Equivalence principle test with microscope: Laboratory and engineering models preliminary results for evaluation of performance

MICROSCOPE is a space mission, scheduled for a launch in 2010, which aims to verify the equivalence principle (EP) with an accuracy of 10-15, over a hundred times better than what has been realized on Earth today. The EP test is based on the measurement of the electrostatic forces to be applied on each test mass of two concentric inertial sensors, in order to maintain these two masses on the same gravitational trajectory. The instrument formed by these two sensors is called a differential accelerometer. On board the MICROSCOPE satellite, two instruments will embark: one for the test itself, and the other as a performance reference. The first of several mechanical models for this instrument have been manufactured. Each is designed to demonstrate a specific part of the development. Associated to the differential accelerometer, a performance software has also been developed. In order to reach the required performance, an in-orbit calibration phase is planned to improve the knowledge of the geometrical dissymmetries and orientation mismatches. Detailed finite element thermal models of the accelerometers have been realized and currently provide information on the behavior of accelerometer parts in response to the satellite thermal perturbations.