CHAMP, GRACE, GOCE instruments and beyond

Abstract

The electrostatic accelerometers of the CHAMP satellite as well as of the GRACE two ones have provided the necessary information to distinguish the satellite actual trajectories from the pure gravitational orbits. By providing the measurements of the satellite non-gravitational forces, one can distinguish the position or velocity fluctuations of the satellite due to the Earth gravity anomalies from those due to the drag fluctuations. In-orbit calibration and validation of on-board instruments, bandwidth, bias stability and resolution proof the success of the mission scientific geodesic return. The basic principle of these sensors stays on the servo-control of one solid mass, maintained motionless from the instrument highly stable structure. Care is paid for the mass motion detection, down to tenth of Angstrom, and to the fine measurement of the servo-controlled forces applied on the mass through electrostatic pressures. With the same concept and technologies, the GOCE inertial sensors have been designed, produced and tested to reach even better performances in order to deal with the milli-Eötvös gradiometer objectives. The performance of the instrument and the interest of the obtained measurements do not only depend on the sensor accuracy itself but also on the on-board environment (magnetic, thermal, vibrational...), on the satellite attitude motions and on the in-orbit configuration and aliasing aspects. Future missions will have also to consider these aspects, especially when envisaging cryogenic electrostatic sensors which can exhibit better self accuracy or when considering satellite to satellite laser tracking. © Springer-Verlag Berlin Heidelberg 2012.