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Europe's satellite-navigation system has taken a big step forward with the signing of new industrial contracts.

Satellite firms EADS Astrium and OHB have been asked to provide spacecraft components that will be needed for the forthcoming constellation.

And rocket company Arianespace has signed the deal which will loft the system's first operational platforms.

The agreements, announced at the Paris air show, are a much needed fillip for the delayed programme.

Galileo came close to collapse in 2007 when a public-private partnership (PPP) set up to construct and run the project fell apart.

The European Commission, which is leading the endeavour, has set aside more than two billion euros to build 26 satellites, buy launch rockets and set up the ground control centres.

Its partner on the venture, the European Space Agency (Esa), is running a procurement contest with the aim of having Galileo up and running by 2013.
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The GPS satellites are not in geo-stationary orbit, but instead orbit twice every time the Earth rotates once. This means that for any observer the satellites appear to orbit once overhead each day. Such an arrangement gives better coverage. It is also clever in the sense that the motion of any GPS satellite will repeat itself each day.

The GPS constellation of 24 satellites are arranged in six different orbital planes, each inclined 55 degrees to the equator. To obtain exactly two orbits per day, the satellites are placed at an altitude of 20,200km.