Satellite phone

A satellite telephone, satellite phone, or satphone is a type of mobile phone that connects to orbiting satellites instead of terrestrial cell sites. They provide similar functionality to terrestrial mobile telephones; voice, short messaging service and low-bandwidth internet access are supported through most systems.

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, varies widely. Early satellite phone handsets had a size and weight comparable to that of a late-1980s or early-1990s mobile phone, but usually with a large retractable antenna. More recent satellite phones are similar in size to a regular mobile phone while some prototype satellite phones have no distinguishable difference from an ordinary smartphone. Satphones are popular on expeditions into remote areas where terrestrial cellular service is unavailable.

A fixed installation, such as one used aboard a ship, may include large, rugged, rack-mounted electronics, and a steerable microwave antenna on the mast that automatically tracks the overhead satellites. Smaller installations using over a two-way satellite broadband service such as BGAN or VSAT bring the costs within the reach of leisure vessel owners. Internet service satellite phones have notoriously poor reception indoors, though it may be possible to get a consistent signal near a window or in the top floor of a building if the roof is sufficiently thin. The phones have connectors for external antennas that can be installed in vehicles and buildings. The systems also allow for the use of repeaters, much like terrestrial mobile phone systems.

Some satellite phones use satellites in geostationary orbit, which are meant to remain in a fixed position in the sky. These systems can maintain near-continuous global coverage with only three or four satellites, reducing the launch costs. The satellites used for these systems are very heavy (approx. 5000 kg) and expensive to build and launch. The satellites sit at an altitude of 35,786 kilometres (22,236 mi); a noticeable delay is present while making a phone call or using data services due to the large distance from users. The amount of bandwidth available on these systems is substantially higher than that of the low Earth orbit (LEO) systems; all three active systems provide portable satellite Internet using laptop-sized terminals with speeds ranging from 60 to 512 kbit per second (kbps).

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