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INTRODUCTION TO SATELLITES

LESSON 2

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DEFINITIONS: SPACE

A place free from obstacles.• An altitude at which an aircraft cannot fly due to

the lack of aerodynamic force.

Outer Space Law Treaty• To ensure that the governments of various

countries have no claim of sovereignty over the space or the moon.

• Most of the members of UN involved in space activities and ITU have signed this treaty.

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CLASSIFICATION OF SPACE

• Air space. Region below 100 km from the earth's surface.

• Outer space: cosmic space and falls between 100 km and 42,000 km: Aerodynamic lift is ineffective and is taken over by the centrifugal force.

• Deep space: Regions beyond 42,000 km fall in this category which is not in use for the communication satellites.

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ACTIVE SATELLITES

• Unlike Passive Satellites, they employ transponders to process and transmit signals.

• They use bend-pipe technology here frequency translation and amplification take place

• Most contemporary communication satellites employ regenerative technology in which demodulation/demultiplexing takes place thus allowing Intersatellite Links (ISL).

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COMPONENTS OF THE SATELLITE SPACE SEGMENT

The space segment of a satellite system consist of:– The satellites – Ground facilities providing the tracking,

telemetry and telecommand (TTC) functions – Logistics support for the satellite stations.

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FIRST LAW OF KEPLER

The trajectory of any satellite which experiences such a central force µ/r2 is a conic section whose focus coincides with the centre of the Earth as shown below.

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SPACE SEGMENT - GSO

• Most communication satellites with a few exceptions (e.g. satellite mobile communication satellites) describe a circular orbit on the equatorial plane at an altitude of about 36 000 km

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ADVANTAGES OF USING STATIONARY ORBITS

This characteristic enables the satellite to provide permanent coverage of a given area with the following advantages:

• Simplified design of earth stations, since they are no longer required to track satellites moving at considerable angular velocities

• More efficient use of the radio spectrum and orbital resources.