Vacuum Chamber Experiments of Beamed Microwave Energy Propulsion
Open Access
- Author:
- Nigay, Natalia
- Graduate Program:
- Aerospace Engineering
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- November 08, 2021
- Committee Members:
- Amy Pritchett, Program Head/Chair
Sven G Bilén, Thesis Advisor/Co-Advisor
Jesse Kane Mc Ternan, Committee Member - Keywords:
- beamed-energy propulsion
electric propulsion
advanced propulsion concept
vacuum chamber experiments
propulsion
spacecraft - Abstract:
- Traditional chemical propulsion is currently the only method to launch a vehicle into orbit, extracting energy from the combustion process to achieve necessary thrust. At this point in time, these systems have nearly maximized efficiency, making further advancements difficult and costly. Beamed-energy propulsion is one of the advanced concepts being explored to further advancement in propulsion systems with potential for space-launch applications. A beamed-energy propulsion device generates thrust by adding energy to heat a propellant via an external power source. In our system, this is microwave energy. There are several methods to transform the beamed microwave energy into thrust, with this research investigating the method of focusing a microwave beam onto a flow of supersonic nitrogen to generate a free-floating plasma that absorbs microwave energy and heats the propellant. Separating the energy source from the vehicle results in mass savings, and since beamed-energy propulsion does not rely on the limited energy stored in a propellant’s chemical bonds, it has the potential to increase efficiency over chemical rockets. Previous work on the beamed-microwave-energy propulsion thruster concluded with the design and construction of a converging--diverging nozzle capable of focusing continuous-wave microwaves to a point along its axis. Theoretically, electric breakdown of a supersonic flow of nitrogen will occur at the focal point, leading to the formation of a gaseous plasma a short distance behind the nozzle's throat. The focus of this research was to test this design inside of a vacuum chamber with the goal of igniting plasma to absorb the beamed microwave energy, heat the flow of nitrogen, and generate thrust at conditions that simulate high altitude flight. To prepare for testing inside of the vacuum chamber, design and construction of a horizontal thrust stand were completed, as well as calibration of the thrust stand, load cell, and pressure transducers. Once the experimental hardware---consisting of the thruster, sensors, propellant system, and microwave waveguides and antenna---was in place, cold flow tests were run to verify supersonic flow in the nozzle. Measurements of pressure and thrust were taken at eight different mass flow rates and plotted. The pressure distribution along the length of the nozzle did not show any pressure discontinuities to indicate a shock wave, so it was concluded that the design of the supersonic nozzle was sound. Once cold flow tests were complete, microwave-heated tests commenced to attempt to ignite plasma inside of the nozzle. Initial tests inputting microwaves into the vacuum chamber did not result in plasma ignition, so a plasma igniter ``spark plug'' was developed. The plasma igniter---a coaxial cable and metal lug acting as electrodes to ionize gas and get discharge---successfully induced breakdown when high voltage was applied. However, the plasma extinguished once voltage was removed, unable to be sustained by the available microwave energy. Attenuation in the waveguide system was measured by replacing the antenna with a power sensor, and revealed a 60% loss in power from the source to the input of the antenna. Potential prohibitive factors to microwave plasma ignition---namely the power loss throughout the waveguide system---were identified and addressed, with methods to decrease attenuation proposed.