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forming composit space station skin in situ



 
 
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  #1  
Old January 31st 05, 05:31 AM
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Default forming composit space station skin in situ

In order to produce the most effective orbiting facility with the least

amount of materials and the least effort, it seems obvious that it
should
be an inflatable sphere. As soon as the internal volume becomes even
the
slightest bit pressurized, the astronauts can begin dispensing with the

bulk of many of the layers of the space suit. This will allow them to
work more efficiently for longer periods of time.
Working inside a huge single sphere is difficult - scaffolding is
nearly
impossible to construct for such a situation. The solution will be to
use
the same technique Brunelleschi used for the dome at the cathedral of
Santa Maria del Fiore - use two closely spaced shells, one inside the
other.
Once the volume is enclosed and the workmen are inside a moderately
pressurized space, the ensuing work can proceed at practically
breakneck speed, unencumbered by a bulky space suit.

I'm considering a sphere 100 meters across, with an internal shell 3
meters inside that. The inner and outer shells will eventually be
augmented with many layers of fabric and epoxy, but initially are
essentially just aluminized mylar and very fragile.
I know plastic at exremely low temperatures is extremely brittle.
Because this is in the vacuum of space, will this aluminized mylar
shatter at the slightest touch, or will astronauts inside the shell be
able to spread strips of fabric and epoxy on it to augment and
reinforce it without too much trouble?
Harmon
Let's light this candle. - Alan Shepard

  #2  
Old January 31st 05, 10:23 PM
Kent Paul Dolan
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"harmoneverett" wrote:

In order to produce the most effective orbiting
facility with the least amount of materials and
the least effort, it seems obvious that it should
be an inflatable sphere.


You might enjoy reading Tim Tyler's work on double
geodesic domes, which might be a bit more practical
as a way to approach the same goal with smaller
bites taken per chew:

http://hex.alife.co.uk/domes/

HTH

xanthian.



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  #3  
Old January 31st 05, 11:50 PM
Andrew Nowicki
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Harmon Everett wrote:

In order to produce the most effective orbiting facility
with the least amount of materials and the least effort,
it seems obvious that it should be an inflatable sphere.


A hotel mogul Robert Bigelow wants to
launch inflatable hotels into orbit.
(http://www.bigelowaerospace.com)

This does not mean that the idea of inflatable
hotels is obvious. Inflatable objects are made
of rubber or plastic, which are sensitive to
temperature extremes and leak air. They are more
suitable as emergency shelters than long term
habitats.

Metals and alloys are better suited for the
harsh space environment than rubber or plastics.
A fairly large cylindrical habitat can be made
from telescoping tubes. Probably the best
design for small habitats is a rotating
torus made of flat or almost flat tiles:
http://www.islandone.org/LEOBiblio/SPBI1GH9.JPG

As soon as the internal volume becomes even
the slightest bit pressurized, the astronauts...


This is a mundane job best suited for telerobots
like Dextre or Robonaut. Astronauts are better
suited for tasks that are too difficult for the
telerobots, for example taking apart and repairing
a digital camera.

I'm considering a sphere 100 meters across, with an internal shell 3
meters inside that. The inner and outer shells will eventually be
augmented with many layers of fabric and epoxy...


100 meter plastic sphere would be too thick and
therefore too expensive. Epoxy produces toxic fumes.

I know plastic at exremely low temperatures is extremely brittle.
Because this is in the vacuum of space, will this aluminized mylar
shatter at the slightest touch...


It is not so brittle, but it would be good idea to
wrap the plastic structure in a metal foil to
protect it from temperature extremes.
  #4  
Old February 1st 05, 05:51 PM
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Very interesting site! I don't think it is applicable, however, as his
domes deal with *compressive* forces, and a space sphere would be
dealing entirely with *tension* forces. I'm also trying to minimize
the amount of work anyone would have to do while wearing a space suit,
and enclose as much volume as possible as quickly as possible. The
more volume that can be enclosed, the more you can rent to more
clients, and the sooner you can ditch the space suit, the easier and
faster it will be to construct the facility. Once the major outer
shell is in place, with a tiny bit of atmosphere - even if it is
nitrogen and carbon dioxide, the bulk of a space suit can be largely
reduced. Smaller internal rooms can be fully developed, hardened,
pressurized, equipped and used or leased out at that point, without
having to fully develop the entire structure. So once the outer skin
is in place, everything else is easier, cheaper, and can be bringing in
income almost immediately. An inflatable that is augmented with fabric
and epoxy is also much easier to pack into a launch vehicle, and erect
once in orbit - no wasted space between components, and relatively few
steps to getting the structure erected once there.
Harmon
Kent Paul Dolan wrote:
"harmoneverett" wrote:

