CME 574 Satellite Communications
Fall, 2007
Dr Hazem Al-Otum
Ref. Ellwood Brem, Instructor
Topics we will cover:
•
History
•
Satellite Mechanics
•
Orbital Mechanics
•
Launch Vehicles
•
Space Segment
•
Earth Segment
•
Link Budget
•
Multiple Accessing
•
Satellite Services:
•
VSAT, MSAT, GPS…
It wasn’t easy!
http://webphysics.ph.msstate.edu/javamirror/ntnujava/projectileOrbit/projectileOrbit
Historical Background
• 1945 Arthur C. Clarke publishes an essay about „Extra Terrestrial Relays“
• 1957 first satellite SPUTNIK
• 1960 first reflecting communication satellite ECHO
• 1963 first geostationary satellite SYNCOM
Historical Background
• 1988 first satellite system for mobile phones and data communication INMARSAT-C
• 1993 first digital satellite telephone system
Historical Background
Passive Sats
•
Moon: (1954-62) USA Navy TX the
first message Earth-moon-earth.
•
(1956)-Relay established between
Historical Background
Passive Sats
Then Came: Sputnik 1, Explorer1
• Launched October 14, 1957
– from the Baikonur
Cosmodrome in Kazakhstan
• 184 pounds
• Orbital period 90 minutes
• Broadcast “beep beep”
– 20 and 40 MHz
• Shocked the US into action
– Started space race
Historical Background
Active Sats
•
(1960) USA Courier – First
transponder-Type Sat. (3W)
•
(1963-64) – USA Syncom-III attempt to
place a GEO Sat.
•
(1965) – IntelSat 1 (Early Bird) 480
VB + 1 TV
Now: Boeing 702 DBS
Satellite
•
134.5 feet long
•
2645 lbs payload
•
11,464 lbs takeoff
weight
•
Over 100 high-power
transponders (94
active/24 spare)
•
Up to 25 kW power
•
Xenon-Ion Propulsion
System
Satellite Regions
•
Region 1:
Europe, Africa, Former Sov. Union & Mongolia
•
Region II:
North, South America and Greenland P
•
Region III:
Asia, Australia, South and West Pacific
Utilization: 24% - USA; 13%-UK; 6% France
Uses of Satellites
(in somewhat chronological order)
• Intercontinental telephone, data, and video
• Photo Reconnaissance
• Scientific research
• Network TV distribution
• Private multipoint data networking (VSATs)
• Strategic military communications
• Signals intelligence
• Mobile satellite services (Inmarsat)
• Satellite radiolocation (GPS/Glonass)
• Direct broadcast satellite (DBS –
Primestar/Echostar)
• Handheld voice/data communications
(Iridium/ICO/Globalstar)
A Platform in Space !
•
In 1945 Arthur C. Clarke wrote an article in
Wireless World
magazine outlining a
system of geo-stationary broadcast satellites
in orbit 22,000 miles above the equator.
Intercontinental telephone,
data, and video relay
•
Initially satellite links were only:
–
One-way video and data traffic
–
Backup to undersea telephone cables
•
Because:
–
Nominal 1-2 second time delay for a
round-trip voice message.
Imagery Reconnaissance
•
Military saw the value !
– Over-fly enemy
– Early “scientific” satellite programs were cover stories
– Discoverer “scientific” satellites
• carried cameras
• returned exposed film by a parachute
•
Modern systems digitally encode imagery
– Radio transmission to earth.
•
Newer systems include radar imaging
Scientific research
• First, scientific satellites
– Space environment near earth
– Unexpected discovery - Van Allen radiation belts in 1958
• Later, scientific satellites took pictures of earth
– Based on military reconnaissance systems
– Weather forecasting
– GOES series of spacecraft now in orbit.
• Today, scientific satellites study
– The Earth
– The solar system
– Deep space
Network TV distribution
•
Early TV network video
– Terrestrial microwave networks
•
C-band satellite systems
– Networks - greater control
– Cable TV – big boost !
– TVRO - dishes in backyards
•
Ku band
– Increased capacity
VSAT - Private Networks
• VSAT
– Very Small Aperture Terminal
• Replaces wireline data connections to businesses
– Convenience stores, malls, restaurants, gas stations
• Common uses
– Muzak background music
– Credit card transactions
– Corporate communications
Strategic Communications
• Strategic communications
– Previously relied on telephone and HF radio systems.
• Satellites
– High data rates
– Increased security
• Early satellites used UHF
• Today frequencies to EHF
• Example – Milstar
– Communications system
Signals Intelligence
• LEO and GEO systems deployed beginning in the 1960’s.
• Designed to intercept radio communications and radar signals.
• Antennas up to 100m in diameter are in orbit now. Receives signals from weak handheld cellular sets
• Other systems allow the
tracking of ships and aircraft based on their transmissions.
Mobile Satellite Services
•
Inmarsat - communications to ships at sea.
•
Expanded
– Aircraft
– Trucks
– Rail locomotives.
– Suitcase sized terminals
• Used extensively in disaster situations and remote exploration.
•
Not suitable for handheld equipment
– Antennas and terminals required
Satellite Radiolocation and Navigation
•
Global Positioning System (GPS)
– Constellation of LEO satellites
– Timing from onboard clocks
•
Earth receivers
– Use stored “ephemeris” data
•
Who uses GPS ?
– Trucks, ships, planes, hikers
DBS - Direct Broadcast Satellite
•
Digital video & audio to home users
– DishNetwork & DirecTV
– High quality pictures
– Competes with cable television
•
Access by subscription
– Set top box
– 18 inch dish antenna
•
Ka & Ku Satellites - Big Ones !
•
New – Satellite to automobile digital radio
Handheld telephone/data
• Iridium & Globalstar
– Many LEO satellites
• Iridium went bankrupt !
– High costs
– Cannot compete with cellular systems
• Globalstar - niche market
– $1 - $3 per call
• Iridium was reborn
– US DOD investment
In the Future
?
Internet backbone services
• Teledesic
– Internet in the sky
– 120 Mb uplink – 720 Mb downlink. – Ka band • LEO constellation – Inter-satellite links – Scalable • Viability in question – Iridium debacle
• System scaled back
– From 240 satellites
– To only 30 satellites
