Space Radiation Environment Impacts on High Power Amplifiers and Solar Cells On-board ...

264 Pages·2015·4.21 MB·English

by  Whitney Lohmeyer

Space Radiation Environment Impacts on High Power Amplifiers
and Solar Cells On-board Geostationary Communications Satellites

Whitney Q. Lohmeyer, Kerri Cahoy

03 2015 SSL # 03-15

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Space Radiation Environment Impacts on High Power Amplifiers
and Solar Cells On-board Geostationary Communications Satellites

Whitney Q. Lohmeyer, Kerri Cahoy

03 2015 SSL # 03-15

This work is based on the unaltered text of the thesis by Whitney Q. Lohmeyer submitted to the
Department of Aeronautics and Astronautics in partial fulfillment of the requirements for the degree
of Ph.D. at the Massachusetts Institute of Technology.
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Space Radiation Environment Impacts on High Power Amplifiers and Solar
Cells On-board Geostationary Communications Satellites

by

Whitney Quinne Lohmeyer

Submitted to the Department of Aeronautics and Astronautics
On March 19, 2015 in Partial Fulfillment of the Requirements for the Degree of Doctor
of Philosophy in Aeronautics and Astronautics

ABSTRACT
Communications satellite operators maintain archives of component telemetry to
monitor system function. Operators generally do not typically use the telemetry data for
scientific analysis of the space radiation environment effects on component anomalies
or performance. We partnered with four geostationary (GEO) operators, acquired >1
million hours of telemetry, and combined these data with space weather observations to
investigate relationships between space weather and hardware performance.

We focused on the effects of space weather on two component types: solar cells and high
power amplifiers. For solar cells, by augmenting >20 years of GEO telemetry with
separate GEO space weather measurements, we calculated both on-orbit degradation of
Si and GaAs solar cells in an annual average sense, and also quantified the degradation
of cells during severe solar proton events (SPEs) of 10 MeV protons > 10,000 pfu. A
functional relationship between the amount of degradation and proton fluence is also
considered. We used the calculated degradation to evaluate several combinations of
space weather environment models with solar cell degradation models and found that
predicted performance is within 1% of the observed degradation. These models had not
previously been validated using multiple on-orbit GEO datasets. We did not find a model
pairing that consistently outperformed the others over all of the datasets.

For high power amplifiers, through the use of statistical analysis, simulations, and
electron beam experiments we conducted a root-cause analysis of solid state power
amplifier (SSPA) anomalies on-board eight GEO satellites. From the statistical
analysis, we identified that the occurrence of anomalies was not random with respect to
the space weather environment, but that there appeared to be a relationship to high-
energy electron fluence for periods of time between 10 – 21 days before the anomalies.
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From the simulations and electron beam lab tests, we demonstrated that internal
charging occurs in the amplifier chain, potentially identifying a cause for the observed
anomalies.

We substantiated an approach toward understanding space weather effects on space
components by obtaining and using long-duration archives of standard commercial
telemetry for scientific analysis. The analysis of large telemetry data sets of similar
components over long periods of time improves our ability to assess the role of different
types of space weather events in causing anomalies and helps to validate models. The
findings in this work that relate deep dielectric charging to component anomalies and
solar proton events to solar cell degradation make use of only a small fraction of the
potentially available commercial geostationary satellite telemetry. Expansion of this
work would provide additional insights on the role of space weather to the science
community and to the satellite design and operator community.

Thesis Supervisor: Kerri Cahoy
Title: Professor of Aeronautics and Astronautics

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Acknowledgments
I would first like to acknowledge and thank my advisor and role-model, Kerri Cahoy. I
aspire to one day be as successful as her. I would also like to thank my parents, Melody
and Bill Lohmeyer, for always being there for me, giving me perspective, and bringing
a smile to my face.

