Variable Output RPG

Hello,
Is it possible to design a RTG so that the daughter products
release more heat at a later date than when it is first assembled. I am
thinking of missions where the early flybys are in the inner system and heat
rejection may be a problem, but once you reach the outer planets the extra
heat and power can be put to good use.

Earl Colby Pottinger


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JRS: In article , seen in
news:sci.space.tech, Earl Colby Pottinger posted at
Fri, 26 Mar 2004 10:55:27 :-

Is it possible to design a RTG so that the daughter products
release more heat at a later date than when it is first assembled. I am
thinking of missions where the early flybys are in the inner system and heat
rejection may be a problem, but once you reach the outer planets the extra
heat and power can be put to good use.

In theory, it may be.

Start the RTG with a supply of Isotope X, which has a twenty-year half-
life and decays into Isotope Y without depositing noticeable energy
nearby; but Isotope Y, also with a 20-year half-life, decays violently.

AFAICS without algebra, that starts out with a zero heating-rate, and
subsequently has a larger heating-rate, thereby doing what you want.

However, ISTM that the chances of finding a decay chain with that
property, and fulfilling all the other conditions, will be rather small.

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In article ,
Earl Colby Pottinger wrote:
Is it possible to design a RTG so that the daughter products
release more heat at a later date than when it is first assembled...

It's not unthinkable, but it strikes me as a major extra complication in
an already rather constrained choice of isotopes. (This wouldn't be
primarily a matter of the RTG's design, but of what isotope you use.)

thinking of missions where the early flybys are in the inner system and heat
rejection may be a problem, but once you reach the outer planets the extra
heat and power can be put to good use.

It's probably easier to go with an orthodox RTG design and use some
variable way of getting rid of the extra heat. (I recall one non-RTG
design which faced the same problem -- the electronics box was heavily
insulated for operation out in the Kuiper Belt, but this obviously made it
prone to overheating early on -- and incorporated a clever no-moving-parts
solution: the innards were cooled by a heat pipe running out to a
radiator, and around the time the bird passed the orbit of Mars, the
heat-pipe fluid froze in the radiator, shutting down the heat pipe.)
--
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Earl Colby Pottinger wrote in message ...
Hello,
Is it possible to design a RTG so that the daughter products
release more heat at a later date than when it is first assembled. I am
thinking of missions where the early flybys are in the inner system and heat
rejection may be a problem, but once you reach the outer planets the extra
heat and power can be put to good use.

There are isotopes which decay as you say, but I don't know if any
would have the combination of properties which would make for a good
RTG...

How about engineering a "baby reactor" which weigh less than 100
pounds? Using tricks like insulated and heat pump cooled moderator,
which would "cool" part of the neutron flux in order to decrease the
fissile fuel mass...

The thermally insulated hot core would be the energy source.

Charles Pooley

Earl Colby Pottinger wrote in message ...
Hello,
Is it possible to design a RTG so that the daughter products
release more heat at a later date than when it is first assembled. I am
thinking of missions where the early flybys are in the inner system and heat
rejection may be a problem, but once you reach the outer planets the extra
heat and power can be put to good use.

Yes!

http://groups.google.com/groups?selm...news.dfncis.de


Someday I'll finish the full paper ... eventually.

Abrigon Gusiq wrote:
Anyway to store the energy you get from the heat in the inner system,
but then you release it when you get to the outer system?
Photosynthesis or better yet heat instead of light?

snip quoted message incorrectly placed at bottom
If you could do that, while remaining light enough, then you wouldn't bother
with the RTG, and just use the energy storage device.
In short, no.
Batteries top out somewhere around 500Wh/Kg (not for current ones),
which a RTG will beat in under a days output, and there is no storage
system that's much better.