Abstract:
A submarine mast simulator as part of a buoyant tow body having a hydrodynamically shaped shell. The mast simulator includes a rigid lower mast section and an inflatable upper mast section extendable from the tow body. A plurality of stabilizer fins extend radially from the tail of the tow body, the fins being actuated to cause the ascent and descent of the tow body. A pressure sensor is positioned on an outer surface of the tow body for detecting a depth of the tow body, and a motor with controller is housed within the tow body, the controller initiating extension of the mast simulator in response to a depth indication.

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 
   This invention generally relates to the art of antisubmarine warfare training and is a device for simulating a submarine mast positioned above a water surface. 
   (2) Description of the Prior Art 
   A submarine mast (e.g., periscope or snorkel) extending above the water surface can be detected by several methods. In a first example of detection, metallic components of the submarine mast will display a radar footprint. In a second example of detection, the submarine&#39;s forward speed will cause the mast to generate a visible wake which is generally much easier to see than the mast itself. In a third example of detection, the thermal plume associated with diesel exhaust from a snorkel can be seen using infrared cameras. Lastly, a sniffer-type chemical sensor can discern various compounds contained within the diesel exhaust. All of these techniques for detection are presently used by aircraft and surface ships to conduct antisubmarine warfare (ASW) operations. 
   The use of naval service or real submarines to train ASW crews is problematic, limited by high expense and risk as well as the low priority of such training relative to a submarine&#39;s other missions. As such, low-cost, low-risk methods of training personnel to detect submarines are needed. 
   One method of detection assistance is to tow a catamaran behind an unmanned underwater vehicle (UUV). The catamaran would have a radar reflector and/or a heat source to mimic submarine characteristics. The catamaran approach lacks realism in that it does not permit the simulator to pop out of the water unannounced and disappear minutes later, as a real submarine mast would behave. Also, a catamaran&#39;s wake and visual appearance are quite different from those of a submarine mast. Finally, the catamaran must be released by the UUV and recovered separately in order for the UUV to perform other tasks during its run. 
   Another method of detection assistance is to deploy a periscope-like mast from a UUV traveling just below the surface. One working prototype extends 26.5 feet in length and weighs 3600 pounds. Bow planes increase the width of the UUV to 67 inches. Furthermore, the capability of the prototype is limited to periscope simulation. However, like all large UUVs, the prototype is expensive to build and operate. It requires a specially trained support crew, a complete logistics system and extensive maintenance, and its size makes the prototype cumbersome to launch, recover and transport. As a result, there is needed a low-cost mast simulator that can be towed and which resembles and operates like the mast of a real submarine. 
   The following references disclose ASW training devices, but do not disclose a mast simulator with the following characteristics: a visual appearance close to that of a submarine periscope or snorkel protruding above the water surface; a radar footprint equal to that of a submarine periscope or snorkel protruding above the water surface; a wake approximating that generated by a submarine periscope or snorkel protruding above the water surface; an infrared signature similar to that of a snorkeling diesel-electric submarine; chemical vapor emissions similar to those of a snorkeling diesel-electric submarine; programmable, submarine-like speed and maneuvering characteristics; an ability to surface/deploy and retract/submerge the mast simulator multiple times during a single run; the minimum drag exerted by the mast simulator when it is not surfaced/deployed; mast simulator hardware which can be jettisoned by the UUV when no longer needed during a mission; low production and maintenance costs; and relatively easy to handle, launch and recover. 
   Mason (U.S. Pat. No. 5,144,587) discloses an expendable moving echo radiator suitable for providing a decoy to attract a homing torpedo and divert the torpedo away from its intended target. The reference further discloses an expandable and collapsible curtain for deployment from a capsule launched from a submarine or other sea vessel. In its expanded configuration, the curtain is characterized by a physical profile sufficient to reflect acoustic waves aid to generate echoes substantially similar to echo signals generated by an actual, full-size submarine or other target. The cited reference further discloses propulsion means, as well as means for capturing a torpedo&#39;s sensors. As such, the expendable device can be used to simulate a submarine for ASW training. In using the echo radiator as a target, the expendable device can be preprogrammed or remotely controlled for self-navigation purposes. 
   Haisfield et al. (U.S. Pat. No. 5,247,894) discloses a decoy which simulates the evasive tactics of a submarine under attack for pulse echo-type search systems and which can be ejected through the flare tube of a submarine. 
   Chace, Jr. et al. (U.S. Pat. No. 5,490,473) discloses an expendable underwater vehicle for use in training naval forces in ASW which is between three and five feet in length and about five inches in diameter. The cited reference further discloses an in-water variable speed feature, a variable tonal levels feature, an autonomous evasion feature, and a high-power integrated pinger feature. 
