GOCE was the first mission selected in ESA's Earth Explorer programme (in November 1999)
The scientific objective of Goce was to map the gravity field of the Earth at high resolution (100 km over the globe, or a gravity field model up to degree 200) with an error smaller than 2-3 cm. An improvement in the accuracy of the gravity field model of about one order of magnitude was expected thanks to the combination of high-performance instruments and a low altitude (the sensitivity of a satellite to the gravity field decreases rapidly at higher altitude).
Goce, unlike GRACE, measured the static or mean part of the gravity field and provided the reference surface, called the geoid, necessary to oceanographers to deduce mean sea level and currents. The gravity field model and gravity gradients, are also very useful to geophysical and geodetic studies.
The satellite was launched from the Plesetsk Cosmodrome on 17 March 2009.
Originally due to complete its gravity-mapping mission in April 2011, it was extend by 18 months to 21 October 2013.
Goce first global gravity model Credits: ESA – Goce High Level Processing Facility
The science payload is consisted of:
- An orthogonal 3-axis gradiometer (radial, along track and normal to the orbit plane), consisting of three pairs of accelerometers (3-axis, precision 10-12 ms-2Hz-0.5) per axis separated by a distance of 50 cm. Gravity gradients were measured with a very high accuracy of 3 mE (milli-Eötvös ; 10-12s-2) within a bandwidth of 0.005 to 0.1 Hz. The accelerometers were built by ONERA (Office National d'Etudes et de Recherches Aerospatiales)
- A Lagrange GPS receiver for precise orbit determination
- A laser retroreflector for precise orbit determination
- Star trackers to measure the satellite's inertial attitude
Goce's inside © ESA
Goce was the first drag-free scientific mission, a requirement necessary to ensure the correct operation of the gradiometer and the satellite's survival. Due to the very low altitude of the mission, at 265 km, the satellite would have been lost in the atmosphere in just a few months without drag compensation, which was achieved using ion thrusters with highly variable thrusts.
CNES's Space Geodesy team is a member of the EGGC consortium (European Gravity Gradient Consortium) selected by ESA to process the mission's data, and particularly for the gravity field modelling by means of the direct numerical method. The following level 2 products have been available from about 6 months after the end of the mission:
World gravity map - Complete Spherical Bouguer Anomaly
- Gravity field model up to degree 200 (minimum) and its variance-covariance matrix
- Precise orbits (by kinematic and reduced-dynamic methods)
- Calibrated and corrected gravity gradients
A national user coordination bureau, FROG (for French Resources Organization for Goce) was also created.
All Goce mission news on ESA's website.