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[aprssig] Balloon warmth

Robert Bruninga bruninga at usna.edu
Wed Mar 24 21:30:12 UTC 2010


> I'll have two identical Styrofoam blocks 
> suspended outside the payload box....
> One will be painted black... and the 
> other will be unpainted white Styrofoam.

If the styrofoam works like it should, painting the outside is
of no value.  The styrofoam is such a good insulator, that even
if the outside  "skin" gets hot, it wont get to the inside
anywhere near like the -60 degree air will.

The whole idea of the Sun is to *avoid* insulation that keeps it
out...  That's why we used concentric a clear coke bottles.  You
still want something soft that bounces when it hits the
windshield of a car.. Or someone's head.

> One will be painted black...
> (or whatever I find that absorbs IR) 

Actually, it is not IR.  Both White and Black absorb IR equally.
Old houses never painted old hot water radiators Black, because
White is just as good at IR absorbtion and emission as black.
The White is for the *sun's" spectrum which is mostly visible
and above.  White only absorbs 30% of the Solar spectrum that
black does. (but it is missleading to call it IR).

Hope that helps.
Bob, WB4APR




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