After years of rigorous planning and testing, NASA scientists say they are convinced that the mid-October launch of the $3.4 billion, plutonium-powered Cassini mission to Saturn poses nearly no risk to the Earth and will provide an astronomical treasure of information about the sixth rock from the Sun. They say that once the mission reaches the Saturnian neighborhood in the year 2004, it also will offer important insights about the planet's icy rings, and about Titan, Saturn's largest moon, which exhibits atmospheric conditions that may have existed on a primordial Earth.
A growing opposition, however, argues that the exploration of Saturn should wait until an alternative electrical generating system is developed. These critics—who include some former NASA employees, scientists, and activists—are concerned that the spacecraft's 72.3 pounds of plutonium 238 poses a potential catastrophic risk to the Earth's population, if the substance is released. Cassini carries the most plutonium ever used on a space mission, and NASA says this is the only means for powering the heavy spacecraft in extremely dim sunlight.