Abstract:
In one aspect, an artillery projectile apparatus is provided that includes a carrier projectile containing a payload, and a fuze disposed at an ogive of the projectile and which is configured to eject the payload when the fuze is detonated. The fuze includes a receiver configured to receive location information from a radionavigation source and a processor configured to acquire position data from the receiver. The processor is also configured to estimate a projectile flight path using the position data, to determine intercept parameters of the artillery projectile relative to an ejection plane of its payload cargo, and to adjust an ejection event initiation command time of the payload in accordance with the determined intercept parameters. In some configurations, the present invention dramatically decreases range errors typically associated with delivering artillery payloads to specific targets.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a low cost munition fuze having increased accuracy, and more particularly to a low cost munition fuze having reduced projectile launch and flight errors. 
   BACKGROUND OF THE INVENTION 
   Studies performed on the long-range accuracy of the current U.S. Army artillery shell stockpile have suggested that at ranges above 20 kilometers, numerous rounds must be fired to achieve a lethal effect on the target. Area saturation can be used to defeat or immobilize a target, at the costs of delaying advancing troops from reaching the target and allowing an enemy some opportunity to evade an assault. Additionally, conventional munition inaccuracies require friendly fire target standoff distances of greater than 600 meters, which prevents suppressive fire in support of target engagement by advancing troops for as much as 20 minutes. 
   Precision weapons are being developed to increase range, to significantly reduce the conventional munition logistic task and to resolve the battle engagement time and mobility issues. However, precision weapons are expensive, and their high accuracy may not be required for conventional munition ranges. 
   SUMMARY OF THE INVENTION 
   Some configurations of the present invention therefore provide an artillery projectile apparatus that includes a carrier projectile containing a payload, and a fuze disposed at an ogive of the projectile and which is configured to eject the payload when the fuze is detonated. The fuze includes a receiver configured to receive location information from a radionavigation source and a processor configured to acquire position data from the receiver. The processor is also configured to estimate a projectile flight path using the position data, to determine intercept parameters of the artillery projectile relative to an ejection plane, and to adjust an ejection event initiation command time of the payload in accordance with the determined intercept parameters. 
   Various configurations of the present invention also provide a method for delivering an artillery projectile payload to a target. The method includes determining a cargo ejection plane between a gun firing the artillery projectile and the target and a nominal ejection event initiation command time to deliver the artillery projectile payload to the target; firing the artillery projectile at the target; acquiring, at the artillery projectile after firing, position and time data; and adjusting, at the artillery projectile after firing, ejection event initiation command time of the artillery projectile payload in accordance with the acquired position and time data. 
   Some configurations of the present invention also provide a fuze that includes a fuze housing; fuze electronics including a processor and a radionavigation receiver contained within the fuze housing; and a power supply configured to power the processor and the radionavigation receiver; an explosive charge responsive to the processor. The processor is responsive to the radionavigation receiver to adjust a time at which the explosive charge is detonated. 
   It will be observed that configurations of the present invention provide a more accurate alternative to conventional munitions systems and a less expensive alternative to precision munitions systems. In some configurations, the present invention contains the artillery fuze functions, is profile-interchangeable with NATO requirements as defined in MIL-Std-333B, and/or incorporates technologically available smart munition updates. 
   Furthermore, it will be observed that some configurations of the present invention provide low cost, mid-range accuracy improvements that can reduce the number of deployed projectiles needed to acquire a target. Some configurations also provide additional cover fire protection to advancing troops by reducing standoff distances and times owing to improved munition accuracies. 
   Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
       FIG. 1  is a cross-sectional drawing representative of various configurations of an artillery projectile of the present invention. 
       FIG. 2  is a partial cross-sectional drawing representative of various configurations of a fuze of the present invention, including a fuze configuration suitable for use in configurations of the artillery projectile represented in  FIG. 1 . 
       FIG. 3  is a drawing showing the relationship of various trajectories and ejection points relative to a nominal cargo ejection plane and a target, where the trajectories intercept the nominal cargo ejection plane at different heights. 
       FIG. 4  is a drawing showing the relationship of various trajectories and ejection points relative to a nominal cargo ejection plane and a target, where the trajectories intercept the nominal cargo ejection plane at different angles. 
       FIG. 5  is a drawing indicating the increased payload delivery accuracy achievable by various configurations of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
   In some configurations and referring to  FIG. 1 , the present invention comprises an artillery projectile  10  that comprises a conventional carrier projectile  11  having a front head part or ogive  12  and a rear base part  14 . Carrier projectile  11  contains one or more payloads such as grenades  18  that are configured to detonate on a target. A fuze  22  is disposed at ogive  12  and is configured to eject the payload when fuze  22  is detonated. In particular, when fuze  22  is detonated, an expanding gas fills a cavity  24  and forces piston  26  to press plate  28  rearward, forcing payload or payloads  18  to push against base  14 . Base  14  is thus forced off carrier projectile  11  and payload or payloads  18  are ejected from projectile  11 . Payload(s)  18  are spin-deployed to control payload dispersion during delivery. The operation and construction of piston  26 , plate  28 , payload  18  and base  14  are conventional and need not be described further. 
   Referring to  FIG. 2 , fuze  22  comprises an outer casing  30 , a fuze setter coil  32 , circuit cards  34 , a power supply assembly including a battery  38 , a safe and arm assembly  40 , and a booster cup  42 . A lead charge  44  is configured to detonate booster pellets  46  in booster cup  42  in response to an ejection command from a processor  48  residing on circuit cards  34 . For safety, the ejection command is preceded by two sensed launch commands in addition to an adjusted firing time command from the processor. Fuze  22  in some configurations is interface-equivalent with MIL-Std-333B specifications. Fuze  22  has screw threads  52  for attachment at ogive  12  of projectile  11 . 
   In some configurations, a global positioning satellite (GPS) receiver  50  is provided in fuze  22  to reduce range errors. Receiver  50  utilizes a ring antenna  36  encircling fuze  22  to receive signals from GPS satellites (not shown). In another embodiment, another GPS-receptive antenna suitable for use with a high-spin-rate projectile could be used. Received GPS data from receiver  50  and time are used by processor  48  to determine a flight trajectory and to adjust payload ejection event initiation command timing for increased range accuracy, for example, by reducing the effects of temperature, gun lay, launch, firing charge, baseburner and projectile flight range errors. In some configurations, to avoid loss of a projectile, processor  48  defaults to a basic M762 fuze mode with fixed ejection times in the event of a GPS subsystem anomaly, such as jamming, inability to acquire satellite transmissions, etc. 
   Under normal conditions, GPS data will be available, and onboard processor  48  will use time data and the acquired GPS position data to calculate a projectile flight path, and to predict an intercept angle, height and time at which artillery projectile  10  will pass through a gun and target-defined ejection plane  62 , as represented in  FIG. 3 . Downrange distance traveled by the payload  18  from an ejection point is a function of the height or elevation of the ejection point. A difference between an actual intercept point and a nominal intercept point  64  of a nominal projectile flight path  68  is determined and utilized to adjust an ejection event initiation command time for ejecting cargo payload (e.g., grenade or other dispensable munitions  18 ). For example, if artillery projectile  10  is more energetic than nominal, it would follow a flight path such as flight path  72 . In this case, the ejection event initiation command time is adjusted so that ejection occurs at a point  74  prior to interception of cargo ejection plane  62  and payload  18  follows path  78 , rather than path  66 , to target  60 . If the projectile is less energetic than nominal, the ejection event initiation command time is adjusted to eject payload  18  at a point  76  after interception of flight path  70  of artillery projectile  10 , and payload  18  follows path  80  to target  60 . These timing adjustments thus effect a more accurate delivery of payload  18  to target  60 . 
   In some configurations, a secondary range adjustment is made by correcting the ejection event initiation command time of payload  18  in accordance with the trajectory slope. More particularly, and referring to  FIG. 4 , if the actual trajectory slope  84  is steeper and the forward or downrange velocity of the cargo at ejection is less than would be the case with a nominal trajectory slope  68 , ejection event initiation command time is delayed so that payload  18  will impact target  60  by ejecting payload  18  at ejection point  86  and payload  18  follows descent path  92 . On the other hand, if the actual trajectory slope  82  is flatter than nominal trajectory slope  68 , the payload will be traveling downrange faster after release than if the payload were following nominal slope  68 . Therefore, the ejection event initiation command time is advanced so that ejection of payload  18  occurs at a point  88  before trajectory slope  82  intersects cargo ejection plane  62 . Payload  18  thus follows a path  90  that allows the payload to travel farther downrange after ejection, and yet still hit at or near target  60 . 
   Referring to  FIG. 5 , by providing a fuze with a first order, or low cost one-dimensional range correction, a footprint representing typical delivery errors to a target  60  is reduced from a footprint  56  representing typical delivery errors in the absence of correction to a reduced size footprint  58  representing the delivery errors of a plurality of artillery projectile configurations and delivery method configurations of the present invention. Configurations of the present invention can be utilized in conjunction with techniques for reducing deflection errors to effect a two-dimensional correction and thus provide additional accuracy. 
   In some configurations of the present invention, power consumption is reduced by increasing the interval between GPS data samples. The sampling intervals can pre-selected in accordance with desired accuracy and power consumption levels, or may be varied during flight in some configurations to obtain a satisfactory trade-off between accuracy and power consumption. Estimated projectile flight parameters may be utilized to adjust GPS sampling intervals. For example, some 60-second projectile flights may require between 6 to 10 samples to adequately estimate the ejection time and trajectory intercept, although the number of samples required may vary from flight to flight. 
   Some configurations of the present invention utilize the following steps to hit a target with artillery projectile  10 . First, using spatial position finding devices, both the target and the artillery projectile firing gun are located in three-dimensional space. The fuze power on sequence is then initiated. GPS gun and target location data and basic fuze initialization data is input to the fuze using the fuze setter. A typical configuration would accommodate turn-on, system initialization, and data entry and/or update within twenty minutes of the projectile firing. 
   An onboard processor  48  establishes, using target location data inputs, a cargo ejection plane  62  that is perpendicular to an azimuth range line between the gun and target  60 . Cargo ejection plane  62  is located up range from target  60  by a distance determined to cause the deployed cargo grenades  18  to land on the target when cargo grenades  18  are dispensed from a nominal flight performance projectile  68 . For example, in some configurations, a nominal projectile flight path  68  intercepts cargo ejection plane  62  at a nominal flight path to ejection plane intercept angle estimated at 52 degrees and at an estimated nominal height of burst altitude of 500 m. Initially, processor  48  is programmed to utilize data from GPS receiver  50  of fuze  22  to eject payload  18  when projectile  10  Intercepts ejection plane  62 . In some configurations, the initialized intercept time is the same as the basic M762 set time, and further the processor  48  is configured to use the initialized intercept time as a default ejection event initiation command time in the event of a GPS anomaly or a fuze processing anomaly, thereby avoiding loss of the projectile. 
   After the fuze is programmed with target and gun location data, the artillery projectile  10  is loaded and fired. During flight, GPS receiver  50  acquires position and time data. Processor  48  is configured to use acquired GPS data to determine a deviation for a nominal projectile flight path to predict an intercept angle, height and time at which projectile  10  will pass through ejection plane  62 . As the flight of projectile  10  continues, ejection plane intercept parameters are updated with each new GPS data set. A convergence test, for example, can be performed following each new set of intercept information to determine if a GPS anomaly has occurred. A detected GPS anomaly causes processor  48  to default to either the last predicted set of ejection plane intercept parameters or to a typical conventional fuze set time. Processor  48  is configured to use either the last predicted ejection plane parameters or a typical conventional fuze set time, dependent upon the number of successful GPS updates before an anomaly occurs, in the event such an anomaly occurs prior to ejection. 
   In some configurations, the intercept point of projectile  10  with ejection plane  62  can be predicted to an altitude of plus or minus 12 m and a range of plus or minus 8 m. Once the ejection plane intercept point is determined, a difference between the nominal impact point and a predicted impact point is used to enhance accuracy by adjusting the ejection event initiation command time. For example, if the predicted ejection plane  62  intercept point and time and nominal impact point  64  and time are coincident then no correction to the ejection event initiation command time is made and a nominal grenade decent trajectory  66  is used for the payload or grenades  18  to impact target  60 . However, if artillery projectile  10  has higher velocity than a nominal artillery projectile, the predicted cargo ejection plane  62  intercept point  94  will be higher than nominal cargo ejection intercept point  64 . Based on an elevation difference between cargo ejection intercept points  64  and  94  and a difference between times corresponding to points  64  and  94 , the ejection event initiation command time is reduced, thus moving the ejection point up range to a point  74  and thereby adjusting payload  18  impact point to more closely coincide with target  60 . Similarly, if artillery projectile  10  has lower velocity than a nominal artillery projectile, the ejection event initiation command time is increased so that the payload or grenades  18  are ejected at point  76  rather than at point  96 , thereby adjusting descending grenade  18  to impact the ground at a point closely coinciding with target  60 . 
   In some configurations, and referring to  FIG. 4 , a secondary range error adjustment is made by correcting the payload ejection event initiation command time for the artillery projectile trajectory intercept angle and time with cargo ejection plane  62 . In this case, if projectile intercept trajectory  84  is steeper than nominal intercept trajectory  68 , the cargo ejection event initiation command time, i.e. the intercept trajectory  84  time, is delayed to allow payload  18  to fly further down range before ejecting its payload at a point  86 . This adjustment allows the grenades to impact the ground at the target range. Similarly, if projectile flight trajectory  82  is flatter than nominal intercept trajectory  68 , the timing is advanced to eject the payload or grenades  18  at point  88 , prior to interception of ejection plane  62  by trajectory  82 . 
   In some configurations, the fuze  22  design may meet some or all of the following specifications: 
   NATO Fuze Configuration, Mil-Std-333B 
   Mil-Std-1316D with overhead safety (Arm 50-msec. prior to Cargo Ejection) 
   M762S&amp;A 
   Inductive set only with EPIAS (No hand set or adjustment) 
   20 minute ground set capability (No 10 day preset) 
   XM982 GPS jamming protection 
   M762 timing is default mode 
   Flight time 100 sec. 
   Accuracy 125 m circular error probability (CEP) at 35 km with 2 hr. met. Data 
   No decrease in lethal area 
   Gun harden—20,000 g setback 
   Gun harden—20,000 rpm spin 
   20 year shelf life 
   In some configurations, the profile of fuze  22  is identical to the M762 profile and satisfies the NATO requirements as defined in Mil-Std-333B. The front end of fuze  22  incorporates the same plastic ogive and fuze setter coil  32  that is used on some conventional configurations of M762 fuzes. The base of fuze  22  also retains the basic M762 design. Booster cap  42  includes explosives  46 , and lead charge  44 . Safe and arm assembly and piston actuator  40  prevents arming until artillery projectile  10  is within 50 msec. from payload  18  ejection. 
   Unlike conventional M762 fuzes, GPS receiver  50  with ring antenna  36  may be provided on circuit boards  34  in fuze  22  and processor  48  may be configured to take advantage of the information received by receiver  50 . In some configurations, a battery  38  is provided to power fuze electronics, including GPS receiver  50  and processor  48 . 
   Some configurations of fuze  22  utilize three double-sided circuit boards  34 , which provide  16  square inches of component mounting surface. GPS receiver  50  and trajectory analysis processor  48  require approximately 10 square inches of circuit board area. Addition fuze electronics on circuit boards  34  utilize the GPS receiver clock and therefore the safety functions and firing circuits can be accommodated on  3  additional square inches of circuit board. Thus, up to three square inches can be provided for additional circuitry and functionality, if required. 
   Battery  38  can provide power for driving GPS receiver  50 , processor  34  and additional fuze circuitry for 20 minutes of ground time followed a 2-second power initialization spike and then a constant power drain for a 100-second flight period. A battery with a volumetric configuration of 1.5 inches in diameter by 0.88 inches high has sufficient capacity in some configurations, although other battery configurations may also be used, depending upon cost and performance requirements. 
   The center section of the configurations of fuze  22  represented by  FIG. 2  feature axial conformal circuit boards  34  mounted in front of battery  38 . The battery can be, for example, a right circular cylinder positioned between safe and arm assembly  40  and circuit boards  34 . Other configurations feature forward or aft mounting locations for battery  38 . Some configurations provide stacked round circuit cards  34  instead of the conformal axial circuit boards  34  shown in  FIG. 2 . A battery  38  and circuit card  34  configuration can be selected in accordance with dynamic environment survival vs. assembly ease and component costs requirements. 
   It will be thus observed that configurations of the present invention provide a more accurate alternative to conventional munitions systems and a less expensive alternative to precision munitions systems. The above-described fuze provides improved accuracy without depleting the spin of a deployed cargo. Because deployment spin is conserved, a historical footprint of the cargo can be preserved. Also, some configurations are profile-interchangeable with the M762 fuze per MIL-Std-333B specifications and some configurations incorporate technologically available smart munition updates. 
   The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.