Abstract:
A battlefield weapon system is proposed to counter the threat posed by small drones. The main system element is an aerodynamically guided missile that is compatible with existing multipurpose shoulder launched weapon systems. The system is fully portable for dispersed deployment among infantry.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    None. 
       FIELD OF THE INVENTION 
       [0002]    This invention is related to battlefield weapons systems and the threat posed by small UAVs (Drones). 
       BACKGROUND OF THE INVENTION 
       [0003]    The low cost and ready availability of simple remote-piloted aircraft systems (RPAS) presents the enemy with an efficient means to achieve battlefield tactical reconnaissance and strike capabilities that would have been unheard of ten years ago. 
         [0004]    In an asymmetric threat scenario, simple, low-cost aircraft remote piloted aircraft (whether directly purchased from hobbyist suppliers, or manufactured along similar lines) can be modified with relative ease to include video downlink and to deliver;
       explosive ordnance   precision, close range shot (rifle, pistol, shotgun)   all manner of chemical, nuclear or biological agents   close-up reconnaissance photography, possibly with GPS   mortar, artillery and sniper spotting       
 
         [0010]    Under a symmetric threat scenario, all of the above-mentioned capabilities are presented, together with:
       threat from semi-autonomous drone aircraft   threat from super-miniature insect- and bird-like aircraft   target marking for terminal guidance of smart munitions.       
 
         [0014]    The small RPAS carries with it the possibility to inflict significant damage, while being difficult to counter. The effective target size may well be as little as 0.01 m 2 , that is to say 50 times harder to hit than a person, as well as moving fast and changing direction. Even for a well-armed and fully supported engagement team, none of the weapons available to the infantryman or rifleman (rifle rounds, hand grenades, RPGs, machine guns, mortar, anti-aircraft missiles, artillery or airstrikes) are effective against this threat. 
         [0015]    The laser-powered weaponry that is currently in trials and early deployment is expensive arid not readily mobile. Truck-mounted systems are not compatible with modern mobile warfare. The need is to create an effective weapon system that can be accessible to every infantryman and practicallideployable at the squad or platoon level. In short, the wish list is:
       Effective   Portable (backpack)   Cost-effective and therefore readily deployable       
 
