Refinement of GRACE-FO Kinematic Orbit by Combining Least Squares Method and Orbital Dynamic Model

Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) satellites are used to map the gravity field of the Earth. The orbit accuracy of GRACE-FO depends on the quality of on-board GPS data, which is key factor affecting GRACE-FO mission execution. To improve the orbit accuracy of GRACE-FO, a dynamical method was developed to reprocess kinematic orbits. First, with known kinematic orbits, the least squares method was used to estimate the initial state and dynamical parameters of GRACE-FO orbits. Second, during data processing, orbit coordinates containing outliers were deleted. Finally, GRACE-FO dynamical orbits with high accuracy were determined by combining initial state and dynamical parameters. To assess the orbit accuracy, dynamical and kinematic orbits were compared with Jet Propulsion Laboratory (JPL) orbits. Three-dimensional root-mean-square (3D-RMS) results show dynamical and kinematic orbit accuracy of 6.3 and 9.5 cm for GRACE-FO-C and 6.6 and 9.7 cm for GRACE-FO-D, achieving improvements of 33.68% and 31.96%, respectively. The RMS of satellite laser range (SLR) residuals was about 4.1 and 5.1 cm for GRACE-FO-C dynamical and kinematic orbit accuracy, and about 4.2 and 5.4 cm for GRACE-FO-D.