National Aeronautics and Space Administration

DRAFT Space Power and Energy Storage Roadmap Technology Area 03

Valerie J. Lyons, Chair Guillermo A. Gonzalez Michael G. Houts Christopher J. Iannello John H. Scott Subbarao Surampudi

November • 2010 DRAFT This page is intentionally left blank

DRAFT Table of Contents Foreword Executive Summary TA03-1 1. General Overview TA03-1 1.1. Technical Approach TA03-2 1.2. Benefits TA03-5 1.3. Applicability/Traceability to NASA Strategic Goals, AMPM, DRMs, DRAs TA03-5 1.4. Top Technical Challenges TA03-5 2. Detailed Portfolio Discussion TA03-6 2.1. Summary Description and TA Breakdown Structure TA03-6 2.2. Description of TABS Elements TA03-6 2.2.1. Power Generation TA03-6 2.2.1.1. Energy Harvesting TA03-6 2.2.1.2. Chemical Power Generation TA03-7 2.2.1.3. Solar Power Generation TA03-9 2.2.1.4. Radioisotope TA03-9 2.2.1.5. Fission TA03-11 2.2.1.6. Fusion TA03-12 2.2.2. Energy Storage TA03-14 2.2.2.1. Batteries TA03-14 2.2.2.2. Flywheels TA03-15 2.2.2.3. Regenerative Fuel Cell Energy Storage TA03-16 2.2.3. Power Management & Distribution (PMAD) TA03-17 2.2.3.1. PMAD Overall TA03-17 2.2.3.2. Wireless Power Transfer TA03-18 2.2.3.3. Distribution & Transmission TA03-18 2.2.3.4. Conversion & Transmission TA03-19 2.2.3.5. Fault Detection, Isolation, and Recovery (FDIR) TA03-19 2.2.3.6. Management and Control TA03-19 2.2.3.7. Major Challenges TA03-19 2.2.4. Cross-Cutting Technology TA03-20 2.2.4.1. Analytical Tools TA03-20 2.2.4.2. Green Energy Impact TA03-20 2.2.4.3. Multi-Functional Structures TA03-21 2.2.4.4. Alternative Fuels TA03-22 3. Possible Benefits to Other National Needs TA03-22 4. Interdependency with Other Technology Areas TA03-23 Acronyms TA03-23 Acknowledgements TA03-23

DRAFT Foreword NASA’s integrated technology roadmap, including both technology pull and technology push strategies, considers a wide range of pathways to advance the nation’s current capabilities. The present state of this effort is documented in NASA’s DRAFT Space Technology Roadmap, an integrated set of fourteen technology area roadmaps, recommending the overall technology investment strategy and prioritization of NASA’s space technology activities. This document presents the DRAFT Technology Area 03 input: Space Power and Energy Storage. NASA developed this DRAFT Space Technology Roadmap for use by the National Research Council (NRC) as an initial point of departure. Through an open process of community engagement, the NRC will gather input, integrate it within the Space Technology Roadmap and provide NASA with recommendations on potential future technology investments. Because it is difficult to predict the wide range of future advances possible in these areas, NASA plans updates to its integrated technology roadmap on a regular basis.

DRAFT Executive Summary teams to develop critical technology needs for fu- The purpose of this study is to assess space pow- ture missions. The team considered the follow- er and energy storage technologies and formulate a ing missions of SMD that require advanced pow- roadmap (Figure R) and a Technology Area Break- er technologies: Jupiter/Europa, Saturn /Titan, down Structure (Figure 3 – discussed in more de- Neptune, Pluto System Missions; the NEO/Small tail in Section 2) which can guide NASA’s invest- body Missions: Comet Nucleus Sample Return, ments to assure the timely delivery of innovative the NEO SEP robotic mission; the Inner Plane- and enabling power and energy storage systems tary Missions: Venus Surface and Venus Sample for future space missions, while also providing Return missions; Mars Missions: Mars In-Situ Re- tangible products for aeronautical and terrestrial source Utilization (ISRU), Mars Plane, Surveyor applications. and Mars Network Landers. The ESMD missions The state of practice power systems are heavy, that require advanced power technologies are: bulky, not efficient enough, and cannot function crewed HEO mission, long duration EVA’s, astro- properly in some extreme environments. The pro- naut suits, crewed NEO SEP/NEP missions and posed power technology will provide power sys- Mars missions. The Space Operations Mission Di- tems with significant mass and volume savings (3 rectorate requires advanced power technologies to to 4X), increased efficiency (2 to 3X) and enable perform ISS upgrades which will include integrat- operation at low and high temperatures and ex- ing updated power and energy storage systems to treme radiation environments. These advanced ca- extend the power system lifetime to match the pabilities will enable power and energy storage for longer ISS mission. Finally, the roadmap includes future science and exploration missions such as: the power technology needs of the Aeronautics missions using electric propulsion, robotic mis- Mission Directorate for “more electric” airplanes sions, lunar exploration missions to NEO and that will rely on power and energy storage tech- MARS, crewed habitats, astronaut equipment, ro- nologies for reducing fuel burn and emissions. botic surface missions to Venus and Europa, po- lar Mars missions and Moon missions, and dis- 1. General Overview tributed constellations of micro-spacecraft. Space The purpose of this study is to assess the state of power systems also offer benefits to other nation- practice of space power and energy storage tech- al needs. This includes national defense systems nologies and formulate a technology roadmap that such as unmanned aerial vehicles (fuel cells, bat- can guide NASA’s investments to assure the time- teries, wireless power), unmanned underwater ve- ly development and delivery of innovative and en- hicles (AUV’s) (batteries, fuel cells, PMAD), and abling power and energy storage systems for fu- soldier portable power systems (PV, batteries, ture space missions. The major power subsystems wireless power, PMAD). Benefits to the terrestrial are:(1) Power Generation/ Conversion, (2) Ener- energy sector include: all-electric and hybrid cars gy Storage, and (3) Power Management and Dis- (batteries, fuel cells, etc.), grid-scale energy stor- tribution (PMAD). Power generation/ conver- age systems (batteries, electrolyzers, fuel cells, fly- sion subsystems include solar arrays, radioisotope wheels, PMAD, etc.), smart grid (PMAD, ana- power generators, reactor power systems and fuel lytical tools), terrestrial solar power systems (high cells. The energy systems employed in space mis- efficiency solar cells, advanced arrays, PV calibra- sions include batteries, regenerative fuel cells and tion, solar concentrators, Stirling convertors, sys- capacitors. PMAD includes power distribution tems analysis), advanced nuclear power systems, and transmission, conversion and regulation, load green energy systems (alternative fuels, advanced management and control. PMAD for wind/solar systems, energy conserva- Power systems are characterized by a number of tion analysis, etc.), and remote, off-grid power performance parameters. One parameter of great systems (crewed vehicles and habitats). importance is specific power (W/kg) that indicates The study team reviewed the: 1) National Space how much power can be delivered per unit mass Policy of the USA (June 2010); 2) NASA strategic of power system. Other related parameters include planning document; 3) SMD next decadal mis- specific energy (Wh/kg) and energy density (Wh/ sion options; 4) Human Exploration Space Sys- m3). However, power systems are not always ame- tem (HESS) of ESMD; 5) Aeronautics research nable to simple characterization in terms of a sin- directorate mission planning document. The Of- gle variable such as specific power. Other ancillary fice of Chief Technologist identified critical de- features can be equally important. These might in- sign reference missions to guide the technology clude temperature sensitivity, stowed volume, cy- DRAFT TA03-1 cle life, storage life, radiation resistance, etc. As cell plants should also be pursued as an option for space missions shift more and more from orbit- maximizing specific energy in power generation al missions to in situ missions with their harsh en- from methane propellants. Radioisotope Pow- vironments, these other factors become more im- er System (RPS) work should focus on ensuring portant. an adequate supply of 238Pu, making efficient use When viewing the power technologies in the of available 238Pu, and developing a 10 Watt class roadmap schematic (shown previously in Figure radioisotope heat source that could be used on a “R”), the technology milestones (shown in blue) variety of missions including sub-surface probes. are at technology readiness level 6. They are as- Power conversion technologies that should be fur- sumed to be ready in 4 years (on average) for mis- ther developed include advanced Stirling and ad- sion use and then are displayed as new capabilities vanced thermoelectric. Work will focus on im- (in orange). The milestones which intersect with proving RPS efficiency and specific power while key propulsion technologies are shown as orange ensuring long life (minimum 14 years). If it ap- with black centers. These technologies will then pears that adequate 238Pu will not be available, it be incorporated into the sample missions (green may be necessary to investigate the use of alterna- milestones) as either mission “pull” (shown by the tive isotopes. RPS work will help enable advanced dotted green lines) or “push” (where the new ca- science missions and new capabilities, such as pabilities can eventually enable or enhance a mis- long-life subsurface probes and radioisotope elec- sion). tric propulsion. Fission Power System (FPS) ef- 1.1. Technical Approach forts should focus on continued technology devel- The road map lays out general technical ap- opment for a 10 – 100 kWe “workhorse” system, development of a 500 – 5000 We fission system proaches for advancing the state of the art in pow- for use on advanced science missions and (poten- er generation, energy storage, power management tially) some “flexible path” missions, and develop- and distribution, as well as their cross-cutting tech- ment of technologies to enable very high power nology areas. For power management and distri- (> 5 MWe) very low specific mass (< 5 kg/kWe) bution (PMAD), the major philosophy associated space fission power. Work on low power (< 100 with the road map is to focus on semiconductor kWe) fission systems should focus on researching device advances resulting in increase breakdown and developing methods for integrating devel- voltage, reduced switching/conduction losses, and oped technologies into a highly useful, long-life improved junction temperature and radiation tol- power supply. Work on high power (> 100 kWe) erance. These advances would be most cross cut- fission systems should focus on advanced fuels ting and have the greatest impact on PMAD, en- and materials, and high temperature power con- abling revolutionary improvements in conversion version. FPS work will help enable affordable use systems. In addition, the road map emphasizes ad- of fission systems for missions not currently possi- vances in power beaming as well power system ar- ble. These include missions requiring >1000 eW in chitecture improvements which are enabled by hostile environments (e.g. heat, dust, radiation) or advanced fault isolation and smart algorithms for in regions where adequate sunlight is not available control. (e.g. outer planets, permanently shaded craters, In solar power generation, the emphasis is on high Martian latitudes, etc.). Technology work re- the development of high efficiency cells, cells that lated to high power fission systems will help en- can effectively operate in low intensity/low tem- able high performance nuclear electric propulsion perature (LILT) conditions (> 3 AU), cells and ar- for cargo and human missions to any destination rays that can operate for long periods at high tem- desired. Fusion power generation technology de- peratures (>200°C), high specific power arrays velopment should focus on ~ 50 MW aneutron- (500-1000 W/kg), electrostatically-clean, radia- ic (p-11B) reactors, direct power conversion (e.g., tion tolerant, dust tolerant, and durable, re-stow- traveling wave) from high energy charged parti- able/deployable arrays. Development of chemi- cle beams, high voltage (~1 MV), high efficien- cal power generation systems should focus on the cy power management and distribution. Related development of PEM and solid oxide fuel cell propulsion work should focus on the develop- plants with passive reactant and water manage- ment of plasma thrusters in which the plasma is ment. Development of small (~2 kW), high reli- heated directly by the high energy charged particle ability heat engine plants (e.g., Stirling, Brayton, beam from an aneutronic fusion reactor. Rankine) for use on the exhaust of solid oxide fuel In energy storage, the technical approach to de-

