Missile Impossible?

Ten...nine...eight...seven..."

On a heavily guarded launchpad at Vandenberg Air Force Base, 125 miles up the Pacific Coast from Los Angeles, a 63-ft.-tall gleaming white rocket sits and waits. Secreted in the nose of the 37-year-old Minuteman II is a 5-ft.-long cone--a mock warhead--and a deflated Mylar balloon. Let's say they are part of an incoming missile from North Korea or Iran. Meanwhile...

Six...five...four...

About 4,800 miles away on Kwajalein Atoll, perched atop a Pacific coral reef, another rocket sits and waits. Nestled inside its nose cone is a $20 million bullet known as the exoatmospheric kill vehicle. It looks more like a mobile moonshine still than a snub-nosed round, but in the vacuum of space, there are no points for style. Its job is to find and then destroy the incoming "warhead" from Pyongyang or Tehran.

"Three...two...one...Ignition."

This Friday, sometime between 7 and 11 p.m. Pacific time, the Pentagon plans to fire the rocket from California, then fire the interceptor from the Pacific. It hopes the resulting collision will persuade President Clinton to give the order to start building a $30 billion system to protect the U.S. from missile attack. Success could signal the most profound change in U.S. national security since Washington decided to contain Soviet expansionism in 1947. That is why so much is riding on this week's test for the military, its contractors and the space shield's many proponents in Washington.

This decisive test is the third in a planned series of 19 for the Pentagon's projected National Missile Defense system. While Pentagon officers insist there will be future chances to halt its construction, a success this week could make that politically all but impossible. Congress is chafing to fund the system (see following story) and was heartened by the first test, in which an interceptor pulverized a fake warhead last October. In a second test in January, however, the interceptor missed its target by 241 ft. when a cooling line clogged and shut down its heat-seeking sensors. As a TIME investigation shows, little is being left to chance this time. So little, in fact, that this may be a test in name only--an expensive piece of Potemkin performance art to win enormous military appropriations. Exactly what is going to be tested on Friday?

There are virtually no unknowns in the procedure. The Pentagon knows the type of rocket launching the target as well as the nature of the target; it knows how powerful the rocket's engine is, where it is coming from and when it is being launched. The crew launching the interceptor will even get to listen in on the countdown of the warhead's rocket as it takes place. All that is valuable intelligence--and much, if not all of it, would be denied to the U.S. if a rogue state decided to strike. Such advantages "place significant limitations" on the value of the test, says Philip Coyle, the Pentagon's chief weapons tester.