The Development of a Pulsed Plasma Thruster as a Solid Fuel Plasma Source for a High Power Helicon Ian Kronheim Johnson A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science The University of Washington 2011 Program authorized to offer degree: Aeronautics and Astronautics University of Washington Graduate School This is to certify that I have examined this copy of a master’s thesis by Ian Kronheim Johnson and have found that is it complete and satisfactory in all respects, and that any and all revisions required by the final examining committee have been made. Committee Members: Professor Robert Winglee, Department of Earth and Space Sciences, Chair Professor Tom Jarboe, Department of Aeronautics and Astronautics Date: The University of Washington ii In presenting this thesis in partial fulfillment of the requirements for a master’s degree at the University of Washington, I agree that the Library shall make its copies freely available for inspection. I further agree that extensive copying of this thesis is allowable only for scholarly purposes, consistent with “fair use” as prescribed in the U.S. Copyright Law. Any other reproduction for any purposes or by any means shall not be allowed without my written permission. Signature: Date: The University of Washington iii University of Washington Abstract The Development of a Pulsed Plasma Thruster as a Solid Fuel Plasma Source for a High Power Helicon Ian Kronheim Johnson Chair of the Supervisory Committee: Professor Robert Winglee Earth and Space Sciences As space exploration shifts to lower mass and lower cost missions, the need for improved on-board propulsion systems is growing. The High Power Helicon (HPH) experiment at the University of Washington is one new possibility in this field. The HPH is currently gas-fed, which creates a number of added concerns during operation. For this reason, a Pulsed Plasma Thruster (PPT) was developed to act as a solid fuel source for the Helicon thruster. The PPT created was 50% smaller in size than the EO-1 satellite PPT [Zakrzwski] and produced electron densities on the order of 1018 m-3, 20 cm downstream of the Teflon surface at 43 J. The thruster had an estimated impulse bit of 138 µN-sec and a specific impulse of 1413 seconds while ablating 44 µg of Teflon per pulse at 4.4% efficiency. The HPH system currently uses a helicon antenna to ionize and accelerate the gas particles with high efficiency. Therefore, the objective of the PPT for the HPH operating system was to produce large numbers of neutral particles traveling at low to medium velocities. This is in comparison to most PPT investigations where higher efficiencies and thrusts are desired. The PPT was successfully fired under vacuum while operated with the HPH magnetic field and is ready to be fully integrated and tested with the HPH system. The University of Washington iv Table of Contents 1 Introduction..............................................................................................................................................1 1.1 Current Propulsion Concepts ...................................................................................................1 1.1.1 Electrostatic Propulsion.....................................................................................................2 1.1.2 Electromagnetic Propulsion.............................................................................................3 1.1.3 Electrothermal Propulsion................................................................................................5 1.1.4 Chemical and Electrical Comparison............................................................................7 1.2 High Power Helicon Thruster...................................................................................................8 1.3 Helicon Thruster Design..........................................................................................................10 1.3.1 Gas vs. Solid Fed Helicon Thruster.............................................................................11 1.4 Pulsed Plasma Thruster...........................................................................................................12 1.4.1 PPT Operation .....................................................................................................................13 1.4.2 PPT Plume .............................................................................................................................15 1.4.3 PPT Flight History..............................................................................................................16 1.5 Outline and Research Goals.................................................................................................... 19 2 Experimental Setup and Electronics Design............................................................................21 2.1 Vacuum System ...........................................................................................................................21 2.2 Control and Data Acquisition ................................................................................................22 2.3 Electronic Control Systems .................................................................................................... 23 2.3.1 Starter Power Processing Unit .....................................................................................23 2.3.2 Main Discharge Power Processing Unit ................................................................... 24 2.4 HPH Base Magnets .....................................................................................................................27 3 Diagnostics.............................................................................................................................................28 3.1 Stangenes Probe..........................................................................................................................28 3.2 Voltage Dividers and the High Voltage Probe ................................................................28 3.3 Langmuir Probes.........................................................................................................................29 3.3.1 Standard Double Probe Theory ...................................................................................30 3.3.2 Probe Construction and Description ......................................................................... 34 3.4 CCD Camera................................................................................................................................... 35 4 Theoretical Models and Data Reduction ...................................................................................36 5 PPT Iterations and Discussion....................................................................................................... 38 5.1 PPT-1................................................................................................................................................38 5.1.1 Spark Plug – PPTv1.0........................................................................................................ 38 The University of Washington v 5.1.2 Spark Wire – PPTv1.1 & 1.2...........................................................................................39 5.2 PPT - 2..............................................................................................................................................41 5.2.1 No Insulation - PPTv2.0................................................................................................... 41 5.2.2 Insulation - PPTv2.1..........................................................................................................42 5.2.3 Electron Density On-axis................................................................................................. 43 5.2.4 Plume Width.........................................................................................................................47 5.2.5 Predicted Electron Densities at 10 cm height........................................................54 5.2.6 Time-of-Flight Velocity Data .........................................................................................54 5.2.7 Mass Ablation Estimates................................................................................................. 57 5.2.8 PPT Performance Estimates..........................................................................................58 5.2.9 Effect of an Applied Magnetic Field............................................................................59 6 Summary.................................................................................................................................................63 7 Bibliography..........................................................................................................................................65 The University of Washington vi List of Figures Figure 1.1. An electrostatic gridded ion thruster schematic (left) [XIPS] and a xenon ion discharge from the NSTAR ion thruster (right) [Ion Propulsion]. .................................2 Figure 1.2. The MPD schematic (left) [Jahn and Choueiri] and (right) a NASA MPD thruster experiment in operation (right) [MPD: NASA Facts]. ...............................................4 Figure 1.3. The Hall thruster schematic (left) [Jahn and Choueiri] and a NASA Hall thruster firing with xenon propellant (right) [Electric Propulsion]. ....................................5