Abstract:
The Trajectory Correction Kit (TCK) is a completely self-contained retrofit kit that is externally and fixedly mounted as an add-on to the rear (aft of the tailfins) of an existing, unguided rocket. The TCK continuously measures the pitch and yaw of the rocket as it is released from the launch tube and during the initial seconds of the flight and calculates the trajectory correction that is necessary to eliminate the measured pitch and yaw. Then it activates selected thrusters among the thrusters that are positioned around the circumference of the rocket body so as to steer the rocket in a direction until the measured pitch and yaw are eliminated. This results in significant reductions in both the rocket flight path dispersion and collateral damage.

Description:
[0001]     The invention described herein may be manufactured, used and licensed by or for the Government for U.S. governmental purposes; provisions of 15 U.S.C. section 3710c apply. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     Unguided artillery rockets, utilized for area suppression fire missions, are most vulnerable to trajectory perturbations during launch and the first several seconds of flight. The trajectory perturbations are manifested as dispersion of the rockets over the target area, with the result that many such rockets must be fired to ensure that the area of interest is sufficiently covered.  
         [0003]     Efforts have been made to add low or medium cost guidance packages to such ballistic rockets to make them impact the selected target more accurately. One system, intended for small and short range rockets, included a semi-active laser seeker and canard guidance package for direct fire guidance all the way to the target. Another system, focusing on large indirect fire artillery rockets for longer ranges, utilized Global Positioning System inputs to an inertial measurement unit along with nose-mounted canards for trajectory control.  
         [0004]     However, such efforts required the development of a new airframe for the rockets. Further, both systems placed the control actuators and the associated electronics in the nose of the weapon and controlled the trajectory all the way until target impact. Even though these systems rendered such rockets more accurate against point or very much smaller objects than area targets, neither system is suitable for use with the large stocks of unguided artillery rockets that are already in existence, because of the incompatibility with the rockets&#39; airframe.  
       SUMMARY OF THE INVENTION  
       [0005]     The Trajectory Correction Kit (TCK) is a completely self-contained retrofit kit that is externally and fixedly mounted onto the rear (aft of the tailfins) of the rocket. The TCK continuously measures the pitch and yaw of the rocket as it is released from the launch tube and during the initial seconds of the flight and corrects the initial flight path perturbations by firing selected thrusters to steer the rocket until the measured pitch and yaw are eliminated. This results in significant reductions in both the rocket flight path dispersion and collateral damage. 
     
    
     DESCRIPTION OF THE DRAWING  
       [0006]      FIG. 1  illustrates the position of the trajectory correction kit on the rocket.  
         [0007]      FIG. 2  shows the housing and the overall shape of the TCK.  
         [0008]      FIG. 3  depicts first hemispherical plate and the components thereon.  
         [0009]      FIG. 4  depicts second hemispherical plate and the components thereon.  
         [0010]      FIG. 5  illustrates how the hemispherical plates are joined together.  
         [0011]      FIG. 6  is a functional diagram of the TCK.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]     Referring now to the drawing wherein like numbers represent like parts in each of the several figures, the structure and operation of the trajectory correction kit (TCK) is described in detail.  
         [0013]     Any and all of the numerical dimensions and values that follow should be taken as nominal values rather than absolutes or as a limitation on the scope of the invention. These nominal values are examples only; many variations in size, shape and types of materials may be used as will readily be appreciated by one skilled in the art as successfully as the values, dimensions and types of materials specifically set forth hereinafter. In this regard, where ranges are provided, these should be understood only as guides to the practice of this invention.  
         [0014]     Free-flight rocket theory and practice have established that the most significant trajectory errors occur within the first few seconds of flight. The most significant error sources are launch-induced errors and aerodynamic effects that occur before the rocket fins deploy and before the rocket velocity is sufficient to generate aerodynamic stability. TCK corrects these errors immediately, whereas the canard type guidance systems, such as previously available, must allow the rocket velocity to build before corrections become effective. Consequently, using canard systems makes the magnitude and duration of the necessary correction larger. Additionally, the canard correction system significantly alters the aerodynamics of the rocket and usually necessitates new firing algorithms for the rocket. In contrast, as will be seen below, the thin cross section of the TCK and its aerodynamic housing has minimal effect on the drag of the rocket on which it is mounted, thus enabling the rocket&#39;s original firing algorithm to be used with little or no modification.  
         [0015]     TCK  101  is intended to be installed on the rear (aft of tailfins  103 ) of rocket  100  so the TCK can be partially aerodynamically obscured by the tailfins. The TCK, which is essentially a tube having an annular vertical cross section, is mounted onto the rocket by being slipped over the rear portion of the rocket body so as to wrap around the rear portion. This is illustrated in  FIG. 1 . The specific mechanism for mounting the TCK so as to secure its attachment fixedly to the rocket prior to and during flight depends on the shape of the airframe of the particular rocket on which it is used.  
         [0016]     One such securing mechanism is explained with respect to the Multiple Launch Rocket System (MLRS) rocket. The general configuration of the MLRS is shown in  FIG. 1  and the external configuration of the TCK is shown in  FIG. 2 . The MLRS has protruding spin lugs on its outer body. To accommodate and take advantage of this feature on an already-existing rocket, cut-outs  209  that match the shape and size of the lugs can be made into the housing of the TCK. The TCK is positioned on the rocket immediately in front of the lugs, with the lugs slipping into the cut-outs. Such mounting allows the lugs to keep the TCK from falling off the rocket and also to prevent the TCK from sliding around the rocket body during flight.  
         [0017]     Other suitable mounting mechanisms may be found for extant rockets that accommodate the unique airframes of the rockets. For rockets yet to be produced, the TCK can be integrated into the airframe during manufacture or internalized and placed in the payload bay or the nose.  
         [0018]     As seen further in  FIG. 2 , for it to be usable as an external add-on to a pre-existing rocket (such as an MLRS that has protruding spin lugs) and for ease of installation, the TCK can be comprised of first and second hemispherical plates  201  and  203  that are joined together to form a complete ring (tubular unit) around the rocket. They may be joined by longitudinal bolts  501  that slide through the holes in plate lugs  503 . This, illustrated in  FIG. 5 , is basically a door hinge type arrangement. Another means for adjoinment is a lap joint that screws the plates together. Yet another means is using high-strength aerospace fasteners in a cross bolt arrangement.  
         [0019]     If the TCK is to be installed on the rocket during the manufacturing process, the plates may be formed as a single, integrated unit.  
         [0020]     Over the first and second hemispherical plates and sharing the same design, including any necessary cut-outs, third and fourth hemispherical plates  205  and  207  can be added to serve as aerodynamic covers. The third and fourth plates together form an annulus and are joined to the first and second plates, respectively, using any suitable aerospace fastening means.  
         [0021]     Due to the high temperature environment of the artillery rocket launch tube, suitable materials for the TCK plates are aluminum, stainless steel or non-metallic materials that are capable of withstanding high temperatures.  
         [0022]      FIG. 3  shows the TCK with the aerodynamic covers removed. Onto the first hemispherical plate are secured first battery pack  307 , angular rate sensor  303 , flight control computer  305  and a multitude of thrusters  301 .  
         [0023]      FIG. 4  shows the second hemispherical plate having thereon addition thrusters  401 , second battery pack  405  and power-conditioning card  403 . The securing of the components onto the first and second hemispherical plates can be achieved by using standard aerospace fasteners.  
         [0024]     It is noted that the placement of any particular component on the first or second hemispherical plate is not critical, except that the multiple thrusters should be positioned in an orderly, pre-determined pattern such that they are distributed around the circumference of the rocket body and render symmetry to the two hemispherical plates with respect to the thrusters.  
         [0025]     Each thruster has therein propellant material, an igniter and an exhaust port  309  through which the exhaust gas can escape. The thrusters can be grouped into blocs, each bloc having several (such as six to seven) thrusters.  
         [0026]     The operation of the TCK begins upon first motion of rocket  100  when it is launched. Powered by battery packs  307  and  405 , angular rate sensor  303  and computer  305  are triggered by the motion of the launch. The computer has therein data as to the normal parameters for the rocket at launch, such as the sustained acceleration (example: 35-80 g&#39;s for MLRS rocket) and the spin acceleration (example: from 0—prior to launch—to 4,000 degrees/second in five feet of travel). The angular rate sensor, in co-operation with the computer, verifies that the rocket motion is within the parameters for launch (i.e. that launch has actually occurred) and that the TCK operation can begin. The trajectory correction begins when the rocket is released from the launch tube after a per-determined time and distance interval from launch. The angular rate sensor continuously measures the pitch and yaw rates of the rocket in flight and inputs these rates into the computer.  
         [0027]     A functional diagram of the TCK is presented in  FIG. 6 , wherein plain lines indicate electrical connections while arrow lines indicate data connections as well as electrical connections. Although only four thrusters are shown in the figure, there can, of course, be many more thrusters.  
         [0028]     The computer uses the pitch and yaw rates to determine which particular thrusters should be fired and when so as to eliminate the measured pitch and yaw and transmits ignition commands to the selected thrusters at the appropriate time.  
         [0029]     The thrusters respond to the ignition commands by igniting the propellant material and expelling the resulting exhaust gas through exhaust ports  309 , thus steering the rocket in a given direction. The pitch and yaw rates are continuously measured and one or more thrusters ignited from time to time to eliminate the measured pitch and yaw until either all of the thrusters have been ignited or there is no more measured pitch and yaw, whichever occurs first.  
         [0030]     A power-conditioning card can be used to maximize the function of the TCK. Card  403  is coupled, as depicted in  FIG. 6 , between the battery packs, angular rate sensor and the computer. The card takes the battery voltage, which can vary based on ambient temperature and the age of the batteries, and converts it to a clean, uniform, constant voltage and current supply for the sensor, the computer and the thrusters.  
         [0031]     Although a particular embodiment and form of this invention has been illustrated, it is apparent that various modifications and embodiments of the invention may be made by those skilled in the art without departing from the scope and spirit of the foregoing disclosure.  
         [0032]     One modification is equipping the TCK with a release mechanism to allow the TCK to fall away from the rocket when trajectory correction has been accomplished. This would reduce the weight of the rocket and remove any aerodynamic drag that may be caused by the TCK. One release mechanism is a means for pulling longitudinal bolts  501  free from the plate lugs  503  and compressed springs mounted on the underside of first and second hemispherical plates. When the bolts are released from the plate lugs, the springs eject the hemispherical plates away from each other as well as away from the rocket itself. Other similar modifications may be made to the TCK to enhance its performance.  
         [0033]     Accordingly, the scope of the invention should be limited only by the claims appended hereto.