The Soyuz launcher for an ambitious mission of developing the Milky Way's most precise three-dimensional map is completing its basic build-up following mating of the vehicle's Block I third stage in French Guiana.

This step occurred in the Spaceport's MIK Launcher Integration Building, enabling checkout of the integrated Soyuz prior to its upcoming transfer to the launch pad - where the European Space Agency's Gaia star-mapper satellite and Fregat upper stage will be installed.

Scheduled for liftoff on December 19, the mission - designated Soyuz Flight VS06 - will be Arianespace's sixth with the workhorse Russian-built launcher from French Guiana since its service entry at the Spaceport in October 2011.

Gaia will make the largest three-dimensional map of the Milky Way by surveying an unprecedented one percent of its 100 billion stars. The Astrium-built spacecraft also is expected to discover hundreds of thousands of unknown celestial objects, including extra-solar planets and failed stars known as brown dwarfs.