I would like to acknowledge my committee, Dan Hastings and Greg Ginet, and other
inspiring professors with whom I have worked or had conversations during my time at
MIT. I sincerely thank Inmarsat, Telenor and ARABSat, for their willingness to
contribute the telemetry data used throughout the entirety of this work, and specifically
Marcus Vilaca, Mark Dickinson, David Bath, the Satellite Operators. I would also like
to thank Dr. Fred DeJarnette, Dan Baker, Scott Messenger, Paul Bauer, Marilyn Good,
Beth Marois, and Hamza Baig.

Lastly, I would like to thank my friends and family. To name only a few of the many
who have provided support over the years – Raichelle Aniceto, Natalya Brikner, Ashley
Carlton, Todd Sheerin, Carolann Belk, Emily Brune, Emily Clements, Leonard
Bouygues, Abhi Butchibabu, Mark Sanchez Net, Annie Marinan, as well as The
Cheung’s (Zoe-Beth, Lilly-Rose, Zachary, Rowena, and Andrew).

Thank you.

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Outline
1. Introduction
1.1 Context
1.1.1 Importance of Geostationary (GEO) Communications Satellites (COMSATs)
1.1.2 Importance of Understanding Space Weather
1.1.2.1 Historical Effects of Space Weather
1.2 Identifying the Research Problem and Opportunity
1.2.1 Access to Space Weather Data and Satellite Telemetry
1.2.2 Commercial Satellite Telemetry
1.3 Problem Statements and Objective
1.4 Thesis Overview
1.5 High Level Review of Contributions
2. The Space Environment: Observations and Models
2.1 Solar Activity
2.1.1 The Solar Cycle
2.2 The Earth's Magnetosphere
2.2.1 Variability in Geomagnetic Activity: The Russell McPherron Effect
2.2.2 Particle Motion
2.2.2.1 The Ring Current
2.2.2.2 Particle Flux and Fluence Definition
2.2.3 The Van Allen Belts
2.2.3.1 Inner Van Allen Radiation Belt
2.2.3.1.1 High-Energy Protons
2.2.3.1.2 Energetic Electrons
2.2.3.1.3 South Atlantic Anomaly
2.2.4 Outer Van Allen Belt
2.2.4.1 High-Energy Electrons
2.2.4.2 GEO Environment
2.2.5 Galactic Cosmic Rays (GCRs)
2.3 Radiation Effects on Components
2.3.1 Total Ionizing Dose (TID)
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2.3.2 Spacecraft Charging
2.3.2.1 Surface Charging
2.3.2.2 Internal Charging
2.3.3 Single Event Effects
2.4 Space Radiation Environment Modeling Tools
2.4.1 Trapped Particle Models
2.4.2 Long-term Solar Particle Fluence Models
2.4.3 Total Ionizing Dose (TID) behind Aluminum Shielding
2.4.4 Low Earth Orbit (LEO) TID Environment and Radiation Requirements
2.4.5 The Modelled GEO Radiation Environment
2.5 Space Environment Indices
2.5.1 Kp Index
2.5.2 Disturbance Storm Time Index (Dst)
2.5.3 Auroral Electrojet (AE)
2.6 Space Weather Data Acquisition and Management
2.6.1 Sunspot Number Data
2.6.2 High-Energy Electron Flux Data
3. Assessment of Space Weather Observations
3.1 Context of this Analysis
3.1.1 Identifying Periods of Increased Activity
3.2 Analysis Approach
3.2.1 Solar Cycle Definition
3.2.2 Data Analysis and Use of Median Absolute Deviation
3.3 Results: Space Environment Baseline
3.3.1 Annual Median Values of the Space Environment Metrics and
Measurements between 1963 and 2012
3.3.1.1 Annual Median of the Kp Index
3.3.1.2 Annual Median of the Dst Index
3.3.1.3 Annual Median of the AE Index
3.3.1.4 Annual Median 10 MeV Proton Flux
3.3.1.5 Annual Median High Energy Electrons
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3.4 Solar cycle Phase Median Values of the Space Environment Metrics and
Measurements for Solar Cycles 20-23
3.5 Likelihood of Increased Activity in the Space Environment
3.5.1 Likelihood of Increased Kp Index over short time intervals
