Development of a counterbalanced pendulum thrust stand for electric propulsion

We have designed and tested a thrust stand conceived for the characterization of RF plasma thrusters. The balance has been employed in the development of small-medium size HPT prototypes, therefore it allows for an high number of tests per day with an accuracy within the 10%. The balance relies on the counterbalanced-type pendulum concept, which allows to achieve high sensitivity while maintaining a low overall size of the system; the displacement is measured by means of an high-accuracy laser interferometer put outside the vacuum chamber. The system can be calibrated with both a calibration mass, before the test, and an electro-magnetic device, during the test session. We have verified the linear behavior of the instrument and we have developed a dedicated algorithm in order to correct the thermal drifts of the balance. We have compared the stand measurements with the thrust estimations derived from Faraday probe measurements within the plasma plume, verifying that the two estimates are in agreement within 20%.