Home > Geosynchronous satellite

1 Definition

According to Kepler's Third Law, the orbital period of a satellite in a circular orbit increases with increasing altitude. Space stations and shuttles in Low Earth Orbit (LEO), typically two or four hundred miles above the Earth's surface make between fifteen and sixteen revolutions per day. The Moon, at an altitude of about 240,000 miles (385,000km), takes thirty days to make a complete rotation. Between those extremes lies the "magic" altitude of 22,300 miles (35,786km) at which a satellite's orbital speed exactly matches the rate at which the earth rotates: once every sidereal day (23 hours 56 minutes). In that case, the satellite is said to be geosynchronous.

If a geosynchronous satellite's orbit is not exactly aligned with the equator, it will appear (when viewed by someone on the ground) to oscillate daily around a fixed point in the sky. As the angle between the orbit and the equator decreases, the magnitude of this oscillation becomes smaller; when the orbit lies entirely over the equator, the satellite remains stationary relative to the Earth's surface – it is said to be geostationary.

2 Application

There are ca. 200 geosynchronous satellites.

Geostationary satellites appear to hover over one spot above the equator. Receiving and transmitting antennae on the earth do not need to track such a satellite. These antennae can be fixed in place and are much less expensive than tracking antennae. These satellites have revolutionized global communications, television broadcasting and weather forecasting, and have a number of important defense and intelligence applications.

One disadvantage of geosynchronous satellites is a result of their high altitude: radio signals take a fraction (approximately 1/4) of a second to reach and return from the satellite, resulting in a small but significant signal delay. This delay increases the difficulty of telephone conversation and reduces the performance of common network protocols such as TCP/IP, but does not present a problem with non-interactive systems such as television broadcasts. There are a number of proprietary satellite data protocols that are designed to proxy TCP/IP connections over long-delay satellite links -- these are marketed as being a partial solution to the poor performance of native TCP over satellite links.

3 History

The concept was first proposed by the science fiction author Arthur C. Clarke around 1945, based on Herman Potocnik's previous work. Working prior to the advent of solid-state electronics, Clarke envisioned a trio of large, manned space stations arranged in a triangle around the planet. Modern satellites are numerous, unmanned, and often no larger than an automobile.

The first geosynchronous satellite was Syncom 2, launched on a Delta rocket B booster from Cape Canaveral 26 July, 1963Events January-March January 11 The Whisky A Go-Go night club in Los Angeles, the first disco in the USA, is opened. January 14 George Wallace becomes governor of Alabama. January 22 Elysee treaty between France and Germany January 28 Black student Harvey. It was used a few months later for the world's first satellite relayed telephoneThe telephone or phone is a telecommunications device that transmits speech by means of electric signals. Generally attributed to the inventor Alexander Graham Bell, the first was built in Boston, Massachusetts, in 1876. However, an Italian inventor Anton call, between U.S. President John F. KennedyJohn Fitzgerald Kennedy ( May 29, 1917 November 22, 1963), often referred to as Jack Kennedy or JFK was the 35th ( 1961 1963) President of the United States. He was the youngest ever to be elected president and the youngest president ever to die in office and NigeriaThe Federal Republic of Nigeria is a country in West Africa. It borders on Benin in the west, Chad and Cameroon in the east, Niger in the north and the Gulf of Guinea in the south. Major cities include the capital Abuja, the former capital Lagos, Abeokutan Prime minister Abubaker Balewa .

See also: Satellite televisionSatellite television is television delivered by way of orbiting communications satellites located 37,000 km (22,300 miles) above the earth's surface. The first satellite television signal was relayed from Europe to the Telstar satellite over North America