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 Documents

U.S. Government Printing Office, Washington, D.C. 20402
Preface

This background paper was prepared by Dr. Ashton B. Carter under a contract with

the Office of Technology Assessment. OTA commissions and publishes such background

papers from time to time in order to bring OTA up to date on technologies that are

the subject of frequent congressional inquiry. After Dr. Carter’s work was under way,

Senators Larry Pressler and Paul Tsongas of the Senate Foreign Relations Committee

requested that the resulting paper be made available to that Committee as soon as

possible. OTA is issuing the paper in the belief that others in Congress and members

of 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 explore emerging technological issues to determine if they merit a fuller, more detailed

assessment. On March 22, 1984, the Technology Assessment Board directed OTA to

carry 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 international 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 PopPage

. . . . . . . . . . . . . . . . . . . . . . 3

. . . . . . . . . . . . . . . . . . . . . . 7

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

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

. . . . . . . . . . . . . . . . . . . . . . 22

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

3.4 Space-Based Particle Beams . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . 28

3.5 Space-Based Kinetic Energy Weapons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.6 Microwave Generators.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

3.7 Other Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4. Other Essential Elements of a Boost-Phase Intercept System . . . . . . . . . . . . . . . . . . . . . . . . . 39

4,1 Target Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

4.2 Aiming and Pointing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

4.3 Intercept Confirmation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

4,4 Command and Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

4.5 Self-Defense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

4.6 Power Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

5. Countermeasures to Boost-Phase Intercept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

5.1 Anti-Satellite (ASAT) Attack, Including Directed-Energy Offense . . . . . . . . . . . . . . . . 46

5.2 Fast-Burn Boosters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

5.3 Counter C3

l Tactics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

5.4 Shielding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

5.5 Decoys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

5.6 Salvo Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

5.7 Offensive Buildup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

5.8 New Targeting Plans.... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

5,9 Other Means of Delivering Nuclear Weapons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

6. A Word on ’’Old’’ BMD and “New” BMD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

7. A Hypothetical System Architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

7.1 System Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60

7.2 Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61

8. Defensive Goals I: The Perfect Defense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

8.1 Nuclear Attack on Society . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

8.2 The Prospects for a Perfect Defense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

9. Defensive Goals ll: Less-Than-Perfect Defense . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

9.1 Goals for Less-Than-Perfect Defense . . . . . . . . . . . . . . . . . . . . . . . . . 73

9.2 Side Effects of BMD Deployment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77

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

Appendix

A. Excerpt From President Reagan’s Television Speech, March 23, 1983 . . . . . . . . . . . . . . . . . 85

B. The ABM Treaty and Related Documents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

C. Other Applications of Directed Energy Weapons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

v

Section 1

INTRODUCTION

This Background Paper describes and assesses

current concepts for directed-energy ballistic

missile defense in space. Its purpose is to provide Members of Congress, their staffs, and the

public with a readable introduction to the socalled “Star Wars” technologies that some suggest might form the basis of a future nationwide

defense against Soviet nuclear ballistic missiles.

Since these technologies are a relatively new

focus for U.S. missile defense efforts, little information about them has been readily available

outside the expert community.

Directed-energy or “beam” weapons comprise

chemical lasers, excimer and free electron lasers,

nuclear bomb-powered x-ray lasers, neutral and

charged particle beams, kinetic energy weapons,

and microwave weapons. In addition to describing these devices, this Background Paper assesses

he prospects for fashioning from such weapons

robust and reliable wartime defense system

esistant to Soviet countermeasures. The assessment distinguishes the prospects for perfect or

ear-perfect protection of U.S. cities and populaon from the prospects that technology will

chieve a modest, less-than-perfect level of performance that will nonetheless be seen by some

xperts as having strategic value. Though the

focus is technical, the Paper also discusses, but

oes not assess in detail, the strategic and arms

ontrol implications of a major U.S. move to develop and deploy ballistic missile defense (BMD).1

This Background Paper grows indirectly out of

resident Reagan’s celebrated television speech

f March 23, 1983, in which he called for a “longerm research and development program to begin

‘ BM D IS the most common of four rough Iy equivalent acronyms

verl 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 this

slgnatlon fell out of favor after the debate over and eventual dese of the Sentinel and Safeguard ABM systems in the late 1960’s

d early 1970’s. BMD largely replaced ABM as the term of choice,

t recently the more self-explanatory Defense Against Ballistic

sslles (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 methods

Ilmltlng damage from nuclear attack besides BMD.

to achieve our ultimate goal of eliminating the

threat posed by strategic nuclear missiles. ”2 Pursuant to the President’s speech, the Department

of Defense established a Defensive Technologies

Study Team under James C. Fletcher (of the University of Pittsburgh) to prescribe a pIan for the

R&D program. A parallel effort, called the Future

Security Strategy Study and headed by Fred S.

Hoffman (of Research and Development Associates), addressed the implications for nuclear

policy of renewed emphasis on BMD. This Paper covers the same technologies and issues as

these Defense Department studies. The ABM

Treaty reached at SALT l3 severely restricts the

development, testing, and deployment of BMD

systems. Though this Background Paper treats the

strategic roles of missile defenses, including many

of their arms control implications, it does not treat

the vital international political implications of a

major U.S. move to BMD.

Focused on directed-energy intercept of missiles in their boost phase, i.e., on “Star Wars”

proper, this paper does not analyze midcourse

and reentry BMD systems or non-BMD applications of directed-energy weapons.4 “Star Wars”

efforts generally further concentrate on intercept

of intercontinental ballistic missiles (ICBMs) rather

than the related but somewhat different problems

of intercept of submarine Iaunched ballistic missiles (SLBMs) or intermediate-range ballistic

missiles (IRBMs). This Paper is therefore not a

substitute for a more complete treatment of the

entire subject of BMD.5 Moreover, BMD itself is

only part of the larger subject of strategic defense,

comprising defense against bombers and cruise

missiles, civil defense, passive defense of military

targets, anti-submarine warfare (ASW), and preemptive counterforce attack in addition to BMD.

2The relevant portions of President Reagan’s speech are

reproduced in Appendix A.

3The ABM Treaty and related documents are reproduced in Appendix B,

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

5For a more complete treatment, see 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 himself

on, and for the Congress and public consequently

to concern themselves with, long-term research

and development. “Star Wars” is thus a somewhat unusual subject for a technology assessment

intended for a public policy audience. It is in the

nature of this subject that unknown or unspecified factors outweigh what is known or can be

presented in concrete detail. Many of the technologies discussed in this Paper, and most certainly all of the schemes for fashioning a defense

system from these technologies, are today only

paper concepts. In the debate over the Safeguard

ABM system a decade ago, or over basing modes

for the MX missile in recent years, one could analyze in detail the technical properties of welldefined systems in engineering development. So

vague and tentative are today’s concepts for “Star

Wars” BMD that a comparable level of analysis

is impossible. Fashions and “front runners” are

likely to change, Nonetheless, one is faced with

assessing the concepts receiving attention today

within the Executive Branch and which underlie

the President’s Strategic Defense Initiative. Fortunately, judgments deduced from generic properties of these concepts, which are unlikely to

change, are sometimes telling.

This Paper is based on full access to classified

information and studies performed for the Executive Branch. But it turns out that a fully adequate

picture of this subject can be presented in unclassified form. One reason is that the important

features of the directed-energy BMD concepts are

based on well-known physics, and many have in

fact been discussed for 20 years. The second

reason is that at this early stage of conceptualize

tion there is simply no point in (and little basis

for) discussion at the detailed level where classified particulars make a difference. The properties

of actual weapon systems in engineering devel

opment, by contrast, are normally and under

standably classified.

The author and OTA wish to thank officials o

the Army’s Ballistic Missile Defense Systems Corn

mand (BMDSCOM), the Lawrence Livermore Na

tional Laboratory, the Los Alamos Nationa

Laboratory, the Defense Advanced Research Proj

ects Agency (DARPA), the Sandia National Labo

ratory, the Air Force Weapons Laboratory (AFWL)

the Office of the Secretary of Defense (OSD), and

the Central Intelligence Agency (CIA) for thei

hospitality and cooperation. Many individual

aided the research for this Background Paper

though none shares the author’s sole respons

bility for errors of fact or judgment. The author

and OTA wish especially to thank Hans Bethe

Richard Briggs, Al Carmichael, Albert Carnesale

Paul Chrzanowski, Robert Clem, Sidney D. Drel

Dick Fisher, John Gardner, Richard L. Garwir

Ed Gerry, Jack Kalish, Glenn A. Kent, Louis Ma

quet, Michael M. May, Tom Perdue, Theodor

A. Postol, George Rathjens, Victor Reis, Jac

Ruina, George Schneiter, David N. Schwartz

Robert Selden, Leon Sloss, Daryl Spreen, Robi

Staffin, John Steinbruner, Sayre Stevens, Thomas

Weaver, Stephen Weiner, and Wayne Winter

This Background Paper contains information

current as of January 1, 1984.
Section 2

BOOSTER CHARACTERISTICS
Section 2

BOOSTER CHARACTERISTICS

Intercept of ICBMs in their boost phase offers

advantages and disadvantages relative to intercept of reentry vehicles (RVs) later in the trajectory. The boosters are fewer and generally more

easily disrupted or destroyed than the RVs. Decoy

boosters would have to match an ICBM’s huge

heat output, making this offensive tactic attractive only in certain circumstances. The disadvantages of boost phase intercept are that boost

phase is only a few minutes long and comprises

the earliest stage of an attack, and that sensing

and intercept must be accomplished from outer

Space and over enemy territory.

Figure 2.1 shows an ordinary (minimum energy) trajectory of a hypothetical future Soviet ICBM

hat has been given, for illustration, the boost profile of the U.S. MX Peacekeeper. Pressure from

a steam generator expel Is the missile from its storage cannister. Once clear of the cannister, the

missile ignites its first stage motor. The first stage

burns for about 55 seconds, burning out at an

altitude of about 22 kilometers. The second stage

also burns for 55 see, burning out at 82 km. The

third stage burns for 60 sec and carries the remainder of the missile to about 200 km, the altitude of the lowest earth orbiting satellites.

When the third stage is jettisoned at the end

of the 3-minute boost phase, the remainder of

the missile consists of the post-boost vehicle (PBV)

or ‘‘bus” and its cargo of 10 reentry vehicles. At

this point the bus and RVs are in ballistic freefall flight to the United States. Even if they are

disrupted in some way or destroyed, these objects or their debris will reenter the atmosphere

over the United States. The last few seconds of

third 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 bussing

decoy (650 sees. after

1200 km Apogee launch)

SOURCE: Author

7
enough speed to reach the United States, so disruption of boost phase any time right up to burnout 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 its

thrusters to make small adjustments to its trajectory. After each adjustment, it releases an RV. RVs

released on different trajectories continue on to

different targets as multiple independently targeted reentry vehicles (MIRVs). Decoys and other

penetration aids for helping the RVs escape defenses later in the trajectory are deployed during busing.

The bus itself is a target of declining value as

it dispenses its RVs. Destroying it early in the deployment process would obviously be useful: the

RVs not yet deployed from the bus would still arrive at the United States, but perhaps nowhere

near their intended targets. If cities are the targets,

relatively small aiming errors might be inconsequential. In any event, tracking the bus to allow

some form of intercept requires a different type

of sensor from that which tracks the booster for

boost phase intercept, since the bus’s thrusters

are small and operate intermittently. Because of

its small size, the bus (or at least critical elements

of it) might be more easily hardened against directed-energy weapons than the booster. For all

these reasons, the value of attempting bus intercept is very unclear, and it usually does not figure prominently in BMD discussions.

From apogee, the slowest point in their freefall trajectory, the RVs and empty bus gain speed

as they fall back to earth. RVs are more resistant

to damage from directed-energy weapons than

boosters, and they might be accompanied by

many decoys. When these objects enter the

upper atmosphere at about 100 km altitude

somewhat over 2 minutes before impact, they begin to heat up, and the lighter objects slow down.

Still lower, below 50 km altitude and less than

a minute before impact, the objects undergo violent deceleration and the bus breaks up. The RVs,

now glowing with heat, streak toward their targets

at an angle of about 23 degrees to the horizontal.

The trajectory shape can be altered at the expense of payload (see Figure 2.2). A lofted trajectory takes longer but reenters faster, and a depressed trajectory can offer unfavorable viewing

angles to defensive sensors late in the trajectory.

The most important trajectory variations from

the point of view of boost phase intercept are variations in boost profile. Boosters like MX were designed with no regard for boost phase BMD, and

optimizing their design gave rise to rather long

boost 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 cannot

penetrate–with relatively little reduction in payload or increase in missile size. Fast burn is accomplished most easily with solid-fueled rockets.

Liquid-fueled boosters like the Soviet SS-18s and

SS-19s burn more slowly and burn out at higher

altitudes. Thus while MX burns out at 200 km

after 3 minutes of boost, the SS-18 burns out at

300-400 km after 5 minutes. The next generation

of Soviet ICBMs will reportedly employ solid propellants.

Studies performed for the Defense Department

showed that with a 25 percent reduction in payload, a booster about the same size as MX could

be built which would burn out in less than 1 minute at only 80 to 90 km, well within the sensible

atmosphere. At 90 km the atmosphere is still too

dense for extremely accurate RV deployment or

for deployment of lightweight RV decoys and

other penetration aids aimed at later defensive

layers: these functions require an additional 10

to 15 seconds of precision deployment betweer

90 and 110 km. If the offense needs precision ac

curacy for some of its ICBMs but fears intercept

during these additional few seconds of high-alti

tude operation, mounting one or two RVs or

each of several “microbuses” instead of all the

RVs on a single bus affords some protection. Each

microbus would contain a simple guidance sys

tern only good enough to carry the RVs from up

per stage burnout to 110 km. Instead of present

ing 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 Commission

on Strategic Forces (the Scowcroft Commission

1“Short Burn Time ICBM Characteristic and Considerations,” Mar

tin 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 carying one warhead. Midgetman’s warhead and

IUS are combined i n one hardened structure.

“able 2.1 shows the characteristics of Midgetman

ariants designed to face a boost-phase intercept

ystem. The fast-burn version burns out at 80 km

fter 50 sees of boost. With a 10 percent increase

7 weight, the fast-burn version can carry a substantial payload of penetration aids. A low-flightprofile version is intended to stay within the atmosphere until burnout, protecting it from some

types of directed-energy weapon. In the hardened version, one gram of ablative or other

hielding material has been applied to each

quare centimeter of the entire booster body (if

le boost-phase intercept system did not begin

operation until a minute or so after launch, the

first stage might not have to be hardened). These

mall boosters are all estimated to cost $10 to $15

million per copy, assuming a buy of 1,000 boosters. Costs for the second and subsequent thousand would of course be substantially smaller.

These costs are two to three times higher per RV

than MX.

The Soviet ICBM arsenal today comprises about

1,400 boosters, more than two-thirds of them

MIRVd. Most are slow-burning liquid-fueled

boosters. The U.S. arsenal contains about 1,000

faster-burning solid-fueled Minuteman boosters,

about half of them MIRVd. Both sides are adding

solid boosters to their arsenals in the 1980’s.

The geographic distribution of offensive boosters can also be important to space-based boostphase defenses. The number of satellites required

in a defensive constellation usually increases if

all opposing ICBM silos are concentrated in one

region and decreases if the silos are spread over
10

o I I I I I I 0
11

wide land areas. (On the other hand, too much

concentration allows defensive satellites to be

focused on one region by choosing the orbits juviciously. ) Soviet SS-18 ICBMs, their largest

MIRVd missiles, are organized into 6 wings of

about 50 missiles each, spread out over a large

region of the U.S.S.R. U.S. Minuteman missiles

are organized into 6 wings of about 150 missiles

each. Figures 2.3 and 2.4 show the geographic

distributions.

react with new and different deployments when

they learn of any U.S. plans to deploy defenses.

It is impossible to project Soviet deployments far

into the future. A reasonable “baseline’ estimate

for the Soviet ICBM arsenal 15 to 20 years from

now might assign them the same number of

boosters they have today, but with burn characteristics similar to the U.S. solid-propellant MX.

This Background Paper indicates where and how

the 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 average

burn times, future Soviet ICBMs could be more potential 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
12

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

Type ICBMs Number

Ss-11 550

SS-13 60

Ss-17 150

SS-18 308

SS-19 330

Total 1398

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

B

ENERGY WEAPONS FOR

OOST-PHASE INTERCEPT
Section 3

DIRECTED ENERGY WEAPONS FOR

BOOST-PHASE INTERCEPT

This section describes the entire set of “beam

weapons” being considered in the United States

today for boost-phase ICBM intercept. Though

these weapons receive the most attention, the

“kill mechanism” that destroys the booster is not

necessarily the most important or technically

challenging part of an overall defense system. The

next section describes other essential elements

of a boost-phase defense.

A revisit to this subject several years from now

might well find a new family of directed energy

concepts receiving attention. But for now the devices described in this section are the basis for

assessments of the prospects for efficient boostphase defense, in the Defense Department and

elsewhere (fig. 3.1 ). Though some of these concepts are new, many have in fact existed in one

form or another for more than twenty years.

Figure 3. I

Gamma

raYs

x

X-rays

TV

Short- Submarine

FM wave AM communications

Far

EHF SHF UHF VHF HF MF LF VLF ELF

1 I 1 I 1 I 1 I 1 1 1 1 J

0.01 01 1 10 01 1 10 0.1 1 1 10 1 10 100 1 10 1 0 0

n 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 3

GHz GHz MHz MHz MHz kHz kHz kHz

Frequency

Earth-to-space Prefixes

transmission (schematic )

Giga (G) Billion 109

Mega (M) Million 106

Kilo (k) Thousand 1 0

3

Some transmissio n

— — 1

MI III (m) Thousandth 10-3

Transparent Micro (μ) Millionth 10-9

Nano (n) Billionth 10

Figure 3.1 The electromagnetic spectrum, showing spectral regions of interest for directed energy BMD. Particle beams and

kinetic energy weapons are not shown because their energy does not consist of electromagnetic radiation, but of atomic and

macroscopic matter, respectively. Source: Author

15
16

For each concept this section attempts to work

through, with some concreteness, the design of

a hypothetical defensive system based on the

concept. The resulting designs are illustrative

on/y; no significance should be attached to

precise numbers. Precision is simply not possible in the current state of technology and study

of these concepts.

In all cases, the “current state of technology”

(however this is defined in each case) is far from

meeting the needs of truly efficient boost-phase

intercept. The systems designed in this section

illustrate the level to which technology would

have to progress to be “in the ballpark.” Much

attention fastens on the guIf between the current

state of technology and the ballpark requirements. This section does not emphasize such

comparisons for several reasons. First, in some

cases details of the precise status of U.S. research

is classified. Second, and more importantly, quantitative comparisons (e.g., “A millionfold increase

in brightness is required to fashion a weapon from

today’s laboratory device”) can mislead unless

accompanied by a deeper explanation of the

technology; and the same quantitative measures

are not appropriate for all technologies. Third,

and most importantly, such comparisons imply

that learning how to build the right device is tantamount to developing an efficient missile defense, which is far from true: equally crucial are

design of a sensible system architecture, cost, survivability, resilience to countermeasures, and the

myriad detailed limitations that do not turn up

until later in development.

3.1 SPACE-BASED CHEMICAL LASERS: A FIRST EXAMPLE

This concept of directed energy weapon has

been the one most frequently discussed in recent

years for boost-phase ICBM intercept. For this

reason (and not necessarily because it is the most

plausible of all the concepts), it will be used to

introduce certain features common to all the

schemes that follow.

Making and Directing Laser Beams

A molecule stores energy in vibrations of its

constituent atoms with respect to one another,

in rotation of the molecule, and in the motions

of the atomic electrons. The molecule sheds

energy in the form of emitted light when it makes

transitions from a higher-energy state to a lowerenergy state. Lasing takes place when many molecules are in an upper state and few are in a lower

state: one downward transition then stimulates

others, which in turn stimulate yet more, and a

cascade begins. The result is a powerful beam

of light.

Energy must be supplied to the molecules to

raise most of them to the upper state. This process is called pumping. In the case of the chemical

lasers considered in this section, the pumping

energy comes from the chemical reaction that

makes the Iasant molecules: hydrogen and fluorine react to form hydrogen fluoride (HF) molecules in an upper state. The other requirement

for Iasing–few molecules in the lower state–is

satisfied simply by removing the molecules from

the reaction chamber after they have made their

transitions to the lower state and replacing them

with freshly made upper state molecules. The

pumping process is not perfect: not all the pumping energy ends up as laser light. The ratio of

pumping energy in to laser energy out is called

the efficiency of the laser.

Laser light is special in two respects: its frequency is precise, since all the light comes from

the same transition in all the molecules; and the

light waves from all the molecules emerge with

crests and troughs aligned, since the waves are

produced cooperatively. These special features

make it possible to focus the laser energy with

mirrors into narrow beams characterized by small

divergence angles (see fig. 3.2). Nonetheless,

there is a limit to the divergence angle that even

a perfect laser with perfect mirrors can produce.

The divergence angle (in radians) can be no

smaller than about 1.2 times the wavelength of

the light divided by the diameter of the mirror.

Thus a laser with 1 micrometer (=1 micron)
17

Figure 3.2

12 megawatt

directed-energy I

weapon

Figure 3.2 Basic power relationships for directed energy

weapons. If the directed energy weapon has a divergence

angle of 1 microradian, the spot size at a range of 4000

kilometers is 4 meters (12 feet). In this figure, the divergence

angle is exaggerated about 1 million times. (For comparison

of scale, the Earth’s radius is about 6,400 km,) If the directed

energy weapon emits 12 megawatts of power, a target within

the spot at 4,000 km receives 100 watts on each square centimeter of its surface. (For comparison, 100 watts is the power

of a Iightbulb, and atypical commercial powerplant produces

1,000 megawatts). Since a watt of power equals one joule of

energy per second this weapon would take 10 seconds to

apply 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 could

have at best a 1.2 microradian divergence angle,

making a spot 1.2 meters wide at a range of 1,000

kilometers (refer to fig. 3.2).1 This perfect performance is called the diffraction limit. Dividing the

laser power output by the size of the cone into

which it is directed (cone size is measured in units

called steradians; a divergence angle of x radians

results in a cone of size 7rxz/4 steradians) yields

the laser’s “brightness,” the basic measure of a

weapon’s lethality.

Destroying Boosters with Lasers

Assuming a high-energy laser with small divergence angle can be formed, stabilized so it does

not 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 patern), is 2.4 times the wavelength divided by the mirror diameter,

Jut most of the energy is in the central fourth of this area: hence

he use in the text of the multiplier 1.2.

clear answer to this question can be given without more study and testing. Estimates of the hardness achievable with future boosters are probably

reliable within a factor of two or three, though

estimates of the hardness of current Soviet

boosters are probably reliable only to a factor of

10 or so.

Roughly speaking, laser light can damage

boosters in two distinct ways. With moderate intensities and relatively Iong dwell times, the laser simply burns through the missile skin. This

first mechanism is the relevant one for the chemical lasers described in this section. The second

mechanism requires very high intensities but perhaps only one short pulse: the high intensity

causes an explosion on and near the missile skin,

and the shock from the explosion injures the

booster. This mechanism, called impulse kill, is

more complex than thermal kill and is less well

understood. it will be discussed in the next

section.

Bearing in mind the uncertainties in these estimates, especially the complex interaction of heating with the mechanical strains of boost, the following estimates are probably reliable: A solidfueled booster can probably absorb without disruption up to about 10 kilojoules per square

centimeter (kJ/cm2

) on its skin if a modicum of

care is taken in the booster’s design to eliminate

“Achilles’ heels. ” This energy fluence would result from 1 second of illumination at 10 kilowatts

per square centimeter (kw/cm2), since one watt

equals one joule per second.2 Applying ablative

(heatshield) material to the skin can probably

double or triple the lethal fluence required. Applying a mirrored reflective coating to the booster

is probably not a good idea, since abrasion during boost could cause it to lose its Iustre. Spinning the booster triples its hardness, since a given

spot on the side of the booster is then only illuminated about a third of the time.3 On the other

ZThe lethal fluence (in kJ/cmZ) must accumulate over a relatively

short 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 sec

of dwell time, but such a slow rate of heating would probably not

damage the booster.

IIt is possible that uniform heating around the circu reference of

the booster introduces lethal mechanisms distinct from those that

apply to heating a single spot on the side of the booster. In that

case, spinning the booster might not lengthen the required dwell

time by the full amount dictated by geometry.
18

hand, currently deployed boosters, especially the

large liquid Soviet SS-18s and SS-19s, might be

vuInerable to I kJ/cm2 or even less. These too

could be hardened by applying heatshield material.

An Orbiting Chemical Laser

Defense System

Consider a space-based BMD system comprised

of 20-megawatt HF chemical lasers with 10 meter mirrors. The HF laser wavelength of 2.7 microns is attenuated as it propagates down into

the atmosphere, but most of the light gets down

to 10 km or so altitude. Deeper penetration is not

really needed, since the laser would probably not

be ready to attack ICBMs until after they had

climbed to this altitude, and in any event clouds

could obscure the booster below about 10 km.

(Substituting the heavier and more expensive

deuterium, an isotope of hydrogen, to make a

DF laser at 3.8 micron wavelength would alleviate

attenuation, but the longer wavelength would require larger mirrors.)

A perfect 10 meter mirror with a perfect HF laser beam yields 0.32 microradian divergence

angle. The spot from the laser would be 1.3

meters (4,0 ft) in diameter at 4 megameters (4,000

kilometers) range. 20 megawatts distributed

evenly over this spot would be an energy flux of

1.5 kw/cm2

. The spot would need to dwell on

the target for 6.6 seconds to deposit the nominal

lethal fluence of 10 kJ/cm2. At 2 megameters

(Mm) range, booster destruction would require

only a fourth of this time, or 1.7 seconds of illumination. Since light takes about a hundredth

of a second to travel 4 megameters and the

booster is traveling a few kilometers per second,

the booster moves about sO meters in the time

it takes the laser light to reach it. The laser beam

must therefore lead the target by this distance.

The next step is to choose orbits for the satellites so that the U.S.S.R.'s ICBM silos are covered

at all times and so that there are enough satellites

overhead to handle all 1,400 of the present Soviet booster population. Equatorial orbits (fig. 3.3)

give no coverage of the northern latitudes where

Soviet ICBMs are deployed. Polar orbits give good

coverage of northern latitudes but concentrate

satellites wastefuIly at the poles where there are

no ICBMs. The optimum constellation consists

Figure 3.3

Figure 3.3 Designing a constellation of directed energy

weapon satellites for optimum coverage of Soviet ICBM

fields. Equatorial orbits (a) give no coverage of northern

latitudes. Polar orbits (b) concentrate coverage at the north

pole. Inclined orbits (c) are more economical. Slight additional

economies are possible in some cases with further

elaboration 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 directed

energy weapon, the lower and more numerous

the satellites must be. For instance, with a lethal

range of 3 Mm, 5 planes containing 8 satellites

each, or a total of 40 satellites, are needed to ensure that Soviet boosters exiting Soviet airspace

would be within lethal range of one satellite. If

the lethal range is increased to 6 Mm, only 3

planes of 5 satellites each are needed. This

dependence of constellation size on weapon

range is displayed in figure 3.4. (It is possible to

adjust these numbers a bit by using slightly elliptical orbits with apogees over the northern hemisphere, adjusting inclinations and phasing, etc.).

In the present example, requiring that at least one

HF laser be no further than 4 Mm from each So200

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 constellation

to ensure that at least one satellite is over each Soviet ICBM

field at all times depends on the effective range of the

directed energy weapon. For every one defensive weapon

required overhead a Soviet ICBM field to defend against

a rapid Soviet attack, an entire constellation must be

maintained on orbit. Since there are many Soviet ICBM fields

distributed over much of the Soviet landmass, more than one

satellite in each constellation would be in position to

participate in a defensive engagement. The ratio of the

number of satellites in the constellation to the number over

or within range of Soviet ICBM fields is called the absentee

ratio. If all Soviet ICBMs were deployed in one relatively small

region of the U. S. S. R., the absentee ratio would be the same

as the number of satellites in the constellation. Source: Author

viet ICBM site at all times (corresponding to no

longer than 6.6 seconds dwell time per booster)

results in the illustrative constellation of 32 orbital positions shown in figure 3.5.

Since the 1,400 Soviet boosters currently deployed are spread out over most of the Soviet

Union, perhaps 3 of the 32 orbital positions would

be over or near the Soviet Union at a time, able

to make efficient intercepts. That is, only one in

11 deployed U.S. battle stations would participate in a defensive engagement. The ratio of the

total number of battle stations on orbit to the

number in position to participate in a defensive

engagement is called the absentee ratio. The inevitable waste reflected in the absentee ratio—

Figure 3.5

O = Cluster of 5 chemical laser battle stations

Total of 32 x 5 = 100 battle stations

Figure 3.5 Constellation of hypothetical directed energy

weapon satellites with 4,000 km range. The orbits are circular

with 1000 km altitude. Each of the four orbital planes consists

of eight positions spaced 45° apart around the circle. In the

example given in the text, five chemical laser battle stations

are 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—offsets an oft-cited

theoretical advantage of boost-phase intercept,

namely, that intercepting one booster saves buying 10 interceptors for the booster’s 10 RVS. On

the other hand, coverage of the U.S.S.R.'s ICBM

fields automatically gives good coverage of essentially all submarine deployment areas. Obviously

the absentee ratio would be 32—the full constellation size—and not 32/3 = 10.7 if Soviet

ICBM silos were not spread out so widely over

Soviet territory but were deployed over a third

or less of the Soviet landmass, so that only one

of the 32 U.S. satellites was within range.

Three of the earlier described laser satellites in

position over the Soviet ICBM fields are not

enough to intercept 1,400 boosters if all or most

of the boosters are launched simultaneously.

Each satellite can only handle a few boosters

because it must dwell for a time on each one.

The time a chemical laser must devote to each

booster depends on the satellite’s position at the

moment of attack—6.6 seconds for 4 Mm range,

1.7 seconds for 2 Mm range, etc. Taking 2 Mm

as an average range for the 32-satellite constellation (hoping the Soviets do not choose a moment

when most of the U.S. satellites are farther than

2 Mm from the ICBM flyout corridors to launch

all their boosters simultaneously), a laser must

devote an average of 1.7 seconds to each booster.

If the boosters in the future Soviet arsenal

resemble the U.S. MX, and the defense waits 30

seconds or so to confirm warning and to wait for

the boosters to climb to an altitude where the HF

laser can reach, each booster is accessible for 150

seconds of its 180 second burn time. Each laser

can therefore handle no more than 90 boosters,

even with instant dewing of the beam from target

to target. If 1,400 Soviet boosters were launched

simultaneously, (1 ,400)/(90) = 15 lasers would

be needed in position, for a worldwide total (multiplying by the absentee ratio) of (10.7) X (15)

= 160 satellites.

If the Soviets doubled their arsenal to 2,800

boosters, the United States would need to deploy

another 160 satellites, possibly an uncomfortable

cost trade for the United States.

What is worse, if the Soviets deployed 1,400

missiles in a single region of the U.S.S.R. (at a

U.S.-estimated cost of $21 billion for MidgetmanIike ICBMs; see section 2 above), the US would

have to build, launch, and maintain on orbit an

additional (32) X(1 400)/(90) = 500 lasers plus

their fuel and support equipment.

If Soviet boosters were covered with shielding

material and spun during flight to achieve an effective hardness of, say, 60 kJ/cm2

, a laser would

have to devote 10 seconds to each booster at 2

Mm range, requiring a sixfold increase in the

number of satellites, to 960. Alternatively, the

average range of each engagement could be reduced to keep the dwell time at 1.7 seconds, with

corresponding increase in constellation density

(fig. 3.4). Either way, the number of U.S. satellites

would grow to nearly the number of Soviet boosters intercepted.

Table 3.1.—Variation of the Number of Chemical Laser Battle Stations Needed to Handle a Simultaneous

Launch of Soviet ICBMs, Depending on Characteristics of the Soviet Arsenal and the U.S. Laser Defense

Laser power Approximate

Number of (MW) and number of

Soviet Booster Geographic Hardness aperture battle stations

Departure from baseline boosters characteristics distribution (kJ/cm2

) diameter (m) needed

Baseline . . . . . . . . . . . . . . . . . . . 1,400 MX-like Current Soviet 10 20/10 160

Booster number . . . . . . . . . . . . 2,800 MX-like Current Soviet 10 20/10 320

Deployment geography . . . . . . 1,400 MX-like One region 10 20/10 500

Booster hardness . . . . . . . . . . . 1,400 MX-like Current Soviet 60 20/10 960

Laser brightness . . . . . . . . . . . . 1,400 MX-like Current Soviet 10 80/50 20-30

(100 times

brighter)

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

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

SOURCE: Author.
21

If the United States developed a battle station

100 times brighter (using, say, a 80 MW laser with

an effective mirror diameter of 50 meters), a few

lasers overhead (20 to 30 total worldwide) could

easily handle an attack of 1400 boosters hardened

to 10 kJ/cm2. If the boosters were hardened to

60 kj/cm2, over 100 such lasers would be needed.

Deployment by the Soviets of 1400 fast-burn

boosters would give the U.S. lasers just 20 to 40

seconds, rather than 200 seconds, to destroy all

the boosters. The U.S. constellation would consequently need to grow by a factor 5 to 10, to

800 to 1600 satellites!

Table 3.1 summarizes how the size of the defensive deployment varies with the parameters

assumed.

Requirements for a Chemical

Laser Defense

Figure 3.6 displays the performance of various

hypothetical HF lasers. Keeping the size of the

battle station constellation down to a hundred

rather than several hundred satellites means lethal ranges of at least 4 Mm with illumination

times less than about 1 second, assuming the defense must be capable of intercepting 1,000 to

2,000 Soviet boosters with launches timed to

keep the boosters as far from the U.S. lasers as

possible. Further assuming Soviet booster hardening to at least 10 kJ/cm2 results in a requirement

for chemical lasers considerably brighter than the

20 MW, 10-meter laser described above. A

hundredfold increase in brightness would be

achieved by a laser with power 80 MW and effective mirror diameter 50 meters.

Such a laser would be about 10 million times

brighter than the carbon dioxide laser on the Air

Force’s Airborne Laser Laboratory. The current

Alpha laser program of the Defense Advanced

Research Projects Agency (DARPA) aims at a construction of an HF laser of just a few megawatts

and built only for ground operation. Nonetheless, there is no fundamental technical reason

why extremely bright chemical lasers cannot be

built. In theory, several lasers can be operated

together so that the brightness of the resulting

beam increases with the square of the number

Figure 3.6

1

1 2 3 4 5 6 , 7 8 9 10

Radius

of Earth Geosynchronous

(6.4 Mm) altitude = 40 Mm

Lethal range (megameters)

Figure 3.6 Lethal range versus booster hardness for HF

chemical lasers of various sizes and dwell times. The labels

on the curves have the format (laser power in megawatts,

mirror diameter in meters) followed by the amount of time

the laser devotes to destroying each booster. Source; Author

of lasers: 10 lasers combined in this way would

produce a beam 100 times brighter than each individual laser. The trick is to arrange for the

troughs and crests of the light waves from all the

lasers to coincide. This theoretical prospect is

unlikely to be realized with H F lasers, since their

light is actually emitted at several wavelengths

and with shifting patterns of crests and troughs.

To yield diffraction-limited divergence, the mirror surface must be machined to within a fraction of a wavelength of its ideal design shape over

its entire surface. Since the mirror is over a million wavelengths across, avoiding small figure errors is a severe requirement. A number of small

mirrors can obviously combine to produce one

large optical surface if their positions are all

aligned to within a fraction of a wavelength. The
2 2

mirrors must maintain perfect surface shape in

the face of heating from the laser beam, vibration from the chemical reaction powering the laser, and vibrations set up in the mirror as it is

slewed. Substantial hardening of mirrors to radiation from nuclear bursts in space and to the xray laser (described below) would be a challenging task. The 2.5-meter diameter mirror on

NASA’s Space Telescope was produced without

these constraints.

An extremely optimistic outcome of HF laser

technology—near the theoretical limit for converting the energy of the chemical reactants to laser energy—would require more than a kilogram

of chemicals on board the satellite for every

megajouIe radiated. A spot diameter of 2 meters

at the target and a lethal fluence of 10 kJ/cm2 over

this area results in an energy expenditure of 300

MJ per booster. Destroying 1,000 Soviet boosters

therefore requires, reckoning very crudely,

300,000 kg of chemicals in position over the Soviet ICBM field, or perhaps 10 million kg on orbit worldwide. The space shuttle can carry a payload of about 15,000 kg to the orbits where the

satellite battle stations would be deployed. About

670 shuttle loads would therefore be needed for

chemicals, with perhaps another half as many for

the spacecraft structures, the lasers and mirrors,

construction and deployment equipment, and

sensors. 1,000 shuttle missions for every 1,000

Soviet boosters (perhaps Midgetmen) deployed

in reaction to the U.S. defense is an impractical

competition for the United States. Use of H F

chemical lasers for BMD therefore requires

remarkably cheap heavy-lift space launch capability in the United States.

The remaining components of the chemical laser defense system—sensors, aiming and pointing

technology, and communications— are for the

most part generic to all directed energy weapons

and are discussed in section 4. Section 5 presents

countermeasures the Soviets might take to offset or nuIlify a chemical laser defense.

3.2 GROUND-BASED LASERS WITH SPACE-BASED MIRRORS

A slight variant of the previous concept puts

the laser on the ground and mirrors in space,

reflecting the light back down toward Earth to attack ascending boosters. This scheme avoids

placing the laser and its power supply in space,

though mirrors, aiming equipment, and sensors

remain. The excimer and free-electron lasers

considered for this scheme are in fact likely to

be rather cumbersome, so ground basing them

might be the only practical way to use them for

BMD. The lasers would emit at visible or ultraviolet wavelengths about ten times shorter than

the near-infrared wavelengths of the HF and DF

chemical lasers in the space-based concept.

Shorter wavelengths permit use of smaller

(though more finely machined) mirrors. The high

power available with ground basing suggests at

least the possibility of impulse rather than thermal kill of boosters.

The term excimer is a contraction of “excited

dimer.” A dimer is a molecule consisting of two

atoms. The dimers considered for these lasers

contain an atom of noble gas and a halogen atom,

making dimers like xenon fluoride (XeF), xenon

chloride (XeCl), and krypton fluoride (KrF). The

laser light comes from dimers in an excited upper

state decaying to a lower state, just like in the HF

laser. Excimer lasers tend to emit light in pulses

rather than in a continuous wave. The population of upper-state molecules is provided by

pumping with electric discharges in a rather complicated process. The population of lower-state

molecules remains small because the lower-state

dimer is unstable and quickly breaks up into its

two constituent atoms. The pumping process for

excimer lasers is inefficient, so only a small fraction of the energy put into the laser in the electric discharge emerges as laser light. Powerful excimer lasers would therefore be large and would

need to vent large amounts of wasted energy;

these characteristics make them unsuitable fot

space basing. Development of excimer lasers is

at an early stage, and no excimer lasers exist with

anything remotely approaching the characteristic:

needed for this boost phase intercept concept.
23

Figure 3.7

10 relay mirrors

(30 m diameter)

Laser beacon

for adaptive

optics 8

12 mountaintop lasers 100 Intercept mirrors

(400 MW, O 5 μ) (5 m diameter)

with 50,000 mirror

subelements for \

adaptive optics

\ I I

Figure 3.7 Illustrative configuration of ground-based excimer

or free-electron laser and space-based mirrors for thermal kill

of Soviet ICBM boosters. Source: Author

Power outputs achieved in the laboratory are still

several orders of magnitude less than the average power needed for thermal kill, and the energy achieved in a single pulse is much smaller

than the single-pulse energies needed for impulse

ki I I.

The working of a free-electron laser (FEL) is

more complicated.4 As the name suggests, the

light-emitter (Iasant) is free electrons emitted from

 particle accelerator. Pumping therefore orignates in the electrical source powering the accelerator. The free electrons from the accelerator

are directed into a tube called the wiggler that

Ias magnets positioned along its length. The

nagnets 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. The

presence of light from one electron causes others

to emit in the usual cooperative manner of a laser, and a cascade begins. By adjusting the positions of the magnets and the energy of the electrons, the wavelength of the light can be tuned

to any value desired. The only advantage of the

FEL over excimer lasers is the high efficiency that

can (theoretically) be obtained with the former.

It has been suggested that it might even be possible to position FELs in space like HF chemical

lasers. FEL operation at visible wavelengths is in

its infancy, and the experimental devices used

are many millions of times less powerful than

those required in this BMD.

The BMD scheme calls for a large ground based

excimer or free electron laser, relay mirrors at

high altitude to carry the laser beam around the

curve of the Earth, and intercept mirrors to focus

the beams on individual boosters (fig. 3.7). The

characteristics of a nominal system for thermal

booster kill are easily ascertained. Suppose first

that there are enough intercept mirrors so that

the average range from mirror to booster is 4 Mm,

and suppose the Soviet boosters are destroyed

with 10 kJ/cm2 deposited on a spot as small as

several centimeters wide. Assume the excimer or

free electron laser operates at about 0.5 microns,

in the visible band. Then a 5 m intercept mirror

will produce a spot 50 cm wide at 4 Mm range.

If a half second of the main laser beam is devoted

to each booster, then the required 10 kJ/cm2 will

be accumulated if the power reflected from each

intercept mirror is 40 MW.

Only about a tenth of the power emitted by

the ground based laser in the United States would

be focused on the booster over the U.S.S.R. The

remainder would be lost in transit through the

atmosphere and in reflection from the two mirrors. Thus a 400 MW laser is required.

Passage through the atmosphere poses a number of problems for the primary laser beam. The

most important source of interference is turbulence in the air, causing different parts of the

laser beam to pass through different optical environments when exiting the atmosphere. Each part

of the beam suffers a slightly different disruption,

and the beam that emerges does not have the
24

orderly arrangement of crests and troughs needed

for diffraction-limited focusing from the intercept

mirror. Without compensation for atmospheric

turbulence, the ground-based laser scheme is

completely impractical. Fortunately, the pattern

of turbulence within the laser beam, though constantly changing, remains the same for periods

of a few milliseconds. Since it takes only 0.1

millisecond for light to make a round trip through

the atmosphere, the effect of turbulence on the

laser beam can be compensated for with the following technique, called adaptive optics: A lowpower laser beacon is positioned near the relay

mirror. A sensor on the ground observes the distortion of the beacon beam as it passes through

the atmosphere. The beam from the groundbased laser is then predistorted in just such a way

that its passage through the same column of air

transited by the beacon beam re-forms it into an

undistorted beam.

Figure 3.7 shows the many components required by the ground-based laser concept. Since

each Soviet booster requires 0.5 sec of beam at

some time during its 200 sec. boost phase, four

beams would be needed to handle 1,400 Soviet

boosters launched simultaneously (assuming no

retargeting delays), The lasers should be deployed

on mountain tops to make atmospheric effects

manageable, and enough should be deployed

that at Ieast four sites are always clear of cloud

cover. The mirror on the ground would need to

be tens of meters across and divided into tens

of thousands of individually adjustable segments

for predistortion of the wavefront. Each relay mirror would need to be accompanied by a beacon.

Four large interception mirrors would be needed

within 4 Mm of each Soviet ICBM flyout corridor,

giving a worldwide constellation of a hundred or

so.

The small laser wavelength means that all mirrors must be more finely machined than the mirrors for the chemical laser and can tolerate

smaller vibrations and stresses due to heating

from the laser beam. The small wavelength also

results in a spot 10 times smaller at the target than

the spot from a chemical laser beam at the same

range. This small spot requires pointing accuracy

ten times finer. Perhaps most important of all, the

plume from the booster motor is too large to

serve as target for such a narrow beam. Some way

of seeing the actual missile body against the

background of the plume is needed for the shortwavelength laser schemes (and for some configurations of chemical lasers). One answer to this

problem, described in section 4 below, is to position near each intercept mirror a low-power laser and a telescope (a laser radar or Iadar): the

laser illuminates the booster and the telescope

observes the reflected laser light, directing the

pointing of the intercept mirror. The Iadar telescope must have a mirror as large as the intercept

mirror, since it must be able to “see” a spot as

small as that made by the beam.

A single immense laser pulse that deposits 10

kJ/cm2 in a very short time–millionths of a second rather than a second— might cause impulse

kill rather than thermal kill, In impulse kill, the

laser pulse vaporizes a small layer of the booster

skin and surrounding air. The superheated gases

then expand explosively, sending an impulsive

shockwave into the booster. A strong enough

shockwave might cause the booster skin to tear.

The advantage of this kill mechanism is that it

would be very difficult to protect boosters from

it. The disadvantages are that impulse kill requires

prodigious laser pulses and mirrors that can withstand them, and that the mechanism is poorly

understood and depends on myriad factors like

the altitude of the booster at the moment it is attacked.

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 genweapon laboratories to use the energy of a nu- eration” of nuclear weapons, the first two generaclear weapon to power a directed beam of x-rays. tions being the atomic (fission) and hydrogen
25

(fusion) bombs. Each succeeding generation represented a thousandfold increase i n destructive

energy, from a ton of high explosive to a kiloton

fission weapon to a megaton fusion weapon. The

third generation weapon uses the same amount

of energy as the fusion weapon, but directs much

of that energy toward the target rather than allowing it to escape in all directions. At the target,

therefore, the energy received is much greater

than the energy that would be received from a

hydrogen bomb at the same range.

x rays lie just beyond ultraviolet light on the

electromagnetic spectrum and have wavelengths

about a thousand times smaller than visible light

(see fig. 3.1 ). Compared to the infrared, visible,

and ultraviolet lasers in the previous sections, the

x-ray laser produces much more energy from its

bomb pump, but the energy is spread out over

a larger cone. The lethal ranges for boosters turn

out to be roughly comparable for all these types

of directed-energy device. Obviously the x-ray

laser delivers all its energy in one pulse, so there

is no question of dwell time on the target. Very

short-wavelength x-rays penetrate some distance

into matter (witness dental and medical x-rays),

but the longer-wavelength x-rays produced by a

laser device do not penetrate very far into matter or into the atmosphere.

orbiting and ground-based “pop-up” systems

have been proposed as ways to make use of the

x-ray laser for boost phase BMD. Both of these

schemes have attractive features but also serious

drawbacks. It could well be that the x-ray laser

device, if a powerful one can eventually be built,

will be more useful in other strategic roles than

boost-phase BMD.

X-Ray Lasers

Little has been revealed about the characteristics of the bomb-pumped x-ray laser being studied by the United States (the so-called Excalibur

device), but some general information can be

deduced from the laws of physics and, to a lesser

extent, from the scientific literature here and in

the Soviet Unions

5F, V. BU nkln, V. 1. Derzhiev, and S. 1. Yakovlenko, %vlet /ourna/ of QuantumE/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 and

L. 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 pumped

to upper energy states by a nuclear bomb. Those cascades

of downward transitions that travel lengthwise build up more

energy than sideways-going cascades. As a result, most of

the energy emerges from the ends of the rod into a cone with

divergence angle equal to twice the rod width divided by its

length. Source: Author

The pumping source for the x-ray laser is a nuclear bomb. The radiant heat of the born b raises

electrons to upper energy levels in atoms of Iasant

material positioned near the detonation (the

chemical nature of the Iasant material has not

been revealed). As the electrons fall back again

to lower levels, it can happen that for a moment

many atoms are in a given upper level and few

in a lower level; this is the necessary condition

for Iasing from the upper level to the lower level.

The wavelength of the emitted x-ray is determined by the energy levels involved. The wavelength of the laser under study in the United

States is classified. We will use a round number

of 1 nm.

Since x-rays are not back-reflected by any kind

of mirror, there is no way to direct the x-rays into

a beam with optics like the visible and infrared

lasers. Nonetheless, some direction can be given

to the laser energy by forming the Iasant material into a long rod. Recall that a laser beam builds

up when light from one Iasant atom stimulates

the upper-to-lower-level transition in another

atom, which stimulates a third, and so on. The

result is a cascade of light heading in same direction as the light from the original atom. The light

pulse gets stronger and stronger as it traverses the

Iasant medium stimulating more and more transitions. In a long rod of Iasant material, cascades

that get started heading lengthwise down the rod

are highly amplified by the time they leave the

rod, whereas sideways-going cascades remain

small. 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 being studied in the U.S. are classified; but it is fairly

easy to determine the upper limit to how powerful such a laser could possibly be. Whether R&D

wiII succeed in making such a perfect laser cannot be said. But it will become clear that something very close to the perfect laser is required

for boost phase intercept, though a less successful

development would still yield a potent antisatellite weapon.

A l-megaton nuclear weapon releases about

4 billion megajoules of energy. By surrounding

the bomb with Iasant rods, most of this energy

can be harnessed to pump the laser. Since the

pumping mechanism for the x-ray laser is rather

disorganized and wasteful, like the pumping

mechanism for excimer lasers, at most a few percent of the bomb energy can be expected to end

up in the laser beam.

The resulting 100 million megajoules or less of

laser energy emerges from the rods into cones

with relatively large divergence angle. It is easy

to see why this divergence angle is much larger

than the divergence angle obtained with the

mirror-directed lasers treated in the previous section, The divergence angle is determined by the

ratio of the width of the rod to its length, as in

figure 3.8. A practical length for a rod is no more

than about 5 meters. Making the rod thinner decreases the divergence angle, but beyond a certain point no further narrowing of the beam cone

is possible. The limit arises from diffraction, just

as with the infrared and visible lasers: the divergence angle of light emitted from an aperture

(mirror, rod tip, or anywhere else) cannot be less

than about 1.2 times the wavelength of the light

divided by the diameter of the aperture. A very

narrow rod therefore actually aggravates diffraction and produces a wide cone. Making the rod

thinner results in no further narrowing of the

beam when (1 .2) (wavelength) /(rod width) s (2)

(rod width)/(rod length). For an x-ray wavelength

of 1 nm and a rod length of 5 meters, this equation yields an optimum rod width of 0.06 mm and

a minimum achievable (diffraction-limited) divergence angle of 20 microradians.

A 1-megaton bomb-pumped x-ray laser can

therefore deposit no more than about 100 million megajoules into a cone no narrower than

about 20 microradians. The x-ray pulse from

detonating such a perfect laser would deposit

about 300 kJ/cm2 over a spot 200 meters wide

at 10 Mm range.

Interaction of X-rays with Matter

X-rays of 1 nm wavelength do not penetrate

very far into matter: all the energy from such a

laser would be absorbed in the first fraction of

a millimeter of the aluminum skin of a missile.

This paper-thin layer would explode, sending a

shockwave through the missile. Thus the x-ray

laser works by impluse kill.

Another consequence of the opacity of matter to x-rays is that the laser beam would not

propagate very far into the atmosphere. The

altitude to which the beam would penetrate

depends on the precise wavelength, which is

classified. For the nominal 1 nm wavelength

described above, boosters below about 100 km

would be quite safe from attack. If the wavelength

were much shorter, the x-rays would penetrate

lower, reaching perhaps 60 km altitude or so. In

what follows, it will be assumed that boosters are

safe from x-ray laser attack below about 80 km.

One last consequence of the physics of x-ray

interaction with matter is noteworthy. When an

atom of matter absorbs an x-ray, it emits an electron. As x-rays are absorbed, it becomes harder

and harder to remove successive electrons. Finally further x-rays cannot remove further electrons, and the matter becomes transparent. This

phenomenon, called bleaching, means that a

strong x-ray laser beam can force its way through

a column of air by bleaching the column, but a

weak laser beam is completely absorbed. An xray laser in the atmosphere might therefore be

able to attack an object in space because the

beam is intense enough in the vicinity of the laser to bleach the air, whereas an x-ray laser in

space could not attack objects within the atmosphere. This fact bodes ill for defensive spacebased x-ray lasers attacked by similar lasers (or
2 7

—

even weaker ones) Iaunched from the ground by

the offense.

As with visible and infrared lasers, the lethality

of a n x-ray laser is subject to large uncertainties.

The proper order of magnitude for the amount

of x-ray energy per square centimeter that needs

to be deposited on the side of a booster to damage it can be estimated fairly easiIy. But the actual hardness of a booster would depend on

many design details in a way that is not fully

understood at this time. A simple calculation indicates that 20 kj/cm2 is a reasonable number to

take for the hardness of a booster. This is about

the same as for impulse kill by visible laser. An

RV would be harder, and a satellite softer.

Orbital Defense Concept

The “perfect” x-ray laser whose characteristics

were deduced above wouId be capable of intercepting a booster from geosynchronous orbit

40,000 km above the Earth. One laser would be

needed for each Soviet booster. At lower altitudes, the rods surrounding the bomb could be

gathered into several bundles and each bundle

aimed at a different booster. At these lower

altitudes, though, the absentee problem means

that roughly one x-ray laser device would still

need to be placed in orbit for each Soviet booster.

Though the x-ray lasers are small and light compared to a chemical laser, the cost tradeoff involved in launching a new laser every time the

Soviets deploy a new ICBM is obviously not a

tolerable one for the United States.

The x-ray laser can attack the boosters after

they have left the protective atmosphere but

before burnout. Simultaneous launch of all Soviet 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 an

m I)U Iw of th IS 5trength to the entl re side of an ICBM booster relulres a fluence F, whose order of magnitude can be estimated

If 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 paperhln 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 orjer (Fa)Y’, 10 ktaps is therefore produced if F =20 kJ/cm’,

In re.allty, not all the deposited energy couples to the booster

n t h If way A more caretu I ca Icu tat Ion of th IS lessened cou pl I ng

1~~ been pertormed by Hans Bet he (private com m u n Icatlon),

the way it is a problem for chemical lasers that

must dwell on each target before passing on to

the next. Fast-burn boosters are Iikewise not a

crippling problem for an orbiting x-ray laser

system unless they burn out before they leave the

atmosphere, Other countermeasures, most notably the vuInerability of U.S. orbital x-ray lasers

to Soviet x-ray lasers, are treated in section 5.

Pop-Up Defense Concept

The pop-up concept represents an attempt to

avoid the one-laser-per-booster cost exchange

and the vulnerability associated with basing the

lasers in space (though crucial sensors remain

space-based even in the pop-up scheme). The

small size and light weight of the bomb-pumped

lasers makes it possible to consider basing them

on the ground and launching them into space

upon warning of Soviet booster launch.

Figure 3.9 shows why basing the pop-up lasers

in the United States is not practical. During the

200 seconds or so of burn time of a Soviet MXFigure 3.9

Lowest altitude

line of fire

clear atmosphere

Burnout of hypothetical

MX-like Soviet ICBM

(200 km altitude

180 sec. after launch)

atmosphere - 100 km

Figure 3.9 X-ray lasers launched from the United States on

warning of Soviet ICBM launch would have to climb at least

as high as the line of fire shown in the figure within three

minutes to intercept an MX-like Soviet ICBM. Such a huge

fast-acceleration defensive booster would be many times

larger 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 would

mb high enough to see the Soviet

boosters over the Earth’s horizon and have a lineof-fire unobstructed by the absorbing atmosphere. Climbing so high so fast requires a booster

for the x-ray lasers that is many thousands of times

larger 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 United

Kingdom, the lasers would be separated from Soviet ICBM silos by only 45 degrees of arc rather

than 90 degrees as with U.S. basing. Even so,

popping up to attack an MX-like Soviet booster

would require an enormous fast-burn booster for

the x-ray laser and would put it into position to

attack the Soviet booster only seconds before

burnout. If the Soviets depressed the trajectory

or shortened the burn time of the offensive

booster very slightly, or if the United States suffered any delay whatsoever in launching the

defensive boosters after Soviet launch (instantaneous warning), this hypothetical U.K.-based

system would be useless.

A final possibility would be launch of defensive lasers from submarines stationed immediately off Soviet coasts—in the Kara Sea or Sea of

Okhotsk, separated from Soviet silos by about 30

degrees of arc–on SLBM-sized fast-burn boosters.

With instantaneous warning, a sea-based laser

might be able to climb to firing position a few

seconds before burnout of a Soviet MX-like ICBM

and would enjoy almost an entire minute of visibility to a slow-burning, high-burnout-altitude

booster like the SS-18. Because of the short range,

each bomb-pumped laser of the perfect design

described above could attack many (over 100)

boosters using many individual Iasing rods. Such

efficiency could well be essential, since a submarine cannot launch all its missiles simultaneously and might only be able to fire one defensive missile in the required few seconds. If the

MX-like Soviet boosters were flown on slightly

depressed trajections, if warning were not communicated to the submerged submarine promptly, if a human decision to launch defensive missiles were required, or if the Soviets deployed

boosters that burned faster than MX, the subIaunched system would be nullified, Last, submarine patrol very near to Soviet shores suggests

the possibility of attacking the submarine with

shore-based nuclear missiles as soon as its position has been revealed by the first defensive

launch. Other countermeasures are discussed in

Section 5.

3.4 SPACE-BASED PARTICLE BEAMS

Beams of atomic particles would deposit their

energy within the first few centimeters of the target rather than at the very surface as with lasers.

The effects of irradiation with the particle beam

could be rather complex and subtle and would

probably depend on design details of the attacking Soviet booster. The result is uncertainty of several factors of ten in the effective hardness of an

ICBM booster to beam weapon irradiation.

neutral particle beams, consisting of atomic

hydrogen (one electron bound to one proton)

deuterium (one electron, one proton, one neutron), tritium (electron, proton, two neutrons) 01

other neutral atoms are considered. To produce

a neutral hydrogen (H°) beam, negative hydro

gen atoms (H –) with an extra electron are accel

erated; the extra electron is removed as the beanemerges from the accelerator,

Only charged particles can be accelerated to Two features of neutral particles beams domi

form high-energy beams, but a charged beam nate their promise as boost phase intercept weap

would bend uncontrollably in the Earth’s mag- ons (leaving aside entirely the issue of counter

netic field. (There is one theoretical exception to measures). The first is the uncertain lethality o

this statement, described below.) For this reason the beam. The second is the fact that the bear-r
29

cannot propagate stably through even the thinnest atmosphere and must wait for an attacking

booster to reach very high altitude.

Generating Neutral Particle Beams

The accelerator that accelerates the negative

hydrogen ion is characterized by its current in

amperes, measuring the number of hydrogen

ions per second emerging from the accelerator;

and by the energy of each accelerated ion in electron volts (eV; 1 eV = 1 watt per ampere).

Multiplying the current by the energy gives the

power of the beam, so that a l-amp beam of 100

MeV particles carries 100 MW of power. Groundbased high-current accelerators and groundbased high-energy accelerators have been built

and are operated daily in laboratories. One of the

challenges for neutral particle beams as weapons

is that they require both high current and high

energy. Another challenge is to provide multimegawatt power sources and accelerators in a

size and weight suitable for space basing.

Magnets focus and steer the beam as it emerges

from the accelerator. The last step is to neutralize

the beam by passing it through a thin gas where

the extra electron is stripped off in glancing collisions with the gas molecules, forming HO from

H-. The divergence angle of the beam is determined by three factors. First, the acceleration

process can give the ions a slight transverse motion as well as propelling them forward. Second,

the focusing magnets bend low-energy ions more

than high-energy ions, so slight differences in

energy among the accelerated ions lead to divergence (unless compensated by more complicated

bending systems). Third, the glancing collisions

that strip off the extra electron give the H atom

a sideways motion. This last source of divergence

Table 3.2.—Neutral Particle Beam Divergence Angle

H“ T“

100 MeV 3.6 microradians 2.0

iOO MeV 1.4 1.0

Divergence angle introduced by stripping electrons from a beam of negative

hIydrogen or tritium ions to produce a neutral beam This source of divergence

j an unavoidable consequence of the Heisenberg uncertainty principle applied

o the sudden stripping of the electron If the satellite. based accelerator of the

egative tons were absolutely perfect, this amount of divergence would remain

is unavoidable and, by the Heisenberg uncertainty principle, cannot be controlled or compensated. It sets a lower limit on the divergence angle

achievable with this method of producing neutral

particle beams. Table 3.2 shows the divergence

angle resulting from this third source, assuming

perfect control of the first two sources. The

divergence cone from a neutral particle beam is

therefore about 10 times larger than the beam

from the chemical laser of section 3.1 and 10

times smaller than from the x-ray laser of section

3.3.

A 100 MeV, 0.5 amp neutral tritium (T°) beam

thus directs 50 MW of power into a cone of divergence angle 2 microradians, producing a spot

10 meters across at 5 Mm range. A target within

this spot receives only 65 watts/cm2

, requiring 1.5

seconds of dwell time to deposit only 100 J/cm2

.

Booster Vulnerability to

Particle Beams

As soon as the neutral particle beam hits the

target, the remaining electron is stripped off, leaving the energetic proton (or deuteron or triton)

penetrating deeply into the target. The proton

scatters electrons in its path, giving up a small

amount of its energy to the electron in each collision. 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 cm

into the propellant in a missile, it deposits about

25 MeV along each cm. Protons penetrate more

deeply than tritons of the same energy, and all

particles penetrate more deeply as they are given

more energy (table 3.3).

Table 3.3.—Penetration Range of Neutral

Particle Beams Into Matter (in centimeters)

H“ TO

100 MeV 250 MeV 100 MeV 250 MeV

Solid propellant or

high explosive

(density 1.0 gm/cm3

) 9.5 46.6 4.2 20.2

Aluminum . . . . . . . . . 3.5 17.2 1.6 7.6

Lead . . . . . . . . . . . . . . 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 grams

1 cm

100 MeV Tritium (T 0, beam

Figure 3.10 A neutral particle beam penetrates farther into

an aluminum target than into a lead target but deposits the

same energy per gram. Though the energy per gram needed

to melt aluminum is well known, the utility of particle beam

BMD concepts rests on the less certain destructive effects

at lower levels of irradiation. Source: Author

Table 3.4.—Effects of Particle Beam Irradiation

Energy deposition

Harmful effect (Joules per gram)

Disruption of electronics . . . . . . . . . . 0.01 –1 .0

Destruction of electronics . . . . . . . . . 10

Detonation of propellants,

high explosive . . . . . . . . . . . . . . . . . 200

Softening of uranium

and plutonium . . . . . . . . . . . . . . . . . hundreds

Melting 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 effects, such as melting of glue and plastic and rate-dependent effects, might also

be Important

SOURCE Author

The target electrons that recoil from collisions

with beam particles eventualy stop, and their energy appears as heat. The 100 MeV T° beam

described above, depositing 100 J/cm2 on an aluminum target, penetrates to a depth of 1.6 cm.

The 1.6 cubic centimeter volume of aluminum

that absorbs this 100 joules of energy weighs

about 4 grams. The effect of the beam is therefore to deposit about 25 joules per gram throughout the first 1.6 cm of the target. The penetration depth is inversely proportional to the density

of the absorbing material, so the same beam on

a lead target would not penetrate as far but would

deposit the same energy per gram as it did in

aluminum (fig. 3.1 O).

The destructive effects of penetrating particle

beams are therefore expressed in joules/gram deposited within the target rather than in joules/cm2

on the surface of the target as with lasers. Table

3.4 shows the energy deposition needed to produce certain harmful effects. Melting the target

is straightforward, but for the other effects at

lower levels of irradiation the criteria are less

clear. Heat effects in solid booster propellants and

in the high explosive and special nuclear materials i n warheads depend on the design of the target. Effects on electronics, particularly transient

disruption of computer circuits when electrons

are scattered by a passing proton, are poorly

known and doubtless quite complicated and specific to the target. Other components not shown

in table 3.4 —plastics, glue, guidance sensors–

make for a very complicated analysis. What is

more, the particle beam might have to suffer the

attenuation of passage through, say, two layers

of aluminum and a layer of plastic before reach

ing a sensitive component.

Uncertainties in the destructive or disruptive

effects of small amounts of radiation from a par

ticle beam weapon is the principal obstacle to

stating what energy, current, and divergent

angle would make this concept a candidate for

boost-phase intercept.

Shielding to protect components from a neutra

particle beam would necessarily be heavy but

could still be an attractive countermeasure. It

discussed in Section 5.

An Orbiting Neutral Particle

Beam System

A critical limitation of neutral particle beam

is that they cannot be aimed through even the

thinnest atmosphere—air so thin that even the ~

ray laser beam could pass through easily. A neutral beam could not attack a Soviet booster unl

the booster reached at least 760 km altitude (ve

sus about 80 km for the x-ray laser)7. Collision

The stripping cross section on oxygen is about 1.5 megabarr

Elastic scattering can also be important for beam loss, since the Rh

scattering angle can be larger than the beam divergence. The auth

is Indebted to Dr. George Gull lespe of Physical Dynamics, Inl

in La Jolla for resu Its of his Born approximation cross sectlt

calculations
31 .

—

between air molecules and H° strip the electron

from the Ho, and gradually all the remaining

protons spiral off the beam axis into 200 km wide

circles under the action of the earth’s magnetic

field.

An MX-like Soviet booster could be attacked

between 160 km altitude and burnout at 200 km,

a period of about 10 seconds. This short attack

window means that the neutral beam cannot

afford to dwell for long on each booster.

It is impossible to state with confidence the resilience of an ICBM booster to irradiation with

a neutral particle beam. But it is likely that faith

would have to be placed in degradation of electronics and other subtle effects, rather than in

gross structural damage, for the beam weapon

to stand a chance as an economical defense

system (ignoring the issue of countermeasures entirely).

Consider again a battle station producing a 0.5

ampere beam of 100 MeV tritium (T°) atoms

with 2 microradian divergence. This beam carries 400 watts/cm2 at 2 megameters range. To do

structural damage to the outer few centimeters

of a missile’s body might take some 2 kJ/cm2

(depositing 500 J/gin in 1.6 cm depth of aluminum, for instance), requiring 5 seconds of dwell

time at this range. Since the available dwell time

is only about 10 seconds, each beam could handle only two boosters. With a constellation size

of almost 100 for 2 Mm range (fig. 3.4), this kill

criterion resuIts in a preposterous system where

the U.S. deploys 50 space-based accelerators for

every one Soviet booster deployed in one region

of the U.S.S.R.

If the assumed Soviet booster hardness is reduced by 100 times, corresponding perhaps to

transient upset of unshielded electronics, each

satellite can destroy 200 boosters at 2 Mm range,

meaning an overall tradeoff of one U.S. accelerator deployed for each two Soviet boosters deployed. Alternatively, the constellation can be

thinned out to an effective range of 5 Mm, where

each satellite at this range can destroy only 32

boosters but the constellation size is only about

16—still a one-to-two trade of battle stations for

Soviet boosters. Such a system scarcely seems

promising in terms of cost exchange.

obviously the neutral particle beam would

stand no chance of intercepting a fast-burn

booster that burns out well within the protective

atmosphere. Even an MX-like booster that flew

a slightly depressed trajectory wouId be invulnerable.

A Theoretical Electron Beam System

Physical theory8 holds out the prospect of one

other type of beam besides the neutral particle

beam. Under certain circumstances, an electron

beam might be able to propagate through the extremely thin air of near-earth space without bending. In this scheme, a laser beam would first

remove electrons from air molecules in a thin

channel stretching from the battle station to the

target, leaving a tube of free electrons and positive ions. The high-energy, high-current electron

beam would then be injected into the channel.

The beam electrons would quickly repel the free

electrons from the channel, leaving the beam

propagating down a positively charged tube. The

attractive positive charge would prevent the electrons from bending off the beam path under the

influence of the geomagnetic field and wouId also

prevent the mutual repulsion of electrons within

the beam from causing the beam to diverge. The

result would be straight-line propagation to the

target, where their effect would be similar in most

respects to the neutral particle beam. This scheme

will not work for a proton beam.

The physics of intense beam propagation

through thin gases is so complex that experiments

will be needed to determine whether this concept is even feasible in principle. If so, the concept would resemble the neutral particle beam,

with the added requirement for the channel-boring laser and perhaps the ability to intercept

boosters at slightly lower altitudes than the neutral

counterpart.

8R, B. MI I Ier, The Physics ot’ Intense Charged Particle Beam5, New

York, 1982, ch. 5.
3.5 SPACE-BASED KINETIC ENERGY WEAPONS

Kinetic energy is the name given to the energy

of a moving projectile. Use of this term makes

ordinary weapons using aimed projectiles into

“directed kinetic energy” weapons.

The phenomenology of high-velocity collisions

between a projectile and a structure like a booster

is surprisingly complex, but in general lethality

is not an issue for kinetic energy boost phase intercept concepts. Rather, the problem is getting

the projectile from its satellite base to the ascending booster in time to make an intercept. Schemes

where the projectile is carried by a small rocket

launched from the satellite suffer most directly

(leaving aside countermeasures) from a combination of the large number and large size of the

rockets needed for adequate coverage. I n particular, the most conspicuous public example of the

kinetic energy approach, the High Frontier Project’s Global Ballistic Missile Defense (GBMD)

concept, 9 has extremely limited capabiIity for

boost phase intercept of current Soviet ICBMs

and would have no capability at all against a

future generation of MX-like boosters.

Kinetic Energy Concepts

Rocket attack of ICBM boosters is obviously not

as novel as beam attack, but it entails rather more

complexity than appears at first blush. The rocket

needs radio or other guidance by long-range sensors on its carrier satellite (or other satellites) to

direct it to the vicinity of its target, since it is impractical to put a long-range sensor on each

rocket. Once in the vicinity of the target booster,

the interceptor needs some form of terminal homing sensor and rather sizeable divert rocket

motors. Homing on the plume of the ICBM booster is not straightforward, since attacking the

plume will obviously not harm the booster: the

booster body must be located in relation to the

plume. These complications introduce opportunities for offensive countermeasures.

An alternative to rocket propulsion would be

to expel the homing vehicles at high velocity from

a gun. So-called rail guns use a clever scheme

9General Daniel O. Graham, The Non-Nuc/ear Defense of Cities: The High Frontier Space-Based Defense Against ICBM Attack

(Cambridge: Abt Books, 1983).

to convert electrical energy to projectile kinetic

energy. Since a 10 kilogram projectile ejected

with 5 km/see velocity carries 125 megajoules of

energy (the amount of energy expended by a 25

megawatt chemical laser in 5 seconds of dwell

on a booster), the power requirements of the gun

schemes are imposing. Providing chemical fuel

or explosives to power a gun therefore involves

the same magnitude of on-orbit weight as the

chemical laser.

Doing away with the homing sensor and replacing the guided projectile with many small

fragments is not an attractive alternative, since

the needed fragments end up weighing far more

than the guided projectile.

The Importance of Projectile Velocity

In the 300 or so seconds from launch to burnout of a slow-burning booster like the SS-18, the

defensive rocket or other projectile must fly from

its satellite to the path of the booster. Such a

booster burns out at about 400 km altitude, so

if the projectile wishes to use the entire 300

seconds of boost phase to travel to its quarry, it

must make its intercept at 400 km altitude.

Suppose now that the projectile’s rocket or gun

launcher can give it a maximum velocity of 5

km/see with respect to the carrier satellite. In the

300 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 carrier therefore has an effective range of 1.5 Mm

(fig. 3.1 la).

Referring to figure 3.4, a constellation of about

240 carrier satellites are needed for continuous

coverage of the Soviet Union. Since Soviet ICBMs

are spread over much of the country, 10 or so

of the carrier satellites might be able to participate

in a defensive engagement. The absentee ratio

is therefore about 24, The 10 satellites over the

U.S.S.R. at the moment of a massive Soviet attack need to be able to handle all 1,400 boosters,

meaning each satellite needs to carry 140 projectiles.

An idealized rocket accelerating a 15 kg guided

projectile to 5 km/see velocity would need to

weigh about 80 kg (a real rocket with this capa-
Figure 3.1 l(a)

-.

.33

Figure 3.1 l(b)

Satellite orbital path

t = 0

SS- 18

boosters

Iaunched

t = 240 sec. A

o 100 200 300

Seconds after launch

I ,

0 800 1600 2400

Kilometers along satellite orbit

Figure 3.11 View from above (looking down on earth) of

coverage by a satellite carrying kinetic energy boost-phase

intercept vehicles. The satellite is deployed in a 400 km orbit.

At time t =0, offensive boosters are launched. The satellite

can make intercepts by shooting downward or wait until the

boosters rise to their burnout altitude and fire nearer to the

horizontal. The longer after launch the intercept is made, the

farther the rocket intercept vehicles can travel from the

satellite to make the intercept. Smaller circles thus

correspond to downward firing, larger circles to horizontal

firing. The satellite moves from left to right in accordance

with its 8 km/see orbital velocity. The area enclosed by all

the circles taken together gives the total coverage of the

satellite and determines how many satellites are needed in

the worldwide constellation for continuous coverage of

opposing ICBM fields. All dimensions are to same scale.

(a) The satellite-based kinetic energy interceptors are

capable of 5 km/see velocity relative to the satellite. The

attack is on a slow-burning Soviet SS-18.

bility would weigh more like 200 kg). Each carrier satellite must therefore weigh (1 40) x (80)

= 11,000 kg. Less than twice this weight can be

carried by the space shuttle into the appropriate

orbits, so establishing the total 240 satellite constellation requires over 120 shuttle launches in

this highly idealized model with idealized rockets

and weightless carrier satellites. (A more carefuI

estimation of interceptor design would more than

double this load.)

From this baseline, we can consider five excursions:

t = 0

MX-like t = 200 Sec.

boosters Booster burnout

launched (200 km altitude)

altitude

o 300

Seconds after launch

o 2400

Kilometers

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

1. Suppose the velocity capability of the inter2

ceptor is doubled to”1 0 km/sec, doubling the

effective flyout range to 3 Mm. At this range,

48 satellites complete the constellation, with

perhaps as many as eight of them in position to participate in the engagement. Each

of the eight satellites must handle 175 Soviet boosters.

Doubling the velocity capability more than

doubles the weight of the rocket required.

The reason is simple: to increase the velocity

requires more propellant, and the extra propellant must itself be accelerated, requiring

yet more propellant. The rocket weight thus

grows exponentially with velocity capability.

