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 ex- plore 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 inter- national Security Division) and Peter Sharfman (Program Manager). Contents Section Page 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Booster Characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Directed Energy Weapon Concepts for Boost Phase Intercept. . . . . . . . . . . . . . . . . . . . . . . 15 3.1 Space-Based Chemical Lasers: A First Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 3.2 Ground-Based Lasers With Space-Based Mirrors . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.3 Nuclear Bomb-Pumped X-Ray Lasers: Orbital and Pop- 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 C3l 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 to achieve our ultimate goal of eliminating the current concepts for directed-energy ballistic threat posed by strategic nuclear missiles. ”2 Pur- missile defense in space. Its purpose is to pro- suant to the President’s speech, the Department vide Members of Congress, their staffs, and the of Defense established a Defensive Technologies public with a readable introduction to the so- Study Team under James C. Fletcher (of the Uni- called “Star Wars” technologies that some sug- versity of Pittsburgh) to prescribe a pIan for the gest might form the basis of a future nationwide R&D program. A parallel effort, called the Future defense against Soviet nuclear ballistic missiles. Security Strategy Study and headed by Fred S. Since these technologies are a relatively new Hoffman (of Research and Development Asso- focus for U.S. missile defense efforts, little infor- ciates), addressed the implications for nuclear mation about them has been readily available policy of renewed emphasis on BMD. This Pa- outside the expert community. per covers the same technologies and issues as these Defense Department studies. The ABM Directed-energy or “beam” weapons comprise Treaty reached at SALT l3 severely restricts the chemical lasers, excimer and free electron lasers, development, testing, and deployment of BMD nuclear bomb-powered x-ray lasers, neutral and systems. Though this Background Paper treats the charged particle beams, kinetic energy weapons, strategic roles of missile defenses, including many and microwave weapons. In addition to describ- of their arms control implications, it does not treat ing these devices, this Background Paper assesses the vital international political implications of a he prospects for fashioning from such weapons major U.S. move to BMD. robust and reliable wartime defense system esistant to Soviet countermeasures. The assess- Focused on directed-energy intercept of mis- ment distinguishes the prospects for perfect or siles in their boost phase, i.e., on “Star Wars” ear-perfect protection of U.S. cities and popula- proper, this paper does not analyze midcourse on from the prospects that technology will and reentry BMD systems or non-BMD applica- chieve a modest, less-than-perfect level of per- tions of directed-energy weapons.4 “Star Wars” formance that will nonetheless be seen by some efforts generally further concentrate on intercept xperts as having strategic value. Though the of intercontinental ballistic missiles (ICBMs) rather focus is technical, the Paper also discusses, but than the related but somewhat different problems oes not assess in detail, the strategic and arms of intercept of submarine Iaunched ballistic mis- ontrol implications of a major U.S. move to de- siles (SLBMs) or intermediate-range ballistic velop and deploy ballistic missile defense (BMD).1 missiles (IRBMs). This Paper is therefore not a substitute for a more complete treatment of the This Background Paper grows indirectly out of entire subject of BMD.5 Moreover, BMD itself is resident Reagan’s celebrated television speech only part of the larger subject of strategic defense, f March 23, 1983, in which he called for a “long- comprising defense against bombers and cruise erm research and development program to begin missiles, civil defense, passive defense of military targets, anti-submarine warfare (ASW), and pre- emptive counterforce attack in addition to BMD. ‘ 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 de- se of the Sentinel and Safeguard ABM systems in the late 1960’s 2The relevant portions of President Reagan’s speech are d early 1970’s. BMD largely replaced ABM as the term of choice, reproduced in Appendix A. t recently the more self-explanatory Defense Against Ballistic 3The ABM Treaty and related documents are reproduced in Ap- sslles (DABM) has gained popularity. Within the Executive pendix B, ~nch, BMD efforts pursuant to President Reagan’s so-called ‘‘Star 4Appendix C describes briefly, but does not assess, other pro- ~rs” speech are referred to as the Strategic Defense Initiative (SD I). posed military applications of directed-energy weapons. )rmally the term strategic defense comprehends other methods 5For a more complete treatment, see f%//;sf;c Missile ~efe~set Ilmltlng damage from nuclear attack besides BMD. ed. Ashton B. Carter and David N. Schwartz (Brooklngs, 1984). 3 4 It is unusual for the President to express himself reason is that at this early stage of conceptualize on, and for the Congress and public consequently tion there is simply no point in (and little basis to concern themselves with, long-term research for) discussion at the detailed level where classi- and development. “Star Wars” is thus a some- fied particulars make a difference. The properties what unusual subject for a technology assessment of actual weapon systems in engineering devel intended for a public policy audience. It is in the opment, by contrast, are normally and under nature of this subject that unknown or unspeci- standably classified. fied factors outweigh what is known or can be The author and OTA wish to thank officials o presented in concrete detail. Many of the tech- the Army’s Ballistic Missile Defense Systems Corn nologies discussed in this Paper, and most cer- mand (BMDSCOM), the Lawrence Livermore Na tainly all of the schemes for fashioning a defense tional Laboratory, the Los Alamos Nationa system from these technologies, are today only Laboratory, the Defense Advanced Research Proj paper concepts. In the debate over the Safeguard ects Agency (DARPA), the Sandia National Labo ABM system a decade ago, or over basing modes ratory, the Air Force Weapons Laboratory (AFWL) for the MX missile in recent years, one could ana- the Office of the Secretary of Defense (OSD), and lyze in detail the technical properties of well- the Central Intelligence Agency (CIA) for thei defined systems in engineering development. So hospitality and cooperation. Many individual vague and tentative are today’s concepts for “Star aided the research for this Background Paper Wars” BMD that a comparable level of analysis though none shares the author’s sole respons is impossible. Fashions and “front runners” are bility for errors of fact or judgment. The author likely to change, Nonetheless, one is faced with and OTA wish especially to thank Hans Bethe assessing the concepts receiving attention today Richard Briggs, Al Carmichael, Albert Carnesale within the Executive Branch and which underlie Paul Chrzanowski, Robert Clem, Sidney D. Drel the President’s Strategic Defense Initiative. For- Dick Fisher, John Gardner, Richard L. Garwir tunately, judgments deduced from generic prop- Ed Gerry, Jack Kalish, Glenn A. Kent, Louis Ma erties of these concepts, which are unlikely to quet, Michael M. May, Tom Perdue, Theodor change, are sometimes telling. A. Postol, George Rathjens, Victor Reis, Jac This Paper is based on full access to classified Ruina, George Schneiter, David N. Schwartz information and studies performed for the Exec- Robert Selden, Leon Sloss, Daryl Spreen, Robi utive Branch. But it turns out that a fully adequate Staffin, John Steinbruner, Sayre Stevens, Thomas picture of this subject can be presented in un- Weaver, Stephen Weiner, and Wayne Winter classified form. One reason is that the important This Background Paper contains information features of the directed-energy BMD concepts are current as of January 1, 1984. based on well-known physics, and many have in fact been discussed for 20 years. The second Section 2 BOOSTER CHARACTERISTICS Section 2 BOOSTER CHARACTERISTICS Intercept of ICBMs in their boost phase offers age cannister. Once clear of the cannister, the advantages and disadvantages relative to inter- missile ignites its first stage motor. The first stage cept of reentry vehicles (RVs) later in the trajec- burns for about 55 seconds, burning out at an tory. The boosters are fewer and generally more altitude of about 22 kilometers. The second stage easily disrupted or destroyed than the RVs. Decoy also burns for 55 see, burning out at 82 km. The boosters would have to match an ICBM’s huge third stage burns for 60 sec and carries the re- heat output, making this offensive tactic attrac- mainder of the missile to about 200 km, the alti- tive only in certain circumstances. The disadvan- tude of the lowest earth orbiting satellites. tages of boost phase intercept are that boost When the third stage is jettisoned at the end phase is only a few minutes long and comprises of the 3-minute boost phase, the remainder of the earliest stage of an attack, and that sensing the missile consists of the post-boost vehicle (PBV) and intercept must be accomplished from outer or ‘‘bus” and its cargo of 10 reentry vehicles. At Space and over enemy territory. this point the bus and RVs are in ballistic free- Figure 2.1 shows an ordinary (minimum ener- fall flight to the United States. Even if they are gy) trajectory of a hypothetical future Soviet ICBM disrupted in some way or destroyed, these ob- hat has been given, for illustration, the boost pro- jects or their debris will reenter the atmosphere file of the U.S. MX Peacekeeper. Pressure from over the United States. The last few seconds of a steam generator expel Is the missile from its stor- 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 dis- pressed trajectory can offer unfavorable viewing ruption of boost phase any time right up to burn- angles to defensive sensors late in the trajectory. out will cause the warheads to fall far short. The most important trajectory variations from For the next 500 seconds or so after burnout— the point of view of boost phase intercept are var- almost until it reaches apogee—the bus uses its iations in boost profile. Boosters like MX were de- thrusters to make small adjustments to its trajec- signed with no regard for boost phase BMD, and tory. After each adjustment, it releases an RV. RVs optimizing their design gave rise to rather long released on different trajectories continue on to boost times. But boost phase can be shortened– different targets as multiple independently tar- giving less time for boost phase weapons to act– geted reentry vehicles (MIRVs). Decoys and other and accomplished within the atmosphere— penetration aids for helping the RVs escape de- where certain directed-energy weapons cannot fenses later in the trajectory are deployed dur- penetrate–with relatively little reduction in pay- ing busing. load or increase in missile size. Fast burn is ac- complished most easily with solid-fueled rockets. The bus itself is a target of declining value as Liquid-fueled boosters like the Soviet SS-18s and it dispenses its RVs. Destroying it early in the de- SS-19s burn more slowly and burn out at higher ployment process would obviously be useful: the altitudes. Thus while MX burns out at 200 km RVs not yet deployed from the bus would still ar- after 3 minutes of boost, the SS-18 burns out at rive at the United States, but perhaps nowhere 300-400 km after 5 minutes. The next generation near their intended targets. If cities are the targets, of Soviet ICBMs will reportedly employ solid pro- relatively small aiming errors might be inconse- pellants. quential. In any event, tracking the bus to allow some form of intercept requires a different type Studies performed for the Defense Department of sensor from that which tracks the booster for showed that with a 25 percent reduction in pay- boost phase intercept, since the bus’s thrusters load, a booster about the same size as MX could are small and operate intermittently. Because of be built which would burn out in less than 1 min- its small size, the bus (or at least critical elements ute at only 80 to 90 km, well within the sensible of it) might be more easily hardened against di- atmosphere. At 90 km the atmosphere is still too rected-energy weapons than the booster. For all dense for extremely accurate RV deployment or these reasons, the value of attempting bus inter- for deployment of lightweight RV decoys and cept is very unclear, and it usually does not fig- other penetration aids aimed at later defensive ure prominently in BMD discussions. layers: these functions require an additional 10 to 15 seconds of precision deployment betweer From apogee, the slowest point in their free- 90 and 110 km. If the offense needs precision ac fall trajectory, the RVs and empty bus gain speed curacy for some of its ICBMs but fears intercept as they fall back to earth. RVs are more resistant during these additional few seconds of high-alti to damage from directed-energy weapons than tude operation, mounting one or two RVs or boosters, and they might be accompanied by each of several “microbuses” instead of all the many decoys. When these objects enter the RVs on a single bus affords some protection. Each upper atmosphere at about 100 km altitude microbus would contain a simple guidance sys somewhat over 2 minutes before impact, they be- tern only good enough to carry the RVs from up gin to heat up, and the lighter objects slow down. per stage burnout to 110 km. Instead of present Still lower, below 50 km altitude and less than ing one target above 90 km, therefore, such a minute before impact, the objects undergo vio- i booster would present several targets. lent deceleration and the bus breaks up. The RVs, now glowing with heat, streak toward their targets The United States is studying a “Midgetman" at an angle of about 23 degrees to the horizontal. missile endorsed by the President’s Commission on Strategic Forces (the Scowcroft Commission The trajectory shape can be altered at the ex- pense of payload (see Figure 2.2). A lofted tra- 1“Short Burn Time ICBM Characteristic and Considerations,” Mar jectory takes longer but reenters faster, and a de- 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 car- million per copy, assuming a buy of 1,000 boost- ying one warhead. Midgetman’s warhead and ers. Costs for the second and subsequent thou- IUS are combined i n one hardened structure. sand would of course be substantially smaller. “able 2.1 shows the characteristics of Midgetman These costs are two to three times higher per RV ariants designed to face a boost-phase intercept than MX. ystem. The fast-burn version burns out at 80 km The Soviet ICBM arsenal today comprises about fter 50 sees of boost. With a 10 percent increase 1,400 boosters, more than two-thirds of them 7 weight, the fast-burn version can carry a sub- MIRVd. Most are slow-burning liquid-fueled stantial payload of penetration aids. A low-flight- boosters. The U.S. arsenal contains about 1,000 profile version is intended to stay within the at- faster-burning solid-fueled Minuteman boosters, mosphere until burnout, protecting it from some about half of them MIRVd. Both sides are adding types of directed-energy weapon. In the hard- solid boosters to their arsenals in the 1980’s. ened version, one gram of ablative or other hielding material has been applied to each The geographic distribution of offensive boost- quare centimeter of the entire booster body (if ers can also be important to space-based boost- le boost-phase intercept system did not begin phase defenses. The number of satellites required operation until a minute or so after launch, the in a defensive constellation usually increases if first stage might not have to be hardened). These all opposing ICBM silos are concentrated in one mall boosters are all estimated to cost $10 to $15 region and decreases if the silos are spread over 10 o I II II I 0 11 wide land areas. (On the other hand, too much react with new and different deployments when concentration allows defensive satellites to be they learn of any U.S. plans to deploy defenses. focused on one region by choosing the orbits ju- It is impossible to project Soviet deployments far viciously. ) Soviet SS-18 ICBMs, their largest into the future. A reasonable “baseline’ estimate MIRVd missiles, are organized into 6 wings of for the Soviet ICBM arsenal 15 to 20 years from about 50 missiles each, spread out over a large now might assign them the same number of region of the U.S.S.R. U.S. Minuteman missiles boosters they have today, but with burn charac- are organized into 6 wings of about 150 missiles teristics similar to the U.S. solid-propellant MX. each. Figures 2.3 and 2.4 show the geographic This Background Paper indicates where and how distributions. the effectiveness of a hypothetical U.S. defense depends on the nature of the offensive arsenal The capabilities of a hypothetical future U.S. it faces. In addition to having shorter average BMD should be measured against the future and burn times, future Soviet ICBMs could be more potential Soviet ICBM arsenal, not against today’s numerous, deployed less widely geographically, arsenal. The future arsenal wiII differ due to the less highly MIRVd, hardened against intercept, natural retirement of old ICBMs and introduction and so on. of new ones, and because the Soviets might well 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 ENERGY WEAPONS FOR BOOST-PHASE INTERCEPT Section 3 DIRECTED ENERGY WEAPONS FOR BOOST-PHASE INTERCEPT This section describes the entire set of “beam A revisit to this subject several years from now weapons” being considered in the United States might well find a new family of directed energy today for boost-phase ICBM intercept. Though concepts receiving attention. But for now the de- these weapons receive the most attention, the vices described in this section are the basis for “kill mechanism” that destroys the booster is not assessments of the prospects for efficient boost- necessarily the most important or technically phase defense, in the Defense Department and challenging part of an overall defense system. The elsewhere (fig. 3.1 ). Though some of these con- next section describes other essential elements cepts are new, many have in fact existed in one of a boost-phase defense. form or another for more than twenty years. Figure 3. I x TV Short- Submarine FM wave AM communications Gamma Far raYs X-rays 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 00 n m nm nm n m µm µm 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 103 Some transmission — — 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 comparisons for several reasons. First, in some through, with some concreteness, the design of cases details of the precise status of U.S. research a hypothetical defensive system based on the is classified. Second, and more importantly, quan- concept. The resulting designs are illustrative titative comparisons (e.g., “A millionfold increase on/y; no significance should be attached to in brightness is required to fashion a weapon from precise numbers. Precision is simply not possi- today’s laboratory device”) can mislead unless ble in the current state of technology and study accompanied by a deeper explanation of the of these concepts. technology; and the same quantitative measures are not appropriate for all technologies. Third, In all cases, the “current state of technology” and most importantly, such comparisons imply (however this is defined in each case) is far from that learning how to build the right device is tan- meeting the needs of truly efficient boost-phase tamount to developing an efficient missile de- intercept. The systems designed in this section fense, which is far from true: equally crucial are illustrate the level to which technology would design of a sensible system architecture, cost, sur- have to progress to be “in the ballpark.” Much vivability, resilience to countermeasures, and the attention fastens on the guIf between the current myriad detailed limitations that do not turn up state of technology and the ballpark require- until later in development. ments. This section does not emphasize such 3.1 SPACE-BASED CHEMICAL LASERS: A FIRST EXAMPLE This concept of directed energy weapon has makes the Iasant molecules: hydrogen and fluor- been the one most frequently discussed in recent ine react to form hydrogen fluoride (HF) mole- years for boost-phase ICBM intercept. For this cules in an upper state. The other requirement reason (and not necessarily because it is the most for Iasing–few molecules in the lower state–is plausible of all the concepts), it will be used to satisfied simply by removing the molecules from introduce certain features common to all the the reaction chamber after they have made their schemes that follow. transitions to the lower state and replacing them with freshly made upper state molecules. The Making and Directing Laser Beams pumping process is not perfect: not all the pump- ing energy ends up as laser light. The ratio of A molecule stores energy in vibrations of its pumping energy in to laser energy out is called constituent atoms with respect to one another, the efficiency of the laser. in rotation of the molecule, and in the motions Laser light is special in two respects: its fre- of the atomic electrons. The molecule sheds quency is precise, since all the light comes from energy in the form of emitted light when it makes the same transition in all the molecules; and the transitions from a higher-energy state to a lower- light waves from all the molecules emerge with energy state. Lasing takes place when many mol- crests and troughs aligned, since the waves are ecules are in an upper state and few are in a lower produced cooperatively. These special features state: one downward transition then stimulates make it possible to focus the laser energy with others, which in turn stimulate yet more, and a mirrors into narrow beams characterized by small cascade begins. The result is a powerful beam divergence angles (see fig. 3.2). Nonetheless, of light. there is a limit to the divergence angle that even Energy must be supplied to the molecules to a perfect laser with perfect mirrors can produce. raise most of them to the upper state. This proc- The divergence angle (in radians) can be no ess is called pumping. In the case of the chemical smaller than about 1.2 times the wavelength of lasers considered in this section, the pumping the light divided by the diameter of the mirror. energy comes from the chemical reaction that Thus a laser with 1 micrometer (=1 micron) 17 Figure 3.2 clear answer to this question can be given with- out more study and testing. Estimates of the hard- ness achievable with future boosters are probably reliable within a factor of two or three, though 12 megawatt estimates of the hardness of current Soviet directed-energy I boosters are probably reliable only to a factor of weapon 10 or so. Roughly speaking, laser light can damage boosters in two distinct ways. With moderate in- tensities and relatively Iong dwell times, the la- ser simply burns through the missile skin. This first mechanism is the relevant one for the chem- ical lasers described in this section. The second mechanism requires very high intensities but per- haps only one short pulse: the high intensity Figure 3.2 Basic power relationships for directed energy weapons. If the directed energy weapon has a divergence causes an explosion on and near the missile skin, angle of 1 microradian, the spot size at a range of 4000 and the shock from the explosion injures the kilometers is 4 meters (12 feet). In this figure, the divergence booster. This mechanism, called impulse kill, is angle is exaggerated about 1 million times. (For comparison of scale, the Earth’s radius is about 6,400 km,) If the directed more complex than thermal kill and is less well energy weapon emits 12 megawatts of power, a target within understood. it will be discussed in the next the spot at 4,000 km receives 100 watts on each square centi- section. meter 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 Bearing in mind the uncertainties in these esti- energy per second this weapon would take 10 seconds to mates, especially the complex interaction of heat- apply a kilojoule per square centimeter (1 KJ/cm2) to the target ing with the mechanical strains of boost, the fol- at 4,000 km range. Source: Author lowing estimates are probably reliable: A solid- fueled booster can probably absorb without dis- wavelength projected with a 1 meter mirror could ruption up to about 10 kilojoules per square have at best a 1.2 microradian divergence angle, centimeter (kJ/cm2) on its skin if a modicum of making a spot 1.2 meters wide at a range of 1,000 care is taken in the booster’s design to eliminate kilometers (refer to fig. 3.2).1 This perfect perform- “Achilles’ heels. ” This energy fluence would re- ance is called the diffraction limit. Dividing the sult from 1 second of illumination at 10 kilowatts laser power output by the size of the cone into per square centimeter (kw/cm2), since one watt which it is directed (cone size is measured in units equals one joule per second.2 Applying ablative called steradians; a divergence angle of x radians (heatshield) material to the skin can probably results in a cone of size 7rxz/4 steradians) yields double or triple the lethal fluence required. Ap- the laser’s “brightness,” the basic measure of a plying a mirrored reflective coating to the booster weapon’s lethality. is probably not a good idea, since abrasion dur- ing boost could cause it to lose its Iustre. Spin- Destroying Boosters with Lasers ning the booster triples its hardness, since a given spot on the side of the booster is then only il- Assuming a high-energy laser with small diver- luminated about a third of the time.3 On the other gence angle can be formed, stabilized so it does ZThe lethal fluence (in kJ/cmZ) must accumulate over a relatively not wave about (jitter), and aimed accurately, short time, so that the booster wall suffers a high rate of heating, what effect will it have on an ICBM booster? No 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 ‘The spot from a perfect laser with perfect mirrors would actually damage the booster. ~e brighter at the center than at the edges. The full angle subtended IIt is possible that uniform heating around the circu reference of )y this spot (the Airy disk from null to null in the diffraction pat- the booster introduces lethal mechanisms distinct from those that ern), is 2.4 times the wavelength divided by the mirror diameter, apply to heating a single spot on the side of the booster. In that Jut most of the energy is in the central fourth of this area: hence case, spinning the booster might not lengthen the required dwell he use in the text of the multiplier 1.2. time by the full amount dictated by geometry. 