03-07-2014, 12:13 AM
Another thought: compression.
The idea of a gravity balloon is that the weight of the shell is balanced against gas pressure. Something I ran into with Hawkings Not Here is shells placed in compressional stress are very vulnerable to buckling, especially large shells. I would've loved to make HNH 50 or 100km in diameter, but the shell thickness became ridiculous (tens of kilometers with diamondoid). HNH, of course, has a vacuum center and is entirely dependent on the structural shell, unlike a gravity balloon.
But in larger volumes, you can't depend on constant air pressure. Differential heating will create differential pressure across many square kilometers.
I suppose you could over-pressurize a bit to keep the shell prestressed in tension against any reasonable pressure drop, but the structure is vulnerable to catastrophic collapse if there's a lot of air loss.
The idea of a gravity balloon is that the weight of the shell is balanced against gas pressure. Something I ran into with Hawkings Not Here is shells placed in compressional stress are very vulnerable to buckling, especially large shells. I would've loved to make HNH 50 or 100km in diameter, but the shell thickness became ridiculous (tens of kilometers with diamondoid). HNH, of course, has a vacuum center and is entirely dependent on the structural shell, unlike a gravity balloon.
But in larger volumes, you can't depend on constant air pressure. Differential heating will create differential pressure across many square kilometers.
I suppose you could over-pressurize a bit to keep the shell prestressed in tension against any reasonable pressure drop, but the structure is vulnerable to catastrophic collapse if there's a lot of air loss.
Mike Miller, Materials Engineer
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"Everbody's always in favor of saving Hitler's brain, but when you put it in the body of a great white shark, oh, suddenly you've gone too far." -- Professor Farnsworth, Futurama
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"Everbody's always in favor of saving Hitler's brain, but when you put it in the body of a great white shark, oh, suddenly you've gone too far." -- Professor Farnsworth, Futurama