I've studied the concept of hollowing out an asteroid and converting it into
a habiat.
One of the plans suggested putting a parabolic reflector and a massive lens
in the sunward pole of the axis in order to provide sunlight.

My question is, is this the best way to provide light for a habitat roughly
30 km long? Is it even feasible?

Comments would be appreciated.

Thanks.

-MKC

I think it's a great idea to hollow out an asteroid. In fact,
that's a staple of my science fiction stories. Why build space
stations when there are hundreds ready-made out there? Even Phobos
and Deimos have enough room in them for whole civilizations.

I never thought of a parabolic reflector -- I figured huge OLEDs
would do the job. They'd last thousands of years -- though maybe
they wouldn't provide enough light. The problem with a reflector
and lens is that all asteroids rotate, and the poles aren't usually
going to perpetually face the Sun. Even if you could stabilize or
stop their rotation, I would guess most asteroids are small enough
that it wouldn't take much to get them rotating again or alter their
rotation.

Oxygen regeneration wouldn't be a problem -- greenhouses or even
regenerating equipment could do that. But how would you produce
heat? I've thought of radioactive decay, but after watching The Day
After, I came to the conclusion that might be dangerous...

Collin

--- In spacesettlers@yahoogroups.com, "Michael Capriola"
wrote:
> I've studied the concept of hollowing out an asteroid and
converting it into
> a habiat.
> One of the plans suggested putting a parabolic reflector and a
massive lens
> in the sunward pole of the axis in order to provide sunlight.
>
> My question is, is this the best way to provide light for a
habitat roughly

--- In spacesettlers@yahoogroups.com, "Michael Capriola"
wrote:

> I've studied the concept of hollowing out an asteroid and converting
> it into a habiat. One of the plans suggested putting a parabolic
> reflector and a massive lens in the sunward pole of the axis in
> order to provide sunlight.

> My question is, is this the best way to provide light for a habitat
> roughly 30 km long? Is it even feasible?

Have you ever been in a modern day mine? Or seen pictures of the
insides of todays mines or even older mines?

Have you noticed all of the bracing?

The problems with hollowing out asteroids is that you're assuming
structural integrity. When you pressurize that asteroid you're going
to have a lot of tensile force exerted on bare rock walls, and this is
harder to compensate for than the bracing used for the compressive
forces in a mina.

Further, the remaining walls cannot safely be considered to be
monolithic, and in fact there may be sections that are loose
aglomerations, which would erupt when subjected to the forces within
atmospheric pressure.

If you have the technology to "melt" a whole asteroid, I'd simply
redeploy it so that you melt out the metals, then remelt the metals
into an engineered product - a Habitat shell.

As for your sunlight question well, let's work it through a bit.

You don't specify a diameter, so I'll assume 6 km. On the cylinder
wall, you've got 565 km^2 of area that needs to be lit. Assuming each
end cap is half of a sphere, the surface area of each end cap is 56.5
km^2. If one end cap is dedicated to your window, then you need to
light a total of 621 km^2 of area. Assuming you want to deliver 1,000
watts of light to each meter^2 of surface area you're going to have to
shine 621 GW through that end cap.

How will you create night and day?
How much heat will be absorbed into the endcap window?
How will the window radiate the heat?
How will you deal with the permanent shadows created by having the sun
be immobile in the endcap?
Will people like the effect of the sun being instantly "turned off"
when nightfall is reached and suddenly turned on at sunrise?
There will be a differential in light intensity between the region
immediately adjacent to the endcap window and the region 30 km away at
the other end of the cylinder.
Will people like to have their windows facing into perpetual shadow?
If you make the endcap window smaller, don't neglect the issue of the
amount of heat that'll be generated. If too small, the window material
might not be able to withstand the heat.

TangoMan

> I think it's a great idea to hollow out an asteroid. In fact,
> that's a staple of my science fiction stories.

How is artificial gravity created in this scenario?

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

> How is artificial gravity created in this scenario?

Well, it's science fiction, so I assume that we've learned to
either "magnify" existing gravitational fields, like lensing light,
or we can manipulate the Casimir effect to either nullify or create
inertia, and therefore manipulate gravity.

Collin

From: victoriatangoman [mailto:tango_dancer@...]

"Have you ever been in a modern day mine? Or seen pictures of the insides
of todays mines or even older mines? Have you noticed all of the bracing?"

