Page "Galileo (spacecraft)" Paragraph 46

As the launch of Galileo neared, anti-nuclear groups, concerned over what they perceived as an unacceptable risk to the public's safety from Galileo's RTGs, sought a court injunction prohibiting Galileo's launch.

RTGs had been used for years in planetary exploration without mishap: the Lincoln Experimental Satellites 8 / 9, launched by the U. S. Department of Defense, had 7 % more plutonium on board than Galileo, and the two Voyager spacecraft each carried 80 % as much plutonium as Galileo did.

However, activists remembered the messy crash of the Soviet Union's nuclear-powered Cosmos 954 satellite in Canada in 1978, and the 1986 Challenger accident had raised public awareness of the possibility of explosive spacecraft failures.

Also, no RTGs had ever been made to swing past the Earth at close range and high speed, as Galileo's Venus-Earth-Earth Gravity Assist trajectory required it to do.

This created a novel mission failure modality that might plausibly have entailed total dispersal of Galileo's plutonium in the Earth's atmosphere.

Scientist Carl Sagan, for example, a strong supporter of the Galileo mission, said in 1989 that " there is nothing absurd about either side of this argument.