Abstract:
A computer based simulation system for virtual training for vehicle crews is disclosed. The vehicle crew training system (VCTS) simulates crew positions for different military vehicles. Two or more crewman modules are networked together to support a partial or full vehicle crew. The crewman modules are self-contained devices that are modular in hardware and software design, easily reconfigurable, and that require minimal facility space, allowing use in restricted environments such as trailers. The VCTS is modular at the crew position level; crewman modules are added or deleted as required to meet a particular training need. One of the crewman modules can be a gunner module, which provides an unrestricted view of the simulated environment to the gunner by means of a display and a simulated vehicle-mounted weapon.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 11/055,708, filed Feb. 11, 2005 (issuing as U.S. Pat. No. 8,864,496), which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The invention pertains to training simulators. 
     BACKGROUND OF THE INVENTION 
     System Design 
     Historically, most virtual crew training has been accomplished with appended trainers or with crew station trainers. An appended trainer consists of equipment added to an actual (parked) combat vehicle such that the vehicle is used to train a full or partial crew in a virtual environment. Examples are Raydon&#39;s Abrams Appended Trainer (A-FIST XXI) and the Bradley Appended Trainer (AB-FIST). A crew station trainer includes a replica of a crew compartment of an actual vehicle. Examples are Raydon&#39;s M-COFT XXI and SIMNET XXI trainers for the Abrams tank and the Bradley fighting vehicle. The appended and crew station trainers typically provide higher fidelity and very little modularity. Here, “fidelity” refers to the physical and functional realism of the man-machine interface, specifically, the realism of the vehicle and/or weapon controls in terms of numbers of controls and control realism; the realism of visual imagery in terms of field of view, resolution, and scene content; and the realism of the physical crew position in terms of the human support structure. Further, these trainers tend to be purpose-built for either individual/crew training or for collective training, but not both. 
     More recently, desktop training systems have emerged that are capable of training individuals and crews of military combat vehicles with less fidelity but at a much lower cost than the appended and crew station trainers. However, these desktop systems are not modular and, like the higher fidelity appended and crew station trainers, tend to be purpose-built for either individual/crew training or for collective training, but not both. 
     Hence, there is a need for a virtual crew training system that is sufficiently flexible to allow both individual/crew training and collective training, is modular, and can provide any level of fidelity. 
     Gunner Module 
     Current simulators for mounted weapons training use video projection screens and a fixed mount weapon mockup. Taken together, this results in a limited field of view for the gunner, i.e., the gunner can only look and shoot at scenes depicted on the projection screen. Typically, these screens are limited to the forward direction only. 
     This approach also requires more space to implement, making it impractical to use in standard trailers or portable shelters. One instantiation of this approach was implemented by the U.S. government at the Mounted Warfare Testbed in Fort Knox, Kentucky. Another instantiation of this approach was implemented by Lockheed Martin for the government&#39;s Virtual Combat Convoy Trainer program, as documented in the Aug. 31, 2004  Orlando Sentinel . Hence, there is a need for a mounted-weapon training simulator module that has a relatively small physical footprint, yet provides realistic perspective, i.e., in all possible directions, for a trainee&#39;s view and aim. 
     SUMMARY OF THE INVENTION 
     System Design 
     The vehicle crew training system (VCTS) is a computer-based simulation system intended to serve the virtual training needs of military users. However, unlike other simulation systems, the VCTS is modular at the crew-position level; crewman modules are added or deleted as required to meet a particular training need. The VCTS provides virtual training for vehicle crew members. “Virtual training” refers to a mode of training in which the trainee is immersed in a simulated environment as a participating entity, and in which results of all actions occur in real-time based on cause and effect. This is also referred to as “real-time, man-in-the-loop simulation.” The simulation system also supports virtual dismounting of a trainee, such that the trainee may virtually exit the virtual vehicle while maintaining the ability to interact with the virtual environment from the vantage point of a dismounted position. Three modes of virtual training are supported: individual training; crew training; and collective training with multiple vehicle crews. The VCTS is able to simulate crew positions for different military vehicles and their associated weapon systems. The VCTS comprises crewman modules networked together to support a partial or full vehicle crew. Moreover, not only is the VCTS modular, but each crewman module is itself modular. The crewman modules are self-contained devices that are modular in hardware and software design, and easily reconfigurable. In addition, the crewman modules occupy a minimal physical footprint. 
     One instantiation of the VCTS is a high mobility multipurpose wheeled vehicle (HMMWV) trainer developed by Raydon Corporation, of Daytona Beach, Fla. This system can be used for virtual combat convoy training in a simulated geographical environment. In an embodiment of the invention, the simulated environment corresponds to an actual urban or rural setting. Future VCTS variants include, but are not limited to, the heavy expanded mobility tactical truck (HEMTT), the standard cargo truck, and the five-ton tactical truck. 
     The VCTS consists of two or more crewman modules networked together. A typical set of crewman modules constituting a VCTS includes a driver module, a commander module, and a gunner module. Via a network, other devices, such as an instructor station and a simulated radio, may be integrated with the VCTS. Additional crewman modules may be added for other crew members, such as an observer/riflemen. Vehicle crew training systems may also be linked together to form groups of simulated vehicles, such as platoons of three or four vehicles, where each vehicle is configured with two or more crewman modules. Two instructor stations may be included in these larger embodiments to facilitate training simultaneously with the conduct of after-action reviews of previously conducted exercises. Additional instructor stations may be added to facilitate individual and crew training. 
     Various embodiments of the invention, therefore, may or may not interface with the instructor station. However, it can be an important component of the overall training system. In embodiments where it is included, it initializes the different VCTS crewman modules, monitors the performance of the trainees, controls the operation of the simulated enemy and friendly forces during the various training exercises, and records all exercise events. In addition, the instructor station supports the conduct of after-action reviews (AARs), wherein previously conducted exercises are played back as an aid to the instructor&#39;s critique of trainee performance. An instructor station can also act as a surrogate driver in the absence of a driver module or any other missing crewmember. If two instructor stations are included, then it is possible to perform the exercise control and monitoring functions with the AAR function simultaneously. 
     The vehicle crew training system is designed in a modular fashion such that systems may be reconfigured to meet different training needs. Reconfiguration may involve adding, deleting, or changing the mix of crewman modules. Modularity also extends to the design of the crewman modules such that the weapon system and/or the vehicle type may be rapidly changed. For example, a .50 caliber machine gun in use on the HMMWV variant of the vehicle crew training system can be swapped for an MK-19 grenade launcher, a 7.62 mm machine gun, an M249 squad automatic weapon, or a tube-launched optically tracked wire-guided (TOW) missile launcher, for example. Note also that the weapon system can alternatively be a non-lethal weapon that might be used for such actions as crowd control, for instance. Examples of such non-lethal weapons include water cannons, devices for firing tear gas canisters or beanbags, and sound and microwave generators. 
     An embodiment of the invention can consist of four simulated HMMWV vehicles, each represented by a VCTS with five Crewman Modules. Two instructor stations and simulated radios can be interfaced with such an embodiment of the VCTS through a network. The system provides individual, crew, and collective training to platoons of HMMWV drivers, commanders, gunners and observer/riflemen. 
     The VCTS is designed to fit into a very constrained space, such as a semi-trailer or a portable shelter. The HMMWV trainer just described fits into two 53-foot semi-trailers. 
     Another embodiment of the VCTS is a HMMWV training system developed for the U.S. Army National Guard. This system can consist of five simulated HMMWV vehicles, where four of the vehicles are represented by VCTS&#39;s consisting of two crewman modules each and the fifth vehicle (external to any VCTS) is represented by an Appended HMMWV containing a driver and gunner position. Simulated radios and an instructor station can also be interfaced to the VCTS. The system provides individual, crew, and collective training to platoons of HMMWV drivers and gunners. The VCTS modules and the instructor station of this embodiment fit in one 53-foot semi-trailer. 
