ABSTRACT
This chapter deals with establishing the fundamental knowledge necessary to understand the elements of air and missile defense (AMD) systems engineering and the initiation of the pre-Phase A planning stage� From a technical perspective, which this book is addressing, there is more than enough material to simply lay the foundation for what the air and missile defense mission need is such that the purpose of this book can be fulfilled� There are no new discoveries presented in this chapter� There are no new revelations for the casual reader of daily newspapers, and TV news program viewers are not already exposed to what is being presented here� The references for this chapter [1-6] will provide the reader sufficient background material to explore in more detail the global expansion of missile weaponry that is no longer contained in the technologically sophisticated centers of the United States, Western Europe, and the former Soviet Union� This book does not address proliferation, which is the particular entity responsible for the spread of first-world weaponry, or treaties intended to reduce proliferation, but simply acknowledges that proliferation has happened and will likely continue to happen� Without any interest in the political interpretation of the reader, the authors acknowledge that the world owes President Ronald Reagan the credit, gratitude, and admiration for his visionary accomplishment of putting in motion the notion that it is necessary, accomplishable, and admirable to establish defenses against missile attacks�
To this end, the remaining sections of this chapter will follow an abridged outline of Figure 2�2 and present the development of the air and missile defense mission need statement and translate it into a technical programmatic plan� The program objectives are established in terms of achievable measures of effectiveness (MOEs)� A top-level set of requirements will then be developed� The remaining pieces defined in Figure 2�2 are left to the practitioner�
The AMD-specific system’s pre-Phase A engineering process is developed and evolved in this chapter� Figure 4�1 shows the proposed multifaceted process flow that incorporates the main body of accomplishments flowing down the center of the diagram and establishes disciplined activity flow to produce the preliminary design and the outline for the remainder of this book�
Recursive arrows to the right of the diagram depict that verification and validation (V&V) and risk analyses are an integral part of the design process� V&V are not left for the final stages of the program activity but are essential to the entire design and development process� Another way of looking at it is that system validation and verification are designed into the system and are not a check at the end� Risk is continuously evaluated, and the results of this analysis are incorporated into design decisions and process activity� V&V and risk analysis techniques and methods are usually specific to agencies and organizations� Techniques and methods are found in the references provided in Chapter 1� The NASA Systems Engineering
Handbook (chapter 1, reference 6) has a mature and executable set of V&V and risk processes�
The recursive arrows on the left-hand side of Figure 4�1 indicate the business processes that must occur� Again, these processes are embedded in the design process and include matters involved with funding your program(s), executing contracts and communicating milestone progress, delays, and hardships� The business activity area is where you account for identifying programmatic and organizational constraints and ensuring that they are communicated to systems engineering�
The mission need statement (MNS) arises from a multitude of occurrences� As Figure 4�1 indicates, a threat is identified through investigations and analysis� The threat is qualified and quantified in both geopolitical and technical terms� The current political and military environment will dictate policy impacting solutions and approaches to accomplishing the mission� The expectations and associated constraints combine with the need to negate the threat to form an MNS�
From this point, the process is product oriented� The products will include a top-level requirements (TLR) document, the concept of operations (CONOPS), system requirements document (SRD), and the architecture design proposal (ADP)� These products will be produced according to the schedule of the phases defined in Chapter 1, along with the other products defined for each phase�
Top-level requirements are part of the pre-Phase A planning and will flow from the MNS� As part of the TLR development process, the measures of effectiveness are developed to initiate a functional requirements analysis that will lead to the SRD�
An MNS might read as follows: There exists a requirement for free and peaceful nations to render offensive missile weapons useless for the purposes of deterrence, to enhance power projection ability, and to produce military advantage when force is necessary� Thus, the MNS establishes a need to construct an air and missile defense system� It would continue that the AMD system(s) must be cost-effective, reliable, and readily available� In addition, this system or set of systems must be upgradeable and responsive in a timely manner�
It is necessary to digress to truly understand the meaning of cost-effective� When discussing defensive systems, cost-effective has often been mischaracterized as the cost ratio of expended engagement asset to offensive missile asset� This is simply not the metric that defines the trade space accurately� This comparison epitomizes the old saying-This is like comparing apples to oranges� The accurate cost-effectiveness trade space in engineering terms is
the cost ratio of expended engagement asset to the protected asset� This is an important distinction� The costs for the user nation to build, deploy, and expend the inbound missile are not a relevant factor� There is no correlation between how much it costs one nation to build a particular missile in terms of both real dollars and with respect to their gross domestic product and another nation to build and deploy the exact same missile and more importantly the AMD system necessary to defeat it� There is, however, a technical, military, and monetary correlation between how much it costs a particular nation to build an asset (ship, port, power plant, etc�) that needs to be protected and the cost for an AMD system to protect it� For example, it can be said that it is too costly to defend a specific asset, but not that it is too costly to shoot down a threatening missile� This is another important distinction that needs to be made� Take a specific example of ship air defense� If each air defense missile (ADM) expended costs $1M to achieve a theoretical probability of kill (Pk ) of 0�99 in self-defense of a $2 billion ship against a hypothetical cruise missile worth $500K to the belligerent nation, three ADMs must be expended� The question is “Does the ship fire only one missile to maintain a reasonable cost ratio?” For this example, the cost ratio is not 2:1 in favor of the defender; it is 4,000,000:1 in favor of the offense� Of course, this is not the computation that needs to be made� The actual approach to determining cost-effectiveness would be to calculate the cost of three expended ADMs to the cost (or more importantly value) of the protected asset, which is a 0�00015 ratio showing conclusively a very cost-effective system� Of course, this does not even put a value on the lives at stake or the consequences of the outcome� These calculations are left for military analysts and are not within the scope of an engineering treatment of the problem� What is important here is to immediately dismiss cost arguments without correlated elements� Defense will surely cost more than offense; however it is the cost and value of the defended asset that is correlated with the cost of its defense�
The term measures of effectiveness implies achieving a specific set of results� Returning to the example in Chapter 2, it is stated that the first part of this process should define the metrics associated with accomplishing the MNS or program charter and that the metrics may also be called the cornerstones of your system� The cornerstones need to define What, When, Where, and How to achieve the mission� The MNS defines Why the mission is to be achieved� The Aegis cornerstones developed by the U�S� Navy [7] are an example of these measures� To properly achieve the desired war-fighting capability in the defense against missile attack, one must examine the intelligence,
surveillance, and reconnaissance (ISR); detection and tracking; weapons control; and engagement processes in the context of the entire defense system mission areas defined earlier� The When, How, and Where are listed as follows:
• Reaction time-How • Firepower-How • Defense penetration technique resistance-When • Environmental resistance-When • Continuous availability-When • Contiguous coverage in theater-Where
Each of these metrics is defined in detail within the context of the overall objectives in what follows�
4.4.1 Reaction Time
Reaction time refers to executing a specific weapon system defense strategy successfully by ensuring that all operations occur within the available engagement timeline� Depending on the mission, as discussed earlier, the engagement timeline requirements will change and the flow down of requirements on the entire system will need to be reevaluated� It is therefore important to lay down the various events associated with the engagement problem� The specific event timing will change depending on the specifics of the engagement problem� For example, a short-range ballistic missile (SRBM) will achieve burnout, apogee, and impact sooner than a medium-range ballistic missile (MRBM)� This, in turn, will require detection and engagement activities to occur sooner for engaging the SRBM� Therefore, first, recognize that there is a target timeline and then develop a defensive weapons system that supports target negation within the engagement timeline� The engagement solution involves careful consideration of both�
The target timeline can be broken down into two major target sets: ballistic targets (targets whose flight path extends outside of the sensible atmosphere and returns through the atmosphere to engage its targets) and air targets (referring to targets that fly strictly within the sensible atmosphere)� First, the ballistic missile defense event timeline is examined, as shown in Figure 4�2�
As the title suggests, Figure 4�2 illustrates a ship-based ballistic missile defense (BMD) engagement timeline but can be generically applied to BMD from any platform� The target has a boost, midcourse, and terminal phase of flight� Within these phases, and not depicted in the graphic, are other possible important events that need to be timed depending on the target� For example, multiple-stage missiles will have staging/separation
events� Most modern ballistic missiles will have attitude control, thrust termination, and other events that may be important to missile defense� The event timing and the details of the events are important to the engagement timeline and must be examined in detail� Separations, terminations, other types of events, and lethal object discrimination requirements can and will contribute to the complexity of the engagement�
The intersection of the target timeline with the defensive system timeline is dependent on the engagement strategy being employed� Figure 4�2 shows, in general, the events that need to be accomplished to consummate a ballistic missile engagement� More detailed engagement events including the weapons fire-control solution, missile discrimination, and other important processes are not discretely depicted� However, Figure 4�2 demonstrates the complex nature of the engagement and that the defensive system must capture the target as early as possible, manage resources efficiently, and engage as early as possible to prosecute an engagement� In this example, it is shown that a detection fence is built with the intent that if the target flies through the fence, it will be detected� This can and most likely will be accomplished with the aid of inorganic assets as part of the ISR process not shown in this diagram� The timeline between detection and missile away will be referred to as the defense system time constant� It is within this period that a number of system functions must take place� The functions will likely have to include computing a fire-control solution (intercept capability) and challenging the validity of the potential target, normally referred to as identification friend or foe (IFF)� It is not possible to completely generalize all AMD system architectures and therefore leaves open the possibility that other critical functions may be required that will utilize time�
4.4.1.1 Engagement Timeline Definitions
The following formal definitions apply for the purposes of this book� System reaction time-sometimes referred to as the defense system time constant shown in Chapter 5-is the time from initial target detection to first missile motion� System reaction time consists of three major components: (1) target detection and transfer of target location from sensor to shooter, (2) combat ID, and (3) missile launcher response time� These times can be stochastic in nature due to performance variations associated with the equipment and operators (for man-in-the-loop systems)� The time required to transfer target information to the shooter is critical in systems that require lock-on before launch (LOBL)� These systems are typically fire-and-forget systems, which no longer require target state data from the sensor that initially detected the target once the missile is launched� These types of missile systems can have their own seeker-active RF seeker, passive IR, or dual-mode systems� Usually, dual-mode systems are both active or passive RF and passive IR seekers� Some missile launchers use a laser to guide the missile to the target�
These systems must either have the laser slaved to the sensor data or acquire the target on their own to maintain laser guide on the target� Both passive IR seeker and laser-guided systems may be severely degraded when operating in fog or rain environments�
The second function that contributes to the overall system reaction time is combat ID� This can be performed at the unit level or in a centralized location� Unit-level combat ID is usually automated and based on both radar data and transponder interrogation to provide identification friend or foe (IFF) data from the combat system� A target at a high inbound speed, which does not respond to IFF interrogations, would normally be classified as hostile� Unit-level combat ID usually takes less time than centralized combat ID� The centralized combat ID typically requires the sensor target data to be transferred via a communication link to the centralized command center� The target information will be reviewed and may be correlated with data from other sensors in order to determine if the contact is threatening� Once the decision is made that the contact is hostile, contact information needs to be relayed back to the firing unit over a command link in order to initiate the engagement process�
Missile initialization: Once a specific missile is chosen for engagement, the third contributor to the engagement timeline includes enabling the missile to be launched and performing in-flight functions� Specifically, pyrotechnic squibs are usually used to initiate battery operation, begin the warhead arming sequence, as well as initiate other functions� Inertial platform initiation may include spinning up gyroscopes unless nonmechanical systems are used such as ring laser gyroscopes� The launcher system also has a response time, which is the time between pushing the launch button and the first missile motion� The launcher response time can include lock-on time for LOBL systems and launcher slew time for systems that need to slew in azimuth and/or elevation� For missiles that are lock-on after launch (LOAL) or are midcourse radar guided via missile uplink commands, launcher response times are generally shorter� LOAL systems with vertical launch cells are preferred and require a minimum amount of launcher preparation time�
Doctrine: Another dimension of the battlespace timeline is the doctrine employed� Doctrine refers to the preplanned approach for engaging targets that can be tailored to mission-specific needs� The doctrine will include the approach to the allocation of resources� More specifically, radar resource management strategy is included in the doctrine� This includes rules and conditions for rolling back radar resources in order to ensure that the highpriority engagement functions always have enough resources to support successful engagements� The weapon employment strategy includes planning the number and type of weapon or weapon variant(s) to expend in a specific engagement opportunity� This also includes consideration of the weapon magazine load out and what weapons remain in the magazine at any given time�
Salvo time: The time interval between successive launches in a specific engagement opportunity is referred to as salvo time� Firing doctrines that include multiple salvos, such as Shoot-Shoot (SS) and Shoot-Shoot-Shoot (SSS), are used to increase overall kill probability; however, this is at the expense of depleting the missiles in the magazine more rapidly� Salvo time generally includes launcher timing limitations and sufficient timing between missile shots to avoid missile fratricide� Missile fratricide can occur when the second shot in the salvo guides to the first missile in the salvo instead of the intended target� Scheduling sufficient salvo time between successive shots is one technique used to prevent fratricide�
In conclusion, all of these times and their management are requirement drivers that must be considered in developing a system-level engagement solution� The requirements’ flow down process will capture these drivers within the appropriate elements to ensure a balanced systems approach�
4.4.2 Firepower
Firepower refers to having the ability to place ordnance on the target when and where they are needed with sufficient numbers to ensure success� There are two firepower requirements that need to be addressed� The first component is being able to reach the target with a sufficient amount of range at intercept between the inbound target and the defended asset that its survivability is ensured� The second component is a homing requirement� The ordnance must also be able to achieve a successful miss distance to achieve a kill or achieve the desired single-shot probability of kill (Pssk)� A flow-back requirement results from the homing requirement� It is also necessary to reach the target with a sufficient number of missiles as possible to achieve the necessary Pssk to ensure the destruction of the target, which will guarantee defended asset survivability� Not only must a sufficient number of ordnance rounds reach their target, but also the right ordnance must reach the target� Not all missiles are created equal� To ensure homing success, choosing the missile to reach and the design to handle any peculiarities of the target must be ensured� The combination of reaching the target at sufficient range with the correct and sufficient number of ordnance and achieving homing success should establish firepower requirements�
The firepower requirement then contributes to defining doctrine requirements mentioned in the previous section� Firepower is heavily dependent on the amount of timeline available for the engagement(s)� Any engagement may and probably will require multiple weapons (ordnance) to be placed on the target to achieve an acceptable success criterion� Each weapon expended will require revisiting the battlespace timeline at least in part� This sequence of expending weapons is also part of the doctrine� This part of the doctrine is referred to as the firepower doctrine� A firepower doctrine requires establishing a defense strategy for successfully negating all incoming targets�
Depending on the mission, other design decisions, and the tactical situation, the firepower doctrine requirements may change and the flow down of requirements on the entire system will then need to be reevaluated�
Five specific firepower doctrine strategies for this book are defined: Shoot; Shoot-Shoot, Shoot-Shoot-Shoot, Shoot-Look-Shoot, and Shoot-ShootLook-Shoot� Each term, shoot, refers to the launching or expending of a weapon (ordnance) to intercept the incoming target� Each time a weapon is expended, it takes battlespace time� Each term, look, refers to a kill evaluation and the cycling to a new and independent shot�
A specific doctrine is chosen to produce a kill while expending a minimum amount of resources and maximizing the amount of resources available to begin a new and independent engagement� The doctrine should also include the policy used to select the correct engagement option and firing doctrine to employ� Firepower doctrine requirements are developed based on the Pssk�
The firing doctrine then establishes essential timeline requirements driving the weapon system time constant requirements� And conversely, the firing doctrine will be driven by the achievable weapon system time constant� This iteration will eventually settle when achievable combinations of engagement solutions, time constants, and firing doctrines are found that will result in the required Pssk for the defined target set overall Pk requirement� This solution set will define firepower�
The required firepower will likely only be accomplished with a layered or tiered approach to AMD� Considering the possible incoming target design variations, including cruise and ballistic missiles and aircraft (manned and unmanned), covering the extent of the atmosphere and beyond, it is unreasonable to expect that deploying one weapon system will handle all possible engagements� Missile speeds ranging from low to high subsonic and supersonic through hypersonic (Mach 5 and above) all need to be engaged thus placing different and competing requirements on the AMD system� The trade space for achieving the firepower objectives is complicated and will involve evaluating different weapon concepts and firepower doctrines� These trades are beyond the scope of this book�
4.4.3 Defense Penetration Technique Resistance
Defense penetration techniques (DPTs) are defined as the design measures employed by the potentially hostile adversary in their offensive air and missile systems that are intended to defeat the defensive systems defending those assets desired to be destroyed� As discussed earlier, cruise or ballistic missile defense is attempted by one of three means� Either a hard or soft kill solution is employed or in combination� The adversarial offensive missile design team can break up the problem into four generic flight phases to design counters necessary to defeat the entire system� This set will be
referred to here as the time-phased defense penetration design options� These options are designated as follows:
1� Countersurveillance and search phase 2� Counterdetection and track phase 3� Counterengagement and missile phase 4� Counterpoint defense phase
It is based on the adversary design approach that resistance to these measures and techniques is found� Performance requirements cannot be established until each of these time-phased defense penetration options (DPOs) are evaluated and a set of them is selected to be addressed in the AMD system design�
Each of the four time-phased defense penetration design options will be described in detail in this section� In adversary studies, the AMD system and a defense penetration design approach are decided upon� The options will consider the strategy necessary to defeat the kill chain by most likely spreading out the challenges across each phase� Speed is the defense penetration fulcrum providing the primary leverage feature dictated by physics for all penetration phases offering advantage to the offensive missile designer� All other defense penetration design measures and techniques become more effective the faster the offensive missile travels� To compress the engagement timeline (collapse the battlespace), the adversary may employ high speed and low radar cross section, high speed and low altitude, or any of a large number of combinations of defense penetration techniques, where speed notably reduces the signature reduction and altitude lowering requirements for the offense [8-15]�
4.4.3.1 Countersurveillance and Search Phase
The first step in the kill chain usually begins with surveillance and search� Within this phase, potentially hostile systems or vehicles are determined to exist or not� When detected, an assessment of their potential hostile intentions or activity is made through the battle management process� If determined to be of a hostile nature, a battle management plan is invoked and appropriate action is taken to transition and designate it as a target and to begin an engagement� This engagement solution will provide the essential time needed for executing the remaining pieces of the kill chain resulting in a successful engagement� As with all the phases, time is the most critical resource to have or deny depending on which side of the problem you are on� Surveillance and search can be accomplished from space-, air-, sea-, subsurface-, and/or ground-borne assets� These assets can be either organic or inorganic to the actual shooter or defense system�
The objective of the adversarial missile design team is to deny, degrade, or confuse surveillance systems to buy time� It is only reasonable to assume that eventually, the target missile will be found and an engagement process will begin� Countersurveillance and search design options include organic, nonorganic, and networked sensor assets� These sensor assets may be from a single system (organic), external systems (inorganic), or a diverse highly interconnected set of platforms (network)� Design options may include stealthy features, concealment CONOPS, deceptive trajectories, and various forms of electronic countermeasures� The mission during this phase of the attack is typically a cat-and-mouse game where each side attempts to understand the likely CONOPS and capabilities of the other� The AMD system requirements include developing methods and techniques to defeat countersurveillance and search techniques�
4.4.3.2 Counterdetection and Track Phase
The AMD system that is protecting a given air space from missile attack will ultimately need to detect and transition to track the target within a fire-control system� The fire-control system and sensor do not necessarily have to be co-located but are part of a system used to conduct the engagement� The search and track sensor(s) may be, and usually are, part of the same system and provide the transition between the first and second time-phased defense penetration design option phases� The distinguishing part of this phase is that it starts after the missile is on its way and heading for a particular target and the search sensor has detected the target� The detection may occur from autonomous search or as a result of a cue from external (inorganic) surveillance systems�
The objective of the target design during this phase is to reduce reaction time by employing various design options aimed at the AMD system� This may include trajectory and altitude variations, jamming, signature reduction, masking schemes, and speed [8-14]� These time-phased defense penetration design options (which will be referred to as DPO from here on) will be employed in a cost-effective manner, which is most advantageous to penetrating a particular AMD system� This means that the DPO design and employment strategy will be dependent on the AMD system it must defeat and penetrate� The DPOs will be employed singularly and in combinations as the task dictates� It is important to remember that the target design need only reduce reaction time and not deny detection to be successful in this phase� The question the offensive missile designer needs to ask and answer is how much time reduction is enough� The answer to this question depends on the counter-DPO capabilities of the defensive AMD system� The objective of the AMD system design is to limit the effectiveness of target DPO through performance trade-offs that will result in robust counter-DPO design requirements�
The longer the time an offensive missile is successful in denying detection and track, the simpler and less difficult it is to defeat the engagement and