In order to produce the most effective orbiting
facility with the least amount of materials and
the least effort, it seems obvious that it should
be an inflatable sphere.


You might enjoy reading Tim Tyler's work on double
geodesic domes, which might be a bit more practical
as a way to approach the same goal with smaller
bites taken per chew:

http://hex.alife.co.uk/domes/

HTH

xanthian.



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  #5  
Old February 1st 05, 10:12 PM
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wrote:

it seems obvious that it should be an inflatable sphere.


Have you looked into NASA's Transhab?

A quick overview of Transhab:
http://www.astronautix.com/craft/traodule.htm

This link details its materials selections and structu
http://faculty.erau.edu/ericksol/pro.../transhab.html

Maker of the Transhab test article:
http://www.ilcdover.com/products/aer...e/habitats.htm

I'm considering a sphere 100 meters across, with an internal shell 3
meters inside that. The inner and outer shells will eventually be
augmented with many layers of fabric and epoxy, but initially are
essentially just aluminized mylar and very fragile.


You can probably start more robustly than that.

If you don't mind developing a big rocket (like Boeing's 7-core Delta
IV concept), then you can launch a sizable, robust sphere immediately.

A 100m sphere pressurized to 4.9psi with oxygen and a dash of nitrogen
would generate 61300psi of stress in a 2mm (1/12") shell. That's well
within the strength capability of a plastic like Kevlar (or the more
modern Zylon). The shell would be about 80-90 metric tons, depending on
the particular shell material selected.

Then, of course, you'd want to look into insulation, debris shields,
additional shells, etc. Scaling up from the 8.2m Transhab cylinder to a
100m sphere suggests about 500-600 metric tons of internal material
would be needed.

Interestingly, the resulting shell (all ~700 tons) is just about as
heavy as the air inside. A 100m sphere of air at sea level pressure
(80/20 nitrogen/oxygen) is 673 metric tons at 25C, if I did my math
correctly.

Actually, that's a thought...the 4.9psi (1/3-bar) initial oxygen
atmosphere I suggested would be 250 metric tons.

This level of bulk material delivery would really encourage the
development of a big launcher.

I know plastic at exremely low temperatures is extremely brittle.


Only if you use the wrong plastic. Some plastics behave very well at
cryogenic temperatures. See the Transhab development notes I linked in
above. Kevlar and polyethylene remain fairly tough and ductile at
cryogenic temperatures.

Mike Miller, Materials Engineer

  #6  
Old February 2nd 05, 06:28 AM
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wrote:
wrote:

it seems obvious that it should be an inflatable sphere.


Have you looked into NASA's Transhab?


Yes, It seemed too much trouble for too little additional volume. More
of a way to put a bigger tin can into space. If you realize you can
augment the outer shells after they are inflated, and add the equipment
as you go along, you can really get a lot of controllable volume from
an inflatable quickly with low cost.

I'm considering a sphere 100 meters across,

You can probably start more robustly than that.

If you don't mind developing a big rocket (like Boeing's 7-core Delta
IV concept), then you can launch a sizable, robust sphere

immediately.

Not interested in developing new launchers. I want it up there NOW.
If not last week. Its going to take a couple years to develop an
internal ecosystem anyway,.. Moving lots of equipment in, shipping up
lots of water. I can send up a crew bunkhouse module, and inflatable
skins - almost off the shelf stuff, within a couple of months of
getting the financing.

A 100m sphere pressurized to 4.9psi with oxygen and a dash of

nitrogen
would generate 61300psi of stress in a 2mm (1/12") shell. That's well
within the strength capability of a plastic like Kevlar (or the more
modern Zylon). The shell would be about 80-90 metric tons, depending

on
the particular shell material selected.


