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The space segment equipment carried aboard the satellite can be
classified under two functional areas, the bus and the payload, as shown
on Figure 2.5.
The bus refers to the basic satellite structure itself and the subsystems
that support the satellite. The bus subsystems are: the physical structure,
power subsystem, attitude and orbital control subsystem, thermal control
subsystem, and command and telemetry subsystem.
The payload on a satellite is the equipment that provides the service or
services intended for the satellite. A communications satellite payload
consists of the communications equipment that provides the relay link
between the up- and down-links from the ground. The communications
payload can be further divided into the transponder and the antenna sub-
systems.
A satellite may have more than one payload. The early Tracking and Data
Relay Satellites (TDRS), for example, had an “Advanced Westar”
communications payload in addition to the tracking and data payload,
which was the major mission of the satellite.
Figure 2.5: Communications satellite subsystem
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Satellite System Elements
