Enhancing GRACE-FO C20 Estimation Precision by Correcting Accelerometer Anomalous Responses to Thruster Firings

The Earth's dynamic oblateness (C₂₀), a crucial component of the time-variable gravity field, is inaccurately estimated by GRACE-FO, currently requiring replacement with Satellite Laser Ranging (SLR) values. This study identifies and corrects a key error source: anomalous accelerometer (ACC) responses to thruster firings. We discovered that the unrealistic response during Roll thruster activations correlates with the ACC's range mode, where increased detection voltage (Vd) heightens sensitivity to platform vibrations.

To address this, we developed a comprehensive physical thruster model, accounting for thrust imbalance (correlated with tank pressure differentials), mounting angle deviations, and center-of-mass (CoM) effects. Calibrated using stable Yaw-thruster data, this model was integrated into an optimized ACC processing workflow, generating new Level-1B products (ACTC1B and ACHTC1B).

Gravity field recovery using the corrected data shows a substantial improvement in C₂₀ estimation. The RMS deviation from the SLR-derived TN-14 solution is reduced to 1.16 × 10^-10, a 21.4% enhancement over the uncalibrated baseline. Spatial-temporal analysis suggests that the clustering of Roll thruster firings near the magnetic equator and their periodic modulation may link these high-frequency perturbations to the C₂₀ bias. 

This work underscores the critical importance of precise accelerometer calibration for reliable gravity field recovery, provides valuable insights for the instrument design and data processing of future gravity missions, and offers a feasible approach to reduce dependency on SLR-derived C₂₀ values in satellite gravity products. This work has been published in Journal of Geophysical Research (JGR): Solid Earth (Shen et al., 2025, https://doi.org/10.1029/2025JB031121).