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So the setting is that we are several hundred years in the future, and scientists are sending humans to the surface of Venus in reinforced vessels similar to submarines or whatnot. We will assume that the tech to pull this off exists in this universe, as that's not what I'm asking about.

I'm mostly concerned about whether such a vessel would float in the air naturally. I would assume it would float in a manner similar to a submarine, given that the air pressure outside would be 90x that the pressure inside, but I don't know how much the fact that it is air instead of water changes this. The fact that airships and hot air balloons float makes me think they would, but I'm not sure if the amount of buoyancy required for such a vessel to float in the high-pressure air would be different than what's required to float underwater.

I'm also somewhat curious what the best way to propel a vessel through this atmosphere would be (propellers, jets, etc), although this question is secondary. (smaller vessels would probably use electricity while larger vessels could potentially have small fusion reactors aboard them).

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  • $\begingroup$ Given the timing of this question, I suspect another Derek Künsken fan. But if not, you may be interested in his recently released hard-SF novel, The House of Styx, which I'm reading now. It features humans living on Venus. $\endgroup$ – Mars Sep 8 '20 at 16:24
  • $\begingroup$ Obligatory xkcd. (Also good source for some of the, errr, issues you'll need to deal with for this experiment...) $\endgroup$ – reirab Sep 9 '20 at 2:50
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Yes. Many unexpected things will float in the atmosphere of Venus.

enter image description here

This 40 ft shipping container weighs 4.2 tonnes, and has a volume of 67.7 cubic meters. Giving it a density of 62 kg/m^3.

The density at the surface is about 65-67 kg/m^3. This means that the shipping container will float upwards off the surface and up into the troposphere, potentially getting up to 65 km off the surface.

That shipping container will behave like a helium balloon.

This should give you an indication of how easy it is to get something to float on Venus. Your vehicle needs to be lighter than a standard Earth submarine (67 kg/m^3 is a lot less dense than seawater), but the concept of a buoyant craft on Venus is sound. (Pressure and temperature will be design issues, however).

Humans won't float, we'll fall to the surface.

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    $\begingroup$ Humans won't float? We are too dense even for the Venusian atmosphere? $\endgroup$ – a4android Sep 8 '20 at 4:46
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    $\begingroup$ Overall, we're a bit less dense than water (source - we can float in the pool but can still submerge/sink easily). Water is ~1000 kg/m^3. Remember that most of the volume of that shipping container is just air -- it's a very-heavily-walled metal balloon. $\endgroup$ – Salda007 Sep 8 '20 at 5:12
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    $\begingroup$ @Renan well, the container, as is, would get crushed in an instant and then drop to the ground. It should be wrapped up in a thin foil of handwanium to avoid being crushed and not letting Venus athmosphere in. Then we could enjoy our container balloon. $\endgroup$ – Duncan Drake Sep 8 '20 at 8:33
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    $\begingroup$ @DuncanDrake: Don’t forget the corrosion!!! $\endgroup$ – Joe Bloggs Sep 8 '20 at 11:47
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    $\begingroup$ @a4android humans won't float, they'll dissolve... $\endgroup$ – leftaroundabout Sep 8 '20 at 11:49
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It depends on how the vehicles are designed. In particular, the ratio of the 1-atmosphere volume occupied by humans needs to be small enough so that the overall density is greater than the density of the Venusian atmosphere.

You could even design the vehicle with varying density, like a submarine. You would let atmosphere into the ballast tanks to descend, pump it out to ascend again. See e.g. Larry Niven's "Becalmed in Hell" https://www.baen.com/Chapters/9781481483605/9781481483605___6.htm

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Short answer: It depends

The density of air at the surface of venus is quite high with around 67kg/m^3 But so is the pressure (yes, these numbers are related).

So as long as the overall density of the vehicle is less than 67km/m^3 AND it is not crushed AND can hold a low pressure inside (either by being gas teight or by pumping gas out faster than it ingresses) AND it can do so in up to 400°C and rain of sulfuric acid (among other nasty things) it will probably float.

It's mostly an engineering challenge to build something that can withstand the pressure AND is still light enough... Maybe a helium filled balloon is still the easier solution.

Good luck!

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Not only near the surface, but even in the Earth-like parts of the atmosphere. Wikipedia has a good run down on ideas for habitats in the atmosphere of Venus: https://en.wikipedia.org/wiki/Colonization_of_Venus#Aerostat_habitats_and_floating_cities

The key part is that "breathable air (21:79 oxygen/nitrogen mixture) is a lifting gas in the dense carbon dioxide atmosphere" (quote from the current version of the Wikipedia section linked above). A human-livable habitat should definitely float in the upper atmosphere, as long as you don't weigh it down too heavily.

Given that, you should definitely be able to have submarine-type vehicles floating in the lower atmosphere.

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