Solar energy spacecraft power supply

Power supply systems provide electricity to feed the onboard spacecraft equipment and can be classified by the primary energy sources chemical, solar, and nuclear. 

Surface missions have significant solar flux available to supply an energy storage system for backup power. Deep space missions do not have a similar capability once the spacecraft travels much beyond the earth s orbit. This availability of solar power provides greater flexibility for a moon or Mars mission in terms of backup power and may affect the number of components and operating strategy compared to a deep space mission. 

Fuel cells are voltaic cells in which the reactants are continuously supplied to the cell and the products are continuously removed. The hydrogen-oxygen fuel cell (Figure 21-17) already has many applications. It is used in spacecraft to supplement the energy obtained from solar cells. Liquid H2 is carried on board as a propellant. The boiled-off H2 vapor that ordinarily would be lost is used in a fuel cell to generate electrical power. 

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