In defense of Cassini

                                 Last update:  11/17/97


Well, the Cassini space probe has been launched without incident, and the controversey about it will presumably receed for awhile... but I've had some thoughts in my head about this for some time, and now I've finally got a moment to get them out.

If you weren't paying attention to this one, here's a quick rundown: The Cassini is a NASA space probe, now on it's way to Saturn. Saturn is pretty far out in the solar system, where the sunlight is quite thin, and anyway, space solar power arrays have a history of jamming when you try to deploy them, so for power they decided to use an RTG (radioisotope thermal generator, if you care). In an RTG, the heat of a radioactive isotope is used to warm up thermocouples (a thermocouple is just a loop made of two dissimilar metals: heat up one junction and you get a small current flowing through the loop). It's not the most efficient way of generating power, but it is simple and reliable and they last a long time, so they tend to get used in deep space missions like this. The Cassini is a big space probe, probably one of the last of the cadillacs NASA has been building (there are virtues to being small, quick and cheap that seem to be sinking in). It needs quite a bit of power, so they used a fair amount of a pretty hot isotope: around 70 pounds of Plutonium-238.

And that's where the fun begins.

in the BaG

The SF Bay Guardian carried a call to action (see Reference below):

'Cassini' countdown Activists try to block launch of nuke-fueled probe.
"We think we are taking too great a risk," coalition member John Selawsky told the _Bay Guardian_. "There have been accidents in the past. We are not infallible, and plutonium is the deadliest substance on Earth."

Yes, there have been "accidents in the past". I understand that there have actually been two accidents with rockets carrying RTGs. What were the consequences? They landed in the ocean, containments intact, and we went out and fished them out. RTGs are actually very simple devices compared to the pressurized water reactors that are usually used to generate nuclear power on earth. Pressurized water reactors have lots of high-pressure plumbing running through the core. RTGs are more like solid lumps of stuff with wires coming out of them. They're pretty easy to seal up, especially considering that they use relatively small quantities of radioactive materials. This is a big one, and it only uses 70 pounds of Plutonium.

Now how about "...plutonium is the deadliest substance on Earth." This is a ridiculous statement, and it's constant repetition from the anti-nuclear people is both frustrating and depressing. It's ridiculous because it's trivial to show that there are other things more deadly than plutonium, for example, arsenic. But it's frustrating because no one seems to care that this is a ridiculous thing to say: in my experience when you explain to someone that arsenic is more deadly than plutonium, they do not find it particularly reassuring. And the fact that the anti-nukes don't actually appear to know anything about what they're talking about never counts against them. This is a heads they win, tails they win, situation.

Where are they getting this stuff from? I'm hardly the first person to challenge this factiod, but it refuses to die. My guess is that it's probably Helen Caldicott... she gets a lot of play in some circles (e.g. her speeches are broadcast on KPFA, the Pacifica station in Berkeley), but as far as I can tell she's a complete crank on this subject. It's as though a bunch of white supremacists kept going around quoting Schockley because they couldn't find anyone else with a PhD who got anywhere near agreeing with them.

Though NASA has touted the mission as a historic opportunity to investigate a planet about which we know little, some scientists and even a few former NASA employees say an accident could expose thousands, even millions, of people to radiation. Critics say an explosion on takeoff from Cape Canaveral could contaminate large parts of Florida or burn up in the atmosphere during its swing past Earth in 1999 on its way to Saturn.
NASA says plutonium is the only viable way to power the six-ton craft, but some specialists maintain that solar cells could be used as a power source.
"Saturn is not going anyplace," said Elliot Cohen, a coalition member and a vigil organizer. "Saturn will still be there when we have safer alternative technologies."

Thanks, but personally I'd like to see this happen in my lifetime.

But even as the national controversy has grown, NASA officials continue to maintain that the possibility of an accident is extrememly small. They say there is almost no chance that the craft will collide with the planet's atmosphere as it passes by Earth two years from now.
Though activists acknowledge that the chances of an accident occuring are relatively small, they maintain that even those odds do not justify what could be catastrophic consequences for very little gain. They say the exploration of Saturn is not worth the possibility of worldwide radiation contamination.

I think they're overestimating both the consequences of an accident and it's likelyhood, but the worst thing about this is that they appear to be completely denying any value in space exploration. Do these people have any soul?

"There are more dangerous consequences than just thousands [of people] getting cancer," Cohen told the _Bay Guardian_. "This stuff causes genetic mutations, birth defects. This is like thalidomide forever."

Fascinating. "Thalidomide forever". Where do they get this stuff? Think about this for just a moment: when was the last time you heard about the genetic mutations resulting from the Hiroshima and Nagisaki blasts? You haven't heard about them, because they didn't happen. How about the fallout from the above ground nuclear testing of the fifties? Noticed any "thallidomide forever" effects from that? Once upon a time, people who knew what they were talking about were afraid that radiation would cause lots of birth defects. Now that it's pretty well been shown that they were wrong, only the people who don't know what they're talking about continue to be afraid of this.

But is there any point in talking about this? Do you care that this is completely wrong, and that the worst case accidents will only result in some additional cases of lung cancer? Or is this another case of heads they win, tails they win?


It would be nice if the risks of doing space exploration could be born only by the people like me who believe in doing them. Just like it would be nice if people driving cars only put their own lives at risk. Unfortunately, it's hard to see how to structure human life that way.

If you put a big sculpture of a foot on top of the Ferry building in San Francisco, there's a finite chance that it could fall over and injure a passerby -- possibly even a passerby that thinks it's really ugly. Should we forbid all public sculpture? After all, we don't need it to survive (at least not in any obvious way). How can we justify even a slight chance that someone could die under that gargantuan heel?

The value of human life is high, but it is not infinite. If we try and act as though it is infinite, it is in danger of becoming worthless.

But there's nothing to get upset about this time, right? After all the good guys won, didn't they? Cassini's in flight, on it's way to Saturn... except that what's going to happen the next time they try and build a space probe using an RTG? Is this another useful technology that's going to be moved to the list of things that are politically untenable?

Heads they win, tails they win.

Appendix 1: Illogical Sentences (?)

This may seem picky, but there are at least two places in this article where the logic seems really peculiar. The last half of the sentence doesn't seem to follow from the first. And both cases are the first sentences of paragraphs...

Though NASA has touted the mission as a historic opportunity to investigate a planet about which we know little, some scientists and even a few former NASA employees say an accident could expose thousands, even millions, of people to radiation.

Is it just me, or is there a complete lack of logic here? "Though NASA has touted the mission as a historic opportunity..." (um, is this in doubt? Or am I just another tout?) "an accident could expose thousands, even millions...". Even if you buy the second part of this sentence, does it negate the first?

But even as the national controversy has grown, NASA officials continue to maintain that the possibility of an accident is extrememly small.

This is getting interesting: another paragraph where there are serious logic problems in the first sentence: "But even as the national controversy has grown, NASA officials continue to maintain that the possibility of an accident is extrememly small." Why would you expect NASA to change it's mind because of a public controversy? "Oh, right: SAFETY. Duh! We didn't think about that guys. Sorry."


The article I quote throughout this piece has a "Jason Mark" byline. It appeared on page 10 of the October 8, 1997 issue of the Bay Guardian -- though if this is available on their web site, I was unable to find it. However, their web site is:
Welcome to the Bay Guardian
The NASA Fact Sheet on "Past Accidental and Incidental Releases of Radioactive Marerial from Space Nuclear Power Sources"
Space Nuclear Power System Accidents

You got a problem with any of this? Let me have it at: