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forming composit space station skin in situ



 
 
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  #21  
Old February 5th 05, 02:28 AM
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Ok, if we consider a 50 m shell, we get 65,449 cubic meters for a total
volume, and for the inside volume of the inner shell, we get 44,602
cubic meters.
Getting it up in one shot is a good goal. But I'm trying to maximize
leasable volume, too. A 100 meter sphere give 523,598 cubic meters of
internal volume, and 434,892 cubic meters inside the inner shell. I
still think the inner and outer shell concept is important for puncture
repair, and sheilding augmentation, and general ease of construction.

The costs are going to be such to develop any sizable facility that we
probably are going to need about 50 tenants, besides the resort/hotel
with about 25 guests per week, (eventually), a large "movie set", a
repair/maintenance /workshack area for contract projects such as a Mars
trip, other larger facilities and so on. I don't think a 50 meter
sphere is going to be big enough. to bring in enough income.

  #22  
Old February 5th 05, 02:50 AM
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Mike:
Zylon is just fibers, right? Kapton would be available in film?
Harmon

  #23  
Old February 5th 05, 03:17 AM
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What are your figures for getting an initial mass of 40 tons for the
initial shell? Are you still figuring on 3 - 4 cm thick of Zylon? I
think it would be easier to bond sheets of Zylon fiber to already
existing inflated walls of Kapton in place, rather than trying to patch
together pieces of a large sphere while in a small room while
weightless. Something like hanging wallpaper, without having to worry
particularly about getting the pattern to match, or leftover bits at
the top and bottom. That way the initial outer shell would only have
to be 5 mil Kapton, which would mass much less.

  #24  
Old February 5th 05, 10:23 AM
Kent Paul Dolan
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"harmoneverett" wrote:

wrote:


You want an environment with enough pressure that
construction workers can promptly ditch their
space suits, or at least reduce them. That's
going to require ~3psi of air pressure (pure
oxygen).


why pure oxygen? The eventual goal is to be able
to breathe in it, but for the moment, an air tank
doesn't weigh anything.


Because if you're going to be sending gases up to
achieve ~3 psi of blood oxygen tension, the minimum
IIUC to sustain human life for extended periods, you
are money ahead to send oxygen, which is breathable,
and thus a money payload, not some inert gas, which
is pure waste (but see below) until and if you go on
to 1 atmosphere.

My hope was that sending a really bare minimum
shell, hardly able to constrain 1 or 2 psi would
allow workers to then work in a much less bulky
pressure suit over the next several years while
they pasted on a couple more of the fabric and
insulation layers for the main shell.


I think you're missing the point that if you put 3
psi of oxygen _inside_ the human body, you have to
put 3 psi _outside_ the human body as well, or the
person just explodes.

Working for long periods of time, like years, in
pressure suits in a container with pressure less
than the breathing gas pressure, is going to involve
too many really unphotogenic industrial accident
fatalities from suit failures to be acceptable.

The base law of gaskets is, now as ever: gaskets
fail. That's from a submariner whose seen far too
many such failures in working plumbing, including
one leaking radioactive fluids from a running
nuclear reactor.

You might as well plan for 3 psi, just to start, and
the space crew lost on the ground years ago because
pure O2 is a hellishly dangerous fire hazard modulo
incredible precautions in what you let come in
contact with it, impractical for a years-long
effort, suggests you plan for a cartload of pressure
capability for inerting gases as well, or some
safety board somewhere is going to set all your
planning efforts to no eventual value.

HTH

xanthian.



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  #25  
Old February 5th 05, 09:08 PM
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wrote:
What are your figures for getting an initial mass of 40 tons for the
initial shell? Are you still figuring on 3 - 4 cm thick of Zylon?


I never figured on 3-4 CENTImeters of Zylon. I was figuring on 0.5
MILLImeters of Zylon for a 3-4psi, 100m-diameter sphere, or 2mm for a
full-pressure 100m sphere.

The 100m sphere with a 0.5mm shell would be 24 tons, though with likely
additions (aluminized exterior, gas barrier film, reinforcements and
rip stops) it would be closer to 40 tons.

I think it would be easier to bond sheets of Zylon fiber to already
existing inflated walls of Kapton in place,


Well, it'd be easier, but the resulting structure isn't something I'd
expect to pass any safety inspection, at least not until it was much
thicker than a shell made of continuous, woven fibers.

Hand lay-up of resin and fibers is prone flaws in ideal factory
conditions. Add in...

