Advanced Charge Control Dynamics Simulation for the LISA Gravitational Reference Sensor

Abstract

A gravitational wave detector in space, the Laser Interferometer Space Antenna (LISA) will be able to detect gravitational waves in the frequency range of 0.1 mHz–1 Hz, adding to humanity's knowledge of the dark cosmos. The LISA gravitational reference sensor contains a test mass (TM) and is used to determine the local inertial reference frame and as endpoints for the interferometry. The TM is surrounded by an electrode housing to detect changes in TM position and orientation, which is fed back to the spacecraft thrusters for drag-free control. As seen on LISA Pathfinder, the TM builds up charge over time from the space environment and needs to be discharged in order to keep the resulting force noise as low as possible. The operation of intelligently discharging the TM is known as charge control, and is one area of improvement to be explored for LISA. To explore new methods of TM discharge, UV LEDs will be pulsed synchronized with an existing 100 kHz high frequency electric field to facilitate photoelectron current direction and to achieve lower UV light powers by duty cycling. This paper addresses new pulsed methods for the LISA Charge Management System, which require in-depth modeling, analysis, and testing because space environment validation will not be possible prior to LISA launch. Therefore, it is necessary to model the dynamics of charge movement to determine the force noise contribution of pulsed continuous charge control. The charge dynamics model is described, and simulation results featured for charge control efficacy in a deep space radiation environment. Experimental testing of the simulation results could be done in the University of Florida Torsion Pendulum, a key technology to testing GRS performance in a space-like environment.