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O TA12 Materials, Structures, Mechanical Systems, and Manufacturing INTRODUCTION The draft roadmap for technology area (TA) 12 Materials, Structures, Mechanical Systems, and Manufactur- ing, is organized into five level 2 technology areas:1 • 12.1 Materials • 12.2 Structures • 12.3 Mechanical Systems • 12.4 Manufacturing • 12.5 Cross-Cutting The TA12 portfolio is extremely broad and differs from most other TAs in that it consists of enabling core disciplines and encompasses fundamental new capabilities that directly impact the increasingly stringent demands of NASA science and exploration missions. These missions depend highly on advancements such as lighter and stronger materials and structures, with increased reliability and with reduced manufacturing and operating costs. Identified technologies are truly interdisciplinary and support virtually all of the other TAs. In TA12, NASA identified two critical areas: human radiation protection and reliability technologies. Long- term human exploration will require new radiation protection technology, i.e., lightweight radiation-shielding mate- rials, multifunctional structural design and innovative manufacturing. Crosscutting technologies will be required to ensure extremely reliable vehicles and systems for safe travel to destinations millions of miles from Earth. Before prioritizing the level 3 technologies included in TA12, the panel considered whether to rename, delete, or move technologies in the technology area breakdown structure (TABS). No changes were recommended for TA12. The TABS for TA12 is shown in Table O.1, and the complete, revised TABS for all 14 TAs is shown in Appendix B. 1 The draft space technology roadmaps are available at http://www.nasa.gov/offices/oct/strategic_integration/technology_roadmap.html. 294
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295 APPENDIX O TABLE O.1 Technology Area Breakdown Structure for TA12, Materials, Structures, Mechanical Systems, and Manufacturing NASA Draft Roadmap (Revision 10) Steering Committee-Recommended Changes The structure of this roadmap remains unchanged. TA12 Materials, Structures, Mechanical Systems, and Manufacturing 12.1. Materials 12.1.1. Lightweight Structure 12.1.2. Computational Design 12.1.3. Flexible Material Systems 12.1.4. Environment 12.1.5. Special Materials 12.2. Structures 12.2.1. Lightweight Concepts 12.2.2. Design and Certification Methods 12.2.3. Reliability and Sustainment 12.2.4. Test Tools and Methods 12.2.5. Innovative, Multifunctional Concepts 12.3. Mechanical Systems 12.3.1. Deployables, Docking, and Interfaces 12.3.2. Mechanism Life Extension Systems 12.3.3. Electro-mechanical, Mechanical, and Micromechanisms 12.3.4. Design and Analysis Tools and Methods 12.3.5. Reliability/Life Assessment/Health Monitoring 12.3.6. Certification Methods 12.4. Manufacturing 12.4.1. Manufacturing Processes 12.4.2. Intelligent Integrated Manufacturing and Cyber Physical Systems 12.4.3. Electronics and Optics Manufacturing Process 12.4.4. Sustainable Manufacturing 12.5. Crosscutting 12.5.1. Nondestructive Evaluation and Sensors 12.5.2. Model-Based Certification and Sustainment Methods 12.5.3. Loads and Environments TOP TECHNICAL CHALLENGES The panel identified six top technical challenges for TA12. These are described briefly below in priority order. While not inconsistent with those identified in the NASA roadmap document itself, they differ in that there was no attempt to explicitly include challenges in each of the level 2 areas represented; that is: materials, structures, mechanical systems, manufacturing, and crosscutting. 1. Multifunctional Structures. Conceive and develop multifunctional structures, including shielding, to enable new mission capabilities such as long-duration human spaceflight, and to reduce mass. Structures carry load and maintain shape. To the extent that a structure can simultaneously perform additional functions, especially those that would normally require add-on systems, mission capability can be increased with decreased mass. Integral shielding to reduce radiation exposure and micrometeoroid and orbital debris (MMOD) risk for human spaceflight missions would be game-changing, and the ISS would be useful to verify such concepts. Other advanced multifunctional structures concepts would enable structures, including joints, to provide thermal protection and control, electrical signal and power transmission, electrical energy and fuel storage, self-sensing
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296 NASA SPACE TECHNOLOGY ROADMAPS AND PRIORITIES and healing, and active shape control. Improved cryogenic boil-off protection, for instance, would considerably reduce the mass required for a Mars mission. Such multifunctional materials and structures will require new design analysis tools and might exhibit new failure modes; these should be understood for use in systems design and space systems operations. 2. Reduced Mass. Reduce mass of launch vehicle, spacecraft, and propulsion structures to increase payload mass fraction, improve mission performance, and reduce cost. Lightweight materials and structures are required to enhance mission performance and enable new mission opportunities. Advanced composites and revolutionary structural concepts would substantially reduce structural weight in launch vehicles, cryo-tanks, propulsion systems, and spacecraft, increasing the payload mass fraction. More energetic propellants would reduce fuel mass in solid motors, and higher-temperature and lower-erosion materials would reduce the weight of engine nozzles. Reduced mass of inflatable habitats and space structures, deployable space systems, and large-scale structures would enable new exploration and science missions. 3. Computational Modeling. Advance new validated computational design, analysis, and simulation methods for materials and structural design, certification, and reliability. First-principles physics models offer the game-changing potential to guide tailored computational materials design. Multi-scale models are needed to encompass composite materials, interfaces, failure, multi-component and deployable structures, and integrated control systems; multi-physics models are needed to address manufacturing processes, operation in extreme environments, and active materials. Conservatism is embedded in established design methodology in several ways, including statistics-based material allowables and traditional factors of safety. Uncertainty management and quantification, if supported by an experimental foundation, offers the potential to reduce weight as well as certification and life-cycle costs by rationalizing sometimes excessive conservatism. Physics-based and computation-based errors can be quantified and compared to required accuracy and confidence levels. A validated computational modeling methodology could provide the basis for certification by analysis, with experimental evidence, as available, used to verify and improve confidence in the suitability of a design. Computational models will be needed to design-in improved reliability, as well as to interpret measurements made by health-monitoring systems. Structures may need to be designed differently to accommodate health monitoring, including unobtrusive sensors and sensor integration, and to enable materials and structures health assessment and sustainability for long-duration missions. 4. Large-Aperture Systems. Develop reliable mechanisms and structures for large-aperture systems. These must be stowed compactly for launch, yet achieve high-precision final shapes. Numerous NASA missions employ mechanical systems and structures that must deploy reliably in extreme environments, often to achieve a desired shape with high precision. Such systems include instrument arms, anten - nas, optical surfaces, solar sails, and some re-entry thermal protection systems. These can be deployed, assembled, or manufactured in space, and may involve flexible materials. Modularity and scalability are desirable features of such concepts, and may require development of autonomous adaptive control systems and technology to address critical functional elements and materials. Concerns include sliding joints and bearings, friction and tribology, coatings and lubrication, as well as their performance and durability over extended periods in storage and extreme operational environments. Performance of large precise space systems cannot be directly verified in the 1- g ground environment, so the ISS would be useful for verification of such concepts. 5. Structural Health Monitoring. Enable structural health monitoring and sustainability for long-duration mis - sions, including integration of unobtrusive sensors, and responsive on-board systems.
