Did you Know??

Dusty · Veteran Member

Did you Know??

10kBq Jaro · Senior Member

Well, with surface pressure being 14.7psia ('a' for absolute), that 30psi at the bottom of a very deep mine shaft corresponds to 2 atmospheres.

I haven't checked the data, and I don't know how deep that mine shaft is (5 kilometers ?), but it seems to me that a doubling of surface air pressure under the effect of 9.8m/s^2 gravity is not very attractive for application on Mars: with much less gravity, at similar depth, you get considerably less than double the surface pressure -- i.e. < twice nothing, is still nothing....

GoogleNaut · Guru

I'd have to agree. Mars would require a really deep shaft, and this would probably be complicated by some of the same things that complicate mines on Earth: geothermal heat (I guess on Mars this would be technically called "ariethermal heat"--but everybody knows what geothermal heat is!) Also, high pressure water seeps and lithoplastic flow of the rock (if the pressure is high enough!) would present large problems. It seems to me that having pressurized surface habitats covered with a layer of Martian soil for radiation shielding makes more sense. The added complications of construction in a near space environment (the surface of mars is pretty similar in many respects) complicated by superfine dust and possibly corrosive surface minerals leads me to believe that these will be challenges enough for now...

But since the surface of Mars is nearly the same atmospheric pressure as 35 km of altitude on earth (about 100,000 feet) then you'd need a shaft close to 350 km deep to get a any significant columnar compression--and even though Mars is apparently mostly dead geologically, this is a non-trivial depth: it's bound to be hot and partially fluid (i.e., molten!) and very, very high pressure down there. Not a pleasant place for a relaxing evening with the wife and kids after a hard days work terraforming Mars!

Dusty · Veteran Member

OK Not such a good idea.

I had been reading "Ringworld Engineers" and got to thinking about Warhead/Canyon.

Oh well

GoogleNaut · Guru

Well, it's not a bad idea. It just works a lot better on Earth because of the thicker atmosphere. With thinner atmosphere, there is a lot less pressure to start with, so the shaft has to be a lot deeper anyway. But because Mars' gravity is about 1/3 that of Earth, the well would have to be almost 3 times deeper again...

Interestingly, along time ago I wondered if it might be possible to bore habitable tunnels all the way through large asteroids like Ceres. In the extremely low gravity at the surface, it seems like it should be possible to core the thing like a gigantic apple and simply build cities inside. Perhaps even spinning them miles beneath the surface for some really interesting habitat spaces. I was thinking about a cool way of utilizing all those volatiles and metals to be found there to build a truly space based industrial civilization. Well, after doing some of the math I found even at the very low surface gravity conditions on the surface of Ceres, there is still enough gravity to generate sufficient pressures below the surface that lithoplastic flow of the rock matrix will still be a problem. Even a hundred kilomoters below the surface, the pressure on tunnels will be substantial. I don't remember the actual numbers, but near the core it would be easily enough to crush anything you put in there. No tunnels to the core I'm afraid--atleast not until you substantially mine out enough surface materials to reduce the overburden enough to reduce the pressure at the core. And that will take a LOT of mining for a body the size of Ceres. I'd have to say that as a general rule, if a body is large enough that internal lithoplastic flows have arranged it into a semblence of a sphere, then core pressures will be high enough to prevent any body spanning tunnels from being made.

However, smaller asteroids should be quite possible to run a tunnel right through the things--and this should make some things easier that way. Even a 'rubble pile' asteroid could be cored this way as long as something like a tunnel boring machine continuously produced or installed a tunnel casing.

Positronium · Member

I would hold off before building any sub-surface dwellings on an asteroid. The fact that Ceres is spherical is probably a good indication that the pressure at its core is high enough to melt rock but it isn't guaranteed. A collection of loose aggragrates would also form a sphere if given enough agitation and time since a spherical matter distribution is a minimal energy state. I don't know if anyone has determined if Ceres is actually solid or not though since no one has actually been there or sent a probe there. There is a picture at the following link that seems to show what may be a polar ice cap which would suggest a decent ice content:

http://hubblesite.org/newscenter/newsdesk/archive/releases/2005/27/

Since Ceres has a density of about 2 g/cm^3 and a random rock has a density around 3 g/cm^3, I think it may be possible that it is made of a gravel and ice mixture, at least partially.

