I've been wondering where we're going to store all of the atmosphere
for a habitat while it's being built.

It doesn't make sense to me to complete the structure of the habitat
and then go and refine material to extract the gases for the
habitat's atmosphere, all the while venting the gases from the
construction process.

I got to thinking about how to build up an atmosphere in the most
efficeint way and would like some feedback from members if they can
point out conceptual flaws and can provide engineering details.

First off we make a very flimsy wire framework of the Habitat. Then
cover it with mylar. Then starting spraying metal on it via vacuum
vapor depostion. Once we have a gas tight shell, with a wall
thickness of (this is where some expert help would be most
appreciated) half a millimeter, we start pumping our waste oxygen
and other needed gases into the Habitat. The gas pressure of the
atmosphere should always be less than the structural strength of the
habitat shell.

Meanwhile, we keep adding more thickness to the shell, thus allowing
more gas pressure to be held.

Now for some Habitat designs the windows issue will not allow this
approach, but the modified cylindrical design that I've already
outlined in this group does allow for this approach.

So other than the windows issue, can anybody supply feedback on this
proposal.

Thanks, TangoMan

Store your gases in liquid form until you need them.

Ron

"victoriatangoman" tango_dancer@...
10/22/02 02:12 PM

I've been wondering where we're going to store all of the atmosphere
for a habitat while it's being built.

It doesn't make sense to me to complete the structure of the habitat
and then go and refine material to extract the gases for the
habitat's atmosphere, all the while venting the gases from the
construction process.

I got to thinking about how to build up an atmosphere in the most
efficeint way and would like some feedback from members if they can
point out conceptual flaws and can provide engineering details.

First off we make a very flimsy wire framework of the Habitat. Then
cover it with mylar. Then starting spraying metal on it via vacuum
vapor depostion. Once we have a gas tight shell, with a wall
thickness of (this is where some expert help would be most
appreciated) half a millimeter, we start pumping our waste oxygen
and other needed gases into the Habitat. The gas pressure of the
atmosphere should always be less than the structural strength of the
habitat shell.

Meanwhile, we keep adding more thickness to the shell, thus allowing
more gas pressure to be held.

Now for some Habitat designs the windows issue will not allow this
approach, but the modified cylindrical design that I've already
outlined in this group does allow for this approach.

So other than the windows issue, can anybody supply feedback on this
proposal.

Thanks, TangoMan

> Store your gases in liquid form until you need them.
>
> Ron
> ******
>

Yeah, that's the obvious solution until you look into the problem.
The problems only become more severe with the larger habitats, so I
used the smallest to illustrate my point. Here's what I did using
the Stanford Torus as an example.

The Stanford Torus is designed to simulate 1 gravity at 1 rpm, thus
for it to have one gravity at the center of the cylindrical torus
section (to give the greatest living area at precisely 1 gravity)
the radius of the torus must be 954.81 meters. The torus section
radius is 60.96 meters. (All figures derived from descriptions in
Heppenheimer's "Colonies in Space.") The Hub radius is 65 meters.
The six spokes are 7.5 meters in radius and 767.89 meters in length.

Thus, the total volume of the Stanford Torus is 72,060,179 m^3 and
its surface area is 2,423,192 m^2.

At 0.5 atmospheric pressure (50% O2,50% N2), if we're using the
conventional wisdom of cryogenically storing the gases until we
finish the Stanford Torus, then we need storage for 36,030,089,500
liters at STP.

O2 has a liquid to gas expansion rate of 875:1, is stored at 5,076
kPa and at a temperature of 154.8 K.

N2 has a liquid to gas expansion rate of 710:1, is stored at 3,394
kPa and at a temperature of 126.3 K.

Thus, the stored volume of liquid O2 is 41,177,245 liters and the
stored volume of liquid N2 is 50,746,605 liters.

To cryogenically store the LO2 in a single spherical pressure vessel
would require a radius of 21.42 meters, with a wall thickness of
31.5 cm.

To cryogenically store the LN2 in a single spherical pressure vessel
would require a radius of 22.96 meters, with a wall thickness of
22.6 cm.

For my pressure vessel calculations I'm using the properties of AISI
1030 Steel, normalized 925C (1700F) and using a safety factor of
2x the Tensile Strength (Yield.) I chose steel because it is easier
and less expensive to refine than aluminum or titanium. Of course,
other metals could be used and that would change the spcifics of
this analysis, but I had to work with something so steel is it :)

http://www.matweb.com/search/SpecificMaterial.asp?bassnum=M1030D

Good luck on welding something that thick!

Alternatively, in order to ease the welding tasks our space workers
will face, we can specify a steel thickness of 2.94 cm. This will
allow a LO2 spherical pressure tank (subject only to longitudinal
forces and thus more efficient than a cylindrical tank) to be 2
meters in radius and a LN2 tank can be 3 meters in radius with the
same steel.

This corresponds to 1,228 LO2 pressure vessels and 449 LN2 pressure
vessels.

The total volume of steel used to construct these pressure vessels
is 3,309 m^3. This is equivelent to covering the surface area of the
Stanford Torus with a skin 1.3 mm thick.

My proposal is to use vacuum vapor deposition to create an extremely
thin pressure vessel. Using the Stanford Torus as an example, vacuum
depositing a skin 100 um thick, would take 242.32 m^3 of the same
steel (using only 7.32% of the metal required for all of the
cryogenic pressure vessels) and at that point the Stanford Torus
could contain an atmosphere of 0.5659 kPa (or 0.0056 atm.) Thus we
could pump in up to 403,537,002 liters at STP. That would translate
to 18,015,045 moles of O2.

