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INTRODUCTION TO

SATELLITE SYSTEM

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المحاضرة اهداف

من • االرضي والجزء الفضائي الجزء على الطالب يتعرف ان

. االصطناعي للقمر الكاملة المنظومة

. الصناعي القمر ومعدات مكونات على الطالب يتعرف ان •

بوضعه الصناعي القمر تحكم كيفية على الطالب يتعرف ان •

االتجاهي.

في للبقاء الصناعي القمر مناورة كيفية على الطالب يتعرف ان •

. المدار في موقعه

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CONTENTS:

• THE SPACE SEGMENT AND THE EARTH SEGMENT

• THE SPACE SEGMENT.

• ATTITUDE CONTROL.

• STATION KEEPING.

• THE EARTH SEGMENT.

• REFERENCES.

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THE SPACE SEGMENT AND THE EARTH SEGMENT

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• The attitude control procedure involves:

1. measuring the attitude of the satellite by sensors;

2. comparing the results of these measurements with the required values;

3. calculating the corrections to be made to reduce errors;

4. introducing these corrections by operating the appropriate

torque units.

• The three axes which define a satellite’s attitude are its roll, pitch,

and yaw (RPY) axes.

• These are shown relative to the earth in Fig. ( 1 ) .

Attitude Control

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Figure(1): (a) Roll, pitch, and yaw axes. (b) RPY axes for the geostationary orbit.

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Station Keeping

• In addition to attitude control, it is important that a geostationary satellite be kept in its correct orbital slot.

• The equatorial ellipticity of the earth causes geostationary satellites to drift slowly along the orbit, to one of two stable points, at 75°E and 105°W.

• Jets are used to counter this drift. This is termed as east-west station-keeping maneuvers.

• The geostationary also will drift in latitude, because of the forces of gravitational pull of the sun and the moon.

• Jets may be pulsed at the appropriate time to return the inclination to (zero north-south station-keeping maneuvers) .

• Orbital correction is carried out by command from the TT&C earth station, which monitors the satellite position.

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The Earth Segment

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TTCM

The main tasks of TTCM are:1) Station-keeping facilities:

a) the satellite must be kept on station within the narrow window formed by the

longitude and latitude assigned to it.

b) its attitude must be monitored and corrected to ensure that the antennas are

always pointed in the right direction towards the Earth.

2) Maintenance in orbital position.

3) Technical control of the satellite, concerning.

4) Attitude control.

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References:

• Satellite Communications By Dennis Roddy / Fourth edition.

• Handbook On Satellite Communications (HSC)

(Edition 3)/Robert W. Jones .• “Brief Overview of Space Market”/By: Yvon Henri /ITU

Radiocommunication Bureau.