Future Air Force Needs for Survivability (2006)

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 Committee on Future Air Force Needs for Survivability concludes firmly that future Air Force requirements and CONOPS will dictate aircraft that are survivable and responsive for timely strike at long range, as well as capable of loiter and persistence in the threat environment. 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.

• 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, countermeasures,¹ 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 airborne interceptors;

• Conduct trade-off studies constrained by the needed or expected technology capabilities;

• 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.

The committee finds that the Air Force technology roadmap for radio-frequency (RF) signature reduction is generally adequate (with some exceptions) to enable, with low to moderate risk, platforms with various combinations of speed and stealth with initial operational capability by 2018. 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 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;

  • 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/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).

Several presentations to the committee emphasized qualitatively the very significant potential of SA to improve vehicle survivability. The question, to what extent does SA impact overall survivability? needs additional analysis. There is no definitive conclusion on the relative effects of speed, stealth, and size on the benefits of situation awareness. 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 begin-

ning, 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.

Finding 5: Countermeasures will continue to have the capability to enhance the survivability of aircraft and offer a significant hedge against future threat advances.

There are other techniques, technologies, and subsystems that can complement signature reduction and offer additional survivability improvements in their own right, including: electronic attack, electronic countermeasures, information warfare, EO/IR countermeasures, RF countermeasures, and self-defense weapons (air-to-air missiles and directed energy). 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 upon 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.

The committee believes that hypersonic missiles available in 2018 could be based on either chemical rocket or air-breathing propulsion. An attempt to field a hypersonic cruise aircraft by 2018 would be very high risk.

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.