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Faster Than a Speeding Bullet
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# : |
19862 |
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Section : |
NATURAL SCIENCE
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| Issue
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5 / 1991 |
2,216 Words |
| Author
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Hank Hogan
Hank Hogan is a science writer in Austin, Texas. |
There's an arms race on. It doesn't grab headlines or invoke superpower summits, and it hasn't disappeared with the end of the Cold War. The war with Iraq showed some rather amazing technology at work, limiting allied and civilian casualities alike. But the guns and cannons, though aimed at their targets with all the precision of modern technology, still depend on chemical techniques that are centuries old.
That may be changing, as a new technology based on electric instead of chemical propulsion emerges. Electric guns may be the weapons with which battles of the next war against tyranny are fought, if another is ever necessary, and the approach may have applications that are literally out of this world.
"The launching of satellites into space is something that's been of interest to a lot of us," says Harry D. Fair, director of the Institute for Advanced Technology in Austin, Texas. The institute is one of the leading electric gun research centers.
Over a barrel
Chemically powered guns and cannons have been around for centuries. Why abandon an approach that has been honed to perfection over half a millennium?
The answer to that question lies in fundamental limitations of the existing technology. In conventional weapons, the barrel walls and the rear of the projectile form a combustion chamber. Burning the appropriate chemicals inside the combustion chamber produces heat, and that makes gases within the chamber expand. The expanding gases push against the projectile and accelerate it forward.
There is an important point about this whole process. The projectile can't move any faster than the gas that's pushing it. And just what is this maximum gas velocity? That turns out to be fundamentally tied, Fair says, to the speed of sound in the high-pressure combustion region behind the projectile.
That upper velocity limits the best of today's cannons to about one mile per second. That's a respectable number, and in the past it would have been adequate for military needs. However, the development of new materials has resulted in stronger armor. Another introduction is known as reactive armor. Because of its construction, reactive armor destroys an incoming projectile before it can do any
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