F’hotocompoaition by Barbara J. Velarde and Mary Louise Garcia
tYISCLAIM1.R TIM! rcporl wab prcpued ● 5 dn a.count of work spon!ored by an agency of the Umted StAIcs Cio.crn. mcnl. Ncilher the Umled St.w.s (%ver.nmcnt ncw any agcn~y thetcwr. nor .ny of Ihcu employees. makes u} wzrr~nty. c\ Iwt’sj w Implied, or ~wumes any l.~al tiabtily or ccspanslbdity for lhc .CCW. 1c7. complclcncss, or uxf.lncss of any [email protected] on, apparatus, product. Or procms di$clowd. or rep. m%nls lhar il$ usc would not mfcmgr prtv. tcly owned nghls. Rcfcremx hcrcm to any $PC,LIIL’corn. mercht Produ.1, pro. css. or strm.c by trade qmc, lradcm~k, manufacrur~, m ~thcrwi~. d~~s not necessarily constitute or imply Its endorsement. recommendation. or lavocmg by the Unihxl States Government or any agemy lhcreof. The views and opinions of authors caprc$$ed hcrrm do not ne.. +xYMily !lal. or reflect thox c.( Ihc United State$ Government or my agency thcleof.
Ballistic Missile Defense: A Potential Arms-Control
.qo% G. E. Barasch
D. M. Kerr R. H. Kupperman’ R. Pollock H. A. Smith**
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— *Los Alamos Fellow. Executive Director, Center for Strategic and International Studies, Georgetown University, 1800 K Street, N.W., Washington, DC 20006. ●
* Los Alamos Consultant.
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Chairman, Mathematics Department, Arizona State
University, Tempe, AZ 85281,
BALLISTIC MISSILE DEFENSE: A POTENTIAL ARMS-CONTROL INITIATIVE by G. E. Barasch, D. M. Kerr, R. H. KuppermQ R. Poilock, and H. A. Smith
SUMMARY United States strategic forces must be restructured to meet national-security objectives in a changing world Growth and modernization of Soviet strategic missile forces are causing our land-based strategic missiles to become increasingly vulnerable to Soviet nuclear attack. American policy for deterring such an attack has evolved from strict reliance on the threat of assured Soviet destruction to include nuclear war-fighting concepts intended to deny Soviet hopes of winning the ensuing conflict. At the same time, events in Iran and Afghanistan have underscored the need to expand and modernize our conventional forces, requiring strict limitation of our strategic investments. For some strategic force configurations, the goals of flexible nuclear deterrence and strategic arms limitations appear mutually inconsistent. With such forces, prospects for arms limitations would degrade further if the current Soviet build-up were to continue, or if the Soviets were to install unilaterally an anti-ballistic missiIe system capable of wide-are% multicity defense, or both. ‘ However, if the United States installs an anti-ballistic missile system along with reduced but modernized offensive strategic forces, arms limitation appears compatible with both assured destruction and war-fighting deterrence policies. This conclusion appears equally valid for expanded Soviet forces even if the Soviets also install ballistic missile defenses. In particular, we have analyzed an American strategic posture including layered defense of MX missiles based deceptively in silos. The exoatmospheric-intercept component of this defense system could also defend some of our cities and industrial and military installations. If the United States were to adopt this strategic posture, we believe it would create incentives for the Soviet Union to restrain strategic-arms expansion. Mutual arms-control initiatives could follow. In addition, this defense system might offer stabfliing features: damage lhnitation for small attacks; nonoffensive crisis response; and relative insensitivity to technological change. These results do not seem to be available by deploying strategic offensive forces alone. Test and installation of the needed defensive systems are now precluded by the Anti-Ballistic-Missile Treaty adopted in 1972. An opportunity for Treaty reconsideration occurs in 1982. Substantiation of our results would suggest that consideration be given to Treaty moditlcations or to replacing the Treaty with other agreements. Such actions could lead to improved national security for the United States by enhancing our deterrent posture an~ at the same time, offer the potential for significant arm=ontrol initiatives.
I. INTRODUCTION Over the past two decades, significant changes have occurred in the long-standing competition between the United States and the Soviet Union. Many of these changes have been adverse to American interests. A shifl in the global balance of power has taken place, as a result of a determined Soviet expansion of its military power through growing defense expenditures. Critical strategic asymmetries between the two superpowers have thus emerged, including ditYering strategic concepts of nuclear deterrence and warfare. For some years American strategy rested on the premise that approximate equality of strategic forces would lead to stable nuclear deterrence, which would be achieved primarily through fear of mutual assured destruction. Consequently, policies on weapons systems that might threaten or undermine Soviet deterrent capabilities were eschewed by the United States as destabilizing. Although the Soviet Union has expressed enthusiasm for the goal of limiting American strategic forces, there is no clear evidence that they have embraced the restraint implicit in our policies. In contrast, the Soviets appear to have developed a strategy of seeking strategic superiority through balanced offensive and defensive forces, with survival as the objective if nuclear war should occur. The Soviets have exploited these asymmetries to attempt to undermine American assurances to its allies and to call into question the guarantee of America’s nuclear umbrella. In recognition of the growing strategic imbalance, the United States recently announced a modification of its nuclear targeting policy.* In addition to a punitive assured-destruction strategy, our retaliation would attempt to deny the Soviets any prospect of achieving war-fighting objectives by destroying a range of needed military installations. Elements of damage limitation in this “countervailing” nuclear strategy are perceived both to enhance deterrence prospects and to provide needed options should deterrence fail. The adoption of the countervailing strategy blurs somewhat the distinction between United States and Soviet doctrines but cannot by itself compensate for existing force asymmetries. Restructuring of our strategic forces is also needed. To allow the flexibility needed within the countervailing policy, American forces must be configured to serve both damage-limiting and assured-destruction roles. Invulnerable ICBMS can contribute to both deterrence policies. In an assured-destruction role, they provide an independent force within the strategic triad that could 2
retaliate if the other triad elements become vulnerable. If the Soviets shelter or harden their strategic industry in an attempt to interfere with our assured-destruction deterrent,z IC BMs have the needed accuracy and yield to counteract these actions. In a war-fighting role, ICBMS are the only strategic element capable of damage-limiting attacks on time-urgent military targets. As offensive technology improves, deterrent strategic forces become more vulnerable to attack, Force-structure or doctrinal changes may therefore be needed. In particular, the ICBMS are becoming increasingly vulnerable to Soviet nuclear attack, Remedies could include technology to reduce vulnerability, expansion of the forces, or changes in strategic doctrine, Doctrinal changes might include launch under attack or launch on warning, and might also necessitate preemptive attack upon time-urgent targets imd disruption of an expected attack. Although such changes in strategic doctrine could be an effective way to counter increased vulnerability, they impose imperatives for action, which, in time of crisis, might increase the probability of nuclear war. To avoid this scenario, our strategic forces must be survivable and our policy for using them must be stable in a crisis: we must be able to gather information and deliberate txfore we have to act. Expansion of strategic forces to compensate for increased vulnerability is not attractive from either an economic or an arms-control perspective. Thus, we are left with the alternative of developing remedial technology to reduce strategic-force vulnerability. There is, however, another constraint on our “selection of strategic-force structures. In recent years, the Soviets have been able to exploit political, economic, and security instabilities in the Middle East, Asia, Africa, and Latin America, without effective opposition from the West. The invasion of Afghanistan by the Soviet Union, coupled with the dilemma posed by the Iranian capture of the American hostages, underscores the inability of our strategic nuclear arsenal to deter attacks of a more limited or conventional nature. These events also give evidence of our failure to project an effective military presence sufficient to achieve American interests in low-intensity conflict. Whhout sufficient conventional forces, we face the increasing risk that nuclear weapons would be used in otherwise conventional contlicts, First use might be by the United States. National frustration, or a Sovietinspired attack on our vital interests, or an initially conventional war, might exceed our conventional-force
response capacity. Depending on our distress, we might then use nuclear weapons under the assumption that a nuclear exchange could remain limited. The Soviets could begin the exchange for similar or disparate reasons. If then our deterrence forces were overly vulnerable, Soviet options would include an all-out counterforce strike as an extremely effective way for them to limit damage to the Soviet Union. Thus, we will need expanded and modernized conventional forces to be able to avoid nuclear escalation from limited conflicts. This need defines a constraint on our strategic-force procurements: we cannot divert effort or funding away from the conventional forces that we need to support measured diplomatic and military responses. Our impotence in the Iranian crisis combined with the Soviet move into Afghanistan have effectively prepared America for remedial action. Before these events, the cold war was thought by liberal strategists to be a thing of the past; the Soviet Union and the United States needed one another or, at leas~ were bent on coexistence. The SALT II agreement, though hotly contested, might well have been ratitied by the Senate. Support for strategic programs was limited. Subsequently, what had sometimes been seen as the professional paranoia of the conservative military strategists began to appear as reality. America suddenly became aware that the Soviets had built up mammoth arsenals of both conventional and nuclear weapons. We now seem ready to seek solutions to the military imbalances. Our objective in this report is to explore technologies that will allow us to reduce forces and still meet both assured-destruction and damage-limiting strategic objectives. We attempt to find forces that will require minimum inventories and investments so as to maximize funds available for conventional forces. With limited inventories, the effectiveness of the strategic forces must be maintained in the face of maturing Soviet technology. Therefore it is essential that the force structure be sufficiently diverse to withstand technological surprise. It must also be relatively insensitive to “cheating” on arms-control agreements; it becomes very ditlcult, in a political context, to acknowledge cheating or even inadequacy of verification once a treaty is accepted. The force structure must be able to respond economically to possible threat growth so that incentives for continued Soviet proliferation are reduced or denied. The force must be able to achieve arms-control, assureddestruction, and damage-limiting objectives regardless of Soviet strategic policy. Finally, it should promote crisis stabilization.
These goals, when coupled with strict force limitations, appear from our analysis to be incompatible if we seek strategies that use only offensive forces and exclude defensive systems. This report, therefore, concentrates on ballistic missile defense technology that could be introduced soon and might measurably foster the goals of deterrence, arms control, and stability. Our analyses indicate that a properly coqflgured force including a ballistic missile defense system may permit deterrence at reduced force levels while resisting erosion of the deterrent by technological advances. Moreover, the effectiveness and structure of such a force do not appear to depend so crucially on treaty-specified actions as to be critically vulnerable to violations of arms-control agreements. Such a ballistic missile defense system would also add elements of crisis stability and damage limitation in case [email protected] were to fail. Defensive systems could be installed economically, together with or separately from the deceptive-basing modes now under development for MX missile deployment. ~ Previous consideration of ballistic missile defense has been seriously constrained by a long-standing and widely held concern: ballistic missile defenses would be destabilizing if capable of defending military, industrial, and urban targets. Such area defenses would presumably interfere with the ihaintenance of assured-destruction retaliatory forces, thus tempting the nation possessing defenses to launch a preemptive strike. Defense installations would presumably also lead to a defensive arms race coupled with the ongoing offensive arms race. These concerns are still current, as stated during 1980 by Secretary of Defense Harold Brown (Ref. 1, p. 99): . . . attempting to construct a complete [ballistic missile] defense against massive nuclear attack would be prohibhively costly, destabilizing, and in the end, almost certain to fail;
and by President Carter’s Deputy Assistant for National Security Affairs, David Aaron:3 I think we can be pleased that we’re not engaged in both a defensive strategic arms race as well as an offensive one. In this report we suggest how prospective ballistic missile defense systems might overcome these concerns. If both the Soviets and the United States are bent on strategic arms reductions, they can apparently retain mutual deterrence by mutually assured destruction with moderate inventories of offensive and defensive strategic
components. The systems need not be costly nor lead to instabilities. If, on the other hand, the Soviets continue their strategic arms build-ups at the current pace, then American force structures that include ballistic missile defense might provide the most economical and flexible options for deterring Soviet attack by the countervailing deterrence strategy. Continued offensive missile proliferation by the Soviets would not need to be mirrored by the United States. Our results suggest that we could instead maintain stable deterrence by moderate increases in hardware, mainly defense components. In this case, the Soviets would not be likely to perceive our response as a threat to which they would have to respond. Reciprocal pressures for an arms race could ease. Of course, the Soviets could continue their arms build-up anyway, and we would have to respond; but our results indicate significant economic advantages for the United States in this scenario. The perceived Soviet/American balance of power rests on military capacities well beyond the maintenance of a reliable assureddestruction (punitive) nuclear deterrent. Thus our derivation of assured-destruction strategic forces represents but a first step in the needed force-structure analysis. We continue the analysis by suggesting some ways in which the countervailing strategy might be enhanced by the capacity for limited defense of military, industrial, and urban targets. The force structures postulated in this study would require defense components whose development and testing are now precluded by the Anti-Ballistic-Missile Treaty, which was adopted in 1972 and is scheduled for review in 1982. At that time either party can withdraw or propose modifications without prejudice to future treaty activities. Strategic defense concepts discussed in this report suggest that serious consideration should be given to modifying the Treaty or replacing it with an agreement that would allow the benefits of the new defensive technologies to accrue in support of both national-security and arms-limitation goals. Consideration of possible treaty actions rests partly on the readiness of ballistic missile defense technology. The Ballistic Missile Defense Program Manager, Major General Grayson D. Tate, Jr., in testimony presented to the Senate Appropriations Committee in March 1980, was subdued but positive in his overall assessment of the technology.’ [Low-altitude defense] technology is low risk and ready for preprototype demonstration now. The exoatmospheric element of layered defense repre4
sents less mature technology. However, . . . advances [in exoatmospheric ballistic missile defense technology] make it feasible to develop autonomous long-range interceptors . . . [This system] is being validated. . . and promises to give defense the cost advantage for the fwst time . . . Based on a brief review of ballistic missile defense technology conducted by Los Alamos during 1980, we concur with General Tate’s optimism. We believe ballistic missile defense soon could be ready to assume the postulated strategic roles. In the next section of this report, we describe some elements of the current technology and summarize our technical assessment, comparing it with the Department of Defense assessment. We then continue our analysis of assured-destruction deterrence postures by describing simple mathematical models and applying them to a set of strategic options available to the United States. We use the results to amplify our suggestions that timing and cost advantages may accrue to strategic options including ballistic missile defense. II. TECHNOLOGY DEFENSE
The ballistic missile defense systems considered in this report can be categorized according to where an offensive weapon is intercepted along its trajectory. System concepts include early-trajectory or boost-phase intercepts, midcourse or exoatmospheric intercepts, and terminal or endoatmospheric intercepts. Systems that specify two groups of intercepts, one after the other, are referred to as layered defense systems. Boost-phase or early-trajectory intercepts by “directed-energy weapons” (intense laser beams or particle beams) hold the potential for an extraordinarily effective defense of all national assets. Directedenergy-weapon development in the United States is at so limited a stage at present that it is extremely unlikely that such systems could improve our strategic position in the coming decade. Well-funded 5- to 10-year research programs wiU be required to establish the needed technology bases in these areas before we can begin to realize their potential. These systems are not part of the present analysis. Our analysis is based on conventional exoatmospheric and endoatmospheric defense systems that intercept between the midpoint of the ballistic trajectory and 1-2 kilometers before impact. These systems operate by
guiding rocket-powered vehicles to intercept incoming warheads. They require ● early warning that a threat has been launched; ● detection and assessment of the approaching threat; ● derivation of trajectories and prediction of impact points; ● discrimination between warheads and decoys; ● commitment, launch, and guidance of interceptors; and ● destruction of the warheads.
These functions are depicted in Fig. 1; the subsequent system descriptions and assessments are discussed in terms of these system functions and the technologies supporting them. Current ballistic missile defense technologies are substantially different from predecessor technologies used by the Safeguard balbstic missile defense system of the earl y 1970s. Safeguard was widely perceived as incapable of fulfilling the missions it faced. It is appropriate, therefore, to contrast Safeguard with current
EXOAT INTE MISSILE
AllACKING / INTERCEPTOR SILO
INTERCEPTOR SILO /“ (NOW EMPTY) .
SILO WITH MX MISSILE
Fig. 1. Layered ballistic missile defense of MX missiles deceptively based in silos. In this depicdon three warheads are on a trajectory aimed at an MX missile in one silo, and three more are airned at an exoatmospheric interceptor in an adjacent silo. The exoatmospheric interceptor is launched and destroys two of the warheads attacking tbe missile. Warheads attacking the now-empty interceptor silo are ignored. The surviving warhead aimed at the missile is intercepted by the terminal defense: Not shown explicitly are the separate threat detection and assessment functions.
systems and show how the deficiencies of Safeguard can be overcome by the new technology.
A. Safeguard Safeguard was a layered defense that used ground-based radars for detection, assessment, tracking, discrimination, and interceptor guidance for both midcourse and terminal defenses. Long-range perimeter acquisition radars provided early warning and determined the size of the attack and its targets. As attackers neared the intercept range, battle management and engagement were taken over by smaller missile site radars, coupled to central computers, with one radar-computer assembly for each wing of the Minuteman force. For the exoatmosphenc layer, multistage Spartan interceptors, guided by the radars, operated out to several-hundred kilometers. The Spartan carried a single high-yield nuclear warhead. Those warheads leaking past the Spartan’s defense layer would be intercepted by fast-reacting Sprint low-yield nuclear interceptors at altitudes of 3-30 kilometers also guided to intercept by radar. Each interceptor would engage one warhead. The large ground-based radars were Safeguard’s weakest point. It was soon recognized that the first Spartan nuclear explosions would render large regions of the atmosphere opaque to radar propagation, thereby blinding the radars and making them vulnerable to attack. Other problems existed as well: ● the computers needed were beyond the state of the art; . discrimination by radar signatures was only marginally effective; and ● the system was easily defeatable by a cost-effective increase in the threat size.
B. Exoatmospheric Defense for the 1980s Current designs for exoatmospheric ballistic missile defense depend on two major innovations: (1) small, high-resolution, sensitive, long-wavelength infrared detectors, installed with computers in space-borne threat-assessment sensors and in interceptors, which replace large ground-based radars and central computers for long-range threat acquisition, assessmen~ tracking and discrimination; and (2) homing infrared guidance that enables each interceptor to disperse many vehicles 6
for multiple nonnuclear intercepts instead of single-vehicle nuclear interceptors. In the current designs, early-warning messages either from satellites or radars trigger the threat detection and assessment functions carried out by infrared sensors. These sensors can be emplaced on satellites or carried alofi on rocket-borne probes launched from the continental United States. Each payload consists of a sensitive infrared telescope, a data-processing computer, and down-link communications equipment. The sensors scan the threat corridor specified by the early-warning message and detect, at ranges of several-thousand kilometers, the attacking reentry vehicles, accompanying objects, and penetration aids. Typical threats could have approximately 5000 reentry vehicles and upwards of 20000 other objects in the field of view; the computer must process information for all of them. The sensor tracks all these objects for minutes, measuring angular information and infrared spectral intensities in several bands as a function of time. The on-board computer stores this information, computes approximate trajectories and launch and impact points, and uses infrared discrimination algorithms to differentiate the reentry vehicles from the other objects in the threat. This information is then relayed to a ground-based battle-management computer in real time via multiple-path communications links. Based on the attack breadth, predicted impact points, and relative strength of the defense, the battle-management computer assigns targets to interceptors and launches them. Impact-point prediction, if accurate enough, permits the battle-management computer to defend targets preferentially, that is, to defend some targets and to ignore warheads attacking others. Such a capability is important if the attack size is larger than the defense can intercept fully, or if deceptive techniques are being used by the attacked party to thin the effective attack on each real target. Following launch, the exoatmospheric interceptor rockets operate autonomously, reacquiring their assigned portions of the threat via infrared sensors, repeating the discrimination procedures, and finally deploying muMple-kill vehicles to engage the attack while still several minutes from impact. Using still anotlm infrared sensor, each kill vehicle homes on a separate warhead, getting close enough to destroy it by direct impact or by tiring a conventional explosive warhead. A fraction of the attack can survive this engagement. Some objectives are deliberately ignored (penetration
aids, accompanying objects, warheads allowed through by a preferential defense). Some engaged objects penetrate the defense (leakage). The surviving warheads either reach their targets or are further depleted by subsequent defense layers. Assessment. The Ballistic Missile Defense Program Oflice is guardedly optimistic about the potential for exoatmospheric technology. General Tate reported that’ The [exoatmospheric component of the] Layered Defense Concept is feasible because [of] advances made in the extensive research and development . . . [The] first two flights [of an experiment] .,. confiied that optical sensors can be used to perform [ballistic missile defense] functions, His Deputy Program Manager, William A. Davis, supplied a more conservative and detailed treatment :s Midcourse technologies are relatively immature, pose a higher technical risk than terminal technologies, and enjoy only a meager data base. There are a host of technical issues to be addressed in [our] research and development program over the next several years, two of which are examined here: optical discrimination and nonnuclear kill. Technical evidence exists that optical discrimination is sufficiently developed to make midcourse operation feasible. Somk optical flight data is available on both reentry vehicles and exoatmospheric penetration aids, and there is extensive laboratory data that correlates well with the flight data. Moreover, the essential finding from simulation exercises carried out jointly with the Air Force’s Advanced Ballistic Reentry Systems (ABRES) shows that all but the most sophisticated penetration aids can be readily discriminated. However, more data and more functional demonstrations are necessary, and there are plans to meet these needs. The evidence is that nonnuclear kill can be achieved in”one of two ways—with a warhead or by direct impact. In both cases, passive homing rather than the conventional radar command guidance will be used, The primary approach is to use a warhead, and actual flight tests (Homing Overlay Experiment) to demonstrate this approach will be
held in several years. Guidance simulations indicate a warhead can be brought close enough to achieve a kill. Impact kill is a back-up approach that was demonstrated in laboratory tests several years ago. Based on our review of exoatmospheric technology, Los Alamos supports the optimism expressed by the Program Office. The technology base for the exoatmospheric systcrn appears to be either in hand or on the immediate horizon. We also are able to add detail to the Program Oflice assessment, Integrated circuit technology is progressing so rapidly that adequate computer capability appears assured. Laboratory models, experiments, and calculations of nonnuclear kill give high confidence in performance capabilities, Infrared detection and discrimination have been studied carefully, and useful techniques and knowledge of their limitations appear in hand, pending proof test within a few years. Impact-point prediction is expected to be capable of permitting preferential exoatmospheric defense of silos,* but it is not expected to be able to resolve impacts among closely spaced shelters of any of the multiple-protective-structure emplacement schemes under consideration. We identified several outstanding technical issues needing further study. These issues are dominated by concern over extreme system complexity. Some analysts have considerable reservations about system operability; others are optimistic. Large-scale simulations in progress lend credence to system operability. Other issues include operability of sensors, computers, communications, and interceptors in a nuclear environment, potential for means of overcoming infrared discrimination, and integration of active defense with an already strained national command-communications-control system. The special problems of attacks launched by nuclear submarines lying close to American shores are particularly stressing to exoatmospheric defense, owing to the short flight times. Intercepting such attacks would require previous placement of threat assessment sensors or—at reduced etliciency-operation without them, In addition, a number of actions could be taken by the Soviets in response to our installation of an exoatmospheric defense ———
*For impact resolution within 5 km, silo-to-silopreferential defense wouId be effective.For poorer resolution, preferential defense of groups of silos would be used.
system that could degrade its capabilities. They inclu
C. Endoatmospheric Defense for the 1980s
Endoatmospheric defense uses radars for all sensing functions. Small radars can be specified because the radars need not have ranges necessary for exoatmospheric defense (a departure from Safeguard). Discrimination against decoys is based on different radar signatures, as objects penetrate the atmosphere, depending on weight, shape, and surface characteristics. Such atmospheric effects begin to be apparent on radar signatures at altitudes below 90 km. Based on time delays associated with discrimination and interceptor flight, a practical upper altitude for intercepts is 20-30 kilometers. The limiting lower altitude for intercept is determined by the capacity of the defended target to withstand defensive weapon bursts and, possibly, nuclear detonation of the intercepted warhead. By this criterion a shelter or silo could be defended successfully with intercepts spaced as closel~meters. Unid States endoatmospheric defense research and development effort is concentrated in two programs: Baseline Terminal Defense and Low-Altitude Defense System. (1) Baseline Termbud Defense is a direct descendant of Safeguard. It uses improved Sprint interceptors, a commercial computer, and phased-array radars considerably smaller than Safeguard’s missile site radar, This system, based on established technology, would be less vulnerable than Safeguard because it would use multiple radars in dispersed sites. Since intercepts would occur in the altitude range of 10-20 kilometers, this system would be useful for soft targets. (2) Low-Altitude Defense System, the major ongoing Iow-endoatmospheric intercept program, is shown schematically in Fig. 2. A derivative of the Baseline Terminal Defense System designed mainly for defense of MX-MPS, it uses single-stage nuclear-warhead interceptors with a range of only a few kilometers. The I.mw-Altitu& Defense System uses phased-array radars of modest power, coupled to minicomputers. Because of 8
small component size, the system can be deceptively based in any of the basing modes proposed so far for MX. In modified configuration it could also be used to defend silos. Assessment. In his Senate testimony regarding terminal defense, General Tate reported:
[Low Altitude Defense System] is considered a low-risk development because of the extensive validation testing accomplished . . . on the Terminal Defense (Site Defense) concept, This testing . . . has proven beyond reasonable doubt that we have the technology to build an effective terminal defense system that can detect, discriminate, and intercept ICBM warheads even in the extreme environment caused by massive ICBM attacks. . . and penetration aids.’ **** The basic technology for Low Altitude Defense—LoAD-has been demonstrated with the exception of nuclear hardness for the radar and the interceptor. Nuclear hardness will be tested and demonstrated . . . prior to MX IOC* and the LoAD preprototype demonstration flight tests.6 As was the case for exoatmospheric defense, we concurred with the Program OffIce assessment of terminal defense technology. We felt that the use of smaller and less complex components make low-altitude defense a relatively low-technical-risk system with less costly components than exoatmospheric systems. However, the stressful nuclear environment envisioned requires interceptor and radar hardness values exceeding those of predecessor systems. Ability to defeat an intense attack against any single target will be limited because, with the very short time available for acquisition, track, and intercept, multiple sequential intercepts witl be ditXcult. The limited space available for interception would also reduce the ability of the system to cope with repeated attack, due to nuclear-fireball interference with radar propagation and to interceptor-interceptor fratricide. In such a dense attack, fratricide between attacking warheads could also be a problem for the attacker. Interceptor technology for endoatmospheric defense is well in hand, provided that nuclear warheads are carried. (Nonnuclear kill may become feasible, particularly for engagements at higher altitudes, but will require further — ———— ●That is, the date currently scheduled for initial operational capability of MX in multiple protective structures.
development in sensor, guidance, warhead, and missile technology.) Distributed data processing and the use of multiple small, hard radars would ensure that the system performance would degrade gracefully against even moderately heavy attack. For low-altitude defense of hard targets, an endoatmospheric system of the Law Altitude Defense System design could be ready for deployment by the mid- 1980s, as reported by General Tate:6 .
[With $25M additional funds starting in Fiscal Year 1981 it would be feasible] to enter engineering development in Fiscal Year 1982 to support a [low-altitude missile defense] deployment concurrent with MX deployment in 1986.* .—— ——— —— ●The BallisticMissileDefense Program received an additional $ 15M in Fiscal Year 198~ funding foUowingGeneral Tate’s testimony.
At the end of the trajectory, as an alternative to conventional hard-target endoatmospheric defense, several last-ditch methods for destroying warheads by nonguided missiles have been proposed. We considered a number of techniques using nonpowered missiles (projectiles, dust clouds) and felt that none was feasible. However, a concept specifying dense barrages of powered but unguided missiles, which recently came to our attention, may offer near-term potential for endoatmospheric defense of hard targets.
D. Layered Defense
Combination of exoatmospheric, infrared, nonnuclear-intercept technology and endoatmospheric, small-radar, nuclear-intercept technology into a layered 9
defense system offers a number of synergistic advantages over either system operated alone: ● leakage factors can be multiplicative, so that two relatively leaky components can combine into a system with very low leakage; ● two different discrimination phenomenologies place severe demands upon decoy designs; ● the low leakage produces lower costs per intercept; ● reduced inventories and complexities accrue to both layers, relative to single-layered defenses; ● the upper layer avoids saturation of the endoatmospheric defense component; and ● exoatmospheric-sy stem threat assessment improves engagement planning for the endoatmospheric defense components. An equivalent set of factors was reported by General Tate (Ref. 4, p. 2872).
On the premise that current ballistic missile defense systems will mature as anticipated, it becomes necessary to consider how such systems would affect the strategic situation. We begin this consideration by exploring, with simple models, the arms-control implications of ballistic missile defense and other strategic options. Alternately, we explore how well these options could do in a world devoid of arms-limiting agreements. We perform the analysis by estimating United States strategic inventories needed to ensure the expected survival of a predetermined deliverable retaliatory strike by the United States after a Soviet first strike. For assured destruction, the retaliatory strike is taken to consist of a fixed number of warheads that can be delivered against Soviet targets of value—cities, industry, transportation, etc. The number of deliverable warheads is taken arbitrarily as 1000 (that is, 100 MX-equivalent payloads). Other numbers can be postulated, but our qualitative conclusions do not change if this assumption is varied. Deterrence could be based alternatively on developing a war-fighting posture, in which forces are so structured as to permit their flexible use throughout a nuclear exchange. In this case the needed analysis is much more complex and is less amenable to simple modeling. Consequently, we are limited to discussing at the end of this section some elements of war-fighting deterrence in qualitative terms, and deferring quantitative treatment.
The needed strategic inventories for deterrence depend on the offensive and defensive systems used. We treat four options: (1) new ICBMS (MX) based nondeceptively in silos, no defenses (extension of current status); (2) new ICBMS (MX) in multiple protective structures “: (MPS), no defenses (current DoD planning);, (3) MX-MPS, defended by terminal missile defenses (extended DoD planning); and (4) MXS based deceptively in silos, defended by layered defenses. We assume that when the United States implements a particular technology, such as exoatmospheric defense, the Soviets can simultaneously implement an equivalent Soviet technology if they choose to do so. We do not attempt in this analysis to account for differences in emplacement dates for American and Soviet inventories. The forces required for the United [email protected] to achieve the specified deterrence criterion also depend on the forces maintained by the Soviet Union. The result achieved by any change in American force structures thus depends strongly on the Soviet response, or lack of response, to the United States initiative. Expectations concerning Soviet responses depend on Soviet motivations and policies. We consider two cases: ● a responsive Soviet behavior in which the Soviet aim is also to maintain a minimal expected deterrent in the face of’ possible United States counterforce attack, and ● an independent Soviet behavior in which the Soviet forces are determined by internal considerations not dependent on American force structures. The initial forces needed to achieve the deterrent criterion can be estimated, based on known, inferred, or assumed capabilities of the opposing force structures and policies for their employment. Such computations must be quite detailed to account properly for design variations within and betsveen Soviet and American forces. Consideration must be given to many aspects and details beyond the capability of the simple sorts of analyses we can attempt here. For example, to model correctly the missile-force exchange we study here, one must consider variations of such parameters as warheads launched on each missile, their accuracies, and their delivery-vehicle performance. However, an estimate of the required force sizes can be obtained from simple models that average over these variables. Such models are much too limited to define actual strategic forces needed, but they are valuable in
estimating how extensive those forces must be to achieve specified deterrence levels. They are thus also useful in comparing force inventories and costs, both between first striker and retaliator, and among the various strategic options considered by the retaliator. Our approach uses such a simple model.
Missiles based nondeceptively in silos, no defense. All silos are assumed to have missiles in them (H = M). S= M(l–p’)@’m
and A. Force-Structure Model W=ps To estimate the required deterrent forces, we assume the following scenario: the Soviets strike fwst, using their entire missile inventory to attack our ICBM fields; we ride out the attack, using any active defenses we have to defend our missiles; our subsequent retaliatory attack is aimed at Soviet value targets; and any Soviet active defenses attempt to intercept the fraction of the retaliatory strike within range of the Soviet defense system. Attack on our land-based ICBMS by the entire Soviet missile force is only one of many possible scenarios, although it is the one often considered in arms-control analyses. This scenario is not realistic, but for our purpose it is conservative in that any lesser attack against the ICBMS either destroys fewer of our missiles or engages fewer of our defenders. The additional survivors would then be usable in damage-limiting roles. Although implications of Soviet reserve forces are neglected in this preliminary study, they are critical and must be treated subsequently in the broader context of countervailing deterrence. To determine force structures, we derived formulas relating survivable, deliverable warheads to initial inventories, based on the above exchange scenario. In the responsive case, both Soviet and American inventories were assumed coupled, Inventories were increased together until the calculations showed each side achieved the specified deterrence criterion, This approach produced minimum inventories and costs for both sides. In the independent case, Soviet missile inventories were postulated at freed levels, and the remaining Soviet and American inventories were varied until the United States achieved the specified deterrence criterion. United States inventories were structured for minimum cost at each threat level. With the notation given in Table I, and using primed quantities for Soviet hardware, the needed formulas are* *The expression (1 — p’)m is rigorously correct in these formulas only for integral values of a For nonintegral values, the correct expressionwould be (1 – p’)rul(1 – p’),where [a] is the integer part of a and the fractional part, For conciseness, we continue to show the simpler form; however, we used the corect form in all our inventory estimates.