The Design Space of a Micro/Nano-Particle Electrostatic Propulsion System.

The Nanoparticle Field Extraction Thruster (NanoFET) is a micropropulsion technology that electrostatically charges and accelerates micro- and nano-particles to generate thrust. Designed in a flat-panel configuration for scalability to different spacecraft power levels, NanoFET is anticipated to provide a large propulsive envelope capable of accomplishing a range of missions not currently possible with a single propulsion system. In addition, NanoFET also has potential applications as a generalized nano-particle accelerator for terrestrial uses in the fields of materials processing, environmental remediation, and biomedicine. Three key challenges facing NanoFET’s development are: 1. How can specific charge be controlled to meet propulsive performance targets with reasonable operating potentials? 2. How can inter-particle cohesive and particle-electrode adhesive forces be overcome to permit charged particle extraction? 3. How can technical and integration risk be mitigated to advance NanoFET’s technology readiness level? 2-D, axisymmetric, finite-element simulations were conducted of particles undergoing electrostatic charging in diode configurations. Maximum charging was obtained for extractor gate aspect ratios (i.e., gate orifice diameter to diode separation) less than unity and for emitter-to-emitter spacings greater than five particle diameters. Thin-shell particles are proposed as an attractive means of maximizing specific charge by reducing the effective particle mass density. Piezoelectrics were considered as an efficient means of applying inertial forces to aid with overcoming cohesive and adhesive forces, which are also mitigated by nanometer-scale surface coatings that increase the effective surface-to-surface separation. The piezoelectrics in NanoFET’s feed system are expected to set the characteristic time scale of thruster operations and provide for throttleable mass flow rates and precise impulse bits. Together with throttling the operating voltage, NanoFET is a variable specific impulse thruster (e.g., 100-900 s) with expectations of high thrust-to-power (e.g., > 1 mN/W) and thrust densities (e.g., ~1 mN/cm2) when used at modest specific impulses. Prototype micro-particle extractors are in the process of being tested for both dry and liquid-suspended propellants, the latter for terrestrial applications. Modeling and experimental results are promising and recommend NanoFET for continued development.PhDAerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/75863/1/liutm_2.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/75863/2/liutm_1.pd