Fully Dynamic Approach for GOCE Precise Orbit Determination

Gravity field and steady-state Ocean Circulation Explorer (GOCE) was launched in 2009 at 250 km altitude to recover the Earth’s static gravity field. As part of the GOCE- Italy project, we carried out GPS-based, fully dynamic Precise Orbit Determination (POD) of GOCE for daily arcs covering about 500 days (November 1, 2009 - May 31, 2011). Three sequences were defined and implemented with the software NAPEOS (ESA/ESOC). A first sequence uses the orbit propagated from the previous day as an a-priori orbit but, to avoid one-day failures compromising all the subsequent POD processing chain, other two sequences were built using the official kinematic Precise Science Orbits (PSO) as a-priori orbits. For those days where the sequences based on the PSO gave less accurate results, or even failure, the a-priori orbit propagated from the previous day was employed. Results show an average post-fit RMS of zero-difference phase measurements below 10 mm for about 90% of the daily arcs. Most orbits compare to less than 6 cm 3D RMS with respect to the official kinematic and reduced-dynamics PSO orbits. To evaluate the quality of the POD results, 366 overlapping arcs of 5 hours were compared, showing an average distance below 1 cm.