Precise orbit determination for TOPEX/Poseidon, Jasons 1,2,3 and Sentinel-6A and the std2400 series of orbits

We have computed updated precise orbits based on Satellite Laser Ranging (SLR) and DORIS data using the NASA Precise Orbit Determination and Geophysical Parameter estimation software, GEODYN. These precise orbits span five core altimeter missions: TOPEX/Poseidon, Jasons 1,2,3, and Sentinel-6A. The new orbits, std2400, are based on SLRF2020 and DPOD2020, improved background gravity modelling, improved nonconservative force modelling, and application of the GOT5.6 ocean tide model. The radial orbit accuracy is evaluated with SLR and altimeter crossover residuals, as well as with orbit difference analyses. The std2400 orbits are compared with the corresponding latest orbits from JPL (JPL_IGS20, based solely on GPS data), the available corresponding CNES export orbits (POEF, based on GPS and DORIS data), and the present SLR+DORIS-based export orbits from GSFC (std2006_cs21). The average radial orbit differences of the new std2400 orbits with the POEF and JPL_IGS20 orbits are 8.4 mm for TOPEX, 6-8 mm for Jason-1, 5-6 mm for Jason-2, 4.7- 6.0 mm for Jason-3 and 4.3 to 6 mm for Sentinel-6A. Analysis with independent altimeter crossovers and SLR data, show the new std2400 orbits have a radial orbit accuracy of 16 mm for TOPEX, 9.9 mm for Jason-1, 7.8 mm for Jason-2, 6.4 mm for Jason-3 and 6.8 mm for Sentinel-6A. We find that mm-level orbit accuracy differences can be detected in altimeter sea level trend analysis and in the altimeter tide gauge verification. The impact of radial drift error shown by the orbit differences from 1993 to 2025 on the global altimeter mean sea level trend estimates was also evaluated. The dominant cause for orbit drift over the 32-year and 4-year timescales between the new std2400 orbits, and the old std2006_cs21 orbits and the POEF series of orbits is found to be due to time-variable gravity modeling error.