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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals Executive Summary After the completion of the National Research Council (NRC) report, Maintaining U.S. Leadership in Aeronautics: Scenario-Based Strategic Planning for NASA's Aeronautics Enterprise (1997), the National Aeronautics and Space Administration (NASA) Office of Aeronautics and Space Transportation Technology requested that the NRC remain involved in its strategic planning process by conducting a study to identify a short list of revolutionary or breakthrough technologies that could be critical to the 20 to 25 year future of aeronautics and space transportation. These technologies were to address the areas of need and opportunity identified in the above mentioned NRC report, which have been characterized by NASA's 10 goals (see Box ES-1) in "Aeronautics & Space Transportation Technology: Three Pillars for Success" (NASA, 1997). The present study would also examine the 10 goals to determine if they are likely to be achievable, either through evolutionary steps in technology or through the identification and application of breakthrough ideas, concepts, and technologies. The Committee to Identify Potential Breakthrough Technologies and Assess Long-Term R&D Goals in Aeronautics and Space Transportation Technology was formed to conduct this study. Between September 1997 and February 1998, the committee visited the NASA research centers that conduct aeronautics and space transportation research and development (R&D) and was briefed by dozens of members of the aerospace and air transportation communities in government, industry, and academia. After gathering information and collecting ideas from a broad cross section of the aerospace community, the committee organized and conducted a Breakthrough Aerospace Technologies Workshop, which was held on February 19 and 20, 1998, to provide additional input; and assist the committee in assessing the technologies and concepts that had been compiled during the previous five months. CANDIDATE BREAKTHROUGH TECHNOLOGIES The committee and the workshop participants adopted a broad definition of "breakthrough technology," which included: (1) discrete technologies that might result in revolutionary improvements in capability; and (2) broad technology areas that might enable dramatic improvements through either evolutionary or revolutionary developments. In addition, the committee and workshop participants recognized that breakthrough capabilities for complex systems, such as air vehicles, launch vehicles, and their related infrastructures, often result from the novel integration of existing "off-the-shelf" technologies, rather than from revolutionary changes or sudden advances in knowledge or techniques.
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals BOX ES-1 NASA's Three Pillars and Ten Enabling Technology Goals to Achieve National Priorities in Aeronautics and Space Transportation Pillar One: Global Civil Aviation Goal 1: Reduce emissions of future aircraft by a factor of three within 10 years and by a factor of five within 20 years. Goal 2: Reduce the perceived noise levels of future aircraft by a factor of two from today's subsonic aircraft within 10 years and by a factor of four within 20 years. Goal 3: Reduce the aircraft accident rate by a factor of five within 10 years and by a factor of 10 within 20 years. Goal 4: While maintaining safety, triple the aviation system throughput, in all weather conditions, within 10 years. Goal 5: Reduce the cost of air travel by 25 percent within 10 years, and by 50 percent within 20 years. Pillar Two: Revolutionary Technology Leaps Goal 6: Provide next-generation design tools and experimental aircraft to increase design confidence and cut the development cycle time for aircraft in half. Goal 7: Invigorate the general aviation industry, delivering 10,000 aircraft annually within 10 years and 20,000 aircraft annually within 20 years. Goal 8: Reduce the travel time to the Far East and Europe by 50 percent within 20 years and do so at today's subsonic ticket prices. Pillar Three: Access to Space Goal 9: Reduce the payload cost to low-Earth orbit by an order of magnitude, from $10,000 to $1,000 per pound, within 10 years. Goal 10: Reduce the payload cost to low-Earth orbit by an additional order of magnitude, from $1,000's to $100's per pound by 2020. The candidate breakthrough technologies identified during the workshop were further refined by three subgroups of the committee, which focused on air vehicle technology, air transportation system technology, and space transportation technology. The findings of these three subgroups are summarized in the following sections.
