Vol. 538
In section 13. Astronomical instrumentation

The astrometric core solution for the Gaia mission

by L. Lindegren, U. Lammers, D. Hobbs, W. O’Mullane, U. Bastian, and J. Hernandez, A&A 538, A78

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The Gaia satellite is the next space astrometry mission, to be launched in 2013. It is expected to measure the positions, parallaxes, and annual proper motions of approximately one billion stars, with accuracies under 10 microarcseconds for brighter stars. The data analysis for Gaia has at its core a simultaneous least-square problem for approximately half a billion parameters, which is obviously not amenable to direct inversion and must be solved iteratively. Lindegren et al. describe the software system and algorithms they developed for this essential task, then demonstrate its convergence on a smaller scale and give a slightly simplified, but realistic simulation of the Gaia mission. Scaling those results to the full Gaia mission shows that its data can be processed with realistic resources, by removing a major potential stumbling block to the overall mission.