This depends on the material being mined. For example, limestone mines -- we
have them all through the Kansas City area -- are supported by columns left
in place during excavation, without any additional bracing. Decades after
these mines were played out, they're still being used as underground
offices, warehouses, industrial parks... even a few restaurants. Still no
added bracing. The limestone being tunnelled through is a mostly
undifferentiated material. Other mines, in other, differentiated, materials,
require the uneven excavation of veins of ore. This type of mine needs the
bracing. The differentiation of the Earth's material is caused by internal
gravity, volcanic and seismic activity, and erosion and re-deposition of
material by wind and (surface *and* underground) water flow. Even the
largest asteroids have only the tiniest fraction of Earth's gravity, and
obviously the other factors are out of the question. Until we get probes
able to drill samples onto a few NEOs, we won't know just how differentiated
the various asteroids are, but without the factors to cause differentiation,
the stony, stony-iron, and metallic classes of asteroids may well have
enough structural integrity to be turned into habitats with minimal bracing.

"When you pressurize that asteroid you're going to have a lot of tensile
force exerted on bare rock walls, and this is harder to compensate for than
the bracing used for the compressive forces in a mina. "

Different, yes. But "harder"? In what way?

"Further, the remaining walls cannot safely be considered to be
monolithic, and in fact there may be sections that are loose
aglomerations, which would erupt when subjected to the forces within
atmospheric pressure. "

This would certainly be a problem with any of the chondritic asteroids, and
even more so with cometary cores. But with some of the other classes, such
as the ones I mentioned earlier, this may be an issue that can be addressed
in much the same way that geologists and mining engineers determine the
subterranean structure of a given piece of real estate here on Earth.

"If you have the technology to "melt" a whole asteroid, I'd simply
redeploy it so that you melt out the metals, then remelt the metals
into an engineered product - a Habitat shell."

Melting the whole asteroid? Is this the `Inside-Outside' idea from `Islands
in Space' by Cole and Cox? That scheme always sounded too expensive -- in
time, resources, and energy -- to be worthwhile. If tunnelling a habitat
into an asteroid *isn't* an option, then I'm with you: Take it apart, and
build the habitat.

Dave

From: flymuffins [mailto:flyingmuffins@...]

> I think it's a great idea to hollow out an asteroid. In fact,
> that's a staple of my science fiction stories.

"How is artificial gravity created in this scenario? "

The same way as the `traditional' designs: spin it. By using solar sails,
solar-powered ion engines (*lots* of them) and/or mass-driver propulsion
systems, a constant force could be applied to bring the asteroid up to
speed. It'd take months to get enough spin for a 1g environment, depending
on the size, but eventually, you're there.

Dave

--- In spacesettlers@yahoogroups.com, "Dave Logsdon" wrote:

> are supported by columns left in place during excavation, without
> any additional bracing.

What's the span between the columns? I'd venture a guess that it's
far, far off from the miles envisioned in a Habitat. The rock in the
ceiling can only support so much force before it needs to be
redirected into the columns. Bracing is like an exoskeleton and helps
distribute the forces.

> Decades after
> these mines were played out, they're still being used as underground
> offices, warehouses, industrial parks... even a few restaurants.

I've been in some. Pretty cool, heh?

> the stony, stony-iron, and metallic classes of asteroids may well
> have enough structural integrity to be turned into habitats with
> minimal bracing.

Here are my assumptions:
The asteroid will have to be spun to induce coriolis forces.
It will have to be pressurized to contain an atmosphere.
There are substandard parts which don't meet specifications for
today's machinary.

To melt out a hollow core and rely on the remainder to be structurally
sound, and to make this decisions at the outset of the process, is
IMO, looking for unexpected trouble. Regions of ore problems can doom
the habitat. Unless you scope the whole asteroid and note the
composition to be uniform throughout and to a certain depth then
you're counting on something you shouldn't be. I'd rather count on
quality control in a steel mill, with the right mixes and
temperatures, and cooling sequences to come out with a uniform
engineered product than count on the thermodynamics involved in
melting iron ore out of a mtallic class asteroid and the uncontrolled
crystallization that results from cooling across spans of, I don't
know, hundreds of meters, maybe.

> "When you pressurize that asteroid you're going to have a lot of
> tensile force exerted on bare rock walls, and this is harder to
> compensate for than the bracing used for the compressive forces in a
> mina. "

> Different, yes. But "harder"? In what way?

There are optimum materials for different tasks. A concrete dam is
more efficient than a steel dam. A steel pressure vessel is more
efficient than a concrete pressure vessel. Different technique would
be used to construct each of these facilities, but I would venture the
opinion that a concrete pressure vessel is going to be, in an
objective sense, a much harder task to engineer and construct than a
steel vessel.

