Gas Storage in Orbit

> 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