On Tue, 23 Oct 2007 07:16:47 -0700, Hop David wrote:

John Schilling wrote:

On Fri, 19 Oct 2007 13:10:07 -0500, "Mike Combs"
wrote:

But it's probably going to be a *lot* less expensive if you allow for
the inhabitants to build, provision, and resupply their habitat using
local resources.

And there's every reason in the world to expect an asteroidal settlement to
be doing this.

Except for the critical shortage of local resources that aren't steel or
coal or glass.

And Mars has a much broader range of useful resources

I'm not sure why you would say this. What resources would be available on
the surface of Mars that you couldn't find in a well-selected CC-type
asteroid?

"CC" meaning "Carbonaceous Chondrite" generally?

OK, let's see: How about useful concentrations of Helium, Lithium,
Beryllium, Boron, Nitrogen, Fluorine, Neon, Sodium, Aluminum, Chlorine,
Argon, Potassium, Titanium, Chromium, Manganese, Copper, Zinc, Arsenic,
Bromine, Krypton, Strontium, Zirconium, Niobium, Molybdenum, Silver, Tin,
Antimony, Iodine, Xenon, Barium, Hafnium, Tantalum, Tungsten, Gold,
Mercury, Lead, Bismuth, Thorium, and Uranium.

While CCs may be poor in some those materials, there are other asteroids
that aren't.

What sort of asteroid do you imagine has useful concentrations of, say,
Boron?

Zinc?

Tin?

Lead?


I acknowledge that one asteroid containing all these resources would be
rare.

An asteroid containing *any one* of those resources is going to be rare
indeed. I didn't just pull the list out of my ass, you know.


On the other hand, there's no superhighways, oceans or rivers that can
be used for transportation on Mars. Transportation will be a substantial
barrier to self sufficiency on Mars as well as among the NEOs.

Transportation by dirt road, is many orders of magnitude cheaper than
space transportation.


Mars definitely has some of those in abundance , and almost certainly has
useful ores of the rest on account of having experienced the same geologic
processes that produced such ores on Earth.

I seem to recall Peter Tillman saying uranium ore was concentrated via
biological processes.

Only a minority of uranium ores, and AIUI it's a minority opinion even
there. Mostly, uranium ores come from abiotic hydrothermal processes,
followed by selective precipitation.


There's certainly some ore concentrating processes on Mars, but I don't
regard it as a given Mars would have all the same ores earth does.

I didn't include any of the minerals for which biologic mechanisms are
necessary. And the purely physiochemical stuff, Mars really does seem
to have had the full range of Earth-style geologic activity. Rather
less active at present, of course, but then there's been nothing going
on to deplete the old ore bodies either.


Carbonaceous chondrites, based on the meteoric evidence, do not.

Meteoric evidence is biased. Some meteorites are much more perishable
than others. If they're not discovered within hours or days of impact,
they're gone. More durable objects are more likely to reach the earth's
surface and become meteorites.

You're talking about iceballs, I assume. Those don't come from NEOs,
except in the "occasionally passes right close to Earth at an ungodly
high relative velocity" definition of NEO. Which is of interest to the
impact-hazards community, but not so much for asteroid mining.

NEOs in the sense of being easily accessible for round-trip travel
from Earth, by definition spend most of their time in a climate too
warm for ice to endure.


Some carbonaceous chondrites may be homogenous aggregates that haven't
experienced any ore concentrating processes. But this isn't the case for
all asteroids. Metallic asteroids are believed to come from the interior
of large asteroids that were massive enough to have differentiated layers.

Which gives you concentrations of iron, nickel, cobalt, and (for a
perverse but economically relevant definition of "concentration"),
the platinum-group elements.

That's it. A really nice grade of stainless steel, a bit of platinum,
and nothing more. Metallic asteroids will make their owners "rich"
in the way Midas was rich.


I also believe there can be ore concentrating processes going on in
objects that outgas when they're closer to the sun.

Such as?

OK, the outgassing of volatiles is by definition a "concentrating process"
for non-volatiles, but there's nothing to concentrate one non-volatile
over another. And the non-volatiles are almost entirely oxides of
silicon, calcium, and magnesium. So there's your glass, and your
magnesium.


Asteroids, are where you get steel and coal and glass, and maybe magnesium
and platinum for the export markets, and that's really about it.

I believe water, ammonia and other volatiles not at the bottom of a
steep gravity well and not far from the earth would be valuable.

Yes, but you're not going to find ammonia in a near-earth asteroid.
Not likely you'll be finding much of any nitrogenous compounds there.

Water, you can get, though only bound up in a mass of carbonaceous
non-volatiles that bears a strong resemblence to coal. And you've
got to be pretty desperate to try and squeeze water from a lump of
coal. But it's at least within the bounds of reason and plausibilty.


On http://clowder.net/hop/railroad/asteroidresources.html I give a list
of reasons (with some web cites) why I believe volatile rich NEOs exist.

I only see reasons to believe volatile-rich asteroids exist. Main belt
asteroids, out where the equilibrium temperature is a nice 200K or less.
If you've got anything for volatile-rich NEOs, I couldn't find it.

And even then, that only gives you nitrogen and somewhat more accessible
hydrogen. That still leaves most of the periodic table that you aren't
going to be squeezing out of an asteroid without invoking elfin magic
as a refining technology.


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