Another way to look at it is to compare the surface acceleration of gravity of Ceres with that of Earth. Since the mass of Ceres is approximately 8.7*10^20 kg and its radius is 466 km roughly, you can use the Gravitational constant to find the surface gravitational acceleration using a = G*m/r^2 (acceleration due to a point mass at a distance is the same as for a spherically distributed mass if you are outside an enclosing Gaussian surface which contains the mass since gravitation is a conservative force). Doing this you get a = 0.267m/s^2 for Ceres which is approximately 0.027 times the surface gravitational acceleration on Earth. A 100 pound (on Earth) person on Ceres would weigh approximately 2.7 pounds.

See also:

http://aa.usno.navy.mil/ephemerides/asteroid/astr_alm/asteroid_ephemerides.html

10kBq Jaro · Senior Member

Positronium wrote:

The fact that Ceres is spherical is probably a good indication that the pressure at its core is high enough to melt rock....

Rock melting inside a planet(oid) has little to do with pressure.

In most cases its caused by heat from NORM (Naturally Occuring Radioactive Materials). This heating is particularly strong in the earliest epoch following solar system formation, because some of the shorter-lived NORMS, like Pu-244, U-235, U-233, etc. are still abundant, following their production in supernovae (note that heat generation is inversely proportional to radiactive decay rate - the shorter the half-life, the greater the energy output).

In some cases, like the Jovian moons Io & Europa, and Saturn's Enceladus, we have also found that gravitational tidal heating can also play a significant role. This would obviously NOT apply to Ceres.

Yet another possibility is the formation georeactors, capable of supplying heat comparable to that of radioactive decay, throughout geologic time.

GoogleNaut · Guru

Asteroid Mining in general

Positronium · Member

RE: Did you Know??

Taylorchef · Member

Ceres is probably a really bad place to start. It has a probable quantity of water ice in the range of 200,000,000 cubic kilometers. Or about the total of about all the fresh water on Earth. The Layer of water ice is from 60 to 120 kilometers thick & starts at from between 20 & 60 kilometers below a high silicate rubble like surface.

GoogleNaut · Guru

I suspect you're right about Ceres having a bit of ice in it--although it sure sounds like it has a lot. This should make Ceres prime realestate for future asteroid volatile mining, and synthetic chemical industry. There's bound to be quite a bit of hydrocarbons there as well, so I would imagine a robust plastics, propellant, and synthetics industry thriving there one day...

I would be interested in learning where you got your data from because Ceres is an enegmatic object as far as data goes--I haven't really found anything to indicate volitiles on that order magnitude--I was just guessing simply in terms of it's position in the solar system.

As far as asteroid mining in general, I can think that mining methods will be strongly influenced by the size of the mined object and its composition. This seems strangely obvious, but there are some subtle things to account for. For instance, a large, silicate 'rubble pile' body may be mined more or less conventionally using a 'strip' mining style operation--virtually scraping material with a drag line and hoppering material. A volitile 'mine' may be operated using a drilled shaft with a downhole heat source to melt and evaporate ices from the interior of bodies and extracting condensates--this is no small technical task. Shafting and removal of solid blocks, followed by retorting may actually be easier---it all depends on the actual composition whether it be ice-bonded regolith (similar to ice-rock mixtures that exist in permafrost or glacial deposit areas on Earth--which are a real Bear to work with!)