If we used the same steel to construct the Torus (I'm not sure we'd
need to use this high strength steel - we could probably do with a
less demanding material because of lower internal pressure - although
we'd now have to factor in rotation stresses) we'd need to refine
5,098,877 Kg Ilmenite to extract 1,876,913 Kg Fe, combine it with
17,120 Kg Mn, 6,468 Kg C, 761 Kg P, and 951 Kg S, in order to refine
1,902,212 Kg of AISI 1030 Steel.

Processing that amount of ilmenite would have yielded 1,075,458 Kg
O2, and 2,146,506 Kg TiO. The O2 would translate to 752,848,832
liters at STP. More than our Habitat can take from a pressure
perspective.

So, the critical path once a refinery is in place might be to first
make some pressure vessels able to withstand 5,076 kPa. Make about
52 - 2m radius pressure vessels. Store the oxygen byproduct from the
Ilmenite reduction process. Use the iron to make steel. Vacuum
deposit the steel to the Habitat framework to the above
specifications. Then release the O2 from 27 pressure vessels into
the habitat and use those pressure vessels to store LH2 (1,297 kPa),
or LN2 that we're getting from somewhere, as well as solar gases
that we're collecting from our refining.

Alternatively, and the option I favor, vent the oxygen away as a
waste product early in our construction phase and do away with the
need to make those first pressure vessels. Afterall, we're producing
about twice as much O2 as we'll need per unit of steel.

From this point forward, it just becomes a matter of adding more
metal to the Torus and adding more atmospheric gas to the Habitat so
that the gas pressure never exceeds the ability of the Habitat walls
to contain it.

We neatly do away with the need to build either complex and massive
pressure vessels or thousands of simpler vessels and their cryogenic
machinary and the necessity to power that machinery in order to
maintain the cryogens.

Now as I stated in my original message, I would appreciate somebody
checking my calculations because I'm not an engineer.

But if my analysis holds true, then I say that the conventional
wisdom of storing gases for later release is an unnecessary and
complex step that can neatly be avoided.

TangoMan

>
> "victoriatangoman"
> 10/22/02 02:12 PM
>
> I've been wondering where we're going to store all of the
atmosphere
> for a habitat while it's being built.
>
> It doesn't make sense to me to complete the structure of the
habitat
> and then go and refine material to extract the gases for the
> habitat's atmosphere, all the while venting the gases from the
> construction process.
>
> I got to thinking about how to build up an atmosphere in the most
> efficeint way and would like some feedback from members if they
can
> point out conceptual flaws and can provide engineering details.
>
> First off we make a very flimsy wire framework of the Habitat.
Then
> cover it with mylar. Then starting spraying metal on it via vacuum
> vapor depostion. Once we have a gas tight shell, with a wall
> thickness of (this is where some expert help would be most
> appreciated) half a millimeter, we start pumping our waste oxygen
> and other needed gases into the Habitat. The gas pressure of the
> atmosphere should always be less than the structural strength of
the
> habitat shell.
>
> Meanwhile, we keep adding more thickness to the shell, thus
allowing
> more gas pressure to be held.
>
> Now for some Habitat designs the windows issue will not allow this
> approach, but the modified cylindrical design that I've already
> outlined in this group does allow for this approach.
>
> So other than the windows issue, can anybody supply feedback on
this

correct me if wrong here, I'm just thinking quickly and not deeply :-)

What happens to liquid items released into space? (I talk here of liquid
waste from astronauts being vented?) It seems to me that it freezes, does
it not? As a frozen block it seems to hold together pretty well in the
vaccuum and cold of space.

Perhaps a mylar sunshade to ensure it stays in the dark of direct sunlight
radiation that would heat it up, but other than that it should be fine until
time you want to reconstitute it to liquid/ gas by heating it up back inside
your vessel...

I'm a forgetting something here?

solves the pressure problem for storage doesnt it?

bob

> correct me if wrong here, I'm just thinking quickly and not
deeply :-)
>
> What happens to liquid items released into space? (I talk here of
liquid
> waste from astronauts being vented?) It seems to me that it
freezes, does
> it not? As a frozen block it seems to hold together pretty well
in the
> vaccuum and cold of space.

The liquids that the astronauts vent are usually water based and
freeze at 0 degrees Celsius or 273 K. Thus, these liquids can
release their heat quickly in the 5 K temperature of space that has
been permanently shadowed from the sun. If you can get away from
planetary sources then the temperature drops to 2.73 K, which is the
Cosmic Microwave Background Temperature, and that's as low as it
gets.

Releasing Oxygen or Nitrogen gas into space from an environment of
293 K, will not give you the same response as water. First off these
gases have a lot more heat to disipate. N2 liquifies at 126.3 K and
O2 liquifies at 154.8 K. So the gases will disperse while they are
cooling. If you could suddenly dump a large enough quantity of gas
into a long-term, well shaded region of space, and were prepared to
accept a large amount of waste, I would think that as that gas is
expanding away and cooling at the same time, some of it MAY cool
down to liquid state before if completely disipated. Intuitively, I
would guess that you may need a ratio of a million to one or so.
This gets into all sorts of gas dispersion ratios that I'm not
familiar with. Maybe somebody else can clarify this matter.

>
> Perhaps a mylar sunshade to ensure it stays in the dark of direct
sunlight
> radiation that would heat it up, but other than that it should be
fine until
> time you want to reconstitute it to liquid/ gas by heating it up
back inside
> your vessel...
>
> I'm a forgetting something here?
>
> solves the pressure problem for storage doesnt it?
>
> bob

If you modify your proposal to liquifying the gases and pumping them
into the pressure vessels and then parking the vessels behind the
mylar, then maintaining the temperature at cryogenic levels becomes
very simple. Net result: you save the electricity costs to keep
gases at cryogenic temperatures.

