Just trying to work through some conceptualization issues with
regard to the Space Manufacturing Facility.

Assume we're trying to build a small Torus structure and the
components are being lifted from earth for assembly in orbit.

The torus "tube" is sectioned into many pieces.

I would prefer that all of the mechanical systems, control systems,
furniture, etc all be outfitted on earth to save assembly time in
orbit.

If this is done, then how much will we have to worry about vacuum
exposure in the open sections damaging all of the equipment.

Should each section be pressure tight, then when sections are
joined, the pressure seals between them are cut out, so that the
many sections start to become a whole with the ends always capped.

What if the sections come in lateral halves or quarters, and we
can't pressure seal them off?

Should then, one of the first built structures in orbit be a large
pressurized assembly bay (assembled piecemeal in a painstakingly
slow process to allow for the large open volume required) where the
quarter sections are assembled, the ends sealed, moved out of the
bay and joined to other completed sections.

If the torus facility will have an intergrated waste heat radiation
facility and other central facilites, how will we process radiant
heat that accumulates during the construction process before the
whole torus functions as one system? Will each sectional piece
require a radiator? Do we wrap the whole thing in mylar to reflect
the heat? Do we extend a large mylar sunscreen behind which we
assemble the torus?

I'm just trying to imagine the asembly of a large facility for
thousands of initial workers and how we would step through that
process. Feel free to bring up your concerns and add to the ones
I've raised.

VictoriaTangoMan wrote:

[Snip]

>Assume we're trying to build a small Torus structure and the
>components are being lifted from earth for assembly in orbit.
>
>The torus "tube" is sectioned into many pieces.
>
>I would prefer that all of the mechanical systems, control systems,
>furniture, etc all be outfitted on earth to save assembly time in
>orbit.
>
Yow! This is the expensive way - I had thought that space
resources, by consensus, were the feed stock to run a SMF. As a
'hand-wave', I'll be able to accept this scenario (ignoring the origin
of the Stanford Torus sections) in order to address the "How do we
assemble it" questions that follow; but I'd like to ask a few questions
of my own as well. Does this scenario assume an SPS already exists? If
so, what was it built out of, and how? If not, should an SPS be built
as a companion to a SMF to provide power and shading? What sort of
resources will an SMF be built from, and how?

>If this is done, then how much will we have to worry about vacuum
>exposure in the open sections damaging all of the equipment.
>
Actually, I had always envisioned the construction of the Torus
being completed before moving any of the smaller equipment (and
certainly furniture!) into it. This means that the equipment could
always be kept in a controlled (or at least pressurized) environment.
The larger pieces of equipment - which have to be built into the Torus
as it is initially constructed - will be made of hardier stuff, and not
suseptible to vacuum damage.

>Should each section be pressure tight, then when sections are
>joined, the pressure seals between them are cut out, so that the
>many sections start to become a whole with the ends always capped.
>
Here you seem to be assuming that the sections will be pressurized
before they are assembled, but that may be problematic. Firstly, you
have to pay the launch cost for the atmosphere inside the sections.
Second, the 'Pressure Seals' will probably be hemispherical, or at
least domed to reduce the stresses on them and the edge of the torus
section where they attach - will your torus "tube" sections even be able
to touch each other? Or will you put an unpressurized ring between each
"tube" section, seal it in place over the end caps of two "tube"
sections, and then remove the end caps? If so, why not just build the
majority of the station as unpressurized ring sections, only joining
them together and pressurizing them when you are ready?

>What if the sections come in lateral halves or quarters, and we
>can't pressure seal them off?
>
The sizes of all of the pieces here are really governed by the sizes
of the launch vehicles which up-port them. Here I'll hop back up onto
my soapbox to say that space resources sidestep this issue by allowing
the entire torus to be built as a single piece, and could provide a much
cheaper solution by eliminating much of the launch costs. Perhaps more
usefully, the pieces in your scenario will have to be carefully designed
to fit together AND sit atop the launch vehicles - I am certain some
clever engineering and prioritization can ensure that those pieces which
must be pressurized will be launched pre-assembled and pre-sealed.
Those pieces which will not need to be constantly pressurized during
assembly (and there will be many) will probably be up-ported first, and
in as many chunks as is convenient.

>Should then, one of the first built structures in orbit be a large
>pressurized assembly bay (assembled piecemeal in a painstakingly
>slow process to allow for the large open volume required) where the
>quarter sections are assembled, the ends sealed, moved out of the
>bay and joined to other completed sections.
>
Here we are at the SMF again - should we build one, how, from what,
and what should it do? If we have one, how much do we really need to
launch? Where will the workers live? Myself I favor building a SMF
early on, but not first. I tend to think that we need to build a
prospecting facility (whether a lunar base or on-orbit NEO retrieval
center, I don't know or really care) and SPS first - mainly because
these are required for harvesting the available space resources. Given
the technology to build large bubbles of (flexible, inflated) plastic in
space, and to reinforce them with slender bands of sprayed on aluminium
(or maybe just more plastic - apparently metal has inferior radiation
sheilding properties), or mirror-coat them, on orbit construction of
these basic facilities should be easy. Given an orbital assembly bay,
should we bother pressurizing it? If you are building something really
big, and have to open the assembly bay up to let it out at the end, how
much atmosphere do you lose? What happens with convection in the bay -
will the welding create areas of superheated air which would be
invisible hazards to the workers? What about frostbite - if the bay is
sheilded, enclosed, and opaque, will it be unbearably cold once you add
an atmosphere to convect away the ambient heat? How will workers get
around this huge volume, now that air restistance is a factor? If we do
not pressurize the assembly bay, what advantages does it have over open
space, and how do we maximize those advantages?

>If the torus facility will have an intergrated waste heat radiation
>facility and other central facilites, how will we process radiant
>heat that accumulates during the construction process before the
>whole torus functions as one system? Will each sectional piece
>require a radiator? Do we wrap the whole thing in mylar to reflect
>the heat? Do we extend a large mylar sunscreen behind which we
>assemble the torus?
>
In an assembly bay (or even just near one) excess heat should not be
a problem - the torus can stay shadowed until it is complete - or at
least until its heat handling systems come on-line.

>I'm just trying to imagine the asembly of a large facility for
>thousands of initial workers and how we would step through that
>process. Feel free to bring up your concerns and add to the ones
>I've raised.
>
I am unconvinced that we will initially need thousands of workers;
we may have to lift some fairly big and heavy equipment initially, but
dozens (perhaps a few hundred) workers should be able to handle the
building of the first, simple facilities. Even with thousands of
workers, I am unconvinced that a Stanford Torus will be the first
habitat. A simple 'Barbell' habitat seems much more likely to me,
probably with a hub at the center of the bar for docking and adding on
of additional habitat sections. It has its own problems; but built as a
temporary lodging alongside of the essential initial orbital facilities
it could work well enough.
Sorry - I seem to have added more concerns and questions than
answers... I hope that some of this will help, and/or get the creative
juices flowing.

On Tuesday, October 1, 2002, at 02:30 PM, Joseph L. Brown wrote:

> Yow! This is the expensive way - I had thought that space
> resources, by consensus, were the feed stock to run a SMF. As a
> 'hand-wave', I'll be able to accept this scenario (ignoring the origin
> of the Stanford Torus sections) in order to address the "How do we
> assemble it"

The most interesting assembly technique I've heard of is:
- create an inflatable with the correct shape (build on ground,
inflate in orbit)
- spray vaporized metal on it.
- If the spray is very fine at first, thermal problems may be
manageable.
- use concentrated solar energy to vaporize the metal
- I'm not sure how to make the spray without a gas, but
perhaps the metal can be ionized and directed with electric fields

This can be automated if a way can be found for the sprayer to around
the structure without using up fuel (just solar power).

The materials in one asteroid (the largest ) are sufficient to make
orbital space colonies with ~500 times the surface area of the Earth in
usable real estate. See http://lifesci3.arc.nasa.gov/SpaceSettlement/
for details.

Al Globus
CSC at NASA Ames Research Center
http://www.nas.nasa.gov/~globus/home.html

> Yow! This is the expensive way - I had thought that space
> resources, by consensus, were the feed stock to run a SMF. As a
> 'hand-wave', I'll be able to accept this scenario (ignoring the
origin
> of the Stanford Torus sections)

No, I see I didn't make myself clear enough. I'm NOT saying build
the Stanford Torus by earth launch.

I'm talking about Heppenheimer's construction shack. Those first
2,000 workers have to live somewhere. It could be the barbell with a
sphere on top that Heppenheimer wrote about. I just chose to look
into the "small" torus option.

in order to address the "How do we
> assemble it" questions that follow; but I'd like to ask a few
questions
> of my own as well. Does this scenario assume an SPS already
exists?

No, this is the first effort to build up the infrastructure. The
housing, the refinery, the fabrication faciliteis, etc.

If
> so, what was it built out of, and how? If not, should an SPS be
built
> as a companion to a SMF to provide power and shading?

Yes, it should. In the future I'll start another thread where we can
discuss the minutae of bootstrapping up to a completed SMF, housing,
lunar facilities, etc.

What sort of
> resources will an SMF be built from, and how?

Earth launched because at the moment there are no lunar or orbital
resources to use, nor means to refine them, nor means to fabricate
anything. I'm premising this thread on that first step into orbit.

>
> >If this is done, then how much will we have to worry about vacuum
> >exposure in the open sections damaging all of the equipment.
> >
> Actually, I had always envisioned the construction of the
Torus
> being completed before moving any of the smaller equipment (and
> certainly furniture!) into it. This means that the equipment
could
> always be kept in a controlled (or at least pressurized)
environment.
> The larger pieces of equipment - which have to be built into the
Torus
> as it is initially constructed - will be made of hardier stuff,
and not
> suseptible to vacuum damage.

Yes, I see your point. I used to hold it myself, until I started
thinking about how expensive it is to keep an astronaut in space. I
don't think it'll be cost efficient to have the astronaut running
systems checks on all of the equipment, checking for bad wiring,
installing lightbulbs, moving in stoves, refrigerators, dishwashers,
computer screens, circuit breakers, etc. . . you get the picture.
Better to have that done by cheaper labor on earth.

I got to thinking about this problem and thought that a pressurized
assembly bay would do it better. As a bonus, the assembly bay can be
attached to the station and be used for construction of orbital
transfer vehicles, deep space probes, etc.
>
> >Should each section be pressure tight, then when sections are
> >joined, the pressure seals between them are cut out, so that the
> >many sections start to become a whole with the ends always capped.
> >
> Here you seem to be assuming that the sections will be
pressurized
> before they are assembled, but that may be problematic. Firstly,
you
> have to pay the launch cost for the atmosphere inside the
sections.

Workers need to breath! We either pay for it when we launch each
section, or we pay for it when we ship up atmospheric gas in bulk
after the station is completed. Where else are you going to get it
from? Not lunar oxygen because that whole mining/refining process
isn't operational yet. Not NEO nitrogen yet. I think it has to come
from earth, so that we can get those other processes started.

> Second, the 'Pressure Seals' will probably be hemispherical, or
at
> least domed to reduce the stresses on them and the edge of the
torus
> section where they attach - will your torus "tube" sections even
be able
> to touch each other? Or will you put an unpressurized ring
between each
> "tube" section, seal it in place over the end caps of two "tube"
> sections, and then remove the end caps?

I favor the latter suggestion because it gives us more usable volume.

If so, why not just build the
> majority of the station as unpressurized ring sections, only
joining
> them together and pressurizing them when you are ready?

Because I'm concerned about the vacuum damage to all of the internal
components.
>
> >What if the sections come in lateral halves or quarters, and we
> >can't pressure seal them off?
> >
> The sizes of all of the pieces here are really governed by the
sizes
> of the launch vehicles which up-port them. Here I'll hop back up
onto
> my soapbox to say that space resources sidestep this issue by
allowing
> the entire torus to be built as a single piece, and could provide
a much
> cheaper solution by eliminating much of the launch costs.

For a habitat, YES, of course. But if you mean the station, then who
will build it? Where will they live? What will they eat? Where will
they get air to breath? Where will the material come from? There's
nothing on the moon or orbit yet. This is the SMF and and housing
that I'm writing about. Have I misunderstood your point?

>
> >Should then, one of the first built structures in orbit be a
large
> >pressurized assembly bay (assembled piecemeal in a painstakingly
> >slow process to allow for the large open volume required) where
the
> >quarter sections are assembled, the ends sealed, moved out of the
> >bay and joined to other completed sections.
> >
> Here we are at the SMF again - should we build one, how, from
what,
> and what should it do? If we have one, how much do we really need
to
> launch? Where will the workers live? Myself I favor building a
SMF
> early on, but not first.

In my mind, the SMF and worker housing go hand in hand. I can't see
how you have one without the other. Perhaps you can lay out your
vision in more detail so that I can see how this can happen. Right
now, I see those first facilities being earth manufactured and then
additional capacity is added to them from lunar derived materials.

I tend to think that we need to build a
> prospecting facility (whether a lunar base or on-orbit NEO
retrieval
> center, I don't know or really care) and SPS first - mainly
because
> these are required for harvesting the available space resources.

Yes, I agree completely. But my question is dealing with the SMF and
housing.

Oh heck, why not . . . check out the new thread on bootstrapping,
right after this message.

Given
> the technology to build large bubbles of (flexible, inflated)
plastic in
> space, and to reinforce them with slender bands of sprayed on
aluminium
> (or maybe just more plastic - apparently metal has inferior
radiation
> sheilding properties), or mirror-coat them, on orbit construction
of
> these basic facilities should be easy.

