MICROSCOPE mission analysis, requirements and expected performance

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.Comment: References update

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

AMONG SPACE FUNDAMENTAL PHYSICS MISSIONS, MICROSCOPE, A SIMPLE CHALLENGING FREE FALL TEST

International audienceSeveral space tests of gravity laws have already been performed but the MICROSCOPE mission is the first one to be fully dedicated to the test of the Equivalence Principle. The dedicated payload is now under qualification and the rather large micro satellite will be produced by Cnes for a launch at beginning of 2015. Each of the two differential accelerometers of the experimental device includes a pair of test-masses whose 720 km altitude orbital motions are constrained along the same purely gravitational trajectory. Evidence of an EP violation is provided by the comparison of the electrostatic configurations needed to maintain the two masses composed of different materials motionless relative to each other. Not only the servo-loop electronics must exhibit very weak level of noise but the geometrical and electrical configuration of the instruments must be very well optimised, accurate, cleaned and steady. Although the accelerometers are saturated on ground by normal gravity, they can be tested on board a free fall capsule in drop tower. These tests complete the fine verification of all mechanical and electrical functions. In addition, the present in flight results of the GOCE mission accelerometers are deeply analysed. Because the sensors of the gravity gradiometer exploits the same technologies, they provide confirmation of the MICROSCOPE instrument models used to extrapolate the in orbit performance and then estimate the expected mission accuracy

MICROSCOPE a micro-satellite for a major corner stone in fundamental physics, from qualification to launch

International audienceThe MICROSCOPE space mission aims at testing the Equivalence Principle with an accuracy of 10e-15. To be launched on April 2016, the CNES microsatellite embarks the instrument that should test for the first time in space the foundation of General Relativity. The expected results whether they confirm or not the Equivalence Principle will bring a major constraint on Physics Models trying to unify Gravity and Quantum Physics.The payload developed by ONERA is composed of two double accelerometers giving full 6-axis measurements to be processed with on-board GPS and star-trackers collected data. The on-ground process of the data takes into account the fine time stamping of the measurement pick up and the position of the satellite along its orbit to correct the Earth’s gravity gradient effect in the difference of the acceleration of two bodies in free-fall. The data once corrected is exploited to extract a potential signal of violation which is along to the Earth’s gravity field.During 2015, the payload flight model has been intensively tested during the qualification campaign of the satellite: environmental tests, EMC tests, electrical tests…. Major results will be presented. They were computed with the Science Mission Center softwares also under development in ONERA. These data complement the simulated data provided by CNES in order to validate the mission ground segment.After a general presentation of the instrument and its performance, the paper will emphasize some return on the particular experience of implementing a high accurate instrument in a small satellite such as MICROSCOPE.As the launch is very close to the presentation, the flight acceptance should be ongoing. A priori no flight data should be available. Nevertheless, the mission flight scenario will be presented as well as the way it will be generated and updated each week by the Mission Center

AMONG SPACE FUNDAMENTAL PHYSICS MISSIONS, MICROSCOPE, A SIMPLE CHALLENGING FREE FALL TEST

International audienceSeveral space tests of gravity laws have already been performed but the MICROSCOPE mission is the first one to be fully dedicated to the test of the Equivalence Principle. The dedicated payload is now under qualification and the rather large micro satellite will be produced by Cnes for a launch at beginning of 2015. Each of the two differential accelerometers of the experimental device includes a pair of test-masses whose 720 km altitude orbital motions are constrained along the same purely gravitational trajectory. Evidence of an EP violation is provided by the comparison of the electrostatic configurations needed to maintain the two masses composed of different materials motionless relative to each other. Not only the servo-loop electronics must exhibit very weak level of noise but the geometrical and electrical configuration of the instruments must be very well optimised, accurate, cleaned and steady. Although the accelerometers are saturated on ground by normal gravity, they can be tested on board a free fall capsule in drop tower. These tests complete the fine verification of all mechanical and electrical functions. In addition, the present in flight results of the GOCE mission accelerometers are deeply analysed. Because the sensors of the gravity gradiometer exploits the same technologies, they provide confirmation of the MICROSCOPE instrument models used to extrapolate the in orbit performance and then estimate the expected mission accuracy

The MICROSCOPE space mission: the first test of the equivalence principle in a space laboratory

