Mumbai University > EXTC > Sem 8 > Satellite Communication and Networks

Marks: 5M

Batteries are used on board the satellite to meet the power requirements when the same cannot be provided by solar panels, as is the case during eclipse periods. Rechargeable batteries are almost invariably used for the purpose. These are charged during the period when the solar radiation is available to the satellite’s solar panels and then employed during eclipse periods or to meet a short term peak power requirements. Batteries are also used during the launch phase, before the solar panels are deployed.

All spacecraft must also carry storage batteries to provide power during launch and during eclipse periods when sun blockage occurs. Eclipses occur for a GSO satellite twice a year,around the spring and fall equinoxes, when earth’s shadow passes across the spacecraft. Dailyeclipses start about 23 days before the equinox, and end the same number of days after. The daily eclipse duration increases a few minutes each day to about a 70-minute peak on equinoxday, then decreases a similar amount each day following the peak.

Sealed nickel cadmium(Ni-Cd) batteries are most often used for satellite battery systems. They have good reliability and long life, and do not outgas when in a charging cycle. Nickel-hydrogen (NiH2) batteries,which provide a significant improvement in power-to-weight ratio, are also used. A power conditioning unit is also included in the power subsystem, for the control of battery charging and for power regulation and monitoring.