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Missiles targeted at US cities and intercepted by President Bush's
proposed missile defence shield could fall on Europe, Canada or middle
America instead, arms researchers warn.
Bush's missile defence 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.
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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.
Booster busting
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."
Success or failure
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." | 