Directed Energy Missile Defense in Space

April 1984

NTIS order #PB84-210111

Recommended Citation:Directed Energy Missile Defense in Space–A Background Paper (Washington, D. C.: U.S.Congress, Office of Technology Assessment, OTA-BP-ISC-26, April 1984).

Library of Congress Catalog Card Number 84-601052

For sale by the Superintendent of DocumentsU.S. Government Printing Office, Washington, D.C. 20402

Preface

This background paper was prepared by Dr. Ashton B. Carter under a contract withthe Office of Technology Assessment. OTA commissions and publishes such backgroundpapers from time to time in order to bring OTA up to date on technologies that arethe subject of frequent congressional inquiry. After Dr. Carter’s work was under way,Senators Larry Pressler and Paul Tsongas of the Senate Foreign Relations Committeerequested that the resulting paper be made available to that Committee as soon aspossible. OTA is issuing the paper in the belief that others in Congress and membersof the public will find it of interest and importance.

An OTA background paper differs from a full-fledged technology assessment.Background papers generally support an ongoing assessment of broader scope or ex-plore emerging technological issues to determine if they merit a fuller, more detailedassessment. On March 22, 1984, the Technology Assessment Board directed OTA tocarry out a full-fledged assessment of “New Ballistic Missile Defense Technologies, ”for which this background paper will serve as one point of departure.

This paper was prepared for OTA’s International Security and Commerce Program,under the direction of Lionel S. Johns (Assistant Director, Energy, Materials, and inter-national Security Division) and Peter Sharfman (Program Manager).

Contents

Section

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2. Booster Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3. Directed Energy Weapon Concepts for Boost Phase Intercept.

3.1 Space-Based Chemical Lasers: A First Example . . . . . .3.2 Ground-Based Lasers With Space-Based Mirrors . . . . .3.3 Nuclear Bomb-Pumped X-Ray Lasers: Orbital and Pop-

Page

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. . . . . . . . . . . . . . . . . . . . . . 15

. . . . . . . . . . . . . . . . . . . . . . 16

. . . . . . . . . . . . . . . . . . . . . . 22p Systems . . . . . . . . . . . . . 24

3.4 Space-Based Particle Beams . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . 283.5 Space-Based Kinetic Energy Weapons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323.6 Microwave Generators.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 353.7 Other Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4. Other Essential Elements of a Boost-Phase Intercept System . . . . . . . . . . . . . . . . . . . . . . . . . 394,1 Target Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394.2 Aiming and Pointing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404.3 Intercept Confirmation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404,4 Command and Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414.5 Self-Defense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414.6 Power Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

5. Countermeasures to Boost-Phase Intercept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 455.1 Anti-Satellite (ASAT) Attack, Including Directed-Energy Offense . . . . . . . . . . . . . . . . 465.2 Fast-Burn Boosters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485.3 Counter C3l Tactics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 485.4 Shielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 495.5 Decoys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505.6 Salvo Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 505.7 Offensive Buildup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515.8 New Targeting Plans.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 515,9 Other Means of Delivering Nuclear Weapons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

6. A Word on ’’Old’’ BMD and “New” BMD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 557. A Hypothetical System Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

7.1 System Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 607.2 Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

8. Defensive Goals I: The Perfect Defense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 658.1 Nuclear Attack on Society . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 668.2 The Prospects for a Perfect Defense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

9. Defensive Goals ll: Less-Than-Perfect Defense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 739.1 Goals for Less-Than-Perfect Defense . . . . . . . . . . . . . . . . . . . . . . . . . 739.2 Side Effects of BMD Deployment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

10. Principal judgments and Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81Appendix

A. Excerpt From President Reagan’s Television Speech, March 23, 1983 . . . . . . . . . . . . . . . . . 85B. The ABM Treaty and Related Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87C. Other Applications of Directed Energy Weapons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

v

Section 1

INTRODUCTION

This Background Paper describes and assessescurrent concepts for directed-energy ballisticmissile defense in space. Its purpose is to pro-vide Members of Congress, their staffs, and thepublic with a readable introduction to the so-called “Star Wars” technologies that some sug-gest might form the basis of a future nationwidedefense against Soviet nuclear ballistic missiles.Since these technologies are a relatively newfocus for U.S. missile defense efforts, little infor-mation about them has been readily availableoutside the expert community.

Directed-energy or “beam” weapons comprisechemical lasers, excimer and free electron lasers,nuclear bomb-powered x-ray lasers, neutral andcharged particle beams, kinetic energy weapons,and microwave weapons. In addition to describ-ing these devices, this Background Paper assesseshe prospects for fashioning from such weapons

robust and reliable wartime defense systemesistant to Soviet countermeasures. The assess-ment distinguishes the prospects for perfect orear-perfect protection of U.S. cities and popula-on from the prospects that technology willchieve a modest, less-than-perfect level of per-formance that will nonetheless be seen by somexperts as having strategic value. Though thefocus is technical, the Paper also discusses, butoes not assess in detail, the strategic and armsontrol implications of a major U.S. move to de-velop and deploy ballistic missile defense (BMD).1

This Background Paper grows indirectly out ofresident Reagan’s celebrated television speechf March 23, 1983, in which he called for a “long-erm research and development program to begin

‘ BM D IS the most common of four rough Iy equivalent acronymsverl ng defense against nuclear ba II istic m issl Ies. Such defenses~re formerly ca I led a ntl-ba I I i st ic m issi [e (ABM) systems, but thisslgnatlon fell out of favor after the debate over and eventual de-se of the Sentinel and Safeguard ABM systems in the late 1960’sd early 1970’s. BMD largely replaced ABM as the term of choice,t recently the more self-explanatory Defense Against Ballisticsslles (DABM) has gained popularity. Within the Executive~nch, BMD efforts pursuant to President Reagan’s so-called ‘‘Star~rs” speech are referred to as the Strategic Defense Initiative (SD I).)rmally the term strategic defense comprehends other methodsIlmltlng damage from nuclear attack besides BMD.

to achieve our ultimate goal of eliminating thethreat posed by strategic nuclear missiles. ”2 Pur-suant to the President’s speech, the Departmentof Defense established a Defensive TechnologiesStudy Team under James C. Fletcher (of the Uni-versity of Pittsburgh) to prescribe a pIan for theR&D program. A parallel effort, called the FutureSecurity Strategy Study and headed by Fred S.Hoffman (of Research and Development Asso-ciates), addressed the implications for nuclearpolicy of renewed emphasis on BMD. This Pa-per covers the same technologies and issues asthese Defense Department studies. The ABMTreaty reached at SALT l3 severely restricts thedevelopment, testing, and deployment of BMDsystems. Though this Background Paper treats thestrategic roles of missile defenses, including manyof their arms control implications, it does not treatthe vital international political implications of amajor U.S. move to BMD.

Focused on directed-energy intercept of mis-siles in their boost phase, i.e., on “Star Wars”proper, this paper does not analyze midcourseand reentry BMD systems or non-BMD applica-tions of directed-energy weapons.4 “Star Wars”efforts generally further concentrate on interceptof intercontinental ballistic missiles (ICBMs) ratherthan the related but somewhat different problemsof intercept of submarine Iaunched ballistic mis-siles (SLBMs) or intermediate-range ballisticmissiles (IRBMs). This Paper is therefore not asubstitute for a more complete treatment of theentire subject of BMD.5 Moreover, BMD itself isonly part of the larger subject of strategic defense,comprising defense against bombers and cruisemissiles, civil defense, passive defense of militarytargets, anti-submarine warfare (ASW), and pre-emptive counterforce attack in addition to BMD.

2The relevant portions of President Reagan’s speech arereproduced in Appendix A.

3The ABM Treaty and related documents are reproduced in Ap-pendix B,

4Appendix C describes briefly, but does not assess, other pro-posed military applications of directed-energy weapons.

5For a more complete treatment, s e e f%//;sf;c Missile ~efe~set

ed. Ashton B. Carter and David N. Schwartz (Brooklngs, 1984).

3

4

It is unusual for the President to express himselfon, and for the Congress and public consequentlyto concern themselves with, long-term researchand development. “Star Wars” is thus a some-what unusual subject for a technology assessmentintended for a public policy audience. It is in thenature of this subject that unknown or unspeci-fied factors outweigh what is known or can bepresented in concrete detail. Many of the tech-nologies discussed in this Paper, and most cer-tainly all of the schemes for fashioning a defensesystem from these technologies, are today onlypaper concepts. In the debate over the SafeguardABM system a decade ago, or over basing modesfor the MX missile in recent years, one could ana-lyze in detail the technical properties of well-defined systems in engineering development. Sovague and tentative are today’s concepts for “StarWars” BMD that a comparable level of analysisis impossible. Fashions and “front runners” arelikely to change, Nonetheless, one is faced withassessing the concepts receiving attention todaywithin the Executive Branch and which underliethe President’s Strategic Defense Initiative. For-tunately, judgments deduced from generic prop-erties of these concepts, which are unlikely tochange, are sometimes telling.

This Paper is based on full access to classifiedinformation and studies performed for the Exec-utive Branch. But it turns out that a fully adequatepicture of this subject can be presented in un-classified form. One reason is that the importantfeatures of the directed-energy BMD concepts arebased on well-known physics, and many have infact been discussed for 20 years. The second

reason is that at this early stage of conceptualizetion there is simply no point in (and little basisfor) discussion at the detailed level where classi-fied particulars make a difference. The propertiesof actual weapon systems in engineering development, by contrast, are normally and understandably classified.

The author and OTA wish to thank officials othe Army’s Ballistic Missile Defense Systems Cornmand (BMDSCOM), the Lawrence Livermore National Laboratory, the Los Alamos NationaLaboratory, the Defense Advanced Research Projects Agency (DARPA), the Sandia National Laboratory, the Air Force Weapons Laboratory (AFWL)the Office of the Secretary of Defense (OSD), andthe Central Intelligence Agency (CIA) for theihospitality and cooperation. Many individualaided the research for this Background Paperthough none shares the author’s sole responsbility for errors of fact or judgment. The authorand OTA wish especially to thank Hans BetheRichard Briggs, Al Carmichael, Albert CarnesalePaul Chrzanowski, Robert Clem, Sidney D. DrelDick Fisher, John Gardner, Richard L. GarwirEd Gerry, Jack Kalish, Glenn A. Kent, Louis Maquet, Michael M. May, Tom Perdue, TheodorA. Postol, George Rathjens, Victor Reis, JacRuina, George Schneiter, David N. SchwartzRobert Selden, Leon Sloss, Daryl Spreen, RobiStaffin, John Steinbruner, Sayre Stevens, ThomasWeaver, Stephen Weiner, and Wayne Winter

This Background Paper contains informationcurrent as of January 1, 1984.

Section 2

BOOSTER CHARACTERISTICS

Section 2

BOOSTER CHARACTERISTICS

Intercept of ICBMs in their boost phase offersadvantages and disadvantages relative to inter-cept of reentry vehicles (RVs) later in the trajec-tory. The boosters are fewer and generally moreeasily disrupted or destroyed than the RVs. Decoyboosters would have to match an ICBM’s hugeheat output, making this offensive tactic attrac-tive only in certain circumstances. The disadvan-tages of boost phase intercept are that boostphase is only a few minutes long and comprisesthe earliest stage of an attack, and that sensingand intercept must be accomplished from outerSpace and over enemy territory.

Figure 2.1 shows an ordinary (minimum ener-gy) trajectory of a hypothetical future Soviet ICBMhat has been given, for illustration, the boost pro-file of the U.S. MX Peacekeeper. Pressure froma steam generator expel Is the missile from its stor-

age cannister. Once clear of the cannister, themissile ignites its first stage motor. The first stageburns for about 55 seconds, burning out at analtitude of about 22 kilometers. The second stagealso burns for 55 see, burning out at 82 km. Thethird stage burns for 60 sec and carries the re-mainder of the missile to about 200 km, the alti-tude of the lowest earth orbiting satellites.

When the third stage is jettisoned at the endof the 3-minute boost phase, the remainder ofthe missile consists of the post-boost vehicle (PBV)or ‘‘bus” and its cargo of 10 reentry vehicles. Atthis point the bus and RVs are in ballistic free-fall flight to the United States. Even if they aredisrupted in some way or destroyed, these ob-jects or their debris will reenter the atmosphereover the United States. The last few seconds ofthird stage burn are crucial for giving the payload

Figure 2.1 .–The Flight of a Hypothetical Future Soviet ICBM With the Booster Characteristics of the U.S.MX Peacekeeper, Drawn to Scale

End bussingdecoy (650 sees. after

1200 km Apogee launch)

SOURCE: Author

7

enough speed to reach the United States, so dis-ruption of boost phase any time right up to burn-out will cause the warheads to fall far short.

For the next 500 seconds or so after burnout—almost until it reaches apogee—the bus uses itsthrusters to make small adjustments to its trajec-tory. After each adjustment, it releases an RV. RVsreleased on different trajectories continue on todifferent targets as multiple independently tar-geted reentry vehicles (MIRVs). Decoys and otherpenetration aids for helping the RVs escape de-fenses later in the trajectory are deployed dur-ing busing.

The bus itself is a target of declining value asit dispenses its RVs. Destroying it early in the de-ployment process would obviously be useful: theRVs not yet deployed from the bus would still ar-rive at the United States, but perhaps nowherenear their intended targets. If cities are the targets,relatively small aiming errors might be inconse-quential. In any event, tracking the bus to allowsome form of intercept requires a different typeof sensor from that which tracks the booster forboost phase intercept, since the bus’s thrustersare small and operate intermittently. Because ofits small size, the bus (or at least critical elementsof it) might be more easily hardened against di-rected-energy weapons than the booster. For allthese reasons, the value of attempting bus inter-cept is very unclear, and it usually does not fig-ure prominently in BMD discussions.

From apogee, the slowest point in their free-fall trajectory, the RVs and empty bus gain speedas they fall back to earth. RVs are more resistantto damage from directed-energy weapons thanboosters, and they might be accompanied bymany decoys. When these objects enter theupper atmosphere at about 100 km altitudesomewhat over 2 minutes before impact, they be-gin to heat up, and the lighter objects slow down.Still lower, below 50 km altitude and less thana minute before impact, the objects undergo vio-lent deceleration and the bus breaks up. The RVs,now glowing with heat, streak toward their targetsat an angle of about 23 degrees to the horizontal.

The trajectory shape can be altered at the ex-pense of payload (see Figure 2.2). A lofted tra-jectory takes longer but reenters faster, and a de-

pressed trajectory can offer unfavorable viewingangles to defensive sensors late in the trajectory.

The most important trajectory variations fromthe point of view of boost phase intercept are var-iations in boost profile. Boosters like MX were de-signed with no regard for boost phase BMD, andoptimizing their design gave rise to rather longboost times. But boost phase can be shortened–giving less time for boost phase weapons to act–and accomplished within the atmosphere—where certain directed-energy weapons cannotpenetrate–with relatively little reduction in pay-load or increase in missile size. Fast burn is ac-complished most easily with solid-fueled rockets.Liquid-fueled boosters like the Soviet SS-18s andSS-19s burn more slowly and burn out at higheraltitudes. Thus while MX burns out at 200 kmafter 3 minutes of boost, the SS-18 burns out at300-400 km after 5 minutes. The next generationof Soviet ICBMs will reportedly employ solid pro-pellants.

Studies performed for the Defense Departmentshowed that with a 25 percent reduction in pay-load, a booster about the same size as MX couldbe built which would burn out in less than 1 min-ute at only 80 to 90 km, well within the sensibleatmosphere. At 90 km the atmosphere is still toodense for extremely accurate RV deployment orfor deployment of lightweight RV decoys andother penetration aids aimed at later defensivelayers: these functions require an additional 10to 15 seconds of precision deployment betweer90 and 110 km. If the offense needs precision accuracy for some of its ICBMs but fears interceptduring these additional few seconds of high-altitude operation, mounting one or two RVs oreach of several “microbuses” instead of all theRVs on a single bus affords some protection. Eachmicrobus would contain a simple guidance systern only good enough to carry the RVs from upper stage burnout to 110 km. Instead of presenting one target above 90 km, therefore, such i

booster would present several targets.

The United States is studying a “Midgetman"missile endorsed by the President’s Commissionon Strategic Forces (the Scowcroft Commission

1“Short Burn Time ICBM Characteristic and Considerations,” Martin Marietta Denver Aerospace, July 20, 1983 (UNCLASSIFIED).

9

Figure 2.2.—Normal (Minimum-Energy), Lofted, and Depressed ICBM Trajectories, Drawn to Scale

SOURCE : Author

with weight 15 to 25 percent that of MX and car-ying one warhead. Midgetman’s warhead andIUS are combined i n one hardened structure.“able 2.1 shows the characteristics of Midgetmanariants designed to face a boost-phase interceptystem. The fast-burn version burns out at 80 kmfter 50 sees of boost. With a 10 percent increase7 weight, the fast-burn version can carry a sub-stantial payload of penetration aids. A low-flight-profile version is intended to stay within the at-mosphere until burnout, protecting it from sometypes of directed-energy weapon. In the hard-ened version, one gram of ablative or otherhielding material has been applied to eachquare centimeter of the entire booster body (ifle boost-phase intercept system did not beginoperation until a minute or so after launch, thefirst stage might not have to be hardened). Thesemall boosters are all estimated to cost $10 to $15

million per copy, assuming a buy of 1,000 boost-ers. Costs for the second and subsequent thou-sand would of course be substantially smaller.These costs are two to three times higher per RVthan MX.

The Soviet ICBM arsenal today comprises about1,400 boosters, more than two-thirds of themMIRVd. Most are slow-burning liquid-fueledboosters. The U.S. arsenal contains about 1,000faster-burning solid-fueled Minuteman boosters,about half of them MIRVd. Both sides are addingsolid boosters to their arsenals in the 1980’s.

The geographic distribution of offensive boost-ers can also be important to space-based boost-phase defenses. The number of satellites requiredin a defensive constellation usually increases ifall opposing ICBM silos are concentrated in oneregion and decreases if the silos are spread over

10

o

I II

I I I

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wide land areas. (On the other hand, too muchconcentration allows defensive satellites to befocused on one region by choosing the orbits ju-viciously. ) Soviet SS-18 ICBMs, their largestMIRVd missiles, are organized into 6 wings ofabout 50 missiles each, spread out over a largeregion of the U.S.S.R. U.S. Minuteman missilesare organized into 6 wings of about 150 missileseach. Figures 2.3 and 2.4 show the geographicdistributions.

react with new and different deployments whenthey learn of any U.S. plans to deploy defenses.It is impossible to project Soviet deployments farinto the future. A reasonable “baseline’ estimatefor the Soviet ICBM arsenal 15 to 20 years fromnow might assign them the same number ofboosters they have today, but with burn charac-teristics similar to the U.S. solid-propellant MX.This Background Paper indicates where and howthe effectiveness of a hypothetical U.S. defense

The capabilities of a hypothetical future U.S. depends on the nature of the offensive arsenal

BMD should be measured against the future and it faces. In addition to having shorter averageburn times, future Soviet ICBMs could be morepotential Soviet ICBM arsenal, not against today’s

arsenal. The future arsenal wiII differ due to the numerous, deployed less widely geographically,less highly MIRVd, hardened against intercept,natural retirement of old ICBMs and introduction

of new ones, and because the Soviets might well and so on.

Figure 23.— Present U.S. ICBM Deployment Areas

SOURCE: OTA, MX Missile Basing, p 274

33-698 0 - 84 - 3 : QL 3

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Figure 2.4.—Present U.S.S.R. ICBM Deployment Areas

Type ICBMs Number

Ss-11 550SS-13 60Ss-17 150SS-18 308SS-19 330

Total 1398

SOURCE: U.S. DOD Soviet Military Power, 2nd cd., P. 14.

DIR CTEDB

ENERGY WEAPONS FOROOST-PHASE INTERCEPT

Section 3

DIRECTED ENERGY WEAPONS FORBOOST-PHASE INTERCEPT

This section describes the entire set of “beamweapons” being considered in the United Statestoday for boost-phase ICBM intercept. Thoughthese weapons receive the most attention, the“kill mechanism” that destroys the booster is notnecessarily the most important or technicallychallenging part of an overall defense system. Thenext section describes other essential elementsof a boost-phase defense.

A revisit to this subject several years from nowmight well find a new family of directed energyconcepts receiving attention. But for now the de-vices described in this section are the basis forassessments of the prospects for efficient boost-phase defense, in the Defense Department andelsewhere (fig. 3.1 ). Though some of these con-cepts are new, many have in fact existed in oneform or another for more than twenty years.

Figure 3. I

GammaraYs

x

X-rays

TV

Short- SubmarineFM wave AM communications

FarEHF SHF UHF VHF HF MF LF VLF ELF

1 I 1 I 1 I 1 I 1 1 1 1 J0.01 01 1 10 01 1 10 0.1 1 1 10 1 10 100 1 10 1 0 0n m nm nm n m µ m µ m µm mm mm cm cm m m m km km km

Wavelength

30 3 300 30 3 300 30 3GHz GHz MHz MHz MHz kHz kHz kHz

Frequency

Earth-to-space Prefixest r a n s m i s s i o n ( s c h e m a t i c )

Giga (G) Billion 109Mega (M) Million 106Kilo (k) T h o u s a n d 1 03

S o m e t r a n s m i s s i o n— — 1

MI III (m) Thousandth 10-3

Transparent Micro (µ) Millionth 10-9Nano (n ) B i l l i on th 10

Figure 3.1 The electromagnetic spectrum, showing spectral regions of interest for directed energy BMD. Particle beams andkinetic energy weapons are not shown because their energy does not consist of electromagnetic radiation, but of atomic and

macroscopic matter, respectively. Source: Author

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For each concept this section attempts to workthrough, with some concreteness, the design ofa hypothetical defensive system based on theconcept. The resulting designs are illustrative

on/y; no significance should be attached toprecise numbers. Precision is simply not possi-ble in the current state of technology and studyof these concepts.

In all cases, the “current state of technology”(however this is defined in each case) is far frommeeting the needs of truly efficient boost-phaseintercept. The systems designed in this sectionillustrate the level to which technology wouldhave to progress to be “in the ballpark.” Muchattention fastens on the guIf between the currentstate of technology and the ballpark require-ments. This section does not emphasize such

comparisons for several reasons. First, in somecases details of the precise status of U.S. researchis classified. Second, and more importantly, quan-titative comparisons (e.g., “A millionfold increasein brightness is required to fashion a weapon fromtoday’s laboratory device”) can mislead unlessaccompanied by a deeper explanation of thetechnology; and the same quantitative measuresare not appropriate for all technologies. Third,and most importantly, such comparisons implythat learning how to build the right device is tan-tamount to developing an efficient missile de-fense, which is far from true: equally crucial aredesign of a sensible system architecture, cost, sur-vivability, resilience to countermeasures, and themyriad detailed limitations that do not turn upuntil later in development.

3.1 SPACE-BASED CHEMICAL LASERS: A FIRST EXAMPLE

This concept of directed energy weapon hasbeen the one most frequently discussed in recentyears for boost-phase ICBM intercept. For thisreason (and not necessarily because it is the mostplausible of all the concepts), it will be used tointroduce certain features common to all theschemes that follow.

Making and Directing Laser Beams

A molecule stores energy in vibrations of itsconstituent atoms with respect to one another,in rotation of the molecule, and in the motionsof the atomic electrons. The molecule shedsenergy in the form of emitted light when it makestransitions from a higher-energy state to a lower-energy state. Lasing takes place when many mol-ecules are in an upper state and few are in a lowerstate: one downward transition then stimulatesothers, which in turn stimulate yet more, and acascade begins. The result is a powerful beamof light.

Energy must be supplied to the molecules toraise most of them to the upper state. This proc-ess is called pumping. In the case of the chemicallasers considered in this section, the pumpingenergy comes from the chemical reaction that

makes the Iasant molecules: hydrogen and fluor-ine react to form hydrogen fluoride (HF) mole-cules in an upper state. The other requirementfor Iasing–few molecules in the lower state–issatisfied simply by removing the molecules fromthe reaction chamber after they have made theirtransitions to the lower state and replacing themwith freshly made upper state molecules. Thepumping process is not perfect: not all the pump-ing energy ends up as laser light. The ratio ofpumping energy in to laser energy out is calledthe efficiency of the laser.

Laser light is special in two respects: its fre-quency is precise, since all the light comes fromthe same transition in all the molecules; and thelight waves from all the molecules emerge withcrests and troughs aligned, since the waves areproduced cooperatively. These special featuresmake it possible to focus the laser energy withmirrors into narrow beams characterized by smalldivergence angles (see fig. 3.2). Nonetheless,there is a limit to the divergence angle that evena perfect laser with perfect mirrors can produce.The divergence angle (in radians) can be nosmaller than about 1.2 times the wavelength ofthe light divided by the diameter of the mirror.Thus a laser with 1 micrometer (=1 micron)

17

Figure 3.2

12 megawattdirected-energy I

weapon

Figure 3.2 Basic power relationships for directed energyweapons. If the directed energy weapon has a divergenceangle of 1 microradian, the spot size at a range of 4000kilometers is 4 meters (12 feet). In this figure, the divergenceangle is exaggerated about 1 million times. (For comparisonof scale, the Earth’s radius is about 6,400 km,) If the directedenergy weapon emits 12 megawatts of power, a target withinthe spot at 4,000 km receives 100 watts on each square centi-meter of its surface. (For comparison, 100 watts is the powerof a Iightbulb, and atypical commercial powerplant produces1,000 megawatts). Since a watt of power equals one joule ofenergy per second this weapon would take 10 seconds toapply a kilojoule per square centimeter (1 KJ/cm2) to the target

at 4,000 km range. Source: Author

wavelength projected with a 1 meter mirror couldhave at best a 1.2 microradian divergence angle,making a spot 1.2 meters wide at a range of 1,000kilometers (refer to fig. 3.2).1 This perfect perform-ance is called the diffraction limit. Dividing thelaser power output by the size of the cone intowhich it is directed (cone size is measured in unitscalled steradians; a divergence angle of x radiansresults in a cone of size 7rxz/4 steradians) yieldsthe laser’s “brightness,” the basic measure of aweapon’s lethality.

Destroying Boosters with Lasers

Assuming a high-energy laser with small diver-gence angle can be formed, stabilized so it doesnot wave about (jitter), and aimed accurately,what effect will it have on an ICBM booster? No

‘The spot from a perfect laser with perfect mirrors would actually~e brighter at the center than at the edges. The full angle subtended)y this spot (the Airy disk from null to null in the diffraction pat-ern), is 2.4 times the wavelength divided by the mirror diameter,Jut most of the energy is in the central fourth of this area: hencehe use in the text of the multiplier 1.2.

clear answer to this question can be given with-out more study and testing. Estimates of the hard-ness achievable with future boosters are probablyreliable within a factor of two or three, thoughestimates of the hardness of current Sovietboosters are probably reliable only to a factor of10 or so.

Roughly speaking, laser light can damageboosters in two distinct ways. With moderate in-tensities and relatively Iong dwell times, the la-ser simply burns through the missile skin. Thisfirst mechanism is the relevant one for the chem-ical lasers described in this section. The secondmechanism requires very high intensities but per-haps only one short pulse: the high intensitycauses an explosion on and near the missile skin,and the shock from the explosion injures thebooster. This mechanism, called impulse kill, ismore complex than thermal kill and is less wellunderstood. it will be discussed in the nextsection.

