Abstract:
This invention proposes to make use of an already developed set of hardware which dispenses and controls the performance of towed decoys capable of defeating radar guided weapons. Using this same hardware, a new and unique payload, payload control and dispensing mechanism is inserted into a decoy towbody. The payload consists of foils and/or foil packs of a pyrophoric material. This material creates an infrared (IR) signature behind the decoy that is more attractive than the infrared plume emitted by the aircraft engine. The fact that the IR decoy is towed insures that it will be kinematically correct by flying the same profile as the aircraft so as to remain within the field of view of the missile&#39;s seeker. Because the pyrophoric material can be metered (dispensed at varying and controllable rates) its radiant intensity can be matched with that of the engine of the towing aircraft. As the burn characteristics of the selected pyrophoric material match the burn profile of hydrocarbon based jet fuels, the towed IR decoy also emits a plume that spectrally matches that of its host aircraft&#39;s engine.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to a infrared (IR) flare dispensing towed decoy, and more particularly, to such an IR flare dispensing towed decoy that is electronically configurable to vary its IR emissions and burn duration. 
     2. Background Art 
     Infrared-guided and radar-guided missiles pose the primary threats to military aircraft engaged in a combat environment. These missiles use their radar and IR guidance to home in on aircraft, thereby substantially increasing their probability of a “hit”. 
     One method of defeating radar-guided missile attacks is to tow a decoy behind the host aircraft that is a more attractive radar target than the aircraft itself, so that the attacking missile chooses the towed decoy as opposed to the aircraft. The assignee hereto has pioneered this particular technology, developing a system for countering radar-guided weapons which is currently entering production for Air Force and Navy combat aircraft under the nomenclature of AN/ALE-50. However, to date no similar capability for defeating non-imaging IR-guided missiles has been developed. 
     Current military aircraft are particularly vulnerable to attack from IR-guided surface-to-air and air-to-air missiles. Statistics gathered from analysis of aircraft losses in hostile actions since 1980 show that almost 90% of these losses have been the result of IR-guided missile attacks. Thus, IR-guided missiles have become a formidable threat to military aircraft. These missiles can either be guided to their target entirely using IR-guidance or can initially utilize radar guidance and then switch over to IR guidance as they come into closer proximity to the target. In regards to the latter approach, IR-guided missiles can be cued via radar, or a passive Infrared Search and Track (IRST) system employed with the missiles can be alerted and properly oriented via a data link from a ground based surveillance or early warning radar. Optimally, however, IR-guided missiles are launched at an aircraft without the use of radar cueing, which often alerts an aircrew to an impending missile attack when the radar signals are detected by an on-board radar warning receiver. These IR-guidance only missiles are essentially passive and can be launched as a result of visual observation of the approaching aircraft, via self cueing or with assistance from a IRST system. In the absence of warning to the target aircraft, these missiles have a high degree of lethality. 
     The number and variety of infrared guided missiles pose a significant challenge to the development of an effective countermeasure in that the missiles tend to employ a wide variety of IR counter-countermeasure (IRCCM) capabilities. This makes it difficult to devise techniques that will be effective across the spectrum of IR guided missile threats and insensitive to the presence/absence or type of IRCCM being employed. 
     A number of methods have been used in an attempt to reduce the lethality of IR-guided missiles. Aggressive maneuvering of the target aircraft is often attempted if there is sufficient warning of an approaching missile. Also, pyrotechnic or pyrophoric flares that are forcibly ejected from on-board magazines using pyrotechnic squibs as the motive source have been employed. However, these devices burn at the necessary intensity for only a short period of time. In addition, gravity quickly separates the flares from the dispensing aircraft removing them from the missile seeker&#39;s field of view—thus limiting or reducing their effectiveness. These IR flares can also be identified by some missiles and rejected because they tend to initially provide more intense IR emissions than the aircraft. Furthermore, some missiles can also identify IR emitting flares by their IR spectrum. 
