Robert J. Chassell wrote:
> Presuming the end caps are mostly low-conductive stone or regolith,
> the major temperature determiner for the end caps should be, I think,
> the air, although indirect light will have an effect.
Erik Reuter <[EMAIL PROTECTED]> responded
I think that would be difficult. Heat conduction between air and a
surface is usually very small compared to heat conduction by a solid,
even a "low conductivity" solid. For example, just a few feet (say,
2m) below ground on earth, the temperature can be quite different than
the air temperature.
Hmmm.... you are right that the temperature is often more or less
constant 2 meters or so underground. However, in my understanding,
dirt and rock are very good insulators, and that heat flows slowly
through them.
What is the heat conductivity of dirt, rock, and nickle-iron? Does
anyone one know?
However, earth insulation is not perfect: In Alaska, I have seen an
airport runway being constructed by digging a bit, putting down mats
of *foam insulation* and then putting gravel over the mats. The
purpose of the foam insulation is to keep the permafrost from melting
in the summer.
Would a spinning space habitat need a layer of insulation below its
rock and regolith, and above its nickle-iron hull? If so, could you
make a good enough insulation by melting rock from an asteroid and
filling it with bubbles of some gas, so it is like vermiculite?
For one thing, the air at the surface near the "equator" (if the
endcaps are the north and south poles) will be warmer than the air
on the axis.
I think it is misleading to speak of them, even metaphorically, as the
`north and south poles' since people think of the poles of earth as
being cold. Only if the end caps are actually colder than the
`surface' (i.e., the rim) does the metaphor work. Or are you meaning
colder in the sense that the parts of the end caps that are closer to
the axis take their surface temperatures from the air at that distance
from the central axis, and those temperatures are colder than the
`surface' (i.e., rim) temperature?
However, the metaphor is obvious and easy; I myself would use it.
(Right hand rule for naming; if you look at a pole of a spinning habit
from outside, if it is spinning counter-clockwise, then that is the
North pole, like on Earth.)
A spinning space habitat as I described it does not have regions with
more slanting sun than other regions. Perhaps the builders of a
habitat would design the central cone to reflect more or less light
over certain regions .... that is an interesting idea.
What are the weather implications of having a region with less light
input than another?
Due to endcap effect, the temperature will also vary along the
length of the habitat.
Is that really the case? Isn't that a question to be determined? I
would expect the opposite: that with sufficiently good insulation,
the surface of the end caps would come to the same temperature as the
air fairly quickly and would neither contribute nor take much heat
from the air.
By the way, from personal experience I can tell you that as a general
rule on a sunny day, air tends to rise over fields and sink over
forests. The top of the `turbulence' layer is at the top of any
clouds that form, if they form. That is to say, a parcel of air does
not rise any further. (This is for a day with a normal lapse rate;
when you have `flat', stratus clouds or an inversion, the
temperature/dew point distribution differs.)
Pleasant, `fair weather' clouds are often no more than 1000 - 2500
feet or 300 - 750 meters thick. So it is helpful to predict the base
of the clouds in a spinning space habitat.
This means that if (`nice') clouds form 4000 ft or 1.2 km above the
surface of the earth, then their tops are likely to be no more than
5000 to 6500 ft or 1.5 to 2 km above the surface.
On earth, with cloud bases at 4000 ft or 1.2 km, you would figure that
the relative humidity at the surface was just a bit more than 50%.
--
Robert J. Chassell Rattlesnake Enterprises
http://www.rattlesnake.com GnuPG Key ID: 004B4AC8
http://www.teak.cc [EMAIL PROTECTED]
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