Gas Storage in Orbit

> 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.