1. Overview of Satellite Systems

Contents • What is satellite communication • The Origin of Satellite • Elements of Satellite Communication • Key input data • Early Satellite Systems • System Design Considerations • Major Problems for Satellite • Limitation for Satellites • Advantages of Satellite • Different Applications • Frequency Allocation & Regulatory Aspects

What is Satellite Communication… • A communication satellite is basically an electronic communication package placed in orbit whose prime objective is to initiate or assist another through space. • Satellite communication is one of the most impressive spin-offs from the space programs and has made a major contribution to the pattern of international communication. • The information transferred most often correspondence to voice (telephone), video (Television) and digital data.

Cont... • Communication satellite are off-course only one means of telecommunication transmission. The traditional means include copper wire and microwave point- to-point links. Newer techniques involves use of optics either point-to-point infrared or fiber optics.

The origin of satellite • The concept of using object in space to reflect signals for communication was proved by Naval Research Lab in Washington D.C. when it use the Moon to establish a very low data rate link between Washington and Hawaii in late 1940’s. • Russia started the Space age by successfully launching SPUTNIK the first artificial spacecraft to orbit of the earth, which transmitted telemetry information for 21 days in Oct. 1957. • America followed by launching an experimental satellite EXPLORER In 1958. • In 1960 two satellite were deployed “Echo” & “Courier” • The first commercial GSO (Geosynhronous Orbit) (Intelsat & Molnya) in 1965 provided video (Television) and voice (Telephone) for their audience

Elements of Satellite Communications • The basic elements of a communication satellite service are divided between; •Space Segment •Ground Segment • The space segment consist of the spacecraft & launch mechanism and ground segment comprises the earth station and network control center of entire satellite system.

Satellite Communications System Uplink Down Link In door Unit IDU RFT RFT IDU RF Transmit Earth Station Receive Earth Station

Concept Transponder Earth station(site B) Earth station (site A) downlink downlink uplink uplink Earth station(site B) Earth station (site A)

Propagation Delay Single Hop 270 ms Double Hop 540 ms

Ground Station _ Anatomy Interfacility Link IFL Indoor Unit Outdoor Unit Antenna (IDU) (ODU) Sub-System 70/140 C/Ku MHz

Satellite Services • The ITU has grouped the satellite services in to three main groups • Fixed Satellite Services (FSS) • Broadcast Satellite Services (BSS) • Mobile Satellite services (MSS)

Space Segment • Space segment consist of a satellite in suitable orbit. • Space segment classified on the basis of orbit; -LEO (Low Earth Orbit) -MEO (Mid Earth Orbit) -HEO (Highly Elyptical Orbit) -GEO & GSO

Ground Segment • The ground segment of each service has distinct characteristics. • Services like; • FSS (Fixed Sat. Serv.) • BSS (Broadcast Sat. Serv.) • MSS(Mobile Sat. Serv.) -Maritime, Aeronautical & Land base • DBS (Direct Broadcast Satellite) • Etc.

Satellite Footprints Satellites beam their signal in a straight path to the earth. The satellite focus these microwaves signals onto the specified portions of the earth’s surface to most effectively use the limited power of their transponders. These focused signals create unique beam patterns called “footprints.” Types of footprints: - Global beam footprint - Hemispheric Beam Footprint - Zone Beam Footprint

Satellite Footprints

Satellite Footprints

Satellite Footprints

Satellite Footprints

Key Input Data... Bands: Beams: C-Band ( ) Ku-Band ( ) Global ( ) Hemi ( ) Zone ( ) Spot ( )

National and Regional Systems 1 Anik, Canada 6 Telecom, France 11 Asiasat, East Asia 12 CS, Japan 2 Morelos, Mexico 7 Kopernikus, Germany 8 Italsat, Italy 3 Panamsat, Americas 13 Palapa, Indonesia 4 Brasilsat, Brazil 9 Arabsat, Arab League 14 Aussat, Australia 5 Eutelsat, Europe 10 Insat, India

Early Satellites Satellite Launching Date Country/Organization Type Height (miles) Comments RELAY 1962 USA/RCA & NASA Active Duplex 942-5303 4.2/1.7 GHz satellite designed to carry telephone signals. SYNCOM 1963 USA/NASA Active Duplex Geostationary First Geostationary communication satellite used to transmit television signals from the Tokyo Olympics. MOLNIYA 1965 U.S.S.R Active Duplex High altitude First Soviet communication satellite elliptical used a high altitude elliptical orbit. EARLY 1965 INTELSAT/COMSAT Active Geostationary First commercial communication BIRD satellite; served the Atlantic ocean region; capacity to carry 240 voice channels INTELSAT 2 1966 INTELSAT/COMSAT Active Geostationary First multiple access commercial satellite with multidestination capability INTELSAT 3 1968 INTELSAT/COMSAT Active Geostationary 3 generation designed to carry 1200 voice circuits

Early Satellites Satellite Launching Date Country/Organization Type Height (miles) Comments Explorer 1958 USA/NASA Broadcast 110 to 920 Very short life; Noted for re-broadcasting an on-board taped message from president Eisnhour ECHO 1960 USA/NASA Passive 1000 100-Foot diameter plastic balloon with an aluminum coating which reflect radio signals COURIER 1960 Department of defense Store & Repeat 600-700 First radio repeater satellite. It accepted and stored upto 360,000 teletype words as it passed overhead and then broadcast to ground stations further along the orbit; only operated for 17 days. TELSTAR 1962 USA/AT&T Active Duplex 682-4030 First satellite to receive and transmit simultaneously; Operated in 4/6 GHz band

Early Satellites Satellite Launching Date Country/Organization Type Height (miles) Comments INTELSAT 4 1971 INTELSAT/COMSAT Active Geostationary COMSAT’s 4th generation; designed to carry 6000 voice circuits. ANIK 1 1972 Canada/Telesat Active Geostationary World’s first domestic satellite; 5000 voice circuits capacity. WESTAR 1974 USA/Western Union Active Geostationary First US domestic satellite

Early Satellites • US Navy bounced messages off the moon • ECHO 1 “balloon” satellite - passive • ECHO 2 - 2nd passive satellite • All subsequent satellites used active communications

ECHO 1 • Photo from NASA

Early Satellites • Relay • Telstar • Syncom 2 - 4000 miles orbit -Allowed live transmission across the Atlantic • Syncom 2 - First Geosynchronous satellite

TELSTAR •

SYNCOM 2 •

Asiasat 2

Satellite Visibility

Contents • When are satellites visible? • Factors Affecting the satellite visibility • Orbit & Altitude Inclination • Earth Shadow • Ground Track • Other factors

Limit of Visibility • When Are Satellites Visible? • Whether or not a satellite is visible to a given observer is dependent upon many factors such as observer location, time of day, satellite altitude, and sky condition. Knowing these details may aid an observer in determining the most favorable times for sightings and is most certainly necessary

Factors Affecting Satellite Visibility • Orbit Altitude And Inclination • Earth's Shadow • Ground Track • Other Factors

Orbit Altitude & Inclination • GEO (~36000 km) • MEO (~15000 km) • LEO (~2000 km) • HEO

Earth's Shadow • The Earth's shadow must also be considered. When shadowed, a satellite is naturally not visible. Such events are dependent upon the satellite's altitude, inclination, the time of year, and the observer's location

Ground Track • Precession of course is not simply a question of watching for a given satellite at the same time each night. Few satellites have an orbital period which is a simple fraction of one day, the geostationary satellites being the obvious exception. The orbital period is dictated by the satellite's altitude. The higher the altitude, the further it has to travel around the Earth. • Many satellites in low Earth orbit go through a similar cycle of visibility. The cycle varies with orbital inclination, altitude, and observer location.

Other Factors • Satellite suffers greater air resistance the lower its orbit. This bleeds off the orbital energy, lowering the orbit yet further as the satellite begins to brush the upper atmosphere. • The forces on the satellite due to the Earth (and Moon, Sun, etc.) vary throughout its orbit giving rise to continual change in the orbit.