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From: karn@petrus.UUCP (Phil R. Karn)
Newsgroups: net.space
Subject: Re: Re: Debris from Upcomming ASAT Test
Message-ID: <628@petrus.UUCP>
Date: Mon, 7-Oct-85 12:08:50 EDT
Article-I.D.: petrus.628
Posted: Mon Oct  7 12:08:50 1985
Date-Received: Tue, 8-Oct-85 04:24:46 EDT
References: <385@aurora.UUCP> <15800003@uiucdcsp> <108@muscat.UUCP> <634@osu-eddie.UUCP>, <620@petrus.UUCP> <6024@utzoo.UUCP>
Organization: Bell Communications Research, Inc
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> Fussy but important point:  the isotope generators use plutonium 238, not
> 239.  238 is much harder to make, but is a fairly pure alpha emitter with a
> relatively short half-life (years), which is exactly what is needed for
> isotope power.  239, the fissionable isotope, has too long a half-life and
> too mixed a radiation output to be useful for this.

You are correct, I should have checked my references first. Pu-238 has a
half life of 86 years, while Pu-239 has a half life of 24,400 years.  Both
decay by spontaneous fission or alpha emission, so Pu-238 will therefore put
out a lot more heat per unit mass than Pu-239. However, I believe that all
reasonably stable isotopes of plutonium are fissionable, and this is why the
nonproliferation people are so concerned about it -- you can't "denature"
it with a non-fissionable isotope like you can with U-235 and U-238.

> Uranium or plutonium-239 can be handled with bare hands, if you aren't
> worried about toxicity.  If you check, I believe you'll find that the
> Apollo crews used tongs for handling the plutonium-238 capsules, because
> they are *thermally* very hot -- sort of obvious given that they are used
> in thermal generators.

There's a comment in my reference (History of Manned Space Flight) that
Pete Conrad had considerable trouble getting the plutonium source out
of its container on Apollo 12. It took him 10 minutes to free it, during
which time his gloves protected his hands.

> > ... shooting one of these [Soviet ocean-surveillance satellites] down
> > with our ASAT would guarantee that its radioactive remains re-enter the
> > atmosphere within a pretty short time...
> 
> A good point.  One wonders why this has not been brought up before.

Probably because shooting down a Soviet satellite would be an act of war,
and we'd have more serious consequences to worry about.

Phil