Ballistic Missile Threat Modeling
John S. McLaughlin
Characterization of the overall missile threat underpins the development of a missile defense system. The Aerospace Corporation has a long history supporting the analysis of intelligence for understanding current and projected missile threats.
Development and operation of an effective missile defense system depends on a sound understanding of the threat—i.e., reliable models of how foreign missile systems look and operate. The most effective threat models are derived through close interaction between defense system designers and intelligence community experts. This interaction improves the designer's understanding of the intelligence driving the system requirements and the intelligence producer's understanding of which aspects of the missile threat are most important. The utility of a threat model may not depend on more degrees of freedom or decimals of precision, but rather, on a solid grasp of general target characteristics and threat model uncertainty and variability.
Aerospace has a 50-year legacy of intelligence analysis that brings a unique combination of historical perspective, insight, and technical expertise to the characterization of an evolving—and now global—ballistic missile threat.
An evolving threat (or threat model) has serious implications for a developmental ballistic missile defense system. The baseline threat drives the design, and design trades early in the concept development stage can be significantly cheaper than even relatively minor design modifications later on. Thus, threat model importance is greatest when least is known. |
Development of a Threat Model
Threat modeling for ballistic missile defense has an outwardly focused component, aimed at characterizing an adversary's missile system, and an inwardly focused component, which considers how a threat model relates to specific needs of the missile defense system. The utility of a model is largely determined by the quality and relevance of the underlying intelligence. The more critical threat models tend to be projections of a future threat, where there is typically limited intelligence to support many of the details. In these cases, consistent assumptions of an adversary's objectives, technological sophistication, and available resources drive a coherent assessment over the full scope of threat characteristics. Well-founded assumptions are as essential to missile threat models as the models are to missile defense designs, particularly in the early stages of the system lifecycle. For example, an adversary that can field a weapon system with an advanced postboost vehicle and sophisticated missile defense countermeasures could presumably also launch several of these missiles at once. In that case, a missile defense system design that could handle only one launch at a time would not be a viable concept.
The long development timelines of both the missile defense system and the adversary's missile system present a challenge to missile threat modeling: sometimes, a missile defense system is intended to counter a threat that has not yet been developed, flight tested, or deployed. In that case, the most critical time to get information on the offensive missile can be in the early days of its development, when details are easiest to conceal or have not yet crystallized.
An additional complicating factor in the development of an accurate threat model is the adversary's motivation to conceal the attributes and vulnerabilities of its missiles. Threat modeling must deal with a situation where threat information is sparse or even deceptive. An intelligence analyst will try to integrate disparate elements of data into a coherent and consistent description of the missile threat, but even the best intelligence data might not provide a sufficiently complete picture. Engineering judgment and historical practice or precedent can be used to help bridge these intelligence gaps. For example, Aerospace familiarity with U.S. space launch and missile programs provides a basis for integrating the available data into a realistic threat model (see sidebar, Project West Wing: Fifty Years of Missile Threat Analysis).
The variability of a threat model further determines its usefulness. Certain characteristics of a missile might be so fundamental that they could be considered invariant—for example, the size of a missile is not likely to change significantly once in production. Other characteristics might be more easily changed, and in these cases, defense system designers must accommodate a range of possibilities, even if high-quality intelligence indicates one particular value. The uncertainty in the easily changed aspects of a threat model is defined more by the potential range of variability than by intelligence uncertainty.
Over time, more intelligence becomes available, and threat models evolve. An evolving threat (or threat model) has serious implications for developmental defense systems. The baseline threat drives the design, and design trades early in the concept development stage can be significantly cheaper than even relatively minor design modifications later on. Thus, it is critical for the early threat description to be rational and realistic.
In general, characterization of a ballistic missile threat for missile defense covers all aspects of a threat system, with a large emphasis on missile flight characteristics and signatures—how a missile behaves and looks to missile defense sensors. Simulated observations of a threat based on models of the underlying physical principles are compared with actual observations, and model parameters are adjusted until a satisfactory match is achieved. Aerospace has been actively involved in this modeling process, contributing new insights on foreign missile programs and relevant threat models to support development and operations of U.S. defense programs. Aerospace engineering and technology expertise has also enabled the development of new threat modeling methodologies that are now widely applied within the intelligence community to more accurately define missile threat characteristics (see sidebar, External Factors Influencing Threat Modeling).
Elements of a Threat Model
Threat modeling for ballistic missile defense systems encompasses a wide range of missile characteristics, gleaned through various methods by the intelligence community. These include performance capabilities, technical aspects, flight trajectories and signatures, countermeasures, basing and deployment, concepts of operation, and employment doctrine.
Performance capabilities include payload type, range, and accuracy. Range is a function of payload mass, and payload mass is strongly correlated with lethality. The ability to hit the continental United States with a weapon of mass destruction is a major concern. Assessments of a weapon system's range, payload, and accuracy should be considered in the context of an adversary's strategic and tactical objectives. For example, a nuclear payload need not be very accurate if targeted against large population centers as a strategic deterrent. Conversely, the utility of a light payload delivered accurately to even long ranges is hard to conceive as a viable missile threat.
Threat modeling for ballistic missile defense systems encompasses a wide spectrum of missile characteristics gleaned through various methods by the intelligence community. These characteristics range from detailed material properties to flight characteristics and signatures to concept of operations and employment doctrine. |
Technical aspects include missile size and weight, materials, propulsion, guidance system, and reentry-vehicle characteristics. Supporting intelligence is not always available, and therefore, threat models at this level of detail typically represent descriptions based on engineered designs constrained to the available intelligence. The desired precision of these details is driven by user requirements, and effective application of these models requires an understanding of the supporting intelligence and underlying assumptions—particularly with respect to admissible variability in the representative descriptions. For example, the assessed length and diameter of a missile might be well supported by intelligence, but whether the airframe is made of steel or aluminum may not be known.
Details about missile flight trajectories and signatures are important for defense system components designed to detect, track, and intercept ballistic missiles. Threat models describe the missile trajectory and how it appears to optical and radar sensors. The nature of the trajectory is closely coupled with guidance system design. For example, a fixed-pitch steering program results in relatively invariant trajectories that differ only in rocket engine burn time, while an energy-management scheme varies flight profiles to achieve desired ranges. In addition to steering, trajectory models depend on the number of stages, stage burn time and burn-time variability, coasts between stages, and payload mass. Optical signatures include the infrared signature of the hot exhaust plume as well as the thermal signature of missile components during unpowered flight. These signatures are influenced by the solar and atmospheric environments as well as sensor characteristics and viewing aspect. Similarly, in the absence of direct observations, radar signature models are based on detailed descriptions of missile components and viewing conditions.
A significant consideration of trajectory and signature modeling relates to a missile's ability to negate defensive measures. The missile designer assesses vulnerabilities to interception based on knowledge of the defense and develops responsive countermeasures to mitigate those vulnerabilities. Designers of both the offensive and defensive systems are strongly motivated to conceal details that reveal vulnerabilities or countermeasures, and this makes threat modeling more difficult. In the absence of intelligence, threat modelers and missile defense designers may consider expected countermeasures based on reasoned assumptions of an adversary's knowledge of the defense, access to technology, and missile constraints such as available volume, mass, and power.
Basing and deployment covers the launch mode, supporting infrastructure, and launch site characteristics. Ballistic missiles have been based at fixed sites, such as silos or towers, and on mobile platforms, such as trains or submarines. Supporting infrastructure depends on missile and payload characteristics and the basing mode; for example, handling requirements for a liquid-propellant missile produce a significantly greater logistical footprint than for a solid-propellant missile of similar range. Deployment models describe the basing locations and (for mobile systems) field deployment areas, the number of launchers, and the number of missiles. Deployment area descriptions include site characteristics, hardness, access, weather, and denial and deception measures such as the use of underground and decoy facilities. Descriptions of deployment area road and rail networks and terrain characteristics are also important to threat mobility and vulnerability assessments.
Employment doctrine and concept of operation are essential elements of a threat model that describe when and how the weapon system might be used. Employment doctrine is driven by strategic or tactical objectives and encompasses targeting, weapon selection, and the warfighting context. The concept of operation includes integration with command, control, and communications elements as well as levels of readiness, camouflage and decoys, technical support, and launch operations.
The Missile Defense Agency has captured a wide spectrum of threat characteristics in its Adversary Capabilities Document to support ballistic missile system development. Aerospace contributed chapters on booster and postboost vehicle characteristics, including specific historical examples to illustrate extremes in parameter bounds. The breadth of the Adversary Capabilities Document helps ensure ballistic missile defense designs address the full scope of the ballistic missile threat.
Application of Threat Models
The lifecycle of a missile defense system begins with a top-level threat assessment that drives a statement of need, leading to system development and operation and ending with decommissioning. System design trades assess performance, cost, and schedule for a number of design options and produce a system specification that is thought to meet requirements within acceptable resource and technology constraints. Because threat missile characteristics are major design drivers, adequate threat models are essential to the system design part of the missile defense system lifecycle. Getting the threat right in this phase is critical because of the major influence it has on downstream system performance and cost.
In the lifecycle, system design leads to system development involving detailed designs and critical technology demonstrations. More detailed threat models are needed here to support specific algorithm development and refinement. Detail does not necessarily mean threat parameter definitions to many decimal places of precision; it may be more useful to characterize the variability of a certain aspect of a threat to promote design robustness. This is a place where close coordination between missile defense system designers and intelligence community subject matter experts helps ensure viable system designs. In several instances, Aerospace has provided models and detailed reports on key stressing missile characteristics to support focused design trades and performance studies.
Threat modeling plays a role in the Ballistic Missile Defense System (BMDS) lifecycle. A top-level threat assessment determines system requirements, leading to system development, testing, and operation. Data generated by operational sensors can be fed back to the intelligence community for improved threat modeling. Because threat missile characteristics are major design drivers, adequate threat models are essential to system design. |
Threat modeling plays a lesser role during the production phase of a missile defense system; however, some systems may incorporate a priori threat information in mission software databases, and threat modeling may be required to suitably populate these databases.
Once up and running, a defense system goes through an operational test and evaluation phase where it is exercised in various scenarios involving simulated threats, dedicated test targets, or targets of opportunity. Threat modeling fidelity requirements are strongly coupled to the objectives of the test application. For example, the objectives may be simply to ensure that components of the system are interacting properly and that inputs and outputs are processed properly; in this case, high fidelity may not be critical to the satisfactory execution of the tests. On the other hand, some testing may seek to demonstrate that the system satisfies technical performance requirements, and in these cases, high threat model fidelity is essential. For example, inadequate fidelity of simulated missile launches used in performance testing could corrupt test results by skewing performance in positive or negative directions. In this case, threat model fidelity should be carefully evaluated relative to the test application to ensure the scenarios faithfully represent those aspects of the threat that might influence system performance. For the last decade, Aerospace has worked closely with operational test and evaluation agencies and missile defense threat modeling organizations to ensure scenarios have sufficient boost-phase fidelity for realistic system testing.
In the operational phase of the missile defense system lifecycle, threat modeling is aimed at optimizing system performance. This may involve ensuring that mission software databases are updated to reflect the intelligence community's latest understanding of the threat. Aerospace has worked in this capacity as part of an interagency working group chartered with managing a priori threat information in mission databases to optimize the performance of operational missile launch warning systems. Near-real-time threat information can be provided to system operators to improve readiness. In addition, operators may receive information on the current weather or defense system configuration and how that might influence the system's response to a launch. Given enough time, the system might be reconfigured to enhance performance against a specific threat—for example, by repositioning or augmenting sensors or interceptors.
Data generated by operational missile defense system sensors can be exploited for improved threat modeling by feeding that data back to the intelligence community. This information may improve the intelligence community's understanding of the threat, which then refines threat models injected into the various aspects of the system lifecycle. In one instance, Aerospace collaboration with a sensor contractor uncovered data revealing startling, and previously unknown, aspects of a foreign missile test.
Conclusion
Characterization of the missile threat underpins missile defense system development. An emphasis on early design trades and system architecture development helps to ensure future missile defense system effectiveness. The most difficult challenge lies in threat projections, which are often based more on conjecture than hard intelligence. This "crystal ball" puts the onus on threat model producers and consumers alike to explicitly consider the context and limitations of the threat assessments to promote development of sufficiently robust defense system designs. The core threat should be adequately represented, and excursions should be recognized and appropriately weighted to avoid design trades that accommodate unlikely threat characteristics at the expense of the core missile threat.