     Another current countermeasure involves the use of an IR jammer. Infrared jammers attempt to confuse missile seekers by “blinking” IR energy at an approaching missile. This energy is modulated at rates designed to confuse the signal processing circuitry of the attacking missile and induce sufficient angle error in its guidance mechanism so as to cause a miss. However, IR jammers have not been particularly successful for a number of reasons. The lamp sources of IR energy have difficulty generating sufficient intensity to overcome the aircraft engine&#39;s IR signature. They normally are required to be omni-directional since the direction of missile attack is not generally known. This further dilutes their energy density. If they are focused into a controlled beam to increase their energy on the IR missile seeker, they require fairly accurate pointing information which is not currently available on fighter aircraft. Finally, since different types of IR-guided missiles rarely use the same signal processing technology, it has not been possible to create a generic jamming modulation effective against all missiles. This can only be accomplished if the jammer designer has intimate knowledge of the missile seeker which allows him/her to exploit its design vulnerabilities. Clearly, this requires knowledge gained via exploitation of captured or covertly obtained missiles or through other intelligence sources. However, this is an impractical approach given the number and variety of IR-guided missile types. 
     In conclusion, the aforementioned approaches have proven to be individually and collectively inadequate to assure the survivability of military aircraft threatened by IR guided missiles. Therefore, what is needed is a system for distracting IR missiles from a target aircraft that tracks with the movement of the aircraft and provides the same IR spectral characteristics as the aircraft to be protected. Furthermore, this system should be able to control its radiant intensity so as to attract IR-guided missiles which are able to more closely discriminate between aircraft IR signatures and IR decoy launched flares. Additionally, the system should exhibit a sufficient burn duration to provide protection over a reasonable length of time against a possible missile attack. 
     SUMMARY 
     These needs are fulfilled by a towed IR decoy that flies the same profile as the aircraft it is protecting, such that the decoy remains in the IR-guided missile&#39;s field of view unlike current aircraft deployed flares which quickly fall away from the aircraft. This decoy also exhibits the same IR spectral characteristics such that the attacking missile cannot discriminate between the decoy and the aircraft to be protected on the basis of these characteristics. Furthermore, this decoy is able to vary its radiant intensity so as to provide an irresistible distraction to the incoming missile. Finally, the decoy is long-lived so that it provides protection against a possible missile attack over an appropriate period of time. This allows the towed IR decoy to be used preemptively (i.e., without need of warning of missile attack) at the option of the aircrew whenever they are likely to be immediately vulnerable to IR missile attack. 
     Generally, the towed decoy of the present invention creates an irresistible distraction which is effective against all of the current generation of attacking IR-guided missile, regardless of the IR counter-countermeasures (IRCCM) employed by the attacking missile. Specifically, the decoy is designed to eliminate, or render ineffective, the key discriminants used by most current generation, non-imaging, IR-guided missiles as IRCCMs. This invention proposes to make use of an already developed set of hardware which dispenses and controls the performance of towed decoys capable of defeating radar-guided weapons (i.e. the AN/ALE-50 system). Using this deployment hardware, a new and unique payload, payload control and dispensing mechanism is inserted into a decoy towbody. The payload consists of foils and/or foil packs (containing multiple foils or packets of powders) of pyrophoric material. Suitable pyrophoric foil flare materials are described in U.S. Pat. No. 5,464,699. This material will create an infrared signature behind the decoy that is more attractive than the infrared plume emitted by the aircraft engine or distracts the missile enough to cause it to miss its intended target. The fact that the IR decoy is towed insures that it will be kinematically correct (flying the same profile as the aircraft and within the field of view of the missile seeker), and because the pyrophoric material will be metered (dispensed at varying and controllable rates) its radiant intensity can be matched with that of the engine of the towing aircraft. In addition, the burn characteristics of the selected pyrophoric material match the burn profile of hydrocarbon based jet fuels. Thus, the towed IR decoy also emits a plume that spectrally matches that of its host aircraft&#39;s engine. The decoy&#39;s ability to meter its payload and it relatively large flare capacity combine to provide a long life that effectively defeats any temporal discriminants used by current IR-guided missiles. 
     One embodiment of a decoy according to the present invention includes a cylindrical housing. This housing is made up of two independent sections which are joined together in the area where a towline is attached. The forward section contains electronics and a motor which act as a motive source for the payload dispensing mechanism. The aft section contains the payload dispensing mechanism and the pyrophoric material payload in hermetically sealed packages. Mounted at the aft end of the aft section are stabilizing fins. 
