Data Processing: Testing of Core Tasks

The implementation and testing of the core processing of Gaia astrometric data has been the main goal of the GDAAS ESA contract (2000-2004). The reduction process, based on the principe of Global Iterative Solution (GIS), involves all the observations of `well behaved' sources and, by solving a minimisation problem in a linearized system of equations, looks for the attitude reconstruction, the derivation of the geometric and photometric calibration, and astrometric and global parameters determination. A first fully operational system has been used to process, in a distributed environment, eighteen months of mission data generated by the Gaia simulator (GASS). Results from several tests are presented, all of them devoted to check if the designed implementation ensures good convergence of the global iterations. We conclude that the system is converging, although at a very slow rate, mainly due to the strong correlation between parallax and light deflection.