Tempting. Very tempting. But too heavy for right now. I have been
reading good things about aluminized Kapton. Get it up and inflated,
harden it with some epoxy and then start sending up regular small
supply shipments of pvc beads to make structural pipes and fabric and
epoxy to reinforce the shells.

Then, of course, you'd want to look into insulation, debris shields,
additional shells, etc. Scaling up from the 8.2m Transhab cylinder to

a
100m sphere suggests about 500-600 metric tons of internal material
would be needed.


Eventually yes, Not right away. There will need to be weekly shipments
of all sorts of materials and equipment. In inexpensive 5, ten and
twenty ton launches. Once the outer shells are in place, individual
smaller rooms can be (and would have to be ) developed on an as needed
basis. But since they would be INSIDE the shell, they can very easily
be put up by astronauts wearing essentially air tanks and flight suits.

The whole shell wouldn't have to be pressurized for a couple of years,
but the individual rooms could be pressurized and used immediately. The
rooms wouldn't have to be developed until a client was willing to pay
for using them.

Eventually, plumbing, trash, wiring, sewage treatment, storage, and all
sorts of stuff will be placed between the two shells. But that can
wait for long term development. Once the shell is up and only slightly
pressurized, the facility is open for business.

Interestingly, the resulting shell (all ~700 tons) is just about as
heavy as the air inside. A 100m sphere of air at sea level pressure
(80/20 nitrogen/oxygen) is 673 metric tons at 25C, if I did my math
correctly.


Sounds about right. But you wouldn't have to go sea level. You could
easily opt for oh, Denver, for half that. Eventually. The thing is,
it wouldn't have to be anywhere near that for the first several years.
And as people worked in it wearing air tanks, the exhaust would just be
vented to the inside of the shell and gradually build up, too. You
need to have the shell there, so that people can be working "inside",
and so there is a little pressure above absolute vacuum, but it doesn't
take much to make it possible to work with just a flight suit, rather
than the whole space suit. What? 1/100 of an atmosphere? And it doesn't
have to be oxygen. initially. And the astronauts won't primarily be
working inside the inner shell - the vacant 400,000 some cubic meters;
mostly they'd be working between the two shells, which they could
pressurize for a lot less. When utility workers have to work down a
manhole in subzero weather, they often set up a tent over it. If the
astronauts have to work inside the inner shell, they could easily set
up a much smaller temporary inflatable dome and work happily inside
that - at pressure, and with air and temperature control. OOh, that's
a new thought.

Actually, that's a thought...the 4.9psi (1/3-bar) initial oxygen
atmosphere I suggested would be 250 metric tons.

This level of bulk material delivery would really encourage the
development of a big launcher.


Once the initial shells are up, a big launcher won't be necessary,
because most of the rest of the deliveries can be in practically
arbitrary amounts. Water, air, plastic beads to feed into the on site
pvc pipe extruder. soil. seeds. fabric. epoxy. The limitation is
that the first couple of inner and outer shells really need to be in
one piece. I think I can get them down to about 25 thousand kilograms.

I know plastic at exremely low temperatures is extremely brittle.


Only if you use the wrong plastic. Some plastics behave very well at
cryogenic temperatures. See the Transhab development notes I linked

in
above. Kevlar and polyethylene remain fairly tough and ductile at
cryogenic temperatures.

Ooops, my mistake. Obviously NOT a materials engineer. And I have
been reading very nice things about kapton.

Mike Miller, Materials Engineer

Thanks Mike!

