GAIA
Gaia aims at obtaining a three-dimensional map of the Milky Way, in order to study the composition, formation and evolution of the Galaxy. Gaia will provide unprecedented positional and radial velocity measurements with high accuracies for about one billion stars in our Galaxy down to magnitude 20. This amounts to about 1 per cent of the Galactic stellar population.
See ESA website (link to http://sci.esa.int/gaia/)