Philip E. Coyle, prop in hand, explains the difficulties of ballistic missile defense. [AAAS/Earl Lane] America's ground-based defense against incoming ballistic missile warheads is unlikely to work as planned because radars and other essential elements of the system are flawed or missing, a leading defense analyst said at a recent panel discussion organized jointly by AAAS and the Federation of American Scientists. Similar issues plague an American-led effort to develop a regional missile defense system for Europe, said Philip E. Coyle, senior science fellow at the Center for Arms Control and Non-Proliferation. Coyle previously held top defense and technology positions in both Republican and Democratic administrations.
Despite billions of dollars invested in technology development, Coyle said, the basic architectures of both anti-missile systems "are in doubt because so many parts don't work, don't exist, or aren't achievable." He cited, among other problems, the poor performance of radars and other sensors essential to discriminate whether an incoming object is a warhead or a decoy.
The current U.S. system for intercepting incoming warheads from space is called the Ground-Based Midcourse Defense or GMD. It has been operational since 2004, with 26 interceptor rockets based in Alaska and four in California. It is intended to defend the United States against limited strikes by intercontinental ballistic missiles (ICBMs) that might be developed by countries such as North Korea or Iran.
George Lewis [AAAS/Earl Lane]
George Lewis, senior research associate at Cornell University's Judith Reppy Institute for Peace and Conflict Studies, also raised serious questions about the adequacy of the U.S. ground-based missile defense, particularly its ability to cope with countermeasures meant to spoof or overwhelm the system. "You're building the world's most complicated machine," Lewis said, "and it has to work the first time it is used."
Despite such concerns, another panelist argued that perceptions about the expected performance of U.S. ballistic missile defenses are at least as important to deterrence as the real capability of the systems. Bruce W. MacDonald, an independent defense consultant and adjunct professor at the Johns Hopkins School of Advanced International Studies, said most U.S. adversaries have a high respect for American military technology.
"To the extent U.S. confidence in its BMD (ballistic missile defense) falls short of perfection," he said, "adversary confidence in its ability to penetrate U.S. missile defenses does not increase by a corresponding amount, or anywhere near it."
The mutual uncertainties give rise to a deterrence that is not trivial, MacDonald said, although he acknowledged that it may not be as robust in the case of an Iran, which can bring far more resources to developing capable long-range missiles, than a North Korea.
For his part, Coyle said the current threat scenarios fail to meet the test of common sense. "I personally don't believe that either North Korea or Iran is so suicidal as to attack the U.S. homeland," he said.
The 6 June discussion on technical, strategic and arms control challenges for ballistic missile defense was held at the AAAS Auditorium. It was moderated by Pierce Corden, a visiting scholar with the AAAS Center for Science, Technology, and Security Policy, and Charles D. Ferguson, president of the Federation of American Scientists.
Coyle and Lewis, citing reviews by the Defense Science Board, the National Research Council, the U.S. Government Accountability Office and others, said some of the goals of the ground-based defense system remain out of reach, including the ability to quickly do "kill assessment" between each shot, selecting those objects that need to be targeted and those that can be ignored.
"This would require sensors and discrimination we don't have, or know how to do," Coyle said.
The system has been tested so far only against shorter range missiles rather than the ICBMs it is designed to bring down. Of the 17 interceptor flight tests since 1997, Coyle said, only eight have been successful, the last of those in 2008.
Lewis said the projected reliability numbers for the system — percentages in the high 90s — are overstated and adding more interceptors will not, by itself, increase the system's effectiveness. The Obama administration, citing concerns about North Korea's long-range missile advances, recently announced plans to add 14 more interceptors, bringing the total to 44 as originally envisioned by the Bush administration.
To accomplish true mid-course interception of a threatening missile, the defense system must track the missile just after it is launched and during its suborbital flight toward its target. The system uses satellite-based sensors to detect the missile's launch and a variety of ground- and sea-based radars to track it during flight. These include four (and eventually six) upgraded early warning radars that date back to the Cold War era, forward-based mobile radars called TPY-2s in Turkey and Japan, Aegis radars on Navy cruisers and destroyers, and a large radar called SBX that is based on a floating platform at sea.
According to Lewis, the early-warning radars can track small targets or clusters of targets but have essentially no ability to distinguish between a warhead and a booster rocket stage or debris. The TPY-2s and the SBX use microwaves in the X-band segment of the electromagnetic spectrum, with wavelengths twenty times smaller than those of the early warning radars. In theory, these shorter wavelengths should provide higher-resolution images of the targets, Lewis said.
Bruce W. MacDonald [AAAS/Earl Lane]
But the measure of how detectable a warhead is by radar (its radar cross section) can be quite small, depending on the size of the object, the material of which it is made, the angle at which the radar beam hits the object, and other factors. That makes it very difficult, even for the available X-band radars, to reliably discriminate between true warheads and countermeasures such as decoys or pieces of chaff made of aluminum or other materials. Moreover, the SBX, the most powerful X-band radar in the system, has been semi-mothballed due to budget constraints, Lewis said. (A National Academy of Sciences study panel has recommended deployment of new X-band radars consisting of stacked TPY-2s at five locations around the world.)
Coyle and Lewis said similar radar discrimination issues surround the proposed missile-defense system for Europe, called the European Phased Adaptive Approach (EPAA). The system is meant to protect Europe from missiles launched from Iran. The Obama administration, like the Bush administration before it, must take into account concerns by Russia and China that efforts to deploy such a regional defense shield might weaken the deterrent effect of their strategic missiles since they could be more vulnerable to interception.
MacDonald said the deployment of defenses against limited missile strikes can work to the geopolitical advantage of the United States, however. He cited the administration's decision to deploy the 14 additional interceptors. For years, China claimed it could do little to curb North Korea's provocative behavior, MacDonald said. But within days after the U.S. announcement, Pyongyang's harsh rhetoric toward South Korea stopped and its border forces stood down. MacDonald said it is likely China brought pressure to bear on North Korea after realizing its behavior could directly threaten the viability of China's nuclear deterrent.
Discussion moderators Pierce Corden and Charles D. Ferguson. [AAAS/Earl Lane]