Plume Composition Measurements of a High-Emission-Density Electrospray Thruster

Abstract

An electrospray thruster designed for nanosatellites is introduced in this paper. The thruster has a compact size featuring a passive propellant transport method through the use of porous materials. Porous electrospray emitters with 1, 25, and 100 emission tips were fabricated using conventional machining techniques. The geometrical features of the emission tips were measured using a high-precision laser profilometer. Thruster prototypes fitted with different emitters were tested in a bipolar operation mode. The emission currents and voltage characteristics were studied, which demonstrated a wide range of operational voltage with relatively high emission currents. The maximum overall emission currents were and achieved using a 100-tip emitter at , and the maximum per-tip emission currents were and achieved using a 25-tip emitter at , respectively. Time-of-flight systems were used to characterize the mass and velocity distribution of the charged particles in the thruster plume, and the results suggest that the electrospray emission were highly ionic, containing mostly monomer ions and dimer ions. The thruster performance was conservatively estimated, with the thrust ranging from approximately 0.92 to , and the specific impulse ranging from 2733 to 5550 s. The maximum thrust per emission tip was approximately in a purely ionic emission regime, which is considerably high in this type of technology.