GeoForschungsZentrum Potsdam, Telegrafenberg, D-14473 Potsdam, Germany
On July 15, 2000 the geoscientific satellite CHAMP has been launched into a near-polar, circular low earth orbit at 460 km altitude. Throughout its anticipated 5-year mission the altitude will decay to 300 km. This mission profile has been chosen to provide full global coverage and to resolve temporal variations.
The CHAMP scientific payload is dedicated to recover the global gravity field, the magnetic field and to perform atmospheric sounding measurements. In addition to these scientific objectives the GPS receiver, star cameras and vector magnetometers are also used as input sensors for the attitude and orbit control system (AOCS).
In order to separate gravitational from non-gravitational orbit perturbations an accelerometer is flown on CHAMP. The non-gravitational perturbations include air drag, solar radiation pressure and attitude control actuator operation. Therefore an attitude control system is needed that sparsely performs thruster firing but predominantly uses magnetic torquing instead. The reason for this is that the latter produce significantly lower angular accelerations and no linear accelerations thus providing a quiet measurement platform.
In this talk we will focus on the early performance of the attitude and orbit sensors and their contribution to a stable attitude control system which is needed for the accelerometer measurements. During nominal operation we observe only 1-2 thust pulses per orbit. The numerous lessons learned of the instrument behavior and the reaction of the attitude control system to it will be presented.
