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Introduction

High-speed flight is a major technological challenge for commercial and business aviation. To help meet this challenge, the National Aeronautics and Space Administration (NASA) asked the National Research Council (NRC) to conduct a study that would identify approaches for achieving breakthroughs in supersonic research and technology (R&T). This report documents the results of that effort.

The report is organized into five chapters. This introduction describes the study process and the committee’s understanding of NASA’s expectations for the study. It also provides background information to set the context for the report’s key findings, conclusions, and recommendations. Chapter 2 briefly reviews how the business case for commercial supersonic aircraft has changed since NASA’s High Speed Research (HSR) Program was cancelled in 1999 and discusses notional vehicles around which technology challenges and research time frames may be grouped. Chapter 3 describes five areas for new focused research to enable industry production by the year 2025 of an environmentally acceptable, economically viable commercial aircraft capable of sustained supersonic flight, including flight over land, at speeds less than approximately Mach 2. Chapter 4 identifies additional critical areas where continued technology development is needed. Chapter 5 presents findings, conclusions, and recommendations that follow from and summarize the earlier discussions. Biographies of committee members are presented in Appendix A. Participants in meetings of the full committee and key subcommittee meetings are listed in Appendix B. Acronyms and abbreviations used in the report are listed in Appendix C.

STATEMENT OF TASK AND STUDY APPROACH

The statement of task for the study was as follows:

  • Based on the results of NASA’s HSR Program, other research, and related studies, identify key customer and design requirements that cannot be satisfied by currently available technology or by adapting technology that is likely to be developed for other applications.

  • Identify breakthrough technologies that may be able to satisfy the high-risk requirements identified above.

  • Prepare a report that qualitatively assesses the most promising breakthrough technologies in terms of their potential value and risk.

The scope of the study included both small aircraft (i.e., supersonic business jets [SBJs]) and large transports. However, the committee was directed not to develop a comprehensive plan addressing all of the R&T needs for a commercial supersonic aircraft. Therefore, this report does not address many important aircraft systems, such as onboard power systems, where government research is not critical to the development of future commercial supersonic aircraft.

The study focused on high-risk, high-payoff technologies where NASA-supported research could make a difference over the next 25 years. It did not focus on any specific vehicle configuration, market segment, or technology readiness level (TRL), although the committee believes that, to have practical value, government-funded research should achieve a TRL range of at least 6 before industry can be expected to incorporate new technologies into commercial aviation products (see Figure 1-1).

The committee conducted hearings and fact-finding meetings to identify technical barriers and promising breakthrough technologies. However, as the study proceeded it became clear that the statement of task presented difficulties with respect to its use of the phrase “breakthrough technology.” Truly breakthrough technologies are likely to be guarded as proprietary and competition sensitive and, as such, are not available to groups such as the NRC committees, which work in a public forum. Thus, even though many committee members knew about potential breakthrough



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Commercial Supersonic Technology: The Way Ahead 1 Introduction High-speed flight is a major technological challenge for commercial and business aviation. To help meet this challenge, the National Aeronautics and Space Administration (NASA) asked the National Research Council (NRC) to conduct a study that would identify approaches for achieving breakthroughs in supersonic research and technology (R&T). This report documents the results of that effort. The report is organized into five chapters. This introduction describes the study process and the committee’s understanding of NASA’s expectations for the study. It also provides background information to set the context for the report’s key findings, conclusions, and recommendations. Chapter 2 briefly reviews how the business case for commercial supersonic aircraft has changed since NASA’s High Speed Research (HSR) Program was cancelled in 1999 and discusses notional vehicles around which technology challenges and research time frames may be grouped. Chapter 3 describes five areas for new focused research to enable industry production by the year 2025 of an environmentally acceptable, economically viable commercial aircraft capable of sustained supersonic flight, including flight over land, at speeds less than approximately Mach 2. Chapter 4 identifies additional critical areas where continued technology development is needed. Chapter 5 presents findings, conclusions, and recommendations that follow from and summarize the earlier discussions. Biographies of committee members are presented in Appendix A. Participants in meetings of the full committee and key subcommittee meetings are listed in Appendix B. Acronyms and abbreviations used in the report are listed in Appendix C. STATEMENT OF TASK AND STUDY APPROACH The statement of task for the study was as follows: Based on the results of NASA’s HSR Program, other research, and related studies, identify key customer and design requirements that cannot be satisfied by currently available technology or by adapting technology that is likely to be developed for other applications. Identify breakthrough technologies that may be able to satisfy the high-risk requirements identified above. Prepare a report that qualitatively assesses the most promising breakthrough technologies in terms of their potential value and risk. The scope of the study included both small aircraft (i.e., supersonic business jets [SBJs]) and large transports. However, the committee was directed not to develop a comprehensive plan addressing all of the R&T needs for a commercial supersonic aircraft. Therefore, this report does not address many important aircraft systems, such as onboard power systems, where government research is not critical to the development of future commercial supersonic aircraft. The study focused on high-risk, high-payoff technologies where NASA-supported research could make a difference over the next 25 years. It did not focus on any specific vehicle configuration, market segment, or technology readiness level (TRL), although the committee believes that, to have practical value, government-funded research should achieve a TRL range of at least 6 before industry can be expected to incorporate new technologies into commercial aviation products (see Figure 1-1). The committee conducted hearings and fact-finding meetings to identify technical barriers and promising breakthrough technologies. However, as the study proceeded it became clear that the statement of task presented difficulties with respect to its use of the phrase “breakthrough technology.” Truly breakthrough technologies are likely to be guarded as proprietary and competition sensitive and, as such, are not available to groups such as the NRC committees, which work in a public forum. Thus, even though many committee members knew about potential breakthrough

