In the years that have passed since President Reagan unveiled the Strategic Defense Initiative (SDI), the United States has witnessed enormous public debate over the security implications of pursuing development of a large-scale defensive system against Soviet ballistic missiles. Few people are neutral about the SDI program. It has been heralded by some as a definitive solution to the dangers of the nuclear age and disparaged by others as a misguided effort leading toward ever greater instability. In the meantime, as the Reagan Administration draws to a close, basic questions concerning the plausible goals, feasibility, and strategic impact of SDI have yet to be resolved. It will be left to a new president and the Congress to decide the fate of SDI in the early 1990s, and to determine what kinds of adjustments to the present program would best suit the country's national security interests.

This will not be an easy task. SDI has left an indelible mark on our country's security debate. In its first three years, SDI emerged as the number one issue on the country's security agenda, in large part because of the President's deep personal commitment to the program. Virtually all issues related to arms control, alliance security, and U.S.-Soviet relations became hostage to SDI in one way or another. Spending on SDI research and development increased rapidly during this period. U.S.-Soviet relations were turbulent. While the Soviets launched blistering propaganda attacks against SDI, the Reagan Administration unveiled a controversial program of field experiments and sought to redefine the 1972 Anti-Ballistic Missile (ABM) Treaty in a way that would enable unfettered development and testing of exotic SDI weapon components in space.

Recent events have combined to soften the sharp focus on SDI. While important technical advances have been made in the program, much of its novelty has worn off. Congress has become more skeptical. Funding has stabilized at well below the levels sought by the Administration. A more sober recognition of the enormous technical hurdles involved has lessened enthusiasm for the idea of a "multilayered" defensive system with major space-based components. Furthermore, SDI no longer appears to be the major stumbling block to improvements in East-West relations that it once was. The Soviets have softened their rhetoric against "space strike weapons" and shifted their focus to urging strict compliance with the ABM Treaty. Soviet leader Mikhail Gorbachev and President Reagan embarked on a series of summits. In late 1987, both sides achieved a major diplomatic breakthrough by agreeing to ban intermediate- and shorter-range nuclear missiles—the so-called INF Treaty—and moved closer to a new regime of reductions in strategic nuclear arms in early 1988.

Nonetheless, major disagreements still exist over how to proceed on SDI and on arms control arrangements governing strategic defensive and offensive weapons. The present SDI program has acquired a vocal constituency of supporters, including some members of Congress, who are committed to fulfilling President Reagan's vision of a defense-dominant world. In addition, new proposals for strategic defense have drawn national attention. These range from the early deployment of "conventional" ground- and space-based interceptor rockets to Senator Sam Nunn's idea of a more limited system to protect against the accidental launching of missiles. Whether the next administration will be able to develop a national consensus on ballistic missile defense (BMD)—and whether it can then translate this consensus into workable arrangements with the Soviet Union—are very much open questions.

The purposes of this volume are to explicate the key security policy issues raised by the SDI program and to explore how they are likely to evolve through the early 1990s. The following issues will figure prominently in debates on future directions for SDI policy, and each, in turn, is examined in the chapters of this book:
—What factors led to the emergence of SDI?
—How have SDI technologies evolved since 1983? How are research and development likely to progress by the early 1990s?
—How will Soviet strategic policies ad just in response to SDI through the early 1990s?
—What are the key SDI issues for U.S. allies?
— How does SDI affect the present structure of offensive and defensive arms control agreements?
— What are the options for negotiating with the Soviet Union future arms control regimes that regulate defensive and offensive forces?
— How will the pursuit of SDI affect the overall U.S. defense posture in the world?

This volume had its origins in a workshop on "The Strategic Defense Initiative and American Security" that was held in August 1986, in Aspen, Colorado. The workshop was sponsored by the Aspen Strategy Group, a program of the Aspen Institute for Humanistic Studies. At that meeting, which was chaired by William J. Perry and Brent Scowcroft, the participants were asked to take stock of the accomplishments of the SDI program over its first three years and to assess its technical prospects and potential impact on security policy through the early 1990s, when SDI research is expected to present options for national decision. Each of the contributors to this volume—Jeffrey Boutwell, Ashton B. Carter, Thomas H. Johnson, Michael M. May, Stephen M. Meyer, Strobe Talbott, and Edward L. Warner III—made major presentations at the workshop. Later, they updated their work to take account of the proceedings and subsequent technological and political developments. Our deepest thanks go to the authors for their excellent contributions.

The introductory chapter proposes a possible SDI research agenda through the early 1990s and draws heavily on the workshop proceedings. We wish to thank Antonia Handler Chayes, John Deutch, Sidney Drell, David C. Jones, Jan Lodal, George Rathjens, John Steinbruner, Albert Wheelon, and Charles Zraket who, as members of the Aspen Strategy Group, participated in the workshop and contributed greatly to the discussion and debate on the ideas presented here. In addition to the authors noted above, the group was very fortunate to have in attendance at the workshop a number of distinguished guests: Solomon Buchsbaum, Albert Carnesale, Richard Garwin, Donald Hicks, Arnold Horelick, Robert C. MacFarlane, Uwe Nerlich, Malcolm O'Neill, David Z. Robinson, James R. Schlesinger, Michael Stafford, James Timbie, Marisol Touraine, and Shirley Williams. We are very grateful to these individuals for their participation and contributions to the discussion.

Generous financial support for this project was provided by the Carnegie Corporation of New York, the John D. and Catherine T. MacArthur Foundation, and the Rockefeller Foundation. We also owe a great debt to those individuals who assisted at various stages in the production of this volume. Ashton B. Carter, Thomas H. Johnson, and Albert Carnesale provided valuable comments on the introductory chapter of the book. Herbert Lin offered much-appreciated technical advice on the various essays. Teresa Pelton Johnson provided valuable editorial services and supervised the production process in its latter stages. Maude Fish prepared the manuscript with the assistance of Yvonne Amundson, Ann Callahan, and Lisa Grumbach. Finally, we are very grateful to William J. Hingst, Linda Owens, W. Daniel Wright and their colleagues at the Aspen Institute, Wye Center, for computer support services.

Readers should note that the opinions and conclusions expressed in this book are those of the authors alone and should not be ascribed to the membership of the Aspen Strategy Group, the Aspen Institute for Humanistic Studies, or to funding or sponsoring organizations.