Europe is building its own satellite-navigation system called Galileo. BBC News looks at why such a network is deemed necessary when we already have the US Global Positioning System (GPS).What is Galileo?
Galileo will be a global network of 30 satellites providing precise timing and location information to users on the ground and in the air. It is costing some 3.4bn euros (£2.3bn; $4bn) of public and private investment and represents the biggest space project yet undertaken in Europe.
Galileo's first demonstrator spacecraft is being launched on 28 December; a second platform will follow in the New Year. They will trial the in-orbit technologies needed to run the system. These include atomic clocks, the heart of any global positioning system.
If all goes according to plan, a full constellation of Galileo satellites will be in operation by the end of 2010.