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64-470: JCSAT-4A , designated JCSAT-6 before launch, is a Japanese geostationary communications satellite which is operated by JSAT Corporation (now SKY Perfect JSAT Group ). It is positioned in geostationary orbit at a longitude of 124° East, from where it is used to provide broadcasting and corporate network communications to Japan. JCSAT-6 was constructed by Hughes, based on the HS-601 satellite bus . It

128-408: A geostationary transfer orbit . From this orbit, the satellite raised itself into a geostationary orbit using an R-4D apogee motor . The final burn to complete its insertion into geosynchronous orbit occurred on 1 March 1999. This article about one or more communications satellites is a stub . You can help Misplaced Pages by expanding it . This article about one or more spacecraft of Japan

192-455: A data network aiming to provide a „Lunar Internet for cis-lunar spacecraft and Installations. The Moonlight Initiative is an equivalent ESA project that is stated to be compatible and providing navigational services for the lunar surface. Both programmes are satellite constellstions of several satellites in various orbits around the Moon. Other orbits are also planned to be used. Positions in

256-518: A medium Earth orbit satellite is about 16,000 kilometres (10,000 mi) above Earth. In various patterns, these satellites make the trip around Earth in anywhere from 2 to 8 hours. To an observer on Earth, a satellite in a gestationary orbit appears motionless, in a fixed position in the sky. This is because it revolves around the Earth at Earth's own angular velocity (one revolution per sidereal day , in an equatorial orbit ). A geostationary orbit

320-591: A more precise match for the capabilities of geosynchronous comsats. Two satellite types are used for North American television and radio: Direct broadcast satellite (DBS), and Fixed Service Satellite (FSS). The definitions of FSS and DBS satellites outside of North America, especially in Europe, are a bit more ambiguous. Most satellites used for direct-to-home television in Europe have the same high power output as DBS-class satellites in North America, but use

384-687: A number of satellites for various purposes; for example, METSAT for meteorological satellite, EUMETSAT for the European branch of the program, and METOP for meteorological operations. These orbits are Sun synchronous, meaning that they cross the equator at the same local time each day. For example, the satellites in the NPOESS (civilian) orbit will cross the equator, going from south to north, at times 1:30 P.M., 5:30 P.M., and 9:30 P.M. There are plans and initiatives to bring dedicated communications satellite beyond geostationary orbits. NASA proposed LunaNet as

448-621: A period (time to revolve around the Earth) of about 90 minutes. Because of their low altitude, these satellites are only visible from within a radius of roughly 1,000 kilometres (620 mi) from the sub-satellite point. In addition, satellites in low Earth orbit change their position relative to the ground position quickly. So even for local applications, many satellites are needed if the mission requires uninterrupted connectivity. Low-Earth-orbiting satellites are less expensive to launch into orbit than geostationary satellites and, due to proximity to

512-545: A radio signal to a telephone system. In this example, almost any type of satellite can be used. Satellite phones connect directly to a constellation of either geostationary or low-Earth-orbit satellites. Calls are then forwarded to a satellite teleport connected to the Public Switched Telephone Network . As television became the main market, its demand for simultaneous delivery of relatively few signals of large bandwidth to many receivers being

576-455: A tape recorder to carry a stored voice message, as well as to receive, store, and retransmit messages. It was used to send a Christmas greeting to the world from U.S. President Dwight D. Eisenhower . The satellite also executed several realtime transmissions before the non-rechargeable batteries failed on 30 December 1958 after eight hours of actual operation. The direct successor to SCORE was another ARPA-led project called Courier. Courier 1B

640-490: A wide range of radio and microwave frequencies . To avoid signal interference, international organizations have regulations for which frequency ranges or "bands" certain organizations are allowed to use. This allocation of bands minimizes the risk of signal interference. In October 1945, Arthur C. Clarke published an article titled "Extraterrestrial Relays" in the British magazine Wireless World . The article described

704-413: Is a stub . You can help Misplaced Pages by expanding it . Communications satellite The radio waves used for telecommunications links travel by line of sight and so are obstructed by the curve of the Earth. The purpose of communications satellites is to relay the signal around the curve of the Earth allowing communication between widely separated geographical points. Communications satellites use

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768-553: Is also possible to offer discontinuous coverage using a low-Earth-orbit satellite capable of storing data received while passing over one part of Earth and transmitting it later while passing over another part. This will be the case with the CASCADE system of Canada's CASSIOPE communications satellite. Another system using this store and forward method is Orbcomm . A medium Earth orbit is a satellite in orbit somewhere between 2,000 and 35,786 kilometres (1,243 and 22,236 mi) above