TA03-2 DRAFT Figure R: Space Power and Energy Storage Roadmap

DRAFT TA03–3/4 This page is intentionally left blank velop advanced space batteries focuses on the de- developed that is cost effective and lightweight, velopment of: 1) High specific energy and long our space exploration will not depend on solar en- life rechargeable batteries (500 Wh/kg, 5000 cy- ergy and we can further our knowledge of outer cles), 2) High specific energy low temperature re- planetary science. Advanced power systems enable chargeable batteries (200 Wh/kg, -100°C ), 3) high power robotic and crewed electric propul- high specific energy primary batteries (1000 Wh/ sion missions as well as in-situ resource utilization kg) with low temperature operational capability missions (ISRU). They enhance the capabilities (-160°C), 4) high temperature (450°C) primary of crewed exploration vehicles (for LEO, HEO, and rechargeable batteries, 5) green battery ma- NEO & Mars missions) and crewed surface hab- terials and processes; and 6) advanced electronics itats. Advances in power system durability and to implement optimized charge methodologies to life enable missions with high radiation and ex- enhance life and safety. treme temperature environments (e.g. Venus, Eu- For flywheel energy storage, development ropa, Mars polar, Lunar polar science missions). should focus on flywheel component miniatur- Miniaturization of power systems, improving im- ization, nanotechnology-based rotors, magnetic pact tolerance for landing and creating novel pow- bearings, reliability, and system development and er system architectures enable nano-satellites and demonstration. small planetary probes. In order to develop high specific energy, high Aeronautics benefits from space power and ener- efficiency, and long life, regenerative fuel cells gy storage products when they are used to produce (RFC), work should focus in the following tech- a more-electric, fuel efficient aircraft. Advanced nical areas: 1) trade studies on the selection of power and energy storage technology can enable most promising RFC systems for a specific appli- missions that are limited only by our imagination. cation (Alkaline, PEM and Solid oxide); 2) devel- 1.3. Applicability/Traceability to NASA opment of high efficiency fuel cells and electrolyz- Strategic Goals, AMPM, DRMs, DRAs ers; 3) reactant storage system mass reduction; 4) The study team reviewed the NASA strategic improved water and thermal management subsys- goals enabled by space power and energy stor- tems; 5) design and fabrication of integrated RFC age, including the Science Missions such as the systems; and 6) test and validation. Outer Planetary Missions: Jupiter/Europa, Sat- In the cross-cutting technology area, some iden- urn /Titan, Neptune, Pluto System Missions; tified technical approaches include multi-func- the NEO/Small body Missions: Comet Nucleus tional structures, physics-based modeling of pow- Sample Return, the NEO SEP robotic mission; er components and systems, nano-technology the Inner Planetary Missions: Venus Surface and based super-capacitors and hydrogen storage ca- Venus Sample Return missions; Mars Missions: pability, biofuels and alternative nuclear fuels for Mars ISRU, Mars Plane, Surveyor and Mars Net- power sources, and the impact of green energy sys- work Landers. The Exploration Mission Direc- tems development both in the aerospace and ter- torate will need this technology for their Crewed restrial communities. Thermal issues are a concern HEO mission, Long Duration EVA’s, Astronaut for all power systems and are addressed as part of Suits, Crewed NEO SEP/NEP Mission and Mars the technology development for each power com- Missions including the Nuclear Electric Propul- ponent and working with the TA-14 Thermal sion Human Mars Mission. The Space Operations Technology Area. Mission Directorate will need to perform ISS up- 1.2. Benefits grades which will include integrating updated Technology advances in space power and en- power and energy storage systems over its now- ergy storage offer significant benefits to space- longer lifetime. The Aeronautics Mission Direc- craft, rovers, spacesuits, tools, computers, habi- torate is interested in “more electric” airplanes that tats, communication networks, and anything that will rely on power and energy storage technologies requires power and energy storage. New missions for reducing fuel burn and emissions. are enabled when a breakthrough in power gener- 1.4. Top Technical Challenges ation or energy storage is attained. For instance, When viewing the system level challenges, the if a novel photovoltaic system is developed that power system composes 20-30 percent of the can operate in low intensity, low temperature con- spacecraft mass based on studies by Joseph Sovie ditions, space systems can be solar powered far- of NASA’s Glenn Research Center (Figure 1). This ther from the sun. If a nuclear power system is demonstrates the value and investment opportu-

DRAFT TA03-5 volume savings (3-4 x SOP) have the challenge of developing components such as high voltage, high power and high specific power solar arrays (1000 V; >100 kW; > 1000 W/kg ), high specific energy batteries (500 Wh/kg), high specific pow- er fuel cells (400 W/kg) and power management and distribution systems with high voltage (100- 1000 V) high power (100 kW–5 MW)—all across the wide range of needs shown in Figure 2. For ex- ample, another top challenge is the need to devel- op nuclear fission power systems in three power

ranges: 2 kWe; 40 kWe; and > 1 MWe with a low Figure 1. Spacecraft System Mass Fractions specific mass less than 5 kg/kW for the highest power system; these likely require very different nities for improving power system mass, capabil- approaches. Also, developing and demonstrating ity, durability in the space environment, lifetime, a revolutionary system (aneutronic fusion) (>50 and cost. Realistic goals for future power and en- MWe) is a major challenge. ergy storage technology development are a four- All of these power systems will need to survive fold reduction in system mass and volume, safe- and be operational in extreme space environments ly lasting over 30 years without replacement, and such as extreme temperatures (-180 to 450°C), being capable of operating in a vacuum in extreme dust-laden and high radiation environments (5 temperatures and radiation fields. MRAD), with high reliability and safety and last The three major subsystems—power gener- from 10- 30 years. ation/energy conversion, energy storage—and Nonetheless, missions that have not even been power management and distribution (PMAD) conceived will be enabled by high risk/high pay- each contribute approximately one-third of the off investments in the development of these pow- mass of the total power system, so all are impor- er and energy storage technologies. Steady invest- tant targets for mass reduction. Another top tech- ments will pay off in huge benefits for both NASA nical challenge is the wide variety of power needs missions and national needs. for aeronautical and space missions. Depending on the power levels and the duration of use, the 2. Detailed Portfolio Discussion power system of choice will vary (Figure 2)—thus requiring a complex suite of technology to be de- 2.1. Summary Description and TA veloped to support NASA's wide ranging needs. Breakdown Structure Power systems that provide the needed mass and The Technology Area Breakdown Structure for Space Power and Energy Systems is shown in Figure 3. 2.2. Description of TABS Elements 2.2.1. Power Generation As shown in Figure 3, this element is made up of all the methods of generating power from chemical, solar and nuclear sources, as well as energy conversion and harvesting technology. 2.2.1.1. Energy Harvesting Energy harvesting is also known as power har- vesting or energy scavenging and defined as ob- taining power from sources that are available or used for other purposes. Currently there are some devices being devel- oped for energy harvesting in industry—such as using the waste heat from nuclear plants and steel Figure 2. Power System Characteristics Based on mills, but not yet used widely for aerospace appli- Mission Need TA03-6 DRAFT program is currently funding development of Stir- ling convertors to improve specific power, reliabil- ity, and life. These devices are very efficient and can make electricity from “waste” heat from oth- er systems, at efficiencies above 60% of Carnot. Government agencies and private industry are in- vesting significant resources in fuel cell, Stirling convertor, and microturboalternator technologies which are energy conversion methods that can be used to harvest unused energy resources. High

power systems (> 100 kWe) may require develop- ment of additional energy conversion technolo-

gies, such as organic Rankine or supercritical CO2 Brayton. In these cases, however, the commercial emphasis on minimizing recurring cost results in technologies and design solutions that rarely sup- port NASA’s requirements. Nonetheless, a NASA effort in this field could be quite synergistic with the nation's desire to identify novel new energy systems. Industry is also seeking to be more en- ergy efficient with their manufacturing processes Figure 3. Technology Area Breakdown Structure for and energy harvesting is one focus area. Anoth- Space Power and Energy Storage er concept for energy harvesting is the retrieval of spent in-space resources for re-use, taking ad- cations. Nonetheless, there is potential for “push” vantage of the energy that was invested in them technologies such as: power from such sources as during launch. Possibly a space processing facili- waste engine heat, warm soil or liquids, kinetic ty could be established to re-cycle these materials. motion, and piezoelectric materials. These novel 2.2.1.2. Chemical Power Generation energy sources can provide local power to improve Power derived from chemical reactants is wide- efficiency, or even provide power to NASA’s equip- ly used in today’s rockets. For example, chemical ment where other power sources could not oper- power supports thrust vector actuation for heavy ate or would be too large or bulky or inefficient. In lift capability and in-space power for spacecraft order to identify beneficial aerospace applications, and surface systems with power requirements in studies should be done to identify all promising the 3-30 kW range. Chemical power systems cur- energy sources such as kinetic energy/momentum, rently in use for thrust vector control are exempli- solar (e.g., Lunar waddis), nuclear (radioisotope/ fied by the hydrazine-fired gas turbines used in the fission/fusion), in-space fuel recovery (e.g., 238Pu, 235 Space Shuttle systems, the hydrazine being kept in He3, U), or local radiation (e.g., Around Jupiter, unique storage. Issues with ground test for these etc.). Also, various energy conversion methodolo- systems have motivated research into electrome- gies need to be studied, such as piezoelectric, ther- chanical actuation for launch vehicle applications, moelectric, Stirling, Brayton, Rankine, and nucle- and, while Paschen corona issues remain a risk, ar fuel processing. Applications that can benefit development of electromechanical actuation will from these power systems should also be identi- likely supplant that of chemical-powered hydrau- fied, e.g., enabling power for remote sensors and lic actuation for the foreseeable future. Chemical controls in spacecraft, aircraft engines, and oth- power systems currently in use for in-space pow- er locations where power was previously not avail- er are exemplified by the Space Shuttle’s alkaline able. Simply put, the challenge for energy harvest- hydrogen/oxygen fuel cells. Opportunities for im- ing systems is to prove that there is enough power proved life and specific power for this application to be gained from these “secondary” systems, and/ have motivated an on-going development pro- or to prove that this is an enabling technology to gram in hydrogen/oxygen PEM fuel cells. Bi-pro- produce power for a novel application, to make it pellant turboalternators have also been developed worthwhile. to TRL 3 for similar applications. Energy conversion technology development can Fuel cells have been used to provide power for enable energy harvesting. NASA’s ETDP/ETDD DRAFT TA03-7 human exploration missions such as Gemini, ic energy). Balance-of-plant components (regula- Apollo, and Space Shuttle. Fuel cells required for tors, valves, circulation pumps) are the source of space applications are considerably different than most failure modes in fuel cell power plants of any terrestrial fuel cells. Space fuel cells developed to chemistry. Stack bipolar plate designs/materials date operate on pure hydrogen (fuel) and pure ox- drive system mass. Catalyst/membrane materials ygen (oxidant), while terrestrial fuel cells operate drive system efficiency and durability. High tem- on hydrogen from reformate and air. Space fuel perature fuel cells (e.g., solid oxide) in particular cells also have to operate in microgravity. Fur- have durability weaknesses when exposed to rapid ther, spacecraft fuel cell technology development load changes. All of these issues must be addressed is focused on maximizing efficiency (which trans- at an integrated subsystem level in order to meet lates into specific energy), while terrestrial fuel cell application challenges. technology development is focused on minimiz- Reliability can be improved by developing mate- ing recurring manufacturing cost. An early ver- rials and stack designs that manage reactants and sion of a Proton Exchange Membrane (PEM) fuel water entirely by passive methods (e.g., wicking), cell was used in Gemini missions (1962-1968). thus eliminating most failure modes. Optimized Alkaline fuel cells were used in the Apollo flights catalysts and membrane electrode assemblies that (1966-1978) and have been used in the Space meet efficiency and durability goals could enable Shuttle (1981- present) missions. Alkaline fuel PEM fuel cells to achieve specific power of up to cells have limited life capabilities (< 5000 hours) 140 W/kg. Advanced polymer alkaline electrolyte and low specific power (~49 W/kg). Further they membrane fuel cells and high temperature PEM are bulky, require frequent maintenance, and can fuel cells could also offer paths to achieve dura- only operate on extremely pure hydrogen and ox- bility and specific power goals. For fuel cells, nan- ygen. Future human exploration and aeronautics otechnology offers electrodes with massively in- missions require fuel cells with more robust ca- creased effective surface area and membranes with pabilities. Some of the future human exploration higher strength and lower ohmic resistance. In the vehicles that may require advanced fuel cells in- limit, this can have the effect of eliminating ohm- clude: crew exploration vehicles, large rovers for ic losses on the cell polarization curve. In the case human surface missions, and astronaut mobili- of the PEM fuel cells, this could increase specif- ty power system. Future aeronautic missions, on ic power beyond 400 W/kg. However, it should the other hand, require green power systems with be noted that, in most spacecraft fuel cell appli- high efficiency and low manufacturing cost. Fuel cations, the mass of reactant storage dominates. cell capability requirements vary from mission to Thus, even an increase in specific power from the mission. Some of the common spacecraft require- Shuttle fuel cell’s 30 W/kg to a nano-engineered ments are: high specific power (200-400 W/kg), cell’s 400 W/kg, only raises specific energy from long life capability (> 10,000 hours), and high ef- 1.5 kWh/kg to 1.6 kWh/kg. ficiency (~80%). NASA’s ETDP/ETDD program Development and test of solid oxide fuel cell and is currently funding development of PEM fuel Stirling/microturbine designs optimized to NASA cells and Stirling convertors with improved specif- specific power/energy and durability requirements ic power, reliability, and life potential , but fund- are required for full demonstration. These designs ing limits may only allow this effort to develop will likely require more expensive materials (e.g., this technology to TRL 4/5. NASA is not current- platinum interconnects in solid oxide fuel cells) ly funding development in heat engine conversion than those being considered for commercial appli- cycles other than Stirling. Aerospace contractors cations. The difficulties involved in managing liq- have conducted some IR&D on small, bi-pro- uid hydrogen feed in microgravity make it unlikely pellant Brayton gas turbines. While NASA col- that chemical power systems can be fed from fuel laborates appropriately with commercial indus- storage common with a hydrogen/oxygen propul- try at the fundamental level, this does not often sion system while in space. However, liquid meth- occur at the subsystem level. Opportunities exist ane can be managed in microgravity. Power can that could push fuel cell mission capability. These effectively be produced from liquid methane/oxy- opportunities include the development of high- gen propulsion storage via high temperature (e.g., ly reliable systems with passive reactant manage- solid oxide) fuel cells, bipropellant turbine or Stir- ment and power generation systems capable of ling engines, or a combination. Further, high tem- drawing reactants from propulsion storage (there- perature solid oxide fuel cells enable heat rejection by improving the total propulsion/power specif- systems that a greatly reduced in mass. Fortunate-

TA03-8 DRAFT Figure 4. Chemical Systems and Fuel Cell Technology Roadmap (Time-phased roadmap (graphic) of ac- tivities necessary to mature technologies) ly, there are potential synergies with other govern- surface missions; 3) PV systems with low intensi- ment programs, which are developing fuel cell and ty/low temperature (LILT) and high radiation tol- heat engine technology with similar requirements erant (5 Mrad) capabilities are required for outer and have a standing vendor team. planetary missions (> 3 AU); 4) Large arrays which 2.2.1.3. Solar Power Generation are structurally and dynamically durable under Solar photovoltaic systems have been used to deployed conditions, while retaining stowed vol- power most of the space science and human explo- ume during launch; 5) High temperature solar ration (space station) missions launched to date. cells and arrays (> 200°C) are required for inner The space science missions that have employed PV planetary missions; and 6) crew exploration vehi- power systems include: Earth orbital, Mars orbit- cles will also require high specific power arrays. al, asteroid fly-bys, lunar orbital, electric propul- As illustrated in Figure 5 NASA applications have sion, Mars surface and lunar surface missions. The much broader environmental requirements and vast majority of space missions now use multi- NASA/other agency/commercial PV common in- junction solar cells (> 29% efficiency) and occa- terests are only in LEO and below, where other sionally use silicon (> 15% efficiency) cells for low agencies are investing in the development of high cost, unique applications. Body-mounted, rigid specific power arrays and in low cost cells and ar- panel (approx 60 W/kg) and flexible deployable rays for terrestrial applications. Unfortunately, de- solar arrays (approx 100 W/kg) are currently be- spite significant need, and major challenges, no ing used in spacecraft – dependent on mission re- significant NASA investment is presently planned quirements and array technology. These state-of- to address the challenges displayed in the other re- practice (SOP) solar power PV power systems are gions of the solar system in Figure 5, leaving a gap mostly suitable for low to medium power (0.5- when addressing NASA needs. Therefore, a new 30 kW) applications. Further they have poten- program needs to be established that emphasizes tially degraded performance at high temperatures the development of high efficiency cells, cells that (above 140°C) and low intensity/low temperature can effectively operate in LILT conditions (> 3 space environments found beyond Mars orbit. AU), cells and arrays that can operate for long pe- Future space science and human exploration mis- riods at high temperatures (>200°C), high specific sions require solar power PV systems with signif- power arrays (500-1000 W/kg), electrostatically- icantly higher performance capabilities compared clean, radiation tolerant, dust tolerant, and du- to SOP systems. The capabilities needed vary sig- rable, re-stowable/re-deployable arrays. For large nificantly from mission to mission. Some of the space power systems, ground testing and verifica- critical requirements of the future space missions tion methods need to be developed. Cost will be are: 1) high voltage and high power arrays (300- a major driver for large PV power systems. Cost 1000 V, > 100 kW) with high specific power ar- reduction can be addressed through reducing cell rays (500-1000 W/kg) capability are needed for cost, modularity of solar cell panels, improved high power electric propulsion missions; 2) dust- manufacturability, and reparability. tolerant PV arrays with high specific power and 2.2.1.4. Radioisotope high efficiency are needed for human and robotic Radioisotope power systems (RPS’s) based on

