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RECENT TRENDS IN SPACECOMMUNICATION

THE ROLE OF

OPTICAL FREE-SPACE ON INTER-SATELLITE

COMMUNICATION

EEE 506- Current Trends in Electronic and Electrical Engineering


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INTRODUCTION

The notion of satellite communication was proposed by Arthur C.Clarke in his article on Wireless World in 1945.

From inception gamut of technologies and operators have beenoperating to uphold satellite communication systems


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Category Year Activity Person/Agency/Country

Geostationary

concept1945

Suggestion of Geostationary satellite communication

feasibility

A. Clark ( U.K )

MoonReflection

1946Detection of Lunar Echo by Radar

J. Mofenson (U.S.A.)

1954Passive relaying of voice by moon reflection.

J.H. Trexler( U.S.A. )

1960Hawaii-Washington, D.C. Communication by

Moon Reflection.

Low altitude

orbit

1958 Observation of signals from Sputnik -1 Satellite.U.S.A. Navy.

1958Tape-recorded voice transmission by Satellite

SCORE.

U.S.S.R., Japan and others.

1960Meteorological facsimile Trans mission by

Satellite Tiros-1.U.S.A. Air Force.

1960Passive relaying of telephone and television by

Satellite Echo-1.U.S.A. NASA

1960Delayed relaying of recorded voice by Satellite

Courier-1B.U.S.A. Army.

1962Active transatlantic relaying of communication by

Satellite Telstar-1.U.S.A. Army.

1962 Communication between manned SatellitesVostok-3 and 4; Space television transmission.

U.S.A., U.K., France.

1963Scatter communication by tiny needles in Orbit.

( West Ford Project 6 )

U.S.A. MIT.

1963Active transpacific relaying of communication by

Satellite Relay 1.U.S.A. NASA, Japan.

Synchronous

Satellite

1963USA-Europe-Africa communication by Satellite

Syncom 2.U.S.A. NASA

1964Olympic Games television relaying by Satellite

Syncom 3

U.S.A., NASA Japan.

1965Commercial Communication (Semi-experimental)

by Satellite Early Bird.INTELSAT.

MAJOR MILESTONES OF SPACE RADIO COMMUNICATIONS


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INTRODUCTION

Motivation to use Satellites

Satellite missions.

Satellite System Elements

Space segment

Ground segment

Transponders

Bent-pipe

Onboard processing

Footprints

Orbits


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INTRODUCTION

Motivation to use Satellites

Satellite missions.


Space segment

Ground segment

Transponders

Bent-pipe

Onboard processing

Footprints

Orbits


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Satellite Orbits

Geosynchronous Orbit (GEO):

36,000 km above Earth, includes

commercial and military

communications satellites,

satellites providing early warning of

ballistic missile launch.

Medium Earth Orbit (MEO): from

5000 to 15000 km, they include

navigation satellites (GPS, Galileo,

Glonass).

Low Earth Orbit (LEO): from 500 to

1000 km above Earth, includesmilitary intelligence satellites,

weather satellites.


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Advantages of Satellite Communication

Can reach over large geographical area

Easy to install new circuits

Circuit costs independent of distance

Broadcast possibilities Terrestrial network "by-pass"

Provision of service to remote or underdevelopedareas

User has control over own network 1-for-N multipoint standby possibilities


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OPTICAL FREE SPACE COMUNICATION IN SPACE

In space, radio frequencies (RFs) are usually used for long-distance

linkage. However, recent progress in optics and laser technologies,

especially in fiber optics, is ushering in an era of inter-orbit communications

using laser beams. Both RFs and optical waves are electromagnetic waves,

but optical waves offer many advantages in space.


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FEATURES OF OPTICAL FREE

SPACE COMMUNICATION LINK SMALLER SIZE

LESS WEIGHT AND POWER CONSUMPTION

HIGH DATA RATE

SECURED

NO REGULATORY RESTRICTION

LESS OVERALL EXPENSES IN ORDER TO ACHIEVETHE SAME MISSION


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LIMITATIONS OF OPTICAL

FREESPACE COMMUNICATION

VIBRATION

INTERNATIONAL INTEROPERABILITY

POINT AHEAD PROBLEM


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POINT AHEAD PROBLEM

RF, even EHF, spreadswhile propagating

Laser light doesnt

spread as much as RF


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FUTURE TREND

LASER COMMUNICATIONS RELAY DEMONSTRATIONMISSION (LCRD) as part of the launches anticipated in2015 and 2016 by NASA Goddard Space Flight Center inGreenbelt MD USA.

LCRD Mission will- Enable reliable, capable and cost effective optical

communication for near earth application and deep spacemissions

- Demonstrate high data rate optical technology

-Identify and develop requirement for future operational opticalcommunication systems

- Develop industrial base for future space optical communicationsystem

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