105-479: SES-11 / EchoStar 105 is a geostationary communications satellite operated by SES and EchoStar and designed and manufactured by Airbus Defence and Space . It has a mass of 5,200 kg (11,500 lb) and has a design life of at least 15 years. The spacecraft had been ready to beam television programming and video services across the Americas for SES and EchoStar. The Falcon 9 launch vehicle has placed
210-479: A delta-v of approximately 50 m/s per year. A second effect to be taken into account is the longitudinal drift, caused by the asymmetry of the Earth – the equator is slightly elliptical ( equatorial eccentricity ). There are two stable equilibrium points sometimes called "gravitational wells" (at 75.3°E and 108°W) and two corresponding unstable points (at 165.3°E and 14.7°W). Any geostationary object placed between
315-427: A geostationary transfer orbit (GTO), an elliptical orbit with an apogee at GEO height and a low perigee . On-board satellite propulsion is then used to raise the perigee, circularise and reach GEO. Satellites in geostationary orbit must all occupy a single ring above the equator . The requirement to space these satellites apart, to avoid harmful radio-frequency interference during operations, means that there are
420-413: A battery (for example when pressing a telegraph key), the electric charge in the wire induces an opposite charge in the water as it travels along. In 1831, Faraday described this effect in what is now referred to as Faraday's law of induction . As the two charges attract each other, the exciting charge is retarded. The core acts as a capacitor distributed along the length of the cable which, coupled with
525-455: A fixed position in the sky. The concept of a geostationary orbit was popularised by the science fiction writer Arthur C. Clarke in the 1940s as a way to revolutionise telecommunications, 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 so that Earth-based satellite antennas do not have to rotate to track them but can be pointed permanently at
630-449: A gain of +33dBm, however again the amount of power that can be fed into the fiber is limited. In single carrier configurations the dominating limitation is self phase modulation induced by the Kerr effect which limits the amplification to +18 dBm per fiber. In WDM configurations the limitation due to crossphase modulation becomes predominant instead. Optical pre-amplifiers are often used to negate
735-415: A geostationary orbit in particular, it ensures that it holds the same longitude over time. This orbital period, T , is directly related to the semi-major axis of the orbit through the formula: where: The eccentricity is zero, which produces a circular orbit . This ensures that the satellite does not move closer or further away from the Earth, which would cause it to track backwards and forwards across
840-576: A geostationary satellite to globalise communications. Telecommunications between the US and Europe was then possible between just 136 people at a time, and reliant on high frequency radios and an undersea cable . Conventional wisdom at the time was that it would require too much rocket power to place a satellite in a geostationary orbit and it would not survive long enough to justify the expense, so early efforts were put towards constellations of satellites in low or medium Earth orbit. The first of these were
945-421: A handful of hours. The first attempt at laying a transatlantic telegraph cable was promoted by Cyrus West Field , who persuaded British industrialists to fund and lay one in 1858. However, the technology of the day was not capable of supporting the project; it was plagued with problems from the outset, and was in operation for only a month. Subsequent attempts in 1865 and 1866 with the world's largest steamship,
1050-547: A higher graveyard orbit to avoid collisions. In 1929, Herman Potočnik described both geosynchronous orbits in general and the special case of the geostationary Earth orbit in particular as useful orbits for space stations . The first appearance of a geostationary orbit in popular literature was in October 1942, in the first Venus Equilateral story by George O. Smith , but Smith did not go into details. British science fiction author Arthur C. Clarke popularised and expanded
1155-399: A known position) and providing an additional reference signal. This improves position accuracy from approximately 5m to 1m or less. Past and current navigation systems that use geostationary satellites include: Geostationary satellites are launched to the east into a prograde orbit that matches the rotation rate of the equator. The smallest inclination that a satellite can be launched into
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#17330862114661260-408: A large area of the earth's surface, extending 81° away in latitude and 77° in longitude. They appear stationary in the sky, which eliminates the need for ground stations to have movable antennas. This means that Earth-based observers can erect small, cheap and stationary antennas that are always directed at the desired satellite. However, latency becomes significant as it takes about 240 ms for
1365-501: A limited number of orbital slots available, and thus only a limited number of satellites can be operated in geostationary orbit. This has led to conflict between different countries wishing access to the same orbital slots (countries near the same longitude but differing latitudes ) and radio frequencies . These disputes are addressed through the International Telecommunication Union 's allocation mechanism under
1470-683: A machine in 1837 for covering wires with silk or cotton thread that he developed into a wire wrapping capability for submarine cable with a factory in 1857 that became W.T. Henley's Telegraph Works Co., Ltd. The India Rubber, Gutta Percha and Telegraph Works Company , established by the Silver family and giving that name to a section of London , furnished cores to Henley's as well as eventually making and laying finished cable. In 1870 William Hooper established Hooper's Telegraph Works to manufacture his patented vulcanized rubber core, at first to furnish other makers of finished cable, that began to compete with
1575-428: A public dispute with William Thomson . Whitehouse believed that, with enough voltage, any cable could be driven. Thomson believed that his law of squares showed that retardation could not be overcome by a higher voltage. His recommendation was a larger cable. Because of the excessive voltages recommended by Whitehouse, Cyrus West Field's first transatlantic cable never worked reliably, and eventually short circuited to
1680-415: A pump laser light to be transmitted alongside the data carried by the cable; the pump light and the data are often transmitted in physically separate fibers. The ROPA contains a doped fiber that uses the pump light (often a 1480 nm laser light) to amplify the data signals carried on the rest of the fibers. WDM or wavelength division multiplexing was first implemented in submarine fiber optic cables from
1785-406: A signal to pass from a ground based transmitter on the equator to the satellite and back again. This delay presents problems for latency-sensitive applications such as voice communication, so geostationary communication satellites are primarily used for unidirectional entertainment and applications where low latency alternatives are not available. Geostationary satellites are directly overhead at
1890-408: A single fiber using wavelength division multiplexing (WDM), which allows for multiple optical carrier channels to be transmitted through a single fiber, each carrying its own information. WDM is limited by the optical bandwidth of the amplifiers used to transmit data through the cable and by the spacing between the frequencies of the optical carriers; however this minimum spacing is also limited, with
1995-407: A solid-state optical amplifier , usually an erbium-doped fiber amplifier (EDFA). Each repeater contains separate equipment for each fiber. These comprise signal reforming, error measurement and controls. A solid-state laser dispatches the signal into the next length of fiber. The solid-state laser excites a short length of doped fiber that itself acts as a laser amplifier. As the light passes through
2100-405: A submarine cable can have a major impact in its capacity. SDM is combined with DWDM to improve capacity. The open cable concept allows for the design of a submarine cable independently of the transponders that will be used to transmit data through the cable. SLTE (Submarine Line Terminal Equipment) has transponders and a ROADM ( Reconfigurable optical add-drop multiplexer ) used for handling
2205-475: A typical multi-terabit, transoceanic submarine cable system costs several hundred million dollars to construct. As a result of these cables' cost and usefulness, they are highly valued not only by the corporations building and operating them for profit, but also by national governments. For instance, the Australian government considers its submarine cable systems to be "vital to the national economy". Accordingly,
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#17330862114662310-464: A wire, insulated with tarred hemp and India rubber , in the water of New York Harbor , and telegraphed through it. The following autumn, Wheatstone performed a similar experiment in Swansea Bay . A good insulator to cover the wire and prevent the electric current from leaking into the water was necessary for the success of a long submarine line. India rubber had been tried by Moritz von Jacobi ,
2415-449: Is a cable laid on the seabed between land-based stations to carry telecommunication signals across stretches of ocean and sea. The first submarine communications cables were laid beginning in the 1850s and carried telegraphy traffic, establishing the first instant telecommunications links between continents, such as the first transatlantic telegraph cable which became operational on 16 August 1858. Submarine cables first connected all
2520-480: Is either not required, the capacity to the country is small enough to be backed up by other means, or having backup is regarded as too expensive. A further redundant-path development over and above the self-healing rings approach is the mesh network whereby fast switching equipment is used to transfer services between network paths with little to no effect on higher-level protocols if a path becomes inoperable. As more paths become available to use between two points, it
2625-586: Is less likely that one or two simultaneous failures will prevent end-to-end service. As of 2012, operators had "successfully demonstrated long-term, error-free transmission at 100 Gbps across Atlantic Ocean" routes of up to 6,000 km (3,700 mi), meaning a typical cable can move tens of terabits per second overseas. Speeds improved rapidly in the previous few years, with 40 Gbit/s having been offered on that route only three years earlier in August 2009. Switching and all-by-sea routing commonly increases
2730-595: Is limited, although this has increased over the years; in 2014 unrepeated cables of up to 380 kilometres (240 mi) in length were in service; however these require unpowered repeaters to be positioned every 100 km. The rising demand for these fiber-optic cables outpaced the capacity of providers such as AT&T. Having to shift traffic to satellites resulted in lower-quality signals. To address this issue, AT&T had to improve its cable-laying abilities. It invested $ 100 million in producing two specialized fiber-optic cable laying vessels. These included laboratories in