Further if you can engineer your gas liquification plant to utilize
the ambient temperature of the shaded space to perform the actual
liquification process, then you save some on the capital cost and
electricity cost, but this is offset by engineering a manufacturing
plant to operate at 5 K. This is not a forgiving environment for
equipment. My guess is that this is more trouble than it's worth.

So, in the end, you still need the expensive pressure vessels and
liquification equipment. But you save costs on maintaining the
cryogenic temperatures.

Good catch on that point. That will save some money.

TangoMan

What do you suppose would happen to has gas once its liquified and then
vented into dark space area?

You would have the relatively small amount of energy to liquify and then
store it as you please as frozen liquid?

curious since I usually dont think these out normally...

> What do you suppose would happen to has gas once its liquified and
then
> vented into dark space area?
>
> You would have the relatively small amount of energy to liquify
and then
> store it as you please as frozen liquid?
>
> curious since I usually dont think these out normally...

It would turn back into a gas.

I modify my previous answer where I thought you might get some gas
turning into a liquid as a million to one shot. I now think its
impossible.

The reason it would turn turn back to a gas is that the liquid state
of O2 and N2 is a function of temperature and pressure. You've
identified one component of the equation with "dark space" but that
still leaves pressure unaccounted for.

That's why we don't have interstellar space freezing solid :) No
pressure.

Why would you store LOX at such a high temperature as 154.8K ?

From http://www.tpub.com/asm/4.htm
"
Description and Properties of Liquid Oxygen
Oxygen can exist as a solid or gas, depending upon the temperature and
pressure under which it is stored. At atmospheric pressure, oxygen exists
as a solid at temperatures below its melting point, - 361F (-281C).
Solid oxygen turns into a
liquid at its melting point and remains in this state until the
temperature rises to its boiling point, -297F (-183C).
At this latter temperature, LOX vaporizes into the gaseous state. Gaseous
oxygen will turn into liquid at atmospheric pressure by cooling to a
temperature below -297F. By increasing the pressure, gaseous oxygen can
be liquified at higher temperatures, up to its critical temperature,
- 182F ( -119C).
"

The -119 C critical temperature mentioned is equal to the 154 K
temperature you mentioned.

Why not store it at -183 C ( 90 K ) at normal atmospheric pressure?

Why not store it at even lower temperature and even lower pressure?

The lower the temperature and pressure, the thinner the walls of your LOX
storage vessel can be.

Ron

"victoriatangoman" tango_dancer@...
10/23/02 12:24 AM

> Store your gases in liquid form until you need them.
>
> Ron
> ******
>

Yeah, that's the obvious solution until you look into the problem.
The problems only become more severe with the larger habitats, so I
used the smallest to illustrate my point. Here's what I did using
the Stanford Torus as an example.

The Stanford Torus is designed to simulate 1 gravity at 1 rpm, thus
for it to have one gravity at the center of the cylindrical torus
section (to give the greatest living area at precisely 1 gravity)
the radius of the torus must be 954.81 meters. The torus section
radius is 60.96 meters. (All figures derived from descriptions in
Heppenheimer's "Colonies in Space.") The Hub radius is 65 meters.
The six spokes are 7.5 meters in radius and 767.89 meters in length.

Thus, the total volume of the Stanford Torus is 72,060,179 m^3 and
its surface area is 2,423,192 m^2.

At 0.5 atmospheric pressure (50% O2,50% N2), if we're using the
conventional wisdom of cryogenically storing the gases until we
finish the Stanford Torus, then we need storage for 36,030,089,500
liters at STP.

O2 has a liquid to gas expansion rate of 875:1, is stored at 5,076
kPa and at a temperature of 154.8 K.

N2 has a liquid to gas expansion rate of 710:1, is stored at 3,394
kPa and at a temperature of 126.3 K.

Thus, the stored volume of liquid O2 is 41,177,245 liters and the
stored volume of liquid N2 is 50,746,605 liters.

To cryogenically store the LO2 in a single spherical pressure vessel
would require a radius of 21.42 meters, with a wall thickness of
31.5 cm.

To cryogenically store the LN2 in a single spherical pressure vessel
would require a radius of 22.96 meters, with a wall thickness of
22.6 cm.

For my pressure vessel calculations I'm using the properties of AISI
1030 Steel, normalized 925C (1700F) and using a safety factor of
2x the Tensile Strength (Yield.) I chose steel because it is easier
and less expensive to refine than aluminum or titanium. Of course,
other metals could be used and that would change the spcifics of
this analysis, but I had to work with something so steel is it :)

http://www.matweb.com/search/SpecificMaterial.asp?bassnum=M1030D

Good luck on welding something that thick!

Alternatively, in order to ease the welding tasks our space workers
will face, we can specify a steel thickness of 2.94 cm. This will
allow a LO2 spherical pressure tank (subject only to longitudinal
forces and thus more efficient than a cylindrical tank) to be 2
meters in radius and a LN2 tank can be 3 meters in radius with the
same steel.

This corresponds to 1,228 LO2 pressure vessels and 449 LN2 pressure
vessels.

The total volume of steel used to construct these pressure vessels
is 3,309 m^3. This is equivelent to covering the surface area of the
Stanford Torus with a skin 1.3 mm thick.