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals Air Vehicle Technology Six technology thrust areas were identified as critical to new air vehicle configurations and the achievement of NASA's eight air transportation-related goals. Advanced Air Vehicle Configurations Advanced air vehicle configurations that include novel wing designs, drag reduction technologies, and aerodynamic/propulsion integration could lead to substantial progress toward meeting four of NASA's goals: reduced air travel costs; reduced noise and emissions levels; increased aviation system throughput; and high-speed air travel. In general, advanced configurations represent high-risk technologies with potentially high payoffs. Embedded Sensing and Control The development of embedded sensors and controls in air vehicles and components could further a number of NASA's air transportation goals. Better health monitoring, more efficient servicing, and improved performance could lead to reduced operating costs and increased safety. In addition, active combustion control in propulsion systems appears to be a promising way to meet NASA's goal for reducing emissions. Critical path items are robust, real-time, highly accurate sensors and actuators. Structures and Materials The development of engineered materials, such as low-cost composites and new corrosion-resistant, damage-tolerant alloys, could lead to reductions in life-cycle costs that would enable reductions in the cost of air travel. Engineered materials could also lead to the expansion of the general aviation market through the introduction of new options for designing more efficient and cost-effective aircraft. High-temperature materials for supersonic engines and airframes could also contribute to meeting NASA's goal of reduced travel time. Advanced Propulsion and Power NASA's goals related to emissions, noise, cost, general aviation, and high-speed air travel will all be affected by advances in propulsion technology. The major opportunities for breakthrough propulsion technologies include alternative fuels, novel concepts for engine components, active control of propulsion processes, and new power and propulsion devices. The desirability of pursuing any of these technologies to the point of application
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals must be assessed early in their development by assessing their benefits in the context of an overall aircraft system. Manufacturing Lower aircraft purchase costs resulting from low-cost manufacturing are necessary for the achievement of NASA's goals of reducing the cost of air travel and reinvigorating the general aviation industry. Lean manufacturing, and automated manufacturing through techniques such as automated and high-velocity machining of parts, sheet metal assembly, and manufacturing by light, should be investigated. Computer-Based Design, Modeling, and Simulation To reduce the costs and shorten the development cycle for future air vehicles with performance characteristics that meet NASA's air transportation-related goals, substantial improvements will have to be made in computer-based design, modeling, and simulation. These improvements include optimizing the flow of information throughout the design process; enhancing linear and nonlinear simulation capabilities for both aircraft and propulsion systems that fully integrate separate models with varying levels of fidelity; and improving the understanding of the optimal integration of humans and computers throughout the design process. Air Transportation Systems Technology Technological changes and the development of new operating procedures for the air transportation system will be required to achieve NASA's air transportation goals. The consensus of the committee is that these improvements will be related in one way or another to advances in information technology. Models to Predict the Impact of New Technologies and Procedures on the Air Transportation System The development of models to predict the impact of technological and procedural changes on the air transportation system will be critical to the long-term future of aeronautics and to meeting NASA's goals relevant to system capacity, environmental compatibility, safety, and cost. These models could be used to identify and address barriers to the incorporation of existing and new technologies into the air transportation system. The development of these models would require cooperation among NASA, the Federal Aviation Administration (FAA), and the aviation industry.
