Europe's Galileo satellite navigation system has been declared viable, with the first determination of a ground location using the four satellites in orbit.
The 10-15m accuracy achieved at the European Space Agency's ground station in Noordwijk, the Netherlands, was as expected given the contribution of the minimum four spacecraft needed to fix a point in three dimensions, according to the agency.
Two were launched in October 2011 and a second pair in October 2012, but a fast-track launch programme beginning this year will have 18 in orbit by the end of 2014 for a functional service and 26 by the end of 2015 for near-global coverage. The full constellation of 27 spacecraft and three orbiting spares should be deployed by 2019.
With only four satellites for the time being, the present Galileo constellation is visible at the same time for a maximum two to three hours daily.
With the validation testing activities under way, users might experience breaks in the content of the navigation messages being broadcast.
In the coming months the messages will be further elaborated to define the "offset" between Galileo System Time and Coordinated Universal Time, enabling Galileo to be relied on for precision timing applications, as well as the Galileo to GPS Time Offset, ensuring interoperability with GPS.
In addition, the ionospheric parameters for single frequency users will be broadcast at a later stage.