*clumsy space suits
*an inability to really squeegee and roll binding resin into the fabric
without tearing the 5-mil Kapton
*A substrate prone to tearing under the mass of an astronaut

...and you're going to end up with a pressure shell laden with flaws
(resin rich areas, inadequate connection between strips of fibers,
etc). It would also be much more dependent on the strength of the
binding resin rather than the fibers. You might be limited to a
fraction of the fiber strength - like 50,000psi instead of 500,000psi.
To make the structure safe, you'd need 2cm or more of thickness in the
strength shell.

Building the shell inside a pressure shell also would make it difficult
to inspect the layers as you lay them down. It generally helps to have
access to both sides (such as during ultrasound examinations).
Stitching and other useful means of binding new patches of the high
strength fiber to the shell would be difficult - you'd need to puncture
the outer hull.

Finally, laying down strips of fiber on any surface work best when you
can really pressure and squeeze down on the surface. For example,
putting a hard mold or plate under two layers of fabric you want to
bond together. That'd be difficult with a 5-mil Kapton outer shell.

rather than trying to patch together pieces of a large sphere
while in a small room while weightless.


Instead of a small room, you can use my suggestion of a 30m (100ft)
starting sphere. Further, that sphere would be an excellent place to
locate large weaving machinery suitable for producing a high strength,
continuously woven shell. It would be easy to inspect the growing
shell, repair any defects, and even strength-test sections. Finally, by
using this separate sphere as a work space to assemble the full-sized
sphere, your assembly processes no longer worry about stressing the
work space's hull - you can push, prod, and strain the full-sized
sphere's material and not worry about poking a hole in it.

Note the Transhab, which had a very enviable safety factor, was
assembled from patches in the manner I suggested.

Mike Miller, Materials Engineer

  #26  
Old February 6th 05, 12:29 AM
Ian Stirling
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Tim McDaniel wrote:
In article ,
Henry Spencer wrote:
you want the insulation external, because that lets you use MLI,
which is superb insulation but works only in vacuum


"MLI"? http://www.acronymfinder.com/ suggests "Multi-Layer
Insulation", but not what's so special about insulation having
multiple layers (putting on a sweater only works in a vacuum?).


It's much, much better than most other sorts of insulation.

It depends for its insulative properties on having lots of shiny reflective
surfaces through which heat has to radiate.

  #27  
Old February 7th 05, 03:44 AM
Harmon Everett
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wrote:
wrote:

Well, it'd be easier, but the resulting structure isn't something I'd
expect to pass any safety inspection, at least not until it was much
thicker than a shell made of continuous, woven fibers.

I was thinking the additional layers of fibers would be continuous
woven fabric. And it wouldn't need to pass a safety inspection until it
was much thicker. In a year or two, after several layers had been laid
down. The first skin would be flexible and fragile, the first fabric
and resin would be much stiffer, but still pretty fragile. The second
layer would be thicker and more capable of being pushed against with
the squeegee, and so on. And each layer would add to the radiation
protection and micrometeorite puncture protection.

Hand lay-up of resin and fibers is prone flaws in ideal factory
conditions. Add in...

*clumsy space suits

Yah. Darn.

*an inability to really squeegee and roll binding resin into the

fabric
without tearing the 5-mil Kapton


I think I can argue this point. I think there are several ways to over
come this problem. Have a moveable curved table to squeegee the resin
into the fabric before the fabric gets moved to its final location. Or
have two part adhesive, one part on the Kapton, one in the fibers. Or
have the first Kapton/fabric/adhesive layer still be somewhat fragile,
but much harder than the Kapton alone. Then the second
Kapton/fabric/adhesive layer you put on can really be rolled on. Then
the third Kapton/fabric/adhesive layer you put on can be practically
applied with a hammer.

*A substrate prone to tearing under the mass of an astronaut


..and you're going to end up with a pressure shell laden with flaws
(resin rich areas, inadequate connection between strips of fibers,
etc). It would also be much more dependent on the strength of the
binding resin rather than the fibers.

Why limited to the strength of the binding resin?

You might be limited to a
fraction of the fiber strength - like 50,000psi instead of

500,000psi.
To make the structure safe, you'd need 2cm or more of thickness in

the
strength shell.

Isn't that what we want anyway? It just doesn't need to happen
immediately.
There's going to be holes and soft spots and attachments. With the
multiple film/fiber blanket/adhesive layers sandwich, you sew in a new
patch of fiber/film/adhesive, epoxy it in and cover it with a patch of
air barrier film, and go on about your business. The only real problem
is a major tear, and you probably criss cross the directions of the
layers of the fabric blankets to minimize that.

