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2 U.S. Boost-Phase Defense BACKGROUND One of the primary perceived benefits of boost-phase defense is the ability to shoot down a missile during its powered phase, when it presents a bright plume signature and before it disperses its payload and countermeasures, thereby clearly identifying the target to be destroyed. This potential to overcome the midcourse discrimination problem has been among the reasons for interest in the pursuit of boost-phase defense. The difficulty is that the boost-phase interceptor (BPI) has to be within range of a point at which it can intercept the target when launch occurs and must be able to respond with a very short action time. This turns out to be much easier said than done. Since the time from detection of a hostile launch until it completes boost is often as little as a minute and, even for slower burning liquid-fueled intercontinental ballistic missiles (ICBMs) is unlikely to exceed 250 sec, any boost-phase intercept—accomplished kinetically or by directed energy—must be launched after detection from a platform that is within the range and action time of the interceptor, essentially intercepting before “booster cut-off” of the hostile missile. While it sounds like a good idea, boost-phase defense presents a unique set of challenges. For starters, whether a solid or liquid rocket motor is used to pro- pel the hostile missile, the boost-phase timeline is very short. In a gross sense, the intercept process must first determine if the launch in fact is a hostile missile and, if it is, determine its trajectory. Then the vehicle providing the “kill” func- tion—known as the kill vehicle (KV)—must acquire and shoot at the target. Here, detection range and kill range capability must be considered. Ground- and ship-based, manned and unmanned aircraft as well as space- 30
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U.S. BOOST-PHASE DEFENSE 31 based interceptor platforms have all been proposed, but either the interceptor platform has to be so close to the threat launch point as to be vulnerable to attack itself, or the velocity of the intercepting projectile has to be very great. The latter is one reason for the interest in using directed-energy (speed of light) weapons for boost-phase interecept. Today’s proposed boost-phase systems originated in the Strategic Defense Initiative era’s research programs. In more recent years, considerable effort has been expended in the development of an in-flight directed-energy platform—a heavily modified Boeing 747-400F airplane. Another option is destroying mis- siles on their launch pads prior to a suspected launch; this could have grave politi- cal consequences should an “innocent” missile be destroyed on the pad. While boost-phase defense has been advocated as the most efficient way to deal with fractionated payloads and exoatmospheric (midcourse) penetration aids, it is extremely sensitive to assumptions about threat booster characteristics. Over time, boost-phase defense tends to be renamed ascent-phase defense when the kinematic realities set in. In fact, ascent-phase defense is code for engagement in the postboost or early midcourse phases of flight. The limitations and complications of a surface-based boost-phase defense lie primarily in the concepts of operations (CONOPS), policy, time, and geography. Since the timelines for engagement in the boost-phase are extremely short, the on-site commander must have authorization from the National Command Author- ity to launch an interceptor immediately after a threat missile has been detected. 1 Also, access must be gained to countries adjacent to the threat country in order to position a boost-phase system close enough, and at the correct geometries, to successfully engage the threat missile. Finally, boost-phase systems are only ef- fective against countries that do not have large enough landmasses to allow them to launch missiles from deep within their territory. The airborne laser is designed to deliver energy at the speed of light to per- form the boost-phase intercept mission. Space-based lasers were also pursued in the past. Virtually no fly-out time is involved, and the beam agility is a function only of how fast the pointing optics can be repositioned. While laser weapons sound like the obvious answer, the energy that a laser can deliver on a target is limited by the power available and the aperture of the device. Atmospheric effects disturb the beam. Much has been accomplished in advancing the pointing and tracking capabilities and the adaptive optics to maintain beam quality, but some fundamental limitations remain. 1 Even if the weapons release delay is assumed to be zero, the range limits make boost-phase defense infeasible.
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32 MAKING SENSE OF BALLISTIC MISSILE DEFENSE PROPOSED SYSTEMS The recently redirected airborne laser (ABL) program was one of two boost- phase systems under development. While the ABL program came from more than 2 decades of military laser development, it could not provide an operation- ally useful boost-phase capability, partly because the inherent range limitations of the atmospheric propagation meant that the Boeing 747-400F would need to operate in hostile airspace. An alternative approach has been to develop a kinetic kill vehicle (KKV) for boost-phase defense by harnessing the successful invest- ments the United States has made over the past several decades for the purpose of midcourse defense, although a KKV for this purpose would have to be much more agile than a KKV for midcourse defense. The Kinetic Energy Interceptor (KEI) program was undertaken for that reason. In principle, boost-phase kinetic interceptors could be launched from land-, sea-, air-, or space-based platforms. However, the efficacy of such interceptors is uncertain. In the following section the committee provides additional information on the U.S. boost-phase systems examined in this report, as called for in the congressional tasking. Specifically, the KEI and ABL programs and other existing boost-phase technology demonstration programs are first described and then analyzed. Kinetic Energy Interceptor The KEI program was initiated in 2002 by the Missile Defense Agency (MDA) based on a recommendation by the Defense Science Board that a boost- phase intercept capability be developed with higher average velocity (high v bo and high acceleration) missiles to enhance ballistic missile defense and as an alternative to the ABL program.2 The Office of the Under Secretary of Defense for Policy also found that a boost-phase intercept capability was required for af- fordability reasons. Furthermore, the ABM Treaty had recently been abrogated, making it possible to develop and deploy such a system. MDA developed a capabilities-based Request for Proposal for a transportable, ground-based boost- phase interceptor system and presented it to industry in December 2002. The KEI program was originally funded as a $4.6 billion (in then-year dol- lars), 8-year development and test boost-phase system using a modified SM-3 seeker and an Exoatmospheric Kill Vehicle Divert and Attitude Control System (EKV DACS) for the KV. Immediately after the contract had been awarded, how- ever, the funding for KEI was significantly reduced and government requirements were added. The mission was expanded in 2004 to include not only boost-phase intercepts but also ascent-phase (prior to countermeasure deployment) and mid- course intercepts. The KEI program was terminated in 2009, just before a planned booster 2 Sean Collins, Missile Defense Agency, “Kinetic Energy Interceptor (KEI) Briefing to the National Academy of Sciences,” presentation to the committee, January 14, 2010.
