4
Conclusions and Recommendations
In the course of responding to the Statement of Task in Chapters 2 and 3, the committee made findings, reached conclusions, and offered suggestions for current and future hypersonics programs. The major conclusions and recommendations are presented below.
Conclusion 1. The Air Force’s HyTech Program, which is a Mach 4 to Mach 8 propulsion technology flow path program, is necessary but not sufficient for the development of a scramjet engine as an integral part of a missile system. Although the limited testing (ground testing only) planned for the propulsion subsystem should indicate its potential engine performance, flight testing over a representative range of operating conditions will be necessary to determine the engine’s operability, reliability, and durability in an integrated system. These parameters are prerequisites to understanding the engine’s utility in an operational system.
Recommendation 1. The Air Force should commit appropriate resources to integrated airframe-engine flight testing, which is vital to demonstrating a hydrocarbon-fueled scramjet in the Mach 4 to Mach 8 range. This recommendation (and the related recommendations that follow) assumes that the Air Force will decide that a hypersonic air-breathing propulsion capability is a potential candidate for fulfilling future system needs (e.g., as part of a hypersonic missile or space access application). If the Air Force is not willing to commit to flight testing, it should reevaluate its goals for the development of air-breathing hypersonic technology.
Conclusion 2a. The HyTech Program itself will not provide the basis for an operational missile system because the development of critical enabling technologies for hypersonic air-breathing missiles are not included in the program and, to the committee’s knowledge, the Air Force is not pursuing them. These critical technologies will have to be mature and validated before the Air Force can proceed with a low-to-moderate risk acquisition program.
Conclusion 2b. Besides propulsion, the five most critical enabling technologies for air-breathing hypersonic missile systems, in order of priority, are (1) airframe and engine thermostructural systems; (2) vehicle integration; (3) stability, guidance and control, navigation, and communications systems; (4) terminal guidance and sensors; and (5) tailored munitions.
Conclusion 2c. If the HyTech Program were expanded to include a full-scale, integrated airframe-engine flight test program, and if the critical enabling technologies were mature, an operational air-breathing hypersonic missile system could be developed with low-to-moderate risk and without concurrency in support of an initial operational capability by 2015.
Recommendation 2a. If the Air Force determines that there is a requirement for a hypersonic missile system, then it should establish a system-oriented program office to manage the system design and the development, integration, and flight testing of critical enabling technologies for a hypersonic missile system.
Recommendation 2b. The program office should establish a road map to reach initial operational capability by 2015. The road map should include six phases: (1) system specification development; (2) system concept development; (3) technology risk reduction; (4) prototype design and flight test; (5) engineering and manufacturing development; and (6) low rate initial production.
Conclusion 3. The Air Force has not established operational requirements or conducted design and requirements trade-off studies in support of an air-launched hypersonic missile system.
Recommendation 3. If the Air Force intends to pursue the development of an air-launched hypersonic missile system
as a viable candidate to meet its future warfighting needs, then it must initiate design and requirements trade-off analyses in the following areas: targets, speed, range, survivability, lethality, aircraft compatibility, risk, and cost.
Conclusion 4. The risk and cost associated with the development of hypersonic air-breathing systems increase significantly with higher cruise speeds. Scramjet technology or existing ramjet technology with nonendothermic fuel-cooled metallic structures could be used for Mach 4 to Mach 6 systems. Systems with a maximum cruise speed of Mach 6 to Mach 6.5 will require a scramjet, which uses nonendothermic fuel cooling or uncooled ceramic composite materials. Mach 8 systems powered by a hydrocarbon-fueled scramjet will require endothermic fuel-cooled engine structures.
Recommendation 4. The Air Force should expedite trade-off studies in three areas: (1) mission parameters, to establish operational requirements; (2) system concepts, to define candidate configurations with optimum ranges of performance, operability, reliability, and affordability; and (3) technology, to redirect HyTech projects toward the most promising alternatives, if necessary.
Conclusion 5. A hypersonic air-breathing missile will affect primarily one aspect of the Air Force support infrastructure, namely, ground testing facilities. Existing test facilities can support full-scale propulsion performance testing only at flight speeds up to approximately Mach 7. Existing test facilities for testing propulsion system operability and reliability are limited. The HyTech Program has plans to upgrade an existing facility for propulsion reliability testing at the Mach 8 cruise condition. Hypersonic missile systems will have no obvious implications for two other areas of the Air Force support infrastructure, high-speed computational facilities and test ranges. Periodic destructive testing of scramjet engines will be necessary in the future.
Recommendation 5. The Air Force should begin planning for the ground test infrastructure to support the development and qualification of the operability, durability, reliability, and performance of integrated hypersonic propulsion systems over the Mach number range from the speed at the end of the rocket-boost phase to the maximum cruise speed. This infrastructure should be completed expeditiously.
Conclusion 6. The Air Force has two broad options for the development of hypersonic technologies for 2015 and beyond. The first is to pursue a broad range of technologies covering a variety of potential applications. The second is to pursue the evolutionary development and deployment of hypersonic weapon systems that derive from established capabilities and clearly stated Air Force requirements.
Recommendation 6. For 2015 and beyond, the Air Force should pursue the evolutionary development of hypersonic weapon systems and develop a long-range plan that incorporates the following four components: operational concepts for future systems and preliminary system designs; scramjet-powered weapon systems using hydrocarbon fuels; hypersonic weapon systems using hydrogen fuel; and combined-cycle systems for space access.
Conclusion 7. The committee is not aware of any other nation that has operational hypersonic scramjet-powered missiles; however, several nations have been working on development, evaluation, and testing, including flight testing, for several years. The Air Force is monitoring foreign developments in hypersonics technology adequately.
