Modeling and Simulation Supports Space and Missile Defense

Written by Erin Flynn Jay

For the U.S. Army Aviation and Missile Research, Development and Engineering Command (AMRDEC), there is a strong push toward simulation-based acquisition where system development is enabled by simulation technology that is integrated across all acquisition phases. This means M&S will play a far more prominent role in system development, integration and assessment, said Tom Barnett, BMDS HWIL Integration Lead for AMRDEC. The AMRDEC supports these areas through basic research, advanced technology development and insertion, system engineering support directly to weapon system program managers, system demonstration, integration, developmental and operational testing, training and performance assessment.

From initial specification and early design M&S is used to “bound the problem” by analyzing the impacts of a new system (or upgrade to existing system) on existing capability. A low- to medium- fidelity force-on-force simulation is typically used at this point to execute “what if” drills to allow the system engineer to understand how the new functionality will perform when inserted into the current force structure.

As system development progresses, M&S is used to analyze trade space within the design and to assess the effectiveness of the design. “Higher fidelity component models are developed to fully wring out the design of all subsystems. These models are then integrated into a full end-to-end system simulation to capture the interdependencies of the components and to assess overall performance under the most stressing conditions,” Barnett told MSMF. “This also allows more robust testing as the M&S input parameters can be quickly reconfigured to test the entire design space.”

M&S then supports early integration by acting as a surrogate for the environment into which the system will be integrated. An example of this is hardware-in-the-loop (HWIL) testing where a component such as a missile seeker with its guidance and control computer is immersed in a simulated tactical environment. The high-fidelity component models mentioned above are adapted to run in real-time and used to “build” the rest of the missile (e.g., propulsion, aerodynamics, divert capability, etc.).

In-band target signatures, backgrounds, environments and countermeasures are then projected into the aperture of the seeker. As the guidance computer reacts to what the seeker “sees,” it sends commands to its (simulated) divert actuators. Barnett said the effects are calculated by complex aerodynamic algorithms, and the resulting forces are applied to the body (also simulated) and to the (sometimes simulated) inertial measurement unit that provide feedback to the guidance computer. This closed-loop simulation capability not only provides significant benefit to the system engineer but is also invaluable to flight test planners.

“While flight testing is the most visible and often spectacular form of testing [whether successful or not] and is extremely valuable to the missile developer, its test objectives tend to be very specific and thus it should not be considered a true indicator of system performance,” Barnett said. On the other hand, flight testing provides an immense amount of verification and validation (V&V) data to the developer of the high-fidelity component models and, by association, all M&S that are benchmarked against them.

This relationship between flight tests and M&S will continue to be a key to successful missile defense development. “In fact, a primary driver of flight test objectives is collection of data related to critical engagement conditions to support M&S validation,” said Barnett. “While several missile defense programs have integrated their system engineering, M&S and flight test efforts in this way, this is a significant paradigm shift for the broader missile defense community.”

As system testing proceeds, the M&S components are gradually replaced by tactical hardware/software and live operators. Ground tests and exercises will test the battle management and fire control capabilities as well as the interoperability of the system. Both automated and operator-in-the-loop functions are tested in these venues. Similar test configurations are used later in the life cycle to support operator training and development of tactics, techniques and procedures. These venues also provide significant anchoring data for the various component and operator models.

A technique used with great success by the AMRDEC is the concept of “integrated simulation and tactical software,” whereby actual tactical code is embedded in the high-fidelity digital simulations, replacing simulated components. Similar to HWIL, Barnett said this “software-in-the-loop” approach allows tactical code to be thoroughly tested but also adds realism to the simulation by reducing the opportunities for errors due to “sim-isms” (errors introduced by the M&S environment).

In summary, M&S provides cradle-to-grave support for space and missile defense by providing a key system engineering resource to investigate interactions and phenomena that are simply not reproducible in any other venue and to assess the system in areas where it is not practical to test. “And because digital simulations and HWIL can be executed many times for a tiny fraction of the cost of a single flight test event, M&S allows substantial cost avoidance while providing significant value added,” said Barnett.

GAPS IN M&S SYSTEMS

“There seems to be a perpetual struggle to increase the fidelity of our system M&S while minimizing runtime,” Barnett said. “A tradeoff of ‘high detail vs. statistical significance’ is a call that all M&S programs are forced to make. As engineers, we expect our M&S to be faithful representations of reality. The art is knowing when the model is ‘good enough.’” There is a tendency to spend far too much time and resources working toward maximum detail/granularity rather than the appropriate level of detail to address the problem.

Since most M&S used for system-level analysis are stochastic in nature, they should be executed many times (i.e., Monte Carlo) to allow the key variables to converge. However, a highly detailed simulation with many entities may take hours or even days to execute, making it prohibitive to run thousands of cases. So AMRDEC can either buy more/faster computers or they can try to be more “efficient” in their M&S engineering.

“Vertical integration” is an approach that allows large-scale system simulations to leverage those higher detailed component models. Typically, the component models are used to generate distributions against which the system simulation makes random draws. In this way, the “fidelity” of the higher detail component model is maintained without the need to run its complex algorithms “inline.” Additionally, since these higher detail component models are also stochastic in nature, running them a single time inline may actually skew the results away from the norm, thereby, in effect, decreasing the fidelity.

In much the same way that vertical integration links the systemlevel simulations to their higher detail component-level counterparts, the same approach should be applied to verification and validation of the M&S. Barnett said the community is working very hard to maximize the return on the flight test dollar by focusing test objectives and data collection on validating key functions and associated data elements and parameters. This is the first step toward implementation of a comprehensive vertical integration strategy.

Appropriately leveraging this data at all “levels” of M&S will significantly improve both the consistency among AMRDEC M&S and, more importantly, the confidence with which they use them.

A weapon system prime contractor typically develops detailed models of components to assist in design and development of that component and possibly to support integration at the weapon system level. “However, little consideration is given to the eventual need to integrate at the system-of-systems level or to independently assess the system prior to fielding,” said Barnett. “Industry could enhance overall M&S efficiency through development of modular and configurable component models that can be integrated into system-level simulations [where appropriate], quickly reconfigured to allow the component to support a different use case and for representing other components that are substantially similar to the first [e.g., a single model for several radars that are built on the same technology].”

Lastly, Barnett said when industry delivers M&S products they should be non-proprietary and robust enough to be used for assessing system performance. Substantial resources are required for the development of these M&S tools as a part of the system engineering and integration of a weapon system. However, when the time comes to assess the delivered system capability, the M&S are sometimes claimed as proprietary, requiring expensive “use rights” negotiations or time-consuming independent model development.

INDUSTRY EFFORTS

One company that is taking the government customers’ desire for efficiencies and a new business model onboard is AGI. The firm has made significant changes to its products and licensing so that its technology is accessible and affordable in any situation.

Travis Langster, director, space superiority, AGI, noted, “The recent release of AGI’s software components—low-level libraries that include the fundamental validated algorithms that comprise our product line—is a breakthrough for the space and missile defense communities, allowing us to offer our capabilities in any form required.” The company’s customer can leverage AGI’s time-based geometry engine as a desktop application, build mission software using AGI’s application engine or extend its applications and Web services with AGI’s new components. “We also have flexible licensing to meet any situation: per user licensing, surge licensing that addresses unexpected needs for additional functionality, enterprise licensing for use organizationwide, and finally, program licensing that makes our software available on a ‘capabilities’ basis, eliminating the need for hard counting of ‘users,’” added Langster. He concluded, “We believe these form factors and licensing options enable a whole new level of support for integrators and users who need to use AGI products for space and missile defense.”

For its part, SAIC’s modeling and simulation expertise extends from “cradle to field” maintaining a comprehensive toolkit to support simulationbased acquisition decisions. SAIC has utilized these M&S tools to support most missile defense system engineering activities, including element design, performance evaluation, concept exploration, concepts of operations, development, asset siting, threat sensitivities; countermeasures/counter countermeasures; test and evaluation; war games and exercises; and warfighter planning, said Ernie Bubb, SAIC vice president.

These M&S tools span the spectrum from very high-fidelity engineering tools to perform component assessments, to force-onforce level simulations to examine architecture-level performance, to integration test beds designed to perform integration and test activities for a complex family of systems. “Threat simulation and signature/scene generations are examples of SAIC’s high fidelity engineering models,” said Bubb. “The SAIC-developed Strategic & Theater Attack Modeling Project simulation models ballistic missile threat trajectories for use in countermeasure analyses and to provide detailed threat input to ballistic missile defense (BMD) architecture effectiveness models.”

The Xpatch toolkit is an electromagnetic code suite for predicting and analyzing high-frequency radar signatures, using the shooting-and-bouncing ray method to predict realistic far-field and near-field radar signatures for 3-D target models. SAIC also uses a suite of models to simulate infrared seeker and overhead sensor images to support weapon system performance analysis, as well as hardware and software development.

SAIC’s WILMA-Suite is an end-to-end modeling and analysis suite for BMD concept exploration used to provide performance predictions of missile defense architectures. “WILMA can be used as a medium-fidelity end-to-end simulation for very responsive evaluation of missile defense architecture effectiveness with consideration for battle planning, communications and integration alternatives,” said Bubb. Or WILMA may be run in higher fidelity mode, used in conjunction with other in-depth element, engineering, environment, phenomenology and threat models to make detailed assessments of missile defense system performance against adversary ballistic missile attacks.

The WILMA-Suite has particular analysis capacity to explore threat and countermeasure sensitivity. The Avatar missile simulation is representative of the higher fidelity M&S tools within the WILMA-Suite. “Avatar is a one-on-one engagement simulation that includes target and interceptor dynamics and kinematics and can be run in three degrees of freedom and six degrees of freedom, depending on problem complexity and desired response time,” said Bubb.

In the air defense domain, a prominent and analytically responsive mission-level tool is SAIC’s Judy model, which is an architecture-level simulation designed specifically to investigate the potential contribution of current and emerging systems, concepts, and technologies to the prosecution of theater targets. “Judy has predominantly been used to evaluate theater architecture performance and concepts of operation in the air and cruise missile defense regime and the C4ISR regime, including attack operations,” Bubb told MSMF. Judy is a medium-fidelity, Monte Carlo, discrete-event system simulation model capable of representing entire theater mission kill chains end-to-end. All entities, threat objects and defense elements are explicitly represented and dynamically interact.

Defense architectures are modeled by defining the elements (C4I, sensor, weapons), their functional assignments, and their communications connectivity. The warfare simulation is carried out against a simulated backdrop reflecting the local environment including terrain and weather. Bubb said that Judy collects a wide variety of statistical metrics for evaluating defense effectiveness including target tracking, sensor utilization, sensor and weapon tasking, weapon expenditures, communications loading, targets killed, threat leakage and keepout distance. Judy was designed to run at a level of 50 times real time (50X), providing rapid trade-space exploration and responsive study turnaround. ♦

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