Achieving geodetic motion for LISA test masses: ground testing result

TL;DR

This study uses a torsion pendulum to evaluate and mitigate forces affecting LISA's test masses, crucial for precise gravitational wave detection, by measuring sensor noise, stiffness, and electrostatic biases.

Contribution

It provides ground testing results that set upper limits on sensor force noise and demonstrates methods to measure and compensate electrostatic effects for LISA.

Findings

Torque noise floor below 10 fNm/√Hz from 0.6 to 10 mHz

Sensor electrostatic stiffness measured at 5% level

Stray DC electrostatic biases detected and compensated

Abstract

The low-frequency resolution of space-based gravitational wave observatories such as LISA (Laser Interferometry Space Antenna) hinges on the orbital purity of a free-falling reference test mass inside a satellite shield. We present here a torsion pendulum study of the forces that will disturb an orbiting test mass inside a LISA capacitive position sensor. The pendulum, with a measured torque noise floor below 10 fNm/sqrt{Hz} from 0.6 to 10 mHz, has allowed placement of an upper limit on sensor force noise contributions, measurement of the sensor electrostatic stiffness at the 5% level, and detection and compensation of stray DC electrostatic biases at the mV level.