The presented research discusses the design, analysis, and testing of a low current, LaB6 heaterless hollow cathode for space propulsion applications. A heaterless design using LaB6 is chosen to reduce complexity and increase electrical power efficiency and robustness. Argon propellant is used due to its more favorable breakdown voltage characteristics compared to xenon.
An original model for the insert region plasma is derived by combining several analyses in literature. This model allows the simultaneous calculation of many plasma and thermal parameters in the cathode using only two completely unobtrusive measurements, and requires several assumptions which are common in hollow cathode research. The design of the cathode and its subsystems are presented in detail. No diagnostics were used in the cathode except direct voltage measurements in the power circuit.
A discussion of emitter poisoning and ignition behavior is presented. The cathode is characterized by measuring anode and keeper voltages as a function of anode current and propellant flow rate, with the cathode discharging directly to a flat metal anode. Results are consistent with those obtained by previous investigations of argon hollow cathodes. This data is used with the derived plasma model to calculate the dependence of various parameters on current and flow rate. A discussion of the spot-plume transition behavior is presented. Finally, insights and design improvements are discussed based on the experimental results. / Master of Science / In recent years, the space industry has seen rapidly accelerating growth due to the continuing advancement of technology. A critical area of spacecraft technology is the spacecraft’s propulsion system, which allows the vehicle to achieve and maintain its desired orbit or trajectory through space. One class of propulsion systems known as “electric propulsion” uses electrical power to accelerate the fuel of the spacecraft. These types of propulsion systems are far more efficient than traditional propulsion systems, which use chemical reactions to create thrust.
One of the main components of certain types of electric propulsion systems is the hollow cathode, which initiates and sustains the thruster operation. In this research, a hollow cathode with several non-conventional characteristics is developed and tested. First of all, standard hollow cathodes use a heater to bring the cathode up to operational temperature, but this design is heaterless which offers several benefits to the cathode and electrical power system designs. Secondly, the cathode uses a non-conventional choice of material for the “emitter”, which emits electrons when heated and allows the cathode to operate. Lastly, while typical electric propulsion systems use xenon for fuel, this cathode uses argon which has several benefits over xenon including cost.
An overview of electric propulsion is presented, as well as a new physics-based model of this type of cathode that allows useful calculations based on simple measurements. The design and test results of the cathode are discussed in detail, with several interesting and insightful behaviors that were noted during testing. Heaterless cathodes have the potential to improve the efficiency, cost, and weight of electric propulsion systems, and this research therefore contributes to an important field for the future of space exploration.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/93959 |
| Date | 20 September 2019 |
| Creators | Nikrant, Alex Warner |
| Contributors | Aerospace and Ocean Engineering, Adams, Colin, Scales, Wayne A., Srinivasan, Bhuvana |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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