Discharge Frequency Modulation of Pulsed Plasma Thruster

Abstract

PPTs. Aston and Pless 14 have concluded that the life of a PPT is lim- ited by the ignition circuit. They have conducted tests to study the igniter plug deposition, erosion, and the manner in which the igniter plug is initiated. 14 The results of these tests indicate that inductive rather than resistive coupling of the igniter plug to the thruster cath- ode, and the use of a high-current, short-pulse-length trigger circuit, offer significant increases in igniter plug lifetime. However, their study was focused on increasing the lifetime of the spark plug, and no experiments were conducted to analyze the dependence of the discharge frequency of the PPT on the pulse duration of the spark plug. Burton and Turchi 8 have speculated that the exact conditions of igniter plasma should not directly affect the performance of the PPT because the energy and mass associated with this spark are much smaller than the corresponding values for the main discharge. However, they have stated that the actual mechanism by which the igniter starts the PPT discharge is not very well understood to date. The present study aims at understanding this dependence of the PPT discharge frequency on the pulse frequency of the spark plug, which can help in better understanding the role of the igniter plug in the discharge initiation of the PPT.