DSCS-III Communication Satellite System

The DSCS-III satellite offers six covert communications channels and is equipped with spatial user-jammer discrimination capability, which sometimes is known as antenna nulling capability, to achieve high discrimination performance. According to the published literature, two channels in this satellite system deploy high-efficiency 40 W TWTAs and the remaining four channels each use only 10 W TWTAs. This means that the total RF output of the TWTAs is 120 W. Assuming a DC-to-RF efficiency of 40% each, the DC input power required for the TWTAs will be close to 300 W. The batteries must supply this amount of DC power. In addition, additional DC power is required to operate the antenna stabilization mechanisms and the various electronics, electro-optic, and microwave sensors onboard the satellite. The solar panels must be capable of charging the batteries to meet all the DC power consumption. 

In the case of multicarrier operation, back-off power is required, which tends to lower the DC-to-RF efficiency for the TWTA units to around 25%. Under such operation, the secondary batteries must be able to supply DC power in excess of 1,200 W for the TWTAs alone. Low-power TWTAs are deployed in DSCS-III systems because of high-gain antennas and the integration of advanced technologies in the receivers. 

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