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!

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

Historical BackgroundPassive Sats

Echo: (1960) 100ft-diameter balloon

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

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– Nothing launched yet