A torsional balance for the characterization of microNewton thrusters

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 muN. 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 muN range, and a micropulsed plasma thruster yielding single impulse bits of 19 muN s. The. low noise figure of the balance (below 0.1 muN/rootHz 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. (C) 2003 American Institute of Physics.