Editing Communications satellite (section)

== Applications ==

=== Telephony ===
{{main|Satellite phone}}
[[Image:Satellite phone.jpg|thumb|Satellite phone ([[Inmarsat]]) in use in [[Nias]], [[Indonesia]], in April 2005 after the [[2005 Nias–Simeulue earthquake|Nias–Simeulue earthquake]]]]

The first and historically most important application for communication satellites was in intercontinental [[long distance telephony]]. The fixed [[Public Switched Telephone Network]] relays [[telephone call]]s from [[land line]] telephones to an [[Earth station]], where they are then transmitted to a geostationary satellite.  The downlink follows an analogous path.  Improvements in [[submarine communications cable]]s through the use of [[fiber-optics]] caused some decline in the use of satellites for fixed telephony in the late 20th century.

Satellite communications are still used in many applications today. Remote islands such as [[Ascension Island]], [[Saint Helena]], [[Diego Garcia]], and [[Easter Island]], where no submarine cables are in service, need satellite telephones. There are also regions of some continents and countries where landline telecommunications are rare to non existent, for example large regions of South America, Africa, Canada, China, Russia, and Australia. Satellite communications also provide connection to the edges of [[Antarctica]] and [[Greenland]]. Other land use for satellite phones are rigs at sea, a backup for hospitals, military, and recreation. Ships at sea, as well as planes, often use satellite phones.<ref>{{cite web | url=http://www.iridium.com/IridiumConnected/IridiumAtWork/Maritime.aspx | title=Connected:Maritime | archive-url=https://web.archive.org/web/20130815171540/http://iridium.com/IridiumConnected/IridiumAtWork/Maritime.aspx | archive-date=2013-08-15 | website=Iridium | access-date=2013-09-19}}</ref>

Satellite phone systems can be accomplished by a number of means. On a large scale, often there will be a local telephone system in an isolated area with a link to the telephone system in a main land area. There are also services that will patch a radio signal to a telephone system. In this example, almost any type of satellite can be used. Satellite phones connect directly to a constellation of either geostationary or low-Earth-orbit satellites. Calls are then forwarded to a satellite [[Earth station#Telecommunications port|teleport]] connected to the Public Switched Telephone Network .

=== Television ===
{{main|Satellite television}}
As television became the main market, its demand for simultaneous delivery of relatively few signals of large [[Bandwidth (signal processing)|bandwidth]] to many receivers being a more precise match for the capabilities of [[Geosynchronous orbit|geosynchronous]] comsats.  Two satellite types are used for North American television and radio: [[Direct broadcast satellite]] (DBS), and [[Fixed Service Satellite]] (FSS).

The definitions of FSS and DBS satellites outside of North America, especially in Europe, are a bit more ambiguous. Most satellites used for direct-to-home television in Europe have the same high power output as DBS-class satellites in North America, but use the same linear polarization as FSS-class satellites. Examples of these are the [[SES Astra|Astra]], [[Eutelsat]], and [[Hotbird]] spacecraft in orbit over the European continent. Because of this, the terms FSS and DBS are more so used throughout the North American continent, and are uncommon in Europe.

[[Fixed Service Satellite]]s use the [[C band (IEEE)|C band]], and the lower portions of the [[Ku band|K<sub>u</sub> band]]. 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, [[remote broadcast|live shot]]s, and [[backhaul (broadcasting)|backhaul]]s), as well as being used for [[distance learning]] by schools and universities, [[business television]] (BTV), [[Videoconferencing]], and general commercial telecommunications. FSS satellites are also used to distribute national cable channels to cable television headends.

[[Free-to-air]] satellite TV channels are also usually distributed on FSS satellites in the K<sub>u</sub> band. The [[Intelsat Americas 5]], [[Galaxy 10R]] and [[AMC 3]] satellites over North America provide a quite large amount of FTA channels on their K<sub>u</sub> band [[transponder]]s.