My proposal is to use vacuum vapor deposition to create an extremely
thin pressure vessel. Using the Stanford Torus as an example, vacuum
depositing a skin 100 um thick, would take 242.32 m^3 of the same
steel (using only 7.32% of the metal required for all of the
cryogenic pressure vessels) and at that point the Stanford Torus
could contain an atmosphere of 0.5659 kPa (or 0.0056 atm.) Thus we
could pump in up to 403,537,002 liters at STP. That would translate
to 18,015,045 moles of O2.

If we used the same steel to construct the Torus (I'm not sure we'd
need to use this high strength steel - we could probably do with a
less demanding material because of lower internal pressure - although
we'd now have to factor in rotation stresses) we'd need to refine
5,098,877 Kg Ilmenite to extract 1,876,913 Kg Fe, combine it with
17,120 Kg Mn, 6,468 Kg C, 761 Kg P, and 951 Kg S, in order to refine
1,902,212 Kg of AISI 1030 Steel.

Processing that amount of ilmenite would have yielded 1,075,458 Kg
O2, and 2,146,506 Kg TiO. The O2 would translate to 752,848,832
liters at STP. More than our Habitat can take from a pressure
perspective.

So, the critical path once a refinery is in place might be to first
make some pressure vessels able to withstand 5,076 kPa. Make about
52 - 2m radius pressure vessels. Store the oxygen byproduct from the
Ilmenite reduction process. Use the iron to make steel. Vacuum
deposit the steel to the Habitat framework to the above
specifications. Then release the O2 from 27 pressure vessels into
the habitat and use those pressure vessels to store LH2 (1,297 kPa),
or LN2 that we're getting from somewhere, as well as solar gases
that we're collecting from our refining.

Alternatively, and the option I favor, vent the oxygen away as a
waste product early in our construction phase and do away with the
need to make those first pressure vessels. Afterall, we're producing
about twice as much O2 as we'll need per unit of steel.

From this point forward, it just becomes a matter of adding more
metal to the Torus and adding more atmospheric gas to the Habitat so
that the gas pressure never exceeds the ability of the Habitat walls
to contain it.

We neatly do away with the need to build either complex and massive
pressure vessels or thousands of simpler vessels and their cryogenic
machinary and the necessity to power that machinery in order to
maintain the cryogens.

Now as I stated in my original message, I would appreciate somebody
checking my calculations because I'm not an engineer.

But if my analysis holds true, then I say that the conventional
wisdom of storing gases for later release is an unnecessary and
complex step that can neatly be avoided.

TangoMan

>
> "victoriatangoman"
> 10/22/02 02:12 PM
>
> I've been wondering where we're going to store all of the
atmosphere
> for a habitat while it's being built.
>
> It doesn't make sense to me to complete the structure of the
habitat
> and then go and refine material to extract the gases for the
> habitat's atmosphere, all the while venting the gases from the
> construction process.
>
> I got to thinking about how to build up an atmosphere in the most
> efficeint way and would like some feedback from members if they
can
> point out conceptual flaws and can provide engineering details.
>
> First off we make a very flimsy wire framework of the Habitat.
Then
> cover it with mylar. Then starting spraying metal on it via vacuum
> vapor depostion. Once we have a gas tight shell, with a wall
> thickness of (this is where some expert help would be most
> appreciated) half a millimeter, we start pumping our waste oxygen
> and other needed gases into the Habitat. The gas pressure of the
> atmosphere should always be less than the structural strength of
the
> habitat shell.
>
> Meanwhile, we keep adding more thickness to the shell, thus
allowing
> more gas pressure to be held.
>
> Now for some Habitat designs the windows issue will not allow this
> approach, but the modified cylindrical design that I've already
> outlined in this group does allow for this approach.
>
> So other than the windows issue, can anybody supply feedback on
this

> Why would you store LOX at such a high temperature as 154.8K ?

First off, my point is that you shouldn't store it at all but send
it into the Habitat after you've built it into a meager pressure
shell.

But if you're not convinced of the validity of that proposition,
then I'll continue with my explanation of why I chose the critical
temperatures of both gases as the environment within which to store
them.

>
> From http://www.tpub.com/asm/4.htm
> "
> Description and Properties of Liquid Oxygen
> Oxygen can exist as a solid or gas, depending upon the temperature
and
> pressure under which it is stored. At atmospheric pressure, oxygen
exists
> as a solid at temperatures below its melting point, - 361F (-281
C).
> Solid oxygen turns into a
> liquid at its melting point and remains in this state until the
> temperature rises to its boiling point, -297F (-183C).
> At this latter temperature, LOX vaporizes into the gaseous state.
Gaseous
> oxygen will turn into liquid at atmospheric pressure by cooling to
a
> temperature below -297F. By increasing the pressure, gaseous
oxygen can
> be liquified at higher temperatures, up to its critical
temperature,
> - 182F ( -119C).
> "

I see that you did your homework. Very good information that I found
useful. Thanks.

>
> The -119 C critical temperature mentioned is equal to the 154 K
> temperature you mentioned.
>
> Why not store it at -183 C ( 90 K ) at normal atmospheric
pressure?

I chose the higher temperature knowing I'd have to make a trade-off
in complexity of pressure vessel design because I:

1.) wanted to avoid changes in the pressure vessel properties at
very low temperatures - i.e. normally ductile materials may become
extremely brittle. Also, in space construction the task and methods
of joining materials that are destined for deep cryogenic
environments will be a difficult task and if IRC is still not a well
understood operating environment so it must also receive careful
study to guide the engineering principles;

2.) wanted to concentrate the refining efforts on construction of a
habitat, not pressure vessels; and

3.) by increasing the pressure, the volume of the gas is reduced.
Even storing the O2 at these high pressures, we'd still need immense
storage facilities.

