Abstract:
A method of autonomously tailoring a detonation delay time of a gun launched munition by utilizing target impact signatures including but not limited to a MOUT target set; earth and timber bunker, triple brick wall, double reinforced concrete, and light armor. While the present method is applicable to countless munition configurations, the projectile architecture used to develop the discrimination algorithm includes a tandem warhead configuration. Upon target impact the forward warhead detonates and pre-damages the target to allow the rear warhead to break through. Target impact data is used to set a detonation delay in the rear warhead providing increased performance behind the target.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 USC §119(e) of U.S. provisional patent application 61/816,845, filed on Apr. 29, 2013, titled “Method For Discriminating Between Military Operations In Urban Terrain (MOUT) Targets,” which is incorporated by reference in its entirety. 
    
    
     GOVERNMENTAL INTEREST 
     The invention described herein may be manufactured and used by, or for the Government of the United States for governmental purposes without the payment of any royalties thereon. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to the field of munitions such as explosive projectiles. Particularly, the present invention relates to a target discriminating munition for use against military operations in urban terrain (MOUT) targets, including but not limited to earth and timber bunkers, triple brick walls, double reinforced concrete, and armored targets. More specifically, the present method relates to an algorithm for use, for example, with a dual warhead design, and is capable of autonomously discriminating between, and defeating numerous targets including a MOUT target set. 
     BACKGROUND OF THE INVENTION 
     The survival of a military unit depends to a great extent on its ability to defeat enemy armor and field fortifications. Substantial improvements in the effectiveness of armor and fortifications to withstand exploding munitions has occurred. Reinforced structures are generally designed to deflect the explosive force of a munition away from a target, or to absorb part of the destructive force as a way to dissipate the damaging effects of the munition. Munitions with a delayed warhead detonation, after target impact, have increased effectiveness in damaging or destroying the target. 
     The delayed timing of an exploding munition, after impact, may be required for several reasons. The purpose of the delay is to produce the greatest target effect or efficiency from the warhead. Some munitions penetrate the target without detonating and then function once inside. Other munitions utilize timing between multiple warheads to create the greatest effect against armor. 
     In addition to delayed timing, target discrimination is an important factor to produce the optimal penetration. Target discrimination has been under continuous development. One such development includes a bunker defeat munition (BDM), which is a shoulder-fired munition that is capable of discriminating between two targets. These targets are classified as either soft or hard, (i.e., sand or armor) to set a detonation delay time. 
     Reference is made to U.S. Pat. No. 8,091,478 that describes an exemplary BDM discrimination method, and which is incorporated herein by reference. The BDM discrimination algorithm samples the state of an acceleration switch during a target impact. Following a predetermined sample period, a circuit determines if the majority of samples were logic high or logic low and uses that determination to set an appropriate detonation delay time. The BDM algorithm uses a binary signal from the switch to decide between two outcomes or two target types. 
     Although this BDM technology has proven to be useful, it would be desirable to present additional improvements. In particular, it would be useful to autonomously discriminate between more than two discrete target media in order to increase munition effectiveness against a wide range of targets. 
     There is therefore a need for a target discriminating algorithm, which can be implemented into a munition, for use against military operations in urban terrain (MOUT) targets, including but not limited to earth and timber bunkers, triple brick walls, double reinforced concrete, and armored targets. The need for such a target discriminating algorithm has heretofore remained unsatisfied. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the challenges of the conventional target discrimination method for munition fuzing, and presents a new target discrimination method for use against multiple discrete targets, including but not limited to earth and timber bunkers, triple brick walls, double reinforced concrete, and armored targets. 
     In one exemplary embodiment, the autonomous target discrimination algorithm is used in conjunction with a dual warhead munition architecture. This dual warhead configuration includes a forward “precursor” warhead and a secondary “bash-through” warhead. 
