A Planar Array of Micro-Fabricated Electrospray Emitters for Thruster Applications

Abstract

This paper reports the design, fabrication, and experimental characterization of a planar array of micro-fabricated electrospray emitters intended for space propulsion applications in micro–satellites. The engine uses the ionic liquid EMI-BF <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$_4$</tex> as propellant. Electrospray engines take advantage of the electrohydrodynamic effect known as Taylor cone to produce thrust. The array is designed with an open architecture and it is composed of a set of spikes, i.e., emitters, coming out from a propellant pool. There are two configurations for the emitters: fully sharpened slender emitters, i.e., pencils, and truncated pyramidal emitters, i.e., volcanoes. The arrays have between 4 and 1024 emitters in an active area of 0.64 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$ cm^2$</tex> . The surface of the engine (tank and emitters) is covered with “black silicon” that acts as wicking material. The micro-fabrication of the engine is described. The paper reports experimental characterization of the hydraulics system including wettability tests, current/emitter–voltage characteristics, and imprints of the exit stream on a collector. Preliminary results demonstrating the feasibility of obtaining substantially larger emission currents at the same extraction voltage by controlling the temperature are also reported. The paper compares the experimental current/emitter–voltage characteristics with relevant theories of field emission of electrons.1433