Asteroid Volatile Extraction

[ARD]

Suppose that one has found an asteroid or extinct comet around 1 kilometer in average diameter, that appears to be loaded with water ice, ammonia ice, methane ice, and all sorts of other wonderful things.  If it's an extinct comet, suppose it has a several centimeter crust that locked its volatiles inside, and which must be broken if these volatiles are to be extracted. 

How would one go about extracting volatiles from an asteroid or comet nucleus?  Strip-mining, which may work on the Moon, would not really be an option (all that dust getting everywhere, the difficulty of movement on an asteroid).  Drilling seems somewhat inefficient, and after one extracts from the immediate area of the drill, one has to move the entire apparatus. 

Would bagging the asteroid in a layer of insulating material work?  Could one simply heat the entire asteroid up until it outgasses its volatiles?  Would the aforementioned crust (present on at least one apparent comet nucleus, 14827 Hypnos) interfere with this? 

And, having caused the asteroid to outgas until you have a bag of gas and rock, how does one go about collecting all this gas and liquefying it for transport?  Would the low gravity present an obstacle to processing the vapors? 

[grondilu]

How would one go about extracting volatiles from an asteroid or comet nucleus?

optical conveyor tractor beam 

Physicists demonstrate an actual tractor beam in the lab

[KelvinZero]

(uninformed opinions follow )
I favor drilling in to contain the mining effects and get protection from cosmic radiation but I think in any cases it would be very useful to be able to process your used material into some form that stays together. Even if you were not mining it would be useful to be able to lock down the surface around landing sites etc.

For this reason it might be worth first comparing options for locking down dust and then using that result to proceed.
Of the top of my head some options are
* bagging (bags brought from earth would be vastly lighter than the volatiles extracted so it could be a cost effective trade.)
* fixative spray (similar argument to bagging)
* sintering.
* concrete. (using a fraction of the water extracted)

I don't like the idea of bagging the entire asteroid to begin with. Maybe that would be more efficient in the long run but in the short term I dont think it would ever get started. I could be wrong. Could be totally reasonable if we end up chasing many tiny rocks only a few meters across rather than one big one. So there is another question: what scale asteroid would be most cost effective to chase?

[alexterrell]

It depends on how advanced you are and how many volatiles you want.

If you want to 50 million tons of volatiles to support your O'Neil Island 4 colony, the bagging it is the way to go. And bring in a few GW of radiative heat. Check the phase diagrams for what minimum pressure you need to condense the volatiles, and that determines the bag pressure, which is going to make for quite an impressive structure. Alternatively, you could build your colony around the asteroid. Once the pressure vessel is done, spread it around to give about 5m of top soild and an atmosphere.

If you want 100,000 tons for your interim colony, you might try digging into it and vaporising it from the inside.

If you want 1,000 tons for your fuel home, then I think you'd scoop it out and process it bit by bit, using the dried out regolith as shielding for your base. Anchoring the scoop may be a challenge - you'd probably want to run a cable right around the asteroid.

I have seen a design to put a bell cone on the asteroid and then heat inside that. It might work depending on the composition and what seal you can get.

[KelvinZero]

Well we are not advanced at all and a 100kg demonstrator would be vastly better than nothing

[Andrew_W]

Bag the sucker.

[ARD]

Well we are not advanced at all and a 100kg demonstrator would be vastly better than nothing

In that case, how might it be done?  A C-type asteroid whose volatiles are accessible from the surface would seem to lend itself to a rather simple technique of scooping material within a robotic arm's length of the lander and heating it like Phoenix did, but on a larger scale.  Larger operations on similar rocks could, I suppose, have rover-like vehicles or even hoppers jump around and scoop up material farther from the processor. 

But suppose you've got a comet nucleus with a depleted crust?  Or just a C-type bombarded to the point where its volatiles are many meters below the surface (as the moons of Mars appear to be)?  Phobos and Deimos in particular are the prompt for this question--extracting water from those bodies would greatly ease any Mars exploration architecture.  However, their water content appears to be tens of meters below the surface. 

Maybe drilling down as far as possible, and then running liquid sodium from a nuclear power source into the pit to cause outgassing? 

[KelvinZero]

But suppose you've got a comet nucleus with a depleted crust?  Or just a C-type bombarded to the point where its volatiles are many meters below the surface (as the moons of Mars appear to be)?  Phobos and Deimos in particular are the prompt for this question--extracting water from those bodies would greatly ease any Mars exploration architecture.  However, their water content appears to be tens of meters below the surface. 

I dont know.. but if you have a way to lock down the regolith you might have an answer. You could build up walls as you advance.

I wonder how big the dust problem will really be in practice. Even if the escape velocity is only 10m/s, couldnt you just make sure you only throw the dust at one meter per second?

Also, whatever you throw, whether it is above or below escape velocity, you won't have circularized its orbit which means it can't float around forever like space junk around earth. each particle will travel on an ellipse that will land back on the asteroid in less than a full orbit (or escape completely). Only a very narrow range of trajectories could even return the dust back to where it came from and you are working.

Finally, some simple 'wind break-like' material could be erected to suck the kinetic energy out of any particles floating around in near-circular orbits, and perhaps to ground any static charge keeping them elevated as well.

[TyMoore]

One of the troubles involved with drilling is the fact that at least for typical hard rock drills on earth, you use water, mud, or compressed air to cool and lubricate the bit and flush cuttings away from the work face. This may be difficult or impossible to do in an asteroid environment of deep cold and vacuum. However, using a powerful linear accelerator to create a say 100kw electron beam you can slab and extract blocks of material.

A combination of industrial lasers or electron beams for creating small boreholes, followed by a hydraulic pneumatic chisel bit (like the units on excavators used to bust up concrete) could be effective in breaking up larger blocks. Use a dragline for the loose material...

I've always thought that sticking the whole thing in a giant 'soup' can and then retorting the whole thing would be very effective.

[grondilu]

I've always thought that sticking the whole thing in a giant 'soup' can and then retorting the whole thing would be very effective.

Not necessarily giant.  It could work more or less like how flies eat.  They inject some enzyme that liquefies food and then they absorb the fluid with their trump.



Instead of using an enzyme, a machine could locally break the asteroid into a powder, mix it up with a liquid and finally absorb the mixture.  (Not sure what kind of liquid will stay liquid in space, though)

[Andrew_W]

"Rubble pile" asteroids are believed to be porous, if you stick the sucker in a black bag the sun will heat it up, the lighter volatiles will vaporize and spread throughout the volume of the bag and the asteroid, slowly warming its whole volume and releasing other volatiles.

You'll only need a very low pressure within the bag for this to happen, and that pressure will be ample to push the volatiles through your shaded and IR radiating distillation plant which will separate off each of the components of the gas as they liquify.

[A_M_Swallow]

{snip}
Instead of using an enzyme, a machine could locally break the asteroid into a powder, mix it up with a liquid and finally absorb the mixture.  (Not sure what kind of liquid will stay liquid in space, though)

A powder is a fluid.  Fluids can be pumped, so a liquid is not needed.

[grondilu]

A powder is a fluid.  Fluids can be pumped, so a liquid is not needed.

I don't know.  I thought a fluid liquid had tensile strength or something that makes it much easier to pump.

[A_M_Swallow]

A powder is a fluid.  Fluids can be pumped, so a liquid is not needed.

I don't know.  I thought a fluid liquid had tensile strength or something that makes it much easier to pump.

You are operating in a vacuum in low gravity.  A liquid that is likely to boil off will make things more difficult.  An Archimedes Screw can move powders.

[grondilu]

Maybe this could help: