The draft roadmap for technology area (TA) 10, Nanotechnology, addresses four level 2 technology subareas:1
• 10.1 Engineered Materials and Structures
• 10.2 Energy Generation and Storage
• 10.3 Propulsion
• 10.4 Sensors, Electronics, and Devices
Nanotechnology manipulates matter and forces at the atomic and molecular levels. The accepted structure size for nanotechnology is between 1 and 100 nanometers in a minimum of one dimension, and includes materials or devices that possess at least one dimension within that size range. Quantum mechanical forces become important at this scale, which means that the properties of nano-sized materials or devices can be substantially different than the properties of the same material at the macro scale. Nanoscale materials or incorporation of them into a matrix have the promise of substantially improving the thermal, electrical, optical, and mechanical properties of a component. Nanotechnology can provide great enhancement in properties, and opens new possibilities due to the novel phenomena that occur only at the nanoscale. Materials engineered at the nano-scale will shift the paradigm in space exploration, sensors, propulsion, and overall system design.
Before prioritizing the level 3 technologies included in TA10, several technologies were renamed or moved. The changes are illustrated in Table M.1. The complete, revised technology area breakdown structure (TABS) for all 14 Tas is shown in Appendix B.
TOP TECHNICAL CHALLENGES
The panel identified five top technical challenges in nanotechnology, listed below in priority order.
1. Nano-Enhanced Materials. Reduce spacecraft and launch vehicle mass through the development of lightweight and/or multifunctional materials and structures enhanced by nanotechnologies.
1The draft space technology roadmaps are available at http://www.nasa.gov/offices/oct/strategic_integration/technology_roadmap.html
TABLE M.1 Technology Area Breakdown Structure for TA10, Nanotechnology
|NASA Draft Roadmap (Revision 10)||Steering Committee-Recommended Changes|
|TA10 Nanotechnology||The steering committee made no changes to the structure of this The steering committee made no changes to the structure of this roadmap, although NASA's draft roadmap renamed or moved|
10.1. Engineered Materials and Structures
10.1.1. Lightweight Structures
|Rename: 10.1.1. Lightweight Materials and Structures|
10.1.2. Damage Tolerant Systems
10.1.5. Thermal Protection and Control
10.2. Energy Generation and Storage
10.2.1. Energy Storage
|Move 10.2.1 to 10.2.2 Energy Storage|
10.2.2. Energy Generation
|Move 10.2.2 to 10.2.1 Energy Generation|
10.2.3. Energy Distribution
|Rename: 10.3.1. Nanopropellants|
10.3.2. Propulsion Components
|Rename: 10.3.2 Propulsion Systems|
10.3.3. In-Space Propulsion
10.4. Sensors, Electronics and Devices
10.4.1. Sensors and Actuators
|Rename: 10.4.2 Electronics|
10.4.3. Miniature Instruments
|Rename: 10.4.3 Miniature Instrumentation|
Development of advanced materials using nanotechnology can improve performance in the following areas: electrical energy generation and storage, propulsion, sensors, instrumentation, signal and power transmission, thermal protection, and active structures sensing, healing, and shape control. Nano-enhanced composites have the capability to enhance mission performance by increasing the strength and stiffness of materials and reducing structural weight. Weight reduction with added material functionality (such as increased strength and stiffness) using carbon nanotube technology has already been demonstrated in numerous materials, and nano-enhanced materials are finding their way into commercial products. Nano-enhanced advanced composites could reduce structural weight in launch vehicles, cryotanks, propulsion systems, and spacecraft, thus increasing the payload mass fraction. Nano-enhanced multifunctional materials and structures may exhibit unique failure modes and thus will require new design analysis tools. Multi-scale models that are valid over scales ranging from nano to macro are needed to understand nano-enhanced composite materials failure mechanisms and interfaces in order to design with them. Multi-physics models are needed to address fabrication processes, operation in extreme environments, and designing with active materials. Additional challenges to the broad use and incorporation of nano-engineered materials into useful products are the limited availability of certain raw nanomaterials and their variable quality. New production methodologies are required, not only to manufacture the raw nanomaterials, but also to controllably incorporate them into other materials. The particular end application may require specific dispersion and ordering of the nanoparticles.
2. Increased Power. Increase power for future space missions by developing higher efficiency, lower mass, and smaller energy systems using nanotechnologies.
Energy generation and energy storage will remain a top technical challenge for all future space-related missions. Batteries and power generation account for a significant amount of weight in any launch vehicle. Efficient methods to generate and recover energy, reduce overall power requirements, and reduce weight will benefit future NASA missions. For long-duration space missions, improved energy generation and storage will play a significant role in the mission success. Nanotechnology can improve performance for energy generation, energy storage, and energy distribution. Nano-enhanced electrode materials used in batteries where the surface area is significantly
increased will allow for faster charge/discharge rates, higher power densities, new battery and fuel cell materials, and increased safety. Nano-engineered devices can also improve existing storage and energy generation technologies making previously inefficient technologies competitive. Large numbers of sensors monitoring system and structural health will result in larger energy needs not only to transmit the information, but also process it. Nanotechnology will enable sensors to be self-powered and allow for distributed sensing in a networked fashion. Nanomaterials are being aggressively studied to improve methods for solar energy harvesting, thermal scavenging, and harvesting energy from the structures themselves. Newer technologies such as nano-structured metamaterials and photonic or phononic crystals with spectral compression will improve collection efficiencies and provide new capabilities.
3. Propulsion Systems. Improve launch and in-space propulsion systems by using nanotechnologies.
Advances in nanotechnology will enable new propellants and improved propulsion technologies. Nanotechnology may impact propellant technology by providing higher combustion efficiency and enabling alternative fuel materials that are less hazardous and require less cooling. More energetic propellants will reduce fuel mass in solid motors, and provide tailorable ignition and reaction rates. Higher-temperature and lower-erosion structural materials based on nanomaterials could reduce the weight of engine nozzles and propulsion structures. In-space electric propulsion (EP) systems, which couple high efficiency and large specific impulse within a relatively small package, will also benefit from performance improvements in nanoparticle propellants and nano-fabricated emission thrusters
4. Sensors and Instrumentation. Develop sensors and instrumentation with unique capabilities and better performance using nanotechnologies.
The success of NASA space missions relies heavily on a variety of sensing methods and sensor technologies for numerous environments in addition to scientific data collection. Structural monitoring of the space vehicle and internal systems self-monitoring, in addition to astronaut health monitoring, will be required as vehicle complexity and mission durations increase. The ability of systems or structures to alert operators and spacecraft systems to changing conditions allows for a proactive approach to maintain capability. Nano-sensor technology allows the incorporation of sensors in structures and systems that are smaller, more energy efficient, and more sensitive, allowing for more complete and accurate health assessments. Nanotechnology also permits targeted sensor applications that improve functional efficiency. Future space missions will also require development of smaller, more efficient excitation sources (photon or electron) for scientific work. Nanotechnology also allows miniaturization of instruments with enhanced performance.
5. Thermal Management. Improve performance of thermal management systems by using nanotechnology.
Thermal management is a key technology area that enables and impacts all of NASA’s missions. Proper thermal management can reduce overall system cost and weight with direct benefit to reducing overall launch vehicle weight. Thermal control is often required at the system level as well as at the subsystem and component level. Often these requirements are at odds; for instance, the samples loaded into an instrument need to be heated, but the detector needs to be cooled. Nanotechnology can be used to tailor the thermal conductivity of materials, making them more efficient conductors or insulators. The use of nanomaterials as fillers in TPS ablators may enhance both char formation and ablator cohesion. This will reduce spalling and total erosion of the TPS materials. Such nanomaterial inclusions can result in a weight savings from using less TPS material.
QFD MATRIX AND NUMERICAL RESULTS FOR TA10
A quality function deployment (QFD) matrix was employed to assist in the ranking of the nanotechnology level 3 technologies and to capture comments and concerns of the panel regarding the technology evaluation
FIGURE M.1 Quality function deployment (QFD) summary matrix for TA10 Nanotechnology. 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.
areas. The QFD matrix is shown in Figure M.1. The weighted scores for all level 3 technologies evaluated with the QFD approach are listed in Figure M.2. As shown in Figure M.2, the weighted scores of three technologies significantly exceeded those of the other technologies, and thus these three were selected as high priority. One technology, 10.4.1 Sensors and Actuators, fell into the medium-priority rating based purely on its QFD score, but the panel chose to designate it as high priority as well; its selection is discussed below in the 10.4.1 Sensors and Actuators individual technology evaluation area.
CHALLENGES VERSUS TECHNOLOGIES
Figure M.3 shows the relationship between the 14 individual level 3 TA10 technologies and the top technical challenges.
Note that the lowest-priority technologies as determined by the QFD rankings tend not to be strongly connected to the top technical challenges. (These are identified by an “L” in the left-most column, and are linked to the top challenges mainly by open circles.) All of the high-priority technologies and many of the medium-priority ones have a strong connection to at least one of the top technical challenges. This correlation shows a good level of consistency in the evaluations by the panel.
Furthermore, many of the TA10 roadmap technologies are connected to each other in support of a common top technical challenge or a crosscutting roadmap technology. For instance, many of the roadmap technologies support challenges related to propulsion, sensors, and instrumentation, and thermal management.
HIGH-PRIORITY LEVEL 3 TECHNOLOGIES
Panel 5 identified four high-priority technologies in TA10. The justification for ranking each of these technologies as a high priority is discussed below.
FIGURE M.2 Quality function deployment rankings for TA10 Nanotechnology
Technology 10.1.1, Lightweight Materials and Structures
Nano-sized materials have the promise of substantially improving the thermal, electrical, and/or mechanical properties of components and structures while reducing weight. The ability of nanotechnology to impact performance on numerous levels allows for the development of multi-functional, lightweight materials and structures that will revolutionize aerospace system design and capability. A clear need for future NASA missions, manned or unmanned, is new advanced nano-enhanced composite materials. The impact of structures based on these materials is broad. Weight reductions can be readily realized in many areas, while improving the strength, damage tolerance, and properties such as thermal, mechanical, and electrical. For future missions, weight reductions and material performance increases that go beyond current capability that uses only carbon fibers are being sought for use in cryotanks and launch vehicles, for radiation protection, and for damage tolerance.
The technology readiness level (TRL) for lightweight materials and structures is difficult to assess as the state of the art is rapidly changing. Any TRL is specific to the individual materials rather than a technology research area. Lower rated technologies (TRL 1-3) include materials using porous carbon fibers and the development of continuous, single-walled carbon nanotube (CNT) fibers. Integration of these materials into composites and structures holds promise for 20 to 30 percent weight reduction and a concomitant increase in strength and stiffness. Higher TRL technologies (TRL 4-6) include using carbon nanotubes for cabling and tapes that are intended for near-term insertion into aircraft as a replacement for conventional copper-based wires and cables.
Lightweight materials and structures enhanced by nanotechnology to reduce weight while improving material performance aligns well with NASA’s expertise and capabilities. NASA has technology requirements that are unique due to long-term deep-space missions and human transport. NASA’s internal development program should focus on the testing and use of nano-enhanced materials and structures and understanding their performance in the extreme environment found in space. Technology development in this area is a worthwhile investment for all launch and space systems. In addition, it will have a broad impact across non-NASA aerospace and non-aerospace applications.
Direct access to the International Space Station is likely to be beneficial to the development of lightweight materials and structures. The performance of these materials and structures can be designed, tested, and evaluated on Earth, however their evaluations will benefit substantially from multiple launch and re-entry tests, and long-term exposure to the space environment.
This technology area received the highest rating of all the level 3 technologies in the QFD matrix analysis. Lightweight materials and structures would represent a large return on investment. This technology is game-changing because reductions in the structural and payload weight of a space vehicle allow for higher efficiency
FIGURE M.3 Level of support that the technologies provide to the top technical challenges for TA10 Nanotechnology.
launches with increased payload capacity. The reduced total launch weight allows NASA greater flexibility in mission design. The expected weight reductions are in the 20 percent-30 percent range, but could be higher especially when including the weight savings due to multifunctionality. This technology will also impact TA12 Top Technical Challenge 2— Reduced Mass, and 4— Large Aperture Systems, and supports 1—Multifunctional Structures. The technology also impacts TA14 Top Technical Challenges 1-4, Thermal Protection Systems, Zero Boil-Off Storage, Radiators, and Multifunctional Materials.
Lack of research into the fabrication methodologies related to scale will slow development of lightweight materials and structures. There is significant cost involved in scaling manufacturing processes to commercial levels if the customer set is limited or the application space for terrestrial uses of the material is limited. Insufficient research into fabrication methodologies will slow development and use of lightweight materials and structures. Additionally, strength and performance gains may not be achieved if control of the nanoparticle dispersion, ordering, and interface properties are not achieved.
Technology 10.2.1, Energy Generation
Energy generation for spaceflight can be improved by leveraging nanotechnology. Current deep space missions rely primarily on stored energy (nuclear or chemical) to power systems aboard spacecraft. Improvements in current energy generation technologies, and the development of other methods of energy generation, can enhance future missions by reducing mass, improving reliability, and increasing mission durations.
The technology readiness level for nanotechnology-enhanced energy generation is dependent on the area of implementation. Lower TRL technologies discussed in the roadmap include quantum dots connected with carbon nanotubes and CNT-enhanced flexible organic photovoltaics (TRL 2-3), while higher TRL technologies involve nano-enhanced electrode materials and optimized nano-engineered structures for anode performance increases (TRL 4-6).
There is excellent alignment between NASA needs and expertise in the area of nanotechnology enhanced power generation. However, the area of research is quite broad and there is already a substantial private and public investment in this area. Consequently, NASA can partner with industry, academia, or other government agencies (e.g., U.S. Air Force, Department of Energy) and leverage promising technologies to deliver extreme environment energy generation systems and energy scavenging methods needed for spaceflight.
The evaluation of energy generation technologies would benefit from access to the ISS. Long-duration testing of energy generating technologies in an extreme environment is critical.
Nanotechnology impacts energy generation by improving the material systems of existing energy storage and generation systems. The QFD matrix evaluation indicates a clear benefit of energy generation research to NASA and excellent alignment with NASA’s needs. As with 10.1.1 Lightweight Materials and Structures, advances in energy generation through nanotechnology is game-changing because lighter, stronger materials and structures allow for more payload devoted to energy generation and power storage, and more efficient energy generation allows for lighter payloads at launch. When improvements are made in materials used for energy generation to increase reliability, performance in extreme environments, and power density, mission space is expanded or extended and costs drop. The ability to scavenge energy such that nano-sensors can be self-powered provides system self-monitoring capability at a fraction of the weight cost and with better sensor coverage. Without this development, the prospect of realizing a virtual digital fleet leader is remote. There is moderate risk involved with development of this technology area for NASA due to the breadth of the area and the numerous technologies that can be leveraged for successful space missions. However, there is substantial risk that commercial technologies developed cannot be adapted to operate with sufficient performance in extreme environments.
Technology 10.3.1, Nanopropellants
Nanopropellants include the use of nano-sized materials as a component of the propellant and as gelling agents for liquid fuels. In both cases, the nano-size provides a material with enormous reactive surface area. The use of nano-sized materials as a component of the propellant can solve several problems associated with current
propellant systems. The problems of most concern are the toxicity and environmental hazards of hypergolic and solid propellants, and the handling requirements for cryogenics. Nanopropellants have the potential to have higher combustion efficiency. If the nanoparticle shape and size can be controlled, the ignition and reaction rates can be tailored. In addition, this technology has the potential to provide long-term propellant storage capabilities in space, and propulsion systems for nano- and pico-satellites. Using the nanoparticle as a gelling agent makes a propellant system easier to handle, but brings problems with pumping and injection. Issues to be resolved for the successful implementation of nanopropellants include passivation and dispersion technologies, scale up of materials and manufacturing, reduction in cost of the nano-sized particles, and system implementation. There are also the safety and health issues associated with use of any new material.
Hydrogen storage is the subject of much research. Nano-structured materials with extremely high surface areas may potentially have a sorption capacity of 8 weight percent. Much work is needed to increase the sorption capacity at operational temperatures. The Department of Energy has done significant work in hydrogen storage technology, which can be leveraged by NASA.
The TRL for nanopropellants is relatively low, with nano-sized fuel components, such as are found in “ALICE,” a mixture of nano-scale aluminum particles and an ice slurry, being the highest (TRL 4). Nano-gelled propellants and nanostructures for hydrogen storage are at a lower level (TRL 2-3).
Research on nanopropellants aligns well with NASA’s expertise and capabilities. NASA can partner with other agencies, such as the U.S. Air Force and the Department of Energy, that also have interests in nanopropellants. Non-aerospace applications of nanopropellants are in the future, and have little industry support at this time.
Access to the International Space Station is not required.
Propellants are critical to NASA’s space mission success. The use of nanopropellants is game-changing because they can provide a 15 to 40 percent increase in efficiency, resulting in a decrease in system weight. In addition, nanopropellants can be multifunctional; that is, the propellant can act as a structural component that is consumed, as well as providing energy storage for in-space power. The development risk of nanopropellants is relatively low.
Technology 10.4.1, Sensors and Actuators
Nano-scaled sensors and actuators are an important research area for NASA’s space mission needs. The nano-scale allows for improvements in sensitivity and detection capability while operating at substantially lower power levels. Nanosensors can be made of variety of materials such as biological materials, inorganic, or polymeric materials, in addition to CNTs or combinations of materials. Due to the wide variety of material choices, nanosensors can be easily integrated with sensor electronics to produce compact and low power systems with ultra-sensitive response to mechanical, thermal, radiation, and molecular perturbations.
The promise of nanosensors and sensor systems is the integration of nano-electronics and nano-power sources to deliver arrays of autonomous sensors suitable for structural health monitoring and other distributed sensing activities. Structural monitoring of the space vehicle and self-monitoring of the internal systems, in addition to astronaut health monitoring, will be required as vehicle complexity and mission durations increase. The ability of systems or structures to alert operators and spacecraft systems to changing conditions allows for a proactive approach to maintain capability. Nanosensors are smaller, more energy efficient, and more sensitive, allowing for more complete and accurate health assessments. Nanotechnology also allows for targeted sensor applications, which improves functional efficiency.
The TRL for nanosensors and nano-actuators is high for specific applications. Trace gas nanosensors have already flown on space missions and on the ISS (TRL 6). However, there is much work to be done in the area of distributive sensing, therefore this TRL is much lower (TRL 2-3). Possible limitations to progress in distributed autonomous sensing are developments in sampling, sensor cleaning, and waste removal if that is required.
Nanotechnology enhanced sensors and actuators are well aligned to NASA’s needs and expertise. The reduction in scale, increase in performance, and concomitant power reductions from these sensors and actuators are required for long-term human mission success. Because NASA requires sensors that can function reliably in extreme environments, it can partner with others to perform joint research to adapt appropriate technologies to fit these specific needs. Research on nanosensors and nanoactuators is widespread in industry, academia, and government labs, and
the rate of progress for this particular technology area is very rapid. Likely aerospace and non-aerospace industries having an interest in this technology include structural monitoring of aircraft and infrastructure such as buildings and bridges. In addition, nanosensors will play a large role in future health care.
Testing and evaluation of nano-enhanced sensors and actuators would benefit from access to the ISS. The knowledge gained from nanosensors embedded into a composite panel to evaluate its structural health during exposure to the extreme space environment would be of tremendous use.
The panel overrode the QFD score for this technology to designate it as a high-priority technology because the QFD scores did not capture the value of this technology in terms of overall benefit to all missions. This technology was given three high-QFD scores (all 9s) for alignment with needs for NASA, non-NASA aerospace, and non-aerospace national goals. NASA uses a variety of sensors for guidance, monitoring of structural health, crew health, engine health, debris damage, fuel and leak detection, detection of life on planets, gas sensing, atmospheric sensing, and for scientific studies, and nanotechnology is expected to significantly impact sensor technology.
MEDIUM- AND LOW-PRIORITY TECHNOLOGIES
TA10 contains 14 level 3 technologies, of which 10 were determined to be of medium or low priority. The QFD matrix indicates that for all the level 3 technologies evaluated, the alignment with NASA needs and non-NASA aerospace technology needs were high. Significant differences appeared with the technology alignment to non-aerospace needs, as well as perceived benefit to NASA.
