(Jeff Root) writes:
Craig Markwardt replied to Jeff Root:

Yes, I can see that. It is why I estimate that only 20% of
the RTG surface area is visible to the back side of the antenna
dish and other parts of the spacecraft sunward of the RTGs,
rather than the approximately 45% that would be visible if they
were plain cylinders.

I think the fractional (i.e. edge-on) area that actually faces
the antenna is much smaller than the outward-facing area. How
do you get 20%?

Just from looking at photos and guessing. Nothing better.

Note that the 20% figure is for the area of the RTG which is
visible to the back of the dish, etc., and is not the most
important thing to measure here, but was a response to Bruce
Woodcock's assertion that:

every RTG is not a spherical black body, but rather has fins
that are "edge on" to the antenna, which means only 2.5% of
the surface area of the RTG is actually facing the antenna.

My 20% figure may be high, but Bruce's 2.5% figure has *got*
to be *way* too low. Or else he mis-stated what the figure

I wouldn't be too quick to dismiss the 2.5% amount without a more
rigorous factual basis. The majority portions of the RTGs which face
the dish are the endcaps, which are designed to be *non*-radiative.
This leaves the edges of the radiator fins, which are pretty thin
indeed, compared to the total surface area.

Don't you agree that 5% looks more like it?

I have no idea. It's a realm where eyeballing it won't help.

Craig


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Craig B. Markwardt, Ph.D. EMAIL:
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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