WHEN NASA's Cassini probe blasted off in October 1997, hundreds of protesters gathered outside Cape Canaveral to demonstrate against the launch. The problem was 150 kilograms of plutonium packed into the craft's nuclear batteries. During Cassini's long journey into the icy depths of space, the plutonium would be needed to produce several hundred watts of power. But should the launch fail, or should NASA miscalculate the trajectory of the craft as it returned to fly past Earth in August 1999, the spacecraft could be destroyed and the plutonium released into the atmosphere.

In the event, everything went without a hitch. But now the anti-nuclear protesters who gathered to send Cassini on its way have something else to worry about. Engineers making the tiny silicon-based devices known as MEMS—microelectromechanical systems—are also looking for a power source for their creations. And some think nuclear batteries could be just the thing.

MEMS will ...