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U.S. BOOST-PHASE DEFENSE 33 flight test. According to MDA, the threat had evolved to the point where the expected capability of the KEI system was inconsistent with the strategy for countering rogue nation threats.3 It is also possible that extremely high costs and delays played a role in termination of the program. By that time, the KEI program had experienced mission changes coupled with technical difficulties, which led to cost growth. The projected cost to complete the contract almost doubled, from $4.6 billion to $8.9 billion (also in then-year dollars). In addition, the develop- ment schedule, originally 5.5 years, was projected to take 14-16 years to com- plete. Over the course of the program, the average unit cost of a KEI interceptor had also increased, from $25 million to over $50 million (in then-year dollars). Prior to termination of the program, the mitigation of technical issues had delayed the first prototype booster flight test date (established in 2007) by over a year. As shown in Figure 2-1, the KEI system consisted of a BMC2 component, a mobile launcher, and an interceptor all up round. KEI had no organic sensors but had direct access to overhead IR sensors and indirect access to other overhead national asset capabilities and to BMD system ground sensors when available. The KEI fire unit consisted of redundant BMC2 systems that received sen- sor input, calculated the fire control solution, and communicated with the inter- ceptor before and during flight. The mobile transporter erector launcher (TEL) transported and launched one round per launcher. It was transportable by C-17 or C-5A aircraft. The interceptor component was a 40-inch diameter, two-stage solid rocket. It carried a third-stage rocket motor (TSRM) in the payload that was used when additional velocity was required. The KV was a derivative of the SM-3 (two-color seeker) and the EKV DACS. It would have been capable in the boost, ascent, and midcourse intercept regions. The CONOPS for the KEI system was very much the same as the CONOPS for tactical air and missile defense systems currently employed by the U.S. Army and the U.S. Navy. The land-based system was mobile and transportable by U.S. Air Force aircraft. The CONOPS called for KEI batteries to be garrisoned at continental United States (CONUS) locations until needed for national defense or defense of an allied country. A fire unit consisting of command and control units and 10 missile launchers with their associated transport vehicles would be transported to the theater of operations. The fire unit would move to its combat position and be emplaced. Emplacement time was estimated at approximately 3 hr. The fire unit commander would receive his rules of engagement (ROE) from his higher headquarters, which during expected periods of combat would require “Weapons Free” (authorization to fire). Upon launch of a threat missile, overhead sensors would detect and report the launch directly to the KEI fire unit. The KEI command and control system would evaluate the threat, classify it, and launch a KEI interceptor at a predicted intercept point in space. Continuous updates would be provided to the interceptor based on overhead sensor data. 3 Ibid.
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34 FIGURE 2-1 KEI system integration. BMDS, ballistic missile defense system; CNIP, C2BMC network interface processor; JNIC, Joint National Integration Center; ROE, rules of engagement. SOURCE: Craig van Schilfgaarde, David Theisen, Steve Rowland, and Guy Reynard, Northrop Grumman Corporation, “An Assessment of Concepts and Systems for U.S. Boost-Phase Missile Defense in Comparison to Other Alternatives: Northrop Grumman Perspective,” presentation to the committee, July 13, 2010. Courtesy of Northrop Grumman Corporation.
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U.S. BOOST-PHASE DEFENSE 35 Airborne Laser The ABL program was planned to provide a boost-phase defense capabil- ity against a range of missile threats. This is no longer a program of record for the MDA but has been downgraded to a research program called the Airborne Laser Test Bed (ALTB), an advanced program for the directed-energy research program. For the purposes of this report, ABL is referred to as if it could provide an operational defense capability; where appropriate, the differences between the original ABL and the present ALTB are noted. The attractiveness of using directed-energy weapons, notably lasers, for boost-phase defense arises out of their potential to deliver a lethal dose of damage to a target at the velocity of light from long distances. The fundamental properties on which the choice of the laser depends include the wavelength, power output, efficiency of conversion of the primary energy into laser energy, and, of course, size and weight. So, in principle, the laser is ideal for boost-phase intercept since it is able to project a large amount of power at the speed of light over several hundred ki- lometers onto a modest-sized (~1 m) spot. To capitalize on these benefits, MDA established the ABL program, which was proposed to consist of a large airframe (a modified Boeing 747-400F airplane) carrying a multimegawatt laser, known as the high-energy laser (HEL). The HEL beam is directed onto the boosting missile body for several seconds. During that time sufficient energy per unit area (fluence) is delivered to cause enough heating to result in mechanical failure of the missile body itself, thus disabling it and preventing the payload from reach- ing its target. The advantage of this system is that it delivers a lethal fluence to the threat missile in a matter of seconds from a great distance. Because the laser beam travels at the speed of light, the distance from which the threat can be intercepted is not limited by the flight time of a rocket interceptor. Rather, the range is limited by the fluence required, the laser power, and the ability to focus the beam onto the target at low elevation angles through the atmosphere. The ability to focus depends on the laser beam quality and issues of light propagation in the atmosphere itself. The beam propagation limitations are complex and are provided in the classified annex (Appendix J).4 Figure 2-2 displays key parts of the ABL system aboard the Boeing 747- 400F. HELs are located in the body of the airframe, and the beam exits the plane at the nose, directed by a large (1.5-m-diameter) movable mirror in a turret. 5 The beam may be directed anywhere within a sphere with a cone cut out in the back- ward and forward directions with respect to the line of flight. The mirror rotates 4 David K. Barton, Roger Falcone, Daniel Kleppner, Frederick K. Lamb, Ming K. Lau, Harvey L. Lynch, David Moncton, et al., 2004. Report of the American Physical Society Study Group on Boost- Phase Intercept Systems for National Missile Defense: Scientific and Technical Issues, American Physical Society, College Park, Md., October 5. 5 Ibid., p. S299.
