Cassini: An Accident Waiting to Happen?

WASHINGTON: Is the Cassini probe, which heads for Saturn Monday, nothing more than a space-bound H-bomb? Despite the spaceship being laden with 72 pounds of highly toxic plutonium, the chances of a nuclear nightmare are actually quite remote. TIME science correspondent Jeffery Kluger reports that "Cassini's opponents have shown an extreme excess of caution. Dozens of spacecraft have flown with nuclear power sources, and so far, there have been no accidents."

What makes an atomic disaster so unlikely? Heat-resistant ceramic jackets around each plutonium pellet, which can easily withstand the temperature of reentry and the force of an explosion. If the system does fail, Cassini's opponents warn, trace amounts of plutonium could be inhaled and cause cancers of the lung, bone and liver. NASA's response: the average exposure would equal about 2 millirems over 50 years, a dose so mild that it makes standing next to your microwave look dangerous.