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Commercial Supersonic Technology: The Way Ahead FIGURE 1-1 NASA technology readiness levels. SOURCE: NASA. System/Subsystem Development technologies, the arrangements under which such knowledge was obtained prevented it from being disclosed or included in this report. This included much of the results of the HSR Program, which are classified as limited exclusive rights data (LERD), details of ongoing work supported by the Defense Advanced Research Projects Agency (DARPA) Quiet Supersonic Platform (QSP) Program, and information collected through work as employees of or consultants to private companies. Because of its limited insight into specific technological solutions to the problems of commercial supersonic flight, the committee was reluctant to accept the role of recommending which individual technical concepts and approaches, many of them in early stages of development, should be funded. For example, one possible breakthrough approach would be the application of “lightcraft technologies,” which are being developed by Lightcraft Technologies, Inc., and Rensselaer Polytechnic University, supported in part by the U.S. Air Force and NASA (David, 2000). This technology suite transcends the conventional notion of a supersonic aircraft by conceptualizing aircraft powered by ground-based lasers. Even if the remaining technical issues are ultimately resolved, however, commercialization as a passenger vehicle will not be achieved in the 25-year time frame that is the focus of this report. Another interesting technology would inject water or other fluid in the engine exhaust to mitigate takeoff noise, allowing the use of smaller exhaust nozzles. The committee also became aware of a proposal for boomless supersonic flight, but the concept has yet to be submitted to peer review and available data are insufficient to allow judging its viability. Rather than attempt to identify, evaluate, and compare the merits of individual breakthrough technologies, the committee concentrated instead on identifying problems and areas where breakthroughs and focused investment are needed to achieve the ultimate objective of sustained commercial supersonic flight, including flight over land. As demonstrated by DARPA’s QSP Program, if the government decides to address a particular problem—such as the challenge of supersonic flight with very low (or no) sonic boom—R&T solicitations would attract proposals for many diverse solutions, which can then be evaluated as part of the solicitation process. Furthermore, NASA has especially good insight into the work of the QSP Program because the program manager is a NASA civil servant on temporary assignment at DARPA. In light of the concerns expressed above, and with the concurrence of the study sponsor, the committee used the following approach to guide it in carrying out the intent of the statement of task: Identify the technical barriers to sustained commercial supersonic flight, including flight over land. Characterize the gap between the state of the art and the technology required to overcome each barrier. Establish the feasibility of closing each gap by considering if at least one promising approach is available. Identify what would have to be demonstrated to show that the gap has been closed.

