Page last updated at 14:48 GMT, Wednesday, 7 May 2008 15:48 UK

EU's sat-nav pioneer calls home

Computer screen. Image: Esa
The first signals from Giove-B were displayed on Esa's giant screen

Giove-B, a test satellite for Europe's Galileo system, has sent its first navigation signals back to Earth.

The European Space Agency (Esa) says the transmission is an "historic step", showing that Galileo will be able to work alongside the US GPS system.

Giove-B carries the most accurate clock ever sent into orbit, key to its intended capacity of providing location information accurate to a metre.

The 30-strong Galileo fleet is intended to be fully operational by 2013.

These constellation satellites will closely resemble Giove-B, which was launched atop a Russian Soyuz rocket on 26 April.

This was a major step forward in creating Galileo
Dr Mike Healy, UK Astrium

The 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.

More sophisticated than its predecessor, it will test further the key Galileo technologies such as the atomic clocks that provide the precise timing underpinning all sat-nav applications.

Despite an early glitch in the system used for orienting the satellite in space, the orbiter now appears to be working well.

Under offer

"Now with Giove-B broadcasting its highly accurate signal in space, we have a true representation of what Galileo will offer," said the system's project manager, Javier Benedicto.

The offer, he said, would include "the most advanced satellite positioning services, while ensuring compatibility and interoperability with GPS".

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

Engineers are now assessing the signal coming down to Earth.

They will be looking for any indications that it is affected by its passage through the atmosphere, and checking that it does not interfere with any systems that use neighbouring bands of the electromagnetic spectrum.

A fundamental focus in coming days will be the in-orbit behaviour of Giove-B's 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 this and its two other atomic clocks, the demonstrator will check the generation of signals across the full spectrum that Galileo intends to use for its five sat-nav services.

Once engineers are happy with all this, the way will be clear to launch the first four satellites in the eventual constellation. These so-called In-Orbit Validation (IOV) spacecraft are expected to fly in 2010.

"We're extremely proud of the critical role we have played on Giove-B, being responsible for the payload and ground segment," commented Dr Mike Healy at UK Astrium.

"'Hearing' the new signal broadcast - this was a major step forward in creating Galileo. It's full speed ahead now for the IOV satellites," he told BBC News.

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 is envisaged as being technologically complementary to GPS, and is touted as a key high-technology venture for the EU.

Esa says that compared with using GPS alone, the combined systems "will provide higher accuracy in challenging environments where multipath and interference are present, and deeper penetration for indoor navigation".


A guide to the main features on Giove-B

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