The Gaia mission to map a billion stars in the Milky Way has been delayed for about two months by the European Space Agency (ESA). X-band transponders used in other satellites have begun to fail, so the ESA has decided to replace those modules prior to launching. The likely blastoff date will be in late December of this year.
The Gaia mission is intended to map the position and velocity of a billion stars in the Milky Way to support ongoing studies on galactic dynamics. The main instrument for this mapping is a gigapixel camera, by far the most complex ever launched into space. The Gaia satellite will orbit near the L2 point positioned about 1.5 million kilometers behind Earth.
Gaia will produce a three-dimensional map of our galaxy. The map will be missing most of the Milky Way's stars (only including one billion of a total of some 400 billion), but this will cover our galactic region in considerable detail, and will provide much needed information about more distant and dust-obscured regions. The positions will be solid to about 24 microarcseconds, which is the width of a human hair at a distance of 1,000 km (621 mi).
As a "free" side result, Gaia is expected to find hundreds of thousands of asteroids and comets in the solar system, perhaps 7,000 exoplanets, 20,000 supernovae, and hundreds of thousands of quasars. Clearly, the analysis of Gaia's petabyte (one million gigabytes) of data will continue long after its five-year mission is complete.