Assessing the Technological Feasibility and Political Desirability of the Strategic Defense Initiative (SDI) (January 6, 1988)

The strategic defense debate has once again returned to the front pages of our major newspapers, with tales of concessions and hard-line stances, negotiations and motivations, strategy and policy. But the underlying debate among the country’s physical and political scientists has been raging since Ronald Reagan first aired his space-shield dream on March 23, 1983. The Strategic Defense Initiative, or “Star Wars” as it has been dubbed by the media,[1] was well-received by the American people, but strong skeptics remain. This paper will attempt to survey the scientific and political arguments as to the technological feasibility and political desirability of SDI. Unfortunately, when arguing SDI, politicians and scientists tend to remain within their areas of expertise and ignore the other half of the issues.[2]  It is our goal to give an interdisciplinary assessment of the prospect of strategic defense, analyzing first the technical and then the political aspects, and then concluding with an appraisal of both in relation to each other.

Ronald Reagan concluded his first SDI speech with an appeal to new technologies: “I call upon the scientific community in our country, those who gave us nuclear weapons, to turn their great talents now to the cause of mankind and world peace, to give us the means of rendering these weapons obsolete.”[3] The SDI plan was to create new technologies which could track down and destroy ballistic missiles, that is, primarily intercontinental ballistic missiles (ICBM) launched from the Soviet Union toward the United States.[4] In May, 1984, Lt. General James Abrahamson detailed the technical elements of the program to the U.S. House Appropriations Committee while recommending $24 billion for Fiscal Year 1985 and $24 billion in expenditures for the FY 1986-1989 period. He divided the program into five technical areas:

  1. Surveillance, Acquisition, Tracking and Kill Assessment (SATKA)

This area involves satellites, using radar and optical imaging (lasers), and other communications devices. “The goal of this program,” states Abrahamson, “is to develop and demonstrate the capabilities needed to detect, track and discriminate objects in all phases of the ballistic missile trajectory.”[5]

  1. Directed Energy Weapons

This program has four components: space-based particle beams, and nuclear driven energy weapons (x-ray lasers).

  1. Kinetic Energy Weapons

Kinetic Energy Weapons will be used to destroy missiles which escape the laser weapon defensive strike during the primary boost phase. As opposed to Direct Energy Weapons, “kinetic energy weapons will rely on nonnuclear kill mechanisms to destroy the intended target.”[6]

  1. Systems Analyses and Battle Management/Command, Control and Communications (BM/C3)

Because of the enormous time constraints on decision-making processes, much of the management of SDI will be handled by computers. Former Secretary of Defense Harold Brown reports that “estimates for the total number of lines of code of software required range from 10 million to 100 million.”[7]

  1. Support Programs

The purpose of the support programs is to “provide timely answers to a variety of critical SDI support related questions.”[8] This means analyzing the effectiveness of each weapon, determining minimum energy needs, and testing the survivability of the system as a whole.

All five of these components present serious technological and strategic problems for the developers of strategic defenses. The first two areas concern primarily the tracking and destroying of missiles during the boost phase, before the rocket leaves the Earth’s atmosphere. The third area, and part of the second, represents our defenses against those missiles which pass through the boost phase.

Proponents of SDI speak of a five-tiered defense, claiming that if each tier has a 90% success rate, the entire system would eliminate 99.999% of the missiles, in other words, allowing one in 10,000 missiles through. This five-tiered concept includes defenses during the boost phase, the warhead deployment phase in space, the re-entry phase, and at two more stages within the Earth’s atmosphere before impact. The commonly quoted estimate of 90% effectiveness at each of these stages is hotly contested by scientists analyzing the specific components of the system, taking into account limitations of the different technologies and effective countermeasures against them.