Four technologies were determined to be medium priority. The overall alignment with non-NASA aerospace technology needs and non-aerospace national goals, while greater than the low-priority technologies, were less than that of the high-priority technologies. The medium-priority nanotechnology areas are: 10.3.2 Propulsion Systems, 10.4.3 Miniature Instrumentation, 10.3.3 In-Space Propulsion, 10.1.5 Thermal Protection and Control, and 10.1.2 Damage Tolerant Systems. It was determined that advances in the 10.1.3 Coatings, 10.1.4 Adhesives, 10.2.1 Energy Storage, 10.2.3 Energy Distribution, and 10.4.2 Electronics level 3 technology areas would not result in game-changing or major benefits to NASA, and thus they were rated low priority. There is an extensive existing infrastructure for development of these technologies in the commercial sector, and the national need is not high. The panel believes that NASA can remain effective in these areas by leveraging and testing commercial technology in extreme environments or by partnering with commercial vendors or other agencies to deliver timely solutions.
All of the technologies had some demonstrated risk and difficulty associated with them.
DEVELOPMENT AND SCHEDULE CHANGES FOR THE
TECHNOLOGIES COVERED BY THE ROADMAP
Future NASA missions depend highly on advancements such as lighter and stronger materials, increased reliability, and reduced manufacturing and operating costs. All of these will be impacted by the incorporation of nanotechnology. The fold-out map included in the TA10 roadmap, Figure R, details various technologies and when they will be needed, but it is unclear from the mission descriptions why specific technologies are required and why a specific insertion date was used. This makes it challenging to suggest any specific modifications to the roadmap schedule. However, development of specific nanotechnologies may be faster than assumed, due to the large international research efforts in this area.
OTHER GENERAL COMMENTS ON THE ROADMAP
It is worth mentioning again that major challenges to the broad use and incorporation of nano-engineered materials into useful products are the limited availability of certain raw nanomaterials and their variable quality. The lack of sufficient materials will negatively impact the proposed roadmap. However, the panel is not advocating that NASA should be active in the large-scale production of nanomaterials.
Nanotechnology is a very broad area of research, and (as can be seen from the table on p. TA10-22 of NASA’s TA10 roadmap), it is crosscutting with and impacts every other roadmap. As stated earlier, research in nanotechnology will also impact TA12 Top Technical Challenge 2— Reduced Mass, and 4— Large Aperture Systems, and supports 1, Multifunctional Structures. Nanotechnology also impacts TA14 Top Technical Challenges 1-4, Thermal Protection Systems, Zero Boil-Off Storage, Radiators, and Multifunctional Materials.
Furthermore, recognizing that much work on a national R&D effort in nanotechnology is underway in government labs, universities, and industry sponsored by NSF and other agencies, the NASA research for space applications should be well coordinated with this national effort.
Even within NASA, its nanotechnology research does not seem to be centrally coordinated, and thus the potential exists for substantial duplication of effort. For example, nanosensor research is being done at NASA-Glenn, NASA-Ames, and JPL, according to information presented to the panel at its January 2011 meeting. The panel suggests that there be substantial coordination between the nanotechnology researchers at the various NASA centers, the national R&D effort, and specific NASA mission end users. In addition, the panel suggests that the nanotechnology researchers collaborate as closely as possible with the researchers involved with the other roadmap level 3 technologies.
PUBLIC WORKSHOP SUMMARY
The workshop for the TA10 Nanotechnology technology area was conducted by the Materials Panel on March 9, 2011, at the Keck Center of the National Academies, Washington, D.C. The discussion was led by panel chair Mool Gupta. He started the day by giving a general overview of the roadmaps and the NRC’s task to evaluate them. He also provided some direction for what topics the invited speakers should cover in their presentations. After the introduction, the day started with an overview of the NASA roadmap by the NASA authors, followed by several sessions addressing the key areas of each roadmap. For each of these sessions, experts from industry, academia, and/or government provided a 35 minute presentation/discussion of their comments on the NASA roadmap. At the end of the day, there was approximately 1 hour for open discussion by the workshop attendees, followed by a concluding discussion by the panel chair summarizing the key points observed during the day’s discussion.
Roadmap Overview by NASA
The presentation by the NASA team provided an overview of the benefits of nanotechnology, including the ability to reduce vehicle mass, increase durability of materials, and improve the performance of propulsion systems, sensors, photovoltaics, and other electronics systems. It was noted that while some areas such as aeronautics— emissions and exploration can provide a technology pull, in general nanotechnology falls into the push category. After providing an overview of the roadmap TABS and the roadmap itself, there was a detailed discussion of several key capabilities. These include 30 percent lighter cryogenic propellant tanks, enabling extreme environment operations, lighter and more efficient thermal protection and management, “smart” airframe and propulsion concepts, adaptive gossamer structures, high-efficiency flexible photovoltaics, enhanced power and energy storage, miniature instruments, enabling low-mass smart satellites capable of formation flying, low-power radiation-hard reconfigurable electronics, improved astronaut health management, and ultrasensitive selective sensing.
