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Comment by pencilguin | Hacker News Reader

At cloud-top level, temperature, pressure, and gravity are all close to Earth-normal, and breathing-air is buoyant.

Numerous materials can be extracted from the outside air, including oxygen, hydrogen, carbon, sulfur, nitrogen, and even some metals.

A day/night cycle is about 100 hours, depending on how close you are to a pole.

A nuclear reactor is as simple as a big fabric tube suspended vertically with a naked atomic pile hanging near the bottom, and a wind turbine turning in an opening at the top, the only moving part.

You need something non-solar because nights are long.

Alternatively, you can store energy with a weight on a cable attached to a generator. Play it out to discharge, winch it back up to charge.

Or maybe different layers of atmosphere circulate at different rates. If so, you can hang a wind turbine in the next layer below.

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I love the mention of gravity storage here. The potential of gravity storage is very real, but you need a lot of weight and a lot of height to achieve meaningful amounts of electricity. And at large scales of weight and height it becomes a surprisingly hard problem. For example, a steel cable can’t stretch much further than a mile under earth gravity before it succumbs to its own weight. But there are other solutions. It’s not rocket science, as they say.

A steel cable one square inch in cross section and a mile long weighs <19k lb on Earth, a bit less on Venus. Cheap mild steel has tensile strength 50k lb/in², and can be as much as 10x as strong. So, self-supporting steel 3 miles to 30 miles.

Getting 250 tons of high-strength steel cable (sheathed against corrosion) to Venus is left as an exercise for the reader. Likewise, a big enough balloon to hold that up. And a strong enough winch.

But in practice, you would make the cable of carbon extracted from atmospheric CO2, instead, and it could support itself all the way down to the surface, 50 mi below. You would need to protect the end against acid vapor corrosion at 470 C: another exercise for the reader.

> At cloud-top level, temperature, pressure, and gravity are all close to Earth-normal ...

... and the cloud is made of sulfuric acid droplets. Don't breathe in, and make sure that nothing important is ever exposed to the outside air.

Maybe just coat the outside of your airship in ten microns of teflon, glass, or lead? As corrosives go, sulfuric isn't that bad.

Ordinary plastic is fine. You can buy concentrated H2SO4 at an auto supply store in a plastic bottle.

Edit: maybe not fine. Resistance to H2SO4 corrosion falls off sharply as its concentration approaches 100%. On Venus, the clouds would be very nearly 100%.

"Plastic" is lots of different things. I'd think polyethylene will be fine but not polylactide.

I was surprised to find that carbon fiber can sit in 50% H2SO4 indefinitely, but degrades above 65%, at normal temperatures.

https://www.gab-neumann.com/Corrosion-resistance-of-impervio...

At low concentration a sulfuric acid solution corrodes only by being an acid.

Neither carbon fiber is affected by acids, nor some types of plastic with carbon-carbon bonds, like polyethylene (but polyesters and other polymers made by polycondensation may be hydrolyzed by acids).

At high concentrations, a sulfuric acid solution begins to have an oxidizing behavior, even if not so strong as nitric acid, so it can convert the carbon from carbon fibers or some plastics into carbon dioxide, damaging them.

The difference in behavior is because the sulfate ions have a very high affinity for water. At low concentrations, they are strongly hydrated, so the attached water shields them from making direct contact with an immersed material. At high concentrations, there is much less water available for hydration and the sulfate ions can make direct contact with an immersed material. Then the oxidized sulfur atoms from the sulfate ions can oxidize any less electronegative elements.

Thank you, that was deeply enlightening.

That was fascinating. As a non- chemist it's easy to think the water is inert and 50% concentration just means 50% as much corrosion, but the water obviously plays an active role.

Neat. Wouldn’t a near 100% cloud be basically a liquid? What would it be like for a spacecraft to fly through that? A big puddle floating in the sky?

A near 100% H2SO4 cloud would be a cloud whose droplets have vanishingly little water in them.

As your balloon drifts up or down through it, the sheen of moisture it collects on its surface is maximum strength sulfuric acid. I hope your balloon is not of a material subject to oxidation, because if it is, you will soon discover a place even worse than in that cloud.

He meant that each droplet would be nearly 100% H2SO4, not the entire volume of the cloud.

> Maybe just coat the outside of your airship in ten microns of teflon, ...

Based on my experience, there's always that one astronaut who forgets and uses a metal spatula.

Long-term we could plant massive new floating plant species in the atmosphere to decarbonize it and form floating soil layers, which eventually would compactify and metamorphosize and spread out latitudinally to form a ring around the planet, thinning out towards the poles and making cliffs and beaches and islands with the atmosphere. The growing regions would not actually stay together but break apart and move technically on top of the atmosphere, with plate boundaries and subduction zones and volcanoes, driven by the pressure below, surface volcanism proper, and weather around the coastal areas.

Keeping carbon persistently out of the atmosphere would be hard, if you are freeing oxygen.

One alternative would be to make diamonds out of the extracted carbon and drop them to the ground. The released oxygen could then bind to crustal aluminum, iron, silicon, calcium, etc.

Venus has sadly little hydrogen, so you won't get oceans.

Just for a sense of scale, the venusian atmosphere has a mass of about half a billion GigaTons, 97% of which is CO2. Here on Earth, with all our industrial infrastructure, the substances we produce the most (iron and concrete) are in the low single digits GigaTons per year. The next ones (fertilizers and plastics) are in the hundreds of megatons per year. If you want to make a difference on Venus, you'd need to make millions of time more diamonds each year in some balloons in the skies than we make iron here on Earth.

It is a matter of how big a hurry you are in.

But, yes, it would be pointless to try terraforming Venus without von Neumann machines, and then it would end up thick with those, instead.

The Kuiper Belt offers more than the inner planets, provided energy is solved e.g. via aneutronic fusion.

> provided energy is solved e.g. via aneutronic fusion

You can use regular fission as a dense energy source. If you are worried about the waste, you can just blow it up. In space there's no fallout. The particles from the explosion will just move radially forever. Most of them (99.9999..%, too many nines to count) will keep moving for billions of years through empty space without encountering anything. Oh, and as a curiosity, if you blow up a nuke in space, there's no fireball. The fireball we see in movies of nuke detonations are due to the air absorbing the X-rays from the nuke and becoming overheated plasma. But there's no air in space, so a nuke explosion is invisible and silent.

Fission is not a good energy solution for the outer solar system (except maybe on Titan) because of the need for a detour through a clunky heat engine. Likewise, hot-neutron fusion.

Layered mirrors concentrating monochromatic solar irradiation into laser cavities, and beaming power to where needed, is the fallback until aneutronic fusion works.

Might the lighter O2 naturally rise away from the organics layer? It may then be able to oxidize metals and meteors sprayed into the upper atmosphere, eventually falling back down with those compounds to fertilize the substrate.

Wind speed is hundreds of km/h. So, "turbulent mixing processes" rule.

There is plenty of un-oxidized material on the ground. Oxygen just needs to be kept off the carbon. And, it needs stirring. Big meteors could do a bit of that.

Earth gets its stirring from tectonics, which Venus lacks.

Just to chip in, that life on Earth produced oxygen from photosynthesis, which over billions of years oxidised the iron in the ocean producing the iron ore beds as it precipitated out.

This occurred in stages.

To work, it needed stirring from plate tectonics.

This is one of the plots in the Space Merchants... https://en.wikipedia.org/wiki/The_Space_Merchants

That book any good?

A 3.85 avg rating with 9,862 ratings on Goodreads, so: average, but ever so slightly tilted towards good?

It's older but considered one of the great classics of sci-fi.

> breathing-air is buoyant

I'm really curious what the temperature, atmospheric makeup, and density is at different altitudes on Venus. I had no idea there could be a theoretically habitable altitude on it.

Atmosphere is mostly CO2, with relatively small amounts of other stuff. O2 and N2 are lighter, so a balloon filled with them could hold stuff up.

So we could live in balloons?

That is the idea. Want to go first? I will watch carefully.

Could be a cool game idea. Where you build in the clouds of Venus.

"You truly belong here with us among the clouds."

What's really interesting to me is that at the right latitude you can dig in and find Mercury quite habitable.

176 Earth days from sunrise to sunrise: 2 local years, half an Earth year. So instead of spring/ summer/fall/winter, you have day/night/day/night.

