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Satellite Communications

Ashaad Rambharos

CSE, Intelsat

Date: October 2014

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Guidelines

• Mobile phones – kindly switch to silent

• Bathrooms

• Questions – please ask

• Health Breaks and Lunch

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Agenda

• Satellite project

• Satellite Launch

• Orbits

• Satellite Eclipse

• Sun Outage

• Frequency allocations

• Polarisation

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Satellite Launch

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Launch Trajectories

Mission Sequence

Stabilization

Multiple burns to achieve GEO orbit

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Launch Trajectories

Successive LAM/LAE burns achieve the final geostationary orbit

Generic Transfer ProfileGeneric Transfer Orbit Profile

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• Show IS20 Launch

• Show video of launch

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Satellite orbits

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Communication Satellite Orbits

•To understand satellite systems better, we must know something about their orbits

•Satellites circle the earth in orbits, balancing gravity against centripetal force

LEO

MEO

GEO

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Satellite Orbits

LEO

MEO

GEO

Type LEO MEO GEO

Description Low Earth Orbit

Equatorial or polar orbit

Medium Earth Orbit

Equatorial or Polar orbit

Geostationary Earth Orbit

Equatorial orbit

Height 100-500 miles 6000-12000 miles 22,282 miles

Signal Availability 15 min 2-4 hrs 24 hrs

Advantages

Lower launch costs

Short round trip signal delay

Small path loss

Tracking antenna

Moderate launch cost

Small round trip delays

Tracking antenna

Covers as much as 42.2% of the earth's surface

Ease of tracking

No problems due to doppler

DisadvantagesShorter life, 5-8 years

Encounters radiation belts

Larger delays

Greater path loss than LEO's

Very large round trip delays

Expensive Earth Stations due to weak signals

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GEO ORBIT

• The orbit must be geosynchronous. Having an

orbital period of ≈ 24Hrs.

• The orbit must be a circle.

The orbit must lie in the earth's equatorial plane

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Satellite Orbits

• GEO Inclined Orbit• Antenna tracking system required

• Uplink beam coverage changes

• Downlink beam coverage changes

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Orbital Drift

• A satellite intended for radio communications among fixed earth

stations must meet two criteria:

• The satellite must remain at a fixed position in the sky, this means

that the satellite must move in a geostationary orbit. The owners of

most geostationary satellites try to maintain their satellites within a

box measuring 0.1° x 0.1°

• The satellite must be maintained at the proper attitude. This term

describes the orientation of the satellite within its box. If the satellite

is not maintained at the proper attitude, its antennas will not be

aimed properly.

• Unfortunately, once a satellite is placed in proper position and

attitude, it doesn't stay there: it tends to drift.

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DRIFT

• Drift degrades satellite performance in two ways: the satellite

may move out of position, or it may assume an improper

attitude.

• Drift results from external forces. While there are hundreds of

external forces acting on the satellite, the primary forces are

these:

• The gravitational pull of the sun. The intensity and direction of

this force changes continuously, in daily and yearly cycles.

• The gravitational pull of other objects in the solar system.

Although these forces are considerably weaker than the sun's

gravity, their effects can be measured and predicted.

• The uneven distribution of land mass on the surface of the

earth.

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Satellite Eclipse

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Eclipse

� Satellite is powered by batteries during the eclipse

period

� When the Earth is between the sun and the satellite

the solar panels do not have sun light - Thus they can

not provide power

� During the spring and fall equinoxes the sun passes

through the equatorial plane

SunEarthEarth

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Sun Outage

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Sun Outage

•During the Spring and Fall equinoxes the sun passes

through the equatorial Plane

� When both the sun and satellite are in the ground

stations field of view, the RF energy from the sun

overpowers the satellite signal

Sun

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Sun Outage (cont)

� Latitude and Longitude of the ground station and Longitude of the satellite determines when the sun outage will occur

� Impact period lasts for Several Days Around the Spring and Fall Equinox

� Per Site Impact Period Lasts 3-10 Days

� Duration 1 – 10 minutes per Day– Antenna Size (Beam Width)

– Satellite Transmit Power (EIRP)

�To calculate sun outage times go to: http://ww2.intelsat.com/resources/satellites/sun.aspx

http://www.satellite –calculations.com

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ITU Satellite Frequency Allocations

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Satellite Frequency Allocations

Maritime Mobile Up

Maritime Mobile Down

Aeronautical Mobile Up

Aeronautical Mobile Down

Land Mobile Up

Land Mobile Down

Emergency/Distress Up

Emergency/Distress Down

Maritime/Land Mobile Up (Co-Primary)

Maritime/Land Mobile Down (Co-Primary)

MSS Up

MSS Down

Legend REGION1

REGION

2

REGION

3

REGION

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ITU Regional Definitions

REGION1

REGION

2

REGION

3

REGION

3

ITU Regional Definitions

BSS = Broadcast Satellite Service FSS = Fixed Satellite Service MSS = Mobile Satellite Service

10700 10950 11200 11450 11700 12200 12750 13250 13750 14500 14800 17300 1810012500 17800

Ku-Band Satellite Frequency Allocations in MHz~ ~ ~ ~

REGION 1

REGION 2

REGION 3Radar

Aero-

nautical

Radar

~ ~ ~ ~

Ka-Band Satellite Frequency Allocations in MHz

17700 20100 21200 27000 30000 310002750019700 29500

REGION 1

REGION 2

REGION 3

~ ~~ ~

L-Band Satellite Frequency Allocations in MHz~ ~

1660.51634.51626.5

REGION 1

REGION 2

REGION 3

1656.51646.51645.516101530 1533 1544 1545 1555 1559

~ ~

1631.515251492

Extended FSS Up

Extended FSS Down

FSS Allotment Plan Up

FSS Allotment Plan Down Government FSS Down

Government FSS Up

BSS Plan Down

BSS Plan Up

Legend

MSS/Government FSS Down (Co-Primary)

MSS/Government FSS Up (Co-Primary)

FSS Up

FSS Down

MSS Up

MSS Down

Space Operation/Earth Exploration/SpaceResearch Down (Co-Primary)

Space Operation/Earth Exploration/Space Research Up (Co-Primary)

Space Research Down

Space Research Up

Meteorological Down

Meteorological Down/MSS Up (Co-Primary)

FSS/MSS Up (Co-Primary)

FSS/BSS Up (Co-Primary)

MSS/Radiodetermination Up(Co-Primary)

~ ~

REGION 1

REGION 2

REGION 3

3400 3700 4200 4500 4800 5850 6425 6725 7025 7250 7750 7900 8400572526552535252025002483.523002200217021602120211020252010198017101675

~ ~

S-Band, C-Band and X-Band Satellite Frequency Allocations in MHz

Fixed

mobile

Fix

ed

mo

bile

Radar

Fixed

mobileAeronautical,

Radio-nav.,

Fixed mobile

~ ~

2290 ~~~ ~~~~ ~

~~

X-BandS-Band C-Band

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•Ka-Band

－Transmit 27.5 – 30.0 GHz

－ Receive 17.7 – 20.0 GHz

Frequency allocations

� C-Band－ Transmit 5.925 - 6.425 GHz (U.S.)

5.625 – 6.425 GHz (I.T.U.)

－ Receive 3.700 - 4.200 GHz (U.S.)

3.400 – 4.200 GHz (I.T.U.)

� Ku-Band－Transmit 14.00 - 14.50 GHz (U.S.)

13.75 – 14.50 GHz (I.T.U.)

－ Receive 11.70 – 12.20 GHz (U.S.)

11.20 – 11.70 GHz (ITU)

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C-Band

•Advantages

– Wide footprint coverage

– Minor effects from rain

– Lower cost for earth station antenna

– Requires larger antennas

� Disadvantages

– Requires larger RF power amplifier

– Effected by terrestrial interference (TI)

– Difficult to obtain transmit license

• Frequency clearance

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Ku-Band

� Disadvantages– Greater effect from rain

– Smaller footprint (beam) coverage

� Advantages

– Smaller antennas

– Smaller RF power amplifiers

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Ka-Band

� Advantages– Smaller antennas

– Smaller RF power amplifier

� Disadvantages– Greater effect from rain

– Smaller footprint (beam) coverage

– High equipment cost

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Polarization

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Polarization

� Provides increased satellite capacity (Allows frequency reuse)

� The directional aspects of the electrical field of a radio signal

� Linear (90o Out of Phase)

－ Horizontal (H)

－ Vertical (V)

－ All Ku-Band satellites are Linear

� Circular (180 o Out of Phase)

－Right Hand Circular (RHCP)

－Left Hand Circular (LHCP)

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Linear Polarization

• Vertical

• Field lies in a plane perpendicular to the earth’s surface.

� Linear Polarization

– The electrical field is wholly in one plane containing the direction of propagation

� Horizontal

– Field lies in a plane parallel to the earth’s surface.

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Circular Polarization

• Left Hand Circular Polarization (LHCP)

• the electric field is rotating counterclockwise as seen by an observer towards whom the wave is moving

� Circular Polarization

– The electrical field radiates energy in both the horizontal and vertical planes and all planes in between

� Right Hand Circular Polarization (RHCP)

– the electric field is rotating clockwise as seen by an observer towards whom the wave is moving

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Linear Polarization

• Advantage

• Lower Cost Antenna System

• Feed Assembly (OMT)

• Better Cross-Pol Isolation

� Disadvantage– Polarization Adjustment Required

– Polarization changes depending on Latitude and Longitude

– Greater chance of problems due to cross-pol interference

– Faraday rotation in the ionosphere

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Circular Polarization

•Advantage

• No polarization adjustment required

• Fixed by Ortho-Mode-Transducer (OMT)

• Less chance of cross-Pol interference

�Disadvantage– Higher cost antenna systems

• Feed Assembly (OMT)

– Slightly lower cross-Pol isolation

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• Questions