The MICROSCOPE (MicroSatellite à traînée Compensée pour l'Observation du Principe d'Equivalence) project is an orbit-based mission to verify the Weak Equivalent Principle with an uncertainty of 10-15. To achieve this goal two differential accelerometer, each equipped with two high precision test masses (made of PtRh10 and TiAl6V4 in the form of hollow cylinders with four flats at the outer shell and six precision countersinks at each face), are to be launched in Spring 2016 and shall orbit the earth for approx. one and a half year.

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.

The paper describes the manufacturing and dimensional measurements of high precision work-pieces by PTB, which shall act as test masses (TM) for the satellite-based experiment MICROSCOPE. The manufacturing involves turning of Ti alloys and PtRh10. The measurements were made by in-process tactile probing, coordinate metrology, and form measurement. The high geometrical demands of the project could be fulfilled on both the manufacturing and the measurement sub-projects.