Abstract:
A projectile defense system uses a rocket exhaust generator to generate a rocket exhaust after an approaching projectile is detected/sensed. The rocket exhaust generator directs the rocket exhaust therefrom in a region that intercepts the trajectory of the approaching projectile.

Description:
STATEMENT OF GOVERNMENT STATEMENT 
   The invention described herein may be manufactured and used by or for the Government of the United States of America for government purposes without the payment of any royalties therefor. 
   FIELD OF THE INVENTION 
   The invention relates generally to defense systems and methods for defending a location. More particularly, the invention is a system and method for defending a location against an incoming projectile using a rocket exhaust. 
   BACKGROUND OF THE INVENTION 
   In a variety of world conflicts today, vehicles and structures are vulnerable to attack from inexpensive shoulder-launched projectiles/munitions such as rocket-propelled grenades (RPGs) and their variants. Propulsion for these projectiles/munitions is typically generated by either rocket motors or Davis-guns. Some have sustainer rockets to maintain or enhance flight velocity. Many have multiple warhead options designed for various threats. The most common types of warheads are shape-charge based anti-armor warheads for attacking tanks and armored vehicles, dual mode warheads for bunkers and lightly armored vehicles, thermobaric warheads for buildings and confined spaces, and some sophisticated threats containing shape charges and fragmenting grenades. Most are designed to impact the target at speeds ranging from 400-1200 feet per second. They have effective ranges from 50-600 meters depending on the system and projectiles used. 
   A passive defense strategy for RPGs involves the use of some type of armor attached to a vehicle or other target to be protected. Unfortunately, turning every vehicle into an improvised tank (or structure into a fortress) is not practical or cost effective. An example of an active defense strategy for RPGs is a reduced-size missile system. For example, one anti-missile system uses radar to detect and locate incoming missiles, and then aims and fires a rapid machine gun burst at the missile threat. However, this type of system can be expensive since it must possess precise target acquisition and aiming capabilities. Furthermore, this type of system can be a threat to friendly forces and noncombatants as any missed intercepts could result in bullets entering a nearby population. 
   Whether passive or active in nature, initiating an RPG (even at a distance) is not necessarily the optimal defeat mechanism. Ideally, the threat would be defeated without incurring a detonation event that generates the resulting jet and/or shrapnel associated with it in the vicinity of the target or nearby personnel. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a projectile defense system. 
   Another object of the present invention to provide a system and method for detecting the approach of an incoming and then deflecting or otherwise defeating the projectile so it does not impact the intended target. 
   Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings. 
   In accordance with the present invention, a projectile defense system and method are provided. An approaching projectile and its trajectory are detected or sensed with a sensing system. A rocket exhaust generator coupled to the sensing system generates a rocket exhaust after the sensing system detects the approaching projectile. The rocket exhaust generator directs the rocket exhaust therefrom in a region that intercepts the trajectory of the approaching projectile to defeat the projectile. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the present invention will become apparent upon reference to the following description of the embodiments and to the drawings, wherein corresponding reference characters indicate corresponding parts throughout the several views of the drawings and wherein: 
       FIG. 1  is a schematic view of a projectile defense system configured to defeat an approaching projectile in accordance with the present invention; 
       FIG. 2  is a schematic view of a projectile defense system of the present invention mounted on a vehicle; 
       FIG. 3  is a schematic view of an embodiment of a rocket exhaust generator for use in the present invention; and 
       FIG. 4  is a schematic view of an embodiment of a rocket exhaust generator in which material particles are mixed in a propellant for ultimate inclusion in the rocket exhaust. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, and more particularly to  FIG. 1 , a projectile defense system in accordance with the present invention is contained within a dashed line box  10 . Projectile defense system  10  can be used to defend a target  100  against a variety of incoming projectile threats such as projectile  200  which, for purposes of this example, is assumed to be traveling on a trajectory  202  that will cause it to impact target  100 . It is to be understood that target  100  can be fixed in its location (i.e., a building, bridge, etc.) or could be a moving vehicle temporarily residing at or moving through a sensitive or protected location. 
   Defense system  10  includes a sensing system  12  and a rocket exhaust generator  14 . The sensing system  12  and the rocket exhaust generator  14  are coupled together for purposes of communication between each other. Sensing system  12  is any system capable of detecting the approach of projectile  200 , and predicting or determining trajectory  202  to see if projectile  200  is a threat to target  100 . Generally, the sensing system  12  is designed to operate autonomously, that is, automatically without manual operation but could be operated manually if required. The sensing system  12  includes at least one sensor  15  and a processing unit  17 , for example, a CPU, which is used, in part, to perform various functions (both not shown). In particular, the sensing system  12  has a processing capability for accomplishing one or more of the following tasks: detecting projectile  200 , determining trajectory  202 , determining velocity of projectile  200 , predicting size of projectile  200 , predicting distance that projectile  200  is from target  100 , and other projectile parameters. In an exemplary embodiment, the processing unit  17  is configured so as to couple the sensing system  12  with the rocket exhaust generator  14  in order to provide communication between the sensing system  12 , including the proximity sensor  15 , and the rocket exhaust generator  14 . 
   A variety of sensors  15  and, in particular, a proximity sensor  15  as part of the sensing system  12 , is used without departing from the scope of the present invention. An example of one type of proximity sensor  15  is an ultra wideband radio-frequency (“rf”) proximity sensor currently used on certain warheads in order to optimize the detonation point thereof. Another example of a proximity sensor  15  is a laser-based proximity sensor. For example, such sensors can be used individually, in combination or in an array depending on the application. Further, the sensors  15  could be adjustably configured to be directionally sensitive to incoming projectiles that are within a defined field-of-view, that is, a detection region, which in  FIG. 1  lies between the two dashed lines referenced by numeral  12 A. 
   Assuming sensing system  12  detected projectile  200  and determined that it was a threat to target  100  as calculated by the processing unit  17 , then the processing unit  17  would send a signal to initiate the rocket exhaust generator  14 . Once initiated, rocket exhaust generator  14  directs a rocket exhaust between lines  16 , which defines an intercept area or region, such that trajectory  202  is intercepted as projectile  200  moves there through. An impulse provided by rocket exhaust  16  alters trajectory  202  so that projectile  200  assumes an alternate trajectory  202 A that is offset from target  100 . The amount of impulse provided by rocket exhaust  16  and an amount of time that such impulse is present are design choices predicated on a variety of factors, which include placement of rocket exhaust generator  14  relative to trajectory  202 , type/size of projectiles that defense system  10  is expected to encounter as well as the size and/or monetary constraints that might be placed on defense system  10 . 
   While it is most desirable to alter trajectory  202  as just described so that target  100  is not directly hit, it is to be understood that the presence of rocket exhaust  16  might also damage projectile  200  to prevent its detonation upon impact with target  100  or the surrounding environment (e.g., buildings, etc.), or cause projectile  200  to detonate prior to impacting target  100 . In each of these cases, there may be some damage to target  100  although such damage would be far less than if target  100  were struck without projectile  200  encountering rocket exhaust  16 . 
   Referring now to  FIG. 2 , the present invention is shown as it might be employed as a defensive system mounted on a moving vehicle  300 . In the illustrated example, two of defense systems  10  are coupled to vehicle  300  with the field-of-view  12 A associated with each one thereof being uniquely directed. It is to be understood that additional defense systems  10  could also be coupled to vehicle  300  without departing from the scope of the present invention. Each of defense systems  10  could be constructed with component elements being separately attached to vehicle  300 . Another option would be for each defense system  10  to comprise a modular unit that is completely self-contained (i.e, sensing system (“SS”)  12  and rocket exhaust generator (“REG”)  14  are coupled together in a single package) and adapted to simply attach to and be removed from vehicle  300 . Another option would be for each defense system  10  to be integrated to each other via the processing unit  17  and/or a second processing unit  19 , for example, a CPU, to conduct activity and/or provide feedback to occupants of the vehicle  300  as well as coordination resources outside the vehicle  300 , for example, by a satellite GPS link. Such attachment/detachment schemes are well understood in the art and are not limitations of the present invention. In this type of embodiment, since vehicle  300  represents the target to be protected, rocket exhaust generator  14  is configured such that rocket exhaust  16  (shown in dashed line form to indicate the location thereof when generator  14  is initiated) would be directed in a direction that could impart at least some degree of a side load to any approaching projectile detected by the defense system&#39;s corresponding sensing system  12 . 
   In each of the above-described embodiments, rocket exhaust generator  14  is any device capable of directing rocket exhaust  16  into a region between an approaching projectile and a target to be protected. For example,  FIG. 3  illustrates one such rocket exhaust generator  14  where a rocket motor  140  includes an exhaust nozzle  142  coupled thereto. Generally, the rocket motor  140  includes an inner portion  19  (not shown). Located in the inner portion  19  are a propellant  140 A and an initiator  140 B for starting the burning of propellant  140 A. The gas produced by propellant  140 A is exhausted as rocket exhaust  16  by exhaust nozzle  142 . 
   If conventional propellants are used in the present invention, rocket exhaust  16  comprises a gas that would be effective at defeating an approaching projectile at relatively short stand-off distances from a target. While advantageous in densely populated areas, the defensive capabilities of such a system may be less than what is required for certain types of hostile projectiles. To enhance the range and/or effectiveness of the present invention without substantially increasing the danger to the nearby population, the pre-burn form of the propellant could have material particles mixed therein where the material particles are selected to survive the burning of the propellant. In other words, the material particles should be a material that has a melting temperature that is greater than the burn temperature of the propellant in which it is mixed. Accordingly,  FIG. 4  illustrates a rocket motor  140 , which includes an inner portion  19  (not shown). Located in the inner portion  19  are a propellant  140 A including material particles  140 C mixed in the propellant  140 A where it will be assumed that a melting temperature of particles  140 C is greater than a burn temperature of propellant  140 A. Upon initiation, propellant  140 A burns while material particles  140 C do not. As propellant  140 A burns, particles  140 C are released in a controlled manner and become fluidized in the turbulent fast moving gasses forming rocket exhaust  16  exiting nozzle  142 . Accordingly, nozzle  142  should be designed for optimal acceleration of small particles in a gas as would be the case for high-efficiency sand blasting types of nozzles. As a result, rocket exhaust  16  includes the gas resulting from the burning of propellant  140 A and material particles  140 C dispersed therein. 
   Material particles  140 C would generally include a powder with particle sizes generally falling in a predetermined range of about 1 to about 500 (about 1-about 500) microns in diameter. A variety of materials could be used for particles  140 C. For example, a suitable material is tungsten, which is heavy, non-toxic, inexpensive, and has a high melting temperature (i.e., greater than 6000° F.). Due to substantial weight and density characteristics of the tungsten, tungsten when accelerated in a high-speed rocket exhaust will impart significant inertia to a projectile upon impact therewith. 
   A powder form of material particles  140 C works well in the present invention because it can be spread (via rocket exhaust  16 ) to a relatively large region as compared to a single object such as a bullet. This means that the present invention does not need to possess expensive and complicated target acquisition capabilities (in sensing system  12 ) or aiming capabilities. Further, the high surface area-to-mass ratio presented by a dispersed powder means that material particles  140 C will slow to a non-lethal velocity at a reasonable distance from their launch point thereby making the present invention reasonably safe even in densely populated regions. 
   The advantages of the present invention are numerous. The projectile defense system and method are simple and can be adapted for protection of a wide variety of targets to include vehicles. The rocket exhaust is capable of deflecting an incoming projectile while remaining substantially non-lethal to nearby personnel. By incorporating dense powder in the rocket exhaust, the effective range of the defense system is increased as are the forces that can be imparted to an approaching projectile. 
   Although the invention has been described relative to a specific embodiment thereof, there are numerous variations and modifications that will be readily apparent to those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described. 
   Finally, any numerical parameters set forth in the specification and attached claims are approximations (for example, by using the term “about”) that may vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of significant digits and by applying ordinary rounding.