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ESA's gravity mission GOCE

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GOCE mission payload

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Housed at the centre of the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite, the gradiometer contains three pairs of proof masses positioned at the outer ends of three 50 cm long orthogonal axes. All experience the gravitational acceleration of Earth slightly differently because of their different position in the gravitational field. The common acceleration of each pair of accelerometers is proportional to non-gravitational forces such as air-drag acting on the satellite. The difference in acceleration for each pair, scaled with the length of the connecting arm, called the gravity gradient, is used for gravity field analysis.

Credits: ESA–AOES-Medialab

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The GOCE gradiometer consists of three pairs of identical ultra-sensitive accelerometers, mounted on three mutually orthogonal arms. One of the arms is aligned with the satellite’s trajectory, one pointing towards the centre of Earth, and the third is perpendicular to the other two. This allows the simultaneous measurement of six independent but complementary components of the gravity field.

Credits: ESA–AOES-Medialab

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Although the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) gradiometer is highly accurate, it is not possible to map the complete gravity field at all spatial scales with the same quality. To overcome this limitation the position of the GOCE satellite is tracked by GPS relative to GPS satellites at an altitude of 20 000 km – this procedure is known as satellite-to-satellite tracking. The gradiometer is used to measure small scales of the gravity field whilst GPS is used to obtain large-scale data.

Credits: ESA–AOES-Medialab

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The need for GOCE to fly in a low orbit means it has to compensate for the atmospheric drag it experiences at this exceptionally low altitude. The animation shows a close-up of the ion-propulsion assembly, which keeps the satellite in a smooth trajectory – free from all effects except those of gravity itself. Two winglets provide additional aerodynamic stability.

Credits: ESA /AOES Medialab

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The GOCE laser retroreflector consists of an array of cubes mounted on a hemispherical frame. It is designed to reflect light back in precisely the same direction it came from to provide independent measurements of the satellite's position.

Credits: ESA

Last update: 16 September 2010

More information

GOCE - ESA's gravity mission (BR-285)GOCE - ESA's schwerkraft mission (BR-209)

In detail

GOCE System Critical Design Review - Executive Summary (pdf)