Abstract:
An unmanned system for investigating underwater regions utilizes an unmanned mothership and a plurality of unmanned underwater vehicles (UUVs). The mothership transports the UUVs to and from the vicinity of an underwater region, releases the UUVs into the water, and facilitates recovery of the UUVs from the water. Each UUV can traverse an underwater region, generate sonar and image data associated with the underwater region, and transmit the sonar and image data through the water for receipt and re-transmission by the mothership. A docking system mounted partially onboard the mothership and partially onboard each UUV couples each UUV to the mothership and selectively releases each UUV into the underwater region. A guidance system mounted partially onboard the mothership and partially onboard each UUV guides each UUV back to the docking system from positions in the water. The mothership and UUVs can also be equipped with a non-contact electrical energy transfer system so that each UUV can return to the mothership and re-charge onboard batteries while underwater.

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 investigation systems, and more particularly to an unmanned system that uses multiple vehicles to investigate an underwater region. 
   BACKGROUND OF THE INVENTION 
   Underwater investigations are conducted for a variety of reasons to include mine hunting, search and rescue operations, bottom mapping, marine life studies, the viewing of maritime accidents and shipwrecks, and environmental investigations. The means for carrying out these investigations are as varied as the types of investigations. For example, in terms of mine hunting, underwater reconnaissance is currently conducted by both manned and unmanned systems, a variety of which will described briefly below. 
   The use of a dedicated mine hunting ship (DMHS) is the traditional method of clearing mines. However, the DMHS is an expensive piece of equipment and is expensive to run owing to the costs associated with the wages of the ship&#39;s crew. The DMHS requires the use of valuable manpower that could be more productively used in other tasks. The DMHS also uses valuable harbor space due to its size. The mine hunting exercise itself cannot be made in a timely manner due to the ship&#39;s lack of speed. Furthermore, the imminent hazards associated with placing a ship and its personnel into a minefield make this method of mine hunting the least attractive. 
   A helicopter towed sensor (HTS) has become a more available and quicker method of mine hunting. However, the HTS is plagued by short duration mission capability due to a helicopter&#39;s fuel requirements. The complexity of launching and recovering the equipment from the helicopter prevents this approach from being performed at night. Finally, the inherent instability of helicopter flight can make the HTS mission an extremely dangerous one. 
   Even more recently, a remote vehicle towed sensor (RVTS) involves the towing of a sensor behind a semi-submersible vehicle. However, the semi-submersible vehicle must be powerful enough to overcome the large drag forces associated with a tow cable. The drag on the tow cable also limits the speed of the RVTS resulting in long missions. The tow cable also inhibits maneuverability. Further, in order to keep the tow cable properly tensioned, the RVTS must make very large and time consuming turns. 
   Another unmanned option utilizes an unmanned underwater vehicle (UUV) equipped with onboard sensors. However, this type of system is not capable of completing the mine hunting mission with the current capabilities of UUVs. The power density of such a craft would require it to travel at extremely slow speeds for the entire time that it is on a mission. The fact that the craft is underwater for the entire mission also prevents communication with the host ship. This lack of communication would require the host to wait for hours or days before critical information is received. Another drawback of this type of system is endurance. That is, current battery technology does not give this type of system enough endurance to complete longer missions. Still another problem is the inaccuracy of a UUV&#39;s inertial guidance system. Specifically, the inaccuracies in an inertial guidance system multiply over the course of the mission until the craft is so “lost” that any information that it recovers would be useless. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a system for performing underwater investigations. 
   Another object of the present invention is to provide a system that can perform unmanned underwater investigations to eliminate risk to personnel. 
   Another object of the present invention is to provide a system for carrying out long-term underwater investigations. 
