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U.S.
National Missile Defense Options
Pugwash
Occasional Papers, II:ii,
By George N. Lewis As a presidential candidate, George W. Bush clearly outlined some of his preferences regarding national missile defense (NMD) options for the United States:
Bush also made it clear that he would not allow continuing Russian objections to prevent deployment:
As these statements indicate, not only is George W. Bush committed to deploying NMD, but he would like to do so rapidly, with a larger system than that planned by Clinton, one that would extend coverage beyond US territory to cover America’s allies and US forces deployed overseas, and he would not allow Russian objections to prevent deployment. Is NMD deployment inevitable? NMD deployment, however, is not yet a certainty. Although candidate Bush strongly endorsed NMD, it is possible that as President his perspective could change, leading to at least a significant deferral of deployment. There are a number of factors that might lead to such an outcome. First, and perhaps most importantly, are the results of upcoming NMD intercept tests. The failure of the second and third intercept tests, in January and July 2000 respectively, certainly had a significant effect on President Clinton’s decision in September 2000 to defer deployment. The fourth intercept test will likely occur within the first six months of the Bush presidency, and several additional tests could occur before a decision to deploy takes place. If all or most of these tests fail, the momentum towards rapid deployment could be seriously dampened. Second is the continuing resistance of Russia to modifying the ABM Treaty. If Russia refuses to accept alterations to the Treaty, the United States would have to withdraw from the Treaty in order to proceed with NMD deployment. Although George W. Bush has stated his willingness to withdraw from the Treaty, the resulting negative international consequences would pose immediate and direct costs that can not be taken lightly by any president. While a faction of Congressional Republicans does indeed favor simply eliminating the ABM Treaty, Bush and his closest advisors do not appear to fall into this camp. Nonetheless, while they are likely to spend at least some time trying to persuade Russia to modify the Treaty, a Bush administration is unlikely to allow Russian resistance to prevent deployment for an extended period of time. Third is continued opposition by US allies to an American withdrawal from the ABM Treaty. Our European allies are almost unanimously opposed to America deploying NMD over Russian objections. This opposition is important because it not only heightens the cost of withdrawing from the Treaty, but it prevents Russia (and China) from being isolated in their opposition to NMD. For over a year, the Clinton administration tried and failed to get the European allies and Canada to endorse its planned NMD system. While the Bush administration will likewise seek allied support, it is unlikely to be any more successful as long as Russia continues to strongly oppose the system. Finally, there are developments that could decrease perceived missile threats that stimulated much of the interest in NMD in the first place. Improved relations with North Korea and Iran, and in particular, an agreement with North Korea curtailing its missile program, are possible and could weaken support for NMD. On the other hand, positive changes in relations with countries such as North Korea and Iran will likely take too long to have much of an effect on Bush’s NMD decision, and there are always other threats, such as China, that can be (and are) used by those arguing for deployment. Even if all the above factors did mitigate against NMD deployment, President Bush and his advisors appear to be firmly committed to NMD. The Republican-controlled (albeit narrowly) Congress, frustrated by what it sees as a series of delaying tactics by the Clinton Administration, will continue to push hard for a rapid deployment. Especially in light of existing legislation (signed by President Clinton) mandating deployment as soon as technologically feasible, it thus appears quite likely that President Bush will take steps to begin NMD deployment by the end of the first year of his administration. Basic NMD Components Should President Bush seek to deploy NMD as rapidly as possible, his system will almost certainly include the same basic components as Clinton’s proposed system, though it could differ significantly in its overall architecture and might add additional components, such has sea-based interceptors. Accordingly, unless President Bush chooses to pursue anentirely new direction, such as a boost phase approach, his NMD system will share many of the same strengths and weaknesses as the Clinton system. The NMD system proposed by Clinton consisted of a relatively small number of component types, most of which were well along in development: ground-based interceptors equipped with homing Exo-atmospheric Kill Vehicles (EKVs), X-band radars, upgraded early warning radars, and the SBIRS-Low space based missile tracking system. These components, which could be deployed in various configurations, would be supported by early warning satellites and would be knit together by command and control facilities and communication relays. The "weapon" of the NMD system is the EKV, which is propelled towards its target by the ground-based interceptor’s high-speed booster rocket. The EKV, which operates above the atmosphere in the relatively long midcourse portion of its target’s flight, uses infrared (and possibly visible light) sensors to home in on its target. It then attempts to destroy the incoming missile’s warhead in a direct, high-speed collision. The EKV has had three intercept tests so far, only the first of which was successful. The key sensor