I tried to find the optimal alternate strategy to storing gases in a
Habitat. I wanted a balance between complexity and resource usage.
So, to store it at a lower temperature will require even more
storage tanks than the scenario I'm using as a comparison. By my
reckoning, that moves away from an optimal solution.

>
> Why not store it at even lower temperature and even lower pressure?
>

Because the volume will increase dramatically. Look at those
expansion ratios I quoted. A lower expansion ratio means more
tankage and cryogenic machinary with less structural stress from
pressure and more materials and fabrication complexity from deep
cryogenic environment.

> The lower the temperature and pressure, the thinner the walls of
your LOX
> storage vessel can be.
>
> Ron
> ***********

Yes, you're correct. But how many more tanks will you need? Your
expansion ratio will not be near the 875:1 that applies to my
example.

That's why I came to the conclusion to vent O2 as a waste until the
Habitat passes as a minimal pressure vessel and use it to store the
gases. You neatly avoid cryogenic storage technology and building
numerous pressure vessels.

>
> "victoriatangoman"
> 10/23/02 12:24 AM
>
> > Store your gases in liquid form until you need them.
> >
> > Ron
> > ******
> >
> Yeah, that's the obvious solution until you look into the problem.
> The problems only become more severe with the larger habitats, so
I
> used the smallest to illustrate my point. Here's what I did using
> the Stanford Torus as an example.
>
> The Stanford Torus is designed to simulate 1 gravity at 1 rpm,
thus
> for it to have one gravity at the center of the cylindrical torus
> section (to give the greatest living area at precisely 1 gravity)
> the radius of the torus must be 954.81 meters. The torus section
> radius is 60.96 meters. (All figures derived from descriptions in
> Heppenheimer's "Colonies in Space.") The Hub radius is 65 meters.
> The six spokes are 7.5 meters in radius and 767.89 meters in
length.
>
> Thus, the total volume of the Stanford Torus is 72,060,179 m^3 and
> its surface area is 2,423,192 m^2.
>
> At 0.5 atmospheric pressure (50% O2,50% N2), if we're using the
> conventional wisdom of cryogenically storing the gases until we
> finish the Stanford Torus, then we need storage for 36,030,089,500
> liters at STP.
>
> O2 has a liquid to gas expansion rate of 875:1, is stored at 5,076
> kPa and at a temperature of 154.8 K.
>
> N2 has a liquid to gas expansion rate of 710:1, is stored at 3,394
> kPa and at a temperature of 126.3 K.
>
> Thus, the stored volume of liquid O2 is 41,177,245 liters and the
> stored volume of liquid N2 is 50,746,605 liters.
>
> To cryogenically store the LO2 in a single spherical pressure
vessel
> would require a radius of 21.42 meters, with a wall thickness of
> 31.5 cm.
>
> To cryogenically store the LN2 in a single spherical pressure
vessel
> would require a radius of 22.96 meters, with a wall thickness of
> 22.6 cm.
>
> For my pressure vessel calculations I'm using the properties of
AISI
> 1030 Steel, normalized 925C (1700F) and using a safety factor of
> 2x the Tensile Strength (Yield.) I chose steel because it is
easier
> and less expensive to refine than aluminum or titanium. Of course,
> other metals could be used and that would change the spcifics of
> this analysis, but I had to work with something so steel is it :)
>
> http://www.matweb.com/search/SpecificMaterial.asp?bassnum=M1030D
>
> Good luck on welding something that thick!
>
> Alternatively, in order to ease the welding tasks our space
workers
> will face, we can specify a steel thickness of 2.94 cm. This will
> allow a LO2 spherical pressure tank (subject only to longitudinal
> forces and thus more efficient than a cylindrical tank) to be 2
> meters in radius and a LN2 tank can be 3 meters in radius with the
> same steel.
>
> This corresponds to 1,228 LO2 pressure vessels and 449 LN2
pressure
> vessels.
>
> The total volume of steel used to construct these pressure vessels
> is 3,309 m^3. This is equivelent to covering the surface area of
the
> Stanford Torus with a skin 1.3 mm thick.
>
> My proposal is to use vacuum vapor deposition to create an
extremely
> thin pressure vessel. Using the Stanford Torus as an example,
vacuum
> depositing a skin 100 um thick, would take 242.32 m^3 of the same
> steel (using only 7.32% of the metal required for all of the
> cryogenic pressure vessels) and at that point the Stanford Torus
> could contain an atmosphere of 0.5659 kPa (or 0.0056 atm.) Thus we
> could pump in up to 403,537,002 liters at STP. That would
translate
> to 18,015,045 moles of O2.
>
> If we used the same steel to construct the Torus (I'm not sure
we'd
> need to use this high strength steel - we could probably do with a
> less demanding material because of lower internal pressure -
although
> we'd now have to factor in rotation stresses) we'd need to refine
> 5,098,877 Kg Ilmenite to extract 1,876,913 Kg Fe, combine it with
> 17,120 Kg Mn, 6,468 Kg C, 761 Kg P, and 951 Kg S, in order to
refine
> 1,902,212 Kg of AISI 1030 Steel.
>
> Processing that amount of ilmenite would have yielded 1,075,458 Kg
> O2, and 2,146,506 Kg TiO. The O2 would translate to 752,848,832
> liters at STP. More than our Habitat can take from a pressure
> perspective.
>
> So, the critical path once a refinery is in place might be to
first
> make some pressure vessels able to withstand 5,076 kPa. Make about
> 52 - 2m radius pressure vessels. Store the oxygen byproduct from
the
> Ilmenite reduction process. Use the iron to make steel. Vacuum
> deposit the steel to the Habitat framework to the above
> specifications. Then release the O2 from 27 pressure vessels into
> the habitat and use those pressure vessels to store LH2 (1,297
kPa),
> or LN2 that we're getting from somewhere, as well as solar gases
> that we're collecting from our refining.
>
> Alternatively, and the option I favor, vent the oxygen away as a
> waste product early in our construction phase and do away with the
> need to make those first pressure vessels. Afterall, we're
producing
> about twice as much O2 as we'll need per unit of steel.
>
> From this point forward, it just becomes a matter of adding more
> metal to the Torus and adding more atmospheric gas to the Habitat
so
> that the gas pressure never exceeds the ability of the Habitat
walls
> to contain it.
>
> We neatly do away with the need to build either complex and
massive
> pressure vessels or thousands of simpler vessels and their
cryogenic
> machinary and the necessity to power that machinery in order to
> maintain the cryogens.
>
> Now as I stated in my original message, I would appreciate
somebody
> checking my calculations because I'm not an engineer.
>
> But if my analysis holds true, then I say that the conventional
> wisdom of storing gases for later release is an unnecessary and
> complex step that can neatly be avoided.
>
> TangoMan
>
> > "victoriatangoman"
> > 10/22/02 02:12 PM
> >
> > I've been wondering where we're going to store all of the
> atmosphere
> > for a habitat while it's being built.
> >
> > It doesn't make sense to me to complete the structure of the
> habitat
> > and then go and refine material to extract the gases for the
> > habitat's atmosphere, all the while venting the gases from the
> > construction process.
> >
> > I got to thinking about how to build up an atmosphere in the
most
> > efficeint way and would like some feedback from members if they
> can
> > point out conceptual flaws and can provide engineering details.
> >
> > First off we make a very flimsy wire framework of the Habitat.
> Then
> > cover it with mylar. Then starting spraying metal on it via
vacuum
> > vapor depostion. Once we have a gas tight shell, with a wall
> > thickness of (this is where some expert help would be most
> > appreciated) half a millimeter, we start pumping our waste
oxygen
> > and other needed gases into the Habitat. The gas pressure of the
> > atmosphere should always be less than the structural strength of
> the
> > habitat shell.
> >
> > Meanwhile, we keep adding more thickness to the shell, thus
> allowing
> > more gas pressure to be held.
> >
> > Now for some Habitat designs the windows issue will not allow
this
> > approach, but the modified cylindrical design that I've already
> > outlined in this group does allow for this approach.
> >
> > So other than the windows issue, can anybody supply feedback on
> this
> > proposal.
> >
> > Thanks, TangoMan
>
Service.

