MICROSCOPE. mission analysis, requirements and expected performance

Abstract

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.

Quantum Physics in Space

“…However, the most stringent upper bound on the violations of the WEP to date comes from space, where one can exploit the possibility to compare the gravitational acceleration of two free falling test-bodies in orbit around the Earth for a very long time. The space mission MICROSCOPE [38,39] of the French space agency CNES, managed in two years of operation to push this upper bound to η ≤ 1.3 × 10 −14 . This bound results from the use of Titanium-Platinum test-bodies, a reference pair of Platinum-Rhodium alloy masses, and the use of data recorded in 120 orbits with free-falling times of up to 8 days.…”

“…However, this is still a preliminary analysis, which employs only 7% of the data collected before the mission was decommissioned in late 2018. Further improvements are expected from the full analysis of the data [39][40][41].…”

“…Following the success of measuring the weak equivalence principle with the MICROSCOPE mission [39] and the need for more precise optical frequency references in space, different experiments and missions have been devised:…”

MICROSCOPE Mission: Final Results of the Test of the Equivalence Principle

“…The bodies are two concentric hollow cylindrical test masses controlled with electrostatic forces in a differential accelerometer. Any difference in the forces required to keep the two test masses in relative equilibrium would provide evidence for an apparent violation of the WEP, originating from an intrinsic violation, or as an effect of extremely small new forces [59]. MICROSCOPE includes two such differential accelerometers called sensor units: in the first one (SUREF), the two test masses have the same composition (Pt:Rh alloy); in the second one (SUEP), they have different compositions [PtRh(90=10) and TiAlV(90=6=4) alloys].…”

“…It is directly related to the Eötvös ratio ηð2; 1Þ ≈ δð2; 1Þ and to the various forces acting on the satellite (see Ref. [59] for a detailed derivation). In the instrument's reference frame,…”