Asteroids as habitats

[aero]

Hollowed asteroids used as habitats are standard fare in science fiction. Often such habitats are made from a nickel-iron asteroid using heat and internal pressure to expand it into a thin spherical shell. Frequently heat is supplied by focused solar radiation or by nuclear devices.

Is it remotely feasible to make a large habitat by hollowing out an asteroid in this manner or by using any other forseeable technique?

[scienceguy]

not enough gravity

[QuantumG]

Vast amounts of literature on the subject: http://en.wikipedia.org/wiki/Colonization_of_the_asteroids

Asteroids provide two advantages over colonizing "free space" such as the Lagrange points:

 * Materials to build that don't need to be sourced from elsewhere
 * Radiation protection

Spinning the asteroid has been the traditional way to obtain artificial gravity. More recently a number of people have recognized that spinning a structure inside a hollowed out cavity of the asteroid is a lot easier and maintains the low gravity environment of the asteroid on the surface, which has manufacturing advantages.

I wrote about one of the simplest ways to generate artificial gravity - a train track inside an asteroid back in July 2010, http://quantumg.blogspot.com/2010/07/living-inside-asteroid.html

[RichardAKJ]

I wrote about one of the simplest ways to generate artificial gravity - a train track inside an asteroid back in July 2010, http://quantumg.blogspot.com/2010/07/living-inside-asteroid.html

What happens when the train breaks down?

[kch]

I wrote about one of the simplest ways to generate artificial gravity - a train track inside an asteroid back in July 2010, http://quantumg.blogspot.com/2010/07/living-inside-asteroid.html

What happens when the train breaks down?

Everybody has to be re-trained? 

[QuantumG]

What happens when the train breaks down?

You fix it?

Not sure I get the question.. the value of the train is that you can imagine getting it running within the first few months of arriving at the asteroid*. That's particularly important if you accept some finite limit to the amount of time humans can spend in zero-g before deleterious health effects kick in.

* The assumption here is that the trip out to the asteroid is brief (no more than 6 weeks) and done in zero-g, with limited radiation protection. If you have a ship with artificial gravity already, then you just need a nice cavity inside an asteroid to park and get the radiation protection. If you have both then all you get from the asteroid is resources.

[aero]

Yes - This is exactly how most sci-fy goes, jumping straight to what has been made and how it is used, totally ignoring the challange or impossibility of making it in the first place. I was hoping for this thread to focus on how the hollow asteroid became a hollow asteroid, not so much on how it was used after it became hollow.

Might it be feasible to guide two modest sized asteroids, each with a similar size crater together so that one crater capped the other and the weak gravity held them together? If not, how much super glue is needed?  Would one cratered asteroid, capped with a moderately flat asteroid be a suitable start to a habitat? How about a larger asteroid with a crater capped by a small nickel-iron asteroid that had been heated and spun into a disk?

[QuantumG]

1. pick an asteroid with an upcoming close approach to Earth
2. send a tunnel digging robot and supplies on a long duration flight
3. dig tunnels
4. flight of the humans to the asteroid
5. setup minimal artificial gravity and life support systems
6. begin excavation of the asteroid and in-situ manufacturing
7. expand the artificial gravity and life support systems to support a growing population
8. continue excavation and construction towards "worldlet" goal
9. develop propulsion systems to take control of the worldlet, so it can be directed towards other asteroids
10. use other asteroids as resources or create more worldlets

Expand humanity ever outwards, colonizing the Oort cloud and eventually to the stars.



Enjoy.

[jedsmd]

Yes - This is exactly how most sci-fy goes, jumping straight to what has been made and how it is used, totally ignoring the challange or impossibility of making it in the first place. I was hoping for this thread to focus on how the hollow asteroid became a hollow asteroid, not so much on how it was used after it became hollow.

Might it be feasible to guide two modest sized asteroids, each with a similar size crater together so that one crater capped the other and the weak gravity held them together? If not, how much super glue is needed?  Would one cratered asteroid, capped with a moderately flat asteroid be a suitable start to a habitat? How about a larger asteroid with a crater capped by a small nickel-iron asteroid that had been heated and spun into a disk?

You might want to Google "Project Plowshare - Peaceful Nuclear Explosions (PNE)".  The US set off a series of 27 atomic bombs to see if they were practical for excavation of harbors and such.  Should be applicable to your project.

[QuantumG]

Gah! What do you imagine these things are made out of?

Consider 25143 Itokawa, visited by Hayabusa. It has a mean density of 1.95 g/cm^3. This is about the same as the density of natural gravel.. which makes perfect sense when you look at it.

You don't need nuclear bombs to dig a hole in this stuff.

[jedsmd]

Gah! What do you imagine these things are made out of?

Consider 25143 Itokawa, visited by Hayabusa. It has a mean density of 1.95 g/cm^3. This is about the same as the density of natural gravel.. which makes perfect sense when you look at it.

You don't need nuclear bombs to dig a hole in this stuff.

Agreed a Tunnel Boring Machine is a far more practical approach.  But AERO wants to hollow the entire asteroid and possibly reshape it and spin it in the processes.  When you consider the amount of material you need to move to complete his vision - nuclear may be the way to go.

[scienceguy]

Gah! What do you imagine these things are made out of?

Consider 25143 Itokawa, visited by Hayabusa. It has a mean density of 1.95 g/cm^3. This is about the same as the density of natural gravel.. which makes perfect sense when you look at it.

You don't need nuclear bombs to dig a hole in this stuff.

If they're like gravel, how will the tunnels hold together after you've tunneled through them?

[aero]

Gah! What do you imagine these things are made out of?

Consider 25143 Itokawa, visited by Hayabusa. It has a mean density of 1.95 g/cm^3. This is about the same as the density of natural gravel.. which makes perfect sense when you look at it.

You don't need nuclear bombs to dig a hole in this stuff.

If they're like gravel, how will the tunnels hold together after you've tunneled through them?

And the material must be strong. Remember it has to withstand pressure - not so much force if there are only small diameter tunnels, but quite a lot of force if the cavity is large.

[QuantumG]

Agreed a Tunnel Boring Machine is a far more practical approach.  But AERO wants to hollow the entire asteroid and possibly reshape it and spin it in the processes.  When you consider the amount of material you need to move to complete his vision - nuclear may be the way to go.

Agreed, it's a nice to have, but you can imagine doing without if necessary.

If they're like gravel, how will the tunnels hold together after you've tunneled through them?

What forces do you imagine hold the asteroid together now?

It's not gravity, that's much too weak.

[jedsmd]

Gah! What do you imagine these things are made out of?

Consider 25143 Itokawa, visited by Hayabusa. It has a mean density of 1.95 g/cm^3. This is about the same as the density of natural gravel.. which makes perfect sense when you look at it.

You don't need nuclear bombs to dig a hole in this stuff.

If they're like gravel, how will the tunnels hold together after you've tunneled through them?

On earth soft bore tunnels are normally lined with concrete.  If there is ice in the asteroid a frozen ice liner might be practical.  But I think QuantumG is right, in that low of gravity a liner isn't necessary as lateral soil pressure might be next to non-existent.

[QuantumG]

If you wanted to pressurize (with air) the tunnels you'd need a liner.

[jedsmd]

If you wanted to pressurize (with air) the tunnels you'd need a liner.

Yes and steel or other tension reinforcement to resist the pressure - ugh that will probably have to come from Earth.

[QuantumG]

If you want to do it early, sure. Resupply from Earth is not so bad, you can do that with long lead times and electric propulsion (like all the asteroid missions to-date).

Do it later, when in-situ manufacturing is happening and local resources of metals can be processed, and imagination becomes the biggest limit to what future generations can achieve.

Taking the long view, there will always be something that it's better to get from Earth than it is to produce locally.. so what can asteroid colonists produce better than people on Earth? Nothing, right? I disagree. They can make stuff in space. So long as launch from Earth remains costly, and people on Earth remain interested in manufactured items in space, those colonists already in space will always have valuable goods.

Maybe that's not so clear. So here's an example: spoons. Even today, people use spoons in space. Sometime in the future there's a need for 1 kg of spoons in Earth orbit. We could launch it from Earth and pay, let's say, $500/kg in launch costs (what an amazing achievement!) or we can put it on the slow boat from the asteroid colony. It's not hard to imagine the marginal cost of transporting those spoons from an asteroid colony to Earth being a lot cheaper, because the energy requirements are so much lower.

[A_M_Swallow]

The tunnel and asteroid will also have to take the force of the train passing.

We may be able to sinter asteroid material to make tunnel liner.  A weak material simply means the liner has to be thick.  If sintering does there are other ways of melting and setting material.

[QuantumG]

The tunnel and asteroid will also have to take the force of the train passing.

Not really. "Train" is an analogy.. we're talking about a ring of steel with a carriage rolling around the inside. The track is transported in parts and put together. It would work fine on the way to the asteroid too, but I think there's more value in a fast transit in zero-g to get to the asteroid than artificial gravity in transit because you can send the track and the train on a slow electric propulsion cargo flight, reducing the mass required on the high impulse crew flight. There's a tradeoff.