Yes, you're right. We could launch big blocks of metal, plastic etc
and vaporize it over an inflatible sphere or cylinder. Then bring up
the airlock doors and then all of the internal ventilation
equipment, heating cooling equipment, etc.

Given an orbital assembly bay,
> should we bother pressurizing it? If you are building something
really
> big, and have to open the assembly bay up to let it out at the
end, how
> much atmosphere do you lose?

Depends on how efficient your vacuum pumps are. After you've
finished constructing your item, you depressureize the bay, open the
doors, send it out, bring in the new components, close the doors,
repressurize.

What happens with convection in the bay -
> will the welding create areas of superheated air which would be
> invisible hazards to the workers?

There will have to be superb air flow througout the bay so that
gases are dispersed. That's why I don't think the bay can just be
a "dumb chamber" a hollow shell. It'll need to be a finely
controlled environment.

What about frostbite - if the bay is
> sheilded, enclosed, and opaque, will it be unbearably cold once
you add
> an atmosphere to convect away the ambient heat?

Well, it's not a dumb chamber. It'll have environmental controls.

How will workers get
> around this huge volume, now that air restistance is a factor?

I envision ropes - one end tied to the bay wall, the other to the
structure being assembled. Now you have zero-g freedom of movement
about the structure, can use ropes for stabilizing the structure,
and for controlling your own motion.

If we do
> not pressurize the assembly bay, what advantages does it have over
open
> space, and how do we maximize those advantages?

Can't really see why there would be an assembly bay that wasn't
pressurized. In that case, don't build a bay.

With a bay, workers don't need to suit up, pre-breathe, limit their
time in space suit, can work without bulk of suit, have more ready
access to tools that they're familiar with and all of the sensitive
equipment in the station sections that are being asembled are
protected.

> >I'm just trying to imagine the asembly of a large facility for
> >thousands of initial workers and how we would step through that
> >process. Feel free to bring up your concerns and add to the ones
> >I've raised.
> >
> I am unconvinced that we will initially need thousands of
workers;

That's a whole other thread :) I'm just using Heppenheimer's figure
of 2,000+ workers in the construction shack scenario. And to me it
rings true considering how many specialized tasks there'll be in the
refining, fabrication, as well as facility and equipment maintenance.

> we may have to lift some fairly big and heavy equipment initially,
but
> dozens (perhaps a few hundred) workers should be able to handle
the
> building of the first, simple facilities. Even with thousands of
> workers, I am unconvinced that a Stanford Torus will be the first
> habitat.

I'm NOT writing about the Stanford Torus. The thread is entitled SMF
Construction process, and I never once wrote Stanford Torus :) You
can have a torus smaller than the Stanford study model.

Check out a graphic called "Torus sections" in the files section.

A simple 'Barbell' habitat seems much more likely to me,
> probably with a hub at the center of the bar for docking and
adding on
> of additional habitat sections. It has its own problems; but
built as a
> temporary lodging alongside of the essential initial orbital
facilities
> it could work well enough.

Yes, that's what I'm saying as well. A barbell station will also run
into most of the concerns I've raised in this thread. Barbell, samll
torus, small sphere, samll cylinder - it doesn't matter to me. It
needs to be built, it needs to come from earth, it needs to be
assembled in orbit, it'll have lots of sensitive equipment in it
that vacuum may damage. It'll have lot's on mundane stuff like
chairs, pillows, pots, pans, forks, lightbulbs as well. Any station
will have to house and support the workers, whether we're using your
figure of a hundred people, or Heppenheimer's (more accurately -
Alan Drigger of the Southern Research Institute who based his work
on earlier space station studies) 2,232 people.

Either way, that's a whole bunch more than 3 guys up in the ISS.

> Sorry - I seem to have added more concerns and questions than
> answers... I hope that some of this will help, and/or get the
creative
> juices flowing.

I enjoyed your response.

victoriatangomanwrote:

>
>> Yow! This is the expensive way - I had thought that space
>>resources, by consensus, were the feed stock to run a SMF. As a
>>'hand-wave', I'll be able to accept this scenario (ignoring the
>>origin of the Stanford Torus sections)
>>
>No, I see I didn't make myself clear enough. I'm NOT saying build
>the Stanford Torus by earth launch.
>
>I'm talking about Heppenheimer's construction shack. Those first
>2,000 workers have to live somewhere. It could be the barbell with a
>sphere on top that Heppenheimer wrote about. I just chose to look
>into the "small" torus option.
>
Sorry I misunderstood you - could you please point me a site with more
info on T. A. Heppenheimer and/or Alan Driger? My google searches on
those terms have turned up overwhelming noise...

>>in order to address the "How do we assemble it" questions that follow; but I'd like to ask a few
>>questions of my own as well. Does this scenario assume an SPS already exists?
>>
>No, this is the first effort to build up the infrastructure. The
>housing, the refinery, the fabrication faciliteis, etc.
>
>>If so, what was it built out of, and how? If not, should an SPS be
>>built
>>as a companion to a SMF to provide power and shading?
>>
>Yes, it should. In the future I'll start another thread where we can
>discuss the minutae of bootstrapping up to a completed SMF, housing,
>lunar facilities, etc.
>
>>What sort of resources will an SMF be built from, and how?
>>
>Earth launched because at the moment there are no lunar or orbital
>resources to use, nor means to refine them, nor means to fabricate
>anything. I'm premising this thread on that first step into orbit.
>
Again, I misunderstood; but - you aren't talking about building a
toroidal habitat, but housing and minimal essential services to support
a minimum number of workers; you also don't seem to be talking about a
prospecting facility (turning space resources into raw materials, eg
asteroids into steel ingots and girders) or a general space
manufacturing facility (with heavy hydraulic presses, industrial cutting
tools, lathes, variety of welding capabilities to suit a wide range of
general manufacturing tasks) but instead an enclosed, controlled
environment where workers can use specific specialized tools to
accomplish only the single task of assembling a pre-fab facility.
Needless to say, the facilities I thought you were talking about are
much larger and more complex than the ones you are actually proposing,
and I didn't realize that I had constructed a strawman. Sorry.
On the whole 'Launch what you use, use what you launch' side of things -
what would you think of using pre-manufactured parts (already on orbit)
to convert Shuttle External Fuel Tanks into the initial construction
shack? I realize that you envision building the construction shack
components here on Terra, as dedicated purpose-built units, but it seems
an awful waste to ignore the ETs which we know will stand up to 1G, can
hold greater than 1 Atmosphere worth of internal pressure, already have
a small amount of insulation pre-built on, and are practically delivered
to orbit for free. There have been several seemingly sound proposals to
build 'Barbell' stations with ETs - could one of those proposals be made
to suit the needs of a mere construction shack? Check out these links:

PERMANENT

Space Islands

SIG - Geode concept

Orbit 6

Space Frontier

and some other Google hits

Aside from all the ET stuff, what about salvaging the existing junk
satellites? They have solar panels, radiation shielding, pumps, perhaps
a little propellant, batteries, various bits of electronics in several
states of repair, and all sorts of other supplies which might be just
fine, but without fuel, or an antenna, or a functional gyro, had to be
written off. I know, not the sort of top-shelf components you would
choose to buy if you had a zillion dollars to spend - but they all work
(or did once) and a precise inventory of what is available can be drawn
up before you ever launch a single gram, not to mention that moving
stuff around in orbit is LOTS cheaper than flinging it into orbit in the
first place. Maybe you would have to buy a launch n the cheap (or two) -
say a Sea-launch or Proton - to carry up essentials. Heck, I'm even
envisioning pre-fab circuit boards, minus the electronics, that hardware
from existing satellites is simply plugged into to provide basic
essential functionality. Also, it is entirely possible that just one or
two ETs could be made to serve as a functional construction shack,
suitable for housing the workers for building the rest of the
construction shack!

>>>If this is done, then how much will we have to worry about vacuum
>>>exposure in the open sections damaging all of the equipment.
>>>
>> Actually, I had always envisioned the construction of the
>>Torus being completed before moving any of the smaller equipment (and
>>certainly furniture!) into it. This means that the equipment
>>could always be kept in a controlled (or at least pressurized)
>>environment. The larger pieces of equipment - which have to be built into the
>>Torus as it is initially constructed - will be made of hardier stuff,
>>and not suseptible to vacuum damage.
>>
>Yes, I see your point. I used to hold it myself, until I started
>thinking about how expensive it is to keep an astronaut in space.
>
Once you have any portion of a functional shack built, the costs of
keeping someone in space should drop dramatically - the most insanely
expensive portion of this initial orbital construction is going to be
launch costs. If your shack can provide even a half or three quarters G,
basic air (not simply scrubbing) and water recycling, then the battle is
half won. Granted that you will have to launch food, but that is
something you would have to have done anyway, and perhaps the workers
could be encouraged to examine the feasiblity of an on orbit garden
(heck, it might be essential anyway - in the form of CELSS).

> I
>don't think it'll be cost efficient to have the astronaut running
>systems checks on all of the equipment, checking for bad wiring,
>installing lightbulbs, moving in stoves, refrigerators, dishwashers,
>computer screens, circuit breakers, etc. . . you get the picture.
>Better to have that done by cheaper labor on earth.
>
How much would it cost to secure all of those lightbulbs, stoves,
computer screens, refridgerators, etc in place well enough to survive
launch? And how much launch cost to you pay to up-port all that packing
material? And if you are worried about vacuum damage to even a single
component, you have to provide full life support (at least air pressure,
humidity, and temperature control) to the whole volume of the entire
section from the moment it is launched to the time when it is fully
installed and ready for your workers to move in. Not too much of a
problem if you already have an SPS, but it does seem kinda wasteful.

>I got to thinking about this problem and thought that a pressurized
>assembly bay would do it better. As a bonus, the assembly bay can be
>attached to the station and be used for construction of orbital
>transfer vehicles, deep space probes, etc.
>
[Snip]

>>>Should then, one of the first built structures in orbit be a
>>>large pressurized assembly bay (assembled piecemeal in a painstakingly
>>>slow process to allow for the large open volume required) where
>>>the quarter sections are assembled, the ends sealed, moved out of the
>>>bay and joined to other completed sections.
>>>
>> Here we are at the SMF again - should we build one, how, from
>>what, and what should it do? If we have one, how much do we really need
>>to launch? Where will the workers live? Myself I favor building a
>>SMF early on, but not first.
>>
>In my mind, the SMF and worker housing go hand in hand. I can't see
>how you have one without the other. Perhaps you can lay out your
>vision in more detail so that I can see how this can happen. Right
>now, I see those first facilities being earth manufactured and then
>additional capacity is added to them from lunar derived materials.
>
I understand now that you were envisioning just an assembly bay, and not
a real generalized SMF; it should actually be trivially easy to build -
though I am still unsure about the wisdom of pressurizing it.

>>Given an orbital assembly bay, should we bother pressurizing it? If you are building something
>>really big, and have to open the assembly bay up to let it out at the
>>end, how much atmosphere do you lose?
>>
>Depends on how efficient your vacuum pumps are.
>
Yes, AND the volume to be emptied. If the assembly bay has a large
enough volume, then even lowering the pressure to a bar or two will
still bleed off a lot of volatiles you paid to launch. Assume an
assembly bay, spherical, and about 101 meters in diameter, giving a
volume of 4.4 *10^6 cubic meters working space. Imagine that you keep
the facility pressurized to .5 Atmospheres, and heated to 0 Centigrade.
4.4 EE6 cubic meters is 4.4 EE9 liters of air, or 2.2 EE9 liters at STP
(Standard Temperature and Pressure); if memory serves this works out to
1 EE9 or 1,000,000,000 moles of air - I thinks this works out to ( .7 *
28 g/m + .29 * 32 g/m + .01 * 18 g/m = 19.6g + 9.28g + .18g = 29.06
grams per mole * 1000000000 moles * .001 kilograms per gram =) 29.06 EE6
kilograms of atmosphere. Please check that.. it does seem a bit high to
me. Assuming it is correct, and we can pay to launch all that (Yipe!),
and that your vacuum pumps can drop the interior of the assembly bay
down to .0005 atmospheres of pressure before openning up to let the
single (of many) finished section leave the bay; you still end up losing
about 29060 Kg of air. Even a bay only about 47 meters in radius (and
one tenth the volume) still loses 2906 Kg (two tonnes?) every times it
cycles open. The workers can bloody well wear pressure suits.

> After you've
>finished constructing your item, you depressureize the bay, open the
>doors, send it out, bring in the new components, close the doors,
>repressurize.
>
>What happens with convection in the bay -
>
>>will the welding create areas of superheated air which would be
>>invisible hazards to the workers?
>>
>There will have to be superb air flow througout the bay so that
>gases are dispersed. That's why I don't think the bay can just be
>a "dumb chamber" a hollow shell. It'll need to be a finely
>controlled environment.
>
>What about frostbite - if the bay is
>
>>sheilded, enclosed, and opaque, will it be unbearably cold once
>>you add an atmosphere to convect away the ambient heat?
>>
>Well, it's not a dumb chamber. It'll have environmental controls.
>
>>How will workers get around this huge volume, now that air restistance is a factor?
>>
>I envision ropes - one end tied to the bay wall, the other to the
>structure being assembled. Now you have zero-g freedom of movement
>about the structure, can use ropes for stabilizing the structure,
>and for controlling your own motion.
>
>>If we do not pressurize the assembly bay, what advantages does it have over
>>open space, and how do we maximize those advantages?
>>
>Can't really see why there would be an assembly bay that wasn't
>pressurized. In that case, don't build a bay.
>
Don't be too quick to dismiss an unpressurized bay - it still provides
sheilding from space debris, galactic and solar radiation, provides even
lighting and heating, and perhaps even energy and anchoring benefits or
psychological support for the workers who no longer have to work over
the bottomless void. This means the workers suits only have to provide
pressure and breathable air - all of the bulky sheilding and temperature
control systems can be left off. Maybe an unpressurized bay can work. Oh
yeah - it also simplifies the process of searching for any possible
leaks in the hull of whatever you are assembling.

>With a bay, workers don't need to suit up, pre-breathe, limit their
>time in space suit, can work without bulk of suit, have more ready
>access to tools that they're familiar with and all of the sensitive
>equipment in the station sections that are being asembled are
>protected.
>
Would a space worker necessarily have to pre-breathe? Presumably, all of
the air mix will be the same for ease of life support, and with lower
than 1 atmosphere of pressure is the bends really a signifigant problem?
The suits could even be a similar pressure to the atmosphere in the
living quarters.

>>>I'm just trying to imagine the asembly of a large facility for
>>>thousands of initial workers and how we would step through that
>>>process. Feel free to bring up your concerns and add to the ones
>>>I've raised.
>>>
>> I am unconvinced that we will initially need thousands of workers;
>>
>That's a whole other thread :) I'm just using Heppenheimer's figure
>of 2,000+ workers in the construction shack scenario. And to me it
>rings true considering how many specialized tasks there'll be in the
>refining, fabrication, as well as facility and equipment maintenance.
>
But the initial work will essentially just be welding together
pre-fabbed pieces, no refining, no fabrication, and minimal maintenance
considering that most systems shouldn't take much wear and tear until
they are installed and activated; and those that are used will be
stressed by fewer workers until the refining and fabrication operations
start up.

>>we may have to lift some fairly big and heavy equipment initially,
>>but dozens (perhaps a few hundred) workers should be able to handle
>>the building of the first, simple facilities. Even with thousands of
>>workers, I am unconvinced that a Stanford Torus will be the first
>>habitat.
>>
>I'm NOT writing about the Stanford Torus. The thread is entitled SMF
>Construction process, and I never once wrote Stanford Torus :) You
>can have a torus smaller than the Stanford study model.
>
True - but I thought the radius of the Stanford Torus was carefully
chosen for minimal size given engineering and psycological
considerations; and despite the title of the thread we have ended up
talking about the construction shack.

>Check out a graphic called "Torus sections" in the files section.
>
>>A simple 'Barbell' habitat seems much more likely to me,
>>
>> probably with a hub at the center of the bar for docking and
>>adding on of additional habitat sections. It has its own problems; but
>>built as a temporary lodging alongside of the essential initial orbital
>>facilities it could work well enough.
>>
>Yes, that's what I'm saying as well. A barbell station will also run
>into most of the concerns I've raised in this thread.
>
I think assembly of a barbell could involve considerably less welding,
and perhaps it would be suitable for housing a small (and expanding)
number of workers even while it is under construction.

> Barbell, samll
>torus, small sphere, samll cylinder - it doesn't matter to me. It
>needs to be built, it needs to come from earth, it needs to be
>assembled in orbit, it'll have lots of sensitive equipment in it
>that vacuum may damage. It'll have lot's on mundane stuff like
>chairs, pillows, pots, pans, forks,
>
How will vacuum damage these items?

> lightbulbs as well.
>
Ok, I'll concede that one.

> Any station
>will have to house and support the workers, whether we're using your
>figure of a hundred people, or Heppenheimer's (more accurately -
>Alan Drigger of the Southern Research Institute who based his work
>on earlier space station studies) 2,232 people.
>
>Either way, that's a whole bunch more than 3 guys up in the ISS.
>
All too true - the ISS is a disastrous white elephant of pork-barrel
political spending on so many disappointing levels. The poor bastards
couldn't even match the habitablity of the pathetically forsaken and
politically betrayed SkyLab. (*Idiots, I live in a country run by idiots*)

>> Sorry - I seem to have added more concerns and questions than
>>answers... I hope that some of this will help, and/or get the
>>creative juices flowing.
>>
>I enjoyed your response.
>
Misguided though much of it was. And thank you; I also enjoy this sort
of mental exercise.

> Sorry I misunderstood you - could you please point me a site with
more
> info on T. A. Heppenheimer and/or Alan Driger? My google searches
on
> those terms have turned up overwhelming noise...

http://www.amazon.com/exec/obidos/tg/detail/-
/0446955590/qid33601044/sr=1-10/ref=sr_1_10/103-4733195-1790246?
v=glance

Heppenheimer (Colonies in Space) and O'Neill (The High Frontier)
both wrote excellent books on subject, both pack a lot of details in
but also write so that a dream is born.

> Again, I misunderstood; but - you aren't talking about building a
> toroidal habitat, but housing and minimal essential services to
support
> a minimum number of workers;

Sometimes I don't make myself clear in my writings. I need to work
on that. When I write Habitat I mean the kind of place with open
spaces, families living there, a BIG place. When I write about a
station, I mean the kind of place where you've got a room, you eat
your chow in the mess hall, you share the restroom. You're there to
work and you call your family on the phone if you get lonely.

Actually, I was talking about building a torroidal Station, not
Habitat, so I completely see how my not clearing up MY distinction
between Habitat and Station, could run afoul of othr people's
definitions.

you also don't seem to be talking about a
> prospecting facility (turning space resources into raw materials,
eg
> asteroids into steel ingots and girders) or a general space
> manufacturing facility (with heavy hydraulic presses, industrial
cutting
> tools, lathes, variety of welding capabilities to suit a wide
range of
> general manufacturing tasks) but instead an enclosed, controlled
> environment where workers can use specific specialized tools to
> accomplish only the single task of assembling a pre-fab facility.

Well, it was your response that was the trigger to get me to finish
writing the huge "Bootstrapping in 60 Easy Steps" post I just upped.
If you can keep awake as you read through that, then you'll see I'm
not ignoring your concerns, or pretending like we don't need space
resources to build stuff in space. WE DO! But we also need worker
housing, and that the one little piece I was talking about in this
thread.

> Needless to say, the facilities I thought you were talking about
are
> much larger and more complex than the ones you are actually
proposing,
> and I didn't realize that I had constructed a strawman. Sorry.

