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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals 6 Breakthrough Technologies to Meet NASA's Goals IDENTIFYING BREAKTHROUGH TECHNOLOGY CATEGORIES At the end of the workshop on breakthrough technologies described in Chapter 1 and Appendix E, the committee identified the technologies that were described in the preceding three chapters. The committee then attempted to identify broad areas of technology development that could lead to breakthrough capabilities in both air and space transportation and that could potentially meet many of NASA's goals for aeronautics and space transportation technology. Because NASA's budget for aerospace R&D is limited, the committee believes that identifying crosscutting technologies is critical. Although all of the technologies discussed in the previous chapters deserve funding consideration by NASA, the five breakthrough technology categories listed in this chapter represent the committee's priority areas of focus (see Table 6-1). 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, 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 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.
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals TABLE 6-1 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 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 believes that five of the cyber technology areas discussed in Chapters 3, 4, and 5 are crucial to meeting NASA's goals. These five areas will not receive adequate levels of R&D focused on aerospace applications without support from NASA. The five cyber technology areas are: 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. Modeling and Simulation Modeling and simulation has developed at a very rapid pace during the past several decades, and NASA's past activities in this area have been noteworthy. For example, the initiation and support of computer programs such as NASTRAN (NASA structural analysis), have provided invaluable design capabilities to the aerospace industry. Today, literally hundreds of models are used to simulate physical systems. However, multiscale models and simulations that can predict the effects of changes in any component or at any scale of a system and propagate them throughout the whole system are still in the development stage. For example, changes in aerospace material properties at the molecular level, such as creep and fracture toughness, can have significant effects at the component level, such as a wing or an airframe, that will alter performance at the macrolevel, in this case, the air vehicle. The capability to link molecular phenomena to macroscale phenomena in an acceptably predictive manner has not been developed. Therefore, a significant area for research in this important area is the integration of models to provide an "unbroken chain" of simulation capability from the atomic scale to the structural scale to the system interaction scale. Models at any given scale must be connected to models at the next larger and next smaller scales.
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals Making the most effective use of simulations in the design process will require a capability to seamlessly integrate models of one level of fidelity with models of a different level. For example, results from a detailed three-dimensional model should be able to be fed back into a less detailed two-dimensional model. The architecture for doing this has yet to be developed. Models of physical properties at a larger scale than the air vehicle will also be necessary to simulate the properties of the entire air transportation system. Here the scale can be thousands of miles and cover the entire airspace of a nation or regional area. An additional challenge posed by the simulation of an entire air transportation system is the modeling of human and socioeconomic behaviors. For simulations of large-scale physical systems or systems comprised of both human and physical behavior, explicit treatment of uncertainties in each fundamental model that comprises the total integrated simulation will be essential. The committee believes NASA's role should be to integrate and verify physically and cognitively accurate models and simulations of aerospace systems. This will require complete knowledge of modeling and simulation R&D being funded by DOD, the NSF, and the aerospace industry so gaps in specific modeling capabilities at various scales can be identified. It will also require that NASA support research on structuring fundamental models to compensate for uncertainties so the realism of the whole simulation will be greater than the sum of its parts. Advanced, Robust, Real-Time Sensors and Actuators Advanced sensor and actuator technologies for aerospace applications should eventually provide for the active, real-time control of vehicle performance and safety. Embedding sensors and actuators within structures and materials will create intelligent or "smart structures" with properties that enhance performance through controlled structural deformation and health monitoring that detects damage and determines remaining useful life. Similarly, closed-loop feedback in propulsion systems could potentially reduce the emissions of environmentally sensitive products of combustion and could control aerodynamic, aerothermodynamic, and aeromechanical instabilities through embedded sensors and controls. Conventional sensor technology will have to be improved in two ways. First, new sensor materials and systems will have to operate at higher turbine inlet temperatures. Second, the scale of conventional sensors will have to be reduced to minimize interference. Nonsilicon-based MEMS have the potential to meet these requirements. Onboard weather detection sensors and systems can affect the safe operation of existing and future air vehicles. The detection of clear-air turbulence and local instabilities, such as trailing edge vortices, could allow pilots to avoid them. In addition, sensors for the early
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals detection of ice and other deposits on wings and lifting surfaces could improve safety during severe weather. Priority areas for R&D on advanced sensor and actuator technologies include: the development of robust actuators and sensors (thermal and chemical) for use in hostile environments; further development of MEMS for use in intelligent systems; and the integration of these systems into air vehicle components. NASA's most practical role in the development of advanced sensor and actuator technologies may be as a systems integrator, in partnership with the private sector, and as a source of basic scientific knowledge related to the physical properties that sensors are designed to observe. NASA research programs could also fill specific technology gaps, such as usable materials for robust sensors. DOD and NSF research in this area should be carefully coordinated with NASA programs. Automated Manufacturing Labor and associated overhead are two of the major cost elements in the manufacture of an aircraft and its component systems. Therefore, reducing these costs through increased automation would reduce the overall cost of acquiring new aircraft. Lower aircraft purchase costs for airlines could contribute to the NASA goal of reducing the cost of air travel, and reducing the cost of new general aviation aircraft could help meet the NASA goal of reinvigorating this sector of the aerospace industry. Manufacturing is an essential element of aerospace product development and should have an influence on the design of an air vehicle beginning with conceptual design. NASA can support the integration of manufacturing into the whole air vehicle production and development process by investigating automated fabrication processes, such as manufacturing by light, that could directly link design databases to finished assemblies. Improved Methods for Developing Flight-Critical Software Virtually all modern systems of any complexity, including aviation systems, are governed by software. As the complexity and size of these software systems grow, their behavior is likely to become less predictable. However, many aviation systems that rely on software are safety critical, meaning that malfunctions would put lives at risk. Therefore, software development methods should focus on ensuring that critical software operates as expected under all conditions. Some approaches may be emerging in current software R&D, but they have only been successfully used in relatively simple digital systems. Verifying complex avionics software, including interfaces to analog components and to human operators, will require continued research. Perhaps the most important software in a commercial aircraft helps the pilot monitor or even fly and land the plane. Chapter 4 in this report points out the growing importance of
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals autonomous flight, the use of precision sensors, and dynamic controls, all of which will be augmented by software. Thus, the behavior of flight-critical software will have to be predictable. Only completely predictable and reliable software will be accepted as a means of improving crew performance. NASA and others have been investigating formal approaches to software development that are still too complex to understand and apply. New development approaches, such as formal methods, may be able to demonstrate that software will do what it is expected to do and can find and exclude unintended actions. The latter task is much more difficult and will require breakthroughs in software design techniques. Such methods will have to reveal functional interactions, intended and unintended, in both the system models and the software that represents them. Because of their underlying complexity, the competitive atmosphere, and possible litigation, industry is not likely to develop these methods itself. However, if these methods could be made usable to software designers, industry would certainly use them. Human-Computer Integration In the past three decades, the power of computation has increased exponentially. Computers today have realized much of their expected potential for controlling and/or simulating complex phenomena in real time through advances like parallel processing. The real potential for terahertz computation rates will further advance the power of computers. Yet the full potential of computing and information technology for aerospace applications, such as the safe and efficient operation of aircraft and the design of aerospace vehicles, will not be realized until interactions between humans and computers have been improved. Although humans are the most advanced sensors and actuators in existence, occasional lapses in action or concentration, and the inability to process information at desired rates, can, and often does, lead to system failures. However, optimized human and machine task allocation and integration could change the situation as dramatically as the advent of the wheel, the mechanical lever, and the airfoil. Improvements in human-computer integration as it relates to the design of aerospace systems, such as aircraft and launch vehicles and their components, will be based on an understanding of the creative process, which is essential to design and cannot be duplicated by machines. If artificial agents, expert systems, and sensory interfaces involving virtual reality can be designed to link human creativity to realistic, physics-based computer models and simulations, complete prototypes could be designed and flown in a fully virtual environment. Thus, near optimum configurations could be realized without ever conducting physical tests.
