A two-stage torsion pendulum for ground testing free fall conditions on two degrees of freedom

Abstract

Ground testing with torsion pendulums played a key role in the development and characterization of the Gravitational Reference Sensor (GRS) of LISA-Pathfinder (LPF). We report on a torsion pendulum facility with 2 soft degrees of freedom (DOF), realized by off-axis cascading two torsion fibers. This instrument, developed for testing on two DOFs the LPF GRS, allows simultaneous measurement of force and torque acting on the suspended test mass (TM), approaching free-fall condition on two DOFs down to a few mHz. We will report on the results of some measurement campaigns devoted in particular to the characterization of force to torque and torque to force actuation cross-talks (CT).