A Relativistic Model for the Gaia Observationsf

Exact general relativistic observation equations for the GAIA concept were derived for a static sphere, i.e., with only stellar angular coordinates as un-knowns. These equations were then put to test in an end-to-end simulation of the current baseline mission. Although the applicability of the present model is limited to the case of an observer in the gravita-tional well of a spherical non-rotating Sun, the results show that, despite cumbersome formalism, measurements of angular distances among stars good to 100 arcsec (as expected for stars of V = 16 mag) can be modeled to yield estimates of the relativistic astrometric parameters with errors of 20 arcsec after only one year of satellite operations.