By Jonathan Amos
BBC News science reporter
Europe and the US have signed a deal to co-operate over satellite navigation.
The Galileo system is scheduled to be fully operational before the end of this decade
It means the EU's planned Galileo system will be compatible with the US GPS - ending a trans-Atlantic dispute.
The agreement determines how Galileo's frequencies should be structured which, crucially, will allow signals to be jammed in war zones if necessary.
US Secretary of State Colin Powell signed the pact with Loyola de Palacio, EU Transport Commissioner, at the EU-US summit at Dromoland Castle, Ireland.
The Galileo project will see its first spacecraft begin to be deployed in 2007.
The final constellation of 30 satellites will more than double the spacecraft providing the American Global Positioning System, increasing the accuracy and reliability of navigation and timing signals that can be received across the planet.
WHAT IS GALILEO?
Europe's own global satellite navigation system
Will work alongside US GPS and Russian Glonass systems
Promises real-time positioning down to just a few metres
Guaranteed under all but most extreme circumstances
Suitable for safety-critical systems - can run trains, guide cars and land planes
Europe believes a sat-nav system that is independent of GPS but inter-operable with it will drive a multi-billion euro industry in which receivers find their way into many more markets - from consumer mobile devices such as cell phones to safety-critical applications such as guided trains and buses.
But the idea of Galileo had irked the US Department of Defense, which controls the existing American system, because of the potential of the European network's signals to interfere with those intended for use by the US military.
The Pentagon feared the frequency structure being demanded by Brussels in the so-called Upper L Band between 1559 and 1591MHz could have prevented American commanders from degrading navigation data in the theatre of war to all but their own forces, as is possible at present.
The new accord between the EU and US sees Europe shift its frequency choices to a standard known as Binary Offset Carrier 1.1.
THE GALILEO FUTURE
Expected to be more than 400 million sat-nav users by 2015
European aerospace and electronics firms say it will create more than 100,000 jobs
Rescue services will be able to pinpoint the exact location of a car driver's accident
Will allow someone to find their way in an unfamiliar city using their mobile phone
The change in technical parameters will allow either side to effectively jam the other's signal in a small area, such as a battlefield, without shutting down the entire system.
More importantly from the civilian perspective, the agreement allows the systems to be meshed seamlessly, greatly benefiting manufacturers, service providers and consumers.
Better accuracy, especially in built-up areas where the current GPS signal can be patchy, should lead to a bigger demand for positioning systems.
Four permanent working groups are being set up to work through all the remaining and future compatibility, trade, development, and security issues.