Earth gravity "surfer" GOCE on course

European satellite explores earth gravity field with the highest precision

Schematic representation of the different fields of application GOCEs: In addition to sea level irregularities, GOCE investigates the effects of seismic activity on the Earth's gravity field. © ESA
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The new GOCE (Gravity field and steady-state Ocean Circulation Explorer) satellite was successfully launched yesterday at 3.21 pm Central European Time from the Russian spaceport Plesetsk. The Rockot launcher brought the satellite into an approximately polar orbit 260 kilometers high.

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From its orbit, GOCE will measure the Earth's gravity field for 20 months in unprecedented precision. The expected results will be particularly important for oceanography, geophysics and sea level research. One and a half hours after launch, at 16:51, the satellite sent the first signals from orbit, indicating the beginning of the measurements. The day before, the countdown to the GOCE launch had been halted due to technical issues. But these could be corrected at short notice.

"Against the background of incalculable climate changes and their serious significance for our habitat, GOCE underscores the great commitment of German and European space travel to sustainable climate research. Space has not only been instrumental in uncovering global change, it also provides the key tools to explore its impact. This helps politics and society to make the necessary decisions to protect our livelihoods, "said Gerold Reichle of the German Aerospace Center (DLR), emphasizing the strategic importance of the mission.

The German GeoForschungsZentrum Potsdam GFZ calculates its own, high-resolution gravitational field from the data of the gravity field "surfer" GOCE. "The so-called 'Potsdamer Kartoffel' became known representation of the earth's gravity field is thus by orders of magnitude more accurate, " said Professor Reinhard Hüttl, CEO of the GFZ. display

Sea currents in the sights

GOCE scans the earth with a spatial resolution of about 100 kilometers and thus provides much more accurate data than all previous satellite missions to the gravitational field. One of the main scientific applications of the GOCE mission will be the study of global ocean currents.

Ocean currents cause sea level elevation deviations from the Earth's gravity equilibrium, which can be up to two meters high and are referred to as marine topography. The knowledge of ocean topography allows conclusions to be drawn about ocean circulation, the changes of which may in turn be linked to climate change.

"By combining GOCE measurements with data from sea level readings from other satellites, it will be possible for the first time to directly measure marine topography and its possible temporal changes on the open oceans" Fle, explains Frank Flechtner, who works on the gravity field evaluation at GFZ. This will be a novel contribution to the knowledge of the oceans and their climate change-related changes.

Other scientific objectives of the GOCE mission include studying the structure of the Earth's crust and mantle convection, as well as the creation of a continental height reference system and the associated accurate recording of the sea level and the understanding of its variations.

Extremely low orbit

The most important sensor for gravity measurement on GOCE is a gravitational gradiometer, which is flown for the first time on a satellite with GOCE. To achieve the required high measurement accuracy, GOCE moves on an extremely low orbit for satellites and is therefore equipped with an ion thruster as a so-called drag-free system, what the forces acting on the satellite St rkr Balances out and allows a flight virtually in free fall.

In addition, GOCE is equipped with a GPS receiver for the centimeter-accurate determination of its orbit position: for the first time, a scientific GPS receiver manufactured in Europe is used on board a satellite.

The GFZ, which has over one-and-a-half years experience in satellite-assisted gravitational field determination, works under the project leadership of the Technical University of Munich and together with institutes from Germany, France, Denmark, Italy, Austria, Switzerland and the Netherlands as co-operation partners in the so-called High Level Processing Facility (HPF) in the GOCE data analysis part.

(GFZ / German Aerospace Center (DLR) / TU Munich, 18.03.2009 - DLO)