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Things That Go Bump in the Night
12/14/2007
Gradually though things got better. By summer parts of the power grid were back on line and emergency transportation was being restored for the distribution of food and medical supplies. Many older vehicles as well as a few newer ones were still operable. At a staggering human cost we'd learned just how fragile our high tech society really was. The Story Was Fictional, but Could It Happen?
The short answer is yes. It sounds like science fiction, but it is based on science fact. If a small nuclear device were detonated 400 kilometers (250 miles) over Kansas, an electromagnetic pulse of destructive force would blanket the continental United States.
We know it could happen because it's already been done. On July 9, 1962 the United States detonated a 1.4 megaton thermonuclear warhead 400 kilometers (250 miles) above Johnston Island in the Pacific Ocean. That test, called Starfish Prime, caused the failure of electronics systems, knocked out streetlights, and fused power lines in Hawaii 1,500 kilometers (930 miles) away. The Soviets had similar experiences during their atmospheric test programs.
The common perception of an atomic explosion is one near the surface of the earth, complete with a mushroom cloud, massive blast and thermal damage, and radioactive fallout. A high-altitude explosion is much different. Blast and thermal damage as well as radioactive fallout are negligible. However, a new phenomenon, an electromagnetic pulse, becomes important. When a nuclear device explodes, it emits a burst of gamma radiation. As the gamma radiation hits air molecules, electrons are knocked loose. These electrons are quickly stopped in the dense air found near the surface of the earth. However, at altitudes between 20 and 40 kilometers (13 to 25 miles), these electrons become trapped in the earth's magnetic field giving rise to an electromagnetic pulse. Since the burst of gamma radiation is almost instantaneous and very brief, on the order of nanoseconds, the electromagnetic pulse is similarly very intense and very brief.
An electromagnetic pulse can be compared to lightning, which has a very high voltage and current, but for a very short duration. The EMP from a high altitude nuclear explosion, however, is more intense and even briefer. The effect of such an EMP would be much like lightning striking every building and every power pole in the United States at precisely the same time. The only difference is that the "surge" protectors that we have all installed to protect our computers wouldn't be fast enough to stop the pulse. Ergo, fried computers.
As less publicized
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