Applications

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ESA / Applications / Observing the Earth / FutureEO / GOCE

Full name: Gravity field and steady-state Ocean Circulation Explorer

Launched: 17 March 2009 from the Plesetsk Cosmodrome, Russia

Duration: After 4 years and 8 months orbiting Earth, the mission came to an end on 11 November 2013, far exceeding its 20-month design life

Mission control: European Space Operations Centre (ESOC), Darmstadt, Germany

Data download: Kiruna (Sweden) and Svalbard (Norway) ground stations

Processing & archiving: ESA’s Earth observation centre in Italy (ESRIN) and the distributed High-level Processing Facilities

Number of instruments: 3

Mission cost: €350 million (including launcher and operations)

Orbit: about 260 km altitude, polar, Sun-synchronous

Mass: 1100 kg

Size: 5.3 m long, about 1 m body diameter

Propulsion tank: 40 kg of xenon

Mission objectives
– to determine gravity-field anomalies with an accuracy of 1 mGal (where 1mGal = 10^–5 ms^–2).
– to determine the geoid with an accuracy of 1-2 cm.
– to achieve the above at a spatial resolution better than 100 km.

Geoid accuracy: 1 - 2 cm vertically with 100 km spatial resolution

Gravitational acceleration at Earth’s surface is about 9.8 m/s², varying from a minimum of 9.788 m/s² at the equator to a maximum of 9.838 m/s² at the poles.

The six accelerometers (three pairs in three orthogonal directions) are some 100 times more sensitive than any previously flown in space.

Industrial Core Team
Thales Alenia Space (Italy) – satellite prime contractor
EADS Astrium GmbH (Germany) – platform contractor
Thales Alenia Space (France) – gradiometer
ONERA (France) accelerometer & system support

The Core Team led a consortium of 41 companies distributed over 13 European countries.

Technical details:

Satellite
Configuration	Minimum cross-section in the direction of motion (1.1 m²) Approx. 9 m² solar array aligned in the orbit plane 1050 kg launch mass
Structure	Several carbon fibre, reinforced plastic structural compartments; load-carrying external structure Structural dynamics: 110 Hz axial, 18 Hz lateral
Thermal control	Passive with heaters High-thermal-stability gradiometer compartment (10 mK @ 5 mHz)
Electrical power	24-32 Vdc unregulated bus; protected and redundant lines Fixed Gallium Arsenide (GaAs) cell solar array, 1300 W Lithium Ion (Li-Ion) battery, 78 Ah, made of 52 strings with 8 cells each
Attitude control	Nadir pointing Only magnetorquers for attitude control Wide-field star trackers hybridised with gradiometer angular acceleration measurement Coarse Sun sensors and magnetometer for acquisition and safe mode AOCS/DFACS application software run in central computer
Drag control	Ion thrusters commanded in closed loop, based on gradiometer common-mode acceleration measurements
Reaction Control System (RCS)	20 mN Kaufman-type ion thrusters (2x)
Data handling	Packet telemetry Flexible and reallocatable packet sizes High-rate (10 Hz) gradiometer-to-computer link via 1553 bus for drag control command synthesis