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals Upwardly Compatible Aerospace Information Systems The expected long lifetimes of current and future aircraft and air traffic management (ATM) systems will necessitate a number of upgrades to their information-based components. To reduce the cost of upgrades that involve new technology or additional functionality, aerospace information systems must be designed to be upwardly compatible. This can be accomplished by developing software that is adaptable, functionally modular, employs an open architecture, and uses well defined interfaces that are unlikely to change. The ability to upgrade information technology-based control systems can contribute to achieving NASA's goals for general aviation, improved safety, reduced operating costs, and increased system throughput. Methodologies for the Development of High Integrity Software New software engineering methodologies could facilitate the development, validation, verification, and maintenance of high integrity software. These methodologies include: formal specification methods, including verifiable high-level languages; formal methods of validating specifications and consequent software; techniques for building and checking models to determine the validity of system components, methods of combining disparate sources of software certification evidence; documentation of safety arguments in the form of safety cases; and models of human operators and their roles and expectations. These approaches to software development address NASA's air transportation goals related to improved safety, increased throughput, and a revitalized general aviation industry. Improved software certification would also reduce aircraft costs and design time. Advanced Human-Automation Systems Although automation has already improved the safety and increased the efficiency of air travel, additional progress can be made through improvements in aviation-related human-automation systems, such as aircraft flight decks. Key issues that require NASA research support include human-machine task allocation and pilot situation awareness. Advances in technology for uninhabited air vehicles (UAVs) may also contribute to the fulfillment of NASA's safety and capacity goals for air transportation operations involving piloted aircraft. Precision Air Traffic Management/Aircraft Operations Precision ATM and aircraft operations will be important to meeting NASA's goals related to air transportation cost, safety, noise and emissions, throughput, high-speed air travel, and general aviation. In the near term, precision ATM will probably be based on emerging technologies now used for weather detection, precise navigation and surveillance, and air-to-ground data transfer and communications. However, achieving NASA's goals in the long
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals term will require the development and implementation of an aircraft-based air traffic control (ATC) capability that is totally independent of ground-based infrastructures. Mitigating Constraints in Terminal Areas Increasing air transportation system throughput depends directly on reducing constraints in terminal areas. Technology developments in this area should focus on reducing runway occupancy time, mitigating the effects of aircraft wake vortices, and enabling vertical/short takeoff and landing (V/STOL) aircraft to operate from existing airports and runways without reducing capacity available for other air traffic. To the extent that these improvements can provide more precise control of aircraft operations or can reduce the potentially harmful effects of wake vortices, they could also improve aviation safety and operating conditions for general aviation aircraft. In the long term, personal air transportation vehicles could be a breakthrough that would achieve NASA's throughput goal by allowing millions of air travelers to bypass existing airports and air travel infrastructures. If these vehicles were produced and sold by general aviation manufacturers, NASA's goal of revitalizing this industry could also be met. Space Transportation Technology NASA's two goals for access to space reflect the view that low-cost is the key to exploiting the commercial potential of space, as well as to expanding space research and exploration. The committee believes that the predominant low-cost attributes of future launch systems will be simplicity, robust design and operating margins, and hardware reusability. The most practical way to achieve NASA's goals for low-cost access to space is to develop robust, reusable launch systems with aircraft-like maintenance and operations. Six related enabling technology areas are described below. Advanced Air Breathing Engines A system study is required to select the most cost effective combined air-breathing/rocket engine for reusable launch vehicles (RLVs). The study must be detailed enough to identify promising technologies and should assess the benefits of engines relative to pure rocket-based propulsion systems incorporating advanced technologies. Pulse Detonation Wave Engine Pulse detonation wave engines could provide the equivalent performance of high chamber pressure conventional rocket engines while operating at one-sixth the pressure, representing an increase of 10 to 15 percent in potential specific impulse. Critical
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals technologies for pulse detonation wave engines include scaling limits, process controllability, and fast acting valves for booster-sized engines. High Thrust to Weight Rocket Engines The thrust-to-weight ratio necessary to enable rocket propulsion-based RLVs to meet the NASA launch cost goals will require significant reductions in the weight of engine components. Advanced materials and fabrication methods will have to be developed to reduce component weight without compromising performance. Variable Expansion Ratio Nozzles Variable expansion-ratio nozzle configurations provide altitude compensation to improve trajectory averaged performance. To be most beneficial to RLVs, these nozzle configurations should be lightweight, should contribute to increases in overall engine thrust-to-weight (T/W), and should reduce overall structural weight requirements. Advanced Propellants and Storage Methods Notable improvements in chemical propellants, which could be important to the achievement of NASA's space transportation goals, are possible. Potential advances include the recombination of highly energetic atomic ingredients, hydrogen storage at high effective densities, and the development of metallic hydrogen. However, the potential of these advances may not be realized unless NASA increases its research support. Integrated Aero-Thermal Structures For RLVs designed to achieve NASA's launch cost goals, lightweight, integrated aerothermal structures will be critical. System studies should be performed to select the most cost-effective integrated thermostructure. Technology development will also be required for a number of critical subsystems. Novel Launch System Concepts Leveraging novel reusable launch vehicle concepts and automated launch operations based on demonstrated technologies and systems approaches aimed at reducing costs and increasing reusability may approach NASA's 10 year launch cost goal.
