Gotcha Marc!
----- Original Message -----
From: "Marc Fries" <[EMAIL PROTECTED]>
To: "Meteorite List" <[email protected]>
Sent: Sunday, May 22, 2005 1:08 PM
Subject: Re: [meteorite-list] OT: Asteroidal and Lunar Materials
Howdy
Interesting, but it needs work. First off, where do you get the
nitrogen? Asteroids are devoid of the stuff, which means hauling large
amounts of liquid nitrogen from the Earth's gravity well ($$$$!).
Second, you've got big metallurgy problems. Fe-Ni is not "stainless
steel", as anyone who has watched their iron meteorite rust can attest
to. Stainless steel is an iron-chromium alloy. Also, asteroidal metal
contains large amounts of sulfides, which acts to embrittle metals. As
a cautionary tale in that regard, it was discovered (far too late) that
the iron used to build the Titanic was very sulfide-rich and the
resulting embrittlement was a likely cause of its' sinking:
http://dwb.unl.edu/Teacher/NSF/C10/C10Links/chemistry.about.com/library/weekly/aa022800a.htm
In addition to sulfides, there will be silicates and minor refractory
components which will basically rip the bubbles as they form:
http://epubl.ltu.se/1402-1617/2002/344/index-en.html
As a macro-scale example look at Coke cans, which have to be made from
an aluminum alloy that is even more pure than aircraft aluminum to keep
from ripping open under extreme plastic deformation when the can is
made. Finally, dropping a kms-long rod of material, no matter how
light, through the Earth's atmosphere at many km/s will break or deform
the surviving pieces considerably. Perhaps this would be better off as
a building material that is not intended to land on a planetary body
(space stations?).
I hate to keep playing the spoil-sport in these emails, but I hope
y'all will look at this as a critical evaluation of the problems
involved and not just a "told-you-so-a-thon". If we understand the
problems then someone can work to overcome them.
Cheers,
MDF
Hi,
A while back there was a mini-thread about the cost of returning
lunar materials to Earth and the effect of economies of scale on that
cost. These cost concerns are similar to a much more analyzed topic:
returning asteroidal materials to Earth. See John Lewis' book "Mining
The Sky."
Even so, to date these discussions have been about materials that
could be obtained on Earth (except for Helium-3). The chief point to
remember about economies is that they change when the material commodity
is both required and can not be obtained elsewhere.
Here's an example: Imagine you want to build a bridge out of iron
across a 100 foot chasm. The simplest way is to take a 100 foot long
slab of iron (or steel), twenty feet wide and 10 feet thick, and flop it
down. Inelegant, but a solution.
More elegant is to take a very thin slab of iron and attach a
variety of iron trusses underneath it, designed to support the stresses
of the bridge. You use much less iron and get a bridge just as strong
or stronger. A more elegant solution.
Even more elegant is build the above example of a bridge very
lightly indeed and support it with iron cables from towers. Now we're
up to Golden Gate elegant, less material, more strength, all gotten by
subdividing the structural shape into smaller and smaller internally
braced "voids."
In older aircraft and race car design, we can see engineers drilling
rows of big holes in beams and such like to create a more favorable
strength/weight ratio. You engineers out there know all about this, of
course.
The next logical step would be to carry the principle down to the
micro scale, where what appear to be solid structural members are
themselves smaller and smaller internally braced voids. But both micro-
and nano- fabrication is too fantastically expensive to contemplate.
Hey, where do the asteroids (and the Moon) come into this?!
Here it is. You've got all this iron (or natural stainless steel)
in free orbit, zero gee, or at least, micro-gee. Melt it in a
cylindrical electric induction furnace and eject it through a special
nozzle at one end. (The furnace is electric because the sunshine is
free and in constant supply.)
The exit nozzle's walls have a multitude of injectors that inject a
whoppingly large number of bubbles of nitrogen gas into the molten steel
as it emerges. The injector banks are computer controlled for rate,
pressure, pulsation pattern, and so forth.
As the molten asteroidal steel foam exits the furnace into vacuum,
it expands from the internal expansion of the nitrogen bubbles that have
been injected into it. The desired goal is to regulate the process so
that the final product contains a very large number of small voids which
butt up to each other forming regular and irregular polyhedra with thin
steel walls separating them.
The result is a material with a density about 1/3rd that of water,
twenty times lighter than a piece of steel the same size and shape, a
structural strength greater than the best aircraft grade aluminum, and a
strength / weight ratio that is an engineer's dream!
Because it's fabricated in zero-gee, it can be produced in virtually
any shape without distortion and made in gigantic sizes limited only by
the capacity of the furnace producing it. ("You want an I-beam how many
miles long?")
If any of you out there are engineers, your mouths should be already
watering. If not, you're no engineer, at least not one in the mold of
Isabard Kingdom Brunel.
Do you want to build a bridge across the 29-mile Straight of
Gibraltar? No problem. Do you want to build a skyscraper five miles
high? No problem. Do you want to build a Tokyo-sized city that will
float on the sea? No problem. Do you want to build a...? You get the
idea.
From fabrication in zero-gee, the huge pieces of Foam Steel will be
spun sprayed with an ablative polymer and gently de-orbited into the
central Pacific Ocean, after which they will be recovered, transported
to the work site, cleaned of polymer, and put in use.
Why the Pacific? Well, you know, there are always these silly folks
who get unreasonably nervous about mile long pieces of steel falling out
of the sky too near them; it's just good public relations to use the
middle of the Pacific. Remember, Foam Steel will float! In fact, the
density of Foam Steel could be only about twice that of Balsa wood!
Foam Steel will float only 1/3rd submerged. No problem. Hello, Hawaii!
The First Iron Age is over. The Second Iron Age is about to begin.
Here is the miracle material of which the future will be built, and it
must come from space because that is the only place where it can be
made, so the raw material is most economically obtained from asteroids
(or the Moon).
It would make no economic sense to boost Earth steel into orbit to
be re-fabricated as Foam Steel! It is conceivable that the demand for
Foam Steel could become so great that one might foresee the growth of an
environmental slash wilderness movement to "Save Our Asteroids!"
So, study those iron asteroids while you've still got them.
Sterling K. Webb
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--
Marc Fries
Postdoctoral Research Associate
Carnegie Institution of Washington
Geophysical Laboratory
5251 Broad Branch Rd. NW
Washington, DC 20015
PH: 202 478 7970
FAX: 202 478 8901
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