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We have designed and tested a thrust stand for RF plasma thrusters characterization. The balance is employed in the development of small and medium size RF plasma thrusters; it allows for a high number of tests per day with an accuracy in the order of 10%. The balance relies on the counterbalanced-type pendulum concept, which allows adjusting the instrument sensibility without changing the overall pendulum size. The range of thrust which can be evaluated depends on the mass of the prototype under test; e.g. for a 0.5 kg prototype the thrust can vary from 20  μ N up to 50 mN. The system can be calibrated with both a calibration mass, and an electric calibrator. We have developed an algorithm which corrects the thermal drifts generated during thruster operation. We have compared the stand results against Faraday cup measurements, finding an agreement within 20%. [ABSTRACT FROM AUTHOR]

The non-intrusive density measurement of the thin plasma produced by a mini-helicon space thruster (HPH.com project) is a challenge, due to the broad density range (between 1016 m-3 and 1019 m-3) and the small size of the plasma source (2 cm of diameter). A microwave interferometer has been developed for this purpose. Due to the small size of plasma, the probing beam wavelength must be small (λ = 4 mm), thus a very high sensitivity interferometer is required in order to observe the lower density values. A low noise digital phase detector with a phase noise of 0.02° has been used, corresponding to a density of 0.5 × 1016 m-3. [ABSTRACT FROM AUTHOR]