Electrokinetic pumping of liquid propellants for small satellite microthruster applications

For most orbital maneuvers, small satellites weighing less than 10 kg require propulsion systems capable of producing thrust in the micro-Newton to milli-Newton force range. At this scale, electrokinetic (EK) pumping offers a method to precisely meter liquid propellants under purely electrical control at pressures and flow rates well-suited for microthruster applications. After exploring a variety of materials and surface treatments for the electrokinetic pumping media, we have demonstrated EK pumping of anhydrous hydrazine using both packed-capillary and larger sintered-monolith pump designs. Hydrogen peroxide has proven difficult to directly pump electrokinetically, but we have shown the utility of delivering peroxide and other electrokinetically incompatible liquids indirectly using in-line reservoirs with fluidic isolation to separate the pump working fluid from the propellant. Directly- and indirectly-pumped propellants have been delivered to novel capillary microthrusters with integrated catalyst beds and plasma-formed micronozzle structures. Specific impulses up to 190 s have been shown for hydrazine in non-optimized capillary thrusters at a mass flow rate of 1.5 mg/s. Controlled thrust pulses with a maximum continuous thrust of 1.5 mN, minimum impulse bit of 7 μN-s, and average specific impulse of 110 s have been demonstrated with the electrokinetically pumped microthruster assembly.