Gaia is the next space-astrometry mission of the European Space Agency, following up on the success of the Hipparcos
mission. With a focal plane containing more than 100 large-area CCD detectors, Gaia will survey the sky and repeatedly
observe the brightest 1,000 million (one billion) objects, down to 20th magnitude, during its 5-year nominal lifetime.
Gaia's science data will comprise absolute astrometry, broad-band photometry, and low-resolution spectro-photometry.
Medium-resolution spectroscopic data (resolving power 11,500) will be obtained for the brightest 150 million sources,
down to 17th magnitude. The extreme thermo-mechanical stability of the spacecraft, combined with the selection of the
L2 Lissajous point of the Sun-Earth/Moon system for operations, allows stellar parallaxes (distances) to be measured
with standard errors less than 10 micro-arcsecond (μas) for stars brighter than 13th magnitude, 20-30 μas for stars at 15th
magnitude, and around 300 μas at magnitude 20. Photometric standard errors are in the milli-magnitude regime. The
spectroscopic data will allow the measurement of radial velocities with errors at the level of 15 km s-1 at magnitude 17.
Gaia's primary science goal is to unravel the kinematical, dynamical, and chemical structure and evolution of the Milky
Way. In addition, Gaia's data will touch many other areas of research, for instance stellar physics, solar-system bodies,
fundamental physics, and exo-planets. The Gaia spacecraft is currently undergoing its critical design review (CDR).
With a launch foreseen in the second half of 2012, the final catalogue is expected in 2020. The science community in
Europe, organized in the Gaia Data Processing and Analysis Consortium (DPAC), is responsible for the processing of
the Gaia data. This formidable task is in full preparation. The calibration of the data presents exciting challenges, in
particular in the area of radiation-damage-induced charge-transfer inefficiency (CTI).