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Satellite Direct - The Future Of Television!
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Introduction and Brief History of Satellites

A satellite is any object that orbits another object (which is known as its primary). All masses that
are part of the solar system, including the Earth, are satellites either of the Sun, or satellites of
those objects, such as the Moon. It is not always a simple matter to decide which is the 'satellite' in
a pair of bodies. Because all objects exert gravity, the motion of the primary object is also affected
by the satellite. If two objects are ufficiently similar in mass, they are generally referred to as a
binary system rather than a primary object and satellite. The general criterion for an object to be a
satellite is that the center of mass of the two objects is inside the primary object. In popular usage,
the term 'satellite' normally refers to an artificial satellite (a man-made object that orbits the Earth
or another body).

In May, 1946, the Preliminary Design of an Experimental World-Circling Spaceship stated, "A
satellite vehicle with appropriate instrumentation can be expected to be one of the most potent
scientific tools of the Twentieth Century. The achievement of a satellite craft would produce
repercussions comparable to the explosion of the atomic bomb..."

The space age began in 1946, as scientists began using captured German V-2 rockets to make
measurements in the upper atmosphere. Before this period, scientists used balloons that went up
to 30 km and radio waves to study the ionosphere. From 1946 to 1952, upper-atmosphere
research was conducted using V-2s and Aerobee rockets. This allowed measurements of
atmospheric pressure, density, and temperature up to 200 km. The U.S. had been considering
launching orbital satellites since 1945 under the Bureau of Aeronautics of the United States Navy.
The Air Force's Project RAND eventually released the above report, but did not believe that the
satellite was a potential military weapon; rather they considered it to be a tool for science, politics,
and propaganda. Following pressure by the American Rocket Society, the National Science
Foundation, and the International Geophysical Year, military interest picked up and in early 1955
the Air Force and Navy were working on Project Orbiter, which involved using a Jupiter C rocket to
launch a small satellite called Explorer 1 on January 31, 1958.

On July 29, 1955, the White House announced that the U.S. intended to launch satellites by the
spring of 1958. This became known as Project Vanguard. On July 31, the Soviets announced that
they intended to launch a satellite by the fall of 1957 and on October 4, 1957 Sputnik I was
launched into orbit, which triggered the Space Race between the two nations.

The largest artificial satellite currently orbiting the earth is the International Space Station, which
can sometimes be seen with the unaided human eye.

Types of satellites

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?Astronomical satellites: These are satellites used for observation of distant planets,
galaxies, and other outer space objects.

·Communications satellites: These are artificial satellites stationed in space for the
purposes of telecommunications using radio at microwave frequencies. Most communications
satellites use geosynchronous orbits or near-geostationary orbits, although some recent systems
use low Earth-orbiting satellites.

·Earth observation satellites are satellites specifically designed to observe Earth from
orbit, similar to reconnaissance satellites but intended for non-military uses such as environmental
monitoring, meteorology, map making etc. (See especially Earth Observing System.)

·Navigation satellites are satellites which use radio time signals transmitted to enable
mobile receivers on the ground to determine their exact location. The relatively clear line of sight
between the satellites and receivers on the ground, combined with ever-improving electronics,
allows satellite navigation systems to measure location to accuracies on the order of a few metres
in real time.

·Reconnaissance satellites are Earth observation satellite or communications satellite
deployed for military or intelligence applications. Little is known about the full power of these
satellites, as governments who operate them usually keep information pertaining to their
reconnaissance satellites classified.

·Solar power satellites are proposed satellites built in high Earth orbit that use microwave
power transmission to beam solar power to very large antenna on Earth where it can be used in
place of conventional power sources.

·Space stations are man-made structures that are designed for human beings to live on in
outer space. A space station is distinguished from other manned spacecraft by its lack of major
propulsion or landing facilities -- instead, other vehicles are used as transport to and from the
station. Space stations are designed for medium-term living in orbit, for periods of weeks, months,
or even years.

·Weather satellites are satellites that primarily are used to monitor the weather and/or
climate of the Earth.

·Miniaturized satellites are satellites of unusually low weights and small sizes. New
classifications are used to categorize these satellites: minisatellite (500-200 kg), microsatellite
(below 200 kg), nanosatellite (below 10 kg).

Orbit types

Many times satellites are characterized by their orbit. Although a satellite may orbit at almost any
height, satellites are commonly categorized by their altitude:

·Low Earth Orbit (LEO: 200 - 1200km above the Earth's surface)

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?Medium Earth Orbit (ICO or MEO: 1200 - 35286 km)

·Geosynchronous Orbit (GEO: 35786 km above Earth's surface) and Geostationary Orbit (
zero inclination geosynchronous orbit). These orbits are of particular interest for communication
satellites and will be discussed in detail later.

