Design and Experimental Validation of a Micro-Newton Torsional Thrust Balance for Ionic Liquid Electrospray Thruster

This work describes the advances on a micro-newton torsional thrust balance for ionic liquid electrospray thruster (ILET) being developed in the National University of Defense Technology. The torsional thrust balance adopts an asymmetric pendulum arm about a flexural pivot, and an electrostatic comb device is used for calibration, which makes the balance compact and allows the measurement of the micro-newton level thrust with high accuracy. To minimize the influence of gravity on the measurement results, a two-dimensional adjustable counterweight mechanism is adapted to balance the entire arm and make its mass center close to the pivot axis. Mechanical oscillations are passively damped with an eddy current damper. A series of experimental studies are carried out in a vacuum chamber; the results provide validation that the balance has good linearity in the range of 2-30 mu N, with the resolution better than 0.21 mu N and the settling time to a step force is less than 7 s, which can meet the thrust measurement requirements of the ILET operating in the mode of alternating work voltage polarity. In addition, we find that the electrostatic force generated by the power supply wire has a non-negligible influence on thrust measurement results, which needs to be considered in the actual thrust measurement.