On a collision course

An upcoming test will require the national missile defense system to strike

down a Minuteman II intercontinental ballistic missile carrying a single

warhead target and a single decoy. The Minuteman will be launched from Vandenburg

Air Force Base, Calif. Twenty minutes later, an interceptor missile carrying

a prototype "kill vehicle" will be launched from Kwajalein atoll in the

Pacific Ocean and should home in on and clash directly with the target warhead.

Intercepting an incoming missile begins with the space-based warning

system, which detects a booster launch. The Defense Support Program is already

in place, and the Pentagon is upgrading that with a system known as Space

Based Infrared System-High, which has greater sensitivity and greater ability

to predict trajectories.

The space-based detection system passes the information through the

command and control system to the early-warning radars, which have already

been deployed in various places around the globe. The radars track the incoming

missiles, providing preliminary data on where the incoming missile is headed

and other information necessary for the intercept.

That information is passed to the so-called X-band radars, which are

small frequency radars that one member of Congress says can detect a golf

ball high over Seattle from hundreds of miles away. It is primarily the

X-band radars that distinguish harmless decoys from destructive warheads.

Once the warheads are pinpointed, the ground-based interceptor is launched.

It consists of a booster and the so-called kill vehicle, which, if necessary,

can receive updated or corrected flight information from the X-band radar

while in flight. The kill vehicle does its own final analysis and zips along

at a smooth 12,000 miles an hour for the hit-to-kill collision.