The American [[Dish Network]] [[Direct-broadcast satellite|DBS]] service has also recently used FSS technology as well for their programming packages requiring their [[SuperDish]] antenna, due to Dish Network needing more capacity to carry local television stations per the [[Federal Communications Commission|FCC]]'s "must-carry" regulations, and for more bandwidth to carry [[HDTV]] channels.

A [[direct broadcast satellite]] is a communications satellite that transmits to small DBS [[satellite dish]]es (usually 18 to 24 inches or 45 to 60&nbsp;cm in diameter). Direct broadcast satellites generally operate in the upper portion of the microwave [[Ku band|K<sub>u</sub> band]]. DBS technology is used for DTH-oriented ([[Direct-To-Home]]) satellite TV services, such as [[DirecTV]], DISH Network and Orby TV<ref>{{cite web|title=Orby TV (United States)|url=https://www.satlaunch.org/packages-orby-tv-117w.htm|access-date=9 April 2020|archive-date=28 July 2020|archive-url=https://web.archive.org/web/20200728194141/https://www.satlaunch.org/packages-orby-tv-117w.htm|url-status=dead}}</ref> in the United States, [[Bell Satellite TV]] and [[Shaw Direct]] in Canada, [[Freesat]] and [[Sky (UK and Ireland)|Sky]] in the UK, Ireland, and New Zealand and [[DSTV]] in South Africa.

Operating at lower frequency and lower power than DBS, FSS satellites require a much larger dish for reception (3 to 8 feet (1 to 2.5 m) in diameter for K<sub>u</sub> band, and 12 feet (3.6 m) or larger for C band).  They use [[linear polarization]] for each of the transponders' RF input and output (as opposed to [[circular polarization]] used by DBS satellites), but this is a minor technical difference that users do not notice. FSS satellite technology was also originally used for DTH satellite TV from the late 1970s to the early 1990s in the United States in the form of [[TVRO]] (Television Receive Only) receivers and dishes. It was also used in its K<sub>u</sub> band form for the now-defunct [[Primestar]] satellite TV service.

Some satellites have been launched that have transponders in the [[Ka band|K<sub>a</sub> band]], such as DirecTV's [[SPACEWAY-1]] satellite, and [[Anik (satellite)|Anik F2]]. NASA and [[ISRO]]<ref>{{cite web|title=GSAT-14|url=http://www.isro.org/satellites/gsat-14.aspx|publisher=ISRO|access-date=16 January 2014|url-status=dead|archive-url=https://web.archive.org/web/20140108052813/http://www.isro.org/satellites/gsat-14.aspx|archive-date=8 January 2014}}</ref><ref>{{cite news|title=Indian GSLV successfully lofts GSAT-14 satellite|url=http://www.nasaspaceflight.com/2014/01/indian-gslv-launch-gsat-14-communications-satellite/|access-date=16 January 2014|newspaper=NASA Space Flight|date=4 January 2014}}</ref> have also launched experimental satellites carrying K<sub>a</sub> band beacons recently.<ref name="spaceref-20050426">{{Cite web |date=26 April 2005 |title=DIRECTV's Spaceway F1 Satellite Launches New Era in High-Definition Programming; Next Generation Satellite Will Initiate Historic Expansion of DIRECTV |url=https://spaceref.com/press-release/directvs-spaceway-f1-satellite-launches-new-era-in-high-definition-programming-next-generation-satellite-will-initiate-historic-expansion-of-directv/ |url-status=live |archive-url=https://archive.today/20231220124331/https://spaceref.com/press-release/directvs-spaceway-f1-satellite-launches-new-era-in-high-definition-programming-next-generation-satellite-will-initiate-historic-expansion-of-directv/ |archive-date=20 December 2023 |access-date=11 May 2012 |publisher=SpaceRef }}</ref>

Some manufacturers have also introduced special antennas for mobile reception of DBS television. Using [[Global Positioning System|Global Positioning System (GPS)]] technology as a reference, these antennas automatically re-aim to the satellite no matter where or how the vehicle (on which the antenna is mounted) 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.

=== Radio broadcasting ===
{{main|Satellite radio}}
Satellite radio offers audio [[broadcast]] services in some countries, notably the United States. Mobile services allow listeners to roam a continent, listening to the same audio programming anywhere.

A satellite radio or subscription radio (SR) is a digital radio signal that is broadcast by a communications satellite, which covers a much wider geographical range than terrestrial radio signals.

=== Amateur radio ===
{{main|Amateur radio satellite}}
[[Amateur radio]] operators have access to amateur satellites, which have been designed specifically to carry amateur radio traffic. Most such satellites operate as spaceborne repeaters, and are generally accessed by amateurs equipped with [[Ultra high frequency|UHF]] or [[VHF]] radio equipment and highly directional [[Antenna (radio)|antennas]] such as [[Yagi antenna|Yagi]]s or dish antennas. Due to launch costs, most current 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.

=== Internet access ===
{{main|Satellite Internet access}}
After the 1990s, satellite communication technology has been used as a means to connect to the [[Internet]] via broadband data connections. This can be very useful for users who are located in remote areas, and cannot access a [[broadband]] connection, or require high availability of services.

=== Military ===
{{main|Military communications satellite}}
{{Further|X Band Satellite Communication}}
Communications satellites are used for [[military communications]] applications, such as [[Global Command and Control System]]s. Examples of military systems that use communication satellites are the [[MILSTAR]], the [[DSCS]], and the [[FLTSATCOM]] of the United States, [[NATO]] satellites, United Kingdom satellites (for instance [[Skynet (satellite)|Skynet]]), and satellites of the former [[Soviet Union]]. India has launched its first Military Communication satellite [[GSAT-7]], its transponders operate in [[UHF]], [[F band (NATO)|F]], [[C band (IEEE)|C]] and {{Ku band}} bands.<ref>{{cite web|url=http://www.ndtv.com/article/india/india-s-first-military-satellite-poor-country-satellite-put-into-earth-s-orbit-414080|title=India's first 'military' satellite GSAT-7 put into earth's orbit|website=NDTV.com|date=2013-09-04|access-date=2013-09-18}}</ref> Typically military satellites operate in the UHF, [[Super High Frequency|SHF]] (also known as [[X-band]]) or [[Extremely high frequency|EHF]] (also known as [[Ka band|K<sub>a</sub> band]]) frequency bands.

=== Data collection ===
Near-ground [[in situ]] [[environmental monitoring]] equipment (such as [[tide gauge]]s, [[weather station]]s, [[weather buoy]]s, and [[radiosondes]]), may use satellites for one-way [[data transmission]] or two-way [[telemetry]] and [[telecontrol]].<ref name="Kramer 2002 pp. 311–328">{{cite book | last=Kramer | first=Herbert J. | title=Observation of the Earth and Its Environment | chapter=Data Collection (Messaging) Systems | publisher=Springer Berlin Heidelberg | location=Berlin, Heidelberg | year=2002 | isbn=978-3-642-62688-3 | doi=10.1007/978-3-642-56294-5_4 | pages=311–328}}</ref><ref>{{cite web | title=Satellite Data Telecommunication Handbook | website=library.wmo.int | url=https://library.wmo.int/fb.php?title=Satellite%20Data%20Telecommunication%20Handbook&url=index.php%3Flvl%3Dnotice_display%26id%3D20662 | access-date=2020-12-21}}</ref><ref>{{cite book |chapter=Equipment needed for Telemetry of Data | title= Manual on sea level measurement and interpretation, volume V: Radar gauges| author=[[Intergovernmental Oceanographic Commission]] 
 |url=https://unesdoc.unesco.org/ark:/48223/pf0000246981 | access-date=2023-08-18}}</ref> It may be based on a secondary payload of a [[weather satellite]] (as in the case of [[GOES]] and [[METEOSAT]] and others in the [[Argos (satellite system)|Argos system]]) or in dedicated satellites (such as [[SCD (satellite)|SCD]]). The data rate is typically much lower than in [[satellite Internet]] access.