Three different time periods were used to outline the top technical challenges facing nanotechnology:
• Next 5 years
— Grand challenge: Controlled growth and stabilization of nanopropellants
— Development of long-life, reliable emission sources
— Development of characterization tools and methodologies to measure coupled properties of nano-structured materials, including non-destructive and in situ techniques
— Optimization of bulk properties of nanomaterials
• Next 5 to 10 years
— Grand challenge: Development of nanostructured materials 50 percent lighter than conventional composites with equivalent or better properties and durability
— Grand challenge: Heirarchical system integration across length scales (from nano to macro)
— Grand challenge: Development of integrated energy generation, harvesting and scavenging technologies
— Development of manufacturing methods, including net-shape fabrication to produce nanomaterials and devices on large scales with controlled structure, morphology and quality
• Next 20 years and beyond
— Grand challenge: Development of graphene electronics
— Development of high-fidelity, high-reliability multiscale models to predict the properties of nanoscale materials and devices/structures
— Development of single molecule detection methods with high specificity (2029+)
The presentation concluded with some discussion of how nanotechnology crosscuts among the majority of the NASA technology roadmaps, as well as outlining how NASA is collaborating in nanotechnology research with the Department of Defense for materials and photovoltaics, and with the Department of Homeland Security for sensors. Also discussed was the National Nanotechnology Initiative (NNI), and how there is a potential avenue for further collaborations in NNI signature initiatives.
Session 1: Nanomaterials
Brian Wardle (MIT) started with a brief introduction, followed by a quick overview of the work his group does at MIT. He commented that the TA10 roadmap provides an “accurate and compelling vision for nanomaterials development with NASA’s broader mission,” and that the main focus of his presentation would be on areas of potential improvement. Wardle noted that the five grand challenges identified by NASA in their roadmap are compelling, there is a mix of specific application areas and crosscutting game changers; Wardle is concerned that the crosscutting aspect is very important and emphasized that this should not get lost in the evaluation process. He sees NASA as a better fit for an integrator role rather than lead developer on nanotechnology with a few small exceptions such as nanopropellants. He commented on several specific areas, including the importance of multiscale modeling and interphase/morphology considerations, as well as questioning what role NASA should take in understanding the environmental health and safety aspects of nanomaterials. Finally, Wardle also noted that there was minimal discussion in the NASA roadmap on nanostructured metals and ceramics, considering NASA’s needs and strengths in these areas.
In the question and answer session following his presentation, Wardle noted that there are reports of nanocomposites having seen 30 percent higher ultimate strength compared with current composite materials and that as a structural material, it is already being incorporated into planned missions like Juno. It was noted that controlling morphology (i.e., alignment, treating nanotubes as structural elements, etc.) currently seems to be trial and error, rather than based on predictive modeling. Wardle indicated that such modeling is beyond current capabilities and is a potential high-value area to invest in but might not be an appropriate area for NASA. Wardle commented that while production volumes are currently significant, the morphology is mixed.
Wade Adams (Rice University) followed Wardle’s presentation with a discussion on observations generated by himself and a small group of colleagues at Rice University. Overall, Adams indicated that the TA10 roadmap was an excellent update and expansion of the 2000 nanotube roadmap that some of his team helped create. While Adams indicated he believed the five grand challenges to be useful, he suggested that the “Hierarchical Systems Integration” challenge merits the most attention, as it is critical to a broad implementation of nano/micro-technology into future systems, and is an area where NASA could potentially show leadership. Adams also highlighted the need for internal expertise, and expressed some concern that limited budget may keep NASA personnel from staying up-to-date on the technologies such that they can be better “smarter buyers.” Adams observed that the NASA roadmap seems to have a longer-term focus, therefore identifying some short-term payoffs might be a good approach. In the end, he noted that NASA will not have enough funding to expect significant NASA leadership
in many of the technical areas, but that focusing funding on a few critical needs might enable NASA leadership in these areas. Finally, Adams strongly encouraged NASA teaming with initiatives from other groups (e.g., the National Nanotechnology Initiative, Department of Defense, Department of Energy, public-private partnerships).
Session 2: Sensors and Nanoelectronics
Avik Ghosh (University of Virginia) started his discussion with a few introductory charts. He noted that for nanomaterials, near-equilibrium properties are reasonably well understood, but that the non-equilibrium regime is less so. He noted that it is becoming more difficult to avoid noise around switching areas, and recent research is attempting to identify ways to use this noise. In terms of the NASA roadmap, Ghosh indicated it was good, but that NASA needs to better spell out the needs versus capabilities; he also agreed with other presenters in that limited funding means it is important for NASA to make sure specific areas do not fall through the cracks. Relative to key challenges, Ghosh discussed that heat dissipation is a primary focus area in electronics, spintronics (and multiferroics) are promising but receiving little funding, and new materials require further research to address current limitations (e.g., graphene is good for some applications, but not for others such as switching). Ghosh commented that there are opportunities in trap dynamics and in improving the engineering of thermal transistors, but also noted that there appear to be gaps in the NASA roadmap as well in thermal conductivity (e.g., significantly less range versus electrical conductivity) and biological computing. He concluded his presentation suggesting that, in addition to partnering with others, NASA could choose a few areas not addressed by other agencies and focus on these niche applications as well.
