1 Preliminary Thrust Characterization of the T-Series Hollow Cathodes for All-Electric Spacecraft

Abstract: This paper characterizes thrust performance of the T5 hollow cathode and a variant of the T6 hollow cathode modified for improved operational characteristics. Both forms of device display impressive propulsive performance and bring to light the potential for application as microthrusters. The T5 hollow cathode is shown to work in an almost purely electrothermal heating mode generating specific impulse as high as 427s with argon while operating below 100W. The variant on the T6 cathode is able to produce specific impulse of over 1050s with xenon and argon; however the acceleration mechanism at this performance is shown to be almost entirely electromagnetic effectively constituting a low power magneto-plasma-dynamic thruster. The T6 cathode also displayed very low discharge voltages ~12V and stable operation while carrying currents of 30-Amps and flow rates of less than 0.1mgs-1 down to a minimum of 0.04mgs-1 with xenon. This investigation highlights the importance of anode/keeper geometry in hollow cathode thruster design and indeed in all space based applications of hollow cathode. Nomenclature α = Degree of ionization A = Area, m2 amu = Atomic mass unit Cp = Specific heat capacity, kJ/kg.K d = Diameter, m εi = Ionization potential, eV e = Electron charge, C E = Electric field, V/m f = View factor I = Current, A J = Current density, A/m2 k = Boltzman’s constant, 1.381 × 10-23 J/K L = Characteristic length, m m = Particle mass, k