The satellite lifted-off from the Baikonur Cosmodrome in Kazakhstan at Saturday evening and was orbiting at an altitude of about 125 miles, carrying the most accurate atomic clock ever flown into space.

The 1,100-pound satellite will continue the testing of critical technologies for Europe's planned $5.3 billion global positioning system that's expected to become operational in 2013.

The satellite, called GIOVE-B -- Galileo in Orbit Validation Element -- carries two redundant small-size rubidium atomic clocks, each with a stability of 10 nanoseconds per day, the ESA said, noting it also is carrying a Passive Hydrogen Maser with a stability better than 1 nanosecond per day. The first of its kind to be launched into space, the PHM is the most stable clock ever to operate in Earth orbit, officials said.

In addition to its technology-demonstration mission, GIOVE-B will also take over GIOVE-A's mission to secure the Galileo frequencies, as the first Galileo satellite -- launched in December 2005 -- is approaching the end of its operational life.