Pulsed Plasma Thrusters (PPTs) are one of the electric propulsions, classified into pulsed electromagnetic propulsions. They have been studied from early stage of space development (1960s). However, after then, the focus of the electric propulsion was on developing a primary propulsion, and research and development of PPTs subsided. However, in recent years, PPTs have attained a lot of attention again as microthrusters. Most PPTs, as below, use solid propellant as propellant; they are called ablation fed PPTs (APPTs).
Sequence of physical events for PPTs
First, a capacitor is charged to high voltage.
A ignitor plug is fired, and provides an initial plasma discharge.
The discharge sublimates and ionizes a part of Teflon.
A main discharge flow through the vaporized or ionized gas, which evaporates and ionizes a Teflon surface more.
Electromagnetic force, which are generated by the main discharge and the self induced field by it, accelerates the plasma between electrodes.
Advantages of APPTs are
engineering simplicity, causing high reliability
no need of storage tank and feed system.
Because of these advantages, APPTs have attained a lot of attention as microthrusters.
They, however, have the following disadvantages at a time.
poor propellant utilization efficiency, and then low thrust efficiency
low reliability of ignitor plug
The former is a serious problem, and it occurs by the following reason. Adjusting the amount of fed propellant in APPTs is very difficult, because APPTs are passively fed propellant by sublimation of Teflon. Especially, even after the main discharge, the temperature of the propellant surface remains still high, and sublimation of the propellant continues. Such a gas experiences no electromagnetic acceleration and has very low velocity. It causes the low thrust efficiency of APPTs. In our laboratory, in order to improve the efficiency, we suggest the use of liquid propellant instead of a solid.