832-565: Is carried out under the auspices of the International Telecommunication Union (ITU). To facilitate frequency planning, the world is divided into three regions: Within these regions, frequency bands are allocated to various satellite services, although a given service may be allocated different frequency bands in different regions. Some of the services provided by satellites are: The first and historically most important application for communication satellites

896-498: Is common to find d {\displaystyle d} measured in kilometers and f {\displaystyle f} in gigahertz , in which case the FSPL equation becomes an increase of 240 dB, because the units increase by factors of 10 and 10 respectively, so: (The constants differ in the second decimal digit when the speed of light is approximated by 300 000 km/s. Whether one uses 92.4, 92.44 or 92.45 dB,

960-490: Is equipped with 32 Ku-band transponders , and at launch it had a mass of 2,900 kg (6,400 lb), with an expected operational lifespan of fourteen and a half years. It was launched atop an Atlas IIAS launch vehicle flying from Launch Complex 36A at the Cape Canaveral Air Force Station . The launch occurred at 01:45:26 UTC on 16 February 1999, and successfully placed JCSAT-6 into

1024-492: 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

1088-558: Is known as a satellite constellation . Two such constellations, intended to provide satellite phone and low-speed data services, primarily to remote areas, are the Iridium and Globalstar systems. The Iridium system has 66 satellites, which orbital inclination of 86.4° and inter-satellite links provide service availability over the entire surface of Earth. Starlink is a satellite internet constellation operated by SpaceX , that aims for global satellite Internet access coverage. It

1152-576: 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

1216-410: Is that a MEO satellite's distance gives it a longer time delay and weaker signal than a LEO satellite, although these limitations are not as severe as those of a GEO satellite. Like LEOs, these satellites do not maintain a stationary distance from the Earth. This is in contrast to the geostationary orbit, where satellites are always 35,786 kilometres (22,236 mi) from Earth. Typically the orbit of

1280-485: Is useful for communications because ground antennas can be aimed at the satellite without their having to track the satellite's motion. This is relatively inexpensive. In applications that require many ground antennas, such as DirecTV distribution, the savings in ground equipment can more than outweigh the cost and complexity of placing a satellite into orbit. By 2000, Hughes Space and Communications (now Boeing Satellite Development Center ) had built nearly 40 percent of

1344-569: The Earth-Moon-Libration points are also proposed for communication satellites covering the Moon alike communication satellites in geosynchronous orbit cover the Earth. Also, dedicated communication satellites in orbits around Mars supporting different missions on surface and other orbits are considered, such as the Mars Telecommunications Orbiter . Communications Satellites are usually composed of

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1408-563: The SHF X band spectrum. An immediate antecedent of the geostationary satellites was the Hughes Aircraft Company 's Syncom 2 , launched on 26 July 1963. Syncom 2 was the first communications satellite in a geosynchronous orbit . It revolved around the Earth once per day at constant speed, but because it still had north–south motion, special equipment was needed to track it. Its successor, Syncom 3 , launched on 19 July 1964,

1472-407: The effective area or aperture of the receiving antenna, which has the units of area, can be thought of as the amount of area perpendicular to the direction of the radio waves from which the receiving antenna captures energy. Since the linear dimensions of an antenna scale with the wavelength λ {\displaystyle \lambda } , the cross sectional area of an antenna and thus

1536-423: The Earth faster, they do not remain visible in the sky to a fixed point on Earth continually like a geostationary satellite, but appear to a ground observer to cross the sky and "set" when they go behind the Earth beyond the visible horizon. Therefore, to provide continuous communications capability with these lower orbits requires a larger number of satellites, so that one of these satellites will always be visible in

1600-415: The Earth's surface. MEO satellites are similar to LEO satellites in functionality. MEO satellites are visible for much longer periods of time than LEO satellites, usually between 2 and 8 hours. MEO satellites have a larger coverage area than LEO satellites. A MEO satellite's longer duration of visibility and wider footprint means fewer satellites are needed in a MEO network than a LEO network. One disadvantage

1664-407: The K u band. The Intelsat Americas 5 , Galaxy 10R and AMC 3 satellites over North America provide a quite large amount of FTA channels on their K u band transponders . Free-space path loss In telecommunications , the free-space path loss ( FSPL ) (also known as free-space loss, FSL) is the attenuation of radio energy between the feedpoints of two antennas that results from

