Measurements taken while monitoring artificial satellites since the 1960s have revealed large irregularities in the Earth’s gravitational field. These irregularities reflect differences in density within the Earth and disturb the motion of satellites by affecting their altitude.

Earth’s gravity, combined with other forces acting on satellites in space, such as atmospheric drag and solar radiation, may change a satellite’s trajectory from as little as 1 mm to as much as several kilometres.

In 1995, the German space agency DLR, in collaboration with CNES and JPL, decided to initiate the CHAMP mission to measure these orbital perturbations with centimetre accuracy. The goal is to create a model of the Earth’s gravity.

The STAR instrument, manufactured by Onera, is used to isolate the non-gravitational forces, and to deduce the shape of the gravitational field of our planet and its large-scale variations.

The first data from CHAMP have already made it possible to calculate a new model of the gravitational field: Eigen-2. And this is just the beginning. CHAMP blazed the trail for the US-German Grace mission (Gravity Recovery and Climate Experiment).

The European satellite GOCE (Gravity Field and Steady-State Ocean Circulation Mission) was launched in March 2009, thus revolutionizing our view of the planet’s gravity.

_{Updated : March 2009}