     By separating the decoy housing into two primary sections, it is possible to adopt a manufacturing approach which gives cognizance to the fact that the payload section contains a hazardous material which is subject to the special handling and treatment requirements normally accorded fuels or munitions. The two sections can be built and tested independently, then joined prior to being encapsulated for extended storage. The forward section encompasses a structure for mounting a number of circuit cards, a towline attachment mechanism, and a structure for mounting an electric stepper motor. It also contains a ballast which assures aerodynamic stability via controlling the decoy center-of-gravity/center-of-pressure. This ballast also provides structural rigidity and attachment points for securing the aft (payload) section. 
     Power is delivered down a towline via appropriate electrical cabling to the decoy from a power supply contained in the on-aircraft launch controller. This power is conditioned in the circuit card area to provide three discrete voltages necessary to operate the decoy. The circuit cards perform communication, motor control and power conditioning functions. More particularly, a modem provides a communication interface between the aircraft and the decoy. This two-way communication involves commands from the aircraft to the decoy for controlling payload dispensing initiation/stop and dispensing rates for the pyrophoric material, and from the decoy to the aircraft for relaying decoy health and status. A motor provides the motive force for the payload dispensing mechanism. This motor is releasably connected to a screw shaft in the aft section of the decoy via a “blind-mating” connector. A motor controller circuit board establishes the parameters of motor operation (e.g. rotation speed) and provides commands directly to the motor. Power conditioning is provided by the power conditioning circuitry which provides appropriate voltages to the motor, motor controller and modem. 
     The aft (payload) section is comprised of a non-rotating piston riding on the aforementioned screw shaft. The screw shaft runs the length of the payload section terminating at a spin-off end cap which seals the payload in the decoy prior to deployment. The payload consists of approximately 6,000-7,000 disks/foils of pyrophoric material which are mounted with a preload on the screw shaft. The preload allows the payload to act as a solid object instead of a compressible object, thus affording accurate metering of the material. In addition, the preload causes each foil to “spring” out of the back of the payload section, thereby facilitating the dispensing of the material. Upon command, the electric motor turns the screw shaft causing the end cap to spin-off and the piston to ride down the screw shaft pushing the pyrophoric foils ahead of it. The rate at which the motor turns determines the rate at which the foils are dispensed into the atmosphere, and in turn, the intensity of the IR signature. The more units of material dispensed per unit time, the higher the radiant intensity generated. The dispensing rates (and so motor speed) are calculated to generate the IR signature necessary to cause an attacking IR missile to miss the host aircraft. The motor speed requirements are programmed into the memory of the on-aircraft launch controller and in turn transmitted to the motor controller of decoy. This controllability allows the decoy to defeat IRCCM intensity discriminants and also provides suitable burn duration to permit preemptive usage. 
     In addition to the just described benefits, other objectives and advantages of the present invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The specific features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims and accompanying drawings where: 
         FIG. 1  is a drawing of the decoy constructed in accordance with this invention showing the two sections of the towbody. 
         FIG. 2  is a block diagram of the major components embodying the present invention. 
         FIG. 3  shows the shifting of the IR centroid calculated by a missile seeker due to the presence of the towed decoy of the present invention. 
         FIG. 4  shows an IR modulation pattern entailing high and low intensity spikes. 
         FIG. 5  shows another IR modulation pattern entailing a high and low intensity spikes followed by a waiting period. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description of the preferred embodiments of the present invention, reference is made to the accompanying drawings, which form a part hereof, and which is shown by way of illustration of specific embodiments in which the invention may be practiced. It is understood that other embodiments may be utilized and structural changes may be made without departing from the scope of the present invention. 
       FIG. 1  provides an overall schematic of a decoy  5  which provides the kinematic, spectral, intensity and temporal features capable of defeating all types of current non-imaging IR missiles.  FIG. 2  provides a block diagram of some of the more important components of the decoy  5 . Referring to these  FIGS. 1 and 2 , the decoy  5  has two basic sections, the forward section  10  and the aft section  20 . The sections can be made separately, and then joined and tested at a later date. Since the decoy  5  is manufactured in two separate sections, it has the advantage of allowing the aft section  20 , which contains hazardous material and is subject to special handling and treatment requirements normally accorded fuels or munitions, to be manufactured and stored separately from the forward section  10 . In the embodiment shown in  FIG. 1  the decoy has a cylindrical housing and is approximately 16.7 inches in length and 2.4 inches in diameter. In general, the forward section contains electronics and a motor which act as a motive source for the payload dispensing mechanism. More specifically, the forward section  10  comprises a towline attachment  11  for attaching a towline  12 , and an electrical interconnect  13 . The electrical interconnect  13  brings power and communications from on-board a host aircraft  30  via appropriate electrical cabling disposed along the towline  12  to an on-decoy communications modem  15 , motor controller  16  and power conditioning circuitry  17 . The communications between the host aircraft  30  and the decoy are two-way. Commands involving dispense initiation start and stop and dispensing rates for the pyrophoric materials  25  in the aft section  20  are sent from the aircraft  30  to the decoy. The decoy  5  sends to the host aircraft  30  decoy health and status information. The motor controller  16  establishes the parameters for motor operation and operates the motor  18 . The motor shaft  18 a has a blindmate connector  19  that connects to a coupling  26  on the aft section  20  of the decoy. The motor  18  is preferably an electric stepper motor. Additionally, the forward section  10  includes a ballast (not shown) which assures aerodynamic stability by controlling the decoy&#39;s center of gravity and center of pressure. The ballast also provides structural rigidity and attachment points for securing the aft section. 
     In general, the aft section  20  contains a payload dispensing mechanism and a payload of pyrophoric materials in hermetically sealed packages. More particularly, the aft section  20  includes a non-rotating piston  21 , a screw shaft  23 , a “spin-off” end cap  24  and several thousand foils or packets of pyrophoric material  25 . There are also four equally space, spring-erected, stabilizing fins  29  mounted at the aft section  20 . These fins  29  spring into place when the decoy is deployed. The piston  21  is prevented from rotating on the screw  23  by an anti-rotation mechanism. This anti-rotation mechanism can be of any appropriate design. However, a wheel-stabilizer configuration is preferred. In this preferred configuration there is a longitudinally oriented slot on the inner surface of the aft section  20  into which extends a portion of a rotating wheel incorporated into the external surface of the piston. The wheel is fitted in a slot within the body of the piston and affixed such that a portion of the wheel extends beyond the surface of the piston and is capable of rotating within the slot. As the piston  21  is driven forward the wheel rotates as it moves through the slot, thereby preventing binding of the piston within the aft housing. However, contact between the sides of the wheel and the walls of the slot prevents the piston from rotating within the aft body. 
     The screw shaft  23  is preferably an acme screw and runs the length of the payload section terminating at the end cap  24 . In this embodiment the foils  25  are doughnut shaped and are mounted on the screw  23 . The foils are preferably 1.5 to 2.0 mils thick and preferably 6000 to 7000 disks/foils of pyrophoric material are used. Packets of pyrophoric powder can also be used, either alone or in conjunction with the foils  25 . 
     Upon command, the electric motor  18  turns the acme screw  23  causing the end cap  24  to spin off and the piston  21  to ride down the screw  23  pushing the pyrophoric foils  25  ahead of it. Each foil and/or powder packet is hermetically sealed using a casing made from, for example, mylar or another plastic material. As the packets are pushed out of the back of the decoy, they are cut open by a sharp projection located at the back of the aft section. The pyrophoric materials  25  burn or glow when exposed to air and emit IR radiation. The packets of pyrophoric material are mounted on the screw  23  with a preload that compresses the packets together in the longitudinal direction within the aft section  20 . The compressed packets act as a solid object when pushed aftward by the piston  21 . As a result, the packets at the aft end of the section  20  begin dispensing immediately when the piston  21  is moved and are dispensed at a rate dictated solely by the speed of the piston. This ensures an accurate metering of the material. In addition, the preload causes each foil to “spring” out of the back of the payload section, thereby facilitating the dispensing of the material. 
     An O-ring  27 , disposed at the back end of the aft section  20 , extends into the interior of the section far enough to contact a peripheral portion of the face of each foil  25  as it reach the back end just prior to being dispensed. This O-ring  27  has a dual purpose. First, it acts as a seal preventing outside air from gaining access to the interior of the aft section  20  where it could react with the remaining pryrophoric foils  25 . In addition, the O-ring  27  imposes a slight resistive force against each foil  25  as it is dispensed from the back end of the aft section  20 . This resistance causes each foil to “spring” out of the back of the payload section, thereby facilitating dispensing of the material. While an O-ring is preferred, it should be noted that any similar structure which provides both the sealing and the resistance function could be employed instead. For example, a shoulder or flap might be employed with equal success. 
     A braking mechanism is contained in a towline reel on the aircraft which holds the towline  12 . The braking mechanism allows the decoy to be towed in a discrete position relative to the host aircraft  30  unique to the type of aircraft and the location on the aircraft where the decoy deploying mechanism is housed. The distance the decoy is positioned behind the aircraft is be chosen to be close enough to allow the decoy to be in proximity to the host aircraft&#39;s exhaust plume such that both the aircraft&#39;s plume and decoy&#39;s flares are in the missile seeker&#39;s field of view at the onset of missile engagement. However, the distance should also be far enough that the decoy clears the aircraft&#39;s superstructure and can provide an effective distraction for an attacking IR missile. This braking mechanism and towline reel are essentially the same as used for the aforementioned radar decoy system and so no greater detail will be provided herein. 
     Power is delivered down the towline  12  to the decoy  5  from a power supply  32  contained on the on-aircraft launch controller  31 . In a tested embodiment a 350V power source was used. The power provided by the source  32  is further conditioned by the power conditioning circuitry  17  in the decoy to provide three discrete voltages necessary to operate the decoy and electronic components. 
     The decoy embodying the present invention is electronically configurable such that it can be made to replicate a variety of aircraft engine infrared plume signatures. This allows the same decoy to be used on a number of tactical and combat support aircraft whose plume signatures appear within a range of approximately 300 to 3000 watts per steradian. This intensity range is accomplished via material dispensing commands transferred from a launch controller  31  onboard the host aircraft  30  down the towline  12  to the decoy and then through the on-decoy modem  15  to the motor control circuitry  16 . The commands instruct the motor controller  16  to control payload dispensing at a rate sufficient to achieve decoy IR signature to aircraft IR signature matching. Specifically, the rate at which the motor  18  turns, which in turn dictates the translation speed of the piston and determines the rate at which the foils are dispensed into the atmosphere (and thus, the intensity of the IR signature). The more units of material dispensed per unit of time, the higher the IR intensity generated. It is noted that the dispensing rate required to mimic a particular aircraft&#39;s IR signature can be readily determined using currently known methods. Therefore, no detailed listing of the dispensing rates associated with particular aircraft will be provided herein. 
     Modeling and analysis of the current generation of non-imaging IR threat missiles, played against an array of aircraft-launched flare decoys deployed from U.S. military aircraft, has resulted in a more comprehensive understanding of the key elements required to be effective against these threat missiles. The key elements are directly related to the methodologies used by IR-guided missiles to discriminate between real (aircraft) targets and decoy (flare) targets. Specifically, current non-imaging IR-guided missile employ kinematic, spectral, radiant intensity, and temporal discriminants to avoid being deceived by the deployment of IR emitting flares. These discriminants will be described below, as well as how the preferred embodiments of the present invention overcome these discriminants. 
     1.0 Kinematic 
     In order to be effective the decoy flare must be kinematically equivalent to its host aircraft. Ideally, it should follow the movements of the aircraft it is protecting. It cannot be allowed to fall out of the field of view of the attacking missile else it loses its ability to divert the attacking missile. Towing the decoy is one way (and perhaps the best way) to accomplish this. A towed IR decoy&#39;s ability to appear kinematically equivalent to the host aircraft is particularly advantageous when the aircraft is diving. Military aircraft usually fly at a sanctuary altitude where they are too high to be reached by any missile threat. The planes then dive on a target, fire and pull back up to sanctuary altitude. IR flares fall away too quickly when the aircraft is in a high speed dive, providing little protection when compared to the towed IR decoy of the present invention. 
     2.0 Spectral 
     In order to be effective the decoy flare must exhibit approximately the same IR spectral characteristics as are exhibited by the aircraft&#39;s exhaust plume. This is necessary to preclude the attacking IR missile from discriminating between real (aircraft) and decoy (flare) targets by seeing or comparing the presence or absence of certain wavelengths within the IR spectrum. The optimal method of achieving this is to use the aforementioned pyrophoric flare materials which burn at approximately the same spectra as hydrocarbon based jet aircraft fuels. 
     3.0 Radiant Intensity 
     In order to be effective the decoy flares must be able to achieve radiant intensity levels exhibited by the engines on the various military aircraft it will be protecting. Obviously, since the engines of these fighter and combat support aircraft tend to produce widely varying levels of IR emissions, the IR decoy&#39;s flares must also be capable of duplicating this range of intensities. 
     Some IR-guided missiles calculate the location of the target aircraft by calculating the centroid of the IR emissions present in the missile seeker&#39;s field of view. These seekers then calculate the distance from the centroid to where the actual aircraft body would most likely be located. For example, as depicted in  FIG. 3 , the host aircraft&#39;s engine plume  50  would normally be perceived by the missile seeker as having an IR intensity centroid at C 1  and would calculate the distance d 1  that the centroid of the plume should be from the aircraft. However, with the addition of the towed decoy  5 , and its IR intensity centroid C 2  at a distance d 2  in the missile seeker&#39;s field of view, the missile seeker will calculate the IR centroid C t  between C 1  and C 2  at a distance d t  behind the aircraft. As a result the missile seeker will miscalculate the position of the aircraft. Hence, the towed decoy of the present invention is placed at a distance close enough to be in the missile seeker&#39;s field of view, but also far enough behind the host aircraft to cause sufficient error in the missile seeker&#39;s infrared centroid calculation such that the missile misses its target aircraft. To counter such missiles, the IR radiation intensity pattern produced by the decoy need not vary and so the IR emitting pyrophoric packets can be dispensed at a steady rate. However, there are advantages to varying the intensity as will be discussed next. 
     Varying the intensity of the IR radiation intensity emitted by the decoy can be used to deceive the seekers of some missile employing intensity discriminants other than just the centroid scheme described above. In one preferred IR radiation intensity modulation pattern depicted in  FIG. 4 , the radiant intensity is varied from somewhat higher to somewhat lower than the aircraft engine&#39;s IR signature. This is accomplished by varying the speed of the of the piston  21  on the screw  23  pushing the pyrophoric payload  25  out of the back of the decoy into the air stream. Some current generation IR missiles attempt to counter IR flare countermeasures by rejecting the brighter IR sources (or weaker in some cases), when more than one source is detected. This is done on the assumption that the presence of an additional source or sources indicates the presence of IR emitting flares. The above-described modulated IR radiation intensity pattern tends to deceive these intensity discriminating missiles by attracting the missile to the decoy or at least away from the aircraft. If the missile is the type that rejects the brighter of the IR sources, the repeated IR bursts having a radiant intensity below that of the aircraft&#39;s exhaust plume will cause the missile to be distracted from the aircraft and toward the decoy instead. However, if the missile is of the type that seeks the brighter IR source, the portion of the modulated IR radiation intensity pattern that exceeds the IR emissions of the aircraft&#39;s exhaust plume will attract the missile and spare the aircraft. Thus, the “high-low” intensity pattern will defeat the missile, regardless of the which CCM it employs. 
     The aforementioned IR radiation intensity pattern exhibiting a high IR energy spike compared to the aircraft&#39;s exhaust plume, followed by a low energy spike compared to the aircraft exhaust plume (as depicted in  FIG. 3 ) will also deceive IR guided missile employing the centroid scheme as a IRCCM. Essentially, the pattern causes the missile&#39;s centroid calculations to be skewed aftward just as it would if the a steady intensity pattern were employed. This will result in the missile miscalculating the location of the target aircraft, causing the attacking missile to miss its mark. 