     The fuzing system of the dual warhead munition includes at least one fuze per warhead. In the description of the exemplary embodiment, a precursor fuze is associated with the forward precursor warhead, and a bash-through fuze is associated with the rear bash-through warhead. 
     Upon projectile impact with the target, the precursor fuze causes the precursor warhead to detonate. The precursor warhead detonation and subsequent bash-through warhead impact event provide a stimulus to the bash-through fuze. This stimulus is used by the bash-through fuze to set a detonation delay time unique to the target impact event. 
     The dual warhead architecture contributes to a series of stimuli that can be used to build capability into the fuzing system. The first recognizable impulse is the initial impact of the projectile (precursor warhead) on the target. This initial impact event is present whether the munition architecture contains a single or dual warhead. 
     The second event is the detonation of the precursor warhead. This second event, while present in a dual warhead configuration, may not be available in differing munition architectures. In the case of a single warhead, the initial impact event can be substituted. 
     The third event is the bash-through warhead target impact. 
     The final stimulus, or impact event is the bash-through warhead detonation. This fourth event, while not used in the current description, could be utilized to include increased capability into the present discrimination algorithm. The present discrimination algorithm is executed during the time period starting with the precursor warhead target impact event and completing before the bash-through warhead detonation event. 
     Although the present invention will be described in connection with a dual warhead architecture, it should be understood that the present invention is applicable to a singular (e.g., bash-through) warhead, and could function independently in the absence of a precursor warhead. 
     To this end, the present method can be used in a munition having a singular warhead, to provide autonomous target discrimination. The method includes the step of sensing an impact between the munition and the target. Upon sensing the impact, the present method allows the munition to break through the target. The present method further uses the impact and the penetration of the munition as stimuli to concurrently monitor a combination of states of a plurality of switches, and to set a selective detonation delay of the munition for providing increased performance behind the target. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention. The embodiments illustrated herein are presently preferred, it being understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown, wherein: 
         FIG. 1  is an isometric view of an exemplary target discriminating munition for use against military operations in urban terrain (MOUT) targets, including but not limited to earth and timber bunkers, triple brick walls, double reinforced concrete, and armored targets, according to the present invention; 
         FIG. 2  is a cross-sectional view of the munition of  FIG. 1 , illustrating the use of a multi-warhead, multi-fuze architecture utilized in the development of the present invention; 
         FIG. 3  is a block diagram of a high-level architecture of a precursor fuze circuitry, forming part of the multi-warhead, multi-fuze architecture of  FIG. 2 ; 
         FIG. 4  is a block diagram of a high-level architecture of a bash-through fuze circuitry, forming part of the multi-warhead, multi-fuze architecture of  FIG. 2 ; 
         FIG. 5  is comprised of  FIGS. 5A and 5B , and represents a flow chart illustrating the method of operation of a munition utilizing the target discriminating algorithm and architecture of  FIGS. 1 through 4 ; and 
         FIG. 6  is a graph illustrating target impact deceleration data utilized by the autonomous target discrimination algorithm, according to the present invention. 
     
    
    
     Similar numerals refer to similar elements in the drawings. It should be understood that the sizes of the different components in the figures are not necessarily in exact proportion or to scale, and are shown for visual clarity and for the purpose of explanation. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to  FIGS. 1 and 2 , the present invention utilizes an exemplary multi-warhead, multi-fuze, target discriminating munition  100 , illustrated herein as a projectile, for use against military operations in urban terrain (MOUT) targets  200 , including but not limited to earth and timber bunkers, triple brick walls, double reinforced concrete, and armored targets, according to the present invention. 
     The munition  100  generally includes a plurality of interconnected sections: a tail for tail section)  111 , a rear body  120 , a main body  130 , and a nose cone  150 . The tail  111  generally includes a plurality of fins and possibly a tail boom, as is known in the field. As a result, the tail  111  will not be described in greater detail. Similarly, the nose cone  150  is known in the field and will not be described herein in detail. The outer shape of the nose cone  150  is selected to maintain standard aerodynamic properties. 
