From New Scientist
In the line of fire New York might feel safe but what about Denver, Edinburgh or Berlin?
MISSILES targeted at US cities and intercepted by Bush's proposed missile defence shield could fall on Europe, Canada or middle America instead, arms researchers warn.
Bush's missile defense plan includes a system to intercept intercontinental ballistic missiles (ICBMs) just minutes after launch, while their rocket boosters are still burning. This "boost-phase interception" should be easier than targeting missiles in mid-flight because tracking a flaming rocket is easier than homing in on a relatively cool and easily disguised warhead sailing high above the atmosphere, experts say.
But destroying only the booster could leave the warhead zinging across the sky, says Ted Postol, a physicist at the Massachusetts Institute of Technology. Precisely where the warhead would land would depend on when the booster was destroyed during its 4 to 6-minute burn. That would be difficult to control, so the warhead could potentially hit anywhere between the launch site and the target city, Postol says.
This means that a nuclear missile fired at the US from North Korea could explode over Alaska or Canada, while one fired from Iraq might strike Britain or mainland Europe.
"Even if you knew all the details, you couldn't be sure of what would happen in any given engagement," Postol says.
The US is considering several options for boost-phase interception. One is a powerful airborne laser mounted inside a modified Boeing 747 that the Air Force is developing to intercept shorter-range missiles. The laser's beam could burn a hole in the thin skin of an ICBM's booster, says Geoff Forden, a physicist at MIT. But it cannot destroy an ICBM warhead, which is designed to withstand tremendous heat while re-entering the atmosphere, he says.
To destroy the warhead itself during the boost phase would need a larger and more manoeuvrable interceptor than anything the US is currently developing, Postol says. It would have to be launched from the ground or the sea, and then specifically target the warhead-perhaps by aiming a stream of shrapnel at it. "There are technologies that overcome this narrowly defined problem," Postol says, "but they look nothing like what the Bush administration is considering."
Researchers disagree on whether a system that simply caused the warhead to fall short could be judged a success or a failure. If it hit land, the warhead would most likely hit a relatively uninhabited area and kill far fewer people than intended, says veteran physicist Richard Garwin, who helped develop the American H-bomb. That fact should deter nations such as North Korea or Iraq from launching a missile at the US, he says, if they were ever tempted to do so.
But Forden questions this. "The guys who might launch this thing probably won't care enough to say if it doesn't hit New York, I don't want to launch it at all."
The shortfall problem could, however, increase tensions between the US and its allies, says George Lewis, a physicist at MIT. "If you ask how many people are going to be killed, on average, you're clearly better off having the warhead fall short," he says. "But the people who it's going to land on may have a different view."
Author: Adrian Cho
New Scientist issue: 1 September 2001
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