Underwater mobile target
United States Patent 1 Hogman et al.  
 [ UNDERWATER MOBILE TARGET [75] Inventors: Mediord N. Hogman, Edmonds;  
 James F. Shedd, Seattle; Keith S. Yett, Seattle; Harold A. Kolve, Seattle, all of Wash.  
 [73] Assignee: The United States of American as represented by the Secretary of the Navy, Washington, DC.  
  22 Filed: Oct. 23. 1973 211 Appl.No.:408,976  
 Primary E.taminerRichard A. Farley Attorney, Agent, or FirmR. S. Sciascia; Charles D. B.  
 Curry {57] ABSTRACT An underwater mobile target that is relatively small Apr. 1,1975  
 and simple in operation. The target has an elongated stream lined body and is battery driven. The target employs a control system that includes elevator fins that are controlled by a pendulum that is responsive to the climb angle of the target. The fluid dynamic characteristics of the target, the center of buoyancy and center of gravity of the target combine with the pendulum controlled elevator fins to cause the target to have a predetermined positive climb angle when powered. A pressure control system is employed wherein the motor is turned on at a lower predetermined depth and turned off at an upper predetermined depth. When launched, the target free falls to the lower predetermined depth where the motor is activated and the target is then powered and maintains the positive climb angle until it reaches the upper predetermined depth where the motor is shut off and the target free falls until it reaches the lower predetermined depth where the motor is again activated. The process is then repeated and the target follows an approximate sawtooth depth trajectory and will present an evasive target to a tracking weapon. The target has an electronic simultation system that employs a sonar frequency transducer and a weapon frequency transducer. The sonar transducer will receive and transmit sonar signals whereas the weapon transducer will transmit only simulated weapon reflected signals.  
 10 Claims, 11 Drawing Figures @{HIEEAFR 1197s SffU 1 BF 3 FlG l TORPEDO INTERROGATION PNENIEDIPII H975 3, 875,552  
 : jlQ  
  f 9 0 /93 9A 99 IT I WEAP WEAP WEAP 35 LOCKOUT PULSE FREQ POWER GEN osG AMP WEAPON b\ e g TRANSDUCER SONAR L SONAR L SONAR 89 PULSE PULSE PULSE GEN 030 AMP HG 7 TRIGGER SIGNAL A TRANS-RCV u j AMPLIFIER SWITCH 33 e? 85 Elf SONAR TRANSDUCER MN W W LOCKED OUT b J l J 1 1 TI TI f zl d &#34;&#34;I h Ta&#39;q  NIIINM WW 9 M MM FIG 8 UN DERWATER MOBILE TARGET BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underwater mobile target and more particularly to a relatively small and simple underwater mobile target that has evasive characteristics.  
 2. Description of the Prior Art Previous evasive underwater mobile targets have been relatively expensive and have employed complex control systems that have been either located internally within the target or have been controlled by an external control communication system. These targets have been somewhat successful; however, their high cost and complexities have been limiting factors. The present invention overcomes these problems by providing an underwater mobile target that is reliable yet relatively simple and inexpensive.  
 SUMMARY OF THE INVENTION Briefly. the present invention is an underwater mobile target that is relatively small and simple in operation. The target has an elongated streamlined body and is battery driven. The target employs a control system that includes elevator fins that are controlled by a pendulum that is responsive to the climb angle of the target. The fluid dynamic characteristics of the target. the center of buoyancy and center of gravity of the target combine with the pendulum controlled elevator fins to cause the target to have a predetermined positive climb angle when powered. A pressure control system is employed wherein the motor is turned on at a lower predetermined depth and turned off at an upper predetermined depth. When launched. the target free falls to the lower predetermined depth where the motor is activated and the target is then powered and maintains the positive climb angle until it reaches the upper predetermined depth where the motor is shutoff and the target free falls until it reaches the lower predetermined depth where the motor is again activated. The process is then repeated and the target follows an approximate sawtooth depth trajectory and will present an evasive target to a tracking weapon. The target has an electronic simulation system that employs a sonar frequency transducer and a weapon frequency transducer. The sonar transducer will receive and transmit sonar signals whereas the weapon transducer will transmit only simulated weapon reflected signals.  
 STATEMENT OF THE OBJECTS OF THE INVENTION An object of the present invention is to provide a relatively simple underwater mobile target.  
  Another object of the present invention is to provide a relatively inexpensive underwater mobile target.  
  Still another object of the present invention is to provide an underwater mobile target that has internal trajectory controls.  