Brunelleschi used the inner and outer shell concept to build his famous
dome. It made the work much easier than trying to do a single shell
with lots of scaffolding. If we consider having these thin plastic
shells floating in orbit, with about 3 meters between them, the
astronauts will still need some way to get around, and station
themselves within the cavity. There will still need to be some sort of
scaffolding. I'm considering sending up a pvc pipe extruder and
setting it up as one of the first rooms inside the shell. Then, run
3/4 inch "great circle" lengths of pipe around the structure, between
the inner and outer shells. Run one from pole to pole, to establish a
meridian so to speak, and then run another at 90° from that, and then
another positioned to attach to the other two at the equator. It seems
to me that then, the best way to organize the placement of further
great circles, is to divide the lengths of pipe between intersections
in half, and attach new great circles at the half way points. Continue
that process until you have intersections oh, about every 10 meters or
so. After the 3rd set of great circles, you have intersections about
every 20 meters, and can probably settle down to a slower pace.
Harmon


  #8  
Old February 3rd 05, 03:01 AM
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wrote:
wrote:
Once the major outer
shell is in place, with a tiny bit of atmosphere - even if it is
nitrogen and carbon dioxide, the bulk of a space suit can be

largely
reduced.


Note that to get the pressure high enough for a pressure suit to be
unnecessary (c3-4psi), you're going to need hundreds of tons of any

gas
except hydrogen or helium.


What volume are you considering? And I didn't say a pressure suit would
be unnecessary, I think the *space* suit would be unnecessary. In
between the shells, the workers would probably need something like a
flight suit pressure suit, but not the full bulk of the space suit.
Does anybody know what the specs for such a pressure suit, that would
deal comfortably with, oh, 1/100 of an atmosphere would be?

In the discussion yesterday, I realized that once the main shells were
in place, a much smaller internal tent could be inflated inside the
inner shell to house - oh, let's say a hemisphere dome 20 meters in
diameter. So the workers that were installing the walls and floors of
the rooms in the interior of the inner shell wouldn't have to wear any
protective gear whatsoever. 4,188 cubic meters of air at Denver air
pressure, oh, half stp, or so, 671 grams/cubic meter times 4,188 cubic
meters=2,810 kilograms or so. Plus probably another ton or two of water
for humidity. Even full atmospheric pressure for that volume would only
be 8,400 kilograms. I don't see a problem with having to heft even a
couple dozen tons of gases up to the station in the first year. Its
going to take several years to develop the entire sphere, but having it
there makes everything else easier. And after 5 or ten years, there
will be hundreds of tons of gases, and hundreds of tons of equipment,
and hundreds of tons of water and hundreds of tons of soil and plastic
and people. That's what an active space station is going to need to
be.
Its not how much its going to cost to get it up there that's important,
it's how much income it can generate to pay for the costs. When Billy
Durant started General Motors, he knew the expenses he was generating
were a substantial portion of the gross national product, but between
1910 and 1920, the economy of the United States more than quadrupled,
and people kept buying the cars and paying his costs.

Once the inner and outer shells are up and minimally hardened, we can
start charging visitors for weekly - working - vacations. How many
people would pay to spend a week in space, even if for part of that
week they were building some of the walls of the station itself?

An inflatable that is augmented with fabric
and epoxy


As Andrew noted, epoxy may not be ideal. However, I'll interpret the
description liberally as "some plastic binder to hold the fabric in
place."

Right.
Harmon

Let's light this candle - Alan Shepard

  #9  
Old February 3rd 05, 02:58 PM
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wrote:
wrote:

Have you looked into NASA's Transhab?


Yes, It seemed too much trouble for too little additional volume.


I was recommending looking into Transhab not because it gave you the
space structure you wanted, but because it answered your material
questions and would give you working mass estimates. I've used
Transhab's shell mass to scale up to assorted hypothetical inflated
stations.

Not interested in developing new launchers. I want it
up there NOW.


Well, alrighty then. I can work with that estimate. But there are some
problems with insisting on

First problem: Shell strength and mass.

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). If you cut the
first shell down to a bare minimum with little margin of safety for
restraining just 3psi, it's still going to need to be 0.5mm thick and
made out of an ultra-strong fiber like Zylon. At a minimum, the shell
will be 24 tons (assuming a fully dense Zylon shell; more likely it'd
be about 36-40 tons). That shell will be inadequate for a 14.7psi
atmosphere.

Aluminized Kapton does not have anywhere near the yield strength to
handle 3psi at 0.5mm thickness. With a 30000psi yield strength (at room
temperature), a Kapton sphere would need to be 3.5-4mm thick, which
would result in a 160-ton shell (just to handle 3psi).

Second problem: air mass.