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals Current assumptions about the allocation of tasks to humans and computers will require significant reappraisal to improve human-computer integration for aircraft operations. This reappraisal will require advanced methodologies to evaluate complex human-computer interactions based on advanced simulation and the collection and analysis of multi-attribute field data. In the meantime, until unpiloted commercial transport aircraft become socially acceptable, information must be organized, refined, and presented to pilots in a manner that effectively maintains their situation awareness. Given the extraordinary amount of data that should be available from inward-looking and outward-looking onboard sensors and external sources of information, a comprehensive systems approach to situation awareness will be critical. More automated space launches will also require improved human-computer interactions. Automation could reduce or eliminate many costs related to launch processing and operations that are currently labor intensive and should contribute to the achievement of NASA's goals to reduce launch costs. Broad, long-term R&D to improve human-computer integration in aerospace systems will probably require substantial support from NASA. Everything from the development of advanced methods for software development to basic research on human cognition would benefit from the oversight and integration that a single sponsor such as NASA could provide. However, the results of research supported by the NIH, NSF, and DOD should also be integrated with the results of NASA's own programs. 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. STRUCTURES AND MATERIALS Over the last three decades, revolutionary advances in structures and materials technology have resulted in significant improvements in aerospace vehicle structural efficiencies and performance characteristics. Progress in this field is expected to continue unabated. Combined with improved 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 monitoring systems, structures and materials technologies will substantially improve aerospace vehicles. Advances in lightweight structures for RLVs and improvements in the general area of high-temperature materials will be critical to meeting a number of NASA's goals.
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals Lightweight Structures for Reusable Launch Vehicles Reducing the weight of the aeroshell or integrated aerothermal structure of a RLV will be necessary for meeting NASA's goals for low cost launch. Lightweight materials and designs will have to be developed for a number of sub-components including: the insulation/thermal protection system; attachments; joints and seals; the cryogenic tank; the composite cold structure; and high-temperature ceramic materials systems. Weight reductions in the propulsion system will also be necessary, with an emphasis on the development of high temperature metallic alloys, ceramics, intermetallics, and polymer composites. These materials will allow both higher operating temperatures and reductions in weight, while maintaining durability and manufacturability. Many systems components, including ducts, valves, manifolds, and casings, could be improved with new materials designed for lower weight. High-Temperature Materials High-performance aerospace vehicles, such as RLVs and supersonic aircraft, require materials systems that can perform satisfactorily in thermal environments ranging from moderate to extreme. For example, the contemporary materials under consideration for a Mach 2.4 high-speed civil transport, including conventional aluminum alloys, titanium alloys, polymer composites, fuel tank sealants, adhesives, and finishes, must perform adequately at temperatures from -65°F to 320°F (350° for leading-edge structures) for a minimum of 60,000 hours at maximum temperature. So far, none of these materials has demonstrated the necessary weight and long-term temperature durability characteristics (NRC, 1997). Therefore, NASA should increase its support for basic materials R&D. Material manufacturability, maintainability and cost must be considered in addition to temperature and weight characteristics. The development of suitable engine materials for the high-speed civil transport should focus on advanced metals, ceramics, intermetallics, and metal-ceramic composites. Other areas for R&D include advanced coatings technology for metals and ceramics, ceramic fibers, and advanced manufacturing technology for net shaped forming. New materials will also be required for the thermal protection systems of RLVs, which must undergo repeated reentry into Earth's atmosphere. Conventional thermal protection systems have not demonstrated the durability or cost properties necessary to meet the NASA 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.
