Progress Towards a Miniaturized Electrospray Thruster for Flexible Propulsion of Small Spacecraft

Abstract

Miniaturized electrical thrusters based on electrospray (or colloid) emitters could revolutionize the spacecraft industry by providing efficient propulsion capabilities to micro and nano satellites (1-100 kg). We report on our recent advances in the development of this technology within the MicroThrust (www.microthrust.eu) European consortium. We present the design and operation of the currently fabricated and next generation emitter arrays, describing their microfabrication process and measured performance. The emitters are out-of-plane internally fed capillaries micromachined in monolithic silicon. They are 100 µm tall and have an inner diameter of 5-10 µm. We operate the devices in both unipolar and bi-polar modes and find that the latest devices operate in a mixed regime, with the emitted spray a composition of ions and droplets. Their specific impulse is consequently in the few hundred seconds, highlighting the need for higher impedance, smaller emitters. Onset voltages are in the range of 800-850V for 200 µm inner diameter extractors, current levels for 19 emitter arrays of 2-3 µA. Preliminary analysis hints to plume half-angles of 35-40 • , although these values depend on the operation mode and beam composition. Nomenclature g Standard gravity (9.80665 m/s 2 )

Microfabricated emitter array for an ionic liquid electrospray thruster

“…One is applying positive and negative voltages alternately, 30) and the other is simultaneously operating two thruster units spraying in opposite polarities. 31) Moreover, the molecular weight of negative ions for typical ionic liquids is similar to that of positive ions. For example, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF 4 ) consists of EMI + with a molecular weight of 100.08 and BF 4…”

Study on the plume self-neutralization of ionic liquid electrospray thruster based on median potential

“…Various satellites in various earth orbits make up the spacebased infrastructure for daily travel, defense construction, weather forecasting, business intelligence and disaster recovery applications [1,2]. Small satellites are recommended for the building of the next-generation global internet due to specific impulse, precise thrust control, low acoustic noise, low power consumption, and reduced structural mass, making it ideal for small satellites [12][13][14][15]. Additionally, ILET generates bipolar particles and achieves self-neutralization of the plume by directly applying positive or negative high voltage to the emitter without external neutralizers [16][17][18].…”