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Sleek probe to map Earth's gravity

16 March 2009

At 14:21 GMT, Monday 16 March 2009, the European Space Agency (ESA) will launch a new satellite to map variations in the Earth's gravity field with unprecedented accuracy.

The satellite will give UK scientists vital information about ocean circulation and sea level change needed to improve climate forecast models.

The Gravity field and steady-state Ocean Circulation Explorer (GOCE) will be the first of ESA's Earth Explorer missions to be launched. Data from GOCE will allow scientists to create a detailed model of the Earth's gravity field.

Artist's impression of the GOCE satellite (Copyright ESA)

"GOCE will yield details of the Earth's gravity field to an accuracy and resolution that is simply unobtainable by existing terrestrial and space techniques," says Professor Philip Moore of Newcastle University, who specialises in gravity research.

By comparing a model of the Earth's gravity field with ocean surface height from other satellite data, oceanographers can track the speed and direction of ocean currents around the globe.

At school, most of us learn that acceleration due to gravity is 9·8 metres per second squared wherever you are on the planet. It turns out it's not quite as simple as this. The shape of the Earth, mountains, trenches deep beneath the ocean and the ground beneath our feet all affect the gravity field, meaning it's not identical everywhere.

"Ocean circulation is important in climate forecast models. Currents carry large quantities of heat from the equator to the poles, such as the system in the north Atlantic, which helps to keep Europe's climate relatively mild. Combined with more than 15 years of existing data on sea-surface height, the data that GOCE delivers will help scientists more accurately measure the role of ocean currents in transporting heat and water around the globe," says ESA's GOCE mission scientist, Mark Drinkwater.

"Researchers at the National Centre for Earth Observation are keen to start using the data that GOCE delivers. We've been working with ESA to make sure we can use the data in the UK's world-leading ocean and climate prediction models. The Met Office and the European Centre for Medium-Range Weather Forecasts have been working with us on this as well. One of the things I'm excited about is finding out about ocean currents in remote regions such as the southern hemisphere for the first time," says Professor Keith Haines, an expert in ocean circulation at the NCEO.

GOCE has other uses. An accurate model of the Earth's gravity field is crucial for defining exactly what height above sea-level actually means. Different countries have their own definitions of sea level, meaning that height is defined differently country to country. With GOCE, scientists will be able to say if two points are at the same height, however far apart they are. This will be important for large-scale surveying and engineering projects such as bridge, tunnel or pipeline building between islands or across seas.

The instrument that GOCE will use to measure gravity is called a gradiometer. It is made up of three pairs of accelerometers that measure tiny differences in gravity at many points as GOCE orbits the Earth. Because the strength of gravity decreases with altitude, the satellite will be in a much lower orbit than other orbiting spacecraft. This makes GOCE one of ESA's most challenging missions to date.

The torpedo-shaped satellite is designed to cut through the edge of the Earth's atmosphere at just 150 miles above the surface of the planet.

GOCE will be launched from the Plesetsk Cosmodrome in Russia into a polar sun-synchronous orbit - its solar panels will always face the sun. It will use the sun's energy to charge and accelerate 40g of xenon particles, which the satellite's ion thrusters will use to combat the effects of air drag. The mission will last around 20 months.

Earth observation is crucial for monitoring changes in the environment. The Natural Environment Research Council makes a large investment in the scientific aspect of the UK's Earth observation programme, investing around £45m in ESA annually. Most of this is used to support Earth Explorer missions under ESA's Earth Observation Envelope Programme. The Earth Explorer missions are designed to answer important scientific questions as well as demonstrate breakthrough technology in Earth observation.

The GOCE mission - costing €350m - involves a large collaboration of European organisations, including UK scientists and engineers working for QinetiQ, Logica and SciSys.

Further information

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

Robert Meisner
ESA press office
Tel: +39 06 941 80 874

Notes

1. GOCE is scheduled to be launched at 14:21 GMT on Monday 16 March 2009 from the Plesetsk Cosmodrome in Russia.

2. The GOCE launch can be watched via an ESA webcast.

3. The Earth Observation Envelope Programme is the science and research element of ESA's Living Planet programme. The EOEP focuses on the atmosphere, biosphere, hydrosphere, cryosphere and the Earth's interior with the overall emphasis on learning more about the interactions between these components and the impact that human activity is having on natural Earth processes.

4. The Natural Environment Research Council is a member of the British National Space Centre, which is at the heart of UK efforts to explore and exploit space. BNSC is a partnership of seven Government Departments, two Research Councils, the Met Office and the Technology Strategy Board. It co-ordinates UK civil space activities and represents the UK at the European Space Agency.

5. The Natural Environment Research Council 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.

6. The NCEO is one of the Natural Environment Research Council's research centres. It has a budget of £33m over five years and involves more than 100 investigators from 26 UK universities and research centres. Its mission is to unlock the full potential of Earth observation to monitor, diagnose and predict climate and environmental changes.

7. NERC invests around £45m in ESA each year. This investment provides the UK with mission opportunities, the associated infrastructure and science support activities, along with access to ESA data for UK researchers. The NCEO is a key user of ESA data.

Press release: 06/09

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