MICROSCOPE

To test the equivalence principle (i.e. the similarity of free fall for two bodies of different composition in an identical gravity field), two differential accelerometers are used successively. If the equivalence principle is verified, the two sets of masses will be subjected to the same acceleration. If different accelerations have to be applied, the principle will be violated.

The principal experiment is the Twin-Space Accelerometer for Gravity Experiment (T-SAGE), built by ONERA and composed of two identical accelerometers and their associated, concentric cylindrical masses. One accelerometer serves as a reference and contains two platinum-rhodium alloy masses, while the other is the test instrument and contains two masses with different neutron–proton ratios: one mass of platinum-rhodium alloy and another mass of titanium-aluminium-vanadium alloy (TA6V). The masses are maintained within their test areas by electrostatic repulsion, designed to render them motionless with respect to the satellite.{{cite web |url=https://directory.eoportal.org/web/eoportal/satellite-missions/m/microscope |title=MicroSCOPE |work=eoPortal |publisher=European Space Agency |accessdate=7 December 2016}}{{cite web |url=https://microscope.cnes.fr/en/MICROSCOPE/t-sage.htm |title=T-SAGE Instrument |publisher=CNES |date=1 July 2016 |accessdate=7 December 2016}}

It is necessary to create a thermally benign environment for the accelerometers. To that end, a Sun-synchronous orbit provides constant illumination; the experiments are mounted on the end of the satellite bus away from the Sun; and to maintain thermal isolation from the satellite itself, the modes of thermal connection were modelled and wire connections were minimised.

The satellite employs a Drag-Free Attitude Control System (DFACS), also called the Acceleration and Attitude Control System (AACS), that uses a double-redundant primary and backup set of four microthrusters (sixteen total) to "fly" the satellite around the test masses. This system takes into account the dynamic forces acting on the spacecraft, including aerodynamic forces due to residual atmosphere, solar pressure forces due to photon impacts, electromagnetic forces within the Earth's magnetosphere, and gravitational forces in the Sun-Earth-Moon system.{{cite web |url=https://microscope.cnes.fr/en/MICROSCOPE/scaa.htm |title=Attitude and acceleration control |publisher=CNES |date=29 June 2016 |accessdate=7 December 2016}}{{cite web |url=http://www.esa.int/Our_Activities/Space_Science/Space_Microscope_to_test_universality_of_freefall |title=Space Microscope to test universality of freefall |publisher=European Space Agency |first=Markus |last=Bauer |date=26 April 2016 |accessdate=7 December 2016}}

MICROSCOPE was successfully launched on 25 April 2016 at 21:02:13 UTC from the Guiana Space Centre outside Kourou, French Guiana.{{cite news |url=http://spaceflightnow.com/2016/04/26/soyuz-blasts-off-with-environmental-satellite-general-relativity-probe/ |title=Soyuz blasts off with environmental satellite, general relativity probe |work=Spaceflight Now |first=Stephen |last=Clark |date=26 April 2016 |accessdate=7 December 2016}} It was carried by a Soyuz ST-A booster with a Fregat-M upper stage.{{cite web |url=http://space.skyrocket.de/doc_sdat/microscope.htm |title=MICROSCOPE |work=Gunter's Space Page |first=Gunter |last=Krebs |date=29 April 2016 |accessdate=7 December 2016}} Other payloads on this flight were the European Space Agency's Sentinel-1B Earth observation satellite and three CubeSats: OUFTI-1 from the University of Liège, e-st@r-II from the Polytechnic University of Turin, and AAUSAT-4 from Aalborg University.{{cite web |url=http://www.arianespace.com/press-release/flight-vs14-a-successful-arianespace-launch-with-soyuz-supporting-sustainable-development-fundamental-physics-and-promoting-space-careers/ |title=Flight VS14 – A successful Arianespace launch with Soyuz, supporting sustainable development, fundamental physics and promoting space careers |publisher=Arianespace |date=25 April 2016 |accessdate=7 December 2016}}

On 4 December 2017, the first results were published. The equivalence principle was measured to hold true within a precision of {{10^|-15}}, improving prior measurements by an order of magnitude.{{cite journal |title=MICROSCOPE Mission: First Results of a Space Test of the Equivalence Principle |journal=Physical Review Letters |first=Pierre |last=Touboul |display-authors=etal |volume=119 |issue=23 |at=231101 |date=8 December 2017 |doi=10.1103/PhysRevLett.119.231101 |pmid=29286705 |arxiv=1712.01176 |bibcode=2017PhRvL.119w1101T|s2cid=6211162 }}

After completing its mission goals and exhausting its supply of nitrogen fuel, the decommissioning of MICROSCOPE was announced on 18 October 2018. The spacecraft was first passivated, then two {{convert|4.5|m|ft|adj=on}} IDEAS (Innovative DEorbiting Aerobrake System) inflatable booms were deployed to passively de-orbit the spacecraft by creating a higher drag profile. By this method, MICROSCOPE is expected to re-enter Earth's atmosphere within 25 years instead of 73 years.

{{Portal|Physics|Spaceflight}}

• Tests of general relativity
• Timeline of gravitational physics and relativity

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• [https://microscope.cnes.fr/en/ MICROSCOPE website] at CNES.fr

{{European Space Agency}}

{{Orbital launches in 2016}}

Category:General relativity

Category:European Space Agency satellites

Category:Satellites orbiting Earth

Category:Spacecraft launched by Soyuz-2 rockets

Category:Spacecraft launched in 2016

Category:Secondary payloads