Investigation of a Micro- and Nano-Particle In-Space Electrostatic Propulsion Concept.

Abstract

A new electrostatic propulsion system that utilizes micro- and nano-particles is under development. At its core, multi-layer grids establish electric fields that charge and accelerate the particles. Before charging, the particles are transported to charging/accelerating zones from storage reservoirs. One method of transport delivers the particles suspended in liquid through microfluidic channels. Another method transports the particles through micro-sieves as a dry powder.

Advantages over current technologies include the ability to tune its operational parameters over a large range, elimination of life-limiting characteristics, and increased design flexibility. Note that other applications such as materials processing and nano-printing may also benefit from emitted high-energy particles.

This thesis investigates several limiting obstacles, which are associated with charging particles, extracting particles from liquids, and overcoming adhesion/cohesion of particles. The results provide new direction towards the final thruster design concept. Here, the obstacles under discussion include:

The ability to accurately charge the particles and to maximize their charge-to-mass ratios is investigated. Theoretical analyses and simulations suggest that restricting the maximum electric field at the particles’ surfaces is a necessary condition to avoid breakdown or field emission. With this constraint, spheres obtain greater charge-to-mass ratios than cylinders because they more uniformly distribute charge over their surfaces. Experimental results suggest that the charging models are reasonable under appropriate conditions.

When transporting particles in a liquid suspension, the ability to extract them with an electric force while preventing the liquid from becoming unstable is critical. Theoretical modeling and experimentation prove that both spherical and cylindrical particles can be extracted successfully. But, it may not be possible to extract particles smaller than the micron range without inducing an instability, which leads to the formation of Taylor cones and limits thruster performance.

When transporting and emitting dry particles, preventing particle adhesion/cohesion is important. Theoretical models developed here, which are supported by experimental results, suggest that an electric force can be use to overcome the adhesion of particles in the nanometer range. A functional micro-sieve thruster prototype capable of operating continuously has demonstrated the ability to overcome adhesion/cohesion in the micron range.