I'm not assuming that the asteroid is a solid chunk or one
undifferentiated element. I assumed rock. My understanding of the
engineering principles is that rock is better suited to compressive
forces than tensile forces. You can engineer it for tensile of course,
but now the challenge is greater, or IOW, harder.

> But with some of the other classes, such as the ones I mentioned
> earlier, this may be an issue that can be addressed in much the same
> way that geologists and mining engineers determine the subterranean
> structure of a given piece of real estate here on Earth.

My assumptions:

We're talking about a Habitat, one with wide open spaces.
We're not talking about a station, with load bearing walls.

If you're referring to a Metallic class asteroid, I'd hate to be
tasked with the job of digging it out. Blowing up whole chunks of
metal in a controlled fashion is not going to be an easy job.

If we're melting the thing, which I think is the premise of the
question, then again, a controlled melting of whole regions, where the
metal is, I assume vaporized rather than liquified, I'm not sure how
we're going to leave load bearing columns standing in the midst of the
furnace that will be the interior of this asteroid.

Further, I'd be concerned about the crystalline structure of the metal
that remained on the interface between the exterior of the shell and
the interior that has been vaporized away.

> If tunnelling a habitat into an asteroid *isn't* an option, then I'm
> with you: Take it apart, and build the habitat.

> Dave

I'd have to go back and check but I thought the premise to the
question was a melt operation. Though, even with tunneling, I think
that the problems discussed above are still present.

TangoMan

From: victoriatangoman [mailto:tango_dancer@...]

"What's the span between the columns? I'd venture a guess that it's
far, far off from the miles envisioned in a Habitat. "

Okay, It seems we're making assumptions about how we each envision the
design. I don't see a completely hollowed-out asteroid, with an interior
similar to an O'Neill design; you're right about the tensile strength issue
in that case. Think instead of a series of large, interconnected man-made
caverns. A better example than those mines I mentioned before would be
Cheyenne Mountain, which has chambers hundreds of feet in length, large
enough to contain multi-story buildings, with enough mountain left over to
survive a direct hit from a multi-megaton nuke. You can check it out at:
http://www.cheyennemountain.af.mil

> Decades after
> these mines were played out, they're still being used as underground
> offices, warehouses, industrial parks... even a few restaurants.

"I've been in some. Pretty cool, heh? "

Very cool. They're small compared to The Mountain, though; I wish my time in
the Air Force had included a tour of duty Inside.

"Here are my assumptions:
The asteroid will have to be spun to induce coriolis forces.
It will have to be pressurized to contain an atmosphere.
There are substandard parts which don't meet specifications for
today's machinary. "

I'll agree with your first two assumptions. As to the third, I'm not really
concerned about part of the rock being "substandard", if there's a hundred
feet or so of it between the floor of the chambers and the outside.
Again, I'm thinking of a floating Cheyenne Mountain, not a stone O'Neill.
I'm with you about the implausibility of the latter.

"If you're referring to a Metallic class asteroid, I'd hate to be
tasked with the job of digging it out. Blowing up whole chunks of
metal in a controlled fashion is not going to be an easy job."

Yeah, I thought about that after I included the M-class in the potential
asteroids I listed. Good point. Still, the stony and stony-iron asteroids
offer at least a few hundred potential sites among the NEOs.

"I'd have to go back and check but I thought the premise to the
question was a melt operation. Though, even with tunneling, I think
that the problems discussed above are still present. "

Somehow, I missed the original post in this thread, so I don't know about
the initial premise. Does my version of an asteroid habitat seem more
plausible, now that I've described it better?

Dave

--- In spacesettlers@yahoogroups.com, "Dave Logsdon" wrote:

> Does my version of an asteroid habitat seem more
> plausible, now that I've described it better?

Absolutely. The principle reason is that each chamber in the station
is structurally sound.

Have you read "Mining the Sky"? I'm thinking in particular about the
Aldrin Cycler. I could see the Cycler looking like this.

Even on this version of the idea I'm left wondering whether it would
be more efficient, time, planning, capital, wise to just build an
engineered Habitat.

Here's why:

To hollow out an asteroid, even when configured into room modules is
going to take effort and a slower pace.

Why not go up to an asteroid, blast a section off, grind it up, cast
it into formed concrete blocks and then in zero-g manoeuver those 100
ton blocks together into a whole, just like a bunch of lego blocks.
The casting process can be automated and no care has to be taken when
blasting segments of the asteroid apart and running those chunks over
to the grinder. This process can accomodate much larger volumes of
material and doesn't have to follow a defined excavating path.

The standards of the engineered product will be uniform and not
limited by by the size and shape of the original asteroid.

Think of it this way - there are plenty of people who live on acerages
that are covered with forests, yet they use lumber from a lumberyard
to build their homes rather than building with the raw logs that they
could get from their property. The house goes up faster, is cheaper to
build, is nore uniform in contruction and is a more efficient use of
material.

TangoMan

--- In spacesettlers@yahoogroups.com, "Collin R. Skocik"
wrote:
>
> I think it's a great idea to hollow out an asteroid. In fact,
> that's a staple of my science fiction stories.

Same here.

> I never thought of a parabolic reflector -- I figured huge OLEDs
> would do the job. They'd last thousands of years -- though maybe
> they wouldn't provide enough light.

I remember the reflector from an old drawing from the 1960s or so.
It helped focus the sunlight and beam it thru a lens and down the
length of the asteroid.

What is an OLED?

> Oxygen regeneration wouldn't be a problem -- greenhouses or even
> regenerating equipment could do that. But how would you produce
> heat?

The problem most likely will be getting rid of excess heat.

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

> the remaining walls cannot safely be considered to be
> monolithic, and in fact there may be sections that are loose
> aglomerations, which would erupt when subjected to the forces
within
> atmospheric pressure.

The article "How to Colonize an Asteroid" (I think the site is now
defunct) mentioned this problem. The suggested answer is to be very,
very careful.

> If you have the technology to "melt" a whole asteroid, I'd simply
> redeploy it so that you melt out the metals, then remelt the metals
> into an engineered product - a Habitat shell.

The method of hollowing out the asteroid, from the article mentioned
above (and from other sources) is to drill a shaft down the length
of the asteroid, stuff it with bags full of water and a
thermonuclear bomb. The bomb goes off, and the steam and shock wave
blow the asteroid up like a balloon.

> As for your sunlight question well, let's work it through a bit.
>
> You don't specify a diameter, so I'll assume 6 km. On the cylinder
> wall, you've got 565 km^2 of area that needs to be lit. Assuming
each
> end cap is half of a sphere, the surface area of each end cap is
56.5
> km^2. If one end cap is dedicated to your window, then you need to
> light a total of 621 km^2 of area. Assuming you want to deliver
1,000
> watts of light to each meter^2 of surface area you're going to
have to
> shine 621 GW through that end cap.

Actually, the diameter is 20 km. I should have told you that. But
thank you for the calculations. Now I have to come up with over 800
GW of light. ;)

> How will you create night and day?

Night is unnecessary in my scenario. Shutters on the bedroom
windows will do nicely. I work graveyard shift, so I know.

> How much heat will be absorbed into the endcap window?
> How will the window radiate the heat?

Very good questions. Anyone have an answer?

> How will you deal with the permanent shadows created by having the
sun
> be immobile in the endcap?

Some people like to sit in the shade. And if the far endcap is
mirrored (or partly so), this might not be that much of a problem.

> There will be a differential in light intensity between the region
> immediately adjacent to the endcap window and the region 30 km
away at
> the other end of the cylinder.

There will be a temperature difference, too, which will affect wind
patterns. I have that info in my files somewhere, and can post it
at some point. Basically, it would operate pretty much the same as
in an Island 3 cylinder.

> Will people like to have their windows facing into perpetual
shadow?

I would assume that windows would face the sun, but when the sun
came up over the mountains this morning and into the coffee shop
window, I changed seats to get it out of my eyes. So perhaps some
windows will face the sun and some would not. Actually, like the
ancient Greeks, people are going to spend most of their time
outdoors.

--- In spacesettlers@yahoogroups.com, "flymuffins"
wrote:
>
> > I think it's a great idea to hollow out an asteroid. In fact,
> > that's a staple of my science fiction stories.
>
> How is artificial gravity created in this scenario?

The asteroid spins on its long axis to provide about 93% Earth
gravity.

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

> To melt out a hollow core and rely on the remainder to be
structurally
> sound, and to make this decisions at the outset of the process, is
> IMO, looking for unexpected trouble. Regions of ore problems can
doom
> the habitat. Unless you scope the whole asteroid and note the
> composition to be uniform throughout and to a certain depth then
> you're counting on something you shouldn't be.

Yes, this is a big drawback. The slightest miscalculation can split
the side of the asteroid wide open.

