Communications satellites play a major role in telephone transmission,television and radio program distribution,computer communications,maritime navigation and military command and control. Satellite communications combines such diverse topics as Radio wave propagation ,antennas, orbital mechanics , modulation , detection , coding and radio electronics.

1. A PAPER PRESENTATION ON
COMMUNICATIONS SATELLITE
FRAMED FOR
“SVITS QUEST-2007”
RAJITHA.T LAVANYA.S
III B-TECH ECE
rajitha_446@ yahoo.co.in
lavanya_419@yahoo.co.in
GUIDED
BY
N.BHEEMLAL(HOD)& YAKOOB REDDY

2. Absract:
Communications satellites play a major role in telephone transmission,television
and radio program distribution,computer communications,maritime navigation
and military command and control.
Satellite communications combines such diverse topics as Radio wave
propagation ,antennas, orbital mechanics , modulation , detection , coding and
radio electronics.
For fixed services, communications satellites provide a technology
complementary to that of fiber optic submarine communication cables. They are
also used for mobile applications such as communications to ships and planes, for
which application of other technologies, such as cable, are impractical or
impossible.

3. Contents:
 Introduction
 1 History
o 1.1 Early missions
o 1.2 Geostationary orbits
o 1.3 Low-Earth-orbiting satellites
o 1.4 Molniya satellites
 2 Applications
o 2.1 Telephony
o 2.2 Television and radio
o 2.3 Mobile satellite technologies
o 2.4 Amateur radio
o 2.5 Satellite broadband
 3 conclusion

4. Introduction:
U.S. military MILSTAR communications satellite
A communications satellite (sometimes
abbreviated to comsat) is an artificial.
Modern communications satellites use History
geosynchronous orbits, Molniya orbits
or low polar Earth orbits.For fixed Early missions
services, communications satellites
The first satellite equipped with on-
provide a technology complementary to
board radio-transmitters was Soviet
that of fiber optic submarine
Sputnik 1, launched in 1957. The first
communication cables. They are also
American satellite to relay
used for mobile applications such as
communications was Project SCORE in
communications to ships and planes, for
1958, which used a tape recorder to store
which application of other technologies,
and forward voice messages. It was used
such as cable, are impractical or
to send a Christmas greeting to the world
impossible.
from President Eisenhower. NASA
launched an Echo satellite in 1960; the
100-foot aluminized PET film balloon
served as a passive reflector for radio
communications. Courier 1B, (built by

5. Philco) also launched in 1960, was the satellite revolves around the earth at a
world’s first active repeater satellite. constant speed once per day over the
equator.
Telstar was the first active, direct relay
communications satellite. Belonging to The geostationary orbit is useful for
AT&T as part of a multi-national communications applications because
agreement between AT&T, Bell ground based antennas, which must be
Telephone Laboratories, NASA, the directed toward the satellite, can operate
British General Post Office, and the effectively without the need for
French National PTT (Post Office) to expensive equipment to track the
develop satellite communication, it was satellite’s motion. Especially for
launched by NASA from Cape applications that require a large number
Canaveral on July 10, 1962, the first of ground antennas (such as direct TV
privately sponsored space launch. Telstar distribution), the savings in ground
was placed in an elliptical orbit equipment can more than justify the
(completed once every 2 hours and extra cost and onboard complexity of
37 minutes), rotating at a 45° angle lifting a satellite into the relatively high
above the equator. geostationary orbit.
An immediate antecedent of the The first geostationary communications
geostationary satellites was Hughes’ satellite was Anik 1, a Canadian satellite
Syncom 2, launched on July 26, 1963. launched in 1972. The United States
launched their own geostationary
Syncom revolved around the earth once
communication satellites afterward, with
per day at constant speed, but because it
Western Union launching their Westar 1
still had north-south motion, special
satellite in 1974, and RCA Americom
equipment was needed to track it.
(later GE Americom, now SES
Americom) launching Satcom 1 in 1975.
Geostationary orbits:
It was Satcom 1 that was instrumental in
A satellite in a geostationary orbit
helping early cable TV channels such as
appears to be in a fixed position to an
WTBS (now TBS Superstation), HBO,
earth-based observer. A geostationary

6. CBN (now ABC Family), and The Low earth orbiting satellites are less
Weather Channel become successful, expensive to position in space than
because these channels distributed their geostationary satellites and, because of
programming to all of the local cable TV their closer proximity to the ground,
headends using the satellite. require lower signal strength (Recall that
Additionally, it was the first satellite signal strength falls off as the square of
used by broadcast TV networks in the the distance from the source, so the
United States, like ABC, NBC, and effect is dramatic). So there is a trade off
CBS, to distribute their programming to between the number of satellites and
all of their local affiliate stations. Satcom their cost. In addition, there are
1 was so widely used because it had important differences in the onboard and
twice the communications capacity of ground equipment needed to support the
Westar 1 (24 transponders as opposed to two types of missions.
Westar 1’s 12), resulting in lower
A group of satellites working in concert
transponder usage costs.
thus is known as a satellite constellation.
Low-Earth-orbiting satellites: Two such constellations which were
intended for provision for hand held
A low Earth orbit typically is a circular telephony, primarily to remote areas,
orbit about 150 kilometres above the were the Iridium and Globalstar. The
earth’s surface and, correspondingly, a Iridium system has 66 satellites. Another
period (time to revolve around the earth) LEO satellite constellation, with backing
of about 90 minutes. Because of their from Microsoft entrepreneur Paul Allen,
low altitude, these satellites are only was to have as many as 720 satellites.
visible from within a radius of roughly
1000 kilometres from the sub-satellite It is also possible to offer discontinuous
point. In addition, satellites in low earth coverage using a low Earth orbit satellite
orbit change their position relative to the capable of storing data received while
ground position quickly. So even for passing over one part of Earth and
local applications, a large number of transmitting it later while passing over
satellites are needed if the mission another part. This will be the case with
requires uninterrupted connectivity.

7. the CASCADE system of Canada’s during the northern portion of the orbit.
CASSIOPE communications satellite. (Elevation is the extent of the satellite’s
position above the horizon. Thus a
Molniya satellites: satellite at the horizon has zero elevation
and a satellite directly overhead has
As mentioned, geostationary satellites
elevation of 90 degrees).
are constrained to operate above the
equator. As a consequence, they are not Furthermore, the Molniya orbit is so
always suitable for providing services at designed that the satellite spends the
high latitudes: for at high latitudes a great majority of its time over the far
geostationary satellite may appear low northern latitudes, during which its
on (or even below) the horizon, affecting ground footprint moves only slightly. Its
connectivity and causing multipathing period is one half day, so that the
(interference caused by signals reflecting satellite is available for operation over
off the ground into the ground antenna). the targeted region for eight hours every
The first satellite of Molniya series was second revolution. In this way a
launched on April 23, 1965 and was constellation of three Molniya satellites
used for experimental transmission of (plus in-orbit spares) can provide
TV signal from Moscow uplink station uninterrupted coverage.
to downlink stations, located in Siberia
and Russian Far East, in Norilsk, Molniya satellites are typically used for
Khabarovsk, Magadan and Vladivostok. telephony and TV services over Russia.
In November of 1967 Soviet engineers Another application is to use them for
created a unique system of national TV mobile radio systems (even at lower
network of satellite television, called latitudes) since cars travelling through
Orbita, that was based on Molniya urban areas need access to satellites at
satellites. high elevation in order to secure good
connectivity, e.g. in the presence of tall
Molniya orbits can be an appealing buildings.
alternative in such cases. The Molniya
orbit is highly inclined, guaranteeing
good elevation over selected positions

8. APPLICATIONS:
TELEPHONY:
Television and radio
There are two satellite types used for
North American television and radio:
A BSS 601 model, owned by SES • Direct Broadcast Satellite (DBS),
Astra, used for DTH television and
broadcasting in Europe • Fixed Service Satellite (FSS).
The first and still, arguably, most A direct broadcast satellite is a
important application for communication communications satellite that transmits
satellites is in international telephony. to small DBS satellite dishes (usually 18
Fixed-point telephones relay calls to an to 24 inches in diameter). Direct
earth station, where they are then broadcast satellites generally operate in
transmitted to a geostationary satellite. the upper portion of the Ku band. DBS
An analogous path is then followed on technology is used for DTH-oriented
the downlink. In contrast, mobile (Direct-To-Home) satellite TV services,
telephones (to and from ships and such as DirecTV, DISH Network , and
airplanes) must be directly connected to Sky Angel in the United States,
equipment to uplink the signal to the ExpressVu in Canada, and Sky Digital in
satellite, as well as being able to ensure the UK.
satellite pointing in the presence of
Fixed Service Satellites use the C band,
disturbances, such as waves onboard a
and the lower portions of the Ku bands.
ship.
They are normally used for broadcast

9. feeds to and from television networks FSS satellites differ from DBS satellites
and local affiliate stations (such as in that they have a lower RF power
program feeds for network and output than the latter, requiring a much
syndicated programming, live shots, and larger dish for reception (3 to 8 feet in
backhauls), as well as being used for diameter for Ku band, and 12 feet on up
distance learning by schools and for C band), as well as using linear
universities, business television (BTV), polarization for each of the transponders'
video-conferencing, and general RF input and output (as opposed to
commercial telecommunications. FSS circular polarization used by DBS
satellites are also used to distribute satellites). FSS satellite technology was
national cable channels to cable TV also originally used for DTH satellite TV
headends. from the late 1970s to the early 1990s in
the United States in the form of TVRO
(TeleVision Receive Only) receivers and
dishes (also known as big-dish, or more
pejoratively known as "BUD" or "Big
ugly dish" systems). It was also used in
its Ku band form for the now-defunct
Primestar satellite TV service.
This all changed when the first
American DBS provider, DirecTV, was
established in 1994, stealing the
limelight from FSS satellite technology
for DTH programming (due to
DirecTV's smaller 18-inch diameter
dishes and lower equipment cost).
However, FSS satellites on the C and Ku
bands still are used by cable and satellite
channels such as CNN, The Weather
Channel, HBO, Starz, and others, for

