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The Microwave Thermal Thruster and Its Application to the Launch Problem


Parkin, Kevin L.G. (2006) The Microwave Thermal Thruster and Its Application to the Launch Problem. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/T337-T709.


Nuclear thermal thrusters long ago bypassed the 50-year-old specific impulse (Isp) limitation of conventional thrusters, using nuclear powered heat exchangers in place of conventional combustion to heat a hydrogen propellant. These heat exchanger thrusters experimentally achieved an Isp of 825 seconds, but with a thrust-to-weight ratio (T/W) of less than ten they have thus far been too heavy to propel rockets into orbit.

This thesis proposes a new idea to achieve both high Isp and high T/W: The Microwave Thermal Thruster. This thruster covers the underside of a rocket aeroshell with a lightweight microwave absorbent heat exchange layer that may double as a re-entry heat shield. By illuminating the layer with microwaves directed from a ground-based phased array, an Isp of 700–900 seconds and T/W of 50–150 is possible using a hydrogen propellant. The single propellant simplifies vehicle design, and the high Isp increases payload fraction and structural margins. These factors combined could have a profound effect on the economics of building and reusing rockets.

A laboratory-scale microwave thermal heat exchanger is constructed using a single channel in a cylindrical microwave resonant cavity, and new type of coupled electromagnetic-conduction-convection model is developed to simulate it. The resonant cavity approach to small-scale testing reveals several drawbacks, including an unexpected oscillatory behavior. Stable operation of the laboratory-scale thruster is nevertheless successful, and the simulations are consistent with the experimental results.

In addition to proposing a new type of propulsion and demonstrating it, this thesis provides three other principal contributions: The first is a new perspective on the launch problem, placing it in a wider economic context. The second is a new type of ascent trajectory that significantly reduces the diameter, and hence cost, of the ground-based phased array. The third is an eclectic collection of data, techniques, and ideas that constitute a Microwave Thermal Rocket as it is presently conceived, in turn selecting and motivating the particular experimental and computational analyses undertaken.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Beamed energy propulsion; Directed energy propulsion; Launch problem; Microwave thermal; Thermal propulsion
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Aeronautics
Minor Option:Electrical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Culick, Fred E. C.
Thesis Committee:
  • Pullin, Dale Ian (chair)
  • Culick, Fred E. C.
  • Shepherd, Joseph E.
  • Barmatz, Martin B.
  • Hunt, Melany L.
  • Worden, Simon P.
Defense Date:26 May 2006
Record Number:CaltechETD:etd-06022006-160023
Persistent URL:
Parkin, Kevin L.G.0000-0003-4521-8559
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:2405
Deposited By: Imported from ETD-db
Deposited On:07 Jun 2006
Last Modified:20 Apr 2020 22:02

Thesis Files

PDF (Parkin-Thesis.pdf) - Final Version
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