Also, sinking a shaft is difficult in the best of conditions here on Earth, but with the added problems of milligravity or microgravity, vacuum, rock-ice-metal matrixes, and many, many other unkowns relatingto faulting and the mechanical properties of the matrix to be mined or tunneled through, it becomes clear that many challenges await astroid mining entrepeneurs. The virtually solid metal matrix of nickel-iron asteroids may be the most challenging, because the natural matrix of iron and nickel will likely be similar to tool steel--tough stuff indeed. Conventional mining methods will probably give way to cutting torches!

This is one reason why I tend to lean toward using an electron beam tool. A linear accelerator can create a reasonably high current beam of electrons which will have a luminosity several orders of magnitude higher than a high power industrial laser.

Using electron beams as the cutting tool could allow thick slabs of material, metal and rock mixtures, to be removed. Further cutting of the slabs into cubes, and then grinding using a centrifugal hammer mill to mechanically seperate out silicate minerals, and then melting in a solar furnace and followed by centrifuging the melt to spray it into a mixxed metal powder. The mixxed metal poweder can then be processed chemically using carbonyl extraction (treatment with carbon monoxide) to remove the bulk of the nickel and iron as the volitle gasses nickel tetracarbonyl and iron pentacarbonyl respectively. The residues will contain mostly cobalt carbonyl and precious metal bearing materials. Further leaching with acid and then electrolysis followed by electrorefining and then casting into ingots will yield up all of the precious metals, of which platinum and rhodium will be the first and among the most economically valuable target minerals of exploitation from the asteroids. The catalyst industry is poised to consume vast quantities of these materials if things like cheap fuel cells for electric vehicles are ever to be made!

But mining and processing requires a lot of equipment and lots of power--and this means a lot of stuff in low earth orbit. Which means a big ship--and this just begs for nuclear power...

Positronium · Member

One way to slice up a large asteroid and collect the volitiles that occurs to me is to just use a large mirror to focus sunlight on it and cut it into little chunks. You could use a thin aluminum coated mylar type mirror that would fold up very small like a solar sail but unfold to the diameter of the Earth or larger depending on the solar flux where you are. Once you cut the asteroid into small enough peices, you can put the chunks into a rather large spherical container (tungsten or quartz perhaps) of some sort, adjust the foccal length of the mirror to make a more diffuse spot to just heat up the sphere and slowly volitalize the ice inside. Collect the gasses that come off and condense them. Put this condensed gas into big balloons and let it refreaze. Now you have larger chunks that are mostly metal and stone that can be processed in a different way but you have removed and collected the volitile stuff so the volume of what remains could be considerably less.

GoogleNaut · Guru

Degassing by retorting (roasting) will certainly be beneficial if the assays indicate significant volatiles--recovery of hydrogen, nitrogen, water, and carbon dioxide will all be necessary, especially to a mature space industrial infrastructure, and will also be necessary for recovery of hydrogen reaction mass for return trips back to home.

On the issue of using solar flux for direct cutting, I've kind of looked at that, but the optics necessary to concentrate, columnate, and direct the solar flux--safely--is a technically difficult enterprise. Such an optical system will likely need lenses, and this may be technically very difficult because if the lenses absorb only 0.1% of say 10 MW of insolation, the energy deposited in a typical lense could be as high as 10KW. An array of lenses will of course absorb proportionately more, and this assumes a transmissance of 99.9% which is a very high figure. 1% absorbance implies 100KW at the lense face--requiring active cooling even for large saphire lenses. Unfortunately we can't yet make optically perfect synthetic diamond on this scale--which is too bad--because diamond would be ideal since it has a very high refractive index (a little over 2) and extremely high thermal conductivity (better than copper if you can believe that!) Still, a solar furnace is a critical technology for s[ace resource utilization because, as you say, it is possible to heat relatively large amounts of material for retorting of volatiles and possibly even melting operations.

Smaller rocks (a few tens of meters across) may be completely 'bagged' or stuck inside a large container and then dissassembled relatively easily by using a large version of a plasma torch. Nitrogen could be used as a carrier gas. A carrier gas thus trapped inside a large 'can' at low pressure, could then be fairly easily extracted using vacuum pumps, where it could be filtered, recompressed, and reused. This would reduce or eliminate the consumption of volatiles for this purpose, however, if the pressence of volatiles were sufficient this may not necessarily even be a problem.

Still, I'm not sure how to approach a cutting, drilling, shafting situation with mixed metal-ice-rock matrix. Drilling in permafrost is not trivial even on Earth! Without expending a lot of volatiles (such as water) for a conventional wet drill to cool and lubricate a diamond bit, I don't see how it would be possible to cut into an asteroid without using some kind of plasma torch cutter, high powered laser, high powered electon or particle beam, or solar concentrator system. A material bit and mechanical power may just not cut it without excessive friction heat and wear.

Taylorchef · Member

The info on Ceres composition comes from NASA & the VLA. NASA has looked at it with various telescopes over the years, & the VLA has hit it with radar a number of times.

Taylorchef · Member

I think the best candidates, in the beginning, for mining are going are going to be the closest ones. It almost does not matter what their composition is, as long as we can get to them, & even move the smaller ones, (100 meters & down in size).

No matter what is in them, they will be useful.

GoogleNaut · Guru

True,

however, candidate bodies composed predominately of volatiles (carbonaceous) and nickel-iron asteroids will be initially the most valuable. What I am interested in is creating a transportation/extraction infrastructure that will primarily concentrate and return platinum group metals, specifically rhodium (currently at almost $4000 US per troy oz) which is an essential catalyst needed for almost all synthetic fuel applications. Platinum will also be extremely useful as a catalyst in conjuntion with rhodium, and also as a standalone catalyst for efficient fuelcells. Most nickel-iron bodies have PGM's (platinum group metals) in excess of 100 parts per million, which would be considered a very high grade ore here on Earth. A 1km diameter spherical equivalent nickel-iron body will mass around 3.6-4.0 billion metric tons, which means that such a body will contain just about 350,000 to 400,000 metric tons of PGM's. Of that, about 1/5 of the PGM's will be rhodium--so anywhere from 70,000 to 80,000 metric tons will be rhodium. Returning even a thousand tons per year will radically alter the supply of this important element causing its price to drop, for sure, but it will open up many new markets for it as well. Creating a ship with a capacity to return 5000 tons of PGM's in one sortie will immediately payback almost $160US billion dollars, assuming a combined 20% platinum + 80% rhodium cargo with a depressed cargo price of $1000US per troy ounce. Even a pessimistic depression of price to $100 per troy ounce still means a return of $16 billion. This is why returning PGM's is so initially important.

Once initial payback is complete, then expansion of existing infrastructure makes a lot more sense. The volatiles then become vastly more important, once this expansion is underway. Initially volatiles will be predominately be used for propellants, but eventually chemical synthesis will make the volatiles useful for everything from creating plastics, soils for agriculture, to eventually pharmeceuticals.

But I believe the only thing that will attract the initial vast amounts of venture capital will be the promise of fairly quick payback with interest by exploiting the initially most valuable commodities out there.

Taylorchef · Member

Your figures are definitely out of this world, (LOL), but I think you are shooting for too high a target, pun intended. There are much smaller asteroids, in the 10 to 100 meter range that are 95% nickel / iron, PMG, or C2 clay matrix types that could actually be moved in total. These would, with our current technology in propulsion, be the better ones to go for economically, because of the other materials in them that could be used in space. We desperately need access to building materials in space, & shipping them from Earths surface is just too expensive.

Maybe instead of discussing what we could do with said materials, we should design a ship that we could use to harvest or relocate these asteroids!!!

Positronium · Member

Thats a good idea. I bet there is sufficient brainpower on this site to design a pretty decent ship.