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals Additional Goals for Space Transportation While attempting to identify potential breakthrough technologies that could achieve NASA's space transportation goals, the committee noted that both focus only on achieving low-Earth orbit (LEO). However, this is only one aspect of the space transportation problem. Most satellites that are launched into Earth orbit, even if it is LEO, require some form of upper stage propulsion or orbital transfer vehicle to boost the satellite into an operational orbit. In addition, space vehicles used for scientific exploration must often travel beyond Earth's orbit into deep space. Providing this additional transport will be expensive and will add considerably to the costs of space missions. Thus, the committee suggests that NASA consider modifying the existing goals or adding additional goals to provide "stretch challenges" for: reducing the overall cost of space transportation, including the launch stage and the final propulsive stage used in orbital transfer minimizing the cost of developing far-reaching space transportation technologies that enable new deep-space missions BREAKTHROUGH TECHNOLOGIES TO MEET NASA'S GOALS The committee's final deliberations were focused on selecting a short list of breakthrough technologies to recommend to NASA as high priorities. Although all of the technologies listed in the three categories above deserve funding consideration from NASA, the committee realizes that in today's environment of constrained budgets NASA may not be able to support all of them simultaneously. Therefore, the five broad technology areas shown in Figure ES-1 and discussed below are the committee's priority areas of focus for a research and development program that would achieve NASA's 10 goals. The committee believes that these five categories are also suited to NASA's role of "pushing the technological envelope" by supporting the development of high risk, but potentially high payoff technologies that are not likely to be supported by U.S. industry based on conventional commercial investment criteria. Although the five categories of research and technology development are discussed separately below, they are interrelated in many ways, just as the 10 national goals defined by NASA for air and space transportation are interrelated. To ensure that meeting any one goal does not adversely affect meeting another, technology must be developed with a broad and comprehensive understanding of the entire air and space transportation system. This will require the cooperation of all organizations involved in the nation's aerospace R&D enterprise, including NASA, the FAA, the U.S. Department of Defense (DOD), universities, and industry. However, NASA is well structured and broad-based enough to play a unique role in the analysis and development of technology for the "aerospace" transportation system. Because NASA's R&D programs intersect engineering and risk exploration, the agency is in a unique position to bring insight to the potential synergism and trade-offs of new component
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals insertion, technology integration, and operational interaction. NASA can act as the steward of crosscutting, "system of systems" technology analysis, which could be called enhanced systems engineering. Cyber Technology The prefix "cyber," when used in words such as cybernetics, cybernation, and recent expressions such as cyberspace, connotes a merging of human control over processes and physical activities with computer-based control. For this reason, the committee has chosen the term cyber technology to encompass a host of technologies and concepts related to the growing importance of computer-based information and control systems to air and space transportation and the design and manufacture of aerospace systems. Cyber technology will be pivotal to the achievement of all of NASA's goals for aeronautics and space transportation technology. However, it would be unrealistic for NASA to play a critical role in R&D related to all of the technologies that fall into this category. For example, continuing improvements in computer microprocessor speed and capability do not require NASA's attention. However, the committee has identified five key cyber technology areas that are crucial to meeting NASA's goals: modeling and simulation for both vehicle design and the characterization of the air transportation system; advanced, robust, real-time sensors and actuators for air vehicle structures, materials, and propulsion systems; automated aerospace manufacturing and space launch operations; improved methods for developing flight-critical software, and optimized human-computer interactions for aircraft flight decks and for the process of aerospace vehicle design. These five areas will not receive adequate levels of R&D focused on aerospace applications without support from NASA. Recommendation. NASA should focus its aeronautics and space transportation research and technology development to meet the 10 goals on the following areas of cyber technology: modeling and simulation applied to both vehicle design and the characterization of the air transportation system; advanced, robust, real-time sensors and actuators for air vehicle structures, materials, and propulsion systems; increased automation of aerospace manufacturing and space launch operations; improved methods for developing flight-critical software; and improvements in human-computer integration for aircraft operations and aerospace vehicle design.
