MICROSCOPE mission: first results of a space test of the equivalence principle

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 nonvanishing 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

La participation française à la mission Ariel de l'ESA

International audienceThe ESA/Ariel mission will address some fundamental questions on the composition and formation of exoplanets, in the frame of the ESA Cosmic Vision Program. Ariel is to be launched in 2029. It will use the technique of transit spectroscopy in the near-infrared (1.1-7.8 μm), observing host stars during planetary transit or eclipses, obtained on around one thousand transiting planets. It will provide an extensive statistical study on planets from Earth-size to gas giants around a range of host star types, in complement to James Webb Space Telescope and ground-based observatories observations. The unique performances of Ariel are to record simultaneously the whole wavelength range from about 1 to 8 μm, to record up to ∼1000 targets for statistical purpose and to study in parallel host star activity with planetary spectra thanks to its visible channel concurrent observations. The international consortium, led by G. Tinetti (UK), will procure to ESA the instrument and subsystems, including the telescope and the spectrometers. The Ariel satellite will consist in a telescope (elliptical mirror 1100 mm x 730 mm size) with radiatively cooled optics below 60K. The telescope feeds two separate instruments :The FGS (Fine Guide Sensor), providing three photometric channels (0.5-0.6 micron ; 0.8-1.1 micron and 1.10-1.95 μm, the latter with coarse spectral resolution R ≥ 15)The AIRS (Ariel Infra-Red Spectrometer) is a two channels grating spectrometer (1.95-3.9 μm with R ≥ 100 and 3.9-7.9 μm with R ≥ 30)The exoplanet spectra are retrieved from transit and/or eclipse observations on the target with data processing including calibration of photometric/spectral science spectra, with timely public release of data to maximize science return of Ariel. Within the consortium, the French participation (co-PIs JP Beaulieu \& PO Lagage) is supported by CNES and will be in charge principally of : - 1. AIRS (Ariel infrared spectrometer) instrument o optical module (including detectors & Cold Front End Electronics) and cryoharnesses including with full calibration at detector and instrument level o AIRS instrument detector control unit t with acceptance by the AMC systems team - 2 Contribution to management and systems engineering o for the Instrument Operations and Science Data Centre (IOSDC); o contribute to algorithm, software definition, and data processing of the SGS and to the observations and scheduling. A description of the AIRS instrument is given in a companion paper(Amiaux et al. this session). In preparation of the Ariel future observations, science schools are annually organized for the training of new PhD students or post-doctoral. The first French Ariel school in 2019 has already been followed by the publication of 4 papers (ARESI, II, III, IV) ReferencesAriel Definition Study Report ESA-SCI (2020) in press.Tinetti, Giovanna, Drossart, Pierre; Eccleston, Paul et al., A chemical survey of exoplanets with ARIEL. 2018ExA, 46, 135TPuig, Ludovic, Pilbratt, Göran, et al. The Phase A study of the ESA M4 mission candidate ARIEL. 2018ExA, 46,211PEncrenaz, Thérèse, Tinetti, G., Coustenis, A. Transit spectroscopy of temperate Jupiters with ARIEL: a feasibility study. 2018ExA, 46, 31EEdwards, Billy, Changeat, Quentin, et al. ARES I: WASP-76 b, A Tale of Two HST Spectra 2020AJ, 160, 8ESkaf, Nour, Bieger, Michelle Fabienne, et al. ARES II. Characterizing the Hot Jupiters WASP-127 b, WASP-79 b, and WASP-62b with the Hubble Space Telescope 2020AJ, 160, 109SPluriel, William; Whiteford, Niall, et al. ARES III. Unveiling the Two Faces of KELT-7 b with HST WFC3 2020AJ, 160, 112PGloria Guilluy, Amelie Gressier, et al. ARES IV: Probing the Atmospheres of the Two Warm Small Planets HD 106315 C and HD 3167 C with HST/WFC3 CAMERA. Submitted to AJ

MICROSCOPE instrument in-flight characterization

Since the MICROSCOPE instrument aims to measure accelerations as low as a few 10$^{-15}$ m s$^{-2}$ and cannot operate on ground, it was obvious to have a large time dedicated to its characterization in flight. After its release and first operation, the characterization experiments covered all the aspects of the instrument design in order to consolidate the scientific measurements and the subsequent conclusions drawn from them. Over the course of the mission we validated the servo-control and even updated the PID control laws for each inertial sensor. Thanks to several dedicated experiments and the analysis of the instrument sensitivities, we have been able to identify a number of instrument characteristics such as biases, gold wire and electrostatic stiffnesses, non linearities, couplings and free motion ranges of the test-masses, which may first impact the scientific objective and secondly the analysis of the instrument good operation

Microscope instrument in-flight characterization

International audienceSince the MICROSCOPE instrument aims to measure accelerations as low as a few 10$^{−15}$ m s$^{−2}$ and cannot operate on ground, it was necessary to have a large time dedicated to its characterization in flight. After its release and first operation, the characterization experiments covered all the aspects of the instrument design in order to consolidate the scientific measurements and the subsequent conclusions drawn from them. Over the course of the mission we validated the servo-control and even updated the PID control laws for each inertial sensor. Thanks to several dedicated experiments and the analysis of the instrument sensitivities, we have been able to identify a number of instrument characteristics such as biases, gold wire and electrostatic stiffnesses, non linearities, couplings and free motion ranges of the test-masses, which may first impact the scientific objective and secondly the analysis of the instrument good operation

MICROSCOPE instrument description and validation

International audienceThis paper focuses on the dedicated accelerometers developed for the MICROSCOPE mission taking into account the specific range of acceleration to be measured on board the satellite. Considering one micro-g and even less as the full range of the instrument with an objective of one femto-g resolution, that leads to a customized concept and a high-performance electronics for the sensing and servo-actuations of the accelerometer test-masses. This range and performance directed the payload development plan. In addition to a very accurate geometrical sensor core, a high performance electronics architecture provides the measurement of the weak electrostatic forces and torques applied to the test-masses. A set of capacitive detectors delivers the position and the attitude of the test-mass with respect to a very steady gold-coated cage made in silica. The voltages applied on the electrodes surrounding each test-mass are finely controlled to generate the adequate electrical field and so the electrostatic pressures on the test-mass. This field maintains the test-mass motionless with respect to the instrument structure. Digital control laws are implemented in order to enable instrument operation flexibility and a weak position detector noise. These electronics provide both the scientific data for MICROSCOPE’s test of the weak equivalence principle and the input for the satellite drag-free and attitude control system

MICROSCOPE: systematic errors

International audienceThe 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

MICROSCOPE: systematic errors

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