The idealized 10 km/sec rocket weighs 420

kg. Each satellite carrying 175 rockets then

weighs 75,000 kg and requires some five

shuttle launches to orbit. The result is that

over 200 shuttle launches are required to orbit the entire (idealized) defense system. Increasing the velocity capability is therefore

no escape from large on-orbit weights.

The current Soviet ICBM force consists

largely of slow-burning liquid-fueled boosters

distributed widely over the Soviet Union.

Consider the consequences for the U.S. kinetic energy defense system if the Soviets de-
34

Figure 3.1 l(c)

300 km radius

260 km radius \

130 km radius

t = 0

SS-18 Boosters at

boosters launched 200 km altitude

t = 280 sec.

Boosters at

300 km altitude

t = 300 sec. /

Booster burnout

(400 km)

- 0 0

0

Seconds after launch

1 I J

o 800 1600 2400

KiIometers

(c) The High Frontier Global Ballistic Missile Defense

(GBMD) concept, with intercept vehicles capable of only 1

km/see velocity relative to the satellite. Intercept of SS-18.

In the actual High Frontier proposal, the satellites are in 600

km orbits, giving them even less coverage than shown here.

Figure 3.11(d)

Satellite must fire straight

down to intercept booster

just before burnout. Satellite

has no lateral coverage at all.

/

boosters launched Booster burnout

&90 km altitude)

0 100 200 300

Seconds after launch

, i

o 800 1600 2400

Kilometers

(d) The High Frontier concept has no capability whatsoever

for boost-phase intercept of MX.

ploy 100 faster-burning MX-like boosters in

one region of the country, so that defensive

interceptors have less time to fly to their

targets and only one satellite overhead participates in the engagement. MX burns out

200 seconds after launch, so each satellite

has an effective range of 1 Mm, requiring a

constellation of 400 satellites (fig. 3.11 b).

3.

4.

5.

In

Each satellite must carry the 100 80-kg rockets needed to handle the attack. An exchange ratio of four 8,000 kg U.S. defensive

satellites for every Soviet offensive booster

deployed is surely an economic advantage

for the U.S.S.R.

Soviet deployment of 1,000 Midgetman-like

boosters would require a compensating deployment of 400 U.S. satellites, each weighing at least 80,000 kg. A system that forces

the United States to such a response is

clearly absurd.

Soviet fast-burn boosters would be totally immune to the kinetic energy defense system.

An interceptor on a satellite in 400 km orbit

(lower orbits shorten satellite lifetimes because of atmospheric drag) could not even

descend straight down to the fast-burn

booster’s 100 km burnout altitude in the required 50 seconds, much less have any lateral radius of action.

Intercepting SS-18 or MX post-boost vehicles

is clearly easier, from the point of view of

flyout velocities, than boost-phase intercept.

Satellites at 700 km or so altitude would have

500 seconds to fly out to meet the bus when

it ascended to their altitude, giving a 2.5 Mm

lethal radius.

conclusion, a rocket-propelled kinetic energy system acting against today’s Soviet ICBM

arsenal (with no Soviet countermeasures) would

require many heavy satellites and would be a

dubious investment for the U.S. Soviet deployment of MX-like or Midgetman-like boosters

wouId nullify the United States defense or force

the U.S. to large investments in new satellites.

Analysis of the High Frontier Concept

The High Frontier Program10 proposes a Global

Ballistic Missile Defense (GBMD) using rocket

propelled interceptors for boost phase intercept.

This concept claims to have some utility, at least

against the present Soviet ICBM arsenal.

The concept consists of 432 satellites (24 planes

of 18 satellites in circular orbits inclined 65

degrees) 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 interceptors are apparently command guided to the

vicinity of the target. The homing sensor is not

specified, but short wave infrared homing on the

hot rocket plume is implied.

Consider this concept defending against the SS18 in its boost phase. Since the SS-18 burns out

at 400 km altitude 300 seconds after launch, each

GBMD satellite has a 0.3 Mm radius of action.

Since the satellites are deployed at 600 km

altitude, the interceptor must descend 200 km

to make an intercept just before burnout, resulting in a lateral radius of action of 0.22 Mm

(compare fig. 3.11c, where the satellites are

assumed deployed at 400 km altitude). With a

range this small, thousands of satellites would be

needed worldwide for continuous coverage of

Soviet ICBM fields. The High Frontier concept

with only 432 satellites would therefore have

meager coverage of Soviet ICBM fields.

The GBMD concept would have no capability

whatsoever against an MX-like booster. Such a

booster would burn out before the interceptor

couId reach it, even if the interceptor were fired

straight down (fig. 3.11 d).

It is possible that the High Frontier concept is

designed for post-boost intercept rather than

3.6 MICROWAVE

Microwaves are short-wavelength radio waves

used in radar, satellite communications, and terrestrial communications relays. A number of ideas

have been conceived for generating microwaves

in space and directing them towards ascending

ICBM boosters. The principal technical problem

with this type of BMD, generator technology

aside, is the uncertain effect the microwaves

would have on their target.

The microwaves would propagate through the

atmosphere unattenuated at all but the highest

power levels. The weapon divergence angle

would be very large, producing a spot many km

boost phase intercept. Its coverage for post-boost

intercept, though greater than for boost-phase intercept, would still be only partial. The only example given in the description’ of the system is

of boost phase intercept of an SS-18, however.

In this example the interceptor is launched 53

seconds before launch of its target booster,

though no explanation is given of how the U.S.

defense knows in advance the precise moment

at which the Soviets would launch a given booster. This early launch allows the interceptor to

reach its target seconds before burnout. Plume

homing, a technique inappropriate for bus intercept, is also implied for the High Frontier concept. Post-boost intercept permits some RVs to

be deployed on trajectories carrying them to the

United States before intercept; and the entire bus,

with its warheads, would continue on to the U.S.

after the interceptor collision, with uncertain consequences.

It would therefore appear that the technical

characteristics of the High Frontier scheme result in a defensive system of extremely limited

capability for boost phase intercept of present Soviet ICBMs and no capability against future MXIike Soviet boosters, even with no Soviet effort

to overcome the defense.

‘ ‘ I bld , p 103.

GENERATORS

wide at a few hundred km range. From these considerations the following concept emerges: As Soviet ICBMs lift off from their silos, a few microwave generators in space bathe the silo fields with

microwaves.

At high power levels, as in a microwave oven,

microwaves cause heating in many materials. But

in the BMD scheme, the divergence cone is so

large that even a prodigious amount of energy

emitted from the generator would lead to very

small energy deposition per square centimeter

on the target (millions of times less than lasers).

The microwave pulse received at the booster
36

would resemble the high frequency component

of the electromagnetic pulse (EMP) from a highaltitude nuclear detonation. However, even weak

microwaves can upset sensitive circuitry if they

can reach it.

A metal skin on the booster would stop the

microwave pulse altogether from reaching internal electronics. The microwave defense must

therefore hope that some aperture or conduit is

available into the booster, whether by design (as

in an antenna), inadvertence, or poor maintenance. If so, and if the electronic circuitry is not

or cannot be made resistant to disruption or burnout, the part of the booster’s performance dependent on those electronics (perhaps accurate

guidance) would be affected.

Because of the very uncertain lethality of microwaves, deployment of space-based generators (if

they can ever be built) would be a harassing tactic rather than a confident-kill ballistic missile

defense.

3.7 OTHER CONCEPTS

Other directed energy concepts suitable in the- single huge pulse for impulse kill of a boostory for ballistic missile defense have been er. All these schemes are at a very early conbroached 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 a

time a revisit to this subject will find a new target just like ordinary particle beams, expanoply of concepts enjoying the front rank of cept that when the antiparticle reached the

discussion. end of its range it would annihilate a parti1. Short-wavelength chemical lasers would

combine the simplicity and efficiency of the

HF chemical laser with the small mirrors of

the short-wavelength excimer and free-electron lasers. Though some ideas have been

advanced along these lines, no laser exists

which can be said to be a candidate to fulfill

this theoretical promise.

2. Explosive-pumped lasers and particle beams

are said to be under study in the Soviet

Union. 12 Such devices might possibly be

quite compact, each bomb generating a

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

cle in the target, freeing a large extra amount

of harmful energy. Acceleration of antimatter beams is accomplished exactly as with

particle beams, and laboratory beams of antimatter have been used routinely in pure

research. One important difference is that

antimatter is not freely available in the universe as is matter; the antimatter for the accelerator would have to be produced by the

defense system, a formidable and complex

undertaking. It is not clear that the extra

energy released in the target by an antimatter beam would justify the trouble of producing the beam.
Section 4

OTHER ESSENTIAL ELEMENTS OF A

BOOST-PHASE INTERCEPT SYSTEM
Section 4

OTHER ESSENTIAL ELEMENTS OF A BOOST-PHASE

The previous section treated only the defensive weapon itself, the so-called “kill mechanism . But if beam weapons ever evolve to the

point where deployment is a serious possibility,

other elements of the overall defensive system

will emerge as equally important determinants

of cost and level of protection. After all, the interceptor missile in traditional BMDs has not been

the central focus of attention or technical debate

since the 1950’s, when it became clear that a

“bullet could hit a bullet. ” Discussion of BMD

at that point passed to the difficuIt issues of radar

performance, data processing capability, and vul4.1 TARGET

INTERCEPT SYSTEM —

Locating and tracking an ICBM booster with

enough precision to aim a directed-energy

weapon is not as straightforward as is sometimes

supposed. it is true that booster motors emit hundreds of kilowatts of power at short- and mediumwave infrared (SWIR and MWIR) wavelengths of

a few microns. Sensors can detect these plumes

at great distances from the earth. Plume sensing

is used today for early warning of missile attack

to support launch of bombers and airborne command posts and launch under attack of ICBMS.

To be useful for directed-energy BMD, however, the sensor must localize the booster within

an area as small as the beam spot. Otherwise the

beam would have to sweep wastefully back and

forth over the area of uncertainty. Small divergence beams must therefore be accompanied by

sensors with small angular resolution.

Diffraction limits the angular resolution of a sensor in the same way it limits the divergence angle

of a laser. A large infrared telescope with 5 m

diameter mirror observing MWIR booster emission at 4 micron wavelength would have angular

resolution no more precise than a micro radian.

Such a sensor affixed to each battle station in a

nerable basing of defensive components—issues

that had nothing to do with the kill mechanism.

In a similar manner, the other essential elements

of a boost-phase intercept system will figure more

prominently in discussion of boost-phase BMD

if and when the kill mechanisms—lasers, mirrors,

accelerators—are in hand. These other essential

elements introduce their own technological problems and opportunities for offensive countermeasures. If traditional BMDs are any guide,

provision of a kill mechanism will be just the

beginning of making an efficient, robust defensive system.

SENSING

defensive constellation would localize ascending

boosters to within a spot 5 m wide at 5 Mm range.

At this range, the (illustrative) systems described

in Section 3 have spot sizes: 1.5 m for the H F laser, 0.6 m for the ground based laser, 10 m for

the neutral particle beam, and 100 m for the xray laser. Even a large infrared sensor on each

battle station would therefore be inadequate for

directing the laser beams at a point source of

MWIR light, marginal for directing the neutral

particle beam, and adequate for directing the xray laser. The actual situation would be worse

still, since the booster is not a point source. The

booster plume would be larger than the laser or

particle beam spots, and the booster body would

need to be located in relation to the plume to

avoid wasting beam time attacking the plume.

For directed-energy weapons with small divergence angles, therefore, sensing the conspicuous

rocket plume is inadequate. Another kind of sensor must be introduced into the BMD system. For

finer angular resolution one looks to shorter

wavelengths, in the visible or ultraviolet. At these

wavelengths the sensor must provide its own illumination. A so-called laser radar or Iadar is the

only practical solution. In a ladar, a low-power

39
40

visible or ultraviolet laser shines on the booster

body, and a telescope on board the battle station senses the reflected light.

Besides the annoyance of a new laser and new

sensor, the necessary introduction of Iadar into

the boost-phase system creates opportunities for

the defense to spoof and blind the offensive

sensor.

Kinetic energy systems do not need precision

long-range sensing, since the rocket or guided

projectile homes on the target when it comes

within short range. The terminal homing might

involve deducing the location of the booster body

in relation to its MWIR plume, homing on lowpower laser light shined from a defensive satellite and reflected from the target, or some other

method. These homing methods are susceptible

to countermeasures.

Though this Background Paper treats only intercept of the booster proper, it is worthwhile

pausing to consider tracking of the post boost

vehicle or bus. The low thrust levels of the post

boost vehicles’s rocket motors, their intermittent

operation, the possibility of dimming them with

propellant additives, and the possibility of

building decoys with small rocket motors all suggest that MWIR plume sensing is not practical for

post boost intercept. The alternatives are Iadar

or radar, suggesting again many opportunities for

countermeasures.

4.2 AIMING AND POINTING

The directed-energy beam must be aimed and In the 15 milliseconds the beam takes to travel

stabilized 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 beam

vergence increases, and the beam wastes energy must therefore lead the target. In one second of

missing the target. The mirrors or other mecha- dwell time, the target moves several km; the

nism steering the beam must be stabilized despite beam must remain on the target, sweeping

vibrations in the battle station caused by the through the sky at the necessary angular rate

beam’s large power source. while still maintaining its aim and jitter control.

4.3 INTERCEPT CONFIRMATION

A desirable, though perhaps not essential, function of BMD systems is confirmation that an attempted intercept succeeded. This function is

sometimes called “kill assessment. ” Intercept

confirmation would allow the beam to move onto

subsequent boosters with more than a statistical

estimate that its previous task was accomplished.

Structural damage to the booster would presumably be revealed by an erratic course or burn pattern, though it might be difficult to say in advance

exactly what the sensor’s view of the wounded

booster would be. Subtle damage inflicted by a

particle beam or microwave generator might not

be visible. Damage to a bus would be difficult

to assess and interpret if the debris, including RVs

(perhaps arranged by the offense to separate from

the bus under extreme circumstances), continue

on their ballistic course to the continental United

States.

Related to intercept confirmation, and ultimateIy more serious, is the question of determining

whether the beam is missing the target (perhaps

by slight misalignment of sensor and beam boresights, miscalibration of aiming mechanisms, etc.)

and, if so, by how much and in what direction.

It might be possible to observe a glowing column

of air where a laser beam passes through the at-
41

mosphere. Some clever but elaborate schemes

have been devised to track a neutral particle

beam. Obviously each new complication added

to the defensive system potentially creates new

opportunities for offensive countermeasures.

4.4 COMMAND AND CONTROL

The crucial infrastructure of command and

control of a complex system is always the last to

take shape, since it integrates the workings of all

the separate components. It is easy to ignore the

difficulty of accomplishing this last step at this

early stage when the other components of a boost

phase system are not yet remotely in hand. The

command and control system of a boost-phase

intercept system would comprise communications links among its far-flung components, data

processing to support sensors and battle station

operations, and “battle management” software

incorporating all the instructions and decisions

needed to run the defensive engagement and to

coordinate the defense with U.S. offensive forces.

Communications and data processing are two

areas of technology where there is the least pessimism—looking two or so decades into the future

when boost-phase systems could presumably be

deployed–that technology will be able to meet

the needs of directed-energy defenses. Compact,

lightweight, and rapid data processing hardware

is virtually assured, though interesting questions

attend on hardening, reliability, and lifetime in

space. Software would be expensive and would

introduce issues of reliability and security from

programmer sabotage. Satellite-to-satellite communication via extremely high frequency radio

and laser offers high data rates and virtual immunity to jamming from earth or from space.

Command and control for BMD does introduce

two interesting issues to which technology cannot provide an answer. The first is the impossibility of testing the whole defense system from

end to end in a realistic wartime setting. Unlike

the air defense systems of World War 11, which

learned through attack after attack to exact kill

rates of several percent, the BMD system would

have to work near perfectly the very first time it

was used. The second issue is the likely need for

the defense to activate itself autonomously, since

there would be no more than a minute for human

decision,

4.5 SELF-DEFENSE

Consideration of anti-satellite (ASAT) attack (see less and until a credible overall approach to satSection 5.1 ), and analogy with traditional BMD ellite survivability is found, one cannot specify

systems (where vulnerability of key radars, data the needed hardware.

processors, and other components is usually the Ground-based BMD lasers and pop-up x-ray chief limitation on defense performance) suggest lasers would obviously need to be protected from that self-defense mechanisms could well end up

being a large part of the defense system. These precursor attack by cruise missiles and other

delivery systems. ‘ mechanisms could include shields, escort weapons, and countermeasures to ASAT sensors. Un-
42

4.6 POWER

Chemical lasers, x-ray lasers, and rocket-propelled kinetic-energy interceptors have power

sources integral to the weapon, but excimer

lasers, free electron lasers, neutral particle beams,

and rail guns would need sources of electrical

power and the equally important means to convert electricity into a form usable by the weapon

(“power conditioning”). Space basing obviously

complicates the task. Large commercial power

plants on the ground produce about 1,000 MW

SOURCES

of power, and directed energy weapons might

require hundreds of MW. On the other hand, the

power plants on defensive satellites need not

work reliably for many years but only once for

a short time, and they need not be very highly

efficient. The three alternatives for space power

are fuel burning, explosives, and nuclear power.

Starting up a large power source in seconds from

a condition of dormancy poses some interesting

design issues.
-

Section 5

COUNTERMEASURES TO BOOSTPHASE INTERCEPT

●
Section 5

COUNTERMEASURES TO BOOST-PHASE INTERCEPT — . . — —

Countermeasures that limit the effectiveness of

traditional ballistic missile defenses—decoys,

radar blackout, defense suppression, etc.—are

well known. A comparable set of countermeasures, no less daunting for being less familiar, faces

the designer of boost-phase defenses.

The need to resort to countermeasures imposes

a cost on the offense. This cost is measured in

money to build more or specialized offensive

hardware, but also in the time needed to do so,

i n constraints upon the type of attack the offense

can incorporate in its nuclear planning, and in

the confidence with which it can predict a “successful” outcome of the strike.

Every BMD system actually proposed for deployment would be accompanied, at least ideally,

by, first, an analysis of its degradation in the face

of an improving Soviet offense and, second, by

an analysis of how much it would cost for the

United States to improve its defense in such a way

as to avoid being overcome. ’

‘See BallIstIc Missile Defense, ed. Ash(on B. Carter and David

N. 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 performance

of a BMD system degrades as the size and sophistication of the attacking force increase.

1

Figure 5.2

Low High

Level of defense performance

Fig. 5.2. The marginal cost exchange ratio measures the outcome of

a race between the Soviet offense to enhance its penetration and a

U.S. defense to maintain its level of protection. In general, modest

defense goals (e.g., “preserve 40 percent of the targets”) are easier

to sustain than high goals (“preserve 95 percent of the targets”)

against improvements in Soviet offensive forces, including deployment of countermeasures.

The first analysis would be expressed in a drawdown curve such as that shown in figure 5.1. The

Soviets can overcome the defense and destroy

a large number of U.S. targets, but to do so the

Soviets must “pay” an “attack price. ”

The second analysis would be encapsulated in

the cost exchange ratio. The marginal cost exchange might be defined as follows: “Assume that

in the year 2000 the U.S. defense and Soviet offense have evolved so that each has a certain

level of effectiveness. Suppose the Soviets wish

to improve their position and the U.S. resolves

to maintain the status quo. Which side spends

more in the competition?” For example, suppose

every time the Soviets add 100 ICBMs to their

arsenal, the United States has to add 20 satellites

to its defensive constellation to intercept them:

Which costs more, 100 ICBMs or 20 satellites?

45
46

In general, high levels of defense performance

are harder to enforce in the face of offensive improvements than low levels: this important fact

is shown schematically in figure 5.2 (see also Section 8.2).

All of the boost-phase intercept schemes discussed in this report are in such an early stage

of conceptualization that nothing remotely like

the analyses represented by Figures 5.1 and 5.2

can be done for them. Nonetheless, countermeasures are known for every boost-phase system devised, and in many cases simple heuristic

estimates of the cost tradeoffs are suggestive. ,

Technical experts disagree not so much about

the facts and calculations underlying these countermeasures as about the interpretation to be

given to them. Should an apparently fatal flaw

uncovered at this early stage of study of a defensive concept be decisive, or should work (and

the inevitable expectations that accompany it)

continue on the chance that a new idea will turn

up to rescue the concept? Would the Soviets

really resort to a subtle tactic or exotic piece of

hardware as a confident basis for their nuclear

policy? Some analysts see BMD as a way of “forcing” the Soviets to take a certain direction in

their pursuit of the arms race, e.g., away from

large, slow-burning MIRVd boosters to singlewarhead Midgetman-like boosters. In this view,

defeat of the BMD is purchased at the price of

a theoretically more stable and desirable Soviet

offensive posture. All these questions of judgment

loom large in making a final assessment of a given

countermeasure.

5.1 ANTI-SATELLITE (ASAT) ATTACK,

INCLUDING DIRECTED-ENERGY OFFENSE

All boost-phase intercept BMD concepts have

crucial components based in space. Even a popup defense would need warning and very probably target acquisition sensors on satellites over

the Soviet Union. Ground-based laser defenses

would have mirrors and sensors—their most fragile components—in space. Vulnerability of these

satellites is a cardinal concern because their orbits are completely predictable (they are in effect fixed targets), they are impractical to harden,

conceal, or proliferate to any significant degree,

and because successful development of effective

directed-energy BMD weapons virtually presupposes development of potent anti-satellite (ASAT)

weapons. ASAT is the clear boost-phase analogue

of familiar defense suppression tactics against

traditional BMDs, where attack is first made upon

the defensive deployment (especially fixed radars)

and then upon the defended targets.

The interplay of ASAT techniques–missiles (nuclear or conventional), space mines, directed

energy—and satellite defense (DSAT) techniques

is a complex one, It is difficult to generalize, but

in the specific case of large battle stations in lowearth orbit it would seem that the advantage is

very likely to lie with ASAT, not DSAT. For one

thing, the offense need not destroy a large number of defensive satellites, but only “cut a hole”

in the defensive constellation. Second, the traditional military refuges all offer complications: concealment from radar, optical, infrared, and electronic detection, while possibly successful for

small payloads in supersynchronous orbits, is impractical for large, complex spacecraft at most a

few thousand km from the earth’s surface; decoy

satellites must generate heat, stationkeep, and

give status reports, and they are in any event only

useful if the ASAT designer is somehow restrained

(perhaps by cost) from shooting at all suspicious

objects; hardening imposes weight penalties, and

massive shields could interfere with the constant

surveillance and instant response required of the

defense; proliferation is useless for expensive

satellites facing inexpensive ASAT methods, As

a consequence, discussions of DSAT for BMD

battle stations usually emphasize large keep-out

zones around the satellites and active self-defense. A third reason why ASAT is likely to prevail over DSAT is that possession by the offense

of the same type of directed energy satellites used

by the BMD probably assures successful first
47

strike. Fourth, the Soviets would pick the time

and sequence of their attack, and it would occur over Soviet territory.

Two rather novel ASAT threats are worthy of

note. The first is the x-ray laser itself. The x-ray

laser, if it could be developed, would constitute

a powerful space mine. Because of its long range,

it could lurk thousands of km from its quarry. The

Soviets might also launch x-ray lasers a few seconds before launch of their main attack. Recall

that the well-known phenomenon of bleaching

(see Section 3.3) would probably allow such xray lasers to shoot out of the atmosphere at a U.S.

x-ray laser defense, but the U.S. x-ray lasers could

not shoot down into the atmosphere at the ascending lasers.

A second ASAT tactic, discussed for many years,

imagines the Soviet Union exploding nuclear

weapons at high altitudes in peacetime with the

intent of shortening the orbital lifetimes of the

U.S. defensive satellites, The nuclear bursts inject further radiation into the van Allen belts that

circle the earth’s equator from about 1,500 to

10,000 km altitude. Satellites (more likely carrying sensors than weapons at these altitudes) passing through the belts accumulate a radiation dose

that gradually degrades electronics, sensors, and

optical surfaces. This possibility, if taken seriously,

would require defensive satellites designed to

withstand rather substantial accumulated radiation doses.

A detailed treatment of the ASAT problem is

beyond the scope of this Background Paper. The

following “parable” illustrates some of the problems encountered in trying to ensure the survivability of a defensive constellation, taking the 20

MW HF lasers of Section 3.1 as an example.

The United States deploys the HF lasers in this

hypothetical system in low orbits at 1,000 km

altitude. Higher altitude would place them too

far from their targets. This is unfortunate: higher

altitude (say, between 2,000 km and semisynchronous orbit at 20,000 km) would move the

satellites further from ground-based ASAT weapons and put them into lesser-used orbits where

staking out a sanctuary would involve less interference with foreign spacecraft.

