Specific charge control for micro/nano-particle electrostatic propulsion
Contact charging of micro- and nano-particles affords the Nanoparticle Field Extraction Thruster (NanoFET) flexibility to adjust its propellant's specific charge. This flexibility permits NanoFET to tune its propulsive performance by adjusting the charging electric fields and acceleration potential. Inherent to the NanoFET design are two features that govern the range of achievable specific charges: the gate electrode configuration (which sets the charging electric fields and the resulting particle charge) and the particle mass density. Electrostatic simulations for various gate electrode configurations were conducted in COMSOL Multiphysics® to provide general scaling relations for the acquired particle charge as a function of gate geometry (i.e., gate orifice diameter DG and inter-electrode gap H) and particle diameter d. The simulation results suggest that configurations with smaller gate aspect ratios (DG/H) provide greater charging and that the charging behavior is consistent until d/H is large and approaches unity. The benefits to performance and operations of using low density, and particularly hollow, particles were examined. Compared to solid gold particles, hollow ceramic particles with shell thicknesses that are 5% and 1% of their diameters have increased specific impulses of 5.3X and 11.5X, respectively. The use of low mass density or hollow particles gives NanoFET the potential for moderate specific impulse and high thrust-to-power performance.
