Satellite Formation for a Next Generation Gravimetry Mission

The technique called “Low-Low Satellite-to-Satellite Tracking” makes use of two-satellite loose formations for detecting the Earth’s gravity field and its space/time variations: the effect of the geopotential shows up as a variation of the inter-satellite distance, which is measured by a suitable metrology. Accelerometers are utilized on each satellite for measuring and separating the effect of the non-gravitational forces. Thales Alenia Space Italia (TAS-I) has studied for the European Space Agency a gravimetric mission of this kind, in which the inter-satellite distance variation is measured by a laser interferometer. The reference mission scenario that has been defined and studied consists of two satellites flying along the same circular orbit at 10 km relative distance and 325 km altitude. The formation control for this mission shall be designed to work in synergy with the drag-free control (necessary for providing quiet operational environment to the accelerometers), to not interfere with the scientific measurement and to minimize the use of the thrusters. Another control system is in charge of maintaining the fine pointing of the interferometer laser beam from one satellite to the other. This chapter summarizes the main results of the studies performed by TAS-I and its team on these subjects 1 2 3.