Patent Publication Number: US-7219589-B2

Title: Bomb fuze event instrumentation

Description:
FIELD OF THE INVENTION 
   This invention relates generally to event detection instrumentation and, more particularly, to instrumentation for detecting the command to initiate a fuze of an air-to-surface weapon. 
   BACKGROUND OF THE INVENTION 
   During the development of the Joint Direct Attack Munition (JDAM) a need arose to precisely determine when the munition&#39;s fusing mechanism under test generated a firing command to trigger the warhead of the weapon. Since the tested weapons were outfitted with inert warheads, a non-explosive method was required to demonstrate fuze functionality. 
   JDAM weapons are designed to be carried aloft while attached to a store point of an aircraft or in the aircraft&#39;s bomb hold. Each JDAM includes an unguided (i.e. “dumb”) bomb and a kit attached thereto that includes a Global Positioning System (GPS) based guidance subsystem. The guidance subsystem includes adjustable fins, actuators, a processor, and other associated components that convert the bomb to a guided (i.e. “smart”) weapon. Service personnel typically load the JDAMs on to the aircraft hours before the intended use of the weapon. At some time prior to release, the GPS coordinates of the intended target are loaded into the guidance system. The aircraft then flies to the vicinity of the target and releases the weapon at a location that is pre-calculated to allow the weapon to fall toward the target. While the JDAM is falling, the guidance system adjusts the trajectory of the weapon to cause it to strike the target with little, or no, positioning error. At a pre-selected altitude nearly coincident with the weapon&#39;s impact, the fuze receives a signal from an on-board DSU-33 (radar altimeter) that indicates that the desired height above the ground has been achieved and the fuze under test initiates the fire signal to a “simulated” explosive charge. The fuze initiates upon receiving the command from the DSU-33 and, if explosives are included in the warhead, triggers the explosive material. Because the bomb typically falls at a speed approaching Mach 1, the pre-selected altitude allows the explosion to propagate through the explosive material in such a manner as to cause the weapon to explode within a short distance from the target. Thus, the JDAM kit allows the user to convert an unguided weapon to a low cost guided weapon with precision strike capabilities. Such precision strike weapons guidance subsystems are available from the Boeing Company of Chicago, Ill. 
   To keep unit costs low, and to avoid undesirable modifications of the associated aircraft (e.g. the addition of a power umbilical), the JDAM is designed to be self sufficient, particularly with regard to power. Thus, each JDAM includes a 28-volt thermal battery to power the guidance subsystem. Because it is likely that the JDAMs will be stored on the aircraft for many hours prior to their use, the power supplied by the thermal battery must be reserved for the guidance system. 
   Nonetheless, it is still necessary to know within about 1 foot of altitude when the fuze commands the detonation to determine the reliability of the fuze, particularly with regard to the timing of the explosion vis-a-vis the approach of the weapon to the target. Thus, a telemetry system is typically added to the test JDAM to transmit the weapon fuze command, engineering information, and other data to the test data system. Unfortunately, as the JDAM nears the ground, the telemetry signal reflects off of the ground and structures thereabout. These reflections interfere with the original signal and therefore cause loss of the transmitted data. The transmitted fuze command suffers disproportionately from this interference because it typically occurs within a few feet of the ground where such multi-path interference is most severe. Thus, a need exists to reliably and precisely determine when and where the fuze command occurred even with the presence of multi-path interference with the telemetry signal. 
   SUMMARY OF THE INVENTION 
   It is in view of the above problems that the present invention was developed. The invention provides systems and methods for determining when a transient electronic event occurs on a mobile platform. More particularly, the invention provides systems and methods for determining when a fuze command occurs on a weapon. 
   In a first preferred embodiment, a flash assembly is provided for indicating when a transient electronic event occurs on a mobile platform and is recorded by an optical motion recording device. Herein, the term “mobile platform” refers to apparatus for transporting payloads such as people or cargo (e.g. a warhead). Thus, for example, aircraft, weapons, and projectiles are included in the term “mobile platform.” The assembly includes a housing and a flash-producing device that communicates with the mobile platform and produces a flash approximately when the event occurs. The housing couples to the body of the mobile platform and contains a flash-producing device in such a manner that the flash is observable. Preferentially, the assembly also includes a faceplate that couples to the housing and maintains an aerodynamic profile associated with a surface of the body. In another preferred embodiment, the assembly is adapted for use with a JDAM weapon and the event is the occurrence of the weapon&#39;s fuze command. The optical recording device (e.g. motion picture camera or video camera) preferentially has a shutter speed fast enough to record the occurrence of the event within the desired accuracy. 
