Scaling up the power of an electrospray microthruster

We report on the development of an electrospray (ES) microthruster that, by emitting fast nanodroplets, covers a wide range of specific impulse and thrust at high (>50%) propulsion efficiency. To achieve a useful thrust, many ES microthrusters must operate in parallel (multiplexing). The multiplexed electrospray microthruster (MES) is packaged in an alumina case that can operate at voltages up to ΔV = 7.56 kV and a reservoir pressure up to 5 bar. We compared nozzle arrays with 7, 37 and 91 capillaries (ID/OD = 10/30 µm). To ensure uniform flow through the various emitters, the hydraulic resistance was increased by filling the capillaries with 2.01 µm beads. The MES devices sprayed the ionic liquid ethylammonium nitrate. The 37-MES device covered a 2.6-fold range of specific impulse reaching 1870 s, and a 4.2-fold range of thrust up to 31.1 µN. The 91-MES device reached higher thrust, but it covered a narrower range. All devices operated stably for hours with modest current fluctuations. The beam cleared the electrodes, with no signs of erosion. The developed microthruster has already reached performances suitable for fine attitude control of microsatellites. Further scaling up by one order of magnitude would enable orbit change and station keeping for small satellites.