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Future Air Force Needs for Survivability Appendix D Glossary Altitude: Altitude can be measured in several meaningful ways. One is the height of the air vehicle above mean sea level, measured along the line between the air vehicle and the center of Earth. Another is the density altitude, which is the equivalent altitude under standard conditions of pressure and temperature at the existing air density outside the air vehicle. In considering the kinematics of a threat missile, it is the density altitude that is important. Countermeasures: Countermeasures refer to a wide range of devices (both active and passive) aimed at defeating the ability of an enemy’s sensor system to find, fix, track, or engage friendly forces. Countermeasures include both radio-frequency (RF) systems (e.g., jammers and so on) and infrared systems (i.e., flares, chaff, and so on) and may be either onboard or offboard systems. Lethality: Weapon lethality must be defined specifically for each class of weapon or munition and each class of target. That said, lethality is expressed as the probability that the desired effects on a target will be achieved by a munition for the conditions of employment. The metric usually used is Pr[kill | hit], where a hit can be by a contact or proximity fuzed munition. For the U.S. munitions inventory, the Joint Munitions Effectiveness Manual is an authoritative source of lethality information.
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Future Air Force Needs for Survivability Maneuverability: Air vehicle maneuverability refers to the acceleration capability of the vehicle in a plane normal to the vehicle velocity vector. Acceleration is generally quoted in terms of “G’s” where 1 g = 9.8 m/s2. Maneuverability is a function of the vehicle shape, mass, orientation, speed, and altitude. Payload: Payload refers to a device or devices carried by the air platform for the purpose of meeting the mission objectives. For intelligence, surveillance, and reconnaissance (ISR) platforms, payload refers to the sensor suite carried. For attack air platforms, payload refers to the munitions that can be deployed. For munitions, payload refers to warhead or submunitions carried. The payload is specified in terms of its impact on the air vehicle by parameters such as mass, volume, power, interface, and so on. The required payload is set by the definition of the mission requirements and can have a significant impact on air vehicle shape and size. Persistence: Persistence refers to the time period that an attacking or ISR platform can engage a target within its window of vulnerability. For air platforms, persistence is measured as time on station. Note that persistence in an attack role can be achieved in three ways: (1) by loitering over the vicinity of a potential target and delivering a gravity bomb, (2) by standing off and using a high-speed weapon to attack within the target’s time of vulnerability, or (3) by standing off at a distance and repeatedly dashing into the battlespace to attack. Range: Range is a distance measurement usually quoted in terms of the relative distance between two points on the surface of Earth. Several range measurements are of importance when considering survivability. The combat range of an aircraft is generally defined as half of the maximum distance (i.e., combat radius) that an aircraft can cover between in-flight refueling operations. Detection range is the maximum linear distance between an air vehicle and the sensing system used to detect the air vehicle at the lowest threshold of the detection system. The weapon range is the maximum distance that a weapon can transit between its carrier platform and target. Signature and/or observability: The general definition of the signature of an air vehicle is any direct or indirect measure of its characteristics or effects. In the context of this study, the most common signature measurement for
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Future Air Force Needs for Survivability RF systems is the radar cross section (RCS, or σ), usually quoted as a log10 of the cross section measured in square meters (dBsm). The RCS of an air vehicle is a function of the RF wavelength and the vehicle shape, size, materials, and orientation. For infrared systems, the signature of a vehicle is quoted in terms of radiant intensity in the waveband of the sensor system of interest and is usually quoted in watts per steradian. The optical signature is a function of the vehicle size and shape, the surface temperature and emissivity, and the exhaust plume. Situation awareness: Situation awareness refers to one’s understanding of the current state of the battlespace. Situation awareness addresses both the knowledge of physical properties of entities within the battlespace (i.e., the position and velocity vector of air vehicles, state of communications systems, location of enemy forces, and so on) and the cognitive understanding of the dynamically evolving environment. As such, the ability of a human to process and act on