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F
TA03 Space Power and Energy Storage
INTRODUCTION
The draft roadmap for technology area (TA) 03, Space Power and Energy Storage, is divided into four level 2
technology subareas:1
• 3.1 Power Generation
• 3.2 Energy Storage
• 3.3 Power Management and Distribution
• 3.4 Crosscutting Technology
NASA has many unique needs for space power and energy storage technologies that require special technol -
ogy solutions due to extreme environmental conditions. For example,
• Venus surface operations require very high sustained temperatures (~460 °C),
• Surface penetrators must survive high-impact decelerations (hundreds of g’s or more),
• Deep space planetary surface missions operate at very cold temperatures,
• Missions that travel very far from the Sun cannot rely on solar energy, and
• Missions to Jupiter and many other destinations must survive high-radiation environments.
These missions would all benefit from advanced technologies that provide more robust power systems with lower
mass. In particular, this technology area encompasses pacing technology challenges for the volume, mass, and
reliability critical space exploration systems. Even in the reduced gravity of the Moon or Mars, the large mass
of EVA suits degrades crew operations. Advanced power and energy storage systems would directly improve the
performance of EVA suits, rovers, surface habitats, and spacecraft.
The ability of space power and energy storage technologies to enable and enhance NASA’s ability to learn
about Earth and the solar system is illustrated by the following quotes from a recently completed decadal survey
on planetary science (NRC, 2011):
1 The draft space technology roadmaps are available at http://www.nasa.gov/offices/oct/strategic_integration/technology_roadmap.html.
131
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132 NASA SPACE TECHNOLOGY ROADMAPS AND PRIORITIES
As future mission objectives evolve, meeting these challenges will require continued advances in several technology
categories, including . . . more efficient power and propulsion for all phases of the missions.
Of all the multi-mission technologies that support future missions, none is more critical than high-efficiency power
systems for use throughout the solar system.
Since more efficient use of the limited plutonium supply will help to ensure a robust and ongoing planetary program,
the committee’s highest priority for near-term multi-mission technology investment is for the completion and valida -
tion of the Advanced Stirling Radioisotope Generator.
The committee recommends that NASA consider making equivalent systems investments in the advanced Ultraflex
solar array technology that will provide higher power at greater efficiency. . .
Investing in these system capabilities will yield a quantum leap in our ability to explore the planets and especially
the outer solar system and small bodies.
Prior to prioritizing the level 3 technologies included in TA03, several technologies were renamed, deleted,
or moved. The changes are explained below and illustrated in Table F.1. The complete, revised technology area
breakdown structure (TABS) for all 14 TAs is shown in Appendix B.
Energy storage can be accomplished using many fundamentally different approaches. The current roadmap
includes three: batteries, flywheels, and regenerative fuel cells. Two other approaches may also prove feasible for
space applications: (1) electric and magnetic field storage and (2) thermal storage (especially for surface power
applications). Accordingly, the structure for this roadmap has been modified by adding two new level 3 technologies:
• 3.2.4. Electric and Magnetic Field Storage
• 3.2.5. Thermal Storage
TABLE F.1 Technology Area Breakdown Structure for TA03, Space Power and Energy Storage
NASA Draft Roadmap (Revision 10) Steering Committee-Recommended Changes
Two technologies have been added.
TA03 Space Power & Energy Storage
3.1. Power Generation
3.1.1. Energy Harvesting
3.1.2. Chemical (Fuel Cells, Heat Engines)
3.1.3. Solar (Photovoltaic & Thermal)
3.1.4. Radioisotope
3.1.5. Fission
3.1.6. Fusion
3.2. Energy Storage
3.2.1. Batteries
3.2.2. Flywheels
3.2.3. Regenerative Fuel Cells
Add: 3.2.4. Electric and Magnetic Field Storage
Add: 3.2.5. Thermal Storage
3.3. Power Management & Distribution
3.3.1. Fault Detection, Isolation, and Recovery (FDIR)
3.3.2. Management & Control
3.3.3. Distribution & Transmission
3.3.4. Wireless Power Transmission
3.3.5. [Power] Conversion & Regulation
3.4. Crosscutting Technology
3.4.1. Analytical Tools
3.4.2. Green Energy Impact
3.4.3. Multi-functional Structures
3.4.4. Alternative Fuels
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133
APPENDIX F
TOP TECHNICAL CHALLENGES
The panel identified four top technical challenges for TA03, all of which are related to the provision of safe,
reliable, and affordable in-space power systems consistent with NASA’s current and potential mission needs. They
are listed below in priority order.
1. Power Availability: Eliminate the constraint of power availability in planning and executing NASA missions.
Power is a critical limitation for space science and exploration. The availability of more power opens up new
paradigms for how NASA operates and even what individual missions can accomplished. Increased power avail -
ability for human exploration missions translates into capabilities to support more astronauts at larger outposts with
higher-capacity in situ resource utilization (ISRU) systems, higher data transmission rates, more capable mobility
systems with shorter turnaround times, and higher capability science instruments. For robotic science missions,
power availability has become critical in determining the scope of a mission that can be planned and how long
it takes to reach mission destinations. This is due to the emergence of electric propulsion systems that enhance
robotic mission design, so that the more power that is available, the shorter the trip time to any destination. Once
at the destination, high power levels enable scientists to develop new approaches to scientific discovery and to
communicate larger volumes of information more quickly back to Earth.
2. High-Power for Electric Propulsion: Provide enabling power system technologies for high-power electric
propulsion for large payloads and planetary surface operations.
Advances in solar and nuclear technologies in the United States and elsewhere during the past decade offer
the potential of developing power generation systems that can deliver tens to hundreds of kilowatts. For example,
inverted metamorphic (IMM) solar cells are being developed to deliver 40 percent efficiency with very little mass
due to removing the thick substrate used to grow the multi-layer photovoltaic semiconductor materials. New light -
weight structures also greatly reduce the mass of solar arrays and enable higher power outputs. As solar arrays
grow to large sizes (such as hundreds of kW for electric propulsion planetary missions), new technology will be
needed for the control and pointing of the large arrays. Nuclear fission system concepts have been developed for
lunar and Mars missions that provide pathways to reasonable mass reactors that can be placed and operated on a
planetary surface to deliver 10 kW to 100 kW. These designs use proven fuels, power conversion technologies,
and reactor materials to reduce the development and operations risk to acceptable levels. Other aspects of fission
systems require technology development including heat exchangers, fluid management, scaling of power conver-
sion devices, heat rejection components, radiation shielding, and aspects of system integration and testing.
3. Reduced Mass: Reduce the mass and stowed launch volume of space power systems.
Power systems typically comprise one third of the mass of a spacecraft at launch, and the volume available
in the launch vehicle fairing can limit the size of solar arrays that can be packaged on the vehicle. New power
generation, energy storage, and power delivery technologies have the potential to cut the mass and volume of these
systems by a factor of two to three. Successfully developing these technologies would enable missions to include
more science instruments, use smaller and less expensive launch vehicles, and/or provide higher power levels.
4. Power System Options: Provide reliable power system options to survive the wide range of environments
unique to NASA missions.
NASA missions require power systems and components to survive many different types of extreme environ -
ments. This can include high radiation levels, very high or very low temperatures, very high impact forces (for
planetary surface penetrators), highly corrosive environments, dusty atmospheres, and other unique extremes. In
all of these challenging environments, the power system must operate predictably and reliably or the mission is
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134 NASA SPACE TECHNOLOGY ROADMAPS AND PRIORITIES
lost. Continued advances in space power technology that improve NASA’s ability to overcome these challenges
will enable NASA to plan and execute a wider array of missions.
QFD MATRIX AND NUMERICAL RESULTS FOR TA03
The panel evaluated 20 level 3 technologies in TA03, Space Power and Energy Storage. Eighteen of these
technologies appear in the draft roadmap for TA03; the other two were added by the panel, as explained above.
The results of the QFD scoring are shown in Figure F.1. Figure F.2 shows the breakdown of the technologies into
high, medium, and low priority categories. Six technologies were assessed to be high-priority technologies:
• Solar (photovoltaic and thermal),
• Fission,
• Distribution and transmission,
• Conversion and regulation,
• Batteries, and
• Radioisotope power systems.
The first five technologies were designated as high-priority technologies because they received the highest QFD
scores based on the panel’s initial assessment. The panel subsequently decided to override the QFD scoring results
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Multiplier 27 5 2 2 10 4 4
0/1/3/9 0/1/3/9 0/1/3/9 0/1/3/9 1/3/9 -9/-3/-1/1 -9/-3/-1/0
Alignment Risk/Difficulty
Technology Name Benefit
60 L
3.1.1. Energy Harvesting 1 3 1 1 3 -3 -1
130 M
3.1.2. Chemical (Fuel Cells, Heat Engines) 3 3 3 3 3 -1 -1
406 H
3.1.3. Solar (Photovoltaic and Thermal Power) 9 9 9 9 9 1 -3
122 H*
3.1.4. Radioisotope (Power) 3 3 1 1 3 1 -3
374 H
9 9 1 1 9 1 -3
3.1.5. Fission (Power)
‐39 L
3.1.6. Fusion 0 3 1 3 1 -9 -9
192 H
3.2.1. Batteries 3 9 9 9 3 1 -1
76 L
3.2.2. Flywheels 1 3 3 3 3 -1 -1
50 L
3.2.3. Regenerative Fuel Cells 1 1 1 1 3 -1 -3
64 L
3.2.4. Electric and Magnetic Field Storage 1 3 3 1 3 -3 -1
118 M
3.2.5. Thermal Storage 3 3 1 3 3 -3 -1
118 M
1 9 9 3 3 -1 -1
3.3.1. (Power) Fault Detection Isolation and Recovery
118 M
3.3.2. Management and Control 1 9 9 3 3 -1 -1
216 H
3.3.3. Distribution and Transmission 3 9 9 3 9 -3 -3
60 L
3.3.4. Wireless Power Transmission 1 3 3 3 3 -3 -3
216 H
3 9 9 3 9 -3 -3
3.3.5. (Power) Conversion and Regulation
106 M
3.4.1. Analytical Tools 1 9 3 1 3 -1 0
54 L
3.4.2. Green Energy Impact 1 1 1 3 3 -3 -1
102 M
3.4.3. Multi-functional Structures 1 9 3 1 3 -1 -1
52 L
3.4.4. Alternative F l
3 4 4 Alt ti Fuels 1 3 1 1 3 -3
3 -3
3
FIGURE F.1 Quality function deployment (QFD) summary matrix for TA03 Space Power and Energy Storage. The justification
for the high-priority designation of all high-priority technologies appears in the section “High-Priority Level 3 Technologies.”
H = High Priority; H* = High Priority, QFD score override; M = Medium Priority; L = Low Priority.
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135
APPENDIX F
0 50 100 150 200 250 300 350 400
3.1.3. Solar (Photovoltaic and Thermal Power)
3.1.5. Fission (Power)
3.3.3. Distribution and Transmission
High Priority
3.3.5. (Power) Conversion and Regulation
3.2.1. Batteries
3.1.2. Chemical (Fuel Cells, Heat Engines)
3.1.4. Radioisotope (Power)
3.2.5. Thermal Storage Medium Priority
3.3.1. (Power) Fault Detection Isolation and Recovery
3.3.2. Management and Control
3.4.1. Analytical Tools
3.4.3. Multi‐functional Structures
3.2.2. Flywheels
3.2.4. Electric and Magnetic Field Storage
Low Priority
3.1.1. Energy Harvesting
3.3.4. Wireless Power Transmission
3.4.2. Green Energy Impact
3.4.4. Alternative Fuels
High Priority (QFD Score Override)
3.2.3. Regenerative Fuel Cells
3.1.6. Fusion
FIGURE F.2 Quality function deployment rankings for TA03 Space Power and Energy Storage.
to designate radioisotope power systems as a high-priority technology to highlight the critical importance of cur -
rently funded and planned programs for Pu-238 production and Stirling engine development and qualification.
Figure F.3 correlates the applicability of the top technical challenges, as described above, to each of the
Space Power and Energy Storage level 3 technologies. This shows that the high-priority technologies, discussed
in the next section, provide the potential solutions that will meet these challenges. The medium- and low-ranked
technologies are judged to have a weak linkage because of the limited benefit of investing in these technologies
regardless of how closely they may overlap with various challenges in terms of subject matter.
HIGH-PRIORITY LEVEL 3 TECHNOLOGIES
Panel 1 identified six high-priority technologies in TA03. The justification for ranking each of these technolo -
gies as a high priority is discussed below.
Technology 3.1.3, Solar (Photovoltaic and Thermal)
Photovoltaic space power systems have been the workhorse of NASA science missions as well as the foundation
for commercial and military space systems. Solar cells directly convert sunlight into electricity. Today’s solar cells are
made from III-V materials2 and are composed of multiple junctions of various band gaps to achieve solar conversion
efficiency of 30 percent. Current emphasis is on the development of high-efficiency cells. NASA also needs
• Cells that can effectively operate in low-intensity/low-temperature (LILT) conditions (which is typical
when spacecraft are more than three astronomical units from the Sun),
• Cells and arrays that can operate for long periods at high temperatures (>200°C),
• High specific power arrays (500 to 1000 W/kg), and
• Electrostatically clean, radiation tolerant, dust tolerant, and durable, re-stowable, and/or deployable arrays.
