Executive Summary

The Air Force Studies Board of the National Research Council (NRC) was asked by the U.S. Air Force (USAF) to investigate combinations of speed and stealth that would provide U.S. aircraft with high levels of survivability1 against potential enemy air defense systems in the 2018 time frame. The missions considered were to include but not be limited to long-range strike. The NRC was also asked to identify changes that might be needed in current research and development (R&D) investment plans to enable such survivable aircraft to have initial operational capability by 2018. Accordingly, the NRC convened the Committee on Future Air Force Needs for Survivability (see Appendix A), which held six meetings at which it received numerous briefings on related matters (see Appendix B). Given the security implications of the subject matter, the committee produced both a classified and an unclassified version of its report.

The committee conducted a somewhat limited analysis, as follows. Chapter 1 provides a brief review of the history of stealth technology development. In Chapter 2, the committee discusses the missions that future U.S. aircraft are expected to undertake, the threats they are likely to face, and the capabilities that are likely to be required to complete these missions. In Chapter 3, it assesses the technical feasibility of achieving various levels of stealth at subsonic, supersonic, and hypersonic speeds by 2018, including consideration of specific aircraft subcomponent technologies (airframe,

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The capability to avoid or withstand a man-made hostile environment.



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Future Air Force Needs for Survivability Executive Summary The Air Force Studies Board of the National Research Council (NRC) was asked by the U.S. Air Force (USAF) to investigate combinations of speed and stealth that would provide U.S. aircraft with high levels of survivability1 against potential enemy air defense systems in the 2018 time frame. The missions considered were to include but not be limited to long-range strike. The NRC was also asked to identify changes that might be needed in current research and development (R&D) investment plans to enable such survivable aircraft to have initial operational capability by 2018. Accordingly, the NRC convened the Committee on Future Air Force Needs for Survivability (see Appendix A), which held six meetings at which it received numerous briefings on related matters (see Appendix B). Given the security implications of the subject matter, the committee produced both a classified and an unclassified version of its report. The committee conducted a somewhat limited analysis, as follows. Chapter 1 provides a brief review of the history of stealth technology development. In Chapter 2, the committee discusses the missions that future U.S. aircraft are expected to undertake, the threats they are likely to face, and the capabilities that are likely to be required to complete these missions. In Chapter 3, it assesses the technical feasibility of achieving various levels of stealth at subsonic, supersonic, and hypersonic speeds by 2018, including consideration of specific aircraft subcomponent technologies (airframe, 1 The capability to avoid or withstand a man-made hostile environment.

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Future Air Force Needs for Survivability key mission sensors, propulsion, and so on). Also in Chapter 3, near-term R&D needs and priorities and far-term R&D opportunities are identified, both for the fielding of a survivable air vehicle in 2018 and for subsequent generations of aircraft. In Chapter 4, the committee analyzes the results of recently published reports in the field and combines these insights with information provided during briefings as well as its own expertise to make observations about the utility of speed and stealth trade-offs against evolving threats. In the limited time available, the committee was not able to conduct a comprehensive analysis of the many variables, including speed and stealth, that affect aircraft survivability, although a framework for conducting such an analysis is presented in Appendix C. A glossary providing the definitions of key terms is presented in Appendix D. The committee’s overall findings and recommendations, including recommendations for changes in the Air Force R&D investment portfolio to achieve these results, are presented in Chapter 5 and discussed below. Note that the committee generally recommends a rebalancing of the R&D portfolio to address Recommendations 3 through 6. Finding 1: The Air Force Global Strike (GS) Concept of Operations (CONOPS) in high-threat environments determines survivability requirements for the long-range strike system and other systems because it simultaneously stresses range, signature reduction, persistence, timeliness, and payload characteristics. The GS CONOPS stresses long range, speed, and payload, while the Global Persistent Attack (GPA) and the persistent Intelligence, Surveillance, and Reconnaissance (ISR) CONOPS stress long range, loiter, and persistence. Separate platforms for GS, GPA, or persistent ISR may be required. However, the committee concludes that emerging technologies might enable multimission capabilities. These technologies promise both system flexibility and affordability. Following are facts to be considered when evaluating these technologies: Range, persistence, and “24/7” (day and night stealth) operations against improved and proliferated threats increase the future survivability challenge. Increasing multimission capabilities tend to increase aircraft size and cost.

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Future Air Force Needs for Survivability Future threat uncertainties call for robust solutions that incorporate speed, stealth, and other important survivability techniques. The committee finds that multiple combinations of speed and stealth capabilities provide equivalent levels of survivability against surface-to-air missile (SAM), airborne interceptor (AI), and integrated air defense system threats. These combinations range from very significant stealth at subsonic speeds to moderate stealth at speeds approaching the hypersonic region. Recommendation 1: The U.S. Air Force should develop and exploit technologies to enable efficient airframe and propulsion operation at both subsonic and supersonic speeds, and at medium and high altitudes, with appropriate levels of signature reduction to enhance survivability against plausible future threats. Finding 2: The USAF has not completely investigated the combinations of speed, stealth, situation awareness (SA), countermeasures,2 and tactics to enable a solid judgment as to what level of speed is required for acceptable survivability in the future. Specifically, neither the Air Force nor industry has invested sufficiently in analysis of the impact of combinations of speed and stealth when employed against postulated future AI and SAM threats. Further in-depth analysis of the potential performance of electro-optical/infrared (EO/IR) and visual sensors based on postulated sensors as well as signatures is needed. Recommendation 2: Before choosing a design point on the speed-stealth performance curve, the Air Force needs to conduct rigorous analyses and trade-off studies as a basis for that decision. The USAF should carry out the following: Perform mission-level analyses (using multiple major combat operation threat baselines and multiple CONOPS) including EO/IR and visual threats, as well as the impact of AIs; Conduct trade-off studies constrained by the needed or expected technology capabilities; 2 The committee considers self-defense technologies to be a subset of countermeasures in this report.

