Abstract:
The invention as disclosed is a recoverable tethered optical fiber buoy and winch assembly that is mounted to the back of the sail or the back of an aft non-moving surface of an underwater vehicle and housed in a configuration to provide very little additional drag to the underwater vehicle when the assembly is not deployed. The invention provides a capability to connect ocean surface visual or radio frequency sensors to an underwater mobile platform with a very high data rate link that is retrievable.

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 therefore. 

   BACKGROUND OF THE INVENTION 
   (1) Field of the Invention 
   The present invention is directed to tethered buoys. In particular, the present invention is directed to a recoverable optical fiber tethered buoy for use with underwater vehicles. The invention provides a capability to connect ocean surface visual or radio frequency sensors to an underwater mobile platform with a very high data rate link that is retrievable. 
   (2) Description of the Prior Art 
   There have been efforts to equip underwater vehicles with buoyant sensors and antennas on a tether that are deployed to the surface for a period of time and then winched back to the underwater vehicle. Prior art winches and buoys are relatively large and cannot be incorporated in the design of next generation underwater vehicles or current underwater vehicles that are near their maximum weight. What is needed is a smaller winch and buoy system that can be mounted to the aft of the sail of a next generation underwater vehicle to provide the critical capabilities of a recoverable tethered buoyed sensor and antenna. 
   SUMMARY OF THE INVENTION 
   It is a general purpose and object of the present invention to provide a winch and buoy assembly that is small enough to be incorporated into the design of the next generation underwater vehicle and will provide the critical capabilities of a recoverable tethered buoyed antenna or sensor. 
   The above object is accomplished with the present invention by a recoverable optical fiber tethered buoy and winch assembly that is mounted to the back of the sail or the back of an aft non-moving surface of an underwater vehicle and is housed in a configuration that causes minimal additional drag to the underwater vehicle. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the invention and many of the attendant advantages thereto will be more readily appreciated by referring to the following detailed description when considered in conjunction with the accompanying drawings, wherein like reference numerals refer to like parts and wherein: 
       FIG. 1  is a cut away view of the buoyant antenna unit, winch, tether and housing mounted to the underwater vehicle; 
       FIG. 2  is a cut away view of the fiber optic tether; 
       FIG. 3  is an illustration of the optical fiber payout/retrieval system; 
       FIG. 4  is an illustration of the deployment, use and retrieval of the buoyant antenna unit. 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1  there is illustrated an embodiment of the recoverable optical fiber tethered buoy assembly  10 , which consists of a housing  12  mated to an integrated buoy  14  and antenna or sensor  16 . The housing  12  contains an optical fiber tether  18  coupled to the antenna or sensor  16 , and an optical fiber payout/retrieval system  20 . The recoverable optical fiber tethered buoy assembly  10  has two configurations, a housed configuration as illustrated in  FIG. 1  and a deployed configuration as illustrated in  FIG. 4 . The housing  12  can be made of a light weight carbon fiber material that is both robust and not subject to corrosion in salt water. The housing  12  can be bonded to an underwater vehicle by means of a water proof seal and retaining hardware. The housing  12  is preferably mounted to an aft non-moving surface of the underwater vehicle such as the sail. When the entire assembly  10  is in the housed configuration, the assembly  10  will provide very little additional drag to the underwater vehicle. The entire assembly  10  is no more than one meter long and weighs approximately thirty pounds. The buoy  14  is buoyant in water and can be filled with air or other gases or it can be made of Styrofoam or other buoyant material. The buoy  14  is cylindrical in shape with one end of the cylinder having a hemispherical shape and the other end having a conical shape. A conical mating system  22  on one end of housing  12  is used during buoy  14  retrieval, whereby the conical end of the buoy  14  fits into the inverse conical end of the housing  12 . The inverse conically shaped end of the housing  12  forms means for mating the buoy  14 . The conical end of the buoy  14  is weighted so that when it floats in water the hemispherical end clears the water&#39;s surface. This ensures that the antenna or sensor  16 , which is integrated into the hemispherical end of the buoy  14 , is able to transmit and receive radio or optic signals above the water&#39;s surface. The buoy  14  is approximately sixteen inches in diameter and about twenty four inches long and weighs approximately one hundred pounds with approximately two hundred forty pounds of buoyancy. 