Building the shell inside a pressure shell also would make it

difficult
to inspect the layers as you lay them down. It generally helps to

have
access to both sides (such as during ultrasound examinations).
Stitching and other useful means of binding new patches of the high
strength fiber to the shell would be difficult - you'd need to

puncture
the outer hull.

A ultrasound gadget on wheels rolls around the outside of the sphere
attached to cables that run exterior on the surface from pole to pole.
Probably going to need it for exterior human work on the outside
surface anyway.
They have sewing machines that work from just one side of the fabric.
There is going to be a lot of that anyway. Once a couple layers of
fabric get adhered to the outer film, that should be minimal danger.
And besides the several layers of fabric getting laid onto the outer
skin, there will probably be another layer or two of inner film.

Finally, laying down strips of fiber on any surface work best when

you
can really pressure and squeeze down on the surface. For example,
putting a hard mold or plate under two layers of fabric you want to
bond together. That'd be difficult with a 5-mil Kapton outer shell.


True. But meanwhile, you have enough internal controlled volume to
lease to paying customers.

rather than trying to patch together pieces of a large sphere
while in a small room while weightless.


Instead of a small room, you can use my suggestion of a 30m (100ft)
starting sphere. Further, that sphere would be an excellent place to
locate large weaving machinery suitable for producing a high

strength,
continuously woven shell.

Why weave it on site? Does it not compress or bend well? I would
think making it on earth and unfolding it in space would be easier.
For that matter, unfolding it between the inner and outer shell of the
100 meter spheres sounds even easier. Then we aren't pressing so much
against the outer Kapton film when we squeegee, as against the Zylon
blanket.
It would be easy to inspect the growing
shell, repair any defects, and even strength-test sections. Finally,

by
using this separate sphere as a work space to assemble the full-sized
sphere, your assembly processes no longer worry about stressing the
work space's hull - you can push, prod, and strain the full-sized
sphere's material and not worry about poking a hole in it.

I'm not worried about poking holes - those can be patched, and are
going to be dealt with on a regular basis. I'm worried about not being
able to lease space to paying customers. With the 100 meter fragile
sphere, we can immediately start leasing space for smaller, functional,
internal pressurized rooms within a non pressurized larger hull while
the external shells get their multiple layers applied over the next
several years.
With the 30 meter concept, the whole structure is being used for
constructing the next size structure, with little room left over to
lease to paying customers or vacationing guests.

Note the Transhab, which had a very enviable safety factor, was
assembled from patches in the manner I suggested.

L'Garde says its lobed (pumpkin shaped) design overcomes much of the
tension requirements of a super pressure inflatable. Something about
the determining factor is the local radius of the individual lobe ( or
gore) rather than the overall diameter of the entire balloon.

Harmon Everett
Let's light this candle - Alan Shepard

  #28  
Old February 7th 05, 05:01 AM
Harmon Everett
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So the argument against working in space suits is that they break and
kill people? Is the same argument valid against the stacking multiple
tin cans with space walks concept in developing the ISS? If you are
working in a space suit inside a volume with 1/2 psi, with the space
suit pressurized to 3 psi, and the space suit develops a leak, are you
more likely to get a slow leak, which you can get back to the fully
pressurized area and patch, or explosive decompression?

  #29  
Old February 7th 05, 02:13 PM
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Harmon Everett wrote:
wrote:
wrote:

Well, it'd be easier, but the resulting structure isn't something

I'd
expect to pass any safety inspection, at least not until it was

much
thicker than a shell made of continuous, woven fibers.


I was thinking the additional layers of fibers would be continuous
woven fabric.


Unless the interior of the sphere is completely empty (of
revenue-generating modules), you're not going to be able to install a
continuous-fiber fabric shell. You're going to have install patches,
which goes right back to the problems of hand lay-ups.

The second layer would be thicker and more capable of
being pushed against with the squeegee, and so on.


Speaking as a materials engineer, I *still* wouldn't trust a composite
shell laid up by hand in that fashion even if you could press and roll
it firmly.

And each layer would add to the radiation
protection and micrometeorite puncture protection.


No, the micrometeorite protection won't increase noticeably with a
slight thickening of the hull. Thick, solid materials are poor means of
stopping micrometeorites.

Why limited to the strength of the binding resin?


