Introduction and Brief History of Satellites and Communication Satellites

Introduction and Brief History of Satellites				Saturn's moon, Titan, the longest relay to
				date. -- January 14, 2005
A satellite is any object that orbits another
object (which is known as its primary). All				Depending on the need the communication
masses that are part of the solar system,				satellites can be placed in various types of
including the Earth, are satellites either of				orbits. We discuss few common types: -
the Sun, or satellites of those objects, such
as the Moon. It is not always a simple matter				(a) Geostationary orbits Satellites: A
to decide which is the 'satellite' in a pair				satellite in a geostationary orbit appears to
of bodies. Because all objects exert gravity,				be in a fixed position to an earth-based
the motion of the primary object is also				observer. A geostationary satellite revolves
affected by the satellite. If two objects are				around the earth at a constant speed once per
ufficiently similar in mass, they are				day over the equator. The geostationary orbit
generally referred to as a binary system				is useful for communications applications
rather than a primary object and satellite.				because ground based antennae, which must be
The general criterion for an object to be a				directed toward the satellite, can operate
satellite is that the center of mass of the				effectively without the need for expensive
two objects is inside the primary object. In				equipment to track the satellite's motion.
popular usage, the term 'satellite' normally				Especially for applications that require a
refers to an artificial satellite (a man-made				large number of ground antennae (such as
object that orbits the Earth or another				direct TV distribution), the savings in
body).				ground equipment can more than justify the
				extra cost and onboard complexity of lifting
In May, 1946, the Preliminary Design of an				a satellite into the relatively high
Experimental World-Circling Spaceship stated,				geostationary orbit.
"A satellite vehicle with appropriate
instrumentation can be expected to be one of				The concept of the geostationary
the most potent scientific tools of the				communications satellite was first proposed
Twentieth Century. The achievement of a				by Arthur C. Clarke, building on work by
satellite craft would produce repercussions				Konstantin Tsiolkovsky and on the 1929 work
comparable to the explosion of the atomic				by Herman Potočnik (writing as Herman
bomb..."				Noordung) Das Problem der Befahrung des
				Weltraums - der Raketen-motor. In October
The space age began in 1946, as scientists				1945 Clarke published an article titled
began using captured German V-2 rockets to				"Extra-terrestrial Relays" in the British
make measurements in the upper atmosphere.				magazine Wireless World. The article
Before this period, scientists used balloons				described the fundamentals behind the
that went up to 30 km and radio waves to				deployment of artificial satellites in
study the ionosphere. From 1946 to 1952,				geostationary orbits for the purpose of
upper-atmosphere research was conducted using				relaying radio signals. Thus Arthur C. Clarke
V-2s and Aerobee rockets. This allowed				is often quoted as being the inventor of the
measurements of atmospheric pressure,				communications satellite.
density, and temperature up to 200 km. The
U.S. had been considering launching orbital				The first geostationary communications
satellites since 1945 under the Bureau of				satellite was Anik 1, a Canadian satellite
Aeronautics of the United States Navy. The				launched in 1972. The United States launched
Air Force's Project RAND eventually released				their own geostationary communication
the above report, but did not believe that				satellites afterward, with Western Union
the satellite was a potential military				launching their Westar 1 satellite in 1974,
weapon; rather they considered it to be a				and RCA Americom (later GE Americom, now SES
tool for science, politics, and propaganda.				Americom) launching Satcom 1 in 1975. It was
Following pressure by the American Rocket				Satcom 1 that was instrumental in helping
Society, the National Science Foundation, and				early cable TV channels such as WTBS (now TBS
the International Geophysical Year, military				Superstation), HBO, CBN (now ABC Family), and
interest picked up and in early 1955 the Air				The Weather Channel become successful,
Force and Navy were working on Project				because these channels distributed their
Orbiter, which involved using a Jupiter C				programming to all of the local cable TV
rocket to launch a small satellite called				headends using the satellite. Additionally,
Explorer 1 on January 31, 1958.				it was the first satellite used by broadcast
				TV networks in the United States, like ABC,
On July 29, 1955, the White House announced				NBC, and CBS, to distribute their programming
that the U.S. intended to launch satellites				to all of their local affiliate stations. The
by the spring of 1958. This became known as				reason that Satcom 1 was so widely used is
Project Vanguard. On July 31, the Soviets				that it had twice the communications capacity
announced that they intended to launch a				of Westar 1 (24 transponders as opposed to
satellite by the fall of 1957 and on October				Westar 1's 12), which resulted in lower
4, 1957 Sputnik I was launched into orbit,				transponder usage costs.
which triggered the Space Race between the
two nations.				By 2000 Hughes Space and Communications (now
				Boeing Satellite Systems) had built nearly 40
The largest artificial satellite currently				percent of the satellites in service
orbiting the earth is the International Space				worldwide. Other major satellite
Station, which can sometimes be seen with the				manufacturers include Space Systems/Loral,
unaided human eye.				Lockheed Martin (owns former RCA Astro
				Electronics/GE Astro Space business),
Types of satellites				Northrop Grumman, Alcatel Space and EADS
				Astrium.
Â· Astronomical satellites: These are
satellites used for observation of distant				(b) Low-Earth-orbiting satellites: A low
planets, galaxies, and other outer space				Earth orbit typically is a circular orbit
objects.				about 150 kilometers above the earth's
				surface and, correspondingly, a period (time
Â· Communications satellites: These are				to revolve around the earth) of about 90
artificial satellites stationed in space for				minutes. Because of their low altitude, these
the purposes of telecommunications using				satellites are only visible from within a
radio at microwave frequencies. Most				radius of roughly 1000 kilometers from the
communications satellites use geosynchronous				sub-satellite point. In addition, satellites
orbits or near-geostationary orbits, although				in low earth orbit change their position
some recent systems use low Earth-orbiting				relative to the ground position quickly. So
satellites.				even for local applications, a large number
				of satellites are needed if the mission
Â· Earth observation satellites are				requires uninterrupted connectivity.
satellites specifically designed to observe
Earth from orbit, similar to reconnaissance				Low earth orbiting satellites are less
satellites but intended for non-military uses				expensive to position in space than
such as environmental monitoring,				geostationary satellites and, because of
meteorology, map making etc. (See especially				their closer proximity to the ground, require
Earth Observing System.)				lower signal strength. So there is a trade
				off between the number of satellites and
Â· Navigation satellites are satellites				their cost. In addition, there are important
which use radio time signals transmitted to				differences in the onboard and ground
enable mobile receivers on the ground to				equipment needed to support the two types of
determine their exact location. The				missions.
relatively clear line of sight between the
satellites and receivers on the ground,				A group of satellites working in concert thus
combined with ever-improving electronics,				is known as a satellite constellation. Two
allows satellite navigation systems to				such constellations which were intended for
measure location to accuracies on the order				provision for hand held telephony, primarily
of a few metres in real time.				to remote areas, were the Iridium and
				Globalstar. The Iridium system has 66
Â· Reconnaissance satellites are Earth				satellites. Another LEO satellite
observation satellite or communications				constellation, with backing from Microsoft
satellite deployed for military or				entrepreneur Paul Allen, was to have as many