The 3psi oxygen atmosphere will be about 250 tons. That's a lot of
tonnage to lift with current launchers. Which brings up problem
three...

Third problem: existing rocket payload capacity.

If you want existing, in-production launchers to get the job done,
you're going to need 11-12 uprated Delta IV heavy launches (22 metric
tons to LEO) or 11 shuttle launches just to get to the stage where you
have a bare minimum, air-filled sphere. However, you'll probably want a
couple more launchers to deliver some climate control equipment (to
keep all that air from overheating), power systems, etc. So you're up
to about 13 launches before the workers get to climb out of their space
suits during construction. Note that the Delta IV heavy, as currently
flown, is not really up to snuff for launching the initial, bare
minimum shell.

Alternately, if you don't want to wait on internal construction
activities for 11 big launches to fill the sphere with air, then you
can deliver the sphere shell (1 launch) and support equipment, probably
including that bunkhouse you mentioned (2 more launches) and get to
work after 3 launches.

But then the astronauts will be spending all their construction time in
suits, at least until 11 more launches have delivered enough oxygen to
give the sphere minimal pressure.

Fourth problem: existing launch capacity

This goal... "There will need to be weekly shipments of all sorts of
materials and equipment. In inexpensive 5, ten and twenty ton
launches." ...requires greater commerical rocket production than is (I
think) currently available.

Boeing would LOVE to expand its factories to help you launch 20-ton
payloads every week. The idea of firing off 12-13 Delta IV Heavies (33
total common core boosters! wee! profits!) just to get the station
started would make Boeing very happy. And you'll eventually need 30
such launches just to bring the sphere up to 14.7psi, not to mention
another 30 launches to get the shell up to full strength, plus an
unknown number of launches to fill the station with that water,
machinery, etc...

Yes, you could be looking at 100 launches of some rocket in the class
of the Delta IV heavy (or a lot more launches of smaller rockets). If
you want that to happen on a weekly basis, using existing rockets, the
rocket maker(s) you contract will need to expand their factories.

Which leads me back to my prior suggestion of taking the time to modify
the rockets. You're already going to have to pay for changes in the
rocket industry, so why not simplify the construction process with
bigger launchers?

The bare minimum shell you want is probably going to be 36-40 tons even
with super strong materials. Just sticking with the Delta IV example so
I don't have to google up alternatives, you can get about 30-35 tons to
LEO with the Delta IV heavy if you strap some solid boosters to it.
Boeing hasn't flown that yet, but it looks like an easy stretch.

Boeing also claims its Delta IV common core booster can be scaled up to
Saturn V payloads. It'll take modifications to the launch pad and some
engineering work, but its mostly just strapping 7 common core boosters
together. It recently flew 3 of them strapped together. With such an
(almost off-the-shelf) rocket, you could launch a full-strength shell
in one leap. You could give a minimum working atmosphere in the shell
in 2 launches, not 11-12.

Alternately, if you're really insistent on launching weekly, perhaps
you should take the time to develop a reusable launcher like the
VentureStar. It'll probably save you headaches in the long run.

Summary of problems:

Getting the station built in exactly the manner you want is somewhere
on the edge of possible/impossible with existing rockets. You need a
shell launched in one piece that's probably going to be 35-40 tons.
Your bare minimum air pressurization ("Once the shell is up and only
slightly pressurized, the facility is open for business") is going to
need 250 tons of oxygen. You want flight rates that are beyond the
immediate abilities of rocketmakers, but could be achieved with a
little development.

I recommend you relax some of your requirements - particularly for
existing rockets - and pay for the development of a higher capacity
rocket. It'll make everything else much more possible.

Mike Miller, Materials Engineer

  #10  
Old February 3rd 05, 07:50 PM
D Schneider
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Andrew Nowicki wrote:

[...]
This is a mundane job best suited for telerobots
like Dextre or Robonaut. Astronauts are better
suited for tasks that are too difficult for the
telerobots, for example taking apart and repairing
a digital camera.


From what I read of the NASA Robonaut tests, it appears that they are
presently not a heck of a lot farther along than handing spanner A from
tool tray B to the astronaut, who then tightens nut C on widget D.

/dps

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