The UK government has published the agreement between it and fellow European governments, and the United States of America, over the promotion, provision and use of the Galileo and Global Positioning System (GPS) systems.

After many years of wrangling, the Galileo project was finally given the go-ahead by the European Union back in December 2007. Galileo is intended to be an independent alternative to America's GPS, which is controlled by the US military.

European nations had wanted for some time their own satellite system that could be relied upon even in times of war or disagreement. As recently as the year 2000, the US only provided limited access to GPS to the general public.

Both the United States and the EU signed an agreement way back in June 2004 that GPS and Galileo signals would be interoperable, but it has taken several years for the agreement to be approved by member states.

Since then two Galileo test satellites have been launched. In late April, the second Galileo test satellite, Giove-B, was carried into space by the Soyuz-Fregat rocket launched from Kazakhstan. A couple of days ago, Giove-B, successfully transmitted radio signals which will one day be used as the basis for satellite navigation in Europe.

"The combined fleet (of both GPS and Galileo satellites) will number roughly 50," according to Ruy Pinto, a Galileo director at Inmarsat, the UK company that owns and operates its own global satellite network. "This will mean more penetration and better accuracy for users, especially within cities with its 'urban canyons'."

The agreement between the EU and the US, specifies that while Galileo satellites will produce Galileo signals, and GPS satellites will produce GPS signals, both signals on the ground will be compatible and interoperable, allowing users in the future to use a device that contains both GPS and Galileo chipsets, which are still to be defined.

Unfortunately, this will mean that existing GPS-based sat-nav devices will require a different chipset to utilise the Galileo signal.

"The use of Galileo requires changes to the current GPS receivers," confirmed Javier Benedicto, Galileo project manager, ESA (European Space Agency) Navigation Department in an emailed reply.

Besides the well-established GPS system, China is building its own network, and the Russians have their own Glonass system, which has a fairly limited geographical range, but is being improved. The US is currently in the process of improving its GPS network (so-called GPS-III).

"By the way the use of future GPS (so-called GPS-III) will also require changes to receivers," added Benedicto.

But will Galileo be able to provide more precise measurements and better accuracy than say GPS or Glonass?

"It is difficult to answer," replied Benedicto, "but in standard user conditions, Galileo will provide an accuracy around one order of magnitude better than current open service GPS."

While civilian GPS and Galileo radio frequencies will be compatible and interoperable at the user level, and the increased number of satellites visible from any location on the Earth will aid accessibility to navigation signals, there will still be an element of Galileo that will remain off limits to civilians.

"Access to Galileo signals will be open to users worldwide, except the so-called Public Regulated signals, which are restricted to European Government official use," said Benedicto.