intelligence applications. Little is known				as 720 satellites. It is also possible to
about the full power of these satellites, as				offer discontinuous coverage using a low
governments who operate them usually keep				Earth orbit satellite capable of storing data
information pertaining to their				received while passing over one part of Earth
reconnaissance satellites classified.				and transmitting it later while passing over
				another part. This will be the case with the
Â· Solar power satellites are proposed				CASCADE system of Canada's CASSIOPE
satellites built in high Earth orbit that use				communications satellite.
microwave power transmission to beam solar
power to very large antenna on Earth where it				(c) Molniya satellites: As mentioned,
can be used in place of conventional power				geostationary satellites are constrained to
sources.				operate above the equator. As a consequence,
				they are not always suitable for providing
Â· Space stations are man-made structures				services at high latitudes: for at high
that are designed for human beings to live on				latitudes a geostationary satellite may
in outer space. A space station is				appear low on (or even below) the horizon,
distinguished from other manned spacecraft by				affecting connectivity and causing
its lack of major propulsion or landing				multipathing (interference caused by signals
facilities - instead, other vehicles are used				reflecting off the ground into the ground
as transport to and from the station. Space				antenna). The first satellite of Molniya
stations are designed for medium-term living				series was launched on April 23, 1965 and was
in orbit, for periods of weeks, months, or				used for experimental transmission of TV
even years.				signal from Moscow uplink station to downlink
				stations, located in Russian Far East, in
Â· Weather satellites are satellites that				Khabarovsk, Magadan and Vladivostok. In
primarily are used to monitor the weather and				November of 1967 Soviet engineers created a
or climate of the Earth.				unique system of national TV network of
				satellite television, called Orbita that was
Â· Miniaturized satellites are satellites				based on Molniya satellites.
of unusually low weights and small sizes. New
classifications are used to categorize these				Molniya orbits can be an appealing
satellites: minisatellite (500-200 kg),				alternative in such cases. The Molniya orbit
microsatellite (below 200 kg), nanosatellite				is highly inclined, guaranteeing good
(below 10 kg).				elevation over selected positions during the
				northern portion of the orbit. (Elevation is
Orbit types				the extent of the satellite's position above
				the horizon. Thus a satellite at the horizon
Many times satellites are characterized by				has zero elevation and a satellite directly
their orbit. Although a satellite may orbit				overhead has elevation of 90 degrees).
at almost any height, satellites are commonly				Furthermore, the Molniya orbit is so designed
categorized by their altitude:				that the satellite spends the great majority
				of its time over the far northern latitudes,
Â· Low Earth Orbit (LEO: 200 - 1200km above				during which its ground footprint moves only
the Earth's surface)				slightly. Its period is one half day, so that
				the satellite is available for operation over
Â· Medium Earth Orbit (ICO or MEO: 1200 -				the targeted region for eight hours every
35286 km)				second revolution. In this way a
				constellation of three Molniya satellites
Â· Geosynchronous Orbit (GEO: 35786 km				(plus in-orbit spares) can provide
above Earth's surface) and Geostationary				uninterrupted coverage.
Orbit ( zero inclination geosynchronous
orbit). These orbits are of particular				Molniya satellites are typically used for
interest for communication satellites and				telephony and TV services over Russia.
will be discussed in detail later.				Another application is to use them for mobile
				radio systems (even at lower latitudes) since
Â· High Earth Orbit (HEO: above 35786 km)				cars traveling through urban areas need
				access to satellites at high elevation in
The following orbits are special orbits that				order to secure good connectivity, e.g. in
are also used to categorize satellites:				the presence of tall buildings.

