MICROSCOPE Instrument Servo-Loops And Digitization

MICROSCOPE is a fundamental physics space mission which aims at testing the Equivalence Principle (EP) with an accuracy of $10^{−15}$. The gravitational signal is measured precisely on-board a drag-free microsatellite by a differential electrostatic accelerometer which includes two cylindrical test masses made of different materials. The masses are servo-controlled along their six degrees of freedom and the MICROSCOPE experiment takes advantage of this specific configuration with 12 data channels. A major point concerns the digitization and computation noise throughout the loop, which should be maintained negligible with respect to the physical noise. This requires dedicated converters, filters and high frequency operations even if the EP test is performed at frequency about $10^{−3}$ Hz.