with the participation of LEO satellite onboard observations can reach 0.27 ns and 0.15 ns, respectively. The improvements in the average RMS and STD are 42.6% and 60.5%, respectively, compared with the ground LEO PCE method. The convergence time and accuracy of LEO/GNSS precise point positioning can be improved by 44.6%, 48.3%, 26.7%, and 20.4% in the east, north, and up directions, respectively, using LEO satellite orbits and clocks from the IKPOD and IPCE methods compared with KPOD and PCE.