   The present invention also provides a mobile platform including a flash-producing assembly thereon. The flash assembly communicates with the fuze command and is triggered to flash when the fuze command occurs. In a preferred embodiment, six flash assemblies positioned around the circumference of the weapon are wired in parallel. Thus, a single optical recording device can record the event despite the orientation of the weapon when the command occurs. 
   More particularly, each of the flash assemblies includes a housing that is adapted to be inserted into the body of the weapon. A preferred embodiment provides a warhead component of a JDAM weapon that has been modified to accept the flash assemblies. Likewise, the warhead component is adapted to receive a battery assembly (e.g. a 1.2 VDC battery), a fuze command distributor assembly, and a set of cables to connect them to the flash assemblies. In operation, the distributor accepts power from the battery and passes it to the flash assemblies. Additionally, the distributor accepts the fuze command from the weapon, amplifies it, and fans it out to the flash assemblies. In another preferred embodiment, the distributor, (preferentially a low current device) communicates with the 28 volts-direct current (VDC) thermal battery of the weapon, but only to sense the status of the weapon for switching the 1.2 VDC flash subsystem battery power on and off. Thus, the flash assemblies draw power only from the 1.2 VDC battery provided herein. 
   In yet another preferred embodiment, a flash assembly is provided. The flash assembly includes a capacitor, a voltage comparator, an oscillator, a switch, an opto-isolator, and a flash tube. The assembly is connected to a 1.2 VDC battery via an external cable set and a fuze command distributor. The battery power flows first to the oscillator where it is stepped up in voltage and then it flows to the capacitor. When the opto-isolator receives the fuze command it is configured to trigger the flash tube thereby discharging the capacitor. Thus, the assembly produces an external indication (a flash) that the fuze command has occurred. Preferably, the voltage comparator communicates with the capacitor to sense the voltage there across. The comparator also communicates with the switch to control the flow of low voltage current to the oscillator. Thus, when the comparator senses that the charge on the capacitor has partially dissipated, the comparator drives the switch to cause the oscillator to re-charge the capacitor. When the capacitor is fully charged the comparator switches the charging circuit off. Thus, weapons constructed in accordance with the current embodiment possess the ability to conserve the power stored by the low voltage battery. Because of this power-saving feature, the present invention provides subsystems that may operate for periods up to about eight hours without requiring a new (or re-charged) battery. 
   Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and together with the description, serve to explain the principles of the invention. In the drawings: 
       FIG. 1  illustrates a weapon constructed in accordance with a preferred embodiment of the present invention; 
       FIG. 2  illustrates a perspective view of the weapon of  FIG. 1 ; 
       FIG. 3  illustrates a schematic of a preferred embodiment of the present invention; 
       FIG. 4  illustrates a schematic of another preferred embodiment of the present invention; 
       FIG. 5  illustrates a schematic of yet another preferred embodiment of the present invention; and 
       FIG. 6  illustrates a flash assembly constructed in accordance with a preferred embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to the accompanying drawings in which like reference numbers indicate like elements.  FIG. 1  illustrates a weapon constructed in accordance with a preferred embodiment of the present invention. 
     FIG. 1  shows an aircraft  10  after releasing a weapon  12  at a target  14 . The weapon  12  falls through the positions where it is designated as  12 ,  12 ′, and  12 ″ for the purpose of destroying the target  14  with an explosion  16 . A telemetry stream  18  transmitted from the weapon  16  to a receiver  20  is also shown schematically along with a nearby structure  22 . The structure  22  and ground create reflections  24  of the telemetry signal  18 , the receipt of which by the receiver  20  interferes with the proper receipt of the original telemetry signal  18 . Thus, the reliability of the telemetry signal degrades as the bomb moves toward the ground and the structures  22 . 
   To cause the explosion  16  to occur at an optimal time, the weapon  12  generates an internal fuze initiation command when the weapon  12  passes through the location at a distance d 1  from the target  14 . The distance d 1  is pre-selected such that the subsequent propagation of the explosion  16  through the warhead occurs while the weapon  12  falls through the distance d 1 . When the weapon is configured to test fuzes (i.e. the weapon includes flash assemblies  26  and an inert war head), a signal from the fuze as the weapon passes d 1  causes the flash assembly  26  to illuminate. A high speed film or video camera records the event. Depending on the characteristics of the weapon  12  and the target  14 , the explosion  16  may be timed to occur above, at, or below the surface of the target  14 . Therefore, the location/altitude of the explosion  16  is critical and must be known with great accuracy (for example, within one foot or 0.001 seconds of its occurrence). In the presence of the reflections  24 , such stringent accuracy may not be guaranteed by the telemetry system. Further, because the command (or at least the leading edge) is a transient electronic event that is internal to the weapon, no indication of its occurrence may be available if the telemetry signal fails. 