Bearing in mind the uncertainties in these esti-mates, especially the complex interaction of heat-ing with the mechanical strains of boost, the fol-lowing estimates are probably reliable: A solid-fueled booster can probably absorb without dis-ruption up to about 10 kilojoules per squarecentimeter (kJ/cm2) on its skin if a modicum ofcare is taken in the booster’s design to eliminate“Achilles’ heels. ” This energy fluence would re-sult from 1 second of illumination at 10 kilowattsper square centimeter (kw/cm2), since one wattequals one joule per second.2 Applying ablative(heatshield) material to the skin can probablydouble or triple the lethal fluence required. Ap-plying a mirrored reflective coating to the boosteris probably not a good idea, since abrasion dur-ing boost could cause it to lose its Iustre. Spin-ning the booster triples its hardness, since a givenspot on the side of the booster is then only il-luminated about a third of the time.3 On the other

ZThe lethal fluence (in kJ/cmZ) must accumulate over a relativelyshort time, so that the booster wall suffers a high rate of heating,Thus a flux of 30 watts/cml would deposit 10 kJ/cmz in 330 secof dwell time, but such a slow rate of heating would probably notdamage the booster.

IIt is possible that uniform heating around the circu reference ofthe booster introduces lethal mechanisms distinct from those thatapply to heating a single spot on the side of the booster. In thatcase, spinning the booster might not lengthen the required dwelltime by the full amount dictated by geometry.

18

hand, currently deployed boosters, especially thelarge liquid Soviet SS-18s and SS-19s, might bevuInerable to I kJ/cm2 or even less. These toocould be hardened by applying heatshield ma-terial.

An Orbiting Chemical LaserDefense System

Consider a space-based BMD system comprisedof 20-megawatt HF chemical lasers with 10 me-ter mirrors. The HF laser wavelength of 2.7 mi-crons is attenuated as it propagates down intothe atmosphere, but most of the light gets downto 10 km or so altitude. Deeper penetration is notreally needed, since the laser would probably notbe ready to attack ICBMs until after they hadclimbed to this altitude, and in any event cloudscould obscure the booster below about 10 km.(Substituting the heavier and more expensivedeuterium, an isotope of hydrogen, to make aDF laser at 3.8 micron wavelength would alleviateattenuation, but the longer wavelength would re-quire larger mirrors.)

A perfect 10 meter mirror with a perfect HF la-ser beam yields 0.32 microradian divergenceangle. The spot from the laser would be 1.3meters (4,0 ft) in diameter at 4 megameters (4,000kilometers) range. 20 megawatts distributedevenly over this spot would be an energy flux of1.5 kw/cm2. The spot would need to dwell onthe target for 6.6 seconds to deposit the nominallethal fluence of 10 kJ/cm2. At 2 megameters(Mm) range, booster destruction would requireonly a fourth of this time, or 1.7 seconds of il-lumination. Since light takes about a hundredthof a second to travel 4 megameters and thebooster is traveling a few kilometers per second,the booster moves about sO meters in the timeit takes the laser light to reach it. The laser beammust therefore lead the target by this distance.

The next step is to choose orbits for the satel-lites so that the U.S.S.R.'s ICBM silos are coveredat all times and so that there are enough satellitesoverhead to handle all 1,400 of the present So-viet booster population. Equatorial orbits (fig. 3.3)give no coverage of the northern latitudes whereSoviet ICBMs are deployed. Polar orbits give goodcoverage of northern latitudes but concentratesatellites wastefuIly at the poles where there areno ICBMs. The optimum constellation consists

Figure 3.3

Figure 3.3 Designing a constellation of directed energyweapon satellites for optimum coverage of Soviet ICBMfields. Equatorial orbits (a) give no coverage of northernlatitudes. Polar orbits (b) concentrate coverage at the northpole. Inclined orbits (c) are more economical. Slight additionaleconomies are possible in some cases with furtherelaboration of the constellation design. Source: Author

of a number of orbital planes inclined about 70°to the equator, each containing several satellites.

The shorter the lethal range of the directedenergy weapon, the lower and more numerousthe satellites must be. For instance, with a lethalrange of 3 Mm, 5 planes containing 8 satelliteseach, or a total of 40 satellites, are needed to en-sure that Soviet boosters exiting Soviet airspacewould be within lethal range of one satellite. Ifthe lethal range is increased to 6 Mm, only 3planes of 5 satellites each are needed. Thisdependence of constellation size on weaponrange is displayed in figure 3.4. (It is possible toadjust these numbers a bit by using slightly ellip-tical orbits with apogees over the northern hem-isphere, adjusting inclinations and phasing, etc.).In the present example, requiring that at least oneHF laser be no further than 4 Mm from each So-

200

150

100

50

0

Figure 3.4

1 I 1 1 I I‘O 1 2 3 4 5 6 7 8 9

Range of directed energy weapon(megameters)

Figure 3.4 The number of satellites needed in a constellationto ensure that at least one satellite is over each Soviet ICBMfield at all times depends on the effective range of thedirected energy weapon. For every one defensive weaponrequired overhead a Soviet ICBM field to defend againsta rapid Soviet attack, an entire constellation must bemaintained on orbit. Since there are many Soviet ICBM fieldsdistributed over much of the Soviet landmass, more than onesatellite in each constellation would be in position toparticipate in a defensive engagement. The ratio of thenumber of satellites in the constellation to the number overor within range of Soviet ICBM fields is called the absenteeratio. If all Soviet ICBMs were deployed in one relatively smallregion of the U. S. S. R., the absentee ratio would be the sameas the number of satellites in the constellation. Source: Author

viet ICBM site at all times (corresponding to nolonger than 6.6 seconds dwell time per booster)results in the illustrative constellation of 32 or-bital positions shown in figure 3.5.

Since the 1,400 Soviet boosters currently de-ployed are spread out over most of the SovietUnion, perhaps 3 of the 32 orbital positions wouldbe over or near the Soviet Union at a time, ableto make efficient intercepts. That is, only one in11 deployed U.S. battle stations would partici-pate in a defensive engagement. The ratio of thetotal number of battle stations on orbit to thenumber in position to participate in a defensiveengagement is called the absentee ratio. The in-evitable waste reflected in the absentee ratio—

Figure 3.5

O = Cluster of 5 chemical laser battle stationsTotal of 32 x 5 = 100 battle stations

Figure 3.5 Constellation of hypothetical directed energyweapon satellites with 4,000 km range. The orbits are circularwith 1000 km altitude. Each of the four orbital planes consistsof eight positions spaced 45° apart around the circle. In theexample given in the text, five chemical laser battle stationsare clustered at each point shown in this figure, for a total

of 32 x 5 = 160 battle stations. Source: Author

20

usually on the order of 10—offs ets an oft-citedtheoretical advantage of boost-phase intercept,namely, that intercepting one booster saves buy-ing 10 interceptors for the booster’s 10 RVS. Onthe other hand, coverage of the U.S.S.R.'s ICBMfields automatically gives good coverage of essen-tially all submarine deployment areas. Obviouslythe absentee ratio would be 32—the full con-stellation size—and not 32/3 = 10.7 if SovietICBM silos were not spread out so widely overSoviet territory but were deployed over a thirdor less of the Soviet landmass, so that only oneof the 32 U.S. satellites was within range.

Three of the earlier described laser satellites inposition over the Soviet ICBM fields are notenough to intercept 1,400 boosters if all or mostof the boosters are launched simultaneously.Each satellite can only handle a few boostersbecause it must dwell for a time on each one.The time a chemical laser must devote to eachbooster depends on the satellite’s position at themoment of attack—6.6 seconds for 4 Mm range,1.7 seconds for 2 Mm range, etc. Taking 2 Mmas an average range for the 32-satellite constella-tion (hoping the Soviets do not choose a momentwhen most of the U.S. satellites are farther than2 Mm from the ICBM flyout corridors to launchall their boosters simultaneously), a laser mustdevote an average of 1.7 seconds to each booster.

If the boosters in the future Soviet arsenalresemble the U.S. MX, and the defense waits 30seconds or so to confirm warning and to wait forthe boosters to climb to an altitude where the HF

laser can reach, each booster is accessible for 150seconds of its 180 second burn time. Each lasercan therefore handle no more than 90 boosters,even with instant dewing of the beam from targetto target. If 1,400 Soviet boosters were launchedsimultaneously, (1 ,400)/(90) = 15 lasers wouldbe needed in position, for a worldwide total (mul-tiplying by the absentee ratio) of (10.7) X (15)= 160 satellites.

If the Soviets doubled their arsenal to 2,800boosters, the United States would need to deployanother 160 satellites, possibly an uncomfortablecost trade for the United States.

What is worse, if the Soviets deployed 1,400missiles in a single region of the U.S.S.R. (at aU.S.-estimated cost of $21 billion for Midgetman-Iike ICBMs; see section 2 above), the US wouldhave to build, launch, and maintain on orbit anadditional (32) X(1 400)/(90) = 500 lasers plustheir fuel and support equipment.

If Soviet boosters were covered with shieldingmaterial and spun during flight to achieve an ef-fective hardness of, say, 60 kJ/cm2, a laser wouldhave to devote 10 seconds to each booster at 2Mm range, requiring a sixfold increase in thenumber of satellites, to 960. Alternatively, theaverage range of each engagement could be re-duced to keep the dwell time at 1.7 seconds, withcorresponding increase in constellation density(fig. 3.4). Either way, the number of U.S. satelliteswould grow to nearly the number of Soviet boost-ers intercepted.

Table 3.1.—Variation of the Number of Chemical Laser Battle Stations Needed to Handle a SimultaneousLaunch of Soviet ICBMs, Depending on Characteristics of the Soviet Arsenal and the U.S. Laser Defense

Laser power ApproximateNumber of (MW) and number of

Soviet Booster Geographic Hardness aperture battle stationsDeparture from baseline boosters characteristics distribution (kJ/cm2) diameter (m) neededBaseline . . . . . . . . . . . . . . . . . . . 1,400 MX-like Current Soviet 10 20/10 160Booster number . . . . . . . . . . . . 2,800 MX-like Current Soviet 10 20/10 320Deployment geography . . . . . . 1,400 MX-like One region 10 20/10 500Booster hardness . . . . . . . . . . . 1,400 MX-like Current Soviet 60 20/10 960Laser brightness . . . . . . . . . . . . 1,400 MX-like Current Soviet 10 80/50 20-30

(100 timesbrighter)

Booster burn time . . . . . . . . . . 1,400 Fast-burn Current Soviet 10 20/10 800-1,600Booster burn time . . . . . . . . . . 1,400 SS-18-like Current Soviet 10 20/10 90

SOURCE: Author.

21

If the United States developed a battle station100 times brighter (using, say, a 80 MW laser withan effective mirror diameter of 50 meters), a fewlasers overhead (20 to 30 total worldwide) couldeasily handle an attack of 1400 boosters hardenedto 10 kJ/cm2. If the boosters were hardened to60 kj/cm2, over 100 such lasers would be needed.

Deployment by the Soviets of 1400 fast-burnboosters would give the U.S. lasers just 20 to 40seconds, rather than 200 seconds, to destroy allthe boosters. The U.S. constellation would con-sequently need to grow by a factor 5 to 10, to800 to 1600 satellites!

Table 3.1 summarizes how the size of the de-fensive deployment varies with the parametersassumed.

Requirements for a ChemicalLaser Defense

Figure 3.6 displays the performance of varioushypothetical HF lasers. Keeping the size of thebattle station constellation down to a hundredrather than several hundred satellites means le-thal ranges of at least 4 Mm with illuminationtimes less than about 1 second, assuming the de-fense must be capable of intercepting 1,000 to2,000 Soviet boosters with launches timed tokeep the boosters as far from the U.S. lasers aspossible. Further assuming Soviet booster harden-ing to at least 10 kJ/cm2 results in a requirementfor chemical lasers considerably brighter than the20 MW, 10-meter laser described above. Ahundredfold increase in brightness would beachieved by a laser with power 80 MW and ef-fective mirror diameter 50 meters.

Such a laser would be about 10 million timesbrighter than the carbon dioxide laser on the AirForce’s Airborne Laser Laboratory. The currentAlpha laser program of the Defense AdvancedResearch Projects Agency (DARPA) aims at a con-struction of an HF laser of just a few megawattsand built only for ground operation. Nonethe-less, there is no fundamental technical reasonwhy extremely bright chemical lasers cannot bebuilt. In theory, several lasers can be operatedtogether so that the brightness of the resultingbeam increases with the square of the number

Figure 3.61

1 2 3 4 5 6 , 7 8 9 10

Radiusof Earth Geosynchronous(6.4 Mm) altitude = 40 Mm

Lethal range (megameters)

Figure 3.6 Lethal range versus booster hardness for HFchemical lasers of various sizes and dwell times. The labelson the curves have the format (laser power in megawatts,mirror diameter in meters) followed by the amount of timethe laser devotes to destroying each booster. Source; Author

of lasers: 10 lasers combined in this way wouldproduce a beam 100 times brighter than each in-dividual laser. The trick is to arrange for thetroughs and crests of the light waves from all thelasers to coincide. This theoretical prospect isunlikely to be realized with H F lasers, since theirlight is actually emitted at several wavelengthsand with shifting patterns of crests and troughs.

To yield diffraction-limited divergence, the mir-ror surface must be machined to within a frac-tion of a wavelength of its ideal design shape overits entire surface. Since the mirror is over a mil-lion wavelengths across, avoiding small figure er-rors is a severe requirement. A number of smallmirrors can obviously combine to produce onelarge optical surface if their positions are allaligned to within a fraction of a wavelength. The

2 2

mirrors must maintain perfect surface shape inthe face of heating from the laser beam, vibra-tion from the chemical reaction powering the la-ser, and vibrations set up in the mirror as it isslewed. Substantial hardening of mirrors to radia-tion from nuclear bursts in space and to the x-ray laser (described below) would be a challeng-ing task. The 2.5-meter diameter mirror onNASA’s Space Telescope was produced withoutthese constraints.

An extremely optimistic outcome of HF lasertechnology—near the theoretical limit for conver-ting the energy of the chemical reactants to la-ser energy—would require more than a kilogramof chemicals on board the satellite for everymegajouIe radiated. A spot diameter of 2 metersat the target and a lethal fluence of 10 kJ/cm2 overthis area results in an energy expenditure of 300MJ per booster. Destroying 1,000 Soviet boosterstherefore requires, reckoning very crudely,300,000 kg of chemicals in position over the So-viet ICBM field, or perhaps 10 million kg on or-

bit worldwide. The space shuttle can carry a pay-load of about 15,000 kg to the orbits where thesatellite battle stations would be deployed. About670 shuttle loads would therefore be needed forchemicals, with perhaps another half as many forthe spacecraft structures, the lasers and mirrors,construction and deployment equipment, andsensors. 1,000 shuttle missions for every 1,000Soviet boosters (perhaps Midgetmen) deployedin reaction to the U.S. defense is an impracticalcompetition for the United States. Use of H Fchemical lasers for BMD therefore requiresremarkably cheap heavy-lift space launch capa-bility in the United States.

The remaining components of the chemical la-ser defense system—sensors, aiming and pointingtechnology, and communications— are for themost part generic to all directed energy weaponsand are discussed in section 4. Section 5 presentscountermeasures the Soviets might take to off-set or nuIlify a chemical laser defense.

3.2 GROUND-BASED LASERS WITH SPACE-BASED MIRRORS

A slight variant of the previous concept putsthe laser on the ground and mirrors in space,reflecting the light back down toward Earth to at-tack ascending boosters. This scheme avoidsplacing the laser and its power supply in space,though mirrors, aiming equipment, and sensorsremain. The excimer and free-electron lasersconsidered for this scheme are in fact likely tobe rather cumbersome, so ground basing themmight be the only practical way to use them forBMD. The lasers would emit at visible or ultra-violet wavelengths about ten times shorter thanthe near-infrared wavelengths of the HF and DFchemical lasers in the space-based concept.Shorter wavelengths permit use of smaller(though more finely machined) mirrors. The highpower available with ground basing suggests atleast the possibility of impulse rather than ther-mal kill of boosters.

The term excimer is a contraction of “exciteddimer.” A dimer is a molecule consisting of twoatoms. The dimers considered for these lasers

contain an atom of noble gas and a halogen atom,making dimers like xenon fluoride (XeF), xenonchloride (XeCl), and krypton fluoride (KrF). Thelaser light comes from dimers in an excited upperstate decaying to a lower state, just like in the HFlaser. Excimer lasers tend to emit light in pulsesrather than in a continuous wave. The popula-tion of upper-state molecules is provided bypumping with electric discharges in a rather com-plicated process. The population of lower-statemolecules remains small because the lower-statedimer is unstable and quickly breaks up into itstwo constituent atoms. The pumping process forexcimer lasers is inefficient, so only a small frac-tion of the energy put into the laser in the elec-tric discharge emerges as laser light. Powerful ex-cimer lasers would therefore be large and wouldneed to vent large amounts of wasted energy;these characteristics make them unsuitable fotspace basing. Development of excimer lasers isat an early stage, and no excimer lasers exist withanything remotely approaching the characteristic:needed for this boost phase intercept concept.

23

Figure 3.7

10 relay mirrors(30 m diameter)

Laser beaconfor adaptive

optics 8

12 mountaintop lasers 100 Intercept mirrors(400 MW, O 5 µ) (5 m diameter)

with 50,000 mirrorsubelements for \adaptive optics

\ I I

Figure 3.7 Illustrative configuration of ground-based excimeror free-electron laser and space-based mirrors for thermal kill

of Soviet ICBM boosters. Source: Author

Power outputs achieved in the laboratory are stillseveral orders of magnitude less than the aver-age power needed for thermal kill, and the en-ergy achieved in a single pulse is much smallerthan the single-pulse energies needed for impulseki I I.

The working of a free-electron laser (FEL) ismore complicated.4 As the name suggests, thelight-emitter (Iasant) is free electrons emitted from particle accelerator. Pumping therefore orig-nates in the electrical source powering the ac-celerator. The free electrons from the acceleratorare directed into a tube called the wiggler thatIas magnets positioned along its length. Thenagnets cause the electrons to wiggle back and~rth as they transit the tube. As they wiggle, the

4See Charles A. Brau, “Free Electron Laser: A Review, ” Laser>CUS, March 1981; f%ywcs Today, December 1983, p. 17.

electrons emit some of their energy as light. Thepresence of light from one electron causes othersto emit in the usual cooperative manner of a la-ser, and a cascade begins. By adjusting the posi-tions of the magnets and the energy of the elec-trons, the wavelength of the light can be tunedto any value desired. The only advantage of theFEL over excimer lasers is the high efficiency thatcan (theoretically) be obtained with the former.It has been suggested that it might even be possi-ble to position FELs in space like HF chemicallasers. FEL operation at visible wavelengths is inits infancy, and the experimental devices usedare many millions of times less powerful thanthose required in this BMD.

The BMD scheme calls for a large ground basedexcimer or free electron laser, relay mirrors athigh altitude to carry the laser beam around thecurve of the Earth, and intercept mirrors to focusthe beams on individual boosters (fig. 3.7). Thecharacteristics of a nominal system for thermalbooster kill are easily ascertained. Suppose firstthat there are enough intercept mirrors so thatthe average range from mirror to booster is 4 Mm,and suppose the Soviet boosters are destroyedwith 10 kJ/cm2 deposited on a spot as small asseveral centimeters wide. Assume the excimer orfree electron laser operates at about 0.5 microns,in the visible band. Then a 5 m intercept mirrorwill produce a spot 50 cm wide at 4 Mm range.If a half second of the main laser beam is devotedto each booster, then the required 10 kJ/cm2 willbe accumulated if the power reflected from eachintercept mirror is 40 MW.

Only about a tenth of the power emitted bythe ground based laser in the United States wouldbe focused on the booster over the U.S.S.R. Theremainder would be lost in transit through theatmosphere and in reflection from the two mir-rors. Thus a 400 MW laser is required.

Passage through the atmosphere poses a num-ber of problems for the primary laser beam. Themost important source of interference is tur-bulence in the air, causing different parts of thelaser beam to pass through different optical envi-ronments when exiting the atmosphere. Each partof the beam suffers a slightly different disruption,and the beam that emerges does not have the

24

orderly arrangement of crests and troughs neededfor diffraction-limited focusing from the interceptmirror. Without compensation for atmosphericturbulence, the ground-based laser scheme iscompletely impractical. Fortunately, the patternof turbulence within the laser beam, though con-stantly changing, remains the same for periodsof a few milliseconds. Since it takes only 0.1millisecond for light to make a round trip throughthe atmosphere, the effect of turbulence on thelaser beam can be compensated for with the fol-lowing technique, called adaptive optics: A low-power laser beacon is positioned near the relaymirror. A sensor on the ground observes the dis-tortion of the beacon beam as it passes throughthe atmosphere. The beam from the ground-based laser is then predistorted in just such a waythat its passage through the same column of airtransited by the beacon beam re-forms it into anundistorted beam.

Figure 3.7 shows the many components re-quired by the ground-based laser concept. Sinceeach Soviet booster requires 0.5 sec of beam atsome time during its 200 sec. boost phase, fourbeams would be needed to handle 1,400 Sovietboosters launched simultaneously (assuming noretargeting delays), The lasers should be deployedon mountain tops to make atmospheric effectsmanageable, and enough should be deployedthat at Ieast four sites are always clear of cloudcover. The mirror on the ground would need tobe tens of meters across and divided into tensof thousands of individually adjustable segmentsfor predistortion of the wavefront. Each relay mir-ror would need to be accompanied by a beacon.Four large interception mirrors would be neededwithin 4 Mm of each Soviet ICBM flyout corridor,giving a worldwide constellation of a hundred orso.

The small laser wavelength means that all mir-rors must be more finely machined than the mir-

rors for the chemical laser and can toleratesmaller vibrations and stresses due to heatingfrom the laser beam. The small wavelength alsoresults in a spot 10 times smaller at the target thanthe spot from a chemical laser beam at the samerange. This small spot requires pointing accuracyten times finer. Perhaps most important of all, theplume from the booster motor is too large toserve as target for such a narrow beam. Some wayof seeing the actual missile body against thebackground of the plume is needed for the short-wavelength laser schemes (and for some config-urations of chemical lasers). One answer to thisproblem, described in section 4 below, is to posi-tion near each intercept mirror a low-power la-ser and a telescope (a laser radar or Iadar): thelaser illuminates the booster and the telescopeobserves the reflected laser light, directing thepointing of the intercept mirror. The Iadar tele-scope must have a mirror as large as the interceptmirror, since it must be able to “see” a spot assmall as that made by the beam.

A single immense laser pulse that deposits 10kJ/cm 2 in a very short time–millionths of a sec-ond rather than a second— might cause impulsekill rather than thermal kill, In impulse kill, thelaser pulse vaporizes a small layer of the boosterskin and surrounding air. The superheated gasesthen expand explosively, sending an impulsiveshockwave into the booster. A strong enoughshockwave might cause the booster skin to tear.The advantage of this kill mechanism is that itwould be very difficult to protect boosters fromit. The disadvantages are that impulse kill requiresprodigious laser pulses and mirrors that can with-stand them, and that the mechanism is poorlyunderstood and depends on myriad factors likethe altitude of the booster at the moment it is at-tacked.

3.3 NUCLEAR BOMB-PUMPED X-RAY LASERS:ORBITAL AND POP-UP SYSTEMS

The U.S. Government has revealed efforts at its Such devices are said to constitute a “third gen-weapon laboratories to use the energy of a nu- eration” of nuclear weapons, the first two genera-clear weapon to power a directed beam of x-rays. tions being the atomic (fission) and hydrogen

25

(fusion) bombs. Each succeeding generation rep-resented a thousandfold increase i n destructiveenergy, from a ton of high explosive to a kilotonfission weapon to a megaton fusion weapon. Thethird generation weapon uses the same amountof energy as the fusion weapon, but directs muchof that energy toward the target rather than allow-ing it to escape in all directions. At the target,therefore, the energy received is much greaterthan the energy that would be received from ahydrogen bomb at the same range.

x rays lie just beyond ultraviolet light on theelectromagnetic spectrum and have wavelengthsabout a thousand times smaller than visible light(see fig. 3.1 ). Compared to the infrared, visible,and ultraviolet lasers in the previous sections, thex-ray laser produces much more energy from itsbomb pump, but the energy is spread out overa larger cone. The lethal ranges for boosters turnout to be roughly comparable for all these typesof directed-energy device. Obviously the x-raylaser delivers all its energy in one pulse, so thereis no question of dwell time on the target. Veryshort-wavelength x-rays penetrate some distanceinto matter (witness dental and medical x-rays),but the longer-wavelength x-rays produced by alaser device do not penetrate very far into mat-ter or into the atmosphere.

orbiting and ground-based “pop-up” systemshave been proposed as ways to make use of thex-ray laser for boost phase BMD. Both of theseschemes have attractive features but also seriousdrawbacks. It could well be that the x-ray laserdevice, if a powerful one can eventually be built,will be more useful in other strategic roles thanboost-phase BMD.

X-Ray Lasers

Little has been revealed about the characteris-tics of the bomb-pumped x-ray laser being stud-ied by the United States (the so-called Excaliburdevice), but some general information can bededuced from the laws of physics and, to a lesserextent, from the scientific literature here and inthe Soviet Unions

5F, V. BU nkln, V. 1. Derzhiev, and S. 1. Yakovlenko, %vlet /our-na/ of Quantum E/ectron/cs 11 (8), August 1981, p. 981. R. C. Elton,R. H. Dixon, and J. F. Seely, Physics of Quantum Electronics 6(1 978), p. 243. Michael A, Duguay, /&d., p. 557. G. Chapllne andL. Wood, Physics Today, June 1975, p. 40.

Figure 3.8

Energy from nuclear bomb

material = 2 (width – length)

Figure 3.8 In an x-ray laser, a rod of Iasant material is pumpedto upper energy states by a nuclear bomb. Those cascadesof downward transitions that travel lengthwise build up moreenergy than sideways-going cascades. As a result, most ofthe energy emerges from the ends of the rod into a cone withdivergence angle equal to twice the rod width divided by its

length. Source: Author

The pumping source for the x-ray laser is a nu-clear bomb. The radiant heat of the born b raiseselectrons to upper energy levels in atoms of Iasantmaterial positioned near the detonation (thechemical nature of the Iasant material has notbeen revealed). As the electrons fall back againto lower levels, it can happen that for a momentmany atoms are in a given upper level and fewin a lower level; this is the necessary conditionfor Iasing from the upper level to the lower level.The wavelength of the emitted x-ray is deter-mined by the energy levels involved. The wave-length of the laser under study in the UnitedStates is classified. We will use a round numberof 1 nm.

Since x-rays are not back-reflected by any kindof mirror, there is no way to direct the x-rays intoa beam with optics like the visible and infraredlasers. Nonetheless, some direction can be givento the laser energy by forming the Iasant mate-rial into a long rod. Recall that a laser beam buildsup when light from one Iasant atom stimulatesthe upper-to-lower-level transition in anotheratom, which stimulates a third, and so on. Theresult is a cascade of light heading in same direc-tion as the light from the original atom. The lightpulse gets stronger and stronger as it traverses theIasant medium stimulating more and more tran-sitions. In a long rod of Iasant material, cascadesthat get started heading lengthwise down the rodare highly amplified by the time they leave therod, whereas sideways-going cascades remainsmall. The result is that most of the laser energy

26

emerges as a beam aligned along the rod axis (fig.3.8).

The projected capabilities of the x-ray lasers be-ing studied in the U.S. are classified; but it is fairlyeasy to determine the upper limit to how power-ful such a laser could possibly be. Whether R&DwiII succeed in making such a perfect laser can-not be said. But it will become clear that some-thing very close to the perfect laser is requiredfor boost phase intercept, though a less successfuldevelopment would still yield a potent antisatel-lite weapon.

A l-megaton nuclear weapon releases about4 billion megajoules of energy. By surroundingthe bomb with Iasant rods, most of this energycan be harnessed to pump the laser. Since thepumping mechanism for the x-ray laser is ratherdisorganized and wasteful, like the pumpingmechanism for excimer lasers, at most a few per-cent of the bomb energy can be expected to endup in the laser beam.

The resulting 100 million megajoules or less oflaser energy emerges from the rods into coneswith relatively large divergence angle. It is easyto see why this divergence angle is much largerthan the divergence angle obtained with themirror-directed lasers treated in the previous sec-tion, The divergence angle is determined by theratio of the width of the rod to its length, as infigure 3.8. A practical length for a rod is no morethan about 5 meters. Making the rod thinner de-creases the divergence angle, but beyond a cer-tain point no further narrowing of the beam coneis possible. The limit arises from diffraction, justas with the infrared and visible lasers: the diver-gence angle of light emitted from an aperture(mirror, rod tip, or anywhere else) cannot be lessthan about 1.2 times the wavelength of the lightdivided by the diameter of the aperture. A verynarrow rod therefore actually aggravates diffrac-tion and produces a wide cone. Making the rodthinner results in no further narrowing of thebeam when (1 .2) (wavelength) /(rod width) s (2)(rod width)/(rod length). For an x-ray wavelengthof 1 nm and a rod length of 5 meters, this equa-tion yields an optimum rod width of 0.06 mm anda minimum achievable (diffraction-limited) diver-gence angle of 20 microradians.

A 1-megaton bomb-pumped x-ray laser cantherefore deposit no more than about 100 mil-lion megajoules into a cone no narrower thanabout 20 microradians. The x-ray pulse fromdetonating such a perfect laser would depositabout 300 kJ/cm2 over a spot 200 meters wideat 10 Mm range.

Interaction of X-rays with Matter

X-rays of 1 nm wavelength do not penetratevery far into matter: all the energy from such alaser would be absorbed in the first fraction ofa millimeter of the aluminum skin of a missile.This paper-thin layer would explode, sending ashockwave through the missile. Thus the x-raylaser works by impluse kill.

Another consequence of the opacity of mat-ter to x-rays is that the laser beam would notpropagate very far into the atmosphere. Thealtitude to which the beam would penetratedepends on the precise wavelength, which isclassified. For the nominal 1 nm wavelengthdescribed above, boosters below about 100 kmwould be quite safe from attack. If the wavelengthwere much shorter, the x-rays would penetratelower, reaching perhaps 60 km altitude or so. Inwhat follows, it will be assumed that boosters aresafe from x-ray laser attack below about 80 km.

One last consequence of the physics of x-rayinteraction with matter is noteworthy. When anatom of matter absorbs an x-ray, it emits an elec-tron. As x-rays are absorbed, it becomes harderand harder to remove successive electrons. Fi-nally further x-rays cannot remove further elec-trons, and the matter becomes transparent. Thisphenomenon, called bleaching, means that astrong x-ray laser beam can force its way througha column of air by bleaching the column, but aweak laser beam is completely absorbed. An x-ray laser in the atmosphere might therefore beable to attack an object in space because thebeam is intense enough in the vicinity of the la-ser to bleach the air, whereas an x-ray laser inspace could not attack objects within the atmos-phere. This fact bodes ill for defensive space-based x-ray lasers attacked by similar lasers (or

2 7—

even weaker ones) Iaunched from the ground bythe offense.

As with visible and infrared lasers, the lethalityof a n x-ray laser is subject to large uncertainties.The proper order of magnitude for the amountof x-ray energy per square centimeter that needsto be deposited on the side of a booster to dam-age it can be estimated fairly easiIy. But the ac-tual hardness of a booster would depend onmany design details in a way that is not fullyunderstood at this time. A simple calculation in-dicates that 20 kj/cm2 is a reasonable number totake for the hardness of a booster. This is aboutthe same as for impulse kill by visible laser. AnRV would be harder, and a satellite softer.

Orbital Defense Concept

The “perfect” x-ray laser whose characteristicswere deduced above wouId be capable of inter-cepting a booster from geosynchronous orbit40,000 km above the Earth. One laser would beneeded for each Soviet booster. At lower alti-tudes, the rods surrounding the bomb could begathered into several bundles and each bundleaimed at a different booster. At these loweraltitudes, though, the absentee problem meansthat roughly one x-ray laser device would stillneed to be placed in orbit for each Soviet booster.Though the x-ray lasers are small and light com-pared to a chemical laser, the cost tradeoff in-volved in launching a new laser every time theSoviets deploy a new ICBM is obviously not atolerable one for the United States.

The x-ray laser can attack the boosters afterthey have left the protective atmosphere butbefore burnout. Simultaneous launch of all So-viet boosters is not a problem for x-ray lasers in

I,tq ~,1 I let or soft h a m mer blow app[ les a n I m pu I se Per u n It area

JI about 1 () kta[]~ (0, 5 kg hammer head, 5 m/see stri kl ng velocity,1 c m radlu~ ( ontac t area; 1 tap = 1 dyne-see/cm’). To apply anm I)U Iw of th IS 5trength to the entl re side of an ICBM booster re-lulres a fluence F, whose order of magnitude can be estimatedIf tt)l low~: The cold mass absorption length (a) for 1 n m x-rays is~ bout () 5 m I I I lgrams/cm2. If a I I the energy absorbed by the paper-hln absorbing layer were converted to klnet Ic energy, the boll-oft/elocity wou Id be (F/a)”, meaning a n impu Ise per unit area of or-jer (Fa)Y’, 10 ktaps is therefore produced if F =20 kJ/cm’,

In re.allty, not all the deposited energy couples to the boostern t h If way A more caretu I ca Icu tat Ion of th IS lessened cou pl I ng1~~ been pertormed by Hans Bet he (private com m u n Icatlon),

the way it is a problem for chemical lasers thatmust dwell on each target before passing on tothe next. Fast-burn boosters are Iikewise not acrippling problem for an orbiting x-ray lasersystem unless they burn out before they leave theatmosphere, Other countermeasures, most no-tably the vuInerability of U.S. orbital x-ray lasersto Soviet x-ray lasers, are treated in section 5.

Pop-Up Defense Concept

The pop-up concept represents an attempt toavoid the one-laser-per-booster cost exchangeand the vulnerability associated with basing thelasers in space (though crucial sensors remainspace-based even in the pop-up scheme). Thesmall size and light weight of the bomb-pumpedlasers makes it possible to consider basing themon the ground and launching them into spaceupon warning of Soviet booster launch.

Figure 3.9 shows why basing the pop-up lasersin the United States is not practical. During the200 seconds or so of burn time of a Soviet MX-

Figure 3.9

Lowest altitudeline of fire

clear atmosphere

Burnout of hypotheticalMX-like Soviet ICBM

(200 km altitude180 sec. after launch)

atmosphere - 100 km

Figure 3.9 X-ray lasers launched from the United States onwarning of Soviet ICBM launch would have to climb at leastas high as the line of fire shown in the figure within threeminutes to intercept an MX-like Soviet ICBM. Such a hugefast-acceleration defensive booster would be many timeslarger than the Saturn V that took astronauts to the moon.

Source: Author

33-698 0 - 84 - 5 : QL 3

28

like ICBM,have to cl

the U.S.-based pop-up lasers wouldmb high enough to see the Soviet

boosters over the Earth’s horizon and have a line-of-fire unobstructed by the absorbing atmos-phere. Climbing so high so fast requires a boosterfor the x-ray lasers that is many thousands of timeslarger than the Saturn V rocket that carried U.S.astronauts to the Moon.

If the British Government allowed the U.S.Government to base x-ray lasers in the UnitedKingdom, the lasers would be separated from So-viet ICBM silos by only 45 degrees of arc ratherthan 90 degrees as with U.S. basing. Even so,popping up to attack an MX-like Soviet boosterwould require an enormous fast-burn booster forthe x-ray laser and would put it into position toattack the Soviet booster only seconds beforeburnout. If the Soviets depressed the trajectoryor shortened the burn time of the offensivebooster very slightly, or if the United States suf-fered any delay whatsoever in launching thedefensive boosters after Soviet launch (instan-taneous warning), this hypothetical U.K.-basedsystem would be useless.

A final possibility would be launch of defen-sive lasers from submarines stationed immedi-ately off Soviet coasts—in the Kara Sea or Sea of

Okhotsk, separated from Soviet silos by about 30degrees of arc–on SLBM-sized fast-burn boosters.With instantaneous warning, a sea-based lasermight be able to climb to firing position a fewseconds before burnout of a Soviet MX-like ICBMand would enjoy almost an entire minute of visi-bility to a slow-burning, high-burnout-altitudebooster like the SS-18. Because of the short range,each bomb-pumped laser of the perfect designdescribed above could attack many (over 100)boosters using many individual Iasing rods. Suchefficiency could well be essential, since a sub-marine cannot launch all its missiles simulta-neously and might only be able to fire one defen-sive missile in the required few seconds. If theMX-like Soviet boosters were flown on slightlydepressed trajections, if warning were not com-municated to the submerged submarine prompt-ly, if a human decision to launch defensive mis-siles were required, or if the Soviets deployedboosters that burned faster than MX, the sub-Iaunched system would be nullified, Last, sub-marine patrol very near to Soviet shores suggeststhe possibility of attacking the submarine withshore-based nuclear missiles as soon as its posi-tion has been revealed by the first defensivelaunch. Other countermeasures are discussed inSection 5.

3.4 SPACE-BASED PARTICLE BEAMS

Beams of atomic particles would deposit theirenergy within the first few centimeters of the tar-get rather than at the very surface as with lasers.The effects of irradiation with the particle beamcould be rather complex and subtle and wouldprobably depend on design details of the attack-ing Soviet booster. The result is uncertainty of sev-eral factors of ten in the effective hardness of anICBM booster to beam weapon irradiation.

neutral particle beams, consisting of atomichydrogen (one electron bound to one proton)deuterium (one electron, one proton, one neu-tron), tritium (electron, proton, two neutrons) 01other neutral atoms are considered. To producea neutral hydrogen (H°) beam, negative hydrogen atoms (H –) with an extra electron are accelerated; the extra electron is removed as the bean-emerges from the accelerator,

Only charged particles can be accelerated to Two features of neutral particles beams domiform high-energy beams, but a charged beam nate their promise as boost phase intercept weapwould bend uncontrollably in the Earth’s mag- ons (leaving aside entirely the issue of counternetic field. (There is one theoretical exception to measures). The first is the uncertain lethality othis statement, described below.) For this reason the beam. The second is the fact that the bear-r

29

cannot propagate stably through even the thin-nest atmosphere and must wait for an attackingbooster to reach very high altitude.

Generating Neutral Particle Beams

The accelerator that accelerates the negativehydrogen ion is characterized by its current inamperes, measuring the number of hydrogenions per second emerging from the accelerator;and by the energy of each accelerated ion in elec-tron volts (eV; 1 eV = 1 watt per ampere).Multiplying the current by the energy gives thepower of the beam, so that a l-amp beam of 100MeV particles carries 100 MW of power. Ground-based high-current accelerators and ground-based high-energy accelerators have been builtand are operated daily in laboratories. One of thechallenges for neutral particle beams as weaponsis that they require both high current and highenergy. Another challenge is to provide multi-megawatt power sources and accelerators in asize and weight suitable for space basing.

Magnets focus and steer the beam as it emergesfrom the accelerator. The last step is to neutralizethe beam by passing it through a thin gas wherethe extra electron is stripped off in glancing col-lisions with the gas molecules, forming HO fromH-. The divergence angle of the beam is deter-mined by three factors. First, the accelerationprocess can give the ions a slight transverse mo-tion as well as propelling them forward. Second,the focusing magnets bend low-energy ions morethan high-energy ions, so slight differences inenergy among the accelerated ions lead to diver-gence (unless compensated by more complicatedbending systems). Third, the glancing collisionsthat strip off the extra electron give the H atoma sideways motion. This last source of divergence

Table 3.2.—Neutral Particle Beam Divergence Angle

H“ T“

100 MeV 3.6 microradians 2.0iOO MeV 1.4 1.0

Divergence angle introduced by stripping electrons from a beam of negativehIydrogen or tritium ions to produce a neutral beam This source of divergencej an unavoidable consequence of the Heisenberg uncertainty principle appliedo the sudden stripping of the electron If the satellite. based accelerator of theegative tons were absolutely perfect, this amount of divergence would remain

is unavoidable and, by the Heisenberg uncer-tainty principle, cannot be controlled or compen-sated. It sets a lower limit on the divergence angleachievable with this method of producing neutralparticle beams. Table 3.2 shows the divergenceangle resulting from this third source, assumingperfect control of the first two sources. Thedivergence cone from a neutral particle beam istherefore about 10 times larger than the beamfrom the chemical laser of section 3.1 and 10times smaller than from the x-ray laser of section3.3.

A 100 MeV, 0.5 amp neutral tritium (T°) beamthus directs 50 MW of power into a cone of di-vergence angle 2 microradians, producing a spot10 meters across at 5 Mm range. A target withinthis spot receives only 65 watts/cm2, requiring 1.5seconds of dwell time to deposit only 100 J/cm2.

Booster Vulnerability toParticle Beams

As soon as the neutral particle beam hits thetarget, the remaining electron is stripped off, leav-ing the energetic proton (or deuteron or triton)penetrating deeply into the target. The protonscatters electrons in its path, giving up a smallamount of its energy to the electron in each col-lision. When it has given up all its energy, it stops.For most of its path, it deposits energy uniformly.Thus if a 100 MeV TO beam penetrates 4 cminto the propellant in a missile, it deposits about25 MeV along each cm. Protons penetrate moredeeply than tritons of the same energy, and allparticles penetrate more deeply as they are givenmore energy (table 3.3).

Table 3.3.—Penetration Range of NeutralParticle Beams Into Matter (in centimeters)

H“ TO

100 MeV 250 MeV 100 MeV 250 MeV

Solid propellant orhigh explosive(density 1.0 gm/cm3) 9.5 46.6 4.2 20.2

Aluminum . . . . . . . . . 3.5 17.2 1.6 7.6Lead . . . . . . . . . . . . . . 0.8 3.9 0.4 1.7

SOURCE Author SOURCE Author

30

Figure 3.10

Solid propellant(density 1 gm/cm3)

(11

4 cm

1 cm

Lead.3 gm/cm3)

4.2 grams 4.2 grams1 cm

100 MeV Tritium (T 0, beam

Figure 3.10 A neutral particle beam penetrates farther intoan aluminum target than into a lead target but deposits thesame energy per gram. Though the energy per gram neededto melt aluminum is well known, the utility of particle beamBMD concepts rests on the less certain destructive effects

at lower levels of irradiation. Source: Author

Table 3.4.—Effects of Particle Beam Irradiation

Energy depositionHarmful effect (Joules per gram)Disruption of electronics . . . . . . . . . . 0.01 –1 .0Destruction of electronics . . . . . . . . . 10Detonation of propellants,

high explosive . . . . . . . . . . . . . . . . . 200Softening of uranium

and plutonium . . . . . . . . . . . . . . . . . hundredsMelting of aluminum. . . . . . . . . . . . . . 1,000

Approximate energy deposition (radiation dose) required to produce various harm.ful effects in components of a missile booster and its payload Many other ef-fects, such as melting of glue and plastic and rate-dependent effects, might alsobe Important

SOURCE Author

The target electrons that recoil from collisionswith beam particles eventualy stop, and their en-ergy appears as heat. The 100 MeV T° beamdescribed above, depositing 100 J/cm2 on an alu-minum target, penetrates to a depth of 1.6 cm.The 1.6 cubic centimeter volume of aluminumthat absorbs this 100 joules of energy weighsabout 4 grams. The effect of the beam is there-fore to deposit about 25 joules per gram through-out the first 1.6 cm of the target. The penetra-tion depth is inversely proportional to the densityof the absorbing material, so the same beam ona lead target would not penetrate as far but would

deposit the same energy per gram as it did inaluminum (fig. 3.1 O).

The destructive effects of penetrating particlebeams are therefore expressed in joules/gram de-posited within the target rather than in joules/cm2

on the surface of the target as with lasers. Table3.4 shows the energy deposition needed to pro-duce certain harmful effects. Melting the targetis straightforward, but for the other effects atlower levels of irradiation the criteria are lessclear. Heat effects in solid booster propellants andin the high explosive and special nuclear materi-als i n warheads depend on the design of the tar-get. Effects on electronics, particularly transientdisruption of computer circuits when electronsare scattered by a passing proton, are poorlyknown and doubtless quite complicated and spe-cific to the target. Other components not shownin table 3.4 —plastics, glue, guidance sensors–make for a very complicated analysis. What ismore, the particle beam might have to suffer theattenuation of passage through, say, two layersof aluminum and a layer of plastic before reaching a sensitive component.

Uncertainties in the destructive or disruptiveeffects of small amounts of radiation from a particle beam weapon is the principal obstacle tostating what energy, current, and divergentangle would make this concept a candidate forboost-phase intercept.

Shielding to protect components from a neutraparticle beam would necessarily be heavy butcould still be an attractive countermeasure. Itdiscussed in Section 5.

An Orbiting Neutral ParticleBeam System

A critical limitation of neutral particle beamis that they cannot be aimed through even thethinnest atmosphere—air so thin that even the ~ray laser beam could pass through easily. A neu-tral beam could not attack a Soviet booster unlthe booster reached at least 760 km altitude (vesus about 80 km for the x-ray laser)7. Collision

The stripping cross section on oxygen is about 1.5 megabarrElastic scattering can also be important for beam loss, since the Rhscattering angle can be larger than the beam divergence. The authis Indebted to Dr. George Gull lespe of Physical Dynamics, Inlin La Jolla for resu Its of his Born approximation cross sectltcalculations

31 .—

between air molecules and H° strip the electronfrom the Hº, and gradually all the remainingprotons spiral off the beam axis into 200 km widecircles under the action of the earth’s magneticfield.

An MX-like Soviet booster could be attackedbetween 160 km altitude and burnout at 200 km,a period of about 10 seconds. This short attackwindow means that the neutral beam cannotafford to dwell for long on each booster.

It is impossible to state with confidence the re-silience of an ICBM booster to irradiation witha neutral particle beam. But it is likely that faithwould have to be placed in degradation of elec-tronics and other subtle effects, rather than ingross structural damage, for the beam weaponto stand a chance as an economical defensesystem (ignoring the issue of countermeasures en-tirely).

Consider again a battle station producing a 0.5ampere beam of 100 MeV tritium (T°) atomswith 2 microradian divergence. This beam car-ries 400 watts/cm2 at 2 megameters range. To dostructural damage to the outer few centimetersof a missile’s body might take some 2 kJ/cm2

(depositing 500 J/gin in 1.6 cm depth of alumi-num, for instance), requiring 5 seconds of dwelltime at this range. Since the available dwell timeis only about 10 seconds, each beam could han-dle only two boosters. With a constellation sizeof almost 100 for 2 Mm range (fig. 3.4), this killcriterion resuIts in a preposterous system wherethe U.S. deploys 50 space-based accelerators forevery one Soviet booster deployed in one regionof the U.S.S.R.

If the assumed Soviet booster hardness is re-duced by 100 times, corresponding perhaps totransient upset of unshielded electronics, eachsatellite can destroy 200 boosters at 2 Mm range,meaning an overall tradeoff of one U.S. acceler-ator deployed for each two Soviet boosters de-ployed. Alternatively, the constellation can bethinned out to an effective range of 5 Mm, whereeach satellite at this range can destroy only 32boosters but the constellation size is only about16—still a one-to-two trade of battle stations for

Soviet boosters. Such a system scarcely seemspromising in terms of cost exchange.

obviously the neutral particle beam wouldstand no chance of intercepting a fast-burnbooster that burns out well within the protectiveatmosphere. Even an MX-like booster that flewa slightly depressed trajectory wouId be in-vulnerable.

A Theoretical Electron Beam System

Physical theory8 holds out the prospect of oneother type of beam besides the neutral particlebeam. Under certain circumstances, an electronbeam might be able to propagate through the ex-tremely thin air of near-earth space without bend-ing. In this scheme, a laser beam would firstremove electrons from air molecules in a thinchannel stretching from the battle station to thetarget, leaving a tube of free electrons and posi-tive ions. The high-energy, high-current electronbeam would then be injected into the channel.The beam electrons would quickly repel the freeelectrons from the channel, leaving the beampropagating down a positively charged tube. Theattractive positive charge would prevent the elec-trons from bending off the beam path under theinfluence of the geomagnetic field and wouId alsoprevent the mutual repulsion of electrons withinthe beam from causing the beam to diverge. Theresult would be straight-line propagation to thetarget, where their effect would be similar in mostrespects to the neutral particle beam. This schemewill not work for a proton beam.

The physics of intense beam propagationthrough thin gases is so complex that experimentswill be needed to determine whether this con-cept is even feasible in principle. If so, the con-cept would resemble the neutral particle beam,with the added requirement for the channel-bor-ing laser and perhaps the ability to interceptboosters at slightly lower altitudes than the neutralcounterpart.

8R, B. MI I Ier, The Physics ot’ Intense Charged Particle Beam5, NewYork, 1982, ch. 5.

3.5 SPACE-BASED KINETIC ENERGY WEAPONS

Kinetic energy is the name given to the energyof a moving projectile. Use of this term makesordinary weapons using aimed projectiles into“directed kinetic energy” weapons.

The phenomenology of high-velocity collisionsbetween a projectile and a structure like a boosteris surprisingly complex, but in general lethalityis not an issue for kinetic energy boost phase in-tercept concepts. Rather, the problem is gettingthe projectile from its satellite base to the ascend-ing booster in time to make an intercept. Schemeswhere the projectile is carried by a small rocketlaunched from the satellite suffer most directly(leaving aside countermeasures) from a combina-tion of the large number and large size of therockets needed for adequate coverage. I n partic-ular, the most conspicuous public example of thekinetic energy approach, the High Frontier Proj-ect’s Global Ballistic Missile Defense (GBMD)concept, 9 has extremely limited capabiIity forboost phase intercept of current Soviet ICBMsand would have no capability at all against afuture generation of MX-like boosters.

Kinetic Energy Concepts

Rocket attack of ICBM boosters is obviously notas novel as beam attack, but it entails rather morecomplexity than appears at first blush. The rocketneeds radio or other guidance by long-range sen-sors on its carrier satellite (or other satellites) todirect it to the vicinity of its target, since it is im-practical to put a long-range sensor on eachrocket. Once in the vicinity of the target booster,the interceptor needs some form of terminal hom-ing sensor and rather sizeable divert rocketmotors. Homing on the plume of the ICBM boost-er is not straightforward, since attacking theplume will obviously not harm the booster: thebooster body must be located in relation to theplume. These complications introduce opportu-nities for offensive countermeasures.

An alternative to rocket propulsion would beto expel the homing vehicles at high velocity froma gun. So-called rail guns use a clever scheme

9General Daniel O. Graham, The Non-Nuc/ear Defense of Cit-ies: The High Frontier Space-Based Defense Against ICBM Attack(Cambridge: Abt Books, 1983).

to convert electrical energy to projectile kineticenergy. Since a 10 kilogram projectile ejectedwith 5 km/see velocity carries 125 megajoules ofenergy (the amount of energy expended by a 25megawatt chemical laser in 5 seconds of dwellon a booster), the power requirements of the gunschemes are imposing. Providing chemical fuelor explosives to power a gun therefore involvesthe same magnitude of on-orbit weight as thechemical laser.

Doing away with the homing sensor and re-placing the guided projectile with many smallfragments is not an attractive alternative, sincethe needed fragments end up weighing far morethan the guided projectile.

The Importance of Projectile Velocity

In the 300 or so seconds from launch to burn-out of a slow-burning booster like the SS-18, thedefensive rocket or other projectile must fly fromits satellite to the path of the booster. Such abooster burns out at about 400 km altitude, soif the projectile wishes to use the entire 300seconds of boost phase to travel to its quarry, itmust make its intercept at 400 km altitude.

Suppose now that the projectile’s rocket or gunlauncher can give it a maximum velocity of 5km/see with respect to the carrier satellite. In the300 seconds of available travel time to its target,the projectile cannot fly more than (5 km/see) x(300 see) = 1.5 Mm from its carrier. Each car-rier therefore has an effective range of 1.5 Mm(fig. 3.1 la).

Referring to figure 3.4, a constellation of about240 carrier satellites are needed for continuouscoverage of the Soviet Union. Since Soviet ICBMsare spread over much of the country, 10 or soof the carrier satellites might be able to participatein a defensive engagement. The absentee ratiois therefore about 24, The 10 satellites over theU.S.S.R. at the moment of a massive Soviet at-tack need to be able to handle all 1,400 boosters,meaning each satellite needs to carry 140 pro-jectiles.

An idealized rocket accelerating a 15 kg guidedprojectile to 5 km/see velocity would need toweigh about 80 kg (a real rocket with this capa-

Figure 3.1 l(a)

-..33

Figure 3.1 l(b)

Satellite orbital path

t = 0SS- 18boostersIaunched

t = 240 sec. A

o 100 200 300Seconds after launch

I ,

0 800 1600 2400Kilometers along satellite orbit

Figure 3.11 View from above (looking down on earth) ofcoverage by a satellite carrying kinetic energy boost-phaseintercept vehicles. The satellite is deployed in a 400 km orbit.At time t =0, offensive boosters are launched. The satellitecan make intercepts by shooting downward or wait until theboosters rise to their burnout altitude and fire nearer to thehorizontal. The longer after launch the intercept is made, thefarther the rocket intercept vehicles can travel from thesatellite to make the intercept. Smaller circles thuscorrespond to downward firing, larger circles to horizontalfiring. The satellite moves from left to right in accordancewith its 8 km/see orbital velocity. The area enclosed by allthe circles taken together gives the total coverage of thesatellite and determines how many satellites are needed inthe worldwide constellation for continuous coverage ofopposing ICBM fields. All dimensions are to same scale.

(a) The satellite-based kinetic energy interceptors arecapable of 5 km/see velocity relative to the satellite. Theattack is on a slow-burning Soviet SS-18.

bility would weigh more like 200 kg). Each car-rier satellite must therefore weigh (1 40) x (80)= 11,000 kg. Less than twice this weight can becarried by the space shuttle into the appropriateorbits, so establishing the total 240 satellite con-stellation requires over 120 shuttle launches inthis highly idealized model with idealized rocketsand weightless carrier satellites. (A more carefuIestimation of interceptor design would more thandouble this load.)

From this baseline, we can consider five ex-cursions:

t = 0MX-like t = 200 Sec.boosters Booster burnoutlaunched (200 km altitude)

altitude

o 300Seconds after launch

o 2400Kilometers

(b) Same as (a), except the target is the faster-burning MX.

1. Suppose the velocity capability of the inter-

2

ceptor is doubled to”1 0 km/sec, doubling theeffective flyout range to 3 Mm. At this range,48 satellites complete the constellation, withperhaps as many as eight of them in posi-tion to participate in the engagement. Eachof the eight satellites must handle 175 So-viet boosters.

Doubling the velocity capability more thandoubles the weight of the rocket required.The reason is simple: to increase the velocityrequires more propellant, and the extra pro-pellant must itself be accelerated, requiringyet more propellant. The rocket weight thusgrows exponentially with velocity capability.The idealized 10 km/sec rocket weighs 420kg. Each satellite carrying 175 rockets thenweighs 75,000 kg and requires some fiveshuttle launches to orbit. The result is thatover 200 shuttle launches are required to or-bit the entire (idealized) defense system. In-creasing the velocity capability is thereforeno escape from large on-orbit weights.The current Soviet ICBM force consistslargely of slow-burning liquid-fueled boostersdistributed widely over the Soviet Union.Consider the consequences for the U.S. ki-netic energy defense system if the Soviets de-

34

Figure 3.1 l(c)

300 km radius

260 km radius \

130 km radius

t = 0SS-18 Boosters at

boosters launched 200 km altitude

t = 280 sec.Boosters at

300 km altitude

t = 300 sec. /Booster burnout

(400 km)

- 0 00Seconds after launch

1 I Jo 800 1600 2400

KiIometers

(c) The High Frontier Global Ballistic Missile Defense(GBMD) concept, with intercept vehicles capable of only 1km/see velocity relative to the satellite. Intercept of SS-18.In the actual High Frontier proposal, the satellites are in 600km orbits, giving them even less coverage than shown here.

Figure 3.11(d)

Satellite must fire straightdown to intercept booster

just before burnout. Satellitehas no lateral coverage at all.

/

boosters launched Booster burnout&90 km altitude)

0 100 200 300Seconds after launch

, io 800 1600 2400

Kilometers

(d) The High Frontier concept has no capability whatsoeverfor boost-phase intercept of MX.

ploy 100 faster-burning MX-like boosters inone region of the country, so that defensiveinterceptors have less time to fly to theirtargets and only one satellite overhead par-ticipates in the engagement. MX burns out200 seconds after launch, so each satellitehas an effective range of 1 Mm, requiring aconstellation of 400 satellites (fig. 3.11 b).

3.

4.

5.

In

Each satellite must carry the 100 80-kg rock-ets needed to handle the attack. An ex-change ratio of four 8,000 kg U.S. defensivesatellites for every Soviet offensive boosterdeployed is surely an economic advantagefor the U.S.S.R.Soviet deployment of 1,000 Midgetman-likeboosters would require a compensating de-ployment of 400 U.S. satellites, each weigh-ing at least 80,000 kg. A system that forcesthe United States to such a response isclearly absurd.Soviet fast-burn boosters would be totally im-mune to the kinetic energy defense system.An interceptor on a satellite in 400 km orbit(lower orbits shorten satellite lifetimes be-cause of atmospheric drag) could not evendescend straight down to the fast-burnbooster’s 100 km burnout altitude in the re-quired 50 seconds, much less have any lat-eral radius of action.Intercepting SS-18 or MX post-boost vehiclesis clearly easier, from the point of view offlyout velocities, than boost-phase intercept.Satellites at 700 km or so altitude would have500 seconds to fly out to meet the bus whenit ascended to their altitude, giving a 2.5 Mmlethal radius.

conclusion, a rocket-propelled kinetic en-ergy system acting against today’s Soviet ICBMarsenal (with no Soviet countermeasures) wouldrequire many heavy satellites and would be adubious investment for the U.S. Soviet deploy-ment of MX-like or Midgetman-like boosterswouId nullify the United States defense or forcethe U.S. to large investments in new satellites.

Analysis of the High Frontier Concept

The High Frontier Program10 proposes a GlobalBallistic Missile Defense (GBMD) using rocketpropelled interceptors for boost phase intercept.This concept claims to have some utility, at leastagainst the present Soviet ICBM arsenal.

The concept consists of 432 satellites (24 planesof 18 satellites in circular orbits inclined 65degrees) at an altitude of 600 km. A velocity

IOlbld

35

capability of I km/see relative to the satellite(“truck”) is attributed to the interceptor. The in-terceptors are apparently command guided to thevicinity of the target. The homing sensor is notspecified, but short wave infrared homing on thehot rocket plume is implied.

Consider this concept defending against the SS-18 in its boost phase. Since the SS-18 burns outat 400 km altitude 300 seconds after launch, eachGBMD satellite has a 0.3 Mm radius of action.Since the satellites are deployed at 600 kmaltitude, the interceptor must descend 200 kmto make an intercept just before burnout, re-sulting in a lateral radius of action of 0.22 Mm(compare fig. 3.11c, where the satellites areassumed deployed at 400 km altitude). With arange this small, thousands of satellites would beneeded worldwide for continuous coverage ofSoviet ICBM fields. The High Frontier conceptwith only 432 satellites would therefore havemeager coverage of Soviet ICBM fields.

The GBMD concept would have no capabilitywhatsoever against an MX-like booster. Such abooster would burn out before the interceptorcouId reach it, even if the interceptor were firedstraight down (fig. 3.11 d).

It is possible that the High Frontier concept isdesigned for post-boost intercept rather than

3.6 MICROWAVE

Microwaves are short-wavelength radio wavesused in radar, satellite communications, and ter-restrial communications relays. A number of ideashave been conceived for generating microwavesin space and directing them towards ascendingICBM boosters. The principal technical problemwith this type of BMD, generator technologyaside, is the uncertain effect the microwaveswould have on their target.

The microwaves would propagate through theatmosphere unattenuated at all but the highestpower levels. The weapon divergence anglewould be very large, producing a spot many km

boost phase intercept. Its coverage for post-boostintercept, though greater than for boost-phase in-tercept, would still be only partial. The only ex-ample given in the description’ of the system isof boost phase intercept of an SS-18, however.In this example the interceptor is launched 53seconds before launch of its target booster,though no explanation is given of how the U.S.defense knows in advance the precise momentat which the Soviets would launch a given boost-er. This early launch allows the interceptor toreach its target seconds before burnout. Plumehoming, a technique inappropriate for bus inter-cept, is also implied for the High Frontier con-cept. Post-boost intercept permits some RVs tobe deployed on trajectories carrying them to theUnited States before intercept; and the entire bus,with its warheads, would continue on to the U.S.after the interceptor collision, with uncertain con-sequences.

It would therefore appear that the technicalcharacteristics of the High Frontier scheme re-sult in a defensive system of extremely limitedcapability for boost phase intercept of present So-viet ICBMs and no capability against future MX-Iike Soviet boosters, even with no Soviet effortto overcome the defense.

‘ ‘ I bld , p 103.

GENERATORS

wide at a few hundred km range. From these con-siderations the following concept emerges: As So-viet ICBMs lift off from their silos, a few micro-wave generators in space bathe the silo fields withmicrowaves.

At high power levels, as in a microwave oven,microwaves cause heating in many materials. Butin the BMD scheme, the divergence cone is solarge that even a prodigious amount of energyemitted from the generator would lead to verysmall energy deposition per square centimeteron the target (millions of times less than lasers).The microwave pulse received at the booster

36

would resemble the high frequency componentof the electromagnetic pulse (EMP) from a high-altitude nuclear detonation. However, even weakmicrowaves can upset sensitive circuitry if theycan reach it.

A metal skin on the booster would stop themicrowave pulse altogether from reaching inter-nal electronics. The microwave defense musttherefore hope that some aperture or conduit isavailable into the booster, whether by design (asin an antenna), inadvertence, or poor mainte-

nance. If so, and if the electronic circuitry is notor cannot be made resistant to disruption or burn-out, the part of the booster’s performance de-pendent on those electronics (perhaps accurateguidance) would be affected.

Because of the very uncertain lethality of micro-waves, deployment of space-based generators (ifthey can ever be built) would be a harassing tac-tic rather than a confident-kill ballistic missiledefense.

3.7 OTHER CONCEPTS

Other directed energy concepts suitable in the- single huge pulse for impulse kill of a boost-ory for ballistic missile defense have been er. All these schemes are at a very early con-broached from time to time. Some of them are ceptual stage.listed below. It is quite possible that in a few years 3. Antimatter beams would penetrate into atime a revisit to this subject will find a new target just like ordinary particle beams, ex-panoply of concepts enjoying the front rank of cept that when the antiparticle reached thediscussion. end of its range it would annihilate a parti-

1. Short-wavelength chemical lasers wouldcombine the simplicity and efficiency of theHF chemical laser with the small mirrors ofthe short-wavelength excimer and free-elec-tron lasers. Though some ideas have beenadvanced along these lines, no laser existswhich can be said to be a candidate to fulfillthis theoretical promise.

2. Explosive-pumped lasers and particle beamsare said to be under study in the SovietUnion. 12 Such devices might possibly bequite compact, each bomb generating a

12A Viation week and Space Technology, JUIY 28, 19801 P. 47.

cle in the target, freeing a large extra amountof harmful energy. Acceleration of antimat-ter beams is accomplished exactly as withparticle beams, and laboratory beams of an-timatter have been used routinely in pureresearch. One important difference is thatantimatter is not freely available in the uni-verse as is matter; the antimatter for the ac-celerator would have to be produced by thedefense system, a formidable and complexundertaking. It is not clear that the extraenergy released in the target by an antimat-ter beam would justify the trouble of pro-ducing the beam.

Section 4

OTHER ESSENTIAL ELEMENTS OF ABOOST-PHASE INTERCEPT SYSTEM

Section 4

OTHER ESSENTIAL ELEMENTS OF A BOOST-PHASE

The previous section treated only the defen-sive weapon itself, the so-called “kill mecha-n i s m . But if beam weapons ever evolve to thepoint where deployment is a serious possibility,other elements of the overall defensive systemwill emerge as equally important determinantsof cost and level of protection. After all, the in-terceptor missile in traditional BMDs has not beenthe central focus of attention or technical debatesince the 1950’s, when it became clear that a“bullet could hit a bullet. ” Discussion of BMDat that point passed to the difficuIt issues of radarperformance, data processing capability, and vul-

4.1 TARGET

INTERCEPT SYSTEM—

Locating and tracking an ICBM booster withenough precision to aim a directed-energyweapon is not as straightforward as is sometimessupposed. it is true that booster motors emit hun-dreds of kilowatts of power at short- and medium-wave infrared (SWIR and MWIR) wavelengths ofa few microns. Sensors can detect these plumesat great distances from the earth. Plume sensingis used today for early warning of missile attackto support launch of bombers and airborne com-mand posts and launch under attack of ICBMS.

To be useful for directed-energy BMD, how-ever, the sensor must localize the booster withinan area as small as the beam spot. Otherwise thebeam would have to sweep wastefully back andforth over the area of uncertainty. Small diver-gence beams must therefore be accompanied bysensors with small angular resolution.

Diffraction limits the angular resolution of a sen-sor in the same way it limits the divergence angleof a laser. A large infrared telescope with 5 mdiameter mirror observing MWIR booster emis-sion at 4 micron wavelength would have angularresolution no more precise than a micro radian.Such a sensor affixed to each battle station in a

nerable basing of defensive components—issuesthat had nothing to do with the kill mechanism.In a similar manner, the other essential elementsof a boost-phase intercept system will figure moreprominently in discussion of boost-phase BMDif and when the kill mechanisms—lasers, mirrors,accelerators—are in hand. These other essentialelements introduce their own technological prob-lems and opportunities for offensive counter-measures. If traditional BMDs are any guide,provision of a kill mechanism will be just thebeginning of making an efficient, robust defen-sive system.

SENSING

defensive constellation would localize ascendingboosters to within a spot 5 m wide at 5 Mm range.At this range, the (illustrative) systems describedin Section 3 have spot sizes: 1.5 m for the H F la-ser, 0.6 m for the ground based laser, 10 m forthe neutral particle beam, and 100 m for the x-ray laser. Even a large infrared sensor on eachbattle station would therefore be inadequate fordirecting the laser beams at a point source ofMWIR light, marginal for directing the neutralparticle beam, and adequate for directing the x-ray laser. The actual situation would be worsestill, since the booster is not a point source. Thebooster plume would be larger than the laser orparticle beam spots, and the booster body wouldneed to be located in relation to the plume toavoid wasting beam time attacking the plume.

For directed-energy weapons with small diver-gence angles, therefore, sensing the conspicuousrocket plume is inadequate. Another kind of sen-sor must be introduced into the BMD system. Forfiner angular resolution one looks to shorterwavelengths, in the visible or ultraviolet. At thesewavelengths the sensor must provide its own il-lumination. A so-called laser radar or Iadar is theonly practical solution. In a ladar, a low-power

39

40

visible or ultraviolet laser shines on the boosterbody, and a telescope on board the battle sta-tion senses the reflected light.

Besides the annoyance of a new laser and newsensor, the necessary introduction of Iadar intothe boost-phase system creates opportunities forthe defense to spoof and blind the offensivesensor.

Kinetic energy systems do not need precisionlong-range sensing, since the rocket or guidedprojectile homes on the target when it comeswithin short range. The terminal homing mightinvolve deducing the location of the booster bodyin relation to its MWIR plume, homing on low-power laser light shined from a defensive satel-

lite and reflected from the target, or some othermethod. These homing methods are susceptibleto countermeasures.

Though this Background Paper treats only in-tercept of the booster proper, it is worthwhilepausing to consider tracking of the post boostvehicle or bus. The low thrust levels of the postboost vehicles’s rocket motors, their intermittentoperation, the possibility of dimming them withpropellant additives, and the possibility ofbuilding decoys with small rocket motors all sug-gest that MWIR plume sensing is not practical forpost boost intercept. The alternatives are Iadaror radar, suggesting again many opportunities forcountermeasures.

4.2 AIMING AND POINTING

The directed-energy beam must be aimed and In the 15 milliseconds the beam takes to travelstabilized as accurately as it is collimated. If the from the battle station to a booster 5 Mm away,beam waves around too much, the effective di- the booster moves about 50 m. A narrow beamvergence increases, and the beam wastes energy must therefore lead the target. In one second ofmissing the target. The mirrors or other mecha- dwell time, the target moves several km; thenism steering the beam must be stabilized despite beam must remain on the target, sweepingvibrations in the battle station caused by the through the sky at the necessary angular ratebeam’s large power source. while still maintaining its aim and jitter control.

4.3 INTERCEPT CONFIRMATION

A desirable, though perhaps not essential, func-tion of BMD systems is confirmation that an at-tempted intercept succeeded. This function issometimes called “kill assessment. ” Interceptconfirmation would allow the beam to move ontosubsequent boosters with more than a statisticalestimate that its previous task was accomplished.Structural damage to the booster would presum-ably be revealed by an erratic course or burn pat-tern, though it might be difficult to say in advanceexactly what the sensor’s view of the woundedbooster would be. Subtle damage inflicted by aparticle beam or microwave generator might notbe visible. Damage to a bus would be difficult

to assess and interpret if the debris, including RVs(perhaps arranged by the offense to separate fromthe bus under extreme circumstances), continueon their ballistic course to the continental UnitedStates.

Related to intercept confirmation, and ultimate-Iy more serious, is the question of determiningwhether the beam is missing the target (perhapsby slight misalignment of sensor and beam bore-sights, miscalibration of aiming mechanisms, etc.)and, if so, by how much and in what direction.It might be possible to observe a glowing columnof air where a laser beam passes through the at-

41

mosphere. Some clever but elaborate schemeshave been devised to track a neutral particlebeam. Obviously each new complication added

to the defensive system potentially creates newopportunities for offensive countermeasures.

4.4 COMMAND AND CONTROL

The crucial infrastructure of command andcontrol of a complex system is always the last totake shape, since it integrates the workings of allthe separate components. It is easy to ignore thedifficulty of accomplishing this last step at thisearly stage when the other components of a boostphase system are not yet remotely in hand. Thecommand and control system of a boost-phaseintercept system would comprise communica-tions links among its far-flung components, dataprocessing to support sensors and battle stationoperations, and “battle management” softwareincorporating all the instructions and decisionsneeded to run the defensive engagement and tocoordinate the defense with U.S. offensive forces.

Communications and data processing are twoareas of technology where there is the least pes-simism—looking two or so decades into the futurewhen boost-phase systems could presumably bedeployed–that technology will be able to meetthe needs of directed-energy defenses. Compact,lightweight, and rapid data processing hardware

is virtually assured, though interesting questionsattend on hardening, reliability, and lifetime inspace. Software would be expensive and wouldintroduce issues of reliability and security fromprogrammer sabotage. Satellite-to-satellite com-munication via extremely high frequency radioand laser offers high data rates and virtual im-munity to jamming from earth or from space.

Command and control for BMD does introducetwo interesting issues to which technology can-not provide an answer. The first is the impossi-bility of testing the whole defense system fromend to end in a realistic wartime setting. Unlikethe air defense systems of World War 11, whichlearned through attack after attack to exact killrates of several percent, the BMD system wouldhave to work near perfectly the very first time itwas used. The second issue is the likely need forthe defense to activate itself autonomously, sincethere would be no more than a minute for humandecision,

4.5 SELF-DEFENSE

Consideration of anti-satellite (ASAT) attack (see less and until a credible overall approach to sat-Section 5.1 ), and analogy with traditional BMD ellite survivability is found, one cannot specifysystems (where vulnerability of key radars, data the needed hardware.processors, and other components is usually the

Ground-based BMD lasers and pop-up x-raychief limitation on defense performance) suggest lasers would obviously need to be protected fromthat self-defense mechanisms could well end upbeing a large part of the defense system. These

precursor attack by cruise missiles and otherdel ivery systems. ‘

mechanisms could include shields, escort weap-ons, and countermeasures to ASAT sensors. Un-

42

4.6 POWER

Chemical lasers, x-ray lasers, and rocket-pro-pelled kinetic-energy interceptors have powersources integral to the weapon, but excimerlasers, free electron lasers, neutral particle beams,and rail guns would need sources of electricalpower and the equally important means to con-vert electricity into a form usable by the weapon(“power conditioning”). Space basing obviouslycomplicates the task. Large commercial powerplants on the ground produce about 1,000 MW

SOURCES

of power, and directed energy weapons mightrequire hundreds of MW. On the other hand, thepower plants on defensive satellites need notwork reliably for many years but only once fora short time, and they need not be very highlyefficient. The three alternatives for space powerare fuel burning, explosives, and nuclear power.Starting up a large power source in seconds froma condition of dormancy poses some interestingdesign issues.

-

Section 5

COUNTERMEASURES TO BOOST-PHASE INTERCEPT

●

Section 5

COUNTERMEASURES TO BOOST-PHASE INTERCEPT— . . — —

Countermeasures that limit the effectiveness oftraditional ballistic missile defenses—decoys,radar blackout, defense suppression, etc.—arewell known. A comparable set of countermeas-ures, no less daunting for being less familiar, facesthe designer of boost-phase defenses.

The need to resort to countermeasures imposesa cost on the offense. This cost is measured inmoney to build more or specialized offensivehardware, but also in the time needed to do so,i n constraints upon the type of attack the offensecan incorporate in its nuclear planning, and inthe confidence with which it can predict a “suc-cessful” outcome of the strike.

Every BMD system actually proposed for de-ployment would be accompanied, at least ideally,by, first, an analysis of its degradation in the faceof an improving Soviet offense and, second, byan analysis of how much it would cost for theUnited States to improve its defense in such a wayas to avoid being overcome. ’

‘See BallIstIc Missile Defense, ed. Ash(on B. Carter and DavidN. Schwartz (The Brookings Institution, 1984), ch, 4.

Figure 5.1

Soviet investment in offense(more ICBMs, new types, special countermeasures, etc.)

Fig. 5.1. Schematic drawdown curve, showing how the performanceof a BMD system degrades as the size and sophistication of the at-tacking force increase.

1

Figure 5.2

Low High

Level of defense performance

Fig. 5.2. The marginal cost exchange ratio measures the outcome ofa race between the Soviet offense to enhance its penetration and aU.S. defense to maintain its level of protection. In general, modestdefense goals (e.g., “preserve 40 percent of the targets”) are easierto sustain than high goals (“preserve 95 percent of the targets”)against improvements in Soviet offensive forces, including deploy-ment of countermeasures.

The first analysis would be expressed in a draw-down curve such as that shown in figure 5.1. TheSoviets can overcome the defense and destroya large number of U.S. targets, but to do so theSoviets must “pay” an “attack price. ”

The second analysis would be encapsulated inthe cost exchange ratio. The marginal cost ex-change might be defined as follows: “Assume thatin the year 2000 the U.S. defense and Soviet of-fense have evolved so that each has a certainlevel of effectiveness. Suppose the Soviets wishto improve their position and the U.S. resolvesto maintain the status quo. Which side spendsmore in the competition?” For example, supposeevery time the Soviets add 100 ICBMs to theirarsenal, the United States has to add 20 satellitesto its defensive constellation to intercept them:Which costs more, 100 ICBMs or 20 satellites?

45

46

In general, high levels of defense performanceare harder to enforce in the face of offensive im-provements than low levels: this important factis shown schematically in figure 5.2 (see also Sec-tion 8.2).

All of the boost-phase intercept schemes dis-cussed in this report are in such an early stageof conceptualization that nothing remotely likethe analyses represented by Figures 5.1 and 5.2can be done for them. Nonetheless, counter-measures are known for every boost-phase sys-tem devised, and in many cases simple heuristicestimates of the cost tradeoffs are suggestive. ,

Technical experts disagree not so much aboutthe facts and calculations underlying these coun-termeasures as about the interpretation to begiven to them. Should an apparently fatal flaw

uncovered at this early stage of study of a defen-sive concept be decisive, or should work (andthe inevitable expectations that accompany it)continue on the chance that a new idea will turnup to rescue the concept? Would the Sovietsreally resort to a subtle tactic or exotic piece ofhardware as a confident basis for their nuclearpolicy? Some analysts see BMD as a way of “for-cing” the Soviets to take a certain direction intheir pursuit of the arms race, e.g., away fromlarge, slow-burning MIRVd boosters to single-warhead Midgetman-like boosters. In this view,defeat of the BMD is purchased at the price ofa theoretically more stable and desirable Sovietoffensive posture. All these questions of judgmentloom large in making a final assessment of a givencountermeasure.

5.1 ANTI-SATELLITE (ASAT) ATTACK,INCLUDING DIRECTED-ENERGY OFFENSE

All boost-phase intercept BMD concepts havecrucial components based in space. Even a pop-up defense would need warning and very prob-ably target acquisition sensors on satellites overthe Soviet Union. Ground-based laser defenseswould have mirrors and sensors—their most frag-ile components—in space. Vulnerability of thesesatellites is a cardinal concern because their or-bits are completely predictable (they are in ef-fect fixed targets), they are impractical to harden,conceal, or proliferate to any significant degree,and because successful development of effectivedirected-energy BMD weapons virtually presup-poses development of potent anti-satellite (ASAT)weapons. ASAT is the clear boost-phase analogueof familiar defense suppression tactics againsttraditional BMDs, where attack is first made uponthe defensive deployment (especially fixed radars)and then upon the defended targets.

The interplay of ASAT techniques–missiles (nu-clear or conventional), space mines, directedenergy—and satellite defense (DSAT) techniquesis a complex one, It is difficult to generalize, butin the specific case of large battle stations in low-earth orbit it would seem that the advantage is

very likely to lie with ASAT, not DSAT. For onething, the offense need not destroy a large num-ber of defensive satellites, but only “cut a hole”in the defensive constellation. Second, the tradi-tional military refuges all offer complications: con-cealment from radar, optical, infrared, and elec-tronic detection, while possibly successful forsmall payloads in supersynchronous orbits, is im-practical for large, complex spacecraft at most afew thousand km from the earth’s surface; decoysatellites must generate heat, stationkeep, andgive status reports, and they are in any event onlyuseful if the ASAT designer is somehow restrained(perhaps by cost) from shooting at all suspiciousobjects; hardening imposes weight penalties, andmassive shields could interfere with the constantsurveillance and instant response required of thedefense; proliferation is useless for expensivesatellites facing inexpensive ASAT methods, Asa consequence, discussions of DSAT for BMDbattle stations usually emphasize large keep-outzones around the satellites and active self-de-fense. A third reason why ASAT is likely to pre-vail over DSAT is that possession by the offenseof the same type of directed energy satellites usedby the BMD probably assures successful first

47

strike. Fourth, the Soviets would pick the timeand sequence of their attack, and it would oc-cur over Soviet territory.

Two rather novel ASAT threats are worthy ofnote. The first is the x-ray laser itself. The x-raylaser, if it could be developed, would constitutea powerful space mine. Because of its long range,it could lurk thousands of km from its quarry. TheSoviets might also launch x-ray lasers a few sec-onds before launch of their main attack. Recallthat the well-known phenomenon of bleaching(see Section 3.3) would probably allow such x-ray lasers to shoot out of the atmosphere at a U.S.x-ray laser defense, but the U.S. x-ray lasers couldnot shoot down into the atmosphere at the as-cending lasers.

A second ASAT tactic, discussed for many years,imagines the Soviet Union exploding nuclearweapons at high altitudes in peacetime with theintent of shortening the orbital lifetimes of theU.S. defensive satellites, The nuclear bursts in-ject further radiation into the van Allen belts thatcircle the earth’s equator from about 1,500 to10,000 km altitude. Satellites (more likely carry-ing sensors than weapons at these altitudes) pass-ing through the belts accumulate a radiation dosethat gradually degrades electronics, sensors, andoptical surfaces. This possibility, if taken seriously,would require defensive satellites designed towithstand rather substantial accumulated radia-tion doses.

A detailed treatment of the ASAT problem isbeyond the scope of this Background Paper. Thefollowing “parable” illustrates some of the prob-lems encountered in trying to ensure the surviv-ability of a defensive constellation, taking the 20MW HF lasers of Section 3.1 as an example.

The United States deploys the HF lasers in thishypothetical system in low orbits at 1,000 kmaltitude. Higher altitude would place them toofar from their targets. This is unfortunate: higheraltitude (say, between 2,000 km and semisyn-chronous orbit at 20,000 km) would move thesatellites further from ground-based ASAT weap-ons and put them into lesser-used orbits wherestaking out a sanctuary would involve less in-terference with foreign spacecraft.

Suppose the battle station designers have suc-ceeded in the considerable task of making thesatellites resilient to multi-megaton nuclear spacemines (bombs, not x-ray lasers) as little as 100 kmaway, To keep all Soviet spacecraft (i.e., all poten-tial mines) at least 100 km away, the United Statesclaims for itself the orbital band between 900 and1,100 km altitude. Perhaps the Soviets areawarded some other orbital zone for their ownmilitary purposes. The United States establishesthe following rules in its zone: 1 ) No foreignspacecraft may transit the zone without prear-rangement; 2) All transiting vehicles must remainat least 100 km from all U.S. battle stations, pass-ing through a “hole” in the constellation; 3)Foreign spacecraft failing to obey these rules maybe destroyed by the U.S. lasers.

Consider first a Soviet kinetic energy ASAT de-ployed at 1,100 km altitude, just outside the U.S.keepout zone. Suppose the rocket interceptorson the Soviet satellites have the same propuIsivecapacity—one km/see—as the proposed HighFrontier Global BMD system. The Soviet ASATsare then just 100 seconds away from the U.S.lasers. The U.S. lasers must therefore be very vig-ilant to avoid surprise attack. Fortunately, at 100km range the 20 MW laser with 10 m mirrorwould burn up even a heavily hardened ASATrocket in short order. Since starting up the mainlaser for self-defense might be awkward, wastefulof fuel, or time consuming, each U.S. battle sta-tion might be escorted by a satellite carrying asmaller laser or rockets for self-defense.