Because the fibers would not be interlinked between layers and between
patches. The resin would be the only source of strength in those areas.
The hand lay-up method is also prone to creating resin-rich areas.

You might be limited to a fraction of the fiber strength -
like 50,000psi instead of 500,000psi.


Isn't that what we want anyway?


Why would we want to cripple the strength of the material?

True. But meanwhile, you have enough internal controlled volume to
lease to paying customers.


Correct. And in the years it takes you to slowly hand-assemble your
giant sphere, those customers might as well be operating in a normal
space station, since the enclosing sphere isn't doing much for their
modules.
In fact, they could go to the competitor who doesn't increase rates to
pay for a big, non-profitable sphere.

If you want that sphere to do something useful, you'll want to build it
quickly to the point it can house occupants without separate,
vacuum-rated modules. This painstaking patchwork method does not seem
good for business.

Why weave it on site? Does it not compress or bend well? I would
think making it on earth and unfolding it in space would be easier.


If you have a rocket that can put a 650-ton shell into orbit, sure,
make it on Earth. If you don't, some on-orbit assembly of individual
full-strength segments will probably be necessary. Of those methods,
the hand lay-up method you like is one of the slower and less safe
methods.

So the argument against working in space suits is that they break and


kill people?


There's multiple arguments against them, including their clumsiness.

Is the same argument valid against the stacking multiple
tin cans with space walks concept in developing the ISS?


Spacesuits are much less of a problem for the ISS. The spacewalks
required for the ISS's construction take much less time than assembling
31416 square meters of multi-layered composite in zero-G. It's about
1900 man-hours for the ISS, while it might be over 3000 man-hours per
layer of the sphere with hand lay-up.

If you are working in a space suit inside a volume with
1/2 psi, with the space suit pressurized to 3 psi, and
the space suit develops a leak, are you more likely to
get a slow leak, which you can get back to the fully
pressurized area and patch, or explosive decompression?


Astronauts exploding in a vacuum is a Hollywood invention, and the
difference between 0.5psi and 0psi isn't significant to the leak rate.

Again: this all gets much easier if you're willing to use somewhat
enhanced launchers. You'll strangle the project if you insist on
countless hundreds of little launches and tedious hand-assembly of the
sphere.

It won't take Boeing much to strap some SRBs onto its Delta IV heavy
and give you a 40-ton payload. With that, you can launch entire 0.5mm
shells into orbit in a single bound. If you go larger, up to a 100- or
120-ton launcher, you can put the full pressure shell into orbit in a
single launch. Then its just a matter of spraying on foam insulation,
inside and out, and laying down some non-structural liners and
insulation.

Mike Miller, Materials Engineer

  #30  
Old February 7th 05, 05:42 PM
Ian Stirling
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In sci.space.tech Kent Paul Dolan wrote:
"harmoneverett" wrote:

wrote:


You want an environment with enough pressure that
construction workers can promptly ditch their
space suits, or at least reduce them. That's
going to require ~3psi of air pressure (pure
oxygen).


why pure oxygen? The eventual goal is to be able
to breathe in it, but for the moment, an air tank
doesn't weigh anything.


Because if you're going to be sending gases up to
achieve ~3 psi of blood oxygen tension, the minimum
IIUC to sustain human life for extended periods, you
are money ahead to send oxygen, which is breathable,


I'd argue slightly about the 3PSI, you can go a fair bit lower if your goal
is "won't die in 5 minutes without exertion".

At the lung wall at 37C is 47 torr (780 torr = 1 atmosphere = 14.7 PSI) of
water vapour.
This can't be reduced, and is a hard limit (barring hypothermia).
About 15 torr of CO2, at normal metabolic rates.


People (nutters) have climbed everest without supplemental oxygen.
At the top, you're looking at 276 torr, of which about 1/5 is O2.

So, at the lung wall, we have 276-62 torr = 214 torr of atmosphere, or
43 torr of oxygen.
So, for pure O2, 43+62 = 125 torr
or 2.35 PSI will get you the same oxygen saturation as on the top of
everest.
About 1.2PSI or so is the pressure at which you're about as well off
as you are holding your breath in normal atmosphere.

Below this, you get rapid de-oxygenation of the blood as it passes through
the lungs.

snip
I think you're missing the point that if you put 3
psi of oxygen _inside_ the human body, you have to
put 3 psi _outside_ the human body as well, or the
person just explodes.


Err, no.

If you try to hold your breath, your lungs rupture.
If you don't, you'r fine until you die from
lack of oxygen (about a minute until you need more
than CPR).
 




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