EFFECT OF PROPELLANT TEMPERATURE ON EFFICIENCY IN THE PULSED PLASMA THRUSTER

A pulsed plasma thruster (PPT) benefits from the inherent engineering simplicity and reduced tankage fraction gained by storing the propella nt as a solid. The solid is converted to the gaseous state and acceler ated by an electric discharge across the propellant face. Previous res earch has concluded that as Little as 10 % of the consumed propellant is converted to plasma and efficiently accelerated. The remaining prop ellant is consumed in the form of late-time vaporization and particula te emission, creating minimal thrust. Critical to improving the PPT pe rformance is improving the propellant utilization. The present work de monstrates one possible method of increasing the PPT propellant effici ency By measuring the PPT thrust, propellant consumption, and propella nt temperature while varying the power level, duration of the experime ntal run, and total propellant mass, a correlation is established betw een decreased propellant temperature and increased propellant efficien cy. The method is demonstrated by performance measurements at 60 W and 5 W,which show a 25% increase in thrust efficiency, while the propell ant temperature decreases from 135 to 42 degrees C. Larger increases i n the efficiency may be realized on-orbit where operating temperatures are commonly subzero. The dependence of propellant consumption on tem perature also creates systematic errors in laboratory measurements wit h short experimental runs, and orbit analyses where the PPT performanc e measured at one power level is linearly scaled to the power availabl e on the spacecraft.