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36 MAKING SENSE OF BALLISTIC MISSILE DEFENSE FIGURE 2-2 Cutaway of the ABL system showing its key parts. SOURCE: Col Laurence Dobrot, USAF, Missile Defense Agency, “Airborne-Laser System Program Office: Pre- sentation to the National Academy of Sciences,” presentation to the committee, January 14, 2010. within the turret so that the beam may be directed by up to about 120 deg from the line of flight.6 The turret rotates so that any angle around the line of flight may be chosen. The ABL must be on station near the location from which the threat missiles would be launched. One or more ABLs would orbit in figure 8-like patterns in that vicinity. Such patterns allow an advantageous side-on view of the potential threat all of the time except when the airframe must turn at the end of the 8; however, a side-on or head-on attitude is always maintained by choosing the correct direction of circulation in the 8. The ABL would fly at an altitude of ap- proximately 12 km in order to minimize the amount of atmosphere through which the beam must travel. For redundancy and for dealing with multiple launches, two ABLs would cover one threat area. Such redundancy would be necessary during refueling operations to avoid gaps in coverage. The ABL would operate autonomously to identify threats by means of on- board IR sensors that detect the exhaust plume of the boosting missile. With knowledge of the location of the threat, the tracking illuminator laser (TILL) is activated to acquire the target, determine the exact aim point desired using the image of the nose, and provide illumination for first-order adaptive optics (AO) corrections. (Astronomers have used AO to at least partially cancel out atmospheric disturbances.) The beacon illuminator laser (BILL) places its beam 6 Ibid., p. S339.
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U.S. BOOST-PHASE DEFENSE 37 on the missile body, and that image provides the higher order correction infor- mation. Finally, the chemical oxygen-iodine laser (COIL) is activated with the HEL focused on the target for long enough to deliver the fluence required to induce mechanical failure of the missile. Mechanical failure results from heating a metal sufficiently to weaken it. It is not necessary to melt the metal to weaken it considerably. The failure itself may come from rupture due to pressure inside the container or from a loss of strength to resist the axial forces of acceleration of the boosting missile. There will probably be a clear optical signature of the mechanical failure to confirm the intercept. The signature may be an explosion or very erratic flight of the booster. It is unlikely that the defense will know when a threat missile is likely to be launched. Therefore, the ABLs must be able to remain on station for extended periods. Providing continuous coverage will require in-flight refueling and a handoff to other airframes to relieve the crew or provide other maintenance for the airframe or its systems. Other Space-Based Interceptors One problem of surface-based (i.e., on land, at sea, or in the air) KKVs is their access to the threat missile. There is a limit on how far a KKV can be based from the intercept point (not the launch point); this limit depends on the fly-out time of the interceptor and the burn time of the threat. A country that is large enough can deliver an array of missile threats that are not vulnerable to surface- based intercept in their boost phase. There may be political constraints on basing interceptors outside enemy territory, in neighboring countries. One way to avoid the geographic constraints suffered by surface-based interceptors is to base them in space, on platforms that carry one or several such interceptors. The enemy may thereby be denied all locations within the latitudes of the orbits. This is the attractive feature of space-based interceptors (SBIs). At this time there is no program of record within MDA for SBIs. This report noted large differences in the size estimates of Lawrence Livermore National Laboratory’s (LLNL’s) KV and that of the more conservative estimate found in the 2004 American Physical Society (APS) report previously noted. The com- mittee’s assessment of these differences and their validity are discussed in the classified annex (Appendix J). In short, the committee believes the LLNL KV was much lighter because it had much less divert velocity propulsion, apparently because it separated from the booster first stage much later than did the APS KV design. The committee believes the sizing methodology used in the APS report
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38 MAKING SENSE OF BALLISTIC MISSILE DEFENSE is more realistic.7 In addition, MDA canceled the Space Test Bed program in its 2010 budget. Moreover, in previous budgets, MDA had established the Space Test Bed to explore con- cepts for and to conduct research to support potential deployment of boost-phase intercept defenses in space. In the 2009 budget, MDA had planned to spend about $300 million for that research, and the Congressional Budget Office’s (CBO’s) projection of DOD’s plans, based on the 2009 future years defense plan (FYDP), incorporated the assumption that an operational space based interceptor system would be developed and fielded.8 The SBI platforms would be placed in multiple rings of satellites, with multi- ple satellites per ring.9 The orbits are inclined with respect to Earth’s equator, and the maximum latitude that the SBIs can cover is a little larger than the inclination angle. Such a constellation of satellites results in nonuniform coverage of the ground, where “coverage” means the number of satellites that are within range to deliver an SBI to a threat missile within the time window. Generally speaking, one wants to have at least one SBI within range, but it may be desirable to have more than one for redundancy or to deal with raids. There is substantially better coverage (i.e., more satellites within range) for latitudes near the orbit inclination angle and poorer coverage at low latitudes. However, coverage at latitudes above the orbit inclination rapidly drops to zero above the latitude of the inclination of the orbit. Airborne-Based Interceptors Recently, ABIs, also known as airborne hit to kills (AHTKs), have been reconsidered and show some potential applications in certain conflict scenarios. The primary difficulty with ABIs, like all other proposed kinetic boost-phase systems, is the need to be close enough (within about 50 km) to the target so that an interceptor with a given speed and a KKV of sufficient agility can reach and successfully home in on the accelerating booster before the boost phase ends. ABI programs have existed in the past, but today only a few low-end ABI systems based on existing interceptors remain on the drawing boards—for example, the network-centric airborne defense element (NCADE), based on a modified advanced medium-range air-to-air missile (AMRAAM) missile, and 7 Ibid. 8 Congressional Budget Office. 2004. Alternatives for Boost-Phase Missile Defense, Washington, D.C., July. 9 The critical number for coverage is the average number of satellites within range, and that is well characterized by the product of the number of rings times the number of satellites per ring. The trade- off between the number of rings and the number of satellites per ring for a fixed product is slowly varying. In addition, the satellites were assumed to have a service life of about 7 years and the disposal of expired platforms is not taken into account.
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U.S. BOOST-PHASE DEFENSE 39 the air-launched hit-to-kill (ALHK) program, based on an air-launched version of the PAC-3 missile. These systems might be able to intercept boosting targets at very short range, but they rely primarily on aerodynamic forces for divert and, consequently, cannot intercept accelerating targets above approximately 30 km in altitude, where most of the boost phase occurs, especially for missiles with ranges beyond 1,000 km. Hence, they cannot provide a robust boost-phase intercept capability. ANALYSIS Overview A boost-phase defense system is one that presumably avoids the midcourse countermeasure problem, provided the system can intercept the hostile missile’s burning booster rocket with its bright exhaust plume before the hostile missile reaches its desired velocity and deploys its payload. If such a boost-phase defense system can achieve that end within the extremely short engagement window available, it can protect a large area against launches from a specific locale. In principle, boost-phase intercept is technically feasible and appears attractive. To take an extreme example, a soldier with a 50-caliber machine gun or handheld rocket launcher 300 yards from a missile launch pad could easily destroy that missile as soon as it lifts off its launch pad. This is so for three reasons: (1) the soldier can see the hostile missile as soon as it emerges from its launcher; (2) the speed and acceleration of the hostile missile at that time are very low compared to the fly-out velocity of the soldier’s firepower; and (3) the hostile missile’s mo- tion at that time is tracked by the soldier’s eyes and is predictable. For the same reasons, an Aegis SM-2 Block IV antiair missile can shoot down a short-range ship-launched Scud-type theater missile during boost if the Aegis ship is down- range within 50 km of the launch. Unfortunately, trying to intercept a hostile booster rocket (solid or liquid propellant) from a significant distance dramatically turns the tables. For one thing, there is not much time between knowledge of where the hostile missile is directed and the time available for the interceptor to reach out to hit the target at a militarily useful range. This is compounded by the fact that the hostile missile is traveling at about the same velocity as the interceptor and its acceleration is less predictable. Even so, it is possible to guide a suitably maneuverable interceptor in order to hit a hostile thrusting booster, assuming the interceptor can get there in time. As noted in Chapter 1, the committee had access to classified information provided by the Missile Defense Agency on its programs of record; however, the committee chose to 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
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40 MAKING SENSE OF BALLISTIC MISSILE DEFENSE not only requested by Congress but also helps improve public understanding of ballistic missile defense issues. The following analysis is based, in large part, on notional data developed by the committee and is stated as such throughout this chapter. While boost-phase defense has been advocated as the most efficient way to deal with fractionated payloads and exoatmospheric (midcourse) penetration aids, such systems are extremely vulnerable depending on threat booster charac- teristics and operational considerations. The committee’s analysis of boost-phase defense concludes that it could be technically possible in some instances but operationally and economically impractical for almost all missions. Time, Range, and Technical Constraints: Iran and North Korea as Examples As previously noted, the committee’s analysis focused on assessing U.S. boost-phase defense systems against ballistic missile threats from Iran and North Korea. Figure 2-3 illustrates the dilemma for all boost-phase defense systems (i.e., the pressing intercept timelines for both solid and liquid threat booster rockets) and specifically displays this dilemma for what most boost-phase defense advocates would call the less onerous of the two ballistic missile defense prob- lems—that is, defense against ICBMs launched from North Korea). Moreover, advocates for boost-phase defense would argue that because of North Korea’s relatively small size and proximity to a coastal boundary, Aegis ships along with military aircraft could get fairly close to the threat boost trajectories in order to minimize the reach required. In Figure 2-3, it is assumed that the threat was detected at an altitude above the cloud cover, which we would assume to be 30 sec after launch of a notional solid-propellant missile and 45 sec after launch of a notional liquid-propellant missile. In understanding the challenges of boost-phase defense of the U.S. homeland and Canada, it is helpful to begin by looking at the ground tracks of trajectories on the rotating Earth from launch to impact and where an ICBM payload lands as a function of where its boost is terminated. Figure 2-4 shows the ground tracks of ICBMs launched from Iran and North Korea to reach the United States. 10 While it is convenient to describe missile performance in a standard way, that is, on a nonrotating Earth basis—it is important, particularly for longer range threats, to consider rotating Earth effects. This is important both for assessing what territory is at risk for a given threat missile performance and for looking at the ability to engage such threats during their boost or early midcourse phase of flight. While there are additional second-order Earth effects—such as Earth’s oblateness (nonspherical shape) and local gravity variations—which must be considered in accurate targeting, these are not of importance for this discussion. 10 Figures 2-4 to 2-8 and Figures 2-11 to 2-16 were generated from the committee’s analysis using Google Earth. © 2011 Google, Map Data©2011 Tele Atlas.
