Re: SPACE: Cassini Mission Consequences

Paul Hager (
Sun, 21 Sep 1997 11:53:39 -0500 (EST)

On Sat, 20 Sep 1997, Natasha V. More (fka Nancie Clark) wrote:

> Although I have been in the periphery of the adversarial panoply of Cassini,
> I'd like to address some data and if anyone has a difference of opinion,
> please do let me know. If this information has already passed through the
> list and either as a solo post or thread of comments, would someone kindly
> advise me and I'll go to the archives and look it up.
> To my knowledge, the plutonium that Cassini is scheduled to carry onboard is
> in the range of 60 - 70 pounds. The size is applicable to lipstick tubes
> and in hardened metal container encasing the chemical.
> Adversaries are alarmed about possible explosion during the launch and
> during earth flyby (gravity assist swing.)
> Advocates of the mission have mitigated the situation by using armored
> containers so that if there is a first stage failure, the integrity of the
> containers are such that there could be no toxic problems. They also state
> that it is literally impossible that there would be a flyby miscalculation,
> and even if there was, it would be known well before a possible collision
> and the course would be corrected.
> Plutonium has been onboard missions for decades: Voyager, Viking, Gemini all
> had plutonium onboard. I'm not sure whether the antagonists are waving
> flags for some personal cause, or there is serious drawbacks to this
> particular missions' load. I have consulted with a few astronomer and space
> architect friends who are actively in the field of space travel. I haven't
> heard any alarm. I'd appreciate hearing your thoughts.
> Natasha Vita More [fka Nancie Clark] -
> "Treat your friends as you do your pictures, and place them in their best
> light." Jennie Jerome Churchill
> More Art Studio -
> BOOK RELEASE: _Create/Recreate - Transhuman Beginnings and Extropic Creativity_
> Press Release: *Extropic Art Manifesto* orbits Saturn -1997-1998

It has been awhile since I have looked into RTGs (Radioactive Thermal
Generators) but your statements are essentially correct. RTGs are powered
by Pu-238. It is a non-fissile isotope of Plutonium that has a half-life
of just under 88 years. It decays by spontaneous fission and energetic
alphas and so generates quite a bit of heat. The fact that Pu-238 is a
good heat source is what makes it so useful on space missions to the outer
planets, particular in view of the short life of batteries and the
insufficiency of solar energy for necessary energy.

The "problem" associated with Plutonium in RTGs is political and has
nothing to do with either health, safety, or proliferation. Much of the
hysteria associated with Plutonium RTGs dates back to the Goffman-Tamplin
"hot particle" hypothesis about plutonium toxicity. The assumption was
that inhaled plutonium in even the smallest amounts would produce cancer.
This hypothesis was invalidated early on but has remained part of the
mythos of anti-nuclear and anti-technology groups. A point that I used to
make when I debated the anti-nuclears back in the late 70s and early 80s
was that it was reliably estimated that atmospheric testing of nuclear
weapons has uniformly dispersd something between 7-10 MILLION tonnes of
plutonium. Thus, if you go for a walk outside, you WILL be exposed to
plutonium and if you work in your garden you will exposed even more if you
kick up any dust. If Goffman and Tamplin were correct we would all be
dead now.

While I am not saying that Plutonium RTGs are benign, the concern focused
on them is way out of proportion to the actual risk. Frankly, I consider
the kinetic energy of a reentering probe and the possible damage it might
produce as being more a matter of concern than the onboard plutonium.

paul hager

"The most formidable weapon against errors of every kind is reason."
-- Thomas Paine, THE AGE OF REASON