Europe’s Arianespace launch consortium has signed a contract with Russia’s Roscosmos space agency for 10 additional Soyuz rockets, locking in prices for vehicles expected to be delivered starting in 2014 or 2015.

The contract, signed June 19 in Moscow, came as Russian and European authorities continue to review possible dates for the inaugural launch of Russia’s Soyuz from Europe’s Guiana Space Center in French Guiana. Construction of the launch pad is nearly complete with the exception of a mobile gantry — the Russian-made piece of equipment that has already caused multiple delays in the start of Soyuz operations.

European and Russian authorities have tentatively set a mid-December date for the inaugural flight. But Arianespace Chief Executive Jean-Yves Le Gall said June 23 this date remains subject to many factors that could permit an earlier flight or push the first launch into 2011.

What is clear is that Arianespace, with a recent contract from Europe’s Eumetsat organization for the launch of a Metop meteorological satellite, continues to accumulate orders for Soyuz missions. The Eumetsat order brings the Soyuz backlog to 19 launches including the inaugural flight, Le Gall said. The first flight is scheduled to carry the Hylas-1 Ka-band consumer-broadband spacecraft for Avanti of London, but the Hylas launch could be transferred to the heavy-lift Ariane 5 rocket under certain conditions, Le Gall said.