     According to a preferred embodiment of the present invention, the munition  100  comprises a precursor warhead  220  (also referred to herein as forward warhead) and a bash-through warhead  222  (also referred to herein as rear warhead). It should however be understood that the munition  100  does not necessarily require dual warheads and could include a larger number of distributed warheads or a single warhead. 
     In this exemplary embodiment, the precursor warhead  220  is the nose cone  150  that impacts the MOUT target  200  before the bash-through warhead  222 . The bash-through warhead  222  is comprised of the rear body  120  and the main body  130 . 
     The precursor warhead  220  is designed to pre-damage the target  200 . The bash-through warhead  222  is designed to penetrate through the damaged target  200  and to detonate after a predetermined delay. 
     Upon impact of the munition  100  with the target  200 , the precursor fuze  240  causes the precursor warhead  220  to detonate. Based on the data collected from the impact of the precursor warhead  220  with the target  200 , the detonation of the precursor warhead  220 , and the impact of the bash-through warhead  222  with the target  200 , the bash-through fuze  242  sets an appropriate detonation delay time for the bash-through warhead  222 . 
     The present dual warhead architecture contributes to a series of stimuli that can be used to build capability into the fuzing system. The first recognizable impulse is the initial impact of the precursor warhead  220  on the target  200 . This event is followed by the detonation of the precursor warhead  220 . Following the latter detonation is the impact of the bash-through warhead  222  with the target  200 . The next stimulus is the detonation of the bash-through warhead  222 . The discrimination algorithm that forms part of the fuzing system is executed during the time period between the precursor warhead  220 /target  200  impact event and the bash-through warhead  222  detonation event. 
     Having summarily described the general mode of operation of the munition  100 , the design and operation of the munition  100  will now be described in more detail. 
       FIG. 3  is a block diagram of a high-level architecture of a precursor fuze circuitry  300  of the precursor fuze  240 . The precursor fuze circuitry  300  generally comprises a power regulator  310 , a source of unregulated input power  320 , a microcontroller  330 , a MEMS G-switch  360 , and a pair of firing capacitors for the piston actuator  370  and the detonator  380 . 
     The precursor fuze circuitry  300  generates an output to a piston actuator  340  and an output to a detonator  350 . The power regulator  310  controls the level of the power delivered to the microcontroller  330 . The microcontroller  330  stores a logic or a software application for authorizing the delivery of the output control signal to the piston actuator  340  included in a safe and arm mechanism (S&amp;A), in order to arm the S&amp;A mechanism. 
     Additionally, the microcontroller logic controls the delivery of the output control signal to the detonator  350  of the S&amp;A mechanism, in order to detonate the precursor fuze  240 . 
     In addition, the microcontroller  330  receives as input, a status signal from the MEMS G-switch  360 , in order to initiate the output to the piston actuator  340  after setback and to initiate the output to the detonator  350  on target impact, as it will be explained later in connection with  FIG. 5 . The MEMS G-switch  360  has a high natural frequency and a small distance that the MEMS G-switch  360  contact must travel during operation. This affords the MEMS G-switch  360  a fast response time under high frequency stimuli. For this reason, the MEMS G-switch  360  is used to sense the projectile initial impact with the target  200 , as it will provide a very fast response. 
       FIG. 4  is a block diagram of a high-level architecture of a bash-through fuze circuitry  400 , forming part of the bash-through fuze  242 . The bash-through fuze circuitry  400  generally comprises a power regulator  410 , an unregulated power supply  420 , a microcontroller  430 , an autonomous target discrimination algorithm (or computer program product)  444 , a MEMS G-switch  460 , a conventional G-switch  470 , an impact switch  480 , and a pair of firing capacitors for an output to a piston actuator  440  and an output to a detonator  450 . 
