Mechanically Amplified Milli-Newton Thrust Balance for Direct Thrust Measurements of Electric Thrusters for Space Propulsion

Direct thrust measurements by means of a balance (TB) are the golden standard for measuring and, concurrently, specific impulse in electric thrusters. To measure these properties novel class electrodeless plasma thrusters, new TB based on Variable Amplitude Hanging Pendulum with Extended Range (VAHPER) concept has been developed. The mechanical amplification mechanism an angular magnification 31°/°.. Using Lagrangian mechanics, we show that loaded 5.2-kg thruster prototype behaves like damped harmonic oscillator natural frequency 0.37 Hz. A variable damping system provides optimal ratio 0.78, which corresponds to settling time only 1.8 s. Both model and calibration have validated. accommodate particularities medium power design includes following features: optical displacement sensor, water cooling, liquid metal connectors, dedicated vacuum-rated electronics autoleveling, remote (in-vacuum) calibration, temperature monitoring. test TB, were performed 500-W Helicon Plasma Thruster breadboard model. When this thruster, measured stiffness was 12.67 ± 0.01 mN/mm. For stiffness, range is 150 mN 0.1-mN resolution. relative uncertainty found be order 2%.