asteroid habitats

--- In spacesettlers@yahoogroups.com, "capcartoonist"
wrote:

> Okay, this is where my ignorance rears its ugly head. Please
> explain about crystallization and why it would be a problem.

OK. First here is a quick summary from a automobile news site:

http://www.autofieldguide.com/articles/090411.html

" "Most metals are crystalline, having atoms arranged periodically in
three dimensions." Except, that is, for those metals that are
amorphous. Their atomic structure is random, not crystallized, so no
crystallization defects occur in its structure. It's highly
non-corrosive, non-magnetic, and many times stronger than conventional
metals.

Three times stronger than high-strength steel at the same weight (its
density is 8 g/cm3, the same as conventional steel), amorphous steel
could challenge aluminum, plastics and composites for domination in
the coming years as the light-weight material of choice for
transportation applications. That is, once researchers work their way
past one little problem with the current batch of amorphous steel:
it's brittle. It shatters like glass when shocked, just like the evil
terminator when he was frozen in Terminator 2: Judgment Day. "There
are various ways of toughening this material so that it is as tough or
tougher than conventional steels," says Shiflet."

Here are two chapters from an on-line course guide:

http://info.lu.farmingdale.edu/depts/met/met205/crystallization.html
http://info.lu.farmingdale.edu/depts/met/met205/imperfections.html

http://www.butschal.de/werkstatt/englisch.html
"The strength between the atoms during crystallization work many
thousand times stronger than any pressure put on the casting from
outside."

Here is some research that actually addresses zero-g crystallization
issues:
http://www.tsniimash.ru/Microgravity/1_5_eng.html
http://www-physics.univer.kharkov.ua/laborat/research/cryst/cryst.htm

And here is some research that looks at crystallization on the
boundary:
http://mhd.sal.lv/contents/1992/1/MG.28.1.14.R.html

So, you're going to reflect light into the interior of an asteroid and
vaporize the metal away. Where ever there is vaporization there will
also be a boundary where there is material that you don't want to
vaporize. The material on the boundary won't be undisturbed when just
an atom away the metal is being vaporized.

You're going to have phase changes galore in the region and
uncontrolled cooling. In fact, the cooling is going to be a rat's nest
of a problem. You're vaporizing all of that metal in the interior of
the asteroid. There is no convection current to swoop that residual
heat out the open endcap. All of that heat has to radiate away,
through the the rock or eventually through the endcap is the
temperature differentials equalize. That's going to cause some issues
for you.

Secondly, because you're operating in space, depending on how quickly
the heat is radiated away, your boundary walls may flash quench.
Crystallization takes time. If the cooling occurs too rapidly the
atoms of the metal walls won't be able to align. Deeper in the wall
where things didn't get so hot, you're going to get crystal
imperfections. Now, imperfections themselves aren't really that big a
problem because they give metal its workability qualities but there
are trade-offs.

Look at this PBS site that focueses on Why The Towers Fell:
http://www.pbs.org/wgbh/nova/wtc/metl_basics.html

Click through to look at the different features.

I guess the best way of putting my concern is that I see the problem
of hollowing out of an asteroid by vaporizing the metal as similar to
digging a road tunnel through a mountain using nuclear bombs.

The processes are uncontrollable.

How will the vaporized metal exit the interior of the asteroid,
especially when you're a few miles into it?

How will the heat escape?

Metal isn't simply metal. Metal beams that we use are the result of
controlled processes in the foundry, and this asteroid plan is
anything but a controlled process.

I just don't see the benefits you see. Can you explain why the
hollowing out process is more efficient than simply blowing the thing
up, refining the metals, producing engineered parts and reassembling
it?

> Vaporized, yes. With a nuke. There would be no load bearing
> columns unless they were installed later.

What holds up the loads until you put up the load bearing columns?

How do you sculpt with a nuclear bomb?

> I was thinking that the floor might be as thick as a km.

Why?

There are always trade-offs.

You wrote that the asteroid was going to be spun to provide "gravity."
If you have floors that are a km thick, that mass also has to be spun.
Further, it takes energy to spin the mass. Also, there are physical
forces to contend with.

Do some quick calculations. Calculate the mass of a 30 km long and
20km diameter cylinder with steel walls a meter thick, compared to the
mass with walls a kilometer thick. How much more energy and reaction
mass are going to be needed to spin that cylinder up to sufficient
speed to create the gravity effect that you want.

Is the extra effort and cost worth the benefit of having a wall a lm
thick? What exactly is that benefit?

Speaking generally now, I've come across these plans before and I've
never understood their appeal. Why are you drawn to it? I don't think
it can be simplicity, because working with uncontrollable equipment
and forces (nuclear bombs, meta vaporization across a moving range) is
going to be a headache.

Why do companies use metal I-beams instead of just carving an I-Beam
out of granite?

TangoMan