fredgiblet wrote:Mining asteroids isn't as simple as most sci-fi would have you believe, just finding and getting to them is gonna be a pain in the ass. You're going to burn a LOT of fuel getting there and back in a reasonable timeframe.
I suspect that when you say "reasonable time" you're thinking about months between (for example) Earth & Mars, or possibly even weeks.
When I say "reasonable time" for this sort of scenario, I'm thinking about
years between Earth and Mars. Moving hydrogen? Package it into a chemical that doesn't leak away so easily (hydrocarbons, for example), shield it from energy sources, and ship it like it's any other bulk commodity. Non-leaky bulk commodities? Ship them in either pressure hulls, or in blocks exposed to the vacuum (in some cases this could even be a metalurgical processing stage). Everything else? Either it's rare materials, or you won't be getting it from an asteroid, unless it was a new station that might as well be built near the materials source.
Asteroids get you bulk commodities instead of this year's iPhone, so you ship them appropriately: with a solar sail. Choose a few distribution points (if you're shipping in-system from the asteroid belt, you'd probably go for Mars, and three of it's Lagrange points), build a free-space warehouse at each, distribute from each according to the arrival season.
fredgiblet wrote:Getting natural resources is significantly more difficult in space than on a planet, expanding is more difficult and expensive in space than on a planet, keeping healthy is more difficult in space than on a planet. The only thing that I see as better about space-born living would be short-term setup, it would probably be faster to get a functional colony set up in a space habitat than on Mars.
Are you counting the time to build the habitat in the set-up time? O'Neill thought that the first station would take ~30 years to build, due to the time needed to build up the industry.
At any rate, the only foreseeable advantage that planets
other than Earth provide for a properly designed system is the lack of a need to provide a gravity replacement... IF you are living on Mars, Venus,
possibly the Moon or Mercury or other objects of that size if you never need to go anywhere else, and the atmospheres of the gas giants. Everywhere else
modifies the challenges faced in living off of the Earth, but doesn't get rid of them:
Mercury has low gravity, no atmosphere, and horrible temperature extremes that only come close to disappearing at the poles; Venus has a horribly hostile lower atmosphere that will melt AND dissolve most things; the Moon has low gravity, no atmosphere, AND high-abrasive dust; Mars has barely any atmosphere, very long-lived dust clouds, and the dust is likely decently abrasive (though it should be much more friendly than on Luna); Jupiter's upper atmosphere is too self-irradiated for habitability with sensible structures; most of Jupiter's moons are bad for the same reason as Jupiter's atmosphere,
including Europa; Callisto, I'll admit, might be a good choice, and if you're willing to go out to Jupiter then it might be considered superior to Mars, but it still has a minor atmosphere and low gravity; If you remove those four major moons of Jupiter, you're left with 0.003% of the mass orbiting Jupiter, so they might as well be asteroids; Saturn is much better than Jupiter for atmospheric colonization, but the lack of a solid foundation means that if your atmospheric colony needs external flotation support, then loss of flotation can result in death even if the colony hull remains intact, adding one potential source of colony destruction, still a decent choice if you're willing to go that far out, though; Titan is reasonably close to a good choice if you're willing to go as far as Saturn, but if you want to terraform then forget it, because both the distance from the sun and the hydrocarbon-dominated environment make that absurd, regretfully it's gravity and temperature are both low, and the atmospheric density actually makes the temperature a concern; Enceladus is a good source of water, but the constant spray suggests that an orbital collection system may be wiser than surface operations, lest your colony turn into a glacier; The rest of Saturn's moons should fall in the same general category as Callisto, Enceladus, or asteroids, since Titan is ~96% of Saturn's orbiting mass; Uranus would probably be the best of the gas giants to place atmospheric colonies in, if not for the distance, as it's escape velocity is lowest, and it's gravity is ~90% of Earths at 1 bar of atmospheric pressure; Saturn's moons are all smaller than Titan, and mostly ice, Titania would probably be the one to aim for if a colony was to be placed on one, since it's the largest; Neptune presumably has no advantages for atmospheric colonization over Uranus; Titan barely has gravity or atmosphere, but it has over 99% of the mass orbiting Neptune, and is suspected to have some potential for geothermal energy; anything further out is basically going to be no better than Titan.
Out of curiosity, what conditions were you thinking favored planets? The only advantage that reliably exists for them is the fact that there's already a floor to stand on.
And, if you think about it, any practical colonization effort (unless you're colonizing to the Moon) is going to call for one or more space-borne habitats on a cycler orbit, since using disposables quickly becomes a unjustified waste.