General status of the Gaia mission and expected performance
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Gaia is an ESA mission to build a census of our Milky Way Galaxy. This is done with a
suite of three instruments combining two fields of view into a single focal plane.
On-board detection of all sources will ensure a bias free survey down to the 20th
magnitude. In addition to astrometry also photometry is done down to the 20th magnitude.
The third, spectroscopic instrument will provide radial velocities down to the 17th
magnitude of the Galactic stellar population. Currently the scientific requirements on
Gaia are largely met except for bright stars for which in astrometry additional efforts
are needed to squeeze the remaining μ arcsecs out of the positional
information error budgets. In the mid-magnitude range (15 mag) the end of mission parallax
errors are from 10 to 25 μ arcsec and photometry errors are between 5 and
16 mmag. Radial velocities are better than 1 km s -1 for the bright stars with
errors increasing to 15 km s -1 for the faintest ones. At the moment there are
no unsolvable technical challenges on the table and Gaia is progressing toward the launch
in 2012.