The geodetic twin satellite mission GRACE delivers gravity field models of the Earth of unprecedented accuracy. However, the originally defined mission baseline is not (quite) reached. Among others, deficiencies in the gravity field sensor system or the related signal processing could be responsible for the degraded performance. In this work the GRACE gravity field sensor system is subject to an integrated sensor analysis. First, models of the satellite environment are derived, including models for the direct gravitational accelerations and non-gravitational forces. The second part contains mathematical models of the individual elements of the gravity field sensor system. The third part consists of the analysis of the raw instrument data. Finally the processing of the raw instrument data to the level that is used for the gravity field determination is investigated.