Suppose the battle station designers have succeeded in the considerable task of making the

satellites resilient to multi-megaton nuclear space

mines (bombs, not x-ray lasers) as little as 100 km

away, To keep all Soviet spacecraft (i.e., all potential mines) at least 100 km away, the United States

claims for itself the orbital band between 900 and

1,100 km altitude. Perhaps the Soviets are

awarded some other orbital zone for their own

military purposes. The United States establishes

the following rules in its zone: 1 ) No foreign

spacecraft may transit the zone without prearrangement; 2) All transiting vehicles must remain

at least 100 km from all U.S. battle stations, passing through a “hole” in the constellation; 3)

Foreign spacecraft failing to obey these rules may

be destroyed by the U.S. lasers.

Consider first a Soviet kinetic energy ASAT deployed at 1,100 km altitude, just outside the U.S.

keepout zone. Suppose the rocket interceptors

on the Soviet satellites have the same propuIsive

capacity—one km/see—as the proposed High

Frontier Global BMD system. The Soviet ASATs

are then just 100 seconds away from the U.S.

lasers. The U.S. lasers must therefore be very vigilant to avoid surprise attack. Fortunately, at 100

km range the 20 MW laser with 10 m mirror

would burn up even a heavily hardened ASAT

rocket in short order. Since starting up the main

laser for self-defense might be awkward, wasteful

of fuel, or time consuming, each U.S. battle station might be escorted by a satellite carrying a

smaller laser or rockets for self-defense.

A constellation of Soviet 20 MW, 10 m HF

lasers (the same technology as the U.S. lasers) at

1,100 km is another matter. These lasers could

attack the U.S. lasers seconds before launch of

a Soviet ICBM attack. The United States would

have to keep these Soviet spacecraft thousands

of km away from the U.S. constellation. That is,

the United States would have to dominate nearearth space. Suppose the United States does so.

Now the Soviets build a fleet of pop-up x-ray

lasers. These lasers climb to 100 km or so altitude,

where information radioed to them from the

ground 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 100

times less bright than the ideal x-ray laser

described in Section 3.3. Nonetheless, by pointing all its Iasing rods at the same target, a Soviet

x-ray laser can destroy a U.S. laser battle station

at 10 Mm range. The U.S. chemical lasers attack

the Soviet x-ray lasers as they ascend, but at this

range long dwell times are required to destroy

the Soviet lasers. By launching enough x-ray

lasers simultaneously, the Soviets succeed in getting some to 100 km altitude, where they can

shoot out through the thin atmosphere, before

the U.S. lasers can destroy them. In this way, the

Soviets “punch a hole” in the U.S. defensive constellation. (At a minimum, the Soviet ASAT attack

consumes precious laser fuel aboard the U.S. battle stations.)

just to make sure, the Soviets also deploy some

powerful ground-based excimer or free electron

lasers to destroy the U.S. battle stations as they

orbit helplessly through space.

5.2 FAST-BURN BOOSTERS

Shortening the boost time and lowering the

burnout altitude is easily accomplished at little

sacrifice in useable ICBM payload (see Section

2). Shorter boost time increases the number of

lasers needed for space-based laser or groundbased laser systems to handle simultaneously

launched boosters. Short burn time makes rocketpropelled kinetic energy systems impractical,

since the radius of action of each satellite

becomes too small. Short burn time, together

5.3 COUNTER

Countermeasures to the crucial functions of

target sensing and command and control are a

relatively unexplored, but probably key, problem

area for directed energy BMD. In the case of terminal and midcourse defenses, the issues of decoy discrimination, confusion caused by chaff

and aerosols, radar blackout and infrared redout,

radar jamming, and traffic handling have always

been and remain central limitations, It is likely

that analogues will be found for boost-phase

systems. Devising countermeasures requires a degree of specificity about the nature of the defense

system which cannot be provided in the present

conceptual stage. There follow a few examples

of C3

l countermeasures, by no means an exhaustive list.

A first point to note is that sensors are likely

to be the most vulnerable part of a defensive satwith low burnout altitude, would severely compromise the effectiveness of x-ray lasers popped

up even from subs near Soviet shores. Low burnout altitude nullifies the neutral particle beam,

which cannot penetrate very far into the atmosphere.

Fast-burn boosters would therefore be a potent,

even decisive, countermeasure against almost all

concepts for boost-phase intercept.

C

3

l TACTICS

ellite. A laser shined into an optical sensor can

daze or injure the focal plane elements, though

viewing in frequency bands absorbed by the atmosphere offers protection from ground-based

lasers. Mirrors would be very susceptible to damage from a Soviet x-ray laser. A Soviet neutral particle beam could disrupt electronic circuits on

U.S. satellites. Radiation pumped into the van

Allen belts by nuclear bursts would affect sensors and electronics.

A single nuclear burst causes the upper atmosphere to glow brightly over areas 100 km in radius for over a minute. Calculated radiances2 are

large enough to cause background problems for

MWIR tracking sensors.

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

(1962).
4 9

Some directed-energy weapons produce spots

only meters wide at the target, requiring target

sensing to commensurate precision via laser radar

(see Section 4.1). Laser radars sense laser light

reflected from the target. A small corner reflector affixed to the target would produce a bright

glint of reflected light, as would other corner

reflectors launched on sounding rockets, ejected

from the target, or attached to the target by expendable booms. These proliferated corner reflectors might force the beam weapon to attack them

all.

The homing sensor of a kinetic energy interceptor could be susceptible to spoofing, depending

on its type.

Jamming satellite-to-satellite communications

crosslinks is probably not an effective offensive

tactic, since the links would have narrow beamwidths, requiring the jammer to locate itself

directly between the two satellites; and wide

bandwidths, requiring high jammer power.

5.4 SHIELDING

A degree of shielding from lethal effects is practical for ail but the kinetic energy weapons but

involves in each case different methods suited to

the different physical principles at work. At the

same time, large uncertainties plague all lethality

estimates, and further testing and study will be

needed before firm answers can be given for any

of the systems. For thermal kill with a laser, a solid

booster designed with some attention to a laser

threat can probably easily be made to withstand

10 kJ/cm2. Application of a gram or so of heatshield material on each square centimeter of

booster skin can probably triple this hardness,

and spinning the booster enhances hardness by

another factor of three. Heatshield material is

ablative, meaning that when heated it burns off,

carrying away the heat in the combustion gases

rather than conducting it through to the missile

ski n underneath. A factor of nine increase in

hardness requires the defensive laser to dwell on

the booster nine times as long or to approach

within a third of the range, Though hardening a

new booster from scratch is clearly easiest, there

is no serious impediment to retrofitting ablative

coatings on existing boosters. Applying a gram

per square centimeter of ablative material to the

entire body of the MX missile would require

removing several RVs from the payload, since the

coating would weigh well over 1,000 kg.

An interesting possibility, requiring further

study, would involve injecting into the atmosphere or producing from atmospheric gases,

either throughout the ICBM flyout corridors or

in the vicinity of individual boosters, smoke or

laser absorbing molecules. Likewise, dust clouds

raised by ground burst weapons (delivered by

cruise missiles or by ICBMs that “leak” through

the defense) might cause serious propagation

problems for the ground-based laser scheme,

Hardening to an x-ray laser involves quite different physical principles. Recall that the x-ray

energy is deposited in a paper-thin layer of the

booster skin. The superheated layer explodes, applying an impulsive shock to the booster. Obviously a paper-thin shield between the booster

and the laser will stop x-rays from reaching the

booster wall. But the problem then becomes the

debris from the exploding shield. One can easily

show by calculation that the debris applies virtually the same impulse to the wall of the booster

as would result from direct impinging of the xrays! A number of schemes can be devised to divert the debris from striking the booster, but these

require more study to implement in practice. One

factor acting in favor of the shield designer is that

the booster is not vulnerable to x-ray attack until

it leaves the atmosphere. The lightweight shields

therefore do not have to be designed to suffer

large drag forces.

The neutral particle beam presents a third distinct type of hardening problem. The energetic

beam particles penetrate into the target, and several centimeters of lead would be required to stop

them. Since the beam cannot penetrate very far

into 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 grams

per square centimeters of lead, the shielding

alone would weigh as much as several RVs. On

the other hand, if the neutral particle beam is only

designed to disrupt or damage sensitive electronics, but is not powerful enough to do damage to

other parts of the missile, only the sensitive components need be shielded. The weight penalty

then becomes small.

neutral particle beam by exploding a few nuclear

weapons at moderate altitudes before the beam

can reach them. The detonations heat the air,

which rises, effectively elevating the altitude at

which the neutral beam is stripped of its remaining electron and bent in the geomagnetic field.

This phenomenon is called atmospheric heave.

It is as yet unresolved whether atmospheric heave

will loft enough air to make a difference to the

engagement altitude of the x-ray laser.

It is possible that the offense can extend the

protection of the upper atmosphere against the

5.5 DECOYS

There is no way for a decoy booster to mimic

closely the hot exhaust plume of an ICBM booster

except by burning a similar rocket stage. One can

add chemicals to the propellants to brighten a

small booster’s plume and dim the ICBM’s, but

as a first approximation a faithful decoy must be

another booster.

Decoy tactics are therefore not as attractive for

boost-phase intercept systems that use plume

sensing as they are for midcourse and reentry

defenses, where large numbers of cheap, lightweight decoys can be carried with negligible offload of RVs. Still, the usefulness of a decoy

depends not on how expensive the decoy is, but

on how the cost of the decoy compares to the

cost of the defense that intercepts it. Booster

decoys would not be nearly as expensive as true

ICBMs, since they carry no warheads or precision guidance system, they need not be highly

reliable, and they might not need to be based in

underground silos but can be deployed above

ground next to the ICBM silos.

Some of the boost phase intercept systems must

grow in the number of their deployed battle stations in direct proportion to the number of Soviet boosters. Deploying one decoy (with a dummy payload) next to each of the 1,400 Soviet

ICBM silos might cause the United States to have

to double the number of battle stations overhead

(and thus worldwide, multiplying by the absentee

ratio) to handle the extra traffic. If the defensive

battle stations were at all expensive, this would

bean unpleasant prospect for the United States.

Many directed energy schemes would not rely

on plume sensing alone (see Section 4.1). Decoy

tactics against laser radars (including corner

reflectors; see Section 5.3) might be much easier

for the offense to implement than mimicking the

booster plume.

5.6 SALVO RATE

The worst-case attack for all the boost-phase A more leisurely salvo rate would allow laser

intercept schemes is massive, simultaneous and particle beam defenses that have to dwell

launch 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 climb

launch then have to handle the entire attack. to intercept position. An attack drawn out 10
51

— —

minutes or longer allows fresh defensive satellites

to move along their orbits into position overhead,

replacing depleted satellites. The orbital period

of satellites in low earth orbit is about 90 minutes.

If there are 8 to 10 satellites in each ring of the

defensive constellation, satellites replace one

another every 10 minutes or so.

An exception to this simultaneous-launch worstcase analysis is the x-ray laser, which delivers alI

its energy in an instant.

There would seem to be few military penalties

for the Soviet Union to adopting plans to launch

all their ICBMs in large attack within a few minutes. Indeed, if one of their objectives is to destroy 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 mounted

on Closely Spaced Basing (Densepack) for MX involve very slow or intermittent salvo rates, however.

More importantly, in many circumstances the

Soviets might wish to launch only a traction of

their ICBM force. A U.S. defense deployment too

small to intercept all boosters in a massive attack

would still be able to handle a small attack. A light

defense might therefore establish a “threshold”

of attack intensity below which Soviet boosters

wouId face intercept. This prospect is discussed

further in Section 9.

5.7 OFFENSIVE BUILDUP

The most straightforward way for the offense

to compete with the defense is to grow in size.

If for every new ICBM added to the Soviet

arsenal, the U.S. defensive satelIite constellation

must be augmented at comparable or greater

cost, the Soviets could challenge the United

States to a spending race to their net advantage.

On the other hand, if the defensive buildup is

cheaper than the offensive buiIdup, the defense

forces the offense either to accept limitations on

its penetration or to resort to qualitative changes

in its arsenal.

As an illustrative example of such a cost tradeoff, consider the hypothetical H F chemical laser

system described in Section 3.1. Each laser in that

system requires 1.7 seconds of dwell time to destroy a booster. During the 200 seconds of boost,

each laser overhead can therefore destroy 120

boosters. But for each laser overhead, 32 are

needed worldwide. Suppose now that the Soviets

deploy, in one region of the U. S. S. R., 1,000

Midgetman missiles at a cost of 10 to 20 billion

U.S. dollars (see Section 2). The U.S. defense

now needs to be “beefed up” with addition of

(1 ,000)X (32)/120 = 270 laser battle stations. A

tradeoff of more than one complex U.S. satellite,

launched and maintained on orbit, for every 4

Soviet boosters (or decoy boosters) deployed on

the ground would certainly appear to be a losing proposition for the United States. This is true

even though the hypothetical HF laser system

represents a very favorable outcome of laser technology.

Note that Soviet deployment of new ICBMs in

one region of the Soviet Union, within coverage

of only a single U.S. satellite, gives them the best

leverage in the cost exchange.

5.8 NEW TARGETING PLANS

Truly efficient ICBM defenses would presum- Iobbed into any target area unimpeded, the suably force upon the superpowers a stricter atten- perpowers have less need to be discriminating

tion to targeting priorities. With thousands of or parsimonious in their nuclear targeting. Such

warheads in today’s arsenals able to be literally a shift might have both desirable and undesirable

33-698 0 - 84 - 6 : QL 3
52

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 hypoures it could no longer afford to threaten the thetical defenses is not clear, but it is probably

other side’s ICBM silos. The warheads “freed up” quite wrong to imagine future defenses acting

from the countersilo mission might then be dedi- against offensive forces targeted according to the

cated 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 efficient

defense against their ICBMs would be increased

emphasis on submarine-launched ballistic missiles (SLBMs), bombers, cruise missiles, and whatever novel methods time and ingenuity might in

the future devise for introducing nuclear weapons

to the United States. As defenses forced up the

cost-per-delivered-warhead of ICBM forces, these

other methods would become relatively more attractive. Though they would sidestep the BMD,

these delivery means have higher pre-launch survivability than ICBMs, and bombers and cruise

missiles have longer times of flight, These attributes are usually seen as “stabilizing.” Shifting

the emphasis of the arms competition away from

ICBMs is therefore sometimes viewed as adequate payoff for the BMD effort.

SLBMs would obviously be vulnerable to the

same boost-phase weapons as ICBMs. The same

worldwide coverage, reflected in the absentee

ratio, that plagues the anti-lCBM cost exchange

means that orbiting boost-phase defenses threaten SLBMs the world over. However, midcourse

and terminal tiers of a layered defense would in

general have much less capability against SLBMs,

because of the latter’s short time of flight, possibly

depressed trajectory, and uncertain direction of

attack. Thus SLBMs could conceivably enjoy

greater penetration of a layered defense than

ICBMs.

If one takes an optimistic view of emerging

defensive technologies, or if one contemplates

technological “breakthroughs,” it is at least conceivable that such developments will spawn new

ways of delivering or aiding the delivery of nuclear weapons as well as new ways of interdicting them.
Section 6

A WORD ON “OLD” BMD

“NEW”

AND

BMD
Section 6

A WORD ON “OLD” BMD AND “NEW” BMD

No one knows whether directed-energy weapons can be built with the characteristics assigned

to the hypothetical systems of Section 3. Even if

such systems can be built, it is not clear that their

performance will match, much less exceed, the

performance of terminal and midcourse BMD systems in level of protection (attack price) and in

cost relative to offsetting offensive improvements.

The boost-phase BMD systems receiving so much

attention today were a year ago at the periphery,

to say the least, of technical discussion of missile

defense. It is important not to lose sight of the

status of traditional reentry and ‘‘advanced” (as

they were called a year ago) “overlay” midcourse

BMDs.

Naturally, the promise of the better-understood

terminal and midcourse systems does not seem

so grandiose, nor the flaws so clear-cut, as they

do for the conceptual boost-phase defenses discussed in this Background Paper. Sounder technical assessments can be made of the “old”

BMDs than of the “new” concepts. Rough concepts gloss over all the difficult design problems

that inevitably limit achievable performance and

turn up serious problems; nonetheless, identifying potentially unsolvable problems at this early

stage of study does not mean they will remain

insurmountable. BMD architectures incorporating boost-phase intercept are not known to be

able to perform better, dollar-for-dollar, than

BMD architectures incorporating only midcourse

and reentry intercept. They are just not known

to be worse. Terminal defense systems have been

studied, designed, and tested for years, and it is

generally agreed that such systems, acting alone,

can enforce a modest attack price of between 2

and 8 RVs (perhaps equivalent to 20 to 80 percent of a booster) per defended aim point. Though

their capabilities are modest, reentry and midcourse defenses suffice for modest defensive

goals. There is no need to incur the technical risk

of “new” boost-phase intercept schemes unless

one aspires to levels of performance clearly beyond those possible with “old” concepts.

Many of the “new” concepts for boost-phase

intercept are not new at all. They have been studied and discussed in one form or another for 20

years. Conversely, there are some new ideas for

improving terminal and midcourse BMDs.1 The

spirit of technical optimism that accompanied the

new emphasis on boost-phase intercept in the

past year affected thinking about “old” BMD as

well.

For terminal defense systems, the new features

receiving attention are, first, non-nuclear warheads on interceptor missiles and, second, airplane-borne infrared sensors as supplements to

ground-based radars. The principal benefit of

non-nuclear intercept is that interceptors can be

deployed nationwide without public concern

about the safety of defensive nuclear warheads.

Non-nuclear kill does not permit the defense to

avoid all the disruptive effects of nuclear bursts,

however, since the offense can still arrange for

RVs to detonate when they sense interceptor impact (“salvage fuzing”). The miss-distance/weight

relationship of the non-nuclear warhead requires

the interceptor to approach more closely to the

RV, and this in turn requires a homing seeker on

the interceptor. Terminal homing obviously

creates new opportunities for offensive countermeasures.

Airborne optical sensors obviously do not suffer radar blackout, but they can suffer the analogous problem of infrared redout. Decoy discrimination remains a problem, though it acquires

some interesting new features. Details of these

new aspects of terminal BMD are obviously classified. Though important, these aspects are fairly

straightforward extensions of traditional techniques rather than revolutionary “breakthroughs. ”

New thought about midcourse defense focuses

on alleviating the Achilles’ heel of systems that

use infrared sensing to support intercept in space:

the ease with which the offense can accompany

attacking RVs with clouds of decoys. One approach receiving attention is simply to cheapen

the interceptor and shoot at everything, RVs and

decoys alike. Another is to probe the attacking

‘See Julian Davidson, “BMD: Star Wars in Perspective, ”

Aerospace America, January 1984, p. 78.

55
56

objects with an active sensor, rather than relying on their thermal emissions, in the hope of discriminating RVs from decoys. Some of these “active discrimination” schemes are complex and

expensive and might in turn be susceptible to offensive spoofing. A third aid to discrimination is

the boost-phase defensive layer itself, which

might constrain the number and type of penetration aids the offense could mount on each booster in addition to reducing the total number of objects approaching the midcourse tier. Fourth,

extensive use of space-based sensors would allow

the defense to observe penetration aids throughout their flight (including during deployment from

the bus) rather than just as they approach the

United States. It remains unclear whether these

techniques will be worth the costs and new countermeasures they would bring to the defense.
Section 7

A HYPOTHETICAL SYSTEM

ARCHITECTURE

●
Section 7

A HYPOTHETICAL SYSTEM ARCHITECTURE

Most analysts of boost-phase BMD assume that

midcourse and terminal BMDs will augment the

boost-phase layer. This section assembles a hypothetical layered defense system in toto. This

system is pure/y illustrative, taking current BMD

concepts at their face value and conveying a concrete image of the defensive architectures analysts

apparently have in mind when they speak of nationwide defense. Obviously there are many

choices for such a “strawman ” system. The particular system described below was chosen for

its illustrative value and not because it represents

some “most plausible” alternative. It would be

meaningless to suggest a “front runner” in the

present state of study and technology development. Rather, the purpose of this example is to

show how the layers interact and to indicate the

overall scale of the deployments contemplated,

without implying that anything remotely like it

ever could or would be built.

A defense with several layers presents the offensive planner with some of the variety of problems that afflicts the BMD designer, who never

knows in advance which attack tactic or countermeasure the offense will choose and must include responses to all of them in the system design. Layered defense forces the offense not only

to develop responses to all the layers, but to develop responses that can be accomplished simultaneously. Thus, for example, the method chosen

to avoid boost-phase intercept must not prevent

deployment of lightweight midcourse decoys.

The synergistic effect of the several layers obviously works strongly in the defense’s favor.

Nonetheless, one must compare the performance of a three-tiered defense to the performance

of a two-tiered defense of the same cost. Thus

it should be no surprise if a $200 billion system

with boost (and possibly even post-boost), midcourse, and terminal layers performs better than

a $50 billion system with no boost phase layer.

The correct questions are whether the additional

$150 billion is worth the extra performance, and

whether spending the $150 billion on more terminal and midcourse defense would in fact be

a better investment.

Occasionally one sees a simplified leakage calculus applied to layered defense. The calculus

assigns a “leakage” of, say, 25 percent (0.25) to

the boost phase layer, 15 percent to the midcourse layer, and 10 percent to the reentry layer,

deducing an “overall leakage” of 0.4 percent on

the basis of the equation (0.25)x (O. 15)x (O. 10)

= 0.004. Though the term leakage can be

defined so that this calculus holds, the result actually bears little relation to the number of targets

preserved by the defense. For one thing, a given

defensive layer does not have an associated leakage fraction independent of attack size: the

leakage fraction for each layer usually increases

with attack size, most obviously (but not only)

when the defensive arsenal becomes saturated.

Second, the performance levels of the individual

layers are not independent. For example, if the

midcourse layer’s interceptor arsenal is sized to

handle only 25 percent of the attack, and the

boost-phase layer works poorly and in fact allows

50 percent of the attack through, the midcourse

layer obviously cannot display the same fractional

efficiency against the attack of double the expected intensity. Conversely, improvements in

one layer might improve performance of another:

effective boost-phase or midcourse layers might

force the offense to abandon the highly structured

“laydowns” of RVs in space and time that limit

a terminal layer’s effectiveness. Third, the raw

number or fraction of leaking RVs does not indicate the number or fraction of targets destroyed

because of the tactics of preferential offense and

defense. For these reasons, the leakage calculus

is not a helpful way to encapsulate layered defense performance.

59
60

7.1 SYSTEM DESCRIPTION

The system design described below takes literally the goal of comprehensive nationwide defense. It seeks the capability (at least on paper)

to engage all attacking Soviet missiles, whether

targeted at cities, U.S. silos, or other military installations. Clearly the precise numbers and kinds

of components in this description can be adjusted

to suit any set of assumptions. The point of this

description is merely to convey the flavor of these

massive architectures. Most assumptions are favorable to the defense.

Suppose that at some time in the future the Soviet ICBM arsenal still consists of 1,400 boosters,

as it does today. For simplicity, suppose further

that each booster is an MX-sized solid propellant

missile carrying 10 RVs and that all silos are located in one large region of the U.S.S.R. The

boosters are not specially shielded against lasers,

but some care in their design has given them an

effective hardness of 10 kJ/cm2

, and they are further spun during ascent. Each booster carries a

small number of decoys, but their small number

is offset by the decoys’ high fidelity. Each RV is

accompanied by 9 lightweight infrared replicas

and 1 high altitude reentry decoy. (This is a very

modest penetration aid loading. One can assume

larger numbers with perhaps poorer fidelity, chaff

and aerosols, etc. )

The hypothetical U.S. defense system comprises both HF chemical laser battle stations and

x-ray laser battle stations for boost-phase intercept, land-based midcourse interceptors carryTable 7.1.—Hypothetical Future U.S. Defense

Designed for Nationwide Protection Against

Hypothetical Future Soviet Offense

U.S. Defense Soviet Offense

5 warning satellites 1,400 MX-like ICBMs

180 HF laser satellites deployed in one

180 laser radars region

900 x-ray laser satellites 10 RVs per ICBM

900 MWIR trackers 9 midcourse decoys

28,000 midcourse intercept per RV

vehicles and boosters 1 reentry decoy per RV

20 LWIR satellites

75 radars

140,000 terminal non-nuclear

interceptors

25 aircraft with LWIR sensors

SOURCE: Author.

ing LWIR homing vehicles (the so-called “Overlay”), and land-based high-endoatmospheric

homing interceptors with non-nuclear warheads

for reentry intercept.

The HF chemical laser system resembles that

described in Section 3.1, except that it has only

five 20 MW lasers at each position in the 32-position constellation, for a worldwide total of 160.

At a range of 2 Mm, a laser must dwell on each

spinning booster for 5 seconds, so each laser at

this range can handle 30 simultaneously launched

boosters if defense begins 30 sec into the 180 sec

boost phase of an MX-like booster. The five lasers

overhead the Soviet silos at any one time can

therefore only handle 150 of the 1,400 Soviet

ICBMs. For small Soviet attacks, however, this

non-nuclear boost-phase layer suffices.

