Actuation system for inertial sensors in high-precision space missions using a torsion pendulum

Precision space inertial sensors are imperative for Earth geodesy missions, gravitational wave observations, and fundamental physics experiments in space. In these missions, the residual acceleration noise of a test mass (TM) caused by the forces generated from inertial sensor components and the environment must be maintained below a specific level. Several forces contributing to residual acceleration are related to the actuation system. Hence, developing a precise actuation system is crucial to eliminate erroneous forces and achieve highly accurate measurements of TM acceleration noise. However, obtaining a ``free-fall'' status of the TM to perform sensitive ground tests for the actuation system poses significant challenges. In this study, a torsion pendulum was employed to analyze the impact of the actuation system on TM torque noise. A closed-loop control system integrating the torsion pendulum with components of the actuation modules was designed to assess the performance of the actuation control algorithm. Experimental findings indicate that certain parameters, such as the maximum torques and DC bias voltages in an actuation system, contribute to additional torque noise, with the peak noise level reaching up to ${10}^{\ensuremath{-}13}\text{ }\text{ }\mathrm{Nm}/{\mathrm{Hz}}^{1/2}$ at 1 mHz. The closed-loop system demonstrates a stable tracking error of approximately ${10}^{\ensuremath{-}7}$, indicating the robust tracking performance and robustness of the integrated system for TM rotation control in varying inertial sensor conditions. The proposed method serves as a reference for advancing actuation systems in diverse space gravitational missions.