GoogleNaut · Guru

Actually, the design of such a vessel was my intention. Using VASIMR (VAriable Specific Impulse Magnetoplasma Rocket technology can achieve the desired specific impulse to achieve reasonably high payload fractions with modest amounts of reaction mass. A nuclear power plant, possibly using a Brayton Cycle gas turbine engine circulating a cooling gas, possibly helium through the reactor, should be compact enough to provide sufficient power for a multimegawatt VASIMR thruster. Some exotic vapor core reactor schemes have been proposed that could get the power levels up even high--but vapor core is pretty cutting edge technology.

There has even been a proposal to create a MiniMag Orion vehicle, a nuclear pulse vehicle, which uses a Zeta Pinch electromagnetic implosion system to create very small fission explosions using Curium or Cerium isotopes as the fuel. Reactor Jet power with such a system could approach 100 GW.

Anyways, it was my intention to identify initial infrastructure requirements for a mining mission to near Earth orbit asteroids: does it make sense to first go after volatiles for use as reaction mass, and as a source for processing chemicals? And then go after a nickel-iron to extract PGM's for quick payoff of investment capital? Granted, long term, almost all materials extracted will be useful, especially materials such as galium and arsenic--not only useful for rad hard semiconductors, but also useful for constructing efficient solar cells. Silicon, aluminum and magnesium, as well as titanium will all be critical use materials. Not to mention the carbon, nitrogen and hydrogen extracted from volatile rich carbonaceous asteroids.

My intention was to find a way to create a relatively quick, high payoff program as a way to minimize short term investment risk. Maximizing profit while simultaneously minimizing risk is essential to any successful venture, and given the size and scope of the needed investment for a successful asteroid mining venture, it seems apparent that relatively quick returns are the only way to attract the venture capital needed. It seems that unless a solid diamond asteroid were found (now wouldn't that be something?!!) the only way to achieve maximum economic value on payload returned is to return the most valuable product one can find: platinum group metals and especially rhodium in particular. All else will fall into place once initial payback is achieved. If values of $100 billion US were returned each trip, and if a payload were returned every year and a half or so, or perhaps every two years, cash flow should be in excess of $50 billion per year. If initial investment is $200 billion US with the current prime rate of 8% this puts interest payments on the initial loan at about $16 billion US per year. This suggests that, neglecting recurring costs, a payback of initial investment could occur in as little as 5 years. A detailed program assessment of the initial program costs and the recurring costs would be needed for a more detailed analysis, but it seems, atleast at first look, plausible that payback of initial investment could occur in as little as ten years of commencement of operations, with operations being entirely in the 'black' after that.

-- Edited by GoogleNaut at 03:40, 2006-06-27

Taylorchef · Member

How about resurecting this thread?

Your idea about using VASMIR, while a good one, I think is still before it's time. NERVA is a tested design & actual working models of it have been built. The MITEE design is anothr one I llke. It is extremely simple, incredibly lightweight, & uses current materiel & thecnologies.

Here are some specifics on both;

NERVA

Diameter: 10.55 m
Length: 43.69 m
Weight empty: 34,019 kg
Weight full: 178,321 kg
Thrust (vacuum): 867 kN
ISP (vacuum): 825 s (8.09 kN·s/kg)
ISP (sea level): 380 s (3.73 kN·s/kg)
Burn Time: 1,200 s
Propellants: Nuclear/LH2
Engines: 1 Nerva-2

MITEE

A new approach for a near-term compact, ultralight nuclear thermal propulsion engine, termed
MITEE (MIniature ReacTor EnginE) is described. MITEE enables a wide range of new and
unique planetary science missions that are not possible with chemical rockets. With U-235
nuclear fuel and hydrogen propellant the baseline MITEE engine achieves a specific impulse of
~1000 seconds, a thrust of 28,000 newtons, and a total mass of only 140 kilograms, including
reactor, controls, and turbo-pump. Using higher performance nuclear fuels like U-233, engine
mass can be reduced to as little as 80 kilograms. Using MITEE, V additions of 20 km/sec for
missions to outer planets are possible compared to only 10 km/sec for H 2 /O 2 engines.

