Mars seems like an introductory class to Venus' horror story. But yes there's plenty to learn, especially from a statistical analysis for finding life in interstellar space type of thing.
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.
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.
... 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.
Based on my experience, there's always that one astronaut who forgets and uses a metal spatula.
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%.
https://www.gab-neumann.com/Corrosion-resistance-of-impervio...
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.
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.
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.
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.
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.
Layered mirrors concentrating monochromatic solar irradiation into laser cavities, and beaming power to where needed, is the fallback until aneutronic fusion works.
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.
This occurred in stages.
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.
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.
https://astronomy.stackexchange.com/questions/26/what-is-the...
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.
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....
Strongly calling B.S. on this claim.
There is no physical reason humans could not have a latent magnetic sense. Other animals are known to have it. So, experiment is determinative.
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.