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62 MAKING SENSE OF BALLISTIC MISSILE DEFENSE Countering Early Deployment of Chemical or Biological Submunitions in Theater Conflicts Chemical or biological submunitions deployed immediately after boost phase are a low-technology threat that could saturate terminal and exoatmospheric de- fenses at shorter missile ranges. Because such weapons are area dispersed and do not require precise delivery, it is not far fetched to contemplate that if each is en- capsulated in an ablative material such as silicone rubber to survive reentry, they could be deployed immediately after boost phase. While not a game changer on the battlefield, such weapons require the donning of protective gear, which would impede and disrupt combat operations. Such weapons are far more disruptive to civilian targets. The latter threat has been studied and found practicable when the short-range reentry heating is modest and the means for thermal protection does not need to be sophisticated. In such a case, the submunitions cannot carry and do not require individual guidance and control systems but simply are ejected at low dispersal velocity. Only boost-phase intercept, prelaunch attack, or midcourse sterilization of the threat volume would be able to counter this type of threat. It is one scenario in which intercepting a hostile missile in its boost phase of flight might be effica- cious. Specifically, carried by multimission aircraft as part of their ordnance load and having as their primary mission the destruction of a missile launch capability or other ground target, such airborne boost-phase interceptors could, once air superiority had been established, engage any weapons that were able to launch in an adversary’s airspace. Alternatively, some form of volume kill—sweeping or sterilizing the threat volume after the payload has been deployed—might be used. The sooner this could be done after submunition dispersal, the smaller the volume that would have to be swept but the more vulnerable the sweeper platform would be. Unfortunately, there is no effective volume kill capability other than the detonation of a nuclear weapon. Countering Ship-Based Theater Ballistic Missiles Launched with Early Deployed Submunitions Against CONUS, Deployed Forces, U.S. Allies, Partners, or Host Nations Some observers consider the possibility of attacks by short-range ballistic missiles launched from ships near U.S. (or allied) shores to be a very serious po- tential threat. Transfers of older liquid-fueled theater ballistic missiles (TBMs) to nonstate actors have already been reported. Ship-launched TBMs with chemical or biological submunition payloads from rogue or nonstate actors aimed at large U.S. coastal population centers would have no immediate return address. While the prospect of a nonstate actor getting nuclear material (at least enough for a dirty bomb) cannot be excluded, a simpler chemical or biological attack could do substantial damage and might be an attractive option for such an actor. Because the launch point for such a threat would, by definition, be relatively
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U.S. BOOST-PHASE DEFENSE 63 close to U.S. territory, boost-phase intercept could be practical. Existing SM-2 Block IV air defense interceptors launched from within 50 km of the ship launch- ing the threat could engage such shorter range threats during boost phase, within the atmosphere. In addition, CONUS-based tactical aircraft carrying weapons if developed for theater boost-phase intercept could be scrambled to fly CAP either over any suspicious ship that evaded detection before reaching a threatening range or until an Aegis ship arrived. For example, a fighter aircraft interceptor platform equipped with an appropriate acquisition sensor and perhaps a modi- fied AMRAAM could be first on the scene for that mission if no Aegis ship was within 50 km. These are not likely to be large-scale threats that warrant the development of a special system to counter them, and modified existing assets could probably play that defensive role at least for the coastal threat. Specifically, Aegis ships with some SM-2 Block IV interceptors that can shadow suspect ships closely enough to engage any launch in its boost phase, followed by a counterbattery strike on the ship itself, could be deployed on both coasts. Countering Long-Range Missiles Launched from North Korea Toward Hawaii or the Mid-Pacific There is a case in which the relative geographical location of a threat coun- try and its potential target would allow boost-phase interceptors to be stationed routinely in positions from which boost-phase intercept would be feasible. This case is the long-range threat trajectory from North Korea to Hawaii or other mid- Pacific islands.22 Here, three conditions would need to be met for such a boost- phase intercept to occur: (1) the threat would be coming toward the interceptor launch platform (an Aegis ship in international waters, say) so the geometry is at a favorable angle; (2) the boost-phase timelines would be long enough to allow a boost-phase engagement in that unique geometry; and (3) an SM-3 sized intercep- tor would have sufficient reach within a rational timeline, it would be externally cued, and its KV would have the necessary additional agility. It has been suggested by some that a capability exists for the essentially instantaneous detection of a missile launch from its silo or launch pad, which would allow earlier commit of a boost-phase interceptor and thereby somewhat extend its range. Of course, very early detection would buy many seconds more of additional fly-out time for interceptors than would waiting for sensor data (from a space-based infrared system (SBIRS)). Here, the idea would be to fire an interceptor toward a nominal point in the fly-out corridor as soon as a launch is detected and to update the interceptor during its powered flight, when better data 22 The “long-range” condition reflects that some potentially significant targets, like U.S. bases on Guam or the Japanese homeland, are so close to North Korea that a ballistic missile aimed at them would have too short a burn time (and too low a burnout altitude) for a boost-phase intercept to be feasible from an Aegis inteceptor on board a ship in the Sea of Japan.
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64 MAKING SENSE OF BALLISTIC MISSILE DEFENSE are available, diverting it to a better-predicted intercept point—with an interven- ing coast, if needed—before igniting a third stage. Boost-phase engagement firing doctrine calls for the interceptor to be used this way to divert during its powered flight in order to reduce the divert velocity and acceleration requirement for the kill vehicle to deal with; however, it does not commit interceptors until the threat’s heading can be estimated.23 Testing of Boost-Phase Defense Systems: Results to Date and Outlook The committee was tasked to assess the past and planned test programs’ value in demonstrating feasibility and the cost-effective utility of the KEI and ABL programs. While the cancellation of KEI and the realignment of the ABL program to an R&D test bed (with which decisions the committee concurs) have made this assessment somewhat moot, the committee has observations about both. Kinetic Energy Interceptor The KEI program was terminated after cost and schedule problems delayed flight testing of the vehicle. Both stages of the booster had been ground tested and were deemed ready for flight test, and simulations using some actual tactical warning and attack assessment (TWAA) elements were conducted with the battle management architecture. That said, the committee believes the foregoing analysis illustrates that no matter how successful tests might one day have been, the system would have had negligible utility as a boost-phase system because it cannot be based close enough to adversaries’ fly-out corridors to engage either long- or short-range mis- siles without being vulnerable to attack. Neither KEI nor any version of SM-3 that will fit on existing launchers has enough reach to have military utility as a boost-phase defense. The committee agrees with the decision to cancel the KEI program as such, but the booster rocket motors could, with some modifications, be used as part of a more effective Ground-Based Missile Defense (GMD) system. The committee returns to this subject—a recommended evolution of the GMD—in Chapter 5 of this report. Airborne Laser Several tests have been conducted with mixed results for one reason or an- other. None of the problems have been fundamental to successful operation of 23 The committee also shows that it is counterproductive to commit an intercept earlier than the timelines shown in Figure 2-3 even if the launch can be detected immediately (see classified annex, Appendix H).