     Further, some missiles that employ the centroid scheme as a IRCCM add a feature by which the missile temporarily ceases tracking the target when a high intensity IR spike is detected on the assumption that it is an IR emitting flare. While temporarily out of its seeking mode, the missile steers toward the projected location for the aircraft based on it last known position. It is believed that when the missile resumes its IR tracking a few seconds later, the flare will have fallen out of the missile seekers field of view and only the aircraft will remain. The intensity spikes exceeding the IR emissions of the aircraft&#39;s engine plume associated with the decoy IR intensity modulation pattern will trigger the above-described missile&#39;s IR tracking shut-down mode. However, when the missile resumes tracking and reacquires what is assumed to be the aircraft alone, it will actually be the aircraft with its decoy. Either this scenario will cause the missile to miscalculate the position of the aircraft in relation to the IR radiation field or it will cause the missile to continuously shut-down its IR seeking function making it unlikely to actually hit the aircraft. 
     To even further skew the IR centroid calculations of missile seekers which calculate the IR centroid in their seeker field of vision, the towed decoy can dispense pyrophoric material in a manner which results in a large IR radiation intensity spike (higher than that of the aircraft&#39;s exhaust plume), a low IR radiation intensity spike (lower than that of the plume), and then wait for a short period of time before repeating the cycle (high spike, low spike, waiting period) as shown in  FIG. 5 . This IR radiation intensity pattern will further skew the centroid that the missile seeker calculates because by waiting after the high spike, low spike combination a series of flare intensities which stretch out further in distance behind the aircraft than with the previously-described alternating high spike, low spike combination. Thus, this pattern would defeat all the IR radiation intensity-based CCMs described previously. 
     4.0 Temporal 
     In order to be effective, the decoy must be able to overcome temporal based IRCCMs employed by some IR-guided missiles. Essentially, these missiles have the capacity to distinguish between the relatively continuous IR emission levels associated with the aircraft&#39;s exhaust plume and the rapidly decreasing IR emissions associated with an IR emitting flare. The towed decoy of the present invention is able to defeat the temporal discriminants of an IR-guided missile because, once activated, the pyrophoric material packets can be continuously dispensed over a relatively long period of time (as compared to current aircraft-launched flare systems), thereby maintaining the desired IR emission levels. It is the decoy&#39;s ability to dispense the IR emitting flares one at a time at controlled rates that provides the relatively long life, i.e. on the order of tens of seconds. Further, if the decoy is damaged or destroyed or simply uses up all its pyrophoric material, it can be automatically and almost instantaneously replaced. For example, if communication is interrupted between the aircraft and the decoy, this event can, at operator option, be used as an automatic cue to deploy another decoy. This provides a nearly continuous protection from IR missiles and allows the towed decoy to be used preemptively by deploying it whenever the aircraft is susceptible to attack from an IR-guided missile. The IR emitting flares are dispensed from the decoy, and the decoys are continuously replaced as long as the aircraft remains in the threat area. The long life of the decoy is also enhanced by a capability to cease dispensing of the flare material if the aircraft successfully evades missile engagement, thereby reserving flare material for potential future missile threats. Finally, when employed, the aforementioned “high-low-pause” IR emission pattern will allow the towed decoy to conserve flare material so as to remain viable for a longer period of time. 
     In summary, the foregoing description has shown the unique towed IR decoy according to the present invention overcomes the key kinematic, spectral, intensity and temporal IRCCMs employed by the current generation of non-imaging IR-guided missiles and significantly increases aircraft survivability against these threats. 
     While the invention has been described in detail by specific reference to preferred embodiments thereof, it is understood that variations and modifications thereof may be made without departing from the true spirit and scope of the invention. For example, different payloads might be used to simulate aircraft IR signatures. Pyrophoric foils of different thicknesses and in different numbers may be used. For instance, the foils can be packaged individually or in groups of foils. This packaging method provides an alternate way of varying the IR intensity of the material that is deployed from the decoy by having greater or lesser numbers of foils packed in one package. Pyrophoric powders can also be used either alone or in conjunction with the foils. The decoy of the present invention could also be different sizes or shapes. For instance, the towed IR decoy could be made with a non-circular cross-section such as a square shape. This square-shaped cross section, or any shape that is not circular, would obviate the need for the wheel-stabilizer or other non-rotation mechanism that is employed in the decoy having a circular cross-section. The towbody of the decoy could also be made of more than two sections, or alternately could take the form of a single integrated structure.