New LISA dynamics feedback control scheme: Common-mode isolation of test mass control and probes of test-mass acceleration

TL;DR

This paper introduces a novel LISA control scheme that isolates common-mode signals, reducing suspension forces and improving test-mass free-fall quality, with implications for data calibration and analysis.

Contribution

A new test-mass suspension method that minimizes control forces by focusing on differential motion, enhancing LISA's measurement precision.

Findings

Significantly reduces suspension forces and torques needed for control.

Derives a new observable for differential acceleration measurement.

Improves calibration and data analysis for LISA.

Abstract

The Drag-Free and Attitude Control System is a central element of LISA technology, ensuring the very high dynamic stability of spacecraft and test masses required in order to reach the sensitivity that gravitational wave astronomy in space requires. Applying electrostatic forces on test-masses is unavoidable but should be restricted to the minimum necessary to keep the spacecraft-test masses system in place, while granting the optimal quality of test-mass free-fall. To realise this, we propose a new test-mass suspension scheme that applies forces and torques only in proportion to any differential test mass motion observed, and we demonstrate that the new scheme significantly mitigates the amount of suspension forces and torques needed to control the whole system. The mathematical method involved allows us to derive a new observable measuring the differential acceleration of test masses projected on the relevant sensitive axes, which will have important consequences for LISA data calibration, processing and analysis.