Design of an interferometric displacement sensor with picometer resolution for the Galileo-Galilei mission

The Galileo-Galilei (GG) mission aims at testing the Weak Equivalence Principle. It requires the measurement of the differential displacement between two test masses with a resolution of 1 pm/√Hz at 1 Hz. An optical interferometer has been designed to the purpose. The principle and the preliminary design of the interferometer will be illustrated.