• noise suppression at acceptable propulsion system weight

Conclusion 2. Candidate technologies for overcoming environmental barriers to a commercial supersonic aircraft with a cruise speed in excess of approximately Mach 2 are unlikely to mature enough to enable operational deployment of an environmentally acceptable, economically viable Mach 2+ commercial supersonic aircraft during the next 25 years.

The ultimate importance of the commercial supersonic aircraft to the U.S. air transportation system is expounded in the long-range technology plans and visions of NASA, the Department of Transportation, and the National Science and Technology Council. Fulfilling these visions of the future will require a long-term investment strategy that looks beyond the short-term economic factors that drive much industry-funded research. The importance of a long-term view is especially important with breakthrough technologies. Unfortunately, both government and industry are reluctant to make the long-term investments necessary to mature expensive, high-risk technologies. In particular, at a time when manufacturers require TRLs of 6 or higher to embrace complex new technologies in safety-critical aeronautics applications, NASA appears to be changing its technology investment strategy so that it reaches TRLs of only 3 or 4. The likely result is a technology maturation gap that could jeopardize U.S. leadership in aerospace technology. To avoid this result—that is, to allow promising technologies to make the transition from the laboratory to the marketplace—NASA must invest enough to achieve TRL 6. With past programs, such as the HSR Program, NASA adopted TRL 6 as the appropriate goal for commercial supersonic research, and the committee is concerned that NASA’s less ambitious goals for much of its ongoing aeronautics research is driven more by the need to curtail aeronautics research because of reduced funding than by an objective assessment of what it will take to achieve the government’s programmatic goals.

Recommendation 3. NASA and other federal agencies should advance the technologies listed in Findings 1 and 2 and Recommendations 1 and 2 to technology readiness level 6 to make it reasonably likely that they will lead to the development of a commercial product.

In summary, the committee identified no insurmountable obstacles to the development of commercial supersonic aircraft and believes that a properly focused research effort by NASA could develop technological solutions to the key problems identified in Finding 1, thereby enabling a successful commercial development program by industry in the relatively near term, especially for aircraft with a cruise speed of less than Mach 2.0. Without continued effort, however, an economically viable, environmentally acceptable commercial supersonic aircraft is likely to languish. National indifference to supersonic technology development would jeopardize longstanding U.S. supremacy in the aviation business segment and significantly harm the nation’s economy. The United States is not the only sponsor of supersonic technology development, and once a commercial supersonic aircraft is developed, users in the United States and other countries will purchase it, regardless of where it is manufactured.

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