Abstract Satellite communications have proliferated worldwide. The trend since about 1965 has been to use the geostationary orbit, where a satellite placed over the equator at the proper distance appeared to an earth station to be stationary. A great advantage for geostationary earth orbit (GEO) satellites is that “stationarity” eliminates the need for tracking in many circumstances. Delay is a principal disadvantage. This is due to the distance involved for a signal to reach a GEO satellite, about 125 ms. A new communication satellite series is evolving using low earth orbit (LEO) satellites. Here the distance to a satellite is greatly reduced (about 500–1500 km above the earth's surface), and hence there is much less delay, 1.6 to 5 ms. Expect LEO satellites to be contenders in two arenas: cellular telephony and data transport. Tracking requirements may be listed as a disadvantage, unless some form of omnidirectional antenna is used. Generally there are much higher elevation angles when compared to their GEO counterparts. This must be listed as an advantage. A brief discussion of LEO satellite systems is provided at the end of the chapter. A large portion of the communication satellites over the Western Hemisphere supports entertainment, particularly TV, supplying service to CATV head‐ends, motels/hotels, and the like. The original intent of GEO satellites was to relay over medium and long distances, multichannel telephony. This is now in decline. Fiber optic cable systems with their far‐reduced propagation delay and nearly infinite bandwidth have caused this decline. One may state that communication satellites have limited bandwidth whereas fiber‐optic cables have nearly unlimited bandwidth. Systems using very small aperture terminals (VSATs) have great promise, and many such systems are in operation. VSATs are commonly used for data connectivities, usually from outstations to a centralized hub. There are three important issues of concern to a satellite system designer: coexistence of satellite communications with terrestrial radio communications (in particular, line‐of‐sight microwave); shortage of desirable frequency assignments for use with geostationary satellites, forcing migration to higher frequencies such as the 30/20‐GHz band with the associated propagation limitations; and the actual orbital crowding where physical separation between GEO satellites is down to 2 degrees. The objective of this chapter is to answer the needs of the satellite link and system designer considering the aforementioned concerns. There is notable lack of standardization, and some sort of standards are set inside a particular system and rarely cross system boundaries. INTELSAT (International Telecommunication Satellite [consortium]) is the largest system operation in the world. This group has set its own standards. If a user wishes an earth station to interoperate with an INTELSAT satellite, that earth station must meet certain standard requirements established by INTELSAT. One of the goals of this chapter is to provide a brief outline of INTELSAT requirements.

and the first satellite to be placed in this kind of orbit was launched in 1963. Communications satellites are often placed in a geostationary orbit A geostationary orbit, also referred to as a GEO or GSO, is a circular geosynchronous orbit 35,786 km (22,236 mi) in altitude above Earth's equator, 42,164 km (26,199 mi) in radius from Earth's center, and following the direction of Earth's rotation. An object in such an orbit has an orbital period equal to Earth's rotational period, one sidereal day, and so to ground observers it appears motionle Most commercial communications satellites, broadcast satellites and SBAS satellites operate in geostationary orbits. List of orbits List of satellites in geosynchronous orbit Orbital station-keeping Space elevator, which ultimately reaches to and beyond a geostationary orbit

Communications satellites are used for television, telephone, radio, internet, and military applications. Some communications satellites are in geostationary orbit A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. Communications satellites are used for television, telephone, radio, internet, and military applications. Some communications satellites are in geostationary Communications satellites usually have one of three primary types of orbit, while other orbital classifications are used to… Geostationary satellites must operate above the equator and therefore appear lower on the horizon as the receiver gets farther from the equator. This will cause problems for extreme northerly latitudes, affecting connectivity and causing multipath interference (caused by signals reflecting off the ground and into the ground antenna). Thus, for areas close to the North (and South) Pole, a geostationary satellite may appear below the horizon. Therefore, Molniya orbit satellites have been launched, mainly in Russia, to alleviate this problem. Molniya orbits can be an appealing alternative in such cases. The Molniya orbit is highly inclined, guaranteeing good elevation over selected positions during the northern portion of the orbit. (Elevation is the extent of the satellite's position above the horizon. Thus, a satellite at the horizon has zero elevation and a satellite directly overhead has elevation of 90 degrees.) The Molniya orbit is designed so that the satellite spends the great majority of its time over the far northern latitudes, during which its ground footprint moves only slightly. Its period is one half day, so that the satellite is available for operation over the targeted region for six to nine hours every second revolution. In this way a constellation of three Molniya satellites (plus in-orbit spares) can provide uninterrupted coverage. The first satellite of the Molniya series was launched on 23 April 1965 and was used for experimental transmission of TV signals from a Moscow uplink station to downlink stations located in Siberia and the Russian Far East, in Norilsk, Khabarovsk, Magadan and Vladivostok. In November 1967 Soviet engineers created a unique system of national TV network of satellite television, called Orbita, that was based on Molniya satellites.