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       MEP thruster under a measurement microscope during alignment of 400 emitter needles and extractor apertures within 10 μm of center of the 40-μm-diameter apertures.
Above: MEP thruster under a measurement microscope during alignment of 400 emitter needles and extractor apertures within 10 μm of center of the 40-μm-diameter apertures.

Electrospray Propulsion

3D Micro-Needles for Microfluidic Electrospray Propulsion Systems

Cecile Jung-Kubiak
Advances in microfabrication capabilities are enabling the development of arrays of silicon electrospray needles for highly compact, integrated, scalable indium-fueled electrospray thrusters. The silicon emitters are patterned using gray-scale electron-beam lithography to write a complex 3-D resist exposure profile and etch mask, which are etched using Deep Reactive Ion Etching (DRIE) techniques. A silicon-pyrex heater is bonded under the array, and is used to melt the propellant, indium, that is deposited onto the emitters.

The thruster assembly also includes an extractor electrode, high-voltage isolator, propellant management device loaded with Indium for replenishment and an assembly structure. Kilovolts are applied between the needles and the extractor with apertures aligned to the needle tips. This is to deform the indium into a liquid cone at the apex of the needles and then extract and accelerate ions to tens of thousands of meters per second to create thrust.

The MEP technology is highly compact, with microfabricated components, a capillary-force-driven feed system, and solid high-density indium metal propellant that are all integrated into the thruster head for a highly distributable propulsion architecture. This technology would provide both primary propulsion and attitude control to enable interplanetary CubeSats and CubeSats for Earth orbit with much greater orbit maneuvering capabilities than large spacecrafts. CubeSat swarms with MEP could be released to characterize asteroids; CubeSats with MEP could return samples from Mars.

Study results suggest that MEP could precision point exoplanet observatories to 40 times better precision than that of the Hubble Space Telescope, which is currently state of the art in pointing precision. They would enable eliminating reaction wheels, vibration isolation hexapods and hydrazine thrusters to off-load them. They will have the capability to operate continuously for years using only hundreds of grams of indium propellant. The high-voltage power-processing units are under development to integrate with single or multiple thrusters on 10x10 cm. It would operate at a specific impulse of > 5000’s to enable 1000 m/s of delta-v capability on a 3U CubeSat with only 60 grams of indium in a volume less than 10 cm3.

Dr. Jung-Kubiak is a microdevices engineer and a member of the E-beam Technologies group. Her research interests include the development of silicon micromachining techniques for ultra-compact submillimeter and THz systems, along with the development of novel micro propulsion systems. She received her PhD from France and joined JPL as a NASA postdoctoral fellow in 2010. She was the recipient of JPL’s Outstanding Postdoctoral Research award in 2011 and the prestigious Lew Allen award in 2018.

        MEP thruster on a micronewton thrust stand in a 2-meter-diameter vacuum chamber for testing. Inset: 100-micronewton prototype MEP thruster in a thermal shield.
MEP thruster on a micronewton thrust stand in a 2-meter-diameter vacuum chamber for testing. Inset: 100-micronewton prototype MEP thruster in a thermal shield.
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