     Gunner Module 
     The gunner module embodies a unique approach to weapon system training for simulated ground vehicles. It provides an unrestricted view of the simulated environment to the gunner by means of a head-mounted display (HMD) and a moveable, vehicle-mounted weapon mock-up. The HMD provides a complete spherical (360-degree) field of regard (FOR) to the gunner; as the gunner moves his head, the instantaneous field of view (IFOV) changes in relation to the direction his head is pointed. The weapon mock-up is cradle/pintle-mounted on a 360-degree traverse ring to allow full 360-degree horizontal traverse, as well as the authentic amount of weapon pitch and yaw. External cabling is routed through a slip ring to allow unlimited rotations of the traverse ring. In addition, weapon mock-ups and the weapon software may be easily changed to simulate different vehicle-mounted weapons. Finally, the gunner module is very compact in size, allowing use in restricted environments such as trailers and mobile shelters. 
     Crewman modules may be of varying fidelity. For example, a lower fidelity desktop version of the gunner module may be used instead of the simulated crew position version described above. “Fidelity” in this context refers to the fidelity or realism of the man-machine interface as experienced by the trainee, i.e., the fidelity of the vehicle and/or weapon controls in terms of numbers of controls and the realism of the controls, the fidelity of visual imagery in terms of field of view, resolution, and scene content, and the fidelity of the physical crew position in terms of the human support structure. 
     The VCTS architecture supports any mix of varying fidelity crewman modules. Since the lower fidelity desktop versions provide subsets of the capabilities embodied in the simulated crew position versions, all discussions of crewman module will refer to the higher fidelity variants, unless specifically stated otherwise. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a diagram illustrating the minimum system configuration of the vehicle crew training system (VCTS), according to an embodiment of the invention. 
         FIG. 1B  is a diagram illustrating a typical full crew configuration of the VCTS, according to an embodiment of the invention. 
         FIG. 1C  is a diagram illustrating multiple VCTS systems linked together to support collective training, in accordance with the embodiments of  FIGS. 1A and 1B ; this configuration is representative of a VCTS training system developed for the U.S. Army National Guard. 
         FIG. 2A  is a diagram showing the major components of a VCTS crewman module, in accordance with the embodiment of  FIG. 1 . 
         FIG. 2B  is a table identifying the types and components that comprise a VCTS crewman module, in accordance with the embodiment of  FIG. 2A . 
         FIG. 3  is a diagram illustrating the componentized architecture of the VCTS software, in accordance with the embodiments of  FIGS. 1 and 2 . 
         FIG. 4A  is a functional block diagram of the VCTS gunner module hardware in accordance with the embodiments of  FIGS. 1, 2 and 3 . 
         FIG. 4B  is a functional software diagram of the VCTS gunner module in accordance with the embodiments of  FIGS. 1, 2 and 3 . 
         FIG. 5A  is a photograph of the overall VCTS gunner module in accordance with the embodiments of  FIGS. 1, 2, 3 and 4 . 
         FIG. 5B  is a photograph of the gunner module weapon mock-up, a simulated .50 caliber machine gun in accordance with the embodiments of  FIGS. 4 and 5A . 
         FIG. 5C  is a photograph of the gunner module traverse ring assembly in accordance with the embodiments of  FIGS. 4 and 5A . 
         FIG. 5D  is a photograph of the gunner module traverse ring encoder m accordance with the embodiments of  FIGS. 4 and 5A . 
         FIG. 5E  is a photograph of the gunner module electronics assembly in accordance with the embodiments of  FIGS. 4 and 5A . 
         FIG. 5F  is a photograph of the gunner module slip ring assembly, head-mounted display and head tracker in accordance with the embodiments of  FIGS. 4 and 5A . 
         FIG. 6  is a photograph of a lower fidelity desktop variant of a gunnery module, according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the invention are discussed in detail below. In describing embodiments, specific terminology is employed for the sake of clarity. The invention is not intended to be limited to the specific terminology so-selected. While specific exemplary embodiments are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations can be used without departing from the spirit and scope of the invention. 
