/sci/ - Science & Math

The reason is not technological limitations, btw. At the height of the "man in the sea" era, there were 70 undersea labs worldwide. The technology necessary to put human workers in the sea for prolonged periods is very mature and established. It's vastly cheaper today thanks to the commoditization of many of the technologies involved.

That era ended primary due to the ongoing expenses of sustaining life undersea (issues which have since been solved with new technology) the development of very cramped, portable ambient pressure habitats intended for temporary use (aka diving chambers) and ROVs.

There was no practical purpose for putting human beings underwater except science, and the world needs only a small number of undersea labs, which is why it currently only has three. (Aquarius, Baylab and Marinelab).

However, with the advent of new oceanic industries, especially those taking place on the continental shelf like power generation and fish farming, there exists a valid business rationale for putting living space for maintinence workers on-site. It is the same principle behind factory/mining towns. They start out spartan and basic, but as more people work there the town grows to meet their needs and provide a better place to raise their families. There is a higher threshold involved in the oceanic equivalent due to the cost of the living structures, but once it is crossed the same thing will happen.

There are in fact already two colonies in the works, one as a luxury community for the rich and the other for diving enthusiasts, with jobs being provided by a nearby gulf stream turbine and a potential deal with the company responsible for the fish farms posted earlier. Pic related, the turbine.

Also, to better explain the significance of a cheap, low power desalinator; Military subs brute force separate oxygen and hydrogen out of water via hydrolysis, an extremely energy hungry and inefficient way to get air out of water that they can afford in terms of energy use only because they have a nuclear reactor onboard. They then use some of the oxygen to replenish the air and recombine the rest to get extremely pure, clean drinking water (having been reconstituted from it's two chemical elements rather than filtered from outside sea water)

Now, there recently came into being a device for separating oxygen out of ocean water using vastly, vastly less electricity. 150 watts per person. It uses a vacuum generating centrifuge, the only downside is it lacks the added desalination capability of hydrolysis. With a low power, cheap desalination device, that's no longer the case. The military has no need of either because of the absurd excess of energy available from the onboard nuclear reactor, but if you're looking to make underwater living space affordable for normal people, these two developments are hugely significant. It eliminates completely the necessity of burning gas to power air compressors to send down fresh air. Now all you need is something like a tidal turbine in the gulf stream, which now exists (pic related)

With this uninterrupted, day and night source of reliable, renewable power, technologically speaking you could meet the life support needs for tens or hundreds of thousands of colonists without any surface interaction and without the use of gas generators or air compressors.