The European Space Agency yesterday said an investigation had been launched into what it said were "the anomolies of the orbit injection" but that the satellites were being safely controlled.
The satellites Doresa and Milena took off from the Kourou space centre in French Guiana aboard a Russian-made rocket on Friday after a 24-hour delay because of poor weather.
"Observations taken after the separation of the satellites from the Soyuz VS09 (rocket) for the Galileo Mission show a gap between the orbit achieved and that which was planned," the Arianespace said in a statement.
The 5.4 billion euro ($7.2 billion) Galileo constellation is designed as an alternative to the existing US Global Positioning System (GPS) and Russia's Glonass, and will have search-and-rescue capabilities.
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Jean-Yves Le Gall, France's Galileo coordinator, told AFP it would be "complicated" to correct the orbit of the two satellites.
"We are trying to see if we can remedy the situation in the coming hours," he said.
Initially, Arianespace had said that the satellites had separated from the mothership to enter into free-flight orbit as planned just under four hours after launch.
"These two satellites are the first of a new type of satellite that are fully owned by the EU, a step towards a fully fledged European-owned satellite navigation system," the European Commission, which funds the project, said Friday.