For a large-scale Soviet attack, the United States

deploys in addition a nuclear boost-phase system

of x-ray lasers. A “perfect” laser with characteristics such as those derived in Section 3.3 can intercept ideally about 50 boosters at 4 Mm range.

Therefore 28 lasers need to be in position over

the Soviet silos at any time to handle a massive

launch, giving a worldwide total of 900 (absentee

ratio 32).

Warning for the boost-phase system is provided

by MWIR warning satellites in synchronous or

supersynchronous orbits. Also, each of the 160

HF laser battle stations has an MWIR telescope

with 4 m mirror and an ultraviolet or visible Iadar

with 2 m mirror for pointing. Each x-ray laser is

accompanied by an MWIR telescope tracker with

1 m mirror.

The 1,400 Soviet boosters carry 14,000 RVs,

126,000 midcourse decoys, and 14,000 reentry

decoys. The United States assumes that only 10

percent of the boosters will survive the boost

phase defense, so the midcourse tier needs to

face 1,400 RVs and 12,600 midcourse decoys.

The midcourse interceptors are given extremely

long range, so only two bases are needed to

cover the entire United States. However, each

base must be prepared to absorb the entire attack, since the Soviets could target one half of

the country more heavily than the other. There-
61

fore the United States needs 14,000 midcourse

interceptors at each base, for a total of 28,000

interceptors. A constellation of 20 satellites with

large LWIR sensors provide long-range acquisition and target assignment to these interceptors.

The United States next estimates that 90 percent of the RVs that enter the midcourse layer

will be successfully intercepted. The terminal defense must handle 140 RVs plus 140 reentry decoys.1 The reentry decoys are, by assumption,

completely faithful in mimicking the signatures

of RVs as seen by ground-based radars and aircraft-borne infrared sensors during early reentry—large decoy numbers have been sacrificed

for this high fidelity. If the U.S. defense takes

literally its charge of nationwide defense, it must

be prepared to make 280 intercepts anywhere

in the country.

I The number of reentry decoys the terminal system must face

actually depends on whether the decoys fool the midcourse as well

as the terminal system’s sensors and on whether the terminal and

midcourse layers cooperate in discrimination. Suppose first that the

reentry decoys look Ilke RVS (and therefore also like midcourse

decoys) to the midcourse layer’s sensor. Then the midcourse layer

will Intercept 90 percent of them (more midcourse interceptors must

be bought to do th@. If, on the other hand, the midcourse layer

correctly identifies the reentry decoys as non-lethal objects, it might

(a) not intercept them, requiring the terminal layer to plan to face

140 RVS plus 1400 reentry decoys, increasing enormously the required arsenal of terminal interceptors; (b) intercept them, in which

case a reentry decoy is a perfect midcourse decoy, making possible a new threat–large numbers of midcourse decoys that look

like reentry decoys rather than RVS; (c) radio the information, objectby-object, to the terminal defense fields.

Each terminal defense site consists of a phasedarray radar and a number of high altitude non-nuclear interceptors. Additional target acquisition

support is provided by a fleet of aircraft patrolling 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. However, an interceptor only covers an area about

50 km in radius. Since the area of the United

States is about 8 million square km, over 1,000

interceptor sites would be needed for nationwide

coverage. Should the defense have to reckon

with intensive Soviet attack on some regions and

no attack on others? Clearly, yes. But equipping

each interceptor site to handle all 280 objects

passing through the first two layers would require

buying 280,000 interceptors! The defense wouId

need to buy this many interceptors if it wanted

to claim the literal capability to engage all Soviet

RVs, no matter where they landed. Suppose,

then, that the United States hopes for a more

evenly distributed Soviet attack and deploys just

half of the arsenal needed for complete coverage— 140 interceptors per region. One radar

might not suffice to handle all the RV traffic in

its sector if the Soviets attack some sectors preferentially, but the United States nonetheless buys

just 75 radars. Five aircraft on patrol at all times

requires a backup fleet totalling perhaps 25.

Table 7.1 summarizes the offensive and defensive deployments.

7.2 ASSESSMENT

It is obviously not possible to assess the performance of a system, such as the hypothetical

layered defense described above, whose components are not (and in many cases cannot be)

designed today, much less assembled in an overall architecture. It is nonetheless worth sketching,

in the illustrative spirit of this section, the issues

that would require analysis if anything resembling

Table 7.1 were ever proposed for deployment.

The first issue concerns the cost of the improvements to the system needed to offset growth in

the Soviet ICBM arsenal—that is, the cost exchange ratio. The number of defensive weapons

is proportional to the number of Soviet ICBMs.

If the Soviets were to double the size of their

ICBM arsenal, the United States would need to

double the number of its x-ray lasers and interceptor missiles. (The number of sensors would

generally have to increase also, though perhaps

not in proportion to the Soviet buildup. The number of HF lasers could remain the same if the

United States continued to intend to use this nonnuclear boost-phase layer to engage only Soviet

attacks of 150 boosters or less. ) Comparison of

the two columns of Table 7.1 indicates that an

arms race of Soviet offense and U.S. defense

seems certain to favor the Soviet side greatly.
62

—

A second issue concerns the huge inventories

of midcourse and reentry interceptors needed for

nationwide defense. The arsenal of reentry interceptors shown in Table 7.1 is in fact only half the

size needed for literally complete nationwide coverage, as remarked above. The cause of these

large interceptor inventories–besides the obvious

presence of decoys–is twofold: first, the low leakage sought by the defense precludes preferential defense, the tactic that makes silo defense so

much more economical; and second, the limited

coverage of each interceptor battery makes preferential offense possible for the attacker. The goal

of nationwide low-leakage defense therefore

forces the BMD system to forfeit the two sources

of leverage that have historically impelled BMD

towards the technically modest mission of defending compact silo deployments to relatively

low survival levels.

Soviet countermeasures–besides straightforward buildup of ICBMs—is a third issue. The particular boost-phase layers described above are

susceptible i n varying degrees to all of the countermeasures described in Section 5, and the midcourse and reentry layers to their respective sets

of countermeasures.

Defensive coverage against submarineIaunched ballistic missiles (SLBMs) is a fourth

issue. The boost-phase layers can intercept SLBMs

launched from all points on the globe. Though

the average range from laser satellite to booster

is larger at equatorial and polar latitudes than at

the mid-latitudes where Soviet ICBMs are located,

the number of SLBMs that could be launched in

a short time from each ocean area is also much

smaller than the huge number of ICBMs that

could lift off simultaneously from the U.S.S.R.

Even the chemical laser deployment alone might

suffice for boost-phase coverage of SLBMs. The

midcourse and reentry layers, however, would

in general not perform as well against SLBMs as

against ICBMs. SLBM trajectories present bad

viewing angles to the midcourse layer’s LWIR

sensors, and the short timeline limits interceptor

coverage. The reentry layer would need to be

augmented with more airborne sensors and more

radars (or radar faces) to cover attack from the

ocean. In general, then, a layered system optimized for ICBM defense could not necessarily

handle 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 and

direct statement of the goal of the deployment.

Though there has been much discussion of the

feasibility of boost-phase BMD, proponents and

skeptics alike frequently leave unstated the standards against which they are judging the technical

prospects. A “successful” BMD deployment

could be defined as anything from a truly impenetrable shield, to a silo defense that merely costs

less to build than it costs the Soviets to overcome,

to a tangled deployment that just “creates uncertainty” for the attacker.

The most ambitious conceivable goal for BMD

would be to take at literal face value the words

of President Reagan in his so-called “Star Wars”

speech of March 23, 1983, when he called for

development of a defense capable of making nuclear weapons “impotent and obsolete.”1 It is not

clear that the President intended his words to be

taken literally, nor that the Administration or anyone else is suggesting the United States seek a

truly perfect or near-perfect defense.2 Nonethe1 Week/y Compilation of Presidential/ Documents, Vol. 19, No.

12, March 28, 1983, pp. 447-448, The text of the relevant part of

the speech is reprinted as Appendix A.

2 Defense Secretary Caspa r Wei nberger appeared to confirm a

literal interpretation In a March 27 interview on NBC’s Meet the

Press, 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 designed to be partial What we want to try to get IS a system which

WIII 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. Responding to the “Congressional Findings” section of the proposed “People Protection Act” (H .R, 3073, 98th Congress, Ist session) which

stated, “The President has called for changes in United States strategjc policy that seek to save lives in time of war, ” Defense Department General Counsel William H. Taft IV wrote:

It IS clear that portions of the “Congressional ftndlngs” section [of

H 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 to

strengthen our ablllty to deter war by, as the President has said,

/, renderl ng [ha llIst Ic m IS; I Ies] Impotent and obsolete. 1 n short,

less, so much writing and debate focuses on this

prospect, and its importance is so great, that it

is taken up in this section. Section 9 treats the

many other possible goals for less-than-perfect

defenses.

There is some confusion in the literature about

the use of the term “mutual assured destruction”

(MAD) in connection with the notion of perfect

defense. In common strategic parlance, MAD refers to the technological circumstance of mutual

vulnerability to catastrophic damage from nuclear

weapons, not to a chosen policy to promote such

vulnerability. There is a strategic school of

thought that advocates a policy usually called

“minimum deterrence, ” maintaining that the capability for assured destruction of Soviet society

is the on/y requirement of U.S. strategic forces.

However, many experts believe that effective deterrence and other national security objectives

require nuclear forces capable of many other

tasks than assured destruction. This section addresses itself to the question of whether MAD is

an avoidable technological circumstance, not to

whether minimum deterrence is a prudent strategic policy.

A sensible start at judging the prospect for nearperfect defense must involve two steps: first, an

exact statement of what perfect defense means

in the context of attack on society with nuclear

weapons; second, some way of gauging the likelihood of success when the technological future

cannot be accurately predicted.

the purpose of the Administration’s policy is to reduce the Ilkellhood

of war. The finding [of H.R. 3073] that the purpose IS to ‘‘sa~ e IIk es

I n tl me of war’ departs from our goal of deterrl ng war

Dr. Charles Townes, a frequent adviser to Secretary of Defense

Weinberger and leader of two DOD task forces studying basing

modes for the MX missile, said that a perfect defense proposal is

“quite impractical. There is no technical solution to safeguarding

man 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 Extent

of Prompt Fatalities in U.S. Urban Areas

 1 0

I I I

500 1000 1500 2000 2500 3000

Attacking warheads

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

SOURCE. Arms Control and Disarmament Agency, U.S. Urban Population

VU/nerabi/ity (ACDA, 1979), quoted in Arthur M. Katz, Life Afrer Nuc/ear

War 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 of

removing from the hands of the Soviet Union the

ability to do socially mortal damage to the United

States with nuclear weapons, so that the Soviet

Union no longer possesses the elemental capability of assured destruction.) What does this

mean?

Figure 8.1 shows how the percent of the U.S.

urban population (about 130 million people in

the 1970 census) killed promptly increases with

the number of Soviet warheads detonating over

U.S. cities. No such curve of the effects of nuclear attacks on cities should be taken as anything

but suggestive: uncertainties are very great in

such estimates, and no attempt has been made

to reflect long-term and indirect effects of the

detonations.3 The curve also accounts only for

3

For discussion of some of the effects of nuclear weapons on

population and cities, see: U.S. Arms Control and Disarmament

Agency, An Analysis of Civil Defense in Nuclear War (ACDA, 1978);

OTA, The Effects of Nuc/ear War (GPO, 1979); ACDA, The Effects

of Nuc/ear War (ACDA, 1979); “Economic and Social Consequences of Nuclear Attacks on the United States, ” prepared for

the joint Committee on Defense ProductIon, 96 Cong. 1 sess., 1979;

fatalities, not for the many additional people injured. If one wishes to account for the possibility

of civil defense evacuation, then the curve should

be taken to represent not the number of people

killed, but the number of people whose homes,

businesses, historic monuments, schools, and

places of worship have been destroyed.

No one supposes that the Soviet Union actually

chooses aim points for its nuclear weapons with

the goal of maximizing human fatalities, as has

been done in preparing Figure 8.1. if the United

States possessed a defense capable of intercepting all but a few of the 8,000 to 10,000 Soviet

nuclear warheads, however, the Soviet Union

might retarget its forces to wreak the most destruction possible with its few penetrating warheads. At any rate, any defense promising U.S.

society genuine immunity from nuclear attack

must reckon with Soviet determination to keep

its arsenal from being “rendered impotent, ” and

therefore with targeting plans contrived to do the

most damage to the fabric of U.S. society.

Where on the curve of Figure 8. 1–after how

many detonations—does one locate the boundaries of “assured destruction, ” “assured surviva l,” “impotent and obsolete, ” and similar

phrases? Clearly there is no analytical prescription for these boundaries: they are the subject

of a broader human judgment. 500 half-megaton

warheads kill half the urban population, injure

most of the rest, and totally destroy all American

cities and large towns. Just 5 megatons, about one

two-thousandth of the Soviet arsenal, detonated

over the 10 largest U.S. cities could kill several

million people and wound over 10 million more.

For the sake of discussion, we shall use 100

megatons—about 1 percent of the Soviet Union’s

arsenal and 1.5 percent of its ICBM force—as the

level 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; National Research Council, Long-Term Wor/~wi~e Effects of Mu/fip/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 “impiously very generous to the notion of perfect de- potent and obsolete. ” Still, it is a definite

fense, 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” that

unknown future technologies will not provide

near-perfect defensive protection of U.S. society

against Soviet ICBMs. The question that needs to

be answered is whether the prospects for nearperfect defense are so remote that such a notion

has no place in reasonable public expectations

or national policy. it is, after all, not provable that

by the next century the United States and

U.S.S.R. will not have patched up their political

differences and have no need to target one

another with nuclear weapons. The issue of the

perfect defense is unavoidably one of technical

judgment rather than of airtight proof,

Four misapprehensions seem common among

non-technical people addressing the prospects for

perfect defense.

The first misapprehension is to equate successful technology development of individual devices—lasers, power sources, mirrors, aiming and

pointing mechanisms—with achievement of an

efficient and robust defensive system. Millionfold

increase in the brightness of some directed-energy device is a necessary, but is far from a sufficient, condition for successful defense. In the

early 1960’s, intercept of RVs with nuclear-tipped

interceptor missiles was demonstrated—”a bulIet could hit a bullet’’–but 20 years later systems

incorporating this “kill mechanism” are still considered relatively inefficient. In general, skeptics

about the future of space-based directed-energy

BMD do not confine their doubts to, or even emphasize, unforeseen problems in developing the

individual components.

A second misappprehension arises in attempts

o equate BMD development to past technological achievements, such as the Manhattan project’s atomic bomb or the Apollo moon landings. Q

The technically minded will recognize a vital difference between working around the constraints

imposed by nature, which are predictable and

unchanging, and competing with a hostile intelligence bent on sabotaging the enterprise. A dynamic opponent makes of BMD, first, a more difficult design problem, since the offense constructs

the worst possible barriers to successful defense;

and second, not one problem but many problems that need to be sidestepped simultaneously

in the design, since the designer cannot be certain which tactics the offense will use.

A third misapprehension concerns the prospect

for a “technological breakthrough” that would

dispel all difficulties. Such breakthroughs are not

impossible, but their mere possibility does not

help in judging the prospects for the perfect defense. For one thing, an isolated technological

breakthrough creating a new defensive component would not necessarily alleviate the system

issues—vulnerability, dependability, susceptibility

to countermeasures, cost—that determine overall

effectiveness. Second, one can just as easily imagine offensive “break throughs,” sometimes involving the same technologies. Thus the x-ray laser, if it matures, might turn out to have been

4Defense Secretary Caspar Weinberger has w rltten (Air Force

Magazine, Nov. 1983):

The nay-sayers have already proclaimed that we WIII never haie

such technology, or that we should never try to acquire It Their

arguments are hardly new In 1945 president Truman’s Chief ot

Staff, Adm William Leahy, said of the atomic bomb “Thatrs the big.

gest fool thing we’ve ever done. The bomb will never go off, and

I speak as an expert in explosives. ” In 1946 Dr. vanne~ ar Bush,

Director of the Office of Scientific Research and Development said

of Intercontinental ballistic missiles, “1 say technically I don’t think

anybody I n the world knows how to do such a thing, and I feel confident [t WIII not be done for a long time to come “ These crltlcs were

proved wrong; what IS more, they were proved wrong quickly

33-698 0 - 84 - 4 : QL 3
better termed a breakthrough in strategic offense

than a breakthrough in strategic defense.

A fourth misapprehension concerns the confidence with which predictions could be made

about the performance of a complex system once

i n place. The “performance” of a system, as

quoted in analyses, is the most likely outcome

of an engagement of offense versus defense.

Other outcomes, though less likely, might still be

possible. Computing the relative likelihoods of

all possible outcomes would be difficult even if

one could quantify all technical uncertainties and

statistical variances. Still, there would remain a

residue of uncertainty about the performance of

a system that had never been tested once in realistic wartime conditions, much less in a statistically significant ensemble of all-out nuclear wars.

The defense would also have no chance to learn

and adapt. In World War II, by contrast, air defense crews learned in raid after raid to inflict

losses of several percent in attacking bombers.

The only reason these modest losses assumed

strategic significance was that they accumulated

over many raids. Of course, the same uncertainties plague the offense as plague the defense. In

general, the offense would tend to overestimate

the defense’s capability. This natural tendency

toward “offense conservatism” is probably vitally

important to the psychological and deterrent value of BMD as it is applied to less-than-perfect

goals. For the perfect defense goal (as defined

above), however, it would seem that the uncertainty weighs heaviest on the defense. To the

reckless, non-conservative defense, a wrong estimate of defense performance spells the difference

between safety and socially mortal damage (or

between deterrence and war). The reckless offense, on the other hand, is presumed desperate

enough to try to inflict such damage on its enemy

and willing to accept the consequences: it stands

to lose little if its estimates are wrong and the defense does work perfectly after all.

With these misapprehensions out of the way,

and recognizing clearly that there can be no question of “proof, “ it would seem that four major

factors conspire to make extremely remote the

prospect that directed-energy BMD (in concert

with other layers if necessary) will succeed in reducing the vulnerability of U.S. population and

society to the neighborhood of 100 megatons or

less.

1. Near-perfect defense of society is much

harder and more expensive than partial defense

of military targets. That is, the marginal cost exchange is much higher for near-perfect defense

than for partial defense (see also Fig. 5.2). There

are two reasons behind this well-known

statement.

The first reason is illustrated schematically in

Figure 8.2. In going from partial silo defense to

perfect city defense, the BMD loses the leverage

of preferential defense. Additionally, the offense

gains the leverage of preferential offense against

the terminal and midcourse layers with their limited geographic coverage, although not against

the boost-phase layer. In Figure 8.2(a), the defense aims to save only 10 percent of the ICBM

force, or one silo. Assuming perfect interceptors

and adopting the tactic of adaptive preferential

defense (using all its interceptors to save just one

silo chosen randomly from the ten at the moment

of attack), the defense concludes it needs to prepare to make one only intercept to counter the

offense’s 10 RVs. In Figure 8.2(b), the offense can

focus all 10 of its RVs on any one of ten cities.

The defense must prepare to make 10 intercepts

for each city, buying a total of 100 interceptors,

if it wants to try to save all the cities. If the Soviets

double their RV arsenal, the United States must

buy just one interceptor to satisfy the defense goal

of Figure 8.2(a), but the United States must buy

100 interceptors to satisfy the defense goal of Figure 8.2(b). The cost exchange ratio is thus 100

times worse for the city defense, even though it

uses the same technology as the silo defense.

The second reason why a near-perfect defensive goal shifts the cost burden in favor of the offense is that the offense can turn all its resources

to improving or replacing just a portion of its

ICBMs to sidestep the defense. The Soviet Union

could therefore harden just 1 percent of its boosters, perhaps concealing exactly which ones were

hardened. Moreover, it could deploy a few fastburn boosters immune to x-ray lasers and neutral

particle beams; build a few different ASAT de-
69

Figure 8.2

10 attacking

ICBM Silos

Radius of BMD

BMD 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 much

greater 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 countermeasures

are avaiIable to the offense if the countermeasures need onIy be implemented on a small scale

rather than throughout the ICBM force. The offense can “experiment” with a number of different tactics with different portions of its force.

The defense’s costs also grow much larger if it

must plan to face a variety of offensive

countermeasures. I n short, the defense must be

able to stop all kinds of attack, but the offense

only has to find one way to get-through.

2. For every defense concept proposed or imagined, including all of the so-called “Star

wars” concepts, a countermeasure has already

been identified. These countermeasures were

enumerated in Section 5 and will not be repeated

here. Three further generalizations about these

countermeasures reinforce a poor prognosis for

cost-effective near-perfect defense: 1 ) In general,

the countermeasures could be implemented with

today’s technology, whereas the defense itself

could not; 2) In general, the costs of the coun-
70

termeasures can be estimated and shown to be

relatively low, whereas the costs of the defense

are unknown but seem likely to be high; 3) In

general, the future technologies presupposed as

part of the defense concept would also be potent weapons for attacking the defense.

3. The Soviet Union does not configure its nuclear missile forces today to maximize damage

to U.S. society and population, but it could do

so if faced with near-perfect U.S. defenses. Targeting plans could focus exclusively on damaging cities. High missile accuracy would be unnecessary, lowering offense costs. Nuclear

weapons could be designed to maximize harmful fallout. ICBM survivability measures–silos,

racetracks, densepacks, etc.—would be unnecessary to a side striking first or possessing its own

defense effective at saving many missiles (but not

all cities); thus basing costs could be diverted to

the city-kill goal, Presumably the Soviet Union

would take these and any other measures necessary to prevent itself from being effectively

disarmed by a U.S. defense, since otherwise it

would be at its enemy’s mercy.

4. BMD by itself will not protect U.S. society

from other methods of delivering nuclear weapons to U.S. soil or from other weapons of mass

destruction. Bombers and cruise missiles (and to

a significant extent SLBMs and IRBMs) present

very different defensive problems than ICBMs.

Today the technical problems of air defense are

no better resolved than the technical problems

of BMD. Novel future offensive delivery vehicles

can only be conjectured along with the future

defense technologies discussed in this Paper. A

desperate Soviet Union could introduce nuclear

weapons into the United States on commercial

airliners, ships, packing crates, diplomatic pouch,

etc. Other methods of mass destruction or terrorism would be feasible for the U. S. S. R., including sabotage of dams or nuclear power plants,

bacteriological attack, contaminating water, producing tidal waves with near-coastal underwater

detonations, 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 or

near-perfect defense assume importance i n certain theories about the workings of nuclear deterrence and the requirements of U.S. security.

Thoughtful observers debate not just the feasibility of achieving these goals but the validity and

importance of the goals as well. The urgency one

attaches to these goals determines the costs, risks,

and harmful side effects one is willing to incur

to fulfill them. Assessing the wisdom of less-thanperfect defense thus involves a complex and subjective balancing of goals and risks, in which

purely technical issues sometimes take a back

seat. In discussion of perfect defense, by contrast,

technical assessment is paramount. This section

therefore calls up many issues of nuclear policy

not subsumed under the title of this Background

Paper, and no pretense is made hereto complete

treatment. 1

Though various strategic goals for BMD can be

distinguished in principle, in practice it might not

be clear or agreed among all parties in the United

States what the purpose of a proposed deployment actually was. Interpretations by the Soviet

Union and other foreign nations of U.S. goals

might 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 Missile

Defense (The Brookings Institution, 1984).

Those familiar with BMD design and assessment wiII recognize that stating a general strategic goal is not enough: the technical specifications are essential. For instance, it makes an

enormous difference in silo defense whether the

defense seeks to charge the offense a price of five

RVs (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 defenses, when better defined, will surpass or even

equal traditional defenses in terms of leakage and

cost exchange, there is no point i n turning to exotic technologies to satisfy modest goals. Virtually

all observers agree, on the other hand, that terminal and midcourse systems are unequal to the

more demanding goals; for these goals one is

forced to direct one’s hopes to the promise of

future technologies.

This section sketches various goals for less-thanperfect defenses and the strategic thinking that

attaches importance to them. It then points out

a number of side effects against which fulfillment

of these goals

section is no

assessment 01

needs to be balanced. This short

substitute for a comprehensive

the pros and cons of BMD.

9.1 GOALS FOR LESS-THAN-PERFECT DEFENSE

1. Strengthen deterrence by preventing preemptive destruction of retaliatory forces. It is

widely recognized that the Soviet Union will soon

have, if it does not already, the combination of

yields, numbers, and accuracy in its ICBM forces

to destroy most U.S. Minuteman ICBMs in their

silos. It is also widely agreed that vulnerable nuclear forces create unwanted temptations for both

sides to strike first if war seems likely. The long

and anguished search for survivable basing

modes for the U.S. MX (Peacekeeper) ICBM has

to date turned up no clear favorites when survivability is balanced against cost, technical risk,

strategic effects, and environmental impacts. z

BMD would substitute for or complement these

other basing modes. By shooting down a fraction

of the opponent’s missiles, BMD would in effect

“de-MIRV” ICBM forces.