Â· Molniya orbits: Is a class of a highly				Applications of Satellites
elliptic orbit. A satellite placed in this
orbit spends most of its time over a				(a) Telephony: One of the major
designated area of the earth, a phenomenon				applications of a communication satellite is
known as apogee dwell. Molniya orbits are				in provision of long distance telephone
named after a series of Soviet/Russian				services. The connectivity is through
Molniya communications satellites that have				frequency division multiple access (FDMA) or
been using this class of orbits since the mid				time division multiple access(TDMA)
1960s.				predominantly. Telephone subscribers can be
				connected through a network of exchanges
Â· Heliosynchronous or sun-synchronous				which are in turn connected to satellite
orbit: A heliosynchronous orbit, or more				earth stations which uplink the traffic to
commonly a sun-synchronous orbit is an orbit				satellite for further processing.
in which an object always passes over any
given point of the Earth's surface at the				(b) Television and Radio: There are two
same local solar time. This is a useful				types of satellites used for television and
characteristic for satellites that image the				radio:
earth's surface in visible or infrared
wavelengths (e.g. weather, spy and remote				(i) Direct Broadcast Satellite (DBS): A
sensing satellites).				direct broadcast satellite is a
				communications satellite that transmits to
Â· Polar orbit : A satellite in a polar				small DBS satellite dishes (usually 18" to
orbit passes above or nearly above both poles				24" in diameter). Direct broadcast satellites
of the planet (or other celestial body) on				generally operate in the upper portion of the
each revolution.				Ku band. DBS technology is used for
				DTH-oriented (Direct-To-Home) satellite TV
Â· Hohmann transfer orbit: For this				services, such as DirecTV and Dish Network in
particular orbit type, it is more common to				the United States, ExpressVu in Canada, and
identify the satellite as a spacecraft. In				Sky Digital in the UK.
astronautics and aerospace engineering, the
Hohmann transfer orbit is an orbital maneuver				(ii) Fixed Service Satellite (FSS): Use the C
that moves a spacecraft from one orbit to				band, and the lower portions of the Ku bands.
another.				They are normally used for broadcast feeds to
				and from television networks and local
Â· Supersynchronous orbit or drift orbit :				affiliate stations (such as program feeds for
orbit above GEO. Satellites will drift in a				network and syndicated programming, live
westerly direction.				shots, and backhauls), as well as being used
				for distance learning by schools &
Â· Subsynchronous orbit or drift orbit:				universities, business television (BTV),
orbits close to but below GEO. Used for				videoconferencing, and general commercial
satellites undergoing station changes in an				telecommunications. FSS satellites are also
eastern direction.				used to distribute national cable channels to
				cable TV headends. FSS satellites differ from
Communication Satellites				DBS satellites in that they have a lower RF
				power output than the latter, requiring a
A communications satellite (sometimes				much larger dish for reception (3 to 8 feet
abbreviated to comsat) is an artificial				in diameter for Ku band, and 12 feet on up
satellite stationed in space for the purposes				for C band). FSS satellite technology was
of telecommunications. Modern communications				also originally used for DTH satellite TV
satellites use geosynchronous orbits, Molniya				from the late 1970s to the early 1990s in the
orbits or low Earth orbits.				USA in the form of TVRO (TeleVision Receive
				Only) receivers and dishes (a.k.a. big-dish,
For fixed services, communications satellites				or more pejoratively known as big ugly dish,
provide a technology complementary to that of				systems). It was also used in its Ku band
fiber optic submarine communication cables.				form for the now-defunct Primestar satellite
For mobile applications, such as				TV service.
communications to ships and planes satellite
based communicationis only the viable means				(c) Mobile satellite technologies:
of communications as application of other				Initially available for broadcast to
technologies, such as cable, are impractical				stationary TV receivers, by 2004 popular
or impossible.				mobile direct broadcast applications made
				their appearance with that arrival of two
Early missions: The origin of satellite				satellite radio systems in the United States:
communication can be traced to an article				Sirius and XM Satellite Radio Holdings. Some
written by Arthur C. Clarke in 1945. He				manufacturers have also introduced special
suggested that a radio relay satellite in an				antennas for mobile reception of DBS
equatorial orbit with a period of 24 hours				television. Using GPS technology as a
would remain stationary with respect to				reference, these antennas automatically
earth's surface and can be used for				re-aim to the satellite no matter where or
long-range radio communication, as it will				how the vehicle (that the antenna is mounted
over come the limitations imposed by earth				on) is situated. These mobile satellite
curvature. Sputnik 1, The world's first				antennas are popular with some recreational
artificial (non communication) satellite, was				vehicle owners. Such mobile DBS antennas are
launched on October 4, 1957. The first				also used by JetBlue Airways for DirecTV
satellite to relay communications was Project				(supplied by LiveTV, a subsidiary of
SCORE in 1958, which used a tape recorder to				JetBlue), which passengers can view on-board
store and forward voice messages. It was used				on LCD screens mounted in the seats.
to send a Christmas greeting to the world
from President Eisenhower. NASA launched an				(d) Amateur radio: Amateur radio
Echo satellite in 1960. This 100-foot				operators have access to the OSCAR satellites
aluminized Mylar balloon served as a passive				that have been designed specifically to carry
reflector for radio communications. Courier				amateur radio traffic. Most such satellites
1B, (built by Philco) also was launched in				operate as space borne repeaters, and are
1960, was the world's first active repeater				generally accessed by amateurs equipped with
satellite. Given below are the details of				UHF or VHF radio equipment and highly
milestones in satellite communcation history:				directional antennas such as Yagis or dish
-				antennas. Due to the limitations of
				ground-based amateur equipment, most amateur
Â· Herman Potocnik - describes a space				satellites are launched into fairly low Earth
station in geosynchronous orbit - 1928				orbits, and are designed to deal with only a
				limited number of brief contacts at any given
Â· Arthur C. Clarke - proposes a station in				time. Some satellites also provide
geosynchronous orbit to relay communications				data-forwarding services using the X.25 or
and broadcast television - 1945				similar protocols.

Â· Project SCORE - first communications				Satellite Broadband Services: In recent
satellite - 1958				years, satellite communication technology has
				been used as a means to connect to the
Â· Echo I - first passive reflector				Internet via broadband data connections. This
satellite - August 1960				is can be very useful for users to test who
				are located in very remote areas, and can't
Â· Courier 1B - first active repeater				access a wireline broadband or dialup
satellite - October 1960				connection.

Â· Telstar - the first active direct relay				Countries with satellite launch capability
satellite designed to transmit television and
high-speed data communications. Telstar was				This list includes counties with an
placed in an elliptical orbit (completed once				independent capability to place satellites in
every 2 hours and 37 minutes), rotating at a				orbit, including production of the necessary
45Â° angle above the equator. July 1962				launch vehicle. Many more countries have
				built satellites that were launched with the
Â· Syncom - first communications satellite				aid of others. The French and British
in geosynchronous orbit. Syncom 2 revolved				capabilities are now subsumed by the European
around the earth once per day at constant				Union under the European Space Agency.
speed, but because it still had north-south
motion special equipment was needed to track				First launch by country
it. 1963
				Country Year of first launch First
Â· OSCAR-III - first amateur radio				satellite
communications satellite - March 1965
				Russia 1957 "Sputnik 1"
Â· Molniya - first Soviet communication
satellite, highly elliptic orbit - October				United States 1958
1965				"Explorer 1"

Â· Early Bird - INTELSAT's first satellite				France 1965
for commercial service - April 1965				"Asterix"

Â· Orbita - first national TV network based				Japan 1970 "Osumi"
on satellite television - November 1967
				China 1970 "Dong
Â· Anik 1 - the first national satellite				Fang Hong I"
television system, Canada, - 1973
				United Kingdom 1971
Â· Westar 1, the USA's first geosynchronous				"Prospero X-3"
communications satellite - April 1974
				European Union 1979
Â· Ekran - first serial Direct-To-Home TV				"Ariane 1"
communication satellite 1976
				India 1980
Â· Palapa A1 - first Indonesia				"Rohini"
communications satellite - July 8 1976
				Israel 1988 "Ofea
Â· TDRSS - first satellite designed to				1"
provide communications relay services for
other spacecraft. - 1983				Iran 2005 "Sina 1"

Â· Mars Global Surveyor - first				In 1998, North Korea claimed to have launched
communications satellite in orbit around				a satellite, but this was never confirmed,
another planet (Mars) - 1997				and widely believed to be a cover for the
				test launch of the Taepodong-1 missile over
Â· Cassini spacecraft relays to Earth				Japan (See Kwangmyongsong).
images from the Huygens probe as it lands on

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One of the best fighter planesthe YAK

Introduction and Brief History of Satellites and Communication Satellites