supporting the NMD system is the X-band radar ("X-band" refers to the radar’s operating frequency of about 10 GHz). This is a large, phased-array radar specifically designed for NMD use, and optimized for precision tracking and discrimination purposes. A prototype X-band radar has been constructed at the US missile test range at Kwajelein atoll in the Pacific and has participated in the intercept tests. Additional radar capabilities would be provided by upgrading the United States’ five existing large phased-array early warning radars to give them the ability to track missile targets accurately enough to guide the interceptors. These modifications involve relatively minor software and processing hardware upgrades and do not change the apertures or average powers of the radars. Despite such improvements, these radars would have little capability for discriminating between actual warheads and decoys and other objects traveling together in the vacuum of space. The third major sensor system is the SBIRS-Low (Space-Based Infrared System – Low earth orbit) missile tracking system. The system, consisting of a constellation of approximately 24 satellites, would use infrared and visible light sensors to track missiles and their warheads with sufficient accuracy to guide the EKV interceptors to their targets, and would also assist with target discrimination. SBIRS-Low inherently provides almost complete global coverage (except for the polar regions) and is also intended to support upper tier theater missile defense (TMD) systems such as Navy Theater Wide and the US Army’s THAAD system. However, SBIRS-Low is unlikely to be available in time to be part of an initial NMD system deployment. Under the Clinton plan, NMD would have been deployed in phases. The initial phase (the C-1 system) would deploy first 20 and then 100 interceptor missiles in central Alaska and a single X-band radar at Shemya, at the western end of the Alaskan Aleutian island chain. These locations are clearly directed against North Korea (although China may well view them as directed against itself). Sensor coverage for missiles approaching from other directions would be provided by upgrading the early warning radars in Alaska, California, Massachusetts, Greenland and Britain. This initial system is intended to be able to defend the entire United States from a few tens of warheads equipped with only "simple" (i.e., ineffective) countermeasures from North Korea, or a smaller number of warheads (because of the limited capabilities of the upgraded early warning radars) from the Middle East. Had President Clinton made a deployment decision in 2000, the C-1 system could have been operational by 2005, although 2007 seems a more realistic date. The full NMD system contemplated by Clinton (the C-3 system) would not have been operational until 2010 at the earliest. The Pentagon’s notional architecture for C-3 added a second interceptor site in North Dakota (the former Safeguard site at Grand Forks), bringing the total number of interceptors up to 200-250. The C-3 system also included a number of X-band missile radars at sites spanning much of the northern hemisphere, as well as the SBIRS-Low space-based missile tracking system. An April 2000 estimate by the Congressional Budget Office put the cost of C-3 at about $60 billion, although the final amount would certainly be higher.3 Supporters of the proposed Clinton NMD system claimed it would be highly effective against small-scale missile attacks. Critics, however, presented analysis showing that the system could be defeated by offensive countermeasures well within the means of countries such as North Korea or Iran.4 Such criticisms, combined with the failure of the January and July 2000 intercept tests, contributed to increased skepticism regarding the effectiveness of the Clinton system, which in turn led to greater interest in NMD alternatives and improvements that might be more effective. The fact that Clinton’s speech on September 1 announcing the postponement of an NMD decision also noted that even the C-1 system was unlikely to be operational until 2007 only increased the interest in some quarters of finding new and more effective NMD alternatives. Bush administration NMD options Proceed with the current system This option would involve either an early decision to deploy, or continued development and testing, of the basic Clinton system. For NMD advocates, the primary advantage of this approach is that the Clinton NMD system technology is the most well developed and rapidly deployable (albeit in 2005-2007). Yet George W. Bush has repeatedly stated that this system is too small and it cannot meet his stated objective of also protecting US allies and forces overseas. Thus, President Bush is likely to proceed with a reconfigured and significantly expanded version of Clinton’s system. However, since many of the potential additions to the basic Clinton system could also be deployed independently as free-standing alternatives, it is useful to first review these systems as alternative options and then return to the possibility of adding them to an expanded version of the Clinton system. Sea-based midcourse defenses There is significant Congressional Republican support for deploying sea-based mid-course interceptors, either as a replacement for or as a supplement to a land-based NMD system. Such a sea-based system could provide earlier and additional intercept attempts, and could be used to expand the coverage of the NMD system to the entire world. Such a use of sea-based interceptors may be what George W. Bush has in mind when he says his NMD system will also defend US allies. Some leading advocates of sea-based defenses, such as the Heritage Foundation, view such systems as a temporary bridge to a space-based NMD system. 