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297 APPENDIX O Mission assurance would be enhanced by an integrated structural health monitoring system that could detect and assess the criticality of in-service damage or fault, then define an amelioration process or trigger a repair in self-healing structures. Such a system requires light, reliable, rugged, unobtrusive, and multifunctional sensors that can be integrated into the structure along with power and data transmission capability. Software to combine disparate data, to diagnose and predict structural health, and to enable the necessary repairs is also a significant challenge. An autonomous integrated on-board systems capability would be game-changing for long-duration, remote missions. 6. Manufacturing. Enable cost-effective manufacturing for reliable high-performance structures and mechanisms made in low-unit production, including in-space manufacturing. Advanced NASA space missions need affordable structures, electronics systems, and optical payloads. Afford - able high-performance structures require advances in manufacturing technology. Such advances include automation using reusable flexible tooling; database- and model-based simulation to ensure selection of the lowest-cost yet reliable and scalable approach; non-autoclave processes for polymer matrix composites to minimize infrastructure investment; in-space manufacture and assembly of large structures such as fuel depots; and means for cost-effective manufacture of lightweight precision optical systems for large structures. In-space manufacturing offers the poten - tial for game-changing weight savings and new mission opportunities; as an example, NASA and DARPA recently pursued the possibility of manufacturing large optical systems in space. The ISS could be used to demonstrate lightweight in-space structures manufacturing capability. QFD MATRIX AND NUMERICAL RESULTS FOR TA12 Figure O.1 shows the panel’s consensus ratings of the 23 level 3 technologies for the TA12 roadmap. Clearly, benefit is the major discriminator among these technologies, while technical risk and reasonableness is the second most important discriminator. Alignment is a less significant discriminator. Most TA12 technologies have the potential to impact multiple NASA missions in multiple areas because every mission would benefit from reduced structural mass, and most would benefit from improved structural reliability and reduced cost. Figure O.2 shows the consensus rankings of the level 3 technologies. As shown in the figure, 12.2.5 Innova - tive Multifunctional Concepts received the highest QFD score. A couple of break points in the consensus scores facilitate sorting into relative high, medium, and low-priority categories. The two top medium-ranked technologies were promoted into the high-priority category because of their close relationship to other high-priority technologies. 12.3.5 Reliability/Life Assessment/Health Monitoring is important in its own right, and it closely supports 12.3.1 Deployables, Docking and Interfaces. 12.4.2 Intelligent Integrated Manufacturing and Cyber Physical Systems 2 supports a number of other high-priority technologies and NASA missions. CHALLENGES VERSUS TECHNOLOGIES Figure O.3 shows the relationship between the 23 individual level 3 TA12 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 shows a good level of consistency in the evaluations by the panel. 2 A cyber-physical system (CPS) features tight coordination between computational and physical elements. A CPS typically involves a network of interacting elements, and is closely tied to concepts of robotics and sensor networks.
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298 NASA SPACE TECHNOLOGY ROADMAPS AND PRIORITIES ls oa ds lG ee na N ch io s at es Te N en o ce er bl pa ds A na os SA ee so er g N A ea in d) -N -A SA R m te on on d A Ti gh an N N N d ei rt ith ith ith an k (W fo y is w w w rit Ef ng R e rio t t t al or en en en ci d ic an lP en Sc nm nm nm it n ef qu ne e ch FD en lig lig lig m Pa Se Te Ti Q B A A A Multiplier 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 236 H 12.1.1. (Materials) Lightweight Structure 3 9 9 9 9 -1 -3 164 M 12.1.2. (Materials) Computational Design 3 9 9 9 1 1 -3 168 M 12.1.3. Flexible Material Systems 3 9 3 3 3 1 -1 156 M 12.1.4. (Materials) Environment 3 9 3 1 3 1 -3 98 L 12.1.5. Special Materials 1 9 1 1 3 -1 -1 244 H 12.2.1. (Structures) Lightweight Concepts 3 9 9 9 9 1 -3 236 H 12.2.2. (Structures) Design and Certification Methods 3 9 9 9 9 -1 -3 106 L 12.2.3. (Structures) Reliability and Sustainment 1 9 3 3 3 -1 -1 94 L 12.2.4. (Structures) Test Tools and Methods 1 9 3 1 3 -3 -1 346 H 12.2.5. (Structures) Innovative, Multifunctional Concepts 9 9 9 9 3 1 -3 216 H 12.3.1. Deployables, D ki 12 3 1 D l bl Docking, and I t f d Interfaces 3 9 3 1 9 -1 1 -1 1 90 L 12.3.2. Mechanism Life Extension Systems 1 9 1 1 3 -3 -1 90 L 12.3.3. Electro-mechanical, Mechanical and Micromechanisms 1 9 1 1 3 -3 -1 228 H 12.3.4. (Mechanisms) Design and Analysis Tools and Methods 3 9 9 9 9 -3 -3 184 H* 12.3.5. (Mechanisms) Reliability / Life Assessment / Health Monitoring 3 9 9 9 3 -1 -1 176 M 12.3.6. (Mechanisms) Certification Methods 3 9 9 9 3 -1 -3 176 M 12.4.1. Manufacturing Processes 3 9 9 9 3 -3 -1 184 H* 12.4.2. Intelligent Integrated Manufacturing and Cyber Physical Systems 3 9 9 9 3 -1 -1 98 L 12.4.3. Electronics and Optics Manufacturing Process 1 9 3 3 3 -3 -1 78 L 12.4.4. Sustainable Manufacturing 1 9 3 3 1 -3 -1 236 H 12.5.1. Nondestructive Evaluation and Sensors 3 9 9 9 9 -1 -3 164 M 12.5.2. Model-Based Certification and Sustainment Methods 3 9 9 3 3 -1 -3 98 L 12.5.3. Loads and Environments 12.5.3. Loads and Environments 1 9 3 3 3 -1 -3 FIGURE O.1 Quality function deployment (QFD) summary matrix for TA12 Materials, Structures, Mechanical Systems, and Manufacturing. 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. 0 50 100 150 200 250 300 350 400 12.2.5. (Structures) Innovative, Multifunctional Concepts 12.2.1. (Structures) Lightweight Concepts High Priority 12.1.1. (Materials) Lightweight Structure 12.2.2. (Structures) Design and Certification Methods 12.5.1. Nondestructive Evaluation and Sensors 12.3.4. (Mechanisms) Design and Analysis Tools and Methods 12.3.1. Deployables, Docking, and Interfaces 12.3.5. (Mechanisms) Reliability / Life Assessment / Health Monitoring 12.4.2. Intelligent Integrated Manufacturing and Cyber Physical Systems Medium Priority 12.3.6. (Mechanisms) Certification Methods 12.4.1. Manufacturing Processes 12.1.3. Flexible Material Systems 12.1.2. (Materials) Computational Design 12.5.2. Model‐Based Certification and Sustainment Methods 12.1.4. (Materials) Environment 12.2.3. (Structures) Reliability and Sustainment 12.1.5. Special Materials Low Priority 12.4.3. Electronics and Optics Manufacturing Process 12.5.3. Loads and Environments 12.2.4. (Structures) Test Tools and Methods 12.3.2. Mechanism Life Extension Systems High Priority (QFD Score Override) 12.3.3. Electro‐mechanical, Mechanical and Micromechanisms 12.4.4. Sustainable Manufacturing FIGURE O.2 Quality function deployment rankings for TA12 Materials, Structures, Mechanical Systems, and Manufacturing.
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Top Technology Challenges 5. Structural Health 1. Multifunctional 6. Manufacturing: Monitoring: Enable 4. Large-Aperture Structures: Conceive Enable cost-effective structural health Systems: Develop 3. Computational 2. Reduced Mass: and develop manufacturing for monitoring and reliable mechanisms Modeling: Advance new Reduce mass of launch multifunctional reliable high- sustainability for long- and structures for large- validated computational vehicle, spacecraft, and structures, including performance structures duration missions, aperture systems. design, analysis and propulsion structures to shielding, to enable new and mechanisms made including integration of These must be stowed simulation methods for increase payload mass mission capabilities in low-unit production, unobtrusive sensors, compactly for launch, materials and structural fraction, improve such as long-duration including in-space and responsive on- yet achieve high- design, certification, and mission performance, human space flight, and manufacturing. board systems. precision final shapes. reliability. and reduce cost. to reduce mass. Priority TA 12 Technologies, Listed by Priority H 12.2.5. (Structures) Innovative, Multifunctional Concepts ● ○ H 12.2.1. (Structures) Lightweight Concepts ○ ● ● H 12.1.1. (Materials) Lightweight Structure ○ ● H 12.2.2. (Structures) Design and Certification Methods ○ ○ ● ○ ○ H 12.5.1. Nondestructive Evaluation and Sensors ● ○ H 12.3.4. (Mechanisms) Design and Analysis Tools and Methods ● ● H 12.3.1. Deployables, Docking, and Interfaces ● H 12.3.5. (Mechanisms) Reliability / Life Assessment / Health Monitoring ○ ● ● 12.4.2. Intelligent Integrated Manufacturing and Cyber Physical Systems H ○ ○ ● M 12.3.6. (Mechanisms) Certification Methods ○ ● M 12.4.1. Manufacturing Processes ○ ● M 12.1.3. Flexible Material Systems ● ○ ○ M 12.1.2. (Materials) Computational Design ○ ○ ● M 12.5.2. Model-Based Certification and Sustainment Methods ● ● 12.1.4. (Materials) Environment M ● ○ ○ L 12.2.3. (Structures) Reliability and Sustainment ○ ○ ● L 12.1.5. Special Materials ○ ○ L 12.4.3. Electronics and Optics Manufacturing Process ○ L 12.5.3. Loads and Environments ○ ● L 12.2.4. (Structures) Test Tools and Methods ○ ○ L 12.3.2. Mechanism Life Extension Systems ○ ○ L 12.3.3. Electro-mechanical, Mechanical and Micromechanisms ○ L 12.4.4. Sustainable Manufacturing ○ 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 [blank] little or no impact in addressing the challenge. FIGURE O.3 Level of support that the technologies provide to the top technical challenges for TA12 Materials, Structures, Mechanical Systems, and Manufacturing. 299
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300 NASA SPACE TECHNOLOGY ROADMAPS AND PRIORITIES Furthermore, many of the TA12 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 reliability, health monitoring, and sustainability. HIGH-PRIORITY LEVEL 3 TECHNOLOGIES Panel 5 identified nine high-priority technologies in TA12. The justification for ranking each of these tech - nologies as a high priority is discussed below. Technology 12.2.5, Innovative, Multifunctional Concepts (Structures) Structures that perform functions in addition to carrying load and maintaining shape can increase mission capability while decreasing mass and volume, potentially benefitting all future space missions. Multifunctional structural concepts involve increasing levels of system integration and provide a foundation for increased autonomy. Habitat structures with integral shielding would reduce radiation exposure and MMOD risk for long-duration human spaceflight missions; these might involve flexible materials and inflatable structures. Other innovative multifunctional concepts would enable load-bearing structures to provide thermal isolation, control and protection in cryo-tanks, habitats, sensor supports and TPS, and address joints as well as primary structure. These concepts would enable on-orbit fuel storage depots and benefit human exploration and science missions by reducing the mass and complexity of thermal control systems. (For instance, improved cryogenic boil-off protection would reduce mass for a Mars mission by 50 percent; Braun, 2011). Sensory and controlled structures would benefit from the ability to conduct electrical signals and power, enabling health monitoring and adaptation. Other multifunctional structures might store energy and autonomously repair damage. Multifunctional structures technology is considered to be at TRL 2 for many level 4 technology items, TRL 3 in several cases, such as integrated MMOD protection, and up to TRL 5 for integrated windows and active control of structural response. The highest-priority technologies are at TRL 2-3. The human spaceflight applications of multifunctional structures technology are unique to NASA and dictate that NASA lead associated technology development. Some multifunctional structures concepts, such as those involving thermal-structural and electrical-structural functionality, are likely to find broader applications in multiple areas and multiple missions, and beyond the aerospace field, including electronics and aircraft. NASA would benefit from partnerships in the development of these technology concepts. One example of a potential cooperative effort might be the commercial development and demonstration of thermally conductive electronics support structures. Some elements of multifunctional structures concepts would benefit from access to the ISS. Specifically, demonstration of habitat structures with integral radiation and MMOD shielding, including long-term exposure to the space environment would increase the TRL of such concepts. While beneficial for other multifunctional technology concepts, access to the ISS would not be required. This technology is game-changing because multifunctional habitat structures with integral shielding could reduce radiation exposure and MMOD risk for human spaceflight, bringing risk levels into acceptable ranges with reduced structural mass and launch vehicle volume. Other multifunctional structures technologies are likely to impact multiple areas and multiple missions and find uses beyond the aerospace field. The development risk is moderate-to-high, perhaps exceeding that of past efforts to develop comparable technology. Technology 12.2.1, Lightweight Concepts (Structures) Lightweight structural concepts could significantly enhance future exploration and science missions and enable new missions. Improved performance of reduced mass launch vehicle systems with increased payload mass fraction could provide benefits for all future space missions. Lightweight cryo-tank concepts could improve launch vehicle performance and potentially enable on-orbit fuel storage depots (crosscutting with TA14). Small-scale inflatable space systems concepts have been demonstrated and commercial scale-up for inflatable crewed systems are planned for later this decade. These concepts and lightweight inflatable ground habitats could enable future exploration
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301 APPENDIX O missions. Lightweight concepts for deployable solar sails, precision space structures, and inflatable, deployable heat shields could provide opportunities for new missions or significantly benefit planned science missions. Advanced composite materials play an important role in developing lightweight structural concepts. Integration of advanced materials and structures technology provide the maximum benefit in development and optimization of lightweight concepts. Lightweight (structural) concepts are considered to be at TRL 2-3 to 5. Some inflatable space systems have been demonstrated at TRL 6. Examples of lightweight structures concepts at TRL 2-3 include cold hibernating elastic memory self-deployable structures and partially flexible composites with shape memory wire. Lightweight structural concepts developed by NASA and the aerospace industry have found extensive appli - cations in transportation, commercial aircraft and military systems. Some space applications of lightweight con - cepts, such as aluminum-lithium cryo-tank structures, solid rocket motor cases, and payload structures, have been demonstrated; however, there are significant new opportunities for adoption of lightweight concepts for future space missions. NASA can partner with other government agencies and/or industry where possible to develop and demonstrate lightweight concepts that will support future NASA missions. An example of a potential cooperative effort is the commercial development and demonstration of an inflatable space habitat that would further NASA’s exploration goals. Some elements of lightweight concepts would benefit from access to the ISS. Specifically, demonstration of in-space manufacturing of lightweight structures, deployment of an inflatable module, and long-term exposure of materials used in these concepts would increase the TRL of lightweight concept technologies. While beneficial, access to the ISS is not required. Lightweight concepts technology could significantly benefit all exploration and science missions and is aligned with NASA’s goals and objectives. The level of risk for lightweight concepts technology ranges from moderate to high depending on the specific technology and application. Many of the lightweight concepts beyond TRL 2-3 are mission dependent, and the timing and effort required to advance from lower TRLs to TRL 6 will depend on the specific application. Weight reductions from lightweight concepts technology could significantly enhance planned exploration and science missions and have the potential to enable new missions. Lightweight structural concepts for habitats, safe havens, and ground-based infrastructure, particularly those technologies that satisfy multifunctional requirements, could enable new human exploration missions to the Moon or Mars. Lightweight deployable structures can enable future science missions with requirements for large-scale structures, precision deployment, and shielding. Technology 12.1.1, Lightweight Structure (Materials) Advanced composite, metallic, and ceramic materials, as well as cost-effective processing and manufacturing methods, are required to develop lightweight structures for future space systems. Further advances are needed if increased benefits from lightweight structures are to be attained. The application of non-autoclave-cured large composite structures to launch vehicles would likely reduce structural weight by more than 30 percent compared to metallic structures. Advanced material systems could enable multifunctional structural designs to reduce radiation levels, improve MMOD protection, and enhance thermal management. Incorporation of nanotechnology-engineered materials in lightweight structures offers the potential for game-changing weight saving and performance improve - ments (crosscutting with TA10). Materials technology for lightweight structures is relevant to all of NASA’s planned and future missions. Lightweight materials are considered to be generally at TRL 2-3, and higher in select areas. Moderate effort is required to reach TRL 6, comparable to that of previous efforts. Lightweight structural materials developed by NASA and other government agencies, academia, and the aerospace industry have found extensive applications in transportation, commercial aircraft, and military systems. Continued NASA leadership in materials development for space applications could result in new materials systems with significant benefits in weight reduction and cost savings. NASA will likely have opportunities to pursue these materials in partnership with other federal agencies and industry.
