MTL Annual Research Report 2011

Electric Propulsion (EP) brings benefits for space missions requiring relatively large changes in satellite velocity, for example by reducing the propellant mass compared to traditional, less fuel-efficient chemical engines. Introducing EP in small satellites would enable them to perform interesting missions, such as long term attitude control/drag cancellation, orbital modification and, perhaps, deep space travel ^[1] . However, most EP technologies are challenging to miniaturize to the required levels, especially for nano/pico-satellites. Our group has developed an ion Electrospray Propulsion System (iEPS) as a candidate of an EP technology amenable for efficient miniaturization. The thruster core is based on a porous metal structure, which is bonded to an oxidized silicon package frame, followed by masking of the metal with a pattern of circles. The metal is then electrochemically etched in a regime that prevents material removal inside the pores, thus forming an array of porous tips ^[2] , as shown in Figure 1. To finalize the device, an extractor silicon grid with a matching array of holes and coated with a gold film is aligned and bonded to the frame holding the porous metal. Electrical isolation is provided by the bonding material and grown silicon oxide layers. A zero vapor pressure ionic liquid (the propellant) is then injected to the device from the back through a port in the silicon frame. The liquid wicks through the porous structure reaching the tips. Ion emission is the produced when applying a voltage of about 1kV between the metal and extractor grid. Figure 2 shows a typical I-V curve and a picture finished devices on a CubeSat ^[3] . A thruster pair should be able to produce 60-70 micro-N, enough to raise the orbit of a 1 kg CubeSat by 400 km in about 25 days of operation consuming 6-7 grams of propellant with 1W of power.