   It should be understood that the present invention would in fact enhance the functionality of the above references by providing a submarine mast simulator having all of the visual, radar, thermal, chemical and wake generation characteristics of a real submarine mast yet is reusable and reliable. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is a general purpose and primary object of the present invention to provide a submarine mast simulator for ASW training. 
   It is a further object of the present invention to provide a submarine mast simulator which simulates the visual appearance, radar footprint, infrared/chemical emissions, and wake generation characteristics of a submarine mast protruding above a water surface. 
   It is a still further object of the present invention to provide a submarine mast simulator which is easy to launch and recover. 
   It is a still further object of the present invention to provide a mast simulator which is towable by a UUV. 
   It is a still further object of the present invention to provide a mast simulator which is inexpensive to manufacture. 
   To attain the objects described, there is provided a tow body having a hydrodynamically shaped shell with a nose and a tail. A mast simulator extendable from the tow body includes a rigid lower mast section and an inflatable upper mast section. A plurality of stabilizer fins extend radially from the tail of the tow body. A pressure sensor is positioned on an outer surface of the tow body for detecting the depth of the tow body. A motor with controller is housed within the tow body; the controller initiates extension of the mast in response to a depth indication by the pressure sensor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the various objects, advantages and novel features of the present invention will be more apparent from a reading of the following detailed description in conjunction with the accompanying drawings wherein: 
       FIG. 1  is a side view of a tow body of the mast simulator of the present invention; 
       FIG. 2  is a top view of the tow body of the mast simulator of the present invention with the view taken from reference line  2 — 2  of  FIG. 1 ; 
       FIG. 3  is a side view of the mast simulator of the present invention in a semideployed position; 
       FIG. 4  is a schematic view of internal components of the mast simulator of the present invention; 
       FIG. 5  is a side view of a fully deployed mast simulator of the present invention being towed; and 
       FIG. 6  is a side view of a retracted mast simulator of the present invention being towed at a cruising depth. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   In general, the present invention is directed to a tow body  10  housing the structure of a mast simulator towed by an unmanned underwater vehicle (UUV)  100  (with  FIGS. 5 and 6  depicting the towing operation and the UUV). 
   Referring now to the drawings wherein like numerals refer to like elements throughout the several views, one sees that  FIG. 1  depicts the tow body  10  generally including a faired shell  12  having a nose  14  and a tail  16  with the tow body  10  being hydrodynamically shaped in order to minimize drag while being towed underwater. 
   A mast recess  18  is formed in the tow body  10  and extends along and into the faired shell  12  so that components retracted in the recess present a streamlined outer surface consistent with that of the faired shell  12 . 
   A center of buoyancy for the tow body  10  is indicated as marking  20 , with the center of buoyancy preferably below the longitudinal centerline of the tow body  10 . The low center of buoyancy of the tow body  10  reduces the tendency of the tow body to roll, both submerged and at the surface. Having the tow body  10  close to neutrally buoyant allows it to follow directly behind the tow vehicle, thereby minimizing drag forces acting upon the tow cable  21 . 
   A plurality of control or stabilizer fins  22  extend radially from the tail  16 . The stabilizer fins  22  are sized and positioned to obtain a desired stability in roll, pitch and yaw, as well as to provide upward lift sufficient to surface the tow body  10  upon command. 
   As shown in  FIG. 2 , the tow body  10  includes a tow harness  24  attached to opposing sides of the faired shell  12  at attachment points  26  with the attachment points equidistant from the nose  14 . The location of the attachment points  26  further improves the stability of the tow body  10  and reduces the likelihood of rolling. The exact location of the attachment points  26  is determined by the need to maximize the angle of attack of the tow body  10  during a surfacing maneuver while minimizing the instability of the tow body. As the attachment points  26  are moved rearward toward the midpoint of the tow body  10 , the angle of attack of the tow body while surfacing increases. However, this rearward attachment causes a tendency for hydrodynamically unstable flight of the tow body  10 . 
   Referring now to  FIG. 3 , the mast simulator  30 , carried by the tow body  10 , is an extending two-part assembly including a rigid lower mast section  32  and an inflatable upper mast section  34 . The lower mast section  32  is hollow with a radial cross-section similar to that of a submarine periscope or snorkel. The upper mast section  34 , coiled and flat when not inflated, is attached to a tip or distal end of the lower mast section  32 . The mast simulator&#39;s physical features provide a realistic simulation of a submarine periscope or snorkel in three respects: visual appearance, radar footprint, and wake generation. However, it is also important to limit the length of the stowed mast simulator  30  in order to minimize tow body length and associated drag, weight, and cost. The lower and shorter mast section  32  must be rigid to withstand the force of water moving past it. The longer, inflatable, upper mast section  34  is actually an elastomeric tube which inflates once the lower mast section  32  has deployed above the water surface. 
