The first line of defense in America's next anti-missile system fails or succeeds in a window of 90 seconds.
That's all the time there is, designers estimate, for a satellite to detect the flash of an enemy launch, determine that it is real and send off a counter-missile from the ground.
It all happens too fast to include a human in the loop.
"Time is of the essence," said Craig van Schilfgaarde, the Northrop Grumman Corp. engineer in charge of the project.
Known as "boost phase" interception, it is designed to be the first "layer" of defense, firing rockets at enemy missiles just after launch, when they are most vulnerable.
The military has deployed parts of the two other layers in the missile defense system - one targeting missiles as they cruise through space in mid-flight and the other aimed at descending warheads when they are just above their targets.
The three layers are the cornerstone of President Bush's plan to defend the United States against rogue nations, such as North Korea and Iran, that are gradually developing the ability to produce weapons with global reach.
But the system has faced serious problems.
The midcourse missile failed a test Dec. 15 when it shut down before leaving its silo at the Ronald Reagan Test Site at Kwajalein Atoll in the central Pacific Ocean. It was the second failure in a major test in two years.
On Dec. 17, the Pentagon announced that it was dropping plans to activate the existing pieces of the missile defense system this year because it had not completed full "shakedown" testing.
The boost phase reaches into an even more complex realm of design, in part because of the speed with which it must identify and destroy an enemy missile.
The payoff could be big. Terry Little, executive director of the government's Missile Defense Agency, said the boost-phase interceptors could destroy 80 percent to 90 percent of enemy ICBMs, leaving the other layers to take care of the rest.
But a recent Congressional Budget Office technical report suggested that the boost-phase system, scheduled for deployment in 2011, would press the far edge of what is physically possible in an anti-missile system.
Philip Coyle, who led the Pentagon's testing office during President Bill Clinton's administration, said the design of the boost-phase system is buckling under its own complexity.
"The [congressional] analysis confirmed that boost-phase missile defense isn't practicable," Coyle said.
