Investigation on operational stability of a pulsed plasma thruster with a pressure probe

The Pulsed Plasma Thruster (PPT) was the first electric propulsion device to be implemented on a spacecraft in orbit (Zond 2) in 1964. However, the pulse ignition mode and the shot-to-shot discharge differences introduce challenges into the evaluation of the performance of PPTs. This work performs impact pressure measurements on a coaxial PPT (Pulsed Electric ThRuster of the University of Stuttgart, PETRUS) using a pressure probe. It is aimed to examine two specific thruster performance values that conventional thrust stands cannot easily obtain: the transient behavior during the phase where the final propellant surface contour is established (i.e., the shot-to-shot difference for the impulse bit during this phase) and the initial operation stability for the lifetime test. The impact pressure difference was measured at various discharge voltages using the pressure probe. To test the thruster's operational stability, a 5000 shots burn-in experiment was conducted on PETRUS. During the operation, the impulse bit variations were measured over 5000 continuous shots using the pressure probe. From the results, the impulse bit curve of PETRUS first shows a trend of decreasing impulse bit (the initial several hundred shots) and then an increasing trend (after 300 shots). After 2151 shots, the thruster's operating condition reaches a steady state with an impulse bit of 144 μN s. Additionally, the reliability of the pressure probe measurement is also evaluated by comparing the results with those from a thrust stand. The results are in good agreement at higher discharge voltages (from 0.9 kV to 1.6 kV), the maximum measured impulse bit difference of the pressure probe over the thrust stand is 9.7%. These results provide a dynamic evaluation of the thruster's operational stability from an engineering aspect. Correspondingly, the comparison results between the pressure probe and thrust stand is a preliminary verification of the pressure probe impulse bit measurement method in this work.