5 Critics of sea-based NMD argue that it will take much longer and be much more difficult and expensive to build than its supporters claim.6 A sea-based midcourse system would use existing or modified launchers and radars on some or all of the over 50 US ships equipped with the Aegis weapons system. The US is currently developing two theater missile defense systems, the Navy Area Defense and Navy Theater Wide systems, based on this equipment. The interceptor for a sea-based NMD system could be a variant of the SM-3 interceptor for the US Navy Theater Wide TMD system that is currently under development, or it could be a larger and faster missile (which might require modifying the launchers on the ships). An infrared homing kill vehicle, likely a modification of either the Light-weight Exo-Atmospheric Projectile (LEAP) developed by SDI or the land-based system’s EKV, would attempt to destroy the missile warhead in a direct high-speed collision. Supporters of sea-based NMD argue that such a system could be deployed rapidly and inexpensively, since it would based on the already existing Aegis infrastructure, and that such a system would be more effective than a land-based NMD system. Quite simply, these claims are incorrect. The Ballistic Missile Defense Organization (BMDO) reported in 1999 that such a sea-based system would both cost more and take longer to deploy than the currently planned land-based system.7 More importantly, sea-based NMD would operate in essentially the same way as the land-based system (i.e., it would use infrared homing, above the atmosphere, hit-to-kill interceptors, supported by radars and space-based infrared sensors), and thus would have all of the same vulnerabilities. In fact, the sea-based system would likely be even less effective because of the smaller size and more limited capabilities of its individual components. In particular, the current ship-borne Aegis radars are clearly inadequate for NMD purposes. Even if these radars are replaced (which would be quite expensive), the resulting radar capabilities would almost certainly be far inferior to those of the ground-based X-band radars. Thus a free-standing sea-based system would almost certainly be both more expensive and inferior in capability compared to a land-based system. However, the BMDO also concluded that a sea-based system incorporating the planned Block-II interceptors (currently scheduled for 22 Pugwash Occasional Papers, March 2001 deployment sometime after 2010) for the Navy Theater Wide TMD system could usefully supplement a land-based NMD system. As noted above, such interceptors could be used to make earlier intercept attempts and to expand the coverage of the NMD system overseas. In this approach, the sensors for the land-based system (including SBIRS-low) can be used to overcome one of the key problems of the free-standing sea-based approach – the limited capabilities of radars on the ships. Given the strong support for sea-based NMD among many Congressional Republicans and the general Republican distaste for anything having to do with President Clinton, it is not inconceivable that Bush could completely scrap the Clinton ground-based approach and proceed with an entirely sea-based (and space-based) approach. This seems quite unlikely, however, given the large cost, long timelines and limited effectiveness of such a system. Rather, it is much more likely, as is discussed below, that sea-based interceptors would be used to supplement a land-based system. Boost-phase defenses The inability of mid-course defenses to defeat a missile armed with many small submunitions released shortly after the end of the boost-phase, instead of a large warhead, plus their vulnerability to countermeasures, has increased interest in boost-phase defenses, several variants of which have been proposed. Boost-phase systems are designed to destroy offensive ballistic missiles early in flight, before the release of the warhead and its decoys or submunitions. Although some countermeasures to boost-phase defenses are possible, they do not face the daunting challenges of target discrimination and multiple submunitions faced by mid-course hit-to-kill interceptors, and so are likely to be more effective. Conversely, however, boost-phase interceptors have only three to four minutes to destroy the ballistic missile during its brief boost phase, and thus must be deployed close to the launch points because of this limited operational envelope. Some types of boost phase defenses may be able to cover a small country such as North Korea, but not larger countries such as Russia or China. Precisely because of this, boost-phase defenses could prove to be less threatening to Russia and China. Yet, while Russian President Putin’s proposal for a European missile defense system is sometimes (and apparently incorrectly) said to involve a boost-phase approach, neither Russia nor China has given any indication that it would find a boost-phase system to be acceptable. Despite these advantages, boost-phase systems face a number of operational constraints. The short range of most boost-phase systems means the general location of the threat must be known in advance, and could expose the boost-phase system to attack. Since most of the proposed boost-phase systems destroy the rocket booster and not the warhead, the issue of where the warhead comes down and what happens when it does is a potential problem. Saturation of boost-phase defenses by multiple simultaneous launches of offensive missiles could also be a problem. Finally, the relatively short response times required, at most a few minutes, have been raised as a concern. The US does have a boost-phase TMD system, the airborne laser, under development and has studied (with Israel) boost-phase TMD systems using interceptor missiles on aircraft. The BMDO reportedly had planned to complete a preliminary study of boost-phase options for NMD by the end of the year 2000. However, other