Measuring the Earth’s gravity

• European Space Agency mission
• The first core mission to be developed as part of ESA’s Living
  Planet Programme
• Launch scheduled 2008

Gravity is not constant for the entire planet. It is weaker at the equator for instance, than at the poles. This is due to the Earth’s rotation and other factors such as its uneven surface and geology.

By measuring tiny variations in the Earth’s gravitational field, scientists will gain a greater insight into how the Earth works; the physics of its interior and changes in sea levels.

The data will be combined with information about sea surface height from other satellites to track the direction and speed of ocean currents.

For more information, visit ESA’s GOCE homepage.

Mission facts

• GOCE is a 5 m long octagonal spacecraft, one metre in diameter.
  
  
• The spacecraft will orbit just 250 km above the Earth’s surface.
  
  
• GOCE will carry three pairs of instruments known as 3-axis electrostatic gravity gradiometers which will measure differences in the Earth’s gravitational field in all directions.
  
  
• GOCE will provide an accurate and detailed global model of the Earth’s gravitational field. The spacecraft will also investigate volcanic regions and provide an estimate of the thickness of polar ice sheets.

Technology

The different sides of the spacecraft will vary in temperature from 140°C to -160°C. GOCE has been tested thoroughly with 400 temperature sensors, 24 hours a day for two weeks, to ensure it can withstand the harsh space environment.

Unlike most satellites, GOCE has no moving parts. This will give it increased stability when making gravity measurements.

GOCE will use two ion thrusters instead of burning fuel. Electricity from the spacecraft’s solar panels is used to produce charged particles or ions from an inert gas and these ions propel the spacecraft.

UK involvement

QinetiQ has supplied the two ion thrusters for the spacecraft.

SciSys Limited developed a satellite simulator for the mission to support satellite operations.