This study focuses on the NNGM mission, whose objective is to measure Earth's gravitational field. This scientific mission has strong requirements in term of AOCS in order to compensate precisely all perturbations. The scope of the study is to find a thruster configuration that firstly satisfies the mission requirements and secondly to save as much fuel as possible. Two simplified models have been made. The first provides the thuster positions and their approximate orientations; the second refines the orientations found by the first model. They gave insights on critical constraints and a first indicative configurations to be used as a starting point for a dedicated local optimization.