Artificial lighting, huh?

On Feb 12, 2008 1:06 PM, Joe Strout wrote:
(...)
> Oh goodness, no, this isn't an issue of materials, it's an issue of
> geometry. For example, the most sensible design for a colony (IMHO)
> is a multi-deck cylinder; you get dramatically more living/working
> space (albiet at lower G in some places), and most of it doesn't need
> any pressure vessel or radiation shielding at all -- it gets that for
> free from the outermost deck.
(...)

I have thought about that too, and I would correct slightly saying
that the most "economic" design is a multi-deck *sphere*: in that case
you would minimize the area of pressure hull/shielding relatively to
the (fully used) internal volume.

HOWEVER, this design has another problem that may increase cost: waste
heat generation. In a single-deck design, the amount of heat generated
is directly proportional to the external surface of the habitat, and I
suppose that there could be a design using the external hull itself as
a heat radiator. In a multi-deck habitat, however, you have the same
"problem" of a planet: for a given habitat radius r, the surface area
of the habitat grows with the square of r (r^2), but the ammount of
volume generating waste heat grows with the *cube* or r (r^3). (For
that reason big planetary bodies tend to overheat inside - because
there is too little surface for too much heat-generating volume - and
have molten cores, as in the case of Earth, while small ones, like the
Moon, tend to cool down to the core.) In the case of a multi-deck
habitat, the tendency would be for the internal volume to overheat
enormously, and so a disproportionately big heat radiation system
would be needed outside the sphere. Depending on the cost of that huge
"tree" of heat radiators that your multi-deck habitat will certainly
need, maybe the economy that you get with the pressure hull and the
radiation shielding would be nullified.

Of course that implies that there is an "optimal radius" for a
multi-deck habitat where the extra cost of radiators balances the
economy in the hull/shield, but I have no idea of what figure would
that optimal radius be. 8-P