Contribution of SLR observations to precise orbit determination and geocenter motion estimation using Galileo and Sentinel-6A satellites as space ties

The GNSS and SLR observation capabilities of both the Galileo and Sentinel-6A satellites provide potential space ties, improving the accuracy of orbit and geocenter motion measurements. This study seeks to evaluate the influence of SLR data on the orbits and geocenter determination by integrating both ground-based and onboard GNSS/SLR data for the Galileo and Sentinel-6A satellites. The experiments utilized 300 days of data from 110 GNSS stations and 27 SLR stations. Both ground- and onboard-GNSS observations, together with SLR data from Galileo and Sentinel-6A, were processed simultaneously to determine the orbits and geocenter motion. Results show that incorporating SLR observations improves Galileo orbit solutions. The std of SLR residuals decreases by 2.5% on average and up to 11% for individual satellites, while orbit overlap consistency improves by 1%–2%. For Sentinel-6A, SLR observations strengthen the estimation of force parameters and reduce parameter correlations by up to 16%. In geocenter motion estimation, Sentinel-6A SLR data lower uncertainties by about 10% and increase the detectability of semiannual and other periodic signals, especially in the Z direction. The combined use of ground- and space-based GNSS/SLR observations also helps to reduce spurious 3CPY signals in geocenter estimation that originate from GNSS solar radiation pressure. Overall, combining GNSS/SLR observations from both MEO and LEO satellites yields more consistent orbit solutions and more reliable geocenter motion estimation.