Thrust measurement of an ion thruster by a force probe approach and comparison to a thrust balance

A key parameter when characterizing the performance of an electric propulsion system is obviously its thrust. The thrust can be either determined directly using a so-called thrust balance or deduced from indirect measurements. Here, we present a comparison of thrust measurements of the same radio frequency ion thruster in the thrust range from 250 μN to 1.5 mN using three different approaches: a conventional direct measurement employing a thrust balance and two indirect measurements, one based on a force probe located stationary in the thruster’s plume in conjunction with a scan of the ion beam profile using a Faraday-array scanner, and another one based on a measurement of the beam current at the grid system and a correction for beam divergence deduced from the Faraday-array scans. The results of the three approaches are compared for different beam currents, and pros and cons of the approaches are discussed.