The MICROSCOPE space mission

The MICROSCOPE mission aims to test the equivalence principle (EP) up to an accuracy of 10(-15) using its well known manifestation: the universality o f free-fall. The mission, implemented in the Cnes programme of 2000, schedu les the launch of the microsatellite for 2004. The satellite payload compri ses four gravitational sensors operating at finely stabilized room temperat ure. The masses of the sensors are controlled to the same orbital motion on -board the satellite, which compensates external surface forces in real tim e by actuation of electrical thrusters. Accurate measurements of the electr ostatic forces applied to the masses, so that they follow the same gravitat ional orbit,are processed in order to reject any common effects on the mass es; then the differential outputs are observed with high precision along th e Earth-pointing axis, with an expected resolution of 5 x 10(-15) m s(-2). The quasi cylindrical test masses are concentric in order to reject gravity gradient effects, and are made of platinum or titanium alloys. The instrum ent's concept and design are presented, and the rationale of the space expe riment is explained.