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals PROPULSION TECHNOLOGY Advanced Air Vehicle Propulsion Concepts NASA's goals related to emissions, noise, cost, general aviation, and high-speed air travel will all be impacted by advances in propulsion technology. Major opportunities include: step changes in the gas turbine engine through the development of novel components using active control, such as aspirated compressors, with fewer, more slowly turning counter-rotating blade rows; and alternative propulsion systems, such as detonation wave engines and fuel cells. Novel Components and Active Control for Gas Turbine Engines Novel methods to control flows in aeropropulsion and fluid machinery components include suction within the inlet and suction and blowing in nozzle/ejector components which would help control tonal noise. Controlled suction in ''aspirated" compressor blades and end-wall surfaces would increase operating margins, improve stall/surge control, and increase T/W (thrust-to-weight) ratios. Active control could also be used to reduce engine emissions created during the combustion process. Real-time, detailed diagnostic sensors, such as optical or MEMS-based sensors, combined with closed-loop controllers and actuators operable at the microscale are areas requiring R&D. Alternative Propulsion Systems Eliminating complicated rotating machinery for high-speed propulsion systems appears to be a worthwhile goal. The detonation-wave engine is one approach that has the potential to increase specific impulse levels based on the basic thermal efficiency benefits of the Humphrey cycle over the turbine engine Brayton cycle. Technological challenges that require additional research include high noise levels, control issues, and the stability of detonation. Fuel cells appear to be a promising source of propulsive power for subsonic air vehicles, but they will require a great deal more development before they will be truly practical. The advantages of fuel cells include low fuel consumption compared to conventional propulsion systems and extremely low (zero, in some cases) production of pollutants (NOx, CO and CO2). In addition, the chemical power conversion efficiency of fuel cells is about twice as high as the thermodynamic power conversion of standard propulsion systems. Determining if fuel cell propulsion technologies can be made feasible from a total vehicle system perspective will require aircraft design studies involving fuel cells. Investments in other areas where NASA has expertise, such as fuels and material development for fuel cells, will also contribute to their potential as useful power sources for air vehicles.
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals 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. Advanced Propellants for Launch Vehicles Despite potential advances in air-breathing launch vehicles and ground-based launch assist techniques, such as magnetically levitated rail guns, the committee believes that rocket-based or combined rocket-air-breathing propulsion systems will continue to be technologies of choice for the commercial launch industry. Therefore, technology breakthroughs in propellant performance, density, and affordability will be crucial to satisfying NASA's space transportation goals. Technologies that should be investigated include cryogenic solid hydrogen, metallic hydrogen, the carbon and carbon-boron absorptivity of hydrogen, and cryogenic solid oxygen. These propellants could provide increases in specific impulse as much as 200 seconds over the current state of the art, and could provide a basis for reducing launch costs to less than $100 per pound of payload to LEO. A number of research projects on the use of hydrogen for various power and propulsion systems, including fuel cells, are under way, but none of these efforts are focused on rocket propellants. Current government-sponsored research in advancing rocket propellant capability is being led by the Air Force, but it is not sufficient to bring new concepts and technologies to meet NASA's goals to fruition. Therefore, the committee believes that aggressive participation by NASA, with close cooperation between the Air Force Rocket Laboratory and NASA's Marshall Space Flight Center, will be necessary. 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 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 to accomplish NASA's goals. However, the committee believes that unconventional advanced configurations have a better potential for achieving these goals.
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals Advanced Configurations The BWB (blended-wing body) is an example of a promising new design concept that could further NASA's goals of reducing costs, emissions, and noise. However, other designs may also have the potential to achieve a number of NASA's goals and should be assessed. In general, overall aerodynamic performance can be enhanced by highly integrated configurations. Although industry may make limited investments in preliminary design studies focused on unconventional configurations, full scale, or even subscale, testing will probably not proceed without substantial participation by NASA. 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 BWB, should undergo extensive virtual testing and/or full-scale experimental vehicle development. PRECISION AIR TRAFFIC OPERATIONS IN TERMINAL AREAS The nation's air transportation system and the air transportation systems of other highly developed areas, such as Europe, are fundamentally constrained in terminal environments. No matter how precise navigation and surveillance become for air traffic en route from one terminal area to another, the total throughput cannot be increased unless more cargo, passengers, and private pilots can take off and land in a given 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. A wide range of candidate improvements in aircraft, airport, and ATM technology should be evaluated to reduce terminal area constraints. Even personal air vehicles (discussed in chapter 4), are a possible solution that should be considered, although their widespread use is probably decades away. However, to meet the 10-year goal of tripling aviation system throughput, the committee believes 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 focused on increasing throughput at airports, such as NASA's capacity and terminal area productivity programs, should support R&D in these three areas.
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals Reduced Runway Occupancy Time Runway occupancy time during landing operations is currently governed by the amount of time it takes an aircraft to proceed from the runway threshold crossing to a runway exit after touchdown. This, in turn, is dependent on the amount of time needed to slow the aircraft sufficiently so that it can safely turn off the runway. Quicker deceleration through the combination of new runway surface materials and aircraft systems, such as actively controlled brakes and brake guidance systems, could increase deceleration profiles and exit speeds. Another way to approach the problem is to allow more than one aircraft to occupy the runway at a given time. Two or more aircraft could land at different touchdown points on the same runway, either in parallel on wide runways or in-trail on long runways. Advanced flight control systems, aircraft-to-aircraft surveillance, and pilot-controller decision aids could ensure that safe spacing between the aircraft is maintained. To be most beneficial, this capability is needed for both visual flight and instrument flight operations. The necessary technologies include very precise control of aircraft position and velocity in all four dimensions and precise position tracking with very rapid updates of aircraft position and intent. Onboard collision avoidance systems would also have to be more highly automated than the systems currently in use. Mitigating Wake Vortices Wake turbulence created by vortices emanating from aircraft wings limits en route in-trail spacing, takeoff and landing spacing, and the spacing of runways at airports. Therefore, the mitigation of wake vortices would have a major impact on reducing terminal area delays. Possible technological approaches to mitigation include the development of sensor systems that can detect and measure wake vortices and the development of methods to reduce or control vortices. Procedural approaches to "managing" wake vortex encounters safely include displaced runway thresholds, variable glide path approaches, precision approach paths for all weather operations, and dynamic encounter aids associated with advanced sensors. NASA should vigorously support research on all of these technologies and procedures. Vertical/Short Takeoff and Landing Aircraft to Enhance Capacity Although V/STOL aircraft usage in the commercial transport market has always been limited because of unfavorable economic projections, these vehicles could serve the short distance air travel markets cost effectively if they could operate from existing airports. If they could also operate without decreasing the capacity available for conventional runway operations, overall throughput would be increased. This potential capability, known as simultaneous noninterfering operations, is currently being investigated by Boeing
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Maintaining U.S. Leadership in Aeronautics: Breakthrough Technologies to Meet Future Air and Space Transportation Needs and Goals Helicopter and NASA Ames Research Center. Simultaneous noninterfering operations would require the same technologies that would enable multi-aircraft runway occupancy. Considerable vehicle technology development for V/STOL aircraft, such as tilt-rotors, will be necessary to make them economical, reliable and safe. Therefore, R&D on propulsion systems, structures and materials, and vehicle configurations should be assessed for their potential applicability to V/STOL aircraft. Recommendation. To further the goal of tripling the aviation system throughput in 10 years, NASA should support R&D 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 throughput at airports, such as the NASA Terminal Area Productivity program, should support R&D in these three areas. REFERENCE NRC. 1997. U.S. Supersonic Commercial Aircraft: Assessing NASA's High-Speed Research Program. Aeronautics and Space Engineering Board, Committee on High Speed Research. Washington, D.C.: National Academy Press.
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