During the discussion period after Ghosh’s presentation, one of the panel members noted that companies such as Intel and IBM will likely drive technology development in these areas, and asked what NASA’s focus should be. Ghosh responded that the industry appears to be focused on near-term applications, whereas the National Science Foundation is more interested in far-term exploratory research; NASA could look to bridge these differences. In responding to a question on specific technologies that NASA should focus on, Ghosh agreed that significant investment in this field is required, and that one possibility is for them to target niche areas that are not currently well funded, as well as trying to identify partnership areas to participate in. As an example of a niche area that NASA might look into, Ghosh noted that utilizing noise in sensor design is not seeing significant funding from other organizations currently. During some discussion on the current TRL of many of the technologies in this roadmap, Ghosh agreed that these typically are in the fundamental/exploratory research phase. He did note, however, that STTRAM does seem closer to feeding into products (e.g., non-volatile memory). He also stated that nanoelectronics technology will be led by industries like IBM, Intel, etc., and NASA can benefit from such developments.
Ashraf Alam (Purdue University) next gave a presentation on his perspectives on the TA10 roadmap. In terms of his overall assessment of the roadmap, Alam noted that a systematic, multi-metric evaluation of available sensor technologies would be very helpful, and that NASA could work with internal and external researchers to achieve this. Over the short term, Alam indicated that sensitivity, variability, and selectivity concerns make many new sensor technologies unsuitable for rapid deployment, and that working to improve this is a worthwhile investment. He also noted that biobarcode sensor and nanonet sensors appear to be especially promising and worthy of future work. Alam identified that one of the challenges for sensors is that the sensitivity line assumes infinitely long sensors; he noted that in reality, the sensor will fail after some period of time (e.g., 1 hour) due to the environment (e.g., salt). Another interesting application, according to Alam, is to mix the sensor with what is being measured, rather than having it at the bottom of the solution, for example. He indicates that these types of sensors can provide much higher sensitivity without much noise. Finally, Alam concluded with three key points: (1) going for high sensitivity can lead to high fluctuations, (2) under extreme environments, sensors can respond very differently, and (3) selectivity is a fundamental issue, in that it is important to cover up the gaps/spaces in sensors if possible. He stated that nanotechnology will play an important role for biosensors.
Session 3: Propulsion
Steve Son (Purdue University) noted in his presentation that the high surface areas in nanopropellants provides benefits, but also has potential negatives as well (e.g., requiring more binder in solid rockets). Regarding the technologies, he indicated that some characteristics do not change at the nanoscale, whereas other characteristics such as reaction rate do change. Son commented that these properties can be used to tailor ignition and reaction rates, control heat release location, and can affect combustion stability. As an example, he indicated that nanotechnology could be used to increase the fuel regression rate of hybrid rocket motors. According to Son, moving from the micro to nano scale can affect rheology—castings, for example, can become more brittle. Relative to green propellants, he indicated that ammonium nitrate might be better than ammonium perchlorate, and that nanoscale techniques might help ammonium nitrate improve in terms of burn rate. As for multifunctional capabilities, Son noted that solid rockets are multifunctional, and investigating liquids and slurries that could potentially be used for things like energy storage (e.g., fuel cell use) could be done. Son did identify several challenges, however, including the rheology of adding high-surface-area particles, controlling the distribution of nanoparticles (where large agglomerations can lead to loss of benefits), and passivation. He also commented that cost is always a challenge, as well as dealing with health and safety issues.
During the discussion period after Son’s presentation, one of the panel members asked what reasonable efficiency increases might be expected in this area. Son responded that it is system dependent; for example, in some cases like a nano-aluminum-ice (nAl-ice) rocket, the propellant is not necessarily higher performance, but enables doing something differently. Another workshop attendee built upon this comment by noting that in the case of nAl-ice, the nano scale is what enables it work, as the propellant will not burn at the micro scale. Son did provide further comments, though, that for hybrid fuels, introducing nanoparticles to increase the regression rate could lead to potentially higher performance. When asked about the status of modeling capability for nanopropellant systems, Son responded that while there have been collaborations with modeling efforts, there is certainly room to do more, and that modeling needs to be tied to experiments to be useful. Finally, in addressing a panel member’s question about TRL, Son indicated that some areas (e.g., making green propellants more viable) are near term, but other areas (e.g., using clusters of engines) is much longer term (i.e., 10 years or more).
Richard Yetter (Pennsylvania State University) next gave a presentation on his views of nanotechnology and propulsion. Regarding nanopropellants, he noted that nanopropellants will not necessarily provide higher energy densities, but can provide improved usage of the stored chemical energy. For example, he indicated that nano-ingredients could produce new gelled and solid propellants, and that nanopropellants may be usable in non-conventional applications. Yetter did note that there have been critical technology issues, where self-assembly and supramolecular chemistry of the fuel and oxidizer elements of energetic materials have lagged far behind chemistries in other disciplines (such as pharmaceuticals, microelectronics, microbiology). He indicated that this has led to limited fundamental understanding of what type of supramolecular structures provide desirable performance in combustion, mechanical, and hazard characteristics. Yetter then went in to some detailed discussion regarding self-assembly, surface passivation, graphene catalysts (e.g., to attain higher reaction rates), nano-engineered energetic materials (e.g., physical vapor deposition), and MEMS devices (e.g., micro-igniter). In terms of multifunctionality, Yetter commented that one application might be having a power system built-into the propulsion system.
During the discussion period after Yetter’s presentation, he was asked about his thoughts on NASA leading in this technology area. Yetter responded that the U.S. Air Force is putting substantial efforts into this area, and that NASA’s efforts are best tuned with a particular mission. He indicated that a good start might be to focus on items at the MEMS scale for self-assembly before moving to much bigger systems. Regarding the top technical challenges, Yetter noted that there is a high risk on passivation and assembly. He also suggested looking at the system implementation— how does using nano affect the system as a whole? Finally, Yetter identified several potential technology gaps, including mass/volume improvements with sensors, the use of graphene as fuel/catalyst, and the fact that safety issues are critical.
Session 4: Energy Generation and Storage
Gary Rubloff (University of Maryland) started his presentation noting that there were three areas in particular that he wanted to address: power generation, integration of nanocomponents, and hierarchical systems. Rubloff provided many detailed comments regarding “random” and “regular” heterogeneous 3D nanostructures, exposed and embedded nanostructures (e.g., applications and differences between the two approaches), engineering aspects of 3D structures (e.g., keeping impurities from impacting performance), process and device integration (e.g., integration at the nano-level to improve volume/weight), and multifunctional nanosystems (e.g., nano-integrated photovoltaic and energy storage systems). Rubloff also discussed what he refers to as the “three self’s”— self-assembly, self-alignment, and self-limiting reactions—and how these can be used to keep costs down. In terms of the NASA roadmap, Rubloff indicated that for the top technical challenges, he saw mechanisms for identifying defects to be lacking the most. He also identified some technology gaps, including using modeling and simulation to guide systems design and prioritization, as well as system level strategies for managing defects and reliability. Correspondingly, Rubloff noted that the high-priority areas that NASA should focus on are defect and reliability mechanisms, integrated systems, and model-based system design. Finally, relative to the time horizon of the NASA roadmap, Rubloff commented that the manufacturing equipment for these materials/systems will need to be there in time.
Public Comment and Discussion Session
The following are views expressed during the public comment and discussion session by either presenters, members of the panel, or others in attendance.
• Technology investment process. One presenter suggested forming a working group across NASA centers that meets regularly and generates consensus on areas with the largest payoffs with some external review. He mentioned that, out of a $1 billion program, spending $100 million on two or three specific areas to demonstrate significant advancement/commitment might make sense.
• Areas for NASA to lead. It was suggested that crosscutting areas like nanotech will be a challenge, and that there is work going in other groups, so it is not clear what NASA should be doing. One response suggested that NASA should take the lead in nanotechnology research related to extreme environments and multifunctional systems. It was raised that on the sensors side, NASA could be a real user/customer but not necessarily a development leader. Another area of suggested emphasis are opportunities in propulsion (e.g., microthrusters). Energy storage was mentioned as another area to look at, but that this might be led by the Department of Energy.
• Nanotechnology research at other agencies. There was a discussion on the substantial research in nano-technology going on at other groups, and it was suggested NASA should look to collaborate and benefit from the large amount invested by nine different agencies. Other agencies were said to be looking at the use of nanotechnology in radiation-hardened electronics, carbon nanotube memory, and ASICs, but no specific agency is coordinating the research. It was noted that the USAF perspective is to compromise between short/high-quality versus long/low-quality carbon nanotubes.
• Timeframe incorporation of nanotubes into structures. Clay nanocomposites have been incorporated into structures in the automotive industry for more than 10 years, whereas nanofiber structures have not been used much in commercial applications yet (ceramics for ballistic protection may be coming online in the next 1 to 2 years). There are examples of layers being used, but that they are not there yet for structural applications. This was seen as similar to the history with carbon fiber—initially it appeared in low-complexity sports equipment, and eventually made its way to more complex systems (e.g., aerospace). It was estimated that high-performance structural applications are likely to happen in the next 10 to 15 years.
• Morphology. It was stated that performance improvements are very dependent on the fiber being used, and single wall nanotube SWNT has been measured at 50 GPa (i.e., 10 x better than carbon fiber PAN). There are currently groups attempting to develop materials at the needed sizes that can be put together as composites are today. Regarding the question on weight savings in composites, it was noted that there is the ability to use nanotubes to control morphology but that alignment requires nanometer scale control, which is something that does not exist currently. Potential gains may not be that great; i.e., potentially up to 50 percent with substantial investment. Another area to look at was the composite matrix—where it was suggested that there is a significant opportunity in affecting performance via this area (e.g., gains at the 30 percent level).
• Thermal system applications. In terms of thermal conductivity, examples were given of nanotubes being used to help carry heat away from electronics/processors. Some groups claim to have seen a 10 percent reduction in the coefficient of thermal expansion (CTE), but that current research has not been focused on this area. It was noted that SWNT have a small but negative CTE, and that designing isotropic materials may be challenging (but also an area in which NASA might benefit).