CME 574 Satellite Communications
Fall, 2007Dr Hazem Al-Otum
Ref. Ellwood Brem, Instructor
To orbit the Earth is to fall down and miss the ground !
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.html
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
• 1982 first mobile satellite telephone system INMARSAT-A
Historical Background
• 1988 first satellite system for mobile phones and data communication INMARSAT-C
• 1993 first digital satellite telephone system
• 1998 global satellite systems for small mobile phones
Historical BackgroundPassive Sats
• Moon: (1954-62) USA Navy TX the first message Earth-moon-earth.
• (1956)-Relay established between WD and Hawaii
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
Historical BackgroundActive 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)
• Internet backbone services
A Platform in Space !
• In 1945 Arthur C. Clarke wrote an article in Wireless World magazine outlining a system of geo-stationary broadcast satellitesin orbit 22,000 miles above the equator.
• The proverbial Sky Hook !
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• Low Earth Orbit (LEO) - typically 200 miles
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
• Hubble Space Telescope, Chandra X-ray Telescope, ISS
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– Direct broadcast (DBS)
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
• 64kbps to 2Mbps
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– Satellite constellation
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• Analog and digital services are used.
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– Almost everyone!
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– Sirius & XM Satellite 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– > $4 per call