[bergoid]

Low gravity is one thing. But the radiation outside the Earth's magnetic field is quite another. People colonizing Mars will need to shield themselves from several types of harmful radiation. Wich means in practice: living underground.

[daxaxelrod]

Could be living underground. Water is also an effective radiation shield. Combined with predictive modeling, we might have a chance.

https://www.nasa.gov/mission_pages/sunearth/spaceweather/ind...

[bergoid]

Agreed. You could cover your above-ground pressurized habitat with blocks of ice. Or with a thick layer of dirt. But the subjective experience remains about the same as living underground.

[allannienhuis]

There are a lot of people who live indoors almost 100% of the time in the winter in northern climates. A lot of the larger northern cities have underground walkways between buildings with subway access etc. No one wants to even walk across the street when it's 40 below. :)

I expect that designs for 'permanently underground/inside' cities would need to include some high-ceiling park-like areas with some bright UV lights, and other considerations, but that sort of thing seems pretty doable. Whether it would be enough to maintain a population's mental heath I guess would need to be seen, but generally speaking I think humans are a pretty adaptable bunch...

[bergoid]

> I expect that designs for 'permanently underground/inside' cities would need to include some high-ceiling park-like areas with some bright UV lights, and other considerations, but that sort of thing seems pretty doable.

Definitely doable. But then there's no longer any special appeal to living on Mars, as opposed to: living in rotating space habitats among the asteroids.

If we reformulate Musk's goal as being: "Create off-site backups of human civilization", then I think asteroid mining & space habitats have a better shot at bootstrapping this process than colonizing Mars.

Once we are leveled up this way in resources and technology, building settlements on Mars can be a side-effect of this outcome. Just like the burgeoning scientific outposts on Antarctica are a side-effect of our current civilization.

[allannienhuis]

I like the idea - why waste all that energy going up and down, and missing out on swimming in zero g? :)

But rotating space habitats might not be as good at replacing gravity as some think. Even with the really-huge 'O'Niell cylinder' scale (8 kilometers diameter), coriolis effects would be noticeable. I suspect a number of industrial processes would be affected by it.

I expect some of the major industrial processes will still need/want to be done on a big pile of rock or sand, rather than in a more fragile object that inherently wants to explode and fling apart all the time :).

[kybernetikos]

And then the big question becomes "How is living underground on Mars better than living underground on Earth?"

[ben_w]

The magnetic field is, by far, the easiest problem. There are many other unsolved problems, but that isn’t one of them.

Now I’m working if making a very large current loop on the ground would double up as a launch/landing system where the planet itself is the reaction mass…

(Probably not; the chances are the requirements for safety and reaction are orders of magnitude different from each other).