Europe to launch four satellite-navigation spacecraft

Europe is about to extend its satellite-navigation system by putting another four spacecraft in orbit.

They will go up on an Ariane 5 rocket from Kourou in French Guiana, with the lift-off scheduled for exactly 10:06 (13:06 GMT) on Thursday, BBC News reports.

It is the first time Europe's premier launch vehicle has been used to loft Galileo satellites. Normally, they go up on a Russian Soyuz, two at a time.

This mission will bring the in-orbit constellation to 18 spacecraft.

That is six short of the planned number for the full network, but more than enough for Galileo to start an initial service, which it is expected to do in the next few weeks.

When that happens, the very latest smartphones and other types of receivers should start picking up the system's signals - either to get a position fix or to make use of its embedded timing information.

"From a technical standpoint we are ready, and the performance is excellent," said Paul Verhoef, director of navigation programmes at the European Space Agency (Esa).

"There are still some small issues that need to be addressed and some formalities that need to be settled, and one of those is making sure the security is in place so that the system is properly protected when the service starts," he told BBC News.