APS Report on Boost-Phase Missile Defense
In July 2003, the American Physical Society (APS) issued a detailed report, of which the Preface and the first paragraphs of the Executive Summary are documented below.
Preface
The American Physical Society (APS) is the largest society for professional physicists in the United States, with more than 40,000 members. The principal functions of the APS are overseeing the publication of professional journals and arranging scientific meetings. The APS also assists the physics community through educational and public outreach programs. In addition, from time to time the APS produces reports on matters of public interest that require technical understanding, and for which an impartial and authoritative analysis would be of particular use to the public and to policy makers. The last such report was on the use of directed energy weapons for missile defense. [1] This is another report in that tradition.
Executive Summary
Boost-phase intercept systems for defending the United States against ballistic missile attack are being actively considered as a major part of a national missile defense strategy. Spending on such systems by the U.S. Department of Defense is growing, and there is a prospect of much larger expenditures in the future. Boost-phase intercept weapons would seek to disable attacking missiles during the first few minutes of flight, while the missiles' boosters are still burning and before they have released nuclear, chemical, or biological munitions. The technical aspects and feasibility of such weapons are the subject of this report.
In spite of the growing interest in boost-phase intercept systems and the increasing resources being committed to developing them, little quantitative information about their technical feasibility, required performance, and potential advantages and disadvantages is available to the public. Consequently, the American Physical Society (APS) convened a study group of physicists and engineers, including individuals with expertise in sensors, missiles, rocket interceptors, guidance and control, high-powered lasers, and missile-defense-related systems, to assess the technical feasibility of boost-phase intercept systems.
The Study Group has based its assessments solely on information found in the open literature about ballistic missiles and missile defense. We have supplemented this information by our expertise in science and engineering and have confined the assessments reported here to those that can be made with confidence by applying the fundamental principles of rocket propulsion, signal detection and processing, guidance and control, and laser beam propagation. In many instances, as documented throughout this report, we have performed our own analyses to address important issues and to assure ourselves of the validity of our conclusions.
Our main conclusions are the following:
Boost-phase defense against intercontinental ballistic missiles (ICBMs) hinges on the burn time of the attacking missile and the speed of the defending interceptor rocket. Defense of the entire United States against liquid-propellant ICBMs, such as those deployed early by the Soviet Union and the People's Republic of China (China), launched from countries such as the Democratic People's Republic of Korea (North Korea) and Iran, may be technically feasible using terrestrial (land-, sea-, or air-based) interceptors. However, the interceptor rockets would have to be substantially faster (and therefore necessarily larger) than those usually proposed in order to reach the ICBMs in time from international waters or neighboring countries willing to host the interceptors. The system would also require the capability to cope with at least the simplest of countermeasures.
Boost-phase defense of the entire United States against solid-propellant ICBMs, which have shorter burn times than liquid-propellant ICBMs, is unlikely to be practical when all factors are considered, no matter where or how interceptors are based. Even with optimistic assumptions, a terrestrial-based system would require very large interceptors with extremely high speeds and accelerations to defeat a solid-propellant ICBM launched from even a small country such as North Korea. Even such high-performance interceptors could not defend against solid-propellant ICBMs launched from Iran, because they could not be based close enough to disable the missiles before they deployed their munitions.
If interceptor rockets were based in space, their coverage would not be constrained by geography, but they would confront the same time constraints and engagement uncertainties as terrestrial-based interceptors. Consequently, their kill vehicles (the final homing stage of the interceptors) would have to be similar in size to those of terrestrial-based interceptors. With the technology we judge could become available within the next 15 years, defending against a single ICBM would require a thousand or more interceptors for a system having the lowest possible mass and providing realistic decision time. Deploying such a system would require at least a five- to tenfold increase over current U.S. space-launch rates.
The Airborne Laser now under development could have some capability against liquid-propellant missiles, but it would be ineffective against solid-propellant ICBMs, which are more heat-resistant.
The existing U.S. Navy Aegis system, using an interceptor rocket similar to the Standard Missile 2, should be capable of defending against short- or medium-range missiles launched from ships, barges, or other platforms off U.S. coasts. However, interceptor rockets would have to be positioned within a few tens of kilometers of the launch location of the attacking missile.
A key problem inherent in boost-phase defense is munitions shortfall: although a successful intercept would prevent munitions from reaching their target, it could cause live nuclear, chemical, or biological munitions to fall on populated areas short of the target, in the United States or other countries. Timing intercepts accurately enough to avoid this problem would be difficult.
The full report and additional information can be found at www.aps.org/public_affairs/
Report to the American Physical Society of the Study Group on Science and Technology of Directed Energy Weapons, Rev. Mod. Phys., Vol. 59, No. 3, Part II, 1987.
