RSIMS: A Case Study in DoD Collaboration

RSIMS: A Case Study in DoD Collaboration

by John Bennett and Brent Waggoner

U.S. Air Force Photo by MSgt Michael Ammons

The Department of Defense (DoD) has used modeling and simulation (M&S) to develop electro-optical and infrared (EO/IR) missile systems for many years. To do this, three basic types of simulations are used: (1) all-digital simulations, (2) scene projection hardware-in-the-loop (HITL) simulations, and (3) signal-injection HITL simulations. This article—which is an updated version of an article previously published in the CSIAC Journal [1]—discusses a DoD community that was formed to collaboratively develop a signal-injection-type HITL simulation architecture called the Reconfigurable Signal-Injection Missile Simulation (RSIMS). As discussed, because of the generic structure and ease of use of RSIMS, it can also be used for many other applications besides signal-injection missile seeker HITL simulations.

BACKGROUND

In an all-digital simulation, everything is modeled mathematically, with the entire simulation performed inside of a computer, with no real missile hardware. For scene projection HITL, the missile seeker (including optics and the detector/gyroscope) is mounted on a three- or five-axis flight motion table (shown in Figure 1). An EO/IR scene projector (shown in Figure 2) is used to present a simulated scene to the missile. This presentation must be done in real time so that the missile is essentially inside of a virtual-reality (VR) type environment, where the missile’s angular orientations, angular velocities, and angular accelerations are provided by the flight motion table.

Figure 1. Five-Axis Flight Motion Table Used in Scene Projection HITL.

Figure 2. Resistive Array EO/IR Scene Projector.

Conversely, a signal-injection HITL simulation, such as RSIMS, is a blend between an all-digital and a full-scene projection HITL simulation. The real missile guidance and tracking electronics are used, but the mechanical and optical components (e.g., detectors, optics, and gyroscopes) are not. The detector signal is generated digitally by the computer and output as an electronic signal that is injected into the missile seeker electronics (as pictured in Figure 3). Any other sensor signals must also be synthetically generated and injected into the seeker.

Figure 3. Signal-Injection HITL Missile Simulation.

In human terms, the difference between scene projection HITL and signal-injection HITL could be likened to the difference between VR achieved with VR goggles (scene projection) and a form of VR where a signal might be injected directly into the optic nerve (signal-injection), bypassing one’s eyes.

RSIMS DESIGN

At its core, RSIMS is a computer architecture for real-time processing that allows the developer to break a problem into subsystem models and implement these models as individual threads each running on a single core of a multi-core Linux personal computer (PC), while providing many utilities for timing control and both analog and digital input/output (I/O).

The basic RSIMS philosophy and design goals are as follows:

• Maximize the use of commercial-off-the-shelf (COTS) hardware (PCs) with custom software.
• Make RSIMS a common simulation architecture between many laboratories/facilities to allow sharing of subsystem models (e.g., gyro, flight motion, sensor/scene, I/O, etc.) and promote joint development, thus allowing entire missile system simulations to be easily shared and reused and greatly reducing overall development times. (For example, when one lab develops a HITL simulation for a particular missile, other labs can quickly duplicate it, thus saving precious time and resources.)
• Make RSIMS open source, where the code is freely shared between participants.
• Enable easy integration of Matlab/Simulink models.
• Minimize cost.

One of the keys to successful real-time operation of an RSIMS simulator is the ability to shield the required number of processor cores from interference from the operating system (OS) or system interrupts so that they can be totally dedicated to real-time processing. If this shielding is not done, interrupts generated by the OS will cause latencies that prevent real-time operation. RSIMS has two options for this service. One is a commercial, real-time version of Linux; the other is a real-time modification to an open-source version of Linux. This modified version is an excellent example of the RSIMS collaborative development environment (discussed later), as it was developed by an RSIMS partner and provided to the rest of the community.

Individual simulation threads can be generated from hand-written C++ code or from Simulink models that have been autocoded using the Mathworks Simulink Coder. Giving the simulation developer the option to mix threads from hand-written C++ and Simulink is extremely powerful. The developer can choose the best format for development of each subsystem model. For example, in the current missile seeker application of RSIMS, simulation timing control, I/O, and object spatial position threads are all hand-written C++ code, while the gyroscope models and missile flight simulation subsystems are both Simulink.

Users can easily spawn RSIMS threads to the PC processor cores for all the simulation subsystems. Once the simulation is running, the threads communicate with each other using the PC system memory. Controls have been developed to make sure that system memory values aren’t accessed while another thread is updating them. Figure 4 illustrates the basic RSIMS modular system design. As shown, the core of RSIMS is the Core Asymmetric Real-Time Threading Structure (CARTS), which isn’t tied to any specific application.

Figure 4. RSIMS Modular System Design.

A CALL FOR COLLABORATION

Historically, each DoD laboratory and contractor that ran signal-injection HITL missile simulations used its own unique, in-house-developed architectures. This approach not only made the sharing of subsystem models or other forms of joint development and collaboration difficult but also required each facility to expend significant resources to maintain and upgrade its individual architecture.

This situation changed, however, in 2003 with the decision to collaboratively develop a common HITL architecture (RSIMS) and the formation of the RSIMS development community, which comprises most of the DoD labs and contractors involved in signal-injection simulation. As a Government-owned product, the RSIMS software is free; all users are thus encouraged to share their code improvements with other developers for the benefit of the entire community.

Additionally, an RSIMS configuration control board (CCB), made up of the RSIMS DoD community members, is currently being planned. Users will continue to be free to make any changes to the RSIMS code they wish, but the CCB will determine which changes will become part of the standard RSIMS distribution.

RSIMS/CARTS has also been distributed to three U.S. allies—Australia, Canada, and the United Kingdom—which provides even more users and, ultimately, more improvements and enhancements that can be shared. Figure 5 shows the three groups that currently make up the RSIMS community: U.S. DoD agencies, U.S. contractors, and allied national labs.

Figure 5. RSIMS Collaborative Development Community.

SIGNAL-INJECTION MISSILE HITL SIMULATION APPLICATION

The specifics of the RSIMS signal-injection missile seeker HITL simulation include EO/IR scene generation using the DoD-owned Fast Line-of-Sight Imagery for Targets and Exhaust Signatures (FLITES) software (shown in Figure 6). Managed by the Air Force Research Laboratory (AFRL), FLITES is currently used by most DoD EO/IR missile simulation facilities, has a large DoD user/developer group, and is closely linked to the RSIMS community. In fact, numerous joint meetings of the RSIMS community and the FLITES User’s Group have been held.

Figure 6. Sample FLITES Images.

The most difficult part of RSIMS development for signal-injection HITL missile simulators was the reticle processor. Most nonimaging EO/IR missile seekers use one or more detector sensors where the EO/IR scene is modulated by a reticle mask to allow tracking of individual sources. This process must be simulated digitally to create the detector signal for injection into the seeker guidance and tracking electronics. The detector sensor reticle mask much be spatially aligned at the correct position on the EO/IR scene with the correct angular rotation. A multiply-accumulate function is used to determine how much EO/IR energy from the scene is transmitted through the reticle mask at each simulation time step.

The detector signal is formed from this operation and output through a digital-to-analog converter for injection into the missile seeker electronics. This process must be done at extremely high rates to ensure proper replication of the analog detector signal, and it is highly challenging to complete this process and output the information within the required time step (typically between 10 and 50 μs, depending on the missile system under test). Figure 7 illustrates the operation of a reticle processor.

Figure 7. Reticle Processor.

In its original design, RSIMS used a COTS PC-based field programmable gate array (FPGA) device for reticle processing. However, the latest version of RSIMS performs this operation on the PC COTS graphics processor unit (GPU), which is also where the EO/IR scene is generated by FLITES. This design is more efficient, as it doesn’t require each scene to be moved (e.g., to the FPGA) before reticle processing can begin.

Figure 8 shows a basic block diagram of an RSIMS HITL missile simulation. Figure 9 shows how each of these processes is used to generate a thread that operates on one core of the multi-processor PC.

Figure 8. RSIMS Block Diagram.

Figure 9. RSIMS Threads on Processor Cores.

Many RSIMS users perform infrared countermeasure (IRCM) effectiveness analysis. High-fidelity expendable IRCM models have been developed for FLITES. Additionally, directed energy/laser-based CM modules are also being developed for RSIMS. As mentioned, the RSIMS I/O interface is designed to be easily adapted for use with any I/O hardware. This gives users great flexibility in choosing the right I/O hardware for their application. Currently, RSIMS has been used with several COTS I/O boards and one Navy-designed board provided by a development partner, the Threat Signal Processor-in-the-Loop (T-SPIL) facility at the Naval Air Warfare Center Weapons Division (NAWCWD) at China Lake, CA.

Another RSIMS partner, the AFRL Dynamic Infrared Missile Evaluation (DIME) Laboratory, is the developer of the all-digital Modeling System for the Advanced Investigation of Countermeasures (MOSAIC). MOSAIC has a good graphical user interface (GUI) and is used by many of the RSIMS partners alongside their HITL simulators. Furthermore, the Navy Integrated Countermeasures Effectiveness Laboratory (NICEL) is working with the DIME Lab to integrate RSIMS and MOSAIC so that the MOSAIC GUI can be used to do simulation runs with both the native MOSAIC all-digital models and RSIMS HITL simulators. This will give users the ability to use a single GUI to set up simulation runs for a study using a suite of both all-digital missile models and HITL simulators.

ACCELERATING THE PACE OF SIMULATOR DEVELOPMENT

As the development of RSIMS progressed, the NICEL realized that the internal development team did not have the capacity to produce all the HITL simulators needed in a reasonable time frame. Thus, the Strategic and Spectrum Missions Advanced Resilient Trusted Systems (S²MARTS) Other Transactional Authority (OTA) contract was leveraged to obtain needed assistance from industry partners. The contract was designed for research, development, and prototyping activities, which was an ideal fit for the development of RSIMS HITL threat missile simulators. And because contract funding can be obligated in just a few weeks, otherwise expiring “sweep up” funds can be tapped. Currently, two threat simulators have been delivered and six threat simulators are in development with industry partners. Once these RSIMS HITL simulators are developed, the designs and software will be shared with the IRCM community and easily replicated at other labs at a fraction of the cost of independent development.

OTHER APPLICATIONS

As discussed, the RSIMS code is extremely flexible and can be used for many other applications besides signal-injection HITL missile simulators. For example, the DIME Lab has used RSIMS as the architecture for a developmental missile seeker. In this application, RSIMS is the architecture for the missile itself, instead of the overall simulation (as in the more traditional RSIMS applications). This application has created a powerful tool called the Open Architecture Surrogate Imaging Seeker (OASIS) (see Figure 10). Because RSIMS is tightly integrated with Matlab and Simulink, the tracking algorithms for this missile can be developed in Simulink and autocoded with the Simulink Coder to run as real-time threads inside the missile processor. Thus, users can quickly and easily change and update the system’s tracking algorithms to optimize performance. Copies of this system are currently in use at several DoD and international facilities.

Figure 10. The OASIS Concept.

Another application of RSIMS is the Fully Immersive Threat Reaction Environment (FITRE) flight simulator being developed by the Arkansas Air National Guard, Defense Intelligence Agency (DIA), and Georgia Tech Research University for several Air Force commands. As pictured in Figure 11, FITRE uses RSIMS to provide real-time, high-fidelity, all-digital models of threat missile systems that are integrated with man-in-the-loop flight simulator training systems. The software provides more realistic threat missile representations/scenarios for aircrews to train. The FITRE implementation of RSIMS replaces the actual missile hardware with a high-fidelity missile simulation that is configured to run in real-time using multiple PC cores via RSIMS. Though the software is still in early development, it has already generated considerable interest across the DoD. In addition, the foundational real-time threading functionality from RSIMS could likewise be easily used for many other real-time applications as well, such as industrial process control or time-critical flight systems for aircraft and unmanned aerial vehicles.

Figure 11. The FITRE VR Flight Simulator (U.S. Army National Guard Photo by Bob Oldham).

ADVANCED THREAT MISSILE SURROGATE PROJECT

Yet another example of RSIMS adaptability, collaboration, and cost-savings involves the DIA’s Missiles and Space Intelligence Center’s (MSIC’s) recent acquisition of hardware for an emerging threat missile system. Only a small number of these systems are available, and they are all currently being used by MSIC for exploitation and testing. The Services, however, would like to begin evaluating the performance of our CM systems against this threat, as well as develop new techniques and devices (if needed), as soon as possible. Unfortunately, an all-digital model cannot be developed until the exploitation is complete, and there are not enough copies of the hardware to build HITL simulators for all the labs that need them.

On two previous occasions in which missile hardware for new threats was in short supply, the NICEL teamed with MSIC and its support contractors to fund development of surrogate electronics for each of these two missiles. These surrogates are electronic analogs of the threat systems that can be used in signal-injection HITL simulators (without detectors, gyros, or other sensors). For this new threat, the development of surrogate hardware was similarly proposed but with a more far-reaching solution. Sponsored by the Test and Evaluation Threat Resource Activity (TETRA), five copies of the surrogate electronics for the threat, along with one turnkey RSIMS HITL simulator, are being developed. The five surrogate copies would go to all the DoD M&S labs interested in developing signal-injection HITL simulators for this threat, including:

• The Guided Weapons Evaluation Facility (GWEF)/AFRL DIME Lab (Air Force)
• The Picatinny Effectiveness and New Countermeasure Evaluation (PENCE) Lab (Army)
• NAWCWD China Lake T-SPIL (Navy)
• Naval Surface Warfare Center Crane Division (NSWC Crane) NICEL (Navy)
• MSIC (DIA).

The turnkey simulator will be used to validate each of the surrogate electronics copies. Each DoD lab will receive its surrogate, power supplies, and the system design and software for the RSIMS HITL simulator. After the completion of the project and delivery of the surrogates, the turnkey simulator will be provided to MSIC. Each of the other activities can then easily (and less expensively) develop its own HITL simulators using the surrogate electronics and simulator design information provided. Once again, this is a good example of the type of collaboration and cost-savings the RSIMS development group has created, not to mention the potentially accelerated development of necessary CM solutions to save Warfighter lives.

SUMMARY

To be sure, developing a common simulation architecture among different organizations can be challenging, especially when each lab has invested heavily in its own architectures. However, RSIMS has ultimately provided partners and users with features (e.g., FLITES scenes, etc.) not always provided in their homegrown systems. Moreover, the benefits of collaborative development and model-sharing between labs have significantly contributed to the success of the RSIMS and its community. A half dozen or so DoD and DoD contractor facilities are currently building or running RSIMS simulators, and it’s hoped that many more applications of this technology will follow. Interested parties are encouraged to contact the authors for more information.

About the Authors

Mr. John Bennett serves as a Software Design Subject-Matter Expert for the Platform Protection and Countermeasure Technologies Division at NSWC Crane’s NICEL. He has more than 34 years of experience in IR and RF expendable CM M&S. He was the developer of the FLAME CM fly-out model and the co-developer of RSIMS and the tri-Service Flare Database, which is a widely used tool for archiving and processing IR expendable radiant intensity data. Mr. Bennett holds a bachelor’s degree in mathematics and computer science from DePauw University and a master’s in mathematics from Indiana University.

Mr. Brent Waggoner serves as the Chief Engineer for M&S at NSWC Crane’s NICEL. He has almost 40 years of experience analyzing, developing, and optimizing IRCM solutions. He’s the co-inventor of the patent on which RSIMS is based, the leader of the Joint Infrared Fundamental Hardware Acceleration Working Group, and the current Chairman of the Military Sensing Symposia (MSS) EO/IR Countermeasures Symposium. Mr. Waggoner holds a bachelor’s degree in aeronautical and astronautical engineering from Purdue University, as well as a master’s in electrical engineering from Rose-Hulman Institute of Technology.

References

1. Bennett, John, and Brent Waggoner. “Reconfigurable Signal-Injection Missile Simulation (RSIMS): A Case Study of Innovation Through the Implementation of a Common Architecture and the Creation of a Collaborative Development Environment.” CSIAC Journal, vol. 7, no. 3, December 2019.