US Army’s creation of SIMNET
SIMNET, the military’s distributed SIMulator NETworking program. Simulators developed prior to the 1980s were stand-alone systems designed for specific task-training purposes, such as docking a space capsule or landing on the deck of an aircraft carrier. Such systems were quite expensive, for example, more than $30-$35 million for an advanced pilot simulator system in the late 1970s, and $18 million for a tank simulator at a time when an advanced individual aircraft was priced around $18 million and a tank considerably less. High-end simulators cost twice as much as the systems they were intended to simulate. Jack A. Thorpe was brought into DARPA to address this situation based on a proposal he had floated in September 1978. Thorpe’s idea was that aircraft simulators should be used to augment aircraft. They should be used to teach air-combat skills that pilots could not learn in peacetime flying, but that could be trained with simulators in large-scale battle-engagement interactions. Thorpe proposed the construction of battle-engagement simulation technology as a 25-year development goal. Concerned about costs for such a system Thorpe actively pursued technologies developed outside the DoD such as video-game technology from the entertainment industries. In 1982 Thorpe hired a team to develop a network of tank simulators suitable to collective training. The team that eventually guided SIMNET development consisted of retired Army Colonel Gary W. Bloedorn, Ulf Helgesson, an industrial designer, and a team of designers from Perceptronics of Woodland Hills, California, led by Robert S. Jacobs. Perceptronics had pioneered the first overlay of computer graphics on a display of images generated by a (analog) videodisc as part of a tank gunnery project in 1979.
The SIMNET project was approved by DARPA in late 1982 and began early in the spring of 1983 with three essential component contracts. Perceptronics was to develop the training requirements and conceptual designs for the vehicle simulator hardware and system integration; BBN Laboratories Inc, of Boston, which had been the principal ARPANET developer, was to develop the networking and graphics technology; and the Science Applications International Corporation (SAIC) of La Jolla, California was to conduct studies of field training experiences at instrumented training ranges at the National Training Center in Fort Irwin, California.
Affordability was the chief requirement Thorpe placed on the development of SIMNET components. Sticking to this requirement led to the most highly innovative aspects of SIMNET. Prior to the late 1980s simulators were typically designed to emulate the vehicles they represented as closely as engineering technology and the available funds permitted. The usual design goal was to reach the highest possible level of physical fidelity — to design “an airplane on a stick,” as it were. The SIMNET design goal was different. It called for learning first what functions were needed to meet the training objectives, and only then specifying the needs for simulator hardware. Selective functional fidelity, rather than full physical fidelity, was SIMNET’s design goal, and as a result, many hardware items not regarded as relevant to combat operations were not included or were designated only by drawings or photographs in the simulator. Furthermore, the design did not concentrate on the armored vehicle per se. Rather, the vehicle simulator was viewed as a tool for the training of crews as a military unit. The major interest was in collective, not individual, training. The design goal was to make the crews and units, not the devices, the center of the simulations. This approach helped minimize costs, thus making possible the design of a relatively low-cost device.
An early crisis that threatened to undo the project was that the visual-display and networking architecture being developed by BBN would not support the SIMNET system concept within the limits of the low-cost constraints. Analyses and expert judgments, from both within and outside of DARPA, indicated that the planned use of available off-the-shelf visual-display technology would not support the required scene complexity within the cost, computer, and communications constraints set by the SIMNET goals. However a proposal from Boeing allowed Thorpe to take advantage of the new generation of DARPA-funded microprocessor advances in VLSI and RISC for development of a new low-cost microprocessor-based computer image generating technology for visual displays. The technology proposed by M. Cyrus of Boeing met the scene complexity (“moving models”) requirements at acceptably low dollar and computational costs. Also, it permitted use of a simpler, less costly networking architecture. The proposed technology would use microprocessors in each tank simulator to compute the visual scene for that tank’s own “virtual world,” including the needed representations of other armored vehicles, both “friendly” and “enemy.” The network would not have to carry all the information in the visual scenes (or potential visual scenes) of all simulators. Rather, the network transmission could be limited to a relatively small package of calibration and “status change” information.
With these architecture and design elements in place SIMNET was constructed of local and long-haul nets of interactive simulators for maneuvering armored vehicle combat elements (MI tanks and M2/3 fighting vehicles), combat-support elements (including artillery effects and close air support with both rotary and fixed-wing aircraft), and all the necessary command-and-control, administrative and logistics elements for both “friendly” and “enemy” forces. A distributed-net architecture was used, with no central computer exercising executive control or major computations, but rather with essentially similar (and all necessary) computation power resident in each vehicle simulator or center?nodal representation.
The terrains for the battle engagements were simulations of actual places, 50 kilometers by 50 kilometers initially, but eventually expandable by an order of magnitude in depth and width. Battles were to be fought in real time, with each simulated element—vehicle, command post, administrative and logistics center, etc.?being operated by its assigned crew members. Scoring would be recorded on combat events such as movements, firings, hits, and outcomes, but actions during the simulated battle engagements would be completely under the control of the personnel who were fighting the battle. Training would occur as a function of the intrinsic feedback and lessons learned from the relevant battle-engagement experiences. Development would proceed in steps, first to demonstrate platoon?level networking, then on to company and battalion levels, and later perhaps on to even higher levels.
Each simulator was developed as a self-contained stand-alone unit, with its own graphics and sound systems, host microprocessor, terrain data base, cockpit with task-training-justified controls and displays only, and network plug-in capability (Figure 2). Thus, each simulator generated the complete battle-engagement environment necessary for the combat mission training of its crew. For example, each tank crew member could see a part of the virtual world created by the graphics generator using the terrain data base and information arriving via the net regarding the movements and status of other simulated vehicles and battle effects. The precise part of the virtual world was defined by the crew member’s line of sight—forward for the tank driver, or from any of three viewing ports in a rotatable turret for the tank commander.
The visual display depended primarily on the graphics generator resident in each simulator. This computer image generation (CIG) system differed in several important characteristics from earlier CIG systems. First, it was microprocessor-based (vs. large mainframe or multiple minicomputer based), and therefore relatively low in cost (less than $100,000 per simulator visual-display subsystem, vs. more than $1 million per visual channel; typical flight simulators have at least five visual channels). Secondly, it was high in environmental complexity with many moving models and special effects, but low in display complexity with relatively few pixels, small viewing ports, and a relatively slow update rate of 15 frames per second (vs. the opposite with earlier CIG systems and the technology being developed to improve and replace them). The development of the essentially unique graphics generator for SIMNET was a principal factor in permitting the system to meet the low-cost-per-unit constraint of the plan.
