[bruce511]

I don't think this really qualifies as a backup survival option.

Power, food, and transport are provided from the surface. So any event that resulted in an extinction of the species would end the habitats, perhaps a month or two later.

Power is the key limiting factor. All the power is derived from the surface, and would likely be damaged or destroyed. Food would be the next factor - yes in some cases there might be local food sources (fish) but that would exhaust quickly as well.

Not to mention air...

[ethbr1]

You can pull power and air out of water, given enough infrastructure. Mix gases would probably be a pain in the ass, depending on what they're using.

Not sure what aquaculture at greater than sunlight depths looks like, but assume you could farm the upper layers of the water column.

The biggest limitation to self-sustainability is probably interior volume, given the need to have manufacturing chains available.

[bruce511]

All this is true, but none applies to the project under discussion.

As an aside, I expect any kind of "backup humanity" goal would almost certainly be easier, more sustainable, and more likely to succeed on land than under water.

On the other hand if we messed up badly enough to require a backup, I'm not sure we deserve it.

[pzo]

Long term this would be still easier to make really sustainable than mars mision.

1) Power:

- power can be from nuclear reactors similar like with nuclear submarines

- you can drill down near some geothermal water

- you can still deploy some floating solar panels with 200m cable linked to habitat and fold back similar like kite in case tsunami

- you can put habitat nearby some water currents (e.g. nearby some 2 underwater mountains/islands and you will have water current because of tidal waves) and deploy some power kite or hydro turbine

2) Oxygen + energy

- just make electrolysis on water molecule to get both oxygen and hydrogen

3)

- grow some seaweed food

- grow fishes and other sea food

Sure this is still hard to pull off but at least 1 order of magnitude easier than on mars. On earth you don't have to worry about gravity, lack of water, lack of geothermal power, radiation from space, protection from micro meteors, -73C temperature during the night on mars (deep water on earth even 200m below is not frozen but between 0-3C). Humanity after 10 years of living underwater can still try to go back to land after things gets better post asteroid impact.

[bruce511]

Oh sure. Colonies on Mars are a complete fantasy right now. They start and end with Mars's lack of a magnetic field.

could we create a self-sufficient habitat underwater? Probably. But given that it would lack key abilities (heavy industry for example) it would inevitably decay (Probably quite quickly.)

[alphan0n]

Someone correct me if I’m wrong, but wouldn’t you need a helium mix at 200 meters?

[6SixTy]

A nuclear reactor could suffice as a local power source. Maybe fusion in another 50 years. With a local power source, electrolytic oxygen generation is possible. Food, hydroponics.

Transportation? Could figure something out.

Most of this tech is stuff we already have or developed with NASA/etc for the ISS gearing it up as a self sustainment environment. Main problem would be internal volume.