Europe's first Galileo satellites lift off

The European Commission (EC) is investing billions of euros in its own version of the American GPS system, BBC News reports.

It expects Galileo to bring significant returns to EU nations in the form of new businesses that can exploit precise space-borne timing and location data.

The Soyuz mission is a long one - it will be several hours before confirmation is received that the satellite pair have been put in their correct orbit 23,000km above the Earth.

The spacecraft are pathfinders for the Galileo system as a whole.

Together with another pair of satellites to be lofted next year, they will prove that Galileo works as designed, from the spacecraft in the sky to all the control and management operations on the ground.

"This phase is called in-orbit validation - IOV," said Javier Benedicto, the Galileo project manager at the European Space Agency (Esa), the EC's technical agent on the project.

"The intention is to test and verify the various system functionalities and the ultimate system performance," he told BBC News.

Deployment of the full Galileo system is likely to take most of the decade.

Sat-nav users themselves will not immediately see any benefits from Galileo, however. That will have to wait until a navigation signal is switched on, and it is likely to be 2015 before there are enough spacecraft in orbit for Galileo to start to show its true capability.

Compared with the Americans' current version of GPS, Galileo carries more precise atomic clocks - the heart of any sat-nav system.

In theory, the data transmitted by Galileo should therefore be significantly better than its US counterpart. Whereas a position fixed by the publicly available GPS signal might have an error of about 10m, Galileo's designers promise metre-scale accuracy when full deployment is achieved.

But the plan is to make the different systems interoperable, meaning the biggest, most obvious benefit to users will simply be the fact that they can see more satellites in the sky at any one time.

So, as the decade progresses and the number of spacecraft in orbit increases, the performance of all sat-nav devices should improve. Fixes ought to be faster and more reliable, even in testing environments such as big cities where tall buildings will often obscure a receiver's view of a transmitting spacecraft.

For full version go to http://www.bbc.co.uk/news/science-environment-15372540