Reconstruction of the Attitude of the Gaia Spacecraft

Gaia is an ESA mission due to be launched in 2013 and will be dedicated to astrometry. The attitude of the spacecraft Gaia is an important part of the data processing of the mission because the astrometry will be calculated with respect to the attitude. Therefore we need a very accurate characterisation of the attitude of the satellite during the observations in order to get the best output from the mission. We simulate the attitude of Gaia using the Dynamical Attitude Model (DAM). It is a simulation developed to achieve a detailed understanding of the Gaia attitude and to provide realistic input data for testing the software pipeline. DAM takes into account perturbations as well as internal hardware components controlling the satellite as the control system, sensors and micro-Newton thrusters. We study the errors in the simulated data, specificall the attitude reconstruction when fittin the Gaia reference attitude with B-splines. We analyse the effect of different parameters and provide an estimation of the expected noise in the scientifi output of the mission due to the noise in the attitude reconstruction.