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302 NASA SPACE TECHNOLOGY ROADMAPS AND PRIORITIES Access to the ISS is not required for development of lightweight materials; however, the ISS could serve as a test bed for evaluation of the exposure of such materials to the space environment. This technology has the potential to significantly reduce the mass of virtually all launch vehicles and payloads—creating opportunities for new missions, improved performance, and reduced cost. The level of risk for materials development and lightweight structures ranges from moderate to high, with non-autoclave- cured composites as a moderate risk, and development and incorporation of nanotechnology materials in high- performance lightweight structures a modestly higher risk. Technology 12.2.2, Design and Certification Methods (Structures) Current structural certification approaches rely on a conservative combination of statistics-based material qualification and experience-based load factors and factors of safety, followed by design development and quali - fication testing. Verification testing and mission history indicates that structures tend to be over-designed and thus heavier than necessary. A model-based “virtual digital certification” methodology could be developed to design and certify space structures more cost-effectively. Advanced physics-based models that predict structural response, failure modes, and reliability using deterministic and probabilistic approaches are a key requirement for such a methodology. This methodology and associated models should be verified and validated with test data at all necessary levels of scale and complexity to ensure confidence in their application. A design and certification methodology based on validated high-fidelity analytical models promises payoffs in weight savings by reducing excess conservatism in the current methodology and in cost reduction by eliminating the large-scale structural tests that are currently required. Methods for advanced design and certification are considered to be generally at TRL 3. This is determined by the availability of validated models for virtual digital certification. NASA has been a leader in developing this technology. Investments from the Air Force Research Labs in similar technologies have contributed significantly and are expected to continue. Several national labs have signifi - cant programs in uncertainty management and quantification. The technology to be developed is not only critical in terms of weight reduction and affordability improvements to NASA’s space missions but also to DOD space structures. NASA can partner with other federal agencies that also have interest in this technology, such as DOD and DOE, to leverage existing expertise. Access to the ISS is not required for this technology development. However, ISS design development and qualification test data may be useful in validating the new models and methodologies resulting from this technol - ogy development. This technology provides another path to lighter and more affordable space structures while assuring adequate reliability. A verified and validated model-based design and certification methodology offers payoffs in lightweight structural designs and affordable certification without extensive testing, while ensuring long-term reliability of space structures. Physics-based models will be required to simulate structural response in a virtual digital fleet leader (VDFL) that would include a digital representation of a vehicle and a real time system to assess vehicle health and identify action necessary to address vehicle performance. Overall, the benefits of this technology rank below those of multifunctional and lightweight structures and materials. Since multiple NASA missions would benefit from improved structural design and analysis capability, the technology alignment was among the highest in this technology area. This high ranking carried over to non-NASA structures as well, since improvements in lightweight structures design, probabilistic design methods, and simulation will also benefit DOD, DOE, and other advanced structural applications. The risk and level of difficulty associated with this technology is high, since significant effort from NASA, industry, academia, and other government agencies will be required to advance the current state of the art. Further, although the objectives have been identified, several challenges need to be over- come, particularly in model development and virtual testing, to reach TRL 6. This technology is applicable to all NASA space vehicles including uncrewed, robotic and human-rated vehicles for use in science missions, and human exploration over extended periods of time.
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303 APPENDIX O Technology 12.5.1, Nondestructive Evaluation and Sensors (Crosscutting) Non-destructive evaluation (NDE) has evolved from its early uses for quality control, product acceptance, and periodic inspection to include continuous health monitoring and autonomous inspection. New NDE and sensor technology, including in situ embedded sensor arrays to assess vehicle and space systems health, integrated analysis to predict vehicle and on-board systems operational capability, and autonomous NDE and sensor operations, will be required for long-duration space missions. Early detection, localization, and mitigation of critical conditions will enhance mission safety and reliability. NASA has proposed an integrated NDE and sensor technology capability in a VDFL that would include a digital representation of a vehicle with real time assessment of vehicle structural health to predict performance and identify operational actions necessary to address vehicle performance. VDFL is an initial step in an overall systems approach to monitor, identify, assess, and respond to on-orbit conditions that impact mission success. Non-destructive evaluation and sensor technology is considered to be at TRL 2-3 for many level 4 technology items. However, some sensor technology is at a higher level and will require integration into vehicle systems to achieve an overall TRL 6. Nondestructive evaluation and sensor development by NASA and other government agencies, industry, and academia has led to improved product quality and reduced failures of space structures. Partnership opportunities exist with academia, industry, and other organizations in the development of new NDE and sensor technology Access to the ISS is not generally required for continued development of nondestructive evaluation and sensor technology. NDE and sensor technology can result in a major increase in reliability of missions. NDE and sensor technology has numerous crosscutting applications and the potential for significant enhancement of safety and mission assur- ance of future long-duration space missions. NASA missions would benefit from an integrated NDE approach to monitor, identify, assess, and respond to on-orbit conditions that impact human exploration and science missions. NASA has proposed a VDFL as an eventual technology development. This concept could be expanded to address not only structural integrity of space vehicles, but to include overall vehicle system performance and operation. The VDFL concept has the potential to be game-changing, though not in a 20-year horizon. NDE and sensor technologies are likely to impact multiple areas and multiple missions, especially as mission durations continue to increase. Assessing and maintaining vehicle integrity with minimal human intervention will be essential for long-duration missions involving complex vehicles and for finding uses beyond the aerospace field. The development risk is moderate-to-high, and consistent with that of past efforts to develop comparable technology. Judgment suggests a clear utility for this technology but no specifically identified users, though the opportunity may exist for partnerships with other agencies. Technology 12.3.4, Design and Analysis Tools and Methods (Mechanical Systems) High-fidelity kinematics and dynamics design and analysis tools and methods are essential for modeling, designing, and certifying advanced space structures and mechanical systems including turbomachinery, landing systems and deployment mechanisms. This technology includes the tools and interfaces required to increase data flow rates between various systems to enable real time use of mechanical system data. A mechanism interrelation/ correlation analysis methodology would enable creation of a single model of spacecraft mechanical systems and would reduce the stack-up of margins across disciplines, e.g., aero-loads, vehicle dynamics, and structural response. Such models could be integrated into a health-management system for diagnosis, prognosis, and performance assessment and in a VDFL system. This technology includes control design techniques for achieving deployment, stiffness control, shape control, and disturbance rejection. This involves perhaps iterative technology development, since the models that yield the best control results are not the same models used for other purposes (stress analysis, for instance). The most appropriate model should be used for control design, and such models may not be totally physics-based. Methods for advanced design and analysis are considered to be generally at TRL 2. This is determined by the availability of interrelation/correlation analysis systems.