missile phase� The AMD requirements challenge is to develop design measures that effectively resist DPO aimed at reducing reaction time� Techniques that can increase system reaction time include the use of elevated sensors to extend the radar horizon and increased radar sensitivity to mitigate the effects of target RCS reduction� Techniques that can maintain performance in reduced system reaction time scenarios are faster missiles to reduce the flyout time and missiles/ordnance with capability to engage at very short ranges� These techniques and methods available to the AMD system designer must be itemized, prioritized, and characterized before achievable requirements can be developed�
4.4.3.3 Counterengagement and Missile Phase
Once the missile target is detected and begins to be tracked, an AMD weapon system fire-control or engagement solution is computed� The time it takes to produce a solution and conduct all of the necessary checks and schedule the other necessary events needed to support the engagement and produce first missile motion is named the weapon system time constant (TWCS), as shown in Figure 4�2� Simply said, this is the time it takes from detection to missile away� It is within this process that the system computes the likely point in time and space where the engagement is likely to end� This spatial location is called the predicted intercept point (PIP), and the time is called the estimated time to go (TGO)� The accuracy of these two parameters is dependent on the precision, accuracy (quality), and resolution of the sensor track information and the computational approach employed to resolve PIP and TGO from the measured data� Subsequently, the accuracy of PIP and TGO will determine the accuracy of the missile midcourse guidance commands used to guide the missile during this phase of flight� A perfect midcourse guidance law will only guarantee that the missile will go where it is being sent� However, it will not be sent to the correct location if all of the supporting data and computations are also not perfect� Imperfect guidance laws, noisy sensor measurements of the target state, and computational inaccuracies contribute to the radar-to-missile handover error� Handover error, simply stated, is defined by the fact that the missile is not placed in space and time at the end of midcourse guidance that would require the missile no additional effort to intercept the target in the remaining engagement time� Homing time is the portion of the engagement where an onboard missile sensor detects and tracks the target and completes the engagement by providing measured data to an onboard guidance computer where acceleration commands are produced and executed through a flight control system� It is during the terminal homing that the handover errors are to be removed� If not, the missile will miss the target and the offensive missile will ingress to the next phase of the engagement�
The objective of the target design team is to explicitly defeat this part of the system and kill chain� To accomplish this, the target design characteristics
must be able to induce unacceptable missile miss distances so as not to be effectively negated or to deny computation of an acceptable fire-control solution� The ways to produce such miss distances are numerous� The methods can start by attacking the quality of the track through deceptive countermeasures or by countering the missile in flight through maneuvers or jamming techniques [9-15]� Fire control and doctrine denial can be accomplished by simply flying so fast through this phase that a successful firecontrol or doctrine solution is unachievable�
The counterengagement and missile phase may be the weakest or most vulnerable link in the engagement chain and may be where most of the defense penetration design options will be employed [9-15]� It is therefore incumbent on the AMD designer set to focus on requirements that minimize system susceptibility to these methods and techniques� Fortunately, physics limits both sides of this problem equally and solutions can be found for the AMD system� Again, the techniques and methods available to the offensive designer must be itemized, prioritized, and characterized before achievable AMD requirements can be developed�
4.4.3.4 Counterpoint Defense Phase
Short-range systems will be employed by the defended asset to add a layer of self-defense for leakers� Leakers are targets that have successfully penetrated the outer layers of the defensive system (the engagement and missile phase of the kill chain)� Short-range self-defense systems can include missiles, guns, and electronic countermeasure techniques [9]� Most of the weapons employed here are simply fire-and-forget systems that do not rely heavily on sophisticated fire-control systems for in-flight guidance�
The objective of the offensive missile design team is to explicitly defeat this part of the system and kill chain as in the previous phase� Again, the way to accomplish this is to induce unacceptable miss distances so as to not incur damage or destruction� The ways to produce such miss distances or render jamming countermeasure systems ineffective are numerous� Trajectory variations and maneuvers are proven means to significantly reduce Pssk and penetrate the last layer of defense [13-15]� Utilizing dual-mode guidance systems to avoid homing in-bands that are being jammed has also been shown to be effective [11-13]� As in the countermissile phase, the AMD requirement here is to focus on minimizing system susceptibility to these methods and techniques� The techniques and methods available to the offensive designer must be itemized, prioritized, and characterized before achievable requirements can be developed�
4.4.4 Environmental Resistance
Environmental resistance establishes the requirement to maintain AMD performance in adverse environments� Originally, this was to include
jamming environments� It is believed that all of the methods and techniques employed by the offensive system(s) to penetrate defensive systems are more effectively captured by measures that resist the target defense penetration techniques (DPTs), which are discussed in the next section� This allows the systems engineer to develop design requirements that focus on operating and fighting in degrading weather and propagation environments against a single measure of effectiveness (MOE)� The environment itself as it affects electromagnetic (EM) and electro-optical (EO) propagation must be met with performance requirements that ensure a graceful degradation of the AMD system engagement performance� In fact, these will evolve as interface requirements for the entire AMD system� Some of the sources for environmental degradation include atmospheric absorption including rain attenuation of the EM and EO spectrums; rain-induced backscatter clutter; sea clutter return; atmospheric refractivity including anomalous propagation (ducting); atmospheric property variations including density, pressure, and temperatures; low-altitude tracking errors including multipath and lobe cutting; background radiation (most prevalent in the EO/IR environment) interferences; and target signature anomalies such as glint and scintillation�
The AMD system requirements must be developed to accommodate reduced performance realities as these environmental effects are analyzed� The good news is that both sides of the fight will need to operate in the same environment and will suffer degraded performance� It is the design that has best accounted for environmental variations that will have the advantage�
4.4.5 Continuous Availability
Continuous availability refers to the elements or components of the AMD system solution that must be operable at all times during deployment� Operable has to be defined as operating with the expected probability of achieving design objectives� Otherwise, the remaining requirement definitions that hinge on achieving a specified Pssk will not be achievable� This book will not dwell or elaborate on this MOE or the requirements it produces as it is not within the desired scope of this book� This falls on the art and engineering of manufacturing and reliability� It is important to this MOE that redundancy is built into the system at critical nodes so as not to field a system with single points of failure or an Achilles heel�
4.4.6 Contiguous Coverage
A reference frame has to be created before it is possible to establish a contiguous coverage MOE� The reference frame can take on many definitions but must include seamlessly enveloping the defended asset with protection from all azimuths out to a specified range and altitude� This is likely accomplished with tiered protection having overlapping engagement area responsibilities� In the surface warfare example, a battle group must be configured to provide
protection of the carriers, LHAs, and possibly civilian assets without gaps in coverage� This can be accomplished with multiple air defense-capable ships working under a specific CONOPS for the situation� These fighting ships may have different capabilities relative to various target sets and range-azimuth sectors� The ships must therefore protect themselves in order to be available to contribute to the AMD system capability� Thus, the AMD system must be required to operate independently as well as part of a larger, more encompassing capability� Attaining and maintaining the contiguous coverage MOE will levy requirements on the AMD system that the elements be interoperable, therefore creating an additional set of interface requirements [9]�
The proper beginning of the top-level requirements is to state or restate the mission need statement� This would not be done here� The TLR must first address the fundamental mission objective� The mission objectives develop the technical facts associated with accomplishing the objective of the MNS and with the MOEs used as constraints and assumptions�
The next task is to clearly define the problem� The problem is the target(s)� Target set engineering characterizations that include flight dynamic envelope and sensor correlated signature details are the essential elements necessary to establish defensive requirements� Moreover, it is necessary to characterize target physical attributes that will affect lethality requirements; employment options that may include coordinated attacks, reattacks, and waypoint usage and varying speed and altitude regimes that may affect timeline requirements; and the active use of deceptive and interference techniques such as electronic countermeasures (ECMs) [11-13]� These characterizations will then need to be mapped into the MOEs�
Performance and interoperability requirements will be formed by identifying the regions of the world where the AMD is to effectively operate, identifying the need for interoperating with different forces and assets, and identifying specific environmental conditions� The TLR includes operational engagement altitude-range regimes, probability of asset survivability requirements, single-shot probability of kill (Pssk) requirements for defensive missile solutions, and time-on-target probability of kill requirements for energy weapons and guns� Raid densities will be incorporated with all Pssk requirements�
The functional performance and interface requirements will evolve from a mapping of these considerations and the target characterizations into the MOEs� The TLR document product will then be used to flow down to the concept of operation (CONOPS) and the development of the system requirements document (SRD)�
