America's "Star Wars" strategic defense system is being designed to stop a Soviet attack by intercepting missiles and warheads in space, where they can supposedly do no harm. In the simulations shown on television, a laser beam or a "kinetic kill" vehicle slams into the attacking missile, which then vanishes in a harmless puff of smoke and flame.
Reality is apt to be much different.
Assume that the worst--and best--happens. Deterrence fails; the Soviets launch, and the American strategic defense system works essentially as imagined. What comes next is not in the TV animator's script: Some attacking warheads are destroyed or disabled above Earth's atmosphere, but most are not; some are simply bumped off-course as they continue their trajectory back down to Earth.
The vehicles that carry the weapons on ballistic missiles and protect them against the stresses associated with their trip back through the atmosphere from space are among the most rugged devices ever built. They must shield against temperatures almost as high as those on the surface of the sun, and be able to take sustained forces of more than 10 times that of gravity. Even the explosion of the booster carrying such re-entry vehicles will not destroy them. The crew compartment of the space shuttle Challenger was far weaker, and yet it survived the fireball essentially intact.
The warheads carried by a Soviet missile destroyed in flight will continue on, following their original trajectories or taking an errant course. The warheads on intercontinental missiles shot down relatively early in their boost phase will not be moving very rapidly, and probably will land in the Soviet Union.
The more time an offensive rocket has to accelerate, the faster its weapons will be traveling if and when the rocket is blown up by a defensive missile. Its warheads will continue in flight for thousands of miles. They might reach the continental United States--or fall just a few miles short or off-target in the ocean, or on Mexico or Canada.
Warheads that successfully re-enter the atmosphere will almost certainly explode, regardless of whether they hit the targets that their makers intended or whether they are far off-course, headed for a Canadian village or an empty cornfield. This possibility makes moot the debate about targeting or defending military installations instead of civilian populations.
Nuclear missiles intercepted in mid-course high above the atmosphere while on ballistic trajectories toward their targets might explode when hit, or might not. An attacker, hoping to interfere with a defender's weapons and strategy, might equip his warheads with "salvage fuzes." A salvage fuze is nothing but a simple sensor that tells the warhead, "We're hit--blow up while you've got a chance!" Salvage fuzes have an edge of several milliseconds to trigger the nuclear weapon before the defending missile can shatter it into impotent pieces.
It would, of course, be best if Soviet warheads exploded high in space, rather than at their targets, but nuclear explosions in space are not without consequences. The electromagnetic pulse from even a single weapon can knock out the electric power grid of half a continent; we cannot even speculate on the immensity of the damage to electrical and electronic systems that dozens or hundreds of near-simultaneous bursts would inflict. In any event, the first few explosions might well cripple the rest of the U.S. defense system and allow the rest of the Soviet attack to get through.
Even if the warheads are intercepted and disabled, the toxic radioactive plutonium that they carry will not vanish. If the weapons burn up on re-entry, the plutonium will burn with them and spread throughout the atmosphere. That radiation, however, will be small in comparison to the fallout from weapons that do explode.
If the warheads reach the ground intact, but without exploding, the plutonium may escape and contaminate an area of up to a few square miles, causing local hot spots. The Soviet arsenal of about 10,000 strategic nuclear warheads probably contains close to 50 tons of plutonium, much of which would be widely dispersed even if U.S. interception efforts turned out to be 100% successful.
Of course, a defended United States would suffer less damage in a nuclear war than if it had no strategic defenses. However, we only would be spared immediate damage, probably at the expense of non-belligerent neighbors. In reality, the end of the cartoon simulation is the beginning of what will be a disaster of incredible magnitude, respecting no boundaries anywhere.
Since strategic defenses, either Soviet or American, may diminish crisis stability, on balance they probably can be viewed as more likely to cause than to avert nuclear disaster--even if they work.