The MICROSCOPE space mission is to test in 2016 the Weak Equivalence Principle (WEP) with an accuracy of 10 −15 . This fundamental physics mission should provide answers to the basic question of the universality of free-falling bodies in a uniform gravity field. During 18 months, the mission should improve the current ground experiments by at least two orders of magnitude. The payload is composed of two electrostatic differential space accelerometers that exhibit a resolution of 2×10 −12 m s −2 Hz −1/2 . By measuring the difference of acceleration between two concentric test masses at the orbital frequency, a possible WEP violation signal is extracted from the measurement where the gravity gradient effect dominates by a factor of one hundred. This paper addresses the scientific objective of the space mission and describes how the performance drives the specification. A particular focus is made on the work jointly performed by ONERA and PTB to fulfil the fabricating requirements.

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