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As currently prorated for the FY02 budget, the Department of the Navy's two FNC programs that are directed toward missile defense have 6.2 and 6.3 funding levels that total $70 million to $80 million per year. The objective of FNC programs is to focus Department of the Navy 6.2 and 6.3 funding to obtain a better return on investment in terms of fielded capabilities. Thus, projects are funded based on requirements, capability gaps, technology feasibility, transition availability, and program manager commitment. There is much to be said for this approach, but a shortcoming is that it tends to focus resources on evolutionary as opposed to revolutionary approaches. The latter are likely to be viewed as technologically risky, and it is intrinsically difficult to identify concrete transition paths for such approaches.

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Although clutter cancellation is the main issue in the development of AMTI radars, radiated system power and sensitivity are not irrelevant. Cruise missiles can and do have very low RCS values, particularly when viewed nose-on. Detection of low-RCS targets requires great system sensitivity. Unfortunately, the lower the RCS of the target to be detected, the lower the detection threshold must be set. Very low threshold levels result in the detection of many spurious targets (e.g., noise spikes, birds, and bugs). Robust discrimination algorithms must be developed that will reject these spurious detections efficiently and there-by minimize the computer resources needed to reject false targets. The development of false target rejection algorithms in order to permit operations at the low thresholds needed to counter low-RCS cruise missiles is certainly an appropriate area of activity for ONR's missile defense FNC.

Other possibilities for the detection of very low RCS objects include the use of multistatic radar configurations. Stealth technology generally reduces the amount of energy that is reflected back to a conventional monostatic radar. Energy reflected from a low-RCS target in other directions can be high, allowing the detection of strong glints by a properly positioned receiver that is not colocated with the radar transmitter. Multiple geometrically dispersed receivers must be available to increase the probability that at least one receiver will detect a strong glint, in effect increasing the target's RCS. The difficulties associated with multistatic operation are formidable. Some of these difficulties may be overcome by the application of current technology. Others will require an extensive R&D program. The committee is optimistic that the heretofore limiting difficulties associated with multistatic operation can be conquered and believes that R&D efforts in this area would be an appropriate component of ONR's missile defense FNC effort.

Another interesting possibility that might be included in ONR's missile defense FNC effort would be the exploitation, by means of image-processing techniques, of the target's obscuration of the background as revealed through its motion—that is, by imaging the target's moving RF shadow. This obscuration is determined by the physical extent of the object, not its apparent RCS.

After having sorted out the cruise missile from low-threshold-induced competing “targets,” the cruise missile defense system must be capable of robust combat identification as part of the discrimination process, for the targeted object could be a friendly cruise missile or aircraft.

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ciency and are supporting the development of technologies that will enable the building of such weapons.

For cruise missile interceptors, target handover prior to terminal engagement is easier than target handover in ballistic missile defense. Typically, the threat is a single object not supported by external penetration aids. Under this condition, semiactive handover and terminal guidance, coupled with an active RF fuze, are adequate. This is the approach used by the Navy self- and area-defense systems today. In the OCMD situation, terrain masking and the effects Earth's curvature preclude the use of surface-based semiactive guidance in most cases. The committee believes that the ONR missile defense FNC should focus on the development of new techniques that will make surface-based semiactive guidance unnecessary.

The development of weapons to support ASCMD was discussed in Chapter 3. R&D for extending the capabilities of ASMD weapons is not a component of ONR's missile defense FNC. However, under ONR's reactive warhead program, a reactive fragmentation warhead is being developed for transition to a number of possible ASCMD and OCMD interceptors.

Under associated programs, R&D for the development of improved electronic warfare techniques is being pursued. Based on briefings provided to it, the committee perceives that the Navy is continuing its impressive program of finding novel extensions for traditional EW techniques. This effort appears to be well funded and is apparently resulting in the near-term deployment of new and highly effective EW capabilities.

At the time of this study, the Navy did not have a program of record for laser or directed-energy weapons. Although it worked intensively for about 30 years on the development of such weapons, no system achieved operational status.

As discussed in Section 4.3, on Air Force R&D programs for missile defense, advances in the technology for the chemical oxygen-iodine laser (COIL) and free electron laser (FEL) show some promise. However, given the present status of these technologies and the lack of a Navy program of record to support them, the committee believes it is unlikely that any laser or directed-energy weapons will achieve IOC on Navy platforms before 2015 or 2020.

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In consideration of the technology needs for missile defense BMC3, the committee finds it useful to distinguish between the BMC3 algorithms per se and the communications links and networks, processors, and software required to implement these algorithms as a distributed information processing system. The requirements for the former are relatively unique to missile defense, while the requirements for the latter strongly overlap those for commercial information processing systems.

Achieving a high-probability kill of a TBM is a difficult problem, so lethality is a key concern for BMD. BMD systems have traditionally been structured in many layers to achieve a cumulative probability of kill exceeding that of any individual layer. The BMDO TMD family of systems has been structured in this way, with the THAAD system and the NTW system providing overlays for the PAC-3 and the NAD system. The Air Force's airborne laser (ABL) could provide a boost-phase layer for shorter range threats.

Exploiting the capabilities of multiple defensive layers in an expeditionary environment requires algorithms for coordinated, distributed weapon-target assignment. Although there are significant CONOPS issues, the development of an appropriate technology base could clarify the trade-offs between coordinated and completely decentralized engagement strategies.