A constellation of Soviet 20 MW, 10 m HFlasers (the same technology as the U.S. lasers) at1,100 km is another matter. These lasers couldattack the U.S. lasers seconds before launch ofa Soviet ICBM attack. The United States wouldhave to keep these Soviet spacecraft thousandsof km away from the U.S. constellation. That is,the United States would have to dominate near-earth space. Suppose the United States does so.

Now the Soviets build a fleet of pop-up x-raylasers. These lasers climb to 100 km or so altitude,where information radioed to them from theground allows them to point their rods at the U.S.lasers and detonate. The Soviets have had poor

48

success at building an x-ray laser; theirs are 100times less bright than the ideal x-ray laserdescribed in Section 3.3. Nonetheless, by point-ing all its Iasing rods at the same target, a Sovietx-ray laser can destroy a U.S. laser battle stationat 10 Mm range. The U.S. chemical lasers attackthe Soviet x-ray lasers as they ascend, but at thisrange long dwell times are required to destroythe Soviet lasers. By launching enough x-raylasers simultaneously, the Soviets succeed in get-ting some to 100 km altitude, where they can

shoot out through the thin atmosphere, beforethe U.S. lasers can destroy them. In this way, theSoviets “punch a hole” in the U.S. defensive con-stellation. (At a minimum, the Soviet ASAT attackconsumes precious laser fuel aboard the U.S. bat-tle stations.)

just to make sure, the Soviets also deploy somepowerful ground-based excimer or free electronlasers to destroy the U.S. battle stations as theyorbit helplessly through space.

5.2 FAST-BURN BOOSTERS

Shortening the boost time and lowering theburnout altitude is easily accomplished at littlesacrifice in useable ICBM payload (see Section2). Shorter boost time increases the number oflasers needed for space-based laser or ground-based laser systems to handle simultaneouslylaunched boosters. Short burn time makes rocket-propelled kinetic energy systems impractical,since the radius of action of each satellitebecomes too small. Short burn time, together

5.3 COUNTER

Countermeasures to the crucial functions oftarget sensing and command and control are arelatively unexplored, but probably key, problemarea for directed energy BMD. In the case of ter-minal and midcourse defenses, the issues of de-coy discrimination, confusion caused by chaffand aerosols, radar blackout and infrared redout,radar jamming, and traffic handling have alwaysbeen and remain central limitations, It is likelythat analogues will be found for boost-phasesystems. Devising countermeasures requires a de-gree of specificity about the nature of the defensesystem which cannot be provided in the presentconceptual stage. There follow a few examplesof C3l countermeasures, by no means an ex-haustive list.

A first point to note is that sensors are likelyto be the most vulnerable part of a defensive sat-

with low burnout altitude, would severely com-promise the effectiveness of x-ray lasers poppedup even from subs near Soviet shores. Low burn-out altitude nullifies the neutral particle beam,which cannot penetrate very far into the at-mosphere.

Fast-burn boosters would therefore be a potent,even decisive, countermeasure against almost allconcepts for boost-phase intercept.

C3l TACTICS

ellite. A laser shined into an optical sensor candaze or injure the focal plane elements, thoughviewing in frequency bands absorbed by the at-mosphere offers protection from ground-basedlasers. Mirrors would be very susceptible to dam-age from a Soviet x-ray laser. A Soviet neutral par-ticle beam could disrupt electronic circuits onU.S. satellites. Radiation pumped into the vanAllen belts by nuclear bursts would affect sen-sors and electronics.

A single nuclear burst causes the upper atmos-phere to glow brightly over areas 100 km in ra-dius for over a minute. Calculated radiances2 arelarge enough to cause background problems forMWIR tracking sensors.

2S. D. Drell and M. A. Ruderman, /nfrared Physics, Vol. 1, p. 189(1962).

4 9

Some directed-energy weapons produce spotsonly meters wide at the target, requiring targetsensing to commensurate precision via laser radar(see Section 4.1). Laser radars sense laser lightreflected from the target. A small corner reflec-tor affixed to the target would produce a brightglint of reflected light, as would other cornerreflectors launched on sounding rockets, ejectedfrom the target, or attached to the target by ex-pendable booms. These proliferated corner reflec-tors might force the beam weapon to attack themall.

The homing sensor of a kinetic energy intercep-tor could be susceptible to spoofing, dependingon its type.

Jamming satellite-to-satellite communicationscrosslinks is probably not an effective offensivetactic, since the links would have narrow beam-widths, requiring the jammer to locate itselfdirectly between the two satellites; and widebandwidths, requiring high jammer power.

5.4 SHIELDING

A degree of shielding from lethal effects is prac-tical for ail but the kinetic energy weapons butinvolves in each case different methods suited tothe different physical principles at work. At thesame time, large uncertainties plague all lethalityestimates, and further testing and study will beneeded before firm answers can be given for anyof the systems. For thermal kill with a laser, a solidbooster designed with some attention to a laserthreat can probably easily be made to withstand10 kJ/cm2. Application of a gram or so of heat-shield material on each square centimeter ofbooster skin can probably triple this hardness,and spinning the booster enhances hardness byanother factor of three. Heatshield material isablative, meaning that when heated it burns off,carrying away the heat in the combustion gasesrather than conducting it through to the missileski n underneath. A factor of nine increase inhardness requires the defensive laser to dwell onthe booster nine times as long or to approachwithin a third of the range, Though hardening anew booster from scratch is clearly easiest, thereis no serious impediment to retrofitting ablativecoatings on existing boosters. Applying a gramper square centimeter of ablative material to theentire body of the MX missile would requireremoving several RVs from the payload, since thecoating would weigh well over 1,000 kg.

An interesting possibility, requiring furtherstudy, would involve injecting into the atmos-phere or producing from atmospheric gases,either throughout the ICBM flyout corridors or

in the vicinity of individual boosters, smoke orlaser absorbing molecules. Likewise, dust cloudsraised by ground burst weapons (delivered bycruise missiles or by ICBMs that “leak” throughthe defense) might cause serious propagationproblems for the ground-based laser scheme,

Hardening to an x-ray laser involves quite dif-ferent physical principles. Recall that the x-rayenergy is deposited in a paper-thin layer of thebooster skin. The superheated layer explodes, ap-plying an impulsive shock to the booster. Obvi-ously a paper-thin shield between the boosterand the laser will stop x-rays from reaching thebooster wall. But the problem then becomes thedebris from the exploding shield. One can easilyshow by calculation that the debris applies vir-tually the same impulse to the wall of the boosteras would result from direct impinging of the x-rays! A number of schemes can be devised to di-vert the debris from striking the booster, but theserequire more study to implement in practice. Onefactor acting in favor of the shield designer is thatthe booster is not vulnerable to x-ray attack untilit leaves the atmosphere. The lightweight shieldstherefore do not have to be designed to sufferlarge drag forces.

The neutral particle beam presents a third dis-tinct type of hardening problem. The energeticbeam particles penetrate into the target, and sev-eral centimeters of lead would be required to stopthem. Since the beam cannot penetrate very farinto the atmosphere, only the upper booster

50

stages need be hardened. But if the third stage,say, of the MX were covered with a few gramsper square centimeters of lead, the shieldingalone would weigh as much as several RVs. Onthe other hand, if the neutral particle beam is onlydesigned to disrupt or damage sensitive electron-ics, but is not powerful enough to do damage toother parts of the missile, only the sensitive com-ponents need be shielded. The weight penaltythen becomes small.

neutral particle beam by exploding a few nuclearweapons at moderate altitudes before the beamcan reach them. The detonations heat the air,which rises, effectively elevating the altitude atwhich the neutral beam is stripped of its remain-ing electron and bent in the geomagnetic field.This phenomenon is called atmospheric heave.It is as yet unresolved whether atmospheric heavewill loft enough air to make a difference to theengagement altitude of the x-ray laser.

It is possible that the offense can extend theprotection of the upper atmosphere against the

5.5 DECOYS

There is no way for a decoy booster to mimicclosely the hot exhaust plume of an ICBM boosterexcept by burning a similar rocket stage. One canadd chemicals to the propellants to brighten asmall booster’s plume and dim the ICBM’s, butas a first approximation a faithful decoy must beanother booster.

Decoy tactics are therefore not as attractive forboost-phase intercept systems that use plumesensing as they are for midcourse and reentrydefenses, where large numbers of cheap, light-weight decoys can be carried with negligible off-load of RVs. Still, the usefulness of a decoydepends not on how expensive the decoy is, buton how the cost of the decoy compares to thecost of the defense that intercepts it. Boosterdecoys would not be nearly as expensive as trueICBMs, since they carry no warheads or preci-sion guidance system, they need not be highlyreliable, and they might not need to be based in

underground silos but can be deployed aboveground next to the ICBM silos.

Some of the boost phase intercept systems mustgrow in the number of their deployed battle sta-tions in direct proportion to the number of So-viet boosters. Deploying one decoy (with a dum-my payload) next to each of the 1,400 SovietICBM silos might cause the United States to haveto double the number of battle stations overhead(and thus worldwide, multiplying by the absenteeratio) to handle the extra traffic. If the defensivebattle stations were at all expensive, this wouldbean unpleasant prospect for the United States.

Many directed energy schemes would not relyon plume sensing alone (see Section 4.1). Decoytactics against laser radars (including cornerreflectors; see Section 5.3) might be much easierfor the offense to implement than mimicking thebooster plume.

5.6 SALVO RATE

The worst-case attack for all the boost-phase A more leisurely salvo rate would allow laserintercept schemes is massive, simultaneous and particle beam defenses that have to dwelllaunch of all Soviet ICBMs. The defensive satel- on their targets more time to handle more targets.Iites over the Soviet silo fields at the moment of Slow attack also allows pop-up defenses to climblaunch then have to handle the entire attack. to intercept position. An attack drawn out 10

51— —

minutes or longer allows fresh defensive satellitesto move along their orbits into position overhead,replacing depleted satellites. The orbital periodof satellites in low earth orbit is about 90 minutes.If there are 8 to 10 satellites in each ring of thedefensive constellation, satellites replace oneanother every 10 minutes or so.

An exception to this simultaneous-launch worst-case analysis is the x-ray laser, which delivers alIits energy in an instant.

There would seem to be few military penaltiesfor the Soviet Union to adopting plans to launchall their ICBMs in large attack within a few min-utes. Indeed, if one of their objectives is to de-stroy U.S. ICBMs in their silos, rapid attack would

be the best Soviet choice. Some, though not all,of the successful attacks that could be mountedon Closely Spaced Basing (Densepack) for MX in-volve very slow or intermittent salvo rates, how-ever.

More importantly, in many circumstances theSoviets might wish to launch only a traction oftheir ICBM force. A U.S. defense deployment toosmall to intercept all boosters in a massive attackwould still be able to handle a small attack. A lightdefense might therefore establish a “threshold”of attack intensity below which Soviet boosterswouId face intercept. This prospect is discussedfurther in Section 9.

5.7 OFFENSIVE BUILDUPThe most straightforward way for the offense

to compete with the defense is to grow in size.If for every new ICBM added to the Sovietarsenal, the U.S. defensive satelIite constellationmust be augmented at comparable or greatercost, the Soviets could challenge the UnitedStates to a spending race to their net advantage.On the other hand, if the defensive buildup ischeaper than the offensive buiIdup, the defenseforces the offense either to accept limitations onits penetration or to resort to qualitative changesin its arsenal.

As an illustrative example of such a cost trade-off, consider the hypothetical H F chemical lasersystem described in Section 3.1. Each laser in thatsystem requires 1.7 seconds of dwell time to de-stroy a booster. During the 200 seconds of boost,each laser overhead can therefore destroy 120boosters. But for each laser overhead, 32 are

needed worldwide. Suppose now that the Sovietsdeploy, in one region of the U. S. S. R., 1,000Midgetman missiles at a cost of 10 to 20 billionU.S. dollars (see Section 2). The U.S. defensenow needs to be “beefed up” with addition of(1 ,000)X (32)/120 = 270 laser battle stations. Atradeoff of more than one complex U.S. satellite,launched and maintained on orbit, for every 4Soviet boosters (or decoy boosters) deployed onthe ground would certainly appear to be a los-ing proposition for the United States. This is trueeven though the hypothetical HF laser systemrepresents a very favorable outcome of laser tech-nology.

Note that Soviet deployment of new ICBMs inone region of the Soviet Union, within coverageof only a single U.S. satellite, gives them the bestleverage in the cost exchange.

5.8 NEW TARGETING PLANS

Truly efficient ICBM defenses would presum- Iobbed into any target area unimpeded, the su-ably force upon the superpowers a stricter atten- perpowers have less need to be discriminatingtion to targeting priorities. With thousands of or parsimonious in their nuclear targeting. Suchwarheads in today’s arsenals able to be literally a shift might have both desirable and undesirable

33-698 0 - 84 - 6 : QL 3

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consequences. For example, the offense might haps cities) as a hedge against poor penetration.decide that in view of the cost of countermeas- How the superpowers would greet these hypo-ures it could no longer afford to threaten the thetical defenses is not clear, but it is probablyother side’s ICBM silos. The warheads “freed up” quite wrong to imagine future defenses actingfrom the countersilo mission might then be dedi- against offensive forces targeted according to thecated to heavier targeting of other aim points (per- war plans of today.

5.9 OTHER MEANS OF DELIVERING NUCLEAR WEAPONS

One additional Soviet response to an efficientdefense against their ICBMs would be increasedemphasis on submarine-launched ballistic mis-siles (SLBMs), bombers, cruise missiles, and what-ever novel methods time and ingenuity might inthe future devise for introducing nuclear weaponsto the United States. As defenses forced up thecost-per-delivered-warhead of ICBM forces, theseother methods would become relatively more at-tractive. Though they would sidestep the BMD,these delivery means have higher pre-launch sur-vivability than ICBMs, and bombers and cruisemissiles have longer times of flight, These at-tributes are usually seen as “stabilizing.” Shiftingthe emphasis of the arms competition away fromICBMs is therefore sometimes viewed as ade-quate payoff for the BMD effort.

SLBMs would obviously be vulnerable to thesame boost-phase weapons as ICBMs. The same

worldwide coverage, reflected in the absenteeratio, that plagues the anti-lCBM cost exchangemeans that orbiting boost-phase defenses threat-en SLBMs the world over. However, midcourseand terminal tiers of a layered defense would ingeneral have much less capability against SLBMs,because of the latter’s short time of flight, possiblydepressed trajectory, and uncertain direction ofattack. Thus SLBMs could conceivably enjoygreater penetration of a layered defense thanICBMs.

If one takes an optimistic view of emergingdefensive technologies, or if one contemplatestechnological “breakthroughs,” it is at least con-ceivable that such developments will spawn newways of delivering or aiding the delivery of nu-clear weapons as well as new ways of interdict-ing them.

Section 6

A WORD ON “OLD” BMD“NEW”

ANDBMD

Section 6

A WORD ON “OLD” BMD AND “NEW” BMD

No one knows whether directed-energy weap-ons can be built with the characteristics assignedto the hypothetical systems of Section 3. Even ifsuch systems can be built, it is not clear that theirperformance will match, much less exceed, theperformance of terminal and midcourse BMD sys-tems in level of protection (attack price) and incost relative to offsetting offensive improvements.The boost-phase BMD systems receiving so muchattention today were a year ago at the periphery,to say the least, of technical discussion of missiledefense. It is important not to lose sight of thestatus of traditional reentry and ‘‘advanced” (asthey were called a year ago) “overlay” midcourseBMDs.

Naturally, the promise of the better-understoodterminal and midcourse systems does not seemso grandiose, nor the flaws so clear-cut, as theydo for the conceptual boost-phase defenses dis-cussed in this Background Paper. Sounder tech-nical assessments can be made of the “old”BMDs than of the “new” concepts. Rough con-cepts gloss over all the difficult design problemsthat inevitably limit achievable performance andturn up serious problems; nonetheless, identify-ing potentially unsolvable problems at this earlystage of study does not mean they will remaininsurmountable. BMD architectures incorporat-ing boost-phase intercept are not known to beable to perform better, dollar-for-dollar, thanBMD architectures incorporating only midcourseand reentry intercept. They are just not knownto be worse. Terminal defense systems have beenstudied, designed, and tested for years, and it isgenerally agreed that such systems, acting alone,can enforce a modest attack price of between 2and 8 RVs (perhaps equivalent to 20 to 80 per-cent of a booster) per defended aim point. Thoughtheir capabilities are modest, reentry and mid-course defenses suffice for modest defensivegoals. There is no need to incur the technical riskof “new” boost-phase intercept schemes unlessone aspires to levels of performance clearly be-yond those possible with “old” concepts.

Many of the “new” concepts for boost-phaseintercept are not new at all. They have been stud-ied and discussed in one form or another for 20

years. Conversely, there are some new ideas forimproving terminal and midcourse BMDs.1 Thespirit of technical optimism that accompanied thenew emphasis on boost-phase intercept in thepast year affected thinking about “old” BMD aswell.

For terminal defense systems, the new featuresreceiving attention are, first, non-nuclear war-heads on interceptor missiles and, second, air-plane-borne infrared sensors as supplements toground-based radars. The principal benefit ofnon-nuclear intercept is that interceptors can bedeployed nationwide without public concernabout the safety of defensive nuclear warheads.Non-nuclear kill does not permit the defense toavoid all the disruptive effects of nuclear bursts,however, since the offense can still arrange forRVs to detonate when they sense interceptor im-pact (“salvage fuzing”). The miss-distance/weightrelationship of the non-nuclear warhead requiresthe interceptor to approach more closely to theRV, and this in turn requires a homing seeker onthe interceptor. Terminal homing obviouslycreates new opportunities for offensive counter-measures.

Airborne optical sensors obviously do not suf-fer radar blackout, but they can suffer the analo-gous problem of infrared redout. Decoy discrim-ination remains a problem, though it acquiressome interesting new features. Details of thesenew aspects of terminal BMD are obviously clas-sified. Though important, these aspects are fairlystraightforward extensions of traditional tech-niques rather than revolutionary “break-throughs. ”

New thought about midcourse defense focuseson alleviating the Achilles’ heel of systems thatuse infrared sensing to support intercept in space:the ease with which the offense can accompanyattacking RVs with clouds of decoys. One ap-proach receiving attention is simply to cheapenthe interceptor and shoot at everything, RVs anddecoys alike. Another is to probe the attacking

‘See Julian Davidson, “BMD: Star Wars in Perspective, ”Aerospace America, January 1984, p. 78.

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objects with an active sensor, rather than rely-ing on their thermal emissions, in the hope of dis-criminating RVs from decoys. Some of these “ac-tive discrimination” schemes are complex andexpensive and might in turn be susceptible to of-fensive spoofing. A third aid to discrimination isthe boost-phase defensive layer itself, whichmight constrain the number and type of penetra-tion aids the offense could mount on each boost-

er in addition to reducing the total number of ob-jects approaching the midcourse tier. Fourth,extensive use of space-based sensors would allowthe defense to observe penetration aids through-out their flight (including during deployment fromthe bus) rather than just as they approach theUnited States. It remains unclear whether thesetechniques will be worth the costs and new coun-termeasures they would bring to the defense.

Section 7

A HYPOTHETICAL SYSTEMARCHITECTURE

●

Section 7

A HYPOTHETICAL SYSTEM ARCHITECTURE

Most analysts of boost-phase BMD assume thatmidcourse and terminal BMDs will augment theboost-phase layer. This section assembles a hy-pothetical layered defense system in toto. Thissystem is pure/y illustrative, taking current BMDconcepts at their face value and conveying a con-crete image of the defensive architectures analystsapparently have in mind when they speak of na-tionwide defense. Obviously there are manychoices for such a “strawman ” system. The par-ticular system described below was chosen forits illustrative value and not because it representssome “most plausible” alternative. It would bemeaningless to suggest a “front runner” in thepresent state of study and technology develop-ment. Rather, the purpose of this example is toshow how the layers interact and to indicate theoverall scale of the deployments contemplated,without implying that anything remotely like itever could or would be built.

A defense with several layers presents the of-fensive planner with some of the variety of prob-lems that afflicts the BMD designer, who neverknows in advance which attack tactic or coun-termeasure the offense will choose and must in-clude responses to all of them in the system de-sign. Layered defense forces the offense not onlyto develop responses to all the layers, but to de-velop responses that can be accomplished simul-taneously. Thus, for example, the method chosento avoid boost-phase intercept must not preventdeployment of lightweight midcourse decoys.The synergistic effect of the several layers ob-viously works strongly in the defense’s favor.

Nonetheless, one must compare the perform-ance of a three-tiered defense to the performanceof a two-tiered defense of the same cost. Thusit should be no surprise if a $200 billion systemwith boost (and possibly even post-boost), mid-course, and terminal layers performs better thana $50 billion system with no boost phase layer.

The correct questions are whether the additional$150 billion is worth the extra performance, andwhether spending the $150 billion on more ter-minal and midcourse defense would in fact bea better investment.

Occasionally one sees a simplified leakage cal-culus applied to layered defense. The calculusassigns a “leakage” of, say, 25 percent (0.25) tothe boost phase layer, 15 percent to the mid-course layer, and 10 percent to the reentry layer,deducing an “overall leakage” of 0.4 percent onthe basis of the equation (0.25)x (O. 15)x (O. 10)= 0.004. Though the term leakage can bedefined so that this calculus holds, the result ac-tually bears little relation to the number of targetspreserved by the defense. For one thing, a givendefensive layer does not have an associated leak-age fraction independent of attack size: theleakage fraction for each layer usually increaseswith attack size, most obviously (but not only)when the defensive arsenal becomes saturated.Second, the performance levels of the individuallayers are not independent. For example, if themidcourse layer’s interceptor arsenal is sized tohandle only 25 percent of the attack, and theboost-phase layer works poorly and in fact allows50 percent of the attack through, the midcourselayer obviously cannot display the same fractionalefficiency against the attack of double the ex-pected intensity. Conversely, improvements inone layer might improve performance of another:effective boost-phase or midcourse layers mightforce the offense to abandon the highly structured“laydowns” of RVs in space and time that limita terminal layer’s effectiveness. Third, the rawnumber or fraction of leaking RVs does not indi-cate the number or fraction of targets destroyedbecause of the tactics of preferential offense anddefense. For these reasons, the leakage calculusis not a helpful way to encapsulate layered de-fense performance.

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7.1 SYSTEM DESCRIPTION

The system design described below takes lit-erally the goal of comprehensive nationwide de-fense. It seeks the capability (at least on paper)to engage all attacking Soviet missiles, whethertargeted at cities, U.S. silos, or other military in-stallations. Clearly the precise numbers and kindsof components in this description can be adjustedto suit any set of assumptions. The point of thisdescription is merely to convey the flavor of thesemassive architectures. Most assumptions are fa-vorable to the defense.

Suppose that at some time in the future the So-viet ICBM arsenal still consists of 1,400 boosters,as it does today. For simplicity, suppose furtherthat each booster is an MX-sized solid propellantmissile carrying 10 RVs and that all silos are lo-cated in one large region of the U.S.S.R. Theboosters are not specially shielded against lasers,but some care in their design has given them aneffective hardness of 10 kJ/cm2, and they are fur-ther spun during ascent. Each booster carries asmall number of decoys, but their small numberis offset by the decoys’ high fidelity. Each RV isaccompanied by 9 lightweight infrared replicasand 1 high altitude reentry decoy. (This is a verymodest penetration aid loading. One can assumelarger numbers with perhaps poorer fidelity, chaffand aerosols, etc. )

The hypothetical U.S. defense system com-prises both HF chemical laser battle stations andx-ray laser battle stations for boost-phase inter-cept, land-based midcourse interceptors carry-

Table 7.1 .—Hypothetical Future U.S. DefenseDesigned for Nationwide Protection Against

Hypothetical Future Soviet Offense

U.S. Defense Soviet Offense

5 warning satellites 1,400 MX-like ICBMs180 HF laser satellites deployed in one180 laser radars region900 x-ray laser satellites 10 RVs per ICBM900 MWIR trackers 9 midcourse decoys28,000 midcourse intercept per RV

vehicles and boosters 1 reentry decoy per RV20 LWIR satellites75 radars140,000 terminal non-nuclear

interceptors25 aircraft with LWIR sensorsSOURCE: Author.

ing LWIR homing vehicles (the so-called “Over-lay”), and land-based high-endoatmospherichoming interceptors with non-nuclear warheadsfor reentry intercept.

The HF chemical laser system resembles thatdescribed in Section 3.1, except that it has onlyfive 20 MW lasers at each position in the 32-po-sition constellation, for a worldwide total of 160.At a range of 2 Mm, a laser must dwell on eachspinning booster for 5 seconds, so each laser atthis range can handle 30 simultaneously launchedboosters if defense begins 30 sec into the 180 secboost phase of an MX-like booster. The five lasersoverhead the Soviet silos at any one time cantherefore only handle 150 of the 1,400 SovietICBMs. For small Soviet attacks, however, thisnon-nuclear boost-phase layer suffices.

For a large-scale Soviet attack, the United Statesdeploys in addition a nuclear boost-phase systemof x-ray lasers. A “perfect” laser with character-istics such as those derived in Section 3.3 can in-tercept ideally about 50 boosters at 4 Mm range.Therefore 28 lasers need to be in position overthe Soviet silos at any time to handle a massivelaunch, giving a worldwide total of 900 (absenteeratio 32).

Warning for the boost-phase system is providedby MWIR warning satellites in synchronous orsupersynchronous orbits. Also, each of the 160HF laser battle stations has an MWIR telescopewith 4 m mirror and an ultraviolet or visible Iadarwith 2 m mirror for pointing. Each x-ray laser isaccompanied by an MWIR telescope tracker with1 m mirror.

The 1,400 Soviet boosters carry 14,000 RVs,126,000 midcourse decoys, and 14,000 reentrydecoys. The United States assumes that only 10percent of the boosters will survive the boostphase defense, so the midcourse tier needs toface 1,400 RVs and 12,600 midcourse decoys.The midcourse interceptors are given extremelylong range, so only two bases are needed tocover the entire United States. However, eachbase must be prepared to absorb the entire at-tack, since the Soviets could target one half ofthe country more heavily than the other. There-

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fore the United States needs 14,000 midcourseinterceptors at each base, for a total of 28,000interceptors. A constellation of 20 satellites withlarge LWIR sensors provide long-range acquisi-tion and target assignment to these interceptors.

The United States next estimates that 90 per-cent of the RVs that enter the midcourse layerwill be successfully intercepted. The terminal de-fense must handle 140 RVs plus 140 reentry de-coys.1 The reentry decoys are, by assumption,completely faithful in mimicking the signaturesof RVs as seen by ground-based radars and air-craft-borne infrared sensors during early re-entry—large decoy numbers have been sacrificedfor this high fidelity. If the U.S. defense takesliterally its charge of nationwide defense, it mustbe prepared to make 280 intercepts anywherein the country.

I The number of reentry decoys the terminal system must faceactually depends on whether the decoys fool the midcourse as wellas the terminal system’s sensors and on whether the terminal andmidcourse layers cooperate in discrimination. Suppose first that thereentry decoys look Ilke RVS (and therefore also like midcoursedecoys) to the midcourse layer’s sensor. Then the midcourse layerwill Intercept 90 percent of them (more midcourse interceptors mustbe bought to do th@. If, on the other hand, the midcourse layercorrectly identifies the reentry decoys as non-lethal objects, it might(a) not intercept them, requiring the terminal layer to plan to face140 RVS plus 1400 reentry decoys, increasing enormously the re-quired arsenal of terminal interceptors; (b) intercept them, in whichcase a reentry decoy is a perfect midcourse decoy, making possi-ble a new threat–large numbers of midcourse decoys that looklike reentry decoys rather than RVS; (c) radio the information, object-by-object, to the terminal defense fields.

Each terminal defense site consists of a phased-array radar and a number of high altitude non-nu-clear interceptors. Additional target acquisitionsupport is provided by a fleet of aircraft patrol-ling the U.S. periphery, carrying LWIR sensors.Each radar has a radius of action of over 200 km,so 75 or so cover the entire United States. How-ever, an interceptor only covers an area about50 km in radius. Since the area of the UnitedStates is about 8 million square km, over 1,000interceptor sites would be needed for nationwidecoverage. Should the defense have to reckonwith intensive Soviet attack on some regions andno attack on others? Clearly, yes. But equippingeach interceptor site to handle all 280 objectspassing through the first two layers would requirebuying 280,000 interceptors! The defense wouIdneed to buy this many interceptors if it wantedto claim the literal capability to engage all SovietRVs, no matter where they landed. Suppose,then, that the United States hopes for a moreevenly distributed Soviet attack and deploys justhalf of the arsenal needed for complete cover-age— 140 interceptors per region. One radarmight not suffice to handle all the RV traffic inits sector if the Soviets attack some sectors pref-erentially, but the United States nonetheless buysjust 75 radars. Five aircraft on patrol at all timesrequires a backup fleet totalling perhaps 25.

Table 7.1 summarizes the offensive and defen-sive deployments.

7.2 ASSESSMENT

It is obviously not possible to assess the per-formance of a system, such as the hypotheticallayered defense described above, whose com-ponents are not (and in many cases cannot be)designed today, much less assembled in an over-all architecture. It is nonetheless worth sketching,in the illustrative spirit of this section, the issuesthat would require analysis if anything resemblingTable 7.1 were ever proposed for deployment.

The first issue concerns the cost of the improve-ments to the system needed to offset growth inthe Soviet ICBM arsenal—that is, the cost ex-change ratio. The number of defensive weapons

is proportional to the number of Soviet ICBMs.If the Soviets were to double the size of theirICBM arsenal, the United States would need todouble the number of its x-ray lasers and inter-ceptor missiles. (The number of sensors wouldgenerally have to increase also, though perhapsnot in proportion to the Soviet buildup. The num-ber of HF lasers could remain the same if theUnited States continued to intend to use this non-nuclear boost-phase layer to engage only Sovietattacks of 150 boosters or less. ) Comparison ofthe two columns of Table 7.1 indicates that anarms race of Soviet offense and U.S. defenseseems certain to favor the Soviet side greatly.

62—

A second issue concerns the huge inventoriesof midcourse and reentry interceptors needed fornationwide defense. The arsenal of reentry inter-ceptors shown in Table 7.1 is in fact only half thesize needed for literally complete nationwide cov-erage, as remarked above. The cause of theselarge interceptor inventories–besides the obviouspresence of decoys–is twofold: first, the low leak-age sought by the defense precludes preferen-tial defense, the tactic that makes silo defense somuch more economical; and second, the limitedcoverage of each interceptor battery makes pref-erential offense possible for the attacker. The goalof nationwide low-leakage defense thereforeforces the BMD system to forfeit the two sourcesof leverage that have historically impelled BMDtowards the technically modest mission of de-fending compact silo deployments to relativelylow survival levels.

Soviet countermeasures–besides straightfor-ward buildup of ICBMs—is a third issue. The par-ticular boost-phase layers described above aresusceptible i n varying degrees to all of the coun-termeasures described in Section 5, and the mid-course and reentry layers to their respective setsof countermeasures.

Defensive coverage against submarine-Iaunched ballistic missiles (SLBMs) is a fourthissue. The boost-phase layers can intercept SLBMslaunched from all points on the globe. Thoughthe average range from laser satellite to boosteris larger at equatorial and polar latitudes than atthe mid-latitudes where Soviet ICBMs are located,the number of SLBMs that could be launched ina short time from each ocean area is also muchsmaller than the huge number of ICBMs thatcould lift off simultaneously from the U.S.S.R.Even the chemical laser deployment alone mightsuffice for boost-phase coverage of SLBMs. Themidcourse and reentry layers, however, wouldin general not perform as well against SLBMs asagainst ICBMs. SLBM trajectories present badviewing angles to the midcourse layer’s LWIRsensors, and the short timeline limits interceptorcoverage. The reentry layer would need to beaugmented with more airborne sensors and moreradars (or radar faces) to cover attack from theocean. In general, then, a layered system opti-mized for ICBM defense could not necessarilyhandle SLBMs as well.

Section 8

DEFENSIVE GOALS 1: THE PERFECT”DEFENSE

Section 8

DEFENSIVE GOALS 1: THE PERFECT DEFENSE

No assessment of whether a defensive system“works” or not is meaningful without a clear anddirect statement of the goal of the deployment.Though there has been much discussion of thefeasibility of boost-phase BMD, proponents andskeptics alike frequently leave unstated the stand-ards against which they are judging the technicalprospects. A “successful” BMD deploymentcould be defined as anything from a truly impen-etrable shield, to a silo defense that merely costsless to build than it costs the Soviets to overcome,to a tangled deployment that just “creates uncer-tainty” for the attacker.

The most ambitious conceivable goal for BMDwould be to take at literal face value the wordsof President Reagan in his so-called “Star Wars”speech of March 23, 1983, when he called fordevelopment of a defense capable of making nu-clear weapons “impotent and obsolete.”1 It is notclear that the President intended his words to betaken literally, nor that the Administration or any-one else is suggesting the United States seek atruly perfect or near-perfect defense.2 Nonethe-

1 Week/y Compilation of Presidential/ Documents, Vol. 19, No.12, March 28, 1983, pp. 447-448, The text of the relevant part ofthe speech is reprinted as Appendix A.

2 Defense Secretary Caspa r Wei nberger appeared to confirm aliteral interpretation In a March 27 interview on NBC’s Meet thePress, when he sa[d (as reported in the Ba/t/more Sun, March 28,1983, p. 1).

Th~> de(enslve systems the president IS talking about are not de-signed to be partial What we want to try to get IS a system whichWIII develop a defense [SIC] that IS thoroughly rellable and total, I

don’t see any reason why that can’t be done.Later, the Defense Department stated that the purpose of the

President’s initiative was not to save Iwes, but to deter war. Respon-ding to the “Congressional Findings” section of the proposed “Peo-ple Protection Act” (H .R, 3073, 98th Congress, Ist session) whichstated, “The President has called for changes in United States stra-tegjc policy that seek to save lives in time of war, ” Defense Depart-ment General Counsel William H. Taft IV wrote:

It IS clear that portions of the “Congressional ftndlngs” section [ofH R 3073] vary from the purpose of the President’s Inltlatlve First,and most I m porta ntly, the purpose of the President’s i nltlatlve IS tostrengthen our ablllty to deter war by, as the President has said,/, renderl ng [ha llIst Ic m IS; I Ies] Impoten t and obsolete. 1 n short,

less, so much writing and debate focuses on thisprospect, and its importance is so great, that itis taken up in this section. Section 9 treats themany other possible goals for less-than-perfectdefenses.

There is some confusion in the literature aboutthe use of the term “mutual assured destruction”(MAD) in connection with the notion of perfectdefense. In common strategic parlance, MAD re-fers to the technological circumstance of mutualvulnerability to catastrophic damage from nuclearweapons, not to a chosen policy to promote suchvulnerability. There is a strategic school ofthought that advocates a policy usually called“minimum deterrence, ” maintaining that the ca-pability for assured destruction of Soviet societyis the on/y requirement of U.S. strategic forces.However, many experts believe that effective de-terrence and other national security objectivesrequire nuclear forces capable of many othertasks than assured destruction. This section ad-dresses itself to the question of whether MAD isan avoidable technological circumstance, not towhether minimum deterrence is a prudent stra-tegic policy.

A sensible start at judging the prospect for near-perfect defense must involve two steps: first, anexact statement of what perfect defense meansin the context of attack on society with nuclearweapons; second, some way of gauging the like-lihood of success when the technological futurecannot be accurately predicted.

the purpose of the Administration’s policy is to reduce the Ilkellhoodof war. The finding [of H.R. 3073] that the purpose IS to ‘‘sa~ e IIk esI n tl me of war’ departs from our goal of deterrl ng war

Dr. Charles Townes, a frequent adviser to Secretary of DefenseWeinberger and leader of two DOD task forces studying basingmodes for the MX missile, said that a perfect defense proposal is“quite impractical. There is no technical solution to safeguardingman kind from nuclear explosives. (New York Times, April 11,1983, p. 14).

65

66.

8.1 NUCLEAR ATTACK ON SOCIETY

Figure 8.1 .-The Effect of Attack Size on the Extentof Prompt Fatalities in U.S. Urban Areas

1 0I I I

500 1000 1500 2000 2500 3000Attacking warheads

Note: Aimpoints chosen to maximize prompt human fatalities. U S. urban popula-tion IS estimated to be 131 million, as in the 1970 census.

SOURCE. Arms Control and Disarmament Agency, U.S. Urban PopulationVU/nerabi/ity (ACDA, 1979), quoted in Arthur M. Katz, Life Afrer Nuc/earWar The Economic and Social Impacts of Nuclear Attacks on the US(Ballinger, 1982) Adapted from Ashton Carter and David N. Schwartz,eds , Ba//istic Miss//e Defense (The Brookings Institution, 1984), p 168

Suppose one wants to take literally the goal ofremoving from the hands of the Soviet Union theability to do socially mortal damage to the UnitedStates with nuclear weapons, so that the SovietUnion no longer possesses the elemental capa-bility of assured destruction.) What does thismean?

Figure 8.1 shows how the percent of the U.S.urban population (about 130 million people inthe 1970 census) killed promptly increases withthe number of Soviet warheads detonating overU.S. cities. No such curve of the effects of nu-clear attacks on cities should be taken as anythingbut suggestive: uncertainties are very great insuch estimates, and no attempt has been madeto reflect long-term and indirect effects of thedetonations.3 The curve also accounts only for

3For discussion of some of the effects of nuclear weapons onpopulation and cities, see: U.S. Arms Control and DisarmamentAgency, An Analysis of Civil Defense in Nuclear War (ACDA, 1978);OTA, The Effects of Nuc/ear War (GPO, 1979); ACDA, The Effectsof Nuc/ear War (ACDA, 1979); “Economic and Social Conse-quences of Nuclear Attacks on the United States, ” prepared forthe joint Committee on Defense ProductIon, 96 Cong. 1 sess., 1979;

fatalities, not for the many additional people in-jured. If one wishes to account for the possibilityof civil defense evacuation, then the curve shouldbe taken to represent not the number of peoplekilled, but the number of people whose homes,businesses, historic monuments, schools, andplaces of worship have been destroyed.

No one supposes that the Soviet Union actuallychooses aim points for its nuclear weapons withthe goal of maximizing human fatalities, as hasbeen done in preparing Figure 8.1. if the UnitedStates possessed a defense capable of intercept-ing all but a few of the 8,000 to 10,000 Sovietnuclear warheads, however, the Soviet Unionmight retarget its forces to wreak the most de-struction possible with its few penetrating war-heads. At any rate, any defense promising U.S.society genuine immunity from nuclear attackmust reckon with Soviet determination to keepits arsenal from being “rendered impotent, ” andtherefore with targeting plans contrived to do themost damage to the fabric of U.S. society.

Where on the curve of Figure 8. 1–after howmany detonations—does one locate the bound-aries of “assured destruction, ” “assured sur-viva l,” “impotent and obsolete, ” and similarphrases? Clearly there is no analytical prescrip-tion for these boundaries: they are the subjectof a broader human judgment. 500 half-megatonwarheads kill half the urban population, injuremost of the rest, and totally destroy all Americancities and large towns. Just 5 megatons, about onetwo-thousandth of the Soviet arsenal, detonatedover the 10 largest U.S. cities could kill severalmillion people and wound over 10 million more.

For the sake of discussion, we shall use 100megatons—about 1 percent of the Soviet Union’sarsenal and 1.5 percent of its ICBM force—as thelevel of penetration for which a defense would

1. Carson Mark, “Global Consequences of Nuclear Weaponry, ”Annua/ Review of Nuc/ear Science, Vol. 26 (1976), pp. 51 -87; Na-tional Research Council, Long-Term Wor/~wi~e Effects of Mu/fi-p/e Nuc/ear- Weapons Detonations (National Academy of Sciences,1 975).

67

be judged “near-perfect.” This definition is ob- regard 100 megatons of explosive force as “im-piously very generous to the notion of perfect de- potent and obsolete. ” Still, it is a definitefense, since most people would presumably not reference for assessment.

8.2 THE PROSPECTS FOR A PERFECT DEFENSE

There is not and cannot be any “proof” thatunknown future technologies will not providenear-perfect defensive protection of U.S. societyagainst Soviet ICBMs. The question that needs tobe answered is whether the prospects for near-perfect defense are so remote that such a notionhas no place in reasonable public expectationsor national policy. it is, after all, not provable thatby the next century the United States andU.S.S.R. will not have patched up their politicaldifferences and have no need to target oneanother with nuclear weapons. The issue of theperfect defense is unavoidably one of technicaljudgment rather than of airtight proof,

Four misapprehensions seem common amongnon-technical people addressing the prospects forperfect defense.

The first misapprehension is to equate success-ful technology development of individual de-vices—lasers, power sources, mirrors, aiming andpointing mechanisms—with achievement of anefficient and robust defensive system. Millionfoldincrease in the brightness of some directed-en-ergy device is a necessary, but is far from a suffi-cient, condition for successful defense. In theearly 1960’s, intercept of RVs with nuclear-tippedinterceptor missiles was demonstrated—”a bul-Iet could hit a bullet’’–but 20 years later systemsincorporating this “kill mechanism” are still con-sidered relatively inefficient. In general, skepticsabout the future of space-based directed-energyBMD do not confine their doubts to, or even em-phasize, unforeseen problems in developing theindividual components.

A second misappprehension arises in attemptso equate BMD development to past technologi-cal achievements, such as the Manhattan proj-

ect’s atomic bomb or the Apollo moon landings. QThe technically minded will recognize a vital dif-ference between working around the constraintsimposed by nature, which are predictable andunchanging, and competing with a hostile intel-ligence bent on sabotaging the enterprise. A dy-namic opponent makes of BMD, first, a more dif-ficult design problem, since the offense constructsthe worst possible barriers to successful defense;and second, not one problem but many prob-lems that need to be sidestepped simultaneouslyin the design, since the designer cannot be cer-tain which tactics the offense will use.

A third misapprehension concerns the prospectfor a “technological breakthrough” that woulddispel all difficulties. Such breakthroughs are notimpossible, but their mere possibility does nothelp in judging the prospects for the perfect de-fense. For one thing, an isolated technologicalbreakthrough creating a new defensive compo-nent would not necessarily alleviate the systemissues—vulnerability, dependability, susceptibilityto countermeasures, cost—that determine overalleffectiveness. Second, one can just as easily im-agine offensive “break throughs,” sometimes in-volving the same technologies. Thus the x-ray la-ser, if it matures, might turn out to have been

4Defense Secretary Caspar Weinberger has w rltten (Air ForceMagazine, Nov. 1983):

The nay-sayers have already proclaimed that we WIII never haiesuch technology, or that we should never try to acquire It Theirarguments are hardly new In 1945 president Truman’s Chief otStaff, Adm William Leahy, said of the atomic bomb “Thatrs the big.gest fool thing we’ve ever done. The bomb will never go off, andI speak as an expert in explosives. ” In 1946 Dr. vanne~ ar Bush,Director of the Office of Scientific Research and Development saidof Intercontinental ballistic missiles, “1 say technically I don’t thinkanybody I n the world knows how to do such a thing, and I feel con-fident [t WIII not be done for a long time to come “ These crltlcs wereproved wrong; what IS more, they were proved wrong quickly

33-698 0 - 84 - 4 : QL 3

better termed a breakthrough in strategic offensethan a breakthrough in strategic defense.

A fourth misapprehension concerns the confi-dence with which predictions could be madeabout the performance of a complex system oncei n place. The “performance” of a system, asquoted in analyses, is the most likely outcomeof an engagement of offense versus defense.Other outcomes, though less likely, might still bepossible. Computing the relative likelihoods ofall possible outcomes would be difficult even ifone could quantify all technical uncertainties andstatistical variances. Still, there would remain aresidue of uncertainty about the performance ofa system that had never been tested once in real-istic wartime conditions, much less in a statisti-cally significant ensemble of all-out nuclear wars.The defense would also have no chance to learnand adapt. In World War II, by contrast, air de-fense crews learned in raid after raid to inflictlosses of several percent in attacking bombers.The only reason these modest losses assumedstrategic significance was that they accumulatedover many raids. Of course, the same uncertain-ties plague the offense as plague the defense. Ingeneral, the offense would tend to overestimatethe defense’s capability. This natural tendencytoward “offense conservatism” is probably vitallyimportant to the psychological and deterrent val-ue of BMD as it is applied to less-than-perfectgoals. For the perfect defense goal (as definedabove), however, it would seem that the uncer-tainty weighs heaviest on the defense. To thereckless, non-conservative defense, a wrong esti-mate of defense performance spells the differencebetween safety and socially mortal damage (orbetween deterrence and war). The reckless of-fense, on the other hand, is presumed desperateenough to try to inflict such damage on its enemyand willing to accept the consequences: it standsto lose little if its estimates are wrong and the de-fense does work perfectly after all.

With these misapprehensions out of the way,and recognizing clearly that there can be no ques-tion of “proof, “ it would seem that four majorfactors conspire to make extremely remote theprospect that directed-energy BMD (in concertwith other layers if necessary) will succeed in re-

ducing the vulnerability of U.S. population andsociety to the neighborhood of 100 megatons orless.

1. Near-perfect defense of society is muchharder and more expensive than partial defenseof military targets. That is, the marginal cost ex-change is much higher for near-perfect defensethan for partial defense (see also Fig. 5.2). Thereare two reasons behind this well-knownstatement.

The first reason is illustrated schematically inFigure 8.2. In going from partial silo defense toperfect city defense, the BMD loses the leverageof preferential defense. Additionally, the offensegains the leverage of preferential offense againstthe terminal and midcourse layers with their lim-ited geographic coverage, although not againstthe boost-phase layer. In Figure 8.2(a), the de-fense aims to save only 10 percent of the ICBMforce, or one silo. Assuming perfect interceptorsand adopting the tactic of adaptive preferentialdefense (using all its interceptors to save just onesilo chosen randomly from the ten at the momentof attack), the defense concludes it needs to pre-pare to make one only intercept to counter theoffense’s 10 RVs. In Figure 8.2(b), the offense canfocus all 10 of its RVs on any one of ten cities.The defense must prepare to make 10 interceptsfor each city, buying a total of 100 interceptors,if it wants to try to save all the cities. If the Sovietsdouble their RV arsenal, the United States mustbuy just one interceptor to satisfy the defense goalof Figure 8.2(a), but the United States must buy100 interceptors to satisfy the defense goal of Fig-ure 8.2(b). The cost exchange ratio is thus 100times worse for the city defense, even though ituses the same technology as the silo defense.

The second reason why a near-perfect defen-sive goal shifts the cost burden in favor of the of-fense is that the offense can turn all its resourcesto improving or replacing just a portion of itsICBMs to sidestep the defense. The Soviet Unioncould therefore harden just 1 percent of its boost-ers, perhaps concealing exactly which ones werehardened. Moreover, it could deploy a few fast-burn boosters immune to x-ray lasers and neutralparticle beams; build a few different ASAT de-

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Figure 8.2

10 attacking

ICBM Silos

Radius of BMDBMD interceptor

coverage

(a)

Figure 8.2. The cost to a U.S. reentry BMD to compete with increases in the size of the Soviet arsenal (the “marginal cost exchange”) IS muchgreater for near-perfect city defense (b) than for partial silo defense (a). In going from (a) to (b), the U.S. loses the leverage of preferential defense

and the Soviet Union gains the leverage of preferential offense.

vices; and so on. More costly countermeasuresare avaiIable to the offense if the countermeas-ures need onIy be implemented on a small scalerather than throughout the ICBM force. The of-fense can “experiment” with a number of dif-ferent tactics with different portions of its force.The defense’s costs also grow much larger if itmust plan to face a variety of offensivecountermeasures. I n short, the defense must beable to stop all kinds of attack, but the offenseonly has to find one way to get-through.

2. For every defense concept proposed or im-agined, including all of the so-called “Starwars” concepts, a countermeasure has alreadybeen identified. These countermeasures wereenumerated in Section 5 and will not be repeatedhere. Three further generalizations about thesecountermeasures reinforce a poor prognosis forcost-effective near-perfect defense: 1 ) In general,the countermeasures could be implemented withtoday’s technology, whereas the defense itselfcould not; 2) In general, the costs of the coun-

70

termeasures can be estimated and shown to berelatively low, whereas the costs of the defenseare unknown but seem likely to be high; 3) Ingeneral, the future technologies presupposed aspart of the defense concept would also be po-tent weapons for attacking the defense.

3. The Soviet Union does not configure its nu-clear missile forces today to maximize damageto U.S. society and population, but it could doso if faced with near-perfect U.S. defenses. Tar-geting plans could focus exclusively on damag-ing cities. High missile accuracy would be un-necessary, lowering offense costs. Nuclearweapons could be designed to maximize harm-ful fallout. ICBM survivability measures–silos,racetracks, densepacks, etc.—would be unnec-essary to a side striking first or possessing its owndefense effective at saving many missiles (but notall cities); thus basing costs could be diverted tothe city-kill goal, Presumably the Soviet Unionwould take these and any other measures nec-essary to prevent itself from being effectively

disarmed by a U.S. defense, since otherwise itwould be at its enemy’s mercy.

4. BMD by itself will not protect U.S. societyfrom other methods of delivering nuclear wea-pons to U.S. soil or from other weapons of massdestruction. Bombers and cruise missiles (and toa significant extent SLBMs and IRBMs) presentvery different defensive problems than ICBMs.Today the technical problems of air defense areno better resolved than the technical problemsof BMD. Novel future offensive delivery vehiclescan only be conjectured along with the futuredefense technologies discussed in this Paper. Adesperate Soviet Union could introduce nuclearweapons into the United States on commercialairliners, ships, packing crates, diplomatic pouch,etc. Other methods of mass destruction or ter-rorism would be feasible for the U. S. S. R., includ-ing sabotage of dams or nuclear power plants,bacteriological attack, contaminating water, pro-ducing tidal waves with near-coastal underwaterdetonations, and so on.

.

●

Section 9

DEFENSIVE GOALS II:LESS-THAN-PERFECT DEFENSE

Section 9

DEFENSIVE GOALS II:LESS-THAN-PERFECT DEFENSE

A host of less grandiose goals than perfect ornear-perfect defense assume importance i n cer-tain theories about the workings of nuclear deter-rence and the requirements of U.S. security.Thoughtful observers debate not just the feasi-bility of achieving these goals but the validity andimportance of the goals as well. The urgency oneattaches to these goals determines the costs, risks,and harmful side effects one is willing to incurto fulfill them. Assessing the wisdom of less-than-perfect defense thus involves a complex and sub-jective balancing of goals and risks, in whichpurely technical issues sometimes take a backseat. In discussion of perfect defense, by contrast,technical assessment is paramount. This sectiontherefore calls up many issues of nuclear policynot subsumed under the title of this BackgroundPaper, and no pretense is made hereto completetreatment. 1

Though various strategic goals for BMD can bedistinguished in principle, in practice it might notbe clear or agreed among all parties in the UnitedStates what the purpose of a proposed deploy-ment actually was. Interpretations by the SovietUnion and other foreign nations of U.S. goalsmight be quite different yet.

I For a more complete treatment of the entire subject of BMD,see Ashton B. Carter and David N. Schwartz, cd., Ballistic MissileDefense (The Brookings Institution, 1984).

Those familiar with BMD design and assess-ment wiII recognize that stating a general strate-gic goal is not enough: the technical specifica-tions are essential. For instance, it makes anenormous difference in silo defense whether thedefense seeks to charge the offense a price of fiveRVs (or half a booster) or 10 RVs (one booster)per silo.

For goals requiring very modest performance,terminal and midcourse defenses might suffice.Since no one knows whether boost phase de-fenses, when better defined, will surpass or evenequal traditional defenses in terms of leakage andcost exchange, there is no point i n turning to ex-otic technologies to satisfy modest goals. Virtuallyall observers agree, on the other hand, that ter-minal and midcourse systems are unequal to themore demanding goals; for these goals one isforced to direct one’s hopes to the promise offuture technologies.

This section sketches various goals for less-than-perfect defenses and the strategic thinking thatattaches importance to them. It then points outa number of side effects against which fulfillmentof these goalssection is noassessment 01

needs to be balanced. This shortsubstitute for a comprehensivethe pros and cons of BMD.

9.1 GOALS FOR LESS-THAN-PERFECT DEFENSE

1. Strengthen deterrence by preventing pre-emptive destruction of retaliatory forces. It iswidely recognized that the Soviet Union will soonhave, if it does not already, the combination ofyields, numbers, and accuracy in its ICBM forcesto destroy most U.S. Minuteman ICBMs in theirsilos. It is also widely agreed that vulnerable nu-clear forces create unwanted temptations for bothsides to strike first if war seems likely. The longand anguished search for survivable basingmodes for the U.S. MX (Peacekeeper) ICBM hasto date turned up no clear favorites when sur-

vivability is balanced against cost, technical risk,strategic effects, and environmental impacts. zBMD would substitute for or complement theseother basing modes. By shooting down a fractionof the opponent’s missiles, BMD would in effect“de-MIRV” ICBM forces.

Of course, turning to BMD to ease ICBM vul-nerability is not without problems. One problemis the prospect of a compensating Soviet BMD.

2MX Missi/e Basing, office of Technology Assessment, U.S. Con-gress, September 1981.

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.

74. .

MX is presumably being bought and made sur-vivable in the first place so that the U.S. can ab-sorb a Soviet strike and retaliate with its ICBMs(in addition to its bombers and submarines)against Soviet targets. But modification or ter-mination of the ABM Treaty to permit a U.S. de-fense would permit a Soviet defense as well. Thesurviving U.S. ICBMs guaranteed by the U.S.BMD might still not result in retaliatory damageto Soviet targets if these targets are defended bySoviet BMD. The U.S. BMD deployment, allbought and paid for, might therefore have beencancel led out by a Soviet counter-deployment,

Other elements of the U.S. retaliatory forcecomprise command and control links, bomberalert bases, and in-port submarines. Bomberbases, sub ports, and fixed command and con-trol facilities are the worst type of target base forBMD to try to defend–a small number of high-value, soft, and interdependent targets. The im-portant remaining category of mobile commandand control facilities, on the other hand, does noteasily lend itself to active defense with BMD.

2. Strengthen deterrence by preventing the useof nuclear weapons as decisive military tools forhigh-confidence “limited” strikes on conven-tional forces. This goal is associated with so-called “warfighting” strategies for nuclear weap-ons. According to analysts who hold this view,today’s “offense dominated” world creates dan-gerous temptations to resort to nuclear weaponsto accomplish militarily well-defined objectives.One can imagine warheads simply being lobbedunopposed into another country in any numberor combination. Though surely the effects ofthese “limited” attacks on nearby communitieswould not be so well-defined, the effect on theopposing military machine might be truly dramat-ic, even decisive. This use of nuclear weaponsin wartime is possible with today’s unopposedoffenses with considerable confidence and mighttherefore be tempting to the combatants. Suchtemptations threaten nuclear deterrence andshould be eliminated. The goal of a comprehen-sive defense would be to make such limited at-tacks infeasible, or at least to complicate the of-fense’s estimations of success to such a degree

that it would not attempt an “experiment.”3

Analysts who favor this approach usually main-tain that Soviet military doctrine inclines theSoviets towards a view of nuclear weapons asmilitary tools to a far greater degree than is com-mon in U.S. thinking. d

To take an explicit example (in this case of So-viet failure to deter the U. S.) of a “war fighting”scenario (chosen randomly from a great manypossibilities), suppose NATO were at war withthe Warsaw Pact, and the Soviets were resupply-ing their ground offensive through just 10 or sorail trunks from the Soviet Union through east-ern Europe. Just 10 well-placed nuclear weapons(according to a hypothetical analyst consideringthis type of scenario) would cut off a large frac-tion of supplies coming to the front, slowing thePact offensive and giving NATO vitally neededtime to marshall its defenses. Wouldn’t theUnited States be sorely tempted to use just a fewICBMs for this decisive intervention in the courseof the war?

Analysts who recommend attention to warfight-ing scenarios and doctrines are surely aware ofthe profound difference between conventionaland nuclear weapons, but they maintain that thethreat of punishment through retaliation upon cit-ies is not an effective deterrent in such scenarios.Wouldn’t it be preferable if these scenarios weresimply closed off by defensive technology?

Critics of this BMD goal object both to the war-fighters’ emphasis upon the risk of this type ofscenario and to the assumption that defensewould materially diminish that risk. In their view,myriad detailed chinks in the armor of deterrencecan always be found, with or without defense,and worrying about them represents a loss of

JPresidential Science Adviser George A. Keyworth, II has stated(interview with US. News and Wor/d Repofl, April 11, 1983, p. 24):

‘‘The objectwe IS to have a system that would convince an adver-sary that an offensive attack WIII not be successful. It has to be a veryeffective system, but It would not have to be perfect to convince apotential adversary that his attack would fall “

Dr. Robert Cooper, director of the Defense Advanced ResearchProjects Agency has also stated this view (The New York Times,Nov. 5, 1983, p. 32): “Even if only 50 percent of all incoming missileswere stopped, the Soviets could then have no confidence in thesuccess of a first strike, and war would be more remote. ”

4Ba//istic Miss;/e Defense, op. cit., Chapter 5.

75—

perspective on the basic difference between nu-clear and conventional instruments of war. Be-sides, they say, suppose the effect of the SovietBMD is to force the United States to attack eachrail line with ten weapons instead of one to assurepenetration: IS there truly a psychological dividebetween using 10 and 100 nuclear weapons,once the divide between O and 10 has beencrossed? Third, would NATO not be adequatelydeterred by the prospect of Soviet retaliation with10 of its nuclear weapons against 10 vital NATOtargets? Last, suppose NATO used 10 cruise mis-siles, against which the BMD was powerless, in-stead of 10 ICBM RVs?

The persuasiveness of this second goal for less-than-perfect BMDs therefore depends on one’sviews of the roles and risks of nuclear weapons—views that are fundamental and deeply held. Thisgoal is therefore one of the most controversialof all.

3. Save lives.5 Another goal for BMD is purelyhumanitarian and seeks no military or strategicadvantage. If the defense did not interfere toomuch with Soviet military targeting objectives(enough for the Soviets to try to overcome it), andassuming the Soviets have no explicit aim to in-flict human casualties, the United States couldexpect some reduction in fatalities in a nuclearwar even from a modest defense. This reductionwould necessarily be limited, since Soviet militaryobjectives include destruction of many targetscollocated with population. BMD and civil de-fense measures would be mutually reinforcing.

Analogous discussion of civil defense has al-ways revealed an inherent tension between thehumanitarian objective of defense and a relatedstrategic objective. The strategic objective seeksto reduce fatalities and damage in order to en-hance U.S. “flexibility” in a crisis, to allow theUnited States to “coerce” the U.S.S.R. (or avoidcoercion) from a position of reduced vulnerability,or to enhance U.S. ability to persist in its war ef-fort despite receiving a Soviet nuclear strike. Thesupposed result of the BMD deployment is to al-low the U.S. President, in dealing with the Sovi-et leadership in time of crisis, to be more willing

‘This d Iscussion borrows from the author’s previous work I nIJ//IsfIc Mlssl/e Defense, op. cit., Chapter 4.

or appear to be more willing to resort to nuclearwar because the consequences to the UnitedStates are presumed smaller.

The coexistence of the humanitarian and stra-tegic objectives for the analogous case of civil de-fense is apparent in the literature on civil defense.The Defense Department6 has argued that theUnited States should have the same crisis reloca-tion options as the U.S.S.R. for two reasons, onestrategic and one humanitarian: 1 ) “to be ableto respond in kind if the Soviet Union attemptsto intimidate us in time of crisis by evacuatingthe population from its cities”; and 2) “to reducefatalities if an attack on our cities appears immi-nent.” Prominent scientists arguing for civil de-fense have also maintained that, “A nation’s civildefense preparedness may determine the balanceof power in some future nuclear crisis. . . . In ouropinion, we must strive for an approximatelyequal casualty rate”.7 More recently, the HighFrontier Study urging strengthened U.S. strategicdefenses stated: “The protection of our citizensmust be prime, but civil defense . . . would re-duce the possibility that the United States couldbe coerced in a time of crisis”. a

In practice, therefore, the humanitarian andstrategic objectives are likely to be difficult todisentangle. Unlike the humanitarian objective,the strategic objective might stimulate a Sovieteffort to put the same number of American livesat risk regardless of the defense. In this way, theSoviet Union could retain the strategic advantagethat, by hypothesis, the BMD deprives them of.The issue then becomes the usual one of the cost-exchange ratio measuring the price to the SovietUnion of retaining its “advantage” relative to theprice of the U.S. defense.

The Defense Department has stated that sav-ing lives in time of war is not the purpose of Presi-dent Reagan’s BMD initiative.9

bAnnual De{ense Department Report, FY 1976, p. 11-24.7Arthur A. Broyles and Eugene P . Wlgner, ‘ ‘C IV I I Defense [n

Llmlted War, ” P h y s i c s Today, VOI 29 (April 1976), pp. 45-46,

‘Daniel 0. Graham, The Non-Nuc/ear Detense ot’ Clfies: The HighFrontier Space-Based Det’ense Against ICBM Attack (Abt Books,1983), p. 122.

‘See footnote 8 2,

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4. Shape the course of the arms competitionand arms control.10 One version of this goal seesthe Soviet tendency to upgrade and proliferateexisting ICBM forces as the principal impedimentto arms control. By introducing BMD (or evendiscussing it), according to this view, the UnitedStates makes the Soviets unsure about the nextstep in the arms competition and thus undercutsthe momentum of Soviet strategic programs, es-pecially ICBM modernization. Though fast-burn-ing Midgetman boosters might defeat boost-phasedefenses, this argument goes, the slow-burningSS-18s and SS-19s will not. BMD might not beable to make all nuclear weapons impotent andobsolete, but it can make large Soviet ICBMs im-potent and obsolete–something the U.S. hasbeen trying to do for a decade. Perhaps efficientdefenses will “force” the Soviets to emphasizesubmarines, bombers, and cruise missiles in theirstrategic arsenal to the same degree the UnitedStates does. (One problem with this line of argu-ment is that by the time the defense is in place,present-generation Soviet ICBMs might alreadybe replaced.)

Another line of argument holds that a majorBMD initiative strengthens the U.S. negotiatingposition at START. An aggressive BMD programdemonstrates U.S. technological prowess andhints at what the Soviets could face if this prow-ess were unleashed. It would seem that newBMD initiatives might not coexist easily with thereductions in offensive arsenals proposed by theUnited States in START, however. Since U.S.BMD is equivalent to attrition of the Soviet ICBMarsenal, any anxieties the Soviets feel at reduc-

IoPreSldentlal science adviser George A. Keyworth, speech beforethe Washington chapter of the Armed Forces Communications andElectronics Association, as reported in Defense Week (Oct. 17,1983):

“Although the strategic defense program’s goal would still be even-tual deployment of a working system, we shouldn’t overlook itspotential beneficial Impact on arms reduction as its progresses. ”

Richard DeLauer, Undersecretary of Defense for Research andEngineering, has said that an arms control agreement is neededto prevent the Soviets from overcoming a defensive system: “Withunconstrained proliferation [of Soviet missiles], no defensive systemwill work.” (Interview with The New York Times, May 18, 1983).

ing the size of their missile inventories would,logically at least, be enhanced by a simultaneousU.S. BMD buildup. Politically, it would seem un-likely, though certainly not impossible, that aclimate favorable to far-reaching offensive armscontrol would also foster an amicable dismantl-ing of the ABM Treaty.

5. Respond to Soviet BMD efforts. Manyanalysts view with alarm Soviet strategic defenseactivities, including upgrading of the MoscowABM, development of a transportable terminalBMD system, construction of a radar in appar-ent violation of the ABM Treaty, development ofdefenses against tactical ballistic missiles, incorpo-ration of limited BMD capability in air defenses,and continued attention to other damage-limitingmethods (civil defense, air defense, antisubma-rine warfare, and countersilo ICBMs). A strongU.S. BMD research and development programmight deter the Soviets from breaking out of theABM Treaty and from continued encroachmentson the Treaty’s provisions. It is frequently notedthat aggressive U.S. research into penetration aidsand other methods for countering defenses mightbe an even more effective way to demonstrateto the Soviets that they would be ill-advised tooverturn the ABM Treaty’s “freeze” on missiledefenses.

6. Protect against accidental missile launchesand attack from other nuclear powers. Thesegoals have been put forward several times in thepast, most notably in the late 1960’s when theJohnson Administration proposed the SentinelABM system to counter Chinese ICBMs, believedat that time to be fast-emerging. Neither goalfigures prominently in today’s discussion of BMDin the United States, though defense against Chi-nese, British, and French missiles could well loomlarger in Soviet thinking. Emerging nuclear pow-ers or terrorists would be unlikely to use ICBMsto deliver their small nuclear arsenals to theUnited States. BMD is therefore of little impor-tance in staving off the threat to U.S. securityposed by nuclear proliferation.

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9.2 SIDE EFFECTS OF BMD DEPLOYMENT

The inevitable side effects of a major strategicinitiative such as BMD might turn out to match,both in magnitude and in duration, the beneficialeffects of satisfying the goal emphasized by thesystem’s purveyors. The public and policy makerswould therefore need to assess the net, long-termeffect of adding BMD to the strategic equation,and not just the achievement of a certain discretegoal as if by surgical intervention. This sectionreviews the well-known list of BMD side effects.Many of these effects are detrimental to U.S. se-curity and would need to be balanced against thebenefits of fulfilling the modest goals of less-than-perfect defense. In making this assessment, it isimpossible to ignore the many unknowns and un-certainties that make it impossible to comparetoday’s world without BMD to a future world withBMD.

1. First strike versus ragged retaliation. It is fre-quently noted that BMD ends up being a betterinvestment for the side that strikes first than forthe side that retaliates. Weapon systems thatcreate relative advantages to striking first in a crisis(rather than risking being struck while seeking apeaceful resolution) are defined to be “destabiliz-ing.” The side striking first uses its full arsenal inan organized penetration of the other side’s de-fense; the retaliating side can only use its surviv-ing arsenal in a possibly disorganized “raggedretaliation” against a forewarned and fully pre-pared defense.

Mitigating factors could in certain circum-stances soften this classical statement of the de-stabilizing effect of BMD. First, truly effectivedefenses might prevent the first striker from de-stroying a substantial fraction of the other side’sretaliatory forces. Second, with proper planning(involving post-attack retargeting and coordinatedtiming), the retaliating forces might still be ableto mount a tailored, efficient strike. Third, therewill seemingly always be a relative advantage tobeing the side that strikes first in a nuclear war,with BMD or without BMD; but this calculus ofrelative advantage is far from being the only fac-tor in deterrence. Other stabilizing factors mightbe strengthened by BMD, offsetting this desta-

bilizing factor. Thus BMD might also discouragetemptations to strike first, by threatening todisrupt the attack.

2. Soviet BMD. A U.S. BMD deployment wouldseem very likely to stimulate a Soviet deployment.Even if the Soviets saw no compelling military ra-tionale for following suit, political appearancescould prove decisive. A Soviet BMD counter-de-ployment would obviously blunt U.S. offensivestriking power, which the U.S. has been spend-ing a great deal to build up. If the U.S. deploy-ment sought to protect its ICBMs from preemp-tive destruction in their silos (Goal 1 above), theSoviet BMD might nonetheless nullify the U.S.ICBMs–this time in flight to their targets. SovietBMD would also introduce a threat to U.S. SLBMs,which are today thought to be virtually immuneto Soviet disruption and to be significantly ad-vanced relative to their Soviet counterparts. If theU.S. deployment sought to prevent “limited”strikes by the Soviets Union (Goal 2), the SovietBMD might in turn preclude a U.S. option to usenuclear weapons selectively and flexibly in sup-port of its NATO allies–an option sometimesseen as central to NATO strategy. Clearly the ac-tual effect of the Soviet BMD counterdeploymentwould depend upon its technical characteristicsand the targets it defended.

3. Demise of the ABM Treaty. An arms con-trol treaty obviously cannot serve as its own jus-tification, and presumably virtually everyonewould agree to the abandonment of the ABMTreaty the moment it ceased genuinely to servethe national security. In addition to its concreteprovisions limiting BMD deployment, however,the ABM Treaty has unavoidably assumed a sym-bolic political meaning in the United States and,in different forms perhaps, in Europe and theU.S.S.R. The Treaty stands for a decade of armscontrol and attempts at superpower understand-ing about nuclear weapons. As a practical mat-ter, it is impossible to overturn the Treaty’s tech-nical provisions without calling into question U.S.commitment to the whole fabric of the SALT/START process. This side effect would have to beweighed against the purely military and strategic

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benefit (if there were, in fact, a net long-term ben-efit) of a U.S. BMD deployment.

4. Allied and Chinese missile forces. The nu-clear missile forces of Britain, France and Chinaare obviously a greater threat to the Soviet Unionthan to the U.S. Most analysts agree that the ex-istence of these forces enhances U.S. security.But a major BMD initiative sparking widespreadSoviet defense would in effect disarm our allies(to a degree depending on the nature of the So-viet deployment).

5. Accompanying strategic programs. A numberof new weapon systems and strategic programswould be natural, though perhaps not necessary,accompaniments to BMD. On the offensive side,the U.S. would need to develop and deploy pen-etration aids against the Soviet BMD and improveits bomber and cruise missile forces to reflectadded reliance on non-missile delivery vehicles.on the defensive side, the overall category of“strategic defense” comprises, in addition toBMD: nationwide air defenses against Sovietbombers and cruise missiles, defensive coverageagainst SLBMs, civil defense shelters and evacua-tion plans, and passive “hardening” of militaryinstallations and industrial facilities.

6. Opportunity Costs. The initial investmentin BMD deployment, the inevitable follow-ens,and any accompanying strategic programs wouldmake a substantial, permanent demand on thedefense budget, competing with other nuclearforces and with conventional forces, not to men-tion with nonmilitary expenditures.

In a more fundamental sense, the transitionfrom a world with a near-total ban on BMD toa world with BMD deployments is probably anirreversible change. Reimposing a defensive“freeze” after a period of unrestrained deploy-ment, much less dismantling defenses and return-ing to zero, would involve all of the problems that

attend upon arms control reductions at STARTtoday. Extra caution seems warranted where stra-tegic actions cannot easily be reversed or re-called: the opportunity for a comprehensive banon missile defense might not arise again.

7. Bean counting. Strategists, politicians, anddiplomats place considerable emphasis on quan-titative measures of the nuclear balance and on“proofs” that “parity” exists. Arms controlnegotiations also reduce themselves quickly tocounting rules. It is unclear whether or how BMDshouId affect such “bean counting. ” For eachU.S. battle station added to a defensive constella-tion, are the Soviets to be credited with fewerICBMs, since the U.S. defense represents poten-tial attrition of the Soviet force? How many So-viet interceptor missiles equals one U.S. laser?Whose estimate of the BMD’s likely wartime per-formance–the defense’s or the offense’s-–gov-erns these counting rules? Experience indicatesthat these types of questions, however far-fetchedand even preposterous they appear in prospect,in the end assume considerable perceived im-portance.

8. Asymmetries. The Soviet BMD deploymentthat could well follow U.S. deployment might notshare the same defensive goal or the same tech-nology, stimulating the usual anxieties about une-qual intentions and capabilities. Defensive sys-tems are also complex, leading different analyststo widely different conclusions about the likelywartime performance of the BMD systems onboth sides. Moreoever the owner of the BMD,aware of all the system’s hidden flaws, mightcredit it with little capability, whereas the offenseplanner will tend to give it the benefit of thedoubt. Though some hypothetical future worldwith mutual BMD deployments might thereforeappeal to one analyst or nation, another couldeasily have a completely different view of thetechnical and strategic “facts.”

Section 10

PRINCIPAL JUDGMENTS ANDOBSERVATIONS

Section 10

PRINCIPAL JUDGMENTS AND OBSERVATIONS

1. The prospect that emerging “Star Wars”technologies, when further developed, will pro-vide a perfect or near-perfect defense system,literally removing from the hands of the SovietUnion the ability to do socially mortal damageto the United States with nuclear weapons, isso remote that it should not serve as the basisof public expectation or national policy aboutballistic missile defense (BMD). This judgmentappears to be the consensus among informedmembers of the defense technical community.

Technical prognosis for such a perfect or near-perfect defense is extremely pessimistic becauseof the concentration and fragility of society; be-cause alI concepts identified as candidates for afuture defense of population are known to be sus-ceptible to countermeasures that would permitthe Soviet Union to retain a degree of penetra-tion with their future missile arsenal despite costlyattempts to improve the U.S. defense; becausethe Soviet Union would almost certainly makesuch a determined effort to avoid being disarmedby a U.S. defense; and because missile defensedoes not address other methods for delivering nu-clear weapons to the United States.

Mutual assured destruction (MAD), if this termis applied to a state of technological existencerather than to a chosen national policy, is likelyto persist for the foreseeable future.

2. The wisdom of deploying less-than-perfectballistic missile defenses remains controversial.Less-than-perfect defenses would still allow theSoviet Union to destroy U.S. society in a massiveattack but might call into question the effective-ness of smaller, specialized nuclear strikes.

Certain theories about nuclear war maintainthat such defenses could lessen the chances ofnuclear war and enhance U.S. security by pro-tecting U.S. retaliatory forces; by interdicting“limited” nuclear strikes; by further confusing So-viet predictions of the outcome of a strike; bydriving Soviet missile deployments in directionsfavored by the United States; by lessening theconsequences of nuclear attack; and/or by fulfill-ing still other strategic goals.

Critics dispute the validity of some of thesegoals; dispute that technology can fulfill the truly

useful goals; and/or argue that the many harm-ful side effects of introducing BMD to the strate-gic equation and altering the Anti-Ballistic Missile(ABM) Treaty regime are not worth satisfyingthese goals.

To address the wisdom of less-than-perfect de-fense, the public and policy makers would needa precise statement of the strategic goal of thedeployment, an assessment of whether technol-ogy could satisfy that goal, and an analysis bal-ancing fuIfillment of the goal against the side ef-fects and uncertainties of introducing a newingredient into the strategic nuclear arena.

3. The strategic goal of President Reagan’sStrategic Defense Initiative calling for empha-sized BMD research—perfect, near-perfect, orless-than-perfect defense against ballistic mis-siles—remains unclear. No explicit technicalstandards or criteria are therefore availableagainst which to measure the technological pros-pects and progress of this initiative.

4. In all cases, directed-energy weapons andother devices with the specifications needed forboost-phase intercept of ICBMs have not yetbeen built in the laboratory, much less in a formsuitable for incorporation in a complete defensesystem. These devices include chemical lasers,excimer and free electron lasers, x-ray lasers, par-ticle beams, lightweight high-velocity kinetic en-ergy weapons, and microwave generators, to-gether with tracking, aiming, and pointingmechanisms, power sources, and other essentialaccompaniments.

It is unknown whether or when devices withthe required specifications can be built,

S. Moreover, making the technological devicesperform to the needed specifications in a con-trolled situation is not the crux of the technicalchallenge facing designers of an effective bal-listic missile defense. A distinct challenge is tofashion from these devices a reliable defensivearchitecture, taking into account vulnerability

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of the defense components, susceptibility to fu-ture Soviet countermeasures, and cost relativeto those countermeasures.

New intercept mechanisms–directed energyweapons and the like—therefore do not by them-selves necessarily herald dramatically new BMDcapabilities.

6. It is clear that potent directed-energyweapons will be developed for other militarypurposes, even if such weapons are never in-corporated into effective BMDs. Such weaponsmight have a role in nuclear offense as well asdefense, in anti-satellite (ASAT) attack, in anti-aircraft attack, and in other applications of con-cern to nuclear policy and arms control. Defenseand arms control policy will thus need to facethe advent of these new weapons, irrespectiveof their BMD dimension.

7. For modest defensive goals requiring less-than-perfect performance, traditional reentryphase defenses and/or more advanced mid-course defenses might suffice. Such defensespresent less technical risk than systems that in-corporate a boost-phase layer, and they couldprobably be deployed more quickly.

New ideas for improving such “old” BMD con-cepts have emerged in the atmosphere of tech-nical optimism enjoyed by the boost-phaseconcepts.

8. Deployment of missile defenses based onnew technologies is forbidden by the Anti-Bal-listic Missile (ABM) Treaty reached at SALT 1. TheTreaty permits only restricted deployment of tra-ditional BMDs using fixed, ground-based radarsand interceptor missiles. Research into new tech-nologies, and in selected cases development andtesting of defense systems based on these tech-nologies, are allowed within the Treaty.

9. There is a close connection, not exploredin detail in this Background Paper, between ad-vanced BMD concepts and future anti-satellite(ASAT) systems. This connection springs fromfour observations: 1) ASAT attack on space-basedweapons and sensors is probably the most attrac-tive countermeasure to boost-phase BMD; 2) di-rected-energy weapons are more likely to suc-ceed in the easier mission of ASAT than in themore difficult mission of boost-phase BMD; 3) toa degree dependent on technical details, earlystages of development of boost phase BMDsmight be conducted in the guise of ASAT devel-opment, stimulating anxieties about the healthof the ABM Treaty regime; 4) to a degree depend-ent on technical details, concluding a treaty withthe Soviet Union limiting ASAT developmentwould impede BMD research at an earlier stagethan would occur under the terms of the ABMTreaty alone.

APPENDIXES

APPENDIX A: THE CONCLUSION OF PRESIDENTREAGAN’S MARCH 23, 1983, SPEECH ON DEFENSE

SPENDING AND DEFENSIVE TECHNOLOGY— —

Weekly Compilation of.

PresidentialDocuments

Monday, March 28, 1983Volume 19—Number 12

Pages 423-466

N O , thus far tonight I’ve shared wi thyou my thoughts on the problems of nation-al security we must face together. My pred-ecessors in the Oval Office have appearedbefore yOU on other occasions to describethe threat posed by Soviet power and haveproposed steps to address that threat. B u tsince the advent of nuclear weapons, thoses t e p s have been increasingly di rectedtoward deterrence of aggression throughthe promise of retaliation.

This approach to stability through offen-sive threat has worked. We and our allieshave succeeded in preventing nuclear warfor more than three decades. In recentmonths, however, my advisers, including in

particular the Joint Chiefa of Staff, have un-derscored the necessity to break out of afuture that relies solely on offensive retali-ation for our security.

Over the course of these discussions, I’vebecome more and more deeply convincedthat the human spir i t must be capable ofrising above dealing with other nations andh u m a n beings by threatening their exist-ence. Feeling this way, I believe we mustthorough])’ examine every opportunity forreducing tensions and for introducing great-er stability into the strategic calculus onboth sides.

One of the most important contributionswe can make is, of course, to lower t h elevel of all arms, and particularly nucleararms. We're engaged right now in severalnegotiations with the Soviet Union to bringabout a mutual reduction of weapons. I willreport to you a week from tomorrow mythoughts on that score. But let me just say,I’m totally committed to this course.

If the Soviet Union will join with us inour effort to achieve major arms reduction,we will have succeeded in stabilizing thenuclear balance. Nevertheless, it will still benecessary to rely on the specter of retali-ation, on mutual threat. And that’s a sadcommentary on the human condition.Wouldn’t it be better to save lives than toavenge them? Are we not capable of dem-onstrating our peaceful intentions by apply-ing all our abilities and our ingenuity toachieving a truly lasting stability? I thinkwe are. Indeed, we must.

After careful consultation with my advis-ers, including the Joint Chiefs of Staff, Ibelieve there is a way. Let me share withyou a vision of the future which offers hope.It is that we embark on a program tocounter the awesome Soviet missile threatwith measures that are defensive. Let u s

turn to the very strengths in technologythat spawned our great industrial base andthat have given us the quality of life weenjoy today.

What if free people could live secure inthe knowledge that their security did notrest upon the threat of instant U.S. retali-ation to deter a Soviet attack, that we couldintercept and destroy strategic ballistic mis-siles before they reached our own soil orthat of our allies?

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I know this is a formidable, technical task,one that may not be accomplished beforethe end of this century. Yet, current tech-nology has attained a level of sophisticationwhere it reasonable for us to begin thiseffort. It will take years, probably decadesof effort on many fronts. There will be fail-ures and setbacks, just as there will be suc-cesses and breakthroughs. And as we pro-ceed, we must remain constant in preserv-ing the nuclear deterrent and maintaining asolid capability for flexible response. B u tisn’t it worth every investment necessary tofree the world from the threat of nuclearwar? We know it is.

In the meantime, we will continue topursue real reductions in nuclear arms, ne-gotiating from a position of strength thatcan be ensured only by modernizing ourstrategic forces. At the same time, we m u s ttake steps to reduce the risk of a conven-tional military conflict escalating to nuclearwar by improving our non-nuclear capabili-ties.

America does possess-now-the technol-ogies to attain very significant improve-ments in the effectiveness of our conven-tional, non-nuclear forces. Proceedingboldly with these new technologies, we cansignificantly reduce any incentive that theSoviet Union may have to threaten attackagainst the United States or its allies.

As we pursue our goal of defensive tech-nologies, we recognize that our allies relyupon our strategic offensive power to deterattacks against them. Their vital interestsa n d o u r s a r c i n e x t r i c a b l y l i n k e d . T h e i rsafety and ours are one. And no change intechnology can or will alter that reality. Wemust and shall continue to honor our com-mitments.