   With reference now to  FIG. 2 , a perspective view of the weapon  12  is illustrated. The weapon  12  includes a plurality of flash assemblies  26 , an inert warhead  30 , a JDAM kit  32  that includes a tail section  34  with fins  36 , a battery  38 , a fuze command distributor  40 , and a set of cables  42  and  44  (shown with cowlings providing mechanical protection and streamlining thereto). The weapon  12  also includes a proximity/radar altimeter  37 , a fuze initiator  39 , and a fuze  41  (which may be, respectively, a DSU-33 proximity/radar altimeter  37  and a FZU-55 fuze initiator). The inert warhead  30  (used for test purposes), preferably does not contain a charge of explosive material. The JDAM kit  32  couples to the aft end of the inert warhead  30 . Within the JDAM kit  32 , a GPS guidance system receives GPS signals and accurately determines the current location of the weapon  12 . The JDAM kit  32  also contains a processor and memory such that the guidance subsystem knows the GPS coordinates of the target and the flight control characteristics of the weapon  12  thereby enabling the JDAM kit to fly the weapon to the target. The JDAM kit also provides power to the telemetry system. Around the outer circumference of the inert warhead  30 , the flash assemblies  26  are spaced apart and positioned to be visible to observers. The tail section  34  is located at the aft end of the JDAM kit  32  and holds the fins  36  in adjustable relation to the weapon  12  for controlling the trajectory of the weapon  12 . 
   Additionally, the inert warhead  30  shown is modified to include an aperture  27  with a recess  29  around the outer end of the aperture  27 . The flash assembly  26  includes a flange  291  (see  FIG. 6 ) extending from a faceplate  233  and that is adapted to fit within the recess  29 . A pair of conventional fasteners  235  is also shown for securely coupling the flash assembly  26  to the inert warhead  30 . 
   In operation, the battery  38  supplies power to the distributor  40  via cable  42 . The distributor  40  allows the power to flow through cable  44  to the flash-producing devices  26  to keep a sufficient charge stored therein for powering the flash (as will be discussed in detail). The processor continuously computes the trajectory necessary to cause the weapon  12  to fall to the target based on the current location of the weapon  12  and the flight characteristics of the weapon  12 . If the weapon&#39;s trajectory begins to deviate from that necessary to strike the target, the processor adjusts the position of the fins  36  to correct for the error. This self-guiding capability is particularly useful on weapons  12  because it allows the weapon  12  to possess precision strike capabilities at low cost. Some time prior to approaching the target  14 , the initiator  39  arms the fuze  41 . As the pre-selected distance d 1  is reached, the altimeter  37  signals the initiator  39 . The initiator  39 , upon sensing the signal, commands the fuze  41  to initiate. In turn, the fuze  41  triggers the warhead  30 . For live warheads, the resulting explosion is timed to maximize damage to the target  14 . But for fuze tests, the warhead  30  is inert. Thus, the distributor  40  is configured to receive the fuze fire signal, amplify it, and pass it on to the flash assemblies  26  with no appreciable delay. The distributed fuze command then communicates through the cable  44  and triggers the flash assemblies  26  which a high speed camera  15  (see  FIG. 1 ) records for determining when the flash occurred. From the occurrence of the fuze command to full flash brilliance less than about 160 microseconds passes. At the speed of the weapon, this time is acceptable for meeting the accuracy requirements of the test. 
   With reference now to  FIG. 3 , the interconnecting wiring of an event detection subsystem  110 , that is constructed in accordance with the principles of the present invention, is shown. The subsystem  110  includes a plurality of flash-producing devices  126 , a low voltage battery  130 , and a fuze command and power distributor  140 . A cable  142  provides a path for the power from the battery  130  to reach the distributor  140 . Another cable  144  provides connectivity between the distributor  140  and the flash assemblies  126 . The distributor includes a number of interfaces to the other cooperating components to form the subsystem  110 . First, the cable  142  connects to a low voltage power input  150  for accepting power from the battery  130 . Likewise, the command from the fuze enters the distributor  140  at a command (or event) input  152 . In a preferred embodiment, the distributor  140  is configured to accept the fuze command from either of two sources via a three pin interface  152 . Opposite the inputs  150  and  152 ,  FIG. 3  shows at least one fuze command output  154  and at least one low voltage power output  156 . These are shown being connected to the cable  144 . Thus, when a flash assembly  126  needs to re-charge, it draws power from the battery  130  through the distributor  140 , as shown. Similarly, the fuze command reaches the flash assemblies  126  via the distributor  140 . 
