L5 satellite workshops.

>>>I'm not sure about the Iron, as to make it into steel you need
Carbon. If we decide to use Lunar materials - which I would suggest
initially because of proximity - there appears to be a lack of carbon
there. In the NASA AMES studies the metal used was Aluminium. Could
the Iron be used in the shield as structural support (the brittleness
may not matter if the Iron is made massive enough as in early bridge-
building and high mass is desirable in the shielding)? In a dumbell
style habitat it may be advantageous to spin the shielding with the
habitat as the geometry would mean a saving in weight if the shield
is built-in rather than separate. A few rough calculations indicate
that a fully shielded habitat of this nature could be built at around
100,000 tonnes or less if the shielding is minimal (i.e. for short-
term workers rather than long-term residents).>>>

The production of Aluminium is quite a power hungry process. It also requires
carbon electrodes. As you stated earlier, carbon is rare in lunar material. On
Earth, about 20KWhrs of electric power are required to produce 1Kg of Aluminium.
In addition to which, you don't have to recycle the carbon on Earth, and high
quality Bauxite ore is available. My guess is that Aluminium will be saved for
applications where its high electrical conductivity put a premium on its use.
Iron, on the other hand, is likely to be an abundant by-product of oxygen
production processes.

The idea of rotating the shielding along with the workshop, is an interesting
one. When one considers that pressurising a pressure vessel to standard
atmospheric pressure, is equivalent to 10 tonnes of Force/square metre, rotation
a shield at 1g with 2.5 tonnes/m2 of shielding on it, would not be a fundamental
problem. So I would guess that even slightly impure iron, could be used to
construct loaded members, within the rotating shield. But, we may want to
consider keeping the revs down. NASA studies suggested that high rates of
rotation caused dizziness & nausea. Rotating the hab to 1/6th or 1/3rd g's may
be easier from a construction point of view as well. Rotating the shielding,
would also allow us the freedom of direct wiring between the inner hab
workshops, and the outer surface of the shielding. This makes the installation
of solar panels on the outer surface of the shield, relatively easy. A dozen or
so panels, 10 by 50 metres each, placed along the circumference of the sphere,
would be able to produce 1 MWe of continuous power. These high power levels
would be essential for magma electrolysis, machining of parts, re-cycling of
scarce materials, the production of Aluminium and Titanium and high data
transmission rates during communications with Earth. It may turn out that is
large amounts of aluminium are required, 1Mwe of continuous power won't be
enough.