     The bash-through fuze circuitry  400  generates the output to the piston actuator  440  and the output to the detonator  450 . The power regulator  410  controls the level of the power delivered to the microcontroller  430 . The microcontroller  430  stores a logic or a software application for further authorizing the delivery of an output control signal to a piston actuator of the safe and arm mechanism (S&amp;A), in order to arm the S&amp;A mechanism. 
     Additionally, the microcontroller logic controls the delivery of the output control signal to the detonator  450  of the S&amp;A mechanism, in order to detonate the bash-through fuze  242 . 
     The microcontroller  430  receives as input, a status signal from each of a MEMS G-switch  460 , a conventional G-switch  470 , and an impact switch  480 , that form part of the bash-through fuze  242 , in order to implement the autonomous target discrimination algorithm, as it will be explained later in connection with  FIG. 5 . While the switch or sensor  470  is referred to herein as “conventional G-switch,” it should be understood that this reference is used for clarity of illustration of the present invention, and does not limit the use of the present invention to conventional switches. The conventional G-switch  470  can alternatively be referred to as a 6000 G-switch, or high acceleration switch, as the algorithm can be modified as required by adjusting the threshold value of the conventional G-switch  470 . 
     The conventional G-switch  470  has a lower relative natural frequency than that of the MEMS G-switch  360 , and requires that a larger relative distance for the conventional G-switch contact to travel during operation. This affords the conventional G-switch  470  a higher trigger threshold and filtering when exposed to high frequency stimuli. For this reason, the conventional G-switch  470  is used to sense the target penetration, as it requires more energy to trigger. 
     The microcontrollers  330  and  430  comprise a commercially available microcontroller. In one embodiment, the software application or program that controls the operation of the munition  100  is stored on the microcontrollers  330  or  430 . Alternatively, the target discrimination application may be hardware, software, or firmware on any integrated or discrete circuitry, or may comprise a similar analog logic with associated hardware. 
     The use and operation of the munition  100  will now be described in more detail, in connection with  FIGS. 5 and 6 .  FIG. 5  includes  FIGS. 5A and 5B , and represents a flow chart that illustrates a method (or process) of operation  500  of the target discriminating munition  100  of  FIGS. 1 through 4 . 
       FIG. 6  is a graph illustrating target impact deceleration data utilized by the autonomous target discrimination algorithm, as it will be described later in more detail. Graph  600  shows three plots  610 ,  612 ,  614  that respectively represent illustrative behaviors of three exemplary MOUT targets  200 . Plot  610  illustrates the behavior of a masonry target; plot  612  illustrates the behavior of an armor target; and plot  614  illustrates the behavior of a sand target. For the purpose of clarity and brevity, the present process  500  will be described in connection with plot  612 . 
     At step  505  of  FIG. 5A , the process  500  is initiated with the application of unregulated input power  320 ,  420 , to both the precursor fuze  240  ( FIG. 3 ) and the bash-through fuze  242  ( FIG. 4 ), respectively. Each of the precursor fuze  240  and the bash-through fuze  242  functions independently (i.e., charging, sensing launch, arming, etc.) beginning at step  505 . 
     A setback event  510  resulting from the launch is sensed by a temporary closure of the Micro Electro Mechanical Systems (MEMS) G-switches ( 360  of  FIGS. 3 and 460  of  FIG. 4 ). At steps  520 ,  522 , and following a predetermined brief delay  512  [e.g., in the range of approximately 50 ms to allow the MEMS G-switches ( 360   FIGS. 3 and 460   FIG. 4 ) to relax and return to the open state] from the onset of the setback event  510 , the microcontrollers ( 330  of  FIG. 3, and 430  of  FIG. 4 ) start monitoring the MEMS G-switches ( 360  of  FIGS. 3 and 460  of  FIG. 4 ) for a subsequent change in state initiated by target impact. It should be clear that while exemplary numeral values are provided throughout the present description for illustration purpose, these values are not exclusive, will vary based on munition configuration, and do not in any way limit the present invention to these specific values. 