   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 unmanned system for investigating underwater regions utilizes an unmanned mothership and a plurality of unmanned underwater vehicles (UUVs) supported by the mothership. The mothership transports the UUVs to and from the vicinity of an underwater region, releases the UUVs into the water, and facilitates recovery of the UUVs from the water. Each UUV includes propulsion and navigation means for traversing an underwater region, sonar means for generating sonar data associated with the underwater region, electro-optic imaging means for generating image data of selected areas of the underwater region, and underwater communication means for transmitting the sonar and image data through the water. The mothership is similarly equipped for navigation through the water. The mothership can include, in modular form, a first module for controlling navigation thereof, a second module for receiving and storing the sonar and image data transmitted through the water from each UUV, a third module for storing and dispensing fuel, a fourth module for propelling and steering the mothership in accordance with instructions received from the first module, and a fifth module for wirelessly transmitting the sonar and image data. A docking system is mounted partially onboard the mothership and partially onboard each UUV. The docking system couples each UUV to the mothership, and selectively releases each UUV into the underwater region. A guidance system is mounted partially onboard the mothership and partially onboard each UUV. The guidance system can guide each UUV back to the docking system from positions in the water. The mothership and UUVs can also be equipped with a non-contact electrical energy transfer system so that each UUV can return to the mothership and re-charge its onboard batteries while underwater. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features and advantages of the present invention will become apparent upon reference to the following description of the preferred embodiments and to the drawings, wherein corresponding reference characters indicate corresponding parts throughout the several views of the drawings and wherein: 
       FIG. 1  is a perspective view of an embodiment of an underwater investigation system that uses multiple unmanned vehicles in accordance with the present invention; 
       FIG. 2  is a side view of an embodiment of the underwater investigative system&#39;s unmanned mothership; 
       FIG. 3  is a head-on view of the mothership taken along line  3 — 3  in  FIG. 2 ; 
       FIG. 4  is a bottom view of the mothership taken along line  4 — 4  in  FIG. 2 ; 
       FIG. 5  is a side view of an embodiment of one of the underwater investigative system&#39;s unmanned investigative vehicles; 
       FIG. 6  is a head-on view of the investigative vehicle taken along line  6 — 6  of  FIG. 5 ; 
       FIG. 7  depicts the mothership and an investigative vehicle during an investigative vehicle recovery operation; 
       FIG. 8  is a schematic view of a non-contact electrical energy transfer system in a non-energy transfer mode; 
       FIG. 9  is a schematic view of a non-contact electrical energy transfer system in an energy transfer mode; and 
       FIG. 10  is a block diagram illustrating the functional relationships of the components of the underwater investigation system. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings, and more particularly to  FIG. 1 , an underwater investigation system using multiple unmanned vehicles is shown and is referenced generally by numeral  100 . By way of illustrative example, underwater investigation system  100  will be described for its use in mine hunting operations. However, as will be understood by one of ordinary skill in the art, system  100  can also be used in a variety of other underwater operations to include, for example, coastal sentry operations, search and rescue operations, undersea survey and/or mapping operations, maritime accident or shipwreck investigations, and marine life studies. Accordingly, it is to be understood that all references to mine hunting operations are not to be considered limitations of the present invention. 
   Underwater investigation system  100  includes an unmanned mothership  200  that can transport two or more (e.g., two are shown) unmanned investigative vehicles  300  underwater to and from an underwater region of interest. In general, mothership  200  is equipped to navigate at and under the water&#39;s surface, release and recover each of investigative vehicles  300 , communicate with each of investigative vehicles  300 , and communicate with a remote location such as a host or launching platform/ship (not shown). In general, each of investigative vehicles  300  can independently navigate underwater, sense and collect data associated with an underwater region, of interest as it traverses same, and communicate with mothership  200  while it is traveling underwater under its own power. 
   Referring additionally now to  FIGS. 2-4 , a more detailed description of mothership  200  will be provided. In the illustrative embodiment, mothership  200  is constructed in a substantially modular fashion to facilitate repairs and/or equipment updates/advances. The forwardmost or nose module  202  houses acoustic signal receiver(s) and transmitter(s) of the type that are well known in the art. For example, nose module  202  will typically house sonar system(s) used for obstacle avoidance and acoustic transceiver system(s) for communicating underwater with each of investigative vehicles  300 . Aft of and coupled to nose module  202  is an electronics module  204  housing various well known navigation and communications electronics utilized for operation of mothership  200 . 
   Aft of and coupled to electronics module  204  is a fuel module  206  that stores and dispenses fuel for mothership  200  as needed. Fuel module  206  is preferably located in the midsection of mothership  200  to minimize changes in the center of gravity caused by fuel usage. As is known in the art, fuel module  206  can house a fuel bladder that collapses with fuel usage. The resulting volume increase within fuel module  206  can be backfilled with seawater to aid in stabilizing the center of gravity and maintaining buoyancy of mothership  200 . 
   Aft of and coupled to fuel module  206  is a propulsion module  208  that houses an engine (e.g., a diesel engine) receiving fuel from fuel module  206 . At the very least, propulsion module  208  supplies power to a propulsor  210  (e.g., a propeller). Additionally, propulsion module  208  can be used to power electric generator(s) that can provide onboard electrical power and can be part of a battery charging system used by investigative vehicles  300  as will be explained further below. 
