[cstross]

However, an interesting aspect of floating habitats in the Venusian stratosphere is that a terrestrial breathable gas mix (80% N2 / 18% O2 / 2% trace others) is a lifting gas that's about as effective as Helium here on Earth. (Venus's atmosphere is > 90% carbon dioxide, which has a significantly higher molecular weight than air.) And it's protected from solar UV and radiation to a considerable extent by the layers of atmosphere above it. So your entire balloon -- or, more likely, dirigible airship -- can be inhabited volume, rather than just a cramped gondola slung underneath.

Photovoltaic power might sound problematic at first in view of the long Venusian night (a single day lasts up to 116 Earth days), but at altitude there are strong jet streams and winds circulate around the equator roughly every hundred hours. So you're not stuck running on battery power for months on end, but you may need some maneuvering capability.

This is not to minimize the problems associated with activity in the Venusian atmosphere -- but it's not quite the impossible hell-hole it's been portrayed as.

[TheOtherHobbes]

You'd be floating in a haze of CO2 and sulphuric acid garnished with hydrogen sulphide, battered by raging convective winds which would make it very hard indeed to stay at a fixed altitude - which means the outer temperature would fluctuate by 10C to 50C or so without massively powerful altitude control.

You can't just drift there as if you're in a hot air balloon eating sandwiches and enjoying the view.

Venus might not be completely impossible, but it's still one of the less hospitable destinations in the solar system.

Also, smelly because of the H2S.

[azernik]

On the other hand, Mars requires you to live in a radiation-shielded pressure vessel.

I think the real killer is that it's hard to build and maintain infrastructure when floating on balloons - much easier to run a spaceport on Mars, or to get to all the useful surface resource deposits. On Venus you'd have to build literal castles in the air, using only only what you can pull out of the atmosphere or ship in from orbit.

Not to mention Mars is at the bottom of a much shallower gravity well.