Of course, turning to BMD to ease ICBM vulnerability is not without problems. One problem

is the prospect of a compensating Soviet BMD.

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

73
.

74

. .

MX is presumably being bought and made survivable in the first place so that the U.S. can absorb a Soviet strike and retaliate with its ICBMs

(in addition to its bombers and submarines)

against Soviet targets. But modification or termination of the ABM Treaty to permit a U.S. defense would permit a Soviet defense as well. The

surviving U.S. ICBMs guaranteed by the U.S.

BMD might still not result in retaliatory damage

to Soviet targets if these targets are defended by

Soviet BMD. The U.S. BMD deployment, all

bought and paid for, might therefore have been

cancel led out by a Soviet counter-deployment,

Other elements of the U.S. retaliatory force

comprise command and control links, bomber

alert bases, and in-port submarines. Bomber

bases, sub ports, and fixed command and control facilities are the worst type of target base for

BMD to try to defend–a small number of highvalue, soft, and interdependent targets. The important remaining category of mobile command

and control facilities, on the other hand, does not

easily lend itself to active defense with BMD.

2. Strengthen deterrence by preventing the use

of nuclear weapons as decisive military tools for

high-confidence “limited” strikes on conventional forces. This goal is associated with socalled “warfighting” strategies for nuclear weapons. According to analysts who hold this view,

today’s “offense dominated” world creates dangerous temptations to resort to nuclear weapons

to accomplish militarily well-defined objectives.

One can imagine warheads simply being lobbed

unopposed into another country in any number

or combination. Though surely the effects of

these “limited” attacks on nearby communities

would not be so well-defined, the effect on the

opposing military machine might be truly dramatic, even decisive. This use of nuclear weapons

in wartime is possible with today’s unopposed

offenses with considerable confidence and might

therefore be tempting to the combatants. Such

temptations threaten nuclear deterrence and

should be eliminated. The goal of a comprehensive defense would be to make such limited attacks infeasible, or at least to complicate the offense’s estimations of success to such a degree

that it would not attempt an “experiment.” 3

Analysts who favor this approach usually maintain that Soviet military doctrine inclines the

Soviets towards a view of nuclear weapons as

military tools to a far greater degree than is common in U.S. thinking. d

To take an explicit example (in this case of Soviet failure to deter the U. S.) of a “war fighting”

scenario (chosen randomly from a great many

possibilities), suppose NATO were at war with

the Warsaw Pact, and the Soviets were resupplying their ground offensive through just 10 or so

rail trunks from the Soviet Union through eastern Europe. Just 10 well-placed nuclear weapons

(according to a hypothetical analyst considering

this type of scenario) would cut off a large fraction of supplies coming to the front, slowing the

Pact offensive and giving NATO vitally needed

time to marshall its defenses. Wouldn’t the

United States be sorely tempted to use just a few

ICBMs for this decisive intervention in the course

of the war?

Analysts who recommend attention to warfighting scenarios and doctrines are surely aware of

the profound difference between conventional

and nuclear weapons, but they maintain that the

threat of punishment through retaliation upon cities is not an effective deterrent in such scenarios.

Wouldn’t it be preferable if these scenarios were

simply closed off by defensive technology?

Critics of this BMD goal object both to the warfighters’ emphasis upon the risk of this type of

scenario and to the assumption that defense

would materially diminish that risk. In their view,

myriad detailed chinks in the armor of deterrence

can 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 adversary that an offensive attack WIII not be successful. It has to be a very

effective system, but It would not have to be perfect to convince a

potential adversary that his attack would fall “

Dr. Robert Cooper, director of the Defense Advanced Research

Projects Agency has also stated this view (The New York Times,

Nov. 5, 1983, p. 32): “Even if only 50 percent of all incoming missiles

were stopped, the Soviets could then have no confidence in the

success 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 nuclear and conventional instruments of war. Besides, they say, suppose the effect of the Soviet

BMD is to force the United States to attack each

rail line with ten weapons instead of one to assure

penetration: IS there truly a psychological divide

between using 10 and 100 nuclear weapons,

once the divide between O and 10 has been

crossed? Third, would NATO not be adequately

deterred by the prospect of Soviet retaliation with

10 of its nuclear weapons against 10 vital NATO

targets? Last, suppose NATO used 10 cruise missiles, against which the BMD was powerless, instead of 10 ICBM RVs?

The persuasiveness of this second goal for lessthan-perfect BMDs therefore depends on one’s

views of the roles and risks of nuclear weapons—

views that are fundamental and deeply held. This

goal is therefore one of the most controversial

of all.

3. Save lives.5 Another goal for BMD is purely

humanitarian and seeks no military or strategic

advantage. If the defense did not interfere too

much with Soviet military targeting objectives

(enough for the Soviets to try to overcome it), and

assuming the Soviets have no explicit aim to inflict human casualties, the United States could

expect some reduction in fatalities in a nuclear

war even from a modest defense. This reduction

would necessarily be limited, since Soviet military

objectives include destruction of many targets

collocated with population. BMD and civil defense measures would be mutually reinforcing.

Analogous discussion of civil defense has always revealed an inherent tension between the

humanitarian objective of defense and a related

strategic objective. The strategic objective seeks

to reduce fatalities and damage in order to enhance U.S. “flexibility” in a crisis, to allow the

United States to “coerce” the U.S.S.R. (or avoid

coercion) from a position of reduced vulnerability,

or to enhance U.S. ability to persist in its war effort despite receiving a Soviet nuclear strike. The

supposed result of the BMD deployment is to allow the U.S. President, in dealing with the Soviet leadership in time of crisis, to be more willing

‘This d Iscussion borrows from the author’s previous work I n

IJ//IsfIc Mlssl/e Defense, op. cit., Chapter 4.

or appear to be more willing to resort to nuclear

war because the consequences to the United

States are presumed smaller.

The coexistence of the humanitarian and strategic objectives for the analogous case of civil defense is apparent in the literature on civil defense.

The Defense Department6 has argued that the

United States should have the same crisis relocation options as the U.S.S.R. for two reasons, one

strategic and one humanitarian: 1 ) “to be able

to respond in kind if the Soviet Union attempts

to intimidate us in time of crisis by evacuating

the population from its cities”; and 2) “to reduce

fatalities if an attack on our cities appears imminent.” Prominent scientists arguing for civil defense have also maintained that, “A nation’s civil

defense preparedness may determine the balance

of power in some future nuclear crisis. . . . In our

opinion, we must strive for an approximately

equal casualty rate”.7 More recently, the High

Frontier Study urging strengthened U.S. strategic

defenses stated: “The protection of our citizens

must be prime, but civil defense . . . would reduce the possibility that the United States could

be coerced in a time of crisis”. a

In practice, therefore, the humanitarian and

strategic objectives are likely to be difficult to

disentangle. Unlike the humanitarian objective,

the strategic objective might stimulate a Soviet

effort to put the same number of American lives

at risk regardless of the defense. In this way, the

Soviet Union could retain the strategic advantage

that, by hypothesis, the BMD deprives them of.

The issue then becomes the usual one of the costexchange ratio measuring the price to the Soviet

Union of retaining its “advantage” relative to the

price of the U.S. defense.

The Defense Department has stated that saving lives in time of war is not the purpose of President Reagan’s BMD initiative.9

bAnnual De{ense Department Report, FY 1976, p. 11-24.

7Arthur A. Broyles and Eugene P. Wlgner, ‘‘CIVII Defense [n

Llmlted War, ” Physics Today, VOI 29 (April 1976), pp. 45-46,

‘Daniel 0. Graham, The Non-Nuc/ear Detense ot’ Clfies: The High

Frontier Space-Based Det’ense Against ICBM Attack (Abt Books,

1983), p. 122.

‘See footnote 8 2,
76

4. Shape the course of the arms competition

and arms control.10 One version of this goal sees

the Soviet tendency to upgrade and proliferate

existing ICBM forces as the principal impediment

to arms control. By introducing BMD (or even

discussing it), according to this view, the United

States makes the Soviets unsure about the next

step in the arms competition and thus undercuts

the momentum of Soviet strategic programs, especially ICBM modernization. Though fast-burning Midgetman boosters might defeat boost-phase

defenses, this argument goes, the slow-burning

SS-18s and SS-19s will not. BMD might not be

able to make all nuclear weapons impotent and

obsolete, but it can make large Soviet ICBMs impotent and obsolete–something the U.S. has

been trying to do for a decade. Perhaps efficient

defenses will “force” the Soviets to emphasize

submarines, bombers, and cruise missiles in their

strategic arsenal to the same degree the United

States does. (One problem with this line of argument is that by the time the defense is in place,

present-generation Soviet ICBMs might already

be replaced.)

Another line of argument holds that a major

BMD initiative strengthens the U.S. negotiating

position at START. An aggressive BMD program

demonstrates U.S. technological prowess and

hints at what the Soviets could face if this prowess were unleashed. It would seem that new

BMD initiatives might not coexist easily with the

reductions in offensive arsenals proposed by the

United States in START, however. Since U.S.

BMD is equivalent to attrition of the Soviet ICBM

arsenal, any anxieties the Soviets feel at reducIoPreSldentlal science adviser George A. Keyworth, speech before

the Washington chapter of the Armed Forces Communications and

Electronics Association, as reported in Defense Week (Oct. 17,

1983):

“Although the strategic defense program’s goal would still be eventual deployment of a working system, we shouldn’t overlook its

potential beneficial Impact on arms reduction as its progresses. ”

Richard DeLauer, Undersecretary of Defense for Research and

Engineering, has said that an arms control agreement is needed

to prevent the Soviets from overcoming a defensive system: “With

unconstrained proliferation [of Soviet missiles], no defensive system

will 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 simultaneous

U.S. BMD buildup. Politically, it would seem unlikely, though certainly not impossible, that a

climate favorable to far-reaching offensive arms

control would also foster an amicable dismantling of the ABM Treaty.

5. Respond to Soviet BMD efforts. Many

analysts view with alarm Soviet strategic defense

activities, including upgrading of the Moscow

ABM, development of a transportable terminal

BMD system, construction of a radar in apparent violation of the ABM Treaty, development of

defenses against tactical ballistic missiles, incorporation of limited BMD capability in air defenses,

and continued attention to other damage-limiting

methods (civil defense, air defense, antisubmarine warfare, and countersilo ICBMs). A strong

U.S. BMD research and development program

might deter the Soviets from breaking out of the

ABM Treaty and from continued encroachments

on the Treaty’s provisions. It is frequently noted

that aggressive U.S. research into penetration aids

and other methods for countering defenses might

be an even more effective way to demonstrate

to the Soviets that they would be ill-advised to

overturn the ABM Treaty’s “freeze” on missile

defenses.

6. Protect against accidental missile launches

and attack from other nuclear powers. These

goals have been put forward several times in the

past, most notably in the late 1960’s when the

Johnson Administration proposed the Sentinel

ABM system to counter Chinese ICBMs, believed

at that time to be fast-emerging. Neither goal

figures prominently in today’s discussion of BMD

in the United States, though defense against Chinese, British, and French missiles could well loom

larger in Soviet thinking. Emerging nuclear powers or terrorists would be unlikely to use ICBMs

to deliver their small nuclear arsenals to the

United States. BMD is therefore of little importance in staving off the threat to U.S. security

posed by nuclear proliferation.
77

9.2 SIDE EFFECTS OF BMD DEPLOYMENT

The inevitable side effects of a major strategic

initiative such as BMD might turn out to match,

both in magnitude and in duration, the beneficial

effects of satisfying the goal emphasized by the

system’s purveyors. The public and policy makers

would therefore need to assess the net, long-term

effect of adding BMD to the strategic equation,

and not just the achievement of a certain discrete

goal as if by surgical intervention. This section

reviews the well-known list of BMD side effects.

Many of these effects are detrimental to U.S. security and would need to be balanced against the

benefits of fulfilling the modest goals of less-thanperfect defense. In making this assessment, it is

impossible to ignore the many unknowns and uncertainties that make it impossible to compare

today’s world without BMD to a future world with

BMD.

1. First strike versus ragged retaliation. It is frequently noted that BMD ends up being a better

investment for the side that strikes first than for

the side that retaliates. Weapon systems that

create relative advantages to striking first in a crisis

(rather than risking being struck while seeking a

peaceful resolution) are defined to be “destabilizing.” The side striking first uses its full arsenal in

an organized penetration of the other side’s defense; the retaliating side can only use its surviving arsenal in a possibly disorganized “ragged

retaliation” against a forewarned and fully prepared defense.

Mitigating factors could in certain circumstances soften this classical statement of the destabilizing effect of BMD. First, truly effective

defenses might prevent the first striker from destroying a substantial fraction of the other side’s

retaliatory forces. Second, with proper planning

(involving post-attack retargeting and coordinated

timing), the retaliating forces might still be able

to mount a tailored, efficient strike. Third, there

will seemingly always be a relative advantage to

being the side that strikes first in a nuclear war,

with BMD or without BMD; but this calculus of

relative advantage is far from being the only factor in deterrence. Other stabilizing factors might

be strengthened by BMD, offsetting this destabilizing factor. Thus BMD might also discourage

temptations to strike first, by threatening to

disrupt the attack.

2. Soviet BMD. A U.S. BMD deployment would

seem very likely to stimulate a Soviet deployment.

Even if the Soviets saw no compelling military rationale for following suit, political appearances

could prove decisive. A Soviet BMD counter-deployment would obviously blunt U.S. offensive

striking power, which the U.S. has been spending a great deal to build up. If the U.S. deployment sought to protect its ICBMs from preemptive destruction in their silos (Goal 1 above), the

Soviet BMD might nonetheless nullify the U.S.

ICBMs–this time in flight to their targets. Soviet

BMD would also introduce a threat to U.S. SLBMs,

which are today thought to be virtually immune

to Soviet disruption and to be significantly advanced relative to their Soviet counterparts. If the

U.S. deployment sought to prevent “limited”

strikes by the Soviets Union (Goal 2), the Soviet

BMD might in turn preclude a U.S. option to use

nuclear weapons selectively and flexibly in support of its NATO allies–an option sometimes

seen as central to NATO strategy. Clearly the actual effect of the Soviet BMD counterdeployment

would depend upon its technical characteristics

and the targets it defended.

3. Demise of the ABM Treaty. An arms control treaty obviously cannot serve as its own justification, and presumably virtually everyone

would agree to the abandonment of the ABM

Treaty the moment it ceased genuinely to serve

the national security. In addition to its concrete

provisions limiting BMD deployment, however,

the ABM Treaty has unavoidably assumed a symbolic political meaning in the United States and,

in different forms perhaps, in Europe and the

U.S.S.R. The Treaty stands for a decade of arms

control and attempts at superpower understanding about nuclear weapons. As a practical matter, it is impossible to overturn the Treaty’s technical provisions without calling into question U.S.

commitment to the whole fabric of the SALT/

START process. This side effect would have to be

weighed against the purely military and strategic
78

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

4. Allied and Chinese missile forces. The nuclear missile forces of Britain, France and China

are obviously a greater threat to the Soviet Union

than to the U.S. Most analysts agree that the existence of these forces enhances U.S. security.

But a major BMD initiative sparking widespread

Soviet defense would in effect disarm our allies

(to a degree depending on the nature of the Soviet deployment).

5. Accompanying strategic programs. A number

of new weapon systems and strategic programs

would be natural, though perhaps not necessary,

accompaniments to BMD. On the offensive side,

the U.S. would need to develop and deploy penetration aids against the Soviet BMD and improve

its bomber and cruise missile forces to reflect

added reliance on non-missile delivery vehicles.

on the defensive side, the overall category of

“strategic defense” comprises, in addition to

BMD: nationwide air defenses against Soviet

bombers and cruise missiles, defensive coverage

against SLBMs, civil defense shelters and evacuation plans, and passive “hardening” of military

installations and industrial facilities.

6. Opportunity Costs. The initial investment

in BMD deployment, the inevitable follow-ens,

and any accompanying strategic programs would

make a substantial, permanent demand on the

defense budget, competing with other nuclear

forces and with conventional forces, not to mention with nonmilitary expenditures.

In a more fundamental sense, the transition

from a world with a near-total ban on BMD to

a world with BMD deployments is probably an

irreversible change. Reimposing a defensive

“freeze” after a period of unrestrained deployment, much less dismantling defenses and returning to zero, would involve all of the problems that

attend upon arms control reductions at START

today. Extra caution seems warranted where strategic actions cannot easily be reversed or recalled: the opportunity for a comprehensive ban

on missile defense might not arise again.

7. Bean counting. Strategists, politicians, and

diplomats place considerable emphasis on quantitative measures of the nuclear balance and on

“proofs” that “parity” exists. Arms control

negotiations also reduce themselves quickly to

counting rules. It is unclear whether or how BMD

shouId affect such “bean counting. ” For each

U.S. battle station added to a defensive constellation, are the Soviets to be credited with fewer

ICBMs, since the U.S. defense represents potential attrition of the Soviet force? How many Soviet interceptor missiles equals one U.S. laser?

Whose estimate of the BMD’s likely wartime performance–the defense’s or the offense’s-–governs these counting rules? Experience indicates

that these types of questions, however far-fetched

and even preposterous they appear in prospect,

in the end assume considerable perceived importance.

8. Asymmetries. The Soviet BMD deployment

that could well follow U.S. deployment might not

share the same defensive goal or the same technology, stimulating the usual anxieties about unequal intentions and capabilities. Defensive systems are also complex, leading different analysts

to widely different conclusions about the likely

wartime performance of the BMD systems on

both sides. Moreoever the owner of the BMD,

aware of all the system’s hidden flaws, might

credit it with little capability, whereas the offense

planner will tend to give it the benefit of the

doubt. Though some hypothetical future world

with mutual BMD deployments might therefore

appeal to one analyst or nation, another could

easily have a completely different view of the

technical and strategic “facts.”
Section 10

PRINCIPAL JUDGMENTS AND

OBSERVATIONS
Section 10

PRINCIPAL JUDGMENTS AND OBSERVATIONS

1. The prospect that emerging “Star Wars”

technologies, when further developed, will provide a perfect or near-perfect defense system,

literally removing from the hands of the Soviet

Union the ability to do socially mortal damage

to the United States with nuclear weapons, is

so remote that it should not serve as the basis

of public expectation or national policy about

ballistic missile defense (BMD). This judgment

appears to be the consensus among informed

members of the defense technical community.

Technical prognosis for such a perfect or nearperfect defense is extremely pessimistic because

of the concentration and fragility of society; because alI concepts identified as candidates for a

future defense of population are known to be susceptible to countermeasures that would permit

the Soviet Union to retain a degree of penetration with their future missile arsenal despite costly

attempts to improve the U.S. defense; because

the Soviet Union would almost certainly make

such a determined effort to avoid being disarmed

by a U.S. defense; and because missile defense

does not address other methods for delivering nuclear weapons to the United States.

Mutual assured destruction (MAD), if this term

is applied to a state of technological existence

rather than to a chosen national policy, is likely

to persist for the foreseeable future.

2. The wisdom of deploying less-than-perfect

ballistic missile defenses remains controversial.

Less-than-perfect defenses would still allow the

Soviet Union to destroy U.S. society in a massive

attack but might call into question the effectiveness of smaller, specialized nuclear strikes.

Certain theories about nuclear war maintain

that such defenses could lessen the chances of

nuclear war and enhance U.S. security by protecting U.S. retaliatory forces; by interdicting

“limited” nuclear strikes; by further confusing Soviet predictions of the outcome of a strike; by

driving Soviet missile deployments in directions

favored by the United States; by lessening the

consequences of nuclear attack; and/or by fulfilling still other strategic goals.

Critics dispute the validity of some of these

goals; dispute that technology can fulfill the truly

useful goals; and/or argue that the many harmful side effects of introducing BMD to the strategic equation and altering the Anti-Ballistic Missile

(ABM) Treaty regime are not worth satisfying

these goals.

To address the wisdom of less-than-perfect defense, the public and policy makers would need

a precise statement of the strategic goal of the

deployment, an assessment of whether technology could satisfy that goal, and an analysis balancing fuIfillment of the goal against the side effects and uncertainties of introducing a new

ingredient into the strategic nuclear arena.

3. The strategic goal of President Reagan’s

Strategic Defense Initiative calling for emphasized BMD research—perfect, near-perfect, or

less-than-perfect defense against ballistic missiles—remains unclear. No explicit technical

standards or criteria are therefore available

against which to measure the technological prospects and progress of this initiative.

4. In all cases, directed-energy weapons and

other devices with the specifications needed for

boost-phase intercept of ICBMs have not yet

been built in the laboratory, much less in a form

suitable for incorporation in a complete defense

system. These devices include chemical lasers,

excimer and free electron lasers, x-ray lasers, particle beams, lightweight high-velocity kinetic energy weapons, and microwave generators, together with tracking, aiming, and pointing

mechanisms, power sources, and other essential

accompaniments.

It is unknown whether or when devices with

the required specifications can be built,

S. Moreover, making the technological devices

perform to the needed specifications in a controlled situation is not the crux of the technical

challenge facing designers of an effective ballistic missile defense. A distinct challenge is to

fashion from these devices a reliable defensive

architecture, taking into account vulnerability

81
8 2

of the defense components, susceptibility to future Soviet countermeasures, and cost relative

to those countermeasures.

New intercept mechanisms–directed energy

weapons and the like—therefore do not by themselves necessarily herald dramatically new BMD

capabilities.

6. It is clear that potent directed-energy

weapons will be developed for other military

purposes, even if such weapons are never incorporated into effective BMDs. Such weapons

might have a role in nuclear offense as well as

defense, in anti-satellite (ASAT) attack, in antiaircraft attack, and in other applications of concern to nuclear policy and arms control. Defense

and arms control policy will thus need to face

the advent of these new weapons, irrespective

of their BMD dimension.

7. For modest defensive goals requiring lessthan-perfect performance, traditional reentry

phase defenses and/or more advanced midcourse defenses might suffice. Such defenses

present less technical risk than systems that incorporate a boost-phase layer, and they could

probably be deployed more quickly.

New ideas for improving such “old” BMD concepts have emerged in the atmosphere of technical optimism enjoyed by the boost-phase

concepts.

8. Deployment of missile defenses based on

new technologies is forbidden by the Anti-Ballistic Missile (ABM) Treaty reached at SALT 1. The

Treaty permits only restricted deployment of traditional BMDs using fixed, ground-based radars

and interceptor missiles. Research into new technologies, and in selected cases development and

testing of defense systems based on these technologies, are allowed within the Treaty.

9. There is a close connection, not explored

in detail in this Background Paper, between advanced BMD concepts and future anti-satellite

(ASAT) systems. This connection springs from

four observations: 1) ASAT attack on space-based

weapons and sensors is probably the most attractive countermeasure to boost-phase BMD; 2) directed-energy weapons are more likely to succeed in the easier mission of ASAT than in the

more difficult mission of boost-phase BMD; 3) to

a degree dependent on technical details, early

stages of development of boost phase BMDs

might be conducted in the guise of ASAT development, stimulating anxieties about the health

of the ABM Treaty regime; 4) to a degree dependent on technical details, concluding a treaty with

the Soviet Union limiting ASAT development

would impede BMD research at an earlier stage

than would occur under the terms of the ABM

Treaty alone.
APPENDIXES
APPENDIX A: THE CONCLUSION OF PRESIDENT

REAGAN’S MARCH 23, 1983, SPEECH ON DEFENSE

SPENDING AND DEFENSIVE TECHNOLOGY — —

Weekly Compilation of

.

Presidential

Documents

Monday, March 28, 1983

Volume 19—Number 12

Pages 423-466

N O , thus far tonight I’ve shared with

you my thoughts on the problems of national security we must face together. My predecessors in the Oval Office have appeared

before yOU on other occasions to describe

the threat posed by Soviet power and have

proposed steps to address that threat. B u t

since the advent of nuclear weapons, those

steps have been increasingly directed

toward deterrence of aggression through

the promise of retaliation.

This approach to stability through offensive threat has worked. We and our allies

have succeeded in preventing nuclear war

for more than three decades. In recent

months, however, my advisers, including in

particular the Joint Chiefa of Staff, have underscored the necessity to break out of a

future that relies solely on offensive retaliation for our security.

Over the course of these discussions, I’ve

become more and more deeply convinced

that the human spirit must be capable of

rising above dealing with other nations and

human beings by threatening their existence. Feeling this way, I believe we must

thorough])’ examine every opportunity for

reducing tensions and for introducing greater stability into the strategic calculus on

both sides.