   Coupled to the top of mothership  200  is a lifting eye block  212  that would typically be coupled atop fuel module  206  (i.e., at or near the craft&#39;s center of gravity) so that mothership can be lifted and lowered thereby from a host platform/ship. Coupled atop propulsion module  208  is a communications module  214  that provides for wireless transmission/reception of signals via an antenna  216 . Antenna can be standard radiowave antenna and can include a GPS antenna for receiving GPS signals that can be used to establish an accurate “own ship” position as is well known in the art. In order to allow mothership to operate covertly under the water&#39;s surface and to reduce space requirements when stowed on a host platform/ship, antenna  216  can be made retractable: Communications module  214  can also include a video camera  218  for providing images from above the water&#39;s surface when mothership  200  is operating at or just under the water&#39;s surface. Manipulation of mothership  200  as it travels through the water is facilitated by actuated wings  220  and a rudder  222 . 
   Mounted on the lower portion of mothership  200  are docking pylons  230 , each of which locks onto one of investigative vehicles  300  during the transport thereof, releases its investigative vehicle  300  into the water when so instructed, and provides the means to guide an investigative vehicle  300  back thereto during recovery of one of investigative vehicles  300 . The capabilities provided by each of docking pylons  230  can be implemented in a variety of ways without departing from the scope of the present invention. However, by way of example, one embodiment of a docking pylon will be described later herein. 
   Referring additionally now to  FIGS. 5 and 6 , a more detailed description of one of investigative vehicles  300  will be provided. Typically, investigative vehicle  300  will be equipped with a variety of sonar capabilities utilizing different types of sonar sensors. For example, mine hunting operations could use a forward look sonar sensor  302  for obstacle avoidance, and one or more of volume search sonar sensors  304 , side look sonar sensors  306 , and gap fill sonar sensors  308 , to collect sonar data about objects (e.g., mine like objects) in a surrounding underwater region as investigative vehicle  300  moves therethrough. The structure and operation of each of these sonar sensors are well known in the art and will not be described further herein. Each of the sonar sensors is coupled to processing electronics (not shown) mounted in an electronics module  310  positioned in the nose portion of investigative vehicle  300 . Electronics module  310  would typically also house an internal guidance system as well as processing control for underwater communication. 
   In addition to being equipped for sonar data collection, investigative vehicle  300  has a conventional electro-optic imaging sensor  312  coupled thereto for collecting image data of any object or area of interest detected by the sonar equipment Imaging sensor  312  is controlled by equipment contained within electronics module.  310 . 
   Sonar and image data collected by electronics module  310  is transmitted through the water acoustically by means of a conventional acoustic transceiver  314  coupled to investigative vehicle  300 . Once again, processing control for acoustic transceiver  314  is housed in electronics module  310 . The structure and operation of such acoustic transmission (and reception) is well understood in the art. 
   Aft of and coupled to electronics module  310  is a propulsion module  316  which can comprise one or more propulsion unit. Typically, propulsion module  316  houses a conventional electric propulsion motor (not shown) and batteries (not shown) for powering same. In-water re-charging of these batteries can be accomplished with a novel battery charging system that will be explained further below. The power from propulsion module  316  is supplied, to a propulsor  318  such as a propeller. Maneuverability of investigative vehicle  300  is controlled by actuated tail fins  320  controlled by systems in electronics module  310 . 
   In the illustrative embodiment, investigative vehicle  300  has a docking rail  322  and an alignment sensor  324  mounted thereon aft of docking rail  322 . Docking rail  322  provides a mechanical coupling designed to cooperate with a docking guide deployable from docking pylon  230  ( FIG. 2 ) of mothership  200 . Alignment sensor  324  cooperates with a guidance signal transmitted from mothership  200  to guide investigative vehicle to mothership  200  during a recovery operation that is depicted in FIG.  7 . 
   Referring additionally to  FIG. 7 , the illustrated embodiment shows a docking guide  232  lowered from docking pylon  230  by means of retraction arms  234 . Docking guide  232  is designed to receive/capture docking rail  322 . To guide investigative vehicle  300  into alignment with docking guide  232 , an alignment transmitter  236  is mounted on the aft end of docking guide  232 . In general, alignment transmitter  236  transmits a signal into the water that alignment sensor  324  detects. Preferably, the signal should provide guidance information to processors (not shown) in electronics module  310  such that investigative vehicle  300  can be steered so that docking rail  322  aligns with docking guide  232  for capture thereby. That is, the signals detected by alignment sensor  324  should identify the navigation maneuvers required to bring docking rail  322  into alignment with docking guide  232  whereby docking guide  232  and docking rail  322  are coupled together. 