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U.S. BOOST-PHASE DEFENSE 65 the laser or its beam conditioning and control. Several target missiles have been destroyed, but all the tests have been at ranges too short to have any military utility for boost-phase defense. The limitations of the ABL are due to the need to sight at low elevation angles through the atmosphere, which fundamentally limits the standoff range for boost-phase engagements. No amount of future testing is likely to change that limitation. Accordingly, the committee concurs with the DOT&E report, which con- cludes that the ABL has no operational utility for missile defense for a variety of reasons, not the least of which is the illogic of placing such an expensive asset in harm’s way because of that range limitation.24 The committee found no reason to believe that ABL could ever be an effective boost-phase defense system, and it believes that the reversion of the ABL to a research and development test bed was a sound decision. There are logical applications that were identified by the Defense Science Board in an unclassified report that do not entail such short reaction times, going in harm’s way, endurance on station, or atmospheric problems at low elevation angles.25 Specifically, the single existing ABL could serve as an emergency anti- satellite (ASAT) device. The aircraft could on its own timeline be positioned to deposit energy on a spacecraft for dwell times limited only by its entire operating time at very high angles of elevation without going anywhere near an adversary’s air defenses. Advanced high-powered solid-state or hybrid lasers could be tested on board as well. FINDINGS Terrestrial-Based Boost-Phase Defense Major Finding 1: While technically possible in principle, boost-phase missile defense—whether kinetic or directed energy, and whether based on land, sea, air, or in space—is not practical or feasible for any of the missions that the com- mittee was asked to consider. This is due to the impracticalities associated with space-based boost-phase missile defense (addressed in Major Finding 2), along with geographical limits on where terrestrial (nonspace) interceptors would have to be placed and the timeline within which such interceptors must function in order to defend the intended targets. • Intercept must take place not just before burnout of the threat booster but also before it reaches a velocity that can threaten any area to be protected. 24 DOD Office of Testing and Evaluation. 2010. “Airborne Laser (ABL) Assessment of Operational Effectiveness, Suitability, and Survivability,” January. 25 Defense Science Board. 2001. Defense Science Board Task Force on High Energy Laser Weapon Applications. Office of Under Secretary of Defense for Acquisition, Technology, and Logistics, Washington, D.C., June.
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66 MAKING SENSE OF BALLISTIC MISSILE DEFENSE Because of the short burn times of even long-range ballistic missile boosters, the interceptor launch platform cannot for its own survivability be so close to the ter- ritory of an adversary as to be vulnerable to the adversary’s perimeter defenses, but it must be close enough to the boost trajectory so that the interceptor can reach the threat missile before it reaches its desired velocity. • Surface-based boost-phase interceptors are not feasible against a large country like Iran for missiles of any kind unless the interceptor platforms are based in the southern Caspian Sea. While it has been suggested that unmanned stealthy aircraft could loiter inside or close to the borders of an adversary, the committee does not believe it to be a feasible approach against a country with an effective air defense like Russian S-300 SAMs, in the face of which stealth aircraft will have a limited time of invulnerability as they maintain station in an environment with a high-density air defense sensor. Range Limits In practice, the operational limits on both kinetic and laser interceptor ranges necessitate that boost-phase defense platforms be located near likely launch sites (or, more precisely, near possible intercept points). Locations that meet the re- quirements are available only in certain limited circumstances—a relatively small threat nation and good access to areas near it over international waters or friendly territory and outside the range of its air defenses. For kinetic interceptors, range is limited by the short duration of powered flight for ballistic missiles—approximately 180-250 sec for ICBMs (although some liquid-fueled types may have longer boost times) and approximately 60-180 sec for short-, medium-, and intermediate-range ballistic missiles. Boost-phase defense of allies or deployed forces against shorter than inter- continental range attacks requires even closer stationing than for longer range threats, because shorter boost times and lower altitudes at burnout—which are the determinants of the windows for boost-phase intercept and of the proximity requirement for both kinetic and laser intercept—are even more demanding. Only in highly favorable geographic situations, e.g., trajectories from North Ko- rea to Hawaii and some other Pacific Ocean targets, is it likely that boost-phase interceptor platforms could be located so as to overcome the time, distance, and altitude constraints. Despite their essentially unlimited speed of “flight,” the use of lasers as the kill mechanism does not avoid the requirement for relatively close-in stationing of the interceptor platform. Lasers operate at the speed of light, but they are range limited because laser power deteriorates with distance from the target. Moreover, although the laser beam reaches the target at the speed of light, it must dwell on the target for several seconds to deposit sufficient energy on the booster to destroy it. The altitude of the target at thrust termination and of the platform for the interceptor also contribute to loss of power on the target, limiting effective
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U.S. BOOST-PHASE DEFENSE 67 ABL range. The dwell time relative to the short duration of an engagement also limits the raid handling capability of any laser ballistic missile defense system. The net effect of these time, altitude, and range constraints is that both ki- netic and laser boost-phase interceptors must be ready to engage from within a few hundred kilometers of the intercept point. As a practical matter, the intercep- tor platforms must be ready to engage on or over international waters or friendly land areas. (It is sometimes claimed that stealth UAVs armed with boost-phase interceptors could operate in an adversary’s air space. However stealth is ex- tremely difficult to maintain for platforms loitering for long periods in airspace under surveillance by a reasonably capable air defense.) Decision Time and Command and Control Missile defense operates within the established military chain of command and employs systems of control and authorization that are consistent with stan- dard operational practices that have withstood the test of time and suit real-world considerations. In standard U.S. practice, weapons release authority is reserved for the higher command echelons, indeed ultimately for the President as commander in chief of the armed forces. Reliable and redundant communication links tie the release authority to the personnel in immediate control of the weapons system in ques- tion. However, it is equally a principle of the command and control system that requirements for higher-level authorization should not be so inflexible