Scientists say the 72 pounds of plutonium is the only means they have of propelling the probe on its 2.2 billion-mile trip. And TIME science correspondent Jeffrey Kluger says the chances of a nuclear nightmare are remote. "Dozens of spacecraft have flown with nuclear power sources," says Kluger, "and so far, there have been no accidents." Ellis Miner, Cassini mission science manager, told CNN an explosion would be "less dangerous than getting an X-ray at the dentists." For Cassini's opponents, wherever they are, the launch — now delayed until Wednesday — will seem more like having teeth pulled.
CAPE CANAVERAL: "Stop Cassini,"raged the protestors' placards. And lo, Cassini did stop, albeit for high winds and a computer glitch rather than complaints over its payload of highly radioactive plutonium. Unfortunately, few of the anti-atomic activists were there to see the Saturn-bound probe stop in its tracks; most had already fled the site Monday morning, fearing a post-launch explosion. "When it comes to your kids," said one area woman who had planned to drive west with her daughter, "you don't take chances."