>Do you know how many Titan-IV launches fail? (1 out of 20 [5%] is my
>understanding. You got any different statistics? If not, why do you
>consider the "risks of a disaster resulting from the Cassini project (to
>be) about as great as the chances that Earth will be hit with an astroid or
>comet?"
>
I do know how many Titans fail. It's very easy to simulate an exploding
booster rocket, and thus it's possible to determine definitively whether the
RTG containment system can withstand a launch mishap.
The risks in this mission are in the possible unintended reentry of the RTG
into the atmosphere. There is no way to precisely simulate every reentry
scenerio. At this point, we are far less likely to face an unintended reentry
of the RTGs than we are to face mass extinction from an astroid. Even if the
RTGs reenter the atmosphere, I don't believe there is any chance of the RTG
causing 1,000,000 deaths.
>Practically speaking, however, can you identify any **specific**
>practical plan presently on the table for "making plutonium virtually
>benign?"
Most plans call for diluting it by mixing it with glass and burying it a few
miles underground in a rock formation which we assume will be stable for at
least 1,000,000 years. I don't mind if they also ship some off the face of
the earth. It is feasible, at the cost of serious launch weight, to package
the plutonium so well that, short of striking an astroid during ascent, there
would be no chance of it's leaking in any accidental reentry scenerio.
>Remember the big propaganda blitz of the early 50's, how they promised that
>nuclear power was going to make electricity so cheap that it would hardly
>be worth metering? Since I think most folks are still just about
>hopelessly naive, I guess we disagree on something here.
Fission energy appears to be on the way out. Nulcear energy, it was originally
thought, would be to too expensive to be economically practical. I think the
energy department convinced investors to finance nuke plants so they could
take a bite out of the cost of nuclear weapons production. Now that the US
isn't producing any nuclear bombs, the nulcear industry is doomed.
>What drew my attention to this thread was noticing Ellen's response
>concerning the Sagan article.
Sagan's article on the Gallileo space probe which use 55lbs of plutonium can be
found at the Cassini Nuclear Safety page.
http://www.jpl.nasa.gov/cassini/rtg/sagan.htm
> Since I've heard more than one professional space engineer claim
>that the Cassini mission could have been fueled by solar power if it were
>only 130 pounds lighter, if you are some kind of physicist, or knowledgable
>layperson, perhaps you can explain to me why the solar power proponents are
>wrong, and/or why RTG's are preferable to solar power.
The intensity of sunlight at Saturn's distance from the Sun is 1% of the
intesity here on Earth. It is also extremely cold there. Even if you could
have a large enough solar array collect and store energy at the orbit of
Saturn, you would have to expend most of that energy just to heat the space
probe up to an operational temperature.
Also, one of the most valuable aspects of the Cassini mission is to radar map
the cloud covered surfaces of Saturn's Moons. You will never operate a radar
system capable of that or the many other things on board Cassini using limited
Solar energy.
There would be no point to going to Saturn using Solar energy. We may as well
just stick to exploring the Earth, Moon, and Mars if we're not going to accept
the risk of using RTGs. Saturn is much like a minature Solar system. Insight
gained from exploring Saturn will certainly help us understand the factors
that determine the risk of Earth being impacted by and astroid or a comet.
This is why I suggested that we should weigh Cassini's risks against the risk
of a medium sized astroid wiping out a large part of Earth.
Thanks for you're reply. Also, my respect is due to people who protest, if not
for what they protest, but certainly for their willingness to protest.
Aaron