Scale-Up Manufacturing and Evaluation of All-metal FEEP/Colloid emitter arrays

1. Scale-Up Manufacturing and Evaluation of All-metal FEEP/Colloid emitter arrays Dr. Craig Friedrich Dr. Jeff Allen Dr. L. Brad King

2. Background and Motivation – Apply Experience and Proven Technology of Mechanical Micromachining Micromilling with 1um lateral x 4um vertical steps Liquid metal jet micromilled in moly – exit 100um Micromilling machine – rebuild to update stages and controls Optical metrology, nm vertical, sub-micron lateral 25um drilled hole and wire thru hair

3. Objective of Research – Mass Fabrication and Large Array Thrusters to Support Testing and Further Thruster Development Taylor cone emission site Micromachined molybdenum substrate with holes and well, tungsten wires inserted, tips chemically etched Single emitter needle Capillary flow of Liquid metal (FEEP) Or ionic liquid (Colloid) Goal is arrays of emitters that have predictable performance and low cost, one piece with no assembly, near net shape with PM, net shape with finish EDM if necessary. Electrochemically Etched Tungsten Emitter Tip

4. Technical Approach – Micromachining of Green Compact Molds and Compaction for Thruster Arrays and Further Thruster Development Green / sintered refractory metal, more complex green molding Touch-up EDM possible if needed Propellant Reservoir Propellant Reservoir Green / sintered refractory metal, easier complex green molding Schematic Only – Not to Scale

5. Technical Approach - Sintering of Compacted Nano / Micropowders • Nanopowder particles are 50 – 100 nanometers in size and have a specific surface area of several square meters per gram; • Michigan Tech has the capability to micromachine molds, produce green compacts, and sinter these powders creating nano / microporous thrusters for efficient indium wetting; • Robust fabrication process will allow further thruster development addressing refractory metal porosity (powder size), indium feed system (interior vs exterior feed, cone geometry), etc.

6. Anticipated Results • A repeatable process whereby FEEP/colloid thruster arrays can be produced quickly and inexpensively via mechanical microfabrication processes and whereby the performance of these thrusters can be established; • Develop a process and fabrication testbed whereby arrays of emitter tips can be manufactured for testing; • Use the fabrication testbed to determine how fabrication process variables affect thruster performance; • Use the fabrication testbed to determine how thruster geometry affects propellant flow and wetting; • Use the fabrication testbed to establish limits on size and number of emitters in an array, and the cost vs performance.