1728-502: The Moon, Earth's natural satellite, acting as a passive relay. After achieving the first transoceanic communication between Washington, D.C. , and Hawaii on 23 January 1956, this system was publicly inaugurated and put into formal production in January 1960. The first satellite purpose-built to actively relay communications was Project SCORE , led by Advanced Research Projects Agency (ARPA) and launched on 18 December 1958, which used

1792-863: 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. In the United States, the National Polar-orbiting Operational Environmental Satellite System (NPOESS) was established in 1994 to consolidate the polar satellite operations of NASA (National Aeronautics and Space Administration) NOAA (National Oceanic and Atmospheric Administration). NPOESS manages

1856-406: The antenna is inversely proportional to the square of distance (The term 4 π d 2 {\displaystyle 4\pi d^{2}} means the surface of a sphere, which has a radius d {\displaystyle d} . Please remember, that d {\displaystyle d} here has a meaning of 'distance' between the two antennas, and does not mean

1920-410: The antennas d {\displaystyle d} must be large enough that the antennas are in the far field of each other   d ≫ λ {\displaystyle \ d\gg \lambda } . The free-space path loss is the loss factor in this equation that is due to distance and wavelength, or in other words, the ratio of power transmitted to power received assuming

1984-409: The antennas are isotropic and have no directivity ( D t = D r = 1 {\displaystyle D_{t}=D_{r}=1} ): FSPL = ( 4 π d λ ) 2 {\displaystyle {\begin{aligned}{\mbox{FSPL}}=\left({\frac {4\pi d}{\lambda }}\right)^{2}\end{aligned}}} Since

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2048-674: The aperture scales with the square of wavelength λ 2 {\displaystyle \lambda ^{2}} . The effective area of an isotropic antenna (for a derivation of this see antenna aperture article) is Combining the above (1) and (2), for isotropic antennas A convenient way to express FSPL is in terms of decibels (dB): using SI units of meters for d {\displaystyle d} , hertz (s ) for f {\displaystyle f} , and meters per second (m⋅s ) for c {\displaystyle c} , (where c=299 792 458 m/s in vacuum, ≈ 300 000 km/s) For typical radio applications, it

2112-506: The assumption that the antennas are lossless, this formula assumes that the polarization of the antennas is the same, that there are no multipath effects, and that the radio wave path is sufficiently far away from obstructions that it acts as if it is in free space. This last restriction requires an ellipsoidal area around the line of sight out to 0.6 of the Fresnel zone be clear of obstructions. The Fresnel zone increases in diameter with

2176-465: The combination of the receiving antenna's capture area plus the obstacle-free, line-of-sight (LoS) path through free space (usually air). The "Standard Definitions of Terms for Antennas", IEEE Std 145-1993, defines free-space loss as "The loss between two isotropic radiators in free space, expressed as a power ratio." It does not include any power loss in the antennas themselves due to imperfections such as resistance. Free-space loss increases with

2240-403: The completion of a fully global network with Intelsat 3 in 1969–70. By the 1980s, with significant expansions in commercial satellite capacity, Intelsat was on its way to become part of the competitive private telecommunications industry, and had started to get competition from the likes of PanAmSat in the United States, which, ironically, was then bought by its archrival in 2005. When Intelsat

2304-416: The diameter of the sphere (as notation usually used in mathematics).) For an isotropic antenna which radiates equal power in all directions, the power density is evenly distributed over the surface of a sphere centered on the antenna The amount of power the receiving antenna receives from this radiation field is The factor A eff {\displaystyle A_{\text{eff}}} , called

2368-455: The edges of Antarctica and Greenland . Other land use for satellite phones are rigs at sea, a backup for hospitals, military, and recreation. Ships at sea, as well as planes, often use satellite phones. Satellite phone systems can be accomplished by a number of means. On a large scale, often there will be a local telephone system in an isolated area with a link to the telephone system in a main land area. There are also services that will patch

2432-692: 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

2496-646: The first transatlantic transmission of television signals. Belonging to AT&T as part of a multi-national agreement between AT&T, Bell Telephone Laboratories , NASA, the British General Post Office , and the French National PTT (Post Office) to develop satellite communications, it was launched by NASA from Cape Canaveral on 10 July 1962, in the first privately sponsored space launch. Another passive relay experiment primarily intended for military communications purposes