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals TABLE ES-1 NASA's Goals for Aeronautics and Space Transportation Technology and the Recommended Breakthrough Technology Categories Breakthrough Technology Category Reduced Emissions Reduced Perceived Noise Levels Reduced Aircraft Accident Rate Triple Aviation System Throughput Reduced Air Travel Costs Increased Design Confidence and Reduced Cycle Time Invigorated General Aviation Industry Reduced Travel Time Reduced Payload Cost to Low Earth Orbit Cyber Technology Modeling and simulation M M H H M H M M M Advanced, robust, real-time sensors and actuators M H M M M M L L M Automated manufacturing L L L L M M H M M Improved methods for developing flight-critical software M M H M M H M L — Human-computer integration M M H M M H H M M Structures and Materials Lightweight structures L L L L M M H H M High-temperature materials M L L L M M M H M Propulsion Technology Advanced air vehicle propulsion concepts H H L L H L M H — Advanced propellants for launch vehicles — — — — — — — — H Aerospace Vehicle Configurations Advanced configurations M M L M M L M H M Precision Air Traffic Operations in Terminal Areas Reduced runway occupancy time L L M H M — M L — Mitigation of wake vortices L L M H M — M L — V/STOL air vehicles L L — H M — M L — L = Low impact on achieving the goal; M = Moderate impact; H = High impact.
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals Structures and Materials Advances in structures and materials, combined with improvements in computational methods, advances in materials science (including increased understanding of material behavior, characterization, and structural analysis), advances in manufacturing methods (including processing science), concurrent, computer-aided design, and intelligent health/performance monitoring systems will yield substantial benefits for aerospace vehicles. Advances in lightweight structures for RLVs and improvements in the general area of high-temperature materials will be critical to achieving a number of NASA's goals. Recommendation. Because immediate breakthroughs in the development of lightweight structures and high-temperature materials suitable for high-speed civil transports and reusable launch vehicles are not readily apparent, NASA should invest in fundamental research on structures and materials research, keeping in mind important end use requirements, such as affordability, manufacturability, and maintenance. Propulsion Technology Step changes in the gas turbine engine through novel components or through the use of active controls, as well as alternative propulsion systems, may have large payoffs in several areas related to the goals for air transportation. Aspirated compressors with fewer, more slowly turning counter-rotating blade rows, for example, would increase operating margins, improve stall/surge control, and increase thrust-to-weight ratios. Detonation wave engines and fuel cells are examples of promising alternative propulsion and power technologies. These technologies will require a great deal of development before they will be practical for air transportation. Recommendation. NASA's investments in propulsion technologies to meet the goals for air transportation should focus on new technologies that offer step changes in the performance of gas turbine engines. NASA should also support research on alternative propulsion and power technologies, which will require aircraft design studies as early in the development process as possible to assess potential benefits. The committee believes that rocket-based or combined rocket/airbreathing propulsion systems will continue to be the technology of choice for the commercial launch industry. Therefore, technology breakthroughs in propellant performance, density, and affordability are imperative for meeting NASA's space transportation goals. Technologies that should be investigated cooperatively by NASA and the Air Force include cryogenic solid hydrogen, metallic hydrogen, carbon and carbon-boron absorptivity of hydrogen, and cryogenic solid oxygen.
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals Recommendation. To reduce launch costs, NASA should become a full partner with the U.S. Air Force in the development of advanced rocket propellants. This joint program should focus on cryogenic solid hydrogen, metallic hydrogen, the carbon and carbon-boron absorptivity of hydrogen, and cryogenic solid oxygen. Aerospace Vehicle Configurations and Integration Concepts The overarching necessity for the total integration of component technologies in the development of air vehicles will require that both conventional and unconventional configurations continue to be explored in pursuit of NASA's goals. However, the committee believes that R&D on unconventional advanced configurations deserves NASA's support because of their high potential for meeting the goals. Recommendation. NASA should continue to support preliminary feasibility studies for advanced air and launch vehicle configurations designed with new levels of propulsion/airframe/aerodynamic integration. Configurations that have the potential to meet several goals, like the blended-wing-body (BWB), should undergo extensive virtual testing and/or full-scale experimental vehicle development. Precision Terminal Area Aircraft Operations The terminal areas of the nation's air transportation system and the air transportation systems of other highly developed areas are fundamentally constrained. No matter how precise navigation and surveillance becomes for air traffic en route from one terminal area to another, total throughput cannot be increased until more commercial cargo and passengers, as well as private aircraft, can take off and land in a terminal area in a given period of time. The committee is not convinced that public use airports will be built or expanded to accommodate projected higher levels of air traffic. Therefore, the solution to increases in terminal area capacity must come from breakthrough technologies and associated procedures. Reducing terminal area constraints in pursuit of NASA's 10-year goal of tripling aviation system throughput will mean that NASA should focus on the development of technologies and procedures for reducing runway occupancy time, mitigating wake vortices, and increasing the use of V/STOL air vehicles at existing airports. Existing government funded initiatives which are seeking to improve throughput at airports, such as the NASA capacity and terminal area productivity programs, should support R&D in these three areas. Recommendation. To further the goal of tripling the aviation system throughput in 10 years, NASA should support research and development focused on mitigating terminal area constraints. The most promising areas of focus include the reduction of runway occupancy time, the mitigation of aircraft wake vortices, and the operation of V/STOL air vehicles at existing airports. Existing government-funded initiatives which are seeking to improve
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals throughput at airports, such as the NASA capacity and terminal area productivity programs, should support research and development in these areas. ACHIEVING THE 10 AND 20 YEAR GOALS Meeting the 10 Year Milestones An examination of the average time it takes to embody technology into commercial aerospace products reveals that research and preliminary technology development under way today will probably not be adopted for at least 10 years. Manufacturers and operators have strong economic incentives for maintaining the technological status quo or adopting only incremental changes. However, meeting NASA's goals for aeronautics and space transportation technology will require that concepts, processes, and technologies be incorporated by industry into commercially viable air and space vehicles and related systems. To accelerate the adoption of new technologies into operational aerospace systems, the committee believes that NASA should focus on the following objectives: reducing the risk of technology adoption by ensuring that it has been fully validated and verified facilitating technology transfer and the reduction of commercial barriers to technology adoption through increased industry participation in the early stages of technology development investigating methods of increasing the pace of the innovation process. Recommendation. NASA should attempt to reduce the time required to introduce new aerospace technology into the commercial marketplace by supporting technology development to a higher level of readiness, by investigating information technology-based methods to speed the pace of innovation, and by maximizing government/industry collaboration in the development of commercially viable technology focused on the 10 goals. Meeting the 20 Year Milestones Although a recommendation that emphasizes technology adoption, technology transfer, rapid innovation, and government/industry collaboration might be misinterpreted as a criticism of long-term, fundamental research, the committee does not intend to convey this message. Many of the technologies identified in the remaining chapters of this report are truly high-risk endeavors that will take much longer than 10 years to develop but could eventually meet NASA's goals. Long-term, high-risk technologies should be pursued through research that is focused specifically on the achievement of the 20 year milestones.
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals The committee also recognizes that many appropriate technologies to achieve these long-term milestones have not been identified because ideal solutions to the challenging problems they represent are currently unknown. The committee believes that the general knowledge pool of the aerospace community should continue to be increased through fundamental research in order to discover these unidentified technology breakthroughs. Therefore, NASA should ensure that appropriate levels of sustained funding and effort continue to be applied to relatively unfocused, long-term, fundamental research in the aerospace sciences. To accomplish these objectives, each NASA center with an aeronautics and space transportation R&D mission should exercise the responsibility and authority to fund researchers with promising ideas that could lead directly to the accomplishment of one or more goals or could eventually lead to revolutionary new aerospace technologies. Recommendation. NASA should ensure that appropriate levels of sustained funding and effort continue to be applied to R&D focused specifically on the 10 goals, and to more general long-term, fundamental research in the aerospace sciences. To accomplish this, each NASA research center with an aeronautics and space transportation technology mission should exercise the responsibility and authority to fund researchers with promising ideas that could lead directly to the accomplishment of one or more goals or could eventually lead to revolutionary new aerospace technologies.
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