Re: Mars colonization versus Stanford Torus

"Mike Combs" <mikecombs@xxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

:"Fred J. McCall" <fmccall@xxxxxxxxxxxxx> wrote in message
:news:th9s429bgr4ljqoq188fdvhsjd96rjfsb4@xxxxxxxxxx
:>
:> There is, but you're not going to leap from 'man in a can' to 'city in
:> the sky' in one swell foop. The money is, at least initially, easier
:> to come by down on the dirt balls.
:
:I'd say SPS represents a business plan where investment money could be come
:by in an orbital location, provided we can get the needed resources there.

That's a really big "provided" there. You also have to make your
business case that getting power from the SPS is cheaper than getting
it by burning natural gas (for example), INCLUDING all capital and R&D
investment required to get your SPS up and running.

Nobody has ever been able to come close to successfully making that
case.

:> I think settling on bodies with
:> lots of resources locally available (the dirt balls) but somewhat
:> shallower gravity wells than Earth is a reasonable and logical
:> stepping stone to your large space structures.
:
:Oh, I would never deny that the process starts with either a moonbase, an
:asteroid base, or an asteroid retrieval mission.

I don't consider the latter two as immediately practical for building
a space habitat. I picture asteroid retrieval as being easier (since
your initial industry is down on your moon base) when you just toss
the asteroid down on the moon and then strip mine it out for smelting
(another process that gravity becomes sort of important for).

:> All I can say is that you have a rather peculiar view of how
:> government contracting works that doesn't seem to be in exact 1:1
:> accord with my experience with it.
:
:Just quoting what I've heard others say. I've certainly had no presonal
:experience with cost-plus contracts.

On can hear "others" say all sorts of silly things and bashing
government contractors is a popular sport.

:> Provide your counter example.
:
:Well, number one, I'm not even sure about your assumption that we've built
:maglevs bigger than the biggest space station. I'm only aware of the
:relatively modest programs in Japan and Germany which are more pilot
:demonstrations. Are any of them bigger in diameter than Skylab?

Skylab had a total volume (including docked Apollo capsule) of around
540 cubic meters. I'm pretty sure that building a maglev train with
that much internal volume isn't hard. The internal volume of a 3-car
maglev train is about half again as large.

A couple other facts to keep in mind are that the maglev cars
mentioned above are being deliberately made small to help with AIR
RESISTANCE and that maglev isn't even necessarily a required
technology. Obviously air resistance is not going to be a problem on
the Moon (for example), so cars could be made much larger. Maglev may
not even be necessary, since you would only need speeds of around 300
kph, which is already being done by more 'conventional' trains, such
as the Japanese Shinkansen trains (which make about 250 kph in air).

:Number two, O'Neill published figures for how large a pressurized structure
:could be built in space with existing materials. While not "proving" we can
:do this in the sense of actually doing it, this at least introduces a
:certain level of numerical rigor to the discussion. I'd have to see a
:comparable study with comparable numerical calculation on the subject of
:maglevs mile across before I'd buy into the assertion that such may be
:simpler than pressure vessels.

Paper studies don't prove much, frankly.

:> Except orbital locations aren't necessarily rich in advantages.
:
:http://members.aol.com/oscarcombs/spacsetl.htm#advantages

I don't find the advantages listed particularly telling. The only one
that can't be done just as well on the Moon is "access to zero-g". The
problem is that we don't know precisely what zero-g is good for right
now, so is that really an 'advantage' or is it a problem to be
addressed?

:> But having that gravity certainly alleviates one set of problems. All
:> the other problems that exist are worse in your orbital location than
:> they are down on a surface, as well.
:
:Not necessarily. We still have the problems of vacuum or near vacuum on the
:moon and Mars. Radiation might be attenuated to 1/2 or 1/3, but is still
:enough that we can't blow off shielding.

But mass for shielding is easier to get when you are already sitting
on a big ball of 'mass' than if you are out in the middle of a whole
bunch of empty.

:> And just where do you think the 'elsewhere' is? You can't just wave a
:> wand and suddenly start from nothing to having millions of people
:> living in space habitats. You have to start somewhere and getting to
:> where you seem to be assuming you are is going to take centuries.
:
:"Elsewhere" could mean Earth.

So now you need to get your launch costs down far enough that it is
practically to lift everything from Earth. How's that working out for
you?

:> You have the same problem only worse in a space habitat. How do you
:> propose to solve it there? Any solution you come up with probably
:> works better down on a surface, where there are greater resources
:> available to implement it.
:
:One thing we can do in orbit which we couldn't do in a gravity field would
:be to build a heat radiator a square mile in area but only 1 inch thick,
:which can simultaneously radiate from both sides.

But why would you want to? You're sitting on a much bigger heat sink
if you're down on the Moon (for example). And good luck with that
huge heat sink, since it can only radiate from both sides if it's in
shadow. On a dirtball, you could simple sink a bunch of rods into the
ground and use the mass of the Moon for your heat sink.

:> Yes, and building the infrastructure to do the latter is easier down
:> on a surface.
:
:So you keep saying. But we don't yet have any experience building a steel
:mill in space and then another one on the moon, in order to compare the two.
:So your assertion is based only on what strikes you as right.

My assertion is based on the fact that current technology requires
gravity to work. You have gravity on the Moon. You don't have it in
space. This leads to some pretty obvious conclusions.

Consider what happens when you get your big chunk of 'ore' and melt it
in zero-g.

:> Retrieving resources is also easier.
:
:This is a much better argument to make.
:
:> Except said 'leveraging' is easier to get started on the Moon.
:
:Versus on an asteroid? Why?

Gravity and lots of available mass.

:> And it's just not that big a problem. The Moon is sufficiently
:> 'light' than something like a catapult ought to be relatively easy.
:
:And I have tremendous enthusiasm for EM launch from the lunar surface. But
:it's important to remember that the launching of ore will preceed the
:launching of finished products, and probably by a good many decades.

Why? I see no reason at all to 'remember' that, since I think it is a
scenario that is very unlikely. Much more likely would be throwing up
pure metals, since it requires lofting less mass and smelting the
stuff is easier down on a surface than up where there's no gravity.

:An
:ore-only launcher can be of modest bore size and essentially unlimited in
:acceleration. Same for launching finished products would have to be bigger
:in diameter, and much, much longer. Hence more expensive.

I don't see why you arrive at the preceding conclusion.

:> And I disagree with you. The space case seems to require much more
:> time and much greater belief in 'magic' technology to solve all
:> problems.
:
:I'm speaking specifically, you've shifted to something more general. I was
:arguing that the maglev lifters in your lunar torus are a component unneeded
:in the orbital version. That's all I ever meant to say.

And your entirely new zero-g industrial processes are something that
isn't needed in a Lunar location. Net advantage - Moon (by a lot).

:> Bedrock is a hell of a lot less likely to fail than some manmade
:> structure.
:
:But why you should make this point is a mystery to me, as if you look back
:you'll see no place where I expressed a concern about failure of the
:underlying bedrock.

Your ring structure in space has to be sufficiently strong to hold
itself together under spin loads. That strength comes from sitting on
rock in the lunar maglev case.

:> Your structure is subject to the same sorts of loads if you intend to
:> spin it to produce gravity. Force is force and doesn't magically
:> disappear just because you move to space.
:
:You still don't seem to understand my point. /Both/ structures are under
:the same loading from centrifugal force, so we can leave that aside. The
:lunar torus is under the /additional/ force of lunar gravity. This is a
:force absent in orbit.

Your analysis is far too superficial. The two structures are actually
under entirely different loads. Your space station must have
sufficient strength to stay together under the spin load - something
has to hold it against the centripetal force so that you get
'gravity'. The strength to do that in the maglev case is provided by
the track sitting on rock, so the cars only need to be able to support
their own weight against the spin gravity, which is an easier problem.

:Rather than just assuming I believe in magic, please be open to the
:possibilty there's a point I'm not getting across to you.

Or a point you don't understand.

:> This just doesn't seem practical if large numbers of people have to
:> get on and off your habitat to 'go to work' every day. Are you
:> assuming everyone stays and all the 'outside' equipment is
:> teleoperated or what?
:
:No. I'd say either rotating seals, or, if that proves impossible to work
:out, some kind of combination elevator/airlock.

This seems impractical if you have large numbers of workers who need
to get in and out every shift.

:Please forgive me for not addressing points beyond here. The conversation
:has quickly become no fun, and nobody is influencing the thinking of the
:other side going in either direction, so further discussion seems pointless.

I'd say the preceding applies to one of us (and it's not me). You're
the one, after all, who STARTED from the position that you were not
going to be convinced no matter what (and stated exactly that).

--
"Some people get lost in thought because it's such unfamiliar
territory."
--G. Behn
.

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