   When fully inflated, the visual appearance and radar footprint of the mast simulator  30  are similar to those of a naval service-type periscope or snorkel. The wake of the mast simulator  30  may differ somewhat from that of a real submarine mast, largely due to hydrodynamic effects caused by the submarine&#39;s large sail, but for training purposes the difference between the mast simulator and a real submarine mast is of minor significance. 
   The mast simulator  30  must be lightweight, to reduce its tendency to tip over when fully extended. As such, the rigid lower mast section  32  is hollow, to accommodate gas tubing and other components described below. However, when not extended, the mast simulator  30  retracts into the mast recess  18  on the faired shell  12  in order to reduce hydrodynamic drag. 
   Turning now to  FIG. 4 , there are shown additional internal components of the tow body  10  contributing to the operation of the mast simulator  30 . In particular, a low-speed reversible electric motor  40  with controller is positioned within the tow body  10  to provide mechanical power to the mast simulator  30 . A pressure sensor  42  is positioned at an outer surface of the faired shell  12  to measure the surrounding seawater pressure. Electromechanical actuators  44  are positioned at the tail  16  of the tow body  10  to drive the stabilizer fins  22 . Mechanical links and gears (not shown) are connected to the lower mast section  32  with a sensor (not shown) determining the angular position of the mast simulator  30 . Each of the mechanical links, gears and the sensor are known in the art such that any suitable arrangement may be applied to the device shown in order to effect operation of the mast simulator  30 . 
   In further description of the mast simulator  30 , an electric air pump  46  is positioned inside the faired shell  12  with inlet piping  48  connecting the lower mast section  32  to an inlet of the air pump. A normally closed (inlet) solenoid valve  50  is located at the atmospheric end of the inlet piping  48 . Outlet piping  52  supplies pressurized air from an outlet port of the air pump  46 . A pressure relief valve  54  is provided for the inflatable upper mast section  34 . 
   An electrically-ignited heat source such as a combustor  56 , supported by a bladder  58  containing hydrocarbon-based fuel, and an electric fuel pump  60  are also housed within the tow body  10 . The piping section  52  connects the outlet port of the air pump  46  to an intake port of the combustor  56 . A second piping section  64  connects an outlet port of the combustor  56  to a base of the inflatable upper mast section  34  via the rigid lower mast section  32 . A three-way, two-position solenoid valve  66  directs an output flow from the air pump  46  to either the combustor  56  or to the inflatable upper mast section  34 . 
   As shown in  FIGS. 5 and 6 , deployment of the mast simulator  30  begins with the tow vehicle  100  going to its minimum depth at a low speed. When the pressure sensor  42  of the tow body  10  indicates that the desired depth has been reached, electromechanical actuators  44  deflect the stabilizer fins  22  in a direction that lifts the nose  14  relative to the tail  16  of the tow body. This positive angle of attack for the tow body  10  forces the tow body to the surface, overcoming the downward drag forces exerted on the tow cable  21 . 
   When the tow body  10  reaches the surface of the water, as indicated by the pressure sensor  42 , the motor controller activates the motor  40 . Through links and/or gears, the activated motor  40  extends the lower mast section  32  into its upright position shown in FIG.  5 . The motor  40  stops when an angle sensor (not shown) indicates that the lower mast section  32  is fully raised a predetermined angle offset from the tow body  10 . 
   Once the lower mast section  32  is raised, the upper mast section  34  is inflated by first energizing/opening the solenoid valve  50  to the atmosphere. The air pump  46  is activated, drawing in fresh air through the solenoid valve  50  and the inlet piping  48  within the lower mast section  32 . The air is pumped into the outlet piping  52 , back through the lower mast section  32 , and into the upper mast section  34  which begins to inflate. Inflation of the upper mast section  34  proceeds with the upper mast section uncoiling upward and expanding outward until it is fully extended. Pumping stops when pressure inside the upper mast section  34  reaches a predetermined value, at which time the solenoid valve  50  closes. The operation of the pressure relief valve  54  precludes an overinflation of the upper mast section  34 . 
   Although not shown, faster inflation of the upper mast section  34  may be accomplished by means of a compressed gas accumulator located within the tow body  10 . The accumulator can be recharged by the air pump  46  while the mast simulator  30  is deployed above the water surface. Recharging the accumulator in this manner expedites the inflation process if multiple mast deployments are to be performed during a single mission. 
