Subject: Re: OT: Voyager watts

From: chris <[email-masked]>
Date: Mon May 12 10:26:00 2003

>In the
>case of a Voyager-class probe, with RTG-sourced power,

For the few of us on the list that are idiots (ok, fine, just for me 
then), what is RTG sourced power?

-chris
<http://www.mythtech.net>

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From: Alexander Schreiber <[email-masked]>
Date: Mon May 12 13:09:00 2003

> then), what is RTG sourced power?

Radionuclear Thermal Generator, a device which contains some suitable
radioactive isotope. The isotope produces heat due to nuclear decay and
this heat is used to produce electric power. A nice longterm source for
considerable amounts of power (depending on size/weight constraints,
they can deliver anything from a few watt to a few kilowatt and even
more).
Disadvantages: guaranteed to not earn you any new friends among the
treehuggers and its power output drops logarithmically over time.

Regards,
      Alex.
-- 
"Opportunity is missed by most people because it is dressed in overalls and
 looks like work."                                      -- Thomas A. Edison

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From: Dan Wright <[email-masked]>
Date: Mon May 12 13:10:16 2003

> then), what is RTG sourced power?

From what I remember, those probes (and most (all?) other deep space probes, I
think), use a radioisotope decay generator for power.  This is a
sub-critical-mass nuclear power plant; it uses the heat produced by a
near-critical lump of plutonium to generate electricity, rather then using
fission to produce heat to produce electricity.

> <http://www.mythtech.net>
- Dan Wright
([email-masked])
(http://www.uiuc.edu/~dtwright)

-] ------------------------------ [-] -------------------------------- [-
``Weave a circle round him thrice, / And close your eyes with holy dread,
  For he on honeydew hath fed, / and drunk the milk of Paradise.''
       Samuel Taylor Coleridge, Kubla Khan

---

From: Ethan Dicks <[email-masked]>
Date: Mon May 12 13:51:00 2003

--- Dan Wright <[email-masked]> wrote:
> From what I remember, those probes (and most (all?) other deep space
> probes, I think), use a radioisotope decay generator for power.
> This is a sub-critical-mass nuclear power plant; it uses the heat
> produced by a near-critical lump of plutonium to generate electricity,
> rather then using fission to produce heat to produce electricity.

Exactly.  Sorry for not being clearer - RTG is "Radioisotope Thermal
Generator" - It's a multi-kg sphere of plutonium with a wad of embedded
thermocouples.  The plutonium just fissions and produces heat (and
neutrons) which the thermocouples turn directly (albeit inefficiently)
into heat.

They are favored for remote devices (deep space, Antarctica, etc.)
because they do not depend on sunlight.  Further out than Mars (and
for ~six months out of the year on the Ice), solar cells aren't a
viable option.

The big worry is that the launch vehicle will explode or the probe will
fall to earth from a failed booster stage and scatter the contents of
the RTG over a wide swath.  They are designed to take a lot of abuse,
but nobody wants to be a test case.

-ethan
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