DRAFT TA03-9 Figure 5. Other Agencies, Commercial Space and NASA Mission Synergies (Overlaps and potential syner- gies across current and planned investments) plutonium-238 and thermoelectric converters advanced Stirling radioisotope generator (ASRG) have been used in space since 1961, with a typi- (10-15 W/kg, 35% efficiency, 15 year life); and cal performance of 3-5 We/kg, 6% efficiency, and 3) small (1-10W) RPS’s that can survive a 5000-g over 30 yr (demonstrated) life. RPS’s operate in- impact, including both the heat source and power dependent of solar proximity or orientation. In conversion system. The radioisotope of choice is addition to enabling sophisticated science mis- plutonium-238, which has excellent power densi- sions (e.g. Pioneer, Viking, Galileo, Ulysses, Cas- ty and lifetime, and minimal radiation emissions. sini, New Horizons) throughout the solar system, The use of a more readily available isotope (e.g., RPS’s were used on Apollo missions 12-17 and the 241Am) instead of 238Pu would result in a perfor- Viking landers. mance penalty for most RPS missions and would Looking forward, RPS’s in the 0.1 – 1000 We require an extensive qualification effort. Howev- power range could continue to enable exciting sci- er, the use of alternative isotopes (in addition to ence missions, and could also be useful in sup- 238Pu) could potentially allow higher power (>1 porting human exploration missions. High specif- kWe) radioisotope systems to be developed and ic power RPS’s could enable radioisotope electric utilized, and allow more extensive use of radio- propulsion for deep space missions, enhancing isotope systems. NASA's Science Mission Direc- or enabling numerous NASA missions of inter- torate is continuing to develop advanced radio- est Specifically, there are three types of radioiso- isotope power systems for future space science tope power systems that need to be developed: 1) missions. The ASRG is making excellent progress advanced radioisotope thermoelectric generators towards the goals of efficiency greater than 28%, (10-15 W/kg, 15-20% efficiency, 15 year life); 2) specific power of 6-8 We/kg, and life exceeding

Figure 6. Photovoltaic Systems Technology Roadmap (Time-phased roadmap (graphic) of activities neces- sary to mature technologies) TA03-10 DRAFT 14 years. in the solar system. Fission systems can support

The major challenges for RPS’s are: (1) to cre- science missions in the 0.5-5 kWe power range ate high efficiency power conversion systems with where 238Pu supply issues may preclude use of ra- very long life capability, (2) the severe impending dioisotope systems. Workhorse 10 – 100 kWe fis- shortage of 238Pu, which is no longer being pro- sion systems can support surface and robotic mis- duced in the U.S. (if the 238Pu availability issue is sions. High power fission systems (MW-class) are not resolved, there is a need to develop and qualify required for nuclear electric propulsion missions alternative nuclear heat sources); and (3) to invent – potentially including crewed missions to Mars, RPS’s which can survive a 5000-g impact. Fore- and other destinations. Fission reactors flown in most is the need for a new program to establish space by the U.S. and the former Soviet Union U.S. plutonium-238 production facilities, or the between 1965 and 1987 operated at coolant out- development and production of alternative nu- let temperatures and thermal powers comparable st clear heat sources. NASA is working with other to those required by a 21 century 40 kWe sys- government agencies to implement this new pro- tem. Space reactor programs not resulting in flight gram. Flight validation of the ASRG and other ra- succeeded in developing high temperature / high dioisotope power systems is very important to en- performance fuels, materials, and heat transport sure the acceptability of these systems on future systems. The experience gained from nearly 7 de- missions. This new program must also focus on cades of terrestrial fission systems can benefit the developing small, impact-resistant radioisotope design and development of future space fission power systems and life-prediction models and ex- systems. Fuel and materials technologies from ter- perimental testing techniques. Advanced RPS’s restrial systems (e.g., FFTF fast fission test facili- could be used on Discovery, Flagship, and Flexi- ty and EBR-II experimental breeder reactor) are ble Path precursor missions . applicable, especially for first generation space fis- 2.2.1.5. Fission sion systems such as those being developed under Fission provides “game-changing” solutions ETDD. High uranium density fuels developed for for powering advanced NASA missions. Game- research and test reactors could also be of use for changing attributes of space fission systems in- ultra-compact systems. NASA ETDD’s ongoing clude virtually unlimited fuel energy density, the space fission power project involves a close part- ability to operate independent of solar proximity nership between NASA and other external orga- or orientation, and the ability to design for opera- nizations. The partnerships are working extremely tion in extremely hostile environments (e.g., high well, with significant progress being made towards dust, high radiation, or high temperature). Fission ground-testing a ¼ -scale technology demonstra- can enable a power-rich environment anywhere tion unit (TDU) by 2013. Components for the

Figure 7. Radioisotope Systems Technology Roadmap (Time-phased roadmap (graphic) of activities neces- sary to mature technologies) DRAFT TA03-11 TDU have been designed, fabricated, and tested. fuels and materials, high temperature / high effi- Fabrication of the integrated TDU is scheduled ciency power conversion, and light-weight, high to begin in FY11. Development and operation temperature radiators. For example at high power of the TDU will provide an excellent foundation levels (> 100 kWe), space fission power system per- for all future space fission power and propulsion formance would benefit from advanced fuels, ad- work, from both an organizational and hardware vanced power conversion, and light-weight radia- standpoint. The current program is focused on a tor technologies. Innovative reactor designs would

40 kWe space fission power system with emphasis also improve performance. Specific technologies on safety, reliability and affordability. The system could include development of high-temperature utilizes reactor and other technologies with signif- (~1800 K) cermet fuels (e.g.,W-UN) and of liquid icant terrestrial heritage. For potential 0.5-5 kWe or vapor core fission reactors (e.g., UF4) capable fission systems, a GRC-led study was completed of operating at temperatures above 2500 K. Ad- in 2010. The study utilized the NASA team that vanced power conversion options could include has been established for the 40 kWe ETDD proj- alkali metal Rankine cycles (building on work per- ect. The 0.5 – 5 kWe systems would also take ad- formed in the 1960s) and Magnetohydrodynam- vantage of ongoing research at NASA (power con- ic (MHD) power conversion. Light-weight radi- version, radiators). ators capable of operating at temperatures above The top technical challenges for fission systems 1000 K could also benefit integrated system per- are application specific. A 0.5-5 kWe fission system formance. would require high uranium density fuel; simple, Next generation systems can be developed to lightweight core-to-power conversion heat trans- TRL 6 via a combination of nuclear testing in col- fer; low mass power conversion (at low power); laboration with the other government agencies and design for safety, reliability, and minimum and fully integrated non-nuclear testing at opera- mass. Existing (or near term) materials, fuels, tional government facilities. Improved conversion power conversion and waste-heat rejection tech- cycles, heat transfer systems, and radiators can all nologies could be used. Simply put, the technol- be developed by NASA and tested to TRL 6. Nu- ogies exist for developing near-term, mission-en- clear testing will be performed as required for ad- abling space fission systems. The major challenge vanced fuels, components, and reactors. Realistic, for these initial systems is integrating the technol- integrated system testing will be used to demon- ogies into a safe, reliable, affordable system. For strate advanced fission systems at TRL 6. second generation space fission systems (and be- 2.2.1.6. Fusion yond), the major challenge is developing technol- ogies to even further improve performance. Specif- Fusion power for electric propulsion could sup- ic technologies include high temperature reactor port human missions to Mars with round-trip