   Another output  160  is shown for communicating the distributed fuze command to the weapon&#39;s data and telemetry subsystem. Preferably, the distributor  140  also includes an input  158  through which the distributor  140  senses whether the weapon is active by the presence of the weapon&#39;s 28 VDC power supply. 
   With reference now to  FIG. 4 , an internal schematic of a preferred distributor  140  is shown. The distributor  140  includes a voltage regulator  162 , a pair of FET transistors  164 , a timer  166 , and a capacitor  168 . When connected as shown, transistors  164  sense whether the weapon is active by determining whether the weapon&#39;s 28 VDC power is present. The purpose of the power sensing section of the distributor  140  is to allow power to pass from the battery input  150  to the low voltage output  156  if the weapon is active (i.e. powered). If the weapon is not active (i.e. un-powered) then no low voltage power is allowed to flow from the battery  130  to the flash assemblies  126 . Thus, the power from the low voltage battery  130  is conserved while the weapon is inactive. Meanwhile, the voltage regulator  162  serves to create 5V to power the fuze detection circuitry and signals to the flash assemblies. 
   In the other portion of the schematic of  FIG. 4 , the fuze command input  152  accepts the fuze command and is connected to the timer  166 . Preferably, the fuze command input  152  includes provisions to accept both a command that transitions from a “low” condition to a “high” condition and a command that transitions from high to low to initiate the fuze. As shown, either type of command triggers the timer  166  with one input, here  152 B being inverted prior to triggering the timer  166 . In addition to being triggered by the fuze command input  152 , the output of the timer  166  is connected to the fuze command output  154  and telemetry output  160 . Preferably capacitors, such as capacitor  168 , are included in the distributor to prevent transients from triggering the timer  166 . Thus, upon receipt of a fuze command, the timer  166  outputs a pulse of a pre-selected length that is communicated to the fuze command outputs  154  and telemetry output  160 . 
     FIG. 5  illustrates a schematic of a flash assembly  126  constructed in accordance with another preferred embodiment of the present invention. The flash-producing device  126  includes a low voltage power input  170 , a fuze command input  171 , a comparator  172 , a high frequency switch  174 , a transformer  176 , a diode  177 , an indicator  178 , three capacitors  180 , a flash tube  182 , a flash tube trigger  184 , and an opto-isolator  186 . As shown, the comparator  172  is configured to sense the voltage stored on the capacitors  180  and to control the switch  174 . The switch  174 , the transformer  176 , and the diode  177  are configured as an oscillator  179  connected between the low voltage power input  170  and the capacitors  180 . Of course, the flash tube is connected in parallel with the capacitors  180 . In another portion of  FIG. 4 , the distributor  140 , the opto-isolator  186  provides a communication path between the fuze command input  171  and the flash tube trigger  184  as shown. 
   In operation, the comparator  172  determines when the voltage across the capacitors  180  has decreased to a pre-selected amount indicative of a partial discharge of the capacitors  180 . When the voltage is low, the comparator  172  biases the switch  174  to an “on” condition, thereby causing the oscillator  179  to generate a pulse of high voltage current that replenishes the charge stored on the capacitors  180 . Thus, the oscillator  179  steps up the low voltage current from the battery to the operating voltage of the flash tube  182 . Preferably, the indicator  178  is configured to produce an observable indication (e.g. a visible neon lamp) when the voltage reaches the minimum operating voltage of the flash tube  182 . When the fuze command arrives from the timer  166  of the distributor  140  (see  FIG. 4 ), the opto-isolator  186  converts the electric pulse to an optically isolated, constant, electric signal that is supplied to the trigger  184 . The trigger  184  steps up the signal from the opto-isolator  186  and causes the flash tube  182  to begin conducting the high voltage charge stored on the capacitor  180 . Thus, the flash-producing device  126  produces an external flash to indicate that the fuze command has occurred. In operation it has been found that subsystems constructed in accordance with the principles of the present invention generate flashes suitable for recording with high-speed cameras within about 159 microseconds of the occurrence of the fuze command. The flash duration (about 0.003 seconds) is long enough to be recorded by a camera at a high frame rate. 
