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1 Introduction This chapter sets forth the overall framework within which the committee performed its task. It also furnishes a road map for the rest of the report. VULNERABILITY IN THE CONTEXT OF OVERALL SURVIVABILITY The purpose of the Air Force's newest combat aircraft, the F-22, is to conduct counter-air missions. According to Air Combat Command, the operational user of the F-22, there are two kinds of counter-air missions. The first, offensive counter air, is to "penetrate deep into heavily defended hostile airspace arid destroy threat capability"; the second, defensive counter air, is to "detect, identify, intercept, and destroy threat aircraft penetrating friendly airspace" (Hinton, ~ 9941. The F-22 design is driven by the aircraft's principal mission, which is offensive counter air (TAF, 1991~.~ Advanced technologies, including steal, are intended to enable the F-22 to penetrate deeply into hostile airspace and shoot down threatening aircraft before they cart detect the F-22. The F-22 has been designed to acquire the enemy target arid shoot first before being acquired. The design philosophy has also emphasized that, if acquired, the F-22 would have ~ A member of the committee who is very familiar with Air Force operations has pointed out that a discrepancy appears to exist between various definitions of the term "offensive counter air." The definition in the Basic Aerospace Doctrine of the United States Air Force (Air Force Manual 1-1) can be read to include the destruction of enemy aircraft on the ground. The definition given in briefings to the committee by representatives of the Air Combat Command and the F-22 System Program Office (Hinton, 1994 and Raggio, 1994) and a discussion in the F-22 Operational Requirements Document (TAP, 1991) state the F-22 mission only in teens of engagements with enemy aircraft in the air (i.e., with no defined air-to-surface requirement). For the purpose of this report, the committee uses the definition that involves only air-to-air engagements. 2 Stealth characteristics are intended to make it difficult or impossible for enemy sensors to acquire or bring weapons to bear on the system. 11

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12 countermeasures, speed, and maneuverability to minimize the likelihood of being hit. The Committee on the Study of Live Fire Survivability Testing of the F-22 Aircraft was charged to study the desirability of waiv- ing, for the F-22, the survivability tests required by law (10 U.S.C. Live Fire Testing of the F-22 ............. _ ,. ~......................................... , ..... , .~ . ~re:ctor..~: ; ems,.. mT ..:~.m Cat. . .. ; ; .. ., ,,, ,, .,, it, ~ ,~ it, q ~ . ~ . , , . . , . , , , . . . . . . . , . . . , . . . , . . . . . ... . . . . . ', . ' . . ' . ' . ' . ' ' ., . . ' ' ' . , , ' . ' . ', ', ' , . ', ' ., ~. 14~. . ~: : : : : : 23661. As part of the study, the committee was asked to determine the sufficiency of the current vulnerability test program for the F-22. The committee was not asked to evaluate the total survivability program for the F-22 and did not do so. However, to assess the vulnerability program, it is important to examine vulnerability within the context of overall survivability. The survivability3 of a weapon system in combat is determined by several factors. First is its ability to avoid detection and interception in performing its mission. If a weapon system is detected and attacked, a second factor is its ability to use attributes like maneuverability to avoid being hit. Factors like these determine susceptibility. Finally, if a weapon system is hit, the inability to complete its mission, return to base safely, or ensure the safety of its personnel is called vulnerability. The survivability of a weapon system is increased by decreasing susceptibility, vulnerability, or both. The F-22 program has placed primary emphasis on decreasing susceptibility, albeit with a significant vulnerability reduction program that includes design and testing. This emphasis has been driven by the advent of stealth technology, advances in avionics, and the blending of other new technologies. Also, the offensive counter-air mission of the F-22 tends to allow avoidance of denser surface-to-air threats at lower altitudes. When the characteristics of a system do not prevent its acquisition and attack by the enemy, Me second aspect of survivability vulnerability- becomes more significant. The DeparDnent of Defense determines how far system designers and manufacturers should go to incorporate vulnerability reduction techniques. Some of the ways system vulnerability can be reduced are Trough redundancy (e.g., redundar~t structural load paws arid electronics), fuel tanks that cannot explode when hit, fire suppression systems, use of nonflammable fluids, arid armor (i.e., shielding of vital components and crew). 3 An acceptable definition of survivability, which was used in the previous National Research Council report Vulnerability Assessment of Aircraft (NRC, 1993), is as follows: "The capability of an aircraft to avoid and/or withstand a man-made hostile environment (Ball, 1985~."