The flight of an ICBM lasts from 29 to 36 minutes. The rocket travels through a five-minute boost phase and spends three to five minutes deploying warheads. The warheads then travel about the atmosphere for about twenty to twenty-five minutes before reentering and striking their target in about one minute.[9]

The primary advantage of space based weapons is that, unhampered by the curvature of the earth, they may strike a missile during the vulnerable boost phase. During the initial ascent the missile has a very large exhaust plume which can be tracked using the current infrared sensors on our early warning satellites. The satellite could feasibly pinpoint the position of the missile and target a laser beam against it. However, one countermeasure which has been proposed is to shorten the boost-phase by increasing the power of the rockets. The Soviets have already begun deploying rockets with boost times around three minutes and experts suggest that it could easily be cut to around one minute. As Harold Brown observes, even chemical lasers, which are much faster than kinetic energy rockets, “will still not be a match for fast-burn boosters of offensive missiles.”[10] In a paper written in 1984 for the International Strategic Institute at Stanford, Sidney Drell, Philip Farley and David Halloway concur with respect to x-ray lasers:

Thus even if we assume that x-ray laser systems are successfully developed with sufficiently high gain—many orders of magnitude beyond current technology—to look promising for destroying boosters at long range, the offense can use the opacity of the atmosphere to defeat them with missiles of high thrust that complete their boost before they can be attacked.[11]

Therefore, a strategic defense which relies on boost phase interception of missiles will most likely be unsuccessful.

Perhaps the most severe handicap of space-based weapons and orbiting surveillance satellites used in the first three tiers of the defense is that they are vulnerable to relatively inexpensive modes of attack. John Tirman and Peter Didisheim, members of the Union of Concerned Scientists, opponents of SDI, point out that satellites will either be traveling in low orbits, which are necessarily periodic and predictable, or in much higher, geosynchronous orbits, which are also predictable because they remain stationary relative to the earth. “It is this fact,” they claim, “that renders defense satellites vulnerable to attacks from anti-satellite weapons. Knowing the exact—or probable—path of an orbiter (and its velocity) is a tremendous advantage to the attacker.”[12] The Soviet Union already possesses two cheap anti-satellite weapons, ABM interceptor missiles and space mines, which could critically debilitate strategic defenses before an attack.[13] Tirman et al. conclude, “As Carter, Gray, and others who have studied the matter agree, space mines—by their sheer simplicity—present a seemingly irresolvable threat to space-based defense.”[14]

Ground based lasers and other defenses used during the last two tiers of the defense are of course invulnerable to attacks by space mines but they also have their drawbacks. As stated before, they cannot hit a rocket during the boost phase due to curvature of the earth and therefore must deal with the ten to twenty warheads which are released from each rocket. The problem here is, as Louis Marquet, Director of Directed Energy Weapons at the SDI Organization admits, “it is relatively straightforward to design decoys that act very much like reentry vehicles.”[15] Marquet claims that the energy lasers will be able to measure the validity of an incoming missile so that the kinetic energy systems, whose job it will be to destroy them, are not wasted. However, Theodore Postol of the Stanford Center for International Security and Arms Control was quoted recently in Time magazine as saying, “the biggest problem [facing SDI is that] nobody knows how to discriminate real objects from false ones. It is the Achilles’ heel of the program.”[16] Indeed, tracking may be so complicated by decoys and other countermeasures that an effective defense may only be possible during the boost phase. As Professor George Rathjens of MIT claims,

One is driven to the acceptance of the essentiality of the boost-phase intercept for a perfect or near-perfect defense of the population. This is not only because of the infeasibility of world coverage with terminal defenses but also because of the extraordinary number of threatening objects that are likely to confront any post-boost defense system: many thousands of warheads at least tens, if not hundreds, of thousands of decoys, not easily distinguishable from warheads prior to reentry.[17]

If, as Rathjens asserts, defense after the boost phase is nearly impossible, and if we accept the conclusion above that interception during the boost phase of a quick-burn rocket is impracticable, we must conclude that these limitations on the weapons and tracking devices make SDI an unrealizable dream.

Whether computer hardware and software can be developed to run the SDI system is as important as the technical feasibility and workability of the weapons themselves. Estimates of the length of the code involved are of course daunting, because the software would be expected to work 100% the first time it is used. A minor programming error could result in a total breakdown of the system. Methods of debugging such a program are not currently known. Proponents of the system can only point to past advances indicating that one cannot predict what the future will bring in the way of computer technology. They rely on breakthroughs as yet unrealized. With a program on the order of ten to one hundred million lines of code, and a necessary reaction time of minutes or seconds, the development of hardware for such a system seems unrealizable for quite some time.

Computer speed is the primary obstacle to a space-based defense which would be required to track thousands of warheads and shoot down a missile second after it is launched. The problem with tracking so many missiles simultaneously is that the number of calculations quickly becomes enormous.

To give perspective to the size of the problem we can take an example from linear programming. Let us assume that we have one satellite per missile (a ridiculous assumption, but one which will only make the result smaller). In order to shoot down every missile, we must assign each satellite a different missile. (We don’t want two satellites to shoot at the same missile and let another missile pass through.) The problem is that not every satellite can reach every missile. The satellites will be in different orbits over different areas of the globe during the attack, and the missiles will be going off in different directions. That means that for n missiles and satellites we have n! ways of assigning them, each with n constraints to check to be sure that every satellite can reach its intended missile. For only 70 missiles that amounts to a maximum of over 10100 calculations! And that it is supposed to be done in a matter of minutes or seconds! Linear programming algorithms can reduce that number considerably, but a problem with 10,000 missiles is out of the question. Marquet boasts that a new Japanese computer can compute 109 operations per second, an enormous feat which does not even comes close to the speed needed to solve the above problem in a reasonable amount of time.[18] Even characteristic advances in computer technology would not allow for a reliable computer program to run our strategic defense.

The technological problems of Reagan’s vision of a strategic defense are enormous. Reagan himself admitted in his 1983 speech that the goal of a nuclear shield might not be reached for decades, and that seems to be an accurate assessment. These technical problems threaten the original purpose of SDI, that is, “to break out of a future that relies solely on offensive retaliation for our security.”[19] For if one cannot guarantee that the system will work as planned, if one cannot counter the counter-measures, if one cannot protect the satellites or debug the software, then the original motivation for SDI has disappeared and the impetus for continuing the program is lost.

The scientific rebuttal of the star wars proposal has led proponents to justify the program with specious political arguments. A proponent of SDI, Alun Chalfont, states emphatically,

the aim is not to provide 100 per cent protection, either for the population of the United States or its retaliatory missile force. It is to demonstrate a capacity to destroy so many attacking missiles that the Soviet Union would not know how many targets, or which targets, would be destroyed. This would make a first nuclear strike an even more problematic option than it is today, thus increasing the credibility of the deterrent.[20]

But Reagan’s initial speech implied that the reason for developing strategic defenses was to assure American survival regardless of deterrence. It was his desire to rid us of MAD (Mutually Assured Destruction) which led him to propose the idea in the first place. If our only goal is to increase deterrence then surely we can achieve that much more effectively by improving our delivery systems and expanding our nuclear submarine fleet. What is more likely is that the Administration wishes to create a defense system which would protect our missiles, not our cities, and therefore increase our retaliatory capabilities in the event of a Soviet first strike. Harold Brown writes, “Technically, [ballistic missile defenses] appear cost-effective for some kinds of strategic retaliatory forces. For defense of population against a responsive threat, they look poor through the year 2010 and beyond.”[21] George Rathjens believes that the Administration is intentionally confusing the issue by claiming the desirability of Reagan’s nuclear shield dream to gain public support while actually working toward the feasible goal of missile defense with the result being somewhat enhanced deterrence.[22] The latter, of course, was rejected in the 1970’s and prohibited by the ABM treaty.

