The GOCE (Gravity field and steady-state Ocean Circulation Explorer) mission is dedicated to measuring the Earth's gravity field and modelling the geoid with unprecedented accuracy and spatial resolution. Since the satellite has to be completely stable to ensure the acquisition of true gravity readings, the spacecraft has no mechanical moving parts. In order to receive the optimum gravity signal GOCE will fly in a particularly low orbit of just 250 km above the surface of the Earth. The slim, octagonal, spacecraft is about 5 m in length and 1 m across – configured to keep aerodynamic drag and torque to an absolute minimum.