Bomb Blocking.

What can we do now? What do we need?

George W. Bush campaigned on the issue of missile defense, criticizing his predecessor for leaving America and her allies undefended. He promised that as President he would pursue robust protections against ballistic missile attack.

But is such a system technologically feasible?

While missile defense does require complex engineering, recent advances in computers, sensors, missile design, and laser construction provide many options for defense against ballistic missiles that would be both affordable and available in the near future. The real question is whether missile defense will receive sufficient funding and national priority. So far it is less technological constraints than the Clinton administration's political decisions that have delayed the arrival of effective missile defense.

Shielding a nation against ballistic missiles is a demanding assignment. A defense must be able to detect a missile launch, track the missile and its payload throughout its trajectory, discriminate between warheads and decoys, then intercept and destroy the warheads, some of which may maneuver evasively once they re-enter the earth's atmosphere, at peak speeds of up to 16,000 miles per hour.

The flight of a ballistic missile can be broken down into three phases: the boost phase, the mid-course phase, and the terminal phase. A ballistic missile is most vulnerable during the boost phase. As it takes off, its speed is relatively slow and it hasn't yet deployed its payload of re-entry vehicles and decoys.

During the mid-course phase, the vehicle leaves the earth's atmosphere, and the warheads and decoys deploy. Since this phase takes place in the vacuum of space, tinfoil decoys and heavy warheads travel at the same velocity, and it is difficult for radar to distinguish between them. On the other hand, infrared sensors are able to tell the difference because the decoys cool in the surrounding space faster than the warheads.