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:

  1. Identify the technical barriers to sustained commercial supersonic flight, including flight over land.

  2. Characterize the gap between the state of the art and the technology required to overcome each barrier.

  3. Establish the feasibility of closing each gap by considering if at least one promising approach is available.

  4. Identify what would have to be demonstrated to show that the gap has been closed.

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