Design and Development of a K-Band Microwave Electrothermal Thruster

Open Access
Author:
Mainwaring, Philip B
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 07, 2016
Committee Members:
  • Sven G Bilen, Thesis Advisor
  • Michael Matthew Micci, Committee Member
  • George A Lesieutre, Committee Member
Keywords:
  • microwave electrothermal thruster
  • electric propulsion
  • space propulsion
  • microwave plasma
  • plasma propulsion
  • resonant cavity
Abstract:
The microwave electrothermal thruster is an electric propulsion technology that has been under development at The Pennsylvania State University since the 1980s. Versions of this thruster have been constructed at 2.45 GHz, 7.5 GHz, 8 GHz, 14.5 GHz, 17.8 GHz, and 30 GHz. This thesis investigates a new 20-GHz thruster based on the 17.8-GHz thruster design. It incorporates new materials and coupling mechanisms in order to investigate their viability and effects on the thruster. Multiphysics modeling and analytical methods are used to design and predict the performance of the thruster. The goal of this work was to design and test a 20-GHz thruster with a specific impulse of 700 s for 100 W of microwave power with helium as a propellant. This work covers the design and simulation of the resonant cavity as well as the selection of new materials. It also details the simulation and prototyping of a new microwave component, a waveguide-to-coaxial transition that uses air as a dielectric. The work included testing of the new 20-GHz thruster with comparisons between the dielectric materials. It also included a comparison of the prototype waveguide transition with commercially available coaxial probes as a plasma coupling mechanism. Preliminary performance results are evaluated with helium as a propellant: 358 s of theoretical specific impulse and 4.28 mN of thrust were achieved with a mass flow rate of 1.22 mg/s. These performance figures were attained with 32 W of delivered microwave power. Ignition of an ammonia plasma was also demonstrated.