Page 42 - SATELLITE AND RADAR COMMUNICATION SYSTEM

3. Attitude control
The attitude of a satellite refers to its orientation in space with respect

to earth. Attitude control is necessary so that the antennas, which usually
have narrow directional beams, are pointed correctly towards earth.

Several forces can interact to affect the attitude of the spacecraft. These
include gravitational forces from the sun, moon, and planets; solar

pressures acting on the spacecraft body, antennas, or solar panels; and
earth’s magnetic field.

4. Orbital control

Orbital control, often called station keeping, is the process required to
maintain a satellite in its proper orbit location. It is similar to, although not
functionally the same, as attitude control.

5. Thermal control

Orbiting satellites will experience large temperature variations, which

must be controlled in the harsh environment of outer space. Thermal
radiation from the sun will heat one side of the spacecraft, whereas the
side facing outer space is exposed to the extremely low temperatures of

space. Much of the equipment in the satellite itself will generate heat,
which must be controlled. Low orbiting satellites can also be affected by

thermal radiation reflected from the earth itself.
The satellite thermal control system is designed to control the large

thermal gradients generated in the satellite by removing or relocating the
heat to provide as stable as possible temperature environment for the sat-

ellite.

6. Telemetry, Tracking, Command and Monitoring (TTCM)

The telemetry, tracking, command, and monitoring (TTC&M) subsystem
provides essential spacecraft management and control functions to keep

the satellite operating safely in orbit. The TTC&M links between the
spacecraft and the ground are usually separate from the communications

system links. TTC&M links may operate in the same frequency bands or in
other bands.

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Satellite System Elements