2835-452: Is that of the launch site's latitude, so launching the satellite from close to the equator limits the amount of inclination change needed later. Additionally, launching from close to the equator allows the speed of the Earth's rotation to give the satellite a boost. A launch site should have water or deserts to the east, so any failed rockets do not fall on a populated area. Most launch vehicles place geostationary satellites directly into
2940-403: Is the gravitational constant , (6.674 28 ± 0.000 67 ) × 10 m kg s . The magnitude of the acceleration, a , of a body moving in a circle is given by: where v is the magnitude of the velocity (i.e. the speed) of the satellite. From Newton's second law of motion , the centripetal force F c is given by: As F c = F g , so that Replacing v with the equation for
3045-670: Is too small to be commercially viable. Some have been used as scientific instruments to measure earthquake waves and other geomagnetic events. In 1942, Siemens Brothers of New Charlton , London, in conjunction with the United Kingdom National Physical Laboratory , adapted submarine communications cable technology to create the world's first submarine oil pipeline in Operation Pluto during World War II . Active fiber-optic cables may be useful in detecting seismic events which alter cable polarization. In
3150-781: Is typically 70°, and in some cases less. Geostationary satellite imagery has been used for tracking volcanic ash , measuring cloud top temperatures and water vapour, oceanography , measuring land temperature and vegetation coverage, facilitating cyclone path prediction, and providing real time cloud coverage and other tracking data. Some information has been incorporated into meteorological prediction models , but due to their wide field of view, full-time monitoring and lower resolution, geostationary weather satellite images are primarily used for short-term and real-time forecasting. Geostationary satellites can be used to augment GNSS systems by relaying clock , ephemeris and ionospheric error corrections (calculated from ground stations of
3255-408: Is used to provide visible and infrared images of Earth's surface and atmosphere for weather observation, oceanography , and atmospheric tracking. As of 2019 there are 19 satellites in either operation or stand-by. These satellite systems include: These satellites typically capture images in the visual and infrared spectrum with a spatial resolution between 0.5 and 4 square kilometres. The coverage
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3360-541: The Australian Communications and Media Authority (ACMA) has created protection zones that restrict activities that could potentially damage cables linking Australia to the rest of the world. The ACMA also regulates all projects to install new submarine cables. Submarine cables are important to the modern military as well as private enterprise. The US military , for example, uses the submarine cable network for data transfer from conflict zones to command staff in
3465-712: The Crimean War various forms of telegraphy played a major role; this was a first. At the start of the campaign there was a telegraph link at Bucharest connected to London. In the winter of 1854 the French extended the telegraph link to the Black Sea coast. In April 1855 the British laid an underwater cable from Varna to the Crimean peninsula so that news of the Crimean War could reach London in
3570-623: The North Pacific Cable system was the first regenerative system (i.e., with repeaters ) to completely cross the Pacific from the US mainland to Japan. The US portion of NPC was manufactured in Portland, Oregon, from 1989 to 1991 at STC Submarine Systems, and later Alcatel Submarine Networks . The system was laid by Cable & Wireless Marine on the CS Cable Venture . Transatlantic cables of
3675-732: The Prussian electrical engineer , as far back as the early 19th century. Another insulating gum which could be melted by heat and readily applied to wire made its appearance in 1842. Gutta-percha , the adhesive juice of the Palaquium gutta tree, was introduced to Europe by William Montgomerie , a Scottish surgeon in the service of the British East India Company . Twenty years earlier, Montgomerie had seen whips made of gutta-percha in Singapore , and he believed that it would be useful in
3780-473: The Radio Regulations . In the 1976 Bogota Declaration , eight countries located on the Earth's equator claimed sovereignty over the geostationary orbits above their territory, but the claims gained no international recognition. A statite is a hypothetical satellite that uses radiation pressure from the sun against a solar sail to modify its orbit. It would hold its location over the dark side of
3885-520: The Rhine between Deutz and Cologne . In 1849, Charles Vincent Walker , electrician to the South Eastern Railway , submerged 3 km (2 mi) of wire coated with gutta-percha off the coast from Folkestone , which was tested successfully. In August 1850, having earlier obtained a concession from the French government, John Watkins Brett 's English Channel Submarine Telegraph Company laid
3990-736: The SS Great Eastern , used a more advanced technology and produced the first successful transatlantic cable. Great Eastern later went on to lay the first cable reaching to India from Aden, Yemen, in 1870. From the 1850s until 1911, British submarine cable systems dominated the most important market, the North Atlantic Ocean . The British had both supply side and demand side advantages. In terms of supply, Britain had entrepreneurs willing to put forth enormous amounts of capital necessary to build, lay and maintain these cables. In terms of demand, Britain's vast colonial empire led to business for
4095-714: The USNS Kingsport docked in Lagos on August 23, 1963. The first satellite placed in a geostationary orbit was Syncom 3 , which was launched by a Delta D rocket in 1964. With its increased bandwidth, this satellite was able to transmit live coverage of the Summer Olympics from Japan to America. Geostationary orbits have been in common use ever since, in particular for satellite television. Today there are hundreds of geostationary satellites providing remote sensing and communications. Although most populated land locations on
4200-430: The centripetal force required to maintain the orbit ( F c ) is equal to the gravitational force acting on the satellite ( F g ): From Isaac Newton 's universal law of gravitation , where F g is the gravitational force acting between two objects, M E is the mass of the Earth, 5.9736 × 10 kg , m s is the mass of the satellite, r is the distance between the centers of their masses , and G
4305-460: The speed of an object moving around a circle produces: where T is the orbital period (i.e. one sidereal day), and is equal to 86 164 .090 54 s . This gives an equation for r : The product GM E is known with much greater precision than either factor alone; it is known as the geocentric gravitational constant μ = 398 600 .4418 ± 0.0008 km s . Hence Submarine communications cable A submarine communications cable
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4410-461: The steel wire armouring gave pests a route to eat their way in. Damaged armouring, which was not uncommon, also provided an entrance. Cases of sharks biting cables and attacks by sawfish have been recorded. In one case in 1873, a whale damaged the Persian Gulf Cable between Karachi and Gwadar . The whale was apparently attempting to use the cable to clean off barnacles at a point where
4515-443: The 1980s, fiber-optic cables were developed. The first transatlantic telephone cable to use optical fiber was TAT-8 , which went into operation in 1988. A fiber-optic cable comprises multiple pairs of fibers. Each pair has one fiber in each direction. TAT-8 had two operational pairs and one backup pair. Except for very short lines, fiber-optic submarine cables include repeaters at regular intervals. Modern optical fiber repeaters use
4620-422: The 1990s to the 2000s, followed by DWDM or dense wavelength division mulltiplexing around 2007. Each fiber can carry 30 wavelengths at a time. SDM or spatial division multiplexing submarine cables have at least 12 fiber pairs which is an increase from the maximum of 8 pairs found in conventional submarine cables, and submarine cables with up to 24 fiber pairs have been deployed. The type of modulation employed in
4725-509: The 19th century consisted of an outer layer of iron and later steel wire, wrapping India rubber, wrapping gutta-percha , which surrounded a multi-stranded copper wire at the core. The portions closest to each shore landing had additional protective armour wires. Gutta-percha, a natural polymer similar to rubber, had nearly ideal properties for insulating submarine cables, with the exception of a rather high dielectric constant which made cable capacitance high. William Thomas Henley had developed
4830-424: The Earth at a latitude of approximately 30 degrees. A statite is stationary relative to the Earth and Sun system rather than compared to surface of the Earth, and could ease congestion in the geostationary ring. Geostationary satellites require some station keeping to keep their position, and once they run out of thruster fuel they are generally retired. The transponders and other onboard systems often outlive
4935-608: The US mainland to Hawaii in 1902 and Guam to the Philippines in 1903. Canada, Australia, New Zealand and Fiji were also linked in 1902 with the trans-Pacific segment of the All Red Line . Japan was connected into the system in 1906. Service beyond Midway Atoll was abandoned in 1941 due to World War II, but the remainder stayed in operation until 1951 when the FCC gave permission to cease operations. The first trans-Pacific telephone cable
5040-516: The United States. Interruption of the cable network during intense operations could have direct consequences for the military on the ground. Almost all fiber-optic cables from TAT-8 in 1988 until approximately 1997 were constructed by consortia of operators. For example, TAT-8 counted 35 participants including most major international carriers at the time such as AT&T Corporation . Two privately financed, non-consortium cables were constructed in
5145-400: The absence of servicing missions from the Earth or a renewable propulsion method, the consumption of thruster propellant for station-keeping places a limitation on the lifetime of the satellite. Hall-effect thrusters , which are currently in use, have the potential to prolong the service life of a satellite by providing high-efficiency electric propulsion . For circular orbits around a body,
5250-466: The cable companies from news agencies, trading and shipping companies, and the British government. Many of Britain's colonies had significant populations of European settlers, making news about them of interest to the general public in the home country. British officials believed that depending on telegraph lines that passed through non-British territory posed a security risk, as lines could be cut and messages could be interrupted during wartime. They sought
5355-456: The cable descended over a steep drop. The unfortunate whale got its tail entangled in loops of cable and drowned. The cable repair ship Amber Witch was only able to winch up the cable with difficulty, weighed down as it was with the dead whale's body. Early long-distance submarine telegraph cables exhibited formidable electrical problems. Unlike modern cables, the technology of the 19th century did not allow for in-line repeater amplifiers in
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#17330862114665460-442: The cable, which permitted design of the equipment for accurate telegraphy. The effects of atmospheric electricity and the geomagnetic field on submarine cables also motivated many of the early polar expeditions . Thomson had produced a mathematical analysis of propagation of electrical signals into telegraph cables based on their capacitance and resistance, but since long submarine cables operated at slow rates, he did not include
5565-510: The cable. Large voltages were used to attempt to overcome the electrical resistance of their tremendous length but the cables' distributed capacitance and inductance combined to distort the telegraph pulses in the line, reducing the cable's bandwidth , severely limiting the data rate for telegraph operation to 10–12 words per minute . As early as 1816, Francis Ronalds had observed that electric signals were slowed in passing through an insulated wire or core laid underground, and outlined
5670-535: The cables in maintaining administrative communications with governors throughout its empire, as well as in engaging other nations diplomatically and communicating with its military units in wartime. The geographic location of British territory was also an advantage as it included both Ireland on the east side of the Atlantic Ocean and Newfoundland in North America on the west side, making for the shortest route across
5775-401: The cause to be induction, using the analogy of a long Leyden jar . The same effect was noticed by Latimer Clark (1853) on cores immersed in water, and particularly on the lengthy cable between England and The Hague. Michael Faraday showed that the effect was caused by capacitance between the wire and the earth (or water) surrounding it. Faraday had noticed that when a wire is charged from
5880-458: The collection of artificial satellites in this orbit is known as the Clarke Belt. In technical terminology the orbit is referred to as either a geostationary or geosynchronous equatorial orbit, with the terms used somewhat interchangeably. The first geostationary satellite was designed by Harold Rosen while he was working at Hughes Aircraft in 1959. Inspired by Sputnik 1 , he wanted to use
5985-509: The concept in a 1945 paper entitled Extra-Terrestrial Relays – Can Rocket Stations Give Worldwide Radio Coverage? , published in Wireless World magazine. Clarke acknowledged the connection in his introduction to The Complete Venus Equilateral . The orbit, which Clarke first described as useful for broadcast and relay communications satellites, is sometimes called the Clarke orbit. Similarly,
6090-608: The creation of a worldwide network within the empire, which became known as the All Red Line , and conversely prepared strategies to quickly interrupt enemy communications. Britain's very first action after declaring war on Germany in World War I was to have the cable ship Alert (not the CS Telconia as frequently reported) cut the five cables linking Germany with France, Spain and the Azores, and through them, North America. Thereafter,
6195-440: The current at 10,000VDC is up to 1,650mA. Hence the total amount of power sent into the cable is often up to 16.5 kW. The optic fiber used in undersea cables is chosen for its exceptional clarity, permitting runs of more than 100 kilometres (62 mi) between repeaters to minimize the number of amplifiers and the distortion they cause. Unrepeated cables are cheaper than repeated cables and their maximum transmission distance
6300-434: The current generation with one end providing a positive voltage and the other a negative voltage. A virtual earth point exists roughly halfway along the cable under normal operation. The amplifiers or repeaters derive their power from the potential difference across them. The voltage passed down the cable is often anywhere from 3000 to 15,000VDC at a current of up to 1,100mA, with the current increasing with decreasing voltage;
6405-402: The data traffic that is crossing oceans is carried by undersea cables. The reliability of submarine cables is high, especially when (as noted above) multiple paths are available in the event of a cable break. Also, the total carrying capacity of submarine cables is in the terabits per second, while satellites typically offer only 1,000 megabits per second and display higher latency . However,
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#17330862114666510-504: The deep-sea sections which comprise the majority of the run, although larger and heavier cables are used for shallow-water sections near shore. After William Cooke and Charles Wheatstone had introduced their working telegraph in 1839, the idea of a submarine line across the Atlantic Ocean began to be thought of as a possible triumph of the future. Samuel Morse proclaimed his faith in it as early as 1840, and in 1842, he submerged
6615-412: The development of submarine branching units (SBUs), more than one destination could be served by a single cable system. Modern cable systems now usually have their fibers arranged in a self-healing ring to increase their redundancy, with the submarine sections following different paths on the ocean floor . One reason for this development was that the capacity of cable systems had become so large that it
6720-438: The distance and thus the round trip latency by more than 50%. For example, the round trip delay (RTD) or latency of the fastest transatlantic connections is under 60 ms, close to the theoretical optimum for an all-sea route. While in theory, a great circle route (GCP) between London and New York City is only 5,600 km (3,500 mi), this requires several land masses ( Ireland , Newfoundland , Prince Edward Island and
6825-400: The effects of inductance. By the 1890s, Oliver Heaviside had produced the modern general form of the telegrapher's equations , which included the effects of inductance and which were essential to extending the theory of transmission lines to the higher frequencies required for high-speed data and voice. While laying a transatlantic telephone cable was seriously considered from the 1920s,
6930-659: The equator and appear lower in the sky to an observer nearer the poles. As the observer's latitude increases, communication becomes more difficult due to factors such as atmospheric refraction , Earth's thermal emission , line-of-sight obstructions, and signal reflections from the ground or nearby structures. At latitudes above about 81°, geostationary satellites are below the horizon and cannot be seen at all. Because of this, some Russian communication satellites have used elliptical Molniya and Tundra orbits, which have excellent visibility at high latitudes. A worldwide network of operational geostationary meteorological satellites
7035-474: The equilibrium points would (without any action) be slowly accelerated towards the stable equilibrium position, causing a periodic longitude variation. The correction of this effect requires station-keeping maneuvers with a maximal delta-v of about 2 m/s per year, depending on the desired longitude. Solar wind and radiation pressure also exert small forces on satellites: over time, these cause them to slowly drift away from their prescribed orbits. In
7140-415: The fabrication of surgical apparatus. Michael Faraday and Wheatstone soon discovered the merits of gutta-percha as an insulator, and in 1845, the latter suggested that it should be employed to cover the wire which was proposed to be laid from Dover to Calais . In 1847 William Siemens , then an officer in the army of Prussia, laid the first successful underwater cable using gutta percha insulation, across
7245-444: The fiber, it is amplified. This system also permits wavelength-division multiplexing , which dramatically increases the capacity of the fiber. EDFA amplifiers were first used in submarine cables in 1995. Repeaters are powered by a constant direct current passed down the conductor near the centre of the cable, so all repeaters in a cable are in series. Power feed equipment is installed at the terminal stations. Typically both ends share
7350-533: The first line across the English Channel , using the converted tugboat Goliath . It was simply a copper wire coated with gutta-percha , without any other protection, and was not successful. However, the experiment served to secure renewal of the concession, and in September 1851, a protected core, or true, cable was laid by the reconstituted Submarine Telegraph Company from a government hulk , Blazer , which
7455-542: The following properties: An inclination of zero ensures that the orbit remains over the equator at all times, making it stationary with respect to latitude from the point of view of a ground observer (and in the Earth-centered Earth-fixed reference frame). The orbital period is equal to exactly one sidereal day. This means that the satellite will return to the same point above the Earth's surface every (sidereal) day, regardless of other orbital properties. For
7560-523: The ground. All geostationary satellites have to be located on this ring. A combination of lunar gravity, solar gravity, and the flattening of the Earth at its poles causes a precession motion of the orbital plane of any geostationary object, with an orbital period of about 53 years and an initial inclination gradient of about 0.85° per year, achieving a maximal inclination of 15° after 26.5 years. To correct for this perturbation , regular orbital stationkeeping maneuvers are necessary, amounting to
7665-415: The gutta-percha cores. The company later expanded into complete cable manufacture and cable laying, including the building of the first cable ship specifically designed to lay transatlantic cables. Gutta-percha and rubber were not replaced as a cable insulation until polyethylene was introduced in the 1930s. Even then, the material was only available to the military and the first submarine cable using it
7770-452: The isthmus connecting New Brunswick to Nova Scotia ) to be traversed, as well as the extremely tidal Bay of Fundy and a land route along Massachusetts ' north shore from Gloucester to Boston and through fairly built up areas to Manhattan itself. In theory, using this partial land route could result in round trip times below 40 ms (which is the speed of light minimum time), and not counting switching. Along routes with less land in
7875-431: The late 1990s, which preceded a massive, speculative rush to construct privately financed cables that peaked in more than $ 22 billion worth of investment between 1999 and 2001. This was followed by the bankruptcy and reorganization of cable operators such as Global Crossing , 360networks , FLAG , Worldcom , and Asia Global Crossing. Tata Communications ' Global Network (TGN) is the only wholly owned fiber network circling
7980-684: The link from Dover to Ostend in Belgium, by the Submarine Telegraph Company. Meanwhile, the Electric & International Telegraph Company completed two cables across the North Sea , from Orford Ness to Scheveningen , the Netherlands. These cables were laid by Monarch , a paddle steamer which later became the first vessel with permanent cable-laying equipment. In 1858, the steamship Elba
8085-678: The mammoth globe-spanning Eastern Telegraph Company , owned by John Pender . A spin-off from Eastern Telegraph Company was a second sister company, the Eastern Extension, China and Australasia Telegraph Company, commonly known simply as "the Extension." In 1872, Australia was linked by cable to Bombay via Singapore and China and in 1876, the cable linked the British Empire from London to New Zealand. The first trans-Pacific cables providing telegraph service were completed in 1902 and 1903, linking
8190-549: The minimum spacing often being 50 GHz (0.4 nm). The use of WDM can reduce the maximum length of the cable although this can be overcome by designing equipment with this in mind. Optical post amplifiers, used to increase the strength of the signal generated by the optical transmitter often use a diode-pumped erbium-doped fiber laser. The diode is often a high power 980 or 1480 nm laser diode. This setup allows for an amplification of up to +24dBm in an affordable manner. Using an erbium-ytterbium doped fiber instead allows for
8295-474: The ocean when Whitehouse increased the voltage beyond the cable design limit. Thomson designed a complex electric-field generator that minimized current by resonating the cable, and a sensitive light-beam mirror galvanometer for detecting the faint telegraph signals. Thomson became wealthy on the royalties of these, and several related inventions. Thomson was elevated to Lord Kelvin for his contributions in this area, chiefly an accurate mathematical model of
8400-444: The ocean, which reduced costs significantly. A few facts put this dominance of the industry in perspective. In 1896, there were 30 cable-laying ships in the world, 24 of which were owned by British companies. In 1892, British companies owned and operated two-thirds of the world's cables and by 1923, their share was still 42.7 percent. During World War I , Britain's telegraph communications were almost completely uninterrupted, while it
8505-418: The only way Germany could communicate was by wireless, and that meant that Room 40 could listen in. The submarine cables were an economic benefit to trading companies, because owners of ships could communicate with captains when they reached their destination and give directions as to where to go next to pick up cargo based on reported pricing and supply information. The British government had obvious uses for
8610-435: The other pumping them at 1450 nm. Launching a pump frequency (pump laser light) at a power of just one watt leads to an increase in reach of 45 km or a 6-fold increase in capacity. Another way to increase the reach of a cable is by using unpowered repeaters called remote optical pre-amplifiers (ROPAs); these still make a cable count as unrepeatered since the repeaters do not require electrical power but they do require
8715-538: The passive Echo balloon satellites in 1960, followed by Telstar 1 in 1962. Although these projects had difficulties with signal strength and tracking, issues that could be solved using geostationary orbits, the concept was seen as impractical, so Hughes often withheld funds and support. By 1961, Rosen and his team had produced a cylindrical prototype with a diameter of 76 centimetres (30 in), height of 38 centimetres (15 in), weighing 11.3 kilograms (25 lb), light and small enough to be placed into orbit. It
8820-476: The planet now have terrestrial communications facilities ( microwave , fiber-optic ), with telephone access covering 96% of the population and internet access 90%, some rural and remote areas in developed countries are still reliant on satellite communications. Most commercial communications satellites , broadcast satellites and SBAS satellites operate in geostationary orbits. Geostationary communication satellites are useful because they are visible from
8925-485: The position in the sky where the satellites are located. Weather satellites are also placed in this orbit for real-time monitoring and data collection, and navigation satellites to provide a known calibration point and enhance GPS accuracy. Geostationary satellites are launched via a temporary orbit , and placed in a slot above a particular point on the Earth's surface. The orbit requires some stationkeeping to keep its position, and modern retired satellites are placed in
9030-477: The resistance and inductance of the cable, limits the speed at which a signal travels through the conductor of the cable. Early cable designs failed to analyse these effects correctly. Famously, E.O.W. Whitehouse had dismissed the problems and insisted that a transatlantic cable was feasible. When he subsequently became chief electrician of the Atlantic Telegraph Company , he became involved in
9135-524: The same plane, altitude and speed; however, the presence of satellites in eccentric orbits allows for collisions at up to 4 km/s. Although a collision is comparatively unlikely, GEO satellites have a limited ability to avoid any debris. At geosynchronous altitude, objects less than 10 cm in diameter cannot be seen from the Earth, making it difficult to assess their prevalence. Despite efforts to reduce risk, spacecraft collisions have occurred. The European Space Agency telecom satellite Olympus-1
9240-580: The satellite into a high-altitude supersynchronous transfer orbit . Geostationary orbit A geostationary orbit , also referred to as a geosynchronous equatorial orbit ( GEO ), 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 motionless, in
9345-537: The ships for splicing cable and testing its electrical properties. Such field monitoring is important because the glass of fiber-optic cable is less malleable than the copper cable that had been formerly used. The ships are equipped with thrusters that increase maneuverability. This capability is important because fiber-optic cable must be laid straight from the stern, which was another factor that copper-cable-laying ships did not have to contend with. Originally, submarine cables were simple point-to-point connections. With
9450-562: The signals in the cable via software control. The ROADM is used to improve the reliability of the cable by allowing it to operate even if it has faults. This equipment is located inside a cable landing station (CLS). C-OTDR (Coherent Optical Time Domain Reflectometry) is used in submarine cables to detect the location of cable faults. The wet plant of a submarine cable comprises the cable itself, branching units, repeaters and possibly OADMs ( Optical add-drop multiplexers ). Currently 99% of
9555-405: The sky. A geostationary orbit can be achieved only at an altitude very close to 35,786 kilometres (22,236 miles) and directly above the equator. This equates to an orbital speed of 3.07 kilometres per second (1.91 miles per second) and an orbital period of 1,436 minutes, one sidereal day . This ensures that the satellite will match the Earth's rotational period and has a stationary footprint on
9660-601: The technology required for economically feasible telecommunications was not developed until the 1940s. A first attempt to lay a " pupinized " telephone cable—one with loading coils added at regular intervals—failed in the early 1930s due to the Great Depression . TAT-1 (Transatlantic No. 1) was the first transatlantic telephone cable system. Between 1955 and 1956, cable was laid between Gallanach Bay, near Oban , Scotland and Clarenville, Newfoundland and Labrador , in Canada. It
9765-441: The thermal noise of the receiver. Pumping the pre-amplifier with a 980 nm laser leads to a noise of at most 3.5 dB, with a noise of 5 dB usually obtained with a 1480 nm laser. The noise has to be filtered using optical filters. Raman amplification can be used to extend the reach or the capacity of an unrepeatered cable, by launching 2 frequencies into a single fiber; one carrying data signals at 1550 nm, and
9870-485: The thruster fuel and by allowing the satellite to move naturally into an inclined geosynchronous orbit some satellites can remain in use, or else be elevated to a graveyard orbit . This process is becoming increasingly regulated and satellites must have a 90% chance of moving over 200 km above the geostationary belt at end of life. Space debris at geostationary orbits typically has a lower collision speed than at low Earth orbit (LEO) since all GEO satellites orbit in
9975-517: The way, round trip times can approach speed of light minimums in the long term. The type of optical fiber used in unrepeated and very long cables is often PCSF (pure silica core) due to its low loss of 0.172 dB per kilometer when carrying a 1550 nm wavelength laser light. The large chromatic dispersion of PCSF means that its use requires transmission and receiving equipment designed with this in mind; this property can also be used to reduce interference when transmitting multiple channels through
10080-821: The world's continents (except Antarctica ) when Java was connected to Darwin, Northern Territory , Australia, in 1871 in anticipation of the completion of the Australian Overland Telegraph Line in 1872 connecting to Adelaide, South Australia and thence to the rest of Australia. Subsequent generations of cables carried telephone traffic, then data communications traffic. These early cables used copper wires in their cores, but modern cables use optical fiber technology to carry digital data , which includes telephone, Internet and private data traffic. Modern cables are typically about 25 mm (1 in) in diameter and weigh around 1.4 tonnes per kilometre (2.5 short tons per mile; 2.2 long tons per mile) for
10185-560: Was spin stabilised with a dipole antenna producing a pancake shaped beam. In August 1961, they were contracted to begin building the real satellite. They lost Syncom 1 to electronics failure, but Syncom 2 was successfully placed into a geosynchronous orbit in 1963. Although its inclined orbit still required moving antennas, it was able to relay TV transmissions, and allowed for US President John F. Kennedy in Washington D.C., to phone Nigerian prime minister Abubakar Tafawa Balewa aboard
10290-634: Was able to quickly cut Germany's cables worldwide. Throughout the 1860s and 1870s, British cable expanded eastward, into the Mediterranean Sea and the Indian Ocean. An 1863 cable to Bombay (now Mumbai ), India, provided a crucial link to Saudi Arabia . In 1870, Bombay was linked to London via submarine cable in a combined operation by four cable companies, at the behest of the British Government. In 1872, these four companies were combined to form
10395-548: Was inaugurated on September 25, 1956, initially carrying 36 telephone channels. In the 1960s, transoceanic cables were coaxial cables that transmitted frequency-multiplexed voiceband signals . A high-voltage direct current on the inner conductor powered repeaters (two-way amplifiers placed at intervals along the cable). The first-generation repeaters remain among the most reliable vacuum tube amplifiers ever designed. Later ones were transistorized. Many of these cables are still usable, but have been abandoned because their capacity
10500-772: Was laid from Hawaii to Japan in 1964, with an extension from Guam to The Philippines. Also in 1964, the Commonwealth Pacific Cable System (COMPAC), with 80 telephone channel capacity, opened for traffic from Sydney to Vancouver, and in 1967, the South East Asia Commonwealth (SEACOM) system, with 160 telephone channel capacity, opened for traffic. This system used microwave radio from Sydney to Cairns (Queensland), cable running from Cairns to Madang ( Papua New Guinea ), Guam , Hong Kong , Kota Kinabalu (capital of Sabah , Malaysia), Singapore , then overland by microwave radio to Kuala Lumpur . In 1991,
10605-654: Was not laid until 1945 during World War II across the English Channel . In the 1920s, the American military experimented with rubber-insulated cables as an alternative to gutta-percha, since American interests controlled significant supplies of rubber but did not have easy access to gutta-percha manufacturers. The 1926 development by John T. Blake of deproteinized rubber improved the impermeability of cables to water. Many early cables suffered from attack by sea life. The insulation could be eaten, for instance, by species of Teredo (shipworm) and