CNN article about nuclear power on space probes

Here's an article that CNN has about nuclear power on space probes. I
list some questions about it below

http://www.space.com/businesstechnol..._focus_040218-
1.html
(Note the line wrap on link.)

One thing that kind of bothers me is the statement that, "The Energy
Department, working with industry, is designing a space-qualified nuclear
fission reactor capable of generating 100 kilowatts of power -- about
1,000 times more than most solar-powered space probes have available
today." Is it true that the average space probe today only uses about
100 Watts? I'm pretty sure that thin film collectors can produce up to
several kilowatts per kilogram of PV panel (at Earth orbit insolation
levels) and that fresnels or other concentrators can improve this power
to weight ratio further. OTOH, the thermal energy produced by a kg of
PU238 is about 500 Watts and a stirling may only allow them to get 30% of
that converted into electricity. Furthermore, new technologies are
allowing for even lighter weight PV and light weight solar thermal
concentrators. I'd think that you'd have to be very far from the sun or
doing fairly exotic things before an RTG only approach would be the best
or the cheapest.

Also, I was wondering about this. It seems to me that rather than using
just Stirlings or just thermal diodes that it should be possible to use
the Stirling as the primary source and the thermal diodes to top off.
The diodes and thermionics are very light weight. They would remove some
of the heat that would otherwise be available to the stirling engine, but
if they didn't drop the overall temperature inordinately then I would
think that they could still produce net power beyond what the Stirling
alone could achieve. Modern thermal diodes can actually be quite
efficient. But, of course, like I said above, these same technologies
could also be used with solar concentrators on many space probes.

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Quibbler (quibbler247atyahoo.com)
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