Characterization of direct current discharge based electric microthrusters

A thesis submitted in fullment of the requirements for the degree of Doctor of Philosophy School of Physics to the Faculty of Science, University of the Witwatersrand, Johannesburg, March 2017.In this work, a novel electrostatic microthruster concept, based on a direct current gaseous discharge, is proposed. The design draws inspiration from the previously developed CorIon system, which utilizes a coupling of the corona ionization mechanism and the acceleration mechanism. The new design is an attempt to develop a space propulsion system for use on microsatellites, such as CubeSats. A proof of concept system is tested to determine if the direct current discharge can be used as a plasma generator for use in electric space propulsion systems. A system representative of the proposed microthruster concept is tested to determine if it operates in a way that will generate thrust, and boundaries on the systems stable operating parameters are ascertained. Lifetime, re- peatability and erosion tests are performed on both the proof of concept system, and the microthruster design to determine if the system is an improvement on the CorIon system. A thrust measurement stand is designed and constructed that utilizes a novel magnetic coupling mechanism to measure the thrust produced by a microthruster. The thrust measurement stand is tested with a cold gas thruster to study the thrust stands repeatability characteristics, and if it produces the expected results for such a system. A theoretical model for the thrust measurement stand is developed, so that the output of the thrust stand can be predicted for various loading conditions. Thrust measurements are performed on the microthruster design as different operating parameters are varied. Measurements of the power used by the microthruster design are taken as different op- erating parameters are varied. Ion current density measurements of the microthruster design are performed as different operating parameters are varied. Ion current density distribution measurements of the microthruster design are performed. Simulations of the microthruster design are developed, using COMSOL Multiphysics, to con rm the hypothesized mechanism of operation of the microthruster design, and to explain the trends observed in experimental data. Two types of simulation are constructed: a base case, where general features in the physical quantities extracted from the simulations are discussed, and simulations where operating parameters are varied, to study the effects these parameters have on the extracted physical quantities. Thrust values are extracted from the simulations and compared with the experimentally measured thrust. Future research to be conducted involving the novel microthruster design is listed.LG201