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Wingnut Ninja
2003-Apr-20, 08:13 PM
How porous are asteroids? Or do we even know exactly? I'm writing a story with a colony in an asteroid, and I was wondering if you could just bore tunnels through it and pressurize them, or if you would have to seal the walls with something more air-tight. I like the idea of having cold, dark tunnels in the rock, but I don't want people getting sucked into crevices, or the asteroid falling apart under stress.
Anyway, are asteroids solid enough to tunnel through safely?

darkhunter
2003-Apr-20, 08:42 PM
Should be. IIRC: There are different types of asteroids: Nickle-iron and chrondite (stony). Of the to I assume that your interested in the nickle iron ones for resources. They should be plenty strong to tunnel through and give the effect you want. Can alway paint the inner walls with a sealent to keep the air in.

Anyone with more knowledge please correct me if I've got it wrong (as if that's a problem here :lol: )

edit: One reference (http://www-astro.physics.uiowa.edu/~srs/Locus27.htm)

aurorae
2003-Apr-21, 12:08 AM
There are different types of asteroids, some appear to be just uncosolidated rubble piles with lots of voids, while others appear to be comparitively solid.

bobjohnston
2003-Apr-21, 02:38 AM
I would agree with aurorae--there are different types. I think it would be a challenge to find a small one sufficiently free of fractures, though.

Calculated densities suggest a significant fraction of asteroids may be rubble piles. If reports on Amalthea are any indication, some objects could have half their volume as voids.

Someone mining an asteroid might prefer to work on a solid one, anyway, to avoid shifting rubble while working. Maybe sealant "spotwelding"...

bobjohnston
2003-Apr-21, 02:40 AM
I would agree with aurorae--there are different types. I think it would be a challenge to find a small one sufficiently free of fractures, though.

Calculated densities suggest a significant fraction of asteroids may be rubble piles. If reports on Amalthea are any indication, some objects could have half their volume as voids.

Someone mining an asteroid might prefer to work on a solid one, anyway, to avoid shifting rubble while working. Maybe sealant "spotwelding"...

beskeptical
2003-Apr-22, 10:44 PM
I am not up on the composition of larger asteroids, but the meteorites that make it to our planet are extremely dense.

Nickel Irons are very hard to cut and drill but it is done with the usual Earth tools like rock saws. There are definitely no gaps inside. The holes you see in ones that have them occur as the meteorite is falling through the atmosphere.

They are made of planetary core material and represent a small percentage of what is hitting the Earth.

Stony meteorites are dense and heavy, no air pockets. There are several types, chondrites, achondrites, carconaceous chondrites, rumurutiites (R-chondrites), and enstatite chondrites (E-chondrites).

Chondrites are dense but you can crumble off an edge of a sliced one if you are not careful.

Many meteorites are mixed.

There has been an extremely rare meteorite with a porous consistency like lava but is not the norm.

Wingnut Ninja
2003-Apr-23, 03:14 AM
Alright, thanks all, I'm satisfied that I can use asteroids without any moral qualms.

Any thoughts on the feasibility of connecting two asteroids with a tether (a really, really strong tether) and spinning them around to make artificial gravity? :D

kilopi
2003-Apr-23, 03:37 AM
Any thoughts on the feasibility of connecting two asteroids with a tether (a really, really strong tether) and spinning them around to make artificial gravity? :D
Well, there is the problem of falling off the backside. Or even the sides. :)

That kinda reduces the useful area. Might as well make 'em totally artificial, and hollow. Let's see, have them going 90mph (3cm/s) in opposite directions, and 900 feet (2 km) apart, that'll give you Earth gravity, but they'd spin around a couple times a minute.

(Specific claim remains even while most every term requires immediate conversion. :) )

QuagmaPhage
2003-Apr-23, 10:56 AM
I gather from your post that you haven't read Heart of the Comet by David Brin & Gregory Benford. Brin & Benford are both physicists and know their stuff. The book is about a exedition to Halley's Comet, where the crew has to colonize the comet to have any hope of surviving. The book was published around 1986 and that is why Halley's Comet is the choosen target, as it last visited the inner solar system that year. But it could apply to any asteroid/comet of a similar composition.

kilopi
2003-Apr-23, 11:05 AM
Me? David Brin wrote The Postman (http://us.imdb.com/Title?0119925).

BigJim
2003-Apr-23, 02:42 PM
There are several distinct classes of asteroid. The three main types are:
S, for stony asteroids, M, for metal, and C, for carbanaceous. One interestring question that would arise while tunneling into an M-type asteroid, which you appear to want to do, is if you could mine it at the same time. Asteroids are extremely rich in minerals and metals. Besides the book Mining the Sky, you can go to

www.matter-antimatter.com/mining_asteroids.htm
www.permanent.com/a_mining.htm
www.mg.mtu.edu/~lgertsch/CSMworkshop99/CSMwhitepaper.htm
neo.jpl.nasa.gov/neo/resource.html
http://science.howstuffworks.com/asteroid-mining.htm

From HowStuffWorks:

John S. Lewis, author of the space mining book Mining the Sky, has said that an asteroid with a diameter of one kilometer would have a mass of about two billion tons. There are perhaps one million asteroids of this size in the solar system. One of these asteroids, according to Lewis, would contain 30 million tons of nickel, 1.5 million tons of the metal cobalt and 7,500 tons of platinum. The platinum alone would have a value of more than $150 billion!

