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Gravity Balloons
#15
(03-07-2014, 12:13 AM)Cray Wrote: 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.

There are some important points in here too, so I'll add another reply.

Compressional stress will lead to problems, and this is why a perfect gravity balloon would have no compressive stress. Only isotropic pressure. But that is for a perfect gravity balloon. In reality, you'll have various stresses due to its imperfections. For extremely large sizes (like Virga), I think there are some major global stability issues. But porosity data suggests that asteroids have at least an order of magnitude more strength than what's needed to keep the intermediate sizes (up to maybe 70 km or more diameter) nice and structurally happy.

Oddly, I went in the completely opposite direction regarding the over/under stressing. My take is that you'll choose to have additional compressional strength. That is, the pressure is lower than what you could sustain via the rock's self-gravity. The reason is because this amounts to asteroid caves as they already exist. Some rearranging might be possible once people have lived there for a long time and have gained lots of understanding of these bodies.
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Messages In This Thread
Gravity Balloons - by stevebowers - 12-08-2013, 08:36 PM
RE: Gravity Balloons - by stevebowers - 12-15-2013, 05:49 AM
RE: Gravity Balloons - by ai_vin - 12-15-2013, 07:25 AM
RE: Gravity Balloons - by ai_vin - 12-15-2013, 07:27 AM
RE: Gravity Balloons - by stevebowers - 12-15-2013, 07:54 AM
RE: Gravity Balloons - by AlanSE - 12-19-2013, 07:15 AM
RE: Gravity Balloons - by stevebowers - 12-21-2013, 06:19 AM
RE: Gravity Balloons - by JohnnyYesterday - 12-21-2013, 05:53 AM
RE: Gravity Balloons - by Cray - 03-06-2014, 11:18 AM
RE: Gravity Balloons - by AlanSE - 05-24-2014, 04:14 AM
RE: Gravity Balloons - by stevebowers - 03-06-2014, 05:49 PM
RE: Gravity Balloons - by Cray - 03-07-2014, 12:13 AM
RE: Gravity Balloons - by AlanSE - 05-24-2014, 04:30 AM
RE: Gravity Balloons - by stevebowers - 03-07-2014, 02:47 AM
RE: Gravity Balloons - by Cray - 03-07-2014, 03:24 AM
RE: Gravity Balloons - by stevebowers - 11-19-2014, 01:18 AM
RE: Gravity Balloons - by Drashner1 - 11-19-2014, 02:09 PM
RE: Gravity Balloons - by stevebowers - 11-19-2014, 05:54 PM
RE: Gravity Balloons - by stevebowers - 11-19-2014, 07:31 PM
RE: Gravity Balloons - by stevebowers - 12-31-2014, 04:32 AM
RE: Gravity Balloons - by AlanSE - 03-25-2015, 04:01 AM
RE: Gravity Balloons - by stevebowers - 03-25-2015, 05:42 AM
RE: Gravity Balloons - by stevebowers - 03-27-2015, 07:24 AM
RE: Gravity Balloons - by sandcastles - 07-02-2016, 11:06 AM
RE: Gravity Balloons - by stevebowers - 07-03-2016, 07:15 AM

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