> the uncontrolled
> crystallization that results from cooling across spans of, I don't
> know, hundreds of meters, maybe.

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

> My assumptions:
>
> We're talking about a Habitat, one with wide open spaces.
> We're not talking about a station, with load bearing walls.
>
> If you're referring to a Metallic class asteroid....
> If we're melting the thing, which I think is the premise of the
> question, then again, a controlled melting of whole regions, where
the
> metal is, I assume vaporized rather than liquified, I'm not sure
how
> we're going to leave load bearing columns standing in the midst of
the
> furnace that will be the interior of this asteroid.

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

> Further, I'd be concerned about the crystalline structure of the
metal
> that remained on the interface between the exterior of the shell
and
> the interior that has been vaporized away.

Again, I don't know anything about crystallization and could use
some input here.

--- In spacesettlers@yahoogroups.com, "Dave Logsdon"
> I don't see a completely hollowed-out asteroid, with an interior
> similar to an O'Neill design; you're right about the tensile
strength issue
> in that case. Think instead of a series of large, interconnected
man-made
> caverns.

That's definately an option, and one they mentioned in "How to
Colonize an Asteroid."

> > There are substandard parts which don't meet specifications for
> > today's machinary. >

> I'm not really
> concerned about part of the rock being "substandard", if there's a
hundred
> feet or so of it between the floor of the chambers and the
outside.

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

> > If you're referring to a Metallic class asteroid, I'd hate to be
> > tasked with the job of digging it out. Blowing up whole chunks of
> > metal in a controlled fashion is not going to be an easy job."
>
> Yeah, I thought about that after I included the M-class in the
potential
> asteroids I listed. Good point. Still, the stony and stony-iron
asteroids
> offer at least a few hundred potential sites among the NEOs.

The problem with stony asteroids is that they may not be
structurally sound. In fact, there's some speculation that many of
them are just loose piles of rubble held together by gravity.

--- 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

From: victoriatangoman [mailto:tango_dancer@...]

"Have you read "Mining the Sky"? "

Oh, yeah! I've been preaching the Gospel of John -- John S. Lewis, that is
-- for years.

"Even on this version of the idea I'm left wondering whether it would
be more efficient, time, planning, capital, wise to just build an
engineered Habitat. "

I can see it going either way, or both ways; it's too early to tell.
Burrowing into the asteroid instead of building a habitat has more appeal to
me on a gut level, but I'm open to whichever idea works best, under various
circumstances. I don't think for a second that the `Flying Cheyenne
Mountain' idea will replace the more traditional, constructed O'Neill
design. I just think there might be room for both designs... and probably
several others we haven't even dreamed up yet.

"To hollow out an asteroid, even when configured into room modules is
going to take effort and a slower pace. "

In a way, that "slower pace" is a good point. Building an asteroid habitat
such as I've described, one chamber at a time, will allow the community
within to develop gradually, somewhat in the way we grow towns here on
Earth. The O'Neill plan, as originally laid out, involves building the
physical structure of a town/habitat of at least 10,000 or so, *then*
introducing a population of strangers to inhabit it. I'm not saying this
*can't* be done. But building the `community' and the structure together, a
step at a time, has proven to work throughout history. Look at the
construction of Arcosanti: http://www.arcosanti.org (Paolo Soleri has a lot
to teach anyone trying to design a self-contained community, on Earth or in
space. Some of the `Space Arcology' designs on the site pre-date O'Neill by
years.) A "slower pace" may very well be a good thing, indeed.

Dave

From: capcartoonist [mailto:capcartoonist@...]

> I'm not really concerned about part of the rock being "substandard",
> if there's a hundred feet or so of it between the floor of the chambers
> and the outside.

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

With a large enough asteroid, that'd be possible, but I can't really see why
you'd want to waste *that* much usable area. Heck, you could cut my original
"hundred feet" example in half, and still have a much thicker, safer hull
than the original O'Neill design.

"The problem with stony asteroids is that they may not be
structurally sound. In fact, there's some speculation that many of
them are just loose piles of rubble held together by gravity."

Not "rubble": chondrules. The 'stony' and 'stony-iron' asteroids -- as
they've been labelled for years -- are more properly named L-class
(low-iron) and H-class (high-iron) ordinary chondrite asteroids. The fact
that they make up some 87% of the "falls" (meteorites) recovered here on
Earth demonstrates that they *aren't* "just loose piles of rubble", or else
they would have all disintegrated in the atmosphere. `Sand' and `Sandstone'
are made of the same substances; let's not confuse one for the other.

Dave

--- In spacesettlers@yahoogroups.com, "Dave Logsdon"
>> From: capcartoonist [mailto:capcartoonist@h...]
> >"I was thinking that the floor might be as thick as a km."
>
> With a large enough asteroid, that'd be possible, but I can't
really see why
> you'd want to waste *that* much usable area. Heck, you could cut
my original
> "hundred feet" example in half, and still have a much thicker,
safer hull
> than the original O'Neill design.

Well, there's a solution to part of the design. 50 meters
thickness? Sure, why not.

>> "The problem with stony asteroids is that they may not be
>> structurally sound. In fact, there's some speculation that many
of
>> them are just loose piles of rubble held together by gravity."
>
> Not "rubble": chondrules....
> The fact
> that they make up some 87% of the "falls" (meteorites) recovered
here on
> Earth demonstrates that they *aren't* "just loose piles of
rubble", or else
> they would have all disintegrated in the atmosphere.

I could be mis-remembering what I read. Rubble was probably the
wrong word to use. Basically, a stony asteroid might be an
aggregate of several smallere asteroids held together by mutual
attraction.

--- In spacesettlers@yahoogroups.com, "Dave Logsdon"
> From: victoriatangoman [mailto:tango_dancer@h...]
>
> "Have you read "Mining the Sky"? "
>
> Oh, yeah! I've been preaching the Gospel of John -- John S. Lewis,
that is
> -- for years.

I haven't read this yet. I should look into it.

> "To hollow out an asteroid, even when configured into room modules
is
> going to take effort and a slower pace. "
>
> In a way, that "slower pace" is a good point. Building an asteroid
habitat
> such as I've described, one chamber at a time, will allow the
community
> within to develop gradually, somewhat in the way we grow towns
here on
> Earth.... building the `community' and the structure together, a
> step at a time, has proven to work throughout history.

I agree. The concept behind my asteroid city was that it was
originally designed as a military base (I'm not going to describe
the politics in my story that led to this), but over the centuries
the asteroid was converted into a city and commercial center. The
idea is that a habitat with thick walls could better withstand an
attack by hostile forces.

But that doesn't explain why it was designed as one big chamber. I
suppose I need to rethink the design. After all, Venice wasn't
built on one island. ;)

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

> 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.

Oops.

> 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.

I believe the idea is that the whole asteroid skin would become
molten and then solidify almost immediately. Don't ask me why. So
crystallization would not occur.

> Speaking generally now, I've come across these plans before and
I've
> never understood their appeal. Why are you drawn to it? I

I saw a cutaway illustration of an asteroid city in an old book from
the 1950s or 1960s. The concept stuck with me and I just assumed
the idea was feasible if somewhat daunting. This was before I heard
of the O'Neil designs.

Anyway, you've given me a lot to think about! And thanks for the
sites info.

If I do decide to stick with the asteroid-city concept I certainly
have a lot of questions to answer. :)

From: capcartoonist [mailto:capcartoonist@...]

"Well, there's a solution to part of the design. 50 meters
thickness? Sure, why not."

My second post suggested 50 *feet*, which is less than 17 meters. Your 50
*meters* idea is thicker by more than half of my original idea. Cut the old
guy a break, okay? We ain't all caught up to this metric stuff...

Dave

"Dave Logsdon" wrote:

>My second post suggested 50 *feet*, which is less than 17 meters. Your 50
*meters* idea is thicker by more than half of my original idea. Cut the old
guy a break, okay? We ain't all caught up to this metric stuff...<

My mistake. When I did the conversion I calculated based on a meter being
what the guy from the Town Water Dept reads. :p

--- In spacesettlers@yahoogroups.com, "Michael Capriola"
wrote:
> I've studied the concept of hollowing out an asteroid and
converting it into
> a habiat.
> One of the plans suggested putting a parabolic reflector and a
massive lens
> in the sunward pole of the axis in order to provide sunlight.
>
> My question is, is this the best way to provide light for a
habitat roughly
> 30 km long? Is it even feasible?
>
> Comments would be appreciated.
>
> Thanks.
>
> -MKC

IMO I can not see this working due to instabilities of the asteroid
perhaps the idea of tumbling the asteroid about its long axis in the
direction of its orbit could be pursued - this would give the
abilite to have multiple habitats along the axis with graduated
artificial gravitys - you can then redirect the light from the
surface into these habitats by the use of mirrors and light tubes.
it is an idea.