A demonstrator spacecraft for Europe's proposed Galileo satellite navigation system has launched from Kazakhstan.
The Giove-B satellite was taken into space atop a Soyuz rocket which left Earth at 2216 GMT, Saturday.
The demonstrator will test the key technologies which will eventually be built into the 30 operational platforms that form the Galileo network.
These include the atomic clocks which provide the precise timing that underpins all sat-nav applications.
Giove-B - a half-tonne, 2.4x1x1m box assembled by EADS Astrium and Thales Alenia Space - is the second demonstrator satellite to go into orbit following the launch of Giove-A in 2005.
The first mission met international obligations to claim the frequencies Galileo will use to transmit its signals to receivers on the ground.
This second mission flies a spacecraft which is, to a large degree, a template for the 30 operational platforms that will follow.
A fundamental focus for Giove-B will be the in-orbit behaviour of its passive hydrogen maser clock.
It is the most stable clock ever put in permanent orbit, and is designed to keep time with an accuracy of better than one nanosecond (billionth of a second) in 24 hours.
As well as its atomic clocks (Giove-B carries three clocks), the latest demonstrator will test the generation of signals across the full spectrum Galileo intends to use for its five sat-nav services.
Saturday's launch from the Baikonur spaceport was an important moment for Galileo which has experienced several delays.
Giove-B was held on the ground for a year because of a component failure during the final stages of its preparation for flight; but more generally, the Galileo programme itself has seen its timeline slip on a number of occasions, and has come close to being abandoned.
Europe has already spent 1.6bn euros ($2.5bn; £1.3bn) on the project and ministers have warned that the additional 3.4bn euros ($5.3bn; £2.7bn) recently approved for sat-nav investments will be the limit on expenditure.
 | GALILEO UNDER CONSTRUCTION A European Commission and European Space Agency project 30 satellites to be launched in batches by end of 2013 Will work alongside US GPS and Russian Glonass systems Promises real-time positioning down to less than a metre Guaranteed under all but most extreme circumstances Suitable for safety-critical roles where lives depend on service  |
Galileo is envisaged as being technologically complementary to GPS, and is touted as a key high-technology venture for the EU.
It is designed to improve substantially the availability and accuracy of timing signals delivered from space.
Users should get quicker, more reliable fixes and be able to locate their positions with an error of one metre compared with the current GPS error of several metres.
"One of the short-comings of GPS has been the ability to rely on it for safety-critical applications such as landing aircraft," said Richard Peckham from EADS Astrium.
"Galileo has a safety-of-life service which is basically an integrity, a monitoring service that checks the signal constantly. With this, we should be able to start relying on satellite navigation much more than we can today with GPS."
If all of the technologies in Giove-B work as predicted, engineers will be clear to launch the first four operational satellites in 2010.
Full capability has been set for the end of 2013.
