Applications
Telephone
An Iridium satellite
The first and historically most important application for communication satellites was in intercontinental satellites who are in spacelong distance telephony. The fixed Public Switched Telephone Network relays telephone calls from land line telephones to an earth station, where they are then transmitted to a geostationary satellite. The downlink follows an analogous path. Improvements insubmarine communications cables, 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 nonexistent, 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 back up for hospitals, military, and recreation. Ships at sea often use satellite phones, and planes.[8]
Satellite phones can be accomplished in many different ways. On larger scale often there will be local telephone system in the isolated area with a link to a telephone system in a main land area. There are services that will patch a radio signal to a telephone system in this example most 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 teleport connected to the Public Switched Telephone Network .