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NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance.
This study was supported by Contract No. DTRA01-00-C-0001 between the National Academy of Sciences and the Defense Threat Reduction Agency. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the organizations or agencies that provided support for the project.
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THE NATIONAL ACADEMIES
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National Research Council
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COMMITTEE ON THERMIONIC RESEARCH AND TECHNOLOGY
TOM MAHEFKEY, Chair, Consultant,
Atlanta, Georgia
DOUGLAS M. ALLEN,*
Schafer Corporation, Dayton, Ohio
JUDITH H. AMBRUS,
Space Technology Management Services, Bridgewater, New Jersey
LEONARD H. CAVENY, Aerospace Consultant,
Fort Washington, Maryland
HAROLD B. FINGER, Consultant,
Chevy Chase, Maryland
GEORGE N. HATSOPOULOS,
Thermo Electron Corporation, Waltham, Massachusetts
THOMAS K. HUNT,
Advanced Modular Power Systems, Inc., Ann Arbor, Michigan
DEAN JACOBSON,
Arizona State University, Tempe, Arizona
ELLIOT B. KENNEL,
Applied Sciences, Inc., Cedarville, Ohio
ROBERT J. PINKERTON,
Spectrum Astro Corporation, Gilbert, Arizona
GEORGE W. SUTTON,
NAE, ANSER Corporation, Arlington, Virginia
Staff
DOUGLAS H. BENNETT, Study Director,
Aeronautics and Space Engineering Board
GEORGE LEVIN, Director,
Aeronautics and Space Engineering Board
ALAN ANGLEMAN, Senior Program Officer
ANNA L. FARRAR, Administrative Associate
BRIDGET EDMONDS (July 2, 2001, until December 27, 2001), Senior Project Assistant
MARY LOU AQUILO (June 12, 2000, until July 2, 2001), Senior Project Assistant
JAN BERGER (September 1, 2001 until October 26, 2001), Project Assistant
VIKTORIA HERSON (January 28, 2000, until June 12, 2000), Project Assistant
AERONAUTICS AND SPACE ENGINEERING BOARD
WILLIAM W.HOOVER, Chair,
United States Air Force (retired), Williamsburg, Virginia
A.DWIGHT ABBOTT,
Aerospace Corporation (retired), Los Angeles, California
RUZENA K.BAJSCY,
NAE, IOM, National Science Foundation, Arlington, Virginia
WILLIAM F.BALLHAUS, JR.,
NAE, Aerospace Corporation, Los Angeles, California
JAMES BLACKWELL,
Lockheed Martin Corporation (retired), Marietta, Georgia
ANTHONY J.BRODERICK, Aviation Safety Consultant,
Catlett, Virginia
DONALD L.CROMER,
United States Air Force (retired), Lompoc, California
ROBERT A.DAVIS,
The Boeing Company (retired), Seattle, Washington
JOSEPH FULLER, JR.,
Futron Corporation, Bethesda, Maryland
RICHARD GOLASZEWSKI,
GRA Inc., Jenkintown, Pennsylvania
JAMES M.GUYETTE,
Rolls-Royce North America, Reston, Virginia
FREDERICK H.HAUCK,
AXA Space, Bethesda, Maryland
JOHN L.JUNKINS,
NAE, Texas A&M University, College Station
JOHN K.LAUBER,
Airbus Industrie of North America, Washington, D.C.
GEORGE K.MUELLNER,
The Boeing Company, Seal Beach, California
DAVA J.NEWMAN,
Massachusetts Institute of Technology, Cambridge
JAMES G.O’CONNOR,
NAE, Pratt & Whitney (retired), Coventry, Connecticut
MALCOLM R.O’NEILL,
Lockheed Martin Corporation, Bethesda, Maryland
CYNTHIA SAMUELSON,
Opsis Technologies, Springfield, Virginia
WINSTON E.SCOTT,
Florida State University, Tallahassee
KATHRYN C.THORNTON,
University of Virginia, Charlottesville
ROBERT E.WHITEHEAD,
NASA (retired), Henrico, North Carolina
DIANNE S.WILEY,
The Boeing Company, Long Beach, California
THOMAS L.WILLIAMS,
Northrop Grumman, El Segundo, California
Staff
GEORGE LEVIN, Director
Preface
Generating electricity from a heat source using no moving mechanical parts is the ultimate goal of the Defense Threat Reduction Agency’s thermionics program. However, developing thermionic energy conversion devices has proven difficult, although much progress has been made. In spite of initial success during the late 1960s and intermittent funding since that time, for a variety of reasons no thermionic system has yet been developed in the United States that can be used today on Earth or in space. The ability of human-kind to reach farther and farther into the solar system and beyond is determined, in part, by our ability to generate power in space for spacecraft use.
