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Comment by garbagetime | Hacker News Reader

You're presenting a false dichotomy. Our options aren't only (a) live only on Earth, and (b) live on Earth and Mars and potentially other planets. There is, for example, (c) live in man-made structures orbiting the sun at a distance of 1AU, which is debatedly much more sensible than trying to live on Mars.

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That's true, but there is no fuel source out in space. Outside of Earth orbit, eg Lagrange points, you need fuel deliveries.

On Mars they can make methane with the Sabatier process.

So you have:

- LEO/MEO - vulnerable to asteroid impact ejecta

- GEO/moon/L-points - avoid ejecta, but need regular refueling. If Earth is toast, there goes resupply

- Mars - close enough to the sun for solar, able to conceivably bootstrap in a few centuries

Actually there is fuel in space - water and sunlight.

You can split water into hydrogen and oxygen using electricity from sunlight.

In long term, most likely both Hydrolox and Methalox will be in use.

I think the parent comment meant to say there is no propellant in space.

There are comets in space, so there is water and water can be made into propellant.

Ceres also seems to have a lot of water: https://astronomy.com/news/2020/08/ceres-an-ocean-world-in-t...

Solar sails can get you to anywhere in the Solar system. Not very fast, but essentially free. So a swarm of drone ships with solar sails can transport an almost infinite amount of propellant to your refueling bases from mining sites.

It is much easier to get protected from radiation on mars, than in the outer space. Nobody knows for certain how would childbirth look like in zero g and it's just the one of many problems. Mars is much more hospitable than pure vacuum.

By building underground structures?

Technically, every structure encapsulating space makes that space "underground" - the distinction between natural rocks or poured concrete as a ceiling is negligible when it comes to radiation protection. Whenever we set up a sunshade, we are protecting ourselves from harmful radiation.

Putting more material between you and radiation by burying into the ground is a good idea, especially when your concrete-pouring capabilities are limited.

Mars is difficult of course, but it does have resources. You can get water, oxygen, rocket fuel, various ores, etc. It's also not a vacuum, and there are places where the temperature profile is vaguely similar to Earth.

None of that is true in space, unless you're thinking of something I'm not, but like another poster has said, none of this is zero sum. The technology developed to try to settle on mars can be devoted to building large, habitable objects in space if people think that's a better plan. We should also have a moon base, etc. etc.

> much more sensible than trying to live on Mars

It's more sensible if you plan to keep a bunch of people there with constant supply from Earth. Elon wants to build a *self-sustaining* city on Mars. There isn't any other choice of location, be it man-made, or in the solar system:

- that has enough resources, atmosphere, gravity, water to allow a non-trivial population to survive without help from Earth

- that is hospitable to life

I suggest you watch his previous presentation where he talks exactly on why Mars is the destination, and not somewhere else.

Yes, we are talking about permanent, Earth-independent settlement in space. I didn't mean to imply that the settlements in the man-made structures would be Earth-dependent.

Atmosphere is possible in man-made structures.

Gravity can be simulated in man-made structures.

I don't believe water is particularly scarce, and it is reusable except for when it's used to create fuel.

With the Sun + plants a lot can be done.

Mars, on the other hand, has low gravity and is far away from the Sun.

How many tons would you need to get out of the gravity well before you had enough orbital manufacturing capacity to begin building that sort of thing? I mean, I love the dream, but I don't know how you can make it a reality.

In the video Elon makes an estimate of a million tons to Mars (if I remember correctly) in order to establish an entirely self-sufficient colony there. Building orbital manufacturing would be a different kind of problem, but in some respects it's kind of similar. I suspect it'll make sense to establish a foothold on Mars first (which has a lot of necessary resources and less gravity means you can transition from the planet to orbit much more cheaply) and then maybe use Phobos and/or Deimos as manufacturing hubs for space-based hardware like habitats. Or maybe it makes sense in the short term (before Mars has the necessary infrastructure for big projects) to do manufacturing on the moon.

> live in man-made structures orbiting the sun at a distance of 1AU, which is debatedly much more sensible than trying to live on Mars.

The resources still need to come from somewhere. Either we mine them on Mars, asteroids, or the moon. Mining is a lot easier when you have gravity you can push against to apply force. Rather than move the resources off-body though, its easier and cheaper to use them directly in-situ.

Your proposed alternative would also benefit from something like Starship.

Of course, we can (and should, eventually) do both.

Better rockets and better spacecraft serve all space exploration and colonization efforts.

Hmm. With Starship's lifting capacity, that might become a side project. Maybe they could even sling something to become part of the orbital station and continue to Mars

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