Precise Orbit Determination for Sentinel-6A using Galileo and GPS observations

The Sentinel-6A satellite, launched on November 21, 2020, is equipped with a dual-constellation (Galileo and GPS) onboard receiver for precise orbit determination (POD). Since launch, there have been significant improvements in the force models and data processing strategies. This has resulted in significant improvements to orbit accuracy. The Gravity Recovery and Climate Experiment-Continuity (GRACE-C) mission, which will be launched in 2028, will carry on a similar onboard receiver to Sentinel-6A. The main purposes of this study are to extend our software to process both Galileo and GPS data for preparing GRACE-C and to investigate how well the orbits of the Sentinal-6A satellite can be currently determined using Galileo or/and GPS data based on the current models and approaches. In this study, we present the results of Sentinel-6a POD solutions. The orbit accuracy is assessed using several tests, which include analysis of orbit fits, Satellite Laser Ranging (SLR) residuals, internal and external orbit comparisons. We show that less than one-cm radial orbit accuracy for the Sentinel-6A satellite has likely been achieved through different orbit accuracy evaluations. The precise Sentonel-6A orbits determined based on Galileo and GPS observations can meet the stringent requirement on radial orbit accuracy (1.5 cm).