Satellite to begin gravity quest

A European spacecraft will begin its quest this week to make the most detailed global map of the Earth’s gravity field.
The arrow-shaped Goce satellite can sense tiny variations in the planet’s tug as it sweeps around the world at the very low altitude of just 255km.
The map will help scientists understand better how the oceans move.
It should also give them a universal reference to compare heights anywhere across the globe.
Goce was launched from the Plesetsk Cosmodrome in north-west Russia in March.
Engineers have since commissioned the spacecraft, satisfying themselves that all its systems are working properly.
But the satellite has had to wait until now for the right conditions to start its science campaign.
“We’ve been in the so-called eclipse mode where the Sun doesn’t shine fully on the solar panels, but now we are entering the measurement mode,” said Dr Volker Liebig, the director of Earth observation at the European Space Agency (Esa).
“Being able to fly low is very good for the measurements, and the Sun is so low in its activity at the moment that we can fly lower than we expected; and that will give us a better signal,” he told BBC News.
The data return will be the first to come from Esa’s Earth Explorer programme, which is sending up a fleet of small satellites tasked with acquiring key information on issues of environmental concern.