Abstract:
A countermeasure launcher system, for use by a submarine, reducing any detectable signature by preventing the escape of pressurized gas into seawater at the forward end of the system&#39;s launch tube upon launching a countermeasure. The pressurized gas that is used in launching the countermeasure is trapped within the launch tube by a unique arrangement of specific components. The pressurized gas is then permitted to slowly exit at a later time via a pressure relief valve in the launch tube&#39;s wall.

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 the payment of any royalties thereon or therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention generally relates to a system for reducing acoustic and visible signatures generated when a submarine countermeasure is launched. More particularly a submarine countermeasure launcher that generates gas to launch a countermeasure has the capacity to capture the gas and therefore reduce the signatures that could be used by an enemy for detection purposes. Countermeasure devices are used to protect submarines from attacking platforms by providing decoys. 
     (2) Description of the Prior Art 
     Ballistic missile submarines currently have eight countermeasure launch device ports positioned outside the submarine&#39;s pressure hull. They are located within the outer hull superstructure forward of the sail. These launch devices are each loaded with an individual countermeasure or another underwater instrument while the submarine is in port. The individual countermeasure or underwater instrument is launched at sea from the submarine&#39;s control room. The launch devices are expendable and cannot be reloaded while the submarine is at sea. 
     Prior to the present invention, the gas generated when firing a countermeasure puts large amounts of acoustic energy and gas bubbles into the water creating a significant detection risk from the resultant acoustic and visual observables. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a general purpose and object of the present invention to provide a system for making a countermeasure launcher more covert at time of launching. It is a further object to achieve this by inhibiting the gas generated during the firing from escaping the launch tube. 
     These objectives are accomplished with the present invention by providing a countermeasure launcher system design centered around capturing the launch tube ram piston at the end of its stroke in such a way that the bubbles produced by a gas generator are contained within the countermeasure launcher&#39;s launch tube. The captured bubbles can be released slowly with reduced acoustic effect. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description of the preferred embodiment taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a partially cutaway pictorial representation of a countermeasure launcher in accordance with the present invention; and 
     FIG. 2 shows a partial sectional view of the launcher tube of FIG.  1  and the components within it prior to launch. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Refer now to the FIG. 1 for a description of the operation of the system and the components required to carry out its operation. A countermeasure launcher  10  comprises a cylinder  12  with a gas generator  14  at the back end of the launcher device  10 . An electrical connector  15  feeds into the back end of the gas generator  14 . A ram plate  16  is disposed in front of the gas generator  14 . The electrical connector  15  provides firing voltage to the gas generator  14 . The edges of the ram plate  16  are sealed by an O-ring  18 . A countermeasure  20  is disposed in launch cylinder  12  forward of ram plate  16 . The rear of the countermeasure  20  is nested in a thrust plate  22  to protect countermeasure  20  from ram plate  16  upon firing. Countermeasure launcher  10  is sealed against the ocean by an end cap  24  held in place by one or more shear pins  26 . 
     Upon issuance of a firing command, an electrical signal is sent to the countermeasure launcher  10 , via electrical connector  15 . This causes gas generator  14  in countermeasure launcher  10  to discharge a large quantity of gas, which creates a high pressure behind ram plate  16 , thereby causing the ram plate  16  to move forward down launch cylinder  12  while pushing countermeasure  20  and thrust plate  22  before it. When countermeasure  20  contacts end cap  24 , the one or more shear pins  26  break, and cap  24  is pushed away enabling countermeasure  20  to exit launch cylinder  12 . 
     In the prior art, after discharge of the countermeasure  20 , thrust plate  22  and ram plate  16  also exit launch cylinder  12 . This causes the gas behind ram plate  16  to rapidly follow through the opening and to disperse into the seawater. This sudden gas discharge causes a great deal of both acoustic energy and visible turbulence. It is audible and visible to any enemy craft monitoring the area in which it occurs, and it compromises the position of a submarine discharging the countermeasure  20 . 
     The present invention provides a countermeasure launcher with a greatly reduced acoustic and visual signature. It achieves this by blocking the escape route of the gasses and then discharging these gasses slowly over a period of time. 
     In order to achieve this a stop ring  28  is added to the launch device  10 . Stop ring  28  is disposed near the outer end of the launch cylinder  12 . A pressure relief valve  30  is positioned behind stop ring  28 . The pressure relief valve  30  can be a disk valve or another valve having quiet operation. A spring plunger  32  retains the ram plate  16  and the thrust plate  22  forward of the pressure relief valve  30  after firing so that neither the ram plate  16  nor the thrust plate  22  inhibits the operation of the pressure relief valve  30 . Spring plunger  32  also minimizes thrust plate  22  oscillations thereby reducing transmitted acoustic energy. Stop ring  28  is positioned in launch cylinder  12  so as to allow the external end of countermeasure  20  to be resting inside of the stop ring  28  prior to firing and to guide countermeasure  20  while exiting from launch cylinder  12  upon firing. Countermeasure  20  has a slightly smaller outer diameter than the inner diameter of stop ring  28  allowing countermeasure  20  to exit upon launch. Thrust plate  22  has a diameter larger than the inner diameter of stop ring  28  so that it is prevented from exiting upon launch. 
     Refer now to FIG. 2 for a further description of many of the components of FIG.  1 . FIG. 2 shows a partial sectional view of launch cylinder  12  and the components within it. End cap  24 , shear pins  26 , gas generator  14 , and electrical connector  15  have been removed from the launch cylinder  12  and are not shown in this view. 
     At the forward end of the launch cylinder  12  is shown the stop ring  28  that is comprised of a spiral retaining ring  34  inserted in a launch cylinder annular groove  36 . In addition the stop ring  28  is made up of a stop/guide ring assembly  38 , having a metallic stop ring  40  and a urethane guide ring  42  bonded together. The guide ring  42  has the countermeasure  20  resting inside it prior to launch and assists in guiding the countermeasure  20  during launch. The stop ring  40  stops the thrust plate  22  and the ram plate  16  upon launching the countermeasure  20 . During launch, thrust plate  22  and ram plate  16  move past spring plunger  32  by causing plunger  32  to depress. Once thrust plate  22  and ram plate  16  move past plunger  32 , plunger  32  returns to its initial position preventing plates  16  and  22  from vibrating because of recoil off of stop ring  28 . This enables the pressure relief valve  30  to be clear of internal components when slowly discharging the contained gas. 
     The gas generator  14  of FIG. 1 is attached to threads  44  positioned on the outer side of the aft end of the launch cylinder  12 . The inner portion of the aft end of the launch cylinder  12 , shown prior to launch, has the ram plate  16  and thrust plate  22 . The ram plate  16  has an annular groove  46  holding the O-ring  18 . The thrust plate  22  is an assembly made up of a urethane guide ring  48  bonded to a thrust plate stop ring  50 . Four equally spaced cap screws  52  connect the thrust plate  22  to the ram plate  16  forming a ram/thrust plate assembly  54 . 
     The launching operation of the inventive device differs from that of the prior art in the following manner. Instead of leaving the launch cylinder  12 , as in the prior art, the ram plate  16  and thrust plate  22  are retained by stop ring  28 . In addition the ram plate  16  and the thrust plate  22  are held between the stop ring  28  and the spring plunger  32 . The pressure relief valve  30  opens due to the pressure contained within the cylinder  12 . Upon opening pressure relief valve  30  slowly bleeds the trapped, compressed gas into the surrounding ocean. 
     There has therefore been described a system for launching a countermeasure with considerably less noise than the former embodiment due to the elimination of suddenly discharged gasses that create noise. 
     Valve  30  can be positioned at any location having access to the high pressure gasses contained within the cylinder. For example, valve  30  can be embodied in the ram portion of the countermeasure. This alternative allows the improved countermeasure launcher to be installed in existing submarines and prevents the necessity of aligning the pressure relief valve with a submarine pressure exit port upon installation aboard the submarine. The valve also can embodied anywhere along the length of the cylinder. 
     Different types of valves can also be used for valve  30  in place of the pressure activated disk valve of the preferred embodiment. Valve  30  can be an electrically actuated valve that will allow release of the high pressure gasses on command rather than automatically as in the preferred embodiment. 
     Alternate means of retaining the ram also exist. One possible retaining means is by use of a retaining cable attached to the back end of the launch tube and the back end of the ram. This alternative also prevents the ram from exiting the launch tube. 
     It will be understood that various changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.