Solar panels were not a practical solution for Galileo's power needs at Jupiter's distance from the Sun (it would have needed a minimum of 65 square metres (700 ft²) of solar panels); as for batteries, they would have been prohibitively massive. The solution adopted consisted of two radioisotope thermoelectric generators (RTGs). The RTGs powered the spacecraft through the radioactive decay of plutonium-238. The heat emitted by this decay was converted into electricity for the spacecraft through the solid-state Seebeck effect. This provided a reliable and long-lasting source of electricity unaffected by the cold space environment and high radiation fields such as those encountered in Jupiter's magnetosphere. Each RTG, mounted on a 5-metre long boom, carried 7.8 kilograms (17.2 lb) of 238Pu [2]. Each RTG contained 18 separate heat source modules, and each module encased four pellets of plutonium dioxide, a ceramic material resistant to fracturing. The modules were designed to survive a range of hypothetical accidents: launch vehicle explosion or fire, re-entry into the atmosphere followed by land or water impact, and post-impact situations. An outer covering of graphite provided protection against the structural, thermal, and eroding environments of a potential re-entry. Additional graphite components provided impact protection, while iridium cladding of the fuel cells provided post-impact containment. The RTGs produced about 570 watts at launch. The power output initially decreased at the rate of 0.6 watts per month and was 493 watts when Galileo arrived at Jupiter. As the launch of Galileo neared, anti-nuclear groups, concerned over what they perceived as an unacceptable risk to the public safety from Galileo's RTGs, sought a court injunction prohibiting Galileo's launch. In fact, RTGs had been safely used for years before in planetary exploration. 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. After the Challenger accident, a study considered additional shielding and eventually rejected it, in part because such a design significantly increased the overall risk of mission failure and only shifted the other risks around (for example, if a failure on orbit had occurred, additional shielding would have significantly increased the consequences of a ground impact). (wiki)
Each RTG, mounted on a 5-metre long boom, carried 7.8 kilograms (17.2 lb) of 238Pu [2]. Each RTG contained 18 separate heat source modules, and each module encased four pellets of plutonium dioxide, a ceramic material resistant to fracturing. The modules were designed to survive a range of hypothetical accidents: launch vehicle explosion or fire, re-entry into the atmosphere followed by land or water impact, and post-impact situations. An outer covering of graphite provided protection against the structural, thermal, and eroding environments of a potential re-entry. Additional graphite components provided impact protection, while iridium cladding of the fuel cells provided post-impact containment. The RTGs produced about 570 watts at launch. The power output initially decreased at the rate of 0.6 watts per month and was 493 watts when Galileo arrived at Jupiter.
As the launch of Galileo neared, anti-nuclear groups, concerned over what they perceived as an unacceptable risk to the public safety from Galileo's RTGs, sought a court injunction prohibiting Galileo's launch. In fact, RTGs had been safely used for years before in planetary exploration. 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.
After the Challenger accident, a study considered additional shielding and eventually rejected it, in part because such a design significantly increased the overall risk of mission failure and only shifted the other risks around (for example, if a failure on orbit had occurred, additional shielding would have significantly increased the consequences of a ground impact). (wiki)
Your Wiki quote fails to mention the very real risk connected to nuclear batteries for space vehicles: contamination after destruction during a crash back to Earth. The likelihood of a space vehicle's crash back on Earth is rather high (much higher than that of a power plant accident), in the order of percents per launch. IIRC there were three US and five Russian cases when an RTG came back on Earth - at least two fell into deep sea (one I know for sure was the Apollo-13 lunar module's, the other was recovered intact), but at least four others did cause contamination, albeit in less populated areas (Canada, Andes).
After the controversy of the weak design of NASA's large planetary satellite series (remember even Cassini was from the same family as the two Voyagers - and that satellite swung by Earth three times, which in case of error would have meant much higher re-entry speeds than during a failed launch), on one hand other power sources were facilitated if possible in satellite designs (also by reducing consumption of instruments), on the other hand, the few RTGs still used were designed to withstand a crash back (for example the Pluto mission's would even have separated during fallback to not be affected by the crash deformations of the rest). *Lunatic*, n. One whose delusions are out of fashion.