Figure 8. Fission Power Systems Technology Roadmap (Time-phased roadmap (graphic) of activities neces- sary to mature fission technologies) TA03-12 DRAFT times under one year and large, high power ro- any heat engine conversion. Also, if no neutrons botic missions throughout the solar system. Such are emitted, little shielding and no radioactive ma- missions start to be enabled by power/propulsion terial handling facilities are required (that are in- systems in the 50+ MW range with total specif- stead necessary for fission or D-T fusion reactors). ic masses (αΤ) less than 2.0 kg/kW. Within the This would reduce the flight development cost of constraints of current (and foreseeable future) fu- an aneutronic fusion reactor to well below that of sion technology, these values of αΤ can only be even a fission power system. Aneutronic reactions achieved via low-neutron or neutron-free (aneu- thus have high potential for low-α space power tronic) fusion reactors. If an electric propulsion generation. However, the high ion energy that is system can be developed with α < 1.0, efficien- required to reach the peak fusion cross section of cy (η) > 0.6 and PMAD with α < 0.5 and η > 0.9, the p-11B reaction is considered unobtainable with delivering αΤ < 2.0 kg/kW would require a fusion the various thermal plasma confinement methods reactor/power conversion system with α < 0.5 kg/ that are being pursued for terrestrial fusion power kW and ηconv > 0.8. Due to the high specific mass reactors. Thus, development of such reactors has of heat-based neutron-to-electric power conver- not been aggressively pursued. The engineering of sion systems, to the residual radiation from neu- direct conversion of fusion product into electrici- tron activation, and to the need of neutron shield- ty (for example the Traveling Wave Direct Energy ing for critical components and crew, delivering Conversion, TWDEC, and the Periodic Focusing this capability requires development of fully aneu- Direct Energy Conversion systems) has progressed tronic fusion power generation. to TRL 3/4 in laboratory experiments. The tech- Fusion power is considered to be most readily nology for using directly the energy from an aneu- attainable through heating and confinement of tronic fusion reactor to create plasma for thruster a D-T plasma until the condition at which the propellant (to be then exhausted through a mag- plasma can heat itself (ignition) is reached. The netic nozzle) is at a similarly low TRL level. D-T reaction releases most (80%) of its energy in As noted above, no significant amount of fund- the form of neutrons, so a D-T fusion reactor re- ing is directed toward engineering for aneutronic quires heavy shielding and heat-based energy con- fusion of potential use in NASA missions. Fund- version to produce electricity. Since the 1960’s fu- ing of research for related direct energy conversion sion research has focused on the D-T reaction, as systems remains almost zero. Whatever the invest- it appears to be the least challenging from the per- ment, the primary technical challenge in aneu- spective of plasma confinement and reactor tech- tronic fusion remains the demonstration of stable nology for utility grid power generation. Steady confinement of plasmas with ions of sufficient en- progress towards the goal of net fusion power gen- ergy to produce high energy yield. With present- eration continues to be made, with most of the ly known magnetic confinement configurations, investments devoted to the magnetic plasma con- thermal plasmas of sufficient energy to sustain finement approach. The primary effort currently these reactions cannot be confined for a sufficient underway is the ITER “Tokomak”, a very large time. Thus, sustaining beam-collider plasmas ap- magnetic confinement device, which is projected pears a more viable solution, yet these have many to lead to net power generation in the 2030’s with unknowns. Other challenges include the develop-

α > 200 kg/kW at ηconv < 0.4 and 10 GW. ment of systems for direct conversion of high-en- The aneutronic fusion reaction p-11B release their ergy alpha particles produced in the fusion reac- energy primarily in the form of charged alpha par- tions. It should also be noted that a propulsion/ ticles and thus enable direct conversion methods power system with αΤ < 1.0 kg/kW is realistical- that are, in principle, much more efficient than ly possible only if a thrust-producing propellant

Figure 9. Fusion Power System Technology Roadmap (Time-phased roadmap (graphic) of activities neces- sary to mature technologies) DRAFT TA03-13 jet can be generated from the energy of the fusion LEO, HEO, and planetary). SOMD requires bat- products of the reactor. teries for ISS astronaut equipment, life support 2.2.2. Energy Storage systems, and as the energy storage element of a photovoltaic based power system, this includes re- This element is made up of all the methods of placements for the existing Ni-H2 batteries with storing energy after it has been generated from so- advanced technology. ARMD requires high spe- lar, chemical and nuclear sources if the energy is cific energy batteries for aviation energy storage in not needed immediately. hybrid and more-electric aircraft. 2.2.2.1. Batteries Advanced batteries with 2-3 X performance ca- Batteries are used in space missions for a wide pability compared to the state of the practice bat- variety of applications. Primary batteries (sin- teries are required for a number of future NASA gle discharge batteries) are used in missions that space missions listed above. These advanced bat- require one-time use of electrical power for few teries will provide significant mass and volume minutes to several hours. Primary batteries have savings and operational flexibility. The require- been used in planetary probes and sample return ments will vary from mission to mission and the capsules (Stardust, Genesis, Deep Impact, and driving requirements for some critical missions Galileo), Mars Landers (MER), and Mars Rov- are: 1) Astronaut /EVA equipment require high ers (Sojourner). Rechargeable batteries (secondary specific energy rechargeable batteries (500 Wh/ batteries) have been used mainly for load-level- kg, 1000 cycles); 2) Human habitat power sys- ing and for providing electrical power for surviv- tems will benefit significantly from batteries with al during eclipse periods on solar powered mis- large storage capability (~MWh, 5000 cycles) sions and as the source of power extravehicular and high specific energy ( 500 Wh/kg); 3) Hu- activity suits. They have been used in orbital mis- man/robotic landers and rovers require high spe- sions (TOPEX, Mars Global Surveyor, and Mars cific energy (500 Wh/kg, 5000 cycles) and ultra Reconnaissance Observer) as well as Mars Land- low temperature rechargeable batteries (-100°C); ers (Mars Pathfinder) and Mars Rovers (Spirit and 4) Crew exploration/rescue vehicles require high Opportunity). State of practice primary and re- specific energy batteries (> 500 Wh/kg); 5) Plan- chargeable batteries are heavy, bulky and have lim- etary probes require high specific energy prima- ited capability to function in extreme space envi- ry batteries (1000 Wh/kg) with low temperature ronments such as high and low temperatures and operational capability (-160°C); 6) Inner plane- radiation. Safety concerns exist with some of the tary missions require high temperature (450°C) primary lithium and rechargeable Li-Ion batter- primary and rechargeable batteries; 7) Earth/ ies. A summary of the characteristics of the state planetary orbiters require long life (> 20 years, of practice primary and rechargeable batteries are 100,000 cycles) and high specific energy recharge- given in Table 1: able batteries (300 Wh/kg); 8) Heavy lift launch Advanced batteries are required for a number of vehicles require high specific energy primary bat- future ESMD, SMD, SOMD, and ARMD mis- teries (1000 Wh/kg) and high rate capability (3 sions. The ESMD missions include astronaut kW/kg). The major technical challenges to devel- equipment and EVA suits, crew exploration vehi- op these advanced space batteries include: 1) de- cles, in-space habitats, surface habitats, humanoid velopment of high specific capacity cathode na- robots, landers, and ISRU. SMD missions include no-materials (500 mA-hr/gm); 2) high specific planetary probes, landers, rovers, orbiters (GEO, capacity anode nano-materials (>1000 mA-hr/

Table 1. Current state-of-the-art/practice for primary and rechargeable batteries SOP System Technology Mission Specific Energy Operating Cycle Life Mission Issues Energy, Density, Temp. Range, Life (Wh/kg) (Wh/l) (°C) (yrs) Primary Ag-Zn, Delta Launch 90-250 130-500 -20 to 60 1 1-9 • Limited operating

Batteries Li-SO2, Vehicles, Cassini temp range, Li-SOCl2 Probe, MER Lander, • Voltage delay Sojourner Rover Rechargeable Ni-Cd, TOPEX, HST, 24-35 10-80 -5 to 30 > 50,000, >10 • Heavy and bulky,

Batteries Ni-H2 Space Station @25% DOD • Limited operating temp range Advanced Li-Ion MER: Spirit & 100 250 -20-30 > 400 >2 Cycle Life Rechargeable Opportunity @50% DOD Batteries Rovers

TA03-14 DRAFT Figure 10. Battery Development Synergies between NASA and Commercial Space. (Overlaps and poten- tial synergies across current and planned investments) gm); 3) high voltage (>5V), highly conducting development of low cost batteries for terrestri- electrolytes; 4) overcharge protection additives al electric vehicle (150-200 Wh/kg) applications, and safety concepts and devices; 5) multi-func- but its focus is on low recurring cost and not high- tional battery structures; 6) extreme temperature est possible performance. To augment the current and radiation-resistant electrolytes and electrodes; investment, a new program is needed to devel- 7) green battery materials and processes; and 8) op advanced primary and rechargeable batteries development of advanced electronics to imple- required for future SMD, ESMD, SOMD and ment optimized charge methodologies to enhance ARMD missions. life and safety is also required. 2.2.2.2. Flywheels As seen in Figure 10, NASA’s energy storage Flywheels offer space craft a novel system for needs span a greater range of environments and combining attitude control (replacing momen- cycle requirements than other organization's ap- tum wheels) and energy storage (replacing batter- plications. NASA’s ETDP/ETDD program is ies) which reduces the overall mass of the com- presently investing ~$2-3M/ year to develop re- bined systems. Flywheels have the advantage of chargeable Li-Ion batteries of 165-260 Wh/kg. being able to quickly deliver their energy, and This current NASA ETDDP program is focused can be fully discharged repeatedly without harm- on meeting the near term ESMD needs. It does ing the system, and have the lowest self-discharge not address the future SMD, SOMD and ARMD rate of any electrical energy storage medium. They needs. Other government agencies are investing have potential to be the best possible storage me- several tens of millions of dollars per year in the dia per unit mass (2700 Wh/kg theoretically) with