2 III-V materials are semiconductor materials made of materials from Groups III and V of the periodic table, such as gallium-arsenide.
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136 NASA SPACE TECHNOLOGY ROADMAPS AND PRIORITIES
Top Technology Challenges
2. High-Power for
Electric Propulsion:
Provide enabling power 4. Power System
system technologies for Options: Provide reliable
1. Power Availability: 3. Reduced Mass:
Eliminate the constraint high power electric Reduce the mass and power system options to
of power availability in propulsion for large stowed launch volume survive the wide range
planning and executing payloads and planetary of space power of environments unique
Priority TA 03 Technologies, Listed by Priority NASA missions. surface operations. systems. to NASA missions.
● ● ● ●
H 3.1.3. Solar (Photovoltaic and Thermal Power)
● ● ● ●
H 3.1.5. Fission (Power)
○ ● ○
H 3.3.3. (Power) Distribution and Transmission
○ ● ○ ○
H 3.3.5. (Power) Conversion and Regulation
○ ● ●
H 3.2.1. Batteries
○ ●
H 3.1.4. Radioisotope (Power)
○
M 3.1.2. Chemical (Fuel Cells, Heat Engines)
M 3.2.5. Thermal Storage
M 3.3.1. (Power) Fault Detection Isolation and Recovery
M 3.3.2. Management and Control
M 3.4.1. Analytical Tools
M 3.4.3. Multi-functional Structures
L 3.2.2. Flywheels
L 3.2.4. Electric and Magnetic Field Storage
L 3.1.1. Energy Harvesting
L 3.3.4. Wireless Power Transmission
L 3.4.2. Green Energy Impact
L 3.4.4. Alternative Fuels
L 3.2.3. Regenerative Fuel Cells
L 3.1.6. Fusion
Strong Linkage: Investments by NASA in this technology would likely have a major
● impact in addressing this challenge.
Moderate Linkage: Investments by NASA in this technology would likely have a
○ moderate impact in addressing this challenge.
Weak/No Linkage: Investments by NASA in this technology would likely have little or
[blank]
no impact in addressing the challenge.
FIGURE F.3 Level of support that the technologies provide to the top technical challenges for TA03 Space Power and Energy
Storage.
Because of the critical importance of photovoltaic power systems, the Department of Defense (DOD) is funding
technology development at the cell level to raise that efficiency first to 33 percent and then to 39 percent. The
most common usage is in planar solar arrays but certain concentrator arrays have flown successfully and two types
are currently under development. Concentrator arrays offer cost reductions due to reduced solar cell material and
efficiency gains.
Nearly all spacecraft flown to date have been powered by solar arrays. Photovoltaic power systems provide
the energy for NASA science missions in low Earth orbit (LEO), including the International Space Station (ISS)
and higher altitude communication systems such as the Tracking and Data Relay Satellite Systems (TDRSS).
They have powered science missions to Mars (both in orbit and on the surface), Venus, and Mercury. Advanced
photovoltaic power systems will be used on the Juno mission to Jupiter and the Solar Probe Plus near the Sun.
Commercial communications satellites in geosynchronous Earth orbit (GEO) rely exclusively on photovoltaic
power systems. NOAA polar orbiting weather satellites also rely on photovoltaic power systems. The DOD uses
photovoltaic power systems for satellites in LEO, GEO and mid-Earth orbits (MEO) for observation, event detec -
tion, navigation (the Global Positioning System), and others applications. The high priority assigned to this level
3 technology is based on the benefit provide by photovoltaic research. The draft roadmap for TA03 also includes
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APPENDIX F
solar thermal systems in technology 3.1.3, but the panel does not perceive solar thermal power technology as a
high priority because it has not been used in space and it has not proven to be cost competitive.
Many photovoltaic power systems have achieved a TRL of 9, including the III-V triple junction solar cells.
Advances in new photovoltaic technology, such as IMM photovoltaic cells (which remove the substrate to leave a
cell that is only a few microns thick and has a power conversion efficiency of more than 30 percent with exceedingly
low mass and inherent radiation tolerance. IMM arrays will be storable and deployable. The increased efficiency
of IMM cells will enable smaller arrays, and the lightweight cells may enable alternate array structures to further
reduce mass. Lightweight solar array structures with specific mass beyond the 100 W/kg offered by the current
state of the art would also be beneficial. These technologies are currently at TRL 3 or below.
As discussed in Appendix E (TA02, In-Space Propulsion Technologies), NASA has a vital interest in photo -
voltaic power system developments for high-power electric propulsion (EP) missions. Because power system mass
reduction is critical to EP missions, advanced array technologies that offer high specific mass (>500 W/kg) and high
power density (>300 W/m2) are critical technology development areas. Increases in solar cell efficiencies offered
by IMM photovoltaic cell technology and lightweight array technology, including both planar and concentrator
approaches (now at TRL 2), is expected to achieve a specific mass of more than 600 W/kg and a power density
of more than 400 W/m2.
The NASA Glenn Research Center has been the primary NASA center developing photovoltaic technolo -
gies, with the Jet Propulsion Laboratory (JPL) and NASA Goddard Space Flight Center (GSFC) also providing
significant capabilities and facilities to advance the state of the art. NASA is well qualified to lead development
of high-power solar array technology because of its expertise and capabilities plus the diversity of its mission
needs, while collaborating with DOD, DOE, commercial industry, and academia. While the DOD has a modest
investment in IMM solar cell technology, NASA is highly motivated to invest in IMM technology to ensure timely
development of next generation solar cells to meet its own mission needs. Continued interactions between NASA
and other countries investing in space photovoltaic technology, including multiple European countries and Japan,
would be beneficial. The ISS has been used to test and qualify new photovoltaic cell technologies in the past, and
it remains available for this function.
Photovoltaic power technology is a high priority because of the game-changing impact that higher power,
lighter weight solar arrays would have on future NASA missions. Solar power generation applies to virtually all
NASA mission areas plus DOD, commercial, and civil space enterprises. Development efforts will therefore lead
to widespread benefits across the user spectrum. The development risks for high-power solar arrays are moderate
to high, which is appropriate for NASA technology investments. Space demonstration tests of lightweight arrays
with power output of 30 to 50 kW level are warranted, and the risks at that size are relatively low. Development
of larger arrays with power output as high as 1 MW will be required to support large-scale exploration missions.