10. distribution to cable TV head ends, and costs quite a bit more than a DBS system
to the DBS providers themselves such as (about US$1500–2000, including
DirecTV and DISH Network who then installation). But most older used TVRO
re-distribute these channels over their systems can be had almost for free, due
own DBS systems. to most people converting over to DBS
systems over the years. Unlike DBS,
The fact that these channels still exist on
big-dish TVRO satellite TV also
FSS satellites (more so for reception and
provides a plethora of unscrambled and
re-distribution by cable TV and DBS
unencrypted channels such as Classic
systems, instead of for DTH viewers)
Arts Showcase, and feeds of syndicated
makes TVRO systems for DTH viewing
TV shows for reception by local TV
a still-viable option for satellite TV,
stations.Free-to-air satellite TV channels
often being a much-cheaper alternative
are also usually distributed on FSS
to DBS, as far as monthly subscription
satellites in the Ku band. The Intelsat
fees are concerned. TVRO-oriented
Americas 5, Galaxy 10R and AMC 3
programming packages sold by
satellites over North America provide a
companies such as National
quite large amount of FTA channels on
Programming Services, Bigdish.com,
their Ku band transponders.The
and Skyvision, are often quite a bit
American Dish Network DBS service
cheaper than their DBS equivalents.
has also recently utilized FSS technology
Motorola still makes digital 4DTV
as well for their programming packages
receivers for DTH TVRO use, and
requiring their SuperDish antenna, due
analog TVRO receivers are still
to Dish Network needing more capacity
available.
to carry local television stations per the
FCC's "must-carry" regulations, and for
However, the hardware for a brand-new
more bandwidth to carry HDTV
TVRO system (dish and receiver, along
channels.Satellites for communication
with a VideoCipher or DigiCipher
have now been launched that have
descrambler, or an integrated
transponders in the Ka band, such as
receiver/decoder (IRD) like a 4DTV
DirecTV's SPACEWAY-1 satellite. The
system, instead of a separate receiver
definitions of FSS and DBS satellites
and descrambler/decoder) nowadays

11. outside of North America, especially in Amateur radio operators have access to
Europe, are a bit more ambiguous. Most the OSCAR satellites that have been
satellites used for direct-to-home designed specifically to carry amateur
television in Europe have the same high radio traffic. Most such satellites operate
power output as DBS-class satellites as spaceborne repeaters, and are
Mobile satellite technologies: generally accessed by amateurs equipped
with UHF or VHF radio equipment and
Initially available for broadcast to highly directional antennas such as
stationary TV receivers, by 2004 popular Yagis or dish antennas. Due to the
mobile direct broadcast applications limitations of ground-based amateur
made their appearance with that arrival equipment, most amateur satellites are
of two satellite radio systems in the launched into fairly low Earth orbits, and
United States: Sirius and XM Satellite are designed to deal with only a limited
Radio Holdings. Some manufacturers number of brief contacts at any given
have also introduced special antennas for time. Some satellites also provide data-
mobile reception of DBS television. forwarding services using the AX.25 or
Using GPS technology as a reference, similar protocols.
these antennas automatically re-aim to
the satellite no matter where or how the Satellite broadband:
vehicle (that the antenna is mounted on)
In recent years, satellite communication
is situated. These mobile satellite
technology has been used as a means to
antennas are popular with some
connect to the Internet via broadband
recreational vehicle owners. Such mobile
data connections. This can be very useful
DBS antennas are also used by JetBlue
for users who are located in very remote
Airways for DirecTV (supplied by
areas, and cannot access a wireline
LiveTV, a subsidiary of JetBlue), which
broadband or dialup connection.
passengers can view on-board on LCD
screens mounted in the seats.
Conclusion:
Amateur radio:
Communicatios Satellites are widely
used to distribute Television

12. programming to terrestrial Tv stations. COMSTAR satelliite systems ,
Marisat is a U.S. system that serves the communications satellite
U.S. Navy and merchant marine , corporation,Washington,D.C.
Comsat general is the system manager  Joseph N.Pelton,”INTELSAT:
and majority stock holder. making the Future happen,”
Space communication and broad
References: casting.Jose l.Alegrettt,”U.S Role
ininternationalSatelliteCommuni
 COMSAT Guide to the
cations II:Leadership Continues”,
INTELSAT,MARISAT and
Satellite Communications.