Emission Characteristics of Passively Fed Electrospray Microthrusters with Propellant Reservoirs

Abstract

We present the characterization of a miniaturized ionic liquid electrospray thruster for Nanosatellite applications. The thruster investigated features an emitter array of 480 emitter tips per square centimeter and a 1 cubic centimeter propellant tank with an entirely passive propellant supply, and is operated at a power level of < 0.15W. The paper presents energy-, and mass-resolving beam spectroscopy of the packaged thruster system, as well as two independent thrust measurements. This allows to derive thruster performance parameters under realistic firing conditions, including individual thruster e ciency contributions, specific impulse and thrust. Total thruster e ciencies of 36%, specific impulse of ⇠ 760s, including all losses, and thrust of 11 12.5µN are presented, at emission currents of 150µA, for a device of ⇠ 1cm 2. Current emission data without current decay of ⇠ 90h is presented, with a maximum of 172h.

Space Propulsion Technology for Small Spacecraft

“…7 shows the throttling capability of selected EP systems, plotting the thrust and specific impulse as a function of input system power. The systems compared show the MIT iEPS system, which features constant specific impulse over the thrust and power range tested [57], the University of Washington VAT thruster that increases delivered impulse bit by increasing the pulsing frequency, the Busek BeP-220 Pulsed plasma thruster with similar operational properties compared to the VAT, the Busek BIT-3 ion thruster with linear specific impulse and thrust increase with increasing power [37], [67], and the Enpulsion IFM Nano thruster with variable thrust/power tradeoff for increasing specific impulse [58]. [67], 15 IFM Nano full system including neutralizer, Enpulsion/Fotec [58], [68].…”

“…While similar in terms of the engineering implementation, electrospray emitters operate by extracting charged particles from an ionic liquid propellant, capable of operating in the pure ionic mode, in which only ions and ions solvated to the n-th degree are emitted [42]. In current versions of thrusters with larger total emission currents achieved by multiplexing the number of emission sites, operation is typically in an ion-dropled mixed regime [57], in which droplets with lower charge-to-mass ratio particles are accelerated to lower exhaust speed, lowering the specific impulse but increasing the thrust produced.…”

An Overview of Cube-Satellite Propulsion Technologies and Trends

“…Their fundamental working mechanism is based on a process by which the conductive liquid surface of the propellant is deformed into a sharp cone-shaped meniscus called Taylor Cone; when a certain threshold of the electric potential is surpassed, ions are extracted from the cone's apex [94][95][96]. Electrospray thrusters accelerate positive or negative ions, respectively generating either a positive or negative ion beams thereby eliminating the need for an external cathode to neutralize the ejected ions unlike in plasma propulsion devices (ion and Hall thrusters) where an external cathode is essential [97].…”

“…Electrospray thrusters accelerate positive or negative ions, respectively generating either a positive or negative ion beams thereby eliminating the need for an external cathode to neutralize the ejected ions unlike in plasma propulsion devices (ion and Hall thrusters) where an external cathode is essential [97]. The propellants used for electrospray thrusters are usually ionic liquids, and their negligible vapor pressure serves as an advantage by resolving the need for propellant pressurization and helps with system miniaturization [96]. The schematic of an electrospray propulsion system is shown in Figure 7, and the major components comprise of propellant storage, emitter and extractor electrode.…”

“…The specific impulse observed in ionic regime is greater than in cone-jet regime [96]. A thruster is typically designed to operate in only one of the two regimes, and the regime defines the specific thruster: either a colloid thruster or a field emission thruster.…”