Patent Publication Number: US-6666402-B2

Title: 2-D projectile trajectory corrector

Description:
RELATED APPLICATION 
     The present application is a continuation of U.S. patent application Ser. No. 10/060,078, filed Jan. 29, 2002, now U.S. Pat. No. 6,502,786 and claims the benefit of U.S. Provisional Application Nos. 60/265,725 and 60/265,794 both dated Feb. 1, 2001. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to artillery projectiles in general and specifically to a device for correcting the range and deflection errors inherent in an unguided spin stabilized projectile. 
     BACKGROUND OF THE INVENTION 
     There is need to improve the accuracy of artillery shells fired by large bore weapons. Technological advances in metallurgy, propulsion, guidance and control now make it feasible for artillery systems to attack targets at ranges greater than 20 miles. Artillery shells, follow a ballistic trajectory, which in an ideal world can be determined mathematically from launch point to target. However, the real world is not as forgiving. Numerous factors affect the trajectory. Variations in temperature, wind and precipitation along with minute differences in manufacturing tolerances of the projectile, the barrel of the weapon, and the charge are just a few of the factors affecting the flight of a projectile. Moreover, there is typically no control of the projectile after launch. Therefore, as the range increases, the potential impact footprint of the projectile grows until it reaches the point where the projectile can no longer be relied upon to accomplish the desired mission. 
     There is a need then to improve the accuracy of artillery projectiles through in-flight control. One proposed solution addressed by prior art is the smart projectile, which is basically a gun-fired guided missile. These weapons are extremely complex. In addition to the normal fuze and payload found in unguided projectiles, these weapons utilize Inertial Measuring Units (IMUs) containing gyros and accelerometers, complex canard assemblies with actuator motors and drive electronics and/or variable angle rocket nozzles, and long grain rocket motors with complex finned base assemblies. 
     The complexity of a smart projectile results in reliability issues. The delicate components of these projectiles are subject to failure due to the high acceleration pressure, temperatures and rotational velocities experienced throughout launch and the flight. The projectile may have to be de-spun prior to flight correction in order to protect the internal components from the high rotational velocities imparted from the rifled barrels. Furthermore, accuracy in such weapons comes at a high cost. Fully guided rounds such as ERGM, XM982 and AGS LRLAP cost between $25,000.00 to $80,000.00 a piece. While simpler, less expensive corrector designs have been proposed, none provide the required two dimensions of control for range and deflection errors. 
     There is a further need then to efficiently utilize the inventory of current artillery pieces. Improvements to the projectile must be compatible with existing rounds. Modem artillery barrels are rifled so as to create spin in the projectile. Without spinning, the projectile has a tendency to tumble which makes it impossible to determine with any level of confidence where the projectile is going to land. One consequence of spin is that it creates a yawing to the right (with right hand refilling twist) or side slip angle called the yaw of repose. When a projectile is fired at a range of 20 miles, the yaw of repose will result in a cross range deflection of about 1 mile. In order to continue using existing weapon systems with rifled barrels, the proposed system must be able to compensate for the affects of rifling. 
     What is needed is a system that can provide two dimensional in-flight projectile trajectory correction more simply and less expensively than a guided projectile. Preferably the system can be used to modify the millions of artillery rounds in the existing inventory or be simply added to new artillery rounds. The system should be safe from electronic jamming, which is likely in a combat environment. The system should improve accuracy so that the corrected projectiles can be used effectively for targets at ranges in excess of 20 miles. 
     SUMMARY OF THE INVENTION 
     The present invention is a two dimensional (2-D) projectile trajectory corrector system for placement on an artillery projectile that includes multiple aerodynamic surfaces which affect drag and spin so that range and cross range deflection may be adjusted in-flight through a deployment method that may include vernier corrections. The two dimensional projectile trajectory corrector system also contains means for receiving positional data and a programmable timer for implementing the deployment strategy necessary for trajectory adjustment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is a device and a method of adjusting a trajectory of a projectile in flight comprising increasing projectile drag to effect a downrange correction and altering the yaw of repose to effect a cross range correction. 