     If at decision step  520 , the microcontrollers ( 330  of  FIG. 3, and 430  of  FIG. 4 ) determine that the MEMS G-switches ( 360  of  FIGS. 3 and 460  of  FIG. 4 ) remain opened, and thus do not detect a change in state, the microcontrollers ( 330  of  FIG. 3, and 430  of  FIG. 4 ) continue monitoring the MEMS G-switches ( 360  of  FIGS. 3 and 460  of  FIG. 4 ), until a change in state is detected by the microcontrollers ( 330  of  FIG. 3, and 430  of  FIG. 4 ). It should be reiterated that the response of the MEMS G-switches ( 360  of  FIGS. 3 and 460  of  FIG. 4 ) are completely independent of one another, as well as the associated responses of the microcontrollers ( 330  of  FIG. 3, and 430  of  FIG. 4 ). 
     Upon target impact of the precursor warhead  220 , the MEMS G-switches ( 360  of  FIGS. 3 and 460  of  FIG. 4 ) will change state (i.e., close). The change of state will be detected by the microcontrollers ( 330  of  FIG. 3, and 430  of  FIG. 4 ) at step  525  of the process  500 . Furthermore, and with reference to plot  612  of graph  600  ( FIG. 6 ), the initial impact of the precursor warhead  200  with the target  200  is shown as peak  605 . 
     The initial precursor target impact  525  is followed by the detonation of the precursor warhead  220  at step  530  of  FIG. 5A , and as further illustrated by peak  625  of the plot  610  ( FIG. 6 ). The detonation of the precursor warhead  220  damages the MOUT target  200 , in preparation for the penetration of the bash-through warhead  222 . 
     With further reference to  FIG. 5B , once the initial precursor warhead target impact event  525  is sensed, the autonomous target discrimination algorithm  444  ( FIG. 4 ) residing on the microcontroller  430  uses both the initial impact event  525  and the detonation of the precursor warhead  530  as stimuli to start two concurrent functions  532 ,  534 . Depending on the performance of the precursor warhead  220  on the target  200 , the bash-through warhead  222  may or may not penetrate the target  200 . The munition  100  does not classify the actual material or construction of the target  200 . Rather, it uses the ability of the bash-through warhead  222  to penetrate the target  200  for timing the detonation of the bash-through warhead  222 . 
     The first function that is initiated by the microcontroller  430  is the commencement of a delay counter at step  532 . In this illustration, an exemplary delay of approximately 750 μs is set at step  532 . As stated earlier, the numerical value of this delay could be modified to any acceptable level, depending on the target signature characteristics. The purpose of this delay is to prevent the microcontroller (or microprocessor)  430  from discriminating the high frequency impact signature. 
     With reference to plot  610  of graph  600  ( FIG. 6 ), this delay is shown as a vertical dashed line  672 . 
     According to the second function  534 , the impact switch (also referred to herein as hard target impact switch or sensor)  480  ( FIG. 4 ) is monitored by the microcontroller  430  for a change in state. The impact switch  480  is designed to open (change of state from high to low), when a threshold acceleration level is exceeded in a specific direction, for example when impact occurs with a heavy armor target, or upon an impact event that causes the bash-though warhead  222  to break apart. The hard target impact switch bypasses the target detection logic and forces detonation of the bash-through warhead  222  on impact, in order to prevent the breakup of the bash-through warhead  222  on heavy armor targets  200 . 
     If the bash-through impact event  531  causes the impact switch  480  to open as determined at decision step  534  of process  500 , then the microcontroller  430  causes the bash-through warhead  222  to detonate immediately at step  535 , on the premise that the MOUT target  200  is not penetrable by the munition  200 . 
     If, however, the bash-through impact event  531  does not cause the impact switch  480  to change state (i.e., to open) as determined at decision step  534 , then process  500 , proceeds to decision step  540 , at the end of the delay period  532 . In other terms, the vertical line  672  ( FIG. 6 ) denotes the initiation of the final determination for the timing of the bash-through warhead  222  detonation. 