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Future Air Force Needs for Survivability Develop enhanced mission-level analytical tools capable of investigating the subtle but critical aspects of detection, tracking, fusion, and cueing of SAM and AI threats; Develop models more accurately representing the human cognitive processes involved in the kill chain command-and-control and decision processes; Assess the impact of speed and stealth on the mission-critical sensor suite; and Strengthen system design and engineering capabilities in the Air Force and in industry. Finding 3: Broad selections of speed and stealth combinations that meet the GS CONOPS capability requirements are technically feasible. Subsonic, supersonic dash, and supersonic cruise, all with appropriate stealth treatments for consistently high levels of survivability, are feasible with increased funding in a few areas. The committee found reasonable consensus on stealth capability achievable at speeds ranging from subsonic to hypersonic. Based on numerous briefings from government and industry sources, the committee concludes that radio-frequency (RF) signature-reduction technology development for supersonic designs needs additional emphasis, including technology for designs incorporating a supersonic dash requirement if value or need is determined. The committee concludes that investment in RF stealth in subsonic regions is currently strong and at the appropriate levels, but that advanced propulsion development is the single technology that can provide the most impact to the success of future aircraft for GS CONOPS. For example, advanced variable-cycle engines could provide the air vehicle with both high speed and efficient loiter capabilities, thus adding greatly to its mission flexibility. Recommendation 3: The USAF should balance its research efforts between speed and stealth to bring advances in various speed regimes: Improve the balance across the speed range by preserving current subsonic programs while increasing funding for supersonic aircraft technology;

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Future Air Force Needs for Survivability Analyze the extent to which all-aspect, RF stealth performance is required for supersonic aircraft and the ability of technology to provide that performance; Provide additional investment in technologies that enable supersonic operations to support fielding in 2018 if required. One such technology is high-temperature radar-absorbing structure materials; Fully fund the Versatile Affordable Advanced Technology Engines program to original program levels for both subsonic and supersonic applications, including increased hot-section capability, improved materials, and thermal-management system technologies; Establish a variable-cycle engine demonstration program to achieve technology readiness level 6 by 2009 in a supersonic cruise aircraft; and Investigate the feasibility of adaptable airframe and skin technology, including morphing technology, to support multimission capabilities. Finding 4: The design balance of speed and stealth will depend on the quality of available friendly and adversary situation awareness. SA has a very significant potential to improve vehicle survivability. However, with the available test results and current modeling and simulation tools, the incremental impact of SA on overall survivability is not quantifiable. The committee also notes that the relative contribution of onboard and offboard sensors to SA remains unresolved. Recommendation 4: The USAF should include SA as a high-priority requirement for all platforms, and include in the design, from the beginning, the essential sensors, apertures, and data links. In addition, it should do the following: Improve modeling, simulation, and analysis tools to enable the development of insight into the trade-offs among speed, signature reduction, and SA in future CONOPS scenarios; and Assess the best mix of onboard and offboard sources for derived SA based on trade-offs of risk and complexity.

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Future Air Force Needs for Survivability Finding 5: Countermeasures will continue to have the capability to enhance the survivability of aircraft and offer a significant hedge against future threat advances. Electronic attack, electronic countermeasures, information warfare, EO and IR countermeasures, RF countermeasures, and self-defense weapons (air-to-air missiles and directed energy) can complement signature reduction and offer additional survivability improvements in their own right. The committee believes that there is insufficient effort on high-speed penetration aids. Recommendation 5: The USAF should continue to implement countermeasure improvements, and: If the Air Force concludes after further trade-off studies and evaluation that sustained supersonic cruise is essential to GS CONOPS, it should implement a high-speed penetration aid effort compatible with contemporary stealth signature levels. The Air Force should evaluate the relative effectiveness of self-defense weapons and define requirements for any new or upgraded capability for next-generation aircraft. This committee urges that, to the maximum extent possible, the basic weapon system be designed with the capability to complete its assigned mission without relying on countermeasures. In other words, although countermeasure systems can significantly enhance the survivability of a weapon, they should be hedges against future threat evolution and improvement and not a requirement for the baseline. The same holds for SA and tactics. Finding 6: Hypersonic missiles with ranges comparable to those of current missiles could increase targeting timeliness and flexibility and thus increase operational utility in the 2018 time frame. It is not clear, however, whether a hypersonic cruise aircraft (other than a missile) designed for long-range flight and recovery offers unique capability and operational utility. Furthermore, it is unlikely that such an air-breathing hypersonic platform, other than a missile, will be available in the near term. An attempt to field a hypersonic cruise aircraft by 2018 would be very high risk.

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Future Air Force Needs for Survivability Recommendation 6: The USAF should increase the investment in hypersonic missile propulsion, materials technologies, and sensor and seeker apertures to be carried on both current and future platforms for long-range strike and begin development as soon as possible, if warranted. It should also conduct a study to determine the technical feasibility, operational utility, and affordability of a hypersonic cruise aircraft with appropriate sensors and weapons. If warranted by the results of the study and the readiness level of the technology, the USAF should begin development of a hypersonic aircraft.

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