Re: coriolis force and air currents in an O'Neil colony

On Sep 19, 1:49 pm, Alfred Montestruc <montest...@xxxxxxxxx> wrote:

I'd politely suggest there might be other goals for
the design than simply a minimal cost, maximum safety one (again,
reference O'Neil's actual work)...

Other goals, OK but by way of introduction I work as a marine engineer
on offshore platforms and rigs, that has the similar situation of a
very harsh dangerous environment that is expensive as all hell to
operate in.

But it's a very *very* different situation in terms of goals. In your
setting, the goal is to get a very small number of highly train,
critically selected people to perform a very specific task, and
*that's it*. Again, this was not O'Neil's goal. It seems a little
silly to state the design is unreasonable, when you don't know what
the design goals are.

Out of curiosity, have you read O'Neil's actual papers on
the subject?

No. Do you know where I can download them?

No I don't. Many reasonable university libraries should have access to
them (IMS, I got them through interlibrary loan while an undergrad).
Again, realizing the constraints and goals of the original project
might be a reasonable starting point before commenting about how
unrealistic the original design was (note, for instance, Isaac's
comments about the state of PV arrays, or the fact that the original
design limited itself to very simple material and electronic
technology... still not a bad thing to consider when planning a
"robust" design).

But you get 100% of the IR associated with sunlight, while if I use a
solar collector and make electricity then use the lights that are of
the right spectra I bet I will have less of an issue that you will,
and produce more crop for the same amount of solar power as I am
converting IR and other freq to useful freq.

OK, that sounds like a good statement. Let's work some numbers.

To grow 1 m^2 of crops under a glass wall will take 1 m^2 of ground
and 1 m^2 of glass, and ultimate requires dissipating about 1400 W (a
very small fraction of which ends up as stored energy in plants... but
even *that* eventually comes out as heat when you eat it :) ). This is
a rather nicely scalable system too, just add more room. The perhaps
downside is that you have to dissipate 1400 W from a surface of
something like 2 m^2 (the front and the back of the flatish "field
module"), and indeed much of the incident energy that you ultimately
have to reject as heat isn't used by the plants anyway

Artificially illuminating a crop takes a couple of steps. You assume
the grow-lighted plants need the same level of illumination as the
"natural" plants above, *but only in the narrow range of spectrum they
need*, which you mention is around 8% of the total energy. So if
that's the case, you need to supply 1 m^2 of plant with just 112 W of
radiant energy in the right region of the spectrum. The luminous
efficiency of an incandescent light is around 2%... in other words,
for every 100 W of energy you put in, you get about 2 W of radiant
energy out in the visual range. The page you pointed to implies a
metal halide bulb is about 7 times as efficient as an incandescent in
the range of interest, so at a rough guess for every 100 W in you get
14 W out - an efficiency of 14% in the range of interest (just because
they're amazingly better than incandescents doesn't make them
amazingly efficient relative to the energy you're putting in). Assume
a PV array efficiency of 30% (a bit on the high side... especially
given how a PV array degrades with time and temperature, relative to a
silica window). So to get that 112 W of energy in the right range of
the spectrum, I need to put in 800 W of electrical power (due to the
losses in electrical to light in the MH florescent bulbs), and to get
that 800 W of electrical power I need to have the PV arrays intercept
2670 W of solar energy. That will require about 1.9 meters of
collecting surface. Optimistically.

So, surface-for-surface, using high-efficiency grow-lamps driven from
high-efficiency PF arrays requires roughly twice the collecting area.
And incidentally, that whole area is collecting heat as well (you may
be doing it on the PV array instead of the bulk habitat, but it's
still heat to be dissipated... and actually PV array drop efficiency
with increasing temperature.

When you have light in the form you need, you use that. Capturing it,
converting it twice, to distribute to multiple-floor greenhouse isn't
a very good system unless you can get the losses down much lower than
currently seems possible. Grow-lights are great options when you don't
have sunlight - where you do have sunlight, you use it instead.

Not to mention the not so minor issue of glass panes with air pressure
on one side and vacuum on the other, vs a ductile material like steel
or aluminum.

Again, you might want to look at what O'Neil actually worked through,
and how, and how "primitive" a technology he did it with, before
maintaining it's a bad idea...

--
Brian Davis

.

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