At the right latitude, and a few meters deep, temperature would be comfortable. But energy would be a problem, with the season-long night.

Axial tilt is <2 degrees. There might be some volatiles frozen in polar craters.

Temperature at a pole would be low, but solar panels mounted vertically (or, better, a wavelength-selective mirror reflecting onto horizontal panels), rotating slowly, would offer continuous power. Constant temperature too low is a lot easier to handle than too high, or varying much. You need to dig down for protection from cosmic radiation.

Gravity is about like Mars, which might or might not be adequate, long term. Nobody knows.

It is remarkably hard to get to and from Mercury. Jupiter is easier.

And the Sun rise/sets would be in the opposite direction from Earth. Imagine watching the sun setting in the East!

https://astronomy.stackexchange.com/questions/26/what-is-the...

To get a sense of it, just visit the opposite hemisphere (edit: on Earth).

What do you mean by that? The sun sets in the west whether you live in the northern or southern hemisphere.

That said, I’m not there’s any appreciable/perceptive difference to which way the sun sets for us anyway. It’s not like we have some internal compass that naturally grounds our cardinal direction. Our only frame of reference during the day on which way is east or west is the movement on the sun. If it suddenly started going the opposite direction it’d be weird if your were experiencing it in a familiar location. If you were somewhere where you’d never experienced a sunrise or sunset before (i.e., as little as a few miles away) I suspect you’d not even notice the difference. You’d have no frame of reference to suggest anything had changed.

> It’s not like we have some internal compass that naturally grounds our cardinal direction.

I'm reminded of "Story of Your Life" [1] / "Arrival" [2] wherein a character's language shapes their thoughts. Those are fiction, but there's also some supporting non-fiction evidence.

Apparently there's a tribe of humans on Earth (in Australia) whose language primarily refers to cardinal directions when describing the location of things - as in "hand me the north cup on the table". I don't think that's the only one - there's also Tenejapan Mayans [4]. From the latter group there's cited examples of an experiment with blindfolded/dizzy Tenejapan in a darkened interior who can identify the cardinal directions accurately. All of this is to say that maybe in fact some humans actually can sense this as if they had an internal compass.

[1] https://en.wikipedia.org/wiki/Story_of_Your_Life

[2] https://en.wikipedia.org/wiki/Arrival_(film)

[3] https://pages.ucsd.edu/~jhaviland/Publications/ETHOSw.Diags....

[4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3095761/

> there's cited examples of an experiment with blindfolded/dizzy Tenejapan in a darkened interior who can identify the cardinal directions accurately

Strongly calling B.S. on this claim.

I doubt a human could directly sense magnetic north, but with practice you could perhaps learn to integrate external cues (like sunrise/set) with your own movements to keep track of the cardinal directions.

Ignorant skepticism is exactly equally as bad as ignorant credulity.

There is no physical reason humans could not have a latent magnetic sense. Other animals are known to have it. So, experiment is determinative.

When I visit the southern hemisphere I’m always struck by how weird it is that the sun is going the wrong way across the sky. It really messes with my sense of the time of day.

If the sun is going the wrong way across the sky, it’s not because of the hemisphere you’re on.

I wonder if this is like an implanted memory that you have or what?

It’s going east-to-west in both hemispheres, that’s for sure. However, in the northern hemisphere the Sun goes from left to right, and in the southern from right to left, when you’re looking at the Sun.

I guess that is true in the higher latitudes on Earth. On Venus the tilt is 2.64 degrees, so it would be even more apparent in lower latitudes.

> I wonder if this is like an implanted memory that you have or what?

As pointed out below, it's because in my normal latitude (south UK) the sun moves from left to right (as you face South) and at a similar distance below the equator, it goes from right to left (as you face North). So at home when I look at the Sun I know that a couple of hours later it be quite a bit to the right of where it is now, and I can use this to assess where shadows will be.

Seems like this would only be true if you’re above the Tropic of Cancer and then comparing to below the Tropic of Capricorn. Between those zones the left/rightness of travel would change dependent on the season.

While sun always moves from east to west, in northern hemisphere, if you look at the sun then it's towards the south and moves left to right; and in southern hemisphere the sun is towards the north and thus moves right to left.

Umm… what?

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