Re-entry nears for ESA’s 'Ferrari of space'
19 September 2013
After more than four years in orbit, ESA’s GOCE mission is nearing its end. In mid-October, the satellite will run out of fuel and its orbit will begin to decay. Re-entry into the atmosphere is expected to happen about three weeks later.
GOCE has been circling Earth since March 2009 at a height of less than 270 km, unusually low for a scientific satellite. Its task has been to map with unrivalled precision the tiny variations in Earth’s surface gravity.
Gravity is the force that pulls everything toward the ground. However, Earth’s gravitational pull varies slightly from place to place. This is partly because the planet is not perfectly round – it is slightly flattened at the poles. Gravity is also affected by high mountains and deep ocean trenches, as well as the thickness and density of oceans and rock layers.
As GOCE passes over regions of different gravitational pull, the spacecraft bobs up and down, and its instruments report these changes to its path. Such precise measurements have been made possible by its low orbit and sleek, aerodynamic design, which led to it being nicknamed the ‘Ferrari of space’. The unique satellite is also extremely stable, without any of the moving parts often used on other spacecraft.
Data from GOCE have been used to study ocean currents, changing sea level, land surface height and the layered structure of Earth’s rocky crust. It even detected winds in space and sound waves that travelled upwards through the atmosphere after the massive earthquake that hit Japan on 11 March 2011. Perhaps the most important result has been a remarkably accurate model (known as the ‘geoid’) of Earth’s gravity. The geoid reveals how Earth would look if gravity was equal everywhere on its surface, so that water would not flow from one point to another.