   One such guidance system for achieving this is described in U.S. patent application Ser. No., 10/609,902 filed Jun. 26, 2003, the contents of which are hereby incorporated by reference. Briefly, this patent application discloses a system whereby guidance is provided to a vehicle as it approaches a position. A guidance transmitter includes light sources arranged in an array and a controller coupled to the light sources. The array defines a primary field-of-view (FOV) from which all light sources are visible. Less than all of the light sources are visible from positions outside of the primary FOV. The light sources are divided into a plurality of sections with each section having a portion of the light sources associated therewith. Operation of the light sources is governed by the controller in accordance with cyclical on/off sequences. Each cyclical on/off sequence is (i) associated with a corresponding one of the sections, (ii) identical for the portion of the light sources associated with the corresponding one of the sections, and (iii) unique for each of the sections. A primary waveform of light energy is defined by the cyclical on/off sequence visible from within the primary FOV. A plurality of secondary waveforms of light energy are defined by the cyclical on/off sequences visible from positions outside of the primary FOV. A guidance receiver is mounted on a vehicle traveling towards the position of the guidance transmitter. The guidance receiver includes (i) sensor(s) for sensing light energy generated by those light sources visible thereto such that either the primary waveform or one of the secondary waveforms is sensed, (ii) a database for storing calibration waveforms where each calibration waveform is indicative of a guidance correction signal that can be used to control navigation of the vehicle, and (iii) processing means coupled to the sensor(s) and database for determining which one of the calibration waveforms matches or is closest to the sensed one of the primary waveform and secondary waveforms. The guidance correction signal associated with the matching calibration waveform can be used to control navigation of the vehicle. 
   As mentioned above, the underwater investigation system of the present invention can include an in-water battery re-charging system for extended investigative missions. In this way, each investigative vehicle  300  can briefly return to mothership  200 , re-charge its onboard batteries, and then continue with its mission. To maintain the watertight integrity of both mothership  200  and investigative vehicle  300 , such battery re-charging is preferably carried out in a non-contact fashion. One such non-contact electrical energy transfer system is described in a co-pending patent application entitled “NON-CONTACT ELECTRICAL ENERGY TRANSFER SYSTEM”, Navy Case number 84899, the contents of which are hereby incorporated by reference. 
   In accordance with the teachings of this patent application, non-contact electrical energy transfer will be described with the aid of  FIGS. 8 and 9 . Specifically, a non-contact electrical energy transfer system is shown and is referenced generally by numeral  10 . Energy transfer system  10  has a core  12  of a ferromagnetic material (i.e., iron, nickel, etc.) that is shaped to define a nearly continuous loop. That is, core  12  is discontinuous such that a gap  14  of width W is defined between ends  12 A and  12 B of core  12 . Although the shape formed by core  12  is not a limitation of system  10 , core  12  is illustrated as a C-shaped core to take advantage of simple iron core transformer concepts. Accordingly, coiled about core  12  at a region thereof that opposes gap  14  is an electrical conductor  16  (e.g., wire, strip of material, a conductive run of material adhered to core  12 , etc.). 
   Energy transfer system  10  further includes a block  18  of the same ferromagnetic material used for core  12 . Preferably, the cross-sectional area of block  18  matches the surface area of each of ends  12 A and  12 B. Block  18  is sized such that its height H is less than width W. The amount of difference between these two dimensions should provide for a small space between block  18  and each of ends  12 A and  12 B when block  18  is positioned in gap  14  as will be explained further below. To maintain such spacing between block  18  and ends  12 A and  12 B, a sleeve  20  can be provided in gap  14  where cross-sectional area of sleeve  20  is configured/sized to slidingly receive block  18 . Sleeve  20  would typically be made from an electrically insulating material such as rubber, nylon, plastic or glass. Coiled about block  18  is an electric conductor  22  (e.g., wire, strip, a conductive run of material adhered to block  18 , etc.). 
   When electrical energy transfer between conductors  1 . 6  and  22  is desired, block  18  is positioned in the gap (i.e., gap  14  illustrated in  FIG. 8  but not shown in  FIG. 9  for sake of clarity) by sleeve  20  as shown in FIG.  9 . With block  18  so positioned, electrical energy (e.g., an AC voltage) is applied to electric conductor  16  by an AC source  30 . The resulting alternating current that passes through electric conductor  16  induces a magnetic field in core  12 . The magnetic field flux lines are concentrated by core  12  as is well understood in the transformer field. The lines of flux pass through the windings of electric conductor  22  thereby inducing an electric current in conductor  22  that is supplied to a load  32 . The inclusion of insulating sleeve  20  prevents any arcing from occurring if AC source  30  is activated while block  18  is being positioned in sleeve  20 . 
