A Russian Soyuz-ST-B carrier rocket, launched on Friday evening from the Kourou space center in French Guiana, has orbited two Galileo-IOV (In-Orbit Validation) communications satellites, Russian space agency Roscosmos said.

The blastoff occurred at 1815 GMT on Friday. Some four hours after, the satellites got separated from the Soyuz-ST-B.

The satellites are the third and fourth in global navigation satellite system Galileo, the European analogue of the US GPS, which is set to eventually expand to 30 satellites, including 27 operational ones and three spares. The first two satellites were put in orbit in 2011 on board a Soyuz carrier rocket.

Galileo is expected to be in full service by 2020, and could become partially operational by 2015. Its satellites will be in 23,200-km (14,415-mile) orbits in three orbital planes with an inclination of 56 degrees. Developers claim the navigation system will be more precise than the GPS.