In article ,
"Mike Combs" wrote:

and the radiator mass needed
to reject all that extra heat,

Undeniably true. But I think one thing this issue hinges on is which is
more expensive per sq meter: simple panels of aluminum tubing, or panels of
PV arrays?

Well, it's the total cost that matters, not the cost per square meter.
Unfortunately that probably requires a more detailed analysis than we
can do here.

as well as severe constraints it imposes
on overall colony geometry, which can have serious impacts on your mass
budget -- for example, it would be hard-to-impossible to make much use
of natural light in a multi-deck design like Kalpana One.

I would agree, but have a personal dislike for multi-deck designs. They
pursue a different design goal, which is "provide as efficiently as possible
living area for X people". I still have a fondness for O'Neill's original
design goal, which was "recreate as closely as possible the most attractive
parts of the Earth's surface".

Yes, this is a very insightful point. To put it another way, O'Neill
was addressing the concern, "People won't want to live in a can." He
pretty much took it as assumed that people could afford to do so if they
wanted to. In my efforts, I'm generally trying to address the concern,
"people can't afford to build a can they can live in." I take it as
assumed that people will want to if they can afford it.

Of course, O'Neill didn't wastefully make his designs expensive, and I
don't wastefully make mine unattractive. But emphasizing one or the
other does lead to some different design decisions.

But getting back to the multi-deck designs, they don't necessarily have
to be less natural than, say, a torus. For example, I've toyed with
(but not yet studied in detail) disk geometries that would have a true
image of the sky on each deck (the image is actually focussed through
long windows on the side wall).

I also think that we might actually be better off with an entirely
artificial sky -- that is, a smooth white surface with a series of
high-power, high-resolution projectors trained on it, like at a
planetarium. This could show an Earthlike sky during the day (including
sunrises and sunsets), and at night, show you the real outside view.
Assuming the sky is sufficiently far away (say, 50 m or more), and the
projection is of sufficiently high quality, this would look as good or
better than real windows.

But I know, our gut tells us that this is a "fake" while windows and
mirrors are "real," and emotionally this is a significant difference.
It's hard to tell which one most people would prefer -- a realistic but
very unnatural sky, or an artificial but very natural-looking one. Some
data points can be gathered from places like the Blue Bijou in
Disneyland, where you can eat under a twilight Louisiana sky, even at
high noon. People know it's fake, but (in my experience) find it quite
pleasant -- and that's a roof only 3 m over your head instead of 50. In
fact, by the time I'm done with lunch and emerge into the real sunlight,
I always feel a bit of a shock, as I had subconsciously forgotten that
it wasn't actually dusk.

Best,
- Joe