Thermionic energy conversion has been pursued since the advent of the space age by virtue of its intrinsic attributes as a compact, high performance space power system candidate. While the revolutionary missions that spawned interest in thermionics 40 years ago have yielded to an evolutionary approach to space utilization and exploration, potential future revolutionary missions prompt interest in maintaining and supporting development and examination of this potential technology option today.
Progress in the technology was substantial during the 1960s but waned in the early 1970s due to a shift in space technology funding priorities. The advent of the Strategic Defense Initiative (SDI) and space exploration initiatives in the late 1970s rekindled interest and investment in thermionics. However, that investment diminished again in the mid 1990s, not as a result of lack of progress, but because of changes in national technology investment priorities. Today, the thermionic technology base and infrastructure stand close to extinction. Only a modest $1.5 million to $3 million per year is directed toward sustaining the technology.
Two complete 5 kilowatt-electric nuclear reactor thermionic systems have been developed and flown in space by the former Soviet Union for experimental purposes, but no follow-up Russian or U.S. development on a high power thermionic system has taken place for a variety of reasons. Among them, the political nature of funding priorities involves decisions based on technology considerations, specifically concerning competing technologies that might accomplish the same system-level mission goals as thermionic systems.
The Committee on Thermionic Research and Technology started by asking a difficult question: In light of past efforts and the lack of apparent success in developing a fully functioning system and uncertain requirements, why do thermionics at all? This report is written to answer that question in view of potential future needs and applications while recognizing the existing technological risks as well as the currently available alternative power conversion technologies, in the context of the present, congressionally mandated, DTRA thermionics technology program (see Appendix A for the statement of task).
This study was sponsored by DTRA and was conducted by the Committee on Thermionic Research and Technology appointed by the National Research Council (see Appendix B).
This report has been reviewed by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the National Research Council’s Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the authors and the National Research Council in making the published report as sound as possible and to ensure that
the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. The committee wishes to thank the following individuals for their participation in the review of this report:
Henry W.Brandhorst, Jr., Space Power Institute, Auburn University,
Lee S.Mason, NASA Glenn Research Center,
Gerald D.Mahan, NAS, Applied Physical Sciences, and
Mohamed S.El-Genk, University of New Mexico, Institute for Space and and Nuclear Power Studies.
Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations, nor did they see the final draft of the report before its release.
The review of this report was overseen by Simon Ostrach, Case Western Reserve University. Appointed by the National Research Council, he was responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.
The committee also wishes to thank others whose efforts supported this study, especially those who took the time to participate in committee meetings and the thermionics workshop held in La Jolla, California.
Tom Mahefkey, Chair
Committee on Thermionic Research and Technology
Tables, Figures, and Boxes
TABLES
ES-1 |
Major Elements of the DTRA Thermionics Program, |
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2–1 |
Major Elements of the DTRA Thermionics Program, |
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3–1 |
Potential Missions for Solar and Nuclear Thermionic Power Systems, |
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3–2 |
Comparison of Flight Demonstrated Power Conversion Technologies, |
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3–3 |
Comparison of Ground Demonstrated Power Conversion Technologies, |
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3–4 |
Comparison of Projected Power Conversion Technology Capabilities, |
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C-1 |
Performance of Chemical and Electrical Propulsion Systems, |
FIGURES
3–1 |
Basic thermionic converter schematic, |
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3–2 |
A cross sectional view of a thermionic fuel element (TFE), |
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3–3 |
Solar thermionic output voltage based on emitter-collector spacing, |
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3–4 |
The current-voltage curve of a typical thermionic converter, |
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3–5 |
Power system options for specific mission durations, |
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3–6 |
Inverse specific mass versus electrical power output, |
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3–7 |
Increase in power density of a nuclear thermionic system as a function of temperature, |
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4–1 |
Artist’s rendition of the HPALM solar thermionic concept, |
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4–2 |
Artist’s rendition of a solar orbital transfer vehicle, |
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5–1 |
Cylindrical inverted multicell cross section, |
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5–2 |
Solar energy flux as a function of distance from the Sun, |
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7–1 |
Effect of emitter bare work function on performance, using computer code TECMDL, |
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7–2 |
Cesiated work function versus bare work function, |
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7–3 |
Effects of cesium oxide vapor on converter performance, |
BOXES