Geology of a recently terraformed planet

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sigi...@yahoo.com

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Feb 17, 2006, 10:49:08 PM2/17/06
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Consider a planet that's broadly Earthlike in size, rotation,
insolation, etc. But it's either lifeless, or has only anaerobic
bacteria. Like Earth in the deep Precambrian, it has a reducing
atmosphere.

Human colonists arrive and terraform it -- algae, then invertebrates,
fungi, land plants, and on up the food chain.

Let us say this takes a thousand years; at the end of which time the
planet has a breathable atmosphere, topsoil, and enough free-living
plants and animals for a human to survive by hunting and fishing.

Now: how will it be different? from Earth?

1) No fossil fuels. FFs were created over millions of years; there
hasn't been time for that here. No oil, natural gas, or coal. Not
even peat.

2) No limestone; limestone is made from the shells of microscopic
marine animals. So, no marbe -- that's just limestone metamorphized
by heat and pressure. (Marble may be a fantastically valuable luxury,
available only as an import from Earth). No limestone caves, either.

3) The soils will be different. Topsoil, okay, but it won't be that
deep except in places where there's been a special effort to create it;
under ideal conditions, prairie topsoil "grows" at something like an
inch per century. And there are hardly any clays... clays are
biogenic; a clay may be 50% organic material by mass.

4) The climate may be very unstable. A thousand years is probably not
long enough to generate a long-term stable climate equilibrium. To
give just one example, a functioning biosphere will shunt a huge amount
of CO2 out of the atmosphere, which will tend to cool the planet.
Eventually it recycles back, thanks to plate tectonics, but there won't
have been nearly enough time for that. Even the weathering cycle may
still be wobbling chaotically. IMS it's something like this that caused
Snowball Earth in the Precambrian.

What else?


Doug M.

Robert A. Woodward

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Feb 18, 2006, 4:03:57 AM2/18/06
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In article
<1140234548.8...@g47g2000cwa.googlegroups.com>,
sigi...@yahoo.com wrote:

> Consider a planet that's broadly Earthlike in size, rotation,
> insolation, etc. But it's either lifeless, or has only anaerobic
> bacteria. Like Earth in the deep Precambrian, it has a reducing
> atmosphere.
>
> Human colonists arrive and terraform it -- algae, then invertebrates,
> fungi, land plants, and on up the food chain.
>
> Let us say this takes a thousand years; at the end of which time the
> planet has a breathable atmosphere, topsoil, and enough free-living
> plants and animals for a human to survive by hunting and fishing.
>
> Now: how will it be different? from Earth?
>
> 1) No fossil fuels. FFs were created over millions of years; there
> hasn't been time for that here. No oil, natural gas, or coal. Not
> even peat.
>
> 2) No limestone; limestone is made from the shells of microscopic
> marine animals. So, no marbe -- that's just limestone metamorphized
> by heat and pressure. (Marble may be a fantastically valuable luxury,
> available only as an import from Earth). No limestone caves, either.

Doug, I believe that there are pre-Cambrian limestone beds.

--
Robert Woodward <robe...@drizzle.com>
<http://www.drizzle.com/~robertaw>

Peter D. Tillman

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Feb 18, 2006, 12:58:53 PM2/18/06
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> Consider a planet that's broadly Earthlike in size, rotation,
> insolation, etc. But it's either lifeless, or has only anaerobic
> bacteria. Like Earth in the deep Precambrian, it has a reducing
> atmosphere.
>
> Human colonists arrive and terraform it -- algae, then invertebrates,
> fungi, land plants, and on up the food chain.
>
> Let us say this takes a thousand years; at the end of which time the
> planet has a breathable atmosphere, topsoil, and enough free-living
> plants and animals for a human to survive by hunting and fishing.
>
> Now: how will it be different? from Earth?

Very likely, few or no significant metallic-mineral deposits, either
(including uranium). Since it's likely that almost all such deposits,
here on earth, are biologically-mediated, and formed in the 10 exp4 to
10exp6 year age-range. [1]

Which is likely to put a severe crimp in the new colony's industrial
base. Not something I recall being addressed in terraforming-SF (except
peripherally (K) in Niven's _Spiral Something_.
______________________
[1] A notable exception are some Pt-group & Cr deposits, which appear to
form by gravity-segregation (fractional crystallization, really) in a
few slow-cooling ultramafic magma-chambers. A slender reed to hang an
industrial civilization on....

Cheers -- Pete Tillman
Geologist & prospector

co...@aol.com

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Feb 18, 2006, 9:07:30 PM2/18/06
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Robert A. Woodward wrote:

> sigi...@yahoo.com wrote:

> > 2) No limestone; limestone is made from the shells of microscopic
> > marine animals. So, no marbe -- that's just limestone metamorphized
> > by heat and pressure. (Marble may be a fantastically valuable luxury,
> > available only as an import from Earth). No limestone caves, either.
>
> Doug, I believe that there are pre-Cambrian limestone beds.

You beat me to it. Calcium carbonate can precipitate out of oceans
abiogenically. So can magnesium carbonate (dolomite, but this gets
complicated).

Thomas Womack

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Feb 19, 2006, 8:11:29 AM2/19/06
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In article <Tillman-EBB7B3...@sn-radius.vsrv-sjc.supernews.net>,

Peter D. Tillman <Til...@toast.net_DIESPAMMERSDIE> wrote:

>Very likely, few or no significant metallic-mineral deposits, either
>(including uranium). Since it's likely that almost all such deposits,
>here on earth, are biologically-mediated, and formed in the 10 exp4 to
>10exp6 year age-range. [1]

10^4 to 10^6 years seems incredibly young -- wasn't the Gabon natural
reactor pure enough uranium-compound to sustain fission two gigayears
ago, aren't the banded iron ore formations things that date from the
advent of oxygen-producing life a gigayear or so back?

Tom

monte...@gmail.com

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Feb 19, 2006, 1:36:33 PM2/19/06
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sigi...@yahoo.com wrote:
> Consider a planet that's broadly Earthlike in size, rotation,
> insolation, etc. But it's either lifeless, or has only anaerobic
> bacteria. Like Earth in the deep Precambrian, it has a reducing
> atmosphere.
>
> Human colonists arrive and terraform it -- algae, then invertebrates,
> fungi, land plants, and on up the food chain.
>
> Let us say this takes a thousand years; at the end of which time the
> planet has a breathable atmosphere, topsoil, and enough free-living
> plants and animals for a human to survive by hunting and fishing.
>
> Now: how will it be different? from Earth?
>
> 1) No fossil fuels. FFs were created over millions of years; there
> hasn't been time for that here. No oil, natural gas, or coal. Not
> even peat.

Not all methane is biological, some dates from the formation of the
earth, and so is prebiological. It is also questionable whether all
heavier petroleum is necessaraly biological.

http://en.wikipedia.org/wiki/Abiogenic_oil

My take is that terraformation will simply take too long to ever be
practical, one can make space habitats cheaper and faster. Their
numbers can make up for their individual vulnerability to asteroid
strikes, and that radiation shielding can be made as thick or thicker
than earth's atmosphere in terms of resistance to all types of
radiation. About 40 feet of ice beats the 14.7 psi of air column.

The 1000 years you indicate is both too short IMHO to get the job done,
and too long to wait. One can build habitats on a time scale of a few
months to a year or so for small ones and 5-10 years for large. The
value of the time of use of the habitat alone would make the
terriformation uneconomic.

Also I suspect that the value of the planet as material to make
habitats would vastly exceed the value of the real estate it would
provide, especially when calculating present worth, as you could
probably make several times the equivalent land area of the surface of
the planet in habitats out of a small fraction of the mass of the
planet in the nominal 1000 years discussed.


------------------snip

Simon Morden

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Feb 19, 2006, 3:18:45 PM2/19/06
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You're also going to have problems with your mudstones: fine clays could
stay in suspension almost indefinitely. Filter feeders and annelids
flocculate the clays so they stay put.

Johnny1a

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Feb 19, 2006, 11:43:51 PM2/19/06
to
monte...@gmail.com wrote:

>
> My take is that terraformation will simply take too long to ever be
> practical, one can make space habitats cheaper and faster. Their
> numbers can make up for their individual vulnerability to asteroid
> strikes, and that radiation shielding can be made as thick or thicker
> than earth's atmosphere in terms of resistance to all types of
> radiation. About 40 feet of ice beats the 14.7 psi of air column.
>
> The 1000 years you indicate is both too short IMHO to get the job done,
> and too long to wait. One can build habitats on a time scale of a few
> months to a year or so for small ones and 5-10 years for large. The
> value of the time of use of the habitat alone would make the
> terriformation uneconomic.
>
> Also I suspect that the value of the planet as material to make
> habitats would vastly exceed the value of the real estate it would
> provide, especially when calculating present worth, as you could
> probably make several times the equivalent land area of the surface of
> the planet in habitats out of a small fraction of the mass of the
> planet in the nominal 1000 years discussed.

There are a couple of hidden assumptions here. They are reasonable,
but it should be noted that they aren't sure things. We don't actually
_know_ that minature self-sustaining biospheres of the sort artificial
habitats would require are viable. They _probably_ are, if one knew
how to set them up and sustain them...but we don't know for sure.
There may be subtle factors (or unsubtle ones we're just missing) that
prevent it, while allowing planet-sized biospheres to operate and
self-sustain.

I tend to agree with you about the time-scale problem of terraforming,
though.

Shermanlee

Johnny1a

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Feb 20, 2006, 12:00:11 AM2/20/06
to

Peter D. Tillman wrote:
> In article <1140234548.8...@g47g2000cwa.googlegroups.com>,
> sigi...@yahoo.com wrote:
>
> > Consider a planet that's broadly Earthlike in size, rotation,
> > insolation, etc. But it's either lifeless, or has only anaerobic
> > bacteria. Like Earth in the deep Precambrian, it has a reducing
> > atmosphere.
> >
> > Human colonists arrive and terraform it -- algae, then invertebrates,
> > fungi, land plants, and on up the food chain.
> >
> > Let us say this takes a thousand years; at the end of which time the
> > planet has a breathable atmosphere, topsoil, and enough free-living
> > plants and animals for a human to survive by hunting and fishing.
> >
> > Now: how will it be different? from Earth?
>
> Very likely, few or no significant metallic-mineral deposits, either
> (including uranium). Since it's likely that almost all such deposits,
> here on earth, are biologically-mediated, and formed in the 10 exp4 to
> 10exp6 year age-range. [1]

I'm no geologist, but something looks very funny about those time
scales. For ex, aren't most of the major iron ore deposits thought to
be biogenic in origin in the pre-oxygenation stage? That would be
hundreds of megayears ago.

But either way, it should be noted that theories about ore availability
are built on a sample set of 1 (maybe 1.1 or 1.2 if we add in what is
known about the other planets).

As it happens, Earth _did_ have a functioning biosphere, so we have no
way to really know what processes would have operated _absent_ that
biosphere, or whether other processes might have produced 'ores' that a
high-tech society could use that the presence of a biosphere
suppresses.

My point is simply that it's risky to generalize from one example, and
for practical purposes Earth is our one example.


Shermanlee

Johnny1a

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Feb 20, 2006, 12:04:50 AM2/20/06
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It's going to make a big difference _how_ it was terraformed, that is,
the techniques used. Different technologies will produce different
results at the detail level.


Shermanlee

sigi...@yahoo.com

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Feb 20, 2006, 12:13:38 AM2/20/06
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Robert A. Woodward wrote:

> Doug, I believe that there are pre-Cambrian limestone beds.

Yep, my bad.

Iron ores? Aren't those biogenic?


Doug M.

monte...@gmail.com

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Feb 20, 2006, 2:10:28 AM2/20/06
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Johnny1a wrote:
> monte...@gmail.com wrote:
>
> >
> > My take is that terraformation will simply take too long to ever be
> > practical, one can make space habitats cheaper and faster. Their
> > numbers can make up for their individual vulnerability to asteroid
> > strikes, and that radiation shielding can be made as thick or thicker
> > than earth's atmosphere in terms of resistance to all types of
> > radiation. About 40 feet of ice beats the 14.7 psi of air column.
> >
> > The 1000 years you indicate is both too short IMHO to get the job done,
> > and too long to wait. One can build habitats on a time scale of a few
> > months to a year or so for small ones and 5-10 years for large. The
> > value of the time of use of the habitat alone would make the
> > terriformation uneconomic.
> >
> > Also I suspect that the value of the planet as material to make
> > habitats would vastly exceed the value of the real estate it would
> > provide, especially when calculating present worth, as you could
> > probably make several times the equivalent land area of the surface of
> > the planet in habitats out of a small fraction of the mass of the
> > planet in the nominal 1000 years discussed.
>
> There are a couple of hidden assumptions here. They are reasonable,
> but it should be noted that they aren't sure things. We don't actually
> _know_ that minature self-sustaining biospheres of the sort artificial
> habitats would require are viable.

As it so happens yes we do, in fact they can be very small, and if
properly cared for can last indefinitly (tested for years at a time).
The below website sells them for from a bit less than $60 USA to around
$200 USA

http://store.yahoo.com/greenfeet/ecospheres.html

Yes these are not large enought to include, but the engineering
principles are the same.

I am a working engineer and I happen to have met and have discussed at
length the issue main designer of the "biosphere II" project. Many
serious mistakes were made in that project, the principle one was
trying to do too much too fast, and letting scientists run the show
with a view to pure research and side scientific issues, rather than
the engineers who would focus on making the bloody thing work.

One of the science projects put a huge amount of active "earth" with
"animal" bacteria that used oxygen and excreted CO2. The mass of earth
was so huge they could not practically remove it w/o major strucural
changes to the building and this screwed over the project as they had
already spent most of the grant money.

Nothing wrong with that sort of earth for open air gardening, but when
a tight balance must be maintined between O2 production and CO2
production, this does not work so good. He agreed with me that the
basic proof of concept should have been done first at small scale
(larger than the above bottles) with human - plant cycle, and that
there is no reason why it would not work. He knew very well what the
problems were with "biosphere II"

Also:

http://spaceflight.nasa.gov/history/shuttle-mir/science/fb/sc-fb-svet.htm

Many types of plants have been proven to grow in space in microgravity
and much higher levels of radiation. I also think that at least one of
the ecosystems discussed above has been to space and back and is still
alive.

I think you objection is basically wrong. Yes you can say that a full
scale ecosystem that could support humans has not been set up in space,
but one was set up on the ground well enough to show it could work (and
did work half assed for a while), and thousands of small scale ones
have been built that work for very long periods of time (years). Also
the basic elements of the concept have been tested in space. The
concept is proven as far as I am concerned.

The structural, centripital accelleration, radiations shielding,
pressure containment, water and air purification, lighting, power,
cooling and heating issues are old hat engineering issues that are not
hard to solve, and have been solved over and over again -- in
spacecraft.


> They _probably_ are, if one knew
> how to set them up and sustain them...but we don't know for sure.

That is the part I disagree with based on the above.

> There may be subtle factors (or unsubtle ones we're just missing) that
> prevent it, while allowing planet-sized biospheres to operate and
> self-sustain.

The closed (sealed) biospheres that are for sale on the above site have
been kept alive for many years and do not die unless you let them get
too cold, or too hot, or not get the right range of light flux (the
green plants in the habitat need light for photo synthasis) or break
the glass, or expose them to too much radiation.


>
> I tend to agree with you about the time-scale problem of terraforming,
> though.


Hard not to.

I think you could make a mostly self-replicating (but for main chips)
system of robots that could be used to construct the physical
strructure of habitats using solar energy and asteroids

A.Mo...@nhm.ac.uk

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Feb 20, 2006, 4:23:54 AM2/20/06
to

sigi...@yahoo.com schrieb:

> Human colonists arrive and terraform it -- algae, then invertebrates,
> fungi, land plants, and on up the food chain.

...


> Let us say this takes a thousand years; at the end of which time the
> planet has a breathable atmosphere, topsoil, and enough free-living
> plants and animals for a human to survive by hunting and fishing.
>
> Now: how will it be different? from Earth?


A recent issue of NATURE (26 January ?) has a paper about something
similar (effects of life on a planets surface).

Andreas


--
Andreas Morlok
Department of Earth and Planetary Science
Kobe University
Kobe
Japan

mau...@itam.mx

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Feb 20, 2006, 4:02:43 PM2/20/06
to

---OT, sort of: have the discoveries of the last few
years changed the conventional wisdom about ter-
raforming Mars? Harder or easier?

Gah. Y'know, these discussions always depress
me. The rest of the solar system is just so ... dull.

Whatever. It's beautiful here in Boston today.

Hasta,

Noel

Johnny1a

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Feb 21, 2006, 1:36:11 AM2/21/06
to

monte...@gmail.com wrote:
> Johnny1a wrote:

> > There are a couple of hidden assumptions here. They are reasonable,
> > but it should be noted that they aren't sure things. We don't actually
> > _know_ that minature self-sustaining biospheres of the sort artificial
> > habitats would require are viable.
>
> As it so happens yes we do, in fact they can be very small, and if
> properly cared for can last indefinitly (tested for years at a time).
> The below website sells them for from a bit less than $60 USA to around
> $200 USA
>
> http://store.yahoo.com/greenfeet/ecospheres.html
>

>


> Nothing wrong with that sort of earth for open air gardening, but when
> a tight balance must be maintined between O2 production and CO2
> production, this does not work so good. He agreed with me that the
> basic proof of concept should have been done first at small scale
> (larger than the above bottles) with human - plant cycle, and that
> there is no reason why it would not work. He knew very well what the
> problems were with "biosphere II"

>


> I think you objection is basically wrong. Yes you can say that a full
> scale ecosystem that could support humans has not been set up in space,
> but one was set up on the ground well enough to show it could work (and
> did work half assed for a while), and thousands of small scale ones
> have been built that work for very long periods of time (years). Also
> the basic elements of the concept have been tested in space. The
> concept is proven as far as I am concerned.
>
> The structural, centripital accelleration, radiations shielding,
> pressure containment, water and air purification, lighting, power,
> cooling and heating issues are old hat engineering issues that are not
> hard to solve, and have been solved over and over again -- in
> spacecraft.
>
>
> > They _probably_ are, if one knew
> > how to set them up and sustain them...but we don't know for sure.
>
> That is the part I disagree with based on the above.

As I said, you're _probably right_. But as you noted, it hasn't been
attempted in space yet, putting all the pieces together. Until we get
to that point, we simply can't be certain.


Shermanlee

Mike Combs

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Feb 23, 2006, 1:59:43 PM2/23/06
to
<monte...@gmail.com> wrote in message
news:1140374193.8...@g44g2000cwa.googlegroups.com...

>
> My take is that terraformation will simply take too long to ever be
> practical, one can make space habitats cheaper and faster.

How refreshing to encounter someone else expressing an opinion I happen to
share.

> The 1000 years you indicate is both too short IMHO to get the job done,
> and too long to wait. One can build habitats on a time scale of a few
> months to a year or so for small ones and 5-10 years for large. The
> value of the time of use of the habitat alone would make the
> terriformation uneconomic.

