The MICROSCOPE mission was designed to test the Weak Equivalence Principle (WEP), stating the equality between the inertial and the gravitational masses, with a precision of 10^-15 in terms of the Eötvös ratio η. Its experimental test consisted of comparing the accelerations undergone by two collocated test masses of different compositions as they orbited the Earth, by measuring the electrostatic forces required to keep them in equilibrium. This was done with ultra-sensitive differential electrostatic accelerometers onboard a drag-free satellite. The mission lasted two and a half years, cumulating five-months-worth of science free-fall data, two thirds with a pair of test masses of different compositions – Titanium and Platinum alloys – and the last third with a reference pair of test masses of the same composition – Platinum. We summarize the data analysis, with an emphasis on the characterization of the systematic uncertainties due to thermal instabilities and on the correction of short-lived events which could mimic a WEP violation signal. We found no violation of the WEP, with the Eötvös parameter of the Titanium and Platinum pair constrained to η( Ti, Pt) = [-1.5 ± 2.3 (stat)± 1.5 (syst)] × 10^-15 at 1σ in statistical errors.

The space mission MICROSCOPE dedicated to the test of the equivalence principle (EP) operated from April 25, 2016 until the deactivation of the satellite on October 16, 2018. In this analysis we compare the free-fall accelerations (a (A) and a (B)) of two test masses in terms of the Eotvos parameter eta(A,B)=2aA-aBaA+aB <i . No EP violation has been detected for two test masses, made from platinum and titanium alloys, in a sequence of 19 segments lasting from 13 to 198 h down to the limit of the statistical error which is smaller than 10(-14) for eta(Ti, Pt). Accumulating data from all segments leads to eta(Ti, Pt) = [-1.5 +/- 2.3 (stat) +/- 1.5 (syst)] x 10(-15) showing no EP violation at the level of 2.7 x 10(-15) if we combine stochastic and systematic errors quadratically. This represents an improvement of almost two orders of magnitude with respect to the previous best such test performed by the Eot-Wash group. The reliability of this limit has been verified by comparing the free falls of two test masses of the same composition (platinum) leading to a null Eotvos parameter with a statistical uncertainty of 1.1 x 10(-15).

The MICROSCOPE mission aimed to test the Weak Equivalence Principle (WEP) to a precision of $10^{-15}$. The WEP states that two bodies fall at the same rate on a gravitational field independently of their mass or composition. In MICROSCOPE, two masses of different compositions (titanium and platinum alloys) are placed on a quasi-circular trajectory around the Earth. They are the test-masses of a double accelerometer. The measurement of their accelerations is used to extract a potential WEP violation that would occur at a frequency defined by the motion and attitude of the satellite around the Earth. This paper details the major drivers of the mission leading to the specification of the major subsystems (satellite, ground segment, instrument, orbit...). Building upon the measurement equation, we derive the objective of the test in statistical and systematic error allocation and provide the mission's expected error budget.

This paper focus on the description of the design and performance of the MICROSCOPE satellite and its Drag-Free and Attitude Control System (DFACS). The satellite is derived from CNES' Myriade platform family, albeit with significant upgrades dictated by the unprecedented MICROSCOPE's mission requirements. The 300kg drag-free microsatellite has completed its 2-year flight with higher-than-expected performances. Its passive thermal concept allowed for variations smaller than 1 $\mu$K at the measurement frequency $f_{\rm{EP}}$. The propulsion system provided a 6 axis continuous and very low noise thrust from zero to some hundreds of micronewtons. Finally, the performance of its DFACS (aimed at compensating the disturbing forces and torques applied to the satellite) is the finest ever achieved in low Earth orbit, with residual accelerations along the three axes are lower than $10^{-12} {\rm m/s}^2$ at $f_{\rm{EP}}$ over 8 days.

The MICROSCOPE mission aims to test the weak equivalence principle (WEP) in orbit with an unprecedented precision of 10 −15 on the Eötvös parameter thanks to electrostatic accelerometers on board a drag-free micro-satellite. The precision of the test is determined by statistical errors, due to the environment and instrument noises, and by systematic errors to which this paper is devoted. Systematic error sources can be divided into three categories: external perturbations, such as the residual atmospheric drag or the gravity gradient at the satellite altitude, perturbations linked to the satellite design, such as thermal or magnetic perturbations, and perturbations from the instrument internal sources. Each systematic error is evaluated or bounded in order to set a reliable upper bound on the WEP parameter estimation uncertainty.

The Weak Equivalence Principle (WEP), stating that two bodies of different compositions and/or mass fall at the same rate in a gravitational field (universality of free fall), is at the very foundation of General Relativity. The MICROSCOPE mission aims to test its validity to a precision of 10^-15, two orders of magnitude better than current on-ground tests, by using two masses of different compositions (titanium and platinum alloys) on a quasi-circular trajectory around the Earth. This is realised by measuring the accelerations inferred from the forces required to maintain the two masses exactly in the same orbit. Any significant difference between the measured accelerations, occurring at a defined frequency, would correspond to the detection of a violation of the WEP, or to the discovery of a tiny new type of force added to gravity. MICROSCOPE's first results show no hint for such a difference, expressed in terms of Eötvös parameter δ(Ti,Pt)=[-1±9 (stat)±9 (syst)] ×10^-15 (both 1σ uncertainties) for a titanium and platinum pair of materials. This result was obtained on a session with 120 orbital revolutions representing 7% of the current available data acquired during the whole mission. The quadratic combination of 1σ uncertainties leads to a current limit on δ of about 1.3×10^-14.

According to the Weak Equivalence Principle, all bodies should fall at the same rate in a gravitational field. The MICROSCOPE satellite, launched in April 2016, aims to test its validity at the 10^-15 precision level, by measuring the force required to maintain two test masses (of titanium and platinum alloys) exactly in the same orbit. A non-vanishing result would correspond to a violation of the Equivalence Principle, or to the discovery of a new long-range force. Analysis of the first data gives δ(Ti,Pt)= [-1 ± 9 (stat) ± 9 (syst)] × 10^-15 (1σ statistical uncertainty) for the titanium-platinum Eötvös parameter characterizing the relative difference in their free-fall accelerations.

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 :