3.5.2 Likelihood of Increased Dst Index across short time intervals
3.5.3 Likelihood of Increased AE over short time intervals
3.5.4 Likelihood of Increased 10MeV Proton Flux Over Short Intervals
3.5.5 Likelihood of increased log (1.8-3.5 MeV Electron Flux) Over Short
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Intervals
3.6 Summary and Discussion of Space Environment Baseline
3.6.1 Kp Index Summary
3.6.2 Dst Index Summary
3.6.3 AE Index Summary
3.6.4 10 MeV Proton Summary
3.6.5 High Energy Electron Summary
3.6.6 Chapter 3 Closing Remarks
4. On-Orbit Solar Cell Degradation: Approach
4.1 Space-based Photovoltaic Power Systems
4.2 Solar Cell Performance Parameters
4.3 The Effects of Radiation on Solar Cells
4.4 Solar Array Degradation in Geostationary Orbit
4.5 Current Models of Solar Cell/Panel Performance
4.6 Analysis Approach
4.7 Solar Array Telemetry Acquisition and Radiation Environment Database
5. On-Orbit Solar Cell Degradation: Analysis
5.1 Annual Degradation of Solar Cells
5.1.1 Annual Degradation of Silicon Cells
5.1.2 Annual Degradation of Gallium Arsenide Cells
5.2 Solar Cell Degradation During SPEs
5.3 Solar Cell Degradation vs. Solar Particle Event Flux
5.4 Comparison of On-Orbit Measurements with Models for Computing Solar Cell
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Degradation
5.5 Analysis Approach for Quantifying Solar Cell Degradation
5.5.1 Model predictions of Si Cell I Degradation for a 15 year GEO mission with
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4 mils of coverglass
5.5.2 Comparison of Measured Si Cell I Degradation and Modeled Solar Cell
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Degradation for a Si Cell behind 4 mils of coverglass
5.5.3 Model predictions of GaAs Cell I Degradation for a 15 year GEO mission
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with 4 mils of coverglass
5.5.4 Comparison between On-Orbit Measurements and Models of GaAs Cell I
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Degradation behind 4 mils of coverglass
5.6 Comparison between On-Orbit Measurements and Models of GaAs Cell I
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Degradation behind 4 mils of coverglass and 2 mils of adhesive
5.6.1 Model predictions of Si Cell I Degradation for a 15 year GEO mission with
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4 mils of coverglass and 2 mils of adhesive
5.6.2 Comparison of On-orbit Si Cell I Degradation and Expected Modelled Solar
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Cell Degradation for a Si Cell behind 4 mils of coverglass and 2 mils of adhesive
5.6.3 Comparison of On-orbit Si Cell I Degradation and Expected Modelled Solar
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Cell Degradation for a GaAs Cell behind 4 mils of coverglass and 2 mils of
adhesive
5.6.4 Comparison of On-orbit GaAs Cell I Degradation and Expected Modelled
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Solar Cell Degradation for a GaAs Cell behind 4 mils of coverglass and 2 mils of
adhesive
5.7 Summary
6. GEO COMSAT Power Amplifiers: Context and Telemetry Data Description
6.1 SSPAs and TWTAs: Current capabilities and Future trends
6.1.1 Traveling Wave Tube Amplifiers (TWTAs)
6.1.1.1 TWTA Failure Mechanisms
6.1.1.2 Advantages and Disadvantages of TWTAs
6.1.1.3 TWTA Configurations
6.1.1.3.1 Flex-TWTAs and Reconfigurability
6.1.1.3.2 TWTA Linearization
6.1.1.3.3 Current TWTA Manufacturer/Supplier Capabilities
6.1.1.4 Future TWTA Technology
6.1.2 Solid State Power Amplifiers (SSPAs)
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