On Apr 17, 2007, at 04:13 UTC, Ed Minchau wrote:

> The logical place for heat radiators would be in the
> shadow of the large mirror (or mirrors, if there is
> one on each side of the hub).

The standard location for them is hanging off the rotational axis,
directly in line with the sun. This way, the radiators do not "see"
the sun in the sky on either side; or from the sun's point of view, it
can't see the radiators except as a thin line. If you look very
closely at
,
you can see this in the torus on the left as a dark red rectangle just
above the torus itself.

Putting it in the shadow of something like the mirror doesn't really
help much, I think, because the mirror is going to be absorbing some
energy (it's not perfectly reflective) and re-radiating it in the
infrared. Some of that infrared radiation would hit your radiator; and
some of the radiation from your radiators would hit the mirror, which
means that it's still in the system and needs to be shed some other
way. What you want instead is for every point on the radiator to "see"
as much empty black sky as possible, so it isn't absorbing anything but
starlight, and any radiation it sheds completely leaves the system.

Best,
- Joe

Joe Strout -- joe@...

On Apr 17, 2007, at 15:58 UTC, Chris Smyth wrote:

> I was thinking along the lines of a horizontally oriented radiator
> in the permanently shadowed crater.

That'll be only 50% (or so) as efficient as a vertical one that sees
black sky on both sides. A radiator radiates in all directions; half
the energy in your example would go down into the floor of the crater.
But regolith (and the Moon in general) is a very poor conductor of
heat, so the crater floor would quickly warm up to the temperature of
the radiator, and from that point on the energy radiated in that
direction is simply trapped, and only the side facing the sky is doing
you any good.

Best,
- Joe

Joe Strout -- joe@...

--- In spacesettlers@yahoogroups.com, joe@... wrote:
>

>
> That'll be only 50% (or so) as efficient as a vertical one that sees
> black sky on both sides. A radiator radiates in all directions; half
> the energy in your example would go down into the floor of the crater.
> But regolith (and the Moon in general) is a very poor conductor...

Hi Joe,

Your point is well taken. I didn't think the problem through very
well. As a general question, if a moon base is constructed underground
at mid-latitudes (using existing lava tubes or man-made tunnels) does
anyone have an idea of how deep those tunnels would need to be in
order to provide adequate radiation shielding and steady ambient
temperatures? I'm thinking any ambient temperatures from 20 to -100
degrees C would do.

Chris

On Apr 18, 2007, at 04:53 UTC, Chris Smyth wrote:

> As a general question, if a moon base is constructed underground
> at mid-latitudes (using existing lava tubes or man-made tunnels) does
> anyone have an idea of how deep those tunnels would need to be in
> order to provide adequate radiation shielding and steady ambient
> temperatures? I'm thinking any ambient temperatures from 20 to -100
> degrees C would do.

A couple of meters down would do it, IIRC.

Best,
- Joe

Joe Strout -- joe@...

--- In spacesettlers, joe wrote:

> On Apr 18, 2007, at 04:53 UTC, Chris Smyth wrote:

>> As a general question, if a moon base is constructed underground
>> at mid-latitudes (using existing lava tubes or man-made tunnels)
>> does anyone have an idea of how deep those tunnels would need to
>> be in order to provide adequate radiation shielding and steady
>> ambient temperatures? I'm thinking any ambient temperatures from 20
>> to -100 degrees C would do.

> A couple of meters down would do it, IIRC.
>
> Best,
> - Joe

Whenever I read about moonbases, it seems they want to bury everything
five metres deep. if two is enough for the orbital habitats which get
radiated from every side, I'm not sure why on the moon you need five.
But if "a couple of meters down" will do the job for both radiation
and for steady temperatures, then five metres down certainly will.

So, what temperature would we be looking at? If it's -100C, then
heating the thing could get expensive. If it's 60C, then keeping
cool is a problem. Still, if it's -100 or 60 ALL THE TIME, then
that's gotta be easier to deal with that a two-week cycle of -173 to
117, over and over and over again forever.

I just looked up the average at Wikipedia. The average is -53C
(-63F). This is probably what we'd be looking at.

On Apr 18, 2007, at 19:04 UTC, Xenophile wrote:

> So, what temperature would we be looking at? If it's -100C, then
> heating the thing could get expensive. If it's 60C, then keeping
> cool is a problem. Still, if it's -100 or 60 ALL THE TIME, then
> that's gotta be easier to deal with that a two-week cycle of -173 to
> 117, over and over and over again forever.
>
> I just looked up the average at Wikipedia. The average is -53C
> (-63F). This is probably what we'd be looking at.

That sounds about right. But it's still cooling (heat rejection) that
will be the problem, not heating. Because regolith is such a good
thermal insulator, it doesn't matter much that the surrounding soil is
-53C -- very quickly the *immediately* surrounding soil is going to be
the same temperature as your habitat, and that'll keep going up until
it radiates heat away as fast as it's produced.

But I agree, it's much easier to deal with a steady temperature than to
be cycling between extremes all the time. So for a lunar base, burial
or siting in a lava tube makes a lot of sense.

Best,
- Joe

Joe Strout -- joe@...