Effects of Propellant and Electrode Geometry on Pulsed Ablative Plasma Thruster Performance

Abstract

A performance level compatible with 30% thrust efficiency at 1500 s specific impulse at 1 mlb (4.45 mN) of thrust was demonstrated with the parallel rail pulsed ablative thruster using Teflon propellant. Parametric variations of interelectrod e spacing and included angle were performed. In addition, Teflon was replaced by other thermoplastics and was also seeded with 10% and 30% LiOH and InBr in an evaluation of alternative propellants. Both the conventional breech-fed and later side-feed electrode/propellant configurations were tested. With the same initial conditions it was shown that the breech-fed geometry yields higher thrust efficiency than the side-fed geometry because of the higher specific impulse generated (i.e., up to 5300 s using Teflon). Results of parametric studies indicate that, for high thrust/power and moderately high specific impulse, virgin Teflon propellant with an interelectrode spacing of 3.0 in. (7.62 cm) and zero degree interelectrode included angle in the side-fed configuration are best. A simple semiempirical analytic model is presented where it is shown that the broad range in performance characteristic of this device is related to the degree to which magnetoplasmadynamic and ordinary gasdynamic acceleration mechanisms can be made more or less dominant in the acceleration of the ablated propellant.