FEEP micro-thrust balance characterization and testing

A micro-thrust stand developed by the National Physical Laboratory under ESA funding was calibrated and characterized. The balance is based on the nulled-pendulum principle. The thruster is positioned in a constrained pendulum that is free to move only along the line of thrust. A capacitive displacement sensor measures the movement of the pendulum and is connected via a servo closed loop to a force actuator that preserves the nulled position of the pendulum. The force exerted by the actuator is the measurement of the thrust generated by the field effect electric propulsion thruster. Part of the environmental vibration noise is cancelled by subtracting the signal produced by a dummy pendulum (not subjected to thrust) from the signal produced by the principal pendulum. The interface between the thruster and balance was designed with the aim of minimizing the interference of the electrical wires. This paper presents the results of the measurements that fully characterize the balance in terms of accuracy, resolution and thrust range. Improvements to the balance are suggested in order to increase its metrological performance.