I did a bit of simple calculation in this article:
http://members.aol.com/oscarcombs/case_spc.htm#Room_To_Grow

It seemed reasonable to me that a space habitat construction program could
equal the surface area of Mars in about 190 years.

> Also I suspect that the value of the planet as material to make
> habitats would vastly exceed the value of the real estate it would
> provide, especially when calculating present worth, as you could
> probably make several times the equivalent land area of the surface of
> the planet in habitats out of a small fraction of the mass of the
> planet in the nominal 1000 years discussed.

O'Neill said the asteroid belt, if converted to habitats, would equal 3,000
times the surface area of the Earth. Yet if it was all lumped together into
a planet, that planet would be smaller than our moon. Yes, space habitats
represent an incredible economy of mass in comparison to planets.

--


Regards,
Mike Combs
----------------------------------------------------------------------
By all that you hold dear on this good Earth
I bid you stand, Men of the West!
Aragorn


monte...@gmail.com

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Feb 24, 2006, 3:06:44 AM2/24/06
to
Mike Combs wrote:
> <monte...@gmail.com> wrote in message
> news:1140374193.8...@g44g2000cwa.googlegroups.com...
> >
> > My take is that terraformation will simply take too long to ever be
> > practical, one can make space habitats cheaper and faster.
>
> How refreshing to encounter someone else expressing an opinion I happen to
> share.
>
> > The 1000 years you indicate is both too short IMHO to get the job done,
> > and too long to wait. One can build habitats on a time scale of a few
> > months to a year or so for small ones and 5-10 years for large. The
> > value of the time of use of the habitat alone would make the
> > terriformation uneconomic.
>
> I did a bit of simple calculation in this article:
> http://members.aol.com/oscarcombs/case_spc.htm#Room_To_Grow

I think you are selling the interstellar stuff way too early. Yes it
is nice to have a long term goal, but that is very long term and
investors do not like to think about things much further away in the
future than about five years. If it cannot make a profit in five years
as a rule you have a hell of a time getting capital to fund a project,
unless you can show some immediate-intermediate term value that is
created that can be sold.

You can fund a 20 plus year-long project, but it will take creation of
intermediate steps that have significant value on their own. Oil firms
for example will look ten or more years into the future for oil
drilling projects if they have the mineral rights to the land, and the
facilities made have intrinsic salvage value like floating production
platforms that are tangible assets that can be sold if the project
fails, even if at a loss - so all the money invested does not get
flushed.

Think about it this way -- if you had 100 billion to invest, would you
not wish to be sure you got some of your money back if the project was
screwed up?

I think the right approach is to focus on automation and start looking
at what can be done both in near earth-lunar space using lunar
materials to make useful things (like communications, weather then
later solar power satellites, and robot exploration spacecraft that can
be sold to whomever wants to buy them), and later in development of the
same in more distant parts of the solar system.

Automation makes sense, as it is so much lighter to lift. As space
capabilities grow you will be able to increase productivity by having
human operators at short light speed communications lags from the
working machines to deal in real time with unusual situations. I think
that keeping a 5-year profit horizon will get you to where you want to
go eventually.

To me the short-term goal is getting more boost-to-orbit capacity in
private hands, which is happening now.

The next step is an early robotic development of lunar materials and
manufacturing facilities. That may require a significant investment,
but if you can show at the end of your first five years that you have
an automated factory on the lunar surface with the capacity to build
useful items (solar power panels, Aluminum structural shapes, Aluminum
tanks filled with Liquid Oxygen whatever) that can be launched from the
lunar surface to earth orbit with a catapult that you also have built
on the lunar surface, that facility would have large tangible value and
so the investors would have confidence that some of their money could
be recovered, and so would be willing to invest on this project if it
could be at that stage in about five years.

This facility can make it much cheaper to have any of a number of space
operations including such mundane but proven commercial successes as
communications, GPS, and weather satellites made cheaper and with much
more powerful transmitters & instruments via use of cheap lunar
materials to build much of the satellite in space.

After that you would see a rush to invest in lunar robotic
manufacturing and mining facilities I think. Then as people realize
that light speed lag is messing with productivity a small contingent of
technical people to deal with problem situations will be added, as they
punch up productivity, the numbers of people rise, and the development
of deep space (asteroid and moons of gas giants) starts, they will need
people to deal with light speed lag issues far more than Lunar
facilities, and so at this point you start building small habitats to
house technical people to trouble shoot a large army of robots to be
sent.

This would be a mining-manufacturing facility not exploration or
prospecting. Exploration should be done by machine, they are much
cheaper to replace then men.

That is an, IMHO, plausible development of space over the next 40 odd
years or so. The next 5-10 years will be spent in development of
launch capacity. I am hoping once reliable private sector launch
capacity is up to it, the lunar mining and manufacturing operation
might start soon after such that in 20 years we may have several
robotic facilities on the moon cranking out things like solar power
panels, liquid Oxygen, and structural Aluminum, Magnesium, and steel,
and even some simple machines and machine parts. Also a small permanent
manned settlement that will be primarily to allow real-time human
oversight of mining and manufacturing robots.

Possibly by then (circa 2026) the first small space habitats will be
being built aimed at housing technical support teams for robotic
mining-manufacturing facilities to be built on asteroids.


> It seemed reasonable to me that a space habitat construction program could
> equal the surface area of Mars in about 190 years.

Maybe -- but you must have an economic reason to build the first one.


> > Also I suspect that the value of the planet as material to make
> > habitats would vastly exceed the value of the real estate it would
> > provide, especially when calculating present worth, as you could
> > probably make several times the equivalent land area of the surface of
> > the planet in habitats out of a small fraction of the mass of the
> > planet in the nominal 1000 years discussed.
>
> O'Neill said the asteroid belt, if converted to habitats, would equal 3,000
> times the surface area of the Earth.

Possibly -- but I think he was not as conservative as I would be about
radiation shielding, and I would never use glass the way he was
proposing, nor any brittle material in a human life safety situation to
contain pressure like that. If the Architects do not like artificial
light -- fire them and hire new Architects. Use of brittle materials
to hold pressure in a life-safety situation is not only bad engineering
practice IMHO, it is gross negligence -IMHO.

Also the whole idea of huge open volumes of air that could have been
made into smaller seal-able pressure holding compartments that would
save lives in the event of a asteroid strike, seems both wasteful and
stupid to me. Wastful in that air is not cheap and air several hundred
feet over your head much of which will whoosh out a hole the first time
a bullet sized asteroid strikes the habitate is a waste.

If you have layers of energy absorbing compartments more people will
live, and you will lose less air and can repair the habitiat sooner.

It seems to me that they have way too many "visionaries" into sci-fi
art, and not enough school of hard knocks engineers in the L-5 society.
Sorry if my years of experiance in marine engineering is showing but
in a harsh environment safety and survivability come a long way before
"form".

My take is that 14.7 mass-pounds per square inch is a minimal level
first cut estimate of the radiation and asteroidal impact shielding
needed as that is the thinnest the earth's protection gets at sea
level, and we know that from time to geologic time radiation events in
.space can kill more complex life forms on earth, and IIRC you do not
see things evolve into very complex forms at high altitude.

Part of that is difficulty of the environment, but part is radiation I
think. You can find some pretty weird complex living organisms on the
ocean bottom in temperatures above 100C near volcano vents, but nothing
more complex than single cell plants and animals on rock at high
altitude?? Hummm maybe radiation shielding is a good idea!

Mike Combs

unread,
Feb 24, 2006, 3:28:38 PM2/24/06
to
<monte...@gmail.com> wrote in message
news:1140768404.0...@e56g2000cwe.googlegroups.com...

>
> I think you are selling the interstellar stuff way too early.

Perhaps you're only being metaphorical in saying "interstellar", but I
consider interstellar travel to be such a distant prospect that there's not
much point discussing it right now. I consider settling solar space to be
an enterprise to busy us for quite some centuries to come.

> I think the right approach is to focus on automation and start looking
> at what can be done both in near earth-lunar space using lunar
> materials to make useful things (like communications, weather then
> later solar power satellites, and robot exploration spacecraft that can
> be sold to whomever wants to buy them), and later in development of the
> same in more distant parts of the solar system.

100 percent agreement.

> This facility can make it much cheaper to have any of a number of space
> operations including such mundane but proven commercial successes as
> communications, GPS, and weather satellites made cheaper and with much
> more powerful transmitters & instruments via use of cheap lunar
> materials to build much of the satellite in space.

But bear in mind that use of lunar resources makes the most sense when the
orbital assets being built are in the megaton range. SPS certainly fits
that bill, but I'm less certain about comm, GPS, and weather sats, even ones
with vastly greater capabilities than at present.

> > It seemed reasonable to me that a space habitat construction program
could
> > equal the surface area of Mars in about 190 years.
>
> Maybe -- but you must have an economic reason to build the first one.

Granted. The scenario O'Neill offered was as housing for the thousands of
SPS workers needed. You seem to emphasize automation, so perhaps one might
take a longer while to work up to a level of 10,000 people needing to live
permanently in HEO. But O'Neill's point was that once one got everything in
place to create SPS from lunar materials, one has nearly everything needed
to make habitats from same as a relatively small side venture.

> Possibly -- but I think he was not as conservative as I would be about
> radiation shielding,

I don't see any reason for controversy in this area. Behind 6 feet of
shielding, radiation levels are no higher than those in many communities on
Earth. Anything beyond that is overkill.

> and I would never use glass the way he was
> proposing, nor any brittle material in a human life safety situation to
> contain pressure like that.

This is a common perception, but I think it owes to viewing the windows of a
habitat as having the characteristics of a christmas ornament. It's
important to remember that the windows are not continuous glass, but 1 meter
square panes set in an aluminum or steel framework. The overall structure
would have significant flexibility and most certainly would not have the
dynamic characteristics of a christmas ornament.

> If the Architects do not like artificial
> light -- fire them and hire new Architects.

This issue is not the preference of the architects but of the intended
residents. We can't point to any examples of significant numbers numbers of
people who have voluntarily chosen to live under artificial illumination for
the rest of their lives. I take confidence from the idea that we can
recreate most of the conditions of the surface of the Earth, and that would
include natural illumination. It's one less potential problem area in a
situtation which will have enough novel circumstances to deal with as it is.

> Also the whole idea of huge open volumes of air that could have been
> made into smaller seal-able pressure holding compartments that would
> save lives in the event of a asteroid strike, seems both wasteful and
> stupid to me.

There are tradeoffs in both approaches. The difficulty with small
compartments is that complete blow-down occurs fairly rapidly. An advantage
of large volumes is that blow-down takes a long time, and repairs can be
more leasiurely.

> Wastful in that air is not cheap

If refining ore, the oxygen might well be quite cheap. But granted, we'll
want to plug holes fairly quickly to save all that precious nitrogen (and
perhaps the hydrogen component of the water vapor).

> and air several hundred
> feet over your head much of which will whoosh out a hole the first time
> a bullet sized asteroid strikes the habitate is a waste.

I don't think you have a realistic notion of the blow-down times. O'Neill
calculated that even an impact from an object the weight of a tennis ball
would still not be an emergency situation.

> It seems to me that they have way too many "visionaries" into sci-fi
> art, and not enough school of hard knocks engineers in the L-5 society.

I paid more attention to what was coming out of the peer-reviewed NASA
studies than what came out of the L-5 Society. I'd like to think that my
FAQ is based more on the former than the latter.


--


Regards,
Mike Combs
http://members.aol.com/oscarcombs/settle.htm

monte...@gmail.com

unread,
Feb 25, 2006, 5:06:35 AM2/25/06
to
Mike Combs wrote:
> <monte...@gmail.com> wrote in message
> news:1140768404.0...@e56g2000cwe.googlegroups.com...
> >
> > I think you are selling the interstellar stuff way too early.
>
> Perhaps you're only being metaphorical in saying "interstellar", but I
> consider interstellar travel to be such a distant prospect that there's not
> much point discussing it right now. I consider settling solar space to be
> an enterprise to busy us for quite some centuries to come.

The site you posted did discuss intersteller travel I think.


>
> > I think the right approach is to focus on automation and start looking
> > at what can be done both in near earth-lunar space using lunar
> > materials to make useful things (like communications, weather then
> > later solar power satellites, and robot exploration spacecraft that can
> > be sold to whomever wants to buy them), and later in development of the
> > same in more distant parts of the solar system.
>
> 100 percent agreement.
>
> > This facility can make it much cheaper to have any of a number of space
> > operations including such mundane but proven commercial successes as
> > communications, GPS, and weather satellites made cheaper and with much
> > more powerful transmitters & instruments via use of cheap lunar
> > materials to build much of the satellite in space.
>
> But bear in mind that use of lunar resources makes the most sense when the
> orbital assets being built are in the megaton range.

After you get the first customer for such that can pay for it. Even
when building 100kg range sattilites, if all but say one kilogram comes
from the moon, and the rest from the earth assembled in orbit one can
get savings I think.


> SPS certainly fits
> that bill, but I'm less certain about comm, GPS, and weather sats, even ones
> with vastly greater capabilities than at present.
>
> > > It seemed reasonable to me that a space habitat construction program
> could
> > > equal the surface area of Mars in about 190 years.
> >
> > Maybe -- but you must have an economic reason to build the first one.
>
> Granted. The scenario O'Neill offered was as housing for the thousands of
> SPS workers needed. You seem to emphasize automation, so perhaps one might
> take a longer while to work up to a level of 10,000 people needing to live
> permanently in HEO.

Yes, start small work your way up. A ~50 odd person habitat seems to
me like a much more reasonable start size.


> But O'Neill's point was that once one got everything in
> place to create SPS from lunar materials, one has nearly everything needed
> to make habitats from same as a relatively small side venture.

yes


>
> > Possibly -- but I think he was not as conservative as I would be about
> > radiation shielding,
>
> I don't see any reason for controversy in this area. Behind 6 feet of
> shielding, radiation levels are no higher than those in many communities on
> Earth. Anything beyond that is overkill.
>
> > and I would never use glass the way he was
> > proposing, nor any brittle material in a human life safety situation to
> > contain pressure like that.
>
> This is a common perception, but I think it owes to viewing the windows of a
> habitat as having the characteristics of a christmas ornament. It's
> important to remember that the windows are not continuous glass, but 1 meter
> square panes set in an aluminum or steel framework. The overall structure
> would have significant flexibility and most certainly would not have the
> dynamic characteristics of a christmas ornament.

I am considering only that the glass is brittle, and that cracks will
run on it. If you make it in 1 meter x 1 meter panes then the
structural load carried by the glass is minimal and the overall
strength must come from the frame and the overall mass gets large. If
the glass panes are intergrated into the structure of the frame such
that it takes significant global loads -- then when -- not if -- when
you have a failure the brittle nature of the glass will make the
failure much worse.

The difference between a brittle material and one that is ductile is
that the ductal material will deform a lot and in the process absorb
kinetic energy. The difference between the energy it takes to fracture
a given sized plate of glass or steel is immense.

Most codes for design of pressure vessels forbid use of brittle
materials.

>
> > If the Architects do not like artificial
> > light -- fire them and hire new Architects.
>
> This issue is not the preference of the architects but of the intended
> residents.

I think the intended residents will care more for their safety and that
of their children than to allow such, at least after the first accident
or two kills large numbers of people that need not have died.

Must we learn the hard way?

> We can't point to any examples of significant numbers numbers of
> people who have voluntarily chosen to live under artificial illumination for
> the rest of their lives. I take confidence from the idea that we can
> recreate most of the conditions of the surface of the Earth, and that would
> include natural illumination.

"Natural illumination" is strongly filtered sunlight, as filtered the
earth's atmosphere, with the filtration variable through the day. Raw
sunlight in space is another animal altogether, and is not safe for
illumination (too much UV).

What is proposed is not "natural illumination". It may indeed be using
filtered sunlight, but it is filtered artificially, and will not match
the filtering of the earth's atmosphere.

My take is that this is not really a valid argument as we are
discussing two types of artifical light, not "natural" light [as humans
evolved using] vs artificial that was designed for human use. I think
that getting the latter close to the real thing in useful spectra is
less hard than the former, and cheaper and safer as well.

Aside from safety and cost issues, controlling heat in a habitat in
space is a big issue. Fully artificial lights can be made that emmit
mostly in useful ranges of light both to man and plant. The flood of
IR that comes with with natrual sunlight heats up the habitate to no
useful end, getting rid of heat is more of a problem than keeping it.
Reflecting it is IMHO a better option.


> It's one less potential problem area in a
> situtation which will have enough novel circumstances to deal with as it is.
>
> > Also the whole idea of huge open volumes of air that could have been
> > made into smaller seal-able pressure holding compartments that would
> > save lives in the event of a asteroid strike, seems both wasteful and
> > stupid to me.
>
> There are tradeoffs in both approaches. The difficulty with small
> compartments is that complete blow-down occurs fairly rapidly.

The relative area of the hole and volume of the compartment is more the
issue I think, and one can design outer compartments to absorb impact
energy.


> An advantage
> of large volumes is that blow-down takes a long time, and repairs can be
> more leasiurely.
>
> > Wastful in that air is not cheap
>
> If refining ore, the oxygen might well be quite cheap.

Yes. But O2 is only 20 odd percent of air on earth.

> But granted, we'll
> want to plug holes fairly quickly to save all that precious nitrogen (and
> perhaps the hydrogen component of the water vapor).
>
> > and air several hundred
> > feet over your head much of which will whoosh out a hole the first time
> > a bullet sized asteroid strikes the habitate is a waste.
>
> I don't think you have a realistic notion of the blow-down times. O'Neill
> calculated that even an impact from an object the weight of a tennis ball
> would still not be an emergency situation.

Depends on the design, impact velocity, and what definition of
"emergency situation" you use. A tennis ball is pretty light by the
way. Mean time between impacts of objects larger than X kg should be
calculatable and deter


> > It seems to me that they have way too many "visionaries" into sci-fi
> > art, and not enough school of hard knocks engineers in the L-5 society.
>
> I paid more attention to what was coming out of the peer-reviewed NASA
> studies than what came out of the L-5 Society. I'd like to think that my
> FAQ is based more on the former than the latter.

I am not all that respectful of NASA, sorry. Look at the sizes of
windows on built manned spacecraft that work. Large ones are not much
seen at all.

Mike Combs

unread,
Feb 28, 2006, 1:41:39 PM2/28/06
to
<monte...@gmail.com> wrote in message
news:1140861995.8...@v46g2000cwv.googlegroups.com...

>
> The site you posted did discuss intersteller travel I think.

If you're referring to my Space Settlement FAQ, I might have mentioned
interstellar travel just once only to make the point that if building
orbital habitats as opposed to terraforming planets, any solar system
becomes a candidate for settlement.

> After you get the first customer for such that can pay for it. Even
> when building 100kg range sattilites, if all but say one kilogram comes
> from the moon, and the rest from the earth assembled in orbit one can
> get savings I think.

Yes, but the savings must pay for estabablishing a mining camp on the moon,
a lunar mass driver, a mass catcher, orbital ore refineries and orbital
manufacturing centers, and then some. I can't see the lift cost savings for
even a hundred 100kg sattelites paying back all of that infrastructure. I
think we have to discuss lift-cost savings in the megatons to justify use of
ET materials. But I'm confident we'll want to build things on that scale.

> Yes, start small work your way up. A ~50 odd person habitat seems to
> me like a much more reasonable start size.

O'Neill was discussing 10,000 person habitats only in the context of
recreating an Earthlike environment. There was universal agreement that
prior to this era there would be many habitats for tens or hundreds of
people which would make no attempt to be Earthlike.

> I am considering only that the glass is brittle, and that cracks will
> run on it. If you make it in 1 meter x 1 meter panes then the
> structural load carried by the glass is minimal and the overall
> strength must come from the frame and the overall mass gets large. If
> the glass panes are intergrated into the structure of the frame such
> that it takes significant global loads -- then when -- not if -- when
> you have a failure the brittle nature of the glass will make the
> failure much worse.

I'm reasonably certain that it was the former, not the latter. But the
original designers did not consider this to make overall mass unacceptable.

> I think the intended residents will care more for their safety and that
> of their children than to allow such, at least after the first accident
> or two kills large numbers of people that need not have died.
>
> Must we learn the hard way?

We'll just have to disagree about the relative levels of danger. I would
stand by a prediction that some people will chose glass-windowed habitats
due to the Earthlike living conditions possible.

> What is proposed is not "natural illumination". It may indeed be using
> filtered sunlight, but it is filtered artificially, and will not match
> the filtering of the earth's atmosphere.

I had hoped my point was clear that by "natural illumination" I meant having
the appearance and sensation of a sun in the "sky", as opposed to living
under small, close, artificial light sources.

> Aside from safety and cost issues, controlling heat in a habitat in
> space is a big issue. Fully artificial lights can be made that emmit
> mostly in useful ranges of light both to man and plant. The flood of
> IR that comes with with natrual sunlight heats up the habitate to no
> useful end, getting rid of heat is more of a problem than keeping it.
> Reflecting it is IMHO a better option.

The heat issue is a valid point. I would simply argue that some will choose
to deal with the heat rejection requirements in exchange for the benefit of
illumination indistinguishable from what we currently enjoy on the surface
of the Earth. Later generations of space settlers may place less of an
emphasis on recreating Earthlike environments, and might well tend more in a
direction of efficiency.

> The relative area of the hole and volume of the compartment is more the
> issue I think, and one can design outer compartments to absorb impact
> energy.

My point was that for the same sized-hole, larger volumes have longer
blow-down times than smaller volumes. The design decision we're discussing
is: Which is worse, catastrophically-sudden complete depressurizations that
affect only a small area, or very slow, gradual pressure drops that affect
large areas?

> Depends on the design, impact velocity, and what definition of
> "emergency situation" you use. A tennis ball is pretty light by the
> way. Mean time between impacts of objects larger than X kg should be
> calculatable and deter

O'Neill used the example of an object the weight of a tennis ball because
it's only objects in that mass range that you're going to routinely
encounter. O'Neill calculated that even for his largest designs, one might
sustain a tennis ball-mass impact about once every three years. It might
take an impact from a 1 ton object to do serious damage, but one should only
expect one of those roughly every million years.

> I am not all that respectful of NASA, sorry. Look at the sizes of
> windows on built manned spacecraft that work. Large ones are not much
> seen at all.

I don't know if we can draw conclusions from design work for spacecraft that
might be manned for a few days at a time when the subject is designing for
permanent, lifetime occupancy.

--


Regards,
Mike Combs

monte...@gmail.com

unread,
Mar 5, 2006, 2:52:27 AM3/5/06
to
Mike Combs wrote:
> <monte...@gmail.com> wrote in message
> news:1140861995.8...@v46g2000cwv.googlegroups.com...
> >
> > The site you posted did discuss intersteller travel I think.
>
> If you're referring to my Space Settlement FAQ, I might have mentioned
> interstellar travel just once only to make the point that if building
> orbital habitats as opposed to terraforming planets, any solar system
> becomes a candidate for settlement.

Perhaps I jumped to confusions. Sorry if that is the case.

>
> > After you get the first customer for such that can pay for it. Even
> > when building 100kg range sattilites, if all but say one kilogram comes
> > from the moon, and the rest from the earth assembled in orbit one can
> > get savings I think.
>
> Yes, but the savings must pay for estabablishing a mining camp on the moon,
> a lunar mass driver, a mass catcher, orbital ore refineries and orbital
> manufacturing centers, and then some. I can't see the lift cost savings for
> even a hundred 100kg sattelites paying back all of that infrastructure.

I think the number of satellites in orbit is in the several thousand
and rising fast. If they were cheaper, then we would have more IMHO.

This below link gives a list of satellites in geostationary orbit. I
count 353 by cutting and pasting to an excell file. That is ONLY
geostationary orbit, which does not include spy, weather, or navigation
satellites, only communications satellites and not all of them. I
think that this kind of shows that the number is large enough that 100
as a market is not even close to a reasonable number.

http://www.satsig.net/sslist.htm

I think a more or less reasonable market projection over 10 years is
more like 10,000.

> I think we have to discuss lift-cost savings in the megatons to justify use of ET
> materials.

Strongly disagree. I think you could get a seed self-sustaining robot
colony on the moon with about 4-5 Saturn V loads of stuff. Put off
real-time correction of robot errors (via humans on the moon able to
work fast remote control, fast as in no ~1/2 second lightspeed gap
between detection of issue and response) till you can afford a habitat
will slow you down a lot [half a second is a long time in control of a
mining machine], but not having any manned craft at all will allow
no-return policy and that can I think get you close to the mass of the
LEM+ Apollo CSM landed per Saturn V, which is nothing to sneeze at, and
low risk and a realistic cap on investment.

That lift would be on the order of 100 - 200 tons of stuff landed on
the moon, not millions of tons, but let it work for 20-30 years and we
could be talking millions of tons lifted off the moon.

> But I'm confident we'll want to build things on that scale.

Agree, eventually.


> > Yes, start small work your way up. A ~50 odd person habitat seems to
> > me like a much more reasonable start size.
>
> O'Neill was discussing 10,000 person habitats only in the context of
> recreating an Earthlike environment. There was universal agreement that
> prior to this era there would be many habitats for tens or hundreds of
> people which would make no attempt to be Earthlike.

Yes that makes more sense, but I think the smaller habitats will be
more commonly lived in, and the places you are talking about will be
more like "Disneyland" that you go to visit on vacation.

It will depend a lot on where the knees of the curves of where economy
of scale in radiation shielding, and use of structural material to
contain pressure is. After some point a larger habitat does not get
you much more economy, and the capital cost and construction time
issues will hold the mean size down. I suspect that more people will
live in habitats that are designed to support in the ballpark of say
100 people or less, than in 10,000 people or more say 200 years after
the first one is built and we have had time for the market to work and
equilibriums be reached.

> > I am considering only that the glass is brittle, and that cracks
will
> > run on it. If you make it in 1 meter x 1 meter panes then the
> > structural load carried by the glass is minimal and the overall
> > strength must come from the frame and the overall mass gets large. If

> > the glass panes are integrated into the structure of the frame such


> > that it takes significant global loads -- then when -- not if -- when
> > you have a failure the brittle nature of the glass will make the
> > failure much worse.
>
> I'm reasonably certain that it was the former, not the latter. But the
> original designers did not consider this to make overall mass unacceptable.

I suspect the designers you speak of have not built many things that
were on the market for sale. Speaking of my personal experience, where
the marine/offshore engineer makes his living is in cutting costs, most
reasonably competent graduates of an engineering school can design a
device that will work. One that will sell like hotcakes on the market
is another story.

On for example a jack-up drilling rig if you can cut 10,000 lbs of
steel out of the hull safely, that is 10,000 more pounds of cargo
(drilling pipe or drilling mud) the rig can jack-up and drill with and
can have on deck for use in operation without having to whistle up a
supply boat to fetch it, at a day rate of US$5,000 or more depending on
the market. These nickels and dimes add up to millions of dollars
saved over the life of the rig, then you get a capital cost reduction
of about (these days) US$0.50 per pound of steel saved, not counting
the reduction in labor time. Another trick commonly pulled is to find
places on a rig where you can use less weld (say ¼ inch fillet
stitched 4 inches every foot rather than continuous), and so reduce
welder labor cost, and even welding rod costs of building it.

My point is that all that mass of material has to be made, then heaved
off the moon to the orbit of the construction site, the braked to match
velocity, then fitted into place, then fastened in by welding or some
other method. Factually the mass of the total project is going to have
a significant impact on the total cost of the product.

So if we have Al's Habitat-yard and Mike's Habitat-yard sitting at
L-5 more or less next door to each other and you build a 1000 person
habitats with windows, and I build a 100 person habitat without
windows, I think I can sell my units for much less than a tenth your
price. I will capture the lower capital market, as those folks cannot
afford your big habitats just as many people cannot afford a large SUV,
and have to buy compact cars.

Also I think I will get a large part of your market if my design is
better and more economical overall, such that I can sell it for less
per person rating, or can alternatively add more features with my
savings. Big firms that need to supply crews with housing for
operations in space will also look at the advantage of having smaller
units, that weigh less per person supported that can be moved to a job
site cheaper, and have more ability to subdivide on future jobs.

If they buy one of your 1000 man Habitats, then say 10 years later they
want to start operations on two new mining locations one with 600 men
and one with 400, then they have to buy at least one more new habitat.
However if they had bought ten of mine, they can recycle them, and buy
no new ones. Also if my habitat design starts out lighter per person
supported, then the cost to move the habitat to a new location is less.
Also having multiple habitats on a jobsite gives you some redundancy
if a critical system breaks on one of the habitats, as the design must
have some redundancy in number of people it can support.