It is clear, however, that SDI, as it was originally conceived, will not be accomplished in the foreseeable future. A poll of members of the National Academy of Sciences in SDI related fields last year reported that,

Of those responding, 78 percent said prospects were either ‘extremely poor’ or ‘poor’ that a survivable and cost-effective system could be built within the next 25 years. Only 4 percent said the odds of success were better than even.[23]

Roy Woodruff, former head of weapons programs at the Lawrence Livermore Laboratory, and an outspoken critic of SDI, was quoted in the New York Times in October as saying, “[Reagan’s] vision of a leakproof shield that makes nuclear weapons impotent and obsolete is not a practical reality.”[24] Yet the Reagan administration continues to push forward SDI as if they had heard nothing of the critics’ objections. On November 24, 1987 the Defense Department announced “that they planned to conduct the first test of a laser weapon in space in the early 1990’s.[25] His successor Frank Carlucci is somewhat less strident but still says, “we ought to deploy SDI as soon as we can.”[26] But deployment and space testing of space weapons may not be accomplished for a long time. As Harvard University Arms Control Specialist Joseph Nye says, “what killed early deployment was the recognition that there was nothing to deploy.”[27]

With the understanding that SDI, as a perfect shield against nuclear weapons, is an unfulfillable dream, we can now analyze the political justifications for continuing the program, assuming that what will eventually be deployed is a defense of missile sites. One argument giving credence just recently is that the U.S. should research SDI because the Russians are researching it. This argument is somewhat paradoxical, because it conflicts with the pro-SDI assertion that an American space shield would not upset the Soviets and provoke them to a first strike. Otherwise formulated, if we do not expect the Soviets to be angered by our space defense and perceive it as a balance-altering advantage, then why should we be angered by their attempts to build a shield? As we showed above, however, a better, i.e. more cost-effective strategy to counter a defense would be to research ways of tricking a ballistic missile defense. The prospect of a Soviet shield should not give us justification for building one of our own.

There is the common perception that it was SDI which brought the Russians to the negotiating table. This would seem reasonable if Gorbachev had not reversed himself one day before arriving in the U.S. for a superpower summit. The Soviets have agreed to postpone discussions about missile defenses to a later date, presumably because the INF agreement was more important to them. SDI could only bring Gorbachev to “the bargaining table” if he thought there was something to bargain. Reagan’s insistence that SDI is not a bargaining chip precludes that reasoning.

The Soviets do have an interest in stopping SDI, though, as does the U.S. Gorbachev’s very real concern about an expansion of the arms race into space justifies his dislike for SDI. Sure, he can make SDI irrelevant by spending $1 for every $1,000 we spend, but he has to spend that $1, and that is what he wants to avoid. Considering the grave state of the Soviet economy, opening up the superpower competition to antisatellite weapons and strategic defenses would be disastrous. The Soviet concern with SDI is real, but it must not be confused with a proof that SDI will work or that it is justified.

One pertinent question to both sides of the debate is whether research on strategic defenses constitutes a violation of the ABM Treaty. Former Chief Arms Negotiator Kenneth Adelman answers that it does not. “The treaty limits deployment of fixed, land-based ABM systems,” he says, “and prohibits development, testing or deployment of space-based, sea-based, air-based, or mobile land-based ABM systems and their components. The treaty unmistakably leaves the research doors wide open.”[28] How he differentiates research and development in the R&D branches of the companies that are doing the SDI research is a mystery. But supposing that research was permitted under the treaty, what could be the goal of such research? Certainly it implies a willingness to violate the treaty if something good shows up. That brash statement of our intention to violate the ABM treaty if it serves our interests is what justifiably worries the Soviets.

The only achievable goal of deployment is the protection of missile silos from Soviet attack. Proponents claim that if the Soviets knew that their weapons had a reduced chance of hitting their targets and knocking out our missiles, they would be deterred from a first strike. Peter Clausen, senior arms analyst for the Union of Concerned Scientists, believes that, “for the purpose of deterring a preemptive attack, Star Wars defenses are at best redundant and at worst counterproductive.”[29] It would seem that our present deterrent force which consists of thousands of land-based warheads as well as those on bombers and submarines would be sufficient. Indeed, our present strategy assumes that enough warheads would survive a Soviet first strike to provide a devastating response. John Holdren, American Director of Pugwash, points out that “even a single medium-size nuclear weapon can destroy a major city.”[30] Therefore it would be virtually impossible for a Soviet first strike to knock out enough of our weapons to eliminate the immense retaliatory threat posed by even just a few surviving missiles. One would only need the added protection of a missile defense if our deterrent threat were insufficient now. But that is far from the case. These arguments were hotly debated during the formation of the ABM Treaty, and SDI adds nothing significantly new to the debate. The only proven method of defense is deterrence through MAD (Mutually Assured Destruction) and arms limitation treaties.