18 hand, currently deployed boosters, especially the Figure 3.3 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 ma- terial. An Orbiting Chemical Laser Defense System Consider a space-based BMD system comprised of 20-megawatt HF chemical lasers with 10 me- ter mirrors. The HF laser wavelength of 2.7 mi- crons is attenuated as it propagates down 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 re- quire larger mirrors.) A perfect 10 meter mirror with a perfect HF la- ser 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 il- lumination. 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 satel- lites 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 So- viet booster population. Equatorial orbits (fig. 3.3) Figure 3.3 Designing a constellation of directed energy give no coverage of the northern latitudes where weapon satellites for optimum coverage of Soviet ICBM Soviet ICBMs are deployed. Polar orbits give good fields. Equatorial orbits (a) give no coverage of northern coverage of northern latitudes but concentrate latitudes. Polar orbits (b) concentrate coverage at the north pole. Inclined orbits (c) are more economical. Slight additional satellites wastefuIly at the poles where there are economies are possible in some cases with further no ICBMs. The optimum constellation consists elaboration of the constellation design. Source: Author of a number of orbital planes inclined about 70° viet ICBM site at all times (corresponding to no to the equator, each containing several satellites. longer than 6.6 seconds dwell time per booster) results in the illustrative constellation of 32 or- The shorter the lethal range of the directed bital positions shown in figure 3.5. energy weapon, the lower and more numerous the satellites must be. For instance, with a lethal Since the 1,400 Soviet boosters currently de- range of 3 Mm, 5 planes containing 8 satellites ployed are spread out over most of the Soviet each, or a total of 40 satellites, are needed to en- Union, perhaps 3 of the 32 orbital positions would sure that Soviet boosters exiting Soviet airspace be over or near the Soviet Union at a time, able would be within lethal range of one satellite. If to make efficient intercepts. That is, only one in the lethal range is increased to 6 Mm, only 3 11 deployed U.S. battle stations would partici- planes of 5 satellites each are needed. This pate in a defensive engagement. The ratio of the dependence of constellation size on weapon total number of battle stations on orbit to the range is displayed in figure 3.4. (It is possible to number in position to participate in a defensive adjust these numbers a bit by using slightly ellip- engagement is called the absentee ratio. The in- tical orbits with apogees over the northern hem- evitable waste reflected in the absentee ratio— isphere, adjusting inclinations and phasing, etc.). In the present example, requiring that at least one HF laser be no further than 4 Mm from each So- Figure 3.5 Figure 3.4 200 150 100 50 0 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 O = Cluster of 5 chemical laser battle stations maintained on orbit. Since there are many Soviet ICBM fields Total of 32 x 5 = 100 battle stations distributed over much of the Soviet landmass, more than one satellite in each constellation would be in position to Figure 3.5 Constellation of hypothetical directed energy participate in a defensive engagement. The ratio of the weapon satellites with 4,000 km range. The orbits are circular number of satellites in the constellation to the number over with 1000 km altitude. Each of the four orbital planes consists or within range of Soviet ICBM fields is called the absentee of eight positions spaced 45° apart around the circle. In the ratio. If all Soviet ICBMs were deployed in one relatively small example given in the text, five chemical laser battle stations region of the U. S. S. R., the absentee ratio would be the same are clustered at each point shown in this figure, for a total as the number of satellites in the constellation. Source: Author of 32 x 5 = 160 battle stations. Source: Author 20 usually on the order of 10—offsets an oft-cited laser can reach, each booster is accessible for 150 theoretical advantage of boost-phase intercept, seconds of its 180 second burn time. Each laser namely, that intercepting one booster saves buy- can therefore handle no more than 90 boosters, ing 10 interceptors for the booster’s 10 RVS. On even with instant dewing of the beam from target the other hand, coverage of the U.S.S.R.'s ICBM to target. If 1,400 Soviet boosters were launched fields automatically gives good coverage of essen- simultaneously, (1 ,400)/(90) = 15 lasers would tially all submarine deployment areas. Obviously be needed in position, for a worldwide total (mul- the absentee ratio would be 32—the full con- tiplying by the absentee ratio) of (10.7) X (15) stellation size—and not 32/3 = 10.7 if Soviet = 160 satellites. ICBM silos were not spread out so widely over If the Soviets doubled their arsenal to 2,800 Soviet territory but were deployed over a third boosters, the United States would need to deploy or less of the Soviet landmass, so that only one another 160 satellites, possibly an uncomfortable of the 32 U.S. satellites was within range. cost trade for the United States. Three of the earlier described laser satellites in position over the Soviet ICBM fields are not What is worse, if the Soviets deployed 1,400 enough to intercept 1,400 boosters if all or most missiles in a single region of the U.S.S.R. (at a of the boosters are launched simultaneously. U.S.-estimated cost of $21 billion for Midgetman- Each satellite can only handle a few boosters Iike ICBMs; see section 2 above), the US would because it must dwell for a time on each one. have to build, launch, and maintain on orbit an The time a chemical laser must devote to each additional (32) X(1 400)/(90) = 500 lasers plus booster depends on the satellite’s position at the their fuel and support equipment. moment of attack—6.6 seconds for 4 Mm range, If Soviet boosters were covered with shielding 1.7 seconds for 2 Mm range, etc. Taking 2 Mm material and spun during flight to achieve an ef- as an average range for the 32-satellite constella- fective hardness of, say, 60 kJ/cm2, a laser would tion (hoping the Soviets do not choose a moment have to devote 10 seconds to each booster at 2 when most of the U.S. satellites are farther than Mm range, requiring a sixfold increase in the 2 Mm from the ICBM flyout corridors to launch number of satellites, to 960. Alternatively, the all their boosters simultaneously), a laser must average range of each engagement could be re- devote an average of 1.7 seconds to each booster. duced to keep the dwell time at 1.7 seconds, with If the boosters in the future Soviet arsenal corresponding increase in constellation density resemble the U.S. MX, and the defense waits 30 (fig. 3.4). Either way, the number of U.S. satellites seconds or so to confirm warning and to wait for would grow to nearly the number of Soviet boost- the boosters to climb to an altitude where the HF ers 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 Figure 3.6 100 times brighter (using, say, a 80 MW laser with 1 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 con- sequently need to grow by a factor 5 to 10, to 800 to 1600 satellites! Table 3.1 summarizes how the size of the de- fensive deployment varies with the parameters assumed. Requirements for a Chemical Laser Defense 1 2 3 4 5 6 , 7 8 9 10 Figure 3.6 displays the performance of various hypothetical HF lasers. Keeping the size of the Radius of Earth Geosynchronous battle station constellation down to a hundred (6.4 Mm) altitude = 40 Mm rather than several hundred satellites means le- thal ranges of at least 4 Mm with illumination Lethal range (megameters) times less than about 1 second, assuming the de- Figure 3.6 Lethal range versus booster hardness for HF fense must be capable of intercepting 1,000 to chemical lasers of various sizes and dwell times. The labels 2,000 Soviet boosters with launches timed to on the curves have the format (laser power in megawatts, keep the boosters as far from the U.S. lasers as mirror diameter in meters) followed by the amount of time the laser devotes to destroying each booster. Source; Author possible. Further assuming Soviet booster harden- ing to at least 10 kJ/cm2 results in a requirement for chemical lasers considerably brighter than the of lasers: 10 lasers combined in this way would 20 MW, 10-meter laser described above. A produce a beam 100 times brighter than each in- hundredfold increase in brightness would be dividual laser. The trick is to arrange for the achieved by a laser with power 80 MW and ef- troughs and crests of the light waves from all the fective mirror diameter 50 meters. lasers to coincide. This theoretical prospect is unlikely to be realized with H F lasers, since their Such a laser would be about 10 million times light is actually emitted at several wavelengths brighter than the carbon dioxide laser on the Air and with shifting patterns of crests and troughs. Force’s Airborne Laser Laboratory. The current Alpha laser program of the Defense Advanced To yield diffraction-limited divergence, the mir- Research Projects Agency (DARPA) aims at a con- ror surface must be machined to within a frac- struction of an HF laser of just a few megawatts tion of a wavelength of its ideal design shape over and built only for ground operation. Nonethe- its entire surface. Since the mirror is over a mil- less, there is no fundamental technical reason lion wavelengths across, avoiding small figure er- why extremely bright chemical lasers cannot be rors is a severe requirement. A number of small built. In theory, several lasers can be operated mirrors can obviously combine to produce one together so that the brightness of the resulting large optical surface if their positions are all beam increases with the square of the number aligned to within a fraction of a wavelength. The 22 mirrors must maintain perfect surface shape in bit worldwide. The space shuttle can carry a pay- the face of heating from the laser beam, vibra- load of about 15,000 kg to the orbits where the tion from the chemical reaction powering the la- satellite battle stations would be deployed. About ser, and vibrations set up in the mirror as it is 670 shuttle loads would therefore be needed for slewed. Substantial hardening of mirrors to radia- chemicals, with perhaps another half as many for tion from nuclear bursts in space and to the x- the spacecraft structures, the lasers and mirrors, ray laser (described below) would be a challeng- construction and deployment equipment, and ing task. The 2.5-meter diameter mirror on sensors. 1,000 shuttle missions for every 1,000 NASA’s Space Telescope was produced without Soviet boosters (perhaps Midgetmen) deployed these constraints. in reaction to the U.S. defense is an impractical competition for the United States. Use of H F An extremely optimistic outcome of HF laser chemical lasers for BMD therefore requires technology—near the theoretical limit for conver- remarkably cheap heavy-lift space launch capa- ting the energy of the chemical reactants to la- bility in the United States. ser energy—would require more than a kilogram of chemicals on board the satellite for every The remaining components of the chemical la- megajouIe radiated. A spot diameter of 2 meters ser defense system—sensors, aiming and pointing at the target and a lethal fluence of 10 kJ/cm2 over technology, and communications— are for the this area results in an energy expenditure of 300 most part generic to all directed energy weapons MJ per booster. Destroying 1,000 Soviet boosters and are discussed in section 4. Section 5 presents therefore requires, reckoning very crudely, countermeasures the Soviets might take to off- 300,000 kg of chemicals in position over the So- set or nuIlify a chemical laser defense. viet ICBM field, or perhaps 10 million kg on or- 3.2 GROUND-BASED LASERS WITH SPACE-BASED MIRRORS A slight variant of the previous concept puts contain an atom of noble gas and a halogen atom, the laser on the ground and mirrors in space, making dimers like xenon fluoride (XeF), xenon reflecting the light back down toward Earth to at- chloride (XeCl), and krypton fluoride (KrF). The tack ascending boosters. This scheme avoids laser light comes from dimers in an excited upper placing the laser and its power supply in space, state decaying to a lower state, just like in the HF though mirrors, aiming equipment, and sensors laser. Excimer lasers tend to emit light in pulses remain. The excimer and free-electron lasers rather than in a continuous wave. The popula- considered for this scheme are in fact likely to tion of upper-state molecules is provided by be rather cumbersome, so ground basing them pumping with electric discharges in a rather com- might be the only practical way to use them for plicated process. The population of lower-state BMD. The lasers would emit at visible or ultra- molecules remains small because the lower-state violet wavelengths about ten times shorter than dimer is unstable and quickly breaks up into its the near-infrared wavelengths of the HF and DF two constituent atoms. The pumping process for chemical lasers in the space-based concept. excimer lasers is inefficient, so only a small frac- Shorter wavelengths permit use of smaller tion of the energy put into the laser in the elec- (though more finely machined) mirrors. The high tric discharge emerges as laser light. Powerful ex- power available with ground basing suggests at cimer lasers would therefore be large and would least the possibility of impulse rather than ther- need to vent large amounts of wasted energy; mal kill of boosters. these characteristics make them unsuitable fot space basing. Development of excimer lasers is The term excimer is a contraction of “excited at an early stage, and no excimer lasers exist with dimer.” A dimer is a molecule consisting of two anything remotely approaching the characteristic: atoms. The dimers considered for these lasers needed for this boost phase intercept concept. 23 Figure 3.7 electrons emit some of their energy as light. The presence of light from one electron causes others 10 relay mirrors to emit in the usual cooperative manner of a la- (30 m diameter) ser, and a cascade begins. By adjusting the posi- Laser beacon tions of the magnets and the energy of the elec- for adaptive trons, the wavelength of the light can be tuned optics 8 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. 12 mountaintop lasers 100 Intercept mirrors It has been suggested that it might even be possi- (400 MW, O 5 µ) (5 m diameter) ble to position FELs in space like HF chemical with 50,000 mirror subelements for \ lasers. FEL operation at visible wavelengths is in adaptive optics its infancy, and the experimental devices used \ II 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 Figure 3.7 Illustrative configuration of ground-based excimer with 10 kJ/cm2 deposited on a spot as small as or free-electron laser and space-based mirrors for thermal kill several centimeters wide. Assume the excimer or of Soviet ICBM boosters. Source: Author 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. Power outputs achieved in the laboratory are still If a half second of the main laser beam is devoted several orders of magnitude less than the aver- to each booster, then the required 10 kJ/cm2 will age power needed for thermal kill, and the en- be accumulated if the power reflected from each ergy achieved in a single pulse is much smaller intercept mirror is 40 MW. than the single-pulse energies needed for impulse Only about a tenth of the power emitted by ki I I. the ground based laser in the United States would The working of a free-electron laser (FEL) is be focused on the booster over the U.S.S.R. The more complicated.4 As the name suggests, the remainder would be lost in transit through the light-emitter (Iasant) is free electrons emitted from atmosphere and in reflection from the two mir- particle accelerator. Pumping therefore orig- rors. Thus a 400 MW laser is required. nates in the electrical source powering the ac- Passage through the atmosphere poses a num- celerator. The free electrons from the accelerator ber of problems for the primary laser beam. The are directed into a tube called the wiggler that most important source of interference is tur- Ias magnets positioned along its length. The bulence in the air, causing different parts of the nagnets cause the electrons to wiggle back and laser beam to pass through different optical envi- ~rth as they transit the tube. As they wiggle, the ronments when exiting the atmosphere. Each part of the beam suffers a slightly different disruption, 4See Charles A. Brau, “Free Electron Laser: A Review, ” Laser >CUS, March 1981; f%ywcs Today, December 1983, p. 17. and the beam that emerges does not have the 24 orderly arrangement of crests and troughs needed rors for the chemical laser and can tolerate for diffraction-limited focusing from the intercept smaller vibrations and stresses due to heating mirror. Without compensation for atmospheric from the laser beam. The small wavelength also turbulence, the ground-based laser scheme is results in a spot 10 times smaller at the target than completely impractical. Fortunately, the pattern the spot from a chemical laser beam at the same of turbulence within the laser beam, though con- range. This small spot requires pointing accuracy stantly changing, remains the same for periods ten times finer. Perhaps most important of all, the of a few milliseconds. Since it takes only 0.1 plume from the booster motor is too large to millisecond for light to make a round trip through serve as target for such a narrow beam. Some way the atmosphere, the effect of turbulence on the of seeing the actual missile body against the laser beam can be compensated for with the fol- background of the plume is needed for the short- lowing technique, called adaptive optics: A low- wavelength laser schemes (and for some config- power laser beacon is positioned near the relay urations of chemical lasers). One answer to this mirror. A sensor on the ground observes the dis- problem, described in section 4 below, is to posi- tortion of the beacon beam as it passes through tion near each intercept mirror a low-power la- the atmosphere. The beam from the ground- ser and a telescope (a laser radar or Iadar): the based laser is then predistorted in just such a way laser illuminates the booster and the telescope that its passage through the same column of air observes the reflected laser light, directing the transited by the beacon beam re-forms it into an pointing of the intercept mirror. The Iadar tele- undistorted beam. scope must have a mirror as large as the intercept mirror, since it must be able to “see” a spot as Figure 3.7 shows the many components re- small as that made by the beam. quired by the ground-based laser concept. Since each Soviet booster requires 0.5 sec of beam at A single immense laser pulse that deposits 10 some time during its 200 sec. boost phase, four kJ/cm2 in a very short time–millionths of a sec- beams would be needed to handle 1,400 Soviet ond rather than a second— might cause impulse boosters launched simultaneously (assuming no kill rather than thermal kill, In impulse kill, the retargeting delays), The lasers should be deployed laser pulse vaporizes a small layer of the booster on mountain tops to make atmospheric effects skin and surrounding air. The superheated gases manageable, and enough should be deployed then expand explosively, sending an impulsive that at Ieast four sites are always clear of cloud shockwave into the booster. A strong enough cover. The mirror on the ground would need to shockwave might cause the booster skin to tear. be tens of meters across and divided into tens The advantage of this kill mechanism is that it of thousands of individually adjustable segments would be very difficult to protect boosters from for predistortion of the wavefront. Each relay mir- it. The disadvantages are that impulse kill requires ror would need to be accompanied by a beacon. prodigious laser pulses and mirrors that can with- Four large interception mirrors would be needed stand them, and that the mechanism is poorly within 4 Mm of each Soviet ICBM flyout corridor, understood and depends on myriad factors like giving a worldwide constellation of a hundred or the altitude of the booster at the moment it is at- so. tacked. The small laser wavelength means that all mir- rors must be more finely machined than the mir- 3.3 NUCLEAR BOMB-PUMPED X-RAY LASERS: ORBITAL AND POP-UP SYSTEMS The U.S. Government has revealed efforts at its Such devices are said to constitute a “third gen- weapon laboratories to use the energy of a nu- eration” of nuclear weapons, the first two genera- clear weapon to power a directed beam of x-rays. tions being the atomic (fission) and hydrogen 25 (fusion) bombs. Each succeeding generation rep- Figure 3.8 resented a thousandfold increase i n destructive Energy from nuclear bomb 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 allow- ing 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 material = 2 (width – length) hydrogen bomb at the same range. Figure 3.8 In an x-ray laser, a rod of Iasant material is pumped x rays lie just beyond ultraviolet light on the to upper energy states by a nuclear bomb. Those cascades electromagnetic spectrum and have wavelengths of downward transitions that travel lengthwise build up more energy than sideways-going cascades. As a result, most of about a thousand times smaller than visible light the energy emerges from the ends of the rod into a cone with (see fig. 3.1 ). Compared to the infrared, visible, divergence angle equal to twice the rod width divided by its and ultraviolet lasers in the previous sections, the length. Source: Author x-ray laser produces much more energy from its bomb pump, but the energy is spread out over The pumping source for the x-ray laser is a nu- a larger cone. The lethal ranges for boosters turn clear bomb. The radiant heat of the born b raises out to be roughly comparable for all these types electrons to upper energy levels in atoms of Iasant of directed-energy device. Obviously the x-ray material positioned near the detonation (the laser delivers all its energy in one pulse, so there chemical nature of the Iasant material has not is no question of dwell time on the target. Very been revealed). As the electrons fall back again short-wavelength x-rays penetrate some distance to lower levels, it can happen that for a moment into matter (witness dental and medical x-rays), many atoms are in a given upper level and few but the longer-wavelength x-rays produced by a in a lower level; this is the necessary condition laser device do not penetrate very far into mat- for Iasing from the upper level to the lower level. ter or into the atmosphere. The wavelength of the emitted x-ray is deter- orbiting and ground-based “pop-up” systems mined by the energy levels involved. The wave- have been proposed as ways to make use of the length of the laser under study in the United x-ray laser for boost phase BMD. Both of these States is classified. We will use a round number schemes have attractive features but also serious of 1 nm. drawbacks. It could well be that the x-ray laser Since x-rays are not back-reflected by any kind device, if a powerful one can eventually be built, of mirror, there is no way to direct the x-rays into will be more useful in other strategic roles than a beam with optics like the visible and infrared boost-phase BMD. lasers. Nonetheless, some direction can be given to the laser energy by forming the Iasant mate- X-Ray Lasers rial into a long rod. Recall that a laser beam builds up when light from one Iasant atom stimulates Little has been revealed about the characteris- the upper-to-lower-level transition in another tics of the bomb-pumped x-ray laser being stud- atom, which stimulates a third, and so on. The ied by the United States (the so-called Excalibur result is a cascade of light heading in same direc- device), but some general information can be tion as the light from the original atom. The light deduced from the laws of physics and, to a lesser pulse gets stronger and stronger as it traverses the extent, from the scientific literature here and in Iasant medium stimulating more and more tran- the Soviet Unions sitions. In a long rod of Iasant material, cascades 5F, V. BU nkln, V. 1. Derzhiev, and S. 1. Yakovlenko, %vlet /our- that get started heading lengthwise down the rod na/ of Quantum E/ectron/cs 11 (8), August 1981, p. 981. R. C. Elton, are highly amplified by the time they leave the R. H. Dixon, and J. F. Seely, Physics of Quantum Electronics 6 rod, whereas sideways-going cascades remain (1 978), p. 243. Michael A, Duguay, /&d., p. 557. G. Chapllne and small. The result is that most of the laser energy L. Wood, Physics Today, June 1975, p. 40. 