> Why would you store LOX at such a high temperature as 154.8K ?
> The -119 C critical temperature mentioned is equal to the 154 K
> temperature you mentioned.
>
> Why not store it at -183 C ( 90 K ) at normal atmospheric
pressure?
>
> Why not store it at even lower temperature and even lower pressure?
>
> The lower the temperature and pressure, the thinner the walls of
your LOX
> storage vessel can be.
>
> Ron
> ***********

After this thread came to an end, I took your questions to heart and
rather than relying on the critical point and temperature data,
which were very easy to find, I started looking for temperature and
pressure data and graphs for cryogenic gas storage .

I did find the data after contacting some liquid gas companies.

If you're interested, I've placed the data in the Excel spreadsheet
I've uploaded to the files section.

TangoMan

Thanks for the information. I presume you mean sheet 'Sheet1' in
'TangoMan's Design Criteria for Space Station.xls'.

But I think that you are ultimately still concluding that we should store
large amounts LOX at 10 bar ( ~150 psi ) at 120 K. I just don't get
it: why do that? That makes your wall thicknesses so excessive.

Drop the temperature and pressure. Put a sun-shield in front of the
tank. LOX and liquid propane are "space-storable" propellants ---- they
require no active refrigeration at 1 bar in space. Your wall thicknesses
would go way down.

One can perform a search on "space storable"+propellant. Here are some
example hits.

Ref 1 for "space-storable": http://www.islandone.org/APC/Chemical/01.html:
"
OF2/C2H6 is also space storable, and has an Isp of 370 lbf-s/lbm. However, all things considered, C2H4 performs better as a fuel since it is denser and provides a higher Isp
"

Ref 2 for "space-storable":
http://quest.arc.nasa.gov/people/journals/space/boyd/primary06-25.html:
"
Lox is cryogenic, but nowhere near the degree that liquid hydrogen is. So
we have propellant combinations that we're studying that involve liquid
oxygen as the oxidizer and various hydrocarbons as a fuel that is
space-storable for long-duration missions, such as a mission to Mars, even
with the cryogenic lox.
"

Ref 3 for "space-storable":
http://www.aleph.se/Trans/Tech/Space/mars.html:
"
These were chosen because CH4/O2 is the highest performing space-storable
chemical propellant, and can be manufactured easily on either Earth, Mars,
or a carbonaceous asteroid.
"

Ron

"victoriatangoman victoriatangoman@... 01/02/03 03:22 PM

> Why would you store LOX at such a high temperature as 154.8K ?
> The -119 C critical temperature mentioned is equal to the 154 K
> temperature you mentioned.
>
> Why not store it at -183 C ( 90 K ) at normal atmospheric
pressure?
>
> Why not store it at even lower temperature and even lower pressure?
>
> The lower the temperature and pressure, the thinner the walls of
your LOX
> storage vessel can be.
>
> Ron
> ***********

After this thread came to an end, I took your questions to heart and
rather than relying on the critical point and temperature data,
which were very easy to find, I started looking for temperature and
pressure data and graphs for cryogenic gas storage .

I did find the data after contacting some liquid gas companies.

If you're interested, I've placed the data in the Excel spreadsheet
I've uploaded to the files section.

TangoMan

> Thanks for the information. I presume you mean sheet 'Sheet1' in
> 'TangoMan's Design Criteria for Space Station.xls'.
>
> But I think that you are ultimately still concluding that we
should store
> large amounts LOX at 10 bar ( ~150 psi ) at 120 K. I just
don't get
> it: why do that? That makes your wall thicknesses so excessive.
>
> Drop the temperature and pressure. Put a sun-shield in front of
the
> tank. LOX and liquid propane are "space-storable" propellants ---
- they
> require no active refrigeration at 1 bar in space. Your wall
thicknesses
> would go way down.
>

Your point is well made and I understand. I hope you're not taking
my observations from our last go 'round, and reaching your
conclusion that the wall thicknesses are excessive. I've conceded to
your argument. Using actual data for cryogenic gases, my
calculations are now more reasonable.

As for the sun shield, if the entire endeavor is as simple as your
statement indicates, then sure, no problem.

Here's why I favored a 120 K storage environment.

First I calculated the temperature in low earth orbit-cislunar space
using the Stefan-Boltzmann law for a black body in space:

S(sun) = xT^4W/m^2

1,360 = (5.67*10^-8W/(m^2K^4))T^4W/m^2

T = 394K

OK, that's kind of hot, but as you wrote all we have to do is keep
the sun from shining on the tanks and the temperature behind that
sunscreen will fall to any point above the 2.73 K microwave
background radiation.

Now I chose 120K for the following reasons:

1.) Steels and other metals start to lose some of their
specification properties at extremely low temperatures. I'm assuming
that the metal refinery in orbit won't be producing all sorts of
steels; rather there will be only a few steel specifications, and
those most likely won't be that complex. But, hey, they may very
well formulate steels for cryogenic use.

2.) I tried to find a temperature environment that would suit many
of the gases so that they could all be stored behind the same sun
shield. I thought that would make the orbital work environment a
little more efficient.

3.) If the tanks are fabricated to exist in an environment behind a
sun shield, then there is an engineering challenge to move the tank
so that no sunlight hits it. How long would it take for a tank to
rupture as the sun is shining on it? I thought better to over-
engineer a bit to a 120 K threshold so that the temperature could
rise to 120K before tank failure was immenent.

4.) With the temperature at 394K and the tanks engineered to 120K,
that means the sun shield has to radiate away 274 K/m^2. I haven't
looked into the issues of sun shield design but I wonder where does
that heat go? How much material and effort have to go into a fairly
large sun shield to protect the tanks of liquid gases? Now I know
that the dark side of the shield will have very low temperatures,
and I've seen comments that indicate the sun shield can be just a
sheet of mylar, but I haven't seen any explanations of how that
mylar radiates the heat. Maybe I'm missing something elementary.

5.) I thought that 120 K was a happy compromise with the O2 tank
having a wall thickness of 16 mm - or 5/8" That doesn't sound
onerous to me.

Feeling it's better to be safe than sorry in orbit, especially when
dealing with our precious and expensive gases. Where have I been too
cautious, or more likely, in error about my assumptions?

TangoMan

A shade can get you down to 30-35K. There's no need to store at 120K.

http://endo.sandia.gov/AIAA_MDOTC/sponsored/lillie_final_web.pdf
"
We allocated to thermal control the objective of passively cooling optics
to ~30 K
"

http://www.astro.utoronto.ca/~lilly/NGST/
"
NGST mission concept is for a large filled-aperture telescope (primary
mirror diameter of around 8m) located far from Earth (likely at the L2
Lagrange point). Shielded from the Sun and Earth by a large deployed
sun-shade, the entire telescope assembly will passively cool to about 35K
"

http://origins.jpl.nasa.gov/meetings/ulsoc/papers/labeyrie.pdf
"
... at cryogenic temperatures (30 degrees K achievable in space with an
umbrella)
"

Ron

"victoriatangoman victoriatangoman@... 01/03/03 03:18 PM

> Thanks for the information. I presume you mean sheet 'Sheet1' in
> 'TangoMan's Design Criteria for Space Station.xls'.
>
> But I think that you are ultimately still concluding that we
should store
> large amounts LOX at 10 bar ( ~150 psi ) at 120 K. I just
don't get
> it: why do that? That makes your wall thicknesses so excessive.
>
> Drop the temperature and pressure. Put a sun-shield in front of
the
> tank. LOX and liquid propane are "space-storable" propellants ---
- they
> require no active refrigeration at 1 bar in space. Your wall
thicknesses
> would go way down.
>

Your point is well made and I understand. I hope you're not taking
my observations from our last go 'round, and reaching your
conclusion that the wall thicknesses are excessive. I've conceded to
your argument. Using actual data for cryogenic gases, my
calculations are now more reasonable.

As for the sun shield, if the entire endeavor is as simple as your
statement indicates, then sure, no problem.

Here's why I favored a 120 K storage environment.

First I calculated the temperature in low earth orbit-cislunar space
using the Stefan-Boltzmann law for a black body in space:

S(sun) = xT^4W/m^2

1,360 = (5.67*10^-8W/(m^2K^4))T^4W/m^2

T = 394K

OK, that's kind of hot, but as you wrote all we have to do is keep
the sun from shining on the tanks and the temperature behind that
sunscreen will fall to any point above the 2.73 K microwave
background radiation.

Now I chose 120K for the following reasons:

1.) Steels and other metals start to lose some of their
specification properties at extremely low temperatures. I'm assuming
that the metal refinery in orbit won't be producing all sorts of
steels; rather there will be only a few steel specifications, and
those most likely won't be that complex. But, hey, they may very
well formulate steels for cryogenic use.