   The optical fiber payout/retrieval system  20  pays out and retrieves the optical fiber tether  18  that is attached at one end to the buoy  14 . The other end of the optical fiber tether  18  is attached to a winch  24 . The optical fiber tether  18  has a core comprising an optical fiber  26  parallel to a small gauge wire  27 , and a strength member  29  surrounded by a flexible jacket  28  made of a buoyant water proof polymer. This core of the optical fiber tether  18  provides power to charge energy storage within the buoy, and the signal path from the underwater vehicle to the antenna or sensor  16  integrated with the buoy  14 . The cross sectional diameter of the optical fiber tether  18  is approximately three millimeters. The length of the optical fiber tether  18  should be at least 1500 meters. The optical fiber tether  18  spools around the winch  24  in the housed configuration and pays out in the deployed configuration similar to fishing line off of a reel. The winch  24  is equipped with an electronic winch sensor  30  that counts each complete revolution of the winch in order to measure the length of optical fiber tether  18  that pays out. The sensor also provides an indicator when the optical fiber tether  18  is completely unwound. The winch  24  is equipped with an electric motor  32  that will spin the winch  24  in order to reel in the optical fiber tether  18 . The winch  24 , the elecronic winch sensor  30  and the electric motor  30  together form means for paying out and retrieving the tether  18 . 
   The electronic components such as the optical fiber tether  18  and the winch sensor  30  and the electric motor  32  interact with electronic and power systems on board the underwater vehicle through an electrical connection  34  that passes through a micro-aperture  36  in the hull of the underwater vehicle. The electrical connection  34  and the micro-aperture  36  together form means for powering the tethered buoy  14  from a power source internal to the underwater vehicle. The signal to and from the optical fiber core  26  as well as the signal from winch sensor  30  are directed to a user command component  38  such as a computer that allows on board means for user command and control of the assembly  10 . 
   In the deployed configuration, as illustrated in  FIG. 4 , the assembly  10  can establish connectivity with the ocean surface as required while the underwater vehicle that it is attached to remains submerged. The buoy  14  will ascend to the surface by virtue of its buoyancy pulling out the optical fiber tether  18  from the winch  24 . The winch  24  within the housing  12  keeps a small drag on the optical fiber tether  18  to prevent fouling. As the winch sensor  30  measures the length of remaining spooled optical fiber tether  18  as deployed, the information is relayed back to the user command component  38 . When the buoy  14  breaks the surface of the water, it provides the antenna or sensor  16  an aperture for line of sight communications and satellite communications, GPS, a basic radar detection function, or visual imaging or laser communications. The buoy  14  stays essentially in one place relative to the ocean surface while the submerged vehicle can continue to move underwater, paying out the optical fiber tether  18  as it does. On command from the user command component  38 , or at the end of the optical fiber tether  18  payout, the winch  24  will start to reel in the optical fiber tether  18  until the buoy  14  is re-docked into the conical mating system  22  of the housing  12 . 
   The recoverable antenna buoy assembly  10  offers a weight advantage to next generation underwater vehicles over prior art systems. It is specifically designed for multiple uses over short periods of time and has decreased complexity and cost over prior art systems. 
   While it is apparent that the illustrative embodiments of the invention disclosed herein fulfill the objectives of the present invention, it is appreciated that numerous modifications and other embodiments may be devised by those skilled in the art. Additionally, feature(s) and/or element(s) from any embodiment may be used singly or in combination with other embodiment(s). Therefore, it will be understood that the appended claims are intended to cover all such modifications and embodiments, which would come within the spirit and scope of the present invention.