Experimental diagnostics for thermal pulsed plasma thrusters

Summary form only given. Although solid propellant pulsed plasma thrusters (PPTs) were developed and flown on small satellites two decades ago, further development of PPTs is needed for orbit control of communication satellites and for attitude control satellites. An advantage to these devices is their simplicity, since they do not require propellant storage or feed systems. However, the efficiency of early generation PPTs was only 6%. Subsequent analysis has suggested that thermal processes are more influential than electromagnetic forces in the acceleration of the plasma propellant. The research presented in this paper concentrated on the diagnostics of the thermal performance of PPTs each of which consisted of a conical cavity machined into a plastic-insulated coaxial configuration. A PPT experimental setup was designed, fabricated and used to investigate the effects of discharge energy, nozzle design, and propellant constituents. A capacitive discharge circuit provided a 7-to-11 kilovolt, 6 microsec energy pulse to the thruster with the driving voltage and current waveforms digitized at 50 MHz. A high-speed framing camera imaged the plasma behavior within a vacuum test cell at 1 microsec increments. A dual-beam acousto-optically-modulated Mach-Zehnder interferometer provided phase shift and electron density information while also giving accurate velocity measurements of the plasma emerging from the PPT nozzle. Time-resolved spectroscopic data was also recorded.