2.) I tried to find a temperature environment that would suit many
of the gases so that they could all be stored behind the same sun
shield. I thought that would make the orbital work environment a
little more efficient.

3.) If the tanks are fabricated to exist in an environment behind a
sun shield, then there is an engineering challenge to move the tank
so that no sunlight hits it. How long would it take for a tank to
rupture as the sun is shining on it? I thought better to over-
engineer a bit to a 120 K threshold so that the temperature could
rise to 120K before tank failure was immenent.

4.) With the temperature at 394K and the tanks engineered to 120K,
that means the sun shield has to radiate away 274 K/m^2. I haven't
looked into the issues of sun shield design but I wonder where does
that heat go? How much material and effort have to go into a fairly
large sun shield to protect the tanks of liquid gases? Now I know
that the dark side of the shield will have very low temperatures,
and I've seen comments that indicate the sun shield can be just a
sheet of mylar, but I haven't seen any explanations of how that
mylar radiates the heat. Maybe I'm missing something elementary.

5.) I thought that 120 K was a happy compromise with the O2 tank
having a wall thickness of 16 mm - or 5/8" That doesn't sound
onerous to me.

Feeling it's better to be safe than sorry in orbit, especially when
dealing with our precious and expensive gases. Where have I been too
cautious, or more likely, in error about my assumptions?

TangoMan

Thanks for the LOX vapor pressure graph, TangoMan.

Heh, heh --- take a look at the vapor pressure at 35K, and tell me what
kind of wall thickness you need !!

Ron

rmenich@...
01/03/03 03:28 PM

A shade can get you down to 30-35K. There's no need to store at 120K.

http://endo.sandia.gov/AIAA_MDOTC/sponsored/lillie_final_web.pdf
"
We allocated to thermal control the objective of passively cooling optics
to ~30 K
"

http://www.astro.utoronto.ca/~lilly/NGST/
"
NGST mission concept is for a large filled-aperture telescope (primary
mirror diameter of around 8m) located far from Earth (likely at the L2
Lagrange point). Shielded from the Sun and Earth by a large deployed
sun-shade, the entire telescope assembly will passively cool to about 35K
"

http://origins.jpl.nasa.gov/meetings/ulsoc/papers/labeyrie.pdf
"
... at cryogenic temperatures (30 degrees K achievable in space with an
umbrella)
"

Ron

"victoriatangoman victoriatangoman@... 01/03/03 03:18 PM

> Thanks for the information. I presume you mean sheet 'Sheet1' in
> 'TangoMan's Design Criteria for Space Station.xls'.
>
> But I think that you are ultimately still concluding that we
should store
> large amounts LOX at 10 bar ( ~150 psi ) at 120 K. I just
don't get
> it: why do that? That makes your wall thicknesses so excessive.
>
> Drop the temperature and pressure. Put a sun-shield in front of
the
> tank. LOX and liquid propane are "space-storable" propellants ---
- they
> require no active refrigeration at 1 bar in space. Your wall
thicknesses
> would go way down.
>

Your point is well made and I understand. I hope you're not taking
my observations from our last go 'round, and reaching your
conclusion that the wall thicknesses are excessive. I've conceded to
your argument. Using actual data for cryogenic gases, my
calculations are now more reasonable.

As for the sun shield, if the entire endeavor is as simple as your
statement indicates, then sure, no problem.

Here's why I favored a 120 K storage environment.

First I calculated the temperature in low earth orbit-cislunar space
using the Stefan-Boltzmann law for a black body in space:

S(sun) = xT^4W/m^2

1,360 = (5.67*10^-8W/(m^2K^4))T^4W/m^2

T = 394K

OK, that's kind of hot, but as you wrote all we have to do is keep
the sun from shining on the tanks and the temperature behind that
sunscreen will fall to any point above the 2.73 K microwave
background radiation.

Now I chose 120K for the following reasons:

1.) Steels and other metals start to lose some of their
specification properties at extremely low temperatures. I'm assuming
that the metal refinery in orbit won't be producing all sorts of
steels; rather there will be only a few steel specifications, and
those most likely won't be that complex. But, hey, they may very
well formulate steels for cryogenic use.

2.) I tried to find a temperature environment that would suit many
of the gases so that they could all be stored behind the same sun
shield. I thought that would make the orbital work environment a
little more efficient.

3.) If the tanks are fabricated to exist in an environment behind a
sun shield, then there is an engineering challenge to move the tank
so that no sunlight hits it. How long would it take for a tank to
rupture as the sun is shining on it? I thought better to over-
engineer a bit to a 120 K threshold so that the temperature could
rise to 120K before tank failure was immenent.

4.) With the temperature at 394K and the tanks engineered to 120K,
that means the sun shield has to radiate away 274 K/m^2. I haven't
looked into the issues of sun shield design but I wonder where does
that heat go? How much material and effort have to go into a fairly
large sun shield to protect the tanks of liquid gases? Now I know
that the dark side of the shield will have very low temperatures,
and I've seen comments that indicate the sun shield can be just a
sheet of mylar, but I haven't seen any explanations of how that
mylar radiates the heat. Maybe I'm missing something elementary.

5.) I thought that 120 K was a happy compromise with the O2 tank
having a wall thickness of 16 mm - or 5/8" That doesn't sound
onerous to me.

Feeling it's better to be safe than sorry in orbit, especially when
dealing with our precious and expensive gases. Where have I been too
cautious, or more likely, in error about my assumptions?

TangoMan