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Authors: William R. Forstchen
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was making.
“Now, if my budget allowed for additional straws, I’d bundle six straws together, then put five on top of them, then four, and so on, and maybe we could build a tower fifty feet high of straws, but in the end it will collapse.
“Which definitely tells us we cannot build this tower of soda straws”—there was a bit of a playful smile—“unless we build a base inside the entire beltway around Washington and cover over the entire city.”
He paused.
“Actually, not a bad idea,” he muttered.
“So,” and he wrote a C next to the downward arrow, “first there is compression, which can be defeated only by expanding the base to an utterly absurd width.”
He then put a finger next to the arrow pointing up.
“So now we have our second problem, and that is vertical tensile strength. Not much of a problem for an earthbound tower a few miles high. But go out 23,000 miles?”
He shook his head.
“The centrifugal force imparted by the rotation of the earth will actually be trying to fling that tower up and away once you get out past…” He paused.
“Around 18,000 kilometers up,” Eva interjected, “but, yes, sir, that upper part will be imparting a tensile or extension pressure. But to a certain extent that relieves the compression. Also—and this is crucial—gravity decreasing at an inverse ratio becomes significant even when just a thousand kilometers up. This is where the entire formula gets very complex. The higher you go, the less the compression weight created by gravity and then eventually the tensile effect of it trying to pull itself apart from above. In part, this does cancel out the issue of compression once above a certain height.”
Erich smiled, as if pleased with an exceptional student, even as he fished a few more straws out of the pack and put all but one aside.
He held up the remaining straw, held one end, then pulled on the other, and it quickly stretched out and became distorted.
“So, even if you have something that can withstand the compression weight, it still has to hold up to the force that will try to stretch it out until it breaks and the upper part just goes flying off into space because of the momentum imparted by the earth’s rotation. That is one tough formula to play with, Miss Eva.”
She nodded without replying. It was obvious the old man had already prepared these responses and was a step ahead of any intern.
“Now, finally, the third force, which is lateral stress.”
This time he held up one straw and pushed at the midpoint: it buckled over.
“The difference in angular momentum the higher up you go and lower down within the atmosphere can be impacted even by terrestrial weather. You ever been up a tall building, like the World Trade Center towers in New York, during a storm? Those buildings are designed to sway as much as six feet, and they are only a thousand feet tall. Some people have to quit their jobs there because they keep getting motion sickness. In fact, NASA has helped more than one building designer with wind-tunnel testing.
“You figure out the square footage of a side of the tower: it gets hit by a hurricane all the way up through and beyond the stratosphere, and the lateral stress loads are enormous. Out in space you even have, of all things, the solar wind, minute but impacting during a major solar event. Along over 20,000 or more miles of structure, it would be noticeable, especially if there is a major solar storm or coronal mass ejection storm.
“Now let’s add in the fact that there are slight but noticeable anomalies in gravity, depending upon where you are above the earth’s surface. That really threw us off-balance when the first satellites were going up and their orbits seemed a bit odd because of that difference in gravity over different locations because the earth is not a perfect sphere. And then let’s add in the influence of the moon’s gravity, even the sun’s gravity. It all adds up to one heck of a
“Now, if my budget allowed for additional straws, I’d bundle six straws together, then put five on top of them, then four, and so on, and maybe we could build a tower fifty feet high of straws, but in the end it will collapse.
“Which definitely tells us we cannot build this tower of soda straws”—there was a bit of a playful smile—“unless we build a base inside the entire beltway around Washington and cover over the entire city.”
He paused.
“Actually, not a bad idea,” he muttered.
“So,” and he wrote a C next to the downward arrow, “first there is compression, which can be defeated only by expanding the base to an utterly absurd width.”
He then put a finger next to the arrow pointing up.
“So now we have our second problem, and that is vertical tensile strength. Not much of a problem for an earthbound tower a few miles high. But go out 23,000 miles?”
He shook his head.
“The centrifugal force imparted by the rotation of the earth will actually be trying to fling that tower up and away once you get out past…” He paused.
“Around 18,000 kilometers up,” Eva interjected, “but, yes, sir, that upper part will be imparting a tensile or extension pressure. But to a certain extent that relieves the compression. Also—and this is crucial—gravity decreasing at an inverse ratio becomes significant even when just a thousand kilometers up. This is where the entire formula gets very complex. The higher you go, the less the compression weight created by gravity and then eventually the tensile effect of it trying to pull itself apart from above. In part, this does cancel out the issue of compression once above a certain height.”
Erich smiled, as if pleased with an exceptional student, even as he fished a few more straws out of the pack and put all but one aside.
He held up the remaining straw, held one end, then pulled on the other, and it quickly stretched out and became distorted.
“So, even if you have something that can withstand the compression weight, it still has to hold up to the force that will try to stretch it out until it breaks and the upper part just goes flying off into space because of the momentum imparted by the earth’s rotation. That is one tough formula to play with, Miss Eva.”
She nodded without replying. It was obvious the old man had already prepared these responses and was a step ahead of any intern.
“Now, finally, the third force, which is lateral stress.”
This time he held up one straw and pushed at the midpoint: it buckled over.
“The difference in angular momentum the higher up you go and lower down within the atmosphere can be impacted even by terrestrial weather. You ever been up a tall building, like the World Trade Center towers in New York, during a storm? Those buildings are designed to sway as much as six feet, and they are only a thousand feet tall. Some people have to quit their jobs there because they keep getting motion sickness. In fact, NASA has helped more than one building designer with wind-tunnel testing.
“You figure out the square footage of a side of the tower: it gets hit by a hurricane all the way up through and beyond the stratosphere, and the lateral stress loads are enormous. Out in space you even have, of all things, the solar wind, minute but impacting during a major solar event. Along over 20,000 or more miles of structure, it would be noticeable, especially if there is a major solar storm or coronal mass ejection storm.
“Now let’s add in the fact that there are slight but noticeable anomalies in gravity, depending upon where you are above the earth’s surface. That really threw us off-balance when the first satellites were going up and their orbits seemed a bit odd because of that difference in gravity over different locations because the earth is not a perfect sphere. And then let’s add in the influence of the moon’s gravity, even the sun’s gravity. It all adds up to one heck of a
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