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America's space-age missile defense sounds like something out of Star Wars. But will it work?

This was only a test of the Pentagon's National Missile Defense System -- with $100 million riding on the results.

Last January, a 60-foot-long American missile loaded with a mock warhead roared out of its silo on the central California coast. Seconds later, nearly 7,000 kilometers (4,350 miles) away in the South Pacific's Marshal Islands, another missile--this one an "interceptor"--streaked into the sky. Nestled inside the interceptor's nose sat the world's most sophisticated high-tech bullet: a 48.5 kilogram (130 pound)-device known as an exoatmospheric kill vehicle, built to destroy enemy missiles in space before they ever reach the U.S.

Here's what was supposed to happen: Posing as an "enemy," the California rocket would soar 1,609 km (1,000 mi) above Earth and release its mock warhead plus a decoy balloon. In an actual nuclear missile, a burst of decoys would serve to lure an interceptor from its intended target. But through an arsenal of Star Wars-type gadgetry, the interceptor with its kill vehicle would hunt its prey at 241 km (4,900 mi) per hour and smash the warhead.

That's not what happened last January, however. Seconds before contact, the kill vehicle veered by 73 meters (241 feet) and missed. The $100 million test proved a real bomb.


Defense scientists say a blown cooling pipe may have caused the failure, but insist the U.S. needs to build the highly controversial $60 billion defense system. "The threat of nuclear missiles is suddenly a major concern again," says Mike Biddle, a U.S. Defense Department spokesman. That's because a few aggressive nations are trying to build nuclear warheads and the missiles needed to launch them. If President Clinton gives the go ahead this fall, the first 25 missile interceptors will be ready within five years. But will it spark a new arms race? Is the new system too pricey? And will it even work? In the first three out of 19 planned tests--including a miss in the most recent test in July--the system has hit a dummy warhead only once.


If an enemy group or country were to attack the U.S., a missile carrying a nuclear warhead would take 30 minutes to reach and decimate a U.S. city. Warheads contain a nuclear bomb, which relies on fusion energy (the joining together under intense heat of two atoms to form a heavier element), the same force that fuels the sun. Hydrogen atoms (a gas, the lightest of all elements) fuse together, producing helium (another gas and the second lightest element). The fusion process releases vast amounts of energy. A typical one-megaton bomb detonates with a force equal to 1 million tons of dynamite at more than 111 million [degrees] C (200 million [degrees] F)--six times as scalding as the sun's center.

Such a bomb would reduce everything within a 3.2 km (2 mi) radius to rubble and kill 98 percent of the immediate population almost instantly. Those living 8 km (5 mi) away might survive the initial blast, but nuclear bombs also release waves of radioactive energy (energy released when an atom loses particles from its nucleus). Known as fallout, the waves travel on wind currents, blanketing Earth with radioactive material hundreds of miles away from the blast. Exposure to fallout causes increased cancer rates and birth defects in humans.


Military scientists say a missile shield would block a nuclear attack. Here's how it would ideally work: When an enemy missile is launched, early-warning satellites 35,406 km (22,000 mi) above Earth detect its presence through infrared sensors that measure heat waves emitted by hot objects. The satellites fire location data to the U.S. Space Command's center inside Cheyenne Mountain in Colorado.

Ground-based radar installations then track the missile. Thrusters propel nuclear missiles high enough into outer space to reach the U.S. from across the globe. Then the missile nose breaks apart into a barrage of warhead-like objects (see diagram, p. 17). All are decoys except for one nuclear warhead capable of catastrophic devastation.


Meanwhile special U.S. X-band radar tracks the warhead and decoys. (Conventional radar determines the position of distant objects by bouncing energy waves off them, but X-band radar beams high-energy waves that can reach outer space with pinpoint accuracy.) "It can be aimed like a flashlight," Biddle says.

Analyzing the radar data, computers in Colorado calculate when to launch a defensive missile, and at the precise moment, a U.S. missile blasts off in Alaska. After a three-stage burn, the boosters fall away, leaving only the kill vehicle. It's equipped with a pair of high-tech "eyes": two infrared sensors cooled to -184 [degrees] C (-300 [degrees] F). The sensors detect even the faintest heat in outer space, and an on-board computer uses algorithms--complex mathematical calculations--to distinguish between a real warhead and fakes.

The kill vehicle smashes the war head on impact. "It locks onto the warhead," says Ronald Kadish, director of the Pentagon's missile defense program, "and collides at a speed of 7.4 km (4.6 mi) per second. At that speed, there's nothing left of the warhead."


Scientists hotly disagree whether a missile defense system would work. Many think a kill vehicle's sensors will never be accurate enough to distinguish between decoys and a nuclear warhead. Other critics say a nuclear shield is outrageously expensive and unnecessary. Still others believe the U.S. needs a complex missile defense system to avert the threat and destruction of nuclear war. What do you think?


The cornerstone of the President's $60 billion program to defend the U.S. from nuclear attack is an interceptor missile that would knock an incoming nuclear warhead out of the sky. Here's an illustration of how it's supposed to work:

enemy missile

Delivers one nuclear warhead and a burst of decoys


Warhead-like objects designed to fake out interceptors


The nuclear bomb--if it gets through, millions could die


Tracks the enemy missile and helps guide the interceptor missile.

interceptor missile

Releases the kill vehicle, whose high-tech sensors hone in on the enemy warhead


The kill vehicle makes a direct hit, smashing the warhead.

What if a Bomb Fell on New York City?

1. The initial blast blows open a 305 m (1,000 ft)-wide, 61 m (200 ft)-deep crater, demolishing all buildings and killing 955,000 people.

2. Nearly all buildings are destroyed; 750,000 people are killed, and 600,000 injured.

3. Buildings are destroyed or damaged, people and debris are thrown onto the streets; 25,000 die, 225,000 are injured.

4. Moderate building damage, few immediate deaths; flying-debris injuries; severe to fatal radiation doses.

A plume of radiation, or fallout, blows east over Long Island, killing many of the 2.8 million residents within two weeks. Some radiation could reach Boston or Washington D.C., poisoning millions more. Result: genetic damage, widespread cancer years later.



Cross-Curricular Connection

History: Read about the long-term health consequences of radiation on the populations of Hiroshima and Nagasaki. What happened to citizens when the bombs fell? Five years later? Today?

Did You Know?

* The U.S. has a virtual constellation of early-warning satellites floating 35,406 kilometers (22,000 miles) above Earth.

* A missile interceptor navigates by finding stars that match a "map" stored in its memory chips.

* X-band radar has shorter waves than conventional radar, allowing it to "draw" a clear image of flying objects up to 1,600 kilometers (995 miles) away.

National Science Education Standards

Grades 5-8: properties and changes of properties in matter * transfer of energy * understanding about science and technology * abilities of technological design

Grades 9-12: atoms * structure and properties of matter * interactions of energy and matter * understanding about science and technology * abilities of technological design


"The Nuclear Shield: Repelling an Attack; A Missile Defense With Limits: The ABC's of the Clinton Plan," The New York Times, June 30, 2000.

National Missile Defense Program:

This Boeing site includes many photos and a video clip: space/nmd/index.html
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Title Annotation:National Missile Defense System; test of National Missile Defense System
Publication:Science World
Geographic Code:1USA
Date:Oct 2, 2000
Previous Article:Sky Show.
Next Article:Can a goldfish live in a can of soda?

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