For BMD, discrimination is a key concern,⁴ and much effort has been devoted to the development of discrimination algorithms for both radar and optical sensors. These algorithms typically extract features from single-sensor data and partition feature space into regions characteristic of reentry vehicles, decoys, and other objects. Extensive training data are needed to select appropriate features and to define these partitions.

The major TBMD systems currently under development have both radar and optical sensors, and the potential benefits of combining the data they collect on various features of the threat objects is becoming increasingly evident. X-band radars being developed allow for the precision measurement of microdynamic features of threat objects.⁵ The passive IR sensors being developed for performing onboard interceptor functions are naturally adept at measuring the thermal characteristics of threat objects. In addition, there is a large class of features, such as macrodynamic body motions, that both sensors can measure. The potential for significant improvements in discrimination capability lies in the effective fusion of these feature vectors.

4 Although conceptually a key element of the BMC3 system, discrimination is often associated with sensor and/or interceptor technology. The committee discusses discrimination in this section, recognizing that discrimination algorithms may be physically hosted on a sensor platform or an interceptor.

5 Microdynamic features of threat objects refer to spin rates or any other irregular motions that provide a unique signature that allows a RV to be discriminated from decoys and debris.

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The limited amount of research in progress on fusing electro-optical and radio frequency sensors can use X-band radar measurements of a target's wobble or nutation in combination with optical measurements of radiant intensity to discriminate the target from replica decoys. The combination of passive optics and LIDAR is also being looked at for similar dual-sensor discrimination modes. There is also extensive investigation of using dual-phenomenology observations to mitigate the effects of various countermeasures; an example is the use of optical sensors to compensate for radar degradation caused by jammers and chaff.

One area where dual phenomenology and electro-optical/RF fusion cannot be implemented in the near term—even though they are clearly needed—is precommitment discrimination (before launch of an interceptor). Precommitment discrimination is needed to allocate and designate interceptors efficiently, but it will not be available until the space-based infrared system-low (SBIRS-low) is deployed.

Unfortunately, with the proliferation of ballistic missile technology, the likelihood of collecting the data needed to train the current generation of BMD discrimination algorithms is diminishing significantly. What is needed is a new generation of discrimination algorithms that reason based on an understanding of sensor and ballistic missile phenomenology. Unlike the current generation of algorithms, such algorithms would be able to cope with new objects and deployment mechanisms for which they have not been explicitly trained. Humans (e.g., missile test analysts) are able to operate in this fashion, but a huge research effort would be required to develop the algorithm technology that would allow discrimination to be automated.

Tracking and identifying cruise missiles in an overland environment with clutter and terrain masking has always been a difficult problem. With the proliferation of signature reduction technology, cruise missiles can defeat current systems. Improved sensor technology is needed to provide a low-cost, distributed sensor network, including bistatic radars and other novel sensing means to obtain track and identification data. Tracking and classification/identification algorithms are needed to exploit data from the sensors. These algorithms must fuse data from multiple sensors, incorporating a knowledge of the terrain and hypothesized missile objectives to extrapolate through coverage gaps. Sensor resource management algorithms are needed to ensure the operation of the sensor network as an integrated sensing system. Sensors must be positioned and tasked to provide assured detection of new threats while supporting the engagement of already detected threats.

Assigning weapons to targets in such an environment has complexities beyond those of the already-difficult BMD problem. Since cruise missiles fly in the same altitude regime as aircraft, UAVs, and certain friendly weapons, real-time, dynamic airspace deconfliction is necessary. Owing to terrain obscuration, it may not be possible to assure the continuous, fire-control-quality track of cruise missiles everywhere, so that engagement areas will have to be selected where sensors

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can support interceptor requirements. With concepts such as the air-directed surface-to-air missile (ADSAM), the platform providing interceptor support may not be the same platform that is launching the interceptor. As a result, there is a need for distributed algorithms to optimally coordinate weapon, sensor, and communications resources to defeat a low-signature cruise missile threat.

Algorithms for missile defense BMC3 are implemented in software on processors tied together by communications links. The software, processing, and communications technologies can heavily leverage commercial technology.

Software issues for missile defense BMC3 include real-time, secure, large-scale, adaptive, distributed processing. While these are areas of intense commercial interest, there are no completely satisfactory solutions available, as evidenced by the difficulties being experienced in current software-intensive DOD programs despite their extensive use of commercial off-the-shelf (COTS) software. Technology is needed to permit the integration of heterogeneous, independently evolving software components. Rigid interface formats and database schemas must be avoided in favor of technologies that permit interface and schema extension and evolution without modifying components that do not use the new data elements that are added. Distributed control mechanisms are needed to quickly reconfigure and execute software components in response to changing environmental conditions.

Commercial processing technology is directly applicable to missile defense BMC3 processing requirements. Where necessary, radiation-hardened versions of commercial systems can be employed. Thus, the development of special-purpose data processors for missile defense BMC3 is unnecessary in general.

As is described in Appendix C, commercial wireless communications technology is an area of great technological ferment. Commercial technology is available in the form of wide-bandwidth radio links and quality-of-service-enabled Internet equipment that more than satisfies military requirements for latency, message loss, bandwidth, and information assurance. Thus, the communications requirements for missile defense BMC3 could be best met by adapting commercial wireless networking technology and equipment (for example, by increasing its jam resistance).

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The importance of discrimination algorithms in TMD and distributed tracking and of resource allocation algorithms in CMD is reiterated.

A concern for both TMD and CMD is the lack of a systems context and an evaluation test bed for BMC3 technologies, such as were developed for national missile defense BMC3 in the early to mid-1990s. For example, the experiment version-88 (EV-88) prototype BMC3 system and associated test bed developed by the Army in Huntsville, Alabama, and the space-based experimental version (SBEV) developed by the Air Force Electronic Systems Center. These test beds provided a means of integrating technology developed by multiple contractors, evaluating the contemporaneous COTS software technologies, and demonstrating the technology to users in a system context. They provided the basis for and led directly into the ongoing development of the national missile defense (NMD) BMC3 system.

The committee believes that a missile defense BMC3 test bed should be established.⁶ This test bed would allow multiple participant organizations to demonstrate their technologies in a system context. The system concept should be relatively unconstrained by current military implementation considerations and CONOPS. Thus commercial wireless communications links and Internet networking technology should be applied. Commercial software technologies should be used in exercises to demonstrate the rapid integration of heterogeneous applications softwares to create a real-time, distributed BMC3 system. The focus would be on future threats, weapons, and sensor systems. This test bed would permit advanced technology to be evaluated in a low-cost environment incorporating it in a development program.

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irreversibly degrade the entire system, and redundancy is needed to overcome this flaw.

The alternative that the committee proposes is to engineer a highly dynamic system in which the entire sensor-to-shooter chain is assembled in real time from whatever components happen to be working and available, very much in the spirit of network-centric operations.⁷ In network-centric operations, information would be shared across the sensing network. Specific sensors would be brought into play and focused on a specific task if they can provide discriminatory power, and airspace is managed dynamically to allow the best use of sensors and the clearest paths for interceptors. Finally, interceptors would be tasked dynamically to afford the most effective protection for the most valuable assets.

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FIGURE 4.1 Theater high altitude area defense (THAAD) system.

DACS. Autonomous onboard navigation, guidance, and target tracking are performed with in-flight updates from the radar. The seeker has a cooled focal plane array with MWIR indium antimonide (InSb) detectors.

Unlike the PAC-3 system, the THAAD system does not have a long history of evolutionary development. It entered the demonstration/validation (Dem/Val) phase of development in 1992. With the experiences and lessons of Desert Storm lending urgency to the development of improved TMD systems, THAAD embarked on an aggressive development schedule. The Dem/Val phase included an objective of first flight in 2 years, and delivery of a user OPEVAL system was targeted for 4 years after first flight. The program experienced a number of quality control and reliability problems in the flight test program, resulting in six consecutive failures to achieve target kill. No two of the failures were for the same reason, and none of them were related to the high-technology features of the system.

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Following a period of internal and red-team reviews, the flight test program was resumed and two successive HTK intercept tests were successful. These flights, on June 10, 1999, and August 2, 1999, demonstrated that the basic design is sound and the HTK strategy is technically feasible. After the two flight tests, THAAD was approved for milestone II and satisfied the exit criteria for the program definition and risk reduction phase. On June 28, 2000, the Army Space and Missile Defense Command awarded the THAAD engineering and manufacturing development (EMD) contract to Lockheed Martin.

The THAAD GBR, formerly an independent radar development project, has become an integral part of the THAAD program and provides surveillance and fire-control support to the system. A large power-aperture, X-band radar provides the long-range search, tracking, and discrimination capability to fully support the fly-out and intercept capability of the missile. It has a single face and does not search all azimuths. The radar incorporates a rich repertoire of waveforms and algorithms to provide the precision tracking and discrimination required to meet the kill probability and coverage objectives of the system. The radar is capable of microdynamic and imaging measurements of objects in the threat cloud to effect precision discrimination, and its broad bandwidth, in the gigahertz range, provides the range resolution to execute such functions as length measurement for discrimination. The radar also tracks the THAAD missile, providing in-flight target updates and a TOM to the kill vehicle. The primary means of performing target kill assessment, critical to SLS and handover decisions, is radar observations.

The engagement sequence for the THAAD system is as follows:

The THAAD system is being developed in two configurations. The first configuration, C-1, will be developed to meet the key performance parameters specified in THAAD's ORD. This phase of development will demonstrate design and operational capabilities through a series of ground and flight tests, qualify the system to enter production, and validate system-manufacturing processes through low-rate initial production. The C-1 configuration will provide a

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substantial war-fighting capability, with delivery of a complete THAAD first unit equipped (FUE) system to the Army by 2007. The second configuration, C-2, will incorporate software enhancements to (1) enable full ORD compliance, (2) keep pace with evolving threats, and (3) apply lessons learned from operational experience. The C-2 materiel release occurs in 2012. The C-1 FUE will include 16 missiles, 1 radar, 2 launchers, and 1 BMC3I subsystem. The C-1 early operational capability (EOC), scheduled for early FY09, will include 48 missiles, 1 radar, 6 launchers, and 1 BMC3 subsystem.

Milestone III for THAAD is scheduled for the start of FY09, and full-rate production (FRP) planning is for 1,250 missiles, 10 radars, 76 launchers, 38 tactical operations stations/launch control stations, and 68 system support groups.

Some of the advanced technology candidates being considered for upgrades to THAAD, along with their potential contributions to meeting advanced threats, are the following:

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FIGURE 4.2 PAC-3 system.

Patriot, largely in radar coverage and missile warhead design, were made only a short time before the Gulf War, leaving little time for test and evaluation before they were used in combat. While the ability of the system to intercept Scud missiles was demonstrated, including field upgrades performed to cope with tumbling missiles, it was not clear if there were any warhead kills, so further improvements were warranted.

The need for a theater ballistic missile defense capability has been recognized by the Army for several decades, and the quest for a defense system to meet this need has been marked by a number of shifts between single- and multiple-mission approaches. In the late 1950s and early 1960s, the field army ballistic missile defense system (FABMDS), a self-contained, mobile defense system designed expressly to engage free-rocket-over-ground (FROG)-type ballistic missiles (Soviet short-range ballistic missiles), was under development, but

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it was phased out largely because of the difficulties of packaging a complete system in a single vehicle. Also, FABMDs gave way to a shift in Army priorities from TMD to air defense, the mission objective of a study conducted from 1963 to 1965 called Air Defense Systems of the 1970s (AADS70).

The SAM-D system, which was the product of AADS70 studies, began with a requirement for a dual-mode capability (TMD and air defense). To reduce its cost, the SAM-D system was reoriented to a single mission, air defense, in the early 1970s, and its name was changed to Patriot. It remained a single-mission air-defense system until the PAC-1 and PAC-2 modifications were incorporated just prior to Desert Storm.

The ABM Treaty, signed in May 1972, prohibited the upgrade of such systems to provide an ABM mode. While the treaty does not proscribe TMD system development or deployment, the ambiguities and controversies surrounding the distinction between TMD and ABM systems inhibited the development of that class of system for a number of years.

The main elements of a PAC-3 battery are a radar set, an engagement control station, and a launch station. The launch station consists of a mobile launcher carrying 16 PAC-3 missiles. In the basic battery, launchers can be located up to 10 km from the engagement control station. With the remote launch communication enhancements upgrade, currently under development, launchers can be located up to 30 km from the basic battery, thus extending the TBM-defended area significantly. The radar is a mobile, multifunction, phased array operating at C-band.

In a modern Patriot battery, there are 8 launchers, 4 of which are loaded with 16 PAC-3 missiles each (total of 64 PAC-3s) and 4 of which are loaded with 4 PAC-2 missiles each (total of 16 PAC-2 missiles). The PAC-2 missiles, originally designed to enhance TBM lethality through the use of large fragment size, are now inventoried for use against all classes of targets. The mixed inventory of PAC-2 and PAC-3 missiles gives the Patriot battery flexibility in engagement of ballistic and air-supported targets.

The original guidance system for the Patriot air defense, still used in PAC-2, was RF semiactive homing, with a downlink to allow implementation of target-via-the-missile (TVM) processing. The TVM approach was initially selected largely because the onboard computers did not have the required throughput, a limitation that has been diminishing rapidly with the march of Moore's law. The PAC-3 missile uses a Ka-band active seeker for endgame homing. This guidance system was developed and demonstrated in the experimental extended-range interceptor (ERINT) program, culminating in three consecutive hit-to-kill intercepts, before transitioning to the Patriot system.

Extensive design trade-off analyses were conducted between a semiactive and an active RF guidance mode and the active seeker before final selection of the active mode for PAC-3. The main factor leading to selection of the active RF guidance mode was its demonstrated hit-to-kill lethality in an endo-atmo-

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spheric environment. Since the hit-to-kill strategy obviates a warhead, the missile is smaller and lighter, allowing a larger number of missiles per launcher (four times as many as PAC-2). This increase in firepower is a significant factor in handling large raid sizes and in implementing a salvo firing doctrine to improve kill probabilities.

The engagement sequence of PAC-3 is (1) inertial fly-out of the missile following initial detection and tracking by the radar to a nominal intercept point in space, (2) onboard seeker acquisition, (3) midcourse homing using rapidresponse attitude control thrusters, and (4) endgame homing to achieve hit-to-kill of the target. Precommitment discrimination is performed by the radar, including a high-resolution waveform that enhances discrimination performance and provides growth options for non-TBM target classification. A critical on-board function is aim-point selection to assure warhead kill, a function that was not accurately executable by Patriot during the Gulf War. Aim-point selection has been effectively executed in the PAC-3 tests conducted to date.

As noted, PAC-3 is an endo-atmospheric, or lower-tier, TBM system, comparable in altitude operating regime to the NAD system. The Army has analyzed PAC-3 from both an effectiveness and an operational viewpoint as an underlay to THAAD in a layered configuration, as well as an autonomous TMD system. Since the elements of the PAC-3 system are separate and distinct from those of THAAD, they can provide a statistically independent tier of defense yielding very low overall leakage. With a lower tier having 20 percent leakage, net system leakage will be 4 percent (0.2 × 0.2 = 0.04). For the defense of high-value theater targets, this layered defense mode can be of immense value in providing a level of protection unachievable with a single system.

The PAC-3 system has had five consecutive successful tests, three tests against ballistic targets and two tests against cruise missiles. The active RF mode has proved to be effective against both classes of targets. Significantly, the tests conducted thus far demonstrate warhead kill against unitary warheads and high lethality against multiple canister warheads.

The PAC-3 system is currently in a low rate initial production phase, with 16 missiles scheduled for the end of FY01 and 32 in FY02. The full system FUE is scheduled for the fourth quarter of FY01, coincident with FUE for the PAC-3 missile. The PAC-3 IOC is scheduled for 2006.

Candidate technologies for block upgrades to Patriot PAC-3 include the following:

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FIGURE 4.3 Joint land attack cruise missile defense elevated netted sensors (JLENS).

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the targets. JLENS can stay aloft for up to 30 days, providing 24-hour coverage over extended areas, and it assists in the development of the SIAP by integrating data from multiple sensors.

JLENS distributes surveillance information via the joint data net and is netted with other theater sensors for distribution of fire control quality data. This netting will initially be accomplished via the CEC network and the joint composite tracking net. The CEC will fuse measurement data from JLENS sensors with data from other CEC-integrated land, sea, air, and space sensors to facilitate development of a SIAP and to provide early warning, cueing, and fire control quality data for over-the-horizon/non-line-of-sight engagements. The JLENS classification, discrimination, and identification data will also be fused via composite identification processing to support identification determinations in distributed command and control nodes.

In addition, JLENS is designed to support attack operation and communication missions. JLENS provides battlefield commanders with surface-moving target tracking and identification to support engagements by attack operation weapons. It also provides the basis for vectoring aircraft to intercept hostile aircraft while still over the horizon. The system assists in maintaining total situational awareness. JLENS has a demonstrated capability to elevate tactical communications and data networks above the battlefield to provide extended range and reliable connectivity and relay capabilities.

JLENS will use a blocked acquisition approach. Block I will design, fabricate, test, produce, and deploy the fire control radar, with sector surveillance integrated into the 71-m aerostat along with the processing station and ancillary equipment. Block II will similarly develop, procure, and deploy the surveillance radar. Block I and Block II configurations will meet the ORD threshold system requirements. Block III will consist of preplanned product improvements to develop and incorporate advanced technologies into Blocks I and II and to bring the JLENS system into compliance with the ORD.

In the FY02 to FY07 program objective memorandum, JLENS is in a program-definition and risk-reduction phase at the start of EMD. It is planned that 12 JLENS units will be built during this phase.

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Because not all of the committee members had interactions with the Air Force R&D programs, only the programs that were briefed to the entire committee by Air Force representatives will be covered here. These programs are related to laser weapon developments and are most significant in the context of the Navy's NTW TBMD effort.

The Air Force's BMD program is focused on the ABL project. The proposed ABL system will consist of a multimegawatt laser carried aboard a modified Boeing 747 aircraft. The system is designed to engage TBMs during their boost phase at standoff ranges of several hundred kilometers. In theater, the ABL will not require penetration into enemy airspace and will be able to engage the shorter range threats. Nevertheless, it will possess a self-defense suite. Furthermore, although its primary mission will be missile defense, the system, by its nature, also opens opportunities for applications in other missions. These might include the following:

The ABL program requires integrating a multi-megawatt COIL into the aircraft to kill boosting TBMs. The ABL laser system consists of three main segments:

The turret assembly contains a 1.5-m-diameter primary mirror mounted on the nose of the aircraft. Six onboard infrared sensors will provide 360 deg of coverage to permit autonomous detection of boosting missiles. The aircraft will cruise at approximately 40,000 ft and thus be substantially above cloud layers. The COIL radiates at a wavelength of 1.3 µ and is being designed to radiate multi-megawatts of energy so that it can heat missile structures to their failing point, causing a destructive kill of the missile.

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If the development of the ABL is successful, it will prove to be a great asset to a theater commander-in-chief. It will have an engagement ability to destroy at least 20 enemy missiles. Depending on engagement geometry, atmospheric turbulence, and missile type, it could destroy up to twice that number or more. With an in-air-refueling capability, the range and on-station endurance of a 747 implies that the availability of local in-theater basing will not be a major limitation of the ABL system. If the system performs as the Air Force projects—that is, as part of a tiered theater missile defense architecture operating in concert with various ground-based and sea-based systems—the ABL should provide a flexible, rapidly deployable response for expeditionary operations.

Although the committee believes that the development risks associated with the ABL are reasonable and that they are likely to be resolved successfully, some development risks do exist. They are as follows:

The Air Force has an active and well-funded effort under way to install and test the laser on a 747 aircraft. An important component of the research and test program deals with propagation and beam spreading, along with the problems associated with holding the beam on the most vulnerable part of the target.

The main operational issue that must be addressed is that the consumables used in the laser cannot be replenished on station. Therefore, any countermeasure that increases the dwell time required for the laser to destroy the target directly decreases the capacity of the system. Coupled with the multiplier effect of the number of aircraft needed to ensure one aircraft continuously on station, this suggests that the mission capacity versus countermeasure trade-off is significant.

Assuming continued funding and no development delays, an airborne laser weapon designed to kill ballistic missiles in their ascent phase is planned for an initial operational capability between 2008 and 2010.

The committee was briefed on the use of a lower powered COIL laser on a low-flying aircraft for defense against cruise missiles. Such a system concept is not funded (nor should it be emphasized) and is not as important to the cruise missile defense problem as ABL is to the ballistic missile defense problem.

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4.4 BMDO MISSILE DEFENSE R&D PROGRAMS

4.4.1 Overview of Theater Ballistic Missile Defense Technology Issues

Technology programs for ballistic missile and cruise missile defense take place in much different programmatic environments. Since the advent of the strategic defense initiative (SDI) in 1983, funding for BMD has been the responsibility of BMDO (originally known as the Strategic Defense Initiative Organization). While the SDI was heavily focused on technology, BMDO currently expends almost all its funding on acquisition and related activities ( Figure 4.4 ). The allocation to BMD technology, exclusive of that earmarked for the spacebased laser program, is only 3 percent of the total BMDO budget, far below the 10 to 12 percent generally viewed as the minimum required to prevent technical obsolescence of the major defense acquisition programs (MDAPs) and keep abreast of the advancing threat.

The committee is deeply concerned about the widening gap between available technology resources and the requirements imposed by a missile threat that is growing rapidly in quality as well as numbers. As described below, the gap creates a major issue with respect to the spiral development strategy that is being used for TMD systems development. Moreover, and of equal concern, there is inadequate funding to develop and evaluate more innovative approaches that could significantly improve system cost and/or performance.

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FIGURE 4.4 BMDO FY01 budget ($4.5 billion).

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A spiral development strategy has been adopted by BMDO, and all BMD program managers have been directed to formulate plans to implement it. According to BMDO officials, the upper-tier TMD programs—THAAD and NTW—are further along in implementation plans than the lower tier, but all programs suffer from a serious mismatch between programmed technology dollars and spiral objectives. BMDO leadership is said to be keenly aware of this mismatch and committed to increasing the technology budget in FY02 and beyond to bring the enabling technologies along to support spiral objectives.

What the Navy is calling spiral development in the missile defense context is basically just evolutionary development to avoid delaying the initial deployment of BMD systems until all objectives are met. The concept is that an 80 to 90 percent solution should be accepted for initial deployment, with the proviso that a systematic plan for periodic upgrades will be implemented. In a number of briefings on spiral development roadmaps that were presented to the committee, the interval between upgrades was relatively short, and the magnitude of the upgrades was smaller than traditionally has been the case. The thinking behind the strategy appears to plug in performance-enhancing technologies when they become ripe for application rather than to wait for some critical mass upgrade.

It is unclear to what extent the program managers are applying their development budgets to technology upgrades instead of looking to the advancedtechnology 6.3 programs to ready the technology for insertion. However, it appears that they are allocating a relatively small proportion of development budgets for technology upgrades and that the projects are highly dependent on 6.3 technology products.

Historically, the process of effecting technology upgrades worked best when the technology program and budget were external to the project. The natural tendency of program managers is to reprogram technology dollars, as necessary, to cover shortfalls in the development program. Because of this, the budgets for some earlier BMD technology programs, such as the Advanced Ballistic Missile Defense Agency, were “fenced” so as to prevent their reallocation to cover nearterm exigencies. The committee believes that this general practice is relevant to the implementation of spiral development and further believes that BMDO and the Navy follow it.

No matter what the size of the BMDO technology budget, the technology investment strategy must be improved to apply the available dollars to the highest priority needs more efficiently. In particular, the committee believes that a more explicit correlation should be established between credible countermeasures and the technology solutions to such countermeasures. In too many cases, the technology projects that are being funded bear only a loose relationship to quantifiable improvements in performance against advanced threats. A tighter relationship will clarify the relevance of the funded technologies and will aid in winning increases in the technology budget.

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The committee believes that the Department of the Navy should take the initiative in creating an all-Service methodology for relating threat drivers to technology solutions that facilitates an understanding of the critical paths and the commonality of technologies between programs. In this regard, two candidate techniques being used in different parts of the BMD community merit consideration. They are (1) a branch-and-block approach that explicitly networks threat branches with candidate technology responses and (2) breakpoint analysis, which extends the severity of the threat elements until they break the system. Both approaches have merit in explicating the rationale for technology programs and evaluating the payoff of candidate technologies. The committee does not endorse a particular implementation of tools of this type but does recognize the need for an explicit methodology that is common to the principal development programs.

In the following subsections, technology needs and issues are discussed, ongoing programs are assessed, and research priorities for theater ballistic missile defense are suggested.

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The increasingly small RCSs that can be achieved by RV technology (rather than the terrain masking that may be encountered in the cruise missile scenarios) are a further challenge. Increased radar transmitter power can increase range performance. All TBMD radars, including SPY-1 and GBR, include high-power module technologies (e.g., GaAs, GaN, and SiC transmit/receive (T/R) modules) that can increase transmitter power and that are under active development in a number of different science and technology organizations.

Power alone is far from the whole solution. The detection of very small targets requires very low detection thresholds, which inevitably produces a large number of additional “targets” (e.g., false alarms and small pieces of debris) that must be sorted out and distinguished from the actual RV by a discrimination logic. Discrimination of the RV from all the other apparent ballistic objects that may accompany or appear to accompany it is the next step in the threat acquisition process and presents formidable challenges. Clearly the radar must be capable of resolving the individual objects—that is, separating them in all spatial dimensions well enough to allow the RV to be successfully identified and tracked. Since measurement resolution depends primarily on signal bandwidth, high-bandwidth radar is needed.

It seems obvious that the greater the number of individual parameters that can be measured about each candidate RV in the cluster (e.g., length, width, body-motion characteristics, reflectivity, effects on polarization), the better the chance that the real RV can be identified. Consequently, BMD radars need to be capable of multimode operation and must have the ability to make a variety of accurate measurements. Algorithms must be developed to exploit these features. Because of the radar reflection properties (i.e., coherence and isolated scattering effects) of typical objects, increasing bandwidth to gain dimensional resolution finer than that already available in today's X-band BMD radars does not produce more useful images (e.g., more accurate measurements of length).

Since any given radar waveform produces only some but not all the measurements that might be desired, a sequence of different measurements must be carried out. The interesting question then arises of how to optimize the order in which the measurements are attempted. Some BMD radars (e.g., GBR in the THAAD program) address this optimization by considering the radar as an adaptive measurement system, not just a “radar.” The waveforms and radar modes utilized at any instant are adaptive responses to the results of the previous measurements. Such adaptive approaches should be explored and extended since they may prove more robust than preplanned approaches in which unexpected RV or countermeasure characteristics are encountered. This approach may also prove useful for the seeker's discrimination tasks as well, with active capabilities expected to be added to the passive sensing currently employed in the exo-atmospheric HTK vehicles.

The final step in the acquisition process—that of establishing fire-control-quality tracks on the candidate RV (or RVs, depending on the success of the

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discrimination process)—is a straightforward and familiar sensor task given the resolution capabilities needed for discrimination. The longer the objects under track can be observed with high resolution and good signal-to-noise, the better the tracking filter estimates will be. In addition, as track quality improves, the volume of the handover basket that is passed on to the HTK vehicle decreases. This in turn minimizes the time required for the onboard seeker to acquire, discriminate, and target the correct RV target. As a result, the kill vehicle divert capability needed to accomplish the intercept will also be minimized.

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maneuvers, thereby minimizing kill-vehicle divert requirements and maximizing the probability of successful intercept.

For ballistic threats, at handover the missile/kill vehicle seeker is typically presented with a many-object target complex depicted and characterized by the measurement capabilities of the initial acquisition radar, from which the target (i.e., RV) must be correctly identified as soon as possible. Clearly, high-resolution “imaging” in all dimensions is required to detect and examine each candidate RV for discrimination. Given the limited aperture imposed by typical missile dimensions, high-frequency systems (i.e., electro-optical and millimeter-wave) must be used. While passive sensors can be adequate for precise azimuth-elevation measurements, for precise range and Doppler measurements, active capabilities via LIDAR or wideband radar adjuncts would be desirable. Current candidate Navy TBMD missile seekers (e.g., SM-2 Block IVA and lightweight exo-atmospheric projectiles) rely entirely on passive optical sensors for the terminal phase, although combined passive/active optical seekers are under development.

Because of the range of possibilities, which includes sophisticated counter-measures, it is clear that the more unique measurements a seeker can make on the totality of objects in the target complex, the better the chance of correctly identifying the real RV. Multiband optical (several IR and possibly visible) sensors with laser detection and ranging (LADAR) and/or millimeter-wave (MMW) radar active adjuncts seem to be called for. If affordable and physically realizable, the combination of multiple optical bands with RF measurements offers good decoy discrimination potential. Although decoys may be produced that are excellent replicas of a RV, the designer of decoys finds it difficult to replicate RV signatures precisely in all-sensing modes.

For many years, BMD discrimination research has concentrated on the development of algorithms derived from observations by a single type of sensor. The more mature discrimination techniques are based on radar measurements, but there is also a significant body of work on passive optical sensor discrimination. Only recently has serious attention begun to be applied to fusing of radar and optical data to enhance discrimination performance.

The main BMD systems currently under development all have both radar and optical sensors, and the enhanced discrimination potential achieved by combining the data they collect on various features of the threat objects is becoming increasingly evident. The radar data, particularly that measurable by the X-band radars being developed, allow the precision measurement of microdynamic features of threat objects. The passive IR sensors being developed for performing onboard interceptor functions are naturally adept at measuring thermal characteristics of threat objects. In addition, there is a large class of features, such as macrodynamic body motions, that both sensors can measure. The potential for a significant improvement in discrimination capability lies in the effective fusion of these feature vectors.

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While passive sensors can make simultaneous measurements (e.g., using FPAs) on multiple objects in multiple modes, active sensors typically employ different waveforms sequentially. Here, as for long-range sensors, treating the seeker's active component (and perhaps the computer resource) as a measurement system rather than simply a radar or an imaging system, may permit effective adaptive procedures to be applied.

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siderably higher in the atmosphere, so guidance-and-control responsiveness is increased. For TBM intercept, the time available to discriminate, close, and hit is shorter than for the exo-atmospheric case. However, the atmosphere helps the defense to filter out lightweight, nonthreatening elements.

The overlapping cross sections of the interceptor and its target define the hit-to-kill lethal radius. As illustrated in Figure 4.5, when all factors are considered, the overall probability of a successful intercept for any given TBMD system increases as the lethal radius increases. The probability is small when the lethal radius is below some critical value, and it is relatively constant above the “knee” in the curve. The goal of any research and development program should be to move the knee as far to the left as possible.

For 30 years, beginning in the mid-1960s, the Navy maintained a high-energy laser program that was oriented toward the development of a shipboard high-energy laser (HEL) that could be used for ASCMD. The result of this extended investment was a realization that in a moisture-laden maritime environment, laser fluences were reduced by scattering and absorption to a point where they would have limited usefulness as a ship self-defense weapon.

More recent appraisals of the value of HEL as an ASCMD weapon have centered on the observation that an HEL can char the nose cone of an incoming missile. If the missile is radar-guided, the charring will result in increased transmission loss through the nose cone and a partial or complete loss of radar guidance. If a radar-guided missile loses its radar capability, it is generally programmed to fly in a straight line to its target based on its IMU.

A missile that flies in a straight line toward its target is more vulnerable to destruction by short-range defensive weapons than a missile that makes evasive

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FIGURE 4.5 Probability of kill vs. lethal radius of intercept (notional).

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maneuvers. Thus, some have argued that a shipboard HEL should be thought of as a complementary weapon that might increase the probability of kill of associated short-range defensive weapons. Others point out that an ability to continue evasive maneuvers based on IMU guidance can be (and in fact has been) programmed into modern missiles as a backup mode of operation in the event that their radar is jammed. Unless unforeseen changes occur in HEL technology, the committee doubts that shipboard HELs will be introduced prior to 2020.

Some directed-energy weapons, in particular lasers, were considered as weapons for the destruction of incoming missiles during late 1980s in the context of the SDI, which envisaged space- as well as land-basing of these systems. Lasers have the potential to deliver a lethal dosage of energy at a great distance with minimal delivery time (velocity of light).

Lasers in the theater ballistic missile defense arena have a role to play principally in the boost phase, when the target size is the largest because the booster is still an integral part of the target. Moreover, the booster is perhaps the softest component of the target. Once the warhead has separated from the propulsion vehicle, the target's size, velocity, and hardness all work together to make the problems for laser weapons a lot more difficult. In the midcourse phase of flight, the opportunities for simulation/antisimulation and decoys abound, making discrimination of the actual warhead difficult. For boost-phase intercept, depending upon the primary boost vehicle, intercept must take place below separation altitude, which is typically less than 100 km. This, in turn, requires the laser platform to be in position to track and engage the target with enough fluence and integration time to create the damage. While the energy is delivered at the speed of light, the rate at which it arrives and is absorbed by the target requires illumination times of several seconds depending on the construction, material, and surface finish of the target.

An extended discussion of the Air Force's laser weapon program is provided in a separate section. The program is based on COIL technology. Another class of lasers, the FEL, attracted much attention during the SDI era. Interest in the FEL appears to be making a comeback because of the wavelength tunability feature, which allows the selective use of a wavelength that has minimal absorption during its transmission through the atmosphere.

The Department of Energy's Thomas Jefferson National Laboratory has been working on a system that appears to be scaleable to the multimegawatt levels of laser power needed for theater missile defense applications. Because of their size and electrical energy requirements, as well as the need for shielding the radiation from the beam dump, FELs would only be suitable for ship (and perhaps also ground-based) deployment. These lasers were proposed by the Los Alamos and Lawrence Livermore National Laboratories and by Boeing and others during SDI development as ground-based lasers that, in conjunction with space-based optics, could be used in ballistic missile defense applications. How-

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ever, the laser power requirements for such applications were seen to be extraordinarily high.

In spite of their promise, FELs are still very much laboratory devices. Their deployment in practical defense systems is farther out in time than the possible deployment of COIL and hydrogen fluoride/deuterium fluoride lasers.

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as a research platform, rather than to defend Israel's northern border, as originally intended (although it still might go to Israel if that nation wants it for an emergency). U.S. and Israeli military authorities would like to develop a smaller, mobile version of the THEL demonstrator at White Sands. Both the Israeli Defense Force and the U.S. Army are interested in fielding a short-range battlefield defensive laser system that would be able to shoot down artillery rockets, mortar shells, and—possibly—aircraft and cruise missiles. The development of a mobile THEL has been estimated to require 5 to 7 years of additional effort.

In tests starting in June 2000, it was fired at 16 rockets and one winged insect that landed on the beam emitter at precisely the wrong time. Some of those rockets were fired simultaneously to test THEL's ability to engage multiple incoming targets. The demonstrator was built with combat capability in mind, and officials had discussed moving it from White Sands to Israel. Despite the successful tests of 2000, there has been a growing concern that the demonstrator was not ready for action. Israel has also expressed concerns that a fixed THEL would become a difficult-to-defend target for attacks. The changing situation in Israel has made a fixed THEL less acceptable. During the summer of 2000, Israel abandoned its occupied territory in southern Lebanon, allowing Hezbollah to launch attacks much closer to the Israeli border. More THELs, or a mobile system, would now be needed to properly defend the border area.

The U.S. and Israeli governments are reported to be completing an agreement that would provide for the development of a mobile THEL. The contemplated mobile system would be carried on a few heavy trucks (one truck would have the laser, another would have the rocket-tracking radar, and others would carry the fuel chemicals). The design objective would be to produce a system light enough to be transported by a C-130 cargo plane.

The committee believes that the Department of the Navy should certainly continue to track the progress of the U.S.-Israeli THEL and consider it for possible application in a maritime environment.

The Israeli Arrow Program is a cooperative program funded largely with BMDO money. It is designed to engage both endo-atmospherically and high in the atmosphere, much like THAAD. While quite large, Arrow uses several technologies similar to those being pursued by the Navy systems and will yield useful information on fragment warhead lethality and seeker phenomenology.