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From: dietz@SLB-DOLL.CSNET (Paul Dietz)
Newsgroups: net.space
Subject: Galileo plutonium
Message-ID: <8602250453.AA05631@s1-b.arpa>
Date: Mon, 24-Feb-86 21:44:54 EST
Article-I.D.: s1-b.8602250453.AA05631
Posted: Mon Feb 24 21:44:54 1986
Date-Received: Fri, 28-Feb-86 01:21:19 EST
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 38

Henry Spencer writes:

>Timothy Wright writes, in part:
>
>>      I read in the latest issue of The Nation that one of the shuttle's
>> planned missions included the Galileo-Jupiter probe, which would have had on
>> board about 46 pounds of Plutonium. A Challenger-type explosion would have
>> either vaporized or finely distributed the stuff all over the greater Cape
>> Canaveral area...
>
>Why?  It didn't vaporize or pulverize the rest of the Challenger, just broke
>it into small pieces for the most part.  The interior of the cargo bay is
>probably the best-protected area on the shuttle, too.

The ET went off with the force of a small atomic bomb, but even an atom
bomb doesn't necessarily destroy everything nearby.  Graphite
covered solid steel spheres have been suspended below A-bombs in
above-ground tests and have suffered only slight ablation of the
surface layer.  The thermal pulse blows off a thin outer layer,
but the heat takes too long to diffuse into the body and most radiates
away.  This phenomenon formed the basis for the Orion-style spaceship.
The radioisotope thermal generators sound somewhat more fragile than
solid steel spheres, though.

Galileo and Ulysses are attached to Centaur upper stages.  These high
energy stages use a lot of LH/LOX fuel, and said fuel sits right next
to the probe in the cargo bay.  A Challenger-type explosion would
certainly rupture and detonate the Centaur tanks.

An aside: 46 pounds of Pu-238 is a lot more dangerous than a similar
amount of Pu-239, since Pu-238 has a much shorter halflife (it has to
to get respectable decay heat).  A solution to the radiation problem
might be to launch the radioisotope source separately and assemble in
orbit (probably not feasible for current probes) or to design probes
that use real nuclear reactors (certainly not possible for current
probes).  The latter solution could allow really high power transmitters
(kilowatts at least) for high data rates from the outer solar system,
and could even power ion engines.