1 clearly recognize that defensive systemshave limitations and raise certain problemsand ambiguit ies. If paired with offensivesystems, they can be viewed as fostering a na g r e s s i v e p o l i c y , and no one wants thatBut with these considerations firmly inmind. I call upon the scientific communityin our country, those who gave us nuclear

for closer consultation with our allies, I’mtaking an important first step. I am direct-ing a comprehensive and intensive effort todefine a long-term research and development program to begin to achieve our ulti-mate goal of eliminating the threat posedby strategic nuclear missiles. This couldpave the way for arms control measures toeliminate the weapons themselves. We seekneither military superiority nor political ad-vantage. Our only purpose-one all peopleshare—is to search for ways to reduce thedanger of nuclear war.

My fellow Americans, tonight we’relaunching an effort which holds the promiseof changing the course of human history.There will be risks, and results take time.But I believe we can do it. As we cross thisthreshold, I ask for your prayers and yoursupport.

Thank you, good night, and Cod blessyou.

Note: The President spoke at 8:02 p.m. fromthe Oval Office at the White House. Theaddress was broadcast live on notion wideradio and television.

Following his remarks, the President metin the White House with o number of ad-ministration officials, including membersof the Cabinet, the White House staff, andthe Joint Chiefs of Staff and former offi-cials of past administrations to discuss theaddress.

APPENDIX B: ABM TREATYAND RELATED DOCUMENTS

—— — . ———-——

1980 EDITION

UNITED STATESARMS CONTROLAND

DISARMAMENTAGENCY

AGREEMENTS

TEXTS AND HISTORIES

WASHINGTON, D. C., 20451

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Treaty Between the United States of America and theUnion of Soviet Socialist Republics on the Limitation ofAnti-Ballistic Missile Systems

Signed at Moscow May 26, 1972Ratification advised by U.S. Senate August 3, 1972Ratified by U.S. President September 30, 1972Proclaimed by U.S. President October 3, 1972Instruments of ratification exchanged October 3, 1972Entered into force October 3, 1972

The United States of America and the Union of Soviet Socialist Republics,hereinafter referred to as the Parties,

Proceeding from the premise that nuclear war would have devastatingconsequences for all mankind,

Considering that effective measures to limit anti-balllstic missile systems would be asubstantial factor in curbing the race in strategic offensive arms and would lead to adecrease in the risk of outbreak of war involving nuclear weapons,

Proceeding from the premise that the Iimitation of anti-ballistic missile systems, aswell as certain agreed measures with respect to the Imitation of strategic offensivearms, would contribute to the creation of more favorable conditions for furthernegotiations on Iimiting strategic arms,

Mindful of their obligations under Article VI of the Treaty on the Non- Proliferation ofNuclear Weapons,

Declaring their intention to achieve at the earnest possible date the cessation of thenuclear arms race and to take effective measures toward reductions in strategic arms,nuclear disarmament, and general and complete disarmament,

Deskiring to contribute to the relaxation of International tension and the strengthen-ing of trust between States,

Have agreed as follows

Article I

1 Each party undertakes to Iimit anti-ballistic missile (ABM) systems and to adoptother measures in accordance with the provisions of this Treaty.

2 Each Party undertakes not to deploy ABM systems for a defense of the territory ofits country and not to provide a base for such a defense, and not to deploy ABMsystems for defense of an individual region except as provided for in Article III of thisTreat y

Article II

1 For the purpose of this Treaty an ABM system is a system to counter strategicballistic missiles or their elements in flight trajectory, currently consisting of:

(a) ABM Interceptor missiles, which are Interceptor missiles constructed anddeployed for an ABM role, or of a type tested in an ABM mode,

8 9

ARMS CONTROL AND DISARMAMENT AGREEMENTS

(b) ABM launchers, which are launchers constructed and deployed for launchingABM interceptor missiles; and

(c) ABM radars, which are radars constructed and deployed for an ABM role, or ofa type tested in an ABM mode.

2. The ABM system components listed in paragraph 1 of this Article include thosewhich are:

(a)(b)(c)(d)(e)

operational;under construction;undergoing testing;undergoing overhaul, repair or conversion; ormothballed

Article Ill

Each Party undertakes not to deploy ABM systems or their components except that.

(a) within one ABM system deployment area having a radius of one hundred and fiftykilometers and centered on the Party’s national capital, a Party may deploy (1) no more

than one hundred ABM launchers and no more than one hundred ABM Interceptormissiles at launch sites, and (2) ABM radars within no more than SIX ABM radarcomplexes, the area of each complex being Circular and having a diameter of no morethan three kilometers; and

(b) within one ABM system deployment area having a radius of one hundred andfifty kilometers and containing ICBM Silo launchers, a Party may deploy’ (1) no more

than one hundred ABM launchers and no more than one hundred ABM InterceptormissiIes at launch sites, (2) two large phased-array ABM radars comparable inpotential to corresponding ABM radars operational or under construction on the dateof signature of the Treaty in an ABM system deployment area containing ICBM Silolaunchers, and (3) no more than eighteen ABM radars each having a potential less thanthe potential of the smaller of the above-mentioned two large phased-array ABMradars.

Article IV

The Iimitations provided for in Article III shall not apply to ABM systems or theircomponents used for development or testing, and located within current oradditionally agreed test ranges, Each Party may have no more than a total of fifteenABM launchers at test ranges.

Article V

1 Each Party undertakes not to develop, test, or deploy ABM systems or

components which are sea-based, air-based, space-based, or mobile land-based2. Each Party undertakes not to develop, test, or deploy ABM launchers for launch-

ing more than one ABM interceptor missile at a time from each launcher, not tomodify deployed launchers to provide them with such a capability, not to develop, test,or deploy automatic or semi-automatic or other similar systems for rapid reload ofABM launchers.

Article VI

To enhance assurance of the effectiveness of the limitations on ABM systems andtheir components provided by the Treaty, each Party undertakes

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SALT ONE – ABM TREATY

(a) not to give missiles, launchers, or radars, other than ABM interceptor missiles,ABM launchers, or ABM radars, capabilities to counter strategic ballistic missiles ortheir elements in flight trajectory, and not to test them in an ABM mode; and

(b) not to deploy in the future radars for early warning of strategic ballistic missileattack except at locations along the periphery of its national territory and orientedoutward.

Article Vll

Subject to the provisions of this Treaty, modernization and replacement of ABMsystems or their components may be carried out.

Article Vlll

ABM systems or their components in excess of the numbers or outside the areasspecified in this Treaty, as well as ABM systems or their components prohibited by thisTreaty, shall be destroyed or dismantled under agreed procedures within the shortestpossible agreed period of time.

Article IX

To assure the viability and effectiveness of this Treaty, each Party undertakes not totransfer to other States, and not to deploy outside its national territory, ABM systems ortheir components limited by this Treaty.

Article X

Each Party undertakes not to assume any international obligations which wouldconflict with this Treaty.

Article Xl

The Parties undertake to continue active negotiations for limitations on strategicoffensive arms

Article XII

1. For the purpose of providing assurance of compliance with the provisions of thisTreaty, each Party shall use national technical means of verification at its disposal in amanner consistent with generally recognized principles of international law.

2. Each Party undertakes not to Interfere with the national technical means ofverification of the other Party operating in accordance with paragraph 1 of this Article.

3. Each Party undertakes not to use deliberate concealment measures whichimpede verification by national technical means of compliance with the provisions ofthis Treaty. This obligation shall not require changes in current construction,assembly, conversion, or overhaul practices.

Article XIII

1. To promote the objectives and implementation of the provisions of this Treaty, theParties shall establish promptly a Standing Consultative Commission, within theframework of which they will:

(a) consider questions concerning compliance with the obligations assumed andrelated situations which may be considered ambiguous;

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ARMS CONTROL AND DISARMAMENT AGREEMENTS

(b) provide on a voluntary basis such information as either Party considersnecessary to assure confidence in compliance with the obligations assumed,

(c) consider questions involving unintended Interference with national technicalmeans of verification,

(d) consider possible changes in the strategic situation which have a bearing onthe provisions of this Treaty;

(e) agree upon procedures and dates for destruction or dismantling of ABMsystems or their components in cases provided for by the provisions of this Treaty;

(f) consider, as appropriate, possible proposals for further increasing the viabilityof this Treaty; including proposals for amendments in accordance with theprovisions of this Treaty,

(g) consider, as appropriate, proposals for further measures aimed at Iimitingstrategic arms.

2 The Parties through consultation shall establish, and may amend as appropriate,Regulations for the Standing Consultative Commission governing procedures,composition and other relevant matters.

Article XIV

1 Each Party may propose amendments to this Treaty Agreed amendments shallenter into force in accordance with the procedures governing the entry into force of

this Treaty.2 Five years after entry into force of this Treaty, and at five-year internals thereafter,

the Parties shall together conduct a review of this Treaty.

Article XV

1 This Treaty shall be of unlimited duration.2. Each Party shall, in exercising its national sovereignty, have the right to withdraw

from this Treaty if it decides that extraordinary events related to the subject matter ofthis Treaty have jeopardized its supreme Interests. It shall give notice of its decision tothe other Party six months prior to withdrawal from the Treaty. Such notice shallinclude a statement of the extraordinary events the notifying Party regards as havingjeopardized its supreme Interests.

Article XVI

1 This Treaty shall be subject to ratification in accordance with the constitutional

procedures of each Party, The Treaty shall enter into force on the day of the exchangeof Instruments of ratification.

2. This Treaty shall be registered pursuant to Article 102 of the Charter of the UnitedNat Ions.

DONE at Moscow on May 26, 1972, in two copies, each in the English and Russianlanguages, both texts being equally authentic.

FOR THE UNITED STATES FOR THE UNION OF SOVIETOF AMERICA SOCIALIST REPUBLICS

President of the UnitedStates of America

General Secretary of the CentralCommittee of the CPSU

9 2

Agreed Statements, Common Understandings, and Uni-lateral Statements Regarding the Treaty Between theUnited States of America and the Union of SovietSocialist Republics on the Limitation of Anti-BallisticMissiles

1. Agreed Statements

The document set forth below was agreed upon and Initialed by the Heads of theDelegations on May 26, 1972 (letter designations added);

AGREED STATEMENTS REGARDING THE TREATY BETWEEN THE UNITEDSTATES OF AMERICA AND THE UNION OF SOVIET SOCIALIST REPUBLICS ONTHE LIMITATION OF ANTI-BALLISTIC MISSILE SYTEMS

[A]

The Parties understand that, in addition to the ABM radars which maybe deployed inaccordance with subparagraph (a) of Article Ill of the Treaty, those non-phased-arrayABM radars operational on the date of signature of the Treaty within the ABM systemdeployment area for defense of the national capital may be retained.

[B]

The Parties understand that the potential (the product of mean emitted power inwatts and antenna area in square meters) of the smaller of the two large phased-arrayABM radars referred to in subparagraph (b) of Article Ill of the Treaty is considered forpurposes of the Treaty to be three million.

[c]

The Parties understand that the center of the ABM system deployment area centeredon the national capital and the center of the ABM system deployment area containingICBM silo launchers for each Party shall be separated by no less than thirteen hundredkilometers.

[D]

In order to insure fulfillment of the obligation not to deploy ABM systems and theircomponents except as provided in Article Ill of the Treaty, the Parties agree that in theevent ABM systems based on other physical principles and including componentscapable of substituting for ABM interceptor missiles, ABM launchers, or ABM radarsare created in the future, specific limitations on such systems and their componentswould be subject to discussion in accordance with Article Xlll and agreement inaccordance with Article XIV of the Treaty.

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ARMS CONTROL AND DISARMAMENT AGREEMENTS

[E]

The Parties understand that Article V of the Treaty includes obligations not todevelop, test or deploy ABM interceptor missiles for the delivery by each ABMinterceptor missile of more than one independently guided warhead.

[F]

The Parties agree not to deploy phased-array radars having a potential (the productof mean emitted power in watts and antenna area in square meters) exceeding threemillion, except as provided for in Articles Ill, IV and VI of the Treaty, or except for thepurposes of tracking objects in outer space or for use as national technical means ofverification.

[G]

The Parties understand that Article IX of the Treaty includes the obligation of the USand the USSR not to provide to other States technical descriptions or blue printsspecially worked out for the construction of ABM systems and their componentsIimited by the Treaty.

2. Common Understandings

Common understanding of the Parties on the following matters was reached duringthe negotiations:

A. Location of ICBM Defenses

The U.S. Delegation made the following statement on May 26, 1972:

Article III of the ABM Treaty provides for each side one ABM system deploymentarea centered on its national capital and one ABM system deployment area contain-ing ICBM silo launchers. The two sides have registered agreement on the followingstatement: “The Parties understand that the center of the ABM system deploymentarea centered on the national capital and the center of the ABM system deploymentarea containing ICBM silo launchers for each Party shall be separated by no lessthan thirteen hundred kilometers.” in this connection, the U.S. side notes that itsABM system deployment area for defense of ICBM silo launchers, located west ofthe Mississippi River, will be centered in the Grand Forks ICBM silo launcher de-ployment area. (See Agreed Statement [C].)

B. ABM Test Ranges

The U.S. Delegation made the following statement on April 26, 1972:

Article IV of the ABM Treaty provides that “the limitations provided for in Article IIIshall not apply to ABM systems or their components used for development or testing,and located within current or additionally agreed test ranges. ” We believe it would beuseful to assure that there is no misunderstanding as to current ABM test ranges. it isour understanding that ABM test ranges encompass the area within which ABMcomponents are located for test purposes. The current U.S. ABM test ranges are atWhite Sands, New Mexico, and at Kwajalein Atoll, and the current Soviet ABM testrange is near Sary Shagan in Kazakhstan. We consider that non-phased array radarsof types used for range safety or instrumentation purposes maybe located outside ofABM test ranges. We Interpret the reference in Article IV to “additionally agreed test

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ranges” to mean that ABM components will not be located at any other test rangeswithout prior agreement between our Governments that there will be such additionalABM test ranges.

On May 5, 1972, the Soviet Delegation stated that there was a commonunderstanding on what ABM test ranges were, that the use of the types of non-ABMradars for range safety or Instrumentation was not limited under the Treaty, that thereference in Article IV to “additionally agreed” test ranges was sufficiently clear, andthat national means permitted identifying current test ranges.

C Mobile ABM Systems

On January 29, 1972, the U.S. Delegation made the following statement:

Article V(l) of the Joint Draft Text of the ABM Treaty includes an undertaking notto develop, test, or deploy mobile land-based ABM systems and their components.On May 5, 1971, the U.S. side Indicated that, in its view, a prohibition on deploymentof mobile ABM systems and components would rule out the deployment of ABMlaunchers and radars which were not permanent fixed types. At that time, we askedfor the Soviet view of this interpretation. Does the Soviet side agree with the U.S.side's Interpretation put forward on May 5, 1971?

On Apri l 13, 1972, the Soviet Delegat ion said there IS a g e n e r a l c o m m o nunderstanding on this matter.

D. Standing Consultative Commission

Ambassador Smith made the following statement on May 22, 1972

The United States proposes that the sides agree that, with regard to initial

Implementat ion of the ABM Treaty’s Art ic le Xl l l on the Standing Consultat ive

Commission (SCC) and of the consultation Articles to the Interim Agreement onoffensive arms and the Accidents Agreement, ’ agreement establishing the SCC willbe worked out early in the follow-on SALT negotiations; until that IS completed, thefollowing arrangements will prevail: when SALT IS in session, any consul tat ion

desired by either side under these Articles can be carried out by the two SALTDelegations, when SALT IS not in session, ad hoc arrangements for any desiredconsultations under these Articles may be made through diplomatic channels.

Minister Semenov replied that, on an ad referendum basis, he could agree that theU.S. statement corresponded to the Soviet understanding

E. Standstill

On May 6, 1972, Minister Semenov made the following statement.

In an effort to accommodate the wishes of the U S side, the Soviet Delegation I S

prepared to proceed on the basis that the two sides will in fact observe theobligations of both the Interim Agreement and the ABM Treaty beginning from thedate of signature of these two documents.

In reply, the U.S. Delegation made the following statement on May 20, 1972:

‘see Article 7 of Agreement to Reduce the Risk of Outbreak of Nuclear War Betweenthe United States of America and the Union of Soviet Socialist Republics, signed Sept.30, 1971

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The U.S. agrees in principle with the Soviet statement made on May 6 concerningobservance of Obligations beginning from date of signature but we would Iike tomake clear our understanding that this means that, pending ratification andacceptance, neither side would take any action prohibited by the agreements afterthey had entered into force This understanding would continue to apply in theabsence of notification by either signatory of its Intent Ion not to proceed withratification or approval

The Soviet Delegation Indicated agreement with the U S. statement

3. Unilateral Statements

The following noteworthy unilateral statements were made during the negotiationsby the United States Delegation

A. Withdrawal from the ABM Treaty

On May 9, 1972, Ambassador Smith made the following statement.

The U.S. Delegation has stressed the Importance the U. S. Government attaches toachieving agreement on more complete Iimitations 011 strategic offensive arms,following agreement on an ABM Treaty and on an Interim Agreement on certainmeasures with respect to the Iimitation of strategic offensive arms The U SDelegation believes that an objective of the follow-on negotiations should be toconstrain and reduce on a long-term basis threats to the survivability of ourrespective strategic retaliatory forces The USSR Delegation has also Indicated thatthe objectives of SALT would remain unfulfilled without the achievement of anagreement providing for more complete Iimitations on strategic offensive arms. Bothsides recognize that the initial agreements would be steps toward the achievement ofmore complete Iimitations on strategic arms. If an agreement providing for more

complete strategic offensive arms Iimitations were not achieved within five years,

U S supreme Interests could be jeopardized Should that occur, it would constitute abasis for withdrawal from the ABM Treaty The U.S. does not wish to see such asituation occur, nor do we believe that the USSR does It IS because we wish toprevent such a situation that we emphasize the Importance the U.S. Government

attaches to achievement of more complete Iimitations on strategic offensive arms

The U.S. Executive will inform the Congress, in connection with Congressionalconsideration of the ABM Treaty and the Interim Agreement, of this statement of theU S position

B. Tested in ABM Mode

On April 7, 1972, the U.S. Delegation made the following statement.

Article II of the Joint Text Draft uses the term “tested in an ABM mode,” in defining

ABM components, and Article VI includes certain obligations concerning s u c htesting. We believe that the sides should have a common understanding of thisphrase. First, we would note that the testing provisions of the ABM Treaty areintended to apply to testing which occurs after the date of signature of the Treaty,and not to any testing which may have occurred in the past, Next, we would amplifythe remarks we have made on this subject during the previous Helsinki phase bysetting forth the objectives which govern the U.S. view on the subject, namely, whileprohibiting testing of non-ABM components for ABM purposes. not to preventtesting of ABM components, and not to prevent testing of non-ABM components for

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non-ABM purposes. To clarify our interpretation of “tested in an ABM mode, ” wenote that we would consider a launcher, missile or radar to be “tested in an ABMmode” if, for example, any of the following events occur: ( 1 ) a launcher IS used tolaunch an ABM Interceptor missile, (2) an Interceptor missile IS flight tested against atarget vehicle which has a flight trajectory with characteristics of a strategic ballisticmissile flight trajectory, or IS flight tested in conjunction with the test of an ABMInterceptor missile or an ABM radar at the same test range, or IS flight tested to analtitude inconsistent with Interception of targets against which air defenses aredeployed, (3) a radar makes measurements on a cooperative target vehicle of thekind referred to in item (2) above during the reentry portion of its trajectory or makesmeasurements in conjunction with the test of an ABM interceptor missile or an ABMradar at the same test range. Radars used for purposes such as range safety orInstrumentation would be exempt from application of these criteria.

C. No-Transfer Article of ABM Treaty

On April 18, 1972, the U.S. Delegation made the following statement:

In regard to this Article [IX], I have a brief and I believe self-explanatory statementto make. The U.S. side wishes to make clear that the provisions of this Article do notset a precedent for whatever provision may be considered for a Treaty on LimitingStrategic Offensive Arms. The question of transfer of strategic offensive arms IS a farmore complex issue, which may require a different solution.

D. No Increase in Defense of Early Warning Radars

On July 28, 1970, the U.S. Delegation made the following statement:

Since Hen House radars [Soviet ballistic missile early warning radars] can detectand track ballistic missile warheads at great distances, they have a significant ABMpotential. Accordingly, the U.S. would regard any increase in the defenses of suchradars by surface-to-air missiles as inconsistent with an agreement.

APPENDIX C: OTHER APPLICATIONSOF DIRECTED ENERGY WEAPONS

This Background Paper treats only one–andprobably one of the most difficult-military ap-plication of directed energy. Many other applica-tions of widely varying plausibility vie for fund-ing and attention. An assessment of all theseschemes is well beyond the scope of this Paper,but the list below is provided for reference. Men-tion of a scheme does not imply that it has anytechnical or military promise; this question wouldhave to be properly studied.

Anti-satellite (ASAT). Directed energy attack onsatellites from space-, air-, or ground-basedweapons is substantially easier than boost phaseBMD. A satellite’s orbit is completely predicta-ble, making it in effect a fixed target. Long dwelltimes and low fluences suffice for ASAT attackon unshielded satellites. For instance, long il-lumination at just a few watts/cm2 (several timesthe sun’s normal irradiance in space) could upsetthe thermal control systems that allow spacecraftto endure the extremes of heat and cold in outerspace. Substantial hardening of large and com-plex satellites (including sensors) to directedenergy weapons from all directions at all timesis impractical. Unlike BMD, which must handlethousands of boosters in a few minutes, ASATswould have fewer targets and longer attack times.Last, BMDs must operate under the most hostilecircumstances imaginable, whereas the super-powers might use ASATs in scenarios short of nu-clear war.

This Background Paper has stressed (see Sec-tion 5.1) that maturation of the same technologiesinvolved in boost phase BMD virtually assures po-tent ASATs. The so-called “Star Wars” systemscould well be their own worst threats. Besidesthe intrinsic ease of ASAT over BMD, a Soviet de-fense suppression ASAT attack on U.S. defensivebattle stations would have three key factors work-ing in its favor: 1 ) The Soviets would pick the timeand sequence of attack on the U.S. BMD systemand launch of their ICBMs; 2) The Soviets neednot destroy the entire defensive constellation, butonly “punch a hole” for their ICBMs to passthrough; 3) The attack would take place over So-viet territory.

Ground-based laser ASATs, presumably usingexcimer or free-electron lasers for best atmos-pheric propagation, would have the advantagesof large size and power supplies. Airborne laserscould avoid some of the propagation disturb-ances introduced by denser air at low altitudes,but turbulence around the airplane skin couldrequire adaptive beam compensation.

Space-based directed energy ASATs are themost interesting category of all, since they wouldbe, in effect, long-range space mines, Rather thanpositioning itself next to its quarry like an ordinaryspace mine, a laser could be thousands of kilom-eters away and still be able to strike withinmilliseconds upon receipt of a radio signal fromthe gound.

Strategic offense. If they mature, the directedenergy devices discussed for BMD might turn outto have been better termed “offensivebreakthroughs” than “defensive breakthroughs.”Consider, for example, a fleet of Soviet x-raylasers launched simultaneously with (or minutesbefore) a Soviet first-stike ICBM attack. The pop-up x-ray lasers’ job would be to intercept any U.S.ICBMs launched before arrival of Soviet silo-kill-ing RVs. The Soviet x-ray lasers wouId thereforedeprive the U.S. of its option for launch underattack. Microwave generators might be used forEMP-like attack on the U.S. command and con-trol system. Another example of offensive use ofbeam weapons would be Soviet ASAT attack onU.S. warning, communications, nuclear detona-tion detection, or navigation satellites importantto the U.S. retaliatory capability. Yet another ex-ample would of course be suppression of anyU.S. BMD that used space-based weapons orsensors.

Bus intercept. This Background Paper hasfocused on intercept of ICBMs before boosterburnout. Intercept of the bus or post boost vehi-cle poses a rather different challenge. Post-boostphase for today’s ICBMs is rather long (severalminutes) but could be shortened drastically onfuture ICBMs. Bus tracking requires a differentsensor than booster tracking, since the bus plume

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is much less conspicuous, and the bus rocketmotor may not operate continuously. The bus isa target of declining value as it dispenses its RVs.Interruption of bus operation would not preventthe bus and its contents from continuing theirballistic flight to the target country, though theaim might be very wide of the target. Operatingabove the atmosphere, the bus can deploy light-weight shields, decoys, and sensor countermeas-ures (e.g., corner reflectors). On the other hand,x-ray lasers and neutral particle beams that can-not penetrate the atmosphere can attack the busin space.

Anti-SLBM. A number of schemes have beensuggested for using directed energy weaponsagainst SLBMs, besides the obvious extensions ofICBM defense. Thus pop-up x-ray lasers could bepositioned on U.S. coasts or ships at sea to in-tercept SLBMs launched from nearby Soviet sub-marines. Aircraft patrolling coastal waters and car-rying lasers could attack ascending SLBMs in theirarea.

Anti-IRBM. Intermediate range ballistic missiles(IRBMs) have short boost phases and potentiallylow trajectories, making anti-lRBM defense ratherdifferent from anti-lCBM defense and perhapsbetter accomplished with ground-based terminalBMD systems deployed in the theater.

Defense of satellites (DSAT). Low-power wide-divergence (small optics) laser satellites (perhapsHF for high specific energy) could serve as “es-corts” for other satellites, defending the othersatellites from hostile objects—mines, ASAT mis-siles —approaching within a given range.

Anti-aircraft. At least four schemes have beenbroached for using directed energy weaponsagainst aircraft or cruise missiles. The most am-bitious would involve a worldwide constellationof trackers (possibly LWIR) and beam weapons(possibly DF or short wavelength lasers) to attackSoviet Blackjack strategic bombers, Backfirebombers attacking U.S. aircraft carriers, Soviet

airborne command post “Doomsday planes, ” So-viet AWACS radar planes, and so on. In a sec-ond scheme, B-1 or B-52 bombers would be out-fitted with lasers (possibly DF) to protect themfrom Soviet fighters, surface-to-air missiles (SAMs),and air-to-air missiles. A third scheme equips car-rier battle groups with lasers or particle beamsto defend themselves against cruise missile attack.Fourth and last, ground-based beam weaponsmight replace surface-to-air missiIes for local airdefense.

Midcourse and terminal BMD. Intense electronbeams have long been studied as replacementsfor interceptors in reentry BMD. In midcourseBMD, beam weapons might not only destroyRVs, but aid discrimination of RVs from light-weight decoys: lasers, particle beams, or x-raylasers would illuminate approaching objects, andsensors would use the response of each objectas an extra piece of data to judge whether it wasa true RV (see Section 6).

Submarine communications. This schemewould use a blue-green laser to communicatewith submerged submarines. Seawater is opaqueto all but VLF and ELF radio frequencies, usedfor submarine communications today, and to theblue-green portion of the visible light spectrum.A blue-green laser beam originating on a satel-lite, reflected from a space-based mirror, or car-ried by an airplane would be modulated in ac-cordance with the message to be transmitted anddirected at a given spot on the ocean. After trans-mission of the full message, the beam woulddwell on a neighboring spot and transmit again,and so on, eventually covering all submarine pa-trol areas. Optical sensors on the submarine hullwould detect the message.

Blinding sensors and seekers. Analysts havestudied a wide range of tactical applications forlasers, involving blinding of battlefield sensors,missile seekers, and even human beings.