     Returning to decision step  540 , the microcontroller  430  inquires if the state of the conventional G-switch  470  is low or high. At this time the impact switch  480  could be disabled by the microcontroller  430 . However, the impact switch  480  could remain enabled if it is determined (or expected) that a secondary hard target event could occur after the initial impact. 
     If at decision step  540  the microcontroller  430  determines that the conventional G-switch  470  has opened (its state is now low), then the microcontroller  430  will cause the bash-through warhead  222  to detonate at step  545  on the premise that the target is not a hard target, and that it has already been penetrated by the munition  100 . Alternatively, the detonation could be scheduled to occur after a short delay, for example in the range of approximately 15 to 25 μs. Such a model will be experienced during an impact with a thin, light target such as plywood, drywall, or glass. 
     If, however, at decision step  540  the microcontroller  430  determines that the conventional G-switch  470  remains closed (its state is still high), then the microcontroller  430  will concurrently schedule a timeout following a predetermined period of time, such as 40 msec, and will also start monitoring the state of the conventional G-switch  470  at step  550 . 
     To this end, the microcontroller  430  uses a preset minimum threshold to decide whether or not the bash-through warhead  222  has penetrated the target  200 . This minimum threshold is denoted by a horizontal line  674  in  FIG. 6  and is set by the threshold trigger level of the conventional G-switch  470 . For illustration purpose only, the threshold for this specific embodiment is set at approximately 6,000 Gs. The microcontroller  430  sets a decision logic feedback loop that is executed between the conventional G-switch  470  and the microcontroller  430 . 
     More specifically, if at decision step  555 , the process  500  determines that the timeout has been reached, even without a change of state of the conventional G-switch  470 , then the microcontroller  430  will cause the bash-through warhead  222  to detonate at step  556 , on the premise that the target is soft by comparison and that the munition has sufficiently buried to allow for efficient function. 
     If however, at decision step  555  the microcontroller  430  determines that, during the current monitor loop, the timeout has not been reached, then the microcontroller  430  inquires at step  557  if the state of the conventional G-switch  470  is low (open) or high (closed). If the state is high, then the microcontroller  430  determines that the minimum threshold  674  ( FIG. 6 ) has not been crossed, and continues to monitor the state of the conventional G-switch at step  550 , as well as the time that it has been looping at step  555 . 
     The process  500  will continue this monitoring loop until the first of two conditions is met: either the conventional G-switch opens (step  560 ), or the timeout has been reached (step  556 ) as explained earlier. Upon determination at step  557  that the state of the conventional G-switch  470  is low (open), then the microcontroller  430  determines that the bash-through warhead  222  has penetrated the target  200 , at step  560 , and sets a predetermined delay at step  565 , prior to detonation at step  570 . 
     With reference to  FIG. 6 , a penetration point  670 , which is the intersection of plot  612  and the minimum threshold line  674 , denotes such penetration of the bash-through warhead  222  through the target  200 . For illustration purpose only, the penetration point  670  occurs after approximately 1.25 msec from the initial precursor warhead/target impact event  525 . 
     The setting of the delay at step  565  is intended to ensure that the bash-through warhead  222  has sufficiently penetrated the target  200  prior to detonation. In this embodiment, the delay is set to approximately 12 ms, although other values can alternatively be used. 
     In this particular embodiment of the munition  100 , the combination states of the impact switch  480  and the conventional G-switch  470 , identifies a total of six targets including but not limited to a hard target/projectile breakup ( 535 ), plywood/drywall/glass target ( 545 ), light armor ( 570 ), triple brick wall/concrete ( 570 ), earth and timber bunker ( 570 ), and circuit timeout ( 556 ). 
     It should be understood that other modifications might be made to the present munition design without departing from the spirit and scope of the invention.