Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 94
Page 94 4 Assessment of Current and Projected Department of the Navy, Other Service, and Defense Agency R&D Programs 4.1 NAVAL MISSILE DEFENSE R&D PROGRAM Research and development efforts related to ballistic missile defense fall under the budgetary jurisdiction of the BMDO. Consequently, the main thrusts of the Department of the Navy R&D programs are related to CMD. However, the Department of the Navy, primarily through ONR's missile defense 1 —and, to a lesser degree, its platform protection 2 future naval capability (FNC) efforts—is pursuing efforts that are relevant to both BMD and CMD in areas such as the following: IR sensors, Combat identification, Advanced ground-based radar technologies, including the advanced multifunction radio frequency system (AMRFS), Various critical radar components—for example, GaN and SiC microwave power amplifiers, and High-speed digital circuits. 1 Cetel, CAPT Alan J., III, USN, “Missile Defense (MD) Future Naval Capability (FNC) Program Overview,” briefing to the committee on April 26, 2000, Office of Naval Research (Code 35)/Office of the Chief of Naval Operations (Code 091), Washington, D.C. 2 Lawrence, Joseph P., III, "Department of Navy S&T Platform Protection FNC," briefing to the committee on April 26, 2000, Naval Research Laboratory, Washington, D.C.
OCR for page 95
Page 95 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. 4.1.1 Department of the Navy Cruise Missile Defense Sensor Research and Development As discussed in Section 3.1, which gives an overview of theater missile defense capability, the Navy is in the process of procuring and developing four major radar systems that have the potential of providing improved sensors for Navy ships. Accordingly, sensor R&D carried out under ONR's missile defense FNC is largely oriented to providing improved sensors for OCMD. In tactical situations, overland cruise missiles are difficult to detect and track because of clutter from the land background. In many situations OCMD is complicated by the fact that the flight path of cruise missiles may be programmed to exploit terrain masking. Another complication is that the engagement may take place at ranges that are below the horizon of sea-based (and even some land-based) radars. Generally, a single land- or sea-based sensor will not allow robust acquisition of remote land-attack cruise missiles. The combined effects of terrain masking and radar horizon limitations necessitate one or more airborne AMTI radar platforms (e.g., JLENS, E-2C RMP, AWACS, JSTARS, and UAVs) or some other form of distributed cooperating short-range electro-optical, acoustic, RF, or other sensors.3 Appropriately, ONR's missile defense FNC program is concentrating on the elevated sensor problem. A sensor by itself does not constitute an OCMD system. Detections and tracks developed by an elevated sensor must be passed to a weapon release authority. If, based on detections by an elevated sensor, a weapon has been released, it must be guided into a collision course with the incoming missile. When the interceptor comes close enough to the target to allow its onboard sensor to acquire the target, the terminal encounter will occur autonomously. ONR's missile defense FNC is engaging in R&D efforts related to all phases of this problem. 3 In Section 184.108.40.206, the Link 16 and CEC legacy discussion applies also to the problem of naval connectivity to these joint sensors.
OCR for page 96
Page 96 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. 4.1.2 Department of the Navy Cruise Missile Defense Weapon R&D Although a full-scale acquisition program apparently does not exist, it is clear that an OCMD concept based on weapon launch from a remote, sea-based platform will require a weapon with unique capabilities not represented in the Navy's current inventory of weapons. ONR managers are aware of this defi-
OCR for page 97
Page 97 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. 4.1.3 Department of the Navy BMC3 Research and Development 220.127.116.11 Background BMC3 provides the glue for connecting weapons to sensors in missile defense systems. Research and development in BMC3 algorithms, software, processors, and communications is required to outpace the threat, to develop lower-cost solutions, and to provide the flexibility to tie together evolving sensors and weapons—naval and other U.S. Services and allied—into a coherent system of systems.
OCR for page 98
Page 98 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.
OCR for page 99
Page 99 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
OCR for page 100
Page 100 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). 18.104.22.168 Department of the Navy BMC3 Technology Programs Theater Ballistic Missile Defense Development of advanced technology for TMD and BMC3 is the responsibility of BMDO. BMDO-sponsored work in BMC3 is discussed briefly in Section 4.4.4, “BMDO and DARPA BMC3 Efforts.”
OCR for page 101
Page 101 Cruise Missile Defense The Department of the Navy's efforts in cruise missile defense come under its missile defense FNC and platform protection FNC programs. A significant portion of the missile defense FNC program is addressing BMC3 issues. In the platform multisensor integration (MSI) program, a sensor fusion capability is being developed for the E-2C. This capability will correlate and fuse radar, infrared, and electronic support measure (ESM) data to better identify and track targets. The objective of the composite combat identification (CCID) program is to attach high-confidence identification to theater-wide tracks to get theater-wide combat identification (CID). The approach is to develop a universal CID engine that will collect CID attributes from all relevant sources in theater, correlate CID attributes to a common track database, reason over the data collected to produce high-confidence CID, and deliver CID with low latency to theater units. The theater collaborative tracking (TCT) program is developing technology for a theater-wide tracking network that would improve bandwidth efficiency and reduce life-cycle costs (by eliminating the need to modify computer software as new sensors are added to the network). The program objectives are to develop and demonstrate a collaborative tracking architecture and algorithms that incorporate need-based data distribution, that have minimal bandwidth increase when participants are added to the network that require no a priori knowledge of sensor or data source location, that require no software changes to accept new sensors, and that include sensor resource management algorithms. In the threat evaluation and weapon assignment (TEWA) program, algorithms are being developed for force-level TEWA in a distributed environment. These algorithms would perform automated threat evaluations that consider all air and missile threats and all assets requiring protection in the theater and then provide automated shooter and weapon recommendations that consider all potential combinations. Work under the platform protection FNC program is focused at the platform level, so there are no BMC3 projects planned. There is an unfunded demonstration program called the horizon extension platform. It would demonstrate a small, long-endurance, tethered hovering platform with electrical power as well as optical fibers provided by the tether. Were this concept to be developed, it could provide a platform for a communications relay for missile defense BMC3 systems and perhaps for look-down sensors as well. BMC3 Technologies Although the committee did not perform an in-depth analysis of the research programs reviewed so briefly in the preceding section, its general impression is that these programs are addressing many of the key BMC3 technology priorities.
OCR for page 102
Page 102 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. Approaches for the Provision of Improved BMC3 Capabilities for Naval Forces The committee believes that BMC3 for TMD will need to undergo a revolutionary redesign. Traditional approaches to BMC3 adopt a design philosophy that is overly static given the highly dynamic environment that will characterize ballistic missile and cruise missile defense. Systems that use these approaches directly link specific preplanned sensors to interceptors, creating a closed-loop control system that guides the interceptor to the target. The fatal flaw of such systems is that a failure, weakness, or unavailability of key components may 6 A previous Naval Studies Board report recommended that Internet Protocol ports would provide valuable evolutionary enhancements (e.g., increased interoperability) and should be pursued (see Naval Studies Board, National Research Council, 2000, Network-Centric Naval Forces: A Transition Strategy for Enhancing Operational Capabilities, National Academy Press, Washington, D.C.). This committee agrees with that approach; however, it believes that merely pursuing the “wrapping” of legacy applications will not get the Navy to the desired modern end state—hence the emphasis on a test bed.
OCR for page 103
Page 103 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. 4.2 ARMY MISSILE DEFENSE R&D PROGRAMS 4.2.1 Theater High Altitude Area Defense System The Army's THAAD system ( Figure 4.1 ) is designed to provide broad area coverage and a deep battle space against short-, medium-, and long-range theater ballistic missiles. It has the unique capability to engage targets at both exo-atmospheric and endo-atmospheric altitudes, giving it enough battle space to achieve multiple shots (the shoot-look-shoot firing doctrine). The SLS capability provides low leakage and minimal expenditure of interceptors. THAAD is an HTK defense system intended to provide high lethality against the full range of theater missiles in the current and projected threat over a wide range of crossing angles. The HTK strategy results in a relatively lightweight interceptor capable of reaching high burnout velocities and providing high firepower per battery. THAAD may be characterized as an upper-tier system in that it has the reach to engage targets at high altitudes in either an autonomous or a layered defense mode. In a layered defense mode, operating cooperatively with a lower-tier system such as PAC-3, it can provide the first filter of a flexible, low-leakage defense in depth. With its high-performance, X-band radar, THAAD can perform kill assessment for either a second upper-tier shot or handover to a lower tier. The THAAD missile has a single-stage, solid-propellant booster with thrust vector control and a separating kill vehicle. The kill vehicle employs a gimbalmounted infrared seeker, providing precision target imagery for tracking and aim-point selection; an uncooled sapphire window; and a liquid, bipropellant 7 Network-centric operations are military operations that exploit state-of-the art information and networking technology to integrate widely dispersed human decision makers, situational and targeting sensors, and forces and weapons into a highly adaptive, comprehensive system to achieve unprecedented mission effectiveness. See Naval Studies Board, National Research Council. 2000. Network-Centric Naval Forces: A Transition Strategy for Enhancing Operational Capabilities. National Academy Press, Washington, D.C., p. 1.
OCR for page 104
Page 104 ~ enlarge ~ 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.
OCR for page 118
Page 118 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
OCR for page 119
Page 119 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. Needed Acquisition Sensor Research Some obvious sensor improvements (e.g., X-band THAAD equivalent ) are not “research” issues but simply need to be done—their pursuit is a priority for the naval forces. Other needed improvements include power and bandwidth improvements via wide-band-gap materials such as GaN and SiC and low-cost T/R modules based on GaAs (X-band) or Si (S-band) microwave/millimeter wave monolithic integrated circuit technology. Digital radar offers flexibility for adaptive measurements—digital waveform generation is often used, but only for limited sets of waveforms (e.g., linear chirps.) Much more flexibility is possible. Any kind of waveform can be generated and processed digitally. The implications of this kind of flexibility should be investigated. Needed Researchon Adaptive Discrimination Full digital with analog-to-digital conversion at each element would offer digital phase shifting with no bandwidth limitations when using digital optical communication technology to transfer microwave signals as digital bit streams and cycle-slip plus digital filtering for interpolation to implement the phase shifting. This is not practical at present owing to the performance limitations of current analog-to-digital converters (ADCs) and their expense. There is a need to develop high-performance, inexpensive ADCs and digital receivers. 22.214.171.124 Seeker Sensors The sensor suite onboard the kill vehicle must first acquire the incoming threats or candidate RVs. Missile seekers have an inherently limited field of view and search capabilities. The acquisition of a target (or target complex, as is likely for ballistic targets) requires the designation of a handover “basket” from the long-range sensors. The better this can be accomplished (i.e., the smaller the basket), the better the capabilities of the seeker sensors can be employed to acquire the target as soon as possible. This efficiency, in turn, will maximize the time available for discrimination, aim-point selection, and vehicle end-game
OCR for page 120
Page 120 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.
OCR for page 121
Page 121 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. Needed Seeker Sensor Research The following seeker sensor research is needed: Multiband IR/visible sensors with laser radar or radar adjunct should be developed to address the discrimination issues that are certain to arise as ballistic missiles continue to become more sophisticated. If one looks at the dramatic advances in focal plane materials and mechanization technologies, it is easy to project continued improvements in quantum efficiency, sensitivity, bias and noise suppression, and resolution. The use of additional resolution and narrower detector bandwidths opens the possibility of other multispectral discriminants, including materials and imaging. Discrimination algorithms that exploit all the signatures that can be detected by multispectral sensors should be developed. LIDAR systems with multipixel FPA, which measure range-to-pixel, need to be developed in order to avoid the mechanical complexity associated with scanning optical systems. More powerful lasers are probably needed to extend the range of the three-dimensional imaging LIDAR adjuncts. RF/MMW adjunct possibilities for enhanced discrimination should be explored, including the possibility of deployable antennas for exo-atmospheric intercepts, to mitigate the limitations of kill-vehicle dimensions. Adaptive discrimination algorithms using the active capability of the seeker as a measurement tool need to be developed. Multiband LWIR sensors and their associated algorithms are able to reject most celestial objects and background by temperature and/or lack of movement; however, visible light sensors must deal with this problem. Background obscuration algorithms should be explored to deal with low-cross-section targets against the stellar background, although because the RVs are so small and the sky background is so complex, this approach seems to be less promising than it was for cruise missile threats.
OCR for page 122
Page 122 4.4.3 BMDO Missile Defense R&D Programs for Weapons 126.96.36.199 Interceptor Technology Issues and Needs The principal goal of TBMD weapons research is to assure that future interceptors can engage incoming missiles with a high probability of success. In this context, success means preventing missile warheads—including weapons of mass destruction—from destroying their intended targets. A need exists to cope with increasingly sophisticated missiles that could be launched in closely coordinated salvos at one or more protected assets. Future missiles may be more difficult to detect, may contain multiple warheads, and may be capable of maneuvering at any point on their trajectory. A field of false targets may surround the warheads that are delivered by future missiles. Secondary goals of TBMD research include the achievement of high reliability at the component and system levels, high effectiveness, and low permissile and total system life-cycle costs. Tertiary goals are the development of backup strategies and alternatives in the event of program failures, increased onboard autonomy, improved performance within existing missile magazine constraints, improved methods for empirical test and evaluation of total effectiveness, and refined algorithms for computer-based analysis and design. Because the missions and interceptors are different for NAD and NTW interceptors, specific needs and issues are different as well. Each TW interceptor is entirely dependent on the satisfactory performance of a single kinetic-kill vehicle (KKV). Since the KKV does not contain an explosive warhead, it must achieve a very small miss distance with respect to its intended aim point on the RV to achieve a successful intercept. There is a four-dimensional set of requirements for KKV performance: discrimination, accuracy, response time, and adaptation. Once the KKV has been delivered to its operational basket with an orientation that places the target in the fields of view of the onboard sensors, it must discriminate the correct target from a field of targets. If the correct target is maneuvering, the accuracy and response time of the KKV's guidance-and-control system must be good enough to ensure collision with the target. There is uncertainty in the predicted maneuvering intercept point and a need to converge the actual miss distance to a sufficiently small value. In statistical terms, not only the mean but also the covariance of the intercept-point error must be close to zero. The margin for error is relaxed considerably if the KKV cross section can be increased (by, for instance, expanding the structural cross section) or if multiple KKVs can be carried by the interceptor, increasing the probability of a hit. This same four-dimensional set of criteria applies for the NAD interceptor. Even if a NAD interceptor is guided to zero-miss distance, its exploding warhead will considerably expand its effective cross section, and the warhead explosive and fragments provide added effect. The likely normal load factors (g levels) for both the maneuvering incoming missile and the interceptor are con-
OCR for page 123
Page 123 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 ~ enlarge ~ FIGURE 4.5 Probability of kill vs. lethal radius of intercept (notional).
OCR for page 124
Page 124 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-
OCR for page 125
Page 125 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. 188.8.131.52 Interceptor Technology Programs Two related programs are the BMDO-sponsored AIT and exo-atmospheric interceptor technology (EIT) programs, led by the Army and Navy, respectively. Key technologies for AIT include low-cost, high-performance strap-down seekers; lightweight and highly reliable solid-propellant, divert and attitude control systems; and accurate modeling of jet interaction for hit-to-kill intercept in the atmosphere. The EIT focus is on the development and demonstration of two-color infrared sensors combined with an active LIDAR sensor and lightweight composite materials for shrouding, construction, and component housing. 184.108.40.206 Technology Priorities Although the committee did not conduct an in-depth analysis of BMD interceptor technology programs, it believes that these programs are addressing the right issues. However, the committee questions the BMDO technology program as a whole—that is, whether it is funded to a level that realistically supports the BMDO spiral development strategy. In developing an enhanced program, the following issues should be considered: Exo- and endo-atmospheric interception of maneuvering targets; Enhancements of, or alternatives to, hit-to-kill strategies; and Improvement of algorithms for multidimensional state vector estimation, and for prediction and control. The committee notes, in addition to inadequate support of spiral development, the lack of high-risk, high-payoff interceptor technologies in the BMDO technology program. Concepts such as multiple, highly minaturized kill vehicles per interceptor need to be under development to provide a counter to future advanced threats and to remedy shortfalls in discrimination and lethality. The committee endorses the development of a 21-in.-diameter second stage for the SM-3 interceptor. Some of the suggested growth paths such as two-color cooled optics interceptor sensors, increased divert-and-maneuver capability, and kill enhancement mechanisms all drive the kill-vehicle weight higher, which in turn requires more boost energy.
OCR for page 126
Page 126 4.4.4 BMDO and DARPA BMC3 Efforts Technology issues and needs for BMD BMC3 are discussed above in Section 220.127.116.11. Here, directly relevant BMDO and Defense Advanced Research Projects Agency (DARPA) BMC3 efforts are briefly discussed. Not much work is being done on BMC3 technology for TMD, although there are technology projects toward BMC3 for NMD. The battle management command, control, communications, computing, and intelligence (BMC4I) advanced technology (BAT) program is developing BMC4I technologies for NMD and TAMD. Technical objectives include improvement of kill assessment processes, communications links with interceptors, high-performance computers, and engagement planning algorithms. Technology for NMD capability 1 includes upgraded early warning radar (UEWR) tracking and fusion algorithms. Technology for NMD capability 2 includes tracking of multiple, closely spaced objects; discrimination algorithms; target engagement and fire control; and kill assessment techniques. BMDO created project Hercules in January 2000 as a National effort to develop robust, adaptive algorithms to counter off-nominal and evolving threats. The project incorporates a spiral development process and aims to develop and transfer algorithms to the MDAPs. It follows a design-to-capability approach, meaning that the algorithms being developed are associated with threat parameters and contain allowances for performance margins. Its primary objective is to develop algorithms that are less dependent on a priori threat data than is currently the case. Project Hercules addresses the critical BMD functions of tracking, discrimination, aim-point selection, and kill assessment, as well as a number of BMC3 functions. A high priority is assigned to discrimination algorithms. The very close relationship that has been established with the other Services is largely fostered by four teams reporting to the project office. In addition, a large number of companies, universities, and federally funded research and development center agencies are participating in the program. A number of specific deliverables to the participating MDAPs have been identified and scheduled by the project. It should be noted that a modest research investment is being made at DARPA in research on how to structure such dynamically assembled systems. Most of these efforts are primarily concerned with agent-based systems (e.g., the control of agent-based systems (COABS) program in DARPA's Information Systems Office (ISO) and the autonomous negotiating teams (ANTS) program in DARPA's Information Technology Office (ITO)). Other efforts at DARPA's ITO are concerned with the use of distributed networks of sensors (e.g., the sensor information technology (SENSIT) program) and with assembling many independent vehicles into a single coherent sensor or effector. While none of these programs have a specific focus on BMD, they do show that DARPA is interested in examining issues relevant to BMD and offer a possible avenue for cross-Service collaboration in early experimentation.
OCR for page 127
Page 127 4.5 INTERNATIONAL PROGRAMS 4.5.1 United States-Japan Cooperative Program In August 1999 the United States and Japan signed a memorandum of agreement to perform cooperative research and development on a ballistic missile defense system. This R&D effort shows promise of a disciplined approach to the system engineering of a capability that would defend Japan from continental threats and potentially serve as the Block II NTW system. The system is scheduled to achieve an initial operational capability sometime after 2015. Task 1 of the effort, currently under way, focuses on conceptual definition. It has delivered or will deliver a threat description, operational system guidelines, a scenario reference mission, technical assessment reports, and a preliminary integrated Dem/Val phase plan. Trade-off studies are being conducted to define the system as a whole and especially its missile element. In particular, cooperative design studies are addressing the missile's guidance unit, its divert and attitude control system, second-stage propulsion, and a lightweight nose cone. Planned follow-on tasks will result in a preliminary design of the Dem/Val missile (in a prime item development specification) and perform risk reduction demonstrations. 4.5.2 United States-Israel Chemical hydrogen fluoride/deuterium fluoride (HF/DF) lasers, which at one time were considered key candidates for ground-based lasers with space-based optical components for SDI, have been reconfigured as a tactical high-energy laser (THEL). In a cooperative activity with Israel, this system has been operated at a power level of 300 to 400 kW and has shown an ability to destroy Katyusha rockets in flight at a standoff distance of about 1 km (or less). Such lasers—which because of their large size and long wavelengths force the use of large optics for targets and long distances—may be candidates for deployment on ships for the defense of Navy assets against cruise missiles and enemy aircraft attacks. They would be in competition with tunable FEL lasers, whose development has shown promise in recent years. Between about 1965 and 1985, the Navy sponsored an extensive program of research in HF/DF lasers. Enthusiasm for shipboard lasers waned as a result of atmospheric adsorption, beam scattering in the maritime atmosphere, and the realization that modern missile nose cones could sustain high levels of damage. The THEL facility is housed in a building at White Sands' High Energy Laser Systems Test Facility. The beam comes from a small turret on top of the structure, attached to which is what amounts to a battlefield chemistry project: tanks of chemicals that, when mixed, generate enough energy to fire the laser. This facility is likely to remain in White Sands, New Mexico, where it will serve
OCR for page 128
Page 128 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.
Representative terms from entire chapter: