LISA Pathfinder Performance Confirmed in an Open-Loop Configuration: Results from the Free-Fall Actuation Mode

TL;DR

This paper demonstrates that the LISA Pathfinder's free-fall mode, where control forces are applied intermittently, confirms previous acceleration noise measurements and can reduce actuation noise, enhancing test mass free-fall precision.

Contribution

It introduces and validates an open-loop free-fall mode for LISA Pathfinder, providing an independent confirmation of acceleration noise levels and demonstrating noise reduction techniques.

Findings

Free-fall mode measurements agree with continuous actuation results.

Free-fall mode eliminates actuation noise contributions.

Larger actuation forces can be used to suppress actuation noise.

Abstract

We report on the results of the LISA Pathfinder (LPF) free-fall mode experiment, in which the control force needed to compensate the quasistatic differential force acting on two test masses is applied intermittently as a series of "impulse" forces lasting a few seconds and separated by roughly 350 s periods of true free fall. This represents an alternative to the normal LPF mode of operation in which this balancing force is applied continuously, with the advantage that the acceleration noise during free fall is measured in the absence of the actuation force, thus eliminating associated noise and force calibration errors. The differential acceleration noise measurement presented here with the free-fall mode agrees with noise measured with the continuous actuation scheme, representing an important and independent confirmation of the LPF result. An additional measurement with larger actuation forces also shows that the technique can be used to eliminate actuation noise when this is a dominant factor.