   By way of illustrative example, the above-described non-contact energy transfer system can be realized in the present invention as follows. Docking guide  232  could be constructed and shaped to serve as core  12  while docking rail  322  could be T-shaped ( FIG. 6 ) with the base portion  322 A thereof serving as block  18  of the re-charging system. 
   In order to provide a better understanding of the operation of the present invention, a functional block diagram of its various systems is provided in FIG.  10 . With respect to mothership  200 , nose module  202  supports or houses sonar sensors  202 A and an acoustic transceiver  202 B. Electronics module  204  houses a sonar processor  204 A coupled to sonar sensors  202 A, a communication processor  204 B coupled to acoustic transceiver  202 B, a navigation/propulsion processor  204 C, and a guidance processor  204 D coupled to  10 , alignment transmitter  236  for controlling the output thereof. 
   Sonar processor  204 A provides its output to navigation/propulsion processor  204 C for navigation corrections in response to obstacle detection. Communications processor  204 B handles underwater communications to/from acoustic transceiver  202 B and wireless communications received at or transmitted from antenna  216 . Navigation/propulsion processor  204 C can implement a pre-programmed navigation route or could be controlled by navigation instructions transmitted from a remote location and received by antenna  216 . 
   As mentioned above, antenna  216  can include a GPS antenna to receive GPS position signals that can be used to generate an accurate “own ship” position by navigation/propulsion processor  204 C. The “own ship” position can then be acoustically transmitted through the water for use by each deployed investigative vehicle  300  to develop navigation connections. The use of GPS in this fashion to develop navigational connections is well understood in the art and will, therefore, not be described further herein. 
   Navigation/propulsion processor  204 C also receives inputs from video camera  218  as an aid to making navigational corrections. Navigation/propulsion processor  204 C controls the dispensing of fuel from tank  206 A by means of dispenser  206 B. Processor  204 C further controls engine  208 A and wings  220 /rudder  222 . The operation of engine  208 A turns a propellor  210 A and electric generators  208 B which, in turn, applies electric energy to core  12  of the battery re-charging system described above. 
   With respect to investigative vehicle  300 , sonar sensors  302 - 308  provide their outputs to a sonar processor  310 A while image sensor  312  provides its output to an image processor  310 B. The respective sonar and image data is provided to a communications processor  310 C that formats the data for (underwater) acoustic transmission by an acoustic transceiver  314 . Navigation/propulsion processor  310 D can implement a pre-programmed navigation plan or could be controlled via navigation instructions transmitted underwater by acoustic transceiver  202 B and received by acoustic transceiver  314 . In either case, navigation and propulsion control is then provided to tail fins  320  and a motor  316 A. In turn, motor  316 A powers a propeller  316 B and is powered by batteries  316 C. Re-charging of batteries  316 C is accomplished when block  18  (e.g., docking rail  322 ) cooperates with core  12  (e.g., rail guide  232 ) as described above. Finally, navigation control for a recovery of an investigative vehicle  300  is provided by a guidance processor  310 E that receives its raw input from alignment sensor  324 . 
   In operation, mothership  200  is deployed in the water with its investigative vehicles  300 ′ coupled thereto. Mothership  200  navigates (e.g., according to a pre-programmed plan, under remote control for a host platform/ship via radio signals received by antenna  216 , etc.) to the vicinity of an underwater region of interest. At a predetermined location(s), mothership  200  releases its investigative vehicles  300  into the water where they begin their independent underwater investigations (e.g., mine hunting sweeps). During such underwater investigations, collected sonar and image data is acoustically transmitted through the water for receipt and storage onboard mothership  200 . At the same time, mothership  200  can re-transmit such data in a wireless fashion to a remote site by means of antenna  216 . For longer missions, investigative vehicles  300  can return to mothership  200  for battery re-charging as described above. When an investigative mission is complete, each of vehicles  300  returns to mothership  200  for recovery and re-transport back to the deploying host platform/ship. 
   The advantages of the present invention are numerous. The underwater investigative system requires no personnel and requires nothing to be towed. By remaining substantially underwater at all times, the covertness of operations is maximized. Collected data is made available to remote locations in a near real-time fashion thereby allowing subsequent operations (e.g., mine destruction, rescue operations, etc.) to proceed in a timely fashion. Long-term missions are made possible by use of a novel non-contact energy transfer system that can be incorporated into the system&#39;s docking mechanisms. 
   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. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described.