The MICROSCOPE space mission

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Abstract
The MICROSCOPE mission aims to test the equivalence principle (EP) up to an accuracy of 10−15 using its well known manifestation: the universality of free- fall. The mission, implemented in the Cnes programme of 2000, schedules the launch of the microsatellite for 2004. The satellite payload comprises four gravitational sensors operating at finely stabilized room temperature. The masses of the sensors are controlled to the same orbital motion on-board the satellite, which compensates external surface forces in real time by actuation of electrical thrusters. Accurate measurements of the electrostatic forces applied to the masses, so that they follow the same gravitational orbit, are processed in order to reject any common effects on the masses; then the differential outputs are observed with high precision along the Earth-pointing axis, with an expected resolution of 5 × 10−15 ms −2. The quasi cylindrical test masses are concentric in order to reject gravity gradient effects, and are made of platinum or titanium alloys. The instrument's concept and design are presented, and the rationale of the space experiment is explained.