Recovering Differential Forces from the GRACE-D Accelerometer

The reduction of non-gravitational accelerations through an onboard accelerometer is a vital part of accurately estimating gravity fields for GRACE-FO. Current accelerometer quality, specifically a defect on the GRACE-D accelerometer, necessitates the use of extensive calibration techniques to optimally utilize the accelerometer measurements. This paper describes these techniques and correction algorithms as they are used for the official GRACE-FO accelerometer products, which rest on the information present in the partially functional GRACE-D accelerometer. First, transplanted data from GRACE-C is used to remove common effects between the spacecraft. Then, GRACE-D data is utilized to compute a correction to the transplanted data to account for solar radiation pressure and albedo using a parity argument and to account for non-common drag and thruster leaks in the attitude control system. The solar radiation pressure and albedo term predominantly improves C3,0 while the drag and leaky thruster term improves the gravity field across the entire spectrum. Finally, some comments on alternative data usage, initial modifications to the algorithms to account for other spacecraft operational modes, and future outlook are provided.