The launcher for Arianespace's next Soyuz mission from the Spaceport in French Guiana is completing its initial checkout for a flight in the second half of 2012, which will carry another two spacecraft for Europe's Galileo satellite navigation constellation.

During activity at the Spaceport's Soyuz Launcher Integration Building - known by its Russian "MIK" designation - the vehicle's four first-stage strap-on boosters have been mated with the Block A core second stage, followed by integration of the Block I third stage.

With its initial build-up concluded, the Soyuz is now undergoing regular maintenance checks that are standard for the Russian-built vehicles that have been in storage prior to their mission. Such verifications include testing of the launcher's pneumatic and electrical systems.

This Soyuz will carry Europe's next two Galileo In-Orbit Validation (IOV) satellites, joining the first pair of spacecraft lofted on Arianespace's historic maiden flight of the Russian-built launcher from French Guiana in October 2011.

Once the four IOV satellites are in orbit, they will provide the minimum information needed for space-based navigation: latitude, longitude and altitude data, along with ranging accuracy; enabling assessment of the Galileo system's performance, while also allowing suppliers to realistically check their receivers and services against actual signals.

Arianespace has been chosen to deploy the entire Galileo constellation of 30 satellites. This began with the launch of the first two experimental satellites, Giove-A and Giove-B, orbited by Arianespace's Starsem affiliate on Soyuz launchers from Baikonur Cosmodrome in 2005 and 2007.

Subsequently, Arianespace lofted the initial pair of In-Orbit Validation spacecraft on Soyuz' October 2011 inaugural mission from the Spaceport. The remaining 24 Galileo constellation satellites will be orbited through 2015, using six additional Soyuz vehicles carrying two spacecraft each, along with three Ariane 5s configured with four per launch. Initial phases of the Galileo program were carried out by the European Space Agency (ESA) in activity co-funded with the European Commission.

Galileo's Full Operational Capability phase is being managed and funded by the European Commission, with ESA and the Commission having signed a delegation agreement by which the space agency acts as design and procurement agent.

The upcoming Galileo mission is designated VS03 in the numbering system for Arianespace's launcher family - which is composed of the medium-lift Soyuz, heavy-lift Ariane 5 and light-lift Vega - all operated at the Spaceport. The "V" represents the French word for "flight" (Vol), while "S" signifies the use of a Soyuz launch vehicle.

Its "3" denotes the third Arianespace mission of Soyuz from French Guiana.