International audienceThis paper introduces the current special issue focussed on the MICROSCOPE mission. This mission is the first experimental test in space of the weak equivalence principle (WEP) using man-made test-masses—as opposed to astronomical tests—with the goal to reach a precision two orders of magnitude better than ground-based experiments. Selected in 1999 by CNES as part of its MYRIADE microsatellite programme, the satellite was launched in 2016 and the mission lasted 2.5 years. This paper summarises the articles of the special issue and highlights the key technological and data analysis aspects that allowed for an unprecedented precision on the test of the WEP

Current results of the Microscope space mission: a test of Equivalence Principle

International audienceLaunched in April 2016, the satellite of the MICROSCOPE space mission should end its operations in autumn 2018. The science objective is the test of the weak Equivalence Principle (EP) with an accuracy of 10-15. The EP is one cornerstone of General Relativity (GR); it states the equivalence between gravitational and inertial mass. Most of the alternative quantum gravity theories or the extensions of GR have to confront this founding principle. In 2017, MICROSCOPE's first results settled a new frontier of the EP lower than 2 x10-14 with only 10% of the available data. Since then, all data are available and are being analysed to accomplish the primary objective. The in-orbit test is based on the comparison of the acceleration of two cylindrical bodies in free-fall around the Earth at 710km altitude. The two bodies are the test-masses of two concentric electrostatic accelerometers which constitutes the science payload of the satellite. The acceleration measurements are also used by the satellite acceleration and attitude control system. This system embarks cold gas thrusters which are capable of micro-newton thrusts in order to maintain the payload case free of surface forces like the atmospheric residual drag or the solar pressure disturbances but also free of the disturbing torques (mainly magnetic or gravitational torques). MICROSCOPE is a dedicated fundamental physics mission with a very accurate acceleration measurement achieved in a rather low orbit. In this talk, after detailing the experiment objective and principle, we will describe the payload with a particular focus on the way it has been characterized in orbit. We will then show some results in terms of acceleration measurements to femto-g resolution. Finally, a status of the science mission results will be given

MICROSCOPE's constraint on a short-range fifth force

The MICROSCOPE experiment was designed to test the weak equivalence principle in space, by comparing the low-frequency dynamics of cylindrical "free-falling" test masses controlled by electrostatic forces. We use data taken during technical sessions aimed at estimating the electrostatic stiffness of MICROSCOPE's sensors to constrain a short-range Yukawa deviation from Newtonian gravity. We take advantage of the fact that in the limit of small displacements, the gravitational interaction (both Newtonian and Yukawa-like) between nested cylinders is linear, and thus simply characterised by a stiffness. By measuring the total stiffness of the forces acting on a test mass as it moves, and comparing it with the theoretical electrostatic stiffness (expected to dominate), it is a priori possible to infer constraints on the Yukawa potential parameters. However, we find that measurement uncertainties are dominated by the gold wires used to control the electric charge of the test masses, though their related stiffness is indeed smaller than the expected electrostatic stiffness. Moreover, we find a non-zero unaccounted for stiffness that depends on the instrument's electric configuration, hinting at the presence of patch-field effects. Added to significant uncertainties on the electrostatic model, they only allow for poor constraints on the Yukawa potential. This is not surprising, as MICROSCOPE was not designed for this measurement, but this analysis is the first step to new experimental searches for non-Newtonian gravity in space

MICROSCOPE’s constraint on a short-range fifth force

International audienceThe MICROSCOPE experiment was designed to test the weak equivalence principle in space, by comparing the low-frequency dynamics of cylindrical ‘free-falling’ test masses controlled by electrostatic forces. We use data taken during technical sessions aimed at estimating the electrostatic stiffness of MICROSCOPE’s sensors to constrain a short-range Yukawa deviation from Newtonian gravity. We take advantage of the fact that in the limit of small displacements, the gravitational interaction (both Newtonian and Yukawa-like) between nested cylinders is linear, and thus simply characterised by a stiffness. By measuring the total stiffness of the forces acting on a test mass as it moves, and comparing it with the theoretical electrostatic stiffness (expected to dominate), it is a priori possible to infer constraints on the Yukawa potential parameters. However, we find that measurement uncertainties are dominated by the gold wires used to control the electric charge of the test masses, though their related stiffness is indeed smaller than the expected electrostatic stiffness. Moreover, we find a non-zero unaccounted for stiffness that depends on the instrument’s electric configuration, hinting at the presence of patch-field effects. Added to significant uncertainties on the electrostatic model, they only allow for poor constraints on the Yukawa potential. This is not surprising, as MICROSCOPE was not designed for this measurement, but this analysis is the first step to new experimental searches for non-Newtonian gravity in space