     FIG. 1 is a perspective view of the present invention in the center position as retrofitted to an existing M549 projectile with representative spin and drag tabs extended; 
     FIG. 2 is a perspective sectional view of the guidance and control subsystem of the present invention for placement in the central or ogive position with a front cutout in which the tabs remain but the structure is removed; 
     FIG. 3 is a perspective view of the present invention in the ogive position with representative spin and drag tabs extended; 
     FIG. 4 is a perspective view of the present invention in the fuze position on the projectile with representative spin and drag tabs extended; 
     FIG. 4A is a perspective view of the fuze of FIG. 4; 
     FIG. 5A is a perspective view of an alternate embodiment 2-D projectile trajectory corrector system incorporated into the fuze assembly with spin and drag tabs deployed; 
     FIG. 5B is a front elevational view of the alternate embodiment of the 2-D projectile trajectory corrector system incorporated into the fuze assembly with spin and drag tabs deployed; 
     FIG. 6A is a front elevational view of the alternate embodiment of the 2-D projectile trajectory corrector system incorporated into the fuze assembly with spin tabs deployed in the spin up position; 
     FIG. 6B is a front elevational view of the alternate embodiment of the 2-D projectile trajectory corrector system incorporated into the fuze assembly with spin tabs deployed in the spin down position; 
     FIG. 7A is a front elevational view of the drag mechanism for the alternate embodiment of the 2-D projectile trajectory corrector system incorporated into the fuze assembly with drag tabs in a pre-launch position; 
     FIG. 7B is a front elevational view of the drag mechanism for the alternate embodiment of the 2-D projectile trajectory corrector system incorporated into the fuze assembly with drag tabs partially deployed; and 
     FIG. 7C is a front elevational view of the drag mechanism for the alternate embodiment of the 2-D projectile trajectory corrector system incorporated into the fuze assembly with drag tabs fully deployed. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Generally, the 2-D projectile trajectory corrector system includes two types of aerodynamic surfaces which deploy from the projectile so as to affect the spin stabilized flight characteristics inherent in a round fired from a rifled barrel. The first type of surface, which provides one-dimensional range correction, is a drag device that acts as an airbrake. These devices are stored within the projectile at launch, then deploy radially from the projectile in-flight so as to eventually lie substantially perpendicular to the line of flight. The timing and sequence of deployment of the drag devices determines the reduction in range. 
     The second type of surface, which provides the second dimension of cross range correction, affects spin and the normal force of the projectile in-flight. The spin device is also stored within the projectile at launch, then deploys radially from the projectile surface but is positioned generally parallel with an angle of attack relative to the line of flight. The spin device is a relatively small swept wing or tab canted at an angle off the streamlined position so as to generate lift to enhance or decrease the spin. The timing and sequence of deployment of the spin devices determines the amount of cross range correction. 
     Deployment of the aerodynamic surfaces is preferably accomplished through firing simple gun-hard pyrotechnic pistons, which force the devices radially from the projectile. This action, combined with the centrifugal force created by the spin of the round, drives the aerodynamic surface out of its chute, through a protective seal, to an active setting. The command to deploy is determined by a system which calculates current trajectory, compares it to the trajectory needed to impact the target, and calculates an adjustment strategy. Deployment commands may be staggered so as to provide initial launch error correction and vernier correction for deviations that develop throughout the flight. 
     The timing of the command to deploy is critical to the correction method. Infinitesimal trajectory errors at launch can result in tremendous errors over a flight span of 20+ miles. The present invention leverages the time of flight for a passive correction technique utilizing the aerodynamic characteristics of a spin stabilized projectile. Range is easily decreased by increasing the drag through an increase of the surface area of the projectile with respect to the direction of flight. The present invention increases drag by deploying surfaces generally perpendicular to the line of flight. The drag surfaces are simply airbrakes. A deployment early in the flight allows for the use of smaller surfaces for they have a longer time to affect the trajectory. Additional increases in the surface area later in-flight provide a residual correction or vernier correction. 
     Likewise, the present invention leverages the physics of a spinning body to vary the deflection. Cross range deflection is affected by two parameters; the pitching moment coefficient and the normal force coefficient. First, a spinning body produces a normal force proportional to its yaw angle in the airstream. The yaw angle, often referred to as the yaw of repose, is proportional to the spin rate. A spin damping device will lower the spin rate and the yaw angle which results in less cross range deflection. Note that a change in spin rate does not occur immediately upon deployment of the spin surfaces. There is a dynamic lag while the projectile decelerates which is taken into account in the deployment calculations. 
     Second, deploying aerodynamic surfaces affects the pitching moment which in turn affects stability. The effect varies with location of the aerodynamic surface as related to the center of gravity of the projectile. Placing fins on the tail of a projectile makes it more stable, like the fletching on an arrow, while fins placed forward of the center of gravity decrease stability. A standard artillery right twist barrel produces a spinning projectile with a drift to the right, which is proportional to the yaw of repose. The yaw of repose varies inversely with the pitching moment coefficient. Finally, the spin surfaces, which preferably have a swept wing appearance, provide some lift to the projectile. The cross range drift is proportional to the lift on the projectile. In summary, adding fins to the projectile can alter cross range deflection by changing the spin rate, by changing the lift and by changing the pitching moment. 
     The present invention provides a method and apparatus for effecting two-dimensional in-flight course correction for artillery shells by deploying pairs of aerodynamic surfaces which affect range and cross range deflection, respectively, to place the projectile on a trajectory which will impact the target. The deployment of the aerodynamic surfaces is preferably determined by a fire control system on the ground in which a projectile tracking radar is used to measure position and velocity of the projectile, calculate course corrections, and uplink commands to the projectile. This method is preferred for it reduces the complexity and quantity of the command/control equipment within the projectile. The 2-D projectile trajectory corrector module then only contains a receiver and a programmable timer to process the commands and deploy the aerodynamic surfaces. Alternatively, the fins may be controlled using a GPS receiver and on-board microprocessor to make the deployment calculations. 
     A vernier correction method is utilized in which multiple deployments of aerodynamic surfaces are made. In a preferred embodiment, each aerodynamic surface has at least one intermediate setting and a fully deployed setting. An initial deployment occurs shortly after launch. Fine targeting corrections, to remove residual errors which develop during flight, is made by deploying selected surfaces to their fully deployed positions later in-flight. Alternatively, additional sets of aerodynamic surfaces maybe included so that the initial correction involves deploying one set of aerodynamic surfaces to a fully deployed position while fine correction is accomplished by deploying one or more additional sets of aerodynamic surfaces to a fully deployed position later in the flight. 
     While drag is increased by simply increasing the exposed surface area of the drag tabs, residual deflection control requires deployment of tabs which will further decrease the spin rate. Therefore, the tab angle of attack will have to be alterable for initially deployed tabs or subsequent additional deployment will occur with tabs having a fixed angle of attack designed to further reduce the spin rate. Clearly, all of the aerodynamic surfaces could have multiple deployment settings so that many corrections could be made during flight. 
     In the preferred embodiment, the aerodynamic surfaces are set in a module to deploy at a fixed angle of attack relative to the direction of flight. For example, at least one pair of surfaces will lie nearly perpendicular to the line of flight so as to increase drag and at least one pair will lie nearly parallel to the line of flight but having a selected angle of attack so as to change the spin rate. This design is preferred due to the simplicity of the design, limited space within the projectile, cost and reliability. In an alternative embodiment, the aerodynamic surfaces could be motor driven so that multiple angles of attack are possible. 
     In a first embodiment of the present invention, a 2-D projectile trajectory corrector module containing multiple pairs of aerodynamic surfaces, (i.e. spin and drag tabs), a receiver and a programmable timer, which processes the directions and deploys the aerodynamic surfaces accordingly, would be retrofitted to an existing artillery round such as the M864 or M549 rounds for use with 155 mm artillery pieces. These rounds are approximately 35 inches in length yet can be stretched to 39 inches (1 meter) and still be fired by existing and planned artillery pieces. The size of the 2-D projectile trajectory corrector system aboard the projectile would be limited to a cylinder four inches in length with a diameter complimentary to the aerodynamic shape of the retrofitted rounds. The tabs, as originally mounted are internal or flush with the periphery of the projectile. During deployment, the tabs are driven to an active aerodynamic position by firing gun hard pyrotechnic pistons. To mate the present invention to an existing round, the warhead is unscrewed from the body and a guidance section containing the present invention is inserted. The projectiles&#39; rocket motor is then attached. This design does not require any changes to the current fuze, warhead or rocket design. Advantageously, none of these components has to be regulated. 
     In a second embodiment of the present invention a 2-D projectile trajectory corrector module containing multiple pairs of aerodynamic surfaces, (i.e. spin and drag tabs), a receiver and a programmable timer which processes the directions and deploys the aerodynamic surfaces accordingly is installed in the ogive position on a projectile, immediately aft of the fuze assembly. One advantage of such a placement involves decreasing the distance of the corrector from the center of gravity which advantageously affects the pitching moment and can be used to decrease deflection. Additionally, with the spin tabs mounted on the periphery of the projectile the spin tab size can be minimized due to the fact that they have a larger moment arm about the spin axis. The 2-D projectile trajectory corrector system has a diameter that is complimentary to the aerodynamic shape of the round while the length of the cylinder is limited by the acceptable overall length of the projectile for the respective weapon. The tabs, as originally mounted are internal or flush with the periphery of the projectile and deployed by pyrotechnic pistons. 
