Abstract:
An underwater intelligence gathering weapon system accurately places a weapon underwater and then communicates therewith from other platform(s). The weapon is equipped to maneuver through the air to a destination at the water&#39;s surface. A first transceiver, mounted onboard the weapon and coupled to the mine&#39;s logic portion, is activated after the weapon is in the water. The first transceiver can send and receive magneto-inductive signals. A second transceiver that sends and receives magneto-inductive signals is remotely located with respect to the first transceiver. Once deployed, the weapon can be controlled from a safe distance and can report any intelligence information collected by onboard sensors.

Description:
ORIGIN OF THE INVENTION 
     The invention described herein was made in the performance of official duties by employees of the Department of the Navy and may be manufactured, used, licensed by or for the Government for any governmental purpose without payment of any royalties thereon. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to underwater weapons, and more particularly to a weapon system that improves underwater placement accuracy while also providing for intelligence gathering and transmission from the weapon, and remote command and control of the weapon once it has been placed. 
     BACKGROUND OF THE INVENTION 
     Mines placed out at sea typically are configured to detect a particular stimulus supplied by an ocean going vessel in order to detonate a large explosive warhead for the purpose of sinking or incapacitating the vessel. Mine fields placed in the littoral regions of the world are used for offensive and defensive purposes. Offensively, placement of mines in a littoral region can destroy an enemy entering a mine field and/or limit the enemy maneuverability. Defensively, a littoral-region mine field can keep an enemy from attacking through a certain region. 
     Currently, underwater mines are placed by aircraft. Placement precision is generally not very good and results in placement errors of hundreds of yards. The higher the altitude of the aircraft when the mine is released, the greater the placement error will be. Thus, in terms of mine placement in littoral regions, aircraft sometimes have to come precariously close to an enemy shore which can result in nullifying a covert mission and/or allow the enemy to target and fire upon the aircraft. 
     In addition to placement problems, mines do not possess the ability to be remotely controlled in an efficient fashion from a safe location. Rather, underwater mines are pre-programmed to respond to seismic, pressure, acoustic and/or magnetic influences to yield detonation. Some efforts are underway to try to remotely command and control mines by use of acoustic signals. However, acoustic signals propagated through water for mine control can be quite unreliable especially in shallow and very shallow water regimes where high surface and bottom reverberation losses exist. Acoustic control can also be negated by the presence of air bubbles, ambient and man-made acoustic noise in the water near the receiver. Acoustic communications through water is further greatly affected by the multipaths, thermoclines and echoes from other sonar sources in the area. 
     Finally, although underwater mines are covert once located, this capability is not currently exploited. That is, mines are not operated as an intelligence gathering post that detects, for example, the number of vessels traversing an area, environmental conditions, etc., and reports back to a remote station. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide an underwater mine system that allows precise placement of and communication with an underwater mine. 
     Another object of the present invention is to provide an underwater mine system that can be released from an aircraft at a safe standoff range. 
     Still another object of the present invention is to provide for remote command and control of an underwater mine. 
     Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings. 
     In accordance with the present invention, an underwater intelligence gathering weapon system uses a mine having a logic portion for controlling explosive operation thereof. Navigation means are physically coupled to the mine for maneuvering it through the air to a destination at the surface of a body of water after being deployed in air from an aircraft. A first transceiver is mounted onboard the mine and is coupled to the mine&#39;s logic portion. The first transceiver is activated after the mine arrives at its destination in the water. The first transceiver will at least receive signals that can control the mine&#39;s logic portion. The signals are magneto-inductive in nature for transmission through the body of water. More specifically, the signals are digital tones modulated on a carrier frequency not to exceed approximately 4000 hertz. A second transceiver that transmits the signals into the body of water is remotely located with respect to the first transceiver. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 depicts an operation scenario using the system of the present invention to accurately place and command/control an underwater mine; and 
     FIG. 2 is a schematic view of one embodiment of a mine used in the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and more particularly to FIG. 1, a deployment sequence and operation scenario for the present invention is shown for use in a deep sea or littoral weapon placement mission. A host vehicle  10  travels to the vicinity (e.g., a typical standoff range of 50-75 nautical miles) of an in-air deployment destination at which point a weapon such as a mine  20  equipped for air travel is released therefrom. In general, host vehicle  10  is an aircraft (e.g., plane, helicopter, etc.) that can travel quickly to and from the vicinity of deployment without being easily detected by enemy surveillance. Once within the desired vicinity at a desired altitude and air speed, host vehicle  10  releases mine  20  which is capable of maneuvering using GPS signals  101  originating from GPS satellites  100  orbiting the earth. Mine  20  can also be equipped with an onboard inertial navigation system to supplement or back-up the GPS navigation capabilities in the event of GPS signal jamming problems. 
     Mine  20  is maneuvered to a ballistic drop zone approximately above a sea-surface deployment destination (referenced by numeral  200 ) located on the surface  201  of a body of water. To accomplish such navigational maneuvering of mine  20 , wings  22  can be attached to a mine body or casing  24  that typically houses explosives and control logic governing the mine&#39;s operation. In accordance with the present invention, communications equipment (not shown in FIG. 1) is also maintained onboard casing  24  to provide for the remote control of the mine&#39;s control logic and, if desired, provide for two-way communication with a remote site as will be explained further below. 
     At a desired altitude and range from deployment destination  200 , wings  22  can be separated from casing  24 . Once wings  22  are jettisoned, a drag device such as a parachute  26  slows the ballistic descent of casing  24 . Upon impact with surface  201  of the body of water, parachute  26  can stay with (as illustrated) or be caused to separate from casing  24 . At this point, casing  24  typically sinks to the bottom  202  under the weight of casing  24  and its contents. 
     Command and control of the contents of mine casing  24  originates from one or more remotely located land, air or sea platform(s). By way of example, a seagoing command and control vessel  30  supplies command and control information to an onboard transceiver  40 . Transceiver  40  includes an antenna  400  capable of transmitting and receiving magneto-inductive communications  44  (e.g., command and control information) through the water. Accordingly, communications  44  is shown as bidirectional. As is known in the art, magneto-inductive communications  44  are low-frequency electromagnetic signals capable of seawater propagation over short distances of approximately 50 nautical miles or less. In terms of the present invention, communications  44  are digital signals that have been converted to audio tone bursts modulated on a carrier frequency as will be described further below. 
     One embodiment of mine  20  is shown schematically in FIG. 2 where casing  24  represents the casing of an underwater mine such as one of the MK60 series used by the U.S. Navy. However, other specially designed mine casings or delivery vehicles can also be used. A wing “kit” is attached to casing  24 . The wing “kit” can deploy wings  22  to allow casing  24  to glide and steer as a winged aircraft and then jettison the wings at a given time or location to allow body  24  to fall ballistically. A variety of such wing “kits” are known in the art and are available commercially. One such commercially available system is the Longshot™ GPS Guided Wing Kit manufactured by Leigh Aero Systems, Carlsbad, Calif. Briefly, this wing kit includes a base  220  mounted to casing  24  using, for example, aircraft lug mounts  25  provided on casing  24 . Wings  22  extend from casing  24  once it is free from the host aircraft. The wing kit has its own GPS system  224  for determining range and altitude. An inertial navigation system (INS)  225  can also be included as a back-up to GPS system  224 . At a given range to a target location and/or altitude, a separation charge  226  is initiated to cause the combination of base  220  and wings  22  to be jettisoned from casing  24 . 
     Base  220  can be coupled mechanically or electromechanically to a parachute assembly  260  at the aft end of casing  24 . Stored within parachute assembly  260  is a parachute (not shown in FIG. 2) that deploys (see parachute  26  in FIG. 1) as base  220  separates from casing  24 . For example, a lanyard  228  can be coupled to base  220  and parachute assembly  260  so that as base  220  and wings  22  are jettisoned, lanyard  228  pulls the parachute from parachute assembly  260 . Lanyard  228  would then release due to the aerodynamic and tensile forces acting on the jettisoned base  220  and wings  22 . 
     A safe-and-arm device  50  is provided in the nose of casing  24 . Safe-and-arm device  50  is coupled to transceiver components onboard casing  24  for at least receiving magneto-inductive communications  44  from transceiver  40 . By way of example, one transceiver arrangement is depicted in FIG.  2 . Safe and arm device  50  is coupled to a battery or other power source  52  that is activated to supply power to transceiver components  54  and, if necessary, to the mine&#39;s control logic  56  and the mine&#39;s target detection device (TDD)  58 . In general, battery  52  is allowed to supply its power when safe and arm device  50  impacts the water&#39;s surface. Such safe and arm devices are well known in the field of airborne munitions. 
     Control logic  56  represents a central processing unit and non-volatile memory storing programming used to control mine operation. Target detection device  58 , when activated, initiates the mine&#39;s explosive operation in response to some stimulus, e.g., noise, pressure change, magnetic field, etc. Control logic  56  and target detection device  58  are systems/devices well understood in the art of mine construction and therefore will not be described further herein. 
     With battery  52  supplying power, transceiver  54  can begin to receive communications  44  originating from remotely located transceiver  40 . Accordingly, transceiver  54  includes an antenna wire  540  wrapped about casing  24 . Antenna  540  is wrapped in this way to effectively increase the useful range of transceiver  54  in terms of magneto-inductive communications. To minimize internal circuit noise while maintaining a high gain, antenna  540  is coupled to a series of high-gain narrow-band filter amplifiers  541 . Amplifiers  541  would typically be arranged in a superheterodyne configuration as is known in the art. The output of amplifiers  541  is supplied to an amplitude modulation (AM) demodulator  542  to detect the smallest amplitude modulation of the carrier frequency used to send magneto-inductive communications  44 . The output of demodulator  542  is supplied to a narrow-band phase locked loop (PLL) based tone decoder  543 . Decoder  543  converts the digital tone bursts of communications  44  into corresponding voltage levels in order to reconstruct the digital data originally used to create communications  44 . The output of decoder  543  is then supplied to control logic  56 . 
     The command and control information contained in communications  44  being supplied to transceiver  54  can simply be a signal causing control logic  56  to begin or cease normal mine operations. That is, control logic  56  could be commanded to activate or deactivate target detection device  58 . However, communications  44  could also be used to completely reprogram control logic  56  in the case of a changing mission scenario. 
     Transceiver  54  can also be used to transmit magneto-inductive communications that might be useful back onboard command and control vessel  30 . Transmission could range from simple acknowledgment of commands received to the supplying of status and/or intelligence gathering surveillance data as will be explained below. Regardless of the type of transmission, digital tones indicative of the data to be sent are input to an audio frequency shift keying modulator (AFSK)  544 . Modulator  544  is supplied with a carrier frequency in the ELF or VLF range. Preferably, the carrier frequency does not exceed approximately 4000 hertz in order to limit areas of transmission interference from other underwater sources and to provide an adequate data exchange rate. The modulated tones are supplied to an output driver stage  545  which, in turn, is coupled to antenna  540 . Note that a similar arrangement of components can be used for transceiver  40  located onboard command and control vessel  30 . 
     As mentioned above, transceiver  54  can be used to transmit a variety of types of transmissions. Simple acknowledgment of commands received could be passed directly from control logic  56  to modulator  544  for retransmission. Status of the mine (e.g., on/off, armed/disarmed, ready to deactivate, etc.) can be provided from target detection device  58  and/or control logic  56  to modulator  544 . Still further, the present invention can be used for underwater surveillance. To do so, environment sensors  60  (e.g., acoustic, pressure, magnetic, etc.) provide sensed data to control logic unit  56 /transceiver  54  for transmission to command and control vessel  30 . Assuming sensors  60  are digital sensors capable of outputting the appropriate digital tones, their outputs could be applied directly to modulator  544  for transmission preparation. Sensors  60  can provide information regarding the number and types of watercraft traveling in the area of the mine and/or simply information on tidal or wave action. 
     An RF receiver  70  can optionally be maintained onboard casing  24 . RF receiver  70  is coupled to control logic  56 . When mine  20  is in flight as illustrated in FIG. 1, host vehicle  10  (or some other platform) can issue commands to update or change the programming of control logic  56 . Then, once casing  24  has impacted water surface  201 , magneto-inductive communications  44  can be used to update or change control logic  56  as described above. In this way, control logic  56  (and thus mine operation) can be remotely controlled during all phases of mine deployment. 
     The advantages of the present invention are numerous. Underwater mines can be remotely delivered from a safe standoff distance and precisely placed at their desired destination. Such precision placement means that a mine field can be accurately mapped by friendly forces. Once placed, the present invention provides for the remote command and control and/or communication with the mine from a safe standoff range. Command and control can include mine arming/disarming, detonation, sterilization, etc. Communication from the mine can also include surveillance data on the area of placement. The surveillance data can be used, for example, to indicate the number of transient ships through the area and store this information for later on-command retrieval. The mine could be commanded to be turned off to allow for the passage of friendly ships and/or forces. 
     Although the invention has been described relative to a specific embodiment thereof, there are numerous variations and modifications that will be readily apparent to those skilled in the art in light of the above teachings. For example, the present invention could be used for pure intelligence gathering, i.e., no weapon is onboard the vehicle housing transceiver  54 . Further, transceiver  40  could be maintained on a buoy as a relay station that includes an RF receiver for receiving RF control signals from an even more remote command platform. The carrier frequency used for tone modulation can be changed based on the depth of the mine. Thus, it is therefore to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described.