Performance Assessment of a Pulsed Thermionic Vacuum Arc Metal−Ion Thruster Through Direct and Indirect Thrust Measurements

This work investigates the propulsion performance of a metal−ion thruster based on thermionic vacuum arc (TVA) discharge operated in direct current (dc) and pulsed regimes using zinc (Zn) as solid propellant. The study focuses on the indirect estimation of thrust and its validation under dc operating conditions through comparison with direct thrust measurements performed under vacuum conditions. Indirect thrust evaluation was carried out using plasma diagnostics, including exhaust ion flux, plasma potential, beam divergence, and propellant consumption measurements. Direct thrust measurements under dc operating conditions were performed using weighing and pendulum deflection methods. The measured thrust ranged between 2 and 10 mN for an applied discharge voltage between 400 and 1000 V. The results showed that the thrust increased with discharge voltage due to enhanced plasma ionization and ion acceleration. For the same average discharge power (200–250 W), pulsed TVA operation produced, on average, slightly more than twice the thrust obtained during dc operation, indicating a higher thrust−to−discharge−power ratio. Under dc operating conditions, the indirectly estimated thrust values were in excellent agreement with those obtained using the two direct measurement methods, supporting the plasma−based thrust estimation methodology. The results demonstrate the capability of TVA discharges to generate propulsion forces in the mN range and indicate the potential of pulsed TVA systems as gridless metal−ion electric thrusters operating with solid propellant.