·High Earth Orbit (HEO: above 35786 km)

The following orbits are special orbits that are also used to categorize satellites:

·Molniya orbits: Is a class of a highly elliptic orbit. A satellite placed in this orbit spends
most of its time over a designated area of the earth, a phenomenon known as apogee dwell.
Molniya orbits are named after a series of Soviet/Russian Molniya communications satellites that
have been using this class of orbits since the mid 1960s.

·Heliosynchronous or sun-synchronous orbit: A heliosynchronous orbit, or more commonly
a sun-synchronous orbit is an orbit in which an object always passes over any given point of the
Earth's surface at the same local solar time. This is a useful characteristic for satellites that image
the earth's surface in visible or infrared wavelengths (e.g. weather, spy and remote sensing
satellites).

·Polar orbit : A satellite in a polar orbit passes above or nearly above both poles of the
planet (or other celestial body) on each revolution.

·Hohmann transfer orbit: For this particular orbit type, it is more common to identify the
satellite as a spacecraft. In astronautics and aerospace engineering, the Hohmann transfer orbit is
an orbital maneuver that moves a spacecraft from one orbit to another.

·Supersynchronous orbit or drift orbit : orbit above GEO. Satellites will drift in a westerly
direction.

·Subsynchronous orbit or drift orbit: orbits close to but below GEO. Used for satellites
undergoing station changes in an eastern direction.

Communication Satellites

A communications satellite (sometimes abbreviated to comsat) is an artificial satellite stationed in
space for the purposes of telecommunications. Modern communications satellites use
geosynchronous orbits, Molniya orbits or low Earth orbits.

For fixed services, communications satellites provide a technology complementary to that of fiber
optic submarine communication cables. For mobile applications, such as communications to ships
and planes satellite based communicationis only the viable means of communications as
application of other technologies, such as cable, are impractical or impossible.

Early missions: The origin of satellite communication can be traced to an article written by Arthur
C. Clarke in 1945. He suggested that a radio relay satellite in an equatorial orbit with a period of
24 hours would remain stationary with respect to earth's surface and can be used for long-range

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radio communication, as it will over come the limitations imposed by earth curvature. Sputnik 1,
The world's first artificial (non communication) satellite, was launched on October 4, 1957. The
first satellite to relay communications was Project SCORE in 1958, which used a tape recorder to
store and forward voice messages. It was used to send a Christmas greeting to the world from
President Eisenhower. NASA launched an Echo satellite in 1960. This 100-foot aluminized Mylar
balloon served as a passive reflector for radio communications. Courier 1B, (built by Philco) also
was launched in 1960, was the world's first active repeater satellite. Given below are the details of
milestones in satellite communcation history: -

·Herman Potocnik - describes a space station in geosynchronous orbit - 1928

·Arthur C. Clarke - proposes a station in geosynchronous orbit to relay communications
and broadcast television - 1945

·Project SCORE - first communications satellite - 1958

·Echo I - first passive reflector satellite - August 1960

·Courier 1B - first active repeater satellite - October 1960

·Telstar - the first active direct relay satellite designed to transmit television and high-
speed data communications. Telstar was placed in an elliptical orbit (completed once every 2
hours and 37 minutes), rotating at a 45° angle above the equator. July 1962

·Syncom - first communications satellite in geosynchronous orbit. Syncom 2 revolved
around the earth once per day at constant speed, but because it still had north-south motion
special equipment was needed to track it. 1963

·OSCAR-III - first amateur radio communications satellite - March 1965

·Molniya - first Soviet communication satellite, highly elliptic orbit - October 1965

·Early Bird - INTELSAT's first satellite for commercial service - April 1965

·Orbita - first national TV network based on satellite television - November 1967

·Anik 1 - the first national satellite television system, Canada, - 1973

·Westar 1, the USA's first geosynchronous communications satellite - April 1974

·Ekran - first serial Direct-To-Home TV communication satellite 1976

·Palapa A1 - first Indonesia communications satellite - July 8 1976

·TDRSS - first satellite designed to provide communications relay services for other
spacecraft. - 1983

·Mars Global Surveyor - first communications satellite in orbit around another planet

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(Mars) - 1997

·Cassini spacecraft relays to Earth images from the Huygens probe as it lands on Saturn's
moon, Titan, the longest relay to date. -- January 14, 2005

Depending on the need the communication satellites can be placed in various types of orbits. We
discuss few common types: -

(a)Geostationary orbits Satellites: A satellite in a geostationary orbit appears to be in a fixed
position to an earth-based observer. A geostationary satellite revolves around the earth at a
constant speed once per day over the equator. The geostationary orbit is useful for
communications applications because ground based antennae, which must be directed toward the
satellite, can operate effectively without the need for expensive equipment to track the satellite's
motion. Especially for applications that require a large number of ground antennae (such as direct
TV distribution), the savings in ground equipment can more than justify the extra cost and onboard
complexity of lifting a satellite into the relatively high geostationary orbit.

The concept of the geostationary communications satellite was first proposed by Arthur C. Clarke,
building on work by Konstantin Tsiolkovsky and on the 1929 work by Herman Potočnik
(writing as Herman Noordung) Das Problem der Befahrung des Weltraums - der Raketen-motor.
In October 1945 Clarke published an article titled "Extra-terrestrial Relays" in the British magazine
Wireless World. The article described the fundamentals behind the deployment of artificial
satellites in geostationary orbits for the purpose of relaying radio signals. Thus Arthur C. Clarke is
often quoted as being the inventor of the communications satellite.

The first geostationary communications satellite was Anik 1, a Canadian satellite launched in
1972. The United States launched their own geostationary communication satellites afterward,
with Western Union launching their Westar 1 satellite in 1974, and RCA Americom (later GE
Americom, now SES Americom) launching Satcom 1 in 1975.
It was Satcom 1 that was instrumental in helping early cable TV channels such as WTBS (now
TBS Superstation), HBO, CBN (now ABC Family), and The Weather Channel become successful,
because these channels distributed their programming to all of the local cable TV headends using
the satellite. Additionally, it was the first satellite used by broadcast TV networks in the United
States, like ABC, NBC, and CBS, to distribute their programming to all of their local affiliate
stations. The reason that Satcom 1 was so widely used is that it had twice the communications
capacity of Westar 1 (24 transponders as opposed to Westar 1's 12), which resulted in lower
transponder usage costs.

By 2000 Hughes Space and Communications (now Boeing Satellite Systems) had built nearly 40
percent of the satellites in service worldwide. Other major satellite manufacturers include Space
Systems/Loral, Lockheed Martin (owns former RCA Astro Electronics/GE Astro Space business),
Northrop Grumman, Alcatel Space and EADS Astrium.

(b)Low-Earth-orbiting satellites: A low Earth orbit typically is a circular orbit about 150 kilometers
above the earth's surface and, correspondingly, a period (time to revolve around the earth) of
about 90 minutes. Because of their low altitude, these satellites are only visible from within a
radius of roughly 1000 kilometers from the sub-satellite point. In addition, satellites in low earth
orbit change their position relative to the ground position quickly. So even for local applications, a

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large number of satellites are needed if the mission requires uninterrupted connectivity.

Low earth orbiting satellites are less expensive to position in space than geostationary satellites
and, because of their closer proximity to the ground, require lower signal strength. So there is a
trade off between the number of satellites and their cost. In addition, there are important
differences in the onboard and ground equipment needed to support the two types of missions.

A group of satellites working in concert thus is known as a satellite constellation. Two such
constellations which were intended for provision for hand held telephony, primarily to remote
areas, were the Iridium and Globalstar. The Iridium system has 66 satellites. Another LEO satellite
constellation, with backing from Microsoft entrepreneur Paul Allen, was to have as many as 720
satellites. It is also possible to offer discontinuous coverage using a low Earth orbit satellite
capable of storing data received while passing over one part of Earth and transmitting it later while
passing over another part. This will be the case with the CASCADE system of Canada's
CASSIOPE communications satellite.

(c)Molniya satellites: As mentioned, geostationary satellites are constrained to operate above the
equator. As a consequence, they are not always suitable for providing services at high latitudes:
for at high latitudes a geostationary satellite may appear low on (or even below) the horizon,
affecting connectivity and causing multipathing (interference caused by signals reflecting off the
ground into the ground antenna). The first satellite of Molniya series was launched on April 23,
1965 and was used for experimental transmission of TV signal from Moscow uplink station to
downlink stations, located in Russian Far East, in Khabarovsk, Magadan and Vladivostok. In
November of 1967 Soviet engineers created a unique system of national TV network of satellite
television, called Orbita that was based on Molniya satellites.

Molniya orbits can be an appealing alternative in such cases. The Molniya orbit is highly inclined,
guaranteeing good elevation over selected positions during the northern portion of the orbit.
(Elevation is the extent of the satellite's position above the horizon. Thus a satellite at the horizon
has zero elevation and a satellite directly overhead has elevation of 90 degrees). Furthermore, the
Molniya orbit is so designed that the satellite spends the great majority of its time over the far
northern latitudes, during which its ground footprint moves only slightly. Its period is one half day,
so that the satellite is available for operation over the targeted region for eight hours every second
revolution. In this way a constellation of three Molniya satellites (plus in-orbit spares) can provide
uninterrupted coverage.

Molniya satellites are typically used for telephony and TV services over Russia. Another
application is to use them for mobile radio systems (even at lower latitudes) since cars traveling
through urban areas need access to satellites at high elevation in order to secure good
connectivity, e.g. in the presence of tall buildings.

Applications of Satellites

(a) Telephony: One of the major applications of a communication satellite is in provision of long
distance telephone services. The connectivity is through frequency division multiple access
(FDMA) or time division multiple access(TDMA) predominantly. Telephone subscribers can be
connected through a network of exchanges which are in turn connected to satellite earth stations
which uplink the traffic to satellite for further processing.

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(b) Television and Radio: There are two types of satellites used for television and radio:

(i)Direct Broadcast Satellite (DBS): A direct broadcast satellite is a communications satellite that
transmits to small DBS satellite dishes (usually 18" to 24" in diameter). Direct broadcast satellites
generally operate in the upper portion of the Ku band. DBS technology is used for DTH-oriented
(Direct-To-Home) satellite TV services, such as DirecTV and Dish Network in the United States,
ExpressVu in Canada, and Sky Digital in the UK.

(ii)Fixed Service Satellite (FSS): Use the C band, and the lower portions of the Ku bands. They are
normally used for broadcast feeds to and from television networks and local affiliate stations (such
as program feeds for network and syndicated programming, live shots, and backhauls), as well as
being used for distance learning by schools & universities, business television (BTV),
videoconferencing, and general commercial telecommunications. FSS satellites are also used to
distribute national cable channels to cable TV headends. FSS satellites differ from DBS satellites
in that they have a lower RF power output than the latter, requiring a much larger dish for
reception (3 to 8 feet in diameter for Ku band, and 12 feet on up for C band). FSS satellite
technology was also originally used for DTH satellite TV from the late 1970s to the early 1990s in
the USA in the form of TVRO (TeleVision Receive Only) receivers and dishes (a.k.a. big-dish, or
more pejoratively known as big ugly dish, systems). It was also used in its Ku band form for the
now-defunct Primestar satellite TV service.

(c) Mobile satellite technologies: Initially available for broadcast to stationary TV receivers, by
2004 popular mobile direct broadcast applications made their appearance with that arrival of two
satellite radio systems in the United States: Sirius and XM Satellite Radio Holdings. Some
manufacturers have also introduced special antennas for mobile reception of DBS television.
Using GPS technology as a reference, these antennas automatically re-aim to the satellite no
matter where or how the vehicle (that the antenna is mounted on) is situated. These mobile
satellite antennas are popular with some recreational vehicle owners. Such mobile DBS antennas
are also used by JetBlue Airways for DirecTV (supplied by LiveTV, a subsidiary of JetBlue), which
passengers can view on-board on LCD screens mounted in the seats.

(d) Amateur radio: Amateur radio operators have access to the OSCAR satellites that have
been designed specifically to carry amateur radio traffic. Most such satellites operate as space
borne repeaters, and are generally accessed by amateurs equipped with UHF or VHF radio
equipment and highly directional antennas such as Yagis or dish antennas. Due to the limitations
of ground-based amateur equipment, most amateur satellites are launched into fairly low Earth
orbits, and are designed to deal with only a limited number of brief contacts at any given time.
Some satellites also provide data-forwarding services using the X.25 or similar protocols.

Satellite Broadband Services: In recent years, satellite communication technology has been used
as a means to connect to the Internet via broadband data connections. This is can be very useful
for users to test who are located in very remote areas, and can't access a wireline broadband or
dialup connection.

Countries with satellite launch capability

This list includes counties with an independent capability to place satellites in orbit, including

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production of the necessary launch vehicle. Many more countries have built satellites that were
launched with the aid of others. The French and British capabilities are now subsumed by the
European Union under the European Space Agency.

First launch by country

Country Year of first launch First satellite

Russia 1957 "Sputnik 1"

United States1958 "Explorer 1"

France 1965 "Asterix"

Japan 1970 "Osumi"

China 1970 "Dong Fang Hong I"

United Kingdom1971 "Prospero X-3"

European Union1979 "Ariane 1"

India 1980 "Rohini"

Israel 1988 "Ofea 1"

Iran 2005 "Sina 1"

In 1998, North Korea claimed to have launched a satellite, but this was never confirmed, and
widely believed to be a cover for the test launch of the Taepodong-1 missile over Japan (See
Kwangmyongsong).

Author has 28 years of experience in the field of Teaching and Management. He is M. Tech from
IIT Kanpur and has worked in different capacities including Signal corps Indian Army, Regional
Manager for a Telecom Company. Currently he is Associate Professor with ITM, Gurgaon that is
rated as best Engineering colleges of North India.

Article Source:
http://EzineArticles.com/?expert=Anil_Nigam

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Satellite Direct - The Future Of Television!
http://doiop.com/satellitedirecthq

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