back in the heroic days of rocket science -- long before Challenger, long before environmental impact statements -- scientists thought big. Big and crazy. Like in 1958, when Ted Taylor, a theoretical physicist and atomic bomb designer, went to the government's Advanced Research Projects Agency with the following idea: Why rely on costly, bulky solid fuel to send tiny payloads into orbit, when a ready source of nearly endless energy was at hand? Why not use atomic bombs to propel our spaceships?
All you needed to do was to detonate a specially designed bomb underneath a giant metal shock-absorber at the base of the ship. The ship would rise up into the air; another bomb would be dropped, and with a series of carefully controlled explosions you could send a ship the size of a 16-story office building rocketing out of our atmosphere on a direct route to the moon or Mars.
Like many postwar nuclear fantasies, the Orion project, as it was called, didn't make it past the drawing board. But space scientists never gave up on the idea of nuclear-powered flight. In fact, they're going to launch one next month. It's called the Cassini probe, a plutonium-laden exploration that is scheduled to rendezvous with Saturn in 2004. To some, it's akin to launching a doomsday machine.
To hear the activists tell it, a Cassini accident could rain deadly plutonium on every living creature on earth, subjecting "millions or billions of people" to various forms of deadly cancer, according to cancer expert Janice Kirsch. Former NASA official Alan Kohn suggests we'll need to provide "permanent fallout shelters for all living beings on the planet." Cassini will be carrying 72.3 pounds of plutonium, enough, according to Australian doctor Helen Caldicott, to kill every human being dozens of times over. "Plutonium is so toxic," she wrote recently in the Nation, "that one pound distributed around the earth in particles small enough to be inhaled could induce lung cancer in every person on the planet."
Such assertions are often unsupported by logic or fact. Caldicott, for example, never spells out exactly how her pound of plutonium would need to be "distributed" in order to do its damage. After all, one pound of nearly anything can cause a good deal of damage if "distributed" properly. One pound of lead, made into bullets and "distributed" via Uzi, could take out at least a good-sized postal sorting facility. One pound of lead sitting in a box in the basement, though, might merely cause you to stub your toe.
But if the activists' claims are notable for their extravagant exaggerations, the complacency and evasions of Cassini's supporters don't exactly inspire confidence. On the Web page of the National Space Society, an "activists toolkit" suggests that whenever pro-Cassini activists find themselves "in doubt" when confronted by journalists asking tough questions, they should simply repeat stock answers like "That's not true," and "Cassini is safe."
In fact, there's a considerable chance Cassini will blow up at launch, potentially sending 72 pounds of plutonium shrapnel into the air. NASA officials, while admitting there is a chance of a launch, er, failure (after all, the Titan IV rocket powering the thing has been known to explode), insist that only a tiny amount of plutonium could possibly escape. It's not as though they're planning to pack the stuff up in a shoe box: The plutonium pellets are encased in many layers of protective coating designed to withstand even the worst accident. On this point, the NASA officials make a pretty good case -- though I'm not going to be eagerly rushing down to Cape Canaveral myself to see Cassini lift off.
Activists are more worried about what might happen after liftoff. The Cassini, you see, is planning to take what you might call the scenic route, slingshotting once around Jupiter, twice around Venus and once again around Earth, to help build up the requisite speed it will need to send it whirling toward Saturn for its final rendezvous.
It's the Earth flyby that inspires the most apocalyptic rhetoric among the mission's critics. Cassini will be traveling more than 40,000 mph as it swings past us. If it were to crash into Earth's atmosphere, it could simply vaporize, potentially sending a fine mist of radioactive material floating into lungs around the world. NASA says that the chances of such a crash are "one in a million" -- and even if it happened, the radiation release might kill 120 people (or maybe a few more) over the course of half a century.
City University of New York physicist Michio Kaku, one of the more sober of the mission's critics, has called the NASA safety analyses "pure guesswork masquerading as physics." True, the probability of a crash during the Earth flyby is very low: It would require an incredible and improbable string of screwups for the ship to go that far off course. Still, according to Kaku, should the worst happen, Cassini's radioactive fallout could kill not 120 people, or 2,300 (as NASA originally estimated), but 200,000.
Kaku's figures are, of course, based upon guesswork as well. But he at least admits as much up front, which is more than can be said for the doomsday scenarists. "Personally, I don't like hearing [Cassini opponents] make these sorts of estimates, and frankly I think most anti-nuclear Cassini scientists are also reluctant to 'play the numbers game' but keep getting pushed into it anyway," says Russell Hoffman, the editor and Webmaster of the STOP CASSINI newsletter and Web site.
Meanwhile, the rest of us get pushed into a miasma of illusory "certainties" provided by dubious statistics and dogmatic assumptions about the safety, or lack thereof, of nuclear energy. If we've learned anything, it is that we know the world less completely than scientists are generally prone to think. So, Hoffman may be justified in saying, "Only providence, chance, or what you might call dumb luck can ultimately 'save us' from a true worst-case scenario with a total incineration of the plutonium over a major population center."
But we also cannot live life -- or at least live a life worth living -- without taking chances. The Cassini probe may well be riskier than NASA would like to pretend; but so risky as to be not worth taking? Ultimately, irrational fear can be as dangerous as irrational confidence. And a lot less glorious.