Defense Secretary Donald H. Rumsfeld has opened the door to the possible use of nuclear-tipped interceptors in a national missile defense system, reviving an idea that U.S. authorities rejected nearly three decades ago as technically problematic and politically unacceptable.
William Schneider Jr., chairman of the Defense Science Board, said yesterday that he had received encouragement from Rumsfeld to begin exploring the idea as part of an upcoming study of alternative approaches to intercepting enemy missiles.
"We've talked about it as something that he's interested in looking at," Schneider said in an interview.
The Pentagon experimented with nuclear-armed interceptors in the 1950s and 1960s and, for a short time in the mid-1970s, deployed an anti-missile system that relied on them. But the notion of nuclear explosions going off high overhead to block incoming missiles proved unsettling for many people. And the prospect that ionized clouds and electromagnetic shock waves associated with the explosions could end up blinding radar on the ground and scrambling electronic equipment eventually helped kill the plan.
Since then, defense officials have focused on developing interceptors to destroy targets without the need for explosives, relying instead on the force of direct impact, a concept known as "hit to kill."
Driving the new interest in arming interceptors with nuclear devices is the problem of dealing with decoys and other measures that an enemy might use to confuse an interceptor, Schneider said.
The hit-to-kill approach depends on interceptors picking out the real enemy targets and homing in on them. By contrast, nuclear-armed interceptors need not distinguish actual targets from clusters of decoys but could rely on explosive power or radiation to wipe out everything in the vicinity.
One other arguable advantage of nuclear interceptors, Schneider suggested, is their potential for ensuring destruction of missile-borne biological warfare agents such as anthrax.
President Bush has made clear his interest in pursuing technological solutions to missile defense, removing long-standing constraints by deciding last December to withdraw the United States from the 1972 Anti-Ballistic Missile Treaty with Moscow.
The Pentagon has embarked on experimental anti-missile programs, including land- and sea-based interceptors as well as airborne lasers and space-based weapons, with the hope of having at least a rudimentary capability in place by fall 2004. But until now, defense officials had shied away from the nuclear option.
An extensive Pentagon review of missile defense alternatives undertaken in the first months of the Bush administration raised the possibility of nuclear-tipped interceptors, according to two officials familiar with the review. But the idea failed to make the list of programs worth funding.
Its return comes in the context of other recent signs of the administration's general readiness to consider broader uses of nuclear weapons. A Pentagon review of U.S. nuclear policy, concluded late last year, put new emphasis on possible nuclear strikes against Third World adversaries and backed development of low-yield nuclear bombs to hit hardened or deeply buried targets.
Russia, which built a missile defense system around Moscow in the 1960s that survives to this day, relied from the start on nuclear-armed interceptors. Although U.S. defense experts regard the Russian system as anachronistic, Russian military officials worry that the United States will eventually adopt the nuclear approach, according to Pavel Podvig, editor of an authoritative book about Russian strategic nuclear forces published last year by the Center for Arms Control Studies in Moscow.
"They believe strongly that you cannot get an effective missile defense system using hit-to-kill," Podvig said.
The Defense Science Board, set up in the 1950s, is a senior advisory body that reports to the secretary of defense on technological, operational and managerial matters. One of its task forces already is looking at some aspects of missile defense, including command and control systems, international cooperation and countermeasures such as decoys. Schneider said he plans to initiate the review of nuclear interceptors and other alternatives to hit-to-kill after the task force completes its study this summer.
"The issue hasn't been looked at for about 30 years," said Schneider, a consultant and undersecretary of state for security assistance under President Ronald Reagan. "The last test involved a four-megaton device on a Spartan interceptor in 1971."
Richard L. Garwin, a senior fellow at the Council on Foreign Relations and prominent missile defense skeptic, said nuclear interceptors still pose several significant technical problems.
"When you actually look at the question, you find that it takes a very large warhead -- more than a megaton -- to destroy anthrax spores in bomblets that may be spread over a distance of five kilometers or more," he said.
"Worse, there are hundreds of civilian satellites as well as many U.S. military satellites vital to our national security that would be imperiled by nuclear explosions. And there are electromagnetic pulse vulnerabilities in an advanced society such as ours that would occur to any point within line-of-sight of the nuclear explosions."
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