George, Jeffrey A.

Go, David B.

NASA Technical Reports Server

1 
2014 Workshop on Thermionic Energy 
Conversion for Space and Earth 
Organizers: 
Jeffrey A. George   Prof. David B. Go  
EP/Propulsion and Power Division   Aerospace and Mechanical Engineering 
NASA Johnson Space Center   University of Notre Dame 
October 14-15, 2014 
NASA Johnson Space Center 
Houston, TX 
https://ntrs.nasa.gov/search.jsp?R=20140013147 2019-08-29T18:17:12+00:00Z
2 
Getting Started 
 
• Welcome 
• Introductions 
• Purpose, Goals, Objectives 
• Logistics 
• Discussion Guidelines 
• Agenda 
• Breakout Sessions 
• Reporting, Next Steps 
2014 Thermionic Workshop 
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Attendees 
2014 Thermionic Workshop 
Name Org Email
NASA/JSC (not traveling)
1 Jeff George NASA/JSC George, Jeffrey A. (JSC-EP311) <jeffrey.a.george@nasa.gov>
2 Jason Wolinsky NASA/JSC WOLINSKY, JASON J. (JSC-EP311) <jason.j.wolinsky@nasa.gov>
3 Eric Malroy NASA/JSC Malroy, Eric T. (JSC-ES411) <eric.t.malroy@nasa.gov>
4 Jonette Stecklein NASA/JSC Stecklein, Jonette M. (JSC-YX111) <jonette.m.stecklein@nasa.gov>
5 John Scott NASA/JSC Scott, John H. (JSC-EP311) (john.h.scott@nasa.gov)
6 John Alred NASA/JSC Alred, John W. (JSC-ES411) <john.w.alred@nasa.gov>
7 Paul Bailey NASA/JSC/Wyle BAILEY, PAUL S. (JSC-EP3)[WYLE INTEG. SCI. & ENG.] <paul.s.bailey@nasa.gov>
NASA/MSFC, JPL, U.S. Army, U.S. Air Force (traveling)
8 Mike Houts NASA/MSFC Houts, Michael G. (MSFC-ZP30) <michael.houts@nasa.gov>
9 Jean-Pierre Fleurial NASA/JPL Fleurial, Jean-Pierre (JPL-3464)[Jet Propulsion Laboratory] <jean-pierre.fleurial@jpl.nasa.gov>
10 Joshua Smith United States Army Research Laboratory Smith, Joshua CTR (US) <joshua.smith133.ctr@mail.mil>
11 Steve Fairchild AFRL/Wright Patterson Steven.Fairchild@us.af.mil
US Institutions (Academic & Commercial)
12 David Go University of Notre Dame David Go (dgo@nd.edu)
13 John Haase University of Notre Dame John Haase (jhaase1@nd.edu)
14 Timothy S. Fisher Purdue University tsfisher@purdue.edu
15 Terence Musho West Virginia University Terence.Musho@mail.wvu.edu
16 Robert Nemanich Arizona State University Robert.Nemanich@asu.edu
17 Franz Koeck Arizona State University franz.koeck@asu.edu
18 "Nick" Nicholas A. Melosh Stanford University nmelosh@stanford.edu
19 Tony Pan Invention Science Fund Tony Pan - Individual <tpan@intven.com>
20 William (Hank) Paxton IOP Technologies, LLC William Paxton <william.f.paxton@gmail.com>
Non-US Institutions (Academic & Commercial)
21 Alireza Nojeh University of British Columbia anojeh@ece.ubc.ca
22 Neil Fox University of Bristol neil.fox@bristol.ac.uk
23 Ian Bickerton University of Bristol Ian Bickerton <Ian.Bickerton@bristol.ac.uk>
24 Amit Tiwari Newcastle University, UK amit.tiwari@ncl.ac.uk
25 Jochen Mannhart Max Planck Gesellschaft J.Mannhart@fkf.mpg.de
26 Robin Wanke Max Planck Institute of Solid State Research Robin Wanke <R.Wanke@fkf.mpg.de>
4 
Workshop Announcement 
2014 Thermionic Workshop 
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Workshop Purpose & Goals 
Purpose:  In light of recent advances in materials, nanotechnology, and microfabrication, to 
bring together interested parties from government, academia, and industry to “restart the 
conversation” on using thermionic energy conversion for Space and Earth applications. 
 
Major Goals: 
• To foster a collaborative intellectual and research community in thermionic emission and 
energy conversion 
• To identify and describe promising applications and “need” 
• To identify rationale and recommendations for focused research 
• To communicate recommendations to stakeholders and policymakers 
• To have effected and advanced the realization and implementation of practical thermionic 
converters 
 
Workshop Topical Areas: 
• Applications, need, requirements, and historical development 
• New and emerging cathode and anode materials for high current density thermionic energy 
conversion (doped diamond, carbon nanotubes, barium oxide, etc.) 
• New and emerging form factors and designs for thermionic energy conversion devices 
(microfabricated structures, diode/triode configurations, photo-enhanced thermionic 
emission, etc.) 
• Testing and characterization apparatus and standards for material characterization, device 
performance and efficiency, and lifetime and robustness tests 
2014 Thermionic Workshop 
6 
Logistics 
• ISS Facility Badging, Rules 
– Visitors badge 
– Core hours 8:00am-5:00pm 
• Wireless 
• Emergencies 
• Break room 
• Restrooms 
• Lunch 
• Tuesday Dinner 
– Landry’s, Kemah Boardwalk 
• Saturn V? 
• Wednesday Dinner? 
• Space Center Houston? 
2014 Thermionic Workshop 
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Discussion Guidelines 
• Public meeting, information, discussion 
• International attendance 
• Export Control rules apply for US attendees 
– Limit discussions to cleared or publicly available info 
• Mind the clock (so we can cover as much ground as possible) 
– 30 min slots 
– ~20 min presentation 
– ~10 min Q&A, discussion 
 
