Fuel cells spacecraft power supply

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. 

Metal-air batteries have proved easier to develop to a state of simplicity and reliability required from a power source than the fuel cells with gaseous or liquid fuels. Hence, although a type of hydrogen-oxygen fuel cell has reached such a state of perfection that it could be assigned the task of the main power supply in the cabin of the Apollo spacecraft, more recently the zinc-air battery seems to have taken its place. 

The situation as regards mobile applications (Table 5) is, with the exception of power supplies for spacecraft, more problematical than static applications. The potential attractions of the fuel cell electric vehicle compared to the conventional internal combustion engined vehicle include ... 

Space applications for Ag-Zn cells include powering the space shuttle, space station, the lunar rover. Mars lander, and deep space probes. They were also used in the Saturn launch vehicles, the Apollo Lunar Lander, and life support jacket and to power space module operations Ml launch and return. In addition, they power spacecraft during launch and reentry. The lunar rover and space-walk suits are powered by the Ag-Zn battery systems. They also supply burst of power to supplement the fuel cell for operations in the command module. 

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