Ronald Reagan’s Strategic Defense Initiative, intended to render nuclear weapons obsolete, may never become a reality. A vast majority of scientists have rejected it, arguing that it is technologically infeasible to create a cost-effective shield against nuclear weapons. Politicians, however, continue to stand by their space laser dreams, arguing that it is the only “humane” strategy, while secretly hoping for a strategic advantage from the more realizable goal of missile defenses. SDI has turned into a public relations campaign designed to circumvent the ABM Treaty. The future of SDI is uncertain. William Broad queries in the December 6, 1987 New York Times Magazine, “Does Star Wars have enough political appeal to survive? The answer is clearly yes. It will remain in one form or another, if only as a hefty research program.”[31] This pessimistic appraisal seems justified considering the sentiment in the U.S. Senate, where in September George Bush had to break a 50-50 tie on a bill which would have cut SDI funding by $2 billion. Certainly, the upcoming presidential election will play a large role in determining the future of SDI. All six Democratic candidates have stated they will eliminate the SDI, whereas all six Republican candidates have indicated that they will continue the program. Of the six Republicans, only former Secretary of State Al Haig has said he would consider not going ahead with the proposed first stage of deployment beginning in 1992. With the political lines drawn so clearly, one would hope that SDI would become a major issue in the 1988 campaign, and that once exposed, the American people would soundly reject it.


Anzovin, Steve. The Star Wars Debate. (New York: The H.W. Wilson    Company, 1986.) A collection of articles on SDI.

Barnaby, Frank, What on Earth is Star Wars? (London: Fourth Estate, 1986)

Bowman, Robert. Star Wars. A Defense Insider’s Case Against the Strategic        Defense Initiative. (Los Angeles;   Jeremy P. Tarcher, Inc., 1986)

Brand, David. “Star Wars’ Hollow Promise.” Time Magazine. December 7,         1987.

Broad, William J. “Star Wars is Coming, But Where is it Going? The New York      Times Magazine. December 6, 1987.

Brzezinski, Zbigniew. Promise or Peril. (Washington: Ethics and Public Policy   Center, 1986.) Collected articles on SDI.

Chalfont, Alun. Star Wars. Suicide or Survival? London: Weidenfeld and            Nicolson, 1985.)

Cimbala, Stephen J. The Technology, Strategy, and Politics of SDI. Westview       Special Studies in National Security and Defense Policy. (Boulder:        Westview Press, 1987.) A collection of articles.

Guerrier, Steven W. and Thompson, Wayne C. Perspectives on Strategic   Defense. Westview Special Studies in National Security and Defense           Policy. (Boulder: Westview Press, 1987.) A collection of articles.

Haley, P. Edward and Merritt, Jack. Strategic Defense Initiative. Folly or Future? (Boulder: Westview Press, 1986.) Collected articles on SDI.

Holdren, John and Rotblat, Joseph. Strategic Defenses and the Future of the          Arms Race. A Pugwash Symposium. (London: Macmillan Press, 1987.)

Jastrow, Robert. How to Make Nuclear Weapons Obsolete. (Boston: Little,          Brown and Company, 1983.)

Snyder, Craig. The Strategic Defense Debate. Can Star Wars Make Us Safe?       (Philadelphia: The University of Pennsylvania Press, 1986.) A collection

of articles.

Tirman, John. Empty Promises. The Growing Case against Star Wars. Union of             Concerned Scientists. (Boston: Beacon Press, 1986.) A collection of            articles on SDI.

Weinrod, W. Bruce. Assessing Strategic Defense. Six Roundtable Discussions.     The Heritage Lectures 38. (The Heritage Foundation, 1985)

Wells, Samuel F. and Liwak, Robert S. Strategic Defenses and Soviet-American      Relations. Cambridge, MA: Ballinger Publishing Company, 1987.)       Papers from a conference on SDI.

[1] Note that this is one of three terms the Reagan Administration has appropriated from George Lucas’ movie, the other two being “Freedom Fighters” and “The Evil Empire”. In fact, the administration criticized the use of the movie title, despite its obvious appropriateness, because they felt it misrepresented SDI as an offensive system. Harvard Professor Richard Pipes, a proponent of SDI, recently admitted in his debate on this campus with Professor Stephen Cohen that he disliked the world “initiative” because the project could more accurately be described as a “response” to Soviet strategic defense research.

[2] For example, one could hear Chief Arms Negotiator Kenneth Adelman begin an answer to a question about SDI in a Woodrow Wilson School speech last year, “Assume SDI only works 90%….”

[3] Strategic Defense Initiative: Folly or Future? Ed. P. Edward Haley and Jack Merritt. (Boulder: Westview Press, 1986.) Page 24.

[4] SDI has no pretensions of stopping submarine-launched cruise missiles or bombs delivered by airplanes. This fact is rarely considered, e.g. the President’s dream of SDI “rendering nuclear weapons impotent and obsolete.”

[5] op. cit. p. 45

[6] ibid.

[7] ibid. page 114

[8] ibid.

[9] Michael May, “Technical Feasibility of the SDI”. Strategic Defenses and Soviet-American Relations. Ed. By Samuel F. Wells, Jr. and Robert S. Litwak. (Cambridge, Mass.: Ballinger Publishing Company, 1987.) Page 125.

[10] Harold Brown, Folly of Future, p. 116

[11] Sidney D. Drell, Philip J. Farley, and David Holloway, “The SDI: A Technological Appraisal” in SDI Folly or Future? Page 99.

[12] John Tirman and Peter Didisheim, “Lethal Paradox: The ASAT-SDI Link” in Empty Promise: The Growing Case Against Star Wars. The Union of Concerned Scientists. Ed. By John Tirman. (Boston: Beacon Press, 1986.) Page 113.

[13] Tirman and Didisheim also note: “There is, perhaps, no finer illustration of the ‘cost-exchange ratio’ than that of space mines versus a Star Wars battle station: a $3 million space mine could destroy a BMD (Ballistic Missile Defense) satellite worth $2 billion to $5 billion.” Page 115.

[14] Tirman et al. p. 116

[15] Louis Marquet, “The Technical Feasibility of SDI” in Perspectives on Strategic Defense. Ed. By Steven W. Guerrier and Wayne C. Thompson. (Boulder: Westview Press, 1987.) Page 105.

[16] Time magazine, December 7, 1987, p. 18

[17] George W. Rathjens, “The Technical (In)feasibility of SDI” in Perspectives on Strategic Defense, op. cit. Page 112.

[18] ibid. p. 105.

[19] Ronald Reagan, Address to the Nation on the Strategic Defense Initiative, March 1983.

[20] Alun Chalfont, Star Wars Suicide or Survival? (London: Weidenfeld and Nicolson, 1985.) Page 84.

[21] Harold Brown, Folly of Future, Page 118.

[22] Rathjens, p. 114

[23] New York Times, October 31, 1986.

[24] New York Times, October 22, 1987. Page A31.

[25] New York Times November 25, 1987 pA13.

[26] Time Magazine Dec. 7, 1987 p. 21.

[27] ibid. p. 21.

[28] Kenneth L. Adelman, “SDI: Setting the Record Straight” in Promise or Peril. Ed. By Zbigniew Brzezinski et al. (Washington, D.C.: The Ethics and Public Policy Center, 1986.) Page 201.

[29] Peter Clausen, “SDI in Search of a Mission” in Promise or Peril. Page 172.

[30] John Holdren, “The Pugwash symposium on Strategic Defences: An Overview” in Strategic Defences and the Future of the Arms Race. (London: The Macmillan Press Ltd, 1987.) Page 12.

[31] William J. Broad, “Star Wars is Coming, But Where is it Going?” in The New York Times Magazine. December 6, 1987. Page 86.