Fundamental Physics with Gaia: A Generic Globals Update Block for Gaia's Astrometric Iterative Solution

Gaia is ESA's ambitious space astrometry mission with a foreseen launch date around mid-2013. Its main objective is to perform a stellar census of the 1000 million brightest objects in our galaxy from which an astrometric catalogue of micro-arcsec level accuracy will be constructed. The Astrometric Global Iterative Solution (AGIS) is the mathematical and numerical framework for creating the astrometric core solution for this catalogue. At past ADASS meetings we have presented the basic working principles of AGIS and the development status of its main constituents. This year we discuss plans for another key step to mature AGIS into an operational system: Global (G) parameters are those influenced by all observations of Gala in a global sense (e.g. the fundamental parameters of the Parametrized Post-Newtonian (PPN) formalism). We outline a scheme that will allow us to define in a very flexible way at run time the list of G-parameters to solve for. The scheme resembles the Generic Calibration concept that is implemented in AGIS since a while already.