Artificial Biospheres In Space

--- In spacesettlers@yahoogroups.com, "babbler36"
> --- In spacesettlers@yahoogroups.com, "ANTIcarrot"
> wrote:
> > > From: Gturner6PPC@y... [mailto:Gturner6PPC@y...]
> >
> > > The optical fiber approach becomes dreadfully expensive very
> > > quickly. Just illuminating a 100 by 100 meter area could
result
> in
> > > a cable that costs $2.4 million dollars a meter, and that's a
> pretty
> > > conservative estimate.
> >
> > Presuming this refers to using lots of little optical fibres?
Why
> not just use one big one? It's not like it'll have to be flexible
> after it's installed.
>
> Why do we have to use opitical fibres? I am sure we can use some
> other material for our purposes.

Light pipes would be a far better alternative, but I don't have good
design data on them. And alternate would be to reflect the rays
through a small window, as when you shine light through a convex
lens (actually use a mirror)through a tiny hole and then onto a
large screen.

> > > Using solar cells and the new argon sulfur sunlight bulbs
would
> > > probably come in at a much lower cost than this, and don't
> require
> > > precision assembly in a vacuum environment. In the near term
> this
> > > might be a much easier option to adopt.
> >
> > Very true and very practical, with just one draw-back: You won't
be
> able to see the stars at night.
>
> It would not work with plants; plants require alot of energy. The
> entire electricial power output of Earth would only be able to
light
> up Rhode Island.

But wasn't one of the justifications of going into space to harness
the limitless energy of the sun? Our current solar panels are
already 20 to 30% efficient, and some of the new lighting
technologies are running around 70%. We need about 1000 watts per
sqsuare meter, whether from direct solar or a lamp that matches the
solar spectrum. The bulbs already can spike on the particular
wavelengths plants rely on for photosynthesis, which could help drop
the heat load.

Given a mirror and window design, I'd estimate
90% reflectivity for the Mylar
98% transmission for MgF2 anti-reflection coated windows, per
surface (total of 96%)
69% transmission though 2.4" of BK7 optical glass (1 meter window
with safety factor of 4).
95% glass area vs. frame (1 meter window, 1" wide frame)
57% transmission, which gives a mirror area 1.75 times larger than
the final illumination area.

The collection area for electric (at 30% cell eff. and 70% lamp
efficiency) is 21%, so the solar panels would be 4.76 times larger
than the illuminated area, or 2.72 times larger than the mirrors,
but their exact geometry is no longer linked to the station layout.
Concentrating collectors and thermal engines might prove more
efficient, or the predicted increases in the efficiency of the lamps
(targeted to reach 80%) and solar cells (to possibly hit 40%) would
only need 1.8 times more collection area than the mirror option. As
an added bonus geometry becomes irrelevant, as does percentage
completion of the station. As you add finish more panels you add
more grow lights.

I'd budget about 100 kW per person (from either direct sunlight or
electrical) based on 1000W delivered/square meter and 100 square
meters - a safety factor of about 4 or 5). That's burning the
lights 24/7, but on a more natural 50% cycle it would cover 200
square meters per person.

The other point is that you're going to have all the electric grid
anyway for indoor lighting, night lighting, and massive and energy
intensive technological production of materials, such as refining
ores, making glass, and rolling steel, titanium, and aluminum for
the construction of the next colony, plus the production of more
solar arrays for other projects.

I don't know if I'd recommend the electric option as the long term
solution, but as an interim measure it has a lot of merit, since
it's just off the shelf technology that allows you to scale an first
generation station to any geometry you want.