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304 NASA SPACE TECHNOLOGY ROADMAPS AND PRIORITIES NASA has been actively developing design and analysis tools and methods for kinematics and rotor dynamics analyses and precursor flight high-data-rate technologies for space vehicle mechanisms. The Air Force Research Laboratory has also invested in deployable mechanisms modeling and testing. The technology is required for both NASA and Air Force space vehicles. NASA could lead or partner with other federal agencies that also have interest in this technology. Access to the ISS is not required for this technology development. However, deployable systems tested on- orbit can provide valuable data for development of analysis tools. This technology can enable a dramatic increase in the reliability of mechanical systems, such as those required for separation, release, and deployment. Improved predictive modeling of spacecraft mechanical systems will reduce overall stack-up of margins across disciplines leading to reduced weight and better performance of con - cepts with minimal ground testing. The overall benefit of this technology is in the same class as 12.2.2 Design and Certification Methods for structures. Since multiple NASA missions would benefit from improved mechanisms design and analysis capability, the technology alignment was among the highest in this technology area. The risk and level of difficulty associated with this technology were rated as high since significant effort from NASA, industry, academia, and other government agencies would be required to advance the state of the art. This technology is applicable to all NASA space vehicles including uncrewed, robotic and human-rated vehicles for use in science missions, and human exploration over extended periods of time. Technology 12.3.1, Deployables, Docking, and Interfaces (Mechanical Systems) Many future science missions involving imaging and scientific data collection will benefit from the com - bination of a large aperture and precision geometry. Achieving such structures within the constraints of antici - pated launch vehicles will most likely involve deployment, possibly including flexible materials, although other approaches including assembly or in-space manufacturing can be considered. Docking and the associated inter - faces provide another approach to building up larger platforms from smaller ones, and these are encountered in human spaceflight missions, along with habitats deployed from flexible materials. These mechanical systems and structures must deploy reliably in extreme environments and achieve a desired shape with high precision; some systems may require the use of a control system to maintain a precise shape under operational disturbances. Such systems include antennas, optical elements, and solar sails. Modularity and scalability are desirable features of such concepts. Deployables, docking, and interfaces technology beyond the current applications for antennas, solar panels, sun shields, and landing systems for science missions and docking systems on the ISS is considered to be at TRL 2-6 for many level 4 technology items, and nominally at TRL 4. Advanced deployables and docking systems have been developed to TRL 6, but typically for smaller systems. The highest-priority technologies are at TRL 3-4. Large precise aperture systems are critical to some NASA science missions as well as to some DOD surveil - lance missions, enabling advanced mission performance. This suggests that NASA lead associated technology development, finding partners when feasible. Some aspects of deployable structures and docking concepts would benefit from access to the ISS. If the systems are relatively large and flexible, their performance cannot be directly verified in the 1- g and 1-atmosphere ground environment. In these cases, the ISS could be used to verify such concepts or to validate design and cer- tification models. This technology will assure the reliable deployment and expected high performance of large precision struc - tures. Without demonstrations associated with this technology, there would continue to be considerable uncertainty and risk involved in fielding such systems. These systems will provide major increases in performance for NASA science missions. Many aspects of precision deployable structures and mechanisms technology are likely to find broader applications in multiple areas and multiple missions, and to a large subset of the aerospace field that requires precise structural geometry. The development risk is moderate-to-high, similar to that of past efforts to develop comparable technology. Judgment suggests a clear utility and clear users, with some possibility of partnerships with other agencies. Space missions have not infrequently failed as the result of failure of a separation, release or
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305 APPENDIX O deployment system. The pursuit of improvements in the reliability of such systems is a critical technology devel - opment area. Technology 12.3.5, Reliability/Life Assessment/Health Monitoring (Mechanical Systems) In recent experience, the reliability of mechanical systems, including deployment, separation and release, and motorized systems, has been a more significant contributor to the failure of space missions than the reliability of structures designed to meet current certification standards. Important technical concerns include sliding joints and bearings, friction and tribology, coatings, and lubrication, as well as their performance and durability over extended periods in storage and extreme operational environments. An integrated sensor system would provide a basis for determining the current state of a mechanical system, as well as prediction of future behavior. To be most effective in assuring mission reliability, the ability to take corrective action must also be designed into the system. Reliability, life assessment, and health monitoring technology is considered to be at TRL 2-3 for many level 4 technology items, TRL 4 for environmental durability testing, and TRL 1 for general life extension prediction and the VDFL concept. Reliability can be advanced significantly for specific classes of mechanical systems at a time. Mission success requires highly reliable spacecraft mechanical systems, especially for long-duration missions. Some elements of mechanical systems reliability would benefit from access to the ISS. For instance, long-term exposure of materials and operation of devices would increase the TRL. While beneficial, access to the ISS is not required. This technology could enable a dramatic increase in the reliability of mechanical systems and structures, espe - cially for long-duration space missions. The intrinsic risk associated with such missions could be reduced through the development of health monitoring systems. This technology area is closely linked with the area of deployables, docking, and interfaces, which itself was ranked high in the QFD evaluation. Significant improvement in the reli - ability of mechanical systems would have a major benefit on assurance of space mission success. Many aspects of reliable mechanisms technology are likely to find applications in multiple areas and multiple missions, to the broad aerospace field, and in some non-aerospace fields. The development risk is moderate-to-high, perhaps exceeding that of past efforts to develop comparable technology. There is a good possibility for outside partnerships. Technology 12.4.2, Intelligent Integrated Manufacturing and Cyber Physical Systems (Manufacturing) As a rule, the fielding of high-performance materials, structures, and mechanisms for space applications requires specialized manufacturing capability. Through advances in technology, largely IT-based, more general but flexible manufacturing methods can be adapted to produce specialized components and systems. A database and data-mining capability would be useful to support a terrestrial and interplanetary design, manufacturing, and opera - tions supply chain. High-fidelity manufacturing process models could be used to simulate various manufacturing scenarios to enable rapid evaluation of process alternatives. An intelligent product definition model could be used to simulate the full behavior of components through all stages of their life cycle. Hardware and software technolo - gies will need to be coordinated to develop the next generation of robotics and automation for space structures. This will require the development of cyber-physical systems that enable adaptable and autonomous manufacturing for long-duration crewed spaceflights, including direct digital manufacturing (DDM). In-space manufacturing has the potential to be game-changing by reducing the structural mass that must be delivered to orbit or to the surface of other worlds. Intelligent integrated manufacturing technology is considered to be at TRL 4, as determined by the availability of validated product definition, and manufacturing process models. In-space manufacturing is at a considerably lower TRL, perhaps 1-2. There are existing industrial capabilities in production process modeling, factory automation and simulation, and product life-cycle modeling. Investments from the Air Force Research Labs in similar technologies have con - tributed significantly and are expected to continue because of the potential impacts on affordability. Manufacturing
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306 NASA SPACE TECHNOLOGY ROADMAPS AND PRIORITIES is an area in which NASA can benefit from monitoring developments in hardware, software, and supply chain management. There is potential to form government, university, and industry consortia to pursue these ends. Access to the ISS is not required for this technology development. However, the ISS could be a useful platform to test in-space manufacturing processes. This technology would enable physical components to be manufactured in space, on long-duration human missions if necessary. For some exploration missions, this could reduce the mass that must be carried into space. Furthermore, this technology promises improved affordability of one-off structures made from high-performance materials. Multiple NASA missions, especially science missions with constrained budgets, would benefit from cradle-to-grave product life-cycle and manufacturing simulation to select affordable designs. For instance, non- autoclave processes would substantially reduce the infrastructure investment needed to manufacture small runs of large polymer matrix composite structures. Additionally, NASA and DARPA recently conducted a study focused on developing larger (>100 m), lighter space-based optical systems using in-space manufacturing. Small-scale (mm) manufacturing concepts were demonstrated, but significant effort would be required to scale up to mean - ingful optical systems. This technology is perhaps at TRL 2, and has potential for ISS demonstration. Therefore, the technology alignment for NASA applications was among the highest in this technology area. This high rank - ing, however, did not carry over to non-NASA applications, where amortization over multiple units changes the manufacturing approach required to ensure affordability. The risk and level of difficulty associated with this technology were rated as high since significant effort from NASA, industry, academia, and other government agencies will be required to advance the current state of the art. This technology is applicable to all NASA space vehicles including uncrewed, robotic and human-rated vehicles for use in science missions, and human exploration over extended periods of time. MEDIUM- AND LOW-PRIORITY TECHNOLOGIES TA12 contains 23 level 3 technologies, of which 14 were determined to be of medium or low priority. Six technologies were rated medium priority, not including the two that were originally rated medium priority but were promoted to the high-priority category, and eight were rated low priority. The ranked QFD results, shown in Figure O.1, provide some insight into the reasons that these technologies did not receive high-priority ratings. For these six medium-priority technologies, the technical risk was considered to be either too low or the required effort was considered unreasonable. A second factor for the lower half of these technologies was reduced alignment with non-NASA aerospace technology and national goals. In the medium-priority technologies there are significant efforts underway in the aerospace industry and other agencies related to manufacturing processes, flex - ible structures, certification methods for mechanical systems, model-based certification and sustainment methods, materials computational design, and environmental materials characterization. Most of the level 4 technology items associated with 12.3.6 Certification Methods are at a low TRL. NASA should be able to partner with others in the development of many of the level 4 items in 12.4.1 Manufacturing Processes, and the panel has included 12.4.1(d) In-Space Assembly, Fabrication, and Repair with the high-priority technology 12.4.2 Intelligent Integrated Manufacturing and Cyber Physical Systems. 12.1.3 Flexible Materials Systems supports 12.2.5 Innovative Multifunctional Concepts, as well as 12.3.1 Deployables, Docking, and Inter- faces. The benefits of research in 12.1.2 Computational Design of Materials are unlikely to be realized within the timeframe addressed by this study. 12.5.2 Model-Based Certification and Sustainment was also regarded as a valuable goal, but with benefits unlikely to be realized within the study timeframe. The likely benefit of pursuing the eight low-priority technologies, broadly defined, was considered to be smaller than that of pursuing the high- and medium-priority technologies. Furthermore, the technical risk associated with these technologies was considered to be either too low, or the required effort was considered unreasonable. Finally, these technologies generally exhibited reduced alignment with non-NASA aerospace technology and national goals. While important in selected aerospace applications, technologies such as special materials, electronics and optics manufacturing processes, electromechanical and micromechanical systems and sustainable manufacturing were identified as areas where industry, other agencies, and academia could partner with NASA in selected technology
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307 APPENDIX O development related to future NASA missions. Technology areas including loads and environment, test tools and methods, and mechanical life extension methods were rated similarly as technology efforts best conducted through industry and academia partnerships. The monitoring aspects of 12.5.3 Loads and Environments might be considered to be included with 12.5.1 Nondestructive Evaluation and Sensors. 12.5.1 Special Materials is a kind of “grab-bag” of unrelated technologies that did not generally fit well with this roadmap. The panel suggests that the associated level 4 technology items be supported as needed by likely users. NASA could partner with others in the development of some of the level 4 items of 12.4.3 Electronics and Optics Manufacturing Process, while the technology related to large ultra-light precision optical structures fits well with other high-priority technology areas. 12.3.3 Electro-mechanical, Mechani- cal, and Micromechanisms includes a variety of perhaps unrelated level 4 technology items. DEVELOPMENT AND SCHEDULE CHANGES FOR THE TECHNOLOGIES COVERED BY THE ROADMAP Perhaps as a result of the need to address such a broad range of technologies in a summary document, the TA12 roadmap devotes little space to discussion of the assumed mission model, or to the inter-dependence of technology development. To some degree, it can be read as a catalog of technology items as much as it can be read as a plan. While such information is included in the Figure 2 foldout in the draft roadmap, detailed interpretation is left to the reader. This makes it challenging to suggest specific modifications to the schedule. OTHER GENERAL COMMENTS ON THE ROADMAP The TA12 roadmap addresses neither improved understanding of the intense vibroacoustic environment of launch nor novel approaches that could reduce structural dynamic response. These extreme loads frequently drive the structural design of spacecraft. This is most closely associated with the following level 3 technologies: Loads and Environments 12.5.3. (Crosscutting); and Design and Certification Methods 12.2.2. (Structures). There is also a crosscutting aspect with active control of vibroacoustic environments and response (TA04). PUBLIC WORKSHOP SUMMARY The workshop for the TA12 Materials, Structures, Mechanical Systems, and Manufacturing technology area was conducted by the Materials Panel on March 10, 2011, at the Keck Center of the National Academies, Wash - ington, 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/discus - sion 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 NASA team presented an overview of the TA12 roadmap. They noted that in developing the roadmap, they focused on innovating and game changing areas instead of incremental improvements. The team also indicated that they looked at both push areas (e.g., physics-based methods, materials, intelligent manufacturing, sustainment, reliability) as well as pull areas (e.g., affordability, multifunctionality, lightweight, environmentally friendly). Overall, the team identified 23 different technologies in the roadmap, and noted that many of these are cut across different disciplines outside the TA12 roadmap. The team also noted that during the roadmap development, they
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308 NASA SPACE TECHNOLOGY ROADMAPS AND PRIORITIES had substantial interaction with the other NASA individuals developing the other TA roadmaps. Finally, the team highlighted that they believed the TA12 roadmap was aligned with the NASA strategic objectives. One topic that the NASA team indicated was a key focus of their roadmap was the VDFL. This technology includes high-fidelity modeling and simulation, design and certification methods, situational awareness, and life prediction and sustainment. According to the team, the VDFL is needed for future NASA endeavors such as deep space travel, where it is difficult to do resupply or provide safe havens in case of emergencies. Essentially, they indicated that the VDFL is a long-term technology aimed at lowering costs and improving reliability for future NASA missions. The NASA team also spent some time discussing the top technical challenges that they developed in the TA12 roadmap. In terms of the overall top challenges, the team noted that radiation protection for humans and reli - ability rose to the top of the list. They also identified top challenges for specific areas, including: materials (e.g., new tailored materials, computational materials technologies), structures (e.g., robust lightweight/multifunctional structures, VDFL), mechanical systems (e.g., higher reliability and predictable performance, precision deployable mechanisms for large space structures), and manufacturing (e.g., advanced manufacturing processes, sustainable manufacturing). After the NASA presentation, a discussion period followed in which several panel members asked the team questions. In responding to a question how the NASA team views the role of nanomaterials in structures, the team responded that they identified products out of the TA10 roadmap that they could use. They noted that materials, manufacturing, and structures work at a larger scale, and there is a need to figure out how to use/implement nano - materials at this larger level. The team noted that areas such as using nanoclays as a toughener and permeability barrier are likely nearer term. Other areas, such as negative CTE materials and platelet materials (to decrease permeability and increase life) have already seen some use in consumer products or flight systems. One workshop attendee also concurred with this viewpoint that applications are becoming nearer term, and that in the next 5 to 10 years much more exploitation should be possible. The concept of the VDFL also generated some discussion. One of the panel members indicated that he viewed the VDFL as a kind of systems engineering technology, rather than a materials/structures technology. He also commented that he felt the VDFL did not go far enough, as it should also include propulsion, guidance/navigation and control (GN&C), on-board sensors, and other features to both monitor and transmit health on all subsystems. Another panel member noted that the NASA team had mentioned certifying models would be part of VDFL, and asked whether this is the overall approach to validation and verification (V&V). The NASA team responded that models for qualification and certification already exist, and that the VDFL is really about making a transition to certifying the models, rather than certifying the program/mission. The team also noted that each vehicle using VDFL will be a test case for improving the models over time. Session 1: Materials Tia Benson Tolle (Air Force Research Laboratory) presented her comments on the NASA roadmap. She indicated she was encouraged to see the acknowledgement in the roadmap of the need for a long-term investment strategy, as well as the push/pull tension built into the roadmap portfolio. She noted that multiple studies have concluded that building in such tension is a proven approach for maximizing innovation and improving product development. Benson Tolle also emphasized that computational design/methods are key to accelerated maturation of complex engineered materials, and they will be relied on more in the future. She noted that while there have been good individual efforts focused on improving computational methods, there is still a need to have a broader and more integrated approach. Benson Tolle also discussed several other materials areas, including hybrid materials, morphing materials, emerging energy harvesting technologies, leveraging TPS investments, and digital manufactur- ing processes. In terms of the top technical challenges, she commented that for the exploitation of nanotailoring, the role of the interface (and its effect on matrix material) is only generally understood, and could use more focus to advance this. Some high-priority technology areas that Benson Tolle emphasized include multifunctional materi - als, and integrated computational materials science and engineering (ICMSE). Finally, she noted that nanotailored
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309 APPENDIX O composites and three-dimensional fiber architectures are near the tipping point where additional investments can help mature these areas. After Benson Tolle’s presentation, workshop participants asked her whether AFRL had formal programs for interacting with NASA research programs. Benson Tolle responded that for her area (i.e., materials), she was not aware of any particular forums for interaction, but that other areas (e.g., engine development) have formal pro - cesses. She did note, however, that there certainly appears to be room for further collaboration with NASA (i.e., in taking advanced materials to the point where they can be exploited for air and space applications). Later in the discussion, another participant asked Benson Tolle about AFRL’s experience in the tradeoffs of multifunctional materials. Benson Tolle answered that first, optimization at the system level must be done early on. Second, she noted that as researchers engineer materials further, the opportunity to change the property tradeoff space may open up. Byron Pipes (Purdue University) followed with a presentation of his views of the NASA roadmap. He noted that while the industry has used composites for more than 30 years, there is still an inability to accurately predict failure modes, and that this results in overdesigning composite structures. Relative to computational materials, Pipes indicated that there are both the “design aided by experiments” and “certification aided by experiments” aspects to consider. He commented that multiscale modeling provides a way to certify materials in ways that do not require experiments. Pipes then suggested that NASA’s goal should be to think about simulation driven materials and structures certification, as well as about simulation driven materials and structures design. He also noted that while NASA serves both aero and space with very different goals (i.e., pervasiveness in aero versus unique solutions in space), human safety is a central issue to both. Pipes indicated that some areas to emphasize might include materials (e.g., computational design materials), structures (e.g., design and certification), cross- cutting model-based certification, and manufacturing (e.g., manufacturing processes). He also noted that micro design models are an area to emphasize with high priority. Pipes then asked the question that, for virtual digital certification, how do you get the FAA and other groups to think more about this? He highlighted this as an area that impacts all missions. Finally, Pipes concluded noting smart materials and devices is another area with a low TRL that might provide benefits to NASA (e.g., health monitoring). After Pipes’ presentation, workshop participants noted that it is important to incorporate early in the process the mechanism for integrating sensors into the structure, and commented that NASA has projects looking into this (e.g., MEMS). Pipes also suggested that there is more to be done in terms of data acquisition analysis and that it is more than just building the sensor into the structure. On another topic, a participant commented that the Boeing 787 symbolizes the state of the art in certification, and asked Pipes what he felt the next steps were. Pipes responded that there are many significant capabilities coming out of the labs that can be taken advantage of. He also indicated that it would be desirable to take some of the uncertainty and empiricism out of the models, as it is becoming increasingly unaffordable to test every piece of structure in every vehicle in the future. Pipes concluded that the science is there, but only recently have has computational power advanced to allow full use of thishe indicated that he believes there will be many more improvements in the next 10 years. Session 2: Structures Les Lee (Air Force Office of Scientific Research; AFOSR) started with a brief overview of AFOSR and its research portfolio. He noted that one of the key areas of focus is in multifunctional design and materials. He notes that in some cases the performance for these may be less than a unifunctional part, but that this is acceptable as long as the overall system improves—system metrics are needed to quantify this. In terms of the NASA roadmap, Lee indicated that the roadmap appeared to be well laid out and contained a good balance between push and pull technologies. He did suggest that the roadmap could use more emphasis on the integration between materials and structures for multifunctional design, as well as providing more coverage of “weakest links” (e.g., joints, discontinuities). On this latter point in particular, a workshop attendee concurred that 90 percent of the issues she deals with are in the interface. Lee also commented that the roadmap coverage on predictive capabilities and VDFL integration appeared to be optimistic; while he indicated he thought this would be useful, he did not think it should be used as an excuse to skip verification testing. Also, Lee noted that although the roadmap coverage
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310 NASA SPACE TECHNOLOGY ROADMAPS AND PRIORITIES of reliability analysis was good, there also needed to be some focus on game changing areas such as autonomic systems. Finally, Lee indicated that self-healing technology is important (e.g., repeated healing), and is critical for deep space missions. Lisa Hill (Northrop Grumman) noted up front in her presentation that cost and affordability are key con - siderations for technology investments, yet this only shows up in the NASA roadmap at a high level. While she indicated that the roadmap does a good job in laying out where we could go, it would also benefit from more quan - tification of why. Hill also commented that the push/pull discussion was done well, as was the concept of linking technologies to a long-term goal (e.g., VDFL). On the other hand, she identified potential gaps (e.g., digital direct manufacturing), as well as areas that could use additional clarification (e.g., the various structures and materials technologies in the roadmap with similar names, the significant connectivity with the TA10 roadmap). Hill also questioned why solar sails were listed as a mission in the roadmap in 2020, as they are already flying at small scales. In terms of VDFL, she noted that currently minimal data is obtained from structures and mechanisms, and that unless forced into the system design, contractors typically will not include these. Hill also commented that the VDFL tools sound useful, but if they are available and used in the design, then the VDFL would not be needed later. Some of the top technical challenges that Hill mentioned include mass producible (e.g., hundreds to tens of thousands annually), modularity, scalability, and obtaining useful performance data on structures (e.g., joints). She did identify some technology gaps in the roadmap, however, including minimal discussion of the production aspects of modular structures, materials and deployments for large optical systems, and concepts for dealing with launch loads in different ways (e.g., friction in joints for damping). Session 3: Mechanical Systems Rakesh Kapania (Virginia Polytechnic Institute and State University) started his presentation by commenting that materials are very important, but so is how they are placed (i.e., direction, geometry). According to Kapania, there are several technology areas that he sees as key to the roadmap: deployables, dockings, and interfaces (e.g., extensibility, correlation between scaled and full-size models), mechanism life extension systems (e.g., under- standing the response of structures to non-stationary random excitations), electro-mechanical systems, design and analysis tools and methods (e.g., connecting analysis with health monitoring, modeling for multifunctional struc - tures, importance of numerical ill-conditioning), reliability/life assessment/health monitoring (e.g., miniaturization, reliability-based structural optimization), and certification methods (e.g., computational-based certification, need for reduced-order modeling, reliability of computers and software). Kapania identified several top technical chal - lenges, including: miniaturization to reduce weight, lack of information on loading environment, effects of radia - tion on material properties, and analysis and design of multidisciplinary systems (e.g., information management, reliable software). In terms of gaps in the roadmap, Kapania noted that energy requirements, energy harvesting, fiber optics based sensors, and distributed sensing could all use more attention. He also commented that there are several high-priority areas for NASA specifically, including: miniaturization and optimization, reliable software for multi-system analysis, and understanding failure modes of multifunctional materials. Kapania also suggested that some aspects of fabrication (e.g., from computer file to three-dimensional object, with sensing, actuation, comput - ing, damage detection, and self-repairing all built in) as well as reliable software able to perform multi-system analysis accurately without conditioning problems are game changing areas. When asked after his presentation on what areas NASA should lead, Kapania responded that one area is in characterizing the space environment—i.e., what it is, what the loads are. He noted that once the requirements are understood, progressing to a solution is straightforward. Kapania also commented that structural health monitoring (which he considers to be near a “tip - ping point” of significant benefit with additional investment) is something desired by most industries, including those outside aerospace (e.g., the automotive industry). Session 4: Manufacturing and Crosscutting Areas Ming Leu (Missouri University of Science and Technology) started his presentation by identifying technologies in the manufacturing and crosscutting areas contained in the NASA roadmap. For in-space assembly, fabrication,