   In another preferred embodiment of the present invention readily available commercial products may be disassembled to obtain the components from which to assemble the flash assemblies  126  disclosed herein. For instance, a flash tube subassembly (including a reflector, a trigger  184 , and a step-up transformer associated with the trigger), an indicator  178 , and transformer  176  may be extracted from a model 887 1428 Single Use camera available from the Kodak Company of Rochester, N.Y. The capacitors  180  are preferably 120 uF, 330 volt, PHOTO-FLASH capacitors available from Rubycon America, Inc. of Gumee, Ill. Preferably, the opto-isolator  186  is a model number H11C6 opto-isolator available from the Digi-Key Corp. of Thief River Falls, Minn. The comparator  172  is preferably a MAX971 CSA comparator available from the Maxim Integrated Products of Sunnyvale, Calif. 
   For the distributor  140  of  FIG. 4 , a preferred embodiment includes components from the following sources. The timer  166  may be a model LMC555CM timer available from the Phillips Semiconductor of Eindhoven, The Netherlands. The voltage regulator  162  may be a model LT1121IZ-5 voltage regulator also available from the Digi-Key Corp. Additionally, the battery  130  may be a model RC-3000HV sub-C, 1.2 volt, high power battery available from the Sanyo Energy (USA) Corporation of San Diego, Calif. While certain components have thus been described, any combination of components suitable for producing a flash or distributing the power or fuze command, as herein described, may be used. With reference now to  FIG. 6 , another preferred embodiment of the present invention is illustrated.  FIG. 6   a  shows a flash assembly  226 , in relation to a weapon warhead, whereas  FIG. 6   b  shoes an exploded view of the flash assembly  226 . The flash assembly  226  includes three capacitors  280 , a flash tube  282 , a printed circuit board  290 , and an adapter  292 . A faceplate  233 , an indicator  278 , a lens  294 , and a housing  296 , are also shown. Generally, the housing  296  contains the other components with the faceplate  233  closing one end of the cylindrical housing  296 . Of the three capacitors  280 , one is positioned in a notch in the printed circuit board  290  and the other two reside adjacent to the circuit board  290 . All three capacitors  280  are electronically connected to the circuit board in accordance with the schematic diagram illustrated by  FIG. 5 . The adapter  292  holds the capacitors  280 , the circuit board  290 , and the flash tube  282  in fixed relation to each other and to the housing  296 . The flash tube  282  and the indicator  278  are, of course, also connected to the printed circuit board  290  in accordance with  FIG. 5 . 
   As shown by  FIG. 6 , the lens  294  fits over the flash tube  282  subassembly and serves to focus and intensify the light generated by the flash tube  282 . When the faceplate  233  is coupled to the end of the housing  296  it holds the flash tube  282 , the lens  294 , and the indicator  278  in fixed relation to each other and the housing  296 . Further, the faceplate  233  ensures that the flash tube  282  and indicator  278  are held in such a manner as to be visible from outside of the housing  296  as well as the aperture  227  of the inert warhead  30 . Additionally, a cable  244  is shown routed from the housing  296 , through the faceplate  233  for connection to a fuze command and power distributor (for example, distributor  140  of  FIG. 4 ). 
   Generally, the flash assembly  226  is adapted to fit within an aperture  227  in the inert warhead  30 . The faceplate  233  of the flash assembly  226  includes a flange  291  that engages a corresponding recess  229  around the top of the aperture  227 . In particular, the oblong faceplate  233  includes a pair of lobes  298  extending from opposite ends of the faceplate  233  to form the flange  291 . Further, when the faceplate  233  abuts the housing  296 , the lobes  298  extend from opposite sides of the housing  296  for engagement with the recess  229  in the weapon. After the flange  291  is seated in the recess  229 , a pair of fasteners  235  is used to securely couple the flash assembly  226  to the inert warhead  30 . Because the lobes  298  rests in the recess  229  the aerodynamic profile of the weapon  12  is maintained. The battery and distributor may also be contained in similar housings with suitable faceplates coupled thereto to further preserve the aerodynamic performance of the weapon. Additionally, cowlings may cover the cables (shown at  42  and  44  in  FIG. 2 ) between the battery, the distributor, and the flash assemblies to provide a flash subsystem compatible with the aerodynamic profile of the weapon. 
   In view of the foregoing, it will be seen that the several advantages of the invention are achieved and attained. A low cost approach to determine the time of a transient event on a mobile platform has been provided. In particular, a flash is produced on the mobile platform to provide an external indication of the time the event occurred. Additionally, the apparatus and methods disclosed herein may operate independently of the mobile platform for up to, and beyond, 8 hours. Thus, the invention requires no power (other than for sensing the status of the mobile platform, if desired) from the mobile platform until it is active, thereby obviating the need for a power umbilical from the mobile platform. 
   The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. 
   As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.