2560-479: The following subsystems: The bandwidth available from a satellite depends upon the number of transponders provided by the satellite. Each service (TV, Voice, Internet, radio) requires a different amount of bandwidth for transmission. This is typically known as link budgeting and a network simulator can be used to arrive at the exact value. Allocating frequencies to satellite services is a complicated process which requires international coordination and planning. This

2624-474: The frequency of a radio wave f {\displaystyle f} is equal to the speed of light c {\displaystyle c} divided by the wavelength, the path loss can also be written in terms of frequency: FSPL = ( 4 π d f c ) 2 {\displaystyle {\begin{aligned}{\mbox{FSPL}}=\left({4\pi df \over c}\right)^{2}\end{aligned}}} Beside

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2688-493: The fundamentals behind the deployment of artificial satellites in geostationary orbits to relay radio signals. Because of this, Arthur C. Clarke is often quoted as being the inventor of the concept of the communications satellite, and the term 'Clarke Belt' is employed as a description of the orbit. The first artificial Earth satellite was Sputnik 1 , which was put into orbit by the Soviet Union on 4 October 1957. It

2752-404: The ground, do not require as high signal strength (signal strength falls off as the square of the distance from the source, so the effect is considerable). Thus there is a trade off between the number of satellites and their cost. In addition, there are important differences in the onboard and ground equipment needed to support the two types of missions. A group of satellites working in concert

2816-469: The ionosphere. The launch of Sputnik 1 was a major step in the exploration of space and rocket development, and marks the beginning of the Space Age . There are two major classes of communications satellites, passive and active . Passive satellites only reflect the signal coming from the source, toward the direction of the receiver. With passive satellites, the reflected signal is not amplified at

2880-515: The late 20th century. Satellite communications are still used in many applications today. Remote islands such as Ascension Island , Saint Helena , Diego Garcia , and Easter Island , where no submarine cables are in service, need satellite telephones. There are also regions of some continents and countries where landline telecommunications are rare to non existent, for example large regions of South America, Africa, Canada, China, Russia, and Australia. Satellite communications also provide connection to

2944-566: The more than one hundred satellites in service worldwide. Other major satellite manufacturers include Space Systems/Loral , Orbital Sciences Corporation with the Star Bus series, Indian Space Research Organisation , Lockheed Martin (owns the former RCA Astro Electronics/GE Astro Space business), Northrop Grumman , Alcatel Space, now Thales Alenia Space , with the Spacebus series, and Astrium . Geostationary satellites must operate above

3008-496: The next two years, international negotiations led to the Intelsat Agreements, which in turn led to the launch of Intelsat 1, also known as Early Bird, on 6 April 1965, and which was the first commercial communications satellite to be placed in geosynchronous orbit. Subsequent Intelsat launches in the 1960s provided multi-destination service and video, audio, and data service to ships at sea (Intelsat 2 in 1966–67), and

3072-470: The northern hemisphere. This orbit provides a long dwell time over Russian territory as well as over Canada at higher latitudes than geostationary orbits over the equator. Communications satellites usually have one of three primary types of orbit , while other orbital classifications are used to further specify orbital details. MEO and LEO are non-geostationary orbit (NGSO). As satellites in MEO and LEO orbit

3136-559: The receiver such that the transmitted signal is received intelligibly. The free-space path loss (FSPL) formula derives from the Friis transmission formula . This states that in a radio system consisting of a transmitting antenna transmitting radio waves to a receiving antenna, the ratio of radio wave power received P r {\displaystyle P_{r}} to the power transmitted P t {\displaystyle P_{t}} is: where The distance between

3200-1047: The same linear polarization as FSS-class satellites. Examples of these are the Astra , Eutelsat , and Hotbird spacecraft in orbit over the European continent. Because of this, the terms FSS and DBS are more so used throughout the North American continent, and are uncommon in Europe. Fixed Service Satellites use the C band , and the lower portions of the K u band . They are normally used for broadcast feeds to and from television networks and local affiliate stations (such as program feeds for network and syndicated programming, live shots , and backhauls ), as well as being used for distance learning by schools and universities, business television (BTV), Videoconferencing , and general commercial telecommunications. FSS satellites are also used to distribute national cable channels to cable television headends. Free-to-air satellite TV channels are also usually distributed on FSS satellites in

3264-468: The satellite, and only a small amount of the transmitted energy actually reaches the receiver. Since the satellite is so far above Earth, the radio signal is attenuated due to free-space path loss , so the signal received on Earth is very weak. Active satellites, on the other hand, amplify the received signal before retransmitting it to the receiver on the ground. Passive satellites were the first communications satellites, but are little used now. Work that

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3328-402: The sky for transmission of communication signals. However, due to their closer distance to the Earth, LEO or MEO satellites can communicate to ground with reduced latency and at lower power than would be required from a geosynchronous orbit. A low Earth orbit (LEO) typically is a circular orbit about 160 to 2,000 kilometres (99 to 1,243 mi) above the Earth's surface and, correspondingly,

3392-454: The square of distance between the antennas because the radio waves spread out by the inverse square law and decreases with the square of the wavelength of the radio waves. The FSPL is rarely used standalone, but rather as a part of the Friis transmission formula , which includes the gain of antennas. It is a factor that must be included in the power link budget of a radio communication system, to ensure that sufficient radio power reaches

3456-418: The transmitting antenna spread out in a spherical wavefront. The amount of power passing through any sphere centered on the transmitting antenna is equal. The surface area of a sphere of radius d {\displaystyle d} is 4 π d 2 {\displaystyle 4\pi d^{2}} . Thus the intensity or power density of the radiation in any particular direction from

3520-447: The wavelength of the radio waves. Often the concept of free space path loss is applied to radio systems that don't completely meet these requirements, but these imperfections can be accounted for by small constant power loss factors that can be included in the link budget . The free-space loss increases with the distance between the antennas and decreases with the wavelength of the radio waves due to these factors: The radio waves from

3584-409: Was Project West Ford , which was led by Massachusetts Institute of Technology 's Lincoln Laboratory . After an initial failure in 1961, a launch on 9 May 1963 dispersed 350 million copper needle dipoles to create a passive reflecting belt. Even though only about half of the dipoles properly separated from each other, the project was able to successfully experiment and communicate using frequencies in

3648-399: Was an aluminized balloon satellite acting as a passive reflector of microwave signals. Communication signals were bounced off the satellite from one point on Earth to another. This experiment sought to establish the feasibility of worldwide broadcasts of telephone, radio, and television signals. Telstar was the first active, direct relay communications commercial satellite and marked

3712-503: Was begun in the field of electrical intelligence gathering at the United States Naval Research Laboratory in 1951 led to a project named Communication Moon Relay . Military planners had long shown considerable interest in secure and reliable communications lines as a tactical necessity, and the ultimate goal of this project was the creation of the longest communications circuit in human history, with

3776-507: Was developed by Mikhail Tikhonravov and Sergey Korolev , building on work by Konstantin Tsiolkovsky . Sputnik 1 was equipped with an on-board radio transmitter that worked on two frequencies of 20.005 and 40.002 MHz, or 7 and 15 meters wavelength. The satellite was not placed in orbit to send data from one point on Earth to another, but the radio transmitter was meant to study the properties of radio wave distribution throughout

3840-428: Was in intercontinental long distance telephony . The fixed Public Switched Telephone Network relays telephone calls from land line telephones to an Earth station , where they are then transmitted to a geostationary satellite. The downlink follows an analogous path. Improvements in submarine communications cables through the use of fiber-optics caused some decline in the use of satellites for fixed telephony in

3904-581: Was launched on 11 February 1965 to explore the feasibility of active solid-state X band long-range military communications. A total of nine satellites were launched between 1965 and 1976 as part of this series. In the United States, 1962 saw the creation of the Communications Satellite Corporation (COMSAT) private corporation, which was subject to instruction by the US Government on matters of national policy. Over

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3968-528: Was launched on 4 October 1960 to explore whether it would be possible to establish a global military communications network by using "delayed repeater" satellites, which receive and store information until commanded to rebroadcast them. After 17 days, a command system failure ended communications from the satellite. NASA 's satellite applications program launched the first artificial satellite used for passive relay communications in Echo 1 on 12 August 1960. Echo 1

4032-492: Was launched, the United States was the only launch source outside of the Soviet Union , who did not participate in the Intelsat agreements. The Soviet Union launched its first communications satellite on 23 April 1965 as part of the Molniya program. This program was also unique at the time for its use of what then became known as the Molniya orbit , which describes a highly elliptical orbit , with two high apogees daily over

4096-684: Was the first geostationary communications satellite. Syncom 3 obtained a geosynchronous orbit, without a north–south motion, making it appear from the ground as a stationary object in the sky. A direct extension of the passive experiments of Project West Ford was the Lincoln Experimental Satellite program, also conducted by the Lincoln Laboratory on behalf of the United States Department of Defense . The LES-1 active communications satellite

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