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311 APPENDIX O and repair, he suggested that NASA could potentially take the lead in this. Leu also added two new areas to the Manufacturing Process area: multi-scale modeling and simulation (as large increases in computer power make this important), and nanomanufacturing (where NASA should look to leverage existing National Science Foundation investments). Leu provided detailed commentary on several technology areas, including: Laser Assisted Material Processing (which is an advanced type of three-dimensional printing applicable to in-space manufacturing and repair), intelligent integrated manufacturing and cyber physical systems, sustainable manufacturing (including consideration of environment, economy, and energy—E3—aspects), Nondestructive Evaluation (NDE), and loads and environments. On NDE in particular, Leu noted that the roadmap appears to focus primarily on ultrasound techniques; he suggested that other methods (e.g., eddy current, microwave, millimeter wave) should also be looked at, and that sensor fusion is another aspect deserving attention. Relative to the top technical challenges in the NASA roadmap, Leu commented that making accurate predictions based on multi-scale modeling will take a long time, and that trying to make complex three-dimensional parts with high precision is difficult. He also commented that there appeared to be some gaps in the roadmap, including: multi-scale modeling and simulation, nanomanufacturing, and lifecycle product and process design (or E3 technologies). Leu indicated several areas that he views as high-priority for NASA, including autonomous fabrication, repair, and assembly at point of use, advanced robotics, functionally gradients composites capable of surviving very-high-temperature environments. In terms of technologies close to a tipping point, Leu noted that composites manufacturing (and polymer matrix composites in particular) could benefit substantially from additional investment. Finally, Leu commented after his presentation that in his view, it is important for NASA to get involved in these areas as the industry is typically not willing to invest. Glenn Light (Southwest Research Institute) followed Leu with a presentation on his perspectives on the NASA roadmap. Light noted that the roadmap stated its goals well in terms of how NDE technologies can feed into the safety/reliability of long-duration space missions and the assessment/maintenance of vehicle integrity with mini - mal human intervention. He also commented that the roadmap provided a good discussion on prognostics (i.e., the ability to detect defects, assess the situation, and provide a prognosis of remaining life or usage), and that this is an area deserving of attention. On the other hand, Light also highlighted some areas that he felt the NASA roadmap did not cover as well, including: types of defects and damage that might be anticipated, practical aspects and effective integration of sensors and sensor life, sensing and monitoring the fields/environment around the structure, technology to route repairing materials through the structure, and wireless power transfer to sensors. In terms of top technical challenges in NDE and sensor systems, Light indicated that these include sensor integration with minimal detrimental effects, sensitivity to early damage, increasing sensor life, sensors and micro-circuitry embedded in the structure, environmental protection for structures (e.g., coatings), and the ability to monitor how coatings are wearing. Light also discussed several areas he felt are high-priority for NASA, including: development of sensors in practical form factors, wireless power transfer to embedded sensors (e.g., local energy harvesting), on-call repair technologies and self-healing metals and composites, and integration of embedded sensors as part of the structural design. As for alignment with NASA, he indicated that many of these areas align well with NASA’s expertise, capabilities, and facilities. Light did suggest that there is a need to set clearly defined national goals for the space program, and minimize the requirement for cost sharing and need to have dual-use technologies (which many federal contracts do). Light also highlighted several technologies that he considers game-changing, including capillary repair materials, practically embedded sensor arrays that positivity impact structural strength, and sending power to all sensors wirelessly. He additionally noted that remote sensing of the environment around the structure is near a tipping point and may benefit from further investment. Regarding embedded sensors, Light indicated that this requires a new concept for teaching structural design. Finally, in responding to a question from a workshop participant on the use of fiber optics embedded for sensing purposes, Light noted that this is good for some things (e.g., stress analysis), but the main issue to date has been the detrimental impact to the structure. 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.
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312 NASA SPACE TECHNOLOGY ROADMAPS AND PRIORITIES • Individual observations on technology development. One workshop attendee provided a relatively detailed set of observations based on his being involved in the technology development efforts at a U.S. government agency. He noted that materials are very different for space systems, as issues with radiation resistance and aggressive environments need to be accounted for. He also commented that space systems are typi - cally low-rate production programs. This attendee then suggested that in computational modeling, most methods do not account for manufacturing variability, and that there have been some spectacular failures when this was used as the basis for validating the system. He emphasized that there is no substitute for testing; while there are many physics-based models out there, there is an issue with not knowing everything that might impact a system. An example he provided of this is for impurities in lithium ion batteries, and the fact that these components still need to be tested for 10 years to understand their 10 year lifetime. Finally this attendee noted the need to think politically to be successful in receiving technology fund - ing; he suggested that looking for dual-use technologies at low manufacturing readiness, and looking at productizing these, might be a way to do this. • Collaboration with other agencies. During the discussions in the day, several presenters and attendees highlighted the need for NASA to look at how to take advantage of other agencies’ investments in technol - ogy development. One workshop attendee indicated that there is a lack of a formal interchange process for technology development among these different groups, and suggested that the NASA Office of the Chief Technologist look to stand up a process like this. This attendee also commented that NASA should look at the National Research Laboratories, AFRL, and other groups, and perform a gap analysis to find out which areas might be most applicable to and worthy of NASA investment. • Radiation protection. One of the panel members noted that NASA had identified radiation protection as one of its top technical challenges in the roadmap. This spurred many comments, including some from the NASA team suggesting that they are looking at materials like metal organic foam in tanks to help as shielding for habitat modules. Another workshop attendee noted that for protecting electronics, there are two approaches: radiation-hardened electronics, or radiation protection for non-radiation-hardened electronics. He commented that if NASA develops better ways to shield spacecraft from radiation, it could have a large benefit for uncrewed spacecraft systems as well. Building on this comment, another attendee noted that taking more of an active materials approach might be beneficial. • Certification of materials. Participants commented that it appears as if there are substantial costs associ - ated with certification, and that this frequently is a barrier to using new materials in actual systems. One participant additionally commented that in the past there were mission requirements to use technologies that were TRL 6 or higher, whereas the organizations developing push technologies frequently stop at about TRL 4—this leads to a “valley of death” that is hard to overcome. Finally, there was a comment from another attendee that improving physics-based modeling is one way to try and streamline certifica - tion, but there is a need to find a good balance between modeling and testing for certification. • Reliability. Toward the end of the public discussion session, one workshop participant asked what others thought about having reliability as a grand challenge for the roadmap. In response, one of the NASA team members noted that having precise knowledge of the structural reliability is important relative to integration and saving mass/volume. A workshop attendee also suggested that it is important to consider whether these technologies are being used because they can, or because they should (e.g., embedded sensors). He commented that the benefit from embedding sensors in laminates versus metals needs to be addressed, for example, and that it is important to take a pragmatic approach in applying these technolo - gies. Another example he provided was self-healing: if a structure has many tubes and holes, there will be a reduction in strength. He noted that there needs to be a filter applied so that these technologies make their way onto a vehicle to make it more robust. REFERENCE Braun, R., National Aeronautics and Space Administration. 2011. “Investments in Our Future: Exploring Space Through Innovation and Tech- nology,” presentation at the Johns Hopkins University Applied Physics Laboratory, Laurel, Md., May 25, 2011. Available at http://www. nasa.gov/pdf/553607main_APL_Bobby_5_27_11_DW2.pdf.