Low Earth Orbit

Introduction to low earth orbit:

LEO stands for Low Earth Orbit.This orbit is very near the earth compared to other orbits hence reduces transmission time of signals. A Low Earth Orbit can also be used for polar satellites which cover polar regions  which the GEOs are unable  accomplish. Since  satellites in Low Earth Orbit are not constantly visible to earth stations,we need automatic systems to track the satellite and align the antenna.Low Earth Orbit satellites are used for a variety of task and application like civil, scientific and military field which includes Earth observation, radar, optical, telecoms and demonstrator.

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Classification of Satellite Orbits


We can classify the satellite orbits as mentioned below:

1.Based on shape of the orbit

Circular with center at thr center of the earth.
Elliptical with one focus at the center of earth.
2.Orbits in different plane around the earth

Equatorial orbit which is above earth’s equator
Polar orbit which passes over both poles
Inclined orbits and other orbits
3.Height of satellites

Geo stationary orbit (GEO) - 36000 km above from the surface of the earth.
Medium earth orbit (MEO) -   6000 - 20000 km above from the surface of the earth.
Low earth orbit (LEO) - 500-1500 km above from the surface of the earth.

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Characteristics and Categories


Characteristics of Low Earth Orbit Satellites

Orbits are circular or slightly elliptical.
Range is 0 to 2000 km from the center of the earth.
Period of revolution or orbit period ranges from 90 minutes to 120minutes.
Diameter of coverage area is about 8000 km.
Signal propagation delay is less than 20ms in one round trip.
Maximum satellite visibility time for earth station is up to 20 min.
Sensitivity of the system must high to handle large Doppler shifts.
Orbital deterioration is caused by atmospheric drag.
Categories of Low Earth Orbit Satellites

Big Low Earth Orbit Satellites

Frequency of operation above 1 GHz.
Data transfer speed is up to few Mbps.
Offers services on global positioning and other voice services.
Little Low Earth Orbit Satellites

Frequency of operation is below 1 GHz.
Bandwidth achieved is 5MHz.
Data transfer speed is up to 10 kbps.
Specially used for paging, tracking, and low-rate messaging.