The rocket is carrying two Galileo navigation system satellites and is fitted with a radar transponder allowing its location to be monitored and controlled in flight.
The Soyuz-ST is a modification of the three-stage Soyuz-2 rocket with a Fregat booster adapted for launch in the conditions prevalent in Kourou where there is high heat and humidity.
“The satellites and the Fregat booster have separated from the carrier rocket at the designated time,” a spokesman for the European Space Agency said.
The satellites on board will be deployed as part of the European Galileo navigation system. At present, two test satellites launched in 2005 and 2008 are working in orbit, and 30 are planned in total.