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Comment by __MatrixMan__ | Hacker News Reader

The general shape of geothermal, where you're up here where it's cool, and you push a fluid down there where it's hot, and you bring the heat back up here to do work... Would a good enough insulator make it thermodynamically feasible to do it from an airship in the Venusian atmosphere?

Like, clearly Earth's crust supports temperature gradients which are steep enough to make the juice worth the squeeze. Presumably you're not going to find gradients so steep in the case of a runaway greenhouse effect, but whatever gradients you do find, are there fundamental limits preventing them from being steep enough?

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The "airships riding on clouds of Venus" is a scifi genre that we need way more of.

To be at 1 atm you need to be way up near 50km, but you'd probably want to be up closer to 55km to get temperatures down, filling it with higher concentration O2 to make it breathable. Making the envelope durable would be pretty crazy in H2SO4, but maybe Ti would self passivate?

Arguably, more dangerous and harder to navigate than vacuum.

You guys are imaginative, I'll give you that.

But there are so many more fundamental problems with the high altitude Venusian colony idea that you would never get to the "temperature gradients > power" pipeline implementation in any case.

I mean right off the bat, imagine building or navigating anything in hurricane Katrina. Then, since we're talking 50km, imagine winds that would make the forces you're dealing with an order of magnitude more problematic.

Yeah, in terms of knowledge and technology, mankind is just not there yet to be perfectly frank.

Wind speed could be fairly irrelevant to the balloon-city; it will never touch "ground". If you can steer away from vortexes (assuming them to be rare), they simply don't matter as a safety issue. (Staying in a desirable temperature zone could create a need for resisting the wind, but that's not a safety issue.)

OTOH, because wind velocity is highly tied to altitude on Venus, wind farming could be an important source of energy generation (along with chemical generation for emergency demand). Drag a fan at a hotter, lower, higher-pressure altitude, and harvest the electricity. In fact, storing an excess of wind-farm energy as chemical energy could power the occasional need to steer away from vortexes.

If the problem of a chemically-inert package can be solved, floating inhabited stations could be feasible.

I hadn't considered the drag-a-fan approach. It brings to mind an interesting kind of sailing where you've got multiple wind directions to solve for. Never mind that an atmospheric colony wouldn't really have a lot of destinations besides itself. Might as well just be one big flotilla.

I expect that a more boring approach would prevail: solar panels. No need for impossibly tall airships to resist wind shear just so they could get at both sides of the hot/cold setup for operating a sterling engine.

Engineering sense aside, I still wanna know if nature would allow the geothermal approach. Something about the idea that a column of air at rest would settle down into such a disequilibrium that it could be harvested of energy in this way feels wrong to me, but I've been unable to muster the thermodynamics chops to align my head with my gut.

The problem is the reflective sulphuric acid clouds of Venus extend quite high up... and of course those eat most anything unprotected. If the wind sheer wasn't so bad, you could try and build tall chimneys with fans in them.. but probably easier to just drag fans.

I still think the temperature and corrosive atmosphere are a lot worse. Two proposed missions come to mind that don't seem concerned with wind or turbulence:

https://www.morningstarmissions.space/samplereturnmission

https://science.nasa.gov/mission/davinci/

Of course anything could happen with funding in the next 5 years that would derail these.

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