So, one of the more persistent criticisms of PlanGen in Traveller is the old "overpopulated hellhole" canard. Specifically, that one can generate Huge populations on profoundly uninhabitable planets. Specifically, Venus (ATM B or C, depending) with 10,000,000,000 inhabitants. Orbital habitats don't seem to be a good enough explanation for serious rules lawyers: they technically "aren't on the planet", and are rather fragile compared to surface based habitats. However, some serious science thought has been put into exactly this issue -and suggest that Venus may actually be the best bet for extraterran settlement - and could support massive populations. How ?
TL:DR version, at 50Km altitude on Venus, conditions are 1psi, temp 0-30c , good abundance of basic earth life elements : (C, H2, O2, Ni ), and lots of solar power opportunities. The basic atmos is unbreathable, but in that mix of atmosphere, normal breathing air (O/N)is a lifting gas ! Build a huge zeppelin protected against the sulfuric acid atmospheric component (easy, really), and live inside. Serious golden age Sci Fi. And since OTU Traveller has Gravitics good enough for floating palaces at Imperial tech levels (12+, IIRC), one doesn't even need the lift provided by the breathable atmosphere except, perhaps, as a backup !
Cool, huh ?
And given that the living space is very thick (probably a kilometer or two before any bad effects of pressure or lack thereof show, there's room for LOTS of people in floating archeologies. So we have these elegant bubbles floating serenely across the sky, occasionally spawning smaller bubbles, using resources drawn from various atmospheric depths as well as the hellish surface of the planet - which is a mine head, only. No one lives there, they just commute in, oh, I don;t know. Armored flying submarines and ground hugging mecha ?
Tell me there isn't a campaign in that.
The linked paper is actually 7 years old at this point: I'm mildly embarrassed that we didn't find this in the play test discussions about habitable worlds. Quite a bit of opinionizing could have been avoided...perhaps. (There was at least one content area "expert source" there that would have argued with his own shadow, as is required in any gaming forum.)
Now, if I can just get some real numbers on the other issue - how long (in actual years) a small world can hold a standard atmosphere ?
Some good fiction led me to this : "Clever Mongoose", and no relation to the present publisher of Traveller: a ripping SF yarn with floating cities, high tech zombies, conspiracies, and alien invasion all with a steam punk scavenger tech sensibility and a high tech background.