POWER SUBSYSTEM- This system provides the necessary DC power to the satellite. All communication satellites derive their electrical power from solar cells. There is also a battery backup facility used during launch and eclipses. The batteries are of sealed Nickel Cadmium type and have good reliability and long life. Everything on board operates electrically. Solar cells are large arrays of photocells connected in various series and parallel circuits as d.c. source. Solar panels are capable of generating many kilowatts. All solar panels always be pointed towards the sun, Solar panels generate a direct current that is used to operate the various components of satellite. D.C. power is used to charge the batteries which provides d.c. current to component of satellite when solar panels are not properly positioned. Voltage regulators are used to power individual electronic circuits. Some components like TWT amplifier in transponder requires very high d.c. voltage to operate, so d.c. to d.c. converter is used to raise the level of low voltages to high voltage.