Artificial lighting, huh?

On Feb 12, 2008, at 10:24 AM, Lucio de Souza Coelho wrote:
> 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.
>
This is true, but it doesn't give you as much area at the maximum
(and presumably most desirable) G-level. It's a trade-off, of
course, but I like having as much living area at full G as we can
reasonably get. The upper decks can be used for other purposes, like
agriculture, recreation, training, mostly-automated factories,
retirement communities, etc... all important functions, leaving even
more space available on the lower deck for most people to live and
work at whatever we decide is the optimal level of gravity.

> 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.

Maybe, but I doubt it -- people smarter than me have looked at heat
management, and concluded that even something as volume-inefficient
as a torus requires big radiators.

The basic point about heat rejection is a good one, though, and this
is the strongest argument for using artificial light at least in the
crop areas: you can tune the spectrum of that light to be most
efficiently absorbed by plants, which otherwise are very inefficient
and generate a lot of waste heat.
> 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.
>
Maybe. That's certainly worth looking into in more detail. There
are many conflicting constraints on the design of something like a
space habitat -- all the more reason not to add another big one, i.e.
a requirement for natural sunlight.

Best,
- Joe