         [0019]    Prior art includes various drone-against-drone systems. Patent U.S. Pat. No. 9,085,362 B1 describes a system for deploying a net from one drone, to entangle another. Also under trials are systems that track the target and provide automatic guidance of a steerable 50 mm projectile to attack a drone. These systems all share the disadvantage that they are not readily deployable among small mobile, combat units on the battlefield. 
         [0020]    Prior art includes various shoulder-launched anti-aircraft missile systems. Existing systems such as the FIM-92 Stinger family are single-purpose, in that they are intended specifically to counter aircraft, and are incompatible with other weapon systems. Furthermore, these weapons lack the accuracy, agility and suitability of guidance system that are all needed to counter a small drone at relatively close range. 
         [0021]    Prior art also extends to shotguns. These provide the spread needed to engage a small target but lack effective range. Under development are frangible rounds for machine guns that have increased range compared do shotguns and similar effect but nevertheless present difficulties in aiming, especially against a maneuvering target. 
         [0022]    It is an object of this invention to provide foot soldiers with a practical means to counter the threat posed by drones. 
         [0023]    It is an object of this invention to provide a drone countermeasure system that is compatible with, and extends the capabilities of, existing equipment that is carried by foot soldiers. 
         [0024]    It is an object of this invention to provide a drone countermeasure system that is inexpensive compared to the current alternatives. 
         [0025]    It is an object of this invention to provide a drone countermeasure that is effective over a range of some hundreds of meters. 
         [0026]    It is an object of this invention to provide foot soldiers with a drone countermeasure system that can be carried in back backs without undue additional weight. 
       SUMMARY OF THE INVENTION 
       [0027]    A missile is launched from a standard shoulder-mounted rocket launch tube, such as SMAW or SMAW II. The missile has fins/wings that make it aerodynamically active and provide lateral acceleration for in-flight maneuverability. A rocket motor boosts the missile to its launch velocity, in a similar manner to other tube-launched rocket projectiles. After launch, there is no need for further thrust; the momentum of the missile is sufficient to carry it to the target. An on-board camera is used to optically track the target and thereby guide the flight of the missile. A proximity-fused charge destroys the target. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0028]      FIG. 1  shows the layout of the missile. 
           [0029]      FIG. 2  shows the missile inside the launch tube. 
           [0030]      FIG. 3  shows the control and guidance dynamics. 
           [0031]      FIG. 4  shows the missile in flight. 
           [0032]      FIG. 5  shows the fragmentation of the missile on close approach to the target. 
           [0033]      FIG. 6  shows the method for initial target designation 
           [0034]      FIG. 7  shows the engagement geometry with respect to the apparent angular deflection of the target in the tracking system resultant from the missile&#39;s maneuvering. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]    With reference to  FIG. 1 , the missile comprises the following components: the fuselage,  1 , provides structural integrity for the missile, contains the control and guidance system and the warhead  6 , as well as creating an aerodynamic envelope for these internal parts and systems; a camera  2  provides images that are used by the tracking and guidance system; wings  3  provide aerodynamic lift and maneuvering capability; tail surfaces  4  stabilize the missile and control its attitude in flight with respect to pitch and yaw; and allerons  5  control attitude in flight with respect to roll. The preferred embodiment uses a regular optical camera, but an infrared camera may be substituted in the skne location and function within the design. 
         [0036]    With reference to  FIG. 2 , the missile  2  is launched from a shoulder mounted rocket tube  1 . Typically this would be of SMAW type, but other types of launch tube or launch mechanism would work. Prior to launch, the tube is aimed at the target. The arming process makes the missile electronically active and the missile&#39;s camera and tracking system (part of the control and guidance system, described below) acquires the target and starts to track it. The wings of the missile  4  are partially retracted so that the missile can fit inside the launch tube. The missile is contained in a sabot  3  to protect it from contact with the walls of the launch tube. The missile is boosted to its launch velocity by a rocket motor  5 . The missile leaves the tube with the rocket motor spent. The rocket motor and sabot detach from the missile, the wings of the missile extend fully, and the missile continues with sufficient momentum to engage the target without the need for subsequent thrust. 
         [0037]      FIG. 3  depicts the control and guidance system. The Target Position in Missile reference axes  1  is the target position relative to the position and orientation of the missile. The camera  2 , which is tracking the target, provides the Guidance Controller with an image of the target. The Guidance Controller processes the sequence of images from the camera and tracks the apparent position of the target. Combining this with known inertial feedback from the Flight Controller  4 , the Guidance Controller Maintains a mathematical model of the position and orientation of the missile and the position of the target and computes and repeatedly updates an intercept path. The resultant guidance information is passed to the MEMS Based Flight Controller  4 . The flight controller provides the control inputs to fly the missile along the flight path dictated by the Guidance Controller. The flight controller uses inertial data from a MEMS (micro-electronic mechanical system) device as its principal feedback mechanism. The inertial data comprises linear acceleration information in three axes and rotational motion about three axes. The flight controller&#39;s control output is to the flight control servos (shown as Servo Dynamics,  5 ) and the servos actuate the aerodynamic control surfaces  6 . The resultant Dynamic Response of Aircraft  7  generates changes in the attitude and acceleration of the missile, and it is these changes that are measured by the MEMS device in the MEMS based flight controller, thus closing the inner control loop that stabilizes the missile and keeps it on its demanded flight path. The Engagement Geometry  9  results from a combination of the flight path of the missile and the flight path of the target. With accurately controlled engagement geometry, the Missile to Target Vector  10  is progressively shortened to the point where the missile directly strikes the target or is close enough for a proximity-fused charge to be effective in destroying the target. Meanwhile, it is the Engagement Geometry that dictates the target position in the missile reference axes, thus closing the outer control loop, of missile guidance. 
         [0038]      FIG. 4  shows the overall target engagement. The missile  2  is launched from tube  1 , and flies along path  4 . Normally the missile path will be curved, in response to offset in initial aim toward the target, and subsequent target motion. The missile computes and establishes an intercept path as opposed to a curve of pursuit, modeling the target&#39;s position, velocity and acceleration. The system may be used to engage target types other than drones. A separate target designator  5  may be used to illuminate the target using a beam of laser light or infrared light of a specific wavelength  6  such that the optical tracking of the target is facilitated, particularly in cases where the target is being tracked against background clutter. 
         [0039]      FIG. 5  shows the final moment of encounter between the missile and the target. The missile is equipped with a proximity fuse and its onboard warhead detonates at a suitable close range. Fragments of the warhead are dispersed at high speed, penetrating the structure of the target and destroying it. 
         [0040]      FIG. 6  shows the initial target designation being performed by aligning the launch tube  1  with the target  2 . The optical tracking system is locked onto target prior to launch. The inertial portion of the guidance system is also initialized so that the missile is fully prepared to enter the target engagement phase of its flight immediately after launch.  FIG. 6  also shows an optional method of target designation in which the view of the target  2  is shown on the screen of a tablet computer  3  and is manually selected. 
         [0041]      FIG. 7  shows the engagement geometry with respect to the camera that is used for guidance. The missile  1  is maneuvering toward the target  2  along flight path  3 . The instantaneous flight vector  4  is displaced by an angle  7 , the angle of attack, from the direction in which the centerline of the missile is pointed. The direction in which the target appears to the missile,  6 , is offset from the centerline of the missile by a different angle,  8 . The angle  8 , the “optical offset angle” changes rapidly in response to changes in the angle of attack  7 . The optical offset angle  8  is important for the tracking camera because it determines the portion of the field of view on which the tracking system needs to focus to maintain lock on the target. Therefore the changes in the angle of attack, as measured by the MEMS chip in the guidance system, are “fed forward” to the camera in order that the camera can compensate for changes in the apparent position of the target. The preferred embodiment uses electronic methods to apply this compensation but there are many ways to accomplish the same result: mechanical, electromechanical and opto-mechanical may also be used. The foregoing discussion applies equally in the missile&#39;s other plane of motion where it is sideslip angle that is varying in response to yaw.