       FIGS. 1A, 1B and 1C  illustrate various embodiments of a VCTS system  100  in accordance with the present invention. The system is comprised of at least two crewman modules  102  and  104  connected via a network  110 . Various embodiments currently comprise crewman modules, which can be, for example, a driver module, gunner module, commander module, and observer/rifleman module. Other crewman module types can be supported as needs dictate. These other modules could include, for example, alternate driver modules, crowd-control/riot-control modules, and non-lethal weapon modules. An embodiment of the system that supports a four-man crew is illustrated in  FIG. 1B ; this configuration of the system includes a driver module  112 , a gunner module  114 , a commander module  116 , an observer/rifleman module  118 , and network  110 . An instructor station is shown connected to the VCTS. The instructor station  120  provides exercise control, monitoring, and evaluation. An embodiment of the invention that supports collective training is illustrated in  FIG. 1C ; four VCTS systems ( 130 ,  140 ,  150 , and  160 ), each consisting of a driver module and a gunner module, and linked via network  110 , support four vehicle crews. The four VCTS systems are linked via network  110  to an instructor station  170  and to an appended trainer  180 , which supports a fifth vehicle crew. 
       FIGS. 2A and 2B  illustrate the components and characteristics of an embodiment of a VCTS crewman module. Crewman modules are self-contained training devices that contain the necessary hardware and software to support virtual training for a single crewman. In an embodiment of the invention, a crewman module consists of a simulated weapon system  186  (or, in the case of a driver module, a driving system  188 ), a display system  190 , a sound system  192 , a computational system  194 , and a crewman station  184 . A simulated weapon system  186  can comprise a weapon mock-up, including all necessary controls such as triggers and arm/safe switches, and the electronics and cabling required to interface it with the computational system  194 . A simulated driving system  188  can comprise a steering wheel, transmission selector, brake and accelerator pedals, and all other necessary controls, electronics and cabling required to drive the vehicle and to interface it with the computational system  194 . The display system  190  consists of the display devices, such as head-mounted displays (HMDs) and liquid crystal display (LCD) panels, and the necessary electronics and cabling required to interface it with the computational system  194 . Sound system  192  consists of amplified speakers and the necessary audio cabling to interface it with the computational system  194 . Weapon and vehicle sounds are broadcast to the trainee via the sound system  192 . The computational system  194  consists of a commercially available PC (or a programmable computing platform of comparable capability, but referred to herein generically as a PC) augmented with standard devices and ports to enable communication with other crewman module hardware components, with other crewman modules, and with external systems such as instructor stations and other vehicle simulators. The crewman station  184  consists of the physical structure that contains and/or supports the trainee, as well as all of the components that comprise a crewman module. 
     The computational system  194  contains the crewman module software. In an embodiment of the invention, the crewman module software consists of a commercially available operating system and application software. The major functions performed by the application software include simulating vehicle movement, weapon aiming, firing, and impact effects, image generation of visual scenes, interfacing with the various hardware components, and interfacing with other crewman modules and with external systems, such as other vehicle simulators, via the network. The application software in the driver module has the additional functions of calculating collision with other objects in the virtual world and of terrain following by the driver&#39;s virtual vehicle. 
       FIG. 3  illustrates the VCTS application software architecture  300  according to an embodiment of the invention. The software architecture can be an object-oriented design comprised of components, which are encapsulated pieces of software with a defined functional purpose and a defined interface. The purpose of componentizing the application software is to minimize rework and maximize reuse as new vehicles and new weapons are incorporated into the VCTS design. 
     Software components are categorized as either being application-specific or reusable. If the latter, they are placed into a library of reusable components. In an embodiment of the invention, one or more application specific components  310  generally links to one or more reusable components  320  to perform a given function. A collection of drivers and application program interfaces (APIs)  330  may also be included with the application software to interface with hardware  340 . Drivers and AP is  330  include drivers for the video and data acquisition cards housed in the PC, as well as network, joystick and sound drivers and the API for the visual software. Underlying the components, drivers and APIs is the real-time executive software  350  that provides the universal means for components, drivers and API&#39;s to communicate via messages, events, and data reflection through its interface. The real-time executive software  350  can also be componentized. 
       FIG. 4A  is a functional hardware diagram of an embodiment of the gunner module, and  FIG. 4B  is a functional software diagram of this embodiment of the gunner module. The illustrated weapon system is comprised of weapon mock-up  402 , traverse ring encoder  404 , calibration button  406 , and an interface device  408 . The weapon mock-up  402 , in one embodiment of the invention, is a simulated .50 caliber machine gun. The position, pitch and yaw of the simulated weapon are measured continuously, and fed back to PC  407  via the interface device  408 . One example of such an interface device  408  is a buffer board, as shown in  FIG. 4A . A calibration signal is fed back to the PC  407  via the interface device  408  when the trainee pushes the corresponding button  406 . The interface device  408  applies signal conditioning to the incoming signals and sends the data to a data acquisition (DAQ) card  410  in the PC  407 . Referring to  FIG. 4B , the weapon I/O software  431  in the PC  407  inputs the data  441  from the DAQ Card  410 , formats it, and outputs the formatted weapon data  442  to the weapon simulation software  432 . Weapon data  442  is received continuously and includes weapon position, pitch, yaw, and trigger pull. The calibration signal is sent only during the weapon calibration process. The weapon simulation software  432  computes a trajectory for the bullets and outputs projectile position data  444  to the network software  434 . The weapon simulation software  432  receives own-vehicle state data  443  continuously from the network software  434 . This data is used to compute the position of the weapon in the virtual environment. 
     In the embodiment illustrated of  FIG. 4A , the display system  190  is comprised of a head-mounted display (HMD)  412  with an attached head tracker (HT) receiver  414 , an HT transmitter  416  mounted above the gunner position and the HMD and HT interface electronics ( 418  and  420 , respectively). In addition, an LCD panel is provided to serve as a video repeater  422  for the benefit of the instructor. In this embodiment of the invention, an acoustic HT system senses the position and attitude of the HMD  412 , and continuously feeds the data to the PC  407  via the HMD/HT data interface. Referring to  FIG. 4B , HT data  446  is continuously input to visual I/O software  460  where it is formatted and then output (see  448 ) to visual simulation software  465 . The visual simulation software  465  uses the formatted HT data  448  to determine the position and look angle of the head relative to the visual scene that is displayed to the trainee wearing the HMD  412 . In an embodiment of the invention, the visual simulation software  465  also performs the following functions:
         Rendering of the visual scene according to the HT-supplied look angle (in data  448 ) and according to own-vehicle state data  449  received from the network software  434 ;   Full color, perspectively correct, anti-aliased and textured image generation;   Imagery affected by atmospheric and weather effects;   Night vision simulation;   Rendering of other vehicles according to vehicle state data  449  received from the network software  434 ;   Input of own.-weapon projectile data  444  and subsequent impact detection processing;   Weapon effect generation and rendering based on own-weapon projectile impact detection;   Weapon effect generation and rendering based on weapon impact data (in data  444 ) received from the network software  434 ;   Output of own-vehicle weapon impact and collision data  450  to the network software  434 ;   Collision detection of the own-vehicle with other objects in the virtual world;   Terrain following by the own-vehicle; and   Output of video  447  to the visual  110  software  460 .
 
The visual I/O software  460  formats the video and sends it to the video card  424  in the PC  407  (see  FIG. 4A ); the video  445  is then output to the display system  190  as standard VGA video.
       

     In the illustrated embodiment, the network software  434  sends and receives data  451  to and from the network  110 . Data sent to the network  110  includes projectile state data received from the weapon simulation software  465 , and weapon impact and collision data received from the visual simulation software  465 . Data received from the network  110  includes own-vehicle state data plus the state of all other vehicles and projectiles that are active in the virtual environment. 
     In the embodiment of the invention shown in  FIG. 4A , a sound system  192  generates aural cues synchronized with and representative of actions and events in the virtual environment. Sounds can caused by, for example, own vehicle and other vehicle movements, own weapon and other weapon firing, weapon impacts and explosions caused by own weapons or other weapons, and could even include environmental “noise” such as crowd noise. 
     The sound system  192  includes amplified speakers  426  that receive audio  452  from the PC  407  via standard audio cables in an embodiment of the invention. The sound I/O software  470  is a sound driver that receives the sound data  453  from sound simulation software  475  and formats it for use by the standard sound hardware in the PC  407 . The sound simulation software  475  creates sounds based on weapon and vehicle state data  454  that is received from the network software  434 . Sound files representing different battlefield sounds are created off-line and then stored in a sound file library; during real-time, the sound simulation software  475  accesses the appropriate sound files and weights them appropriately to create aural cues for the trainee. 
     In an embodiment of the invention, the computational system  194  consists of a commercially available PC equipped with 2 GB of main memory and a Pentium 4® CPU; Windows XP® maybe used as the operating system. In this embodiment, the DAQ  410  card is a commercially available PCI card that supports both analog and digital signals. The video card  424  may be a commercially available PCI graphics card. 
       FIG. 5A  is a photograph illustrating the overall mechanical design of a gunner module  500 , according to an embodiment of the invention. The gunner module  500  is built on a gunner station  505 , which is a large aluminum box with a large circular hole cut in the top panel. A traverse ring  510  is fastened to the top of the box. The traverse ring  510  consists of a pallet carousel modified for use with the gunner module  500 . An electronics assembly  515 , an HMD/HT support structure  520 , and a weapon mock-up  525  are attached to the traverse ring  510  such that they move with the traverse ring  510  in response to trainee pressure. A slip ring support structure  530  is attached to the gunner station  505 , such that it remains fixed in space regardless of traverse ring rotation. A slip ring  535  and a video repeater  540  are attached to this support structure. Each of these items is described in more detail in the following paragraphs. 
       FIG. 5B  is a photograph illustrating an embodiment of the mechanical design of the weapon mock-up  525 , which in this embodiment of the invention is a .50 caliber machine gun. A mounting base  542  for the simulated weapon is attached to the traverse ring  510 , such that the simulated weapon moves when the traverse ring  510  moves. The main body of the gun is attached to the mounting base  542  via a cradle/PINTLE mount  544  that permits simultaneous pitch and yaw aiming of the simulated weapon. Pitch and yaw sensors  546  and  548  built into the cradle/PINTLE mount  544  consist of potentiometers that change voltage in direct proportion to the rotation of the simulated weapon in each axis. Attached to the back end of the main body of the simulated weapon are hand grips  550  and a trigger  552  that are used by the trainee to aim and fire the weapon. A charging handle  554  is included in the mechanical design, but it is not functional in the illustrated embodiment. A counterweight  556  is attached to the front end of the main body of the simulated weapon in order to provide a realistic heft and balance to the trainee. 
       FIG. 5C  is a photograph illustrating the mechanical design of the traverse ring  510  and attached components, according to an embodiment of the invention. As shown, the traverse ring  510  is a circular carousel attached to the top panel of the gunner station  505 . It rotates freely in both directions in response to trainee pressure applied to a gunner back rest  558 . A cover  560  is attached to the traverse ring  510  to simulate the space constraints of a HMMWV-mounted .50 caliber machine gun; it is also used to mount the calibration button  562  and, on the underside of the cover  560 , the traverse ring encoder (not shown). A weapon mock-up mounting base  564  and a bustle plate  566  are also attached to the traverse ring  510 , such that all of the components mounted to these support surfaces move with the traverse ring  510 . 
       FIG. 5D  is a photograph of an embodiment of the traverse ring optical encoder  568  which, as mentioned above, is attached to the underside of the traverse ring cover  560 . A sensing wheel  570  is a metal wheel with a rubber o-ring that is positioned against the inside of the traverse ring  510 , such that the wheel moves when the traverse ring  510  moves. Optical encoder  568  senses the rotation and converts it to an eight-bit digital signal. This signal is routed back to the data acquisition card in the PC via the interface device. 
       FIG. 5E  is a photograph illustrating the mechanical design of the electronics assembly  515  of the gunner module  500 , according to an embodiment of the invention. This assembly is attached to the bustle plate  566  such that the entire electronics assembly  515  moves with the traverse ring  510 . The components that comprise the electronics assembly  515  can include the following:
         A commercially available PC with DAQ and video cards,  572 ;   Amplified speakers  574 ;   HMD interface electronics  576 ;   Head tracker (HT) interface electronics  578 ; and   Enclosure containing power strips and the interface device,  580 .       

       FIG. 5F  is a photograph illustrating the mechanical design of the superstructure of the gunner module  500 , according to an embodiment of the invention. The HMD/HT support structure  520  is attached to the bustle plate  566  which, in turn, is attached to the traverse ring  510 , such that the HMD/HT support structure  520  and components attached to it move with the traverse ring  510 . The HMD  582  can be hung on the HMD/HT support structure  520  when not in use. In the illustrated embodiment, the HMD  582  is a commercially available display device that provides a view of the virtual environment to the trainee directly in front of his eyes. Standard VGA video is fed to the HMD  582 . A sensor is attached to the top of the HMD  582 ; this is the HT Receiver  584 . The HT receiver  584  works in concert with an HT transmitter  586 , which is attached to a mounting plate on the top of the HMD/HT support structure  520 . For this embodiment of the invention, an acoustic HT system is employed; acoustic signals are transmitted by the HT transmitter  586  and received by the HT receiver  584 . As the trainee head (and therefore the HMD  582 ) moves, the time required for the acoustic signals to travel the distance between the HT transmitter  586  and the HT receiver  584  continuously changes in direct proportion to the distance between the transmitting and receiving devices. The visual simulation software computes the position and orientation of the HMD  582  (and therefore the trainee&#39;s head) based on these signals. 
     For this embodiment of the invention, the slip ring  535  is attached to the slip ring support structure  530 , which is attached to the main body of the gunner station  505 . Therefore, the slip ring  535  stays fixed in space as the traverse ring  510  moves. The slip ring  535  is a commercially available device that routes wires through the slip ring  535  to the HMD/HT support structure  520 . As the traverse ring  510  moves, slip ring cabling  588  moves in a circular motion around the slip ring  535 , but cable connections are maintained. Since most of the electronics are mounted on the bustle plate  566  or otherwise attached to the traverse ring  510 , only a few wires are passed over the slip ring cabling  588 . They include:
         Ethernet cabling for the ethernet network that connects the gunner module  500  to other crewman modules or to external systems;   VGA video cabling for the video repeater  540  attached to the slip ring support structure  530 ; and   Power cabling for the various electronic devices attached to the traverse ring  510 .
 
In another embodiment of the invention, the slip ring could be integrated into the traverse ring.
       

     Note that, in addition to the HT apparatus discussed above, other mechanisms could be used to track the position and/or orientation of the head of the gunner trainee. Examples include inertial head trackers and eye trackers, both of which are known in the art. 
       FIG. 6  is a photograph of an embodiment of a lower fidelity desktop variant  600  of the gunner module. This version of the gunner module provides all of the functionality of the higher fidelity gunner module described above. Differences include those relating to the fidelity of the device. For example:
         The gunner simulates moving a traverse ring using foot pedals  610  and software that moves a weapon mock-up  620  around the simulated ring; the imagery displayed to the gunner on an HMD  630  presents the view that the gunner would see if he moved the traverse ring with his feet and back as he would on the higher fidelity variant of the gunner module.   A lower fidelity HMD  630  is used with reduced resolution and with angular tracking only, i.e., only in the direction that the Gunner&#39;s head is pointed is sensed by the head tracker.       

     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail may be made therein without departing from the spirit and the scope of the invention.