My design will not have big windows, but it could have swimming pools,
and other nice facilities that I can afford to add on the difference in
cost of materials lifted from the moon, and reduced fabrication cost
(fitting those windows). If you add those facilities, then I still
beat you on cost.

The heat build-up of the windows will also add a lot of weight and cost
in the cooling system and necessary redundancy for it.


> > I think the intended residents will care more for their safety and that
> > of their children than to allow such, at least after the first accident
> > or two kills large numbers of people that need not have died.
> >
> > Must we learn the hard way?
>
> We'll just have to disagree about the relative levels of danger.

OK

> I would
> stand by a prediction that some people will chose glass-windowed habitats
> due to the Earthlike living conditions possible.

I think it will be far less than a majority after they compare price,
operational costs (Like needing a much bigger cooling plant and the
power to feed it.) and safety issues.

Money screams - customers listen.


> > What is proposed is not "natural illumination". It may indeed be using
> > filtered sunlight, but it is filtered artificially, and will not match
> > the filtering of the earth's atmosphere.
>
> I had hoped my point was clear that by "natural illumination" I meant having
> the appearance and sensation of a sun in the "sky", as opposed to living
> under small, close, artificial light sources.
>
> > Aside from safety and cost issues, controlling heat in a habitat in

> > space is a big issue. Fully artificial lights can be made that emit


> > mostly in useful ranges of light both to man and plant. The flood of

> > IR that comes with natural sunlight heats up the habitat to no


> > useful end, getting rid of heat is more of a problem than keeping it.
> > Reflecting it is IMHO a better option.
>
> The heat issue is a valid point. I would simply argue that some will choose
> to deal with the heat rejection requirements in exchange for the benefit of
> illumination indistinguishable from what we currently enjoy on the surface
> of the Earth.

Disagree that it is identical, but I agree some will like it, but I
think you are aiming more at the "Disneyland" market, not the real
working folks place to live and work market.

> Later generations of space settlers may place less of an
> emphasis on recreating Earthlike environments, and might well tend more in a
> direction of efficiency.

I suspect the direction will be the reverse. As the space society
becomes wealthy enough to afford this - it will. Early settlers will
be living in harsher situations.


> > The relative area of the hole and volume of the compartment is more the
> > issue I think, and one can design outer compartments to absorb impact
> > energy.
>
> My point was that for the same sized-hole, larger volumes have longer
> blow-down times than smaller volumes. The design decision we're discussing
> is: Which is worse, catastrophically-sudden complete depressurizations that
> affect only a small area, or very slow, gradual pressure drops that affect
> large areas?

But meteors come in a wide variety of sizes and velocities. If your
big volume gets hit with a big object or smaller one at high velocity
making a big hole, the air rushes out in one big whoosh, and everybody
dies fast. If it is compartmentalized, more of the crew will have a
better chance to live.

> > Depends on the design, impact velocity, and what definition of
> > "emergency situation" you use. A tennis ball is pretty light by the
> > way. Mean time between impacts of objects larger than X kg should be

> > calculateable and deter


>
> O'Neill used the example of an object the weight of a tennis ball because
> it's only objects in that mass range that you're going to routinely
> encounter.

Umm - maybe. I think this will depend on what part of space you are
operating at. I suspect that the moons of a gas giant will have a lot
more junk in orbit moving at significant speeds, parts of the asteroid
belt might be bad. Also low earth orbit is getting dirtier in terms of
more and more junk. Then you have the potential for accidental
collisions with common types of spacecraft that will be operating close
to the habitat, which as a marine engineer designing rigs one is
required to consider, collisions between drilling rigs and supply boats
are common event. Collisions between two ships or a ship and a rig are
also not unheard of, and one must make reasonable precautions in the
design of the ship or rig to minimize loss of life and property. While
Dr. O'Neill's calculation may indeed be 100% right given his
assumptions, I think his perhaps hidden or unrealized assumption of
only natural objects colliding with the habitat can be a killer.

What happens when a common design of space cargo tug or passenger ferry
smacks into the window of the habitat with a closing velocity of say
10% the delta-vee that she is designed for? I doubt that a say a 1,000
-10,000 kg spacecraft hitting the window at oh lets say 500 m/s is
going to bounce off, or that the hole it makes will be a small one.

Nor is this going to be all that uncommon an accident. Collisions
between small craft and the large craft they have to load or unload are
to be expected. Perhaps the speed I mention is high, but one must
design for a worse case accident that is plausible. It is probable
that on occasion pilots of such small craft will lose control or make
serious mistakes in handling of the craft that will cause a collision,
such as falling asleep and forgetting to do a retro burn. The point is
the designer generally says that is just tough for the small craft, but
that is not acceptable for the large craft to be destroyed as a result,
as it will probably happen several times over the life of the large
craft with no operational fault on the crew. Ergo the engineer has to
design around it.


> O'Neill calculated that even for his largest designs, one might
> sustain a tennis ball-mass impact about once every three years. It might
> take an impact from a 1 ton object to do serious damage, but one should only
> expect one of those roughly every million years.

Natural ones I agree. Accidental collisions, I disagree. Also one must
consider criminal acts short of war that may cause collisions, like
hijacking of spacecraft.

War is like an act of god, you cannot deal with it as an engineer, but
one can anticipate common types of crime, or accidents.


> > I am not all that respectful of NASA, sorry. Look at the sizes of
> > windows on built manned spacecraft that work. Large ones are not much
> > seen at all.
>
> I don't know if we can draw conclusions from design work for spacecraft that
> might be manned for a few days at a time when the subject is designing for
> permanent, lifetime occupancy.

Point taken.

Peter D. Tillman

unread,
Mar 6, 2006, 1:01:22 PM3/6/06
to
In article <1140412418.6...@g43g2000cwa.googlegroups.com>,
sigi...@yahoo.com wrote:

> Robert A. Woodward wrote:
>
> > Doug, I believe that there are pre-Cambrian limestone beds.
>
> Yep, my bad.
>

But still biogenic (sfaik).

> Iron ores? Aren't those biogenic?
>

Yup. With minor exceptions (Kiruna-type, maybe)

Cheers -- Pete Tillman

Mike Combs

unread,
Mar 10, 2006, 2:14:22 PM3/10/06
to
<monte...@gmail.com> wrote in message
news:1141545147.5...@u72g2000cwu.googlegroups.com...

> I think a more or less reasonable market projection over 10 years is
> more like 10,000.

OK, I would agree that /if/ there were a market for 10,000 satellites, it
would probably justify use of ET resources.

> That lift would be on the order of 100 - 200 tons of stuff landed on
> the moon, not millions of tons, but let it work for 20-30 years and we
> could be talking millions of tons lifted off the moon.

Have you seen the NASA study about self-replicating lunar industrial
systems? I think it's on the web somewhere. O'Neill was also very
interested in self-replicating systems.

> It will depend a lot on where the knees of the curves of where economy
> of scale in radiation shielding, and use of structural material to
> contain pressure is. After some point a larger habitat does not get
> you much more economy, and the capital cost and construction time
> issues will hold the mean size down.

True enough. But just know that Gerard O'Neill, the acknowledged expert on
orbital habitats, placed that knee at the scale of Island 3.

> I suspect the designers you speak of have not built many things that
> were on the market for sale.

I suppose not, at least in the sense of things on the open market. But some
of them had experience designing and building particle accelerators which
were over a mile across, and which faced the more difficult requirement of
standing up under external, rather than internal, air pressure.

> So if we have Al's Habitat-yard and Mike's Habitat-yard sitting at
> L-5 more or less next door to each other and you build a 1000 person
> habitats with windows, and I build a 100 person habitat without
> windows, I think I can sell my units for much less than a tenth your
> price.

Oh, please don't misunderstand me. I totally agree that space settlement
will start out at a scale closer to what you're talking about than Island 1.
I'm just saying that long term, I expect large habitats which by and large
recreate the most pleasant areas found on our planet. I think once
established in space, there will be the wealth to pay for these kinds of
things, and that subsequent large, Earthlike habitats will only cost a small
fraction of the price of the first one.

It occurs to me that I stand in an intermediate postion between you and the
megastructures people. I think making one 10,000 person habitat might be
more economical than making a hundred 100 person habitats. But looking at
the megastructure dreams of single structures which house thousands or
millions of times the population of the entire Earth, I agree that a smaller
subdivision of units is probably better, safer, and more economically
feasible.

> My design will not have big windows, but it could have swimming pools,
> and other nice facilities that I can afford to add on the difference in
> cost of materials lifted from the moon, and reduced fabrication cost
> (fitting those windows). If you add those facilities, then I still
> beat you on cost.

A difference in our assumptions is that I don't think there's going to be an
enormous cost difference between a pressure vessel wall of windows and a
pressure vessel wall made any other conceiveable way.

> I suspect the direction will be the reverse. As the space society
> becomes wealthy enough to afford this - it will. Early settlers will
> be living in harsher situations.

We're just looking at different timescales. My view is that the initial
space settlers will live in rather spartan quarters because making anything
more elaborate won't be economically feasible. Timescale: A few years to
perhaps a decade or two after the start of space industrialization. Then
we'll see the era of "Island" type Earthlike habitats. Built initially for
space workers, later a market will develop for imigrants from Earth, who
will value Earthlike living conditions. Then we might see later generations
of space-born types who don't really care about what is or isn't Earthlike.
They might well seek efficiencies which might be gained by doing things like
growing food in radically new and different ways. Timescale: Beyond 2 or 3
generations or perhaps a century.

> But meteors come in a wide variety of sizes and velocities. If your
> big volume gets hit with a big object or smaller one at high velocity
> making a big hole, the air rushes out in one big whoosh, and everybody
> dies fast. If it is compartmentalized, more of the crew will have a
> better chance to live.

