Scale-Up Manufacturing and Evaluation of

All-metal FEEP/Colloid emitter arrays

Dr. Craig Friedrich

Dr. Jeff Allen

Dr. L. Brad King

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

Optical metrology, nm vertical, sub-micron lateral

25um drilled hole and wire thru hair

Micromilling machine – rebuild to update stages

and controls

Objective of Research – Mass Fabrication and Large Array Thrusters to Support Testing and Further Thruster Development

Taylor cone emissionsite

Single emitterneedle

ElectrochemicallyEtched Tungsten Emitter Tip

Capillary flow ofLiquid 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.

Micromachined molybdenum substrate with

holes and well, tungsten wires inserted, tips chemically etched

Technical Approach – Micromachining of Green Compact Molds and Compaction for Thruster Arrays and Further Thruster Development

Propellant Reservoir

Green / sintered refractory metal, more

complex green molding

Propellant Reservoir

Green / sintered refractory metal, easier complex green molding

Schematic Only – Not to Scale

Touch-up EDM possible if needed

Technical Approach - Sintering of Compacted Nano / Micropowders

Material Rel. Density

Rel. Resistivity

Rel. Therm. Cond.

Rel. Therm. Exp.

Sinter Temp C

Sinter time (min.)

Molybdenum 1 2.48 2.4 1.07 2050 120

Tantalum 1.62 1.01 1 1.4 2400 480

Tungsten 1.87 1 3.01 1 2350 480

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.

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.