DTIC ADA516394: Charging Effects on Fluid Stream Droplets for Momentum Exchange Between Spacecraft

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21-01-2010 Doctoral Thesis
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Charging Effects on Fluid Stream Droplets for Momentum Exchange Between 5b. GRANT NUMBER

Spacecraft

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S) 5d. PROJECT NUMBER
Thomas B. Joslyn (University of Colorado)

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50260542
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AANirD F AoDrcDeR REeSsSe(aErSc)h Laboratory (AFMC)
AFRL/RZSA AFRL-RZ-ED-TP-2010-027
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Approved for public release; distribution unlimited (PA #10048).

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For submission to the Graduate Faculty of the University of Colorado at Colorado Springs, CO.
14. ABSTRACT

This dissertation presents the results of research on a novel satellite propulsion concept that relies on the constant transfer of
momentum through projection of silicon oil droplet streams through space. The system is primarily applicable to satellites flying
side-by-side in formation that require a constant distance between them in order to conduct certain missions such as
interferometric synthetic aperture radar observations. Rational for selection of the silicone oil DC705 as the best working fluid is
presented. Droplet size, velocity, and spacing needed for station keeping of various satellite mass and separation distance
combinations is evaluated. Droplet streams of diameters demonstrated in this study and speeds demonstrated in past research can
satisfy propulsion needs of reasonably sized satellites in any earth orbit with at least a kilometer of separation. A continuous
droplet stream system requires an order of magnitude less mass than comparable electric propulsion systems and two orders of
magnitude less power. The focus of this study is droplet charging in space due to various mechanisms associated with ambient
plasma and photoemissions.
15. SUBJECT TERMS

16. SECURITY CLASSIFICATION OF: 17. LIMITATION 18. NUMBER 19a. NAME OF RESPONSIBLE
OF ABSTRACT OF PAGES PERSON
Dr. Andrew Ketsdever
a. REPORT b. ABSTRACT c. THIS PAGE 19b. TELEPHONE NUMBER
SAR 196 (include area code)
Unclassified Unclassified Unclassified N/A
Standard Form 298 (Rev. 8-98)

Prescribed by ANSI Std. 239.18
CHARGING EFFECTS ON FLUID STREAM
DROPLETS FOR MOMENTUM EXCHANGE
BETWEEN SPACECRAFT
by

THOMAS B. JOSLYN

A dissertation submitted to the Graduate Faculty of the

University of Colorado at Colorado Springs

in partial fulfillment of the

requirements for the degree of

Doctorate in Philosophy

Department of Mechanical and Aerospace Engineering

2009
ii

Copyright 2009, Thomas B. Joslyn.
All Rights Reserved.
iii

This dissertation for Doctorate of Philosophy degree by
Thomas B. Joslyn
has been approved for the
department of Mechanical and Aerospace Engineering
by

