Some Questions

--- Chris Smyth wrote:

> Hi Space Settlers,
> I'm new to the group but I've followed the
> discussion about colonies
> in space since the days of the L5 Society. I have a
> number of
> questions, the answers to which continue to elude
> me. Here goes
> (just two questions to start):
> 1)I had great hopes for the ill-fated Biosphere 2
> project in Arizona.
> I understand that they're in virtual bankruptcy at
> this time and are
> hoping that the University of Arizona will rescue
> them. It may well be
> that the project lacked the proper engineering and
> financial
> commitment to make it a viable space colony test
> bed. Nonetheless,
> I've always thought that a populated and functional
> earth-bound full
> scale space colony prototype would be the most
> prudent way to test the
> many assumptions and conjectures about how such a
> colony would work
> mechanically and socially. Any thoughts on this
> subject?

The Biosphere II project was a great idea. I think
the experiment needs to be replicated, though with
some modifications. They actually did manage to
survive for a couple of years inside that environment,
recycling all their air and water. It was only the
curing concrete absorbing oxygen that forced them to
inject some oxygen into the system. I'd consider the
Biosphere II project a success, even with that
injection of O2 into the system.

So, what would I do differently? First of all, I'd
have the experiment repeated in a windowless facility.
That way, all the energy usage could be precisely
metered, and it would avoid having that large "lung"
to handle the pressure differences due to the
day/night cycle. It is nice having those windows and
lowering the energy costs, but until it is precisely
known what the energy requirements are, one cannot
design a space colony - you'd either end up with too
much energy getting into the system (and hence heat
problems) or too little energy.

Secondly, I would not try to replicate every single
ecosystem on earth in one experiment. I would stick
with just a few species, and just a few environments -
just enough to recycle the air and water in the
system. After all, for the first space colony, it is
unlikely that there would be more than a couple of
dozen species at most.

> 2)The question of shielding is one of the key issues
> in the design
> criteria for proposed space colonies (of any type).
> One popular
> suggestion is to use lunar regolith to serve as
> shielding. I wonder if
> a sufficient thickness of water ice applied to the
> exterior of the
> structure and thermally protected both internally
> and externally would
> make a better shield (a so-called double hull
> construction).

Any shield constructed out of low atomic weight atoms
would be good. If one goes with water or just plain
H2 gas, then the shield needs to be thicker than if
one went with something like paraffin or regolith.
One thing that needs to be avoided is the use of heavy
elements like lead, as although they will stop the
primary radiation they would generate lethal secondary
radiation.

> I realize
> that this would add greatly to the mass of the
> structure and obtaining
> the vast quantities of water would be problematic
> (to say the least).

The mass would probably be the same no matter what the
material used. IIRC the mass needs to be about 10000
kg per square meter of surface area. So a denser
material would just mean a thinner shell, and a
lighter material a thicker shell.

> Still, I wonder if, in the long run, -200 degree
> water ice would
> provide a structural stiffness, radiation absorbing
> capability, and
> micrometeorite shield superior to other materials.
> Your comments on this?
>

Most likely any shell/hull would have several
different materials arranged in layers, each with its
own properties. For instance, you might have a layer
of aluminum a few atoms thick on the outside, followed
by a layer of kevlar, then maybe a layer of paraffin
wax, then a layer of polyethelene, then a layer of
water ice, a layer of polyethelene, etc etc etc. The
various properties of each layer would each contribute
something to the hull/shell - reflectivity from the
aluminum, micrometeorite impact absorption from the
kevlar, radiation shielding from the paraffin and
water, holding the air pressure inside with the
polyethelene, and so on.

Ed