Part of ESA's Living Planet Programme are the Earth Explorer missions. One of these is the GOCE (Gravity field and steady-state Ocean Circulation Explorer) satellite. GOCE will provide data to determine the global and regional models of Earth's gravity field to an unprecedented accuracy. It is seeking to determine A global geoid of 1 cm accuracy at about 100 km spatial resolution and a gravity field model with 1-2 mGal precision accuracy and the same spatial resolution. The geoid is an equipotential surface of the Earth, as opposed to the shape of the actual crust. Without movements, the surface of the oceans would follow such an equipotential surface - the geoid. GOCE's measurements will be more than just an excercie in geodesy (which is very important in itself), but will bring important data to geophysicists, and even more importantly for oceanography.
The experiments requires basically just two components: the so-called Electrostatic Gravity Gradiometer (EGG) - which consists of ultra-sensitive accelerometers, and a GPS-based Satellite-to-Satellite Tracking System (SSTI). To be more sensitive, th^e satellite will be orbiting at a very low height of 250 km. However, the thin atmosphere at this height has an effect of a gentle push on the satellite. To compensate for these forces, it has high precision ion thrusters made by QinetiQ. These will be used in such a way that the satellite feels absolute free fall, without any net forces. The satellite itself doesn't contain any moving elements (so that they don't interfere with the measurements).
GOCE will be launched in spring 2008 from Plesetsk, Russia, to a sun-synchronous polar orbit.