🚀 go-pugleaf

On Tue, 7 Aug 2012 17:59:42 -0500, "Tim Williams"
<tmoranwms@charter.net> wrote:

>"Jon Kirwan" <jonk@infinitefactors.org> wrote in message 
>news:e0q228956bpb829qehome35ab6mcfoaps6@4ax.com...
>> Which reminds me of another thing. How do they convect the
>> internally generated heat away. I recall hearing about
>> multiple power systems, operating around 32V at near 2A. More
>> than one. This power must be convected/conducted away -- no
>> way they want to radiate it. I wonder if they push it
>> (costing more heat) towards a vane or arm and drag it around
>> on the surface to get rid of it? The atmosphere won't help
>> much.
>
>In addition to what the others have said, keep in mind the thing floated 
>through space for six months -- you can't cool Pu238 down, so *all* that 
>heat had to be dissipated, as radiation, from the backshell and heat shield, 
>into space.  The vehicle itself may've had cooling to the shell, but the 
>shell still had to dissipate it.

The shell is now gone. I was curious about Curiosity, itself.

You can only emit so many watts into space via radiation
given a surface area: A*e*s*T^4. There is no convection or
conduction, of course. But as George pointed out, the
existing atmosphere likely provides some relief here.

But speaking only about radiation outward, even with e at 0.9
(it usually isn't -- but I've measured silicon carbide, for
example, at around .9), this works out to about 490 watts/m^2
of radiating surface with e=0.9 and T=40C. (Anodized aluminum
is about 0.75.)

The problem is compounded by the fact that the same (or
nearby) surfaces will absorb insolation. On Mars, this is
about 1/2 the amount Earth gets, per m^2. But the Gale Crater
is at 4.5 degrees south latitude (basically on the equator)
and so it would experience, I think, on the order of 1362/2
or 680 Watts/m^2 of insolation, ignoring the albedo of the
atmosphere (which probably [but I don't really know] doesn't
reflect or thermalize a lot away before it reaches ground
level.) There would also be differential heating (sides where
sun is striking vs other sides), too.

All this poses some interesting questions, at least.

Cyclic heating and cooling can seriously cut down on the
lifetime of instrumentation, structures, solar panels, and so
on. UV radiation, also, is energetic enough to break polymer
bonds such as C-C and C-O, as well as many functional groups.
Obviously, still higher radiation from the sun causes
ionization, photon excitation, and atomic displacement. I
remember also that tests on a CCD not so long ago showed that
100 Rads generated hot spots on 10% of the CCD exceeding the
limits of an 8 bit ADC.

The ISS, for example, used hundreds of kilograms of silicon
purely for thermal protection. 

I'm curious how these issues were examined, explored, and
either discounted or solved. Anyone know the details?

Thanks,
Jon