A thruster for nanosatellites was entirely additively manufactured using a combination of 3D printing and hydro-thermal growth of zinc oxide nanowires. The thruster produces pure ions from the ionic liquids used to generate propulsion. The pure ions make the thruster more efficient than similar state-of-the-art devices, giving it more thrust per unit flow of propellant.
The thrust provided by the device, which is about the size of a dime, is minuscule. The force can be measured on the scale of a few tens of micronewtons, a thrust about equal to half the weight of one of the sesame seeds in a hamburger bun. But in the frictionless environment of orbit, a CubeSat or similar small satellite could use these tiny thrusts to accelerate or maneuver with fine control.
The miniaturized thruster operates electrohydrodynamically, producing a fine spray of accelerated, charged particles that are emitted to produce a propulsive force. The particles come from a sort of liquid salt called ionic liquid. The 3D-printed body holds a reservoir of ionic liquid along with a miniature forest of emitter cones coated with zinc oxide nanowires hydro-thermally grown on the cone surfaces. The nanowires act as wicks to transport the liquid from the reservoir to the emitter tips. By applying a voltage between the emitters and a 3D-printed extractor electrode, charged particles are ejected from the emitter tips.
The researchers experimented with printing the emitters in a type of stainless steel as well as a polymer resin. They were able to detect the pure ion jet using mass spectrometry, which can identify the composition of particles based on their molecular mass. Typically, an electrospray produced from ionic liquids would contain ions plus other species made of ions mixed with neutral molecules.
Producing a jet of pure ions means that the thruster can utilize more efficiently the propellant onboard and propellant efficiency is key for objects in orbit because refueling satellites is rarely an option. Electrospray designs can have many applications beyond space. The technique can emit not just ions but also things like nanofibers and droplets. The fibers could be used to make filters or electrodes for energy storage; the droplets could be used to purify seawater by removing brine.