Figure 1. NanoFET-related activities.
The Air Force sponsors development of NanoFET thruster prototypes and investigation of associated physics..
Figure 2. Concept view of NanoFET
. Scalability is shown from the emitter (upper right: particles in reservoir not shown; lower right: cross-sectional view) up to the chip (upper left) and array (lower left) size scales.
An integrated NanoFET propulsion module is shown (lower left) taking up half the volume of a 1-unit cubesat.
Small spacecraft such as micro-, nano-, and pico-satellites are increasingly being used for low cost, rapid response, or distributed space missions.
To enable deployment of ever smaller and more versatile fleets of spacecraft, there is a logical progression toward in-space propulsion systems with high efficiency, small footprints, and low mass.
The Nanoparticle Field Extraction Thruster (NanoFET) electrostatically charges and accelerates pre-fabricated nano-particles for thrust.
Potential advantages of NanoFET as a micropropulsion system include:
- No ionization energy loss due to electrostatic charging
- High thrust-to-power at modest Isp for dynamic retasking
- Precise thrust control governed by piezoelectric feed system
- Flat-panel scalability and redundancy
- Self-neutralizing via bi-polar operations
- Environmentally stable propellants
- Cubesat platform compatibility
As shown conceptually in Figure 2, backpressure (e.g., from a constant-force spring) passively feeds the electrically conductive particle propellant in dry powder form towards a charging sieve.
There, particle aggregates are dispersed upon passage through the sieve with the aid of piezoelectric-induced inertial forces.
Individual particles undergo contact charging and extraction due to the electric field imposed between the charging sieve and the extractor gate.
The charged particles are then accelerated to the exhaust velocity by electric fields generated between the extractor and accelerator gate electrodes.
While NanoFET can operate with just a single gate electrode, having dual, stacked gate electrodes permits the charging and acceleration stages to be decoupled; such a setup enables voltage throttling of NanoFET without adversely impacting particle charging.
Individual emitters are arranged in a scalable planar array sized for the desired thrust range.
In conjunction with ElectroDynamic Applications, Inc., testing of the M1 micro-particle prototype demonstrated the feasibility of a piezoelectric-based particle feed system along with charging and acceleration of 1-10 µm particles.
An upgraded prototype (M2) is currently undergoing performance testing as a precursor to scaling down to nanoparticle propellant.
Figure 3. M1 proof-of-concept testing
. (Left) Laser velocimetry conducted inside the ultra-high vacuum (UHV) chamber. (Center) Representative emission seen with high-speed camera. (Right) Three M1s being prepared for vacuum integration.
Selected Relevant Publications
Liu, T., Peterson, P., Gallimore, A., Gilchrist, B, and Mirecki-Millunchick, J., "Nano-Particle Electrostatic Propulsion,"
JANNAF 4th Spacecraft Propulsion Subcommittee Meeting, Colorado Springs, CO, 3-7 May 2010.
Liu, T., Wagner, G., Gallimore, A., Gilchrist, B, and Peterson, P., "Mapping the Feasible Design Space of the Nanoparticle Field Extraction Thruster,"
IEPC-2009-004, 31st International Electric Propulsion Conference, Ann Arbor, MI, 20-24 September 2009.