Superb1rd

1.7 dla

' Beams shaped to fOiBitlnats specific land masses

' Beams shaped to fOiBitlnats specific land masses

The mass of a satellite antenna, including feed, depends largely on its size and the materials used in its construction. These factors are in turn a function of the frequency and beamwidth or gain. Table 13-16 lists some examples of satellite antenna weights, showing that the more complex shaped-beam antennas have relatively high mass because of their complex feed networks. Multiple and scanning beam antennas have comparable masses.

The power efficiency and mass of a satellite transmitter are often key factors in sizing a satellite. Figure 13-15 shows how the transmitter input power and mass varies with output RF power, based on actual satellite equipment We can see that the solid-

state transmitter has lower mass but requires more input power compared to the traveling wave tube amplifier. In general, solid-state transmitters are preferred for power outputs up to 5 or 10 W, except at frequencies below 2 GHz, where power outputs up to 80 W are achievable. Solid-state amplifiers are more reliable than the traveling wave tube amplifier, mostly because they require lower voltages. We expect improved solid-state amplifiers with higher powers and frequencies will become available during the next 10 years.

Fig. 13-15. Satellite Transmitter Power and Mass vs RF Power Output. The curves derive from actual flight hardware. The data Is relatively independent of output frequency.

Table 13-17 lists the payload parameters for FireSat, based on the link budgets in Table 13-13 and the payload characteristics found in Table 13-16 and Fig. 13-15. These parameters also enter into the total satellite power and mass budget discussed in Chap. 10.

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