16879 orbital effects

7/28/2019 16879 ORBITAL Effects

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Doppler Shift The Doppler effect in satellite communications is the change in

frequency of an electromagnetic signal that results from the

relative speed of the satellite and the Earth terminal.

When transmitter is moving towards the receiver, the received

frequency will be higher than true transmitting frequency.

When transmitter is moving away from the receiver, the

received frequency will be lower than true transmitting

frequency.



Solar Eclipse A satellite is said to be in eclipse when earth prevents

sunlight from reaching it.

For GEO satellites, eclipses occur during two periodsthat begin 23 days before the equinoxes and end 23days after the equinoxes. (About march 21 andSeptember 23).

During eclipse, satellite does not receive any powerand rely fully on batteries.



Batteries are designed to operate with maximum depthof discharge.

The Depth of Discharge (DOD) of a battery determines the fraction of power that can be withdrawn from the battery.

Ground controllers perform battery conditioning prior

to eclipse operation to ensure best battery performance.



In eclipses not only main power source is withdrawn,but also the rapidity with which satellite enters andexits the shadow can cause extreme change in powerand heating effects.



Sun Transit Outage A Sun-transit outage occurs due to the particularly

strong interference that results when the geometry of

an orbit is such that the beam of an Earth stationantenna is pointed directly at the Sun.

The sun temperature is about 6000 to 10000 K, which

will add noise to our signal and hinders the

communication.



The days on which maximum solar interference

occurs varies according to the latitude of the Earth

station; the time of day on which the interferenceoccurs depends on the longitude of the Earth station.

Noticeable interference may be experienced for as

long as ten minutes a day for several days, duringwhich time the receiving Earth station can do nothing

except wait for the Sun to move out of the antenna’s

main lobe.

Although the time lost may seem insignificant(approximately 0.01% of the year), Sun-transit

outages always occur in the daytime during peak

traffic loads.



In the northern hemisphere, sun outages occur beforethe March equinox (February, March) and afterthe September equinox (September and October), andin the southern hemisphere the outages occur after theMarch equinox and before the September equinox.



Range Variations Even with best station keeping system available, the

position of satellite w.r.t earth exhibits a cyclic daily

variation. This will led to variation in range between satellite

and user terminals.

If TDMA is used, special attention needed so that

particular frames reach their requisite destination.

16879 orbital effects

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