I can't seem to find a table of data on how quickly the lunar
surface temperature flucuates. Does the temp go from -140c just
before dawn to 120C an hour after sunrise? Is it hottest at noon?
How quickly does the temperature drop after sunset? Is it coldest
before the dawn?
When the temperature on Earth is being reported, it is usually the air
temperature measured by a thermometer in an air stream in the shade. I
hate to seem academic, but one must define their terms. There is no air
(atmosphere) on the Moon, so what object's temperature are you asking about?
In the shade, for example, in the bottoms of craters at the poles where the
Sun never shines, the temperature is probably below 40 K (- 230 or so C). A
meter under the surface at the equator, the temperature is nearly constant
at about - 50 C. The temperature of engineered objects on the Moon would be
very much like the same objects on orbit, hot in the Sun and cold in the
shade, but how hot and how cold would depend on how much heat was being
conducted or convected to the object from elsewhere. The surface of a
balloon with a little gas in it would be hot on the Sun side, cold on the
shade side, and the gas would carry heat between the two. How much heat
would be transported would depend on the gas pressure, composition,
convection and so on. A solar day on Earth is 24 hours, but on the Moon it
is 709 hours or so. During this time, the temperature on small "isolated"
surface grains of regolith range from about 100 K to 400 K or so. A large
rock with good internal thermal conductivity would vary a lot less. One
can't say with out more information. Hope this helps. Sincerely, Jay
Huebner
Yes Jay, your response helped quite a bit. While I was aware of the
facts you mentioned I erred in not being specific about my question.
Sloppy on my part.
objects. The first would be the actual lunar mining habitat. It
would be radiating heat, I'm thnking that ISRU such as lunar
concrete is making a lot of sense. How much of a thermal shock will
the structure go through? That depends on how much is buried, how
much surface area radiates, the thickness of the concrete, how much
of the concrete is a heatsink, and a host of other factors, but what
I think is an important issue is the rate of temperature change.
After sunrise or sunset does the temperature change gradually or is
is like a quenching process where a piece of hot metal is dipped in
cold water. So, implicit in my question, is that the temperature is
referring to the temperature of the lunar surface and the building
structure.
The second class of object is what I'm most concerned about because
they would be more fragile than a building envelope, and this class
of objects would the the base support equipment that is exposed on
the lunar surface. Objects such as heliostats, their support
framework, stationary mining equipment, and mining equipment that is
operated during the night. A possible outcome of this consideration
is whether it is necessary or economically feasible to design mobile
mining equipment which is optimized to work in a specific
temperature range, so that one set of equipment can handle the
thermal environment of the lunar day and another set is engineered
or the lunar night. I don't presume that one piece of complicated
machinary can operate over a temperature range of 260C. Further, if
it can, it may not be able to take a drastic thermal change, so
perhaps a strategy of bringing the equipment into a buidling
envelope and while the temperature is rapidly changing on the lunar
surface, the equipment in the shop is changing at a lower rate and
eventually brought into equilibrium with the temperature of the
lunar surface. That's why I'm curious about how suddenly the
temperature changes on the surface as a factor of the sun's position
over the course of a lunar day.
As for the stationary equipment which must stay on the surface and
survive the thermal change, the question for me then becomes can the
equipment be engineered to survive the thermal shock or do we have
to mitigate the thermal change to a lower rate.
So, in the end, that's the discussion I'm throwing out. If anyone
has some hard data on the rate of temperature change on the lunar
surface, that would be most helpful, as I've been unable to locate
it.
> When the temperature on Earth is being reported, it is usually the
air
> temperature measured by a thermometer in an air stream in the
shade. I
> hate to seem academic, but one must define their terms. There is
no air
> (atmosphere) on the Moon, so what object's temperature are you
asking about?
> In the shade, for example, in the bottoms of craters at the poles
where the
> Sun never shines, the temperature is probably below 40 K (- 230 or
so C). A
> meter under the surface at the equator, the temperature is nearly
constant
> at about - 50 C. The temperature of engineered objects on the
Moon would be
> very much like the same objects on orbit, hot in the Sun and cold
in the
> shade, but how hot and how cold would depend on how much heat was
being
> conducted or convected to the object from elsewhere. The surface
of a
> balloon with a little gas in it would be hot on the Sun side, cold
on the
> shade side, and the gas would carry heat between the two. How
much heat
> would be transported would depend on the gas pressure, composition,
> convection and so on. A solar day on Earth is 24 hours, but on
the Moon it
> is 709 hours or so. During this time, the temperature on
small "isolated"
> surface grains of regolith range from about 100 K to 400 K or so.
A large
> rock with good internal thermal conductivity would vary a lot
less. One
> can't say with out more information. Hope this helps. Sincerely,
Jay
>...
> Here's what I'm curious about. Actually there are two classes of
> objects. The first would be the actual lunar mining habitat. It
> would be radiating heat, I'm thnking that ISRU such as lunar
> ...
> The second class of object is what I'm most concerned about because
> they would be more fragile than a building envelope, and this class
> of objects would the the base support equipment that is exposed on
> the lunar surface. Objects such as heliostats, their support
> framework, stationary mining equipment, and mining equipment that is
> operated during the night. A possible outcome of this consideration
chararteristeics of each type of material in a vaccum coupled with a
thermal flow anaylsis.
A thought that your questions brought to my mind is about structures
that are in full sun with part of the structure in shade. There could
be serious fracture problems depending on the coefficent of expansion
and the thermal characteristics of the material. I have been attempting
to make items out of glass (pyrex type COE 90) for a current project and
it is very important to control the rate of cooling to avoid having the
glass explosivly shatter due to stress from the interior being hotter
than the exterior.
Mitchell James
> I can't seem to find a table of data on how quickly the lunar
> surface temperature flucuates. Does the temp go from -140c just
> before dawn to 120C an hour after sunrise? Is it hottest at noon?
> How quickly does the temperature drop after sunset? Is it coldest
> before the dawn?
>
> Anybody have a website with this data? I coudn't find anything.
Data Book - http://www.asi.org/adb/), but Peter Eckart's "Lunar Base
Handbook" has all the tables you could want on this sort of thing.
Surface temperature is pretty well defined (Apollo measurements
showed temperature rising 1 or 2 degrees C with 1 meter depth).
In general, aside from the effects of a body's shape the main parameter
is the thermal inertia (p. 140 of Eckart's book).
At the equator there would be a broad temperature maximum at around
390 K at lunar noon. Temperature drops quickly at sunset to
about 150 K, then falls slowly through the night to about 110 K, rising
quickly with the sunrise again.
Arthur Smith (apsmith@...