__________________________
Andrew Ketsdever, Chair

__________________________
Scott Trimbolli

__________________________
James Stevens

__________________________
Linda Krause

__________________________
Steven Tragesser

_____________
Date
iv

Abstract
This dissertation presents the results of research on a novel satellite propulsion concept that relies
on the constant transfer of momentum through projection of silicon oil droplet streams through space. The
system is primarily applicable to satellites flying side-by-side in formation that require a constant distance
between them in order to conduct certain missions such as interferometric synthetic aperture radar
observations. Rational for selection of the silicone oil DC705 as the best working fluid is presented.
Droplet size, velocity, and spacing needed for station keeping of various satellite mass and separation
distance combinations is evaluated. Droplet streams of diameters demonstrated in this study and speeds
demonstrated in past research can satisfy propulsion needs of reasonably sized satellites in any earth orbit
with at least a kilometer of separation. A continuous droplet stream system requires an order of magnitude
less mass than comparable electric propulsion systems and two orders of magnitude less power.
The focus of this study is droplet charging in space due to various mechanisms associated with
ambient plasma and photoemissions. Droplet charging is modeled analytically and numerically, primarily
with the in-space material charging software called NASCAP. Predicted low earth orbit (LEO) charging is
less than a few volts relative to the ambient plasma. Droplets in GEO charge slightly positive in the sun and
slightly negative in eclipse during nominal geomagnetic conditions. During high geomagnetic activity,
droplets in GEO reach several kilovolts negative potential, which is sufficient to induce Coulomb break-up.
Eclipsed polar orbiting droplets reach negative charge potentials of -26V. Lorentz forces will impair droplet
collection in the GEO and polar environments but can be mitigated by producing larger droplets and using
faster transit speeds between satellites.
A numerical model was developed to simulate droplet stream dispersion caused by electric fields
acting between charged droplets. This dispersion can be abated substantially by increasing droplet spacing,
which is possible using solenoid valve technology evaluated in laboratory testing. Laboratory charging of
DC705 using an extreme ultraviolet lamp in vacuum was conducted. Droplet charge potentials measured in
more than 200 experiments were within 4% of NASCAP photoemission simulation predictions. This close
correlation indicates that the DC705 material properties determined in this study and the NASCAP
algorithm are appropriate for prediction of photoemission charging of DC705.
v

Acknowledgements

Credit for devising the concept of using fluid stream propulsion to maintain a set distance between
side-by-side formation satellites belongs to two individuals at the University of Colorado. Dr. Steve
Tragesser realized the need for such a propulsion system and Dr. Andrew Ketsdever realized that
momentum transfer with fluid streams could satisfy that need.
Many individuals contributed to my pursuit of identifying and then analyzing the challenges
associated with this topic. My advisor Dr. Andrew Ketsdever provided guidance and instruction every step
of the way, with both this topic and a previous one that proved to be a dead end. Taylor Lilly has also
provided technical support and advice with both topics and helped troubleshoot problems from computer
code to vacuum chamber components. Dr. Linda Krause of the Physics Department at the U.S. Air Force
Academy was very helpful with charge modeling and learning to use NASCAP. Dr. Victoria Davis at SAIC
was also helpful in understanding the capabilities, limitations and intricacies of NASCAP.
Several research assistants have also helped me at various times: Jeff Atkinson with droplet
generation, Jordan Olliges with Labview and with my previous topic, Barry Cornell with vacuum chamber
operation, Sean Hammerlan with high-speed camera operation, and Shawn Laabs with Thermal Desktop.
Ron Wilkinson, Calvin Roberts and Steve Jernigan provided the advice and skill needed to build and
operate dozens of components and instruments for various experiments.
My work was supported by two organizations within the Air Force: The Astronautics Department
at the Air Force Academy sponsored my PhD slot and I am very grateful to General (ret.) Mike DeLorenzo
and Col Martin France who allowed me the opportunity to pursue it. Air Force Research Lab (Propulsion
Directorate: Advanced Concepts Division) provided funding for the equipment and materials needed to
carry out experimentation in this study.
My deepest debt of gratitude is to my family, especially my two sons, Ben and Taylor, who have
sacrificed countless irreplaceable hours of quality time with Dad and endured many boring weekend hours
in the lab “with” Dad. Your love, support and patience is truly appreciated!
vi

Table of Contents

CHARGING EFFECTS ON FLUID STREAM DROPLETS FOR MOMENTUM EXCHANGE
BETWEEN SPACECRAFT i
Abstract iv
Acknowledgements v
Tables ix
Figures x
Chapter 1: Introduction and Related Research 1
A. Motivation for Tandem Satellites 2
B. Fluid Selection and Droplet Generation 4
C. System Performance and Comparison with Ion Engines 8
D. Summary of Non-Charging Impediments to Droplet Stream Propulsion 12
E. Relevance of Droplet Charging to Droplet Stream Propulsion 13
Chapter 2: Analytic Models of Charging of Droplets in Space 14
A. Characterizing the LEO and Auroral Charging Environments 14
B. Characterizing the Geosynchronous Charging Environment 21
C. Space Charging Theory 23
D. Space Charging Theory Applied to Silicone Oil Droplets 29
E. Droplet Charge Prediction by Analytic Methods 32
F. Properties Affecting Secondary Emission of Electrons 39
G. Photoemission of Electrons in DC705 48
Chapter 3: Numerical Charging Simulations 51
A. NASA Charging Analyzer Program (NASCAP) Limitations 52
vii

B. Material Properties in NASCAP 55
C. Results of GEO Simulations 61
D. Results of LEO and Auroral Simulations 69
E. Summary of Droplet Charging in LEO, GEO, and Auroral Environments 76
Chapter 4: Effects of Electric and Magnetic Fields on Droplet Motion 79
A. Small Charge Induced Drift Forces Considered 79
B. Lorentz Forces Caused by Earth’s Magnetic Field 82
C. Charge Induced Droplet Breakup 86
D. Electric Field Forces Acting Between Droplets 88
E. Droplet Drift Due to Electric Field Interactions 90
F. Computer Simulation of Electric Field Induced Droplet Dispersion 93
G. Plasma Damping of Electric Fields between Droplets 97
Chapter 5: Droplet Charging Experimentation 101
A. Experimental Method and Setup 101
B. DC705 Capacitor Charging Experiment Setup 106
C. Droplet Charging and Deflection Experiment Setup and Method 111
D. Droplet Charging Experimental Results 114
E. Comparison of Experimental Results to NASCAP Results 119
F. Comparison of Experimental Results to SimIon Simulation Results 120
Chapter 6: Conclusions and Recommendations 123
Appendix 1: Tandem Satellite Propulsion Needs and Droplet Stream Capabilities 126
Appendix 2: Past Droplet Stream Research 132
Appendix 3: Heat Transfer Considerations for Fluid Stream Propulsion 136
viii

Appendix 4. Droplet Stream Formation 144
Appendix 5. Evaporation Losses and Additional Fluid Requirements 153
Appendix 6. Effects of Drag in LEO 156
Appendix 7. Effects of Solar Radiation Pressure 160
Appendix 8. Effects of Atomic Oxygen on Candidate Fluids 162
Appendix 9: Optimization and Design Tools 164
Appendix 10: Lee Solenoid Micro Valve Specifications 167
Appendix 11: Photodiode Specifications and Output 170
Appendix 12: Droplet Dispersion Simulation Code (for Matlab) 173
Bibliography 177
References 178
ix

Tables

Table 1. Candidate LDR Fluids and their Properties at 20°C.6 ....................................................................... 5
Table 2. Low and High Altitude Auroral Environment Fontheim Parameters Used in this Study. ............... 20
Table 3. GEO Charging Environments Used in this Study. .......................................................................... 23
Table 4. DC705 Material Properties Selected for Use by NASCAP. ............................................................ 55
Table 5. Dielectric Constants and Strength of Select Materials and Silicone Oil.52 ...................................... 56
Table 6. Summary of Equilibrium Potentials (maximum sunlit surface and minimum eclipsed surface) and
Time to Reach Equilibrium in the Environments Analyzed .................................................................. 76
Table 7. Cyclotron Periods for 1mm Droplet at Several Voltage Potentials ................................................. 80
Table 8. Secondary Lorentz Force Drift Due to Transit Velocity ................................................................. 85
Table 9. Direction and Speed Stability of DC704 Droplet Streams. ............................................................. 90
Table 10. DC705 Capacitor Results. ........................................................................................................... 107
Table 11. Capacitance Change in Second DC705 Capacitor Experiment. .................................................. 109
Table 12. Droplet Diameter Statistical Results............................................................................................ 115
Table 13. Radiation Equivalent Biot Numbers for a 1mm Droplet ............................................................. 138
Table 14. Radiation from Fluid Stream Pairs at Similar levels of Thrust (100m Transit) ........................... 143
Table 15. Drift of Droplets due to Solar Radiation Pressure in 50 seconds ................................................ 160
Table 16. Notional Mission Parameters and Resulting Stream Propulsion Specifications .......................... 166