Gradiometer accommodation on board a drag-free satellite

Accommodation of the GRADIO instrument, composed of eight three-axis ultrasensitive accelerometers located at the corners of a cubic structure on a Geopotential Research Mission spacecraft is discussed. A two-stage DISCOS configuration with a magnetically suspended inner-stage; and a very fine control of the Earth pointed inner-stage taking into account the GRADIO accelerometer measurements in order to limit the variations of the angular accelerations are required. For diagonal tensor components and an averaging time of 4 sec, the overall goal is 0.1 Eotvos at 160 km altitude.