MICROSCOPE instrument description and validation

Abstract

This 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.

Result of the MICROSCOPE weak equivalence principle test

“…The typical temperature of the SUEP was about 10 • C while it was about 19 • C for the SUREF. The higher temperature in SUREF was due to two defective capacitors used for house-keeping data [34]. Note also the higher temperatures during sessions 452 and 454 when the two SUs ran simultaneously.…”

“…• The sensor unit (SU) used: as explained in [34], the payload is composed of 2 SUs, each SU enclosing 2 co-axial concentric test masses. SUREF has 2 test masses with the same composition and is used as a null check of the experiment; SUEP aims at comparing the free falls of a test mass in platinum and of a test mass in titanium.…”

“…x between the 2 test masses along the most sensitive axis X (see [38] and [34] for the description of the axis), which was analysed in this work, is directly computed from these data.…”

“…5.5.4). • The temperature which is measured by several probes inside the mechanical and electrical subsystems of each SU [34]. The corresponding systematic effects are estimated in [43].…”

“…size of the satellite and global cost); for a more detailed presentation of MICROSCOPE the reader is referred to other papers of this volume (Ref. [34,37,38,[43][44][45][46][47][48]).…”