Page last updated at 16:40 GMT, Friday, 25 April 2008 17:40 UK

Mission to prove Europe's sat-nav

By Jonathan Amos
Science reporter, BBC News

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A guide to the main features on Giove-B

Europe's quest to build its own version of GPS is about to take an important step forward with the launch of a test spacecraft, Giove-B.

The demonstrator must prove the key technologies in the Galileo satellite navigation system before the full network begins its roll-out in 2010.

These include the atomic clocks which provide the precise timing that underpins all sat-nav applications.

The launch is a big moment for Galileo which has suffered severe delays.

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

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.

Giove-B will be lofted by a Soyuz-Fregat vehicle from the Baikonur spaceport in Kazakhstan. The rocket is timed to leave Earth at 0416 local time, Sunday (2216 GMT, Saturday).

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.

Giove-B will be 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.

"We're already cutting metal on the first four of those," said Richard Peckham, from EADS Astrium, which has led the development of the demonstrator.

"Giove-B is therefore a significant step in that direction. There are new technologies in Europe which haven't yet flown. This is the opportunity to test their performance in space," he told BBC News.

A fundamental focus for Giove-B will be the in-orbit behaviour of its passive hydrogen maser clock.

Giove-B (Astrium)
The hydrogen maser (silver box) is pictured during payload integration


It will be 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.

"It is the firm intention of Galileo to improve what GPS is providing now but also to be compatible," explained Javier Benedicto, Galileo project manager at the European Space Agency (Esa).

"Currently GPS operates with one open signal in a particular frequency band. With Galileo, we are going to broadcast up to 10 signals and the combination of these signals will allow us to provide a number of services which we cannot achieve today with the current system."

If all of these technologies work as predicted, the project will be clear to launch the first four operational satellites in 2010.

Full capability has been set for the end of 2013 - a target that will challenge a rocket industry that already has a long queue of satellite customers waiting for launch opportunities.

BUILDING THE SPACE SEGMENT OF GALILEO
x
Demonstrators will test key technologies; Giove-B follows Giove-A into orbit
In addition, 30 satellites are needed for the full Galileo system
First 4 spacecraft in the constellation have already been ordered
Remaining 26 yet to be ordered; they will be launched in batches
A mix of medium- and heavy-lift rockets could do the job
The timeline is challenging whichever rocket system is used

Further delays are unlikely to be tolerated. The patience of many politicians in Europe is running out.

The project came close to collapse last year when the private consortium chosen to construct and run the system failed to meet a deadline to take development work forward.

European ministers were forced into a review and decided to abandon their public-private model for Galileo's construction in favour of a solution that is fully funded from taxes.

The continued commitment to Galileo is based on the belief that huge returns to the European economy will accrue from the investment.

Already, GPS is said to have spawned global markets that are worth several tens of billions of euros annually.

The new European constellation is expected to deepen and extend those markets as sat-nav functionality becomes ubiquitous in consumer devices such as mobile phones.

"The biggest benefit will come when GPS and Galileo operate together," said Richard Peckham.

"Users will see twice as many satellites and they will get better performance; they won't lose the signal when they are walking around city centres for example."

This past week saw agreement between the European Parliament and the European Council of Ministers on the legal instrument releasing the funds to finish Galileo.

Invitations to tender for the work to finish building the system will be issued in the next few months.

THE FIVE GALILEO SERVICES

OPEN ACCESS NAVIGATION This will be 'free to air' and for use by the mass market; Simple timing and positioning down to 1m
COMMERCIAL NAVIGATION Encrypted; High accuracy at the cm scale; Guaranteed service for which service providers will charge fees
SAFETY OF LIFE NAVIGATION Open service; For applications where guaranteed accuracy is essential; Integrity messages will warn of errors
PUBLIC REGULATED NAVIGATION Encrypted; Continuous availability even in time of crisis; Government agencies will be main users
SEARCH AND RESCUE System will pick up distress beacon locations; Feasible to send feedback, confirming help is on its way

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Launching the 'space clock' on Giove-B

Jonathan.Amos-INTERNET@bbc.co.uk


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