Abstract:
A steerable projectile comprises a pressure chamber to hold gas in a pressurized state; and a body section coupled to the pressure chamber, the body section having a flight system to use the pressurized gas for adjusting a trajectory of the projectile. The pressure chamber comprises an orifice in a wall of the pressure chamber; and a check valve corresponding to the orifice, the check valve configured to allow gas that results from ignition of a propellant to enter the pressure chamber via the corresponding orifice and to prevent the gas, once inside the pressure chamber, from exiting the pressure chamber via the corresponding orifice.

Description:
BACKGROUND 
     There are different techniques for steering or guiding a projectile during flight. For example, guided projectiles can be fin-stabilized or spin-stabilized and can use internal and/or external air-actuated control methods. As used herein guided projectiles include, but are not limited to, bullets, artillery projectiles (e.g. shells and shots), and tube-launched missiles. The Defense Advanced Research Projects Agency (DARPA) EXtreme ACcuracy Tasked Ordinance (EXACTO) project and the United States Army&#39;s Excalibur artillery projectile are examples of systems which use guided projectiles. 
     Typical guided projectiles which use internal air-actuated control methods include a chemical gas generator which is responsible for generating pressurized gas. The pressurized gas is then released through one or more orifices in the projectile to adjust the trajectory of the projectile. However, the chemicals used to generate the gas have a limited shelf-life which means that the guided projectile must either be used or replaced periodically. In addition, the components necessary for generating the pressurized gas and controlling the amount of pressure of the generated gas can be costly. 
     SUMMARY 
     In one embodiment, a steerable projectile is provided. The steerable projectile comprises a pressure chamber to hold gas in a pressurized state; and a body section coupled to the pressure chamber, the body section having a flight system to use the pressurized gas for adjusting a trajectory of the projectile. The pressure chamber comprises an orifice in a wall of the pressure chamber; and a check valve corresponding to the orifice, the check valve configured to allow gas that results from ignition of a propellant to enter the pressure chamber via the corresponding orifice and to prevent the gas, once inside the pressure chamber, from exiting the pressure chamber via the corresponding orifice. 
    
    
     
       DRAWINGS 
       Understanding that the drawings depict only exemplary embodiments and are not therefore to be considered limiting in scope, the exemplary embodiments will be described with additional specificity and detail through the use of the accompanying drawings, in which: 
         FIG. 1  is an exploded perspective view of one embodiment of a projectile. 
         FIG. 2  is a cross-sectional view of one embodiment of a pressure chamber. 
         FIG. 3  is a perspective view of another embodiment of a pressure chamber. 
         FIG. 4  is a cross-sectional view of the pressure chamber of  FIG. 3 . 
         FIG. 5  is a cross-sectional view of another embodiment of a pressure chamber. 
         FIG. 6  is a block diagram of one embodiment of a projectile cartridge. 
         FIG. 7  is a block diagram of one embodiment of a projectile launching system. 
     
    
    
