Accelerometry Aboard CHAMP

Abstract

One of the key instruments aboard the CHAMP geoscientific small satellite is the three-axes STAR accelerometer, which shall measure the resultant acceleration of the spacecraft due to non-gravitational forces. Then, the purely gravitational signal in CHAMP’s orbit, measured with GPS satellite-to-satellite tracking, can be extracted for use in Earth gravity field modelling. Besides the noise in the accelerometer measurements, environmental systematic error sources may affect the accelerometer data: e.g. accommodation at CoG, orientation knowledge and spurious, linear and rotational accelerations from the attitude control system and due to boom oscillations. A crucial point in the exploitation of the measured accelerations is the determination of the instrument’s calibration parameters, i.e. bias, and scale factor which shall be done with an in-flight data adjustment. Results of numerical simulations of CHAMP’s tracking and accelerometer scenario, taking into account the GPS and accelerometer error sources and the estimation of calibration and nuisance parameters, are presented with regard to impacts on orbit and gravity field recovery accuracy. The objective is to develop an optimal data processing approach which can be applied to real mission data after the launch of CHAMP, end of 1999.