The European Space Agency (ESA) is about to launch the most sophisticated mission ever to investigate the Earth’s gravitational field and to map the reference shape of our planet, known as the geoid, with unprecedented resolution and accuracy. The Gravity field and steady-state Ocean Circulation Explorer (GOCE) will be placed into a low altitude near sun-synchronous orbit by a Russian Rockot vehicle launched from the Plesetsk Cosmodrome in Northern Russia, some 800 km north of Moscow. Lift-off is scheduled to take place at 16:21 CEST (14:21 UTC) on Wednesday, September 10th. The launcher is operated by Eurockot Launch Services, a joint venture between EADS Astrium and the Khrunichev Space Centre (Russia). ESA’s 1-ton spacecraft carries a set of six, state-of-the-art, high-sensitivity accelerometers to measure the components of the gravity field along all three axes. The data collected will provide a high-resolution map of the geoid (the reference surface of the planet) and of gravitational anomalies. Such a map will greatly improve our knowledge and understanding of the Earth’s internal structure and will also be used as a much better reference for ocean and climate studies. Such will include sea-level changes, oceanic circulation, and ice caps dynamics survey. Numerous applications are expected in climatology, oceanography, and geophysics, as well as for geodetic and positioning activities.

To make this mission possible, ESA, its industrial partners (45 European companies led by Thales Alenia Space), and the science community, had to overcome an impressive technical challenge by designing a satellite that will orbit the Earth close enough to gather high-accuracy gravitational data, while being able to filter out disturbances caused by the remaining traces of the atmosphere in low Earth orbit (at an altitude of only 260 km). This resulted in a slender, 5-m-long arrowhead shape for aerodynamics, with low power ion thrusters to compensate for the atmospheric drag. GOCE is the first Core Mission of the Earth Explorer program that was started by ESA in 1999 to foster research on the Earth’s atmosphere, biosphere, hydrosphere, cryosphere and interior. Two more Core Missions are already under development: ADM-Aeolus for atmospheric dynamics (2010), and EarthCARE to investigate the Earth’s radiative balance (2013). Three smaller Earth Explorer Opportunity Missions are also in preparation: CryoSat-2 to measure ice sheet thickness (2009), SMOS to study soil moisture and ocean salinity (2009) and Swarm to survey the evolution of the magnetic field (2010).