You still don't see the implications of the O'Neill calculation. The kinds
of objects which would do the damage you're concerned with might come along
only once in a millenia, or once every million years. We really should be
designing for the tennis-ball-mass impacts, which will happen every few
years, rather than the space boulders, which will be vanishingly rare.

> Also low earth orbit is getting dirtier in terms of
more and more junk.

True, but O'Neill never advocated building habitats in any orbit which gets
frequently eclipsed from the sun.

> Then you have the potential for accidental
> collisions with common types of spacecraft that will be operating close
> to the habitat, which as a marine engineer designing rigs one is
> required to consider, collisions between drilling rigs and supply boats
> are common event.

I would agree that this is a greater cause for concern. And certainly our
experience with Mir suggests that this is the bigger danger. But we should
be reassured by the fact that shielding for cosmic rays will necessitate
slag walls 6 feet thick.

> While
> Dr. O'Neill's calculation may indeed be 100% right given his
> assumptions, I think his perhaps hidden or unrealized assumption of
> only natural objects colliding with the habitat can be a killer.

Most man-made debris is in LEO, with some in GEO. O'Neill never recommended
any orbit closer than half-way to lunar orbit. So in that context it's
correct to view the threat mostly in terms of meteroids.

> What happens when a common design of space cargo tug or passenger ferry
> smacks into the window of the habitat with a closing velocity of say
> 10% the delta-vee that she is designed for? I doubt that a say a 1,000
> -10,000 kg spacecraft hitting the window at oh lets say 500 m/s is
> going to bounce off, or that the hole it makes will be a small one.

In the smaller kinds of habitats that we'll see in any near-term future,
there will be no direct straight-line path to the windows past the radiation
shields. Sunlight will be bounced around the shields by mirror
arrangements. The same strategy which will guard agains a cosmic ray
particle coming through a window ought to keep a runaway space tug from
doing the same.

Bryan Derksen

unread,
Mar 10, 2006, 10:58:29 PM3/10/06
to
On Fri, 10 Mar 2006 13:14:22 -0600, "Mike Combs"
<mike...@nospam.com_chg_nospam_2_ti> wrote:
>Have you seen the NASA study about self-replicating lunar industrial
>systems? I think it's on the web somewhere. O'Neill was also very
>interested in self-replicating systems.

AASM senses tingling! My favourite subject's been mentioned! :)

http://en.wikisource.org/wiki/Advanced_Automation_for_Space_Missions

>It occurs to me that I stand in an intermediate postion between you and the
>megastructures people. I think making one 10,000 person habitat might be
>more economical than making a hundred 100 person habitats. But looking at
>the megastructure dreams of single structures which house thousands or
>millions of times the population of the entire Earth, I agree that a smaller
>subdivision of units is probably better, safer, and more economically
>feasible.

How about borging each individual person's brain into their own
self-contained self-propelled robotic space pod? That's probably the
farthest extreme on the small end of the subdivision scale. :)

>> While
>> Dr. O'Neill's calculation may indeed be 100% right given his
>> assumptions, I think his perhaps hidden or unrealized assumption of
>> only natural objects colliding with the habitat can be a killer.
>
>Most man-made debris is in LEO, with some in GEO. O'Neill never recommended
>any orbit closer than half-way to lunar orbit. So in that context it's
>correct to view the threat mostly in terms of meteroids.

Any place with a large space habitat is going to attract all sorts of
space traffic by its very existence, though. It's by no means an
insurmountable problem but it seems worth considering.

>> What happens when a common design of space cargo tug or passenger ferry
>> smacks into the window of the habitat with a closing velocity of say
>> 10% the delta-vee that she is designed for? I doubt that a say a 1,000
>> -10,000 kg spacecraft hitting the window at oh lets say 500 m/s is
>> going to bounce off, or that the hole it makes will be a small one.
>
>In the smaller kinds of habitats that we'll see in any near-term future,
>there will be no direct straight-line path to the windows past the radiation
>shields. Sunlight will be bounced around the shields by mirror
>arrangements. The same strategy which will guard agains a cosmic ray
>particle coming through a window ought to keep a runaway space tug from
>doing the same.

Radiation shielding will only be a few meters thick in most designs,
won't it? http://books.slashdot.org/article.pl?sid=00/12/29/1637242
says six feet, the first reference I found in Google that gave a
number. A 10,000 kilogram spacecraft at 500 m/s is probably going to
go through that.

monte...@gmail.com

unread,
Mar 13, 2006, 3:04:33 AM3/13/06
to

Mike Combs wrote:
> <monte...@gmail.com> wrote in message
> news:1141545147.5...@u72g2000cwu.googlegroups.com...
>
> > I think a more or less reasonable market projection over 10 years is
> > more like 10,000.
>
> OK, I would agree that /if/ there were a market for 10,000 satellites, it
> would probably justify use of ET resources.
>
> > That lift would be on the order of 100 - 200 tons of stuff landed on
> > the moon, not millions of tons, but let it work for 20-30 years and we
> > could be talking millions of tons lifted off the moon.
>
> Have you seen the NASA study about self-replicating lunar industrial
> systems? I think it's on the web somewhere. O'Neill was also very
> interested in self-replicating systems.

Not yet but I see someone posted a link to it. I will browse it soon.

>
> > It will depend a lot on where the knees of the curves of where economy
> > of scale in radiation shielding, and use of structural material to
> > contain pressure is. After some point a larger habitat does not get
> > you much more economy, and the capital cost and construction time
> > issues will hold the mean size down.
>
> True enough. But just know that Gerard O'Neill, the acknowledged expert on
> orbital habitats, placed that knee at the scale of Island 3.

Humm.


>
> > I suspect the designers you speak of have not built many things that
> > were on the market for sale.
>
> I suppose not, at least in the sense of things on the open market. But some
> of them had experience designing and building particle accelerators which
> were over a mile across, and which faced the more difficult requirement of
> standing up under external, rather than internal, air pressure.


OK - but I caution you that being competent to design a machine that
will work is a much lower level of competence in a given area, than
being able to design one that will both work and be economically
competitive among a large field of contenders.


> > So if we have Al's Habitat-yard and Mike's Habitat-yard sitting at
> > L-5 more or less next door to each other and you build a 1000 person
> > habitats with windows, and I build a 100 person habitat without
> > windows, I think I can sell my units for much less than a tenth your
> > price.
>
> Oh, please don't misunderstand me. I totally agree that space settlement
> will start out at a scale closer to what you're talking about than Island 1.
> I'm just saying that long term, I expect large habitats which by and large
> recreate the most pleasant areas found on our planet.

No question about it, you will need more internal space and so a much
larger structure to do that. However, I point out that even in some of
the most beautiful outdoor environments in the world, the first thing
humans tend to do is build tiny shelters with small rooms and, if large
enough, narrow hallways. I think we have more of a psycological
problem with needing relitively close quarters than one with needing
open space.

> I think once
> established in space, there will be the wealth to pay for these kinds of
> things, and that subsequent large, Earthlike habitats will only cost a small
> fraction of the price of the first one.

Or we will be so rich it will not matter.

>
> It occurs to me that I stand in an intermediate postion between you and the
> megastructures people. I think making one 10,000 person habitat might be
> more economical than making a hundred 100 person habitats.

!!!!!

Where are they going to get the capital to build structures that
blasted big and tie up that capital for the decades that it will take
to build them?

It has been physically possible to build million person archology type
cities on earth for around 100 years or so. Show me even one 10,000
person plus arcology on earth.

Why not? I suspect the return on investment is too low and too long
term for it to be practical. Alos people do not like them, too
impersonal I think. ~1000 person apartment complexes seem to be near
the top of what people will live in. Most people perfer single family
unit dwellings. When you need to enclose pressure and have radiation
shielding, then I think larger is more practical, but the economic and
human psycological pressures will make the mean much closer to the 100
person size than the 100,000 person size.

----------------snip

Logan Kearsley

unread,
Mar 13, 2006, 6:04:39 PM3/13/06
to
<monte...@gmail.com> wrote in message
news:1142237073....@j52g2000cwj.googlegroups.com...

>
> > Oh, please don't misunderstand me. I totally agree that space
settlement
> > will start out at a scale closer to what you're talking about than
Island 1.
> > I'm just saying that long term, I expect large habitats which by and
large
> > recreate the most pleasant areas found on our planet.
>
> No question about it, you will need more internal space and so a much
> larger structure to do that. However, I point out that even in some of
> the most beautiful outdoor environments in the world, the first thing
> humans tend to do is build tiny shelters with small rooms and, if large
> enough, narrow hallways. I think we have more of a psychological
> problem with needing relatively close quarters than one with needing
> open space.

Methinks that's more a function of it being much easier and cheaper to build
smaller shelters with smaller rooms than it is to build really big ones.
You'll notice that people with more money to spend tend to have larger
shelters with larger rooms. Additionally, you'll find that a great number of
people, especially in some of the most beautiful outdoor environments in the
world, spend a great deal of time outside of those shelters- some to such an
extent that *most* of their time is spent outside of those shelters.

-l.
------------------------------------
My inbox is a sacred shrine, none shall enter that are not worthy.


monte...@gmail.com

unread,
Mar 14, 2006, 1:03:24 AM3/14/06
to


Could be, but I don't think that you are refuting my point, that even
in really good outdoor environments, people want shelter AKA enclosed
environments.

Logan Kearsley

unread,
Mar 14, 2006, 12:21:54 PM3/14/06
to
<monte...@gmail.com> wrote in message
news:1142316204.8...@j33g2000cwa.googlegroups.com...

