The most advanced gravity measurement satellite prepares for launch

3 April 2008

A new satellite that will measure the Earth's global gravity field considerably more accurately than is currently achievable by other satellite and terrestrial means is being prepared for launch in Russia at the end of May.

Part of the European Space Agency's Living Planet Programme, the GOCE mission (Gravity Field and Steady-State Ocean Circulation Explorer) will help UK researchers to locate gravity anomalies around the world and link them to the deep Earth processes that cause earthquakes and volcanic activity.

Professor Philip Moore from Newcastle University, who specialises in gravity research, said, "One of the problems in observing gravity from space is that the strength of the Earth's gravity field diminishes with altitude. GOCE will skim the edge of our atmosphere, orbiting at a low altitude where the satellite will be sensitive to the strongest possible gravity field signal. For the first time a gradiometer will be used in space so the measurements will be far more accurate."

The gradiometer is based on six ultra-sensitive accelerometers and is able to achieve very accurate measurements. GOCE will gather the data at an altitude of around 270km above the Earth and will capture spatial scale measurements at around 100km. The best scale measurement we can obtain from existing satellites is around 600km.

The Earth's near elliptical shape, due to its rotation, means that you are further from the Earth's centre at the equator than at the poles; so you would weigh more at the North or South Pole than in the tropics. The Earth's interior is also not uniform. The surface is covered with mountains, and trenches and ridges under the oceans; all these cause deviations in the gravitational pull at the surface.

GOCE will map these differences and create a model for an ideal surface (known as the geoid), that best approximates mean sea-level for seas devoid of tides, wind or currents. The geoid provides both a gravity standard and a universal height reference system, on which all data can be measured and compared. The mission has a limited life-span of around 20 months, but this should be sufficient to produce the most accurate geoid model to date. Once its fuel has been used up the satellite will be allowed to fall to Earth where it will burn up in the atmosphere.

Professor Moore said, "This is a very challenging mission as GOCE will be constantly battling against the effects of air-drag to obtain these measurements. However, the benefits to oceanographers, geophysicists, glaciologists and many other researchers will be vast. The data will add to our knowledge of the interior of the Earth and sea level change. It will provide us with a better understanding of ocean circulation and volcanism and even the processes that lead to accumulation of stresses and the triggering of earthquakes."

Further information

ESA Media Relations Office
Paris
Tel: +33 1 5369 7155
Fax: +33 1 5369 7690

NERC Press Office
Natural Environment Research Council
Polaris House, North Star Avenue
Swindon, SN2 1EU
Tel: 01793 411561
Mob: 07917 557215

Notes

1. ESA held a media day today (3 April 2008) at the European Space and Technology Centre (ESTEC) in the Netherlands. Their press release and more information about GOCE can be found on their website, or e-mail wil.stangenberg@esa.int to request a hard copy of their press pack.

2. Professor Philip Moore from Newcastle University and Dr Arwyn Davies, Head of Earth Observation for NERC and the British National Space Centre are available for interview. Please contact the NERC press office if you would like to speak to either of them.

3. GOCE is a slim, octagonal cylinder shaped rocket, 5m long and 1m in diameter, with solar panelled wings and stabilising tail fins. It weighs around 1,000kg.

It will be launched from Plesetsk in Russia on 31 May 2008 into a Sun-synchronous near-circular orbit and will travel with a speed of around 8km/s. It is the first ESA satellite employing drag-free control, and the first ever satellite to use electric propulsion to continually compensate for atmospheric drag.

The spacecraft faces the danger of literally falling from the sky within weeks of being launched. Failure of the ion propulsion system would mean that air-drag would not be compensated for, the orbit would decay and the satellite would burn up in the atmosphere.

4. NERC is a member of the British National Space Centre (BNSC, which is a partnership of ten Government Departments, Research Councils and the Met Office and is at the heart of UK efforts to explore and exploit space. BNSC co-ordinates UK civil space activities to benefit science, enterprise and the environment and represents the UK at the European Space Agency and at other international forums.

5. The Natural Environment Research Council (NERC) funds world-class science, in universities and its own research centres, that increases knowledge and understanding of the natural world. It is tackling major environmental issues such as climate change, biodiversity and natural hazards. NERC receives around £400m a year from the government's science budget, which is used to provide independent research and training in the environmental sciences.

The most advanced gravity measurement satellite prepares for launch

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