   When inflated, the mast simulator  30  presents the visual appearance of a submarine mast. Additionally, a radar-reflective coating  28  applied to the mast simulator  30  causes the mast simulator to exhibit the radar footprint of a submarine mast. In a third described, but nonexhaustive method of detection, the lower mast section  32  generates a realistic wake as it travels on the water surface. The size, shape, and other physical characteristics of the mast simulator  30  can be varied to mimic the visual appearance, radar footprint, and wake characteristics of most known submarine masts. It should be noted that the wake signature is also a function of the speed, orientation, and physical features of the tow body  10 . 
   Simulation of infrared and chemical vapor emissions is accomplished as follows. At any time after the inlet solenoid valve  50  is opened and the air pump  46  is activated, the three-way solenoid valve  66  is energized. The solenoid valve  66  directs the flow of pumped air to the combustor  56 , into which a hydrocarbon fuel from the fuel bladder  58  is pumped by the fuel pump  60  and electrically ignited in the combustor. Hot combustion gasses are directed by the tubing  64  into the upper mast section  34 . Once the upper mast section  34  is fully inflated, the combustion gasses are automatically released to the atmosphere through the exhaust solenoid valve  70  and/or pressure relief valve  54 . To prevent overinflation of the upper mast section  34  during activation of the air pump  46 , the exhaust solenoid valve  70  may be continually cycled open and closed. The resulting infrared signature of released combustion gasses, both convective and radiative, mimics that of a snorkeling diesel submarine. By varying fuel type and operating characteristics of the combustor  56 , the exact composition of the vapor emissions can be tailored to simulate those of diesel exhaust gasses. 
   The fuel bladder  58  is in communication with ambient and pressurized seawater by inlet port  72 , thereby allowing the seawater to displace fuel as the fuel is consumed. Otherwise, the fuel would be displaced by gaseous vapors, greatly altering the buoyancy of the tow body  10 . 
   A flexible antenna (not shown) integral to the upper mast section  34  can serve several functions. One such function is to receive global positioning system (GPS) signals, providing the tow vehicle  100  a precision navigation capability. The antenna might also serve as a radio frequency (RF) beacon to aid vehicle recovery efforts. In a general sense, the flexible antenna can be used to send or receive any type of data when deployed, via shielded wires within the tow cable. 
   Upon completion of a detection exercise using the mast simulator  30 , the inlet solenoid valve  50  is closed and the air pump  46  is deactivated. In the same instant, the exhaust solenoid valve  70  opens, allowing the upper mast section  34  to deflate. As it deflates, the upper mast section  34  reverts to its original flattened and coiled condition. Once the upper mast section  34  is deflated, the exhaust solenoid valve  70  closes and the low-speed motor  40  lowers the mast simulator  30  into a retracted position within the mast recess  18 . The tow vehicle  100  then dives and increases speed, pulling the tow body  10  behind it, to perform other duties or operations (see FIG.  6 ). 
   Alternatively, the tow vehicle  100  can release the tow cable  21  and/or tow body  10  prior to continuing its mission. In this case, the tow body  10  must be recovered separately and the upper mast section  34  should remain inflated to aid in its location and recovery. If the tow vehicle  100  and the tow body  10  have completed their mission and must be recovered together, the upper mast section  34  can remain inflated in order to facilitate a sighting of the tow body. Further, positive buoyancy provided by the inflated mast section  34  reduces the likelihood of the tow body  10  sinking in the event of seawater leaking into normally dry parts of the tow body. 
   Power for the motors  40 , actuators  44 , pumps  46  and  60 , solenoid valves  50 ,  66 , and  70 , combustor  56 , and sensors  42  is provided by the tow vehicle  100  and delivered through wires embedded within the tow cable  21 . Communication between the tow vehicle  100  and the tow body  10  electronic subsystems is conducted in the same manner. 
   It will be appreciated that the present invention provides a tow body  10  with mast simulator  30  which simulates the geometric, radar, wake, infrared, and chemical vapor characteristics of a submarine&#39;s periscope, snorkel, or other type of mast. Surfacing is achieved through the use of active control surfaces  22 , rather than buoyancy changes caused by bladder inflation. The tow body  10  becomes a mast simulator by raising a radar-reflective, wake-generating mast after the tow body surfaces. Infrared and chemical vapor emissions, which mimic a snorkeling diesel-electric submarine, are generated by means of the combustor  56  and a hydrocarbon-based fuel supply contained within the tow body  10 . 
   In view of the above detailed description, it is anticipated that the invention herein will have far-reaching applications other than those of antisubmarine warfare training. 
   This invention has been disclosed in terms of certain embodiments. It will be apparent that many modifications can be made to the disclosed apparatus without departing from the invention. Therefore, it is the intent of the appended claims to cover all such variations and modifications as come within the true spirit and scope of this invention.