I believe a NERVA could be built, using modern materiel & techniques for a whole lot less weight than the last one built in 1972.

One of these engines is a good place to start for our Asteroid Harvester Spacecraft.

-- Edited by Taylorchef at 23:55, 2006-11-04

GoogleNaut · Guru

What I was thinking, and a NERVA or Pratt & Whitney "Triton" engine (LOX afterburning) will work too, was to use a spacecraft in conjunction with something like the CaLV launch vehicle (this is the Shuttle Derived Launch Vehicle currently on the books for the US return to the moon.) I haven't worked out the details but my intention was to study in detail a resource pipeline of materials flowing from deepspace (Near Earth orbit crossing Asteroids and comet reminants) to High Earth Orbit Logistics Station and a Low Earth Orbit Depot. I even have suggested names for them: Clarke Station in Low Earth Orbit, O'Neil Station in High Earth Orbit. The purpose of the O'Neil Station was to recieve and process materials from asteroids and comets and to act as a staging area for deep space missions. The location of this station is unclear to me, but may be located well above geosynchronous orbit, but perhaps not as far as the moon. As such it must be massive enough to provide its own shielding from solar flares and such. Very quickly this station would be the centerpoint of almost all commerce outbound from or inbound to Earth. The Clarke LEO Station would be an initial resource depot, staging and construction area for initial sorties. The functional kernel or Core Functional Block of the O'Neil station would be constructed at Clarke Station and moved to high earth orbit.

It would seem to make sense to design launch vehicles with easy to dissassemble propellant tankage that can be easily converted into livable space, shops, storage containers, etc. The philosophy of maximizing materials utilization right down to reclaiming propellant residuals from vehicles delivering payload to the station is a key design philosophy. By thinking of spent stages and propellant residuals as a resource, we can significantly increase the total value of product delivered to the station. Using some of those reclaimed resources to build to the first deep space vehicle. Dispatching this vehicle initially to a comet or comet reminant to bring back thousands of tons of volatiles (mostly water.) Initial missions to bring back volatiles will be essential to 'prime the pipe' as it were by filling Clarke Station's storage tanks with water and other commodities needed to manufacture additional hydrogen and oxygen propellants. Once that propellant reserve has been created, enough to fully fuel several sorties, then it becomes favorable to go to other places, like the nickel-iron asteroids.

So my first impressions about building only a vehicle were not large enough--it is necessary to create a whole transportation infrastructure--and this explains why it has not yet been done!

The idea of using VASIMR was to attmept to exploit an interesting feature of the engine--it can be multifuel. By this I mean that by thoughtful engineering of the engine, it can be made to process different propellant streams. I have actually contacted Dr. Franklin Ramon Chang-Diaz, the inventor of the VASIMR concept, and they do have intentions of exploiting different propellant streams for the engine. This is very important if one wants to capilalize on the different resources out there: for instance, you could 'burn' hydrogen for an outbound leg to an asteroid., load up on volatiles, and then refill your empty hydrogen tanks with liquid oxygen instead (after emptying them of residuals and venting them to space first!) Hydrogen can give from 3000 to 10000 sec of specific impulse on the outbound leg, and oxygen processed in the same engine may give you about 1/4 of this (750 sec to 2500 seconds of specific impulse.) But since liquid oxygen is 16 times denser than liquid hydrogen, then instead of a cargo penalty you gain 16*1/4 = 4 times as much cargo on the return leg as the outbound leg--which is ideal if you want to return a lot more stuff than you go out with! Using liquid oxygen as a denser reaction mass makes sense if you can do it. VASIMR maybe could do it with clever engineering (I e-mailed Dr. Chang-Diaz about this very possibilty--and erosion of the helicon antennas is definately a concern, especially with something as chemically reactive as oxygen.) NERVA cannot handle liquid oxygen because oxide fuel structures and oxide ceramics cannot conduct heat fast enough to do so without melting...

Still, a more conventional NERVA system could be used, and these are all possibilities I want to explore further.