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Commercial Supersonic Technology: The Way Ahead BACKGROUND Commercial supersonic aircraft have been the object of many development programs. The first major effort by the United States, the Supersonic Transport (SST) Program, was terminated in the early 1970s prior to completion. France and Great Britain, however, were able to complete development of the Concorde, which has shown both the possibilities and problems of commercial supersonic aircraft. NASA’s HSR Program began in 1985 with the objective “to establish the technology foundation by 2002 to support the U.S. transport industry’s decision for a 2006 production of an environmentally acceptable, economically viable, 300-passenger, 5,000 nautical mile, Mach 2.4 aircraft” (NRC, 1997). The first flight of a commercial supersonic aircraft was envisioned around 2010, with the first production aircraft to be operational around 2013. As shown in Table 1-1, NASA expected that program goals would require a large investment. The HSR Program was conducted in two phases. Phase 1, from 1985 to 1990, focused on environmental compatibility issues. Phase 2, from 1990 until 1999, focused on development of airframe and propulsion technologies. A proposed but never implemented Phase 2A would have focused on affordable manufacturing technologies starting in 1997. The HSR Program was canceled in 1999, largely because NASA was unwilling to continue the program without a stronger commitment from industry to the commercial development of a 300-passenger, Mach-2.4 aircraft. As a result, NASA’s supersonic R&T efforts were greatly curtailed. Regulatory standards are a key factor in determining the viability of commercial supersonic aircraft. Because environmental standards are becoming more strict, delays in developing a supersonic commercial aircraft mean that when one is built, it might have to meet more stringent standards than originally anticipated by the HSR Program. Just before the program was closed out, HSR managers solicited new ideas on how to meet more stringent environmental standards. This admittedly hasty exercise was intended to provide a technology development roadmap in anticipation of future efforts to develop supersonic technology. The 1997 NRC report that assessed NASA’s HSR Program emphasized the importance of relating aircraft performance requirements to the needs of customers—that is, passengers, airlines, manufacturers, and society. It concluded that the focus on Mach 2.4 was too aggressive and probably not justified by the business analysis. The report prioritized aircraft performance requirements based, in part, on their contribution to meeting customer needs and the level of risk and concluded that more advanced R&T is needed to establish the feasibility of sustained supersonic commercial flight. It presented a plan to achieve a flight demonstration aircraft that would fully validate aerodynamic, propulsion, and flight control technologies. The United States is not the only sponsor of supersonic technology. The governments of France, Japan, Russia, and the United Kingdom are also sponsoring development of supersonic technology with commercial applications, although none has embarked on a formal program to produce a new commercial supersonic aircraft. The development of a commercial supersonic transport that can meet international environment standards and compete successfully with subsonic transports may be a larger effort than the industry of any single nation, including the United States, might wish to undertake. As with many such innovations, the first manufacturer to market will have the potential to dominate the market. If only one commercial supersonic transport is available, airlines from the United States and other countries will purchase it regardless of where it is manufactured. A small supersonic jet could be developed by a single aircraft manufacturer and might lead to important technological innovations. The ultimate importance of commercial supersonic aircraft to the U.S. air transportation system is set forth in long-range technology plans and visions promulgated by NASA (NASA, 1998), the Department of Transportation (DOT, 1999), and the National Science and Technology Council (NSTC, 2000). Fulfilling these visions of the future will re- TABLE 1-1 Total NASA Funding for the HSR Program from Program Inception in FY 1990 Through Planned Completion in FY 2002 (millions of dollars) Program Element FY 1990–1996 FY 1997 FY 1998-2002 Total Propulsion 459.3 114.1 312.5 885.9 Airframe 322.6 110.5 286.8 719.9 Systems Integration 144.0 29.7 107.0 280.7 Total 925.9 254.3 706.3 1,886.5 SOURCE: NRC (1997).

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Commercial Supersonic Technology: The Way Ahead quire a long-term investment strategy that looks beyond the shorter-term economic factors that drive much industry-funded research. A long-term view is especially important when it comes to breakthrough technologies. By nature, these technologies require long-term investments to increase their maturity and reduce their risk enough to convince the aerospace manufacturing industry to turn them into commercial products that the Federal Aviation Administration (FAA) will certify and airlines (or other users) will buy. Unfortunately, both government and industry are reluctant to make the long-term investments necessary to advance expensive, high-risk technologies. In particular, at a time when manufacturers require a TRL 6 or higher to embrace complex new technologies in safety-critical aeronautics applications, NASA appears to be redirecting its technology investment strategy to achieve an end point of TRL 3 or 4. The likely result is a technology maturation gap that could jeopardize U.S. leadership in aerospace technology. To avoid this consequence—that is, to allow promising technologies to make the transition from the laboratory to the marketplace— NASA must accept the challenge of investing enough to achieve TRL 6. REFERENCES David, L. 2000. “Laser-Boosted Rocket Sets Altitude Record.” Space.com. November 3. Available online at <http://www.space.com/businesstechnology/technology/laser_craft_001103.html>. Accessed on September 13, 2001. DOT (Department of Transportation). 1999. Effective Global Transportation in the Twenty-First Century: A Vision Document. U.S. Department of Transportation Research and Technology Coordinating Council “One DOT” Working Group on Enabling Research, September. Available online at <http://www.volpe.dot.gov/infosrc/strtplns/dot/glbtrn21/index.html#toc>. Accessed on September 13, 2001. NASA (National Aeronautics and Space Administration). 1998. NASA Technology Plan, December. Available online at <http://technologyplan.nasa.gov/default.cfm?id=1.0>. Accessed on September 13, 2001. NRC (National Research Council). 1997. U.S. Supersonic Commercial Aircraft. Available online at <http://www.nap.edu/catalog/5848.html>. Accessed on September 13, 2001. NSTC (National Science and Technology Council) Committee on Technology, Subcommittee on Transportation Research and Development. 2000. National Transportation Strategic Research Plan. May. Available online at <http://www.volpe.dot.gov/infosrc/strtplns/nstc/srplan00/index.html>. Accessed on September 13, 2001.