Island A

Over the weekend, I made some rough calculations for the pressure vessel that we
would need, for the outer hull of Island A. I assumed an Iron pressure vessel.
This would be constructed from lunar Ilmenite derived Iron, that was processed
in a small initial facility, within a shuttle external tank. Depending upon how
the Iron is treated, a wide range of material properties are possible. So I
assumed that we would be dealing with a soft, pure iron, purified using the
Carbonyl process. In this case, the tensile strength of the soft iron would be
about 500MN/m2, and its properties would closely resemble those of mild steel. I
assumed a safety factor of 8. This probably is not excessive, given that the
pressure vessel is all that stands between the crew and oblivion. I also assumed
that the facility would be pressurised to 1/2 atm. The thin walled pressure
vessel equation, yields a wall thickness of 0.8cm. Given that the density of
pure iron is 7900Kg/m3, and the radius of our pressure vessel is 20m, the mass
of the vessel comes out to be 317.677 tonnes. In order to produce this much
Iron, we would need to reduce 862 tonnes of Ilmenite, into Fe, TiO2 and O2. The
pressure vessel itself could be formed using vacuum deposition, so the initial
external tank facility would only need to reduce and purify the the iron. This
could be achieved by hitting lunar Mare soil, with hot carbon monoxide and
passing the resulting vapour through a fractionating column. The pure iron
carbonyl, will condense out at its own specific temperature. It could then be
decomposed into carbon monoxide and pure iron. The depleted lunar soil residue
from the process, can be used as a shielding material.