GEOSTATIONARY (GEO)

GEO systems orbit the Earth at a fixed distance of 35,786 kilometers (22,300 miles). The satellite's speed at this altitude matches that of the Earth's rotation, thereby keeping the satellite stationary over a particular spot on the Earth. Examples of GEO systems include INTELSAT, Inmarsat, and PanAmSat.

Geostationary satellites orbit the Earth above the equator and cover one third of the Earth's surface at a time. The majority of communications satellites are GEOs and these systems will continue to provide the bulk of the communications satellite capacity for many years to come.

GEOs support voice, data, and video services, most often providing fixed services to a particular region. For example, GEO satellites provide back-up voice capacity for the majority of the U.S. long distance telephone companies and carry the bulk of nation-wide television broadcasts, which commonly are distributed via from a central point to affiliate stations throughout the country.

Until recently, the large antennae and power requirements for GEO systems limited their effectiveness for small-terminal and mobile services. However, newer high-powered GEO satellites using clusters of concentrated "spot beams" can operate with smaller terrestrial terminals than ever before and can support some mobile applications. GEO satellite coverage typically degrades beyond 20 degrees North Latitude and 20 degrees South Latitude.

GEO systems have a proven track record of reliability and operational predictability not yet possible for the more sophisticated orbital designs now being deployed. GEO systems are also less complicated to maintain because their fixed location in the sky requires relatively little tracking capability in ground equipment. In addition, their high orbital altitude allows GEOs to remain in orbit longer than systems operating closer to Earth. These characteristics, along with their high bandwidth capacity, may provide a cost advantage over other system types.

However, their more distant orbit also requires relatively large terrestrial antennae and high-powered equipment and are subject to transmission delays. In addition, since only a few large satellites carry the load for the entire system, a GEO satellite loss is somewhat more consequential than for the systems described below.

Summary of GEO Pros and Cons

* PRO: GEO systems have significantly greater available bandwidth than the LEO and MEO systems described below. This permits them to provide two-way data, voice and broadband services that may be unpractical for other types of systems.
* PRO: Because of their capacity and configuration, GEOs are often more cost-effective for carrying high-volume traffic, especially over long-term contract arrangements. For example, excess capacity on GEO systems often is reserved in the form of leased circuits for use as a backup to other communications methods.
* CON: GEO systems, like all other satellite systems, require line-of-sight communication paths between terrestrial antennae and the satellites. But, because GEO systems have fewer satellites and these are in a fixed location over the Earth, the opportunities for line of sight communication are fewer than for systems in which the satellites "travel" across the sky. This is a significant disadvantage of GEO systems as compared to LEO and MEO systems, especially for mobile applications and in urban areas where tall buildings and other structures may block line-of-sight communication for hand-held mobile terminals.
* CON: Some users have expressed concern with the transmission delays associated with GEO systems, particularly for high-speed data. However, sophisticated echo cancellation and other technologies have permitted GEOs to be used successfully for both voice and high-speed data applications.