Application of Accelerometer Data in Precise Orbit Determination of GRACE -A and -B

We investigate how well the GRACE satellite orbits can be determined using the onboard GPS data combined with the accelerometer data. The preprocessing of the accelerometer data and the methods and models used in the orbit determination are presented. In order to assess the orbit accuracy, a number of tests are made, including external orbit comparison, and through Satellite Laser Ranging (SLR) residuals and K-band ranging (KBR) residuals. It is shown that the standard deviations of the position differences between the so-called precise science orbits (PSO) produced by GFZ, and the single-difference (SD) and zero-difference (ZD) dynamic orbits are about 7 cm and 6 cm, respectively. The independent SLR validation indicates that the overall root-mean-squared (RMS) errors of the SD solution for days 309 - 329 of 2002 are about 4.93 cm and 5.22 cm, for GRACE-A and B respectively; the overall RMS errors of the ZD solution are about 4.25 cm and 4.71 cm, respectively. The relative accuracy between the two GRACE satellites is validated by the KBR data to be on a level of 1.29 cm for the SD, and 1.03 cm for the ZD solution