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Suggested Citation:"4 Technology Issues." National Research Council. 2008. U.S. Conventional Prompt Global Strike: Issues for 2008 and Beyond. Washington, DC: The National Academies Press. doi: 10.17226/12061.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

4 Technology Issues Overview The key goal for conventional prompt global strike (CPGS) systems, the ability to hit distant targets quickly and accurately, delivering damage only to the well-defined target area, entails serious technical challenges. A wide range of concepts has been proposed to meet the CPGS challenge, as illustrated in Figure 4-1. These solutions include modest modifications to existing ballistic missiles (such as the Conventional Trident Modification [CTM]), boost-glide missiles, and hypersonic cruise missiles. The weapons themselves can be launched from the continental United States (CONUS) or from forward-deployed land bases, submarines, or aircraft. The principal proposals for CPGS build on technology designed for the rapid, long-range ballistic delivery of nuclear weapons. Since a conventionally armed prompt global strike system must be much more precise in its targeting accuracy and weapon delivery than a nuclear delivery system, no existing system can be used without modification. CPGS systems are being considered with varying degrees of modification from a ballistic trajectory, as illustrated in Figure 4-2. The simplest modification requires developing sufficient control, navigation, and guid- ance during reentry to enable the required terminal accuracy, as in the left-most options shown in Figure 4-2. For some options a gliding reentry vehicle (RV) is used to increase range, trajectory flexibility, and maneuverability, as illustrated in the two right-most options shown in Figure 4-2. In addition to the terminal accu- racy challenge, these approaches also must solve the serious issues of managing the heat generated when traveling at high speed within the atmosphere. A wide variety of CPGS payloads has also been proposed for use, as illus- 87

88 FIGURE 4-1 Candidate concepts for conventional prompt global strike include ballistic missiles, boost-glide vehicles, and hypersonic cruise missiles. The range of these concepts varies from 1,000 to 3,000 nmi for forward-deployed systems to more than 10,000 nmi for land-based sys- tems. Options are being investigated to attack a range of targets from soft to hard to mobile. NOTE: Acronyms are defined in Appendix A. Figure 4.1, bitmapped, uneditable, color top is portrait size bottom is landscape size if caption is only 1 line

CTM SLGSM CSM-1 CSM-2 • Built on E2 and • Built on Mk 500 RV • Built on AMaRV • Technology being LETB experience experience experience developed in • Small warhead • 300-s TPS • 800-s TPS FALCON program • Error correction • Large warhead • Large warhead • 3,000-s TPS • Limited footprint • Moderate trajectory • Footprint expansion • Large payload with expansion flexibility with RV having dispense capability • Error correction moderate lift-to-drag • Significant footprint • Trajectory flexibility ratio expansion with RV and footprint having high lift-to- expansion with RV drag ratio having moderate lift-to-drag ratio FIGURE 4-2  Illustration of the reentry vehicles (RVs) proposed for different stages of conventional prompt global strike (CPGS) systems. A previously developed modification to ballistic reentry, E2, is the basis for the proposed short-term Conventional Trident Modification (CTM) op- tion. For the ­Submarine-Launched Global Strike Missile (SLGSM), a scaled-up version of the previously developed Mk 500 is the proposed RV, which is designed to have a glide range less than 1,000 nmi. The Conventional Strike Missile (CSM)-1 concept builds on theAMaRV vehicle and is considered to have an 800-second glide segment to its trajectory. The CSM-2 concept builds on a high lift-to-drag (L/D) vehicle, which is be- ing developed by the Defense Advanced Research Projects Agency FALCON program, that has a 3,000-second thermal protection system (TPS). NOTE: AMaRV, advanced maneuvering reentry vehicle; E2, Enhanced Effectiveness (one of two test beds for demonstrating proof-of-principle concepts for ballistic missile delivery in CPGS and discussed in Chapter 4 in the subsection entitled “Guidance, Navigation, and Control Ac- curacy Issues”); LETB, Life Extension Test Bed (the second of two test beds for demonstrating proof-of-principle concepts for ballistic missile delivery in CPGS and discussed in Chapter 4 in the subsection entitled on “Guidance, Navigation, and Control Accuracy Issues”). 89

90 U.S. Conventional Prompt Global Strike trated in Figure 4-3. In the terminal phase of flight, the RV or cruise missile may attack the target with a unitary warhead (which may be designed for penetration), or a warhead that disperses kinetic energy projectiles (KEPs). The reentry vehicle may fly a nominally ballistic flight path with entry angles of less than 30°, or the reentry vehicle may maneuver aerodynamically for vertical attack of the target. Alternatively, the delivery platform may slow sufficiently to deploy existing munitions, sensors, communication relays, or unmanned aerial vehicles (UAVs). The dispensing sequence may occur at low speed following deceleration of a low-β reentry or may be required to occur at supersonic or hypersonic speeds for survivability reasons. The following sections review the CPGS options and technology challenges, including the system requirements, system concepts, research and development (R&D) issues, and technology readiness time lines. Requirements In its most general definition, the mission of a CPGS system is to provide the capability to attack and defeat with conventional weapons a time-sensitive target anywhere in the world. In considering a CPGS capability, one must address the complete end-to-end system-of-systems capability to identify potential targets, determine their geolocation, define attack options, estimate collateral damage, communicate effectively with a decision maker who chooses to go forward with the strike, deconflict flight through air and space domains, engage the target, and assess the impact of the attack. The time required to complete the entire target prosecution time line must lie within the target’s period of vulnerability. A version of the attack time line is shown in Figure 4-4 as consisting of the following phases: Find, Fix, Track, Target, Engage, and Assess (F2T2EA). As illustrated in Figure 4-4, the development of a robust and flexible CPGS capability requires shorten- ing all aspects of the target prosecution time line. With respect to the engagement portion of the F2T2EA process, CPGS options that have the potential to engage a target within 1 hour are being explored. Compression of the time line to the extent required will necessitate seamless integration of disparate systems; development of detailed tactics, techniques, and procedures (TTPs); and personnel training. It appears likely that time lines consistent with the CPGS mission can be achieved, but additional development work will be required. For the near to mid-term, some of the steps will need to have been accomplished in advance of when the 1-hour clock begins. In the mid- to-long term, improved procedures and technology may make it possible that the entire process could be accomplished within the hour under some conditions. In fact, in examining several scenarios and looking at historical cases analogous to what is envisioned (see Chapter 2), the committee found that many of the missions postulated for this capability can largely be preplanned on a contingency basis, reducing the stress on these enabling activities. What cannot be preplanned is the

FIGURE 4-3 The need to attack different types of targets drives a requirement for different terminal-phase maneuvering and warhead charac- teristics. Terminal-phase options for conventional prompt global strike include minimal error corrections to the ballistic trajectory to achieve terminal accuracy, aerodynamic maneuvering for vertical impact to allow attack of buried structures, long-range glide for range extension and Figure 4.3, bitmapped, uneditable, color potential dispensing of munitions, and low-β reentry with deployment of an unmanned aerial vehicle (UAV) for attack of a moving target. top is portrait size NOTE: Acronyms are defined in Appendix A. 91 bottom is landscape size if caption is only 1 line

92 U.S. Conventional Prompt Global Strike Days Find Fix Track Target Engage Assess Today Decide Hours F2T2 E A CPGS Decide FIGURE 4-4 Conventional prompt global strike (CPGS) will require compression of the time line across the entire Find, Fix, Track, Target, Engage, and Assess (F2T2EA) strike process. With strategic warning and preparation, Days key aspects of this process can be ac- complished in advance. For those portions of the process that need to occur inside the compressed time, technical means for seamlessly integrating systems that are currently Find Fix Track Target not interoperable will need to be developed. Engage Assess Today decision and validation time when the contingency actually occurs. The speed of execution time required in CPGS decision and validation, including the time for Decide earlier steps in those limited cases when preplanning has not occurred, exacerbates an already difficult command, control, communications, computers, intelligence, surveillance, and reconnaissance (C4ISR) situation for the U.S. military, as dis- cussed in a recent report of the National Research Council. The “global” requirement for a CPGS system places significant requirements on potential engagement systems, one that the committee concluded should not be taken literally. The “prompt” requirement for a CPGS system also significantly   ational Research Council. 2006. N Hours C4ISR for Future Naval Strike Groups. The National Academies Press, Washington, D.C.   f “global coverage” were free, it would not be an issue, but the committee found, from its own I analysis, that modest restrictions of coverage (e.g., not worrying about a sudden need to fire on Antarctica) would in some cases allow material improvements in payload and more flexibility in A F2T2 E system choice. CPGS Decide

TECHNOLOGY ISSUES 93 impacts the design characteristics of potential engagement systems. In assessing the requirements for CPGS, it is important that the terms “global” and “prompt” be viewed in the context of the realistic time lines associated with gathering and evaluating credible intelligence, surveillance, and reconnaissance (ISR) data, planning of force packages for a precision strike, and the decision process autho- rizing the strike. The range of scenarios considered in this report is intended to illuminate the full spectrum of mission options. The concept of a prompt global strike capability initially evokes ideas involv- ing strategic ballistic missiles—either land- or sea-based—that can deliver pay- loads over enemy defenses to targets 6,000 or more nautical miles away within 30 to 40 minutes of their launch. If one defines the term “global strike” to mean the ability to strike anywhere in the world without depending on basing or overflight rights, but perhaps with foresight in positioning launch platforms, one is led to look at approaches other than intercontinental ballistic delivery. In this approach, “prompt” might be measured from the time of decision or target-cue to the time of weapon effect. That is, preparations and decisions would have been made in advance. A number of technical system options are potentially available for CPGS. Specifically, platforms (e.g., submarines, land-based aircraft, carrier-based air- craft) can be moved forward to an area of interest and can loiter (in some cases covertly) with long persistence—for many days at a time—while the planning and approvals for the force package are proceeding in parallel. These platforms can carry fast-flying shorter-range stand-off weapons that have flight times of 30 minutes or less to arrival on target. Armed remotely piloted vehicles have been employed on several occasions and represent one end of the spectrum of this concept, as does a cruise missile with loiter capability, but both have far less loi- ter endurance than needed and are likely to be detected while they loiter. A naval battle group (with aircraft, cruise missiles, or both) can sometimes run undetected in an area for days or weeks, but it might be observed at any time. In contrast, a nuclear-powered attack submarine (SSN) or a nuclear-powered ballistic missile submarine (SSBN) deployed in a region of interest with medium-range ballistic missiles would meet the criteria of covertness and persistence without significant limitations, if necessary technical capabilities are developed and weapon effec- tiveness is demonstrated. Two other important desirable characteristics are embodied in the CPGS con- cept. One is the need to have a high probability of penetrating defenses and reach- ing the target, and the other is the ability to do this without risking U.S. personnel. These concerns are highest in the leading edge of an attack against a formidable adversary when the adversary’s air defenses have not been suppressed. These considerations favor longer-range ballistic missiles or boost-glide missiles or hypersonic cruise missiles that could be launched from submarines, long-range aircraft, or land bases. Some systems that would launch from CONUS, however, might be constrained by concerns about overflight (e.g., a missile over-

94 U.S. Conventional Prompt Global Strike flying Europe, Russia, or China) and about debris from booster stages (which might, for example, fall into Canada). Whatever scheme is proposed, there are ambiguity issues, potential compromise of other mission capabilities, and inter­ national policy and arms stability questions to be considered (see Chapter 3). In discussing the range requirement for a CPGS system, it is helpful to look at the geography of the world overlaid with range contours and azimuths to and from various locations. The (nonrotating Earth) ranges from the coasts of the United States (where CONUS-based systems may be based) to various parts of the world are shown in Figure 4-5. One can see that a CONUS-based CPGS system must have a range of 6,500 to 7,000 nmi to reach most parts of the world if bal- listic trajectories are flown. If overflight considerations constrain operations, the required range may be as much as 16,000 nmi, since the system may be required to fly the long way around. Figure 4-6 shows ranges from a potential operating region in the Arabian Sea. One can see that a CPGS system operating from this area requires a range of approximately 2,500 to 3,500 nmi to reach most of the troubled regions of the area. With range requirements defined, the speed requirements for candidate con- cepts are shown in Figure 4-7, where the capabilities of existing conventional forces, hypersonic cruise missiles, and ballistic missiles are overlaid on lines of average Mach number (defined as the range divided by the time-to-target and stratospheric sound speed, assumed to be 968 ft/sec). The existing capability for conventional force projection is limited to subsonic speeds. With a 1-hour engage- ment window, this limits the range to approximately 460 nmi. The range-time trade-off for ballistic missiles is also shown in Figure 4-7. In this case, the time-to-target was calculated assuming maximum-range ballis- tic flight for each range. Ballistic missiles can engage targets within the 1-hour engagement window for both forward-deployed and CONUS-based systems. From forward-deployed platforms, ballistic missiles can engage targets in approx- imately 25 minutes, whereas CONUS-based ballistic missiles require a flight time of approximately 40 minutes. Finally, the capabilities of hypersonic cruise missiles are shown correspond- ing to flight at speeds of between Mach 4 and Mach 8. (In this report, the term “hypersonic cruise missiles” will be used to refer to missiles that cruise at speeds at or above Mach 4.) Even hypersonic air-breathing cruise missiles are not capable of deployment from CONUS in the 1-hour engagement window, but they can be deployed from forward-deployed forces with flight times between 30 and 60 minutes.   nless U specifically expressed otherwise, the range contours in this report are presented as nonro- tating Earth ranges.   ach 1 defined in this context as the speed of sound in the stratosphere = 968 ft/sec (or equivalently M 0.159 nmi/sec, or, 1,062 km/hr).

8000 5000 6000 7000 5000 6000 7000 8000 5000 6000 7000 FIGURE 4-5 Sample great circle ranges (nmi) from (left) Kennedy Space Center, Florida, and (right) Vandenberg Air Force Base, California, illustrating the need for 6,500 to 7,000 nmi to reach most parts of the world for a continental United States–based system. Overflight restric- tions can result in significantly longer-range requirements, since the vehicle may be required to travel the long way around the globe. Figure 4.5, editable, color top is portrait size 95 bottom is landscape size

96 U.S. Conventional Prompt Global Strike 3000 2000 FIGURE 4-6 Sample ranges (in nautical miles) from a notional nuclear-powered guided missile submarine (SSGN) launch location in the Arabian Sea illustrating the need for a conventional prompt global strike range capability of 2,500 to 3,500 nmi when launched from an SSGN. Target Figure 4.6, editable, color Types and Information Required The targets sets that are most relevant to CPGS can be divided into three general categories: (1) fixed soft targets (both point and area targets), (2) fixed hard targets (both hardened point targets and deeply buried complexes), and (3) mobile targets or targets with uncertain location. Only the subset of targets within these general categories that are considered to be time-sensitive will be candidates for attack with a CPGS system. Fixed Soft Targets A fixed soft target is one whose geolocation is known with accuracy accept- able for attack, whose location remains constant during the engagement window,

FIGURE 4-7 Flight time versus range for existing subsonic systems, proposed hypersonic cruise missiles, and ballistic missiles. Overlaid are lines of average Mach number, defined as the ratio of block speed (range divided by flight time) to the sound speed at 390 degrees Rankin. For continental United States (CONUS)-based systems, only ballistic missiles are capable of meeting a 1-hour time line. For forward-deployed systems, hypersonic cruise missiles are candidates. 97 Figure 4.7, bitmapped, uneditable, color top is portrait size bottom is landscape size if caption is only 1 line

98 U.S. Conventional Prompt Global Strike and whose construction is sufficiently light that penetrating warheads are not required. Examples include personnel at a fixed location (potentially located in an non-reinforced building or structure), missiles loaded on gantries, and relo- catable systems such as trucks, ships, air defenses, and missile launchers during time periods when they are in fixed positions. A special case of soft targets is the soft large-area case in which a personnel target is known to be in a given area that contains multiple buildings, tents, or vehicles, such as a training camp. If the target’s location within the large area is not determined, then the probability of an effective hit would be reduced, subject to the area of uncertainty and the radius of dispersion of the KEPs. The use of multiple offset weapons would increase the odds of an effective strike, but at the cost of increased collateral damage. For many parts of the world, those where the National Geospatial-Intel- ligence Agency (NGA) has built a Digital Point Positional Data Base (DPPDB), mission planners can geolocate targets within minutes with an accuracy measured in meters once the target has been found. However, if a target lies within an area not covered by a DPPDB, it can take a prolonged period to achieve the accurate geolocation. Greater efforts are needed to speed up this process. Specifically, NGA needs to accelerate the production of the DPPDB to extend its geographic coverage and develop a means to determine rapidly and accurately the geographic coordinates of any visually identified point (e.g., from a recent photo taken in the field) when that point lies outside DPPDB coverage. Whether or not the target lies in an area covered by a DPPDB, a principal additional challenge will often lie in intelligence efforts to find the target and verify the information indicating that a strike is warranted. In summary, the committee has evaluated technical enablers associated with finding and locating fixed, time-sensitive soft targets, as discussed in Chapter 2, and has concluded that some credible scenarios exist where a target could be found and geolocated in a time frame consistent with the CPGS mission. Fixed Hard Point Targets A fixed hard target is one whose geolocation is known with accuracy accept- able for attack and whose hardness or construction is sufficiently strong that a penetrating warhead is required. Examples include buried structures or hardened command-and-control (C2) bunkers and hardened aircraft and missile shelters. The payloads proposed for the earliest versions of a CPGS system have limited capability for seriously damaging such targets, as discussed in the subsec- tion “Weapons Effectiveness,” below. More capability will be available in later versions. Some fixed hardened targets can be identified and geolocated prior to the period when they take on a time-sensitive urgency and some (those that lie in an area covered by a DPPDB) can be quickly geolocated once identified. In summary, the committee evaluated technical enablers for this class of target

TECHNOLOGY ISSUES 99 and determined that, with sufficient planning, the time line associated with the upfront technical portions of the F2T2EA process could in some cases support the CPGS mission. Mobile Targets or Targets with Uncertain Location Both mobile targets and targets whose geolocation accuracy is insufficient to attack with conventional coordinate-seeking weapons present significant chal- lenges to a CPGS system. One type of example includes personnel not known to be in a fixed location such as a particular meeting room (see above for soft large-area targets) or land vehicles and ships that are underway. A second type of example would be mobile intercontinental ballistic missile (ICBM) launchers that move to the field but then sit at poorly known fixed positions when firing weapons. This class of target places significant extra technical requirements on a CPGS system, with different constraints for the two types of example. Three general approaches to overcoming this challenge have been considered in this study (others are possible): (1) continued observation combined with in-flight target updates, a topic not addressed in detail in this study; (2) the deployment of submunitions capable of independent target acquisition and prosecution; or (3) ballistically delivered UAVs with onboard sensors, communications, and weapons and sufficient endurance to search for, acquire, prosecute, and assess damage to targets. The committee believes that development of the capability to attack this class of target is important and that research, development, testing, and evaluation (RDT&E) in this area must continue. Countermeasures All approaches to targeting with CPGS will, of course, be subject to counter- measures, and some of the proposed CPGS options specifically address approaches to deal with countermeasures, such as the use of terrain to protect against attack. Continuing effort against countermeasures will be a military necessity as oppo- nents become aware of CPGS capabilities and adopt tactics such as using terrain well, deception in locating things underground, using large underground facilities, “hiding” among civilians, jamming, decoys, and so on. System Concepts Strike missiles are held by developed military forces the world over. Figure 4-8 plots the range and gross launch weight of existing missiles, together with shaded regions indicating sizing trends related to CPGS. The shaded regions for subsonic and hypersonic cruise missiles and boost-glide vehicles are based on analyses conducted by the committee, which are described later in this chapter.

10,000 s cle 100 s V ehi eM issile lide Cruis st-G onic Boo Subs 1,000 iles Miss ets uise ock ic Cr cR rson llisti Hype Ba Antiship Ramjet Antiship Rocket 100 Antiship Turbine Air-to-Surface Ramjet Range (nmi) Air-to-Surface Rocket l Rockets ica Air-to-Surface Turbine Tact 10 Surface-to-Surface Rocket Surface-to-Surface Turbine Rocket-Powered Missiles 1 1,000 10,000 100,000 1,000,000 Launch Mass (lbm) FIGURE 4-8 Worldwide inventory of missiles. The blue data points represent rocket-powered systems, which can be broadly divided into tactical and long-range ballistic missile domains. The light-blue shaded region designated “Boost-Glide Vehicles” illustrates the range ben- efit of gliding reentry vehicles compared with ballistic missiles. The red data points represent subsonic cruise missiles powered by turbojet engines. The committee considered the potential of larger subsonic cruise missiles, and the red shaded region represents the trend of range Figure 4.8 considered hypersonic cruise missiles. While no strategic hypersonic versus launch mass for subsonic cruise missiles. The committee also Color, editable cruise missiles exist in the world currently, the trend of missile range versus launch mass is also shown. SOURCE: Based on data in Aviation Week and Space Technology Aerospace Source Book 2006, January 16, pp. 184-199.

TECHNOLOGY ISSUES 101 While this presentation of missile capability hides important factors such as war- head weight, number of stages, and launch platform, several interesting trends can be observed. Missiles capable of operation from CONUS (range > 6,500 nmi) are ballistic or boost-glide in nature. For intermediate ranges (2,500 nmi < range < 3,500 nmi), ballistic, boost-glide, and hypersonic cruise missiles are all candidates. A number of engagement system concepts to support the CPGS mission were presented to the committee by both government and industry sources. These systems can be broadly classified as ballistic missiles, boost-glide missiles, and hypersonic cruise missiles. The committee also considered some additional ideas. Of these, one system concept, which the committee refers to as CTM-2, seems quite worthy of more serious consideration, for reasons indicated in Chapter 2. The sections that follow provide brief descriptions of various system concepts. Proposed Systems The USAF Space Command is currently conducting an analysis of alterna- tives (AoA) for CPGS systems. Candidate systems under consideration within the AoA are outlined in Table 4-1. The Conventional Trident Modification is the only system (with the possible exception of CTM-2) capable of near-term deployment. The mid-term option, called the Conventional Strike Missile (CSM), serves as the basis for two alternatives discussed in this report, CSM-1 and CSM-2. Within the AoA, four long-term options are being considered: CONUS-based missile (similar to the committee-proposed CSM-2), forward-based missile, Submarine-Launched Global Strike Missile (SLGSM); and Mach 6 missile. These options are discussed in the subsections below. As discussed below, CTM could also serve as the first step in the evolution- ary development of technology for other high-speed delivery systems that offer additional capability and flexibility. In this development scenario, technology development would begin with a demonstration of the necessary control on lim- ited-maneuverability ballistic reentry vehicles, followed by the development of maneuverable endoatmospheric reentry flight paths of increasing range that would support more flexible and powerful military options. This evolutionary path was suggested in Figure 4-2. The path draws from test trajectories: the Enhanced Effectiveness (E2) test, which is the basis for the proposed CTM; and the Life Extension Test Bed (LETB), which is the basis for the proposed SLGSM and for proposed developments involving longer reentry flight paths, as discussed below in the subsections on SLGSM and CSM-1 systems (see below the subsection on “Guidance, Navigation, and Control Accuracy Issues” for a discussion of the E2 and LETB tests). The final reentry vehicle type shown (designated CSM-2) minimizes the initial ballistic phase and exploits long-range hypersonic glide. This option is discussed in the subsections below on CONUS-based boost-glide missiles and advanced hypersonic weapons.

102 TABLE 4-1 Potential Candidates for Achieving Conventional Prompt Global Strike Capability Used in the Air Force Space Command Analysis of Alternatives (AoA) Near Term Mid-Term Materiel Solutions Examined in PGS AoA (Long Term) Conventional Conventional CONUS Missile Forward-Based SLGSM Mach 6 Missile Trident Strike Missile Missile Modification Projected IOC FY10 FY14/15 FY20 FY20 FY20 FY20 Funded FY08 Demo Program Conceptual Conceptual Conceptual Conceptual President’s Funded FY08 (No funding) (No funding) (No funding) (No funding) Budget President’s Budget Launch Vehicle Trident D-5 Minotaur III Minotaur III Minuteman III Two-stage Solid B-52 Class Booster Class Boostera Class Booster Rocket Booster Payload Modified Mk-4 Biconic Biconic Biconic Biconic Medium Cruise Missile Delivery (68 in.) Hypersonic Glide Hypersonic Hypersonic Re-entry Vehicle (Scram Jet with Vehicle Vehicle Glide Vehicle Glide Vehicle (96 in.) Rocket Booster) (161 in.) (161 in.) (161 in.) Max Range Classified 10,300 nmib 9,000 nmi+ 4,200 nmi 3,500 nmi with 2,000 to 2,800 1,150 lb Payload nmic Payload 1,000 lb 2,000 lb 2,000 lb 2,000 lb 900 lb 1,000 to 2,000 lb Capacity (4 250 Mk-4s)

Payload Modified Mk-4 Biconic Biconic Biconic Biconic Medium Cruise Missile Delivery (68 in.) Hypersonic Glide Hypersonic Hypersonic Re-entry Vehicle (Scram Jet with Vehicle Vehicle Glide Vehicle Glide Vehicle (96 in.) Rocket Booster) (161 in.) (161 in.) (161 in.) Max Range Classified 10,300 nmib 9,000 nmi+ 4,200 nmi 3,500 nmi with 2,000 to 2,800 1,150 lb Payload nmic Payload 1,000 lb 2,000 lb 2,000 lb 2,000 lb 900 lb 1,000 to 2,000 lb Capacity (4 250 Mk-4s) Payload 1.25 ft3 22 ft3 22 ft3 22 ft3 6 ft3 22 ft3 Volume Potential KEP Dispensed Dispensed Dispensed KEP, Unitary Blast Dispensed Payload Munitions, KEP, Munitions, KEP, Munitions, KEP, Fragments or Munitions, KEP, Concepts Penetrator Unitary Blast Unitary Blast Penetrator Unitary Blast Fragments or Fragments or Fragments or Penetrator Penetrator Penetrator NOTE: The mid-term Conventional Strike Missile and long-term CONUS missile concepts are similar to the CSM-1 and CSM-2 in this report. Acronyms are defined in Appendix A. This table, taken from the Air Force’s analysis of alternatives, is shown for comparative information purposes only. The committee’s Table 4.1 configurations and assessments of alternate CPGS systems differ in some cases. aDifferent booster stack from CSM. b18,600 nmi with advanced TPS. cDoes not include B-52 fly-out range extension. SOURCE: Maj. Steven Kravitsky, USAF, Headquarters, Air Force Space Command, “Prompt Global Strike Payload Development,” presentation to the commit- tee, May 11, 2007, Washington, D.C. 103

104 U.S. Conventional Prompt Global Strike Sea-Based Missiles Figure 4-9 shows the time line for near-term and longer-term CPGS system options that could be deployed on a submarine platform. The baseline system is the CTM, which could be fielded by 2011 depending on funding decisions in 2008. CTM-2 (not shown in Figure 4-9) could be a second step in CTM’s evolutionary path, or a first-step development itself. The development and demonstration of technology to meet the performance goals of either of these options would con- tribute to the rapid development of the proposed SLGSM. Conventional Trident Modification CTM is the proposed U.S. Strategic Command (STRATCOM) near-term CPGS solution. It involves an adaptation of the Trident II (D5) missile for 2 of the 24 missile tubes on each SSBN. Each missile would nominally carry four modi- fied Mk4 reentry vehicles. The proposed deployment on the existing SSBN fleet allows the existing infrastructure of crews and training to be used, thus minimizing the costs of deploying the system and giving high confidence in its reliability. The baseline Trident II (D5) is a stellar-navigated, inertially guided ballistic missile with a range of more than 4,000 nmi. Powered by a three-stage solid- rocket propulsion system, the vehicle achieves velocities in excess of 20,000 ft/sec. D5 missiles are carried in each of the 24 launch tubes on the 12 deployed Ohio-class SSBNs, which operate in both the Pacific and Atlantic Oceans. The Trident II (D5) has been deployed for more than 15 years, and extensive end- to-end system testing has shown the system to be extremely reliable, with 117 consecutive successful flight-tests as of this writing. Overall the CTM is proposed as a modification of the baseline Trident system through (1) the replacement of the nuclear warheads with a conventional warhead consisting of dispersable KEPs on two missiles; (2) modification of the Mk4 reen- try bodies through the addition of an aft extension (called a backpack) containing an aerodynamic control system, and a Global Positioning System (GPS) receiver and inertial navigation package to improve accuracy; and (3) modification of the launcher control system and its interface with the missile to allow positive con- trol of mixed nuclear and conventional loads. The existing Trident warheads are unguided after they leave the third-stage “bus.” The KEP warhead is an area weapon capable of attacking soft targets whose position is known with accuracy on the order of meters. The warhead consists of many tungsten rods deployed by an explosive charge to create a relatively uniform dispersion of individual small rods. The technical issues associated with the KEP warhead are described below in the subsection “Weapons Effectiveness.”   he T Navy uses the term “reentry body, or RB” as opposed to “reentry vehicle, or RV.” This report uses both terms interchangeably.

2006 2007 2008 2009 2010 2011 2011 2012 2012 2013 2013 2014 2015 IOC First PGS to CTM (As Proposed) Field SSBN Deploy SLGSM on SSBN (Expand Global Reach) SLIRBM SLIRBM SLIRBM FS BSD Demo SS BSD Demo BSD II Demo Production and Deployed Support IOC to be determined Global Strike Expand SSGN PGS SLGSM SSGN Technology Demo Capability (Notional) Using Existing FBM ALLIANT TECHSYSTEMS Industry/ Navy Team to Raise TRL Deploy SLGSM or Derivative on SSBN(X) Figure 4-9 The prompt global strike (PGS) baseline system is the Conventional Trident Modification (CTM). The submarine-launched intermediate-range ballistic missile (SLIRBM) technology demonstrations in parallel with the CTM technology development provide the basis for subsequent development of the Submarine-Launched Global Strike Missile (SLGSM). NOTE: FS, First Stage; BSD, Booster Sys- tem Demonstration; SS, Second Stage. Remaining acronyms are defined in Appendix A. SOURCE: Office of the Technical Director (Navy), Figure 4.9, editable, color 105 Strategic Systems Programs, provided tolandscape (size if caption is onlyWashington, D.C. the committee on December 18, 2007, 1 line)

106 U.S. Conventional Prompt Global Strike The key vehicle components are the modified reentry body and its integrated backpack for guidance and control. The primary issues in system development are navigation, guidance, and control, and weapon dispersal. The CTM proposal is backed by detailed design, analysis, and flight-testing. Non-nuclear reentry vehicles with the backpack have been flight-tested as described later in the sub- section “Guidance, Navigation, and Control Accuracy Issues,” and KEP payloads have been evaluated in sled tests and other short-range flights at White Sands Missile Range, New Mexico. The backpack contains a GPS-aided inertial guid- ance system and a four-flap aerodynamic control system (derived from the E2 test) for the maneuvering required to achieve the desired terminal accuracy. As discussed below in the subsection “Guidance, Navigation, and Control Accuracy Issues,” testing to be carried out in the CTM development will provide crucial demonstrations of the achievable military utility of the ballistic delivery of con- ventional munitions. If CTM R&D is delayed, it may delay any other CPGS by years because of the need to do careful component-level and full-system-level testing on many more components. Without special precautions, the proposed CTM program would raise the specter of an accidental launch of a nuclear weapon when the intent is to launch a conventional weapon because (1) both kinds of weapons would be carried on the same submarine platform, and (2) prompt global strikes may often allow little time for second checks. The technical issues associated with the nuclear surety of a mixed load were discussed in Chapter 2. CTM with Modifications to Increase Payload Capabilities Reentry Vehicle Modification for Vertical Attack  There are significant advan- tages for the reentry vehicle to maneuver sufficiently at all ranges to be able to dive on the target vertically. This capability is needed to deny an adversary the option of positioning key assets in steep terrain or between structures that might shield them from weapons coming in at ballistic reentry angles, which typically are less than 30 degrees from the local horizontal for long-range ballistic flight. The Navy’s current CTM proposal for initial conventional payloads does not offer this capability at the ranges of interest; however, the LETB test (see also the sub- section “Guidance, Navigation, and Control Accuracy Issues”) illustrated such a capability for a shorter-range application. The configuration tested was a biconic “bent-nose” variant of the baseline CTM payload, a larger variant of which is also the basis for the proposed SLGSM reentry vehicle. For CTM’s longer ranges, this reentry payload would require a thicker heat shield and somewhat larger flaps than the version flight-tested most recently. The bent-nose biconic vehicle with the thicker heat shield is very similar to the Navy Strategic Systems Mk 500 evader maneuvering reentry body (see Figure 4-2), which was flight-tested numerous times on Trident I and on Minuteman missiles during the 1970s. It appears that this would be a minimum-risk development that would defeat an existing tactical

TECHNOLOGY ISSUES 107 countermeasure and that it ought to be evaluated for possible deployment as part of the initial CTM program. A primary difference between this proposed option and the SLGSM reentry vehicle is the size of the warhead that can be carried. A Committee-Proposed Additional CPGS Option: The CTM-2  CTM as proposed is constrained to small conventional payloads primarily for missions against fixed soft targets. Another possibility discussed by the committee is a two-stage Trident configuration (CTM-2), a minimum-modification natural evolution from CTM, with payload volume and weight capacity offering a great deal of flexibility on what can be carried. A basic Trident missile with its third stage and two of its four post-boost control-gas generators removed (a simple modification that would not invalidate the D5’s long test history) could carry a very large single- or multiple- weapon payload as long as it fits under the existing nose fairing or shroud. These modifications would expand the set of CPGS missions that could be effectively performed. This report refers to this two-stage Trident modification as CTM-2. Figure 4-10 illustrates this flexibility, showing as examples that one 3,000 lb penetrator weapon can be carried by a CTM-2 missile to a ballistic range of about 4,000 nmi, and that a 1,500 lb penetrator weapon can be carried to more than Payload Capability 8,000 7,000 6,000 Payload Weight (lb) 5,000 UAV IN LOW β RV 4,000 3,000 (C) 2,000 (B) (A) 1,000 2,000 2,500 3,000 3,500 4,000 4,500 5,000 5,500 6,000 Range (nmi) FIGURE 4-10 Candidate configurations for the committee-proposed Conventional Trident Modification (CTM)-2 illustrating concepts for integrating large payloads on a two-stage Trident missile, and results for range versus payload trade-offs for ballistic flight.

108 U.S. Conventional Prompt Global Strike 5,000 nmi. In order to attack small, hardened buried targets, an earth-penetrator munition weighing on the order of 1,000 lb is required. Housed in a larger ver- sion of the biconic maneuvering RV just described, the total vehicle weighs about 1,500 lb. The maneuvering capability would not only allow this weapon to arrive on target vertically, but by choice of maneuver, the impact velocity could be con- trolled to be the roughly 0.5-1.0 km/sec that is best for penetrator effectiveness. The maneuver used to reduce velocity is typically a pull-up followed by a pull- down to vertical flight. Development issues for guidance, navigation, and control capabilities in this case are more severe than for CTM, as discussed below in the subsection “Guidance, Navigation, and Control Accuracy Issues.” For the biconic vehicle, several hundred additional miles in range and foot- print are achieved by aerodynamic maneuvering to dump energy for best pen- etrator-munition performance. Four CTM KEP warheads also could be carried to the same range. On a longer development timescale, a ballistically delivered armed UAV with a half-hour endurance and its own search-and-target-acquisition capability could be developed with a gross weight of less than 3,000 lb, enabling mobile targets to be held at risk. This concept is discussed along with dispensed munitions later in this chapter. While this CPGS option was not proposed by the Navy, the committee views the two-stage conventional Trident CTM-2 as an interesting evolutionary approach to CPGS because it may allow relatively early introduction (i.e., 2 years after CTM), and it has great payload flexibility and growth potential. It might or might not be different enough from the traditional three-stage Trident missile to satisfactorily address the ambiguity problem that some have been concerned about (see Chapter 3). Submarine-Launched Global Strike Missile For the longer-term CPGS role, the Navy proposes a small new, single- warhead, two-stage missile known as the Submarine-Launched Global Strike Missile, or SLGSM. The SLGSM is an intermediate-range ballistic missile that would be launched primarily from forward-deployed SSGN platforms and also, to increase geographic coverage, from SSBNs. The SSGNs are four Ohio-class submarines that were modified in ways that prevent carriage of the D5 missile. SSGN missions currently focus on Special Operations Forces and strike using Tomahawk missiles. The SLGSM concept involves the development of a new, two-stage solid-rocket propulsion system which, together with a reentry vehicle capable of a limited amount of gliding, is planned to deliver a 1,000-lb-class warhead to ranges in excess of 3,000 nmi. The missiles are sized such that two or   wo T 1,500 lb weapons could in principle be carried to 4,000 nmi but would require irreversible structural changes to the base frame of the missile, making this a less flexible option.

TECHNOLOGY ISSUES 109 three SLGSMs could be held in a multiple all-up-round canister (MAC) within a single SSGN launch tube. Once the technical solutions developed for the CTM have been tested, the more substantial investment needed to develop a more powerful CPGS system can be evaluated. A submarine-launched system allows global strike to be achieved with a smaller required delivery range and thus a less powerful ballistic launch motor. The correspondingly slower reentry speed results in a less-stressing lift into a glide path that allows long-range steering, as demonstrated for the LETB (see the subsection below titled “Guidance, Navigation, and Control Accuracy Issues”) and envisioned for all the more-advanced delivery systems. Thus, the development path shown in Figure 4-9 for the SLGSM has strong feasibility of concept. The specific plan for the SLGSM is to achieve greater military utility by providing a prompt strike capability from forward-based naval platforms, spe- cifically SSGNs, allowing larger payloads compared to those of the CTM and a more flexible terminal trajectory through the use of a reentry vehicle with a moderate lift-to-drag ratio. The system requires the development of a new missile, including new solid-propellant booster motors and scaled derivatives of existing reentry vehicles. Rocket motor technology consistent with a shorter-range sub- marine-launched, intermediate-range ballistic missile (SLIRBM) has undergone two static firing tests (the SLIRBM demonstrations illustrated in Figure 4-9). The terminal maneuverability and accuracy will be effected with a medium-lift reentry vehicle, which is a scale-up of the LETB-tested bent-nose design, as illustrated in Figure 4-11, and is envisioned to provide the flexibility to contain different types of warheads. Experience from testing of the CTM reentry body will be important in the final development of SLGSM’s RV. For SLGSM’s RVs, the challenges of pull-up into the glide path and thermal management during the glide are much less than those of the longer-range sys- tems. Because similar boost stages and the payload have been tested for a similar concept, the committee considers that planning for SLGSM is a useful path in the evolution of technical capabilities beyond the CTM. Range, Payload, and Size Trade-offs The committee has concerns about two aspects of the Navy’s current concept for the SLGSM. First, it has a slenderness (length to diameter) ratio substantially greater than that of any existing underwa- ter-launched vehicle. Second, it is planned to house two per SSGN tube, while the committee recommends that there be three per tube to increase firepower. The Navy’s current concept for SLGSM has a 38-inch-diameter missile with a slenderness ratio substantially greater than 12. The committee is concerned that a missile so long and slender may be subject to excessive bending stress as it leaves the tube of a submarine underway and enters the cross-flowing water. Shortening the missile would reduce its range for a given diameter. Figure 4-12 shows the results of independent missile simulations done by this committee, constraining the length-to-diameter ratio to 12. The figure shows payload versus range for

110 U.S. Conventional Prompt Global Strike FIGURE 4-11 Relationship of the proposed Conventional Trident Modification (CTM) and Submarine-Launched Global Strike Missile (SLGSM) reentry bodies to the tested Enhanced Effectiveness (E2) Test Bed and Life Extension Test Bed (LETB) designs. The larger SLGSM would allow larger and more diverse payloads. SOURCE: Office of the Technical Director (Navy), Strategic Systems Programs, provided to the committee on December 18, 2007, Washington, D.C. two- and three-stage missiles of different diameters and propellant classes. In its proposed two-stage configuration, when limited to length-to-diameter ratio of 12, a 38-inch-diameter SLGSM can carry a 1,500 lb payload to a ballistic range on the order of 2,000 nmi. The maneuvering biconic reentry vehicle can extend that range several hundred miles as it dissipates velocity. Since this range appears adequate for CPGS, the committee recommends that the Navy’s Strategic Systems Programs (SSP) Office conduct a careful analysis of structural bending loads dur- ing launch before exceeding a slenderness ratio of 12 in the SLGSM design. Shown in parentheses in Figure 4-12 is the number of missiles of each size that fit in a MAC in an SSGN tube. Three 38-inch-diameter SLGSM mis- siles should fit in each launch tube if the MAC for SLGSM is designed for the depth-charge shock levels currently used for Trident in SSBNs. (The MAC used in SSGNs with Tomahawk missiles is designed to a greater shock-mitigation requirement.) The committee believes that the 50 percent increase in firepower

2,500 2,000 1,500 1,000 Payload (lb) g h e d 500 c f b a 0 500 1,500 2,500 3,500 4,500 5,500 6,500 Range (nmi) a 33 Stg 34" x3434(4) (4) a Stg 34" x ft ft e 22 Stg 34"xx34ft (4)(4) e Stg 34" 34 ft b 33 Stg 21" x 21 ft (9) b Stg21x21 (9) -a f 33 Stg 30" x 30(5) (5) f Stg 30"x30 ft ft 3 Stg 27"" x 27 ft 140s c 3 Stg 27“ 27 ft 140s (7) (7) g 2Stg27"x27ft"100s (7) 100s (7) g 2 Stg 27" x 27 ft d 3 Stg 38"x38ft (3) (3) d 3 Stg 38 " x 38 ft h 2Stg 38"x38ft (3)38 ft (3) h 2 Stg 38" x FIGURE 4-12 Payload versus ballistic range capability for notional two- and three-stage Submarine-Launched Global Strike Missile (SLGSM) configurations. All vehicles are constrained to a length-to-diameter ratio of 12. The number in parentheses indicates the number of missiles that can fit in a single launch tube of a nuclear-powered guided missile submarine. 111 Figure 4.12 landscape,editable color

112 U.S. Conventional Prompt Global Strike is important enough to consider a reduction in the shock specifications, and the committee recommends that SSP look carefully at this issue. The committee is concerned that the DOD’s current plans for CPGS may be too sanguine in terms of its predictions of target geolocation accuracy, weapon delivery accuracy, and lethality of weapons. To some degree, these concerns could be addressed by carrying three missiles per tube and firing a patterned laydown. Figure 4-12 explores these possibilities. Figure 4-12 also shows that the same missiles with a third stage added can carry a smaller Mk 5 RV delivering about 700 lb of throw weight to a range of at least 5,500 nmi. SLGSM design is driven by many factors that the committee cannot, of course, examine in adequate depth. It recommends that the Navy continue to explore the trade-offs that Figure 4-12 addresses. Land-Based Missiles The long history of U.S. nuclear-armed land-based ballistic missile programs provides a solid foundation for land-based CPGS concepts. These concepts can be divided into conventional ballistic missiles and boost-glide missiles, which can be CONUS-based or forward-deployed. This section discusses current Ser- vice programs, alternative concepts under active study, and other possible system concepts that come immediately to mind but are not being pursued, together with the reasons why. Conventional Ballistic Missile: Conventional Minuteman Just as the Navy has proposed to develop a Conventional Trident Modifica- tion, the U.S. Air Force could develop a Conventional Minuteman Modification (CMM). Warhead technology the Navy is developing for CTM could be applied as well to Minuteman, drawing on the several hundred boosters available in stor- age. Land-basing would avoid whatever additional risks to the nation’s nuclear deterrence capability are engendered by mixed loads on SSBNs. Similar to CTM, this CMM concept would be effective against a limited class of targets and would be indistinguishable from its nuclear-armed progenitor externally and in-flight. In the committee’s opinion, even if consensus were to emerge suddenly on the desir- ability of this CMM concept, it would probably take several years longer to field than would CTM because of real-world issues relating to the current-day status of programs, organizations, authorization delays, and other factors. A new land-based conventionally armed ballistic missile could be developed with a more capable warhead, evolving later to even greater capabilities, as is the case for sea-launched concepts discussed above. However, it would have the basing and arms agreement issues discussed in Chapter 3. It also would have no significant performance advantage over a sea-launched missile, with the excep- tion of potentially being able to deliver a larger warhead, which could increase

TECHNOLOGY ISSUES 113 effectiveness against some buried targets—although the relative ease with which facilities can be deeply buried makes this a losing game. Gauging the balance of its advantages and disadvantages, the U.S. Air Force has decided not to pursue the development of a purely ballistic land-based con- ventionally armed ballistic missile, and the committee supports the Air Force’s decision, as discussed in Appendix I. Boost-Glide Missiles: Conventional Strike Missile and Advanced Hypersonic Weapon A proposed alternative to a conventional ballistic missile is a (hypersonic) boost-glide vehicle—here a rocket is used to boost to high speed an aerodynami- cally controlled glide vehicle that maneuvers to the target. Concepts in which the initial phase of flight includes a ballistic segment have been proposed, while other concepts fly entirely endoatmospheric trajectories. Following apogee, the glide vehicle descends into the atmosphere where a pull-up maneuver is executed to position the vehicle on an equilibrium glide slope. The vehicle then glides unpowered to the target area. Both CONUS-based and forward-deployed boost- glide vehicles have been proposed. Compared with forward-deployed systems, prompt strike from within the CONUS requires a larger rocket and results in a flatter reentry angle and higher reentry speeds. The larger systems allow larger payloads than those that could be carried by CTM or SLGSM; however, the higher reentry speed renders more difficult the control, guidance, and navigation needed for accurate targeting, and the long exposure to high heat flux complicates thermal management. Nevertheless, developing a longer-range glide capability for the reentry vehicle in the form of a 161-inch boost-glide vehicle (larger than the modification proposed for the SLGSM) is the basis for the land-based options listed in Table 4-1. Additional details on the proposed boost-glide systems are provided below. The reader is also referred to Appendix G for additional details on the characteristics of the boost-glide trajectory. CONUS-Based Boost-Glide Vehicle: Conventional Strike Missile  The primary concept for a CONUS-based Conventional Strike Missile is based on a modified ballistic launch vehicle together with a scaled version of the advanced maneuver- ing reentry vehicle (AMaRV). The CSM concept uses a Minotaur III-class booster, a configuration using no longer operationally deployed Peacekeeper rocket motors. The reentry vehicle will have capabilities for pull-up and hypersonic glide similar to those proposed for SLGSM, but at much higher reentry speeds and for much longer times in the atmosphere. The Air Force has programmed $477.7 million over the period FY 2008 to FY 2013 to develop and demonstrate CSM in three flight-tests, as illustrated in Figure 4-13. The weapon system is proposed to be based at Vandenberg Air Force Base, California, and Cape Canaveral Air Force Base, Florida (pending resolution of

Activity Name 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 114 CSM Demonstration Program System definition Weapon Weapon Demo Demo Demo Risk reduction demonstrations MTD-1P Flight 3 Demo-1 Demo-2 Flight 1 Flight 2 System design, development, integration Vandenberg site preparation Conventional Payload Delivery Vehicle Technology Development • Guidance • Payload Dispensing • Nose Tip • Flight Control Technologies • Thermal protection/nose/flaps • Flaps FALCON Demonstration Program Initial weapons work focuses on CSM Aerodynamic hypersonic performance dispensing of “seeker/sensor” payloads Advanced GN&C Demo Demo Thermal protection } Flight Flight In-flight 2-way communications AFSPC Funding ($M) 13.81 9.0 30.1 44.5 83.0 84.2 86.1 1 Congressional Plus Up Demo Location Description Demo Location Description Weapon Demo -1 Eglin AFB BLU-108 weapon software qualification Demo Flight 1 Vandenberg Assess vehicle control/instrumented submunition control/instrumented submunition Weapon Demo -2 Eglin AFB BLU-108 lethality demo Demo Flight 2 Vandenberg Demonstrate 800 second flight/BLU -108 dispense flight/BLU-108 dispense MTD -1P White Sands BLU-108 dispense/environment demo Demo Flight 3 Vandenberg Demo advanced thermal protection/global reach FIGURE 4-13 The focus of the Conventional Strike Missile (CSM) Technology Demonstration Plan is on early weapons demonstrations to test the dispensing of existing off-the-shelf munitions, to address environmental testing and weapon requalification, with a priority given to “seeker/sensor”-type weapons that may address target location error4.13 collateral damage issues. Ongoing research on thermal protection, Figure and guidance, navigation, and control, and in-flight communication will feed into later planned flight demonstrations. NOTE: Acronyms are defined landscape,editable in Appendix A. SOURCE: Maj. Steven Kravitsky, USAF, Headquarters, Air Force Space Command, “Prompt Global Strike Payload Develop- color ment,” presentation to the committee, May 11, 2007, Washington, D.C.

TECHNOLOGY ISSUES 115 treaty issues), and to be capable of delivering KEP and penetrator warheads and many of the Service’s air-launched weapons. The CSM’s ability to alter its trajec- tory significantly would reduce overflight issues, enable significant cross-range diverting capability for in-flight retargeting, and permit tailoring the end-game approach angle for improved weapon system effectiveness. The CSM concept pushes the performance envelope in the areas of thermal protection systems and air-launched weapon dispensing mechanisms. While a ballistic reentry body typically spends less than 60 seconds in the oxidative hyper- sonic environment, the first version of CSM is proposed to fly in it for about 800 seconds, stressing current technology. A planned second version of CSM would increase the maximum glide range to 9,000 nmi, which would require the devel- opment of new thermal protection technology to operate for up to 3,000 seconds in the stressing hypersonic environment. The CPGS AoA is modeling hypersonic boost-glide vehicles as slowing to Mach 5 to dispense their weapons. This speed seems at the same time aggressively high for dispensing and questionably low for surviving strong local air defenses. These technical risks are discussed in more detail below, along with a description of the Defense Advanced Research Proj- ects Agency (DARPA) Force Application and Launch from CONUS (FALCON) Program that CSM is intended to leverage. In the committee’s view, the CSM effort planned and funded by the U.S. Air Force is optimistic for a program intended to result in a highly reliable, highly effective presidential-release weapon. In the committee’s judgment, a prudently scheduled, well-funded program with adequate testing would have an initial operational capability (IOC) of about 2017 for an initial version of CSM (which is referred to in this report as CSM-1) that has an 800-second glide phase and is capable of delivering either KEP or penetrator warheads, and an IOC of about 2022 for a second version (referred to in this report as CSM-2) that is proposed to have a 3,000-second glide phase and to be capable of dispensing a wide variety of air-launched weapons at high speed or delivery of KEP or penetrator warheads. Forward-Deployed Boost-Glide Missiles: Advanced Hypersonic Weapon  An- other design concept examined by the U.S. Army is a shorter-range but forward- based endoatmospheric hypersonic boost-glide vehicle, sometimes called the Advanced Hypersonic Weapon (AHW). It would have a range of approximately 4,200 nmi and could be based in Guam, at Diego Garcia in the Indian Ocean, and in Puerto Rico, with four missiles available at each launch site. The Army Space and Missile Defense Command in Huntsville, Alabama, received additional congressional funding of $1.6 million in FY 2006 and $8.9 million in FY 2007 to do technology studies to support a similar weapon concept, but the Army has not programmed substantial out-year funds for serious weapon

116 U.S. Conventional Prompt Global Strike system development. Army officials informed the committee that technology developed in this effort would flow into the Air Force’s CSM program. Hypersonic Cruise Missiles In addition to ballistic and boost-glide missiles, hypersonic cruise missiles launched from submarines, surface ships, or aircraft potentially offer capability for the CPGS mission. In concept, these systems consist of two stages: the first- stage rocket-powered and the second stage powered by an air-breathing ramjet or scramjet (i.e., supersonic combustion ramjet) engine. The advantage of the cruise missile is that the air-breathing engine uses oxygen from the atmosphere instead of carrying an oxidizer, allowing for a mis- sile capable of large speed variation and diverting maneuvers, flexible approach to the target area, and the ability to control the trajectory for the deployment of submunitions, with potential for loitering and searching for mobile targets. One disadvantage is the relative immaturity of the air-breathing propulsion technology for missiles operating at speeds above Mach 4. Propulsion technology issues and readiness levels are discussed more completely below. At present, cruise missiles such as the Tomahawk and conventional air- launched cruise missile (CALCM) are limited to subsonic speeds, with ranges of approximately 1,000 to 2,000 nmi (see the data presented in Figure 4-8). Figure 4-14 shows the results of independent calculations done by the committee on the characteristics of long-range subsonic and hypersonic cruise missiles. The poten- tial performance variation is bounded on the lower end with an assumption that aerodynamic and propulsion efficiency remains constant with increasing missile size and on the upper end by an assumption that aerodynamic and propulsion efficiencies will increase with increasing missile size. For the lower performance numbers, the baseline engine and aerodynamic performance are constant with increasing missile diameter and consistent with those obtained from flight and laboratory tests for short-range tactical missiles. The upper curves account for potential performance improvements that can be realized for larger-scale flight vehicles. In these curves, the assumed improvement in aerodynamic efficiency is a 67 percent increase in the vehicle lift-to-drag ratio (increasing from 12 to 20 for subsonic missiles and from 3 to 5 for hypersonic missiles) over the range of missile diameters considered. This increase is consistent with the incorpora- tion of larger, more efficient lifting surfaces on the larger missile. The assumed improvement in propulsion efficiency is a 33 percent improvement in engine specific impulse over the range of missile diameters considered. This improve- ment consists of an assumed increase from 2,656 seconds to 3,600 seconds for   Col Paul Gydesen, USAF, Chief, Deterrence and Strike Division, Plans and Requirements Director- ate, U.S. Air Force Space Command, discussion with the committee, February 23, 2007, Washington, D.C.

TECHNOLOGY ISSUES 117 Range (nmi) Missile Diameter (in.) Range (nmi) Missile Diameter (in.) FIGURE 4-14 The impact of missile diameter and payload on range of notional (a) subsonic and (b) hypersonic cruise missiles. The solid curves are based on flight- or laboratory- demonstrated aerodynamic and propulsion technology. The dashed curves illustrate the potential performance improvements that result from potential aerodynamic and propulsion efficiency gains. NOTE: TFSC, thrust specific fuel consumption. Figure 4.14, bitmapped, uneditable, color subsonic missiles. For hypersonic missiles, the engine specific impulse varies with speed, and the 33 percent improvement in specific impulse was applied as a scale factor across the speed range to account for the anticipated performance improve- ment associated with larger engines. When designed to constraints of the Vertical Launch System carried on surface ships, a hypersonic cruise missile would have

118 U.S. Conventional Prompt Global Strike a maximum range of approximately 1,000 nmi if operated at a cruise speed of Mach 4. While this range is much shorter than that envisioned for a CPGS system, this capability could become an important element of a future tactical system if routinely installed on forward-deployed ships and submarines. The possibility of employing hypersonic cruise missiles from the SSGN platform also provides an interesting potential. In designing the cruise missile for integration into an SSGN canister, the missile cross-sectional shape will likely not be circular, but rather designed to fit within a pie-segment of the cylindrical launcher. In this case, a larger effective missile diameter can be achieved. If the SSGN launch tubes are modified to hold three hypersonic cruise missiles, calcula- tions indicate that the powered range of the missile would be greater than 2,000 nmi (i.e., roughly the same range capability of a submarine-launched, intermedi- ate-range ballistic missile). Air-launched, hypersonic cruise missiles have been proposed in order to satisfy the demands of the CPGS mission (see Mach 6 Missile in Table 4-1). Launched from a bomber, the cruise missile would be a two-stage system consist- ing of a solid-rocket-powered first stage and a second-stage air-breathing cruise vehicle powered by either a ramjet or a scramjet engine. The air-launched missile would be capable of carrying a 2,000 lb warhead to a range of approximately 2,000 nmi. The air-breathing propulsion system would offer advantages in terms of trajectory flexibility and energy management, allowing for in-flight rerouting, avoiding overflight, and optimizing the terminal approach geometry. Thermal management issues associated with hypersonic cruise missiles are quite different from those involving ballistic or boost-glide systems. Operating at a maximum speed of Mach 6, the heat transfer to the external air vehicle is substantially lower than that of reentry vehicles, and metallic structures can be used. In the internal portion of the flow-path, either high-temperature ceramic- matrix composites or fuel-cooled metallic structures can be used. Thus, many of the issues associated with ablative thermal protection systems, which are required for ballistic and boost-glide systems, are avoided. Research and Development Issues To varying degrees, the CPGS concepts described above share challenges associated with reliably operating in an extremely stressing and unforgiving environment. In the following subsections, several of the most important technol- ogy issues are described and discussed. But first a few comments on operating environment are needed. The first concerns the characteristics of ballistic reentry. One of the principal design factors is called the ballistic coefficient, β, which is defined as follows: W β= CD A

TECHNOLOGY ISSUES 119 where W is the weight of the reentry vehicle, CD is the drag coefficient, and A is the cross-sectional area. Manned reentry vehicles typically operate with a low β, such that the reentry vehicle slows significantly in the upper portion of the atmosphere where the blunt vehicle shapes produce strong shock waves with sig- nificant energy dissipation through heating of the atmosphere, which minimizes the overall thermal challenge to the vehicle. This type of reentry was used in the Apollo program and the early photo reconnaissance missions. Low-β reentry could be useful in a CPGS mission context for concepts that deploy munitions or ISR assets, as discussed earlier. Ballistic missile reentry vehicles are typically designed with a high β so that the reentry vehicle plunges into the deep atmosphere at high speeds. This makes defense very difficult (which was an early consideration in the development of ballistic missiles) and enables high accuracies with unguided RVs because of the short atmospheric transit time and resulting small drift in the inertial naviga- tion system. The high-β reentry leads to an increased heat transfer, and thus the requirement for a robust thermal protection system. A CONUS-based ballistic missile with a range of 7,500 nmi has a reentry speed of approximately 24,640 ft/sec. A forward-deployed ballistic missile with a range of 2,500 nmi has a reentry speed of approximately 18,300 ft/sec. While this velocity difference may not appear overly large, one must note that the kinetic energy is proportional to the velocity squared, so that the shorter-range reentry vehicle enters the atmosphere with a kinetic energy that is approximately 45 percent lower than that of the long-range system. This difference in entry kinetic energy results in significant differences in the stress placed on the thermal protec- tion and guidance, navigation, and control systems. Thermal Protection System Conventional Approaches Existing high-β ballistic reentry vehicles are designed with thermal protection systems (TPSs) that use ablative materials to survive an extremely high-heat-flux environment for the short reentry times. Modern reentry vehicles use a shape- stable carbon material nosetip with a carbon-phenolic heat shield for thermal protection downstream of the nosetip. Through extensive development and testing, carbon-phenolic material has proven to be the best choice based on its density, ablation characteristics, and relatively low thermal conductivity. The CTM, SLGSM, and the initial variant of CSM are all based on exist- ing TPS technology and existing thermal design and analysis techniques. Only CTM uses the existing TPS materials in the manner for which they were origi- nally developed (i.e., in a ballistic reentry mode with minimal endoatmospheric maneuvering). CSM-1, and to a much lesser degree SLGSM, uses existing TPS

120 U.S. Conventional Prompt Global Strike technology in a boost-glide trajectory in which the TPS is exposed to the environ- ment for longer time periods than for conventional ballistic RVs. As discussed above, SLGSM is an intermediate-range missile that delivers its RV on a conventional ballistic trajectory. Its Maneuverable RV (MaRV) is similar to the Mk 500 MaRV, which was developed and tested at much longer ranges for glides, error correction, and desired terminal conditions. While it therefore must dissipate less heat input and has a shorter soak time (atmospheric flight) than long-range CONUS-based concepts, the soak time effects must be tested. (If that payload were also used for CTM-2, it would need to be capable of handling total heating and soak times closer to the CONUS-based CSM-1 requirement if a gliding trajectory was flown.) This longer exposure time introduces uncertainties in the TPS performance due to the potential for nonlinear coupling of the body shape changes with aerothermodynamics, especially with respect to uncertainty in the prediction of aerodynamic boundary layer transition. Application of existing TPS technology to SLGSM and CSM-1 concepts will need to be fully evaluated as part of the RDT&E associated with these systems. Thermal protection issues must also be addressed in designing for weapons effectiveness. Penetrating warheads are limited by structural considerations to impact speeds of approximately 1 km/sec. Thus, ballistic and boost-glide delivery systems must be operated in such a manner that the kinetic energy of the warhead is dissipated sufficiently prior to impact. For the dispersal of dispensed muni- tions or UAVs, even slower final speeds may be necessary. For CONUS-based global range systems that reenter at 7.9 km/sec, 30.7 MJ/kg of kinetic energy must be dissipated if the impact speed is limited to 1 km/sec. For high-β reentry vehicles, the slender aerodynamic shapes result in minimal heating of the atmo- sphere, with most of this dissipated energy entering the vehicle prior to being released as radiation cooling or ablation products. For a shorter-range SLGSM or forward-deployed land-based boost-glide system with an initial glide velocity of approximately 6 km/sec, the kinetic energy to be dissipated is approximately 17.5 MJ/kg. Advanced Thermal Protection System Concepts The development of a capability for extremely long range glide vehicles, as envisioned in the advanced CSM-2 concept, will require the development of a novel thermal protection system capable of operating at hypersonic speed in the atmosphere for times up to 3,000 seconds. With the RV based on carbon-carbon (C/C) material rather than carbon-phenolic material, the aim is to develop an integrated TPS system with a shape-stable nosetip, an acceptable ablation rate over the flight trajectory, and minimal heat transfer to the internal portion of the reentry vehicle. Numerous technical challenges exist with the development of this type of thermal protection system, including the development of techniques for the accu-

TECHNOLOGY ISSUES 121 rate prediction of aerothermodynamic loads and ablation rates, manufacturing processes for the production of large-scale C/C aerostructures, and insulation for the protection of internal components. The challenges associated with the development of a 3,000-second TPS system have been undertaken by the DARPA FALCON Program. In this effort, two hypersonic test vehicles (HTVs) will be flown between Vandenberg Air Force Base and Kwajalein Atoll (location of the U.S. Army’s Reagan Test Site) to demonstrate the performance of a long-duration TPS (as well as demonstrating guidance, navigation, and control accuracy and in-flight communications). The flights are scheduled for 2009 and 2010, so early information on the performance of this new class of TPS will be available to support decisions on the development of long-range systems. Guidance, Navigation, and Control Accuracy Issues As noted earlier, ballistic missile delivery systems were developed for nuclear weapons delivery for which, owing to the large damage area of the weapon, achieving the required accuracy in the placement of the weapon is relatively easy to accomplish. In contrast, for conventional weapons, accuracy of placement (technically referred to in terms of the circular error probable [CEP] or spheri- cal error probable [SEP]) is essential in order to obtain the desired effects on the target. Obtaining this increased delivery accuracy is a key technological challenge in developing a conventional prompt global strike capability. Obtaining high delivery accuracy for a ballistic missile requires that the reentry vehicle be steerable. Because the vehicle is moving extremely rapidly and thus spends a relatively short time within the atmosphere, controlled steering to the desired target is technically challenging. Preliminary design solutions have been field-tested, specifically using modified Mk4 reentry bodies, and serve as the “proof of principle” for the proposals for ballistic missile delivery in CPGS. The two field-tests were the submarine-launched E2 Test Bed and the LETB (see Figure 4-11). The E2 evaluation was conducted in October 2002 using a D5 missile. The modified Mk4 reentry body had an added flap actuator system for control and a GPS-aided Inertial Navigation System (INS). During a substantial part of reentry, GPS reception was lost owing to a plasma-induced blackout. Nevertheless, the flaps deployed and operated as predicted to provide three-axis flight control (roll, yaw, and pitch). Under flap control, the reentry body (RB; see footnote 5, above) was able to turn to its target, and guidance and control were sufficient to steer the RB to the target within several meters of the onboard navigation solution. In other words, the RB came within several meters of where the navigation system calculated that the target was located. There was, however, a large navigational error, so that the actual impact point was well off the target. The correction for the navigational error is expected to be technically feasible. Design analysis has

122 U.S. Conventional Prompt Global Strike been performed which indicates that a properly integrated GPS/INS, incorporating accurate alignment initialization (and, probably, adaptive control algorithms), will make it possible to reduce navigational errors to GPS-like accuracy. The LETB modification to the Mk4 included, in addition to the flaps, a 2 degree offset biconic nose for extended range and added flight stability and maneuverability. The navigation system was similar to that flown in E2. During the terminal phase of the trajectory, the RB executed a pitch-up maneuver, divert- ing the RB an additional 25,000 feet downrange from the ballistic impact point and turning to its selected target. A 3-second loss of GPS reception of most satel- lites was attributed to a failure to maintain lock on the carrier during the high-g pitch-up maneuver. As discussed in the following subsection, it is believed that this problem can be addressed by using newer technologies able to withstand the effects of maneuvers up to 40 g’s. The proposed CPGS ballistic delivery systems build on these earlier results, as illustrated in Figure 4-2. As has been discussed, the simplest proposal is the CTM, which builds on the E2 results to allow fine control of targeting around the normal ballistic reentry trajectory. The longer-term proposals would include extended reentry trajectories enabled by the adaptation of the biconic nose design used in the LETB. Thus, resolving the issues regarding guidance, navigation, and control that were demonstrated in the E2 and LETB tests remains a crucial step in establishing the feasibility and military utility of the proposed systems for CPGS. GPS/INS Navigation To achieve weapons effectiveness in all of the intended use-cases, strike accu- racy within a few meters in each dimension is needed. Reducing miss distance to this level is a sizable challenge given the numerous sources of error (target loca- tion, guidance, navigation, and control) that contribute to it. Here the navigation error is addressed, that is, the terms in the error budget that relate to the knowledge of position, velocity, acceleration, and attitude of a delivery vehicle under naviga- tion with a combined GPS/INS. Both GPS and INS have strengths and weaknesses. The main advantage of GPS is that it provides positional data with considerable accuracy and bounded errors; however, it is susceptible to loss of signal. GPS uses a low-power signal that makes it fairly easy to compromise reception. Plasma formation, loss of carrier lock during maneuvers, and jamming are each capable of compromis- ing reception for CPGS applications. An INS offers precision navigational data (acceleration, velocity, position, and attitude) in real time based on the gyroscopic inertial measurement unit (IMU), and it is far more resistant to denied service than GPS is. Thus, IMU can provide precision navigation in the vicinity of the ground target in the presence of GPS jamming or GPS blackout due to plasma sheath attenuation. An INS tends to accumulate errors over time, but feedback of

TECHNOLOGY ISSUES 123 accurate position from GPS can provide the needed corrections. Thus, the respec- tive strengths of GPS and INS are complementary. When combined into a tightly integrated GPS/INS system, the shortcomings of either component operating individually are better managed. Early versions of GPS/INS have suffered from susceptibility to loss of lock on the carrier loops during large-g maneuvers. However, integrated systems are now guaranteeing service at up to 40 g’s. Within this limitation, which is reported to be manageable for CTM, present GPS/INS systems, properly implemented, are sufficient to guarantee navigational accuracy currently measured in meters, with continuing improvements in capability likely to be available. For the larger reentry vehicles, faster reentry speeds, or more stressing envi- ronment of highly maneuverable vehicles, the issues of maintaining GPS/INS lock will have to be addressed again. Similar issues will also arise for energy dissipation maneuvers prior to the release of penetrating warheads, dispensed munitions, or UAVs (see below). Energy dissipation maneuvers can be performed by the reentry vehicles, but acceleration-sensitive drifts in the IMU may impact accuracy. A complete assessment of the accuracy associated with such maneuvers will be required on a case-by-case basis. Guidance and Control Given the likelihood that GPS/INS solutions are sufficient for the require- ments of CTM, the precision and accuracy of the aerodynamic response of the RV to guidance and control information are crucial to achieving delivery accuracy. Engineering analyses of proposed design for the CTM reentry vehicle have been performed; they indicate that achieving the control necessary for the required few-meter accuracy is feasible, if all systems perform at their expected technical capability.10 Thus it is essential that flight-tests planned for CTM be carried out and that they be designed to demonstrate RV-delivery accuracy (e.g., relative to a specific target of known absolute GPS coordinates) and the factors contributing to the miss distances. The results from these tests will serve as essential information for design decisions in the more-advanced proposed systems concepts.   APT Terry J. Benedict, USN, Technical Director, U.S. Navy Strategic Systems Programs, “CTM C Brief to NAS (U),” presentation to the committee, February 23, 2007, Washington, D.C. (classi- fied).   JASON Study for STRATCOM on Prompt Global Conventional Strike,” JSR-05-450, July 29, “ 2005, presentation to the Defense Science Board, January 2007, Washington, D.C. (This document contains other restricted/controlled unclassified information as described in 5 U.S.C. 552(b).) 10 CAPT Terry J. Benedict, USN, Technical Director, U.S. Navy Strategic Systems Programs, “CTM Brief to NAS (U),” presentation to the committee, February 23, 2007, Washington, D.C. (classified).

124 U.S. Conventional Prompt Global Strike Munitions and Sensor Deployment The technical demands on guidance, navigation, and control for high terminal accuracy of the reentry vehicle could be dramatically reduced if the reentry vehicle dispensed a secondary, steerable weapons delivery body. Several CPGS system concepts rely on dispensing submunitions, weapons, or UAVs; the dispensing may occur at either high-speed or low-speed conditions, following reentry, hypersonic glide, or cruise. High-speed dispensing of submunitions presents significant chal- lenges regarding control of the dispensing munition to avoid recontact with the RV, while simultaneously enabling aerodynamic capture of the munition. If the dispensing occurs at hypersonic speeds, additional thermal protection will likely be required for the munition. As an alternative to a high-speed dispensing, the reentry vehicle may slow to low speeds, at which the challenges associated with dispensing munitions have largely been solved. Slowing a high-β RV to low supersonic speeds presents chal- lenges associated with dissipating the large-vehicle kinetic energy while simul- taneously maintaining accuracy in the dispensing position, as discussed earlier. By contrast, the use of a low-β vehicle (as proposed in the DARPA Rapid Eye program) to slow to acceptable speeds is straightforward. An example of a promising dispensing system is the UAV envisioned for CTM-2, which would have ballistic delivery with a very low-β reentry vehicle. A blunt reentry heat shield is proposed to slow the payload down to a velocity at which a ballute or drogue chute can deploy (á la Apollo or early film-recovery capsules). Then when the vehicle slows sufficiently, the proposed design is for the drogue to deploy the main parachute, slowing the system to a velocity at which it can safely extract the UAV from the back of the reentry shell, and the UAV can then search for and acquire the target with its onboard sensors and, upon verifica- tion and authorization, can engage the target. This type of concept greatly reduces the need for accuracy in the navigation of the reentry vehicle, but challenges exist in the development of the extraction, erection, and control of the UAV. DARPA recently solicited industry for demon- stration of a similar concept to rapidly deliver a long-endurance ISR UAV. Propulsion System Development Rocket Propulsion New ballistic missile or boost-glide vehicles for the CPGS mission will require new solid-propellant booster motors. These motors will generally be classified as either Class 1.1 or 1.3 explosives, depending on the sensitivity of the propellants. Class 1.1 propellants are highly energetic propellants that may detonate under stressing conditions. Class 1.3 propellants, while not as energetic,

TECHNOLOGY ISSUES 125 will not detonate. Whether a propellant is designated Class 1.1 or 1.3 defines requirements for handling, storage, and so on. The DOD prefers, for good reasons, that all new weapon systems incorporate insensitive (nondetonating) munitions, which requires a booster propellant to be Class 1.3. Since Class 1.1 propellants offer better performance, system develop- ers, facing volume constraints, often “buy into” the handling issues of Class 1.1 propellants. The committee recommends that the potential advantages of any new system incorporating Class 1.1 propellants be evaluated in detail to ensure that the risk and complexity of using Class 1.1 propellants are warranted. Air-Breathing Propulsion Hypersonic cruise missiles require the development of air-breathing engines such as ramjets or scramjets. Ramjet engines are capable of powering the mis- sile to speeds up to approximately Mach 4. Ramjets were first flown at speeds of Mach 4 in the early 1960s. The technology basis for ramjet propulsion systems is very mature, and ramjet-powered systems are currently operational in many countries. The development of scramjet engines will be required to power air-breathing cruise missiles operating at speeds above Mach 5. This engine technology has been investigated extensively in a laboratory environment since the late 1950s, but the transition to flight demonstrations only began with the Kholod scramjet demonstration test-flights conducted between 1991 and 1998 (in concert with France and NASA), the Australian HySHOT II scramjet test in 2002, and the NASA X-43A Mach 7 and 10 flight demonstrations conducted in 2003 and 2004, respectively. Continuing technology demonstrations include the DARPA/Office of Naval Research (ONR)-funded Hypersonic Flight Demonstration (HyFLY) and USAF/DARPA-funded X-51 programs aimed at demonstrating technologies for Mach 6+ cruise-missile applications. In-Flight Communications Communicating to a CPGS weapon in the midcourse or terminal phases of its trajectory offers significant operational advantages for all proposed CPGS options. This subsection discusses those advantages and candidate means of accomplishing the communication. Applications For all CPGS options, in-flight communication is needed to support flight aborting and battle damage assessment (BDA). Owing to its importance, BDA is discussed separately in a later subsection. For boost-glide missiles and hypersonic

126 U.S. Conventional Prompt Global Strike cruise missiles, in-flight communications would enable in-flight targeting update and target reacquisition and verification. In-Flight Targeting Update  As discussed in earlier reports of the Naval Studies Board11 in-flight targeting update is an essential part of any long-range system for hitting moving ground targets. This is because it enables an appropriate bal- ance of the burden of performance between the off-board targeting system and its geolocation accuracy and report frequency on the one hand, and the weapon and its seeker’s ability to detect and classify on the other. As a practical matter, boost-glide missiles or hypersonic cruise missiles must be given a steady stream of reports in order to intercept the right moving target. Brought into the vicinity of the right target by the in-flight targeting updates, the boost-glide missile or hypersonic cruise missile can dispense a seeker-guided weapon (subject to the technical constraints of real systems as discussed below in the subsection “Mobile Targets”) for target kill. Commanders may also want or need the capability to terminate a mission after launch. Retargeting and Loitering Capability  It is possible that a more valuable target may emerge after the launch of a CPGS weapon, or that a primary target may be lost (e.g., may have gone underground), and as a result a secondary target becomes more desirable. In-flight communication would give the commander flexibility to make the changes necessary in these cases. Boost-glide missiles and hypersonic cruise missiles have the significant advantage of being able to maneuver to updated target coordinates following a launch. In-flight communication can exploit this capability by giving the weapon a new pop-up target that had not been detected prior to launch. Because of the expense of the weapon, there must be a sufficiently valuable target available as a default if no pop-up target arises. The committee believes that retargeting capability would be of relatively little value in a presidential-release CPGS weapon, because it is intended to be used against only one or a few high-value targets in a given area. Communications Means The most promising means of communicating with a CPGS weapon in-flight is through existing ultrahigh-frequency (UHF) satellites. This frequency band per- mits the weapon to employ a simple, omnidirectional antenna. At UHF, the trans- mission data rate is limited, but achievable rates would accommodate all of the 11  aval N Studies Board, National Research Council, 2000, Network-Centric Naval Forces: A Transi- tion Strategy for Enhancing Operational Capabilities, National Academy Press, Washington, D.C.; Naval Studies Board, National Research Council, 1993, Space Support to Naval Tactical Operations (U), National Academy Press, Washington, D.C. (classified).

TECHNOLOGY ISSUES 127 applications discussed here, including battle damage assessment. With sufficient priority (and a presidential-release weapon should have it), satellite channels can be made available reliably. The Tactical Tomahawk has such a link. The potential for establishing such capabilities for CPGS may be influenced by the plasma sheath that can form during reentry, interfering with radio-frequency communica- tions channels (see the subsection “GPS/INS Navigation” above). The formation of a plasma sheath is highly dependent on the specific characteristics of the reen- try vehicle. Vehicle speeds above Mach 10 may result in a plasma sheath, while speeds about Mach 20 virtually guarantee it. Altitude is also a factor, with plasma effects occurring between approximately 30,000 feet and 300,000 feet. The shape of the reentry body is important, with blunt bodies causing higher-density plasma. Finally, ablative materials and materials high in plasma-inducing contaminants are likely to increase plasma density. Thus, careful design and testing to evaluate the impact of plasma formation around the reentry vehicle will be important for in-flight communication, as well as for GPS reception, as discussed above. Weapons Effectiveness One of the warheads proposed for employment in some proposed CPGS systems is a cluster of segmented tungsten rods that are explosively deployed through the heat shield of the RV at a time determined by a fuze. The result is a selectable pattern of the rod segments or KEPs that are dispersed over the desired target area, impacting at a velocity of more than 5,000 ft/sec. If the fuze is set not to fire, the resulting densely packed cluster of rods serves as a 250 lb unitary slug (penetrator) which, along with a RV structure, impacts with kinetic energy sufficient potentially to penetrate a multistory building or to create a crater several meters across and deep. The issues of the effectiveness of such kinetic energy weapons against various types of targets are discussed below. Fixed Soft Targets Most fixed soft targets are susceptible to attack by unitary blast-fragmenta- tion or kinetic energy warheads. As previously noted, the initial CTM would carry up to four reentry vehicles equipped with advanced navigation, guidance, and control capabilities. Each reentry vehicle would carry a warhead consisting of dispersible KEPs. Using approximately 1,000 small tungsten rods deployed by explosive charge, a relatively uniform pattern of small KEPs is created. The kinetic energy of a single rod is approximately the same as that of a 50-caliber bullet. The dispersion radius of the pattern can be varied by varying the height at which the warhead is triggered, with constraints imposed by atmospheric drag on the dispensed rods. If a completely uniform pattern could be achieved and a single rod placed in each square meter on the ground, the dispersion pattern would have a diameter

128 U.S. Conventional Prompt Global Strike of 35.7 meters. If the target is such that a denser pattern is required with, say, 16 rods per square meter, a 1,000-rod warhead would be capable of producing a dispersion diameter of 8.9 meters. In both cases, the dispersion diameter is greater than the expected miss distance, so the KEP warhead is anticipated to be effective against soft targets. If the target location error was somewhat larger and a dense pattern was needed over a larger area, the multiple RV capability offers the option of patterning entirely on the single target. In understanding the military effects of KEP weapons,12 it is important to realize that there is no explosive blast (other than that used to disperse the projec- tiles), and thus the extended damage due to overpressure does not occur. Instead, direct structural damage is dependent on the materials response of the target. Many structural elements, such as the wall of a vehicle, the face of a radar dish, or the roof a building, will experience local damage directly at the point of impact, comparable to the type of limited damage caused by meteor strikes, as shown in Figure 4-15. While an increased speed of the projectile increases its kinetic energy, the efficiency with which the energy is transferred to cause lateral damage to the target generally does not increase correspondingly. The size of the damage region will be comparable to the size of the projectile, as shown in Figure 4-15. In the case of the small tungsten rod fragments of a KEP, the structural damage area per particle will be much smaller. Thus, estimating the actual military weapons effectiveness has been the topic of analysis in terms of the susceptibility of the target to the specific action of the small kinetic energy particles of the CPGS warhead.13 In addition, the types of damage must be ranked in terms of how long lasting the damage is. Effectiveness rankings can include an attack that merely delays enemy action for a few seconds or minutes, or an attack that requires the enemy to delay action until a repair can be effected. The timescale required for the repair then becomes a further criterion for ranking the effectiveness. Analyses of a wide range of target types under con- sideration for CPGS have been performed. The results indicate that in most cases, a single CTM KEP will have a high kill probability against fixed soft targets if target geolocation accuracy and guidance, navigation, and control accuracy are as predicted. Current plans call for high-speed sled tests of the KEP warhead and for continued modeling of the effectiveness of the KEP warhead against classes 12  APT Terry J. Benedict, USN, Technical Director, U.S. Navy Strategic Systems Programs, “CTM C Brief to NAS (U),” presentation to the committee, February 23, 2007, Washington, D.C. (classified); and David W. Lando, Distinguished SLBM Expert, Naval Surface Warfare Center, Dahlgren Division, “CTM: Weapon Effectiveness Presentation (U),” presentation to the committee, July 29, 2007, San Diego, Calif. (classified). 13  APT Terry J. Benedict, USN, Technical Director, U.S. Navy Strategic Systems Programs, “CTM C Brief to NAS (U),” presentation to the committee, February 23, 2007, Washington, D.C. (classified); and David W. Lando, Distinguished SLBM Expert, Naval Surface Warfare Center, Dahlgren Division, “CTM: Weapon Effectiveness Presentation (U),” presentation to the committee, July 29, 2007, San Diego, Calif. (classified).

TECHNOLOGY ISSUES 129 FIGURE 4-15 Damage to a tile roof and the interior ceiling caused by the strike of a m ­ eteorite of estimated mass 0.7 kg with an impact speed of less than 500 ft/sec, illustrat- ing the limited damage potential of kinetic energy warheads. Increased speed of impact on structural elements such as walls and roofs does not cause proportional increases in lateral damage, but primarily increases the number of walls and such that can be penetrated. SOURCE: “The Glanerbrug Meteorite Fall,” posted by the Dutch Meteor Society, Leiden, The Netherlands, May 18, 1998; see <http://www.xs4all.nl/~dmsweb/meteorites/­ glanerbrug/glanerbrug.html>. Figure 4.15, bitmapped, uneditable, color of targets. The committee recommends that efforts to define the effectiveness of the KEP warhead against targets of interest be continued, as this information will be relevant to several of the envisioned CPGS systems. The CSM concept envisions the deployment of existing weapons, such as the BLU-108, following deceleration from the reentry conditions. As discussed above, there are technology issues that must be addressed with respect to the dispensing of weapons at high speeds. In addition, the deployed weapons have been well characterized for most target classes of interest, and they are limited in utility for some cases. Some of the difficult issues in addressing mobile targets are described below in the subsection “Mobile Targets.” Fixed Hard Targets Hardened targets include above-ground hardened structures, shallow under- ground structures, and deeply buried targets. The issue of lethality against hard-

130 U.S. Conventional Prompt Global Strike ened targets was studied recently by the National Research Council. 14 This study concluded that many strategic hard and deeply buried targets can only be attacked directly with nuclear weapons. By their conventional nature, CPGS weapons will not solve the existing shortcomings concerning the attack of these strategic targets. CPGS systems, with the exception of the initial version of CTM, will be capable of attack of hardened above-ground facilities and shallow underground facilities. The lethality against a hardened target depends on the ability of the weapon to penetrate the hardened features of the target, the ability to fuse the weapon properly, and the ability of the warhead to create the desired effects. Currently, penetrating warheads are limited by structural considerations to impact speeds of approximately 3,000 ft/sec, which sets the upper limit to the capability to penetrate hardened structures. Reducing reentry vehicles speeds to this level also creates technical issues of thermal protection and guidance, navigation, and control, as discussed above. The more significant challenges lie in the areas of fuse development and effects generation, although these challenges are not significantly different from those for tactical penetrating weapons. Additional R&D is required prior to the deployment of a smart fuse that is reliable and can operate in the presence of easily implemented countermeasures. Techniques to tailor the delivered effects are also required, especially with respect to buried structures containing or manufacturing components and systems for weapons of mass destruction (WMD). The commit- tee recommends robust investigation of techniques necessary to defeat hardened structures, with specific attention paid to the defeat of WMD components and systems. Mobile Targets Mobile targets represent one of the most challenging types of target for attack by a CPGS system. The problems are different depending on whether the targets move from time to time but are fixed when weapons arrive (e.g., mobile ICBMs parked somewhere in a dispersal area), or whether they are actually ­moving when weapons arrive (e.g., a caravan of terrorist leaders moving on a country road). Three technical approaches can be considered for attacking moving targets: (1) terminal sensors, (2) remote sensors and weapon data links, or (3) a combi- nation of both. A terminal sensor can be added to a CPGS system to correct for moderate uncertainties in target location. Incorporating the sensor directly in a high-b RV or hypersonic cruise-missile body presents significant challenges relat- ing to the integration with the thermal protection system. Incorporating the termi- nal sensor in a deployed weapon, as proposed in the CSM-2 concept, avoids the 14  ational N Research Council. 2005. Effects of Nuclear Earth-Penetrator and Other Weapons, The National Academies Press, Washington, D.C.

TECHNOLOGY ISSUES 131 challenging integration with the TPS but requires a high-b RV or cruise missile to slow to an acceptable dispensing speed, which will likely increase its vulnerability in a heavily defended area. The approach of launching a low-b RV to dispense a UAV, as discussed earlier in this chapter, appears an attractive one. Hitting the right moving target is a significant technical challenge. Boost-glide missiles and hypersonic cruise-missile options are assumed capable of deploying BLU-108 submunitions with Skeet warheads. These submunitions are capable of reliably finding motor vehicles (via infrared signatures) and striking them. They cannot discriminate one vehicle from another, however. Originally developed to stop a line of armored tanks, they can be usefully employed if collateral damage is of little importance or if the target vehicle is virtually alone—more than, say, a mile from any other motor vehicle. As a practical matter, in those situations where the target vehicle is moving among other vehicles and collateral damage is to be avoided if possible, human-in-the-loop operations will be required for a CPGS weapon. The committee believes that this will be as true in the year 2020 as it is now. Autonomous target-recognition technology is not advancing at a rate fast enough to solve the significant challenges associated with reliably differentiating one vehicle from another. In large part this is because one cannot predict how, in a given operational situation, the target vehicle will differ from the rest. Perhaps the target vehicle will be identified as “the middle one of three white SUVs traveling in a row.” Perhaps it will be identified by its license plate number. The UAV delivered by the CTM-2 (with UAV) option is assumed to have the necessary capabilities to (1) give remotely located human controllers the visual information that they need to identify the intended target, and (2) permit human control of the UAV, including authorizing it to attack. In this report, it is assumed that CSM-2 and the hypersonic cruise missile could deploy a 2,000 lb UAV capable of the same functions, although it would have less payload and/or range (or loiter time). One possibility for a weapon to arm the UAV is the Hellfire missile. It appears that carriage of at least two Hellfire missiles, at 100 lb each, on either a 3,000 lb or 2,000 lb UAV would be suitable. Battle Damage Assessment Near-real-time battle damage assessment is difficult in most strike situa- tions. Better BDA is seemingly always near the top of the commander’s list of most-desired capabilities. Unique aspects of CPGS option design, along with the application of modern technology, can potentially give CPGS weapons much better BDA capability than the military is used to with any of its existing strike weapons. The essence of a CPGS BDA is to carry in the delivery vehicle a deployable device that can hang in the air above the target as the weapon is delivered, take snapshots of the target before and after the target is (one hopes) hit, take a moment to compress the photos into fewer bits of data, and linger in the air long enough

132 U.S. Conventional Prompt Global Strike to communicate the compressed photos through a UHF satellite link back to the commander who launched the weapon. What makes this concept potentially better than any existing capability is that the camera is very close to the scene, the photo sequence enables a direct comparison of “immediately before” with “immediately after,” taking time for photo compression and communication after the strike should enable a high-quality image, and the commander has the photos quickly. Any CPGS option could, in principle, incorporate this concept, as could any weapon system capable of carrying and releasing the BDA device. For example, in a later version of CTM, one of the reentry bodies could be such a BDA device. In the boost-glide missile or hypersonic cruise-missile concepts, the delivery vehicle itself could possibly perform the function or, probably better, it could dispense a BDA device along with the weapon. The evaluation of this concept is certainly possible outside the context of CPGS, and if it is technically reasonable, incorporating it within a CPGS system would be a valuable addition. Implications of a Possible Prohibition on Research and Development of Trident-Based Systems Some in the Congress have called for the Department of Defense (DOD) to proceed in its CPGS program in a manner that excludes systems based on the Trident missile. The intent is to maximize an alleged “bright line” between conventional and nuclear systems. The committee strongly recommends that no such prohibition be adopted or imposed. In particular, it believes that CTM R&D would be very valuable even if the CTM were not deployed. It further believes that the CTM-2’s two-stage rocket may sufficiently differentiate it from the full three-stage Trident when tracked by a sophisticated satellite-based system (see Chapter 3 and Appendix H for further discussion of nuclear ambiguity). Turning the issue around, the committee concludes that if Trident-based R&D were proscribed, the effect would be to delay—perhaps substantially—the devel- opment and deployment of any CPGS capability, without actually doing much to reduce the ambiguity problem. It is not that the knowledge gained from CTM (or CTM-2) R&D could not be gained in other ways in time, but rather that much would have to be done from scratch—squandering the many years of base-laying by the Trident Missile Program. In addition, the DOD would have to do substantial component testing for the other options, because the other options simply do not have the advantages of building incrementally from a firm foundation. The least delay (perhaps 2 years or so) would be caused if the alternative system approved were the SLGSM. Technology Readiness Levels and Time frames Many of the advanced technologies that are needed to provide CPGS system capabilities have been under development in laboratory environments or flown as

TECHNOLOGY ISSUES 133 part of the advanced-configuration development programs. An approximate time line for the various CPGS technology options discussed above is shown in Figure 4-16. These technologies build on the development of existing RV and technology development and existing demonstration programs such as the FALCON, X-43, HyFLY, and X-51. Capabilities beyond the basic ballistic missile and limited boost-glide sys- tems will require the development of more advanced technologies. Boost-glide concepts that use a significant endoatmospheric glide segment will require the operation of a reentry system in a manner that has not been previously demon- strated. One option for development of the CSM involves the exploitation of the reentry vehicle technology developed under the AMaRV program. As envisioned in the initial version of the CSM, the AMaRV vehicles would be scaled up to the size needed to carry the conventional payloads, and the vehicle would be flown with an extended glide segment. The capability of this extended glide segment would be limited by the existing capabilities of thermal protection systems. It is anticipated that this initial capability (labeled CSM-1 in Figure 4-16) would allow for an 800-second glide segment. The committee believes that there are significant technical risks in the operation of existing reentry vehicles in this new flight mode with an extended glide range and that these risks can only be mitigated through system-level demonstration testing. Very long range glide segments will require the development of new thermal protection systems. The DARPA FALCON flight-test program will explore one approach to the thermal protection system in a reentry vehicle with the high lift- to-drag ratio needed for long-range gliding flight. With demonstrations planned for 2009 and 2010, the FALCON program plans a near-term demonstration of the basic operating characteristics of a vehicle technology that may provide a long-range capability for the CPGS mission. The DARPA FALCON technology is envisioned to feed into a second-generation CSM system (labeled CSM-2 in Figure 4-16). If the FALCON program is successful in demonstrating the tech- nologies necessary for long-range gliding reentry vehicles, the ultimate capability of the CSM system could possibly be developed in a single effort, as opposed to a two-stage process. The forward-deployed AHW builds on technologies developed under the Sandia Winged Reentry Vehicle (SWERVe) program conducted in the 1980s. For deployment as a CPGS, the SWERVe vehicle technologies will need to be upgraded to enable flight at higher speeds and longer glide range within the atmosphere. The development of the thermal protection system necessary for a forward-deployed boost-glide system will be similar in nature to the development of the TPS for the CSM system. Significant overlap in technology development for boost-glide systems will likely occur if the forward-deployed boost-glide missiles continue to be seriously considered. The air-breathing Mach 6 missile (hypersonic cruise missile) represents a new class of delivery system, which is immature relative to the ballistic systems.

MK-4 RB E2 and LETB 134 CTM GN&C accuracy Sea-launched KEP effectiveness Corona/Apollo ballistic CTM-2 with missiles deployed UAV CTM-2 RV scaling MK-500 RB Lethality Assessment SLGSM Medium lift-to-drag shape Sea-launched Intermediate TPS boost-glide missile FALCON 3600 s TPS 3000 s TPS Hypersonic L/D High lift-to-drag AMaRV In-flight CSM-2 Communications CONUS-based boost-glide CSM-1 800 s TPS missile GN&C accuracy SWERVe Forward-deployed AHW boost-glide Advanced TPS GN&C accuracy missile ASALM X-51 Mach 4 Missile Mach 6 Missile HyFLY Sea- or air- X-43 A/B propulsion launched hypersonic Thermal management missile GN&C accuracy 1970 1980 1990 2000 2005 2010 2015 2020 2025 Year FIGURE 4-16 Technology development time lines illustrating a legacy to all proposed conventional prompt global strike systems. The time lines for future technologies are based on an assumption that investments will continue to be made in critical research and development activi- ties. NOTE: A/B propulsion refers to the four gas generators in the Post Boost Propulsion System on the Trident equipment section (bus) that burn in two stages: the first two burn together called “A” propulsion; once they burn out, a transition is made to the next two gas generators Figure 4.16 called “B” propulsion. The remaining acronyms are defined in Appendix A. landscape,editable color

TECHNOLOGY ISSUES 135 Technology associated with air-breathing hypersonic propulsion systems has been under development in a laboratory environment for the past 30 years and has recently begun transition to the flight-test environment in programs such as the NASA-funded X-43, DARPA/ONR-funded HyFLY, and USAF/DARPA-funded X-51 programs. These programs have demonstrated or will demonstrate critical aspects of the propulsion technology necessary to enable a Mach 6 cruise missile. Furthermore, the Air Force Research Laboratory is exploring the technologies associated with a Mach 6 hypersonic cruise missile under its Robust Scramjet Technology program. In 1998, the National Research Council conducted a study evaluating the U.S. Air Force Hypersonic Technology (HyTECH) program.15 This study concluded that the development of a Mach 6 missile in 2015 was feasible. Although not all recommendations in that report were implemented, the technology readiness of hypersonic cruise missiles is such that this type of capability can be deployed in about 2020. Summary The desire for conventional prompt global strike capabilities with the fewest constraints has led to proposals based on ballistic and hypersonic delivery sys- tems. While establishing such capabilities appears feasible, for some concepts it is at the cutting edge of aeronautic technology. The most-effective development of CPGS capabilities will require a spiral technology evolution in which interme- diate capabilities are developed and tested, with the results serving as the basis for evaluating and developing more-advanced capabilities. Preliminary testing of the CTM system is an excellent first step in such a development process, because it is strongly connected to proven capabilities and allows key new technologies to be evaluated at relatively low cost. Furthermore, the technologies that must be demonstrated for the success of CTM are common to the success of other proposed ballistic/hypersonic programs for CPGS. The development of CPGS options beyond the relatively limited capabilities of CTM will require additional investments in thermal protection and weapons dispensing. Supporting develop- mental efforts in these areas as proposed for Falcon and CSM also provides an important step in the future evolution to the most-effective future systems. Findings and Recommendations Finding 1. The command, control, communications, computer, intelligence, surveillance, and reconnaissance (C4ISR) systems needed to enable conventional prompt global strike (CPGS) are only sufficient to meet the CPGS time lines under 15  ational N Research Council. 1998. Review and Evaluation of the Air Force Hypersonic Technology Program, National Academy Press, Washington, D.C.

136 U.S. Conventional Prompt Global Strike limited conditions. Significant additional effort will be required to provide seam- less integration of numerous disparate systems and to increase the global coverage of the Digital Point Positional Data Base. Recommendation 1. The Office of the Secretary of Defense (OSD) should fund the National Geospatial-Intelligence Agency (NGA) to speed production of the Digital Point Positional Data Base (DPPDB) to increase its geographic cover- age and to develop a means to determine rapidly and accurately the geographic coordinates of any visually identified point (e.g., from a recent photo taken in the field) when that point lies outside DPPDB coverage. Finding 2. Conventional Trident Modification (CTM) represents the only near- term option for a CPGS capability, but the system accuracy has not been demon- strated, and the kinetic energy projectile (KEP) warhead will likely be effective against only a subset of candidate targets. In addition, the limited maneuverability of the proposed CTM reentry vehicle will result in an inability to attack targets in many urban and mountainous regions. Recommendation 2.1. The accuracy of the CTM system needs to be demon- strated in end-to-end system tests. This accuracy demonstration will provide needed information for the CTM system concept, as well as providing important technical information applicable to all CPGS candidate systems. Recommendation 2.2. Evaluation of the KEP warhead effectiveness should be included in the CTM system tests and defined against candidate target sets. War- heads capable of defeating a wider range of targets should be developed. Recommendation 2.3. The baseline CTM system concept should include the development and use of reentry vehicles capable of vertical impact to allow the attack of targets in urban or mountainous environments. Finding 3. A modified version of the Trident missile system, designated in this report as CTM-2, could provide enhanced weapons effectiveness with larger and more flexible payloads. Recommendation 3. The Navy Strategic Systems Programs Office should con- duct a detailed technical assessment of the CTM-2 concept. If deemed feasible, CTM-2 research, development, testing, and evaluation should be provided to address overall system accuracy and weapons effectiveness. Finding 4. More-advanced concepts for CPGS, such as CTM-2, Conventional Strike Missile (CSM), and Advanced Hypersonic Weapons (AHWs), offer the potential for improved system performance through more flexible payloads and

TECHNOLOGY ISSUES 137 trajectories, but these concepts carry high technical risk that must be mitigated prior to any deployment decision. Recommendation 4. OSD should fund the technology development of the longer- term CPGS concepts to address the technical issues associated with thermal pro- tection systems; hypersonic aerodynamics and air-breathing propulsion systems; guidance, navigation, and control accuracy; and munitions dispensing systems. Finding 5. The attack of moving targets and incorporation of battle damage assessment in a CPGS setting will require the development of significant new capability, which could be accomplished with a combination of deployed terminal sensors and weapon data links. Recommendation 5. OSD should fund the technical evaluation of system con- cepts to address the attack of moving targets and incorporation of battle damage assessment, including the dispensing of unmanned aerial vehicles from ballistic missiles or boost-glide vehicles.

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Conventional prompt global strike (CPGS) is a military option under consideration by the U.S. Department of Defense. This book, the final report from the National Research Council's Committee on Conventional Prompt Global Strike Capability, analyzes proposed CPGS systems and evaluates the potential role CPGS could play in U.S. defense.

U.S. Conventional Prompt Global Strike provides near-, mid-, and long-term recommendations for possible CPGS development, addressing the following questions:

  1. Does the United States need CPGS capabilities?
  2. What are the alternative CPGS systems, and how effective are they likely to be if proposed capabilities are achieved?
  3. What would be the implications of alternative CPGS systems for stability, doctrine, decision making, and operations?
  4. What nuclear ambiguity concerns arise from CPGS, and how might they be mitigated?
  5. What arms control issues arise with CPGS systems, and how might they be resolved?
  6. Should the United States proceed with research, development, testing, and evaluation (RDT&E) of the Conventional Trident Modification (CTM) program5 and, ultimately, with CTM production and deployment?
  7. Should the United States proceed with the development and testing of alternative CPGS systems beyond CTM?
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