data and information is an important aspect of situation awareness. Situation awareness is important for both the attacking forces (i.e., knowledge of surface-to-air missile system locations, targets, defensive doctrine, and so on) and the defensive forces (i.e., targeting and tracking of attacking systems, determining intent, weapon-target pairing, and so on). Speed: The normal definition of speed is the instantaneous magnitude of the velocity vector. The speed of an air vehicle represents the relative motion of the air vehicle with respect to the air mass surrounding it. This vector is normally not coincident with the axes of the vehicle, which results in an angle-of-attack or angle-of-yaw with respect to its direction of motion. The normal way to express speed for modern military aircraft and missiles is Mach number, M, which is the ratio of air vehicle speed to the local speed of sound in the air mass. (Since the sound speed is a function of temperature, the sound speed is generally taken to be with respect to the standard atmosphere unless otherwise noted.) The Mach number is used to characterize speed ranges or regimes: subsonic (M < 1); transonic (M ~ 0.8-1.1);1 supersonic (1 < M < 4); and hypersonic (M > 4). Mach number is an important similarity parameter regarding the aerodynamics of the vehicle. When tied to a specific altitude, Mach number can also be used to define the aerothermal environment that the air vehicle must oper- 1 Strictly speaking, the transonic regime, which begins when M = 1, is first reached somewhere on the vehicle, usually at the maximum thickness point on the wing.
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Future Air Force Needs for Survivability ate within. Air vehicle block speed, Vblock, is also an important parameter for analysis. Block speed is defined as the distance covered along a ground track divided by the flight time. Block speed is sometimes quoted in terms of a Mach number, but Mach number is ambiguous in this context, since altitude (and hence temperature and speed of sound) can vary throughout a trajectory. Within this report, Mach number used to denote a block speed is defined as the block speed divided by the standard-day sea-level sound speed. The design speed of an air vehicle system strongly impacts air vehicle and propulsion system requirements. Survivability: In terms of combat, survivability refers to the capability of an aircraft to avoid a man-made hostile environment. Survivability is defined as the probability that an air vehicle is not killed during its mission. Survivability consists of susceptibility and vulnerability. Within this report, the focus is on the susceptibility portion of aircraft survivability. Susceptibility: Susceptibility is a measure of the probability that an air defense system can physically make contact with the air vehicle. With a hit-to-kill interceptor system, susceptibility defines the probability that a portion of the interceptor actually impacts the air vehicle. With an interceptor system using a blast-fragmentation warhead, susceptibility defines the probability that a warhead fragment impacts the air vehicle. Tactics: Tactics are the processes that are executed to achieve the desired mission results and typically are designed to synergistically maximize capabilities and strengths and to minimize weaknesses. An example is a fighter that has a speed advantage against a threat, but also has a turn-rate disadvantage. This fighter would generally be deployed with tactics that utilize high-speed “blow through” techniques while taking shots of opportunity, as opposed to tactics that utilize a low-speed “dogfight” approach with a steady-state weapons engagement zone as the goal. The functional components of tactics include available assets, support assets, associated capabilities, timing synchronization, threat environment, weather, terrain, fuel, communications, weapons, operator experience, and mission objectives. Key trade-offs include the ability to achieve surprise versus the capability to execute, comprehensive planning versus the ability to dynamically respond, risk versus value of mission accomplishment, risk versus assets committed, and risk versus timing.
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Future Air Force Needs for Survivability Threat: Threat is a general term that can be applied to the enemy systems and subsystems that impact the detectability, susceptibility, and ultimately, the survivability of U.S air vehicles. The term is applied, for example, to an enemy integrated air defense system, early warning sensors, acquisition sensors, surface-to-air missiles, and air-to-air missiles. Vulnerability: Vulnerability addresses the response of the air vehicle after it is hit by an interceptor system. Vulnerability is defined as the probability that the air vehicle is killed once it is impacted by an interceptor system. (Note that the vehicle’s mission could well be compromised prior to this kill if it were forced to maneuver or turn back to avoid the threat.)
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