than the Space-Based Laser, a holdover from the SDI Program that is two decades or more away from deployment, there are currently no NMD boost-phase programs underway. Future candidates for boost-phase defenses currently under discussion include: (1) a sea-based system that would adapt interceptors currently under development (but not designed for boost-phase intercepts) for boost-phase use; (2) a sea-based or land-based system using large interceptors specifically designed for boost-phase intercepts; (3) deployment of boost-phase interceptors on unpiloted aerial vehicles; and (4) use of the Airborne Laser TMD system currently under development as an NMD boost-phase system. Boost-phase options Some have suggested adapting near-term or future planned missile defense interceptors and deploying these on ships near suspected launch points.8 However, the use of near-term terminal-phase interceptors, such as those of the Patriot PAC-3, Navy Area Defense, or Arrow systems, does not appear workable except under extremely favorable conditions (for example, a launch site near a coastline). These interceptors are both too slow and cannot operate above the atmosphere (which limits them to intercepts only during the first part of the boost-phase). Longer-term, exo-atmospheric midcourse interceptors, such as those for the THAAD, Navy Theater Wide and NMD systems, may have some capabilities if deployed and used in a boost-phase role. However, these interceptors have not been designed to intercept accelerating targets such as missile boosters, which requires significantly greater divert capabilities than needed to intercept midcourse targets, which travel on predictable trajectories. Thus it is currently at best unclear if any of these approaches could work. Boost-phase defense using interceptors specifically built for boost-phase use has been proposed by Theodore Postol and Richard Garwin, who developed similar (but not identical) concepts that would use large (ICBM-sized) interceptor missiles equipped with homing kill vehicles deployed on ships, submarines, or fixed sea platforms, or on land in cooperation with Russia.9 The large size of these interceptors is driven by the need for high burnout speeds and by a large divert capability requirement for the kill vehicle, which leads to a larger kill vehicle mass than in midcourse interceptors. While such interceptors would almost certainly be more effective than mid-course or terminal interceptors used as boost-phase interceptors, none is under development at present. The use of small, high-speed interceptor missiles on unpiloted aircraft for NMD boost-phase purposes has also been suggested. At present, it is unclear if the kill vehicle and missile can be made small enough to make this approach practical. Instead of interceptor missiles, a boost-phase defense could use lasers. The US is currently developing the Airborne Laser (ABL), which would put a megawatt-class laser aboard a Boeing 747 aircraft for defense against theater missiles. Current plans call for a first test against a missile target (SCUD class) in 2003 and for deployment (of seven ABLs) beginning in 2007. The technical feasibility of the ABL is not yet firmly established, and probably cannot be until it is actually tested. Even if it is feasible, there are significant engineering problems that could substantially delay its deployment. If it works as anticipated, the ABL could have a range of perhaps 300 to 500 km against short-range theater missiles. However, it would likely have a greater range against intercontinental-range missiles, because these have longer boost phases, burn out higher in the atmosphere (so the laser beam has to pass through less atmosphere), and usually have thinner walls. If it works as planned, the ABL could cover a launch area comparable to or larger than that of interceptor-based systems. Theater missile defenses and NMD As previously noted, the Navy Theater-Wide (and more marginally THAAD) theater missile defense system could be formally incorporated into a land-based NMD system and used to supplement and extend its coverage. The Airborne Laser TMD system could similarly be incorporated into an NMD system as a boost-phase system. However, these systems could also be deployed independently of NMD to defend US allies and overseas forces from short and medium range missiles. In this way, these TMD systems could be viewed as supplementing the NMD system. Other planned, lower-altitude TMD systems, such as Patriot PAC-3, Navy Area Defense, Arrow, and MEADS, have no significant ability to engage intercontinental-range missiles, and thus can not play a significant role in defense of US territory. However, some of these systems could be used to defend against relatively short-range (1,500 km and less) missiles. For countries for which the missile threat is seen as coming from shorter-range missiles, such TMD systems would in effect be NMD systems. Thus in conjunction with an NMD deployment, President Bush could choose to forward deploy TMD systems to satisfy his requirement that US allies and forces deployed overseas be defended. However, such systems may not be as effective as the NMD system against missiles, particularly of intercontinental-range, unless fully supported by sensor systems equivalent to those available to the NMD system. Space-based weapons Any NMD system will involve space-based sensors. At a minimum, it will use the existing Defense Support Program (DSP) early warning satellite system or its replacement, the Space-Based Infrared System – High Earth Orbit (SBIRS-High). More importantly, Clinton’s full NMD system would also have included the SBIRS-Low space-based missile tracking system. This system is intended to provide high quality missile tracking data – adequate for guiding interceptors – over almost the entire world. However, Clinton’s plan did not include any space-based interceptors, lasers or other weapons. The only space-based weapon currently under development is the Space-Based Laser. The US is presently spending about $140 million per year on this system, which is intended to provide a boost-phase capability on a global basis. Current plans call for a possible in-orbit technology demonstration in the period 2012-2015, with possible deployment after 2020. Both of these are likely to be delayed, however, and recent BMDO program cost estimates are as high as $75 billion. It is clear that space-based weapons will not be available in time to play any role in a near-term NMD deployment. It is also likely that, if their high cost does not completely preclude deployment, such weapons would not be available until at least 2020. However, given the strong support for such weapons among some elements of the Republican party, it is quite possible that there could be a significant boost in spending on the Space-Based Laser, with the objective of accelerating its potential deployment and, less likely, that some development of space-based interceptors could begin. An expanded NMD system based on the components of the current system In this approach, the basic NMD components (X-band radars, Upgraded Early Warning Radars, EKVs on Ground-Based Interceptors, SBIRS-PAC-3 Intercept Sequence [BMDO] Low, etc.) developed for the Clinton system would be used as the basis of Bush’s NMD system, but the system would be significantly expanded. The Clinton system was specifically designed to be expandable, which is one of the reasons it causes such problems for nuclear arms control. This expansion could be accomplished in one or both of two ways. First, the system could deploy additional numbers of basic components (e.g., more interceptors at more locations). Second, different components, such as sea-based interceptors or the Airborne Laser, could be added to the system. This approach has a number of political advantages over other approaches, and thus seems likely to be the one adopted by the Bush administration. Because initial deployments would be similar to those of the Clinton plan, this approach could achieve an initial operational capability on about the same time scale as Clinton’s system, and probably faster than any other alternative approach. Second, the greater size of the final system could be portrayed as addressing some of the vulnerabilities of the Clinton system, although simply adding more of Clinton’s components might not actually accomplish this, since their fundamental vulnerability to countermeasures and submunitions would not be changed. Third, the inclusion of additional components, such as sea-based interceptors, would allow coverage to be extended to US allies, a stated Bush objective. Finally, even though the system would rely heavily on components developed during the Clinton administration, the complete system would be clearly different than that proposed by Clinton, leaving no doubt that this was a Bush administration system. It thus seems most likely that the Bush administration will opt for a reconfigured and expanded (additional interceptor sites and/or more interceptors) version of Clinton’s land-based NMD system. This system would be deployed in phases in order to get an early initial operational capability. To this core system, the Bush Administration would then add naval, boost-phase, and/or TMD components (with sea-based interceptors the most likely). As noted above, there is strong Republican support for sea-based NMD, and the BMDO has already stated that sea-based interceptors could be incorporated into a land-based NMD system. Ultimately, if sea-based NMD interceptors are deployed, technological forces seem likely to drive a convergence of land-based and sea-based systems. It has already been proposed that sea-based interceptors could use the land-based EKV kill vehicle, and both land- and sea-based interceptors would rely on essentially the same sensor network. In this scenario, naval ships would essentially become remote, mobile launch platforms for the land-based NMD system, extending its coverage over the entire globe. President Bush could additionally decide to formally incorporate the Airborne Laser into the NMD system, giving the system a boost-phase component. Perhaps somewhat less likely, this could also be done by deploying sea-based boost-phase interceptors. Summary In the months following his inauguration, President Bush will likely conduct a formal review of NMD options while trying to persuade Russia to abandon its opposition to modifying the ABM Treaty. At some point in 2001, however, it seems highly likely that President Bush will move rapidly to begin NMD deployment. Although he conceivably could completely scrap the Clinton administration’s NMD technology and move to an entirely different NMD approach, this would impose a substantial delay in achieving an initial NMD capability and thus seems improbable. Rather, what seems most likely is that the Bush administration will seek to deploy an NMD system whose initial phase (2005-2007) would be similar to that of the Clinton system, although larger and somewhat reconfigured. The Bush NMD system would then be subsequently expanded, with sea-based interceptors the most likely addition and with a boost-phase component also a strong possibility. George Lewis is Associate Director of the Security Studies Program at the Massachusetts Institute of Technology. He has a Ph.D. in physics from Cornell University. Prior to coming to MIT, he was at Cornell’s Peace Studies Program and at the Center for International Security and Arms Control at Stanford. For the last decade his work has focused on technical analysis of arms control and international security problems, with an emphasis on ballistic missile defense issues. Endnotes
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