26 emerges as a beam aligned along the rod axis (fig. A 1-megaton bomb-pumped x-ray laser can 3.8). therefore deposit no more than about 100 mil- lion megajoules into a cone no narrower than The projected capabilities of the x-ray lasers be- about 20 microradians. The x-ray pulse from ing studied in the U.S. are classified; but it is fairly detonating such a perfect laser would deposit easy to determine the upper limit to how power- about 300 kJ/cm2 over a spot 200 meters wide ful such a laser could possibly be. Whether R&D at 10 Mm range. wiII succeed in making such a perfect laser can- not be said. But it will become clear that some- thing very close to the perfect laser is required Interaction of X-rays with Matter for boost phase intercept, though a less successful development would still yield a potent antisatel- X-rays of 1 nm wavelength do not penetrate lite weapon. very far into matter: all the energy from such a A l-megaton nuclear weapon releases about laser would be absorbed in the first fraction of 4 billion megajoules of energy. By surrounding a millimeter of the aluminum skin of a missile. the bomb with Iasant rods, most of this energy This paper-thin layer would explode, sending a can be harnessed to pump the laser. Since the shockwave through the missile. Thus the x-ray pumping mechanism for the x-ray laser is rather laser works by impluse kill. disorganized and wasteful, like the pumping Another consequence of the opacity of mat- mechanism for excimer lasers, at most a few per- ter to x-rays is that the laser beam would not cent of the bomb energy can be expected to end propagate very far into the atmosphere. The up in the laser beam. altitude to which the beam would penetrate The resulting 100 million megajoules or less of depends on the precise wavelength, which is laser energy emerges from the rods into cones classified. For the nominal 1 nm wavelength with relatively large divergence angle. It is easy described above, boosters below about 100 km to see why this divergence angle is much larger would be quite safe from attack. If the wavelength than the divergence angle obtained with the were much shorter, the x-rays would penetrate mirror-directed lasers treated in the previous sec- lower, reaching perhaps 60 km altitude or so. In tion, The divergence angle is determined by the what follows, it will be assumed that boosters are ratio of the width of the rod to its length, as in safe from x-ray laser attack below about 80 km. figure 3.8. A practical length for a rod is no more than about 5 meters. Making the rod thinner de- One last consequence of the physics of x-ray creases the divergence angle, but beyond a cer- interaction with matter is noteworthy. When an tain point no further narrowing of the beam cone atom of matter absorbs an x-ray, it emits an elec- is possible. The limit arises from diffraction, just tron. As x-rays are absorbed, it becomes harder as with the infrared and visible lasers: the diver- and harder to remove successive electrons. Fi- gence angle of light emitted from an aperture nally further x-rays cannot remove further elec- (mirror, rod tip, or anywhere else) cannot be less trons, and the matter becomes transparent. This than about 1.2 times the wavelength of the light phenomenon, called bleaching, means that a divided by the diameter of the aperture. A very strong x-ray laser beam can force its way through narrow rod therefore actually aggravates diffrac- a column of air by bleaching the column, but a tion and produces a wide cone. Making the rod weak laser beam is completely absorbed. An x- thinner results in no further narrowing of the ray laser in the atmosphere might therefore be beam when (1 .2) (wavelength) /(rod width) s (2) able to attack an object in space because the (rod width)/(rod length). For an x-ray wavelength beam is intense enough in the vicinity of the la- of 1 nm and a rod length of 5 meters, this equa- ser to bleach the air, whereas an x-ray laser in tion yields an optimum rod width of 0.06 mm and space could not attack objects within the atmos- a minimum achievable (diffraction-limited) diver- phere. This fact bodes ill for defensive space- gence angle of 20 microradians. based x-ray lasers attacked by similar lasers (or 27 — even weaker ones) Iaunched from the ground by the way it is a problem for chemical lasers that the offense. must dwell on each target before passing on to the next. Fast-burn boosters are Iikewise not a As with visible and infrared lasers, the lethality crippling problem for an orbiting x-ray laser of a n x-ray laser is subject to large uncertainties. system unless they burn out before they leave the The proper order of magnitude for the amount atmosphere, Other countermeasures, most no- of x-ray energy per square centimeter that needs tably the vuInerability of U.S. orbital x-ray lasers to be deposited on the side of a booster to dam- to Soviet x-ray lasers, are treated in section 5. age it can be estimated fairly easiIy. But the ac- tual hardness of a booster would depend on Pop-Up Defense Concept many design details in a way that is not fully understood at this time. A simple calculation in- The pop-up concept represents an attempt to dicates that 20 kj/cm2 is a reasonable number to avoid the one-laser-per-booster cost exchange take for the hardness of a booster. This is about and the vulnerability associated with basing the the same as for impulse kill by visible laser. An lasers in space (though crucial sensors remain RV would be harder, and a satellite softer. space-based even in the pop-up scheme). The small size and light weight of the bomb-pumped Orbital Defense Concept lasers makes it possible to consider basing them on the ground and launching them into space The “perfect” x-ray laser whose characteristics upon warning of Soviet booster launch. were deduced above wouId be capable of inter- cepting a booster from geosynchronous orbit Figure 3.9 shows why basing the pop-up lasers 40,000 km above the Earth. One laser would be in the United States is not practical. During the needed for each Soviet booster. At lower alti- 200 seconds or so of burn time of a Soviet MX- tudes, the rods surrounding the bomb could be Figure 3.9 gathered into several bundles and each bundle aimed at a different booster. At these lower Lowest altitude altitudes, though, the absentee problem means line of fire 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 com- clear atmosphere pared to a chemical laser, the cost tradeoff in- volved in launching a new laser every time the Burnout of hypothetical MX-like Soviet ICBM Soviets deploy a new ICBM is obviously not a (200 km altitude tolerable one for the United States. 180 sec. after launch) The x-ray laser can attack the boosters after they have left the protective atmosphere but before burnout. Simultaneous launch of all So- viet boosters is not a problem for x-ray lasers in atmosphere - 100 km 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 re- lulres 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 paper- Figure 3.9 X-ray lasers launched from the United States on hln absorbing layer were converted to klnet Ic energy, the boll-oft warning of Soviet ICBM launch would have to climb at least /elocity wou Id be (F/a)”, meaning a n impu Ise per unit area of or- as high as the line of fire shown in the figure within three jer (Fa)Y’, 10 ktaps is therefore produced if F =20 kJ/cm’, minutes to intercept an MX-like Soviet ICBM. Such a huge In re.allty, not all the deposited energy couples to the booster fast-acceleration defensive booster would be many times n t h If way A more caretu I ca Icu tat Ion of th IS lessened cou pl I ng larger than the Saturn V that took astronauts to the moon. 1~~ been pertormed by Hans Bet he (private com m u n Icatlon), Source: Author 33-698 0 - 84 - 5 : QL 3 28 like ICBM, the U.S.-based pop-up lasers would Okhotsk, separated from Soviet silos by about 30 have to cl mb high enough to see the Soviet degrees of arc–on SLBM-sized fast-burn boosters. boosters over the Earth’s horizon and have a line- With instantaneous warning, a sea-based laser of-fire unobstructed by the absorbing atmos- might be able to climb to firing position a few phere. Climbing so high so fast requires a booster seconds before burnout of a Soviet MX-like ICBM for the x-ray lasers that is many thousands of times and would enjoy almost an entire minute of visi- larger than the Saturn V rocket that carried U.S. bility to a slow-burning, high-burnout-altitude astronauts to the Moon. booster like the SS-18. Because of the short range, each bomb-pumped laser of the perfect design If the British Government allowed the U.S. described above could attack many (over 100) Government to base x-ray lasers in the United boosters using many individual Iasing rods. Such Kingdom, the lasers would be separated from So- efficiency could well be essential, since a sub- viet ICBM silos by only 45 degrees of arc rather marine cannot launch all its missiles simulta- than 90 degrees as with U.S. basing. Even so, neously and might only be able to fire one defen- popping up to attack an MX-like Soviet booster sive missile in the required few seconds. If the would require an enormous fast-burn booster for MX-like Soviet boosters were flown on slightly the x-ray laser and would put it into position to depressed trajections, if warning were not com- attack the Soviet booster only seconds before municated to the submerged submarine prompt- burnout. If the Soviets depressed the trajectory ly, if a human decision to launch defensive mis- or shortened the burn time of the offensive siles were required, or if the Soviets deployed booster very slightly, or if the United States suf- boosters that burned faster than MX, the sub- fered any delay whatsoever in launching the Iaunched system would be nullified, Last, sub- defensive boosters after Soviet launch (instan- marine patrol very near to Soviet shores suggests taneous warning), this hypothetical U.K.-based the possibility of attacking the submarine with system would be useless. shore-based nuclear missiles as soon as its posi- A final possibility would be launch of defen- tion has been revealed by the first defensive sive lasers from submarines stationed immedi- launch. Other countermeasures are discussed in ately off Soviet coasts—in the Kara Sea or Sea of Section 5. 3.4 SPACE-BASED PARTICLE BEAMS Beams of atomic particles would deposit their neutral particle beams, consisting of atomic energy within the first few centimeters of the tar- hydrogen (one electron bound to one proton) get rather than at the very surface as with lasers. deuterium (one electron, one proton, one neu- The effects of irradiation with the particle beam tron), tritium (electron, proton, two neutrons) 01 could be rather complex and subtle and would other neutral atoms are considered. To produce probably depend on design details of the attack- a neutral hydrogen (H°) beam, negative hydro ing Soviet booster. The result is uncertainty of sev- gen atoms (H –) with an extra electron are accel eral factors of ten in the effective hardness of an erated; the extra electron is removed as the bean- ICBM booster to beam weapon irradiation. emerges 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 thin- is unavoidable and, by the Heisenberg uncer- nest atmosphere and must wait for an attacking tainty principle, cannot be controlled or compen- booster to reach very high altitude. sated. It sets a lower limit on the divergence angle achievable with this method of producing neutral Generating Neutral Particle Beams particle beams. Table 3.2 shows the divergence angle resulting from this third source, assuming The accelerator that accelerates the negative perfect control of the first two sources. The hydrogen ion is characterized by its current in divergence cone from a neutral particle beam is amperes, measuring the number of hydrogen therefore about 10 times larger than the beam ions per second emerging from the accelerator; from the chemical laser of section 3.1 and 10 and by the energy of each accelerated ion in elec- times smaller than from the x-ray laser of section tron volts (eV; 1 eV = 1 watt per ampere). 3.3. Multiplying the current by the energy gives the A 100 MeV, 0.5 amp neutral tritium (T°) beam power of the beam, so that a l-amp beam of 100 thus directs 50 MW of power into a cone of di- MeV particles carries 100 MW of power. Ground- vergence angle 2 microradians, producing a spot based high-current accelerators and ground- 10 meters across at 5 Mm range. A target within based high-energy accelerators have been built this spot receives only 65 watts/cm2, requiring 1.5 and are operated daily in laboratories. One of the seconds of dwell time to deposit only 100 J/cm2. challenges for neutral particle beams as weapons is that they require both high current and high energy. Another challenge is to provide multi- Booster Vulnerability to megawatt power sources and accelerators in a size and weight suitable for space basing. Particle Beams Magnets focus and steer the beam as it emerges As soon as the neutral particle beam hits the from the accelerator. The last step is to neutralize target, the remaining electron is stripped off, leav- the beam by passing it through a thin gas where ing the energetic proton (or deuteron or triton) the extra electron is stripped off in glancing col- penetrating deeply into the target. The proton lisions with the gas molecules, forming HO from scatters electrons in its path, giving up a small H-. The divergence angle of the beam is deter- amount of its energy to the electron in each col- mined by three factors. First, the acceleration lision. When it has given up all its energy, it stops. process can give the ions a slight transverse mo- For most of its path, it deposits energy uniformly. tion as well as propelling them forward. Second, Thus if a 100 MeV TO beam penetrates 4 cm the focusing magnets bend low-energy ions more into the propellant in a missile, it deposits about than high-energy ions, so slight differences in 25 MeV along each cm. Protons penetrate more energy among the accelerated ions lead to diver- deeply than tritons of the same energy, and all gence (unless compensated by more complicated particles penetrate more deeply as they are given bending systems). Third, the glancing collisions more energy (table 3.3). that strip off the extra electron give the H atom a sideways motion. This last source of divergence Table 3.3.—Penetration Range of Neutral Table 3.2.—Neutral Particle Beam Divergence Angle Particle Beams Into Matter (in centimeters) H“ T“ H“ TO 100 MeV 3.6 microradians 2.0 100 MeV 250 MeV 100 MeV 250 MeV iOO MeV 1.4 1.0 Solid propellant or high explosive Divergence angle introduced by stripping electrons from a beam of negative (density 1.0 gm/cm3) 9.5 46.6 4.2 20.2 hIydrogen or tritium ions to produce a neutral beam This source of divergence j an unavoidable consequence of the Heisenberg uncertainty principle applied Aluminum . . . . . . . . . 3.5 17.2 1.6 7.6 o the sudden stripping of the electron If the satellite. based accelerator of the Lead . . . . . . . . . . . . . . 0.8 3.9 0.4 1.7 egative tons were absolutely perfect, this amount of divergence would remain SOURCE Author SOURCE Author 30 Figure 3.10 deposit the same energy per gram as it did in aluminum (fig. 3.1 O). Solid propellant (density 1 gm/cm3) The destructive effects of penetrating particle beams are therefore expressed in joules/gram de- posited within the target rather than in joules/cm2 Lead on the surface of the target as with lasers. Table (11.3 gm/cm3) 3.4 shows the energy deposition needed to pro- 4 cm duce certain harmful effects. Melting the target is straightforward, but for the other effects at 1 cm lower levels of irradiation the criteria are less 4.2 grams 4.2 grams clear. Heat effects in solid booster propellants and 1 cm in the high explosive and special nuclear materi- als i n warheads depend on the design of the tar- get. Effects on electronics, particularly transient disruption of computer circuits when electrons 100 MeV Tritium (T 0, beam are scattered by a passing proton, are poorly known and doubtless quite complicated and spe- Figure 3.10 A neutral particle beam penetrates farther into an aluminum target than into a lead target but deposits the cific to the target. Other components not shown same energy per gram. Though the energy per gram needed in table 3.4 —plastics, glue, guidance sensors– to melt aluminum is well known, the utility of particle beam make for a very complicated analysis. What is BMD concepts rests on the less certain destructive effects at lower levels of irradiation. Source: Author 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 Table 3.4.—Effects of Particle Beam Irradiation ing a sensitive component. Energy deposition Uncertainties in the destructive or disruptive Harmful effect (Joules per gram) effects of small amounts of radiation from a par Disruption of electronics . . . . . . . . . . 0.01 –1 .0 ticle beam weapon is the principal obstacle to Destruction of electronics . . . . . . . . . 10 Detonation of propellants, stating what energy, current, and divergent high explosive . . . . . . . . . . . . . . . . . 200 angle would make this concept a candidate for Softening of uranium boost-phase intercept. and plutonium . . . . . . . . . . . . . . . . . hundreds Melting of aluminum. . . . . . . . . . . . . . 1,000 Shielding to protect components from a neutra Approximate energy deposition (radiation dose) required to produce various harm. particle beam would necessarily be heavy but ful effects in components of a missile booster and its payload Many other ef- could still be an attractive countermeasure. It fects, such as melting of glue and plastic and rate-dependent effects, might also be Important discussed in Section 5. SOURCE Author An Orbiting Neutral Particle Beam System The target electrons that recoil from collisions with beam particles eventualy stop, and their en- A critical limitation of neutral particle beam ergy appears as heat. The 100 MeV T° beam is that they cannot be aimed through even the described above, depositing 100 J/cm2 on an alu- thinnest atmosphere—air so thin that even the ~ minum target, penetrates to a depth of 1.6 cm. ray laser beam could pass through easily. A neu- The 1.6 cubic centimeter volume of aluminum tral beam could not attack a Soviet booster unl the booster reached at least 760 km altitude (ve that absorbs this 100 joules of energy weighs sus about 80 km for the x-ray laser)7. Collision about 4 grams. The effect of the beam is there- fore to deposit about 25 joules per gram through- The stripping cross section on oxygen is about 1.5 megabarr out the first 1.6 cm of the target. The penetra- Elastic scattering can also be important for beam loss, since the Rh tion depth is inversely proportional to the density scattering angle can be larger than the beam divergence. The auth of the absorbing material, so the same beam on is Indebted to Dr. George Gull lespe of Physical Dynamics, Inl in La Jolla for resu Its of his Born approximation cross sectlt a lead target would not penetrate as far but would calculations 31 . — between air molecules and H° strip the electron Soviet boosters. Such a system scarcely seems from the Hº, and gradually all the remaining promising in terms of cost exchange. protons spiral off the beam axis into 200 km wide obviously the neutral particle beam would circles under the action of the earth’s magnetic stand no chance of intercepting a fast-burn field. booster that burns out well within the protective An MX-like Soviet booster could be attacked atmosphere. Even an MX-like booster that flew between 160 km altitude and burnout at 200 km, a slightly depressed trajectory wouId be in- a period of about 10 seconds. This short attack vulnerable. window means that the neutral beam cannot afford to dwell for long on each booster. A Theoretical Electron Beam System It is impossible to state with confidence the re- Physical theory8 holds out the prospect of one silience of an ICBM booster to irradiation with other type of beam besides the neutral particle a neutral particle beam. But it is likely that faith beam. Under certain circumstances, an electron would have to be placed in degradation of elec- beam might be able to propagate through the ex- tronics and other subtle effects, rather than in tremely thin air of near-earth space without bend- gross structural damage, for the beam weapon ing. In this scheme, a laser beam would first to stand a chance as an economical defense remove electrons from air molecules in a thin system (ignoring the issue of countermeasures en- channel stretching from the battle station to the tirely). target, leaving a tube of free electrons and posi- Consider again a battle station producing a 0.5 tive ions. The high-energy, high-current electron ampere beam of 100 MeV tritium (T°) atoms beam would then be injected into the channel. with 2 microradian divergence. This beam car- The beam electrons would quickly repel the free ries 400 watts/cm2 at 2 megameters range. To do electrons from the channel, leaving the beam structural damage to the outer few centimeters propagating down a positively charged tube. The of a missile’s body might take some 2 kJ/cm2 attractive positive charge would prevent the elec- (depositing 500 J/gin in 1.6 cm depth of alumi- trons from bending off the beam path under the num, for instance), requiring 5 seconds of dwell influence of the geomagnetic field and wouId also time at this range. Since the available dwell time prevent the mutual repulsion of electrons within is only about 10 seconds, each beam could han- the beam from causing the beam to diverge. The dle only two boosters. With a constellation size result would be straight-line propagation to the of almost 100 for 2 Mm range (fig. 3.4), this kill target, where their effect would be similar in most criterion resuIts in a preposterous system where respects to the neutral particle beam. This scheme the U.S. deploys 50 space-based accelerators for will not work for a proton beam. every one Soviet booster deployed in one region The physics of intense beam propagation of the U.S.S.R. through thin gases is so complex that experiments If the assumed Soviet booster hardness is re- will be needed to determine whether this con- duced by 100 times, corresponding perhaps to cept is even feasible in principle. If so, the con- transient upset of unshielded electronics, each cept would resemble the neutral particle beam, satellite can destroy 200 boosters at 2 Mm range, with the added requirement for the channel-bor- meaning an overall tradeoff of one U.S. acceler- ing laser and perhaps the ability to intercept ator deployed for each two Soviet boosters de- boosters at slightly lower altitudes than the neutral ployed. Alternatively, the constellation can be counterpart. 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 8 R , 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 to convert electrical energy to projectile kinetic of a moving projectile. Use of this term makes energy. Since a 10 kilogram projectile ejected ordinary weapons using aimed projectiles into with 5 km/see velocity carries 125 megajoules of “directed kinetic energy” weapons. energy (the amount of energy expended by a 25 megawatt chemical laser in 5 seconds of dwell The phenomenology of high-velocity collisions on a booster), the power requirements of the gun between a projectile and a structure like a booster schemes are imposing. Providing chemical fuel is surprisingly complex, but in general lethality or explosives to power a gun therefore involves is not an issue for kinetic energy boost phase in- the same magnitude of on-orbit weight as the tercept concepts. Rather, the problem is getting chemical laser. the projectile from its satellite base to the ascend- ing booster in time to make an intercept. Schemes Doing away with the homing sensor and re- where the projectile is carried by a small rocket placing the guided projectile with many small launched from the satellite suffer most directly fragments is not an attractive alternative, since (leaving aside countermeasures) from a combina- the needed fragments end up weighing far more tion of the large number and large size of the than the guided projectile. rockets needed for adequate coverage. I n partic- ular, the most conspicuous public example of the The Importance of Projectile Velocity kinetic energy approach, the High Frontier Proj- In the 300 or so seconds from launch to burn- ect’s Global Ballistic Missile Defense (GBMD) out of a slow-burning booster like the SS-18, the concept,9 has extremely limited capabiIity for defensive rocket or other projectile must fly from boost phase intercept of current Soviet ICBMs its satellite to the path of the booster. Such a and would have no capability at all against a booster burns out at about 400 km altitude, so future generation of MX-like boosters. if the projectile wishes to use the entire 300 seconds of boost phase to travel to its quarry, it Kinetic Energy Concepts must make its intercept at 400 km altitude. Rocket attack of ICBM boosters is obviously not Suppose now that the projectile’s rocket or gun as novel as beam attack, but it entails rather more launcher can give it a maximum velocity of 5 complexity than appears at first blush. The rocket km/see with respect to the carrier satellite. In the needs radio or other guidance by long-range sen- 300 seconds of available travel time to its target, sors on its carrier satellite (or other satellites) to the projectile cannot fly more than (5 km/see) x direct it to the vicinity of its target, since it is im- (300 see) = 1.5 Mm from its carrier. Each car- practical to put a long-range sensor on each rier therefore has an effective range of 1.5 Mm rocket. Once in the vicinity of the target booster, (fig. 3.1 la). the interceptor needs some form of terminal hom- ing sensor and rather sizeable divert rocket Referring to figure 3.4, a constellation of about motors. Homing on the plume of the ICBM boost- 240 carrier satellites are needed for continuous er is not straightforward, since attacking the coverage of the Soviet Union. Since Soviet ICBMs plume will obviously not harm the booster: the are spread over much of the country, 10 or so booster body must be located in relation to the of the carrier satellites might be able to participate plume. These complications introduce opportu- in a defensive engagement. The absentee ratio nities for offensive countermeasures. is therefore about 24, The 10 satellites over the U.S.S.R. at the moment of a massive Soviet at- An alternative to rocket propulsion would be tack need to be able to handle all 1,400 boosters, to expel the homing vehicles at high velocity from meaning each satellite needs to carry 140 pro- a gun. So-called rail guns use a clever scheme jectiles. An idealized rocket accelerating a 15 kg guided 9General Daniel O. Graham, The Non-Nuc/ear Defense of Cit- projectile to 5 km/see velocity would need to ies: The High Frontier Space-Based Defense Against ICBM Attack (Cambridge: Abt Books, 1983). weigh about 80 kg (a real rocket with this capa- -. .33 Figure 3.1 l(a) Figure 3.1 l(b) t =0 MX-like t = 200 Sec. Satellite orbital path boosters Booster burnout launched (200 km altitude) t =0 SS- 18 boosters Iaunched t = 240 sec. A altitude o 300 Seconds after launch o 2400 o 100 200 300 Kilometers Seconds after launch I , (b) Same as (a), except the target is the faster-burning MX. 0 800 1600 2400 Kilometers along satellite orbit Figure 3.11 View from above (looking down on earth) of 1. Suppose the velocity capability of the inter- coverage by a satellite carrying kinetic energy boost-phase ceptor is doubled to”1 0 km/sec, doubling the intercept vehicles. The satellite is deployed in a 400 km orbit. effective flyout range to 3 Mm. At this range, At time t =0, offensive boosters are launched. The satellite can make intercepts by shooting downward or wait until the 48 satellites complete the constellation, with boosters rise to their burnout altitude and fire nearer to the perhaps as many as eight of them in posi- horizontal. The longer after launch the intercept is made, the tion to participate in the engagement. Each farther the rocket intercept vehicles can travel from the satellite to make the intercept. Smaller circles thus of the eight satellites must handle 175 So- correspond to downward firing, larger circles to horizontal viet boosters. firing. The satellite moves from left to right in accordance Doubling the velocity capability more than with its 8 km/see orbital velocity. The area enclosed by all the circles taken together gives the total coverage of the doubles the weight of the rocket required. satellite and determines how many satellites are needed in The reason is simple: to increase the velocity the worldwide constellation for continuous coverage of requires more propellant, and the extra pro- opposing ICBM fields. All dimensions are to same scale. (a) The satellite-based kinetic energy interceptors are pellant must itself be accelerated, requiring capable of 5 km/see velocity relative to the satellite. The yet more propellant. The rocket weight thus attack is on a slow-burning Soviet SS-18. grows exponentially with velocity capability. The idealized 10 km/sec rocket weighs 420 bility would weigh more like 200 kg). Each car- kg. Each satellite carrying 175 rockets then rier satellite must therefore weigh (1 40) x (80) weighs 75,000 kg and requires some five = 11,000 kg. Less than twice this weight can be shuttle launches to orbit. The result is that carried by the space shuttle into the appropriate over 200 shuttle launches are required to or- orbits, so establishing the total 240 satellite con- bit the entire (idealized) defense system. In- stellation requires over 120 shuttle launches in creasing the velocity capability is therefore this highly idealized model with idealized rockets no escape from large on-orbit weights. and weightless carrier satellites. (A more carefuI 2 The current Soviet ICBM force consists estimation of interceptor design would more than largely of slow-burning liquid-fueled boosters double this load.) distributed widely over the Soviet Union. From this baseline, we can consider five ex- Consider the consequences for the U.S. ki- cursions: netic energy defense system if the Soviets de- 34 Figure 3.1 l(c) Each satellite must carry the 100 80-kg rock- ets needed to handle the attack. An ex- 300 km radius change ratio of four 8,000 kg U.S. defensive 260 km radius \ satellites for every Soviet offensive booster 130 km radius deployed is surely an economic advantage for the U.S.S.R. t =0 3. Soviet deployment of 1,000 Midgetman-like SS-18 Boosters at boosters would require a compensating de- boosters launched 200 km altitude ployment of 400 U.S. satellites, each weigh- t = 280 sec. ing at least 80,000 kg. A system that forces Boosters at 300 km altitude the United States to such a response is t = 300 sec. / clearly absurd. Booster burnout 4. Soviet fast-burn boosters would be totally im- (400 km) - mune to the kinetic energy defense system. 