A torsional balance for the characterization of microNewton thrusters

Abstract

We describe the performance of a torsional balance suitable for the study of microNewton thrusters. A design based on flexural pivots and electrostatic forces (for calibration and active damping) makes it possible to test thrusters with a mass of a few kilograms, and measure submicroNewton level forces with high accuracy and a resolution better than 0.03 μN. The usefulness of the balance is proved by measuring the performance of two different electric propulsion accelerators: a colloid thruster generating thrust in the 2–13 μN range, and a micropulsed plasma thruster yielding single impulse bits of 19 μN s. The low noise figure of the balance (below 0.1 μN/Hz in the 7 mHz–1 Hz bandwidth) will make it possible to measure the thrust noise requirements imposed in colloid thrusters by missions such as the Space Technology 7 and the Laser Interferometer Space Antenna.