A second pair of satellites that will help supply Europe with its own navigation system have been launched from French Guiana.

The satellites launched Friday join two others launched a year ago as part of the European Union s nascent Galileo navigation system. A minimum of four satellites are needed so officials can perform an in-orbit validation of the system.

A total of 30 satellites ultimately will be launched. By 2014, the system is expected to operate as a free consumer navigation service, and by 2020 it will be fully operational and provide more specialized services.

The taxpayer-funded program is expected to rival the American GPS network, with EU officials touting it as more precise and reliable.