Fighter Combat

FIGHTER WEAPONS 39The various forms of horning guidance generally offer improved capabilityagainst airborne targets, especially highly maneuverable targets. Moreefficient trajectories and better guidance accuracy in the critical terminalphase of the intercept are often available. Each guidance method, however,has some advantage over the others in certain situations, so combinationsystems are sometimes employed. An example is the use of preset orcommand guidance during the early portion of a long-range shot to get themissile close enough to the target to allow passive or active homing.Advances in solid-state electronics technology have made it practical toplace more sophisticated guidance and sensor capability in small, lightweightmissile packages.Missile SeekersThe seeker system of a missile is responsible for sensing and tracking thetarget and providing the information necessary for performance of theguidance system. Preset and command guidance do not require a seeker inthe missile, since the tracking function is accomplished by the launching/guidanceplatform. Beam-rider missiles usually have a receiver in thetail to collect information from the host guidance/tracking beam. Passivemissiles generally require a sensor receiver in the nose, as do semi-activehomers; but semi-active homers may also include a rear receiver forinterception of information directly from the illuminating platform whichcan be compared to the reflected energy received by the forward sensor toderive additional guidance data. Active homers require both a transmitterand a receiver, generally located forward.The maximum range of its seeker operation often limits the effectiverange of a missile system. Passive seekers have an inherent advantage here,because their received power is inversely proportional to the square of thetarget range, while the max-range of active and semi-active systems variesinversely with the fourth power. Several other factors also are involved.For passive systems these include the intensity of the target radiation inthe direction of the sensor, the type of radiation (which determines the rateof signal attenuation by the atmosphere), and the seeker sensitivity. Foractive and semi-active systems maximum range depends on, in addition totransmitted power and receiver sensitivity, the reflective characteristics ofthe target relative to the type of illumination used. These reflective characteristicsare usually sensitive to target size, and also to the target's constructionmaterial, shape, surface contours, and aspect, all of which maycombine to increase or decrease reflectivity.The most common passive seeker now in use is the heat seeker. Thisdevice contains a material (the detector) which is sensitive to heat (infrared—IR—radiation)that is produced primarily by the target's propulsionsystem. The detector is often cryogenically cooled to eliminateinternally generated thermal "noise" and allow detection of even verysmall amounts of IR energy coming from an external source. The seekermust still have the capability to discriminate between target radiation andbackground radiation, however. Such differentiation is essential for all