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Comment by terramars | Hacker News Reader

agreed Lagrange point asteroid is much easier than any of the other options. you don't even need a big one, you just need enough of a continuous supply of resources to build a really big space station. centripetal gravity really doesn't work for this scenario though since most practical arrangements for overcoming bone loss require ~1km radius which means carbon nanotubes.

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> ~1km radius which means carbon nanotubes

You can build an 8km diameter O'Neill cylinder[1][2] with titanium. From memory his calculations used a 200% safety margin.

Where does the titanium come from? The moon, which absolutely lousy with the stuff.

Where does the energy to work titanium come from? Your friendly neighbourhood fusion lamp: the sun.

If you have mature carbon nanotech, you can jump up to McKendree cylinders[3]. These are O'Neill cylinders scaled up to a 920km diameter.

[1] http://en.wikipedia.org/wiki/ONeill_cylinder

[2] http://en.wikipedia.org/wiki/The_High_Frontier:_Human_Coloni... (worth reading if you can find it)

[3] http://en.wikipedia.org/wiki/McKendree_cylinder

Link [1] is broken :). Need the encoded apostrophe in the URL: http://en.wikipedia.org/wiki/O%27Neill_cylinder

Gack!

Thanks.

First, we would need some time to get the experience to reach that rock.

Then, considering the effort spent acquiring experience, it would be better to focus on a large asteroid.

In fact, it would be even better if we could find a way to spare some of the effort to put it on a stable earth orbit.

Wait then, couldn't we put this big rock already in stable earth orbit called "the moon" to some good use?? It's not like we've never been there tens of years ago!!

EDIT: gravity and chemical composition are valid reasons to mine an asteroid, you are totally right. Yet if we wanted not to mine but to have a colony to edge our bets for a meteor strike, IMHO the moon seems to be a better choice. However, I should have been clearer with my thoughts, I stand corrected :-)

The biggest strike against the Moon is gravity - its gravity well is deep enough to make rocketry expensive, even if nowhere near as expensive as on Earth. Even very large asteroids are mostly much less massive than the Moon.

For the same reason (mass), asteroid mining is probably more lucrative than Lunar mining (barring materials similar to Helium-3). The Moon seems to have a less diverse composition, with some useful minerals (which are mostly more massive) buried beyond easy reach.

The truth is that the Moon is more like a planet than like an asteroid. It is easier to reach.

IIRC some asteroids are even less delta-v away than the moon is. It'd be convenient to have one in Earth orbit, but not necessary.

I also question whether the structural integrity of these things is enough for them to withstand centripetal gravity without ripping themselves apart. We haven't even really confirmed that the large asteroids are really even one solid piece of rock as apposed to being a bunch of debris chunks stuck together.

Then rip them apart by design. There's an artist fixation on making one big non-redundant volume, but other than some surface area to volume vs mass issues there's no reason not to make something that looks more like a sea urchin than a baseball. Once you get over 100 or so little modules chained together you get some interesting dynamic stability problems but it gives the computers something to think about.

Worst design I can imagine is one single huge volume like the classic artists interpretation of an oneil cylinder. One hole and they all die and/or the thing rips itself to shreds.

"large asteroids are really even one solid piece of rock"

You'd be surprised what can be figured out from albedo and rotation measurements. The other thing is the line between asteroid and planet is purely arbitrary, but hovers around the self circularizing point where gravity is intense enough that it has to be more or less spherical. So the biggest asteroids are gravitationally guaranteed to be rounder and smoother, almost like a planet, at least compared to a smaller asteroid. And we've got direct imaging on small asteroids WRT scaling.

The reason there are no planets the size of the earth that are cigar shaped or whatever is gravitational. A giant asteroid would be a bit "bumpier" relatively than a small planetary moon, but its not gravitationally possible to be a cigar or a swiss cheese.

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