The platinum would be about ten times better than the best terrestrial ore and the iron and nickel would be very pure. And this is only for an S asteroid- imagine an M asteroid being mined![/url]

QuagmaPhage
2003-Apr-23, 07:44 PM
Me? David Brin wrote The Postman.

No not you kilopi, sorry for the confusion. I meant the original poster Wingnut Ninja.
Yes David Brin wrote the book The Postman. From what I have read about the movie, they have very little in common except the basic premise. The book was rather good actually. IIRC it was his second or third full length novel.

Another hard SF novel which feature mining and colonization of a asteroid is Time by Stephen Baxter. As BigJim points out asteroids are very rich in minerals and metals and the novel's protagonist tries to mount a expedition to get one pushed into orbit around the Earth.

gethen
2003-Apr-23, 08:37 PM
Hey, I loved the book The Postman! But the movie was strictly a Kevin Costner vehicle. Except for Tom Petty.

ToSeek
2003-Apr-23, 08:37 PM
Hey, I loved the book The Postman!


It was actually a short story (and a classic one) before it was a novel.

kilopi
2003-Apr-24, 02:12 AM
No not you kilopi, sorry for the confusion. I meant the original poster Wingnut Ninja.
Wheeuww, thank the L*rd. Still, the OP was talking about asteroids, not comets.

Wingnut Ninja
2003-Apr-24, 04:59 AM
Actually, I have read Heart of the Comet; that and some other stories are what gave me the idea of using asteroids (I'm a big fan of David Brin :) ). In HotC, they have to line the tunnels with a sealed tube, but an asteroid would be made of hardier stuff than a comet, so hopefully that would be unneccessary. It would also prevent people from "falling off the bottom;" you just stay inside.
There's also an Asimov story that I read a while ago (I forget the name... it deals with sewage) that takes place in a colonized asteroid. At one point one of the inhabitants explains to a visitor that because they can tunnel all the way through the asteroid, they have more livable surface area than the earth!
Of course, I want to avoid the cheap way out of "generated" artificial gravity, so I'm going with the spinning tether approach. If it's a few kilometers long they wouldn't have to spin very quickly. Tank Farm Dynamo (another Brin short story) has something along those lines.
I forgot about the mining potential, though. I'll make sure to make it a very wealthy place.

traztx
2003-Apr-24, 02:25 PM
How massive is the asteroid? Your tether needs to support all that weight when you spin the pair up to 1G. I suppose you could make it out of those magical nanotubes.

Maybe one benefit to spinning around is that approaching spacecraft don't have to retro to match orbital velocity. They can retro to the velocity tangent to the inside edge of the colony's rock and let it catch them for a landing. I realize that's a little more delta-v in the long run, but you arrive a little faster.

Wingnut Ninja
2003-Apr-24, 05:22 PM
It's a very, very strong tether. It's basically one of those things where I say, "They managed to do it, don't complain." Also, they aren't spinning at a full 1 G, more like a third of a G or so.

And my arrangement has three asteroids; two spinning on the tether and a third one in the middle (not directly attached to the tether) that is used for docking and storage. To dock on one of the ends, you would need to line up with the plane of the spin, and then have to deal with weight once you land, and all kinds of other annoying problems. Zero g docking is a lot easier.

daver
2003-Apr-24, 06:30 PM
It's a very, very strong tether. It's basically one of those things where I say, "They managed to do it, don't complain." Also, they aren't spinning at a full 1 G, more like a third of a G or so.

You're still going to have to support your asteroid. Your tether is going to look a lot like a web. It may as well be a web--multiple strands for redundancy.

Obviously construction would be easier with less gravity. It's your story, you can determine that there is a minimum gravity above which no bad medical effects occur, or that medicine has learned to compensate for them. Regardless, you might extend one of the tethers to have a 1 g environment for a tourist hotel.



And my arrangement has three asteroids; two spinning on the tether and a third one in the middle (not directly attached to the tether) that is used for docking and storage. To dock on one of the ends, you would need to line up with the plane of the spin, and then have to deal with weight once you land, and all kinds of other annoying problems. Zero g docking is a lot easier.

That gets kind of messy--you're going to have a spinning section and a non-spinning section, and some sort of bearing joining the two. You might just want to have everything spin, and have the docking spacecraft roll to match your spin (a la 2001). It's going to be a pretty leisurely roll rate anyway--probably less than 1 rpm.

traztx
2003-Apr-25, 04:16 PM
I'd love to hang out at the recreation center in the middle rock :)

OK Maybe "hang out" is a bad phrase... "float around"?

I wonder if they could have a "swimming drop" instead of a swimming pool. It would be a huge drop of water held together by surface tension and kept steady by fans perhaps. Would the surface tension eject any swimmer out of the drop if they were only partially in it? What happens to any bubbles a diver makes deep inside the drop?

ToSeek
2003-Apr-25, 04:19 PM
I wonder if they could have a "swimming drop" instead of a swimming pool. It would be a huge drop of water held together by surface tension and kept steady by fans perhaps. Would the surface tension eject any swimmer out of the drop if they were only partially in it? What happens to any bubbles a diver makes deep inside the drop?

I think Clarke had a story like that: the space station had a big sphere of water in the middle, with a hollow bubble of air right at the center. Don't recall how the air at the center was kept oxygenated, though.

Wingnut Ninja
2003-Apr-26, 05:33 AM
Zero-g football is where it's at. Use little Spock-style rocket boots to move around.