Electrical power supply in space

Silicon solar cells are used as the primary satellite power source in normal operation. When the Sun, for the satellite, is eclipsed by the Earth, power is maintained by nickel cadmium or nickel hydrogen secondary batteries. Full shadow eclipse for geostationary satellites occurs on 44 nights in spring and 44 nights in the autumn, the longest eclipses occurring at the equinoxes and giving 65 minutes of full shadow. Research on new types of storage cell, such as the silver hydrogen cell, seeking longer life, lower mass and higher efficiency, is in progress.

Spinning body satellites have body mounted arrays of solar cells, typically producing about 10 watts per kilogram of solar array mass. Body stabilised satellites using extendable arrays, which can be rotated so that they always face the Sun, deliver up to 23W/kg. Current research is aimed at increasing the dimensions of de-ployable solar panels and reducing their mass. Values are reaching 50 to 60 watts per kilogram and a few tens of kilowatts per panel. High efficiency solar cells now being developed could cut substan­tially the mass and size of arrays.

One disadvantage of deployed arrays is the limited amount of power available before the array can be deployed, that is, while the satellite is still in its transfer orbit.

Figure 51.4 INTELSAT V satellite configuration

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