  Other objects advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein:  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic diagram of the overall underwater mobile target of the present invention;  
  FIG. IA is a schematic diagram of the front view of the mobile target of FIG. 1 taken at section IAIA;  
  FIG. 2 is a diagram illustrating the trajectory of the mobile target with relationship to the launching vessel and the tracking weapon;  
  FIGS. 3, 3A and 3B illustrate the pendulum control system of the underwater mobile target of FIG. 1;  
  FIG. 4 is a schematic diagram of the mobile target during free fall.  
  FIG. 5 is a schematic diagram of the mobile target during powered operation;  
  FIG. 6 is a schematic diagram of the overall electrical system of the mobile target of FIG. 1;  
  FIG. 7 is a schematic diagram of the simulation system of the mobile target of FIG. 1; and  
  FIG. 8 is an illustration of signal waveforms at points a through g of FIG. 7.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT As illustrated in FIG. I the present invention relates to an underwater mobile target II that is of relatively small configuration and is relatively simple in operation. The target includes a body I3 having a battery 15 in the nose section, an electronics simulation system 17 in the center section and a motor 19 and pendulum control system 21 in the tail section. The motor I9 drives a propeller 23 by shaft 25. A pair of fixed rudder fins 27 are attached to the tail of the target at l angles from each other. A pair of movable elevator fins 29 are pivotally attached to the tail of the target at 180 angles from each other and at angles with respect to fixed rudder fins 27. The pendulum control system controls the position of elevator fins 29 by means of linkage 31. A sonar frequency transducer/receiver 33 has a toroidal configuration and is positioned at the nose section. A weapons frequency transducer 35 has a toroidal configuration and is positioned at the aft section of the body I3. A pressure switch 37 is mounted forward of the weapons frequency transducer 35 and senses the hydrostatic pressure of the surrounding medium at the depth of the target.  
  In FIG. 2 is illustrated a typical operation of the under water target 11 of the present invention in relationship to a sonar tracking vessel 39 and an acoustic homing weapon 41. The target 11 is dropped from the vessel 39 and sinks and follows a trajectory such as in dicated by dotted line 43. When the target reaches a first predetermined depth. for example 400 feet. the electro acoustic and propulsion systems are energized. This occurs at point A wherein the target 11 follows a shallow climb angle 6 until it reaches a second predetermined depth, point B, where the propulsion system is turned off. The second predetermined depth may be about 300 feet. for example. The target then sinks to the first predetermined depth. point C. where the propulsion system is again activated and the process is repeated until the batteries expire. From this it can be seen that the target is following an evasive trajectory. After the target is in operation and the sonar of the vessel, operating at a predetermined frequency, is tracking the target. then homing weapon 41 is released. and starts its own acoustic interrogation of the target. The  
 homing weapon is operating at a predetermined weapons frequency which is different than the frequency of the vessel&#39;s sonar signal. When the sonar signal from the vessel 39 is received by the sonar frequency transducer 33 then the target generates a dual response. First. the weapons frequency transducer 35 transmits a signal that is selected to be the same as the transmitted frequency of weapon 41. Second. the sonar frequency transducer 33 transmits a signal that is selected to be the same as the vessel&#39;s sonar frequency. In practice. after the ships sonar is consistently tracking the target. the weapon is launched and vessel&#39;s sonar becomes passive. Now the weapon will transmit its own signal which will be received by sonar frequency transducer 33, which is a broad band receiver and will respond to both the sonar and weapon transmitted signals. Upon receipt of the weapons transmitted signal the target will transmit. by weapon frequency transducer 35, a signal to be received by weapon 41 which will see it as its reflected signal. Immediately following the weapon frequency transmitted signal from transducer 35, is a sonar frequency Signal transmitted by sonar frequency transducer 33. This sonar signal will not be detected by weapon 4] (through rejection circuitry) but will be detected by the vessels sonar. The process is then repeated with each weapons transmission that is received by the target. In this manner the vessel 39 will know whether the weapon 4] is tracking the evasive target 11 and will know the target bearing in azimuth to enable weapon recovery. The particular technique for achieving this above described target operation will be hereinafter described in detail.  
  As best depicted in FIG. IA. the target has a weight offset system to offset the effect of propeller torque and prevent the target from having roll and to also assure that fixed rudder fins 27 remain vertical in the water. This is achieved by employing a weight 75 that creates a pull around torque TO: about the center line of the target that is equal and opposite to the torque TO that is the reactive torque induced about the center line of the target by the propeller.  
