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forming composit space station skin in situ



 
 
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  #11  
Old February 4th 05, 05:16 AM
Kent Paul Dolan
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" wrote:

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.


An alternative that has lots of obvious arguments
going for it, like redundancy for safety reasons,
more reasonable single-launch lift requirements,
and a stageable startup, would be to replace the
"one big sphere" concept with a "bunch of grapes"
design.

Yes, the eventual surface area, mass, and so forth
would be greater [but not that much greater when the
partitioning for the unit sphere design is counted
in], but the project could be practical and feasible
with current technology, instead of straining at
every seam.

Also, the "bunch of grapes" has room to grow if the
project succeeds, again in chewable sized bites.

xanhian.


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  #12  
Old February 4th 05, 02:26 PM
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Kent Paul Dolan wrote:
An alternative that has lots of obvious arguments
going for it, like redundancy for safety reasons,
more reasonable single-launch lift requirements,
and a stageable startup, would be to replace the
"one big sphere" concept with a "bunch of grapes"
design.


That's a reasonable point.

By halving the diameter of the sphere to 50m, you
quarter the mass of shell that needs to be launched
at once. The mass of air drops 1/8th that of
a 100m sphere, too.

In fact, with a 50m sphere, you would be able to
launch a shell of the same weight as the 100m sphere
but able to handle 4x the internal pressure. That's
a 40-ton payload that gives you the immediate
capability to handle 1 atmosphere of pressure.

Further, if you're playing around with Saturn V-grade
launchers, the required air mass for 1 atmosphere of
pressure (80ish tons) can be delivered in one payload
rather. A single off-the-shelf Delta IV Heavy can
deliver a breathable, 3-4psi oxygen atmosphere for
a 50m sphere.

but the project could be practical and feasible
with current technology, instead of straining at
every seam.


Yep. And at 30-33m spheres (100ft across), you can
much more easily use existing launchers. The shell of
a 33m, 1atm sphere would be about 20 tons.

wrote:

Does anybody know what the specs for such
a pressure suit, that would
deal comfortably with, oh, 1/100 of an atmosphere
would be?


Yes. It would be something like a normal spacesuit,
minus the thermal and debris protection. The bulk
of the suit would still be present because the
bulk (if not the weight) of a spacesuit is the
pressure-resistant shell and the constant-volume
joints that allow the astronaut to move despite
being stuck in a rigidly-inflated, human-shaped
balloon. A simple flight suit would not be adequate.

The 1/100th atmosphere environment you're
proposing is not much different than a vacuum,
though I think it'll complicate cooling by
making normal sublimative cooling difficult.

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.


That's a fairly reasonable approach. However,
you still have some logistical concerns to
deal with, because the initial shell will still
be fairly heavy (c40 tons). That runs into
launch problems.

If you're willing to use a tent approach but
not bend on developing/modifying rockets for
heavier payload capacity, perhaps you should
extend the tent approach to its logical end:

Assemble sections of the main sphere in a
smaller "workshack."

As I noted above, a 30m sphere with a normal
environment would be within the capability of
existing rockets to launch (in perhaps 2 launches).

Over the next 30-35 launches, you could assemble
enough material in the "workshack" to build the
complete, 1atm 100m sphere (with debris shields
and insulation). Workers in the workshack could
(somehow) stitch, glue, and bond this supersized,
multi-walled balloon together and then kick it
out an airlock.

Another 11 launches later, you'd have a minimum
breathable atmosphere in the main sphere, then
about 30 launches later, you'd have a full
atmosphere in the main sphere.

Mike Miller, Materials Engineer

  #13  
Old February 4th 05, 06:20 PM
Andrew Nowicki
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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.


D Schneider wrote:

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.


This is a highly politicized issue because
jobs are at stake. Dextre or Robonaut makers
claim that these telerobots can do anything.
Astronauts and Shuttle makers claim that they
are totally useless unless the astronauts are
nearby to help them.

Louis J. Lanzerotti, chair of the Hubble report,
changed his mind after President George W. Bush
nominated him to serve on the National Science
Board (NSB), the 24-member governing body of the
National Science Foundation (NSF) in September
of 2004. The nomination looks to me like a bribe
to persuade Lanzerotti to scuttle the foreign-made
Dextre.
  #14  
Old February 4th 05, 08:01 PM
Henry Spencer
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In article .com,
wrote:
...you're going to need hundreds of tons of [gas]...


What volume are you considering?


For any big unobstructed volume at any breathable pressure, gas mass is
going to be serious. Air at 1atm weighs about 1.25kg/m^3 -- rather more
than people think.

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.


Unfortunately, the big problem of working in spacesuits is the stiffness
resulting from suit pressurization. Getting rid of the outer
thermal/micrometeorite protection would help only a little.

I'm not sure what you mean by "flight suit pressure suit", but note that
the suits worn (for example) for shuttle ascent are *emergency* suits,
which get their lighter weight and greater *unpressurized* flexibility
partly by accepting that they will be uncomfortable and very difficult to
work in when pressurized.

Does anybody know what the specs for such a pressure suit, that would
deal comfortably with, oh, 1/100 of an atmosphere would be?


It would have to be essentially a full spacesuit.

...4,188 cubic meters of air at Denver air
pressure, oh, half stp, or so...


Uh, no, sorry, Denver pressure is much higher than that. Even if we make
it Quito instead -- nearly twice as high as Denver -- air pressure and
density are still about 75% of sea level. (And if you're doing physical
work at that pressure, you'll want higher than normal oxygen content, as
anyone who has been to Quito will tell you...)
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |
  #17  
Old February 4th 05, 10:12 PM
Tim McDaniel
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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?).
I gather that the abbrev. is a little imprecise.
http://www.nasatech.com/Briefs/Sept03/KSC12092.HTML says

The present thermal-insulation systems are layer composites based
partly on the older class of thermal-insulation systems denoted
generally as "multilayer insulation" (MLI). A typical MLI
structure includes an evacuated jacket, within which many layers
of radiation shields are stacked or wrapped close
together. Low-thermal-conductivity spacers are typically placed
between the reflection layers to keep them from touching. MLI can
work very well when a high vacuum level (10-4 torr) is maintained
and utmost care is taken during installation, but its thermal
performance deteriorates sharply as the pressure in the evacuated
space rises into the "soft vacuum" range [pressures 0.1 torr (13
Pa)]. In addition, the thermal performance of MLI is extremely
sensitive to mechanical compression and edge effects and can
easily decrease from one to two orders of magnitude from its ideal
value even when the MLI is kept under high vacuum condition.

--
Tim McDaniel; Reply-To:
  #18  
Old February 4th 05, 11:16 PM
Del Cotter
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On Fri, 4 Feb 2005, in sci.space.tech,
" said:

Kent Paul Dolan wrote:
An alternative that has lots of obvious arguments
going for it, like redundancy for safety reasons,
more reasonable single-launch lift requirements,
and a stageable startup, would be to replace the
"one big sphere" concept with a "bunch of grapes"
design.


That's a reasonable point.

By halving the diameter of the sphere to 50m, you
quarter the mass of shell that needs to be launched
at once.


Even more than that. The larger the sphere, the stronger the skin has
to be to contain the same pressure. In general, wall thickness goes up
linearly with diameter, if pressure is the overriding factor determining
wall thickness. In other words, for a given pressure and material
strength, wall thickness/diameter is a design constant, and shell mass
goes up with the diameter cubed, not squared.

Halving the diameter probably wouldn't reduce the mass by a factor of
eight, because there are other drivers to the wall thickness than just
pressure containment, but if pressure containment is not irrelevant to
the design, then it will be a factor of more than four.

--
Del Cotter
Thanks to the recent increase in UBE, I will soon be ignoring email
sent to . Please send your email to del2 instead.
  #19  
Old February 4th 05, 11:40 PM
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wrote:
wrote:
wrote:


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.


multi layered sandwich and insulation and such. Ok. Point taken.

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).


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.

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.


Sure, reinforced with some sort of ultra strong fiber and adhesive
matrix. What about Zylon degrading in UV light?
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.(Sent up in much smaller, easier and less expensive shipments)
Of course the main shell wouldn't be able to be fully pressurized for
years, but with it up, you could easily set up smaller interior rooms
that COULD be fully pressurized. And which you could lease out for
income while you worked on augmenting the entire shell.

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.

Yes. I was SO disappointed when informed that the current launchers
only can carry 20 tons or so. Even if the workers have to use full
space suits for a while, working INSIDE, they don't have to worry about
falling, or dropping things, or drifting away, so I think it would
still be much easier.


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).


What about a multilayer sandwich - aluminized Kapton outer shell to
help shield from UV,(oh, 2 mil thick. Check me on this, wouldn't that
be 1.46 grams for 200 square centimeters? Then, with Zylon fabric inner
shell bonded to it? Perhaps with another layer of Kapton inside it?
The separate layers could even be launched separately and inflated
inside each other before the bonding agent sets up, not necessarily
with anything near 3 psi, just enough to push them together under
tension.

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...


We don't need to start out with anything near 3 psi, or 1 psi or 1/2
psi. The outside of the space station is vacuum. The inflatable will
inflate with practically nothing. What was the inside pressure of ECHO
I?

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.


We don't need to start with an air filled sphere. We just need the
sphere. Once we have the sphere up - everything else is easier.

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.


3 launches is what I've been figuring lately. 4 when I consider an
inner shell. At $250 million per.


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.


NO! you inflate a much smaller tent inside the sphere, and fully
pressurize that to do most of the construction in, a couple of rooms at
a time. In your shirt sleeves. The main sphere NEVER gets fully
pressurized for years. You just don't worry about it until some
contractor is willing to pay to do it.
Meanwhile, the folks pasting the extra layers on the inside of the
exterior shell will probably have to wear almost a full space suit,(per
Henry) and the folks constructing interior walls and rooms will be
inside a much smaller (oh, 20 meter diameter) inflated tent, working in
their shirt sleeves.

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.


And I'd LOVE to pay them to do so!

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...


Eventually. Sure.. It could take years. What a boring thought. :-)
Meanwhile, we'll be developing an internal ecosystem, plumbing, going
from one or two paying guests per week to 10 or 20, and from one
lessee, paying to use one 10 meter by 10 meter by 10 meter cube to 25
paying contractors, and giving the passenger space flight industry time
to develop. But meanwhile, THEY would have a destination to take
customers too - and would be able to charge the $5 million dollars per
round trip flight that they will have to, in order to make a profit.
Good development all the way around.


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?


I think simple is what I can do now. More complicated is something
that will take maybe a couple years to develop the concept.
I think I can do this now.

Once the launch market starts heating up (I really think I can use two
launches per week -- Yes, I'll pay what you are wanting to charge...)
Somebody out there will develop bigger capacity. I don't have to worry
about that.
And when we start turning a profit, we can think about bigger projects.
Once this is up and operating, outfitting a Mars expedition will be
much simpler. And we will once again need 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.

No it won't! It will only take a couple of tons of air to make a couple
of rooms fully operational and able to be leased out. A big skyscraper
doesn't wait to start leasing and opening stores and rooms until all
the floors are finished - as soon as a couple of floors are finished,
they move in paying clients and open for business.


You want flight rates that are beyond the
immediate abilities of rocketmakers, but could be achieved with a
little development.


If I start paying for regular launches, the launch market will develop
on its own.

This is good, Mike. You want to go into business?
Harmon

  #20  
Old February 5th 05, 01:53 AM
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Henry Spencer said:
It would have to be essentially a full spacesuit.

...4,188 cubic meters of air at Denver air
pressure, oh, half stp, or so...


Uh, no, sorry, Denver pressure is much higher than that. Even if we
make
it Quito instead -- nearly twice as high as Denver -- air pressure and
density are still about 75% of sea level. (And if you're doing
physical
work at that pressure, you'll want higher than normal oxygen content,
as
anyone who has been to Quito will tell you...)

Gee, Henry, pop my bubble...

 




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