Capacitive sensing of test mass motion with nanometer precision over millimeter-wide sensing gaps for space-borne gravitational reference sensors

Abstract

Capacitive sensing of test mass motion with nanometer precision over millimeter-wide sensing gaps for space-borne gravitational reference sensors. Physical Review D, 96(6), 062004.There may be differences between this version and the published version. You are advised to consult the publisher's version if you wish to cite from it.http://eprints.gla.ac.uk/148989/ We report on the performance of the capacitive gap-sensing system of the Gravitational Reference Sensor (GRS) onboard the LISA Pathfinder (LPF) spacecraft. From in-flight measurements, the system has demonstrated a performance, down to 1 mHz, that is ranging between 0.7 aF Hz −1/2 and 1.8 aF Hz −1/2 . That translates into a sensing noise of the test mass motion within 1.2 nm Hz −1/2 and 2.4 nm Hz −1/2 in displacement and within 83 nrad Hz −1/2 and 170 nrad Hz −1/2 in rotation. This matches the performance goals for LPF and it allows the successful implementation of the gravitational waves observatory LISA. A 1/f tail has been observed for frequencies below 1 mHz, the tail has been investigated in detail with dedicated in-flight measurements and a model is presented in the paper. A projection of such noise to frequencies below 0.1 mHz shows that an improvement of performance at those frequencies is desirable for the next generation of GRS sensors for space-borne gravitational waves observation. 2PACS numbers: 04.80. Nn, 95.55.Ym

LISA Pathfinder platform stability and drag-free performance

“…green) or by enhancing the reddening of the noise of z 1 and z 2 sensors. To remove this ambiguity, the reddening (1/f behaviour) has been measured independently by [13]. Figure 5 shows the behaviour of the z 2 sensing output.…”

“…We used therefore the results of independent and dedicated investigations that were performed during the mission. For the capacitive sensing noises, we refer to [13] which showed that these noises had a 1 / f (in amplitude) dependence below 1mHz whereas, for the capacitive actuation noises, [14] showed a 1 /f dependence (in amplitude) below 1mHz. We have performed an analysis of all the observables (x, y, z, θ, η and φ) associated to TM 1 for a number of noise only runs.…”

“…The LISA Technology Package (LTP ), the main payload of LPF , was built to demonstrate the feasibility of the targeted sensitivity [10] and includes high performance sensing and actuation subsystems. The Gravitational Reference Sensor (GRS ) [12] includes the 1.93kg Au-Pt test mass, surrounded by a conducting electrostatic shield with electrodes that are used for simultaneous capacitive position sensing and electrostatic force actuation of the TM [13,14]. The Optical Metrology System (OMS ) [15][16][17] uses heterodyne interferometry for high precision test mass displacement measurements.…”

Design of a Carrier Wave for Capacitive Transducer with Large Dynamic Range

“…A pair of carrier waves, which are +V p and −V p with equal amplitude and opposite phase, are injected into the two fixed plates. Therefore, the differential capacitance ∆C information is converted to voltage information and picked up by the charge amplified by V charge [17].…”

Analysis of the accuracy of actuation electronics in the laser interferometer space antenna pathfinder

“…The other TM (labeled TM2) is actuated, such that it follows the spacecraft and TM1. The main LPF observable, Dg, is the total residual acceleration of the two TMs in free fall condition, along the main measurement axis x, and it is calculated by 6,7 Dg(t) =ẍ 12…”