Island A

Rotation seems to me to be a nice-to-have rather than a minimal requirement
for an initial orbital workshop.

Ron Menich

hollroa@...
Please respond to
ssi_list

Given the enormous start-up costs of the O'neill vision, it seems unlikely
that
Island one will be the first colony to be built. I have been looking at a
different approach. My idea centres around placing a workshop in L5, that
is
specifically designed to construct SPS modules. For lack of a better name,
I
will call this island A. The basic element of the workshop is an iron
sphere,
approximately 40 metres in diameter. The sphere rotates twice per minute.
The
sphere is divided into cylindrical floors. The floors are divided into crew
quarters, manufacturing workshops, ore processing facilities, a hydroponics
bay
and a satellite assembly hall. The satellite assembly hall is a cylinder
that
lies along the axis of rotation. At each end of this assembly hall, there
lies
an airlock. These are used both during the launch of finished SPS modules
and
for the docking of supply ships, ore carrying ships and various other
spacecraft. The assembly hall is 10 metres in diameter and 40 metres long.
Lunar ores are delivered to the facility through its axial airlocks.
The
ores are then taken to a small workshop, where they are processed into
manufacturing materials such as Calcium, Titanium, Iron, Aluminium,
Magnesium,
Silicon, Rutile, Ilmenite, e.t.c. These materials are then used in various
other
small workshops for the manufacture SPS parts.
The assembly hall is far too small to house a full scale SPS satellite.
For
this reason it may be easier to produce the SPS in modules and assemble
them
tele-robotically outside of the habitat. If a 20MWe SPS can be manufactured
and
assembled in one week, then a 1000MWe SPS could be built in 1 year. If we
assume
a 40 year life time, and a 0.1$/KWhr rate of return, the SPS will be
produce
$35billion through out its life time. This amount would certainly exceed
the
cost of producing it.

The facility itself could be produced almost entirely from lunar derived
iron. Out of all lunar derived metals, iron is the easiest to produce. It
is a
by-product of oxygen production. The entire facility could be formed by
vacuum
deposition of iron, onto a thin shell of polymer. The Polymer shell would
need
to be brought up from Earth, but would only weigh a few hundred kilos. The
interior cylindrical floors and assembly hall would be constructed in the
similar way. The oxygen that is liberated from the iron, will be useful
when the
time comes for habitat pressurisation. The entire habitat might weigh in at
200-300 tonnes, minus the furnishings. Most of this mass will be lunar
materials.

The construction crew could be housed within a converted shuttle
external
tank, during construction. This would be fitted out in LEO, and lifted to
L5
using low thrust ion engines. The crew housing, would probably resemble a
Zubrin
style Mars hab. The external tank could be shipped back to LEO and fitted
out as
a ferry, after construction of the workshop is completed. A solar electric
propelled ferry, would be extremely useful for shipping people and
materials
between low-Earth orbit and L5.

Despite its small size, island A will require a relatively large amount of
shielding. If we assume that 250g/cm2 of shielding (about 1/4 of what we
get on
Earth) is an adequate amount, roughly 12,000 tonnes of shielding would be
required. A lunar mass driver, equipped with a 1Mwe nuclear power source,
would
deliver this amount of shielding to L2 in about 1 year.

Tony