Modelling the Torques Affecting the Hipparcos Satellite

Abstract

Reconstructed attitude data for the Hipparcos mission as obtained in the final stages of the data analysis for the published catalogue is used to derive detailed information on the dynamics of the satellite. Most elements of the inertia tensor of the satellite could be calibrated from the observed acceleration data, which are also used to reconstruct torques due to solar radiation and gravity gradient, and the magnetic moment of the satellite and it's interaction with the magnetic field surounding the Earth. The effects of the oblateness of the Earth on the gravity gradient are evaluated and shown to be negligable. The magnetic field model includes both the `main' and the `disturbance' fields. The remaining systematic effects in residual torques are most likely attributed to variations in the magnetic field that are local and are beyond the models used to describe it. The angular momentum vector for one of the gyros was reconstructed from the torque it asserted on the satellite while it was running in redundant mode.