Missile Impossible?

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The trouble is that in this week's test the interceptor won't rely solely on satellites and early-warning radars to trace its target. It will be looking for a target traveling a familiar path--the same California-to-Kwajalein arc used in the previous two tests. And this relatively short distance--as well as safety concerns--means the mock warhead won't be traveling as fast as a genuinely hostile one. This "single end-game geometry," said an independent review panel headed by retired General Larry Welch last fall, "raises questions about the ability of the flight-test program to verify system performance." The Pentagon says it will use computer simulations to replicate other attack angles and ensure that the system can defend against incoming warheads following different paths.

The Pentagon concedes its tests don't mirror reality. Pentagon test watchdog Coyle tells TIME that all attempted intercepts until 2004 will occur with the defenders fully briefed in advance on the "timing, direction and countermeasures" employed. And, Coyle adds, because of safety concerns, even in later tests "the soldiers may have a pretty good idea about the timing, direction and nature of the threat."

In Friday's test, the interceptor will have other advantages that the final product will not possess. The mock warhead, in fact, will basically shout, "Here I am!" to those trying to shoot it down. That's because it will carry a global-positioning-system transmitter, the same satellite technology that keeps motorists from getting lost. Although Pentagon documents say GPS data will help guide the interceptor during test flights, program officials say the data will be used only if other methods fail. Any use of GPS data, says Coyle, "does not suitably stress the system in a realistic enough manner to support acquisition decisions."

In the minutes following the target's launch, the interceptor will receive updated maps as the mock warhead soars over the ocean. Then, like a thirsty traveler about to cross a desert, the interceptor will take a final gulp of data on its nemesis' whereabouts and expected route just before blasting off some 20 minutes after the California launch.

Less than three minutes after leaving Kwajalein, the interceptor--having discarded its boosters--will be flying solo. Zipping across the heavens at 4,900 m.p.h., it will be about 1,500 miles from its target. Over the next six to eight minutes, the interceptor will try to hunt down its prey and guide itself into a suicidal collision with the warhead. It will be receiving guidance from far below as early-warning radar systems detect the incoming warhead. These systems hand off data to a so-called X-band radar system based on Kwajalein, which stabs the sky with a narrow beam of electronic pulses. The X-band's shorter wavelengths and advanced signal-processing capabilities give it the power to "draw" a clear image of the incoming warheads and surrounding decoys from up to 1,000 miles away. (Ultimately, the system's $500 million X-band radar will be based on storm-tossed Shemya Island, Alaska.)

The X-band radar will send its data to the interceptor by way of a supersonic cell-phone system known as the in-flight interceptor communications system. Eventually, 14 IFICS stations will be built, arrayed in pairs in yet to be determined geographic regions. The Pentagon's environmental-impact statement says the pairings are needed to meet unspecified "reliability requirements." The Federation of American Scientists posits that placing the stations in pairs, fairly far apart, reduces the chances that in-flight communications will be lost because of storms that may develop over a single IFICS site.

Once free of its boosters, the interceptor's first job is to confirm where it is. It will do that by finding stars that match a map stored in its memory chips. Having fixed its own location, the interceptor will turn its telescope toward the target's expected location. As the interceptor and mock warhead travel to within 500 miles of each other, the interceptor should pick up the warhead, along with the decoy balloon and launch container. From here on out--in the final 100 seconds--the interceptor will be on its own, getting no guidance from the ground. But it will still be getting help. At this point, the balloon, the designated hindrance, will become the sly helper.

In Friday's test, the big, bright balloon will be the major decoy. (The launch container will play a similar but subordinate role.) But even Pentagon officials acknowledge that the balloon will act more like a beacon that alerts the interceptor to the nearby presence of the real target. The Pentagon concedes the October test might not have succeeded if the decoy hadn't appeared so vivid to the interceptor's sensors. "The large balloon aided in acquisition of the target," Coyle says. "It is uncertain whether the interceptor could have achieved an intercept in the absence of the balloon." In short, the decoy is hardly a decoy. Critics maintain that future interceptors will be unable to distinguish more muted decoys from warheads, especially at long distances and supersonic speeds.