One of the most important contributions

we can make is, of course, to lower t h e

level of all arms, and particularly nuclear

arms. We're engaged right now in several

negotiations with the Soviet Union to bring

about a mutual reduction of weapons. I will

report to you a week from tomorrow my

thoughts on that score. But let me just say,

I’m totally committed to this course.

If the Soviet Union will join with us in

our effort to achieve major arms reduction,

we will have succeeded in stabilizing the

nuclear balance. Nevertheless, it will still be

necessary to rely on the specter of retaliation, on mutual threat. And that’s a sad

commentary on the human condition.

Wouldn’t it be better to save lives than to

avenge them? Are we not capable of demonstrating our peaceful intentions by applying all our abilities and our ingenuity to

achieving a truly lasting stability? I think

we are. Indeed, we must.

After careful consultation with my advisers, including the Joint Chiefs of Staff, I

believe there is a way. Let me share with

you a vision of the future which offers hope.

It is that we embark on a program to

counter the awesome Soviet missile threat

with measures that are defensive. Let u s

turn to the very strengths in technology

that spawned our great industrial base and

that have given us the quality of life we

enjoy today.

What if free people could live secure in

the knowledge that their security did not

rest upon the threat of instant U.S. retaliation to deter a Soviet attack, that we could

intercept and destroy strategic ballistic missiles before they reached our own soil or

that of our allies?

85
8 6

I know this is a formidable, technical task,

one that may not be accomplished before

the end of this century. Yet, current technology has attained a level of sophistication

where it reasonable for us to begin this

effort. It will take years, probably decades

of effort on many fronts. There will be failures and setbacks, just as there will be successes and breakthroughs. And as we proceed, we must remain constant in preserving the nuclear deterrent and maintaining a

solid capability for flexible response. B ut

isn’t it worth every investment necessary to

free the world from the threat of nuclear

war? We know it is.

In the meantime, we will continue to

pursue real reductions in nuclear arms, negotiating from a position of strength that

can be ensured only by modernizing our

strategic forces. At the same time, we must

take steps to reduce the risk of a conventional military conflict escalating to nuclear

war by improving our non-nuclear capabilities.

America does possess-now-the technologies to attain very significant improvements in the effectiveness of our conventional, non-nuclear forces. Proceeding

boldly with these new technologies, we can

significantly reduce any incentive that the

Soviet Union may have to threaten attack

against the United States or its allies.

As we pursue our goal of defensive technologies, we recognize that our allies rely

upon our strategic offensive power to deter

attacks against them. Their vital interests

and ours arc inextricably linked. Their

safety and ours are one. And no change in

technology can or will alter that reality. We

must and shall continue to honor our commitments.

1 clearly recognize that defensive systems

have limitations and raise certain problems

and ambiguities. If paired with offensive

systems, they can be viewed as fostering a n

agressive policy , and no one wants that

But with these considerations firmly in

mind. I call upon the scientific community

in our country, those who gave us nuclear

for closer consultation with our allies, I’m

taking an important first step. I am directing a comprehensive and intensive effort to

define a long-term research and develop

ment program to begin to achieve our ultimate goal of eliminating the threat posed

by strategic nuclear missiles. This could

pave the way for arms control measures to

eliminate the weapons themselves. We seek

neither military superiority nor political advantage. Our only purpose-one all people

share—is to search for ways to reduce the

danger of nuclear war.

My fellow Americans, tonight we’re

launching an effort which holds the promise

of changing the course of human history.

There will be risks, and results take time.

But I believe we can do it. As we cross this

threshold, I ask for your prayers and your

support.

Thank you, good night, and Cod bless

you.

Note: The President spoke at 8:02 p.m. from

the Oval Office at the White House. The

address was broadcast live on notion wide

radio and television.

Following his remarks, the President met

in the White House with o number of administration officials, including members

of the Cabinet, the White House staff, and

the Joint Chiefs of Staff and former officials of past administrations to discuss the

address.
APPENDIX B: ABM TREATY

AND RELATED DOCUMENTS

—— — . ———-——

1980 EDITION

UNITED STATES

ARMS CONTROL

AND

DISARMAMENT

AGENCY

AGREEMENTS

TEXTS AND HISTORIES

WASHINGTON, D. C., 20451

8 7
8 8

Treaty Between the United States of America and the

Union of Soviet Socialist Republics on the Limitation of

Anti-Ballistic Missile Systems

Signed at Moscow May 26, 1972

Ratification advised by U.S. Senate August 3, 1972

Ratified by U.S. President September 30, 1972

Proclaimed by U.S. President October 3, 1972

Instruments of ratification exchanged October 3, 1972

Entered 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 devastating

consequences for all mankind,

Considering that effective measures to limit anti-balllstic missile systems would be a

substantial factor in curbing the race in strategic offensive arms and would lead to a

decrease in the risk of outbreak of war involving nuclear weapons,

Proceeding from the premise that the Iimitation of anti-ballistic missile systems, as

well as certain agreed measures with respect to the Imitation of strategic offensive

arms, would contribute to the creation of more favorable conditions for further

negotiations on Iimiting strategic arms,

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

Nuclear Weapons,

Declaring their intention to achieve at the earnest possible date the cessation of the

nuclear 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 strengthening of trust between States,

Have agreed as follows

Article I

1 Each party undertakes to Iimit anti-ballistic missile (ABM) systems and to adopt

other measures in accordance with the provisions of this Treaty.

2 Each Party undertakes not to deploy ABM systems for a defense of the territory of

its country and not to provide a base for such a defense, and not to deploy ABM

systems for defense of an individual region except as provided for in Article III of this

Treat y

Article II

1 For the purpose of this Treaty an ABM system is a system to counter strategic

ballistic missiles or their elements in flight trajectory, currently consisting of:

(a) ABM Interceptor missiles, which are Interceptor missiles constructed and

deployed 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 launching

ABM interceptor missiles; and

(c) ABM radars, which are radars constructed and deployed for an ABM role, or of

a type tested in an ABM mode.

2. The ABM system components listed in paragraph 1 of this Article include those

which are:

(a)

(b)

(c)

(d)

(e)

operational;

under construction;

undergoing testing;

undergoing overhaul, repair or conversion; or

mothballed

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 fifty

kilometers 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 Interceptor

missiles at launch sites, and (2) ABM radars within no more than SIX ABM radar

complexes, the area of each complex being Circular and having a diameter of no more

than three kilometers; and

(b) within one ABM system deployment area having a radius of one hundred and

fifty 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 Interceptor

missiIes at launch sites, (2) two large phased-array ABM radars comparable in

potential to corresponding ABM radars operational or under construction on the date

of signature of the Treaty in an ABM system deployment area containing ICBM Silo

launchers, and (3) no more than eighteen ABM radars each having a potential less than

the potential of the smaller of the above-mentioned two large phased-array ABM

radars.

Article IV

The Iimitations provided for in Article III shall not apply to ABM systems or their

components used for development or testing, and located within current or

additionally agreed test ranges, Each Party may have no more than a total of fifteen

ABM 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-based

2. Each Party undertakes not to develop, test, or deploy ABM launchers for launching more than one ABM interceptor missile at a time from each launcher, not to

modify 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 of

ABM launchers.

Article VI

To enhance assurance of the effectiveness of the limitations on ABM systems and

their components provided by the Treaty, each Party undertakes
90

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 or

their 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 missile

attack except at locations along the periphery of its national territory and oriented

outward.

Article Vll

Subject to the provisions of this Treaty, modernization and replacement of ABM

systems or their components may be carried out.

Article Vlll

ABM systems or their components in excess of the numbers or outside the areas

specified in this Treaty, as well as ABM systems or their components prohibited by this

Treaty, shall be destroyed or dismantled under agreed procedures within the shortest

possible agreed period of time.

Article IX

To assure the viability and effectiveness of this Treaty, each Party undertakes not to

transfer to other States, and not to deploy outside its national territory, ABM systems or

their components limited by this Treaty.

Article X

Each Party undertakes not to assume any international obligations which would

conflict with this Treaty.

Article Xl

The Parties undertake to continue active negotiations for limitations on strategic

offensive arms

Article XII

1. For the purpose of providing assurance of compliance with the provisions of this

Treaty, each Party shall use national technical means of verification at its disposal in a

manner consistent with generally recognized principles of international law.

2. Each Party undertakes not to Interfere with the national technical means of

verification of the other Party operating in accordance with paragraph 1 of this Article.

3. Each Party undertakes not to use deliberate concealment measures which

impede verification by national technical means of compliance with the provisions of

this 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, the

Parties shall establish promptly a Standing Consultative Commission, within the

framework of which they will:

(a) consider questions concerning compliance with the obligations assumed and

related situations which may be considered ambiguous;
9 1

ARMS CONTROL AND DISARMAMENT AGREEMENTS

(b) provide on a voluntary basis such information as either Party considers

necessary to assure confidence in compliance with the obligations assumed,

(c) consider questions involving unintended Interference with national technical

means of verification,

(d) consider possible changes in the strategic situation which have a bearing on

the provisions of this Treaty;

(e) agree upon procedures and dates for destruction or dismantling of ABM

systems or their components in cases provided for by the provisions of this Treaty;

(f) consider, as appropriate, possible proposals for further increasing the viability

of this Treaty; including proposals for amendments in accordance with the

provisions of this Treaty,

(g) consider, as appropriate, proposals for further measures aimed at Iimiting

strategic 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 shall

enter 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 of

this Treaty have jeopardized its supreme Interests. It shall give notice of its decision to

the other Party six months prior to withdrawal from the Treaty. Such notice shall

include a statement of the extraordinary events the notifying Party regards as having

jeopardized 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 exchange

of Instruments of ratification.

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

Nat Ions.

DONE at Moscow on May 26, 1972, in two copies, each in the English and Russian

languages, both texts being equally authentic.

FOR THE UNITED STATES FOR THE UNION OF SOVIET

OF AMERICA SOCIALIST REPUBLICS

President of the United

States of America

General Secretary of the Central

Committee of the CPSU
9 2

Agreed Statements, Common Understandings, and Unilateral Statements Regarding the Treaty Between the

United States of America and the Union of Soviet

Socialist Republics on the Limitation of Anti-Ballistic

Missiles

1. Agreed Statements

The document set forth below was agreed upon and Initialed by the Heads of the

Delegations on May 26, 1972 (letter designations added);

AGREED STATEMENTS REGARDING THE TREATY BETWEEN THE UNITED

STATES OF AMERICA AND THE UNION OF SOVIET SOCIALIST REPUBLICS ON

THE LIMITATION OF ANTI-BALLISTIC MISSILE SYTEMS

[A]

The Parties understand that, in addition to the ABM radars which maybe deployed in

accordance with subparagraph (a) of Article Ill of the Treaty, those non-phased-array

ABM radars operational on the date of signature of the Treaty within the ABM system

deployment area for defense of the national capital may be retained.

[B]

The Parties understand that the potential (the product of mean emitted power in

watts and antenna area in square meters) of the smaller of the two large phased-array

ABM radars referred to in subparagraph (b) of Article Ill of the Treaty is considered for

purposes of the Treaty to be three million.

[c]

The Parties understand that the center of the ABM system deployment area centered

on the national capital and the center of the ABM system deployment area containing

ICBM silo launchers for each Party shall be separated by no less than thirteen hundred

kilometers.

[D]

In order to insure fulfillment of the obligation not to deploy ABM systems and their

components except as provided in Article Ill of the Treaty, the Parties agree that in the

event ABM systems based on other physical principles and including components

capable of substituting for ABM interceptor missiles, ABM launchers, or ABM radars

are created in the future, specific limitations on such systems and their components

would be subject to discussion in accordance with Article Xlll and agreement in

accordance with Article XIV of the Treaty.
93

ARMS CONTROL AND DISARMAMENT AGREEMENTS

[E]

The Parties understand that Article V of the Treaty includes obligations not to

develop, test or deploy ABM interceptor missiles for the delivery by each ABM

interceptor missile of more than one independently guided warhead.

[F]

The Parties agree not to deploy phased-array radars having a potential (the product

of mean emitted power in watts and antenna area in square meters) exceeding three

million, except as provided for in Articles Ill, IV and VI of the Treaty, or except for the

purposes of tracking objects in outer space or for use as national technical means of

verification.

[G]

The Parties understand that Article IX of the Treaty includes the obligation of the US

and the USSR not to provide to other States technical descriptions or blue prints

specially worked out for the construction of ABM systems and their components

Iimited by the Treaty.

2. Common Understandings

Common understanding of the Parties on the following matters was reached during

the 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 deployment

area centered on its national capital and one ABM system deployment area containing ICBM silo launchers. The two sides have registered agreement on the following

statement: “The Parties understand that the center of the ABM system deployment

area centered on the national capital and the center of the ABM system deployment

area containing ICBM silo launchers for each Party shall be separated by no less

than thirteen hundred kilometers.” in this connection, the U.S. side notes that its

ABM system deployment area for defense of ICBM silo launchers, located west of

the Mississippi River, will be centered in the Grand Forks ICBM silo launcher deployment 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 III

shall 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 be

useful to assure that there is no misunderstanding as to current ABM test ranges. it is

our understanding that ABM test ranges encompass the area within which ABM

components are located for test purposes. The current U.S. ABM test ranges are at

White Sands, New Mexico, and at Kwajalein Atoll, and the current Soviet ABM test

range is near Sary Shagan in Kazakhstan. We consider that non-phased array radars

of types used for range safety or instrumentation purposes maybe located outside of

ABM test ranges. We Interpret the reference in Article IV to “additionally agreed test
94

SALT ONE–AGREED STATEMENTS

ranges” to mean that ABM components will not be located at any other test ranges

without prior agreement between our Governments that there will be such additional

ABM test ranges.

On May 5, 1972, the Soviet Delegation stated that there was a common

understanding on what ABM test ranges were, that the use of the types of non-ABM

radars for range safety or Instrumentation was not limited under the Treaty, that the

reference in Article IV to “additionally agreed” test ranges was sufficiently clear, and

that 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 not

to 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 deployment

of mobile ABM systems and components would rule out the deployment of ABM

launchers and radars which were not permanent fixed types. At that time, we asked

for 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 April 13, 1972, the Soviet Delegation said there IS a general commo n

understanding 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

Implementation of the ABM Treaty’s Article Xlll on the Standing Consultative

Commission (SCC) and of the consultation Articles to the Interim Agreement on

offensive arms and the Accidents Agreement, ’ agreement establishing the SCC will

be worked out early in the follow-on SALT negotiations; until that IS completed, the

following arrangements will prevail: when SALT IS in session, any consultation

desired by either side under these Articles can be carried out by the two SALT

Delegations, when SALT IS not in session, ad hoc arrangements for any desired

consultations under these Articles may be made through diplomatic channels.

Minister Semenov replied that, on an ad referendum basis, he could agree that the

U.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 the

obligations of both the Interim Agreement and the ABM Treaty beginning from the

date 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 Between

the United States of America and the Union of Soviet Socialist Republics, signed Sept.

30, 1971
95

ARMS CONTROL AND DISARMAMENT AGREEMENTS

The U.S. agrees in principle with the Soviet statement made on May 6 concerning

observance of Obligations beginning from date of signature but we would Iike to

make clear our understanding that this means that, pending ratification and

acceptance, neither side would take any action prohibited by the agreements after

they had entered into force This understanding would continue to apply in the

absence of notification by either signatory of its Intent Ion not to proceed with

ratification or approval

The Soviet Delegation Indicated agreement with the U S. statement

3. Unilateral Statements

The following noteworthy unilateral statements were made during the negotiations

by 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 to

achieving agreement on more complete Iimitations 011 strategic offensive arms,

following agreement on an ABM Treaty and on an Interim Agreement on certain

measures with respect to the Iimitation of strategic offensive arms The U S

Delegation believes that an objective of the follow-on negotiations should be to

constrain and reduce on a long-term basis threats to the survivability of our

respective strategic retaliatory forces The USSR Delegation has also Indicated that

the objectives of SALT would remain unfulfilled without the achievement of an

agreement providing for more complete Iimitations on strategic offensive arms. Both

sides recognize that the initial agreements would be steps toward the achievement of

more 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 a

basis for withdrawal from the ABM Treaty The U.S. does not wish to see such a

situation occur, nor do we believe that the USSR does It IS because we wish to

prevent 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 Congressional

consideration of the ABM Treaty and the Interim Agreement, of this statement of the

U 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 suc h

testing. We believe that the sides should have a common understanding of this

phrase. First, we would note that the testing provisions of the ABM Treaty are

intended 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 amplify

the remarks we have made on this subject during the previous Helsinki phase by

setting forth the objectives which govern the U.S. view on the subject, namely, while

prohibiting testing of non-ABM components for ABM purposes. not to prevent

testing of ABM components, and not to prevent testing of non-ABM components for
96

SALT ONE–AGREED STATEMENTS

non-ABM purposes. To clarify our interpretation of “tested in an ABM mode, ” we

note that we would consider a launcher, missile or radar to be “tested in an ABM

mode” if, for example, any of the following events occur: ( 1 ) a launcher IS used to

launch an ABM Interceptor missile, (2) an Interceptor missile IS flight tested against a

target vehicle which has a flight trajectory with characteristics of a strategic ballistic

missile flight trajectory, or IS flight tested in conjunction with the test of an ABM

Interceptor missile or an ABM radar at the same test range, or IS flight tested to an

altitude inconsistent with Interception of targets against which air defenses are

deployed, (3) a radar makes measurements on a cooperative target vehicle of the

kind referred to in item (2) above during the reentry portion of its trajectory or makes

measurements in conjunction with the test of an ABM interceptor missile or an ABM

radar at the same test range. Radars used for purposes such as range safety or

Instrumentation 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 statement

to make. The U.S. side wishes to make clear that the provisions of this Article do not

set a precedent for whatever provision may be considered for a Treaty on Limiting

Strategic Offensive Arms. The question of transfer of strategic offensive arms IS a far

more 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 detect

and track ballistic missile warheads at great distances, they have a significant ABM

potential. Accordingly, the U.S. would regard any increase in the defenses of such

radars by surface-to-air missiles as inconsistent with an agreement.
APPENDIX C: OTHER APPLICATIONS

OF DIRECTED ENERGY WEAPONS

This Background Paper treats only one–and

probably one of the most difficult-military application of directed energy. Many other applications of widely varying plausibility vie for funding and attention. An assessment of all these

schemes is well beyond the scope of this Paper,

but the list below is provided for reference. Mention of a scheme does not imply that it has any

technical or military promise; this question would

have to be properly studied.

Anti-satellite (ASAT). Directed energy attack on

satellites from space-, air-, or ground-based

weapons is substantially easier than boost phase

BMD. A satellite’s orbit is completely predictable, making it in effect a fixed target. Long dwell

times and low fluences suffice for ASAT attack

on unshielded satellites. For instance, long illumination at just a few watts/cm2 (several times

the sun’s normal irradiance in space) could upset

the thermal control systems that allow spacecraft

to endure the extremes of heat and cold in outer

space. Substantial hardening of large and complex satellites (including sensors) to directed

energy weapons from all directions at all times

is impractical. Unlike BMD, which must handle

thousands of boosters in a few minutes, ASATs

would have fewer targets and longer attack times.

Last, BMDs must operate under the most hostile

circumstances imaginable, whereas the superpowers might use ASATs in scenarios short of nuclear war.

This Background Paper has stressed (see Section 5.1) that maturation of the same technologies

involved in boost phase BMD virtually assures potent ASATs. The so-called “Star Wars” systems

could well be their own worst threats. Besides

the intrinsic ease of ASAT over BMD, a Soviet defense suppression ASAT attack on U.S. defensive

battle stations would have three key factors working in its favor: 1 ) The Soviets would pick the time

and sequence of attack on the U.S. BMD system

and launch of their ICBMs; 2) The Soviets need

not destroy the entire defensive constellation, but

only “punch a hole” for their ICBMs to pass

through; 3) The attack would take place over Soviet territory.

Ground-based laser ASATs, presumably using

excimer or free-electron lasers for best atmospheric propagation, would have the advantages

of large size and power supplies. Airborne lasers

could avoid some of the propagation disturbances introduced by denser air at low altitudes,

but turbulence around the airplane skin could

require adaptive beam compensation.

Space-based directed energy ASATs are the

most interesting category of all, since they would

be, in effect, long-range space mines, Rather than

positioning itself next to its quarry like an ordinary

space mine, a laser could be thousands of kilometers away and still be able to strike within

milliseconds upon receipt of a radio signal from

the gound.

Strategic offense. If they mature, the directed

energy devices discussed for BMD might turn out

to have been better termed “offensive

breakthroughs” than “defensive breakthroughs.”

Consider, for example, a fleet of Soviet x-ray

lasers launched simultaneously with (or minutes

before) a Soviet first-stike ICBM attack. The popup x-ray lasers’ job would be to intercept any U.S.

ICBMs launched before arrival of Soviet silo-killing RVs. The Soviet x-ray lasers wouId therefore

deprive the U.S. of its option for launch under

attack. Microwave generators might be used for

EMP-like attack on the U.S. command and control system. Another example of offensive use of

beam weapons would be Soviet ASAT attack on

U.S. warning, communications, nuclear detonation detection, or navigation satellites important

to the U.S. retaliatory capability. Yet another example would of course be suppression of any

U.S. BMD that used space-based weapons or

sensors.

Bus intercept. This Background Paper has

focused on intercept of ICBMs before booster

burnout. Intercept of the bus or post boost vehicle poses a rather different challenge. Post-boost

phase for today’s ICBMs is rather long (several

minutes) but could be shortened drastically on

future ICBMs. Bus tracking requires a different

sensor than booster tracking, since the bus plume

9 7
9 8

is much less conspicuous, and the bus rocket

motor may not operate continuously. The bus is

a target of declining value as it dispenses its RVs.

Interruption of bus operation would not prevent

the bus and its contents from continuing their

ballistic flight to the target country, though the

aim might be very wide of the target. Operating

above the atmosphere, the bus can deploy lightweight shields, decoys, and sensor countermeasures (e.g., corner reflectors). On the other hand,

x-ray lasers and neutral particle beams that cannot penetrate the atmosphere can attack the bus

in space.

Anti-SLBM. A number of schemes have been

suggested for using directed energy weapons

against SLBMs, besides the obvious extensions of

ICBM defense. Thus pop-up x-ray lasers could be

positioned on U.S. coasts or ships at sea to intercept SLBMs launched from nearby Soviet submarines. Aircraft patrolling coastal waters and carrying lasers could attack ascending SLBMs in their

area.

Anti-IRBM. Intermediate range ballistic missiles

(IRBMs) have short boost phases and potentially

low trajectories, making anti-lRBM defense rather

different from anti-lCBM defense and perhaps

better accomplished with ground-based terminal

BMD systems deployed in the theater.

Defense of satellites (DSAT). Low-power widedivergence (small optics) laser satellites (perhaps

HF for high specific energy) could serve as “escorts” for other satellites, defending the other

satellites from hostile objects—mines, ASAT missiles —approaching within a given range.

Anti-aircraft. At least four schemes have been

broached for using directed energy weapons

against aircraft or cruise missiles. The most ambitious would involve a worldwide constellation

of trackers (possibly LWIR) and beam weapons

(possibly DF or short wavelength lasers) to attack

Soviet Blackjack strategic bombers, Backfire

bombers attacking U.S. aircraft carriers, Soviet

airborne command post “Doomsday planes, ” Soviet AWACS radar planes, and so on. In a second scheme, B-1 or B-52 bombers would be outfitted with lasers (possibly DF) to protect them

from Soviet fighters, surface-to-air missiles (SAMs),

and air-to-air missiles. A third scheme equips carrier battle groups with lasers or particle beams

to defend themselves against cruise missile attack.

Fourth and last, ground-based beam weapons

might replace surface-to-air missiIes for local air

defense.

Midcourse and terminal BMD. Intense electron

beams have long been studied as replacements

for interceptors in reentry BMD. In midcourse

BMD, beam weapons might not only destroy

RVs, but aid discrimination of RVs from lightweight decoys: lasers, particle beams, or x-ray

lasers would illuminate approaching objects, and

sensors would use the response of each object

as an extra piece of data to judge whether it was

a true RV (see Section 6).

Submarine communications. This scheme

would use a blue-green laser to communicate

with submerged submarines. Seawater is opaque

to all but VLF and ELF radio frequencies, used

for submarine communications today, and to the

blue-green portion of the visible light spectrum.

A blue-green laser beam originating on a satellite, reflected from a space-based mirror, or carried by an airplane would be modulated in accordance with the message to be transmitted and

directed at a given spot on the ocean. After transmission of the full message, the beam would

dwell on a neighboring spot and transmit again,

and so on, eventually covering all submarine patrol areas. Optical sensors on the submarine hull

would detect the message.

Blinding sensors and seekers. Analysts have

studied a wide range of tactical applications for

lasers, involving blinding of battlefield sensors,

missile seekers, and even human beings.