INTRODUCTION TO SATELLITE SYSTEM

اهداف المحاضرة • ان يتعرف الطالب على الجزء الفضائي والجزء الارضي من المنظومة الكاملة للقمر الاصطناعي. • ان يتعرف الطالب على مكونات ومعدات القمر الصناعي. • ان يتعرف الطالب على كيفية تحكم القمر الصناعي بوضعه الاتجاهي. • ان يتعرف الطالب على كيفية مناورة القمر الصناعي للبقاء في موقعه في المدار.

CONTENTS: THE SPACE SEGMENT AND THE EARTH SEGMENT THE SPACE SEGMENT. ATTITUDE CONTROL. STATION KEEPING. THE EARTH SEGMENT. REFERENCES.

THE SPACE SEGMENT AND THE EARTH SEGMENT

Attitude Control The attitude control procedure involves: measuring the attitude of the satellite by sensors; comparing the results of these measurements with the required values; 3. calculating the corrections to be made to reduce errors; 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 .

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

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.

The Earth Segment

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.

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.