  In FIGS. 3, 3A and 3B is illustrated the pendulum control system 21 of the rear section of target 11. The pendulum control system 21 includes a pendulum weight 45, that is attached to pendulum arms 47 and 49 respectively by two pairs of bolts 51 and 53. Pendulum arms 47 and 49 are rotatably mounted on pin 55 which is supported by mounting bracket 57 which is supported by body 13. Linkage 31 is rotatably mounted on pin 59 which is mounted on pendulum arm 47 and 49 at a position below the pi\ot point of the pendulum. Linkage 31 is held in its centered position by spacers 61 and 63. As best depicted in FIGS. 3 and 3B fins 29 are attached to ring support 65 by pins 67 and pins 67 are rotatably mounted in bearings 69. Linkage 31 is m tatably mounted on the upper part of ring support 65 by means of support 71 and pin 73.  
  when the target undergoes free fall the nose is downward and the pendulum weight 45 swings forward causing the elevator fins 29 to rotate counter clockwise as illustrated in FIG. 4. However, the force on fins 29 are insufficient to cause the target to rotate substantially about its center of gravity (CG). At a predetermined depth the target propulsion is turned on, and since the fins 29 are of sufficient size and are rotated a maximum amount counter clockwise, the target will rotate clockwise until it reaches a predetermined positive climb angle 6 as shown in FIGS. 2 and 5.  
  In FIG. 5 is illustrated a moment or torque diagram which illustrates the technique by which the climb angle 6 is determined while the target is being propellcd. Several factors enter into the climb angle which include speed of target, body surface area. weight of target, buoyancy force. angle and size of elevator fins 29, distance between the pivot point of fins 29 and the center of buoyancy (CB). and the distance between the center of gravity (CG) and the center of buoyancy (CB). The weight distribution of the target is selected so that the center of gravity (CG) is forward of the center of buoyancy (CB). As the target travels through the water. an angle of attack, a exists as illustrated in FIG. 5. For small variations in the climb angle, 01 remains constant. This angle of attack produces an upward force which counteracts the net force (W-B). In addition. a moment acts about the center of buoyancy due to the angle of attack. This moment acts in the clockwise direction as shown in FIG. 5. Since the target nose is upward, the pendulum causes the elevation fins to move clockwise resulting in a force F that generates a counter-clockwise torque. Note that the weight W generates a counter-clockwise torque. It follows that the system stabilizes during propulsion when M wl F 1 wherein the various forces, surface angles and areas, weight. buoyancy. speed. moment arms and the like result in the target achieving a climb angle 6.  
  An example of parameters that have resulted in a successful system are set forth below. It will be understood by those skilled in the art that these parameters may be modified or changed provided these modifications are compatible with the teachings of the present invention.  
 TABLE OF PARAMETERS target weight 16 pounds target buoyancy 15 3/4 pounds target diameter 3.5 inches target length 51 1/4 inches negative buoyancy 1/4 pound speed 5 knots distance between CB and CG .120 inch to .140 inch area of elevator fins 3 3/4 square inches distance between CG and elevator fins pivot 24 inches elevator fin map angle 11 pull around torque 7 inch oz. motor dc type, 4000 rpm, 30 volt. nominally 1 amp. current drain In FIG. 6 is illustrated a schematic diagram showing the overall electrical system of the target 11. Battery 15 has one output applied to one side of pressure switch 37 and to one side of switch 79 which is part of latching relay 81. The other side of pressure switch 37 is connected to one side of the coil of latching relay 81 through diode 82 and to one pole of motor 19. The other side of switch 79 of latching relay 8] is connected to one of the power inputs to simulation system 17. The other output of battery 15 is connected to the other end of the coil in latching relay 81, to the other power input of simulation system 17 and to the other pole of motor 19. From this it can be seen that no power is applied to the simulation system 17, to motor 19 and to latching relay 81 in the position shown in solid lines. In the position shown, in solid lines, pressure switch 37 has not been activated such as when the target is still on board the vessel or hen the target has been initially dropped over board and is in its initial free fall. When the target reaches a predetermined depth. pressure switch 37 closes. as shown in dotted line. which results in power being applied to motor I) and to simulation system 17 and to the relay coil through diode 82. vv hen the target rises in the water to a predetermined depth then switch 37 will open. as shown in solid line Therefore. power is removed from motor 19 and the target will free fall. However. power will be still applied to simulation system 17 during the free fall. This is because power will be applied to the relay coil via switch 79 but will be blocked by diode 82 for being applied to motor 19. When the target reaches a predetermined depth the pressure switch 37 is again closed and the target motor is again activated. This process will repeat until the battery expires.  
  In FIG. 7 is illustrated by block diagram the simulation system 17 of the present invention Curves a through g of FIG. 8 represent the signals shown at points a through g of HO. 7. Sonar transducer 33 receives a signal from either the vessels sonar system or from the weapon system. When either signal is received it is transmitted through transmitter/receiver switch 85. that is applied through amplifier 87 to trigger circuit 89. The trigger signal is applied to lockout device 91 which generates a pulse having a time duration T as illustrated in curve C of FIG. 8. Point a is the incoming sonar signal from the vessel or the incoming signal from the weapon. Point I) is the square wave output of trigger 89 that exists for the same time duration as does the sig nal at point a. The lockout device 91 provides an output signal that exists for a time duration T that is greater than the sum of the two transmission times T- and T The leading edge of signal at point r activates the weapon pulse generator 93 which generates a square pulse at point (1 having a time duration T The trailing edge of the pulse at point (I activates the sonar pulse generator 95 which generates a square wave pulse at point 0 having a time duration T;, The pulse at point (1 activates weapon frequency oscillator 97, for the time period T which is applied through amplifier 99 to weapon frequency transducer 35. The pulse at point e activates sonar frequency oscillator 101. for a time period T which is applied through amplifier 103 and switch 85 to sonar transducer 33. From the foregoing it can be seen that during the time period T, that no incoming signals applied to sonar transducer 33 (including the feedback signal caused by transmission signals from transducer 33 and 35) will retrigger the weapon pulse generator 93 and the sonar pulse generator 95 because they are locked out of the system by lockout device 9].  
  The signals at point it are shown as examples to illus trate the behavior of the system in an ideal sense. In ac tual operation. signals at point (I, and thus point b. con sist of not only interrogation signals. but also the sonar pulse transmission a as amplified by amplifier 103 and seen on the signal line \ia trans-Rei switch Nov 85, and a replica of the weapon frequency transmission from transducer l\o 35 as it is sensed by sonar transducer No. 33. The lockout time. T prevents these signals from falsely activating the electronic system. The duration of T is great enough to allow for the termination of the sigl&#39;lals on line a.  
 What is claimed is;  
 l. A device comprising:  
 a. an elongated body having a forward section and a rearward section;  
 b. said body including a control system;  
 c. said control system including at least one movable control member operatively connected to the cxterior ofthe rearward section of said elongated body;  
 (1. sensing means for sensing the position of the longitudinal axis of said body with respect to horizontal;  
 c. actuator means responsive to said sensing means for actuating said at least one movable control member;  
 f. a motor for propelling said body in the forward direction; and  
 g. control means for periodically turning said motor on and off.  
 2. The device of claim 1 wherein:  
 a. said actuator means moves said movable control member at a positive angle with respect to the lon gitudinal axis of said body when said sensing means senses that the longitudinal axis of said body is at a negative angle with respect to horizontal; and  
 b. said actuator means moves said movable control member at a negative angle with respect to the longitudinal axis of said body when said sensing means senses that the longitudinal axis of said body is at a positive angle with respect to horizontal.  
 3. The device of claim 2 wherein:  
 a. the weight and buoyancy distribution of said body is selected whereby the center of gravity of said body is forward of the center of buoyancy of said body.  
 4. The device of claim 3 wherein:  
 a. said at least one movable control member comprises at least one movable elevator fin;  
 b. said sensing means comprises a pendulum; and  
 c. said pendulum being mounted in said body whereby its axis of rotation is about perpendicular to the longitudinal axis of said body.  
 5. The device of claim 1 wherein said control means includes:  
 a. pressure responsive means mounted on said body for sensing the pressure acting on the exterior surface of said body; and  
 b. motor actuating means responsive to said pressure responsive means for turning on said motor when the pressure on the exterior surface of said body is greater than a first predetermined pressure and turning off said motor when the pressure on the exterior surface of said body is less than a second predetermined pressure.  
 6. The device of claim 5 wherein:  
 a. said first predetermined pressure is greater than said second predetermined pressure.  
 7. The device of claim 6 wherein:  
 a. said body moves in a forward direction at a predetermined positive angle with respect to horizontal when said motor is on; and  
 b. said body free falls when said motor is off.  
 8. The device of claim 1 including:  
 a. a simulation system mounted within said body;  
 b. said simulation system including first means in cluding a first receiving means for sensing signals in a first predetermined frequency range and a first transmitting means for transmitting signals in a second predetermined frequency range; and  
  8 first transmitting means is transmitting.  
 10. The device of claim 9 including:  
 a. means for activating said second transmitting means before said first transmitting means is activated and while said first receiving means is inactivated.