Patent Publication Number: US-6666144-B1

Title: Warhead decoupling bearing

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without payment of any royalties thereon or therefor. 
     BACKGROUND OF THE INVENTION 
     1. Field Of The Invention 
     The present invention pertains to mechanisms to decouple a warhead from a rocket motor to improve the precision of the rocket motor and more particularly to a bearing system to decouple a warhead from a rocket motor. 
     2. Description Of The Related Art 
     The precision of current rocket motors relates directly to the spin rate that they are capable of obtaining during use. When the spin rate is increased, this improves the precision of the rocket motor. In certain rocket motor systems, flutes are machined in the rocket nozzle body in order to generate torque, which, in turn, generates spin of the rocket motor during use. For example, flutes within a typical 2.75 inch rocket motor can generate a maximum of approximately 3 ft-lbs of torque. The spin rate that is generated from this torque relates directly to the weight of the warhead/rocket motor system. 
     One method that has been employed to reduce the weight of rocket motor portion of the system in order to increase the spin rate of the rocket motor, is to decouple the warhead from the rocket motor during use so the warhead spins separately from the rocket motor. Therefore, the same torque as discussed above can be applied to only the rocket motor, which weighs significantly less without the warhead attached, thus creating a higher spin rate. Many larger warhead/rocket motor systems use ball bearing systems to decouple the warhead from the rocket motor. However, in order to meet the precision requirements for military applications, such a ball bearing must be custom made. Also, because ball bearings require liquid lubrication in order to operate effectively, in order to maintain the systems over a long shelf life, regular service is required for such systems. Thus, for smaller warhead/rocket motor systems, it is not cost effective to employ such a decoupling system. 
     Therefore, it is desired to provide a low-cost system to decouple a warhead from a rocket motor during use for smaller warhead/rocket motor systems. 
     SUMMARY OF THE INVENTION 
     The present invention comprises annular bearings that allow a warhead to decouple from a rocket motor during use to increase the spin rate of the rocket motor, and, in turn, increase the precision of the rocket motor. The present invention is designed to be a low-cost, maintenance free alternative to ball bearing decouplers. 
     Accordingly, it is an object of this invention to provide a low-cost alternative to ball bearing decouplers for rocket motor and warhead systems. 
     It is a further object of this invention to provide a maintenance free bearing decoupler for rocket motor and warhead systems. 
     A still further object of this invention is to provide a more precise rocket motor and warhead system. 
     This invention accomplishes these objectives and other needs related to rocket motor and warhead systems by providing an improved precision rocket motor and warhead system by increasing the spin rate of the rocket motor. The system comprises a rocket motor tube with an outer housing segment attached to one end. An annular sleeve placed within the outer housing segment so that the end of the sleeve is aligned with the end of the outer housing segment. At least two annular bearings are placed around the outer surface of the sleeve. Normally the annular bearings will be made of a plastic type material that can be “stretched” around the outside of the sleeve prior to placing it within the outer housing segment. The inner surface of the sleeve will include a warhead attachment mechanism to secure the warhead to the inner surface. Finally, the invention includes a locking mechanism that locks the sleeve in place within the outer housing segment while attaching the warhead to the sleeve and unlocks to allow the sleeve to rotate independently of the rocket motor tube. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawing, which is incorporated in and constitutes a part of the specification, illustrates an embodiment of the invention, and, together with the description, serves to explain the principles of the invention. 
     FIG. 1 is an exploaded, angled view of an embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention, as embodied herein, comprises an improved precision rocket motor and warhead system using annular bearings to decouple the rocket motor from the warhead during use, thereby reducing the weight of the rocket motor and increasing its spin rate. The annular bearings are preferably made of a plastic material that is low-cost, easily manufactured and requires little or no maintenance over the length of the systems&#39; shelf-life. The invention also comprises a method of increasing the precision of a rocket motor and warhead system using the annular bearings described herein to decouple the rocket motor from the warhead during use. 
     Referring to FIG. 1, the invention comprises a rocket motor tube  100  having an open end  102  that is attached to an outer housing segment  101 . The outer housing segment  101  is attached on the outside of the end  102  so that the inner diameter of the outer housing segment  101  is slightly larger than the inner diameter of the rocket motor tube  100 . Numerous methods of attachment can be used including threads or tabs. The embodiment of the invention shows two tabs  105  that click into place when the outer housing segment  101  is placed over the end  102  of the rocket motor tube  100 . An annular sleeve  104  has at least two annular bearings  106  placed around it. The annular sleeve  104  is placed within the outer housing segment  101 . The sleeve  104  will normally be placed with the end  116  of the sleeve  104  proximately aligned with the open end  103  of the outer housing segment  101 . The outer diameter of the sleeve  104  plus the bearings  106  is such that the sleeve  104  will not slide into the rocket motor tube  100  due to the smaller diameter of the rocket motor tube  100  versus the outer housing segment, but, the bearings  106  still allow the sleeve  104  to spin within the outer housing segment when force is applied to the sleeve  104 . In this configuration, the sleeve  104  may spin independently of the rocket motor tube  100 . The invention also includes a locking mechanism  108 ,  110  that locks the sleeve  104  in place within the outer housing segment  101 . This allows the warhead  112  to be attached to the sleeve using the warhead attachment mechanism  114 . 
     The present invention was developed for use in the 2.75-inch rocket motor and warhead system, however, the invention may be employed within any rocket motor  100  and warhead  112  system. The sleeve  104  and the outer housing segment  101  will normally be constructed of a metal material with one preferred material being aluminum (the rocket motor tube  100  is normally constructed of the same material). The inner diameter of the outer housing segment  101 , as noted above, will be slightly larger than the inner diameter of the rocket motor tube  100 . The width of the outer housing segment  101  will be slightly larger than the width of the sleeve  104  as discussed below to allow the sleeve  104  to fit within the outer housing segment  101 . The outer diameter of the sleeve  104  will depend upon the rocket motor  100  and warhead  112  system. The sleeve  104  should be designed to fit within the outer housing segment  101  so that it will not slide into the rocket motor tube  100 . The outer diameter of the sleeve  104  plus the bearings  106  should also allow the bearings to spin within the outer housing segment  101 . The width of the sleeve  104  can vary and may be determined by one skilled in the art as long as it fits within the outer housing segment  101 . The width of the sleeve will normally increase with the size of the rocket motor  100  due to the normal forces at work on the sleeve  104  placed upon it by the rocket motor  100  and warhead  112 . 
     The annular bearings  106  preferably are made from a plastic material that can be stretched around the sleeve  104  like a sock. The plastic material may be selected by one skilled in the art as long as the coefficient of friction of the material is low enough to allow the sleeve  104  to spin within the outer housing segment  101 . Examples of preferred materials include polytetrafluoroethylene (teflon) and acetal. The coefficient of friction between teflon and aluminum is approximately is 0.04 and the coefficient of friction between aluminum and aluminum is approximately 1.04. Therefore, the material selected should comprise a coefficient of friction below 1.04 and more preferably below 0.20. By using a plastic material, the bearings  106  can be moldable parts, which significantly decrease manufacturing costs compared to parts such as custom ball bearings. Furthermore, plastics degrade very little over time, so the bearings  106  do not need to be sealed from the environment to improve shelf-life. For specific purposes, if a lower friction is desired between the bearings  106  and the outer housing segment  100 , a dry film lubricant may be applied. Unlike lubricants used in conjunction with ball bearings (oil, etc.), dry film lubricants have proven to resilient against long term degredation. 
     The locking mechanism  108 ,  110  is needed to hold the sleeve  104  in place within the outer housing segment  101  while attaching the warhead  112  to the sleeve  104 . Many possible locking mechanisms may be used and can be selected by one skilled in the art. One preferred example is set forth in FIG.  1 . Four notches  108 , approximately equidistant from one another, are made on the end  103  of the outer housing segment  101  and on the sleeve  104  on the side  116  aligned with the end  103 . These notches  108  may be aligned and rods  110  can be placed through the notches  108  in order to hold the sleeve  104  immobile within the outer housing segment  101  while the warhead  112  is attached to the sleeve  104 . The term “rods” within this application means any shape that fits through the notches  108  to hold the sleeve  104  immobile within the outer housing segment  101 . 
     The warhead attachment mechanism  114  merely attaches the warhead  112  to the inner surface  118  of the sleeve  104 . Many attachment mechanisms  114  are possible and, again, may be selected by one skilled in the art, including sealant and a screwing mechanism. One preferred warhead attachment mechanism, shown in FIG. 1, are matching threads on the inner surface  118  of the sleeve  104  and the outer surface of one side  120  of the warhead  112  that allow the user to screw the warhead  112  into the sleeve  104 . 
     The invention also includes a method for improving the precision of a rocket motor and warhead system by using the annular bearing system described above. The user places the outer housing segment  101  on the rocket motor tube  100  and places annular sleeve  104 , having the two annular bearings  106 , within the outer housing segment  101 . Then the user attaches the warhead  112  to the sleeve  104  and the rocket motor and warhead system is launched. The rocket motor tube  100  will spin from torque created by flutes within the rocket motor. The sleeve  104  and warhead  112  will spin independently due to the bearings  106  between the sleeve  104  and the outer housing segment  101 . Thus, all of the torque created by the flutes will be used on only the weight of the rocket motor tube  100 , to spin that portion of the system. The greater spin rate will result in improved precision of the system. 
     What is described are specific examples of many possible variations on the same invention and are not intended in a limiting sense. The claimed invention can be practiced using other variations not specifically described above.