Power: nuclear, 8 solar, 8. thermoelectric

Space exploration relies heavily on solar energy when the spacecraft is in the inner solar system. However, solar power is insufficient for spacecraft that have to journey to the outer planets. Chemical energy sources, typically batteries, tend to be relatively heavy and have rather short lifetimes for missions that are to last many years. The solution adopted to date is to combine a radioactive solid with a thermoelectric generator (see Section 15.2.3). The advantages of this solution are that there are no liquids to spill and no moving parts to wear, and a nuclear isotope with a long half-life will continue to provide power over the lifetime of the craft. 

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