The potential value of defense systems deployed forward, near the launch areas of hostile ballistic missiles, was studied in the mid-1960s almost as soon as ballistic missiles were first deployed.1 In particular, forward-based air- and sea-launched defense systems were evaluated and a space-based scheme called the Ballistic Missile Boost Intercept (BAMBI) was even proposed.
The Nike X System, which eventually led to the Sentinel and Safeguard programs, evolved from air defense missiles that were deemed the most realistic solution to defense of the continental United States (CONUS). The later systems consisted of radar-command-guided Spartan area interceptors designed to engage threats above the atmosphere, as well as radar-command-guided Sprint terminal interceptors (with very high acceleration) that were launched after atmospheric filtering of light decoys. While Sentinel was aimed at defending population and infrastructure, the system evolved into Safeguard when the objective became to defend land-based retaliatory forces.
The Safeguard program was declared operational and deployed at Grand Forks, North Dakota, at about the time the Antiballistic Missile (ABM) Treaty between the former Soviet Union and the United States was signed, but it was dismantled 2 years later. In addition to being susceptible to certain countermeasures, the Safeguard program was meant to detonate defensive nuclear warheads overhead to prevent enemy nuclear detonations in the United States, which did not engender support for it.
1For additional reading, see Ashton B. Carter and David V. Schwartz, 1984, Ballistic Missile Defense, Brookings Institution Press, Washington, D.C.
Even before the Safeguard program was deployed and then dismantled, the U.S. Army’s Advanced Ballistic Missile Defense Agency (ABMDA) began to exploit the emerging long-wave infrared sensor technology that allowed detecting and tracking objects against the cold space background. Studies conducted in the mid- to late 1960s defined midcourse defense options based on interceptors with long-wave infrared sensors capable of detecting potential intercontinental ballistic missile (ICBM) threats thousands of kilometers away on their ballistic trajectories, observing them for more than 100 sec while closing on the threat, thereby maximizing the opportunity for discriminating warheads from countermeasures and other objects in the threat complex and finally homing on the object that posed the most credible threat to intercept it. Simulations in 1969 lent confidence to the notion that this optical homing could be accomplished with sufficient accuracy to achieve a direct hit, thereby destroying the target by the force of the collision, at closing velocities approaching or exceeding 10 km/sec. At the same time, technology was dramatically improving the ability to track rocket boosters from space and predict their trajectories with handover volumes compatible with the acquisition-and-divert capabilities of the interceptors. With a moderate-sized onboard long-wave infrared (LWIR) track (while scan or staring mosaic sensor uncapped once above 80 km altitude), the interceptor could view the threat against the deep space background as it closed in and could thus search and acquire individual objects hundreds of miles away, typically about one-third the range of the threat missile. Moreover, the same sensor could be used to home in on the target once it was designated to achieve miss distances consistent with nonnuclear kill. This work led to flight experiments for verification, but because of the ABM treaty, more than 10 years elapsed before a technology flight experiment—called the Homing Overlay Experiment—was initiated that led to the successful intercept of an ICBM reentry vehicle (RV) launched from Vandenberg Air Force Base in California in 1984. This experiment was followed by the Exoatmospheric Reentry Interceptor System (ERIS), which reduced the size of the kill vehicle (KV) to a more operational configuration that successfully intercepted in 1991. While all of these experimental interceptors had, in varying degrees, the onboard processing to track and discriminate among tens of objects, including celestial objects, in the field of view, there was still concern about the ease of creating relatively lightweight countermeasures that would be effective above the atmosphere.
In 2001, the National Missile Defense (NMD) program transitioned to the Ground-Based Midcourse Defense (GMD) system and was directed to be deployed by 2004. It is currently emplaced at Fort Greely, Alaska. The attraction of midcourse (exoatmospheric) defense is that interceptors at a few sites can protect targets anywhere in the entire country, committing the earliest intercepts only after assessing an attack with multiple phenomenology. Put another way, in principle, it can adapt in real time to defend against whatever is threatened and still have sufficient shot opportunities to deal with imperfections in target desig-
nation and intercept failures. On the other hand, it must at some point also deal with exoatmospheric countermeasures, which in principle can be light in weight yet credible and are easily deployed. The midcourse discrimination controversy has contributed to interest in the pursuit of boost-phase defense.
Surface-to-surface ballistic missiles have proliferated in recent years. Today, many countries beside Russia and China possess such missiles. These countries include several that are hostile to the United States, notably Iran, North Korea, and Syria, and several that are not very stable. While the number of countries deploying ballistic missiles is not expected to increase dramatically in the next decade, there is a possibility that other countries whose relations with the United States are problematic could acquire them in the near future. More importantly, countries that already possess ballistic missiles are likely to improve their systems in terms of number, capability, and technological sophistication. For the purposes of this report, the committee’s analysis focused on North Korea and Iran.
So far no countries other than Russia and China (and U.S. allies such as the United Kingdom and France) have ballistic missiles of intercontinental range, although a number have space launch programs that could, in principle, be adapted for ICBM purposes. Moreover, both Iran and North Korea have deployed missiles capable of striking U.S. allies and friends and U.S. forward-deployed forces, and they are working on nuclear weapons with which to arm them and on missiles with still longer ranges.
In the case of Iran, while the regime’s long-term goals in its pursuit of ballistic missile development are unclear, it seems likely that deterrence of conventional (or nuclear) attacks on its territory and coercion of its neighbors within the Middle East are two of those goals. The growing inventory of older, liquid-propellant shorter-range missiles is a threat primarily to Iran’s closest neighbors, but the appearance of longer-range liquid- and solid-propellant ballistic missiles, some with multiple stages, is a harbinger of longer-range threats to come.
Perhaps most important to this study is the rapid development of Iran’s indigenous solid-propellant missile capability. The new solid-propellant ballistic missile has an estimated range of approximately 2,000 km. All of Israel and the Arabian peninsula are within range of such a missile, as shown in Figure 1-1.2 Here, the smaller circle represents the rotating Earth coverage of this new solid-propellant ballistic missile, or of a 2,000-km-range variant of the Shahab-3.3 Iran is working to develop larger solid rocket motors that could soon show up
2Figure 1-1 was generated from the committee’s analysis using Google Earth. ©2011 Google, Map Data©2011 Tele Atlas.
3Department of Defense. 2010. Ballistic Missile Defense Review Report, Washington, D.C.: February, pp. 5-6.
FIGURE 1-1 Hypothetical range of Iranian ballistic missiles.
as two- or three-stage intermediate-range ballistic missiles (IRBMs). The larger circle in Figure 1-1 shows that a notional three-stage missile employing Iran’s currently demonstrated solid-propellant technology could reach approximately 5,600 km, thus threatening virtually all of Europe, including the United Kingdom, the Eurasian landmass, and much of northern Africa. To the southeast it would reach almost to the straits of Malacca and considerably beyond Diego Garcia. With this capability, there may be little need to add ICBM capability to dissuade U.S. or NATO intervention to thwart Iran’s ambitions.
North Korea is a somewhat different story compared to Iran. To date, it has shown little interest in long-range solid-propellant missiles, instead focusing on building bigger and more capable liquid-propellant systems. While some view the Taepo Dong 2 as a potential threat to the United States, the committee thinks this is unlikely. A more immediate threat is a new 3,200 km IRBM North Korea is developing that can threaten Japan, Guam, and Okinawa—all staging areas for a U.S. response to aggressive behavior by North Korea.4
4Ibid., p. 5.
An open question is whether Iran’s solid-propellant capability will be shared with North Korea and others in the way that liquid-propellant technology has flowed in the other direction. In this study, the committee has tried to look at the broad spectrum of threats, current or that may emerge over several years, rather than parsing the details of shifting projections of specific programs. While there is uncertainty as to the pace of either state’s progress, prudence dictates that the United States assume, in the absence of verifiable evidence to the contrary, that both North Korea and Iran will eventually have ballistic missiles capable of reaching CONUS with nuclear weapons, and that both will attempt to adapt their programs to offset U.S. defense efforts. Generic but representative examples of potential ballistic missiles, available in the open literature, and actual threat assessments from the intelligence community are provided in classified Appendix F, which accompanies this unclassified report.5
The principal hurdles in developing a true ICBM for Iran and North Korea to overcome are achieving reliability and a sufficient range, developing a workable RV, and producing a nuclear (or conceivably chemical or biological) weapon that can be used in an ICBM RV. Estimates of how long it will be before either country first tests an ICBM vary greatly, from a few months to a decade or more. Of course, a first test, even if successful—North Korea’s initial tests of a Taepo Dong 2 nominally for space launch failed—would not be equivalent to deploying an operational system, which could take additional years. Nor is it clear how soon either country could develop a workable RV and nuclear warhead for their missiles. However, the consensus of the intelligence community is that both countries could have an operational ICBM capability within a decade.
Based on the information presented to the committee, it appears any ICBM that Iran or North Korea could deploy initially would be relatively unsophisticated. However, the U.S. intelligence community expects that most of the countries that are developing ballistic missiles will improve their capabilities over time. In addition to their indigenous technological capacity, Iran and North Korea—and others seeking ballistic missile capability—are likely to be able to tap into one another’s technologies and the technologies of other missile-possessing countries, whether with those countries’ consent or otherwise.
In addition to increasing survivability and effectiveness of their ballistic missile force by measures such as mobile basing and increased accuracy, emerging ballistic missile states will likely make other improvements of significance for U.S. missile defense efforts, notably the adoption of solid-propellant systems, more energetic missiles, and the development and integration of countermeasures against missile defense systems. So far the countermeasure efforts of both appear to be directed against theater-level terminal defenses, but some—such as multiple near-simultaneous launches, which both Iran and North Korea have
5Some believe theater ballistic missiles launched by ships is a serious threat, particularly for nonstate actors, and there may be potential responses that would involve intercepting missiles.
demonstrated—would also have potential against defenses designed to deal with longer-range threats.
Our nation’s ability to anticipate and understand the details of an Iranian or North Korean ICBM (or other missiles) would depend substantially on the extent of their flight testing. While both countries are likely to do some testing—both to confirm the performance of their systems and in the hopes of gaining political advantage by exhibiting their prowess—they are unlikely to follow the extensive testing practices of the United States and the former Soviet Union during the Cold War or those of China.
Although Russia and China will certainly maintain and modernize their strategic nuclear arsenals, U.S. policy states that missile defense is not intended or designed to counter those forces—and any attempt to do so would be an expensive and destabilizing failure. Accordingly, and consistent with its congressional tasking, this study does not consider the ability to defend against Russian or Chinese strategic forces as an evaluation criterion for proposed missile defense systems.
In addition to developing its strategic deterrent, however, China is also very active in developing conventionally armed tactical and theater missile capabilities for “anti-access, area-denial” missions. Such missile systems could pose serious threats to U.S. allies and U.S. power projection forces in the western Pacific. A case of particular concern—though far from the only one—is the development of a much publicized anti-ship ballistic missile, with a maneuvering conventional warhead designed to attack naval forces at sea. Dealing with this potential threat is, in contrast to the strategic force question, very much a potential mission for U.S. missile defense.6
The congressional tasking for this study requested an assessment of the concepts and systems for U.S. boost-phase missile defense in comparison with non-boost ballistic missile alternatives. It calls for attention to the systems for two purposes: (1) countering short-range ballistic missile (SRBM), medium-range ballistic missile (MRBM), and IRBM threats from rogue states to the deployed forces of the United States and its allies and (2) defending the territory of the United States against limited ballistic missile attack.7
To provide a context for analysis of present and proposed U.S. boost-phase and non-boost concepts and systems, the committee considered the following to be the missions for ballistic missile defense (BMD): (1) protection of the
6Department of Defense. 2010. Ballistic Missile Defense Review Report, Washington, D.C.: February, p. 7.
7The term “systems” is used in place of “concepts and systems” throughout this report, recognizing that the term can be either existing or proposed.
U.S. homeland against nuclear attacks, attacks involving other weapons of mass destruction (WMD), or conventional ballistic missile attacks; (2) protection of U.S. forces, including military bases, in theaters of operation against ballistic missile attacks armed with WMD or conventional munitions; and (3) protection of U.S. allies, partners, and host nations against ballistic-missile-delivered WMD and conventional weapons.8 A fourth mission, protection of the U.S. homeland, allies, and partners against accidental or unauthorized launch, was considered as a collateral benefit of any ballistic mission defense but not as a goal that drives system requirements.9 Consistent with U.S. policy and the congressional tasking, the committee conducted its analysis on the basis that it is not a mission of U.S. BMD systems to defend against large-scale, deliberate nuclear attacks by Russia or China.10
BMD intercept can, in principle, be accomplished in any of the three phases of flight of the target missile: boost phase, midcourse phase (which can in turn be subdivided into early, ascent, and postapogee or decent phases), and terminal phase. Further elaboration of this terminology is provided in Box 1-1.
Figure 1-2 displays the present and proposed U.S. BMD systems for countering SRBM, MRBM, IRBM, and ICBM threats in the context of their phases of flight. In addressing the congressional tasking, the committee examined a wide range of present and proposed BMD systems, along with their supporting sensors. The BMD systems examined in this report are shown in Table 1-1, where they are displayed in terms of their applicability to a given protected area and mission (i.e., protecting the U.S. homeland, allies, or U.S. forces) and to a given layer of defense (terminal-, midcourse-, or boost-phase defense). The programs of record for the particular defense systems are described in Chapters 2 and 3. In addition, the committee examined two other defense systems—CONUS-based evolved GMD (denoted as GMD-E in Chapter 5) and Forward-Based Evolved GMD—that resulted from its analysis and simulation work, where it found significant weaknesses in the current systems.
While the committee had access to classified information provided by the Missile Defense Agency on its programs of record, the committee chose to
8For brevity, missions (2) and (3) are usually considered together because they so often involve defense against hostile missiles of similar character although being defended against for different purposes.
9Any BMD system would provide some inherent capabilities for defense against accidental or unauthorized launch of a Russian or Chinese missile or, for that matter, one owned by another power. However, defense against such attacks should not drive the design or evaluation of defense concepts, because the greater sophistication (or numbers) of such an attack would tend to establish unrealistic and perhaps infeasible or unaffordable requirements compared to those appropriate for defenses focused on the rogue state threat.
10Aside from political and stability effects, such defense is not practical, given the size, sophistication, and capabilities of Russian and Chinese forces and both countries’ potential to respond to U.S. defense efforts, including by increasing the size of the attack to the point at which defenses are simply overwhelmed by numbers.
Ballistic Missile Defense Intercept Technology
For purposes of this report, ballistic missile defense intercept can occur in three phases of flight: boost phase, midcourse phase, and terminal phase. This terminology is defined below:
“Boost-phase intercept” (BPI) will be used exclusively for intercept of the threat missile prior to the end of powered flight of the main stages of the missile. Intercept during this phase is noteworthy because, if successful, the missile’s payload cannot reach its intended target. Whether the payload itself survives boost-phase intercept depends on where on the target missile the intercept occurs. The degree of payload shortfall depends on when during the target missile’s boost phase the intercept occurs. The main challenge associated with boost-phase intercept is the short time associated with powered flight, typically between 60 and 300 seconds depending on the missile’s range and propellant type.
“Midcourse intercept” refers to exoatmospheric intercept after threat booster burnout. During this phase, all objects follow ballistic trajectories under the sole influence of Earth’s gravitational field. The midcourse phase is noteworthy because it is the longest phase of a missile’s flight (for those missiles that leave the atmosphere), thereby providing more time for observing and reacting to the threat. However, it is also the phase where decoys may be most effective because all objects follow ballistic trajectories regardless of their mass. The terms “ascent phase intercept” and “early intercept” are redundant because they refer to intercept after the end of the boost phase of flight but prior to apogee, which makes them part of midcourse intercept. Intercepting threat missiles as early as possible during the midcourse phase increases battle space and defends large footprints from a single forward site, thereby adding shot opportunities that use interceptors more efficiently.
“Terminal defense intercept” refers to endoatmospheric intercept after the midcourse defense opportunity. The presence of substantial dynamic forces make this phase unique as far as ballistic missile defense is concerned because light objects such as decoys, which slow down faster due to atmospheric drag, follow substantially different trajectories than heavy objects such as reentry vehicles. The altitude at which the transition from midcourse to terminal defense occurs is somewhat ambiguous, with light decoys being slowed appreciably relative to reentry vehicles at altitudes between 70 and 100 km and appreciable aerodynamic forces on the reentry vehicle occuring at altitudes below approximately 40 km.
NOTE: Postboost, predeployment intercept (PBDI) refers to intercept of a missile’s postboost vehicle (PBV) or payload deployment module, if any, after the main rocket engines burn out and prior to the complete deployment of multiple objects contained in the missile’s payload (reentry vehicles, decoys, and other countermeasures). This distinction is important because intercepts during the PBDI phase potentially eliminate some objects depending on how early in the PBDI phase the intercept occurs, PBVs are more easily detected and tracked, and PBVs may undergo lower power maneuvers as they deploy their multiple objects. The duration of the PBDI phase depends on PBV design and mission. However, it can be very or vanishingly short as noted in a recent Defense Science Board report entitled Science and Technology Issues of Early Intercept Ballistic Missile Defense Feasibility (September 2011).
FIGURE 1-2 Notional ballistic missile defense (BMD) systems against short-range ballistic missile, medium-range ballistic missile, intermediate-range ballistic missile, and intercontinental ballistic missile threats. In this figure, all notional BMD systems are illustrated independent of their operational or developmental status. As this figure shows, numerous BMD systems have been proposed and considered for boost- and ascent-phase intercept in an attempt to build a layered defense system. PAC-3, Patriot advanced capability 3; ABI, airborne laser interceptor; GBI, ground-based interceptor.
TABLE 1-1 BMD Systems Examined in This Report in Terms of Their Potential Mission Applicability
|SM-3 Block IIB
|SM-2 Block IV
|SM-3 Block I
SM-3 Block II
|SM-3 Block IIA
SM-3 Block IIB
|SM-2 Block IV
|SM-3 Block I
SM-3 Block II
|SM-3 Block IIA
NOTE: blue, operational; green, in development; purple, being considered; red, inactive, terminated, or redirected.
develop a set of notional threat missiles, notional interceptor designs, and notional sensors to explore the basic physical limitations of missile defense system performance, with the understanding that a public report was not only requested by Congress but also helps improve public understanding of ballistic missile defense issues. As such, the analysis included in this unclassified report (as distinct from the classified annex) is based on illustrative calculations that, in the committee’s view, reasonably capture various missile defense architecture trade-offs. None of these calculations use classified threat missiles characteristics or classified system specifications for U.S. missile defense assets.
Current policy guidance for missile defense is provided in three DOD reports—the 2010 Quadrennial Defense Review, the 2010 Nuclear Posture Review, and the 2010 Ballisic Missile Defense Report, with the last report calling for limited but effective missile defense of the U.S. homeland, of U.S. deployed forces abroad, and of the host nations for those forces. In addition, as part of U.S. policy of extended deterrence, the last of the three reports calls for cooperation with allies to provide a defense umbrella against belligerent states, particularly North Korea and Iran, that are hostile to the collective interests of the United States and its friends and allies on which it depends.
The title of this report, Making Sense of Ballistic Missile Defense, underscores the four primary objectives in meeting the congressional tasking. One is to provide a sound basis for resolving once and for all some of the claims for BMD systems (including sensors): Do present and proposed ballistic missile defense systems offer capability and capacity to handle situations beyond those constituted by an unrealistically constrained view of the threat? Given the kinematics and time constraints of the engagement problem, are intercepts realistically achievable? The second objective is to independently assess from a user’s perspective the effectiveness and utility of the BMD systems being fielded as well as those being contemplated for future deployment. The third, as per the statement of task, is to examine the resource requirements for each BMD capability in relation to its mission utility. This resource examination is based on currently available program cost data as well as on historical cost data for systems with similar elements and takes into consideration realistic, achievable concepts of operations. The final objective is to propose a way forward for U.S. missile defense efforts, including midcourse discrimination.
The chapters of the committee’s unclassified report are organized as follows: Chapter 2 provides the committee’s assessment of systems for U.S. boost-phase missile defense. Chapter 3 addresses non-boost alternatives. Chapter 4 compares the various systems in terms of their utility, maturity, and cost. Chapter 5 recommends a path forward, including those activities that in the committee’s judgment should be redirected or terminated and the various supporting sensors that will be required. The committee believes systems engineering and analysis need improvement and that the current ballistic missile defense capability for U.S. homeland defense—the GMD system—should evolve to improve its overall effectiveness. The committee also produced a separate classified annex, which does not modify any of the report’s findings or recommendations but provides supporting material and analyses employing classified data.