as to delay action to the point of ineffectiveness. Rules of engagement—which can change as threat conditions change—are guidelines for action, including when time or other considerations make seeking higher authority infeasible. The special circumstances of missile defense—the potential of a missile at- tack to do massive damage, the ramifications of mistakenly destroying a foreign nation’s space launch vehicle (or even a routine developmental test missile), the possibility of creating space debris (or debris or even weapons falling to Earth), the compressed timelines and heavy reliance on sensor data—make it difficult to strike the appropriate balance between higher level—ultimately Presidential— control and sufficiently rapid response. These problems arise for any missile defense. The flight time for an ICBM attacking the United States from Iran would be only about 40 minutes, and all other flight times can be shorter. The time needed to detect and characterize a threatening launch—probably on the order of 1 min—and the time needed to conduct the intercept after weapon release—on the order of 15-17 min for mid- course intercept—leave a window of only a few minutes for requesting release authority, for the decision maker to consider and make the decision, and for that decision to be communicated to personnel who control the interceptor system. The problem is challenging enough for midcourse intercept, where the win- dow for engagement would be a few tens of minutes. Even more daunting would
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68 MAKING SENSE OF BALLISTIC MISSILE DEFENSE be the authorization of a boost-phase intercept, for which there would be virtu- ally no time because the interceptor would have to begin the engagement within seconds of the sensors reporting that a hostile launch had occurred. The short boost period not only imposes limits (far more significant for ki- netic than for laser-kill systems) on the time available for the intercept itself, it also means—for either laser or kinetic kill—that there be very rapid detection of the launch; its classification as threatening; tracking; decision and release author- ity to engage; and execution of release with all of these in addition to whatever time is needed for the engagement itself. Accomplishing this in the time available is a formidable operational challenge. The short time for intercept raises an important policy question. To allow boost-phase interceptors to be fired within a few tens of seconds of detection of the launch of the attacking missiles, authority to engage would have to be del- egated to the military personnel with immediate control of the system. Indeed, in practice, the “decision” to intercept would need to be made largely by a computer program, with human input essentially limited to confirming that the system ap- pears to be functioning properly. Accordingly, civilian and higher level military authority would have to be exercised by determining the rules of engagement that were embodied in the computer program rather than in real time during an actual attack. Other Issues A significant technical limitation of boost-phase intercept, in addition to those presented by the short powered flight of the target, arises from the fact that ballistic missiles are accelerating nonuniformly during powered flight, not to mention almost discontinuously at staging events. This further complicates predicting the target’s future location, which for kinetic-kill intercepts increases the divert requirements for the kinetic-kill vehicle. Also, the target is accelerating rapidly, which means that the interceptor must have a comparable acceleration capability. As a result, kinetic-kill vehicles designed for midcourse intercepts will have limited boost phase intercept capability even if one assumes they are stationed within range of the intercept point. These requirements for boost-phase kinetic kill can be met technically, but they add to the weight and complexity of boost-phase intercept systems. A further technical and operational issue for boost-phase intercepts is that even a successful intercept has the “shortfall” problem—that is, the potential not just for fragments of engines, fuel tanks, and the like but also for an intact and armed nuclear weapon to fall on friendly or neutral territory. Moreover, it is a misconception that a boost-phase intercept could cause threat missile debris to fall on the country of origin. In short, it is physically impossible for this to happen unless the interceptor is based in the country of origin and is close enough to the threat launch point to intercept the threat in the atmosphere.
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U.S. BOOST-PHASE DEFENSE 69 Indeed, by the time of intercept, which would take place relatively late in powered flight and well above the atmosphere, the reentry vehicle (RV) would already have been given sufficient velocity to continue on a trajectory that could extend into the original target area, or at least into friendly or neutral territory, and produce a nuclear detonation on impact. In principle, a kinetic-kill boost-phase interceptor could be aimed so as to impact the RV containing the warhead (as contrasted to the booster itself), but ensuring such impact would be challenging, because of uncertainties about the position of the RV relative to the hot rocket exhaust, which is guiding the interceptor. A laser kill mechanism, even if properly aimed, would probably not be powerful enough to destroy a warhead carried on an RV hardened to survive reentry. It might, however, be possible to count on midcourse defense to deal with RVs that “escape” from a boost-phase intercept. It can therefore also be concluded that none of these measures to mitigate “short- fall” are likely to be effective, and that the consequences of a nuclear detonation on land “caused” by a U.S. intercept would be so severe that a boost-phase system must constrain intercepts to windows that minimize the risk of an RV falling on land. Such a constraint would, however, add another significant limitation to the already extremely tight window for intercept. Finally, boost-phase intercepts are not immune from countermeasures, in- cluding hardening to reduce the booster’s vulnerability to lasers, spoofing precur- sor launches, and the like. Iran has conducted tests in which several missiles of various types were launched nearly simultaneously. A nation could seek to defeat a boost-phase defense by launching several decoy boosters at the same time as the actual missile in the hope of confusing, or even overwhelming, the defense’s sensors and data processors. Even more sophisticated countermeasures can be postulated—for example, fractionated upper stages—though typically they come at a price to the offense in terms of complexity and reduction in volume available for the weapons payload.26 Overall Evaluation As a practical matter, however, these other potential disadvantages would be dwarfed by the fact that both kinetic and laser interceptors would have to be on platforms relatively close to the targets. Even leaving aside how such proximity would expose the interceptor platforms to attack, this range-determined constraint makes boost-phase intercept operationally infeasible, because, except in a few cases, it would not be realistic to count on a boost-phase intercept platform being close enough to effect intercept. • In particular, Iran is too large geographically (and its northern neighbors 26 Additional discussion on decoys and countermeasures is provided in the classified annex (Ap- pendix J).
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70 MAKING SENSE OF BALLISTIC MISSILE DEFENSE too unlikely to consent to U.S. boost-phase intercept overflights or basing) to make boost-phase operationally feasible, even against liquid-propellant ICBMs. • By contrast to Iran, the small size of North Korea and its long coastlines mean that boost-phase intercept for ICBMs is not ruled out by geography, as long as North Korea sticks to liquid-propellant engines, and a large enough interceptor such as KEI could be based at sea, as explained below. • In general, boost-phase intercept systems are more feasible the longer the boost time of the target missile. Therefore, they tend to be more feasible against liquid-propellant missiles than solid-propellant missiles, owing to the longer boost times associated with the former. However, it would be imprudent to justify boost-phase intercept development based on its potential against liquid-propellant missiles when solid-propellant missiles are an obvious countermeasure; such a system could become obsolete as soon as it is deployed. In fact, the deployment of a boost-phase intercept system would likely stimulate the development of solid-propellant systems if they were not already being pursued for other reasons (e.g., solid-propellant missiles are more suitable for mobile deployment and hence can survive better against air attack). For example, Iran already has tested a two-stage solid-propellant medium-range ballistic missile (MRBM). Boost-phase intercept deployment against liquid-propellant missiles would be justified only if a hostile country does not, or cannot, deploy solid-propellant ICBM technology, as was the case for the former Soviet Union for almost 40 years. So far, there is no sign that North Korea is working on solid-propellant rockets for longer range missiles, but it could shift toward solid propellant, possibly with assistance from Iran, with which it has significant cooperation. The question becomes, Should the United States invest in a boost-phase system with some capability against liquid-fuel North Korean ICBMs if that country might shift to solid-fuel rockets before or soon after the system becomes operational? • There may be specialized cases in which boost-phase defense is feasible because either the threat must come toward the platforms or the platforms can be placed close enough to the threat and in an adequately benign environment. For example, a boost-phase intercept might be workable if the threat is North Korean medium- or long-range missiles heading toward U.S. bases in the western Pacific and therefore flying toward the Sea of Japan, on or over which boost-phase in- tercept platforms could be stationed. In this situation, and comparable situations elsewhere, the platform proximity problem is manageable, because the threat is coming toward the interceptor. Space-Based Boost-Phase Defense Major Finding 2: While space basing for boost-phase defense would in principle solve the problems of geographical limits that make surface-based boost-phase intercept impractical, the size and cost of such a constellation system is extremely
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U.S. BOOST-PHASE DEFENSE 71 high and very sensitive to the timeline in which interceptors must be launched. As a result it is susceptible to countermeasures such as salvo launches that either delay and reduce its coverage or squander space-based intercepts. • In principle, a constellation of satellites equipped with boost-phase interceptors could be configured so as always to be geographically in range for an intercept. The number of satellites required depends, in part, on the burn time and altitude of the threat missiles. Shorter powered flights of solid-fueled threat missiles require many more satellites for coverage. Shorter range missiles with their shorter burn times and lower burnout altitudes cannot be engaged by space- based boost-phase intercepts. • The total life-cycle cost of placing and sustaining the constellation in orbit is at least an order of magnitude greater than that of any other alternative and impractical for that reason alone. Overall Evaluation Space-basing for boost-phase intercept would, in theory, solve the problems of proximity that make surface- and air-based boost-phase interceptors generally impractical. In principle, a constellation of satellites equipped with boost-phase interceptors could be configured so as always to be geographically in range for an intercept. The number of satellites required would depend in part on what threats are to be defended against. Shorter powered flight times for the threat missiles would require more satellites for coverage. A space-based system would have to overcome objections (and, arguably, legal obstacles) to “weapons in space.” More important, a space-based system would be vulnerable to the sort of primitive ASAT device that a country capable of deploying an ICBM would probably be able to develop. The most powerful objection to a space-based system, however, is the total acquisition cost (both initial and replacement satellite costs plus launch costs) for the large number of satellites needed for continuous coverage of potential threat launch locations because of the relative motion of satellites in orbit to Earth below (see Appendix J in the classified annex). Some 700 satellites would be required for defense against liquid-fueled ICBMs and some IRBMs, with some residual capability against solid-fueled ICBMs. For confident defense against solid-fuel ICBMs, as many as 1,600 to 2,000 satellites would be needed. The total life-cycle cost of developing, building, launching into orbit, and maintain- ing in orbit, even an austere and limited-capability network of 650 satellites, for example, would be approximately $300 billion (in FY 2010 dollars). The cost for greater capability would be correspondingly greater. From an annual acquisi- tion cost perspective, these relatively high costs over the time frame estimated to provide operational space-basing for boost-phase interceptors would probably prove unaffordable.
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72 MAKING SENSE OF BALLISTIC MISSILE DEFENSE Airborne-based interceptors (ABIs) have been proposed for boost-phase defense and possibly for terminal defense. All near-term systems on which the committee was briefed have very limited boost-phase capability (intercept ranges on the order of 50 km). The limited ranges of which a system would be capable do not allow boost-phase intercepts from outside the territory of even a small country such as North Korea. Such a system would be viable only if the aircraft could fly CAP for extended periods of time over enemy territory after air su- premacy had been achieved.