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> Getting resources from the moon seems out-of-date these days because the moon is far away in terms of energy even if it is close in distance. Getting resources from asteroids makes more sense.

You're right about raw energy, but one advantage of the moon is that you can build electromagnetic mass drivers that can sling raw material into orbit without affecting the natural orbit of the body (technically you are but only negligibly). For asteroids, you probably have to haul the whole thing back into Earth orbit for it to be useful, and you'd probably have to use some kind of propellant.

Also asteroid missions have much longer timelines if you have to go all the way out to the belt to get them. Less so if you get a near-earth rock, but those missions are pretty complex if trying it in Kerbal Space Program is any indication, and getting it wrong can be catastrophic. Many countries might not take too kindly to people wanting to sling city-destroying rocks around. Moon seems safer in that sense as a first option.

The two aren't mutually exclusive of course, and there are advantages to both. I imagine we'll see both strategies employed in a variety of different ways.

Still, moon has some gravity, making it possible to use some terestrial mining techniques and hardware and has more or less unlimited energy once you have a self-sustaining solar panel plant going.

The general idea for ONeil cylinders has been to build them in Moon-Earth Lagrange points with lunar material launched by solar powered electromagnetic mass drivers.

So the distance from Moon is not really an issue.

The L4 and L5 Lagrange points that O'Neill advocated in the 1970s really make no sense.

Halo orbits around Moon-Earth and Sun-Earth L1 and L2 make a lot more sense because they are energetically cheap to get to. L4 and L5 are a ghetto.

Tech like the mass drivers can move material from the asteroid belts in more cheaply than it can from the lunar surface. You also have to consider what it costs to stop the projectiles when they get where they are going (one reason to use the Earth-Moon L1 because you can hit it with nearly no excess velocity)

Ringworlds and orbitals are significantly bigger and harder to build than O’Neill cylinders. O’Neill cylinders are potentially feasible within a century or two; ringworlds and orbitals would take much longer.

>O’Neill cylinders are potentially feasible within a century or two

Is there anything fundamentally holding us back from building one right now? I mean there's the obvious problem that nobody has a good reason to build one, and only a hand full of entities have the funding to do so. But the engineering challenges seem to be on the level of building LHC or ITER: not nessesarily easy, but very doable.

They're enormous, and enormous things are difficult and expensive to build. They're also in space, and building things in space is difficult and expensive. So that's quadratically difficult and expensive.

SpaceX is claiming in the neighborhood of $1500/kg to put something into LEO. If you want to put a structure on the order of billions of kilograms into orbit it would make more sense to get that mass from something already out there and park it in high orbit instead - and space-based mining technology doesn't exist yet.

I wonder if we could circularize the orbit of a near earth asteroid like https://en.wikipedia.org/wiki/3908_Nyx which is outside of earth orbit always (less likely to run into the earth, and 10% farther up the sun's gravity well.

At the same time a fully loaded Falcon 9 uses about $10/kg of fuel to put something into LEO. The cost mainly comes from building the rockets, and to a lesser degree operating them (mission control, landing ships, etc). All of those costs would come down dramatically once you reach the scales nessesary for building such a structure. Economies of scale could easily bring the price down an order of magnitude or more.

For a small-ish cylinder that might be enough. For a cylinder that's multiple kilometers long we would want to do asteroid mining and rockets engineered to bring stuff up cheaply (at the expense of loosing a few rockets, loosing dirt is a lot more acceptable than loosing billion dollar satellites).

Note that such prize is most likely for low Earth orbit - and I don't think you want a 30 km long orbital there when if you could get it there.

There is still signifficant air drag in LEO that would get it down rather quickly, ruining someones day on the surface.

Closer to $1100 per kg for Falcon Heavy.

And something like $300 per kg for Starship (on the assumption of roughly $30M for a fully reusable launch - Musk says it should be cheaper than F9 per launch - and 100 tonnes to LEO) if they're successful in minimizing refurbishment between launches, and there's enough business to spread the development costs over enough launches.

Does it need to be a full ring from the start?

No, but consider: O'Neill cylinders can be part of a Dyson swarm, and they certainly don't need to be a full Dyson swarm from the start!

Getting resources from the moon seems out-of-date these days because the moon is far away in terms of energy even if it is close in distance.

Being close in time is still a factor for manned missions when starting out. If something goes very wrong, rescue is only a few days away.

If space missions become common enough then we'll probably have some kind of navy designed to accommodate for this problem.

Like a stellar breakdown service, always in the area

Space is really big, though. If you're in the asteroid belt, it doesn't really help if the Space Coast Guard is also in the asteroid belt because they might still be multiple AU's away.

That's true, but in all likelihood companies will cluster their operations together for this very reason. It's worth sharing some kind of common infrastructure in a specific location to protect workers/assets.

Besides, a few days/weeks is a better response time than a few months.

Sure, but then you need at least two central points for the Space Coast Guard to operate from: Earth itself (inevitably) and whichever "cluster" in the asteroid belt you want.

And there's really a limited size of an asteroid belt cluster you could get. If you start from Ceres and go a few hundred (even dozen!) meters either towards or away from the sun to reach another nearby asteroid, that asteroid has a completely different orbital velocity and will not line up with Ceres again until either it or Ceres completes another full revolution. That means you have to be in essentially the same orbit and travel either clockwise or counterclockwise, which is most efficiently done by making a more eccentric orbit (so your aphelion is the same as Ceres' but your perihelion is lower, or alternatively your perihelion is the same as Ceres' but your aphelion is higher) and then readjusting once you reach the target. But even this maneuver requires going the long way around the sun. Similarly if you want to go up or down relative to your orbital plane (i.e. change inclination).

If you want a cluster of bodies in space that stays relatively the same distance from each other, you have to have a smallish orbital system. The Earth/Moon system is one of these, and it's going to be a lot more feasible to capture near-Earth asteroids and stash them in Earth orbit than to try and find a meaningful cluster of belt asteroids that actually stay close together over the long term.

Consider that the delta V from Mars to Earth is 15 km/s, and we use gravity boost to make that delta V.

Assume we invented engines that could manage that delta V in half an hour. If my math is right, if you wanted enough 'fire departments' to reach every asteroid within one hour, you'd need about 67,000 of them, and you'd have to figure out how to pull that delta V without running into any other asteroids (probably out of the ecliptic?)

The good news is your paramedics would only pull about .8Gs which, while perfectly comfortable for earthers would still be tolerable for belters. My point is that if you try to decrease the number of stations to, say, 100, you're going to turn any human occupants into a fine mist in the process.

I'm not suggesting to cover the entire asteroid belt, only a tiny fraction - still more than enough room.

Did you look at any of my math at all? 1/67000 is a pretty tiny fraction alright.

Ok, here’s some more math. The average distance between asteroids in the belt is apparently over twice as far as the moon. The moon is still very far away for us. There will be no rescues for a very long time and remember that humans die at 10Gs, so when I say very long time I’m not just talking about faster rockets. I’m talking about basic research in human physiology.

More NASA videos and The Expanse for you, less Star Trek.

remember that humans die at 10Gs

This is not exactly true. Arguably, it's half false. In any case, this is more nuanced than what you state. There may be some humans who die at 10G. Prolonged exposure to high G might increase the death toll. People could be maintained at 10G unconscious, if they are in the right position, on the right kind of couch.

Humans have survived much higher G loads.

https://en.wikipedia.org/wiki/John_Stapp

I was about to argue with you and then realized I misspoke. Humans begin to die at 10Gs, as in survivability starts to drop at that point and if the point is to get the humans there and back again, that’s not very good.

Regardless, if people can survive 20Gs that still only doubles your range. And since we are discussing a category error of orders of magnitude, my point still stands.

I don't know why I always get voted down pointing out the obvious on moon vs. asteroids...

https://www.permanent.com/asteroids-vs-moon-private.html