0 00 An interceptor on a satellite in 400 km orbit Seconds after launch 1 I J (lower orbits shorten satellite lifetimes be- o 800 1600 2400 cause of atmospheric drag) could not even KiIometers descend straight down to the fast-burn (c) The High Frontier Global Ballistic Missile Defense (GBMD) concept, with intercept vehicles capable of only 1 booster’s 100 km burnout altitude in the re- km/see velocity relative to the satellite. Intercept of SS-18. quired 50 seconds, much less have any lat- In the actual High Frontier proposal, the satellites are in 600 km orbits, giving them even less coverage than shown here. eral radius of action. 5. Intercepting SS-18 or MX post-boost vehicles is clearly easier, from the point of view of Figure 3.11(d) flyout velocities, than boost-phase intercept. Satellites at 700 km or so altitude would have Satellite must fire straight 500 seconds to fly out to meet the bus when down to intercept booster it ascended to their altitude, giving a 2.5 Mm just before burnout. Satellite has no lateral coverage at all. lethal radius. / In conclusion, a rocket-propelled kinetic en- ergy system acting against today’s Soviet ICBM Booster burnout arsenal (with no Soviet countermeasures) would boosters launched &90 km altitude) require many heavy satellites and would be a 0 100 200 300 dubious investment for the U.S. Soviet deploy- Seconds after launch ment of MX-like or Midgetman-like boosters , i o 800 1600 2400 wouId nullify the United States defense or force Kilometers the U.S. to large investments in new satellites. Analysis of the High Frontier Concept (d) The High Frontier concept has no capability whatsoever for boost-phase intercept of MX. The High Frontier Program10 proposes a Global Ballistic Missile Defense (GBMD) using rocket ploy 100 faster-burning MX-like boosters in propelled interceptors for boost phase intercept. one region of the country, so that defensive This concept claims to have some utility, at least interceptors have less time to fly to their against the present Soviet ICBM arsenal. targets and only one satellite overhead par- The concept consists of 432 satellites (24 planes ticipates in the engagement. MX burns out of 18 satellites in circular orbits inclined 65 200 seconds after launch, so each satellite degrees) at an altitude of 600 km. A velocity has an effective range of 1 Mm, requiring a constellation of 400 satellites (fig. 3.11 b). IOlbld 35 capability of I km/see relative to the satellite boost phase intercept. Its coverage for post-boost (“truck”) is attributed to the interceptor. The in- intercept, though greater than for boost-phase in- terceptors are apparently command guided to the tercept, would still be only partial. The only ex- vicinity of the target. The homing sensor is not ample given in the description’ of the system is specified, but short wave infrared homing on the of boost phase intercept of an SS-18, however. hot rocket plume is implied. In this example the interceptor is launched 53 seconds before launch of its target booster, Consider this concept defending against the SS- though no explanation is given of how the U.S. 18 in its boost phase. Since the SS-18 burns out defense knows in advance the precise moment at 400 km altitude 300 seconds after launch, each at which the Soviets would launch a given boost- GBMD satellite has a 0.3 Mm radius of action. er. This early launch allows the interceptor to Since the satellites are deployed at 600 km reach its target seconds before burnout. Plume altitude, the interceptor must descend 200 km homing, a technique inappropriate for bus inter- to make an intercept just before burnout, re- cept, is also implied for the High Frontier con- sulting in a lateral radius of action of 0.22 Mm cept. Post-boost intercept permits some RVs to (compare fig. 3.11c, where the satellites are be deployed on trajectories carrying them to the assumed deployed at 400 km altitude). With a United States before intercept; and the entire bus, range this small, thousands of satellites would be with its warheads, would continue on to the U.S. needed worldwide for continuous coverage of after the interceptor collision, with uncertain con- Soviet ICBM fields. The High Frontier concept sequences. with only 432 satellites would therefore have meager coverage of Soviet ICBM fields. It would therefore appear that the technical characteristics of the High Frontier scheme re- The GBMD concept would have no capability sult in a defensive system of extremely limited whatsoever against an MX-like booster. Such a capability for boost phase intercept of present So- booster would burn out before the interceptor viet ICBMs and no capability against future MX- couId reach it, even if the interceptor were fired Iike Soviet boosters, even with no Soviet effort straight down (fig. 3.11 d). to overcome the defense. It is possible that the High Frontier concept is designed for post-boost intercept rather than ‘ ‘ I bld , p 103. 3.6 MICROWAVE GENERATORS Microwaves are short-wavelength radio waves wide at a few hundred km range. From these con- used in radar, satellite communications, and ter- siderations the following concept emerges: As So- restrial communications relays. A number of ideas viet ICBMs lift off from their silos, a few micro- have been conceived for generating microwaves wave generators in space bathe the silo fields with in space and directing them towards ascending microwaves. ICBM boosters. The principal technical problem At high power levels, as in a microwave oven, with this type of BMD, generator technology microwaves cause heating in many materials. But aside, is the uncertain effect the microwaves in the BMD scheme, the divergence cone is so would have on their target. large that even a prodigious amount of energy The microwaves would propagate through the emitted from the generator would lead to very atmosphere unattenuated at all but the highest small energy deposition per square centimeter power levels. The weapon divergence angle on the target (millions of times less than lasers). would be very large, producing a spot many km The microwave pulse received at the booster 36 would resemble the high frequency component nance. If so, and if the electronic circuitry is not of the electromagnetic pulse (EMP) from a high- or cannot be made resistant to disruption or burn- altitude nuclear detonation. However, even weak out, the part of the booster’s performance de- microwaves can upset sensitive circuitry if they pendent on those electronics (perhaps accurate can reach it. guidance) would be affected. A metal skin on the booster would stop the Because of the very uncertain lethality of micro- microwave pulse altogether from reaching inter- waves, deployment of space-based generators (if nal electronics. The microwave defense must they can ever be built) would be a harassing tac- therefore hope that some aperture or conduit is tic rather than a confident-kill ballistic missile available into the booster, whether by design (as defense. in an antenna), inadvertence, or poor mainte- 3.7 OTHER CONCEPTS Other directed energy concepts suitable in the- single huge pulse for impulse kill of a boost- ory for ballistic missile defense have been er. All these schemes are at a very early con- broached from time to time. Some of them are ceptual stage. listed below. It is quite possible that in a few years 3. Antimatter beams would penetrate into a time a revisit to this subject will find a new target just like ordinary particle beams, ex- panoply of concepts enjoying the front rank of cept that when the antiparticle reached the discussion. end of its range it would annihilate a parti- cle in the target, freeing a large extra amount 1. Short-wavelength chemical lasers would of harmful energy. Acceleration of antimat- combine the simplicity and efficiency of the ter beams is accomplished exactly as with HF chemical laser with the small mirrors of particle beams, and laboratory beams of an- the short-wavelength excimer and free-elec- timatter have been used routinely in pure tron lasers. Though some ideas have been research. One important difference is that advanced along these lines, no laser exists antimatter is not freely available in the uni- which can be said to be a candidate to fulfill verse as is matter; the antimatter for the ac- this theoretical promise. celerator would have to be produced by the 2. Explosive-pumped lasers and particle beams defense system, a formidable and complex are said to be under study in the Soviet undertaking. It is not clear that the extra Union.12 Such devices might possibly be energy released in the target by an antimat- quite compact, each bomb generating a ter beam would justify the trouble of pro- 12A Viation week and Space Technology, JUIY 28, 19801 P. 47. ducing the beam. Section 4 OTHER ESSENTIAL ELEMENTS OF A BOOST-PHASE INTERCEPT SYSTEM Section 4 OTHER ESSENTIAL ELEMENTS OF A BOOST-PHASE INTERCEPT SYSTEM — The previous section treated only the defen- nerable basing of defensive components—issues sive weapon itself, the so-called “kill mecha- that had nothing to do with the kill mechanism. nism. But if beam weapons ever evolve to the In a similar manner, the other essential elements point where deployment is a serious possibility, of a boost-phase intercept system will figure more other elements of the overall defensive system prominently in discussion of boost-phase BMD will emerge as equally important determinants if and when the kill mechanisms—lasers, mirrors, of cost and level of protection. After all, the in- accelerators—are in hand. These other essential terceptor missile in traditional BMDs has not been elements introduce their own technological prob- the central focus of attention or technical debate lems and opportunities for offensive counter- since the 1950’s, when it became clear that a measures. If traditional BMDs are any guide, “bullet could hit a bullet. ” Discussion of BMD provision of a kill mechanism will be just the at that point passed to the difficuIt issues of radar beginning of making an efficient, robust defen- performance, data processing capability, and vul- sive system. 4.1 TARGET SENSING Locating and tracking an ICBM booster with defensive constellation would localize ascending enough precision to aim a directed-energy boosters to within a spot 5 m wide at 5 Mm range. weapon is not as straightforward as is sometimes At this range, the (illustrative) systems described supposed. it is true that booster motors emit hun- in Section 3 have spot sizes: 1.5 m for the H F la- dreds of kilowatts of power at short- and medium- ser, 0.6 m for the ground based laser, 10 m for wave infrared (SWIR and MWIR) wavelengths of the neutral particle beam, and 100 m for the x- a few microns. Sensors can detect these plumes ray laser. Even a large infrared sensor on each at great distances from the earth. Plume sensing battle station would therefore be inadequate for is used today for early warning of missile attack directing the laser beams at a point source of to support launch of bombers and airborne com- MWIR light, marginal for directing the neutral mand posts and launch under attack of ICBMS. particle beam, and adequate for directing the x- ray laser. The actual situation would be worse To be useful for directed-energy BMD, how- still, since the booster is not a point source. The ever, the sensor must localize the booster within booster plume would be larger than the laser or an area as small as the beam spot. Otherwise the particle beam spots, and the booster body would beam would have to sweep wastefully back and need to be located in relation to the plume to forth over the area of uncertainty. Small diver- avoid wasting beam time attacking the plume. gence beams must therefore be accompanied by sensors with small angular resolution. For directed-energy weapons with small diver- gence angles, therefore, sensing the conspicuous Diffraction limits the angular resolution of a sen- rocket plume is inadequate. Another kind of sen- sor in the same way it limits the divergence angle sor must be introduced into the BMD system. For of a laser. A large infrared telescope with 5 m finer angular resolution one looks to shorter diameter mirror observing MWIR booster emis- wavelengths, in the visible or ultraviolet. At these sion at 4 micron wavelength would have angular wavelengths the sensor must provide its own il- resolution no more precise than a micro radian. lumination. A so-called laser radar or Iadar is the Such a sensor affixed to each battle station in a only practical solution. In a ladar, a low-power 39 40 visible or ultraviolet laser shines on the booster lite and reflected from the target, or some other body, and a telescope on board the battle sta- method. These homing methods are susceptible tion senses the reflected light. to countermeasures. Besides the annoyance of a new laser and new Though this Background Paper treats only in- sensor, the necessary introduction of Iadar into tercept of the booster proper, it is worthwhile the boost-phase system creates opportunities for pausing to consider tracking of the post boost the defense to spoof and blind the offensive vehicle or bus. The low thrust levels of the post sensor. boost vehicles’s rocket motors, their intermittent operation, the possibility of dimming them with Kinetic energy systems do not need precision propellant additives, and the possibility of long-range sensing, since the rocket or guided building decoys with small rocket motors all sug- projectile homes on the target when it comes gest that MWIR plume sensing is not practical for within short range. The terminal homing might post boost intercept. The alternatives are Iadar involve deducing the location of the booster body or radar, suggesting again many opportunities for in relation to its MWIR plume, homing on low- countermeasures. power laser light shined from a defensive satel- 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, func- to assess and interpret if the debris, including RVs tion of BMD systems is confirmation that an at- (perhaps arranged by the offense to separate from tempted intercept succeeded. This function is the bus under extreme circumstances), continue sometimes called “kill assessment. ” Intercept on their ballistic course to the continental United confirmation would allow the beam to move onto States. subsequent boosters with more than a statistical estimate that its previous task was accomplished. Related to intercept confirmation, and ultimate- Structural damage to the booster would presum- Iy more serious, is the question of determining ably be revealed by an erratic course or burn pat- whether the beam is missing the target (perhaps tern, though it might be difficult to say in advance by slight misalignment of sensor and beam bore- exactly what the sensor’s view of the wounded sights, miscalibration of aiming mechanisms, etc.) booster would be. Subtle damage inflicted by a and, if so, by how much and in what direction. particle beam or microwave generator might not It might be possible to observe a glowing column be visible. Damage to a bus would be difficult of air where a laser beam passes through the at- 41 mosphere. Some clever but elaborate schemes to the defensive system potentially creates new have been devised to track a neutral particle opportunities for offensive countermeasures. beam. Obviously each new complication added 4.4 COMMAND AND CONTROL The crucial infrastructure of command and is virtually assured, though interesting questions control of a complex system is always the last to attend on hardening, reliability, and lifetime in take shape, since it integrates the workings of all space. Software would be expensive and would the separate components. It is easy to ignore the introduce issues of reliability and security from difficulty of accomplishing this last step at this programmer sabotage. Satellite-to-satellite com- early stage when the other components of a boost munication via extremely high frequency radio phase system are not yet remotely in hand. The and laser offers high data rates and virtual im- command and control system of a boost-phase munity to jamming from earth or from space. intercept system would comprise communica- Command and control for BMD does introduce tions links among its far-flung components, data two interesting issues to which technology can- processing to support sensors and battle station not provide an answer. The first is the impossi- operations, and “battle management” software bility of testing the whole defense system from incorporating all the instructions and decisions end to end in a realistic wartime setting. Unlike needed to run the defensive engagement and to the air defense systems of World War 11, which coordinate the defense with U.S. offensive forces. learned through attack after attack to exact kill Communications and data processing are two rates of several percent, the BMD system would areas of technology where there is the least pes- have to work near perfectly the very first time it simism—looking two or so decades into the future was used. The second issue is the likely need for when boost-phase systems could presumably be the defense to activate itself autonomously, since deployed–that technology will be able to meet there would be no more than a minute for human the needs of directed-energy defenses. Compact, decision, lightweight, and rapid data processing hardware 4.5 SELF-DEFENSE Consideration of anti-satellite (ASAT) attack (see less and until a credible overall approach to sat- Section 5.1 ), and analogy with traditional BMD ellite survivability is found, one cannot 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 precursor attack by cruise missiles and other being a large part of the defense system. These delivery systems. ‘ mechanisms could include shields, escort weap- ons, and countermeasures to ASAT sensors. Un- 42 4.6 POWER SOURCES Chemical lasers, x-ray lasers, and rocket-pro- of power, and directed energy weapons might pelled kinetic-energy interceptors have power require hundreds of MW. On the other hand, the sources integral to the weapon, but excimer power plants on defensive satellites need not lasers, free electron lasers, neutral particle beams, work reliably for many years but only once for and rail guns would need sources of electrical a short time, and they need not be very highly power and the equally important means to con- efficient. The three alternatives for space power vert electricity into a form usable by the weapon are fuel burning, explosives, and nuclear power. (“power conditioning”). Space basing obviously Starting up a large power source in seconds from complicates the task. Large commercial power a condition of dormancy poses some interesting plants on the ground produce about 1,000 MW design issues. - Section 5 COUNTERMEASURES TO BOOST- PHASE INTERCEPT l Section 5 COUNTERMEASURES TO BOOST-PHASE INTERCEPT — . . — — Countermeasures that limit the effectiveness of Figure 5.2 traditional ballistic missile defenses—decoys, radar blackout, defense suppression, etc.—are well known. A comparable set of countermeas- ures, 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 1 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 “suc- cessful” outcome of the strike. Every BMD system actually proposed for de- ployment would be accompanied, at least ideally, by, first, an analysis of its degradation in the face of an improving Soviet offense and, second, by Low High an analysis of how much it would cost for the Level of defense performance United States to improve its defense in such a way Fig. 5.2. The marginal cost exchange ratio measures the outcome of as to avoid being overcome. ’ a race between the Soviet offense to enhance its penetration and a U.S. defense to maintain its level of protection. In general, modest ‘See BallIstIc Missile Defense, ed. Ash(on B. Carter and David defense goals (e.g., “preserve 40 percent of the targets”) are easier N. Schwartz (The Brookings Institution, 1984), ch, 4. to sustain than high goals (“preserve 95 percent of the targets”) against improvements in Soviet offensive forces, including deploy- ment of countermeasures. Figure 5.1 The first analysis would be expressed in a draw- down 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 ex- change might be defined as follows: “Assume that in the year 2000 the U.S. defense and Soviet of- fense 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 Soviet investment in offense every time the Soviets add 100 ICBMs to their (more ICBMs, new types, special countermeasures, etc.) arsenal, the United States has to add 20 satellites Fig. 5.1. Schematic drawdown curve, showing how the performance to its defensive constellation to intercept them: of a BMD system degrades as the size and sophistication of the at- tacking force increase. Which costs more, 100 ICBMs or 20 satellites? 