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Introduction 13 The subject of this report is F-22 vulnerability, not susceptibility. However, both are significant aspects of survivability, and neither should be considered in a vacuum by decision makers. Both aspects influenced the committee's recommendations, even though susceptibility was not explicitly evaluated. Use of the F-22 for roles other than offensive or defensive courter air, such as surface-attack operations, is being considered as a future possibility. Other missions and new threats that affect aircraft configuration, performance, and radar signature (for example) could make the terms of the survivability equation extremely dynamic influencing the balance between . . .... . . .... , , ~ susceptibility and vulneran111ty and require expect~t~ous and prudent consideration of vulnerability design and testing. Major modifications resulting from arty new mission would require the Air Force to reassess vulnerability and implementation of the law on live fire testing. VULNERABILITY TESTING OF AIRCRAFT VERSUS GROUND VEHICLES The law governing live fire testing had its origin in ground vehicle vulnerability. One should be careful, however, to differentiate between a fighter that has a mission of offensive counter air with its high dependency on stealth, countermeasures, speed, and maneuverability and a ground vehicle that is difficult to make stealthy and is not fast or agile. The relative weights riven tn ~ . . ~ ~ . . . ... ~ . .. . .. .. suscept~y and vulnerably and their realization in a design are different for fighters and ground vehicles (or even for aircraft with other missions). Also, it is more difficult to simulate, accurately and completely, the environment experienced by a fighter than that experienced by a ground vehicle. With respect to susceptibility and vulnerability, high-performance fighters are the result of a finely tuned optimization-in which aerodynamic shape, lifting capacity, payload volume, structural weight, avionics, and hydraulic systems are put into a balance along with manufacturing costs, reliability, maintenance, and repair-that is significantly different from ground vehicles. The effect of any vulnerability deficiency corrections on susceptibility (and, for that matter, on such elements of system performance as payload, range, and speed) must be considered. Changes in many aspects to reduce vulnerability are considerably more likely to affect system performance adversely for aircraft than for ground vehicles. In simulating the operational environment, two important considerations are (~) the stress state of the aircraft structure, normally a great deal higher than that of ground vehicles, and (2) the potentially large aerodynamic forces that can result when surface materials are distorted into the airspeed or holes of significant dimensions expose inner airframe spaces to free airstream pressures. Both considerations imply significantly more complex and expensive live fire testing for

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14 Live Fire Testing of the F-22 aircraft, if all potentially important phenomena are to be represented fully in such tests (e.g., the imposition of realistic Toads and sufficiently high air velocities before arranging projectile impact). REPORT ORGANIZATION The report is organized to reflect the subtasks in the Statement of Task (set forth in the Preface). Chapter 2 includes a discussion of circumstances affecting the F-22 survivability program that have occurred since Milestone Il. which is the decision point that initiated engineering and manufacturing development of the F-22. Chapter 3 deals with questions concerning practicality and affordability of full-up, full-scale live fire testing. Chapter 4 addresses the sufficiency of the F-22 test program. Chapter 5 treats vulnerability assessment tools, which are very important to survivability testing of the F-22 as well as other aircraft. Finally, Chapter 6 presents the committee's recommendations. There are, in addition, four appendices. Appendix A provides information about the meetings, site visits, and discussions of the committee. Appendix B is the Live Fire Test Law (10 U.S.C. 2366~. Appendix C provides the text of documents associated with the Department of Defense F-22 waiver request. Appendix D reproduces pertinent material from the National Research Council's ~ 993 report Vulnerability Assessment of Aircraft.

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Introduction' 15 REFERENCES Ball, R.E. 1985. (Cited in NRC, 1993.) The Fundamentals of Aircraft Combat Survivability Analysis and Design. New York: American Institute of Aeronautics and Astronautics, Inc. Hinton, W.S. 1994. Threat, Mission, and Operational Requirements for the F-22. Presentation to the Committee on the Study of Live Fire Survivability Testing of the F-22 Aircraft, National Academy of Sciences, Washington, D.C., December 21. NRC (National Research Council). ~ 993. Vulnerability Assessment of Aircraft: A Review of the DeparDnent of Defense Live Fire Test and Evaluation Program. Air Force Studies Board, NRC. Washington, D.C.: National Academy Press. Raggio, R.F. ~ 994. Overview of the F-22 Program. Presentation to the Committee on the Study of Live Fire Survivability Testing of the F-22 Aircraft, National Academy of Sciences, Washington, D.C., December 21. TAP (Tactical Air Force). 1991. Advanced Tactical Fighter (ATE) System Operational Requirements Document (SORD) TAP 304-3-/-A. March I. (S/NF)