No problem. I hope I've presented you with the largese and
complexity you crave in the "Bootstrapping" post :))))

> On the whole 'Launch what you use, use what you launch' side of
things -
> what would you think of using pre-manufactured parts (already on
orbit)
> to convert Shuttle External Fuel Tanks into the initial
construction
> shack? I realize that you envision building the construction shack
> components here on Terra, as dedicated purpose-built units, but it
seems
> an awful waste to ignore the ETs which we know will stand up to
1G, can
> hold greater than 1 Atmosphere worth of internal pressure, already
have
> a small amount of insulation pre-built on, and are practically
delivered
> to orbit for free. There have been several seemingly sound
proposals to
> build 'Barbell' stations with ETs - could one of those proposals
be made
> to suit the needs of a mere construction shack? Check out these
links:
>
> PERMANENT
>
> Space Islands

>
> SIG - Geode concept

>
> Orbit 6
>
> Space Frontier
>use.htm>
>
> and some other Google hits
>
le/External_Tank/>
>

I admire the thought these people have put into their proposals and
I too think that a use can be found for those Extrnal Tanks. Here
are some things to consider:

You can get the tanks for FREE. The National Commission on Space in
1986, Congress in 1987 and 1988, and President Reagan in 1988
directed NASA to make the ETs available to entrepreneurs. NASA
signed Memoranda of Understanding in 1987, 1989, 1992 to provide ETs
to the External Tanks Corporation (ETCO) of Boulder CO and Global
Outpost Inc. of Las Cruces, NM. But there are some strings attached.
You've got to take delivery in orbit with no extra work for NASA.
You have to stabilize their orbit so they don't come tumbling
uncontrollably into the atmosphere. NASA won't permit any
modifications to the tank prior to launch. That means no prebuilt
structures in the tank through which the fuel or oxidizer would flow.

So let's say, unlike the two companies above, you actually met all
of the conditions. That means you've got your own orbital
capability. So you can take the tanks off of NASA's hands. Now,
you've got to purge the thing and bring up all of your equipment and
workers to transform it while its in orbit. I've got one word for
you: EXPENSIVE. You've got to launch all of your gear and the
workers to install it. Working in zero-g is a lot less productive,
especially in a space suit, than working in an automated factory,
with cranes, robotic welders, jigs, every tool you could want within
reach, an equipment failure can be repaired by getting on the phone
(hey, do you think MAYTAG would send up their lonely repairman to
fix your broken dryer in orbit? :) All you're saving is the
cost of the pressure shell. I can't see it working out. What I can
see though is taking these ETs and using them as fuel storage tanks.
That makes sense to me. Or using them for their chopped metal value.
Or for some cheap open storage/warehouse space, light assembly. But
not as a space station. But hey, that's my opinion.

>
> Aside from all the ET stuff, what about salvaging the existing
junk
> satellites? They have solar panels, radiation shielding, pumps,
perhaps
> a little propellant, batteries, various bits of electronics in
several
> states of repair, and all sorts of other supplies which might be
just
> fine, but without fuel, or an antenna, or a functional gyro, had
to be
> written off.

Well, I'd venture a guess that the amount of fuel you'd expend in
matching orbits would more than outweight the value gained. Solar
panels degrade over time in space. Even new panels degrade by, IIRC,
>10% as they journey through the Van Allen Belts on their way to
GSO. The propellent is either Hydrogen peroxide, which degrades
about 1% a year. Or it's hydrazine or nitrogen tetroxide, both of
which are explosive. So you do run some risk in going to salvage old
fuel. How much risk? Couldn't tell you. I guess I'm left wondering
what you'd do with this salvage?

I know, not the sort of top-shelf components you would
> choose to buy if you had a zillion dollars to spend - but they all
work
> (or did once) and a precise inventory of what is available can be
drawn
> up before you ever launch a single gram, not to mention that
moving
> stuff around in orbit is LOTS cheaper than flinging it into orbit
in the
> first place. Maybe you would have to buy a launch n the cheap (or
two) -
> say a Sea-launch or Proton - to carry up essentials. Heck, I'm
even
> envisioning pre-fab circuit boards, minus the electronics, that
hardware
> from existing satellites is simply plugged into to provide basic
> essential functionality. Also, it is entirely possible that just
one or
> two ETs could be made to serve as a functional construction shack,
> suitable for housing the workers for building the rest of the
> construction shack!

I kind of touch on the housing issue in my bootstrapping post. To
address your question of knowing what you're going to go after
before you even launch. Yes, that sounds like good planning to me.
But I still can't get my head around, why do you want those spare
parts? How much expense are you going to incur in zipping around,
changing your delta-v to match all of those satellites' orbits and
doing your handiwork. And then somebody has to ctrack open that ET
and make it livable. As Al Globus pointed out to me, the complexity
of just the ISS radiator/truss section is pretty impressive. Having
thought about it, I have to agree that space is a harsh environment
and that translates into money. I think that same principle has to
be applied to the ET conversion proposal. All it is is a pressure
tank. To make it into a livable space for 1 to ,you name it, people
is not going to be cheap.

> Once you have any portion of a functional shack built, the costs
of
> keeping someone in space should drop dramatically - the most
insanely
> expensive portion of this initial orbital construction is going to
be
> launch costs. If your shack can provide even a half or three
quarters G,
> basic air (not simply scrubbing) and water recycling, then the
battle is
> half won. Granted that you will have to launch food, but that is
> something you would have to have done anyway, and perhaps the
workers
> could be encouraged to examine the feasiblity of an on orbit
garden
> (heck, it might be essential anyway - in the form of CELSS).

Yeah, I agree with you.
>
> > I
> >don't think it'll be cost efficient to have the astronaut running
> >systems checks on all of the equipment, checking for bad wiring,
> >installing lightbulbs, moving in stoves, refrigerators,
dishwashers,
> >computer screens, circuit breakers, etc. . . you get the picture.
> >Better to have that done by cheaper labor on earth.
> >
> How much would it cost to secure all of those lightbulbs, stoves,
> computer screens, refridgerators, etc in place well enough to
survive
> launch? And how much launch cost to you pay to up-port all that
packing
> material? And if you are worried about vacuum damage to even a
single
> component, you have to provide full life support (at least air
pressure,
> humidity, and temperature control) to the whole volume of the
entire
> section from the moment it is launched to the time when it is
fully
> installed and ready for your workers to move in. Not too much of a
> problem if you already have an SPS, but it does seem kinda
wasteful.

Good point. That's what I'm trying to figure out. The pressurization
doesn't have to be a full 1 atm. Just enough not to damage the
components. And if they're not launched with the assembly, they've
got to be launched seperately. So the way I see it, we're just
delaying the cost to a future date and adding the expense of
integrating those components by having the astronaut do it.

You know the problem with forums like this is that we often know
more than we write in a post, so that what the reader gets is only a
partial picture. That's what I'm sensing from you. I'm reading that
you keep referring to the SPS making things easy. I'm sure you know
exactly what you're trying to say, but all I get is that somehow
there's a SPS in orbit and you've got lot's of power, but I have no
clue how you got that SPS up there I'm not getting the full
nature of your response.

Take a look at the Bootstrapping thread and tell me if you see
another way of getting from a to z. I tried to be comprehensive in
all of the steps that I could foresee. Then maybe we can reference
back to these concerns.