     In a third embodiment of the present invention, the 2-D projectile trajectory corrector module contains single pairs of aerodynamic surfaces, (i.e. spin and drag tabs), the receiver and the programmable timer which processes the directions and deploys the aerodynamic surfaces accordingly will be installed within the fuze assembly of an existing round. From an economic standpoint, this location allows the 2-D projectile trajectory corrector to be installed on millions of existing rounds. A further advantage of such a placement involves the distance of the corrector surfaces from the center of gravity which affects the pitching moment and can be used to decrease deflection. However, the spin tabs mounted on the periphery of the projectile have to be larger than the central body and ogive positions due to the fact that they have a smaller moment arm about the spin axis. 
     The size of the 2-D projectile trajectory corrector system mounted within the fuze is limited. The fuze may be lengthened, but overall length of the projectile must not exceed 1 meter, and while diameter of the fuze increases from the nose to the aft portion, internal space is at a premium due to the necessary fuze components. The tabs, therefore are limited to single pairs which pivot from the body of the projectile but have at least two settings. 
     In practice, target coordinates are determined and the projectile, fitted with the present invention, is fired with an initial aim point down range and to the right of the target. With the corrector surfaces mounted forward of the center of gravity, the spin tabs are used to decrease spin which results in less deflection, thus the spin tabs draw the projectile to the left. In the preferred embodiment of the present invention, the trajectory of the projectile is calculated by a radar system either coincident to the weapon or a stand alone radar system. Based on the tracking results, commands are uplinked to the projectile for an initial deployment of the drag and spin tabs to eliminate errors caused by muzzle exit velocity and elevation error. The tracking radar maintains contact with the projectile throughout the flight. Consequently, additional deployments of drag and spin tabs are made to remove residual errors. Through the present invention, the projectile can be guided to either strike within an acceptable distance from the target or, if the projectile is clearly off course due to weather or the target has moved, the projectile can be directed to impact in a safe area. 
     The 2-D projectile trajectory corrector system of the present invention is shown generally at  10  in the figures. It is generally comprised of an annular support structure  12 , drag tabs  14 , and spin tabs  16 . In a first embodiment, depicted in FIG. 1, the preferred projectile onto which the present invention is retrofitted is designated a M549 rocket assisted projectile  20 . The projectile  20  is comprised of a fuze assembly  22 , a warhead  24 , a rocket assembly  26 , and an obturator band  28  whose diameter is slightly greater than the projectile  20 . The obturator band  28  imparts the rotation to the projectile  20  as it follows the rifling of the barrel. The 2-D projectile corrector  10  is installed forward of the obturator  28 , between the warhead  24  and rocket assembly  26 . As depicted in FIG. 1, the spin tabs  16  and drag tabs  14  are deployed. 
     FIG. 2 depicts a cut away view of the annular support structure  12  of the 2-D projectile trajectory corrector  10 . Detailed specifications as to the thickness and diameter of the annular structure  12  are well known to those skilled in the art for they correspond with dimensions and design tolerances of the M549 round  20 . The annular structure  12  maintains the same outer diameter as the adjacent sections of the projectile  20 . The thickness of the support body  32  corresponds to that needed to withstand the longitudinal and radial pressures associated with initial launch and subsequent firing of the rocket assembly structure  26 . Note that placement of the projectile trajectory corrector  10  forward of the obturator band  28  avoids the extreme conditions aft of the obturator band  28  seal, which exist in that region due to the propulsion of the projectile  20 . 
     The aerodynamic tabs  14 ,  16  are housed in a fixed position within a deployment ring  34  prior to launch. As shown in the first embodiment, the drag tabs  14  are preferably rectangular while the spin tabs  16  preferably have a streamlined triangular shape with the base of the triangle on the aft end and a restraining pin  36  mounted on the fore end which holds the tab  16  in its slot  17  when fully deployed. The tabs  14 ,  16  are located within individual chutes  30 . The tabs  14 ,  16  are deployed by firing a gun hard pyrotechnic piston  38 , the detailed specifications of which are well known to those skilled in the art. The piston  38  drives the tabs  14 ,  16  down their respective chutes  30  and through a protective seal in the slot  17  to the desired deployment. In this embodiment there are multiple sets of spin tabs  16  and drag tabs  14 . The vernier effect is accomplished by deploying at least one opposing set of tabs  14 ,  16  for the initial correction and at least a portion of the remaining tabs  14 ,  16  for residual correction. 
