Smooth operation

The electric propulsion system on the ESA GOCE (Gravity field and steady-state Ocean Circulation Explorer) gravity measuring satellite has shown that it is able to keep the satellite completely free from drag as it cuts through the remnants of Earth's atmosphere.

Launched in March and currently progressing through the commissioning phase, GOCE is set to measure Earth's gravity field with unprecedented accuracy.

However, to do this means that the satellite has to orbit Earth as low as possible where the gravitational signal is stronger, but also where the fringes of the atmosphere remain.

To ensure that the gravity measurements taken by GOCE are of true gravity, the satellite has to be kept stable and in 'free fall'. Any buffeting from residual air the satellite encounters along its orbital altitude of just 250km could potentially drown the gravity data.

This posed a technical challenge - the satellite structure had to be as aerodynamic as possible and a system had to be developed that would continually and instantaneously compensate for variations in air drag.