2014 Thermionic Workshop 
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ROM Primary Focus 
2014 Thermionic Workshop 
Thermionic Energy Conversion for 
Space Missions  
Jeff George, NASA 
Michael Houts, NASA 
Jean-Pierre Fleurial, JPL 
Emerging Thermionic Emission 
Materials 
Tim Fisher, Purdue University 
Nicholas Melosh, Stanford University 
Terrence Musho, West Virginia University 
Steven Fairchild, AFRL 
Emerging Thermionic Energy 
Conversion Devices 
*Jochen Mannhart, Max Planck Institute 
*Alireza Nojef, University of British 
Columbia 
Joshua Smith, Army Research Lab 
Tony Pan, Invention Science Fund 
David Go, University of Notre Dame 
Diamond-Based Thermionic Energy 
Conversion  
Neil Fox, University of Bristol 
Hank Paxton, IOP Technologies 
*Robert Nemanich, Arizona State 
University 
Amit Tiwari, Newcastle University 
Commercial 
Academia 
Government 
*Breakout Session Leader 
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Agenda 
2014 Thermionic Workshop 
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Getting Started 
 
• Welcome 
• Introductions 
• Purpose, Goals, Objectives 
• Logistics 
• Discussion Guidelines 
• Agenda 
• Breakout Sessions 
• Reporting, Next Steps 
2014 Thermionic Workshop 
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Why Explore Mars? 
• Most similar planet to Earth. (though still different) 
• Compare Geography, Geology, Development History 
• Once had a warm, wet Climate.  (What happened?) 
• Did Life once exist?  (Or still exist?) 
• Humans Can Explore Mars. 
– Not too far or hot or cold, sunlight, gravity, resources 
• Humanity could Live there. (a second home to Earth) 
• Our Next Big Challenge! 
• What will we Learn? 
• What will we Invent? 
 
JSC Nuclear Systems Team 
12 
Mars: The Need for Speed… 
Increased Mission Duration       
  Increased Risk, Health Concerns, Consumables, Spares 
 
• Radiation 
– SPE 
– GCR 
– (Reactor) 
• Depressed Immune System 
• Bone Loss 
• Muscle Loss 
• Away from Family, Friends, Joys of Life 
• Mental Well Being / Morale 
• Catastrophic Environmental Events 
• System Failures (&/or massive redundancies/spares to mitigate) 
• Increased Food & Consumables load 
• <Good Thing  Power-rich can enable 3D printers to make spares, better/lighter ECLSS 
S/S’s, etc.> 
 
If we can’t find a way to break the 3.5 year Mars mission paradigm,  
we may never get to Mars. 
 
2014 Thermionic Workshop 
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Six Month Mars Mission: Case 1 Q-thruster 
• 2 month outbound leg (Earth SOI  Mars SOI) 
• 2 month Mars stay (orbital maneuver, EDL, Surface) 
• 2 month return leg (Mars SOI  Earth SOI) 
• 6 month Round Trip (Earth SOI  SOI) 
JSC Nuclear Systems Team 
Thrust Q-thr. Metric Power
(N) (N/kWe) (kWe)
2180 0.4 5450
2180 1 2180
2180 4 545
Feb 4 2031 
May 4 2031 
Opposition 
Apr 4 2031 
Jun 4 2031 
Aug 4 2031 
Copernicus runs by EG / Tim Dawn 
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Mars Vehicle Concepts 
2014 Thermionic Workshop 
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“Converter X” Design Ref. & Performance Goals 
~ Initial Working Concept for Thermionic Converter: 
• “Reasonable” unit scale, system quantity 
• 25mm x 25mm area 
• 20% system efficiency, 25% converter efficiency 
• 20 We / cm^2 
• 125 We converter 
• Voltage = 1-2 V 
• Current = 10-20 amps / cm^2 
• Thot = 1600-1800 K 
• Tcold = 900-1100 K 
• Gap = TBD 5-10, or 100 micro-m (0.01-0.1 mm vacuum vs. mag. assist) 
• Emitter Material/Surface = Nanostructured Tungsten w/ adsorbed BaO 
• Emitter Work Function = 2 eV 
• Collector Material/Surface = Doped diamond nano crystals 
• Collector Work Function = 1 eV 
• Other structural, insulating materials = Alumina 
• Space Charge Mitigation = Small vacuum gap, Magnetic assist, Cesium plasma 
• Design Approach, Morphology = tbd 
• Microfabrication Approach / Techniques = tbd 
2014 Thermionic Workshop 
X 
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“21st Century” Pathways for Improvement 
• New Emitter and Collector Materials with Lower Work Functions 
 
• Nano-fabricated Surface Topologies to Lower Work Functions 
 
• Microfabrication 
 
• New Converter Design / Topography Approaches to Reduce or 
Eliminate Space Charge Effects 
 
• Photon Enhanced Thermionic Emission (PETE) 
 
• Others? 
2014 Thermionic Workshop 
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Thermionic Conversion Applications 
SPACE POWER: 
• Nuclear thermal sources 
• Solar thermal sources 
• Others? 
 
 
TERRESTRIAL POWER: 
• “Topping” of fossil fuel plants 
• Energy harvesting / scavenging 
• Others? 
JSC Nuclear Systems Team 


2014 Workshop on Thermionic Energy Conversion for Space and Earth

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