Date: 26 Aug 89 04:54:57 GMT
From: gem.mps.ohio-state.edu!csd4.csd.uwm.edu!mailrus!jarvis.csri.toronto.edu!utgpu!utzoo!henry@tut.cis.ohio-state.edu  (Henry Spencer)
Subject: Re: How is Voyager powered?

In article <1910@crdgw1.crd.ge.com> oconnordm@CRD.GE.COM (Dennis M. O'Connor) writes:
>There is another kind of "no-moving-part" radioisotope generator.
>Don't know the name. It uses isotopes that emit charged particles
>( usually beta particles, I think. i.e. high-energy electrons ). The
>beta-emitter is in the middle of an exacuated sphere. The
>electrons are emmited by the beta-emitter and travel to the
>sphere wall. The sphere wall becomes negatively charged,
>and the central mass of beta-emitting material becomes
>positive. Connect wires to each and you have a battery.

Nuclear batteries have been built with this system, but the power output
is very low.  A related scheme with much better power output is to use
heat from an isotope or a reactor to "boil" electrons off a suitable
cathode.  This scheme, thermionic conversion, is used in the Topaz
high-power space reactor that the Soviets have flown experimentally
(and are now offering for sale).

>I've heard that high-power radarsats use actual reactors
>( with control rods, coolant, et cetera ), but have no idea 
>how the heat is made into electricity.

The Soviet radarsats do indeed use reactors, mostly because they want to
operate at the lowest possible altitude (radar effectiveness requires
the shortest possible range) and with fairly high power output, and
the necessary solar arrays would produce too much air drag.  I think
their operational reactor uses thermocouples, just like the Voyager
RTGs.  Topaz may be intended as a replacement.
-- 
V7 /bin/mail source: 554 lines.|     Henry Spencer at U of Toronto Zoology
1989 X.400 specs: 2200+ pages. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu