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GOCE satellite payload is activated

14 April 2009

Thales Alenia Space developed the sophisticated Electrostatic Gravity Gradiometer for measuring the terrestrial gravitational field, and relies on a set of six ultra sensitive capacitive sensors.

Cannes, April 14, 2009 - Following the successful launch of the GOCE satellite on March 17, the sophisticated Electrostatic Gravity Gradiometer for measuring the terrestrial gravitational field and main payload instrument, was gradually activated from April 3 to 7 for in-orbit acceptance tests.

Thales Alenia Space developed the sophisticated Electrostatic Gravity Gradiometer for measuring the terrestrial gravitational field, and relies on a set of six ultra sensitive capacitive sensors. The six high-tech, very-high-precision accelerometers that are the heart of this instrument perfectly withstood the launch, and the instrument's performance is fully in line with forecasts.

GOCE, the first satellite in the European Space Agency's Earth Explorer family, is designed to map the Earth's gravitational field in three dimensions, to a degree of accuracy never before achieved. The satellite and its main instrument, the gradiometer, were integrated by Thales Alenia Space, industrial prime contractor for the project. The six ultrasensitive accelerometers were produced by French aerospace research agency Onera in Châtillon.

Each of the accelerometers measures the intensity of the electric field needed to keep a proof mass levitated, and can therefore detect the miniscule disturbances caused by changes in the gravitational field on the movement of the mass. Teams from Thales Alenia Space and Onera have analysed the initial data transmitted by the satellite, which indicate that: the reference flyweights are levitated, the measurements of the electrical field around each electrode inside the accelerometers are consistent, and the projected performance based on this preliminary data is promising. Thanks to these sophisticated technologies, GOCE will be the only satellite capable of capturing all the terrestrial gravitational changes, providing accurate and complete data on the internal structure and dynamics of the Earth, particularly the large-scale circulation of sea and ocean waters and their effect on the climate.

After a perfect launch on March 17, and initial verification of the onboard system, on March 31 and April 2, ESA teams activated the two ion microthrusters designed to compensate for the tiny amount of aerodynamic drag caused by the residual atmosphere in low Earth orbit. These two very-low-thrust ion microthrusters are operating perfectly.

Initially injected into orbit at 283 kilometers, the satellite is now slowly descending towards its operational orbit of 268 kilometers, solely due to this aerodynamic friction. Once it arrives at an altitude of 273 kilometers, GOCE will start the "drag free" orbital control mode, using data from the accelerometers to control the microthrusters and effectively compensate for atmospheric drag.

Over the next phase, the satellite will be finely stabilised and the gradiometer calibrated. The satellite will shortly enter an eclipse period, where its orbit will regularly take it into the shadow of the Earth, thus limiting its onboard energy potential. This phase will last until the end of August, at which point it will be ready to kick off its scientific operational mission.

About Thales Alenia Space
The European leader in satellite systems and a major player in orbital infrastructures, Thales Alenia Space is a joint venture between Thales (67%) and Finmeccanica (33%). Thales Alenia Space and Telespazio embody the two groups' "Space Alliance". Thales Alenia Space sets the global standard in solutions for space telecoms, radar and optical Earth observation, defense and security, navigation and science. The company has a total of 7,200 employees and 11 industrial sites, with locations in France, Italy, Spain and Belgium.