Right
> >now, I see those first facilities being earth manufactured and
then
> >additional capacity is added to them from lunar derived materials.

I agree with you wholeheartedly.

> >
> I understand now that you were envisioning just an assembly bay,
and not
> a real generalized SMF; it should actually be trivially easy to
build -
> though I am still unsure about the wisdom of pressurizing it.

Well here's a point that we can each take a side on and investigate
and argue. We keep it on topic and see where it leads us.

>
> >>Given an orbital assembly bay, should we bother pressurizing
it? If you are building something
> >>really big, and have to open the assembly bay up to let it out
at the
> >>end, how much atmosphere do you lose?
> >>
> >Depends on how efficient your vacuum pumps are.
> >
> Yes, AND the volume to be emptied. If the assembly bay has a large
> enough volume, then even lowering the pressure to a bar or two
will
> still bleed off a lot of volatiles you paid to launch. Assume an
> assembly bay, spherical, and about 101 meters in diameter, giving
a
> volume of 4.4 *10^6 cubic meters working space. Imagine that you
keep
> the facility pressurized to .5 Atmospheres, and heated to 0
Centigrade.
> 4.4 EE6 cubic meters is 4.4 EE9 liters of air, or 2.2 EE9 liters
at STP
> (Standard Temperature and Pressure); if memory serves this works
out to
> 1 EE9 or 1,000,000,000 moles of air - I thinks this works out to
( .7 *
> 28 g/m + .29 * 32 g/m + .01 * 18 g/m = 19.6g + 9.28g + .18g =
29.06
> grams per mole * 1000000000 moles * .001 kilograms per gram =)
29.06 EE6
> kilograms of atmosphere. Please check that.. it does seem a bit
high to
> me.

Well, I'd have to crack open my Physics books and then figure out
what your numbers were referencing.

Assuming it is correct, and we can pay to launch all that (Yipe!),
> and that your vacuum pumps can drop the interior of the assembly
bay
> down to .0005 atmospheres of pressure before openning up to let
the
> single (of many) finished section leave the bay; you still end up
losing
> about 29060 Kg of air. Even a bay only about 47 meters in radius
(and
> one tenth the volume) still loses 2906 Kg (two tonnes?) every
times it
> cycles open. The workers can bloody well wear pressure suits.

You make a good case. Assuming the numbers compute properly, I would
definitely take my idea back to the drawing board.

Just as an aside, if people are breathing bottled air via a ace
mask, how low can the pressure in their environment go before its
unhealthy for them.

Maybe a solution is a very low pressure, enough to mitigate against
vacuum damage, enough to allow people to work in shirtsleeves, but
with their own air supply. Any thoughts?

> Don't be too quick to dismiss an unpressurized bay - it still
provides
> sheilding from space debris, galactic and solar radiation,
provides even
> lighting and heating, and perhaps even energy and anchoring
benefits or
> psychological support for the workers who no longer have to work
over
> the bottomless void. This means the workers suits only have to
provide
> pressure and breathable air - all of the bulky sheilding and
temperature
> control systems can be left off. Maybe an unpressurized bay can
work. Oh
> yeah - it also simplifies the process of searching for any
possible
> leaks in the hull of whatever you are assembling.

Here too, you raise some worthy points. You're right, there might
indeed be some benefits to an unpressurized bay.

> Would a space worker necessarily have to pre-breathe? Presumably,
all of
> the air mix will be the same for ease of life support, and with
lower
> than 1 atmosphere of pressure is the bends really a signifigant
problem?
> The suits could even be a similar pressure to the atmosphere in
the
> living quarters.

Well, if suit and envirnoment are all the same pressure then no
prebreathing is necessary. But coming back to earth is going to be a
problem, especially if you're the pilot.

> But the initial work will essentially just be welding together
> pre-fabbed pieces, no refining, no fabrication, and minimal
maintenance
> considering that most systems shouldn't take much wear and tear
until
> they are installed and activated; and those that are used will be
> stressed by fewer workers until the refining and fabrication
operations
> start up.

We're mixing apples and oranges. I was writing about constructing a
station to house thousands of worker to perform the tasks of
refining, fabrication etc.

It appears to me that you're writing about the workers needed to
build the shack that will house the workers that build the SPS and
the big habitat.

I'm not far from your viewpoint. Again, look at my bootstrapping
post. There is a smaller housing station that initially is ued to
get the shack started in LEo, then it's moved to the moon, then it's
moved to L1.

>
> True - but I thought the radius of the Stanford Torus was
carefully
> chosen for minimal size given engineering and psycological
> considerations; and despite the title of the thread we have ended
up
> talking about the construction shack.

I'm not exactly sure what you meant by that closing remark. I'm
going to take a guess and venture a clarification, no offense
intended. The SMF in the title refers to Space Manufacturing
Facility, a prettier moniker for what started us as the Construction
Shack.

As for the Stanford study, I think they premised it a wide cross
section of the population so that NO ONE would sense discomfort from
the increased rpm. I contend that our initial workers will be chosen
for psychological stability in cramped quarters, higher rpm
environment, etc. Not just anybody's granny can go and be a elite
astronaut welder/fabricator/miner, etc.

Torus' can be smaller and rotate faster than the Stanford model,
it's just that now some people will experience discomfort, while
other won't. I saw a study where no one had discomfort a 1 rpm, only
a few at 2 rpm, a significant jump at 3 rpm, and everybody at 5 rpm.

> I think assembly of a barbell could involve considerably less
welding,
> and perhaps it would be suitable for housing a small (and
expanding)
> number of workers even while it is under construction.

Sure, OK. I'm not proposing torus. I just happened to chose it as
the form factor because I had just run a whole slew of numbers on
it. Barbell works for me just as well.

>
> > Barbell, samll
> >torus, small sphere, samll cylinder - it doesn't matter to me. It
> >needs to be built, it needs to come from earth, it needs to be
> >assembled in orbit, it'll have lots of sensitive equipment in it
> >that vacuum may damage. It'll have lot's on mundane stuff like
> >chairs, pillows, pots, pans, forks,
> >
> How will vacuum damage these items?

That's a compare and contrast statement. It may damage the sensitive
stuff, but it won't damage the mundane stuff, but you still need to
haul both into orbit. That's all I was trying to say.

> >Depends on how efficient your vacuum pumps are.
> >
> Yes, AND the volume to be emptied. If the assembly bay has a large
> enough volume, then even lowering the pressure to a bar or two
will
> still bleed off a lot of volatiles you paid to launch. Assume an
> assembly bay, spherical, and about 101 meters in diameter, giving
a
> volume of 4.4 *10^6 cubic meters working space. Imagine that you
keep
> the facility pressurized to .5 Atmospheres, and heated to 0
Centigrade.
> 4.4 EE6 cubic meters is 4.4 EE9 liters of air, or 2.2 EE9 liters
at STP
> (Standard Temperature and Pressure); if memory serves this works
out to
> 1 EE9 or 1,000,000,000 moles of air - I thinks this works out to
( .7 *
> 28 g/m + .29 * 32 g/m + .01 * 18 g/m = 19.6g + 9.28g + .18g =
29.06
> grams per mole * 1000000000 moles * .001 kilograms per gram =)
29.06 EE6
> kilograms of atmosphere. Please check that.. it does seem a bit
high to
> me. Assuming it is correct, and we can pay to launch all that
(Yipe!),
> and that your vacuum pumps can drop the interior of the assembly
bay
> down to .0005 atmospheres of pressure before openning up to let
the
> single (of many) finished section leave the bay; you still end up
losing
> about 29060 Kg of air. Even a bay only about 47 meters in radius
(and
> one tenth the volume) still loses 2906 Kg (two tonnes?) every
times it
> cycles open. The workers can bloody well wear pressure suits.

This was just bugging me no end so I did check your numbers:

here's the way I figure it using your examples for bay size.

Example #1
radius of bay . . . 101 meters . . this is HUGE
volume of bay . . . 4,317,344 m^3
1 mole = 22.4 liters @ STP = 22.4 liters/mole (ANY GAS)
atmosphere = 80% Nitrogen = 28g = 0.8 * .28 = 22.4g
20% Oxygen = 32g = 0.2 * .32 = 6.4g
28.8 g/mole = 0.0288 kg/mole
101 meter radius sphere contains 4,317,344,000 liters/22.4 L/mole
thus contains 192,738,571 moles * .0288 kg/mole * 0.5 atm 2,775,435 kg of air.

Example #2
radius of bay . . . 47 meters
volume of bay . . . 435,057 m^3
1 mole = 22.4 liters @ STP = 22.4 liters/mole (ANY GAS)
atmosphere = 80% Nitrogen = 28g = 0.8 * .28 = 22.4g
20% Oxygen = 32g = 0.2 * .32 = 6.4g
28.8 g/mole = 0.0288 kg/mole
47 meter radius sphere contains 435,057,000 liters/22.4 L/mole
thus contains 19,422,187 moles * .0288 kg/mole * 0.5 atm 279,680 kg of air.

In my post I proposed a torus section of 100 feet in length and a
completed diameter of 67 ft. To keep things consistent 30.5m length
and 20.5 diameter. So even your 47 meter radius is too big. I would
propose a radius of 21 meters, which is still 38% larger than the
30.5 meter length of the section. So my example follows.

Example #3
radius of bay . . . 21 meters
volume of bay . . . 38,807 m^3
1 mole = 22.4 liters @ STP = 22.4 liters/mole (ANY GAS)
atmosphere = 80% Nitrogen = 28g = 0.8 * .28 = 22.4g
20% Oxygen = 32g = 0.2 * .32 = 6.4g
28.8 g/mole = 0.0288 kg/mole
21 meter radius sphere contains 38,807,000 liters/22.4 L/mole
thus contains 1,732,457 moles * .0288 kg/mole * 0.5 atm 24,947 kg of air.

Your figure of vacuum pump efficiency is 0.0005. This translates to:
1 atm = 760 Torrs
0.0005 atm = .38 Torrs

Thus:

Exp #1 2,775,435 kg air * 0.0005 atm lost = 1,388 kg lost per cycle.

Exp #2 279,680 kg air * 0.0005 atm lost = 140 kg lost per cycle.

Exp #3 24,947 kg air * 0.0005 atm lost = 12.5 kg lost per cycle.

By my calculation we'd have a vacuum pump as good as something NASA
has (and I'm not talking a table top model either) which is a 24 ft
by 75 ft chamber capable of going down to 10 * E-7 Torrs.

Granted a 21 meter radius bay is larger, but I'll calculate by their
figures and leave it up to the reader to determine by how much to
adjust performance.

Exp #1 2,775,435 kg air @ 380 Torrs before cycling airlock
. . . 7,304 kg air lost @ 1 Torr after cycling
. . . 0.0007 kg air lost @ 10E-7 Torr after cycling (NASA Standard)

Exp #2 279,680 kg air @ 380 Torrs before cycling airlock
. . . 736 kg air lost @ 1 Torr after cycling
. . . 0.00007 kg air lost @ 10E-7 Torr after cycling (NASA Standard)

Exp #3 24,947 kg air @ 380 Torrs before cycling airlock
. . . 66 kg air lost @ 1 Torr after cycling
. . . 0.000007 kg air lost @ 10E-7 Torr after cycling (NASA Standard)

COSTING

Using a Shuttle Launch cost of $10,000/kg to replace the air lost in
one cycle.

Example #1
.0005 atm . . . 1,388 kg * $10,000 = $13,880,000
1 Torr . . . . 7,304 kg * $10,000 = $73,040,000
10E-7 Torr. . . 0.0007 kg * $10,000 = $7

Example #2
.0005 atm . . . 140 kg * $10,000 = $1,400,000
1 Torr . . . . 736 kg * $10,000 = $7,360,000
10E-7 Torr. . . 0.00007 kg * $10,000 = $0.7

Example #3
.0005 atm . . . 12.5 kg * $10,000 = $125,000
1 Torr . . . . 66 kg * $10,000 = $660,000
10E-7 Torr. . . 0.000007 kg * $10,000 = $0.07

Conclusion:

Well, after running through the numbers I have to withdraw my
concession to your point. Your first assembly bay is too huge to be
relevant to my example. You could build the Starship Enterprise in
there :) Your second example is still twice as large as I'd
comfortably need. With an assembly bay 21 meters in radius, using
your numbers, I'd lose 12.5 kg of air or $125,000 in replacement
launch costs per airlock cycle, or if I used NASA standard
technology, I'd lose 7/1000 of a gram of air, worth 7 cents in
Shuttle replacement launch cost.

Also consider the issue of lifting the mass of that air at a cost of
$10,000/kg.

67 ft diameter * 100 ft length = 352,707 ft^3
35.3147 ft^3 per m^3 ----> 9,988 m^3 ----> 9,988,000 L / 22.4L/mole
thus 445,900 moles * .0288 kg/mole * 0.5 atm = 6,421 kg of air.

6,421 kg air * $10,000 = $64,210,000 for six Launches.
4,994 kg Nitrogen * $10,000 = $49,936,117 for six Launches.
1,427 kg Oxygen * $10,000 = $14,273,883 for six Launches.

Actually, having run the numbers and looked into the technology out
there, I'm more comfortable with the idea of construction within an
assembly bay now than before.

And considering we'd have to mount an expedition to a NEO to capture
the Nitrogen, then refine it in orbit, I actually think the cost is
reasonable (especially because I'm using $10,000/kg as the cost
basis.)

So what do you think?

check this site
http://www.bmpcoe.org/bestpractices/internal/nasam/nasam_19.html