45 46 In general, high levels of defense performance uncovered at this early stage of study of a defen- are harder to enforce in the face of offensive im- sive concept be decisive, or should work (and provements than low levels: this important fact the inevitable expectations that accompany it) is shown schematically in figure 5.2 (see also Sec- continue on the chance that a new idea will turn tion 8.2). up to rescue the concept? Would the Soviets really resort to a subtle tactic or exotic piece of All of the boost-phase intercept schemes dis- hardware as a confident basis for their nuclear cussed in this report are in such an early stage policy? Some analysts see BMD as a way of “for- of conceptualization that nothing remotely like cing” the Soviets to take a certain direction in the analyses represented by Figures 5.1 and 5.2 their pursuit of the arms race, e.g., away from can be done for them. Nonetheless, counter- large, slow-burning MIRVd boosters to single- measures are known for every boost-phase sys- warhead Midgetman-like boosters. In this view, tem devised, and in many cases simple heuristic defeat of the BMD is purchased at the price of estimates of the cost tradeoffs are suggestive. , a theoretically more stable and desirable Soviet Technical experts disagree not so much about offensive posture. All these questions of judgment the facts and calculations underlying these coun- loom large in making a final assessment of a given termeasures as about the interpretation to be countermeasure. given to them. Should an apparently fatal flaw 5.1 ANTI-SATELLITE (ASAT) ATTACK, INCLUDING DIRECTED-ENERGY OFFENSE All boost-phase intercept BMD concepts have very likely to lie with ASAT, not DSAT. For one crucial components based in space. Even a pop- thing, the offense need not destroy a large num- up defense would need warning and very prob- ber of defensive satellites, but only “cut a hole” ably target acquisition sensors on satellites over in the defensive constellation. Second, the tradi- the Soviet Union. Ground-based laser defenses tional military refuges all offer complications: con- would have mirrors and sensors—their most frag- cealment from radar, optical, infrared, and elec- ile components—in space. Vulnerability of these tronic detection, while possibly successful for satellites is a cardinal concern because their or- small payloads in supersynchronous orbits, is im- bits are completely predictable (they are in ef- practical for large, complex spacecraft at most a fect fixed targets), they are impractical to harden, few thousand km from the earth’s surface; decoy conceal, or proliferate to any significant degree, satellites must generate heat, stationkeep, and and because successful development of effective give status reports, and they are in any event only directed-energy BMD weapons virtually presup- useful if the ASAT designer is somehow restrained poses development of potent anti-satellite (ASAT) (perhaps by cost) from shooting at all suspicious weapons. ASAT is the clear boost-phase analogue objects; hardening imposes weight penalties, and of familiar defense suppression tactics against massive shields could interfere with the constant traditional BMDs, where attack is first made upon surveillance and instant response required of the the defensive deployment (especially fixed radars) defense; proliferation is useless for expensive and then upon the defended targets. satellites facing inexpensive ASAT methods, As a consequence, discussions of DSAT for BMD The interplay of ASAT techniques–missiles (nu- battle stations usually emphasize large keep-out clear or conventional), space mines, directed zones around the satellites and active self-de- energy—and satellite defense (DSAT) techniques fense. A third reason why ASAT is likely to pre- is a complex one, It is difficult to generalize, but vail over DSAT is that possession by the offense in the specific case of large battle stations in low- of the same type of directed energy satellites used earth orbit it would seem that the advantage is by the BMD probably assures successful first 47 strike. Fourth, the Soviets would pick the time Suppose the battle station designers have suc- and sequence of their attack, and it would oc- ceeded in the considerable task of making the cur over Soviet territory. satellites resilient to multi-megaton nuclear space mines (bombs, not x-ray lasers) as little as 100 km Two rather novel ASAT threats are worthy of away, To keep all Soviet spacecraft (i.e., all poten- note. The first is the x-ray laser itself. The x-ray tial mines) at least 100 km away, the United States laser, if it could be developed, would constitute claims for itself the orbital band between 900 and a powerful space mine. Because of its long range, 1,100 km altitude. Perhaps the Soviets are it could lurk thousands of km from its quarry. The awarded some other orbital zone for their own Soviets might also launch x-ray lasers a few sec- military purposes. The United States establishes onds before launch of their main attack. Recall the following rules in its zone: 1 ) No foreign that the well-known phenomenon of bleaching spacecraft may transit the zone without prear- (see Section 3.3) would probably allow such x- rangement; 2) All transiting vehicles must remain ray lasers to shoot out of the atmosphere at a U.S. at least 100 km from all U.S. battle stations, pass- x-ray laser defense, but the U.S. x-ray lasers could ing through a “hole” in the constellation; 3) not shoot down into the atmosphere at the as- Foreign spacecraft failing to obey these rules may cending lasers. be destroyed by the U.S. lasers. A second ASAT tactic, discussed for many years, Consider first a Soviet kinetic energy ASAT de- imagines the Soviet Union exploding nuclear ployed at 1,100 km altitude, just outside the U.S. weapons at high altitudes in peacetime with the keepout zone. Suppose the rocket interceptors intent of shortening the orbital lifetimes of the on the Soviet satellites have the same propuIsive U.S. defensive satellites, The nuclear bursts in- capacity—one km/see—as the proposed High ject further radiation into the van Allen belts that Frontier Global BMD system. The Soviet ASATs circle the earth’s equator from about 1,500 to are then just 100 seconds away from the U.S. 10,000 km altitude. Satellites (more likely carry- lasers. The U.S. lasers must therefore be very vig- ing sensors than weapons at these altitudes) pass- ilant to avoid surprise attack. Fortunately, at 100 ing through the belts accumulate a radiation dose km range the 20 MW laser with 10 m mirror that gradually degrades electronics, sensors, and would burn up even a heavily hardened ASAT optical surfaces. This possibility, if taken seriously, rocket in short order. Since starting up the main would require defensive satellites designed to laser for self-defense might be awkward, wasteful withstand rather substantial accumulated radia- of fuel, or time consuming, each U.S. battle sta- tion doses. tion might be escorted by a satellite carrying a A detailed treatment of the ASAT problem is smaller laser or rockets for self-defense. beyond the scope of this Background Paper. The following “parable” illustrates some of the prob- A constellation of Soviet 20 MW, 10 m HF lems encountered in trying to ensure the surviv- lasers (the same technology as the U.S. lasers) at ability of a defensive constellation, taking the 20 1,100 km is another matter. These lasers could MW HF lasers of Section 3.1 as an example. attack the U.S. lasers seconds before launch of a Soviet ICBM attack. The United States would The United States deploys the HF lasers in this have to keep these Soviet spacecraft thousands hypothetical system in low orbits at 1,000 km of km away from the U.S. constellation. That is, altitude. Higher altitude would place them too the United States would have to dominate near- far from their targets. This is unfortunate: higher earth space. Suppose the United States does so. altitude (say, between 2,000 km and semisyn- chronous orbit at 20,000 km) would move the Now the Soviets build a fleet of pop-up x-ray satellites further from ground-based ASAT weap- lasers. These lasers climb to 100 km or so altitude, ons and put them into lesser-used orbits where where information radioed to them from the staking out a sanctuary would involve less in- ground allows them to point their rods at the U.S. terference with foreign spacecraft. lasers and detonate. The Soviets have had poor 48 success at building an x-ray laser; theirs are 100 shoot out through the thin atmosphere, before times less bright than the ideal x-ray laser the U.S. lasers can destroy them. In this way, the described in Section 3.3. Nonetheless, by point- Soviets “punch a hole” in the U.S. defensive con- ing all its Iasing rods at the same target, a Soviet stellation. (At a minimum, the Soviet ASAT attack x-ray laser can destroy a U.S. laser battle station consumes precious laser fuel aboard the U.S. bat- at 10 Mm range. The U.S. chemical lasers attack tle stations.) the Soviet x-ray lasers as they ascend, but at this just to make sure, the Soviets also deploy some range long dwell times are required to destroy powerful ground-based excimer or free electron the Soviet lasers. By launching enough x-ray lasers to destroy the U.S. battle stations as they lasers simultaneously, the Soviets succeed in get- orbit helplessly through space. ting some to 100 km altitude, where they can 5.2 FAST-BURN BOOSTERS Shortening the boost time and lowering the with low burnout altitude, would severely com- burnout altitude is easily accomplished at little promise the effectiveness of x-ray lasers popped sacrifice in useable ICBM payload (see Section up even from subs near Soviet shores. Low burn- 2). Shorter boost time increases the number of out altitude nullifies the neutral particle beam, lasers needed for space-based laser or ground- which cannot penetrate very far into the at- based laser systems to handle simultaneously mosphere. launched boosters. Short burn time makes rocket- Fast-burn boosters would therefore be a potent, propelled kinetic energy systems impractical, even decisive, countermeasure against almost all since the radius of action of each satellite concepts for boost-phase intercept. becomes too small. Short burn time, together 5.3 COUNTER C3l TACTICS Countermeasures to the crucial functions of ellite. A laser shined into an optical sensor can target sensing and command and control are a daze or injure the focal plane elements, though relatively unexplored, but probably key, problem viewing in frequency bands absorbed by the at- area for directed energy BMD. In the case of ter- mosphere offers protection from ground-based minal and midcourse defenses, the issues of de- lasers. Mirrors would be very susceptible to dam- coy discrimination, confusion caused by chaff age from a Soviet x-ray laser. A Soviet neutral par- and aerosols, radar blackout and infrared redout, ticle beam could disrupt electronic circuits on radar jamming, and traffic handling have always U.S. satellites. Radiation pumped into the van been and remain central limitations, It is likely Allen belts by nuclear bursts would affect sen- that analogues will be found for boost-phase sors and electronics. systems. Devising countermeasures requires a de- A single nuclear burst causes the upper atmos- gree of specificity about the nature of the defense phere to glow brightly over areas 100 km in ra- system which cannot be provided in the present dius for over a minute. Calculated radiances2 are conceptual stage. There follow a few examples large enough to cause background problems for of C3l countermeasures, by no means an ex- MWIR tracking sensors. haustive list. A first point to note is that sensors are likely 2S. D. Drell and M. A. Ruderman, /nfrared Physics, Vol. 1, p. 189 to be the most vulnerable part of a defensive sat- (1962). 49 Some directed-energy weapons produce spots The homing sensor of a kinetic energy intercep- only meters wide at the target, requiring target tor could be susceptible to spoofing, depending sensing to commensurate precision via laser radar on its type. (see Section 4.1). Laser radars sense laser light Jamming satellite-to-satellite communications reflected from the target. A small corner reflec- crosslinks is probably not an effective offensive tor affixed to the target would produce a bright tactic, since the links would have narrow beam- glint of reflected light, as would other corner widths, requiring the jammer to locate itself reflectors launched on sounding rockets, ejected directly between the two satellites; and wide from the target, or attached to the target by ex- bandwidths, requiring high jammer power. pendable booms. These proliferated corner reflec- tors might force the beam weapon to attack them all. 5.4 SHIELDING A degree of shielding from lethal effects is prac- in the vicinity of individual boosters, smoke or tical for ail but the kinetic energy weapons but laser absorbing molecules. Likewise, dust clouds involves in each case different methods suited to raised by ground burst weapons (delivered by the different physical principles at work. At the cruise missiles or by ICBMs that “leak” through same time, large uncertainties plague all lethality the defense) might cause serious propagation estimates, and further testing and study will be problems for the ground-based laser scheme, needed before firm answers can be given for any of the systems. For thermal kill with a laser, a solid Hardening to an x-ray laser involves quite dif- booster designed with some attention to a laser ferent physical principles. Recall that the x-ray threat can probably easily be made to withstand energy is deposited in a paper-thin layer of the 10 kJ/cm2. Application of a gram or so of heat- booster skin. The superheated layer explodes, ap- shield material on each square centimeter of plying an impulsive shock to the booster. Obvi- booster skin can probably triple this hardness, ously a paper-thin shield between the booster and spinning the booster enhances hardness by and the laser will stop x-rays from reaching the another factor of three. Heatshield material is booster wall. But the problem then becomes the ablative, meaning that when heated it burns off, debris from the exploding shield. One can easily carrying away the heat in the combustion gases show by calculation that the debris applies vir- rather than conducting it through to the missile tually the same impulse to the wall of the booster ski n underneath. A factor of nine increase in as would result from direct impinging of the x- hardness requires the defensive laser to dwell on rays! A number of schemes can be devised to di- the booster nine times as long or to approach vert the debris from striking the booster, but these within a third of the range, Though hardening a require more study to implement in practice. One new booster from scratch is clearly easiest, there factor acting in favor of the shield designer is that is no serious impediment to retrofitting ablative the booster is not vulnerable to x-ray attack until coatings on existing boosters. Applying a gram it leaves the atmosphere. The lightweight shields per square centimeter of ablative material to the therefore do not have to be designed to suffer entire body of the MX missile would require large drag forces. removing several RVs from the payload, since the The neutral particle beam presents a third dis- coating would weigh well over 1,000 kg. tinct type of hardening problem. The energetic An interesting possibility, requiring further beam particles penetrate into the target, and sev- study, would involve injecting into the atmos- eral centimeters of lead would be required to stop phere or producing from atmospheric gases, them. Since the beam cannot penetrate very far either throughout the ICBM flyout corridors or into the atmosphere, only the upper booster 50 stages need be hardened. But if the third stage, neutral particle beam by exploding a few nuclear say, of the MX were covered with a few grams weapons at moderate altitudes before the beam per square centimeters of lead, the shielding can reach them. The detonations heat the air, alone would weigh as much as several RVs. On which rises, effectively elevating the altitude at the other hand, if the neutral particle beam is only which the neutral beam is stripped of its remain- designed to disrupt or damage sensitive electron- ing electron and bent in the geomagnetic field. ics, but is not powerful enough to do damage to This phenomenon is called atmospheric heave. other parts of the missile, only the sensitive com- It is as yet unresolved whether atmospheric heave ponents need be shielded. The weight penalty will loft enough air to make a difference to the then becomes small. 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 underground silos but can be deployed above closely the hot exhaust plume of an ICBM booster ground next to the ICBM silos. except by burning a similar rocket stage. One can add chemicals to the propellants to brighten a Some of the boost phase intercept systems must small booster’s plume and dim the ICBM’s, but grow in the number of their deployed battle sta- as a first approximation a faithful decoy must be tions in direct proportion to the number of So- another booster. viet boosters. Deploying one decoy (with a dum- my payload) next to each of the 1,400 Soviet Decoy tactics are therefore not as attractive for ICBM silos might cause the United States to have boost-phase intercept systems that use plume to double the number of battle stations overhead sensing as they are for midcourse and reentry (and thus worldwide, multiplying by the absentee defenses, where large numbers of cheap, light- ratio) to handle the extra traffic. If the defensive weight decoys can be carried with negligible off- battle stations were at all expensive, this would load of RVs. Still, the usefulness of a decoy bean unpleasant prospect for the United States. depends not on how expensive the decoy is, but on how the cost of the decoy compares to the Many directed energy schemes would not rely cost of the defense that intercepts it. Booster on plume sensing alone (see Section 4.1). Decoy decoys would not be nearly as expensive as true tactics against laser radars (including corner ICBMs, since they carry no warheads or preci- reflectors; see Section 5.3) might be much easier sion guidance system, they need not be highly for the offense to implement than mimicking the reliable, and they might not need to be based in 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 be the best Soviet choice. Some, though not all, to move along their orbits into position overhead, of the successful attacks that could be mounted replacing depleted satellites. The orbital period on Closely Spaced Basing (Densepack) for MX in- of satellites in low earth orbit is about 90 minutes. volve very slow or intermittent salvo rates, how- If there are 8 to 10 satellites in each ring of the ever. defensive constellation, satellites replace one More importantly, in many circumstances the another every 10 minutes or so. Soviets might wish to launch only a traction of An exception to this simultaneous-launch worst- their ICBM force. A U.S. defense deployment too case analysis is the x-ray laser, which delivers alI small to intercept all boosters in a massive attack its energy in an instant. would still be able to handle a small attack. A light defense might therefore establish a “threshold” There would seem to be few military penalties of attack intensity below which Soviet boosters for the Soviet Union to adopting plans to launch wouId face intercept. This prospect is discussed all their ICBMs in large attack within a few min- further in Section 9. utes. Indeed, if one of their objectives is to de- stroy U.S. ICBMs in their silos, rapid attack would 5.7 OFFENSIVE BUILDUP The most straightforward way for the offense needed worldwide. Suppose now that the Soviets to compete with the defense is to grow in size. deploy, in one region of the U. S. S. R., 1,000 If for every new ICBM added to the Soviet Midgetman missiles at a cost of 10 to 20 billion arsenal, the U.S. defensive satelIite constellation U.S. dollars (see Section 2). The U.S. defense must be augmented at comparable or greater now needs to be “beefed up” with addition of cost, the Soviets could challenge the United (1 ,000)X (32)/120 = 270 laser battle stations. A States to a spending race to their net advantage. tradeoff of more than one complex U.S. satellite, On the other hand, if the defensive buildup is launched and maintained on orbit, for every 4 cheaper than the offensive buiIdup, the defense Soviet boosters (or decoy boosters) deployed on forces the offense either to accept limitations on the ground would certainly appear to be a los- its penetration or to resort to qualitative changes ing proposition for the United States. This is true in its arsenal. even though the hypothetical HF laser system represents a very favorable outcome of laser tech- As an illustrative example of such a cost trade- nology. off, consider the hypothetical H F chemical laser system described in Section 3.1. Each laser in that Note that Soviet deployment of new ICBMs in system requires 1.7 seconds of dwell time to de- one region of the Soviet Union, within coverage stroy a booster. During the 200 seconds of boost, of only a single U.S. satellite, gives them the best each laser overhead can therefore destroy 120 leverage in the cost exchange. boosters. But for each laser overhead, 32 are 5.8 NEW TARGETING PLANS Truly efficient ICBM defenses would presum- Iobbed into any target area unimpeded, the su- ably force upon the superpowers a stricter atten- perpowers have less need to be 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 hypo- ures 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 worldwide coverage, reflected in the absentee defense against their ICBMs would be increased ratio, that plagues the anti-lCBM cost exchange emphasis on submarine-launched ballistic mis- means that orbiting boost-phase defenses threat- siles (SLBMs), bombers, cruise missiles, and what- en SLBMs the world over. However, midcourse ever novel methods time and ingenuity might in and terminal tiers of a layered defense would in the future devise for introducing nuclear weapons general have much less capability against SLBMs, to the United States. As defenses forced up the because of the latter’s short time of flight, possibly cost-per-delivered-warhead of ICBM forces, these depressed trajectory, and uncertain direction of other methods would become relatively more at- attack. Thus SLBMs could conceivably enjoy tractive. Though they would sidestep the BMD, greater penetration of a layered defense than these delivery means have higher pre-launch sur- ICBMs. vivability than ICBMs, and bombers and cruise If one takes an optimistic view of emerging missiles have longer times of flight, These at- defensive technologies, or if one contemplates tributes are usually seen as “stabilizing.” Shifting technological “breakthroughs,” it is at least con- the emphasis of the arms competition away from ceivable that such developments will spawn new ICBMs is therefore sometimes viewed as ade- ways of delivering or aiding the delivery of nu- quate payoff for the BMD effort. clear weapons as well as new ways of interdict- SLBMs would obviously be vulnerable to the ing them. same boost-phase weapons as ICBMs. The same Section 6 A WORD ON “OLD” BMD AND “NEW” BMD Section 6 A WORD ON “OLD” BMD AND “NEW” BMD No one knows whether directed-energy weap- years. Conversely, there are some new ideas for ons can be built with the characteristics assigned improving terminal and midcourse BMDs.1 The to the hypothetical systems of Section 3. Even if spirit of technical optimism that accompanied the such systems can be built, it is not clear that their new emphasis on boost-phase intercept in the performance will match, much less exceed, the past year affected thinking about “old” BMD as performance of terminal and midcourse BMD sys- well. tems in level of protection (attack price) and in For terminal defense systems, the new features cost relative to offsetting offensive improvements. receiving attention are, first, non-nuclear war- The boost-phase BMD systems receiving so much heads on interceptor missiles and, second, air- attention today were a year ago at the periphery, plane-borne infrared sensors as supplements to to say the least, of technical discussion of missile ground-based radars. The principal benefit of defense. It is important not to lose sight of the non-nuclear intercept is that interceptors can be status of traditional reentry and ‘‘advanced” (as deployed nationwide without public concern they were called a year ago) “overlay” midcourse about the safety of defensive nuclear warheads. BMDs. Non-nuclear kill does not permit the defense to Naturally, the promise of the better-understood avoid all the disruptive effects of nuclear bursts, terminal and midcourse systems does not seem however, since the offense can still arrange for so grandiose, nor the flaws so clear-cut, as they RVs to detonate when they sense interceptor im- do for the conceptual boost-phase defenses dis- pact (“salvage fuzing”). The miss-distance/weight cussed in this Background Paper. Sounder tech- relationship of the non-nuclear warhead requires nical assessments can be made of the “old” the interceptor to approach more closely to the BMDs than of the “new” concepts. Rough con- RV, and this in turn requires a homing seeker on cepts gloss over all the difficult design problems the interceptor. Terminal homing obviously that inevitably limit achievable performance and creates new opportunities for offensive counter- turn up serious problems; nonetheless, identify- measures. ing potentially unsolvable problems at this early Airborne optical sensors obviously do not suf- stage of study does not mean they will remain fer radar blackout, but they can suffer the analo- insurmountable. BMD architectures incorporat- gous problem of infrared redout. Decoy discrim- ing boost-phase intercept are not known to be ination remains a problem, though it acquires able to perform better, dollar-for-dollar, than some interesting new features. Details of these BMD architectures incorporating only midcourse new aspects of terminal BMD are obviously clas- and reentry intercept. They are just not known sified. Though important, these aspects are fairly to be worse. Terminal defense systems have been straightforward extensions of traditional tech- studied, designed, and tested for years, and it is niques rather than revolutionary “break- generally agreed that such systems, acting alone, throughs. ” can enforce a modest attack price of between 2 and 8 RVs (perhaps equivalent to 20 to 80 per- New thought about midcourse defense focuses cent of a booster) per defended aim point. Though on alleviating the Achilles’ heel of systems that their capabilities are modest, reentry and mid- use infrared sensing to support intercept in space: course defenses suffice for modest defensive the ease with which the offense can accompany goals. There is no need to incur the technical risk attacking RVs with clouds of decoys. One ap- of “new” boost-phase intercept schemes unless proach receiving attention is simply to cheapen one aspires to levels of performance clearly be- the interceptor and shoot at everything, RVs and yond those possible with “old” concepts. decoys alike. Another is to probe the attacking Many of the “new” concepts for boost-phase intercept are not new at all. They have been stud- ‘See Julian Davidson, “BMD: Star Wars in Perspective, ” ied and discussed in one form or another for 20 Aerospace America, January 1984, p. 78. 55 56 objects with an active sensor, rather than rely- er in addition to reducing the total number of ob- ing on their thermal emissions, in the hope of dis- jects approaching the midcourse tier. Fourth, criminating RVs from decoys. Some of these “ac- extensive use of space-based sensors would allow tive discrimination” schemes are complex and the defense to observe penetration aids through- expensive and might in turn be susceptible to of- out their flight (including during deployment from fensive spoofing. A third aid to discrimination is the bus) rather than just as they approach the the boost-phase defensive layer itself, which United States. It remains unclear whether these might constrain the number and type of penetra- techniques will be worth the costs and new coun- tion aids the offense could mount on each boost- termeasures they would bring to the defense. Section 7 A HYPOTHETICAL SYSTEM ARCHITECTURE l Section 7 A HYPOTHETICAL SYSTEM ARCHITECTURE Most analysts of boost-phase BMD assume that The correct questions are whether the additional midcourse and terminal BMDs will augment the $150 billion is worth the extra performance, and boost-phase layer. This section assembles a hy- whether spending the $150 billion on more ter- pothetical layered defense system in toto. This minal and midcourse defense would in fact be system is pure/y illustrative, taking current BMD a better investment. concepts at their face value and conveying a con- crete image of the defensive architectures analysts Occasionally one sees a simplified leakage cal- apparently have in mind when they speak of na- culus applied to layered defense. The calculus tionwide defense. Obviously there are many assigns a “leakage” of, say, 25 percent (0.25) to choices for such a “strawman ” system. The par- the boost phase layer, 15 percent to the mid- ticular system described below was chosen for course layer, and 10 percent to the reentry layer, its illustrative value and not because it represents deducing an “overall leakage” of 0.4 percent on some “most plausible” alternative. It would be the basis of the equation (0.25)x (O. 15)x (O. 10) meaningless to suggest a “front runner” in the = 0.004. Though the term leakage can be present state of study and technology develop- defined so that this calculus holds, the result ac- ment. Rather, the purpose of this example is to tually bears little relation to the number of targets show how the layers interact and to indicate the preserved by the defense. For one thing, a given overall scale of the deployments contemplated, defensive layer does not have an associated leak- without implying that anything remotely like it age fraction independent of attack size: the ever could or would be built. leakage fraction for each layer usually increases with attack size, most obviously (but not only) A defense with several layers presents the of- when the defensive arsenal becomes saturated. fensive planner with some of the variety of prob- Second, the performance levels of the individual lems that afflicts the BMD designer, who never layers are not independent. For example, if the knows in advance which attack tactic or coun- midcourse layer’s interceptor arsenal is sized to termeasure the offense will choose and must in- handle only 25 percent of the attack, and the clude responses to all of them in the system de- boost-phase layer works poorly and in fact allows sign. Layered defense forces the offense not only 50 percent of the attack through, the midcourse to develop responses to all the layers, but to de- layer obviously cannot display the same fractional velop responses that can be accomplished simul- efficiency against the attack of double the ex- taneously. Thus, for example, the method chosen pected intensity. Conversely, improvements in to avoid boost-phase intercept must not prevent one layer might improve performance of another: deployment of lightweight midcourse decoys. effective boost-phase or midcourse layers might The synergistic effect of the several layers ob- force the offense to abandon the highly structured viously works strongly in the defense’s favor. “laydowns” of RVs in space and time that limit Nonetheless, one must compare the perform- a terminal layer’s effectiveness. Third, the raw ance of a three-tiered defense to the performance number or fraction of leaking RVs does not indi- of a two-tiered defense of the same cost. Thus cate the number or fraction of targets destroyed it should be no surprise if a $200 billion system because of the tactics of preferential offense and with boost (and possibly even post-boost), mid- defense. For these reasons, the leakage calculus course, and terminal layers performs better than is not a helpful way to encapsulate layered de- a $50 billion system with no boost phase layer. fense performance. 59 60 7.1 SYSTEM DESCRIPTION The system design described below takes lit- ing LWIR homing vehicles (the so-called “Over- erally the goal of comprehensive nationwide de- lay”), and land-based high-endoatmospheric fense. It seeks the capability (at least on paper) homing interceptors with non-nuclear warheads to engage all attacking Soviet missiles, whether for reentry intercept. targeted at cities, U.S. silos, or other military in- The HF chemical laser system resembles that stallations. Clearly the precise numbers and kinds described in Section 3.1, except that it has only of components in this description can be adjusted five 20 MW lasers at each position in the 32-po- to suit any set of assumptions. The point of this sition constellation, for a worldwide total of 160. description is merely to convey the flavor of these At a range of 2 Mm, a laser must dwell on each massive architectures. Most assumptions are fa- spinning booster for 5 seconds, so each laser at vorable to the defense. this range can handle 30 simultaneously launched Suppose that at some time in the future the So- boosters if defense begins 30 sec into the 180 sec viet ICBM arsenal still consists of 1,400 boosters, boost phase of an MX-like booster. The five lasers as it does today. For simplicity, suppose further overhead the Soviet silos at any one time can that each booster is an MX-sized solid propellant therefore only handle 150 of the 1,400 Soviet missile carrying 10 RVs and that all silos are lo- ICBMs. For small Soviet attacks, however, this cated in one large region of the U.S.S.R. The non-nuclear boost-phase layer suffices. boosters are not specially shielded against lasers, For a large-scale Soviet attack, the United States but some care in their design has given them an deploys in addition a nuclear boost-phase system effective hardness of 10 kJ/cm2, and they are fur- of x-ray lasers. A “perfect” laser with character- ther spun during ascent. Each booster carries a istics such as those derived in Section 3.3 can in- small number of decoys, but their small number tercept ideally about 50 boosters at 4 Mm range. is offset by the decoys’ high fidelity. Each RV is Therefore 28 lasers need to be in position over accompanied by 9 lightweight infrared replicas the Soviet silos at any time to handle a massive and 1 high altitude reentry decoy. (This is a very launch, giving a worldwide total of 900 (absentee modest penetration aid loading. One can assume ratio 32). larger numbers with perhaps poorer fidelity, chaff and aerosols, etc. ) Warning for the boost-phase system is provided by MWIR warning satellites in synchronous or The hypothetical U.S. defense system com- supersynchronous orbits. Also, each of the 160 prises both HF chemical laser battle stations and HF laser battle stations has an MWIR telescope x-ray laser battle stations for boost-phase inter- with 4 m mirror and an ultraviolet or visible Iadar cept, land-based midcourse interceptors carry- with 2 m mirror for pointing. Each x-ray laser is Table 7.1.—Hypothetical Future U.S. Defense accompanied by an MWIR telescope tracker with Designed for Nationwide Protection Against 1 m mirror. Hypothetical Future Soviet Offense The 1,400 Soviet boosters carry 14,000 RVs, U.S. Defense Soviet Offense 126,000 midcourse decoys, and 14,000 reentry 5 warning satellites 1,400 MX-like ICBMs decoys. The United States assumes that only 10 180 HF laser satellites deployed in one percent of the boosters will survive the boost 180 laser radars region 900 x-ray laser satellites 10 RVs per ICBM phase defense, so the midcourse tier needs to 900 MWIR trackers 9 midcourse decoys face 1,400 RVs and 12,600 midcourse decoys. 28,000 midcourse intercept per RV The midcourse interceptors are given extremely vehicles and boosters 1 reentry decoy per RV long range, so only two bases are needed to 20 LWIR satellites 75 radars cover the entire United States. However, each 140,000 terminal non-nuclear base must be prepared to absorb the entire at- interceptors tack, since the Soviets could target one half of 25 aircraft with LWIR sensors SOURCE: Author. the country more heavily than the other. There- 61 fore the United States needs 14,000 midcourse Each terminal defense site consists of a phased- interceptors at each base, for a total of 28,000 array radar and a number of high altitude non-nu- interceptors. A constellation of 20 satellites with clear interceptors. Additional target acquisition large LWIR sensors provide long-range acquisi- support is provided by a fleet of aircraft patrol- tion and target assignment to these interceptors. ling the U.S. periphery, carrying LWIR sensors. Each radar has a radius of action of over 200 km, The United States next estimates that 90 per- so 75 or so cover the entire United States. How- cent of the RVs that enter the midcourse layer ever, an interceptor only covers an area about will be successfully intercepted. The terminal de- 50 km in radius. Since the area of the United fense must handle 140 RVs plus 140 reentry de- States is about 8 million square km, over 1,000 coys.1 The reentry decoys are, by assumption, interceptor sites would be needed for nationwide completely faithful in mimicking the signatures coverage. Should the defense have to reckon of RVs as seen by ground-based radars and air- with intensive Soviet attack on some regions and craft-borne infrared sensors during early re- no attack on others? Clearly, yes. But equipping entry—large decoy numbers have been sacrificed each interceptor site to handle all 280 objects for this high fidelity. If the U.S. defense takes passing through the first two layers would require literally its charge of nationwide defense, it must buying 280,000 interceptors! The defense wouId be prepared to make 280 intercepts anywhere need to buy this many interceptors if it wanted in the country. to claim the literal capability to engage all Soviet I The number of reentry decoys the terminal system must face RVs, no matter where they landed. Suppose, actually depends on whether the decoys fool the midcourse as well then, that the United States hopes for a more as the terminal system’s sensors and on whether the terminal and evenly distributed Soviet attack and deploys just midcourse layers cooperate in discrimination. Suppose first that the half of the arsenal needed for complete cover- reentry decoys look Ilke RVS (and therefore also like midcourse decoys) to the midcourse layer’s sensor. Then the midcourse layer age— 140 interceptors per region. One radar will Intercept 90 percent of them (more midcourse interceptors must might not suffice to handle all the RV traffic in be bought to do th@. If, on the other hand, the midcourse layer its sector if the Soviets attack some sectors pref- correctly identifies the reentry decoys as non-lethal objects, it might (a) not intercept them, requiring the terminal layer to plan to face erentially, but the United States nonetheless buys 140 RVS plus 1400 reentry decoys, increasing enormously the re- just 75 radars. Five aircraft on patrol at all times quired arsenal of terminal interceptors; (b) intercept them, in which requires a backup fleet totalling perhaps 25. case a reentry decoy is a perfect midcourse decoy, making possi- ble a new threat–large numbers of midcourse decoys that look Table 7.1 summarizes the offensive and defen- like reentry decoys rather than RVS; (c) radio the information, object- by-object, to the terminal defense fields. sive deployments. 7.2 ASSESSMENT It is obviously not possible to assess the per- is proportional to the number of Soviet ICBMs. formance of a system, such as the hypothetical If the Soviets were to double the size of their layered defense described above, whose com- ICBM arsenal, the United States would need to ponents are not (and in many cases cannot be) double the number of its x-ray lasers and inter- designed today, much less assembled in an over- ceptor missiles. (The number of sensors would all architecture. It is nonetheless worth sketching, generally have to increase also, though perhaps in the illustrative spirit of this section, the issues not in proportion to the Soviet buildup. The num- that would require analysis if anything resembling ber of HF lasers could remain the same if the Table 7.1 were ever proposed for deployment. United States continued to intend to use this non- nuclear boost-phase layer to engage only Soviet The first issue concerns the cost of the improve- attacks of 150 boosters or less. ) Comparison of ments to the system needed to offset growth in the two columns of Table 7.1 indicates that an the Soviet ICBM arsenal—that is, the cost ex- arms race of Soviet offense and U.S. defense change ratio. The number of defensive weapons seems certain to favor the Soviet side greatly. 62 — A second issue concerns the huge inventories Defensive coverage against submarine- of midcourse and reentry interceptors needed for Iaunched ballistic missiles (SLBMs) is a fourth nationwide defense. The arsenal of reentry inter- issue. The boost-phase layers can intercept SLBMs ceptors shown in Table 7.1 is in fact only half the launched from all points on the globe. Though size needed for literally complete nationwide cov- the average range from laser satellite to booster erage, as remarked above. The cause of these is larger at equatorial and polar latitudes than at large interceptor inventories–besides the obvious the mid-latitudes where Soviet ICBMs are located, presence of decoys–is twofold: first, the low leak- the number of SLBMs that could be launched in age sought by the defense precludes preferen- a short time from each ocean area is also much tial defense, the tactic that makes silo defense so smaller than the huge number of ICBMs that much more economical; and second, the limited could lift off simultaneously from the U.S.S.R. coverage of each interceptor battery makes pref- Even the chemical laser deployment alone might erential offense possible for the attacker. The goal suffice for boost-phase coverage of SLBMs. The of nationwide low-leakage defense therefore midcourse and reentry layers, however, would forces the BMD system to forfeit the two sources in general not perform as well against SLBMs as of leverage that have historically impelled BMD against ICBMs. SLBM trajectories present bad towards the technically modest mission of de- viewing angles to the midcourse layer’s LWIR fending compact silo deployments to relatively sensors, and the short timeline limits interceptor low survival levels. coverage. The reentry layer would need to be augmented with more airborne sensors and more Soviet countermeasures–besides straightfor- radars (or radar faces) to cover attack from the ward buildup of ICBMs—is a third issue. The par- ocean. In general, then, a layered system opti- ticular boost-phase layers described above are mized for ICBM defense could not necessarily susceptible i n varying degrees to all of the coun- handle SLBMs as well. termeasures described in Section 5, and the mid- course and reentry layers to their respective sets of countermeasures. Section 8 DEFENSIVE GOALS 1: THE PERFECT” D E F E N SE Section 8 DEFENSIVE GOALS 1: THE PERFECT DEFENSE No assessment of whether a defensive system less, so much writing and debate focuses on this “works” or not is meaningful without a clear and prospect, and its importance is so great, that it direct statement of the goal of the deployment. is taken up in this section. Section 9 treats the Though there has been much discussion of the many other possible goals for less-than-perfect feasibility of boost-phase BMD, proponents and defenses. skeptics alike frequently leave unstated the stand- There is some confusion in the literature about ards against which they are judging the technical the use of the term “mutual assured destruction” prospects. A “successful” BMD deployment (MAD) in connection with the notion of perfect could be defined as anything from a truly impen- defense. In common strategic parlance, MAD re- etrable shield, to a silo defense that merely costs fers to the technological circumstance of mutual less to build than it costs the Soviets to overcome, vulnerability to catastrophic damage from nuclear to a tangled deployment that just “creates uncer- weapons, not to a chosen policy to promote such tainty” for the attacker. vulnerability. There is a strategic school of The most ambitious conceivable goal for BMD thought that advocates a policy usually called would be to take at literal face value the words “minimum deterrence, ” maintaining that the ca- of President Reagan in his so-called “Star Wars” pability for assured destruction of Soviet society speech of March 23, 1983, when he called for is the on/y requirement of U.S. strategic forces. development of a defense capable of making nu- However, many experts believe that effective de- clear weapons “impotent and obsolete.”1 It is not terrence and other national security objectives clear that the President intended his words to be require nuclear forces capable of many other taken literally, nor that the Administration or any- tasks than assured destruction. This section ad- one else is suggesting the United States seek a dresses itself to the question of whether MAD is truly perfect or near-perfect defense.2 Nonethe- an avoidable technological circumstance, not to whether minimum deterrence is a prudent stra- 1 Week/y Compilation of Presidential/ Documents, Vol. 19, No. tegic policy. 12, March 28, 1983, pp. 447-448, The text of the relevant part of the speech is reprinted as Appendix A. A sensible start at judging the prospect for near- 2 Defense Secretary Caspa r Wei nberger appeared to confirm a literal interpretation In a March 27 interview on NBC’s Meet the perfect defense must involve two steps: first, an Press, when he sa[d (as reported in the Ba/t/more Sun, March 28, exact statement of what perfect defense means 1983, p. 1). in the context of attack on society with nuclear sig T n h~ e > d d t e o (e b ns e l v p e a rt s ia ys l t W em h s a t t w he e p w r a e n si t d t e o n t t r IS y t a t l o k i g n e g t a IS b a o u s t y s a t r e e m n o w t h i d c e h - weapons; second, some way of gauging the like- WIII develop a defense [SIC] that IS thoroughly rellable and total, I lihood of success when the technological future don’t see any reason why that can’t be done. Later, the Defense Department stated that the purpose of the cannot be accurately predicted. President’s initiative was not to save Iwes, but to deter war. Respon- ding to the “Congressional Findings” section of the proposed “Peo- ple Protection Act” (H .R, 3073, 98th Congress, Ist session) which the purpose of the Administration’s policy is to reduce the Ilkellhood stated, “The President has called for changes in United States stra- of war. The finding [of H.R. 3073] that the purpose IS to ‘‘sa~ e IIk es tegjc policy that seek to save lives in time of war, ” Defense Depart- I n tl me of war’ departs from our goal of deterrl ng war Dr. Charles Townes, a frequent adviser to Secretary of Defense ment General Counsel William H. Taft IV wrote: Weinberger and leader of two DOD task forces studying basing It IS clear that portions of the “Congressional ftndlngs” section [of modes for the MX missile, said that a perfect defense proposal is 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 “quite impractical. There is no technical solution to safeguarding strengthen our ablllty to deter war by, as the President has said, man kind from nuclear explosives. (New York Times, April 11, /, renderl ng [ha llIst Ic m IS; I Ies] Impotent and obsolete. 1 n short, 1983, p. 14). 65 66 . 8.1 NUCLEAR ATTACK ON SOCIETY Figure 8.1.-The Effect of Attack Size on the Extent fatalities, not for the many additional people in- of Prompt Fatalities in U.S. Urban Areas jured. 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 intercept- ing all but a few of the 8,000 to 10,000 Soviet 10 nuclear warheads, however, the Soviet Union 500 10 I 00 15 I 00 20 I 00 2500 3000 might retarget its forces to wreak the most de- struction possible with its few penetrating war- Attacking warheads heads. At any rate, any defense promising U.S. Note: Aimpoints chosen to maximize prompt human fatalities. U S. urban popula- tion IS estimated to be 131 million, as in the 1970 census. society genuine immunity from nuclear attack SOURCE. Arms Control and Disarmament Agency, U.S. Urban Population VU/nerabi/ity (ACDA, 1979), quoted in Arthur M. Katz, Life Afrer Nuc/ear must reckon with Soviet determination to keep War The Economic and Social Impacts of Nuclear Attacks on theU S its arsenal from being “rendered impotent, ” and (Ballinger, 1982) Adapted from Ashton Carter and David N. Schwartz, eds , Ba//istic Miss//e Defense (The Brookings Institution, 1984), p 168 therefore with targeting plans contrived to do the most damage to the fabric of U.S. society. Suppose one wants to take literally the goal of Where on the curve of Figure 8. 1–after how removing from the hands of the Soviet Union the many detonations—does one locate the bound- ability to do socially mortal damage to the United aries of “assured destruction, ” “assured sur- States with nuclear weapons, so that the Soviet viva l,” “impotent and obsolete, ” and similar Union no longer possesses the elemental capa- phrases? Clearly there is no analytical prescrip- bility of assured destruction.) What does this tion for these boundaries: they are the subject mean? of a broader human judgment. 500 half-megaton Figure 8.1 shows how the percent of the U.S. warheads kill half the urban population, injure urban population (about 130 million people in most of the rest, and totally destroy all American the 1970 census) killed promptly increases with cities and large towns. Just 5 megatons, about one the number of Soviet warheads detonating over two-thousandth of the Soviet arsenal, detonated U.S. cities. No such curve of the effects of nu- over the 10 largest U.S. cities could kill several clear attacks on cities should be taken as anything million people and wound over 10 million more. but suggestive: uncertainties are very great in For the sake of discussion, we shall use 100 such estimates, and no attempt has been made megatons—about 1 percent of the Soviet Union’s to reflect long-term and indirect effects of the arsenal and 1.5 percent of its ICBM force—as the detonations.3 The curve also accounts only for level of penetration for which a defense would 3For 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); 1. Carson Mark, “Global Consequences of Nuclear Weaponry, ” OTA, The Effects of Nuc/ear War (GPO, 1979); ACDA, The Effects Annua/ Review of Nuc/ear Science, Vol. 26 (1976), pp. 51 -87; Na- of Nuc/ear War (ACDA, 1979); “Economic and Social Conse- tional Research Council, Long-Term Wor/~wi~e Effects of Mu/fi- quences of Nuclear Attacks on the United States, ” prepared for p/e Nuc/ear- Weapons Detonations (National Academy of Sciences, the joint Committee on Defense ProductIon, 96 Cong. 1 sess., 1979; 1 975). 67 be judged “near-perfect.” This definition is ob- regard 100 megatons of explosive force as “im- piously very generous to the notion of perfect de- potent and obsolete. ” Still, it is a 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 ect’s atomic bomb or the Apollo moon landings. Q unknown future technologies will not provide The technically minded will recognize a vital dif- near-perfect defensive protection of U.S. society ference between working around the constraints against Soviet ICBMs. The question that needs to imposed by nature, which are predictable and be answered is whether the prospects for near- unchanging, and competing with a hostile intel- perfect defense are so remote that such a notion ligence bent on sabotaging the enterprise. A dy- has no place in reasonable public expectations namic opponent makes of BMD, first, a more dif- or national policy. it is, after all, not provable that ficult design problem, since the offense constructs by the next century the United States and the worst possible barriers to successful defense; U.S.S.R. will not have patched up their political and second, not one problem but many prob- differences and have no need to target one lems that need to be sidestepped simultaneously another with nuclear weapons. The issue of the in the design, since the designer cannot be cer- perfect defense is unavoidably one of technical tain which tactics the offense will use. judgment rather than of airtight proof, A third misapprehension concerns the prospect Four misapprehensions seem common among for a “technological breakthrough” that would non-technical people addressing the prospects for dispel all difficulties. Such breakthroughs are not perfect defense. impossible, but their mere possibility does not help in judging the prospects for the perfect de- The first misapprehension is to equate success- fense. For one thing, an isolated technological ful technology development of individual de- breakthrough creating a new defensive compo- vices—lasers, power sources, mirrors, aiming and nent would not necessarily alleviate the system pointing mechanisms—with achievement of an issues—vulnerability, dependability, susceptibility efficient and robust defensive system. Millionfold to countermeasures, cost—that determine overall increase in the brightness of some directed-en- effectiveness. Second, one can just as easily im- ergy device is a necessary, but is far from a suffi- agine offensive “break throughs,” sometimes in- cient, condition for successful defense. In the volving the same technologies. Thus the x-ray la- early 1960’s, intercept of RVs with nuclear-tipped ser, if it matures, might turn out to have been interceptor missiles was demonstrated—”a bul- Iet could hit a bullet’’–but 20 years later systems incorporating this “kill mechanism” are still con- 4Defense Secretary Caspar Weinberger has w rltten (Air Force sidered relatively inefficient. In general, skeptics Magazine, Nov. 1983): about the future of space-based directed-energy The nay-sayers have already proclaimed that we WIII never haie BMD do not confine their doubts to, or even em- such technology, or that we should never try to acquire It Their arguments are hardly new In 1945 president Truman’s Chief ot phasize, unforeseen problems in developing the Staff, Adm William Leahy, said of the atomic bomb “Thatrs the big. individual components. 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 A second misappprehension arises in attempts of Intercontinental ballistic missiles, “1 say technically I don’t think o equate BMD development to past technologi- anybody I n the world knows how to do such a thing, and I feel con- fident [t WIII not be done for a long time to come “ These crltlcs were cal achievements, such as the Manhattan proj- proved wrong; what IS more, they were proved wrong quickly 33-698 0 - 84 - 4 : QL 3 better termed a breakthrough in strategic offense ducing the vulnerability of U.S. population and than a breakthrough in strategic defense. society to the neighborhood of 100 megatons or less. A fourth misapprehension concerns the confi- dence with which predictions could be made 1. Near-perfect defense of society is much about the performance of a complex system once harder and more expensive than partial defense i n place. The “performance” of a system, as of military targets. That is, the marginal cost ex- quoted in analyses, is the most likely outcome change is much higher for near-perfect defense of an engagement of offense versus defense. than for partial defense (see also Fig. 5.2). There Other outcomes, though less likely, might still be are two reasons behind this well-known possible. Computing the relative likelihoods of statement. all possible outcomes would be difficult even if one could quantify all technical uncertainties and The first reason is illustrated schematically in statistical variances. Still, there would remain a Figure 8.2. In going from partial silo defense to residue of uncertainty about the performance of perfect city defense, the BMD loses the leverage a system that had never been tested once in real- of preferential defense. Additionally, the offense istic wartime conditions, much less in a statisti- gains the leverage of preferential offense against cally significant ensemble of all-out nuclear wars. the terminal and midcourse layers with their lim- The defense would also have no chance to learn ited geographic coverage, although not against and adapt. In World War II, by contrast, air de- the boost-phase layer. In Figure 8.2(a), the de- fense crews learned in raid after raid to inflict fense aims to save only 10 percent of the ICBM losses of several percent in attacking bombers. force, or one silo. Assuming perfect interceptors The only reason these modest losses assumed and adopting the tactic of adaptive preferential strategic significance was that they accumulated defense (using all its interceptors to save just one over many raids. Of course, the same uncertain- silo chosen randomly from the ten at the moment ties plague the offense as plague the defense. In of attack), the defense concludes it needs to pre- general, the offense would tend to overestimate pare to make one only intercept to counter the the defense’s capability. This natural tendency offense’s 10 RVs. In Figure 8.2(b), the offense can toward “offense conservatism” is probably vitally focus all 10 of its RVs on any one of ten cities. important to the psychological and deterrent val- The defense must prepare to make 10 intercepts ue of BMD as it is applied to less-than-perfect for each city, buying a total of 100 interceptors, goals. For the perfect defense goal (as defined if it wants to try to save all the cities. If the Soviets above), however, it would seem that the uncer- double their RV arsenal, the United States must tainty weighs heaviest on the defense. To the buy just one interceptor to satisfy the defense goal reckless, non-conservative defense, a wrong esti- of Figure 8.2(a), but the United States must buy mate of defense performance spells the difference 100 interceptors to satisfy the defense goal of Fig- between safety and socially mortal damage (or ure 8.2(b). The cost exchange ratio is thus 100 between deterrence and war). The reckless of- times worse for the city defense, even though it fense, on the other hand, is presumed desperate uses the same technology as the silo defense. enough to try to inflict such damage on its enemy The second reason why a near-perfect defen- and willing to accept the consequences: it stands sive goal shifts the cost burden in favor of the of- to lose little if its estimates are wrong and the de- fense is that the offense can turn all its resources fense does work perfectly after all. to improving or replacing just a portion of its With these misapprehensions out of the way, ICBMs to sidestep the defense. The Soviet Union and recognizing clearly that there can be no ques- could therefore harden just 1 percent of its boost- tion of “proof,“ it would seem that four major ers, perhaps concealing exactly which ones were factors conspire to make extremely remote the hardened. Moreover, it could deploy a few fast- prospect that directed-energy BMD (in concert burn boosters immune to x-ray lasers and neutral with other layers if necessary) will succeed in re- 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 2. For every defense concept proposed or im- are avaiIable to the offense if the countermeas- agined, including all of the so-called “Star ures need onIy be implemented on a small scale wars” concepts, a countermeasure has already rather than throughout the ICBM force. The of- been identified. These countermeasures were fense can “experiment” with a number of dif- enumerated in Section 5 and will not be repeated ferent tactics with different portions of its force. here. Three further generalizations about these The defense’s costs also grow much larger if it countermeasures reinforce a poor prognosis for must plan to face a variety of offensive cost-effective near-perfect defense: 1 ) In general, countermeasures. I n short, the defense must be the countermeasures could be implemented with able to stop all kinds of attack, but the offense today’s technology, whereas the defense itself only has to find one way to get-through. could not; 2) In general, the costs of the coun- 70 termeasures can be estimated and shown to be disarmed by a U.S. defense, since otherwise it relatively low, whereas the costs of the defense would be at its enemy’s mercy. are unknown but seem likely to be high; 3) In 4. BMD by itself will not protect U.S. society general, the future technologies presupposed as from other methods of delivering nuclear wea- part of the defense concept would also be po- pons to U.S. soil or from other weapons of mass tent weapons for attacking the defense. destruction. Bombers and cruise missiles (and to 3. The Soviet Union does not configure its nu- a significant extent SLBMs and IRBMs) present clear missile forces today to maximize damage very different defensive problems than ICBMs. to U.S. society and population, but it could do Today the technical problems of air defense are so if faced with near-perfect U.S. defenses. Tar- no better resolved than the technical problems geting plans could focus exclusively on damag- of BMD. Novel future offensive delivery vehicles ing cities. High missile accuracy would be un- can only be conjectured along with the future necessary, lowering offense costs. Nuclear defense technologies discussed in this Paper. A weapons could be designed to maximize harm- desperate Soviet Union could introduce nuclear ful fallout. ICBM survivability measures–silos, weapons into the United States on commercial racetracks, densepacks, etc.—would be unnec- airliners, ships, packing crates, diplomatic pouch, essary to a side striking first or possessing its own etc. Other methods of mass destruction or ter- defense effective at saving many missiles (but not rorism would be feasible for the U. S. S. R., includ- all cities); thus basing costs could be diverted to ing sabotage of dams or nuclear power plants, the city-kill goal, Presumably the Soviet Union bacteriological attack, contaminating water, pro- would take these and any other measures nec- ducing tidal waves with near-coastal underwater essary to prevent itself from being effectively detonations, and so on. . l 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 Those familiar with BMD design and assess- near-perfect defense assume importance i n cer- ment wiII recognize that stating a general strate- tain theories about the workings of nuclear deter- gic goal is not enough: the technical specifica- rence and the requirements of U.S. security. tions are essential. For instance, it makes an Thoughtful observers debate not just the feasi- enormous difference in silo defense whether the bility of achieving these goals but the validity and defense seeks to charge the offense a price of five importance of the goals as well. The urgency one RVs (or half a booster) or 10 RVs (one booster) attaches to these goals determines the costs, risks, per silo. and harmful side effects one is willing to incur For goals requiring very modest performance, to fulfill them. Assessing the wisdom of less-than- terminal and midcourse defenses might suffice. perfect defense thus involves a complex and sub- Since no one knows whether boost phase de- jective balancing of goals and risks, in which fenses, when better defined, will surpass or even purely technical issues sometimes take a back equal traditional defenses in terms of leakage and seat. In discussion of perfect defense, by contrast, cost exchange, there is no point i n turning to ex- technical assessment is paramount. This section otic technologies to satisfy modest goals. Virtually therefore calls up many issues of nuclear policy all observers agree, on the other hand, that ter- not subsumed under the title of this Background minal and midcourse systems are unequal to the Paper, and no pretense is made hereto complete more demanding goals; for these goals one is treatment.1 forced to direct one’s hopes to the promise of Though various strategic goals for BMD can be future technologies. distinguished in principle, in practice it might not This section sketches various goals for less-than- be clear or agreed among all parties in the United perfect defenses and the strategic thinking that States what the purpose of a proposed deploy- attaches importance to them. It then points out ment actually was. Interpretations by the Soviet a number of side effects against which fulfillment Union and other foreign nations of U.S. goals of these goals needs to be balanced. This short might be quite different yet. section is no substitute for a comprehensive I For a more complete treatment of the entire subject of BMD, assessment 01 the pros and cons of BMD. see Ashton B. Carter and David N. Schwartz, cd., Ballistic Missile Defense (The Brookings Institution, 1984). 9.1 GOALS FOR LESS-THAN-PERFECT DEFENSE 1. Strengthen deterrence by preventing pre- vivability is balanced against cost, technical risk, emptive destruction of retaliatory forces. It is strategic effects, and environmental impacts. z widely recognized that the Soviet Union will soon BMD would substitute for or complement these have, if it does not already, the combination of other basing modes. By shooting down a fraction yields, numbers, and accuracy in its ICBM forces of the opponent’s missiles, BMD would in effect to destroy most U.S. Minuteman ICBMs in their “de-MIRV” ICBM forces. silos. It is also widely agreed that vulnerable nu- Of course, turning to BMD to ease ICBM vul- clear forces create unwanted temptations for both nerability is not without problems. One problem sides to strike first if war seems likely. The long is the prospect of a compensating Soviet BMD. and anguished search for survivable basing modes for the U.S. MX (Peacekeeper) ICBM has 2MX Missi/e Basing, office of Technology Assessment, U.S. Con- to date turned up no clear favorites when sur- gress, September 1981. 73 . 74 . . MX is presumably being bought and made sur- that it would not attempt an “experiment.”3 vivable in the first place so that the U.S. can ab- Analysts who favor this approach usually main- sorb a Soviet strike and retaliate with its ICBMs tain that Soviet military doctrine inclines the (in addition to its bombers and submarines) Soviets towards a view of nuclear weapons as against Soviet targets. But modification or ter- military tools to a far greater degree than is com- mination of the ABM Treaty to permit a U.S. de- mon in U.S. thinking. d fense would permit a Soviet defense as well. The To take an explicit example (in this case of So- surviving U.S. ICBMs guaranteed by the U.S. viet failure to deter the U. S.) of a “war fighting” BMD might still not result in retaliatory damage scenario (chosen randomly from a great many to Soviet targets if these targets are defended by possibilities), suppose NATO were at war with Soviet BMD. The U.S. BMD deployment, all the Warsaw Pact, and the Soviets were resupply- bought and paid for, might therefore have been ing their ground offensive through just 10 or so cancel led out by a Soviet counter-deployment, rail trunks from the Soviet Union through east- Other elements of the U.S. retaliatory force ern Europe. Just 10 well-placed nuclear weapons comprise command and control links, bomber (according to a hypothetical analyst considering alert bases, and in-port submarines. Bomber this type of scenario) would cut off a large frac- bases, sub ports, and fixed command and con- tion of supplies coming to the front, slowing the trol facilities are the worst type of target base for Pact offensive and giving NATO vitally needed BMD to try to defend–a small number of high- time to marshall its defenses. Wouldn’t the value, soft, and interdependent targets. The im- United States be sorely tempted to use just a few portant remaining category of mobile command ICBMs for this decisive intervention in the course and control facilities, on the other hand, does not of the war? easily lend itself to active defense with BMD. Analysts who recommend attention to warfight- 2. Strengthen deterrence by preventing the use ing scenarios and doctrines are surely aware of of nuclear weapons as decisive military tools for the profound difference between conventional high-confidence “limited” strikes on conven- and nuclear weapons, but they maintain that the tional forces. This goal is associated with so- threat of punishment through retaliation upon cit- called “warfighting” strategies for nuclear weap- ies is not an effective deterrent in such scenarios. ons. According to analysts who hold this view, Wouldn’t it be preferable if these scenarios were today’s “offense dominated” world creates dan- simply closed off by defensive technology? gerous temptations to resort to nuclear weapons Critics of this BMD goal object both to the war- to accomplish militarily well-defined objectives. fighters’ emphasis upon the risk of this type of One can imagine warheads simply being lobbed scenario and to the assumption that defense unopposed into another country in any number would materially diminish that risk. In their view, or combination. Though surely the effects of myriad detailed chinks in the armor of deterrence these “limited” attacks on nearby communities can always be found, with or without defense, would not be so well-defined, the effect on the and worrying about them represents a loss of opposing military machine might be truly dramat- ic, even decisive. This use of nuclear weapons JPresidential Science Adviser George A. Keyworth, II has stated in wartime is possible with today’s unopposed (interview with US. News and Wor/d Repofl, April 11, 1983, p. 24): offenses with considerable confidence and might ‘‘The objectwe IS to have a system that would convince an adver- sary that an offensive attack WIII not be successful. It has to be a very therefore be tempting to the combatants. Such effective system, but It would not have to be perfect to convince a temptations threaten nuclear deterrence and potential adversary that his attack would fall “ Dr. Robert Cooper, director of the Defense Advanced Research should be eliminated. The goal of a comprehen- Projects Agency has also stated this view (The New York Times, sive defense would be to make such limited at- 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 tacks infeasible, or at least to complicate the of- success of a first strike, and war would be more remote. ” fense’s estimations of success to such a degree 4Ba//istic Miss;/e Defense, op. cit., Chapter 5. 75 — perspective on the basic difference between nu- or appear to be more willing to resort to nuclear clear and conventional instruments of war. Be- war because the consequences to the United sides, they say, suppose the effect of the Soviet States are presumed smaller. BMD is to force the United States to attack each The coexistence of the humanitarian and stra- rail line with ten weapons instead of one to assure tegic objectives for the analogous case of civil de- penetration: IS there truly a psychological divide fense is apparent in the literature on civil defense. between using 10 and 100 nuclear weapons, The Defense Department6 has argued that the once the divide between O and 10 has been United States should have the same crisis reloca- crossed? Third, would NATO not be adequately tion options as the U.S.S.R. for two reasons, one deterred by the prospect of Soviet retaliation with strategic and one humanitarian: 1 ) “to be able 10 of its nuclear weapons against 10 vital NATO to respond in kind if the Soviet Union attempts targets? Last, suppose NATO used 10 cruise mis- to intimidate us in time of crisis by evacuating siles, against which the BMD was powerless, in- the population from its cities”; and 2) “to reduce stead of 10 ICBM RVs? fatalities if an attack on our cities appears immi- The persuasiveness of this second goal for less- nent.” Prominent scientists arguing for civil de- than-perfect BMDs therefore depends on one’s fense have also maintained that, “A nation’s civil views of the roles and risks of nuclear weapons— defense preparedness may determine the balance views that are fundamental and deeply held. This of power in some future nuclear crisis. . . . In our goal is therefore one of the most controversial opinion, we must strive for an approximately of all. equal casualty rate”.7 More recently, the High Frontier Study urging strengthened U.S. strategic 3. Save lives.5 Another goal for BMD is purely defenses stated: “The protection of our citizens humanitarian and seeks no military or strategic must be prime, but civil defense . . . would re- advantage. If the defense did not interfere too duce the possibility that the United States could much with Soviet military targeting objectives be coerced in a time of crisis”. a (enough for the Soviets to try to overcome it), and assuming the Soviets have no explicit aim to in- In practice, therefore, the humanitarian and flict human casualties, the United States could strategic objectives are likely to be difficult to expect some reduction in fatalities in a nuclear disentangle. Unlike the humanitarian objective, war even from a modest defense. This reduction the strategic objective might stimulate a Soviet would necessarily be limited, since Soviet military effort to put the same number of American lives objectives include destruction of many targets at risk regardless of the defense. In this way, the collocated with population. BMD and civil de- Soviet Union could retain the strategic advantage fense measures would be mutually reinforcing. that, by hypothesis, the BMD deprives them of. The issue then becomes the usual one of the cost- Analogous discussion of civil defense has al- exchange ratio measuring the price to the Soviet ways revealed an inherent tension between the Union of retaining its “advantage” relative to the humanitarian objective of defense and a related price of the U.S. defense. strategic objective. The strategic objective seeks to reduce fatalities and damage in order to en- The Defense Department has stated that sav- hance U.S. “flexibility” in a crisis, to allow the ing lives in time of war is not the purpose of Presi- United States to “coerce” the U.S.S.R. (or avoid dent Reagan’s BMD initiative.9 coercion) from a position of reduced vulnerability, or to enhance U.S. ability to persist in its war ef- fort despite receiving a Soviet nuclear strike. The supposed result of the BMD deployment is to al- bAnnual De{ense Department Report, FY 1976, p. 11-24. low the U.S. President, in dealing with the Sovi- 7Arthur A. Broyles and Eugene P. Wlgner, ‘‘CIVII Defense [n Llmlted War, ” Physics Today, VOI 29 (April 1976), pp. 45-46, et leadership in time of crisis, to be more willing ‘Daniel 0. Graham, The Non-Nuc/ear Detense ot’ Clfies: The High Frontier Space-Based Det’ense Against ICBM Attack (Abt Books, ‘This d Iscussion borrows from the author’s previous work I n 1983), p. 122. IJ//IsfIc Mlssl/e Defense, op. cit., Chapter 4. ‘See footnote 8 2, 76 4. Shape the course of the arms competition ing the size of their missile inventories would, and arms control.10 One version of this goal sees logically at least, be enhanced by a simultaneous the Soviet tendency to upgrade and proliferate U.S. BMD buildup. Politically, it would seem un- existing ICBM forces as the principal impediment likely, though certainly not impossible, that a to arms control. By introducing BMD (or even climate favorable to far-reaching offensive arms discussing it), according to this view, the United control would also foster an amicable dismantl- States makes the Soviets unsure about the next ing of the ABM Treaty. step in the arms competition and thus undercuts 5. Respond to Soviet BMD efforts. Many the momentum of Soviet strategic programs, es- analysts view with alarm Soviet strategic defense pecially ICBM modernization. Though fast-burn- activities, including upgrading of the Moscow ing Midgetman boosters might defeat boost-phase ABM, development of a transportable terminal defenses, this argument goes, the slow-burning BMD system, construction of a radar in appar- SS-18s and SS-19s will not. BMD might not be ent violation of the ABM Treaty, development of able to make all nuclear weapons impotent and defenses against tactical ballistic missiles, incorpo- obsolete, but it can make large Soviet ICBMs im- ration of limited BMD capability in air defenses, potent and obsolete–something the U.S. has and continued attention to other damage-limiting been trying to do for a decade. Perhaps efficient methods (civil defense, air defense, antisubma- defenses will “force” the Soviets to emphasize rine warfare, and countersilo ICBMs). A strong submarines, bombers, and cruise missiles in their U.S. BMD research and development program strategic arsenal to the same degree the United might deter the Soviets from breaking out of the States does. (One problem with this line of argu- ABM Treaty and from continued encroachments ment is that by the time the defense is in place, on the Treaty’s provisions. It is frequently noted present-generation Soviet ICBMs might already that aggressive U.S. research into penetration aids be replaced.) and other methods for countering defenses might Another line of argument holds that a major be an even more effective way to demonstrate BMD initiative strengthens the U.S. negotiating to the Soviets that they would be ill-advised to position at START. An aggressive BMD program overturn the ABM Treaty’s “freeze” on missile demonstrates U.S. technological prowess and defenses. hints at what the Soviets could face if this prow- 6. Protect against accidental missile launches ess were unleashed. It would seem that new and attack from other nuclear powers. These BMD initiatives might not coexist easily with the goals have been put forward several times in the reductions in offensive arsenals proposed by the past, most notably in the late 1960’s when the United States in START, however. Since U.S. Johnson Administration proposed the Sentinel BMD is equivalent to attrition of the Soviet ICBM ABM system to counter Chinese ICBMs, believed arsenal, any anxieties the Soviets feel at reduc- at that time to be fast-emerging. Neither goal IoPreSldentlal science adviser George A. Keyworth, speech before figures prominently in today’s discussion of BMD the Washington chapter of the Armed Forces Communications and in the United States, though defense against Chi- Electronics Association, as reported in Defense Week (Oct. 17, 1983): nese, British, and French missiles could well loom “Although the strategic defense program’s goal would still be even- larger in Soviet thinking. Emerging nuclear pow- tual deployment of a working system, we shouldn’t overlook its ers or terrorists would be unlikely to use ICBMs potential beneficial Impact on arms reduction as its progresses. ” Richard DeLauer, Undersecretary of Defense for Research and to deliver their small nuclear arsenals to the Engineering, has said that an arms control agreement is needed United States. BMD is therefore of little impor- to prevent the Soviets from overcoming a defensive system: “With unconstrained proliferation [of Soviet missiles], no defensive system tance in staving off the threat to U.S. security will work.” (Interview with The New York Times, May 18, 1983). posed by nuclear proliferation. 77 9.2 SIDE EFFECTS OF BMD DEPLOYMENT The inevitable side effects of a major strategic bilizing factor. Thus BMD might also discourage initiative such as BMD might turn out to match, temptations to strike first, by threatening to both in magnitude and in duration, the beneficial disrupt the attack. effects of satisfying the goal emphasized by the 2. Soviet BMD. A U.S. BMD deployment would system’s purveyors. The public and policy makers seem very likely to stimulate a Soviet deployment. would therefore need to assess the net, long-term Even if the Soviets saw no compelling military ra- effect of adding BMD to the strategic equation, tionale for following suit, political appearances and not just the achievement of a certain discrete could prove decisive. A Soviet BMD counter-de- goal as if by surgical intervention. This section ployment would obviously blunt U.S. offensive reviews the well-known list of BMD side effects. striking power, which the U.S. has been spend- Many of these effects are detrimental to U.S. se- ing a great deal to build up. If the U.S. deploy- curity and would need to be balanced against the ment sought to protect its ICBMs from preemp- benefits of fulfilling the modest goals of less-than- tive destruction in their silos (Goal 1 above), the perfect defense. In making this assessment, it is Soviet BMD might nonetheless nullify the U.S. impossible to ignore the many unknowns and un- ICBMs–this time in flight to their targets. Soviet certainties that make it impossible to compare BMD would also introduce a threat to U.S. SLBMs, today’s world without BMD to a future world with which are today thought to be virtually immune BMD. to Soviet disruption and to be significantly ad- 1. First strike versus ragged retaliation. It is fre- vanced relative to their Soviet counterparts. If the quently noted that BMD ends up being a better U.S. deployment sought to prevent “limited” investment for the side that strikes first than for strikes by the Soviets Union (Goal 2), the Soviet the side that retaliates. Weapon systems that BMD might in turn preclude a U.S. option to use create relative advantages to striking first in a crisis nuclear weapons selectively and flexibly in sup- (rather than risking being struck while seeking a port of its NATO allies–an option sometimes peaceful resolution) are defined to be “destabiliz- seen as central to NATO strategy. Clearly the ac- ing.” The side striking first uses its full arsenal in tual effect of the Soviet BMD counterdeployment an organized penetration of the other side’s de- would depend upon its technical characteristics fense; the retaliating side can only use its surviv- and the targets it defended. ing arsenal in a possibly disorganized “ragged 3. Demise of the ABM Treaty. An arms con- retaliation” against a forewarned and fully pre- trol treaty obviously cannot serve as its own jus- pared defense. tification, and presumably virtually everyone Mitigating factors could in certain circum- would agree to the abandonment of the ABM stances soften this classical statement of the de- Treaty the moment it ceased genuinely to serve stabilizing effect of BMD. First, truly effective the national security. In addition to its concrete defenses might prevent the first striker from de- provisions limiting BMD deployment, however, stroying a substantial fraction of the other side’s the ABM Treaty has unavoidably assumed a sym- retaliatory forces. Second, with proper planning bolic political meaning in the United States and, (involving post-attack retargeting and coordinated in different forms perhaps, in Europe and the timing), the retaliating forces might still be able U.S.S.R. The Treaty stands for a decade of arms to mount a tailored, efficient strike. Third, there control and attempts at superpower understand- will seemingly always be a relative advantage to ing about nuclear weapons. As a practical mat- being the side that strikes first in a nuclear war, ter, it is impossible to overturn the Treaty’s tech- with BMD or without BMD; but this calculus of nical provisions without calling into question U.S. relative advantage is far from being the only fac- commitment to the whole fabric of the SALT/ tor in deterrence. Other stabilizing factors might START process. This side effect would have to be be strengthened by BMD, offsetting this desta- weighed against the purely military and strategic 78 benefit (if there were, in fact, a net long-term ben- attend upon arms control reductions at START efit) of a U.S. BMD deployment. today. Extra caution seems warranted where stra- tegic actions cannot easily be reversed or re- 4. Allied and Chinese missile forces. The nu- called: the opportunity for a comprehensive ban clear missile forces of Britain, France and China on missile defense might not arise again. are obviously a greater threat to the Soviet Union than to the U.S. Most analysts agree that the ex- 7. Bean counting. Strategists, politicians, and istence of these forces enhances U.S. security. diplomats place considerable emphasis on quan- But a major BMD initiative sparking widespread titative measures of the nuclear balance and on Soviet defense would in effect disarm our allies “proofs” that “parity” exists. Arms control (to a degree depending on the nature of the So- negotiations also reduce themselves quickly to viet deployment). counting rules. It is unclear whether or how BMD shouId affect such “bean counting. ” For each 5. Accompanying strategic programs. A number U.S. battle station added to a defensive constella- of new weapon systems and strategic programs tion, are the Soviets to be credited with fewer would be natural, though perhaps not necessary, ICBMs, since the U.S. defense represents poten- accompaniments to BMD. On the offensive side, tial attrition of the Soviet force? How many So- the U.S. would need to develop and deploy pen- viet interceptor missiles equals one U.S. laser? etration aids against the Soviet BMD and improve Whose estimate of the BMD’s likely wartime per- its bomber and cruise missile forces to reflect formance–the defense’s or the offense’s-–gov- added reliance on non-missile delivery vehicles. erns these counting rules? Experience indicates on the defensive side, the overall category of that these types of questions, however far-fetched “strategic defense” comprises, in addition to and even preposterous they appear in prospect, BMD: nationwide air defenses against Soviet in the end assume considerable perceived im- bombers and cruise missiles, defensive coverage portance. against SLBMs, civil defense shelters and evacua- tion plans, and passive “hardening” of military 8. Asymmetries. The Soviet BMD deployment installations and industrial facilities. that could well follow U.S. deployment might not share the same defensive goal or the same tech- 6. Opportunity Costs. The initial investment nology, stimulating the usual anxieties about une- in BMD deployment, the inevitable follow-ens, qual intentions and capabilities. Defensive sys- and any accompanying strategic programs would tems are also complex, leading different analysts make a substantial, permanent demand on the to widely different conclusions about the likely defense budget, competing with other nuclear wartime performance of the BMD systems on forces and with conventional forces, not to men- both sides. Moreoever the owner of the BMD, tion with nonmilitary expenditures. aware of all the system’s hidden flaws, might In a more fundamental sense, the transition credit it with little capability, whereas the offense from a world with a near-total ban on BMD to planner will tend to give it the benefit of the a world with BMD deployments is probably an doubt. Though some hypothetical future world irreversible change. Reimposing a defensive with mutual BMD deployments might therefore “freeze” after a period of unrestrained deploy- appeal to one analyst or nation, another could ment, much less dismantling defenses and return- easily have a completely different view of the ing to zero, would involve all of the problems that technical and strategic “facts.” Section 10 PRINCIPAL JUDGMENTS AND OBSERVATIONS Section 10 PRINCIPAL JUDGMENTS AND OBSERVATIONS 1. The prospect that emerging “Star Wars” Critics dispute the validity of some of these technologies, when further developed, will pro- goals; dispute that technology can fulfill the truly vide a perfect or near-perfect defense system, useful goals; and/or argue that the many harm- literally removing from the hands of the Soviet ful side effects of introducing BMD to the strate- Union the ability to do socially mortal damage gic equation and altering the Anti-Ballistic Missile to the United States with nuclear weapons, is (ABM) Treaty regime are not worth satisfying so remote that it should not serve as the basis these goals. of public expectation or national policy about To address the wisdom of less-than-perfect de- ballistic missile defense (BMD). This judgment fense, the public and policy makers would need appears to be the consensus among informed a precise statement of the strategic goal of the members of the defense technical community. deployment, an assessment of whether technol- Technical prognosis for such a perfect or near- ogy could satisfy that goal, and an analysis bal- perfect defense is extremely pessimistic because ancing fuIfillment of the goal against the side ef- of the concentration and fragility of society; be- fects and uncertainties of introducing a new cause alI concepts identified as candidates for a ingredient into the strategic nuclear arena. future defense of population are known to be sus- 3. The strategic goal of President Reagan’s ceptible to countermeasures that would permit Strategic Defense Initiative calling for empha- the Soviet Union to retain a degree of penetra- sized BMD research—perfect, near-perfect, or tion with their future missile arsenal despite costly less-than-perfect defense against ballistic mis- attempts to improve the U.S. defense; because siles—remains unclear. No explicit technical the Soviet Union would almost certainly make standards or criteria are therefore available such a determined effort to avoid being disarmed against which to measure the technological pros- by a U.S. defense; and because missile defense pects and progress of this initiative. does not address other methods for delivering nu- clear weapons to the United States. 4. In all cases, directed-energy weapons and Mutual assured destruction (MAD), if this term other devices with the specifications needed for is applied to a state of technological existence boost-phase intercept of ICBMs have not yet rather than to a chosen national policy, is likely been built in the laboratory, much less in a form to persist for the foreseeable future. suitable for incorporation in a complete defense system. These devices include chemical lasers, 2. The wisdom of deploying less-than-perfect excimer and free electron lasers, x-ray lasers, par- ballistic missile defenses remains controversial. ticle beams, lightweight high-velocity kinetic en- Less-than-perfect defenses would still allow the ergy weapons, and microwave generators, to- Soviet Union to destroy U.S. society in a massive gether with tracking, aiming, and pointing attack but might call into question the effective- mechanisms, power sources, and other essential ness of smaller, specialized nuclear strikes. accompaniments. Certain theories about nuclear war maintain It is unknown whether or when devices with that such defenses could lessen the chances of the required specifications can be built, nuclear war and enhance U.S. security by pro- tecting U.S. retaliatory forces; by interdicting S. Moreover, making the technological devices “limited” nuclear strikes; by further confusing So- perform to the needed specifications in a con- viet predictions of the outcome of a strike; by trolled situation is not the crux of the technical driving Soviet missile deployments in directions challenge facing designers of an effective bal- favored by the United States; by lessening the listic missile defense. A distinct challenge is to consequences of nuclear attack; and/or by fulfill- fashion from these devices a reliable defensive ing still other strategic goals. architecture, taking into account vulnerability 81 82 of the defense components, susceptibility to fu- 8. Deployment of missile defenses based on ture Soviet countermeasures, and cost relative new technologies is forbidden by the Anti-Bal- to those countermeasures. listic Missile (ABM) Treaty reached at SALT 1. The Treaty permits only restricted deployment of tra- New intercept mechanisms–directed energy ditional BMDs using fixed, ground-based radars weapons and the like—therefore do not by them- and interceptor missiles. Research into new tech- selves necessarily herald dramatically new BMD nologies, and in selected cases development and capabilities. testing of defense systems based on these tech- 6. It is clear that potent directed-energy nologies, are allowed within the Treaty. weapons will be developed for other military 9. There is a close connection, not explored purposes, even if such weapons are never in- in detail in this Background Paper, between ad- corporated into effective BMDs. Such weapons vanced BMD concepts and future anti-satellite might have a role in nuclear offense as well as (ASAT) systems. This connection springs from defense, in anti-satellite (ASAT) attack, in anti- four observations: 1) ASAT attack on space-based aircraft attack, and in other applications of con- weapons and sensors is probably the most attrac- cern to nuclear policy and arms control. Defense tive countermeasure to boost-phase BMD; 2) di- and arms control policy will thus need to face rected-energy weapons are more likely to suc- the advent of these new weapons, irrespective ceed in the easier mission of ASAT than in the of their BMD dimension. more difficult mission of boost-phase BMD; 3) to 7. For modest defensive goals requiring less- a degree dependent on technical details, early than-perfect performance, traditional reentry stages of development of boost phase BMDs phase defenses and/or more advanced mid- might be conducted in the guise of ASAT devel- course defenses might suffice. Such defenses opment, stimulating anxieties about the health present less technical risk than systems that in- of the ABM Treaty regime; 4) to a degree depend- corporate a boost-phase layer, and they could ent on technical details, concluding a treaty with probably be deployed more quickly. the Soviet Union limiting ASAT development would impede BMD research at an earlier stage New ideas for improving such “old” BMD con- than would occur under the terms of the ABM cepts have emerged in the atmosphere of tech- Treaty alone. nical optimism enjoyed by the boost-phase concepts. APPENDIXES APPENDIX A: THE CONCLUSION OF PRESIDENT REAGAN’S MARCH 23, 1983, SPEECH ON DEFENSE SPENDING AND DEFENSIVE TECHNOLOGY — — Weekly Compilation of . particular the Joint Chiefa of Staff, have un- derscored the necessity to break out of a Presidential future that relies solely on offensive retali- ation for our security. Over the course of these discussions, I’ve Documents 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 exist- ence. Feeling this way, I believe we must thorough])’ examine every opportunity for reducing tensions and for introducing great- er stability into the strategic calculus on both sides. One of the most important contributions we can make is, of course, to lower the 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 Monday, March 28, 1983 thoughts on that score. But let me just say, Volume 19—Number 12 I’m totally committed to this course. Pages 423-466 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 retali- ation, 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 dem- onstrating our peaceful intentions by apply- ing all our abilities and our ingenuity to achieving a truly lasting stability? I think we are. Indeed, we must. After careful consultation with my advis- ers, including the Joint Chiefs of Staff, I NO, thus far tonight I’ve shared with believe there is a way. Let me share with you my thoughts on the problems of nation- you a vision of the future which offers hope. al security we must face together. My pred- It is that we embark on a program to ecessors in the Oval Office have appeared counter the awesome Soviet missile threat before yOU on other occasions to describe with measures that are defensive. Let us the threat posed by Soviet power and have turn to the very strengths in technology proposed steps to address that threat. But that spawned our great industrial base and since the advent of nuclear weapons, those that have given us the quality of life we steps have been increasingly directed enjoy today. toward deterrence of aggression through What if free people could live secure in the promise of retaliation. the knowledge that their security did not This approach to stability through offen- rest upon the threat of instant U.S. retali- sive threat has worked. We and our allies ation to deter a Soviet attack, that we could have succeeded in preventing nuclear war intercept and destroy strategic ballistic mis- for more than three decades. In recent siles before they reached our own soil or months, however, my advisers, including in that of our allies? 85 86 I know this is a formidable, technical task, for closer consultation with our allies, I’m one that may not be accomplished before taking an important first step. I am direct- the end of this century. Yet, current tech- ing a comprehensive and intensive effort to nology has attained a level of sophistication define a long-term research and develop where it reasonable for us to begin this ment program to begin to achieve our ulti- effort. It will take years, probably decades mate goal of eliminating the threat posed of effort on many fronts. There will be fail- by strategic nuclear missiles. This could ures and setbacks, just as there will be suc- pave the way for arms control measures to cesses and breakthroughs. And as we pro- eliminate the weapons themselves. We seek ceed, we must remain constant in preserv- neither military superiority nor political ad- ing the nuclear deterrent and maintaining a vantage. Our only purpose-one all people solid capability for flexible response. But share—is to search for ways to reduce the isn’t it worth every investment necessary to danger of nuclear war. free the world from the threat of nuclear My fellow Americans, tonight we’re war? We know it is. In the meantime, we will continue to launching an effort which holds the promise pursue real reductions in nuclear arms, ne- of changing the course of human history. gotiating from a position of strength that There will be risks, and results take time. can be ensured only by modernizing our But I believe we can do it. As we cross this strategic forces. At the same time, we must threshold, I ask for your prayers and your take steps to reduce the risk of a conven- support. tional military conflict escalating to nuclear Thank you, good night, and Cod bless war by improving our non-nuclear capabili- you. ties. America does possess-now-the technol- Note: The President spoke at 8:02 p.m. from ogies to attain very significant improve- the Oval Office at the White House. The ments in the effectiveness of our conven- address was broadcast live on notion wide tional, non-nuclear forces. Proceeding radio and television. boldly with these new technologies, we can Following his remarks, the President met significantly reduce any incentive that the in the White House with o number of ad- Soviet Union may have to threaten attack ministration officials, including members against the United States or its allies. of the Cabinet, the White House staff, and As we pursue our goal of defensive tech- the Joint Chiefs of Staff and former offi- nologies, we recognize that our allies rely cials of past administrations to discuss the upon our strategic offensive power to deter address. 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 com- mitments. 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 an 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 APPENDIX B: ABM TREATY AND RELATED DOCUMENTS —— — . ———-—— 1980 EDITION AGREEMENTS TEXTS AND HISTORIES UNITED STATES ARMS CONTROL AND DISARMAMENT AGENCY WASHINGTON, D. C., 20451 87 88 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 strengthen- ing of trust between States, Have agreed as follows Article I 1 Each party undertakes to Iimit anti-ballistic missile (ABM) systems and to 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, 89 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) operational; (b) under construction; (c) undergoing testing; (d) undergoing overhaul, repair or conversion; or (e) 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 launch- ing 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; 91 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 General Secretary of the Central States of America Committee of the CPSU 92 Agreed Statements, Common Understandings, and Uni- lateral 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 contain- ing 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 de- ployment area. (See Agreed Statement [C].) B. ABM Test Ranges The U.S. Delegation made the following statement on April 26, 1972: Article IV of the ABM Treaty provides that “the limitations provided for in Article 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 common 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 IS 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 such 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 Ground-based laser ASATs, presumably using probably one of the most difficult-military ap- excimer or free-electron lasers for best atmos- plication of directed energy. Many other applica- pheric propagation, would have the advantages tions of widely varying plausibility vie for fund- of large size and power supplies. Airborne lasers ing and attention. An assessment of all these could avoid some of the propagation disturb- schemes is well beyond the scope of this Paper, ances introduced by denser air at low altitudes, but the list below is provided for reference. Men- but turbulence around the airplane skin could tion of a scheme does not imply that it has any require adaptive beam compensation. technical or military promise; this question would Space-based directed energy ASATs are the have to be properly studied. most interesting category of all, since they would Anti-satellite (ASAT). Directed energy attack on be, in effect, long-range space mines, Rather than satellites from space-, air-, or ground-based positioning itself next to its quarry like an ordinary weapons is substantially easier than boost phase space mine, a laser could be thousands of kilom- BMD. A satellite’s orbit is completely predicta- eters away and still be able to strike within ble, making it in effect a fixed target. Long dwell milliseconds upon receipt of a radio signal from times and low fluences suffice for ASAT attack the gound. on unshielded satellites. For instance, long il- lumination at just a few watts/cm2 (several times Strategic offense. If they mature, the directed the sun’s normal irradiance in space) could upset energy devices discussed for BMD might turn out the thermal control systems that allow spacecraft to have been better termed “offensive to endure the extremes of heat and cold in outer breakthroughs” than “defensive breakthroughs.” space. Substantial hardening of large and com- Consider, for example, a fleet of Soviet x-ray plex satellites (including sensors) to directed lasers launched simultaneously with (or minutes energy weapons from all directions at all times before) a Soviet first-stike ICBM attack. The pop- is impractical. Unlike BMD, which must handle up x-ray lasers’ job would be to intercept any U.S. thousands of boosters in a few minutes, ASATs ICBMs launched before arrival of Soviet silo-kill- would have fewer targets and longer attack times. ing RVs. The Soviet x-ray lasers wouId therefore Last, BMDs must operate under the most hostile deprive the U.S. of its option for launch under circumstances imaginable, whereas the super- attack. Microwave generators might be used for powers might use ASATs in scenarios short of nu- EMP-like attack on the U.S. command and con- clear war. trol system. Another example of offensive use of beam weapons would be Soviet ASAT attack on This Background Paper has stressed (see Sec- U.S. warning, communications, nuclear detona- tion 5.1) that maturation of the same technologies tion detection, or navigation satellites important involved in boost phase BMD virtually assures po- to the U.S. retaliatory capability. Yet another ex- tent ASATs. The so-called “Star Wars” systems ample would of course be suppression of any could well be their own worst threats. Besides U.S. BMD that used space-based weapons or the intrinsic ease of ASAT over BMD, a Soviet de- sensors. fense suppression ASAT attack on U.S. defensive battle stations would have three key factors work- Bus intercept. This Background Paper has ing in its favor: 1 ) The Soviets would pick the time focused on intercept of ICBMs before booster and sequence of attack on the U.S. BMD system burnout. Intercept of the bus or post boost vehi- and launch of their ICBMs; 2) The Soviets need cle poses a rather different challenge. Post-boost not destroy the entire defensive constellation, but phase for today’s ICBMs is rather long (several only “punch a hole” for their ICBMs to pass minutes) but could be shortened drastically on through; 3) The attack would take place over So- future ICBMs. Bus tracking requires a different viet territory. sensor than booster tracking, since the bus plume 97 98 is much less conspicuous, and the bus rocket airborne command post “Doomsday planes, ” So- motor may not operate continuously. The bus is viet AWACS radar planes, and so on. In a sec- a target of declining value as it dispenses its RVs. ond scheme, B-1 or B-52 bombers would be out- Interruption of bus operation would not prevent fitted with lasers (possibly DF) to protect them the bus and its contents from continuing their from Soviet fighters, surface-to-air missiles (SAMs), ballistic flight to the target country, though the and air-to-air missiles. A third scheme equips car- aim might be very wide of the target. Operating rier battle groups with lasers or particle beams above the atmosphere, the bus can deploy light- to defend themselves against cruise missile attack. weight shields, decoys, and sensor countermeas- Fourth and last, ground-based beam weapons ures (e.g., corner reflectors). On the other hand, might replace surface-to-air missiIes for local air x-ray lasers and neutral particle beams that can- defense. not penetrate the atmosphere can attack the bus Midcourse and terminal BMD. Intense electron in space. beams have long been studied as replacements Anti-SLBM. A number of schemes have been for interceptors in reentry BMD. In midcourse suggested for using directed energy weapons BMD, beam weapons might not only destroy against SLBMs, besides the obvious extensions of RVs, but aid discrimination of RVs from light- ICBM defense. Thus pop-up x-ray lasers could be weight decoys: lasers, particle beams, or x-ray positioned on U.S. coasts or ships at sea to in- lasers would illuminate approaching objects, and tercept SLBMs launched from nearby Soviet sub- sensors would use the response of each object marines. Aircraft patrolling coastal waters and car- as an extra piece of data to judge whether it was rying lasers could attack ascending SLBMs in their a true RV (see Section 6). area. Submarine communications. This scheme Anti-IRBM. Intermediate range ballistic missiles would use a blue-green laser to communicate (IRBMs) have short boost phases and potentially with submerged submarines. Seawater is opaque low trajectories, making anti-lRBM defense rather to all but VLF and ELF radio frequencies, used different from anti-lCBM defense and perhaps for submarine communications today, and to the better accomplished with ground-based terminal blue-green portion of the visible light spectrum. BMD systems deployed in the theater. A blue-green laser beam originating on a satel- lite, reflected from a space-based mirror, or car- Defense of satellites (DSAT). Low-power wide- ried by an airplane would be modulated in ac- divergence (small optics) laser satellites (perhaps cordance with the message to be transmitted and HF for high specific energy) could serve as “es- directed at a given spot on the ocean. After trans- corts” for other satellites, defending the other mission of the full message, the beam would satellites from hostile objects—mines, ASAT mis- dwell on a neighboring spot and transmit again, siles —approaching within a given range. and so on, eventually covering all submarine pa- Anti-aircraft. At least four schemes have been trol areas. Optical sensors on the submarine hull broached for using directed energy weapons would detect the message. against aircraft or cruise missiles. The most am- Blinding sensors and seekers. Analysts have bitious would involve a worldwide constellation studied a wide range of tactical applications for of trackers (possibly LWIR) and beam weapons lasers, involving blinding of battlefield sensors, (possibly DF or short wavelength lasers) to attack missile seekers, and even human beings. Soviet Blackjack strategic bombers, Backfire bombers attacking U.S. aircraft carriers, Soviet