Microscope: A Scientific Microsatellite Development

MICROSCOPE is a CNES-ESA-ONERA-CNRS-OCA-DLT-ZARM scientific mission developed in the frame of Myriade Microsatellite family. The scientific objective consists to test the Equivalence Principle between gravitational mass and inertial mass with an relative accuracy of 10 ; i.e. one hundred times better than the one obtained today on Earth . Satellite has been launched the 25 of April 2016 for a 2 years in orbit lifetime. This paper begins with a introduction of the scientific goals, a presentation of the mission and the payload definition, explaining how the S/C has evolved in time in order to fulfil the stringent mission requirement always keeping in line with microsatellite development approach. The main part of the paper is focused on the description of actual spacecraft design with a presentation of all the functional chains, their performances and the ground validation process. Most innovative elements are the AACS (Attitude and Acceleration Control System) running simultaneously 38 control loops in order to keep the payload in drag-free condition during scientific sessions and (CGPS) Cold Gas Propulsion System generating and modulating a continuous thrust in the range from 1 to 300 μN with an accuracy of 0.1 μN. A special attention is given to micro perturbation control plan and satellite validation logic due to high sensitivity of PL and the impossibility to perform full representative test on ground. It is shown how the design of the satellite is optimized, melting new advanced technology and low cost, well proven methods coming from Myriade family. The paper will end with a presentation of first in-flight results especially the commissioning phase. MICROSCOPE MISSION OVERVIEW MICROSCOPE, an acronym for ”MICROSatellite with drag free Control for the Observation of the Principle of Equivalence”, is a space mission in universe’s science proposed by ONERA and CERGA Institutes, satellite has been launched the 25 of April 2016 by Soyouz with VS14 flight. This mission has been developed in the frame of the scientific missions exploiting the MYRIADE microsatellite product line. Equivalent Principle Mass could be defined in two different ways : as a inertial mass mi , i.e. the term of proportionality between the external force acting on a body and its acceleration : γ  ⋅ = i F m (1) where F = external force; γ = acceleration; and mi = inertial mass. as a gravitational mass mg , i.e. the term of proportionality of gravitational force : 2 r g M g m G g F ⋅ ⋅ = (2) where Fg = gravity force; G = universal constant of gravitation, r = the distance between the two body; Mg the mass of the body generating the gravitation field and mg = the gravitational mass. The Equivalence Principle (EP) postulates a perfect proportionality between the inertial mass and the gravitational mass of a body, whatever its chemical composition. For two different bodies of inertial masses m1i , m2i and gravitational masses m1g , m2g we should then have :