Batteries are also problematic. For example, if we powered the Galileo space probe using conventional batteries instead of Radioctive Thermal Generators (RTGs) and expected the same duration for the mission (70000 hours), the probe would have batteries weighing 47T! This does not include the fact that the batteries themselves need to be kept warm.
Robert Zubrin in his excellent book Entering Space, discusses the use of nuclear power in space. He goes one step further and recommends the use of an actual nuclear reactor.
Not only do we need RTG's, we need to move beyond them to actual space nuclear power reactors that use nuclear fission, rather than mere radioisotope decay, to generate tens or hundreds of kilowatts. The reason for this is very simple. On Earth, it has been said, knowledge is power. IN the outer solar system, power is knowledge.Perhaps its time to get past the neo-luddites and start to look at nuclear power more rationally.