Solar arrays with such a high power output would be game changing. Structures large enough for such a large array
have not been developed, however, and a focused development program for large arrays, that addresses control and
pointing issues and the higher risk associated with higher power arrays, is warranted to support NASA exploration
missions.
Technology 3.1.5, Fission
Space fission power systems use heat generated by fission of a nuclear fuel to power a thermal to electric
conversion device to generate electric power. Key subsystems include the reactor, heat exchanger (to move the heat
out of the reactor and into the power converter), power converter, heat rejection radiator, and radiation shield. As
noted in an earlier study that focused on space applications of fission reactor systems (NRC, 2006, pp. 10-11):
Nuclear reactor systems, which can provide relatively high power over long periods, make it possible to design mis -
sions with more numerous and more capable science instruments, high-bandwidth communications systems, shorter
transit times, and greater flexibility to change the course and speed of spacecraft enough to conduct extended investi -
gations (rather than brief flybys) of bodies of interest; visit multiple bodies much more easily; and significantly alter
a spacecraft’s trajectory in response to information collected during a particular mission. Nuclear reactors have the
potential to overcome limitations associated with low energy and power. They do this by providing electricity and
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138 NASA SPACE TECHNOLOGY ROADMAPS AND PRIORITIES
propulsion over a wide range of power levels for extended periods (years to decades), including during both transit
and surface operations, without regard to the availability of either solar energy or large quantities of chemical fuel.
Nuclear reactor systems, however, are expensive to develop, and their potential will be realized only if key technol -
ogy issues can be overcome.
Space fission technology is currently assessed to be at TRL 3. While some components are demonstrated at
higher TRLs, many of the required elements require technology development to advance beyond TRL 3. Other
components have reached higher TRLs in past programs such as the SP-100 and Prometheus programs, but tech -
nology capability has been lost and must be redeveloped. Key subsystems that must be addressed include the reac -
tor (including instrumentation and control/safety), energy conversion, heat transfer, heat rejection, and radiation
shields.
NASA has some of the expertise needed to develop space fission power system technologies, but it will need to
work in collaboration with the DOE and private industry in order to advance the technology to TRL 6 and beyond.
Because of their unique capabilities and statutory requirements, DOE must take the lead on the development reac -
tor components and technologies, including the fuel. NASA centers including the Glenn Research Center and the
Marshall Space Flight Center have the expertise and facilities to lead development of the energy conversion and heat
rejection subsystems. NASA is also qualified to lead overall systems engineering efforts, with DOE assistance for
nuclear subsystems. This is a technology that is primarily suited to space exploration needs, and therefore NASA
is best positioned to take the lead in maturing the technology to TRL 6 or beyond. There may be opportunities to
collaborate with some international partners that have capabilities and facilities in fast reactor technologies, such
as Russia, Japan, and France. Use of the space station is not appropriate for developing this technology.
Space fission power systems would be game-changing due to the potential (1) to provide a power rich envi -
ronment to planetary surface exploration missions, especially for crewed missions, and (2) to enable high-power
electric propulsion systems for deep space exploration and science missions. The alignment of this technology
with NASA’s needs is high because of the game-changing impact it would make on both robotic science and
human exploration capabilities. Alignment with other aerospace and national needs is considered to be low because
space power reactors will be designed as fast neutron reactors, and there are no significant terrestrial applications
for fast neutron reactor technology. The risk is assessed to be moderate to high, which is appropriate for NASA.
(This risk level assumes that NASA will set realistic goals for the fission system to be developed; otherwise the
risk could increase to the “very high” level.) The next space fission development program would hopefully adopt
performance and life goals that are not as ambitious as the fission power system goals incorporated in the cancelled
Jupiter Icy Moons Orbiter (JIMO) mission, so that entirely new materials or fuels will not need to be developed.
A space reactor concept based on liquid metal cooling, stainless steel structures, and UO 2 fuel would have the
strongest technology base, drawing on decades of development. The pursuit of higher temperature systems has
been the primary source of technical problems and associated cost and schedule overruns in prior space fission
power system development projects. The cost of the power system development is expected to be high, in the range
of $1 billion to $2 billion over 10 to 12 years. This cost is easily justified, however, by the potential benefits that
can be realized in both the human and robotic exploration of the outer solar system and beyond. Thus, fission is
judged to be a high-priority technology.
Technology 3.3.3, Distribution and Transmission
Interest in the components of a spacecraft electrical power system often centers on the power generation and
storage functions, and many resources have been devoted to exploring options, developing alternatives, and improv-
ing the specific power and energy of the systems that serve these two functions. As game-changing science and
human exploration missions of the future are examined, the need for significant increases in electrical power on
spacecraft becomes a clearer and higher priority. With these higher power levels, an extrapolation of the current
technologies for the distribution and transmission (D&T) of power would result in unacceptably high mass and
complexity. Thus, D&T is judged to be a high-priority technology area.
Distribution and transmission on a space system is comprised primarily of cables (copper conductors and
insulation) and connectors. Currently, electrical power on spacecraft is distributed by direct current (DC) at fixed
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APPENDIX F
voltages ranging from 28V DC to 100V DC. The ISS is the exception to this rule, with a 120V DC distribution
architecture. As higher power systems are developed, higher voltage distribution will be required to avoid very
heavy wire bundles. This can be done with either DC or alternating current (AC) architectures. Paschen’s law
limits high-voltage DC systems to a maximum of about 270 V DC. Therefore, high power levels will require more
attention to AC systems, probably at relatively high frequencies. The demand for lower mass will challenge the
traditional copper materials for the bus, and the need to operate at higher temperatures (to increase the efficiency
of the thermal management systems as well as electronics efficiencies) may appear counter to the need to reduce
ohmic losses in transmission lines.
Proposed research under technology 3.3.3 would increase the voltage of D&T subsystems, develop high-
frequency AC distribution options for space systems, and identify alternate materials to replace copper conductors.
Copper wire has long been a conductor of choice for spacecraft, but as power levels increase, so too will current
and voltage and with them the conductor mass will grow. With DC currents, to reduce the mass penalty of larger
cables, alternate materials such as superconductors or nano-material conductors may need to be developed, along
with lighter space-qualified insulating materials capable of protecting systems at high voltage. With AC power
systems, advancing beyond the 116 V AC system in the space shuttle may require very high operating frequen -
cies; for example, NASA funded development of a 440 volt, 20 kHz AC power system for Space Station Freedom
until it was reconfigured to use a DC power system (Patel, 2005). Technical needs include keeping transmission
losses to a minimum, reducing transformer masses, incorporating fault protection and smart telemetry into power
distribution architectures, and developing new connectors.
Ultimately, the nature of future missions will dictate the architecture and technologies used for vehicle power
systems, and that, in turn, will define the requirements for electrical power D&T. For example, the electrical
power from a nuclear reactor-turboalternator system will likely be high-voltage AC, while power from photovol -
taics is always generated as a DC voltage. If electric thrusters are needed for the mission, very-high-voltage DC
power (kilovolts) will be required, perhaps from a nuclear prime-power source. Each of these options will impose
D&T technology requirements that are, in most cases, not yet at TRL 3. The risks associated with developing the
needed D&T technologies are high over the next two decades, but there may be no alternative to addressing those
needs if the needed power is to be delivered to the load with acceptable mass, volume, and efficiency constraints.
NASA is well suited to lead development of advanced D&T technologies. Advances in this technology will
likely require significant participation from both industry and academia for voltage selection, architecture technol -
ogy option development, and advanced transmission and insulation materials. The ISS provides limited benefit to
the development this technology, as testing can be accomplished on the ground using vacuum chambers and test
fixtures. In addition, the introduction of high voltages on the ISS could pose safety risks, which would increase
the cost and schedule of any ISS test program. However, in-space testing is ultimately required (on the ISS or
some other platform) to validate new D&T technology in the space environment. For example, in-space testing is
needed to address plasma interactions and micro-meteoroid impacts.
The panel determined that advanced D&T technology could provide significant benefits in terms of system
mass reduction due to the major reductions in cable harness mass that could be achieved with high-voltage sys -
tems. Advanced technologies in this area would be broadly applicable to many classes of NASA and non-NASA
space systems, and potentially to a broad range of terrestrial systems as well. The risk was judged to be medium
to high, within the typical range of NASA technology programs.
Technology 3.3.5, Conversion and Regulation
The voltage and current of electrical power available on any particular spacecraft will be dictated by the power
source and the power management and distribution architecture. Various payloads will then most likely require the
power in a different form, such as higher voltage for electric propulsion. The purpose of electrical power conver -
sion and regulation is therefore to provide the necessary bridge between the power source and payloads, and to
regulate this power to within the tolerances required by the payloads.
Currently unresolved issues include the need to (1) space qualify existing terrestrial high-voltage components
and (2) replace space qualified components that currently lag significantly behind the commercial state of the
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140 NASA SPACE TECHNOLOGY ROADMAPS AND PRIORITIES
art. Important parameters for improving power conversion and regulation devices include increasing conversion
efficiency, operating temperature range, and radiation tolerance. Advanced conversion and regulation technology
with relatively near-term application is at TRL 4.
Future space power generation and distribution systems are likely to operate at high voltages than current
systems to increase efficiency. Higher current ratings, lower switching and conduction losses, and higher junction
temperature tolerances would improve the functionality of future system components. The need for high-voltage
regulation is also associated with some electric propulsion technologies that require high voltages (kilovolts) to
function. Development of high-voltage regulation capabilities would require a major project that includes the
development of many new technologies and facilities. The next generation technology for power conversion and
regulation is at TRL 2 to 3.
An example of advanced conversion and regulation technology is a higher band gap material such as silicon-
carbide or gallium-nitride that would replace the traditional silicon materials in switching components, thereby
increasing device operating temperature and efficiency while decreasing mass and volume. Another example is
advanced magnetics for improved conversion and regulation devices.
NASA has the extensive capabilities, equipment, and facilities needed to lead research and technology develop -
ment of advanced conversion and regulation technology. NASA will need to collaborate with industry and academia
to leverage the power electronics advances being made for other applications, including commercial uses. Advance -
ments that NASA makes in this area will have application to future electric vehicles and commercial smart-grid
systems where power is generated and regulated close to its point of use. Some aspects of technology development
can potentially be accomplished jointly with offices of the DOD and DOE. Qualification of the hardware in the
space environment could be facilitated by attaching an experimental payload externally to the ISS, providing a
low-risk, in-space demonstration.
Conversion and regulation of power was highly ranked because it was identified as potentially providing
a major improvement in mission performance, as well as having broad applicability across several NASA mis -
sion areas. The main benefits of advanced power conversion and regulation on system performance come both
directly in the form of lower subsystem mass, as well as indirectly in the form of better conversion efficiencies
that provide higher power margin. These benefits are especially important at the higher power levels needed for
electric propulsion systems or high-bandwidth communications. Increasing the efficiency of power conversion
could potentially reduce the size of solar arrays, batteries, and thermal control systems by more than 10 percent
on lower power systems, with a bigger impact for higher power systems. Conversion and regulation was assessed
to have broad application across the general aerospace community, as all spacecraft use power conversion and
regulation components. The technical risk associated with future advancement of this technology is moderate to
high, which is a good fit to NASA’s level of risk tolerance for technology development, and the likely cost to
NASA and the timeframe to complete technology development is not expected to substantially exceed that of past
efforts to develop comparable technologies.
Technology 3.2.1, Batteries
Batteries are electrochemical energy storage devices that have been flown in space since the beginning of
the space age. Battery technology has advanced continuously, and further high-payoff improvements are possible
through recent scientific discoveries. In space, batteries must survive a variety of harsh, sometimes unique envi -
ronments and load profiles are more demanding than for most terrestrial applications. Many batteries are already
proven in space, at TRL 9, but a variety of advanced chemistry alternatives have yet to be developed and qualified
for spaceflight.
After relying on nickel-cadmium and nickel-hydrogen rechargeable batteries for decades, the aerospace indus -
try is now moving to lithium-ion (Li-ion) batteries as the standard energy storage component for space systems.
Li-ion technology provides a substantial improvement in specific energy, charge and discharge rates, and cycle
life at high depths-of-discharge. Li-ion batteries are also being used as a primary battery (where the battery is used
once and not recharged) in applications such as launch vehicle electric power systems.
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NASA missions would benefit from new electrochemical power technologies that offer higher specific energy
and/or higher specific power. NASA has world-class expertise in space battery technology, with capabilities at
multiple centers including JPL, Glenn Research Center, Goddard Space Flight Center, and Ames Research Center.
NASA is best qualified to lead development of advanced battery technology for their unique mission needs. Ide -
ally, research in this technology would leverage commercial technology developments, as NASA did with the
development of Li-ion batteries for space applications.
Rechargeable battery technology is advancing rapidly to meet the commercial needs of electric vehicles, cell
phones, laptop computers/tablets, and renewable energy systems. NASA would therefore benefit from collabora -
tions with DOE and commercial industry in developing advanced battery technology. DOE’s Advanced Research
Projects Agency-Energy (ARPA-E) is pursuing a wide range of advanced battery technologies, and the commercial
automotive industry is investing in efficient batteries for plug-in hybrid/electric vehicles (where longevity, energy
density, and reliability are quite important, as they are in space applications. The ISS can be an asset in testing
some advanced batteries (such as those with liquid electrodes or electrolytes) in a relevant thermal, electrical, and
microgravity environment.
The steering committee assessed the benefit of battery technology to be significant due to the potential to
reduce mass for many space systems and to enable missions in extreme environment missions. The alignment of
this technology with NASA’s needs is high due to its potential impact on both robotic science and human explora -
tion capabilities; its alignment with other aerospace and national needs is also high because batteries are so widely
used. NASA can capitalize on the investments by other government and commercial organizations that are making
substantial investments in advanced battery technologies. However, the unique requirements posed by NASA mis -
sions in extreme environments do require NASA-specific research and development with moderate risk.
Technology 3.1.4, Radioisotope
Radioisotope power systems (RPSs) provide power to scientific and human exploration missions over long
periods almost anywhere in the solar system and beyond. RPSs have enabled many unique deep space and plan -
etary exploration missions, making important scientific discoveries possible. RPSs used plutonium-238 (Pu-238)
as a heat source, and they have used thermoelectric converters since 1961 to provide reliable electrical power for
many missions throughout the solar system, including Pioneer, Viking, Viking landers, Galileo, Ulysses, Apollo
12-17, Cassini, and New Horizons. Demonstrated mission operating lifetimes have exceeded 30 years. Future
RPSs could be developed to deliver both lower power levels (watts or fractions of a watt) and higher power levels
(hundreds of watts up to 1 kW). The higher power systems would enable radioisotope electric propulsion for deep
space missions, making several new classes of missions possible.
While RPSs have a well-established foundation, there are significant technology issues that must be overcome
to maximize the effectiveness of the United States’ dwindling supply of available Pu-238. DOE no longer has the
ability to produce Pu-238 (except for very small amounts for research), and the United States has purchased all
available Pu-238 from Russia. No other country, including Russia, is currently producing Pu-238, and multiple
studies have shown that there is no other available radioisotope material that can meet even a significant fraction
of NASA’s RPS needs. Supported by recent NRC studies (NRC, 2010, 2011), NASA and DOE have been attempt -
ing to restart production of a limited annual quantity of Pu-238 for the past few years, but Congress has not yet
provided funding to the DOE and/or NASA for this purpose.3
NASA and DOE have been developing advanced RPSs that would use Stirling engines to replace thermoelectric
converters. Because the energy conversion efficiency of the Stirling engine under development is about 5 times that
of thermoelectric converters, Stirling engines require significantly smaller quantities of Pu-238 to achieve similar
power levels. Given the scarcity of Pu-238 (which will persist for years even after Pu-238 production is approved
and funded), the much higher efficiency of Stirling engines is necessary if RPSs are to be available for NASA’s
3 By statute, the U.S. DOE is the only federal agency authorized to produce nuclear material. Congressional action through October 2011
indicates that the 2012 budget for DOE will include no funds to restart production of Pu-238. The NASA budget for 2012 may include up to
$10 million for this purpose, but it remains to be seen when the DOE will be able to restart production of Pu-238.
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142 NASA SPACE TECHNOLOGY ROADMAPS AND PRIORITIES
planned science and exploration missions. As discussed in Chapter 3, establishing a reliable, recurring source of
Pu-238 and maturing Stirling engine technology are both critically important to provide power for NASA’s future
science and exploration missions that cannot rely on solar power.
Radioisotope technology using Stirling engines is currently assessed to be at TRL 6. Although some compo -
nents have been demonstrated at higher TRLs, a flight test is needed to advance beyond TRL 6. Using the ISS to
demonstrate this technology is not an option due to restrictions regarding operation of nuclear power systems in
LEO. RPS technology is somewhat unique to NASA, as interplanetary space missions are the only driving need
that has been identified to justify restarting Pu-238 production. NASA and DOE have the unique capabilities and
facilities necessary to develop RPSs. By statute, DOE must be responsible for the nuclear aspects of RPS technol -
ogy development. NASA Glenn Research Center has led the development of Stirling engines and the Jet Propulsion
Laboratory leads NASA efforts in RPS development and spacecraft integration.
In assigning the QFD scores for this technology, the panel assumed that Pu-238 production and Stirling
technology development would continue as currently planned by NASA. As noted above, RPS technology was
selected as a high-priority technology despite its relatively modest QFD score because this technology is criti -
cally important to the future of NASA’s deep space missions. The committee assessed the benefit of additional
investments in RPS technology to be low because there are few good options with the potential to improve on the
performance of RPSs that couple Stirling engines with Pu-238 heat sources. However, as noted above, this rating
would be much higher if those technologies were not already being developed. The alignment of this technology
to NASA’s needs is high due to the high impact on both robotic science and human exploration capabilities, while
alignment with other aerospace and national needs is considered to be low. The risk is assessed to be moderate
to high, within the bounds of NASA’s acceptable risk levels for technology development. The cost of the power
system development is expected to be moderate. Thus, RPS technology would be assessed as a medium-priority
technology based on its QFD score, which is based on two assumptions: (1) the current program for Stirling engine
development is continued and (2) domestic production of Pu-238 is restored in a timely fashion. Given that the
second assumption remains in doubt, the panel overrode the QFD score to assign this technology a high priority.
MEDIUM- AND LOW-PRIORITY TECHNOLOGIES
TA03 includes 14 level 3 technologies that ranked low or medium priority. This includes two technologies
that were added to the TABS for completeness. Thermal storage was added due to its potential to improve energy
storage mass, as compared to advanced batteries, for many special purpose applications. For example, if a heat-
engine-based power system is used, energy can be efficiently stored thermally instead of using an electrochemical
system. In situ resource utilization (ISRU) is another application where thermal energy storage might be preferable,
especially if thermally based processes are used. Electric and magnetic field storage was added as a technology
to cover many advancing technologies such as super-capacitors, ultra-capacitors, and superconducting magnetic
energy storage. In general, these technologies are useful options when storage times are very short such as peak
load management for a high-power-radar instrument.
Seven of the eight technologies that were assessed to be low priority were judged to have marginal benefits
to NASA missions within the next 20 to 30 years. These technologies included energy harvesting, flywheels,
regenerative fuel cells, electric and magnetic field storage, green energy impact, alternative fuel storage, and
wireless power transmissions. The marginal benefit (less than 10 percent improvement) evaluation was based on
an assessment of the expected improvement, at the system level, in the primary parameter of interest for each
technology. In most cases, this was improvement in spacecraft mass or reliability that the panel believed could be
achieved given reasonable investments in that technology. While higher claims have been made for some of these
technologies, such as flywheels or electric and magnetic field storage, the panel’s review of available information
did not produce any credible technology development paths that would achieve the ambitious performance levels
specified in the draft roadmap with reasonable investments. Also, currently available approaches for advancing
these technologies tended to have a lower risk level than is usually appropriate for NASA technology investments.
The remaining low-priority technology, fusion, was judged to provide no likely value to NASA in the next 20 to
30 years due to a very low probability of success during that timeframe.
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The six power and energy storage technologies that were ranked as medium priority included four that had
marginal benefit scores and two that had more substantial benefits, but application of those benefits was limited
to a small set of mission areas. The four with marginal benefits included fault detection, isolation, and recovery
(FDIR), management and control, analytical tools, and multi-functional structures. While the benefit of these
technologies was assessed to be similar to the low-priority technologies discussed previously, all four ranked
higher because any advancement would apply to all or nearly all NASA and non-NASA space missions in all or
most mission classes. In other words, success in these technologies helps everyone. The remaining two medium-
priority technologies, thermal storage and chemical power generation, were judged to provide substantial benefit
to a smaller set of mission opportunities. Thermal storage applications include heat engine power systems and
ISRU, as described above. Chemical power generation, including fuel cells and heat engines, may be valuable in
human exploration missions where large quantities of hydrogen and oxygen are being used for propulsion. In these
cases, power can be generated essentially for free using the boil-off from the propellant tanks.
DEVELOPMENT AND SCHEDULE CHANGES FOR THE
TECHNOLOGIES COVERED BY THE ROADMAP
Schedules for Space Power and Energy Storage technologies are highly dependent on the level of funding
applied to the development programs. The schedules depicted in the roadmap are generally feasible if sufficient
resources are applied to each item in the roadmap.
OTHER GENERAL COMMENTS ON THE ROADMAP
Space Power and Energy Storage is related to several other technical areas. Many challenging requirements
arise from high-power electric propulsion applications discussed in TA02. Heat rejection from power and energy
storage components relies on technologies from the thermal control systems covered by TA14. Advances in many
power technologies are possible due to advancing materials technologies discussed under the materials and struc -
tures technologies in TA12 and nanomaterials covered by TA10.
PUBLIC WORKSHOP SUMMARY
The workshop for the Space Power and Energy Storage technology area was conducted by the Propulsion and
Power Panel on March 21, 2011, on the campus of the California Institute of Technology in Pasadena, California.
The discussion was led by panel member Douglas Allen, who began with a general overview of the draft roadmap
and the NRC’s task for this study. He also provided some direction for what topics the invited speakers should
cover in their presentations. Experts from industry, academia, and government were invited to lead a 25 minute
presentation and discussion of their perspective on the draft NASA roadmap for TA03. At the end of the session,
there was a short open discussion by the workshop attendees that focused on the recent session. At the end of the
day, a concluding discussion led by Allen summarized the key points observed during the day’s discussion.
Session 1: Solar Arrays
Ed Gaddy (Applied Physics Laboratory) started the solar arrays session with a discussion on properly mea -
suring the impact of technology improvements. His argument was that often the cost impact of weight saving
technology improvement is significantly underestimated. This can lead to under-investment in advanced technolo -
gies. He also observed that solar array history has shown that slow and steady investments, which lead to slow and
steady technology improvements can be highly successful and, over time, this approach can yield revolutionary
improvements in capabilities. He advocated support for Inverted Metamorphic Multijunction (IMM) photovoltaic
cells as the next evolutionary step forward in this technology. Finally, he stated operational missions need better
insight into the benefits of adopting specific new technologies and/or incentives should be established to encourage
mission managers to adopt advanced technologies that have achieved an appropriately high TRL.
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Alan Jones (ATK) began his review of the TA03 roadmap by saying that its near-term goals were generally
achievable, but the long-term goals would be much more challenging. He then reviewed the solar power array chal -
lenges that are specific to NASA missions, such as very low or very high environmental temperatures. He endorsed
NASA investment in IMM photovoltaic cell technology, but added that support for advanced array technologies is
also needed. In particular, he suggested that investing in wing-level structural platforms is needed to fully realize
the benefits of the new cells.
Ted Stern (Vanguard Space Technologies) discussed integrated array manufacturing methods that could reduce
array cost and weight and increase array reliability. He also discussed a concept of modular solar arrays that would
simplify spacecraft design by making all arrays using the same method, which would allow for easier qualification.
He also discussed the advantages and disadvantages of near-term technology for solar concentrators to improve
solar array performance. For the long-term, he supported investments in spectrum converting and multi-photon
enabled photovoltaics that may provide game-changing performance. Finally, he noted the value in showing the
relevance of improved solar arrays to terrestrial spinoffs.
Paul Sharps (Emcore Photovoltaics) began by providing some information on Emcore and noting that it is
one of two U.S. developers and manufacturers of high-efficiency multi-function solar cells and arrays for space
applications. He noted that while solar cells have received continuous DOD funding for 25 years, there has been
little improvements in cell integration and array technologies. He provided his perspective on IMM technology,
stating that Emcore had achieved 34 percent energy conversion efficiency with this technology in the laboratory,
and work is progressing with concepts that may achieve 37 percent efficiency. (State-of-the-art cells have less
than 30 percent conversion efficiency.) Sharps believes that a 34 percent efficient, radiation hard IMM cell is 2 to
3 years away from being inserted into flight hardware. He suggested that NASA focus its photovoltaic cell invest -
ments on this technology, adapting it for NASA specific requirements such as very-high- and very-low-temperature
environments and the very low light intensity experienced in deep space.
In the group discussion the speakers were asked to forecast where state-of-the-art array technology might be
in the next 20 years. The speakers seemed to generally agree that a power density of 400 W/kg will be available in
the near term, but that long-term forecasting is very difficult given that the next generation of technology that will
be successful beyond IMM remains to be determined. The group discussion also covered the benefits that NASA
is likely to receive from investing its own resources in solar array technology. The responses included arrays built
for NASA specific environments (particularly missions to outer planets, the inner planets, and the Sun), quicker
deployment of advanced technologies, and the ability to act as a smart buyer of array technology provided by
industry.
Session 2: Power Storage
Joe Troutman (ABSL Space Products) started the session on power storage by noting that Li-ion technology
has driven recent advances in battery performance. He said that basic Li-ion battery technology has been proven,
but more work is needed to improving cell performance and safety, primarily through the use of advanced cathode
materials and anode coatings. He also suggested that increasing cell voltage would lead to higher energy density
and cycle life.
Michael Tomcsi (Quallion) said that Li-ion batteries have shown a steady improvement in energy density
(W-hr/kg) of about 6 to 8 percent per year for the past 15 years. He then discussed the different materials that can
be used to improve batteries in the future. He suggested that small improvements of a few percent per year are
achievable. Tomcsi asserted that metallic lithium batteries may provide a leap in performance, although significant
safety issues must be overcome.
In the group discussion both speakers agreed that cathode advancements will be the biggest challenge in
future battery improvements. For advancements needed to support NASA specific needs, they suggested that low-
temperature performance could be improved with some loss in performance, but the high-temperature requirements
stated in the draft roadmap for TA03 are very challenging and may be achievable only with a completely new
type of battery. There was also some discussion on better modeling for battery development and the challenge of
developing good physics-based battery models to replace current empirical models.
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Session 3: Power System Engineering
The purpose of this session was to obtain insights into how solar-based power systems work as a whole and
the performance improvements that could arise from advanced technology.
Robert Francis (The Aerospace Corporation) began the session by discussing some of the general issues
related to improving solar-based power systems. He noted that the DOD has a technology roadmap with specific
performance numbers in terms of energy density and volumetric efficiency for solar arrays. This DOD roadmap
projects improvements that are about half the level of improvement proposed in the draft NASA roadmap for
TA03. Francis thinks that most of the mass savings in future solar power systems will come from improvements
to solar array supporting structures—not from improvements in the solar cells mounted on the arrays. He noted
some of the challenges in moving to very-high-power arrays include the need for higher voltages for the spacecraft
electrical bus and difficulties in ground testing.
Azam Arastu (Boeing) focused most of his talk on the two advanced, lightweight, and compact, solar arrays
currently under development at Boeing with the support of the Defense Advanced Research Projects Agency
(DARPA) and the U.S. Air Force Research Laboratory. Both the Fast Access Testbed Spacecraft (FAST) and
the Integrated Blanket/Interconnect System (IBIS) arrays are capable of generating very high power and employ
highly efficient IMM solar cell technology and advanced deployment structural concepts to provide significant
improvements in the specific power over the current state of the art. The FAST array uses linear solar concentra -
tors and is less expensive as it uses fewer solar cells. It also is more tolerant to radiation and more effective in
the low-light environments of deep space, but it has more precise pointing requirements. The IBIS array, which is
constructed using thin, flexible, and planar solar modules, packs more compactly than FAST and has less precise
pointing requirements. Both array systems are designed to be highly modular and scalable so they can eventually
be assembled into systems providing solar arrays capable of generating upwards of 300 kW of power.
The group discussion spent some time on the issue of modularity with both speakers saying that the slight
increase in weight caused by modular systems is outweighed by the savings due to simplicity and the ability
to mass produce components. When asked why NASA needs to invest in arrays when there is already a robust
technology development, the speakers suggested that NASA can focus its investment on spacecraft integration
issues and the unique environmental requirements for operation in space. One of the speakers also said that even
non-financial support from NASA could help ensure technological progress continues. Finally there was some
discussion on bus voltage: 200 V DC was identified as a near term possibility; 300 V DC possible over the long
term; and improving performance beyond that achievable with 300 V DC may require shifting from a DC power
system to an AC power system.
Session 4: Nuclear Systems
Joseph Nainiger (Alphaport) began the session on nuclear systems by discussing the history of RPSs and fis -
sion power systems. He noted that while the United States has extensive flight experience with RPSs, it has only
flown one fission power system (in 1965) and has not manufactured and ground tested a fission nuclear thermal
rocket since 1972. Over the near term, RPSs will continue to fill the need for a reliable source of electrical power
in environments that cannot use solar power (even with advances in solar power technology). Fission systems are
enabling for missions with high power demands independent of sun proximity or illumination. Nainiger praised the
current effort at NASA to develop and test the non-nuclear components of a fission power system, while adding
that a system capable of producing at least 1 MW of electrical power will only be possible with a sustained and
aggressive technology development effort. He noted that fission power systems will require a significant invest -
ment in infrastructure, and he suggested that efforts should be taken to capture technology developed in the past.
Naininger also asserted that restarting the production of Pu-238 is a critical national need.
Gary Bennett (formerly with NASA) concurred that NASA has a critical need for Pu-238. He postulated that
more than half of the missions proposed in the recent planetary decadal survey (NRC, 2011) would benefit from
an RPS, if enough Pu-238 were available. He discussed the new RPSs under development and urged NASA to
focus on the Stirling engine power converter that is at the heart of the Advanced Stirling Radioisotope Generator
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(ASRG). To advance fission power technology, he recommended starting small, using ideas that are known to
work and evolving over time with an emphasis on safety and reliability. He said that NASA should acknowledge
the high cost and complexity of fission space power systems, and he cautioned against chasing new fission power
concepts that are unrealistic and unproven, with no technological foundation.
H. Sterling Bailey (formerly with General Electric) focused his remarks on fission power systems, which he
supports as a game-changing technology that could dramatically expand NASA’s science and exploration mission
capabilities. He noted the programmatic challenges of fission power and the legal requirement that NASA partner
with DOE in developing nuclear systems. He also said that the history of fissions space power systems has been
characterized by bold efforts that are cancelled before development of operational systems is completed. As a
result, confidence in this technology is low and the pool of personnel experienced with this technology is small and
shrinking. He advocated the development of a fission space power system that could produce 1 kW of electricity,
and he strongly supported ongoing work by NASA’s Fission Surface Power System Technology Project. Bailey
cautioned against adopting a megawatt-class system as a goal for a new fission space power program; it would be
better to start small.
The group discussion period spent some time on what size fission system should be built. Most of the speakers
supported development of the 40 kW system that NASA is currently funding. (The current effort, which is funded
entirely by NASA, does not include the development of nuclear technology.) In the end, system performance
requirements should be based on the requirements of whatever missions are expected to use the system. Several
speakers noted that efforts to develop new nuclear power systems typically face both technological and political
challenges. A member of the NRC panel noted that the latter is outside the scope of this study, which is focused
on technology.
REFERENCES
NRC (National Research Council). 2006. Priorities in Space Science Enabled by Nuclear Power and Propulsion. The National Academies
Press, Washington, D.C.
NRC. 2010. Radioisotope Power Systems: An Imperative for Maintaining U.S. Leadership in Space Exploration. The National Academies Press,
Washington, D.C.
NRC. 2011. Vision and Voyages for Planetary Science in the Decade 2013-2022. The National Academies Press, Washington, D.C.
Patel, M.R. 2005. Spacecraft Power Systems. CRC Press, Boca Raton, Fla.
