Sun transit outage occurs for geostationary satellites around the equinoxes for up to 10 minutes, interrupting signals due to interference from solar radiation. A satellite experiences a solar eclipse when the Earth or Moon prevents sunlight from reaching it. For geostationary satellites, eclipses due to Earth occur in the 23 days before and after equinoxes. To avoid eclipses impacting operations, satellites should be positioned west of Earth stations.

1. Arpan Deyasi
Dept of ECE, RCCIIT, Kolkata, India
Course: MCE203A
Sun Transit Outage
5/18/2020 1Arpan Deyasi, RCCIIT, MCE203A

2. Sun transit outage
is an phenomena
where
geostationary
satellite signals are
interrupted caused
by interference
from solar
radiation
What is Sun Transit Outage?
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3. Features of Sun Transit Outage
This effect lasts for 6 days around the equinoxes
This effect occurs for a maximum period of 10 minutes
Generally, sun outages occur in February, March,
September, October
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4. Solar Eclipse on Satellite
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5. A satellite is said
to be in eclipse
when sunlight is
prevented to
reach it by the
earth or the
Moon
Solar Eclipse on Satellite
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6. If Earth’s orbital plane around Sun coincides with
Earth’s equatorial plane, then geostationary orbit will
be eclipsed by the earth. This is called the earth
eclipse of satellite.
Solar Eclipse on Satellite
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7. For geostationary satellite, the Solar eclipse due to
Earth occurs during two periods
begins 23 days before equinox
and
ends 23 days after equinox
Features of Solar Eclipse
During eclipse, satellite receives no power from its solar
panels and it has to operate on its onboard standby
batteries which reduce satellite life
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8. Mathematical formulation of Solar eclipse
ie(t): inclination angle of earth’s equatorial plane
w.r.t Sun’s direction
2
( ) 23.5sine
t
i t
T
π 
=  
 
where T = 365 days
ie(t): maximum is summer and winter solstices
zero in spring and autumn solstices
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9. Mathematical formulation of Solar eclipse
Maximum shadow angle of Earth
1 e
max
e 0
R
180 2cos
R R
φ −  
= °−  
+ 
Re: Earth radius
R0: satellite distance
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10. Mathematical formulation of Solar eclipse
Re = 6378 km
R0 = 35786 km
Φmax = 17.4°
Duration of eclipse considering 24 hours period
max
17.4
24
360
t hr
°
= ×
°
max 1.16t hr=
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11. Mathematical formulation of Solar eclipse
Relative position of Sun is calculated from first eclipse day
before equinox and last day after equinox
max( ) 0.5 8.7ei t φ= = °
Corresponding time ‘t’ is
1365 87
sin
23.5
t
π
−  
=  
 
21t days
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12. Features of Solar Eclipse
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13. 5/18/2020 13Arpan Deyasi, RCCIIT, MCE203A

14. When moon passes in front of sun, moon eclipse
occurs
It is less important as it takes place for short
duration (twice in every 24 hours for an average of
few minutes)
Lunar Eclipse
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15. Way to avoid eclipse during satellite lifetime
When satellite longitude is East of the Earth station, then it enters
in the eclipse during daylight and early morning
This is undesirable if the satellite has to operate on reduced battery
power
Conclusion: Satellite longitudes should be set at
West of Earth station
When satellite longitude is West of the earth station, eclipse does
not occur until the Earth station is in darkness when usage is
likely to be low
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16. Doppler frequency shift
LEO satellite is in relative motion w.r.t Earth station terminal
GEO satellite appears stationary w.r.t Earth station terminal
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17. Doppler frequency shift
As GEO satellites moves w.r.t Earth station, frequency of
satellite transmitter varies w.r.t receiver of Earth station
Doppler shift
R T T
T T P
f f f v
f f v
∆ −
= =
fR: transmitted signal frequency
fT: received signal frequency
vT: component of satellite transmitter velocity directed towards
Earth station receiver
vP: phase velocity of e.m wave in free space
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18. http://archive.mu.ac.in/myweb_test/Satelight%20Comm..pdf
A. K. Maini, V. Agarawal, “Satellite Communications”, Wiley, 1st Ed.,
2019
References
S. Katiyar, “Satellite Communication”, S. K. Kataria & Sons, 1st Ed., 2007
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