     In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize specific features relevant to the exemplary embodiments. 
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments. However, it is to be understood that other embodiments may be utilized and that logical, mechanical, and electrical changes may be made. The following detailed description is, therefore, not to be taken in a limiting sense. 
     The embodiments described below provide pressurized gas for use in an air-actuated control system of a guided projectile, also referred to herein as a steerable projectile. In particular, the embodiments described below have a practically limitless self-life. In addition, the embodiments described below substantially reduce the complexity of the gas generation system as compared to typical chemical gas generators. 
       FIG. 1  is an exploded perspective view of one embodiment of a projectile  101 . The projectile  101  can be implemented, for example, as a bullet, an artillery shell, or a tube-launched missile. Notably, the projectile  101  is provided by way of example and not by way of limitation. In particular, the projectile  101  may include other components in addition to those shown in  FIG. 1  when implemented. 
     The projectile  101  includes a body section  102  and a pressure chamber  104 . The body section  102  includes flight system  105  and navigation or guidance system  107 . Notably, flight system  105  and guidance system  107  are depicted in  FIG. 1  by way of example. In particular, flight system  105  and guidance system  107  can be located in any portion of the body section  102 . In this example, the body section  102  and the pressure chamber  104  are cylindrical. However, it is to be understood that, in other embodiments, the body section  102  and pressure chamber  104  are not required to be cylindrical. 
     Flight system  105  is configured to alter or adjust the flight path of projectile  101  based on information received from guidance system  107 . In particular, the flight system  105  is an internal air-actuated control system which releases pressurized gas from one or more orifices  115  in the projectile  101  to control the trajectory of the projectile  101 . For example, the release of the pressure may be a jet of gas that deflects the projectile as it exits orifices  115 . In other embodiments, the pressurized gas is used to pop out a fin/control surface which steers the projectile  101 . Suitable air-actuated flight control systems are known to one of skill in the art of guided projectiles. The guidance system  107  can be a laser-guided system, a radar-based tracking system, an infrared tracking system, an inertial measurement unit, a global positioning system (GPS) sensor, or any combination thereof, as known to one of skill in the art. In addition, one of skill in the art is aware of other appropriate guidance systems which can be used to implement guidance system  107 . 
     The projectile  101  also includes a pressure chamber  104  which holds the pressurized gas used by flight system  105  to maneuver the projectile  101 . The pressure chamber  104  includes an orifice  106  located along a center axis  107  of the pressure chamber  104 . The orifice  106  is disposed in an external wall of the pressure chamber to permit gas from outside the pressure chamber  104  to enter the pressure chamber  104 . In particular, when a propellant is ignited to propel the projectile  101  out of a tube, such as a gun barrel, an artillery cannon or a missile launch tube, the gas produced by the ignited propellant enters the pressure chamber  104  through the orifice  106 . As used herein, a propellant is an explosive substance which produces a force when ignited that imparts motion to a projectile. 
     Hence, the projectile  101  does not need a chemical reaction gas generator as used in conventional guided projectiles. Since, the projectile  101  uses pressurized gas from the ignited propellant, the projectile  101  essentially has an unlimited shelf-life as long as the propellant can be ignited. In addition, the relative simplicity of the pressure chamber  104 , as compared to typical gas generators, reduces the cost of manufacturing the projectile. 
       FIG. 2  is a cross-sectional view of one embodiment of the pressure chamber  104  used in the projectile  101 . As shown in this exemplary embodiment, the pressure chamber  104  includes an orifice  106  and a check valve comprised of a spring  212  and a cover  208  coupled to the spring  212 . In this example, the cover  208  is implemented as a sphere. However, it is to be understood that other shapes of the cover  208  can be used in other embodiments. 
     The cover  208  is configured to prevent gas from entering or leaving the pressure chamber  104  when it covers the orifice  106 . In particular, based on its spring constant, the spring  212  provides a force on the cover  208  which causes the cover  208  to cover or block the orifice  206 . When a propellant is ignited, the pressure from the explosion provides enough force to overcome the force applied on the cover  208  by the spring  212 . Thus, the pressure from the ignited propellant moves the cover  208  to open the orifice  106  and allow gas to enter the pressure chamber  104 . Gas continues to enter the chamber  104  until the pressure of the gas reaches a desired range. In particular, if the pressure in the chamber  104  is too low, the projectile  101  will not steer well. However, if the pressure is too high, the pressurized gas can rupture the wall of the pressure chamber  104 . Once the desired range is reached, the spring  212  will then cause the cover  208  to press against and cover the orifice  106  to prevent entry or exit of more gas through the orifice  106 . Since the ignition of the propellant will generally produce more than sufficient pressure, the lower pressure limit is controlled by the spring  212  and cover  208  which prevent the pressurized gas from exiting the pressure chamber  104 . The upper pressure limit is controlled by the diameter of the orifice  106 , the value of the external pressure produced by ignition of the propellant, and the time the external pressure is applied. 
     In addition, the pressure chamber  104  optionally includes a filter  210 . The filter  210  is needed in embodiments in which particles in the gas from the propellant could clog or block channels in the flight system  105  through which the pressurized gas travels. For example, in the embodiment of  FIG. 2 , the filter  210  is placed at the opening of the orifice  106  to prevent the particles from entering the pressure chamber  104 . However, in other embodiments, the filter  210  can be placed in other locations. For example, in one embodiment, the filter  210  is placed at an opening through which the gas in the pressure chamber exits to the flight system  105  leaving the particles in the pressure chamber  104 . 
     Furthermore, although a single orifice  106  is shown in  FIGS. 1 and 2 , it is to be understood that in other embodiments more than one orifice can be used. For example, in  FIGS. 3 and 4 , another embodiment of a pressure chamber  304  has two orifices  306 - 1  and  306 - 2 . Orifices  306 - 1  and  306 - 2  are placed along the perimeter of the pressure chamber  304  and located symmetrically about the center axis  307  of the pressure chamber  304 . By placing the orifice along the perimeter of the pressure chamber  304 , the center of the back surface  311  of the pressure chamber  304  can be used for other purposes, such as for sensors used for laser-guidance. 
     As shown in the cross-sectional view of  FIG. 4 , the pressure chamber  304  includes a check valve for each orifice  306 . The check valve for each orifice  306  includes a spring  412  and a cover  408  as described above with respect to  FIG. 2 . It should be noted that, although a spring and cover are shown and described herein, the check valve for each orifice  306  can be implemented in other ways. For example, a flap and joint can be used in other embodiments, as shown in  FIG. 5 . Furthermore, although two orifices  306  are shown in this example, more than two orifices symmetrically placed about the center axis  307  can be used in other embodiments. 
       FIG. 5  is a cross-sectional view of another embodiment of a pressure chamber  504 . In the exemplary pressure chamber  504 , the check valve is implemented as a flap  509  and a joint  513 . The joint  513  is biased to a position that maintains the flap  509  in a position to close or block the orifice  506 . Hence, the flap  509  and joint  513  prevent pressurized gas inside the pressure chamber  504  from exiting through the orifice  506  similar to the spring  212  and cover  208  discussed above. Additionally, gas that results from the ignition of a propellant is able to enter the pressure chamber  504  by providing enough force to overcome the bias in the joint  513 . Also, in the example of  FIG. 5 , the optional filter is not included in the pressure chamber. 
       FIG. 6  is a block diagram of an exemplary embodiment of a projectile cartridge  600 . The projectile cartridge can be a bullet cartridge or an artillery projectile cartridge. The projectile cartridge  600  includes a projectile  601 , casing or shell  614 , propellant  616 , and primer  618 . The projectile  601  is disposed in an opening in a first end of the casing  614  and the primer  618  is disposed in a second end of the casing  614 . The propellant  616  is disposed within a cavity formed by the casing  614  as shown in  FIG. 6 . 
     The primer  618  is used to ignite the propellant  616  located in the casing  614  as known to one of skill in the art. The pressure that results from igniting the propellant  616  forces the projectile  601  out of the casing  614  and out of a tube such as a gun barrel or artillery canon. In addition, the projectile  601  includes a body section  602  and a pressure chamber  604  similar to the exemplary embodiments of a body section and a pressure chamber described above. In particular, the pressure that results from igniting the propellant  616  also causes the pressure chamber  604  to be filled with gas as described above. The projectile  601  then uses the pressurized gas in pressure chamber  604  for controlling the trajectory of the projectile  601  during flight as described above. 
       FIG. 7  is a block diagram of one embodiment of a projectile launching system  703 . The projectile launching system includes a projectile  701 , a tube  722 , a propellant  716 , and a firing mechanism  720 . The projectile  701  includes a body section  702  and a pressure chamber  704  similar to the exemplary embodiments of a body section and a pressure chamber described above. In this embodiment, the projectile  701  is part of a projectile cartridge  700  similar to projectile cartridge  600  described above. In particular, the projectile  701  is disposed in an opening in a first end of a casing  714  and a primer is disposed in a second end of the casing  714 . A propellant  716  is disposed inside the casing  714 . However, it is to be understood that projectile launching system  703  is provided by way of example only. In particular, in some embodiments, the projectile  701  is not part of a projectile cartridge. For example, projectile  701  can be implemented as a tube-launched missile. In such embodiments, the propellant  716  is located in a section of the projectile  701 . Alternatively, in other embodiments, a projectile, such as an artillery shot can be placed in a tube  722  without a cartridge. In such a case, the propellant  716  is loaded into the tube  722  separately. 
     The firing mechanism  720  causes the propellant to ignite which propels the projectile  701  out of the tube  722 . For example, in some embodiments, the tube  722  is implemented as a gun barrel and the projectile  701  is a bullet. In such a case, the firing mechanism is a hammer which strikes the primer  718  to ignite the propellant  716 . The ignition of the propellant  716 , thus, causes the bullet to be propelled out of the barrel. In other embodiments, the tube  722  is an artillery canon and the projectile  701  is an artillery shell. The gas produced by the ignition of the propellant  716  enters the pressure chamber  704 , as described above. 
     A flight system in the projectile  701  uses the pressurized gas to adjust the trajectory of the projectile  701 , as described above, and known to one of skill in the art. Hence, as described above, the projectile  701  has a substantially limitless shelf-life since it does not depend on chemical reactions to generate the pressurized gas as in typical guided projectiles. In addition, the projectile  701  is relatively less expensive to manufacture by leveraging the pressure produced by the ignited propellant  716  to fill the pressure chamber  704  with pressurized gas. 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiments shown. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.