Calibration and adjustment of center of mass (COM) based on EKF during in-flight phase

Abstract

The electrostatic accelerometer, assembled on gravity satellite, serves to measure all non-gravitational accelerations caused by atmosphere drag or solar radiation pressure, etc. The proof-mass center of the accelerometer needs to be precisely positioned at the center of gravity satellite, otherwise, the offset between them will bring measurement disturbance due to angular acceleration of satellite and gradient. Because of installation and measurement errors on the ground, fuel consumption during the in-flight phase and other adverse factors, the offset between the proof-mass center and the satellite center of mass is usually large enough to affect the measurement accuracy of the accelerometer, even beyond its range. Therefore, the offset needs to be measured or estimated, and then be controlled within the measurement requirement of the accelerometer by the center of mass (COM) adjustment mechanism during the life of the satellite. The estimation algorithm based on EKF, which uses the measurement of accelerometer, gyro and magnetometer, is put forward to estimate the offset, and the COM adjustment mechanism then adjusts the satellite center of mass in order to make the offset meet the requirement. With the special configuration layout, the COM adjustment mechanism driven by the stepper motors can separately regulate X, Y and Z axes. The associated simulation shows that the offset can be controlled better than 0.03 mm for all the axes with the method mentioned above.