Following the success of the European GOCE mission, which provided a static global map of the Earth’s gravity field, the European Space Agency started several studies for a Next Generation Gravity Mission (NGGM). The objective of this mission is to measure the temporal variations of the Earth’s gravitational field over a long period with a level of accuracy never achieved before. NGGM will consist of two satellites flying drag-free in a low-altitude inclined orbit. Variations in the distance between the two satellites, which will be measured by laser interferometry, corrected by measurements of non gravitational acceleration, represent gravity anomalies. This thesis focuses on a fundamental aspect of the mission, i.e.