Cassini, a NASA craft HQ’d out at JPL, will achieve Saturn orbit sometime in November, 2004. At some point it will deposit the Huygens space probe, compliments of the European Space Agency, which will parachute into Titan’s atmosphere, measuring its pressure, temperature, and density. Tonight is our last chance to be near these probes till, one day, we follow their trail.

Adding to the intrigue is the possibility that Cassini could disintegrate in the upper atmosphere and hasten all our deaths. It carries 72 pounds of plutonium. One Arjun Makhijani, a nuclear engineer from the Institute for Energy and Environmental Research, claims that if Cassini’s plutonium vaporized in our atmosphere it could release more radiation than all the open-air nuclear explosions since the very first Los Alamos blast in 1945, combined. This would be very serious business: Berkeley professor and Manhattan Project veteran John Gefman, who has an MD as well as a PhD, attributes an increase in lung cancer since the mid-1960s to the TRANSMIT 5BN-3 spacecraft, which fell back to Earth in 1964, and which carried about a third the plutonium Cassini’s packing.

Michio Kaku, a man sufficiently visionary to be one of the first popular champions of string theory (I refer to his fine book, Hyperspace), has been perhaps even more vigorous in his denouncing of Cassini. He has written extensively-to a nonscientist such as myself, numbingly-about the potential dangers. Peace activists who protested Cassini’s launch now protest the flyby; they’ll be out tonight, you can count on it. These are people many are quick to dismiss, but, having marched with them a few times on other causes, I find it difficult to do so. I do find in them a nearly mystical fear of anything nuclear, and their propensity to link Cassini to a general "militarization of space" seems absurd. At the end of the day, though, I’m in something like their position: a nonscientist picking among the conflicting testimonies of scientists in order to support my opinion about a scientific project.

The pro-Cassini side has some solid scientific credentials of its own. NASA can claim to have safely used radioisotopic thermoelectric generators-the "nukes" under discussion-on its Apollo, Pioneer, Viking, Voyager, Galileo and Ulysses missions. No incident. No problem. NASA’s estimation of the odds for a failure in Earth’s upper atmosphere are 1 in 1.2 million. Bob Mitchell, Cassini’s Program Manager, has said of such a failure, "It’s not a credible event. I’m not telling you it’s impossible, but it’s just not credible." Apparently the anti-Cassini faction has been saying that the nuclear-powered RTGs could have been replaced by solar cells; NASA’s response is that solar cells just won’t work as far out as Saturn because of the faintness of the sun’s energy at such a distance.

This puts me, and, perhaps, you, back in the ring with the peace activists, picking scientists. Finally, the act of choice, for myself and for national policy generally, must fall back upon personal preference:

Do you choose to favor this supremely cool mission, and accept the risk that it might, just might, lead to the deaths of millions by cancer? I do. I’m not entirely comfortable with the choice, but I’m not going to lose any sleep over it, either. It would be easy to theatricalize such a concern, to convey, through writing, something akin to Bill Clinton’s quivering bottom lip, but I won’t do that. I’ll be blunt: I want this mission, and will choose to believe the scientists who say there ain’t gon’ be no accident. I know I’m "picking scientists" when I want Kaku to be wrong about Cassini but right about string theory. If you’re pro-Cassini, and not, yourself, a scientist, you probably feel the same way. You may nod in mock-sympathy when confronted by someone deeply concerned about the project’s dangers, but on the inside, you’re lying. We are both inwardly delighted that no protest is going to stop this mission (and while we’re being honest, let’s not pretend that the protest’s failure has anything to do with a general public interest in space exploration. Cassini benefits not from our enthusiasm, but from the public’s indifference). Even deeper within us rests a conviction that we don’t dare speak: that the success of this mission would, in the long run, do more for humanity than its failure would cost us, even if that failure be measured in human lives.

(Something, though, must voice this position, or mark my words, we’re going to lose space exploration-and that something might well be a philosophically and artistically serious Hard Science Fiction. Dan Goldin, space science’s left jab, can’t hold off the mundane forever.)

So I hope you got out in spirit Tuesday night, brethren. We might not say what’s in our hearts, but we can stand up for ourselves.