Satellite phone
From Free net encyclopedia
A satellite telephone, satellite phone, or satphone is a mobile phone that communicates directly with orbiting communications satellites. Depending on the architecture of a particular system, coverage may include the entire Earth, or only specific regions.
The mobile equipment, also known as a terminal or earth station, varies widely. A satellite phone handset has a size and weight comparable to that of a late 1980s or early 1990s cell phone, but with a large retractable antenna. These are popular on expeditions into remote areas where terrestrial cellular service is unavailable.
A fixed installation, such as used shipboard, may include large, rugged, rack-mounted electronics, and a steerable microwave antenna on the mast that automatically tracks the overhead satellites.
Geostationary services
Some satellite phones use satellites in geostationary orbit. These systems can maintain near-global coverage with only three or four satellites, reducing the launch costs. The major satellite system in civilian use is Inmarsat.
The disadvantage of geostationary satellite systems is that the inverse square law means that a comparatively large antenna system is required for signal transmission and reception for the phone. The phone system must therefore be quite physically large, compared to the tiny terrestrial mobile phones.
Low Earth orbit
LEO telephones utilizes LEO (low Earth orbit) satellite technology. The advantages include providing worldwide wireless coverage with no gaps. All satellite phones tend to be LEOs. LEO satellites orbit the earth at high speed, low altitude orbits with an orbital time of 70–90 minutes, an altitude of 640 to 1120 kilometres (400 to 700 miles), and provide coverage cells. Since the satellites are not geosynchronous, they must fly complete orbits and thus further guarantee complete coverage over every area by at least one satellite at all times. Blimps are being considered as an alternative to satellites.
The two deployed LEO satellite systems are Iridium and Globalstar. Customer numbers for both systems never matched the levels required to fund the large number of satellite launch costs, and both went into bankruptcy. They are now operated by new owners who bought the assets for a fraction of their original cost.
There are several models of satellite phones available.
Satellite phones in pop culture
In the movie Jurassic Park III, Alan Grant lends his satellite phone (Globalstar handset) to Nash. Then, the dinosaur eats him and the phone is found in the dinosaur's feces. The satellite phone was also used many times on the show Relic Hunter. The main character, Sydney Fox, would use it to communicate back home when she found interesting relics. Also such phones are said to be difficult to tap or trace which makes them a popular favorite for both terrorists and drug lords alike.de:Satellitentelefon et:Satellittelefon ja:衛星電話 fi:Satelliittipuhelin sv:Satellittelefon