Figure 11. Battery Technology Roadmap. (Time-phased roadmap (graphic) of activities necessary to ma- ture technologies) DRAFT TA03-15 the application of nanotechnology. For example, stage of development. The major subsystems of the development of carbon nano fibers which can an RFC are: fuel cell, electrolyzer, reactant stor- be wound to form ultra strong, lightweight rotors age, thermal management, and control. Space would enable higher energy storage capability for RFC systems are considerably different than ter- flywheels. These rotors will also be much safer, re- restrial RFC systems. Air-based RFCs (recycling quiring lighter weight shroud material. Bearing only hydrogen and water) are being developed for technology development such as superconducting commercial terrestrial and military applications. magnetic bearings and advanced generators would Space RFC systems have no air available and must also advance flywheel technology. be designed for operation with oxygen. Further- During the last 10 years, NASA's research and more, space RFC systems have to be optimized technology efforts created engineering mod- for multi-gravity environment operations (0g – el units which were fabricated and tested (25-30 launch loads) and also for thermal and water man- Wh/kg) to be able to replace the batteries on the agement in space thermal vacuum environments. ISS. Ground demonstrations were very successful Space-quality RFC technology feasibility demon- and a prototype system was readied for potential strators have been assembled and tested to demon- installment on the ISS. Nonetheless, today, there strate technology viability and determine system is no planned NASA funding for flywheels. At the operations. Currently PEM RFCs are no further same time, there is increasing military, industrial advanced than a TRL of 3-4 and have been dem- and commercial terrestrial power grid storage in- onstrated only in terrestrial experimental test beds terest. at 50 % round trip efficiency and operated at less The major challenges are to advance flywheel than 100 cycles. technology to achieve the potential to store ener- NASA’s ETDD and SBIR programs are current- gy for kWh & MWh systems at a specific energy ly funding limited development of critical compo- of up to 2700 Wh/kg with carbon nano fiber ro- nents and devices for hydrogen/oxygen PEM fuel tors (as mentioned above) and to attain a charge cells and electrolyzers with improved specific pow- life of greater than 50,000 cycles and lifetime of er, reliability, and life potential. Both discrete (sep- greater than 20 years with high reliability and safe- arate fuel cell and electrolyzer stacks) and unitized ty. To meet these challenges, NASA could pursue (one stack) systems have been examined. The pri- flywheel component miniaturization, nanotech- mary focus in technical development to date has nology-based rotors, magnetic bearings, reliabili- been on the fuel cell portion. ETDP plans were ty, and system development and demonstration. to begin addressing electrolysis via SBIR efforts 2.2.2.3. Regenerative Fuel Cell Energy (which has been implemented), then begin to sup- Storage port with project funds in FY11-12 time frame. Despite the termination of RFC funding under Regenerative fuel cell systems (RFCs) are attrac- ETDD, there is a defined need for advanced space tive for space missions that require large scale en- quality electrolysis systems, thus fuel cell and elec- ergy storage of the order of several MWh. This trolysis work are planned to continue as separate is especially important for large-scale energy stor- elements. Other government agencies are invest- age applications such as space habitats and plan- ing in a similar system in support of energy stor- etary surface systems requiring 10’s of kW elec- age for blimps. Other government agencies and trical power. Unlike batteries which become very private industry are investing significant resources large when designed to address long periods of op- in PEM fuel cell technologies, but fuel cell design, eration, regenerative fuel cells only require larg- cathode catalyst, water management and opera- er storage containers and additional reactants to tional conditions are not the same as the oxygen- extend their operational period. Regenerative fuel fed system required for NASA. Commercial em- cells required for large scale energy storage appli- phasis is primarily placed on minimizing cost and cations would be enhanced by high specific ener- in technologies, and design solutions for terrestri- gy (Up to 1500 Wh/kg), high charge/discharge ef- al operations rarely support NASA spacecraft re- ficiency (up to 70%), high reliability, and long life quirements. capability (~10,000 hours). A new technology program is needed to devel- Three RFC chemistries are in development: 1) op high specific energy, high efficiency, and long Polymer Electrolyte Membrane (PEM), 2) Alka- life, regenerative fuel cells that are required for the line, and 3) Solid oxide. Among these three chem- large scale energy storage needs of future ESMD istries, PEM RFC system is at the most advanced and ARMD missions. This program needs to fo-

TA03-16 DRAFT Figure 12. Regenerative Fuel Cell Systems Technology Roadmap. (Time-phased roadmap (graphic) of activities necessary to mature technologies) cus efforts in the following technical areas: 1) kg is at or just above what can be achieved with trade studies on the selection of most promising custom power converters (in the range of 1kW RFC chemistries for a specific application (Alka- to 1MW) using the latest commercially available line, PEM and Solid oxide); 2) development of parts. It should be noted that these parts often high efficiency fuel cells and electrolyzers; 3) reac- outperform space grade parts significantly due to tant storage system mass reduction; 4) improved the intrinsic “inertia” of class S (space grade) pro- water and thermal management subsystems; 5) duction lines. As such, in general it’s very hard for design and fabrication of integrated RFC systems; a space based PMAD system to achieve this mark and 6) test and validation. A NASA effort in this due to poor performance in terms of losses. In ad- field could be quite synergistic with another agen- dition, although high voltage parts are commer- cy's program, which is developing a similar RFC cially available above 1000V, the rigor and over- and is working with an established vendor team. head of tracking and screening that comes with Any PEM and Solid Oxide electrolysis develop- the higher part grades means you can’t find simi- ment effort for regenerative fuel cells could be larly rated high voltage parts in any manufactur- completely in common with that for life support er’s space grade offering. In fact, while commer- oxygen generation, such as is operating on Space cial grade MOSFETs are available with ratings of Station, and with ISRU. at 1200V and 600A (Powerex), no space grade an- 2.2.3. Power Management & Distribution alog exists. As a result, generally electronic com- (PMAD) ponent voltage ratings (usually semiconductor de- vice as well as capacitor ratings) limit the system PMAD is the “backbone” that holds a pow- bus voltage. Further these factors are more con- er system together. It is often neglected in discus- straining than the issues arising from cable insu- sions of technology development and innovation lation effectiveness and/or the separation issues in favor of the more visible larger power compo- (arcing/corona) associated with the higher voltage nents and is often thought of with a “buy it by system. In terms of environmental limitations, sil- the yard” mentality. However technology devel- icon based semiconductors junctions often carry a oped for reducing the mass of the PMAD system practical limit to junction temperature at or near would impact one-third of the mass of the whole 150°C which has a direct impact on the level of power system. For the time period from now un- heating a device can withstand due to its internal- til 2016, the need is to qualify a range of space- ly generated losses. This also has an impact on ra- grade high voltage active power semiconductor diator size when, for a given internal loss level and transistors (comparable to the commercial offer- junction to case thermal resistance, the temper- ing) and passive components and adapt terrestri- ature sink must be low enough to accommodate al advances in power management and control to the ΔT required to stay beneath the 150°C junc- new space power system architectures. For 2017- tion temp with margin. In addition, for a given 2022, the challenge is to improve qualified power silicon based device, there is often a tradeoff that semiconductors by increasing the current rating, exists between breakdown voltage and conduction lowering switching and conduction losses, and in- loss (on state resistance) as well as a trade between creasing junction temperature tolerance. For the switching and conduction losses. These trades col- period 2023 – 2028 another top challenge would lectively present an obstacle to increasing power be to develop a viable power beaming approach, as density. In addition to these aforementioned lim- described later in this section. itations, capacitors, a key component in the ener- 2.2.3.1. PMAD Overall gy balancing function within PMAD conversion Typically, PMAD power density around 5kW/ steps, typically employ electrolytic variants. Elec-

DRAFT TA03-17 trolytic Capacitors: Tantalum and Aluminum – overall, the parts in these systems must be better Aluminum capacitors are used on ground or pres- suited to the space environment for both earth- sure controlled areas in space. Tantalum non-solid orbiting as well as interplanetary missions while (MIL-PRF-39006) and tantalum solid capacitors needed performance improvements are simulta- (MIL-PRF-39003) are hermetically sealed and are neously achieved. In particular, we need semicon- currently being used in space applications. How- ductor parts with improved junction temperature ever, they often carry limited operating tempera- operating tolerance and radiation tolerance, pos- ture range and present poor density. In terms of sibly via nontraditional semiconductor materi- external pressure: Aluminum electrolytic capaci- als. Further, for EDL systems, power systems and tors can operate up to 80,000 feet and pressures as their associated hardware need to be capable of low as 3 kPa. Exceeding these limits can damage withstanding extremely high g impacts delivered capacitor. Temperature ratings: In addition, since on landing. temperature is one of the main factors in capacitor 2.2.3.2. Wireless Power Transfer life, temperature ratings need to be increased. For Wireless power transfer can be split into two cat- example, tantalum capacitors (MIL-PRF-39006) egories based on transmit power and throw dis- currently have an operating temperature between tance. In the smaller class, analogous to recharge- -55°C and 85°C. These capacitors are de-rat- able toothbrushes and cell phone charging pads, ed when operated between 85°C and 125°C. In electric or magnetic fields are used with a pickup many cases super capacitors promise improved ca- mechanism to charge without electrical contact; pability in a number of these areas but current- these are useful to power small rechargeable bat- ly carry their own limitations. Super capacitors, teries such as those used in wireless sensors. In the also known as Electric Double Layer Capacitor larger class, commonly referred to as high intensi- (EDLC), have the highest energy density. Cur- ty power beaming, power could be transmitted via rently in production we find 30Wh/kg which is laser beam or over microwaves that can be used for thousands of times greater than what we achieve launch capabilities to deliver a payload from Earth with electrolytic capacitors. However, in general, to LEO, electrically refuel UAVs or geosynchro- supercaps have low voltage ratings. Cells have to nous satellites, or for numerous deep space appli- be connected in series to get higher voltages which cations. Further, power beaming techniques could increases ESR and decreases the reliability. conceivably have a drastic effect on energy storage Across all the areas within PMAD, focus areas mass in the system as strategically placed transmit- for technology push should target improved pow- ters could reduce the power system’s required on- er density and environmental tolerance. Each of board energy storage capability. In the case of high these overarching PMAD focus areas will be ad- intensity power beaming, 50% efficiency has been dressed first in the paragraphs that follow. In achieved at the receiver. The final output electri- terms of mass, distribution system weight is driv- cal power density at the receiver has reached 20 en by system cable/buss mass. Since a higher op- 2 erating voltage can yield a lower (distribution sys- W/cm , which has been limited primarily by the tem) weight for the same power level, it is both source and the collimating optics. a near term and a long term goal across all ar- 2.2.3.3. Distribution & Transmission eas of PMAD. For higher PMAD power density, Cryogenically cooled conductors, motors, etc. the emphasis must be on improved semiconduc- have greatly reduced conduction losses and resul- tor device and passive device characteristics. This tant power densities can be factors greater than would include including a higher operating volt- those at ambient temperatures, however, the ap- age to enable smaller distribution system mass. plication of cryogenic technology needs to be In addition, this also drives the need for devic- done on a case by case basis after analyzing the es with higher break down voltages as well as re- added value against risk and complexity trades. duced switching and conduction losses. In addi- Another possibility is embedding signal paths tion to the limitation these active devices impose, in composite structures. An interesting concept, passive devices also become limiting factors. Ca- originally proposed by members of the mili- pacitors used today in space applications need to tary aircraft community, would embed electrical- have higher densities, higher operating voltages, ly reconfigurable signal pathways into composite and higher temperature tolerance to achieve fu- structures. The pathways could be multipurpose ture space missions. delivering low power levels to loads such as sen- From an environmental perspective for PMAD sors, act as communications links, sense space-

TA03-18 DRAFT craft structural damage, and even reroute signals 2.2.3.7. Major Challenges around damaged structure and any resulting bro- Major challenges to the development of high ken pathways. power, high voltage PMAD are directly related 2.2.3.4. Conversion & Transmission to part capability and availability and limited ex- For conversion, in addition to the overarching pertise in high voltage design. To elaborate, high issues raised above, building blocks, common- power systems require higher distribution voltag- ly known as Power Electronics Building Blocks es. This means both power semiconductors as well (PEBB), that are modular and scalable need to be as passive components at this voltage rating need developed. These modules should be able to be re- to be developed that enable the higher bus voltage. applied to new designs and scaled for appropri- These parts are not commercially available at this ate voltages/power levels with minimal recurring time. In addition to the voltage and current rat- analysis and as such have a high level of reusabil- ing of these power semiconductor parts, improved ity. junction temperature tolerance, radiation toler- ance coupled with reduced switching and conduc- 2.2.3.5. Fault Detection, Isolation, and tion losses must be developed to accomplish the Recovery (FDIR) mission. While these issues are being partially ad- For FDIR, a common, highly capable/configu- dressed through commercial development efforts, rable semiconductor-based protection and switch- military and space grade parts are not seeing this ing design should be developed. Commonly called same level of innovation due to a variety of factors a Remote Power Controller (RPC), these devices related to supply and demand on the worldwide serve as both power control and circuit protection commercial market. In addition, NASA and its in typical space PMAD systems. The implemen- partners lack the expertise needed in high voltage tation of these devices is often customized from design at this power level. NASA’s previous work project to project. Within FDIR, an area where in this area was limited to high voltage, low pow- we should push technology would be the devel- er sources for instrument development and those opment of a highly competent, configurable RPC knowledgeable in this area are also few and get- design that implements data bus communica- ting fewer. tions, can operate at high voltage ratings, be low There are a number of technology pushes with- loss and high current capable while implement- in PMAD that NASA will have to champion in ing a user selectable variety of advanced protec- order to achieve revolutionary rather than evo- tion algorithms such as programmable set points, lutionary advances. NASA will have to augment current limit, I2t, etc. This standard design could its current efforts in the R&D of wireless pow- be qualified once, be useful in any NASA mission, er transfer to include low power magnetic and and reduce overall cost/ weight while improving electrically coupled methods as well as the higher fault protection and isolation characteristics. power beaming techniques that employ mediums 2.2.3.6. Management and Control such as lasers and microwaves in order for these In control and management of power, the terres- technologies to be useful and game changing. In trial renewable energy boom as well as our nation’s addition, NASA should invest in the develop- interest in a power grid topology termed ‘Smart ment of beamed power distribution. A new con- Grid” dovetails into the technology push strategies cept for beamed energy involves use of fiberoptic that NASA should focus on. Smart Grids, with a transmission of light power from a laser source. multitude of interconnected sources and loads re- This could revolutionize the way we conduct ro- quire advanced power flow control algorithms that botic surface exploration (it is already revolution- promise more efficient more reliable power system izing deep sea exploration). Continued develop- operations. These same concepts can and should ment could enable use of this method of power be developed into space power systems. In addi- distribution for a wide range of space and aero ap- tion, power system control algorithms need to be plications. This development activity would be highly reliable but also be resilient when faults do in addition to the development of convention- occur to enable the long term autonomous oper- al beaming approaches described here via free la- ation that interplanetary space systems or surface ser light and microwaves. In terms of power semi- power systems would need much in the same way conductor development, while we see incremental terrestrial smart grid technologies are advancing. improvement, this is constrained primarily to the commercial markets. NASA will have to develop the space grade market segment for the commer-

DRAFT TA03-19 cial suppliers leveraging an increased demand in 2.2.4.1. Analytical Tools the commercial market for many of these same at- The development of analytical models and pre- tributes (less the radiation and temperature toler- dictive tools to model and characterize subcom- ance) from nation’s focus on terrestrial renewable ponents and systems for power and energy storage energy sources and their associated conversion are a cross-cutting technology which will provide and distribution functions. In addition, with re- capability to all NASA missions which require spect to lowered switching /conduction loss, in- power. creased temperature and radiation tolerance, new The capabilities needed are physics-based mod- materials for semiconductor parts should be fur- els of all power-related components, sub-systems ther explored such as the advances currently in and whole power systems. Also, needed is an over- work on SiC active switches. This kind of revolu- all algorithm to join the models together to ana- tionary advance in the State of the Art could result lytically predict the performance of any innova- in significantly reduced internally generated losses tive new technologies and to determine the overall while at the same time improve the junction tem- impact on a power system. The analysis could in- perature limit by a factor or 4x or more. The com- clude prediction of overall system efficiency, max- pound effect of these improvements will result in a imum and minimum power levels, reliability, life, much smaller and lighter power system particular- and cost of operation. The models could also help ly when PMAD conversion system magnetic and in determining design parameters and the cost of heat rejection mass are considered. In the area of building and testing the prototype, engineering super capacitors, NASA should sponsor research unit, and flight hardware. that would move to hermetically seal the EDLCs, Current power system modeling often relies on decrease their operating temperature (via a reduc- empirical modeling using experimental data from tion of core to case the thermal resistance), im- existing components. The system models are high prove their operating voltage, decrease their equiv- level and often do not capture the actual impact alent series resistance, and ultimately quality this of new technology when introduced. NASA has robust design for space applications. in the past (1970’s) invested in such analysis tools Much of what NASA needs in the area of as the Environmental Workbench, to predict the PMAD, as well as many of the power disciplines performance of solar arrays in the space environ- are in large part similar to the advances the coun- ment. Though effective, commercially developed try needs in its terrestrial green power initiatives tools are in use throughout the aerospace indus- that are prevalent in government and venture cap- try and other government agencies have worked ital funded R&D efforts today. High voltage, high in this area, no current joint development pro- power, DC distribution systems are center stage as grams exist. Physics-based models of power sys- are increased efficiency PV arrays and higher effi- tem elements and an overall system to connect the ciency conversion steps. In addition, the nation- models will not be trivial to develop and demon- al focus on the smart grid concept (a move away strate to TRL6. First, it will be necessary to inven- from centralized generation and load aggregation tory the available models (if any) per power sys- to a distributed interconnected approach) is very tem technology element to determine how they much aligned with the advance power manage- are written, what the inputs/outputs are, how they ment and control techniques NASA will need in work in general and how we would like them to future PMAD designs. Future designs that might work. Then, a gap analysis of the available models leverage these new concepts in the terrestrial mar- needs to be conducted along with how they need ket to be immensely more efficient in converting to interact and model an entire power system. their source to electric power and further, be more 2.2.4.2. Green Energy Impact effective in distributing power and minimizing/re- claiming lost energy. In addition, the smart grid This section does not address a particular tech- concepts could change the way NASA designs its nology, but it involves an approach to energy tech- EPS architectures by reframing the way power de- nology development which is related to power and signers think of source load interconnection. energy storage. Stimulus to the development of high efficiency, clean power generation and energy 2.2.4. Cross-Cutting Technology storage is probably the most important contribu- Cross-cutting technology is complementary to tion that NASA’s space exploration program can the power and energy storage technologies while provide to improving the environment and bring- not being directly in line with delivery of an ad- ing about energy independence for the United vanced power system itself. TA03-20 DRAFT States. Any of the energy technologies developed pollutants. NASA work could also contribute to under this roadmap could find commercial ap- the development of higher efficiency nuclear sys- plications and have significant impact despite the tems that would reduce excess heat generation as differences in performance requirements between well as reduce the amount of spent fuel generat- aerospace and terrestrial applications. Aerospace ed for a given amount of electricity. NASA thus applications require maximizing reliability and can make its most effective contributions to solv- specific power/energy, while most commercial ap- ing the world’s energy problems by pursuing mis- plications also require minimizing cost and max- sions that aggressively pull new technologies out imizing production capability. NASA’s mission of the laboratory and display them to the world. requirements create problems which have nev- 2.2.4.3. Multi-Functional Structures er before been defined, and the solutions require Many NASA missions (cross-cutting) would new thinking and new technology. Thus, NASA’s benefit from the mass reduction resulting from contribution to advances in the energy field result the use of multi-functional structures in the power from the efforts to generate novel power systems systems. The idea of incorporating power system for NASA needs. This leads to spin-off technolo- elements into the structure of a vehicle or habitat gies for the commercial world and the creation of would be beneficial in reducing weight and could new companies and teams of engineers who will also enhance reliability and safety through en- apply NASA’s power system technologies to ter- hanced capability for redundancy. Current struc- restrial needs. tural elements are not electrically active. How- An historical example is the low temperature ever, if power system components and structural (e.g., PEM and alkaline) fuel cell. Such fuel cells elements were designed together in a system with were a solution in search of a problem until the part of the power system providing the structure, advent of the human spaceflight program. NASA’s or part of the structure providing a power system interest in fuel cell technology had nothing to function, it would be possible to provide “dual do with “alternative energy”. The Human Space- use” elements in place of current “single purpose” flight Program had no “alternative.” In a classic elements. case of “mission pull”, NASA had to make fuel cell One concept would involve using the space/air- technology work in order to carry out the Gemi- craft structure as the electrode materials for batter- ni, Apollo, and Shuttle programs. NASA actively ies. The electrolyte could be sandwiched between funded both PEM and Alkaline technology devel- two electrode plates which would be part of the opment through the 1970’s. This put technology structure. This would require the electrodes (an- vendor teams in place in the 1990’s to respond odes and cathodes) to have sufficient strength to to the “green energy” and “hydrogen economy” bear structural loads. This is clearly possible with movements that generated strong interest in PEM the advancement of nanotechnology. For exam- fuel cells. In fact, all the major players (automo- ple, carbon nanotubes incorporated in electrodes bile companies and power technology firms) can could provide the strength. The opportunities trace their intellectual property heritage and, in would probably be greater for a multifunction- some cases, their corporate and technical person- al structure incorporating super capacitors. Bo- nel heritage to the three companies where NASA ron nitride (BN) nanotube-based super capaci- funded fuel cell development in the 1960’s and tors are currently of great interest. The structure 70’s. NASA in effect created a new industry that can be strengthened by BN nanotubes, which can brought a laboratory experiment to the current also be used as super capacitors for energy stor- widespread contributions to the energy economy. age. Another possibility is to use the structure as Such can happen with any of the technologies the main power bus bar where the power could being explored on this roadmap. Some especial- pass through the structure and could automatical- ly promising contributions to green energy are ly find the path of least resistance and could “heal” photovoltaics, energy storage systems, energy har- itself if damaged. In effect, it could be a “smart vesting, power management and distribution (e.g. structure”. smart grid), and space nuclear power. NASA’s For a multifunctional structure incorporating space nuclear power research could contribute super capacitors, it would be necessary to first to the development of “grid-appropriate” reac- demonstrate concept feasibility (to TRL 3) in tors which would allow remote users and small three years, complete subcomponent testing in six or developing countries to utilize nuclear power years and provide a concept demonstration in ten instead of power systems that emit CO2 or other DRAFT TA03-21 years. For multifunctional materials that can bear such as the benefits to national defense. Some ex- load and act as electrode materials, initial materi- ample applications would be the use of fuel cells, als could be developed in five years, then a struc- batteries and wireless power transmission to un- tural sub-system demonstrated in six years and a manned aerial vehicles for longer flights before re- system level demonstration performed in 10-12 fueling and quieter operation. Also, unmanned years. Also, nanotube-based super capacitors will electric submarines could also benefit from ad- provide novel high energy density future energy vanced batteries, fuel cells and PMAD systems. storage capability as well as being excellent candi- Portable power systems for the soldier would be dates for inclusion in multi-functional structures. very beneficial by providing lightweight, possibly 2.2.4.4. Alternative Fuels solar-powered systems to keep the soldier cool and Alternative fuels could greatly impact the gen- power tools, lights, and computers without rely- eration of power. For instance, if a novel way to ing on a delivery truck to supply fuel or a load of produce energy dense biomass fuels were available new batteries. to be produced on the moon or on Mars, then Another visible national need is for energy inde- that could become a source of energy for produc- pendence and green energy (discussed previous- ing power. If a novel in-situ resource became avail- ly). NASA's work on batteries and fuel cells and able to generate a new fuel, then that fuel could possibly PMAD could have spin-offs to all electric be used in a power generation system. One major and hybrid cars. Grid scale energy storage systems issue facing the space nuclear community is the would benefit from improved batteries, electrolyz- scarcity of 238Pu. If a viable alternative fuel could ers, fuel cells, flywheels, and PMAD. The "Smart be discovered, or if a novel process for generating Grid" would take advantage of PMAD and Ana- 238 lytical Tools developed to design planetary outpost Pu were discovered, this would have a major im- power systems and terrestrial solar power systems pact on how we power our future space missions. which would consist of high efficiency solar cells, 3. Possible Benefits to advanced arrays, solar concentrators, and Stir- Other National Needs ling convertors. Advanced nuclear power systems could benefit from NASA's efforts to design mod- NASA's work in space power and energy storage ern, lightweight, novel fission and fusion power could have great benefits to other national needs systems. Green energy systems would benefit from Table 2. Interdependencies with other technology areas Relevant Technology Areas Deliverables or Requirements Launch Propulsion Systems (TA 1) High reliability, autonomous, high specific power, long life power and energy storage systems are needed for launch vehicles. In-Space Propulsion Systems (TA 2) High Power Systems (100 kW–5 MW) for electric propulsion; Fuel cell power from liquid propulsion reactants; Fusion beam power for plasma thrusters. Robotics, Tele-robotics, and Autonomous High specific Energy Storage Systems ( >500 Wh/kg); High specific power nuclear and solar power Systems (TA 4) systems Communication and Navigation Systems (TA 5) Communications systems produce clearer, more data-rich signals when enabled with high power sources. Long-life power and energy storage are critical to communication and navigation.

Human Health, Life Support and Habitation EVA Power Systems; Human Habitat Power Systems; Efficient electrolyzers for producing O2 from water. Systems (TA 6) Human Exploration Surface Systems (TA 7) Very high power and energy storage requirements are needed to support human exploration—such as drilling, crewed rovers, high powered instrumentation, etc. Scientific Instruments, Observatories, and Require very long life, ultra reliable, both low and high power systems with high specific energy storage Sensor Systems (TA 8) capability and innovations in power scavenging and beaming. Entry, Descent, & Landing (TA 9) High g power systems (e.g., low power nuclear; and rugged, deployable, high temperature solar arrays) are required. Nanotechnology (TA 10) TA 3 needs input from TA 10 for high specific energy batteries materials, fuel cell catalysts, thermo- electric and photovoltaic materials, etc. Modeling, Simulation, Information technology TA 3 needs to collaborate with TA 11 to generate power and energy storage physics-based models that and Processing (TA 11) can be incorporated into a full system simulation. Materials, Structural and Mechanical Systems, Novel, efficient, multi-functional structures with imbedded power systems and high specific power and Manufacturing (TA 12) solar arrays are needed from TA 12. Ground and Launch Systems Processing (TA 13) High reliability, autonomous, high specific power, long life power and energy storage systems are needed for launch systems. Also: innovative, renewable, portable systems. Thermal Management Systems (TA 14) Advances in power and energy storage systems require advanced thermal management technology, such as advanced radiators, heat pipes, Stirling coolers, etc.

TA03-22 DRAFT NASA’s work on alternative fuels for aviation, ad- kWe kilowatts electric vanced PMAD for wind/solar systems, and energy LEO low earth orbit conservation analysis. Remote, off-grid power sys- LILT Low Intensity/Low Temperature tems could be patterned after NASA's crewed ve- MER Mars Exploration Rover hicles and habitats. MHD Magneto-hydrodynamics p-11B Proton – Boron 11 (fusion reaction). 4. Interdependency with PEBB Power Electronics Building Blocks Other Technology Areas PEM Proton Exchange Membrane The interdependencies with other technology PMAD Power Management and Distribution areas are shown in Table 2. PV Photovoltaic RPC Remote Power Controller RPS Radioisotope power system Acronyms SEP Solar Electric Propulsion αΤ Total Specific Mass kg/kW SiC Silicon Carbide η Efficiency SLA Stretched Lens Array 238Pu Plutonium 238 SOFC Solid Oxide Fuel Cell 241Am Americium 241 (isotope) TDU Technology Demonstration Unit ASRG Advanced Stirling Radioisotope Generator TRL Technology Readiness Level D-D Deuterium – Deuterium (fusion reaction) UAV unmanned aerial vehicle

DRM Design Reference Mission UF4 A cermet fuel D-T Deuterium – Tritium (fusion reaction) TABS Technology Area Breakdown Structure EDLC Electric Double Layer Capacitor aka W-UN Tungsten Uranium supercapacitor EPS Electric Power System Acknowledgements ETDD Enabling Technology Development and Demonstration The NASA technology area draft roadmaps were ETDP Exploration Technology Development developed with the support and guidance from Program the Office of the Chief Technologist. In addition EVA Extravehicular Activity to the primary authors, major contributors for the FDIR Fault Detection Isolation and Recovery TA03 roadmap included the OCT TA03 Road- GPHS General Purpose Heat Source mapping POC, Howard Ross; the reviewers pro- HST Hubble Space telescope vided by the NASA Center Chief Technologists ISIS Integrated Sensor in Structure and NASA Mission Directorate representatives, ISS International Space Station and the following individuals: Douglas Bearden, ITER International Tokomak Experimental Jeffrey George, Steven Howe, Lee Mason, David Reactor Poston, and Isaac Spaulding.

DRAFT TA03-23 November 2010

National Aeronautics and Space Administration

NASA Headquarters Washington, DC 20546 www.nasa.gov TA03-24 DRAFT