I don't think anybody disagrees that most people want shelters (houses). All
of the artists conceptions of Island habitats I've ever seen do, in fact,
have houses in them. What I'm refuting is the implication that people will
want their tiny enclosed spaces over the opportunity for wider, open spaces.
If somebody provides a habitat that contains a beautiful lakeside vista (for
example), and doesn't allow any extra structures to be put inside, of course
nobody's going to want to live there! But similarly, if somebody provides a
beautiful lakeside vista with beachfront houses, and somebody else provides
a block of cozy enclosed spaces, only weirdoes like me and Isaac Asimov are
going to go for the latter, modulo price considerations.

Mike Combs

unread,
Mar 15, 2006, 1:57:20 PM3/15/06
to
"Bryan Derksen" <bryan....@shaw-spamguard.ca> wrote in message
news:jvh412h6iqqhsljv9...@4ax.com...

>
> Any place with a large space habitat is going to attract all sorts of
> space traffic by its very existence, though. It's by no means an
> insurmountable problem but it seems worth considering.

True. At least in this area, as opposed to LEO, we can have sensible rules,
stringently enforced, from the beginning.

> won't it? http://books.slashdot.org/article.pl?sid=00/12/29/1637242
> says six feet, the first reference I found in Google that gave a
> number. A 10,000 kilogram spacecraft at 500 m/s is probably going to
> go through that.

Sure, but I think the most likely scenario for collision is the one we saw
for Mir: A spacecraft loses control while on final approach for docking. At
that point, I would expect relative velocities to be just a few meters/sec.
As far as collisions from objects in significantly different yet
intersecting orbits, true, even a 6 foot wall is scarce protection, and the
only real answer there is to never permit this.

Jordan

unread,
Mar 17, 2006, 3:01:12 PM3/17/06
to
Pete Tillman said:

>
Very likely, few or no significant metallic-mineral deposits, either
(including uranium). Since it's likely that almost all such deposits,
here on earth, are biologically-mediated, and formed in the 10 exp4 to
10exp6 year age-range. [1]
>

I'm not sure that we know yet that these deposits can't be formed
abiotically on a planet that lacked life, because on Earth presumably
micro-organisms long ago incorporated all such accessible metals into
their bodies and then formed new depsoits out of them. In any case, I
strongly suspect that a level of technology permitting terraforming
(and especially the amount of time which terraforming takes) would mean
that the civilization colonizing the planet could:

1) exploit asteroidal metals, and

2) use at least the deuterium-tritium, and probably also the
deuterium-trihelium, nuclear fusion reactions as a power source.

Sincerely Yours,
Jordan

Mike Combs

unread,
Mar 20, 2006, 2:04:24 PM3/20/06
to
"Jordan" <JSBass...@yahoo.com> wrote in message
news:1142625672.0...@j33g2000cwa.googlegroups.com...

>
> In any case, I
> strongly suspect that a level of technology permitting terraforming
> (and especially the amount of time which terraforming takes) would mean
> that the civilization colonizing the planet could:
>
> 1) exploit asteroidal metals, and

I'd agree. In fact, I'd go even further, and say that a level of technology
permitting terraforming would also permit exploitation of asteroidal metals
to build orbital habitats, and that the amount of time which terraforming
takes would allow doing so on a scale to rival the surface area of a planet.
In which case one might question the sensibility of sticking with the
original plan.

http://members.aol.com/oscarcombs/case_spc.htm#Room_To_Grow

Jordan

unread,
Mar 20, 2006, 2:35:08 PM3/20/06
to
Mike Combs said:

>I'd agree. In fact, I'd go even further, and say that a level of technology
permitting terraforming would also permit exploitation of asteroidal
metals
to build orbital habitats, and that the amount of time which
terraforming
takes would allow doing so on a scale to rival the surface area of a
planet.
In which case one might question the sensibility of sticking with the
original plan. <

I think that humans will do both -- terraforming and space hab
construction. I also think that in many cases people will simply live
in habs on or under the surface of non-terraformed planets, too.
People historically have adopted a variety of ways of life, and I think
they will continue to do so in the future.

Sincerely Yours,
Jordan

Jordan

unread,
Mar 20, 2006, 4:43:31 PM3/20/06
to
Mike Combs said:

> As far as collisions from objects in significantly different yet intersecting orbits, true, even a 6 foot wall is scarce protection, and the only real answer there is to never permit this. <

One way to prevent this is through active defense, and past a certain
technological point I would expect _all_ spaceships or habs to carry
anti-collision lasers and charged particle beams, and magnetic
shielding (the lasers to vaporize/deflect through thermal explosion
incoming junk; the CPB's to vaporize/deflect/charge them; and the
magnetic shielding to deflect charged objects).

Sincerely Yours,
Jordan

Jordan

unread,
Mar 20, 2006, 6:27:49 PM3/20/06
to
Well, this is hardly an either-or. Why not build a big, open L-5
cylinder and on the inside build houses _which can be sealed against
vacuum in emergencies?_ If everyone has a pressure-tight house and an
emergency vacuum suit handy (this can be far less than a
full-capability space suit because it doesn't need anywhere near as
much resistance to radiation, nor does it need an EVA manuever
thruster), then they have the best of both worlds, don't they?

Sincerely Yours,
Jordan

Logan Kearsley

unread,
Mar 20, 2006, 9:32:32 PM3/20/06
to
"Jordan" <JSBass...@yahoo.com> wrote in message
news:1142897269....@v46g2000cwv.googlegroups.com...

Because most people would see that as drastic overkill?
Sure, it could happen, and it would provide the best of both worlds, and it
wouldn't even be particularly hard to make it happen. But I doubt it would
happen with any degree of regularity.

Mike Combs

unread,
Mar 21, 2006, 3:00:40 PM3/21/06
to
"Jordan" <JSBass...@yahoo.com> wrote in message
news:1142883308.3...@i39g2000cwa.googlegroups.com...

>
> I think that humans will do both -- terraforming and space hab
> construction. I also think that in many cases people will simply live
> in habs on or under the surface of non-terraformed planets, too.
> People historically have adopted a variety of ways of life, and I think
> they will continue to do so in the future.

In the final analysis, I have to agree. The future will see more variety,
which means some people living on planets, and some not. I have strong
feelings that the orbital folk will have significant advantages over the
planetary folk, but some will disagree and insist on making a go of it on
another planetary surface.

It's kind of like when people ask will we genetically modify ourselves,
technologically modify ourselves, or remain in our present human form.
Well, the answer is all of the above. Not everybody will go charging off in
the same direction.

Mike Combs

unread,
Mar 21, 2006, 3:14:30 PM3/21/06
to
"Logan Kearsley" <chrono...@verizon.net> wrote in message
news:4BJTf.6660$wD1.997@trnddc02...

> "Jordan" <JSBass...@yahoo.com> wrote in message
> news:1142897269....@v46g2000cwv.googlegroups.com...
> > Well, this is hardly an either-or. Why not build a big, open L-5
> > cylinder and on the inside build houses _which can be sealed against
> > vacuum in emergencies?_ If everyone has a pressure-tight house and an
> > emergency vacuum suit handy (this can be far less than a
> > full-capability space suit because it doesn't need anywhere near as
> > much resistance to radiation, nor does it need an EVA manuever
> > thruster), then they have the best of both worlds, don't they?
>
> Because most people would see that as drastic overkill?
> Sure, it could happen, and it would provide the best of both worlds, and
it
> wouldn't even be particularly hard to make it happen. But I doubt it would
> happen with any degree of regularity.

It all turns on whether Gerard O'Neill was right or wrong in his
calculations. If right, then we can expect about every 3 or 4 years an
incident which will result in a very slow, gradual drop in air pressure
which presents no problem provided that the hole can be sealed in a day or
so. Alternately, the kind of collision which might make you glad you live
in a hermetic house with a spacesuit in the hall closet might happen once
every million years. In that situation, I doubt seriously anyone will spend
any kind of money whatsoever against that eventuality.

I can't see a reason for feeling that O'Neill miscalculated other than that
"Lost In Space" left us with a different impression of the situation.

Jordan

unread,
Mar 21, 2006, 5:02:16 PM3/21/06
to

Logan Kearsley wrote:
> "Jordan" <JSBass...@yahoo.com> wrote in message
> news:1142897269....@v46g2000cwv.googlegroups.com...
> > Well, this is hardly an either-or. Why not build a big, open L-5
> > cylinder and on the inside build houses _which can be sealed against
> > vacuum in emergencies?_ If everyone has a pressure-tight house and an
> > emergency vacuum suit handy (this can be far less than a
> > full-capability space suit because it doesn't need anywhere near as
> > much resistance to radiation, nor does it need an EVA manuever
> > thruster), then they have the best of both worlds, don't they?
>
> Because most people would see that as drastic overkill?
> Sure, it could happen, and it would provide the best of both worlds, and it
> wouldn't even be particularly hard to make it happen. But I doubt it would
> happen with any degree of regularity.

Well, it's not just meteoric penetration that you'd have to worry
about. Remember, a big open cylindrical space hab has a big shared air
space in its main compartment which is nevertheless tiny by the
standards of a planetary atmosphere. This main compartment could be
ruptured or contaminated by all sorts of military or terrorist acts,
and all sorts of accidents.

Yes, it wouldn't happen very often. And ocean liners don't sink very
often. But when they do, you're glad they carry lifeboats.

Sincerely Yours,
Jordan

Madalch

unread,
Mar 21, 2006, 6:18:21 PM3/21/06
to
> In that situation, I doubt seriously anyone will spend
> any kind of money whatsoever against that eventuality.

You don't know my wife.

($500 worth of earthquake preparedness equipment, and when was the last
noticable earthquake in BC?)

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