     In a second embodiment, as depicted in FIG. 3, the projectile  40  onto which the present invention  10  is fitted is an advanced 155 mm round  40  for the Advanced Gun System (AGS). The AGS, originally designed to support the US Navy&#39;s DD land-attack destroyer program, is capable of engaging targets at ranges in excess of 40 miles. The projectile  40  is comprised of a fuze assembly  22 , a warhead  24 , a rocket assembly  26 , and an obturator band  28 . The 2-D projectile trajectory corrector system  10  is installed behind the fuze  22  in the ogive position of the projectile  40 . As depicted in FIG. 3, the multiple sets of the spin tabs  16  and drag tabs  14  are deployed. The annular structure  12  is tapered from fore to aft to maintain the same outer diameter as the adjacent sections of the projectile  40 . The thickness of the annular structure  12  corresponds to that needed to withstand the radial and axial pressures associated with initial launch and subsequent firing of the rocket assembly structure. 
     The aerodynamic tabs  14 ,  16  are housed in a fixed position within the annular ring  12  prior to launch. The drag tabs  14  are preferably rectangular in shape while the spin tabs  16  preferably have a streamlined triangular shape with the base of the triangle on the aft end. The tabs  14 ,  16  are located within individual chutes  30  to which a piston  38  is attached (See FIG.  2 ). The tabs  14 ,  16  are deployed by firing the gun hard pyrotechnic piston  38 . The piston  38  drives the tabs  14 ,  16  down its respective chute  30 . In this embodiment there are multiple sets of spin tabs  16  and drag tabs  14  so the vernier effect is accomplished by deploying at least one opposing set of tabs  14 ,  16  for the initial correction and at least a portion of the remaining tabs  14 ,  16  or less for residual correction. 
     In an alternate embodiment, the present invention could be retrofitted to any projectile through the use of a specially designed fuze which incorporates both spin and drag inducing surfaces. FIG. 4 depicts a 2-D projectile trajectory corrector system  10  which is incorporated into a new fuze design. Because of space constraints within the fuze assembly  22  there is only room for two spin tabs  16 . The surface area of the individual spin tabs  16  must be greater than the previously described embodiments where multiple tabs  14 , 16  are used (See FIGS.  1  and  3 ). The tabs  16  are depicted in FIG. 4 as fully deployed. The shape of the spin tabs  16  is generally triangular with the base at the aft end. The leading edge of the spin tab  16  has a swept wing so as to reduce drag. 
     When only two spin tabs  16  exist, the vernier effect is accomplished by a spin tab  16  design which incorporates at least two deployment settings so as to provide initial and residual trajectory correction. The initial correction may be accomplished by partial deployment of the spin tab  16 . Residual correction is accomplished by achieving a full deployment setting of the spin tab  16  with a new angle of attack at the appropriate point along the trajectory. 
     An alternate fuze design embodiment  60 , is depicted in FIGS. 5 and 6, is comprised of one set of drag tabs  14  and one set of spin tabs  16 . Spin tab  16  must have a variable angle of attack setting in order to provide residual correction. FIGS. 5A and 5B depict a swept wing shaped spin tab  16  fully deployed. The tab  16  is stored pre-launch in chute  61 . The spin tab wing tip  65  has a leading edge  63  with extends outboard greater than the trailing edge  64  so as to facilitate rotation out of the tab chute  61 . The wing shaped tab  16  is released by a pyrotechnic piston (not shown) internal to the fuze assembly  22  which pushes the tab  16  out of the chute. Centrifugal force from the spinning projectile rotates the tab  16  about the leading edge  63  of the tab root  66  through a pivot (not shown) to a fully deployed position. 
     Initially, spin tab  16  is in a streamlined position which does not influence the spin characteristics of the projectile, accept to minimally increase drag. The leading edge of the tab root  66  is mounted within a fitting  62  which can pivot about the streamlined position. The fitting  62  allows the tab  16  to be rotated so as to spin up, FIG. 6A, or spin down, FIG. 6B, the projectile. Putting a spin up torque on the projectile increases the draft of the projectile to the right. The aft end of the tab root  66  extends aft of the fitting  62  and is radially displaced from the fuze body  22  so as to facilitate rotation about fitting  62 . In addition, the fitting  62 , is designed for multiple settings in order to increase or decrease spin for correction of residual error. The rotation of the fitting may be made to preset angles through firing a pyrotechnic piston or allow for any variation by way of an electric motor. 
     The drag tab surfaces  14  are also subject to space constraints when incorporated into a fuze  60 . FIGS. 4 and 5 depict two separate approaches. FIG. 4 depicts multiple smaller drag tabs  14  radially deployed around the base of the fuze  60 . Note that the individual tabs are shaped to maximize surface area within the constraints of the diameter of the fuze. The outboard edge of the drag tab  51  is wider than inboard edge  52 . The outboard edge  51  is curved so that when in the stored position, the outboard edge tracks the arc of the fuze assembly  22  proximate the tab. The inboard edge  52  is sized to correspond with the decreased radius when in the stored position. The vernier effect is, accomplished by deploying at least one opposing set of drag tabs  14  for the initial correction and the remainder or less for residual correction. As depicted in FIG. 4, all of the drag tabs  14  are deployed so the projectile is in the residual correction mode. 
     FIGS. 5 and 7 depict an alternate drag tab  14  configuration in which only one pair of aerodynamic surfaces is deployed. In contrast to the spin tabs  16 , the drag tabs  14  are deployed incrementally in two steps, FIGS. 7A-7C. The drag tabs  14  are mounted to the aft end  71  of the fuze assembly  60  so as to maximize their potential surface area and avoid the internal circuitry of the fuze. Each tab  14  is comprised of three sides: a curved outer edge  72 ; a radial edge  73 ; and an inboard edge  75 . The tab rotates radially about a pivot point  76  located proximate the juncture of the outboard  72  and inboard  75  sides. The curved outer edge  72  follows the same arc as the base of the fuze  71  when in the pre-deployment position, FIG.  7 A. The radial edge  73  is angled so that its tangent would bisect the center of the fuze  22 . 
     As installed on the projectile, the drag tabs  14  are nested within slots  67  internal to the fuze with the outer edge  72  flush with the periphery of the projectile. The inner edge  75  abuts a drag tab base  78  which has the same thickness as the drag surfaces  14  and outer faces reciprocal to the inner edge  75  of the respective tabs  14 . Two pyrotechnic pistons  79 , one for each tab, are mounted on the drag tab base  78  for driving the tabs  14  out of their respective slots  67  upon initial deployment. As depicted in FIG. 7B, the drag tab base  78  contains two slots  81  which correspond with an interim deployment notch  74  on the radial edge  73  which allows for an interim deployment setting. The inboard edge  75  contains a hook  82  adjacent the pivot point  76  for engaging a protrusion  80  on the drag tab base  78  which acts as a stop once the drag tabs  14  reach maximum deployment. The drag tab base  78  contains a central opening  77  for passage of command and control wiring to the projectile warhead and rocket assembly which lies aft of the fuze  22 . 
     In operation, the projectile with the present invention  10  installed is fired long and to the right of the true target due to the naturally existing yaw of repose which creates a deflection to the right. Command and control of the projectile may be accomplished through a combination of a phased array radar system and a fire control system. The fire control system may comprise a microwave link, which gives the projectile&#39;s position, a unit for calculating the trajectory and the trajectory correction vector. A ballistics computer on the ground calculates actual impact point of the projectile and extrapolate initial range and deflection corrections. Spin and drag tab  14 ,  16  deployment is communicated to the guidance corrector on the projectile  20  through the tracking/command radar uplink which is orders of magnitude stronger than a GPS uplink. The pyrotechnic pistons  38  fire deploying spin  16  and drag tabs  14  to their required initial position. Initial deployment of the drag tabs  14  reduce range. Initial deployment of the spin tabs  16  slowly de-spins the projectile. The lower rotational rate reduces the cross range deflection. 
     Additional corrections may be made in-flight to remove residual error created by the environment or flight characteristics of the projectile. The result is a range correction through either full deployment of the drag tabs  14  or deployment of additional drag tabs  14  and a decrease in deflection by deploying spin tabs  16  with a new angle of attack which will further draw the projectile  20  to the left. In the alternative, if the fire control system determines that it is impossible to reach the target based on initial launch parameters, the fire control system may direct the projectile  20  to a safe impact point. 
     It is obvious to those skilled in the art that other embodiments of the device and method, in addition to the ones described herein, are indicated to be within the scope and breadth of the present application. Accordingly, the applicant intends to be limited only by the claims appended hereto.