Development of inflatable volumes is a reasonable step towards us becoming a spacegoing species. If you have a decent bag and enough air to pressurise it, you can have as much room as you want in space. There's no external pressure working to collapse it.
Of course, there are questions to answer about safety, shielding against debris and radiation protection, but that's the point of doing the research. I love this kind of stuff. It serves to remind people that space travel isn't just launch vehicles. Part of, as you say, providing a place in space for humans to live, is providing spacecraft that aren't utterly cramped.
Inflatable habitats actually scale worse than ridged structures. The problem is as you inflate a structure the air pressure is constant but the surface area increases. And you must carry the load around the edges.
The advantage is actually in mid-sized structures where you can more easily compact them for transport where rigid structures are sent up in a single piece for strength.
PS: This is also why you need buttressing around above ground pools. For comparison 1ATM = 33.9 feet of water. Above ground pools rarely go above 1/3 ATM at there base. Granted, they are also not made out of Kevlar, but the same basic problems apply in space.
Interesting. I would expect that both air pressure and the tensile strength of your enclosure would scale directly in proportion with the area of the enclosure.
But some thought experiments about enormous pools - ponds, really - make me think that you're correct.
Indeed, looking it up, in a sphere, the stress (in units of pressure) is equal to (pressure x radius) / (2 X thickness). In a cylinder, it's worse - axial stress is the same as a sphere, but hoop stress is (pressure x radius) / (thickness)! You also have to think about increased stretching in the hoop direction compared to the ends of a flat-plate cylinder, which should probably be a sphere or complicated ellipsoidal shape to best deal with the stress.
Applying these equations, an ideal steel (assume an alloy with tensile strength 700 MPa) sphere with 1cm thick walls would have a maximum radius of 138.2m. A cylinder would have half the radius. Using Kevlar (tensile strength 3620 MPa) increases the radius by 3.62.
Doubling the thickness doubles the allowable radius but also increases the mass of our sphere from an already staggering 136 metric tons (3 Falcon Heavy payoloads) to an astonishing 546 metric tons, or more than 10 Falcons Heavy.
Kevlar is, of course, lighter than steel by about 5 times, but that many tons of Kevlar will not be cheap. That's about 0.5% of the total world annual production of the stuff!
We won't be going up to inflatable planets anytime soon.
You could have multiple membranes wrapping one another, each with a lower pressure than the last until vacuum. That way you substantially reduce pressure forces, and improve ballistic resistance.
Make it big enough, and vaguely cylindrical, and you could spin it up to provide simulayed gravity - you'd just need internal webbing to prevent it bulging from centripetal forces.
This all adds mass of course, but it still be lighter and more compact than an equivalent rigid structure.
Your mistake is in assuming we're simply optimizing for volume and nothing else.
Factor in each of size, cost, and deployment complexity, and it's clear many feel that inflatable structures represent huge potential wins.
Besides, it's not like you actually need to build single, huge volumes. Space-based habitats built of multiple, smaller linked structures makes more sense, anyway, as it enables module isolation in case of failure.
We are still thinking in terms of tiny structures. Picture a space station with 100,000+ people.
From a safty standpoint you want modular structures. But, you also want to minimize the areas directly linked to space. Thus you end up with something like a nuclear submarine vs an ever expanding ant hill.
Remember apartment builds give every room a view, but that's high risk in space. You can also reuse walls, between areas to cut down on mass without compromising if there is a leak.
Of course, there are questions to answer about safety, shielding against debris and radiation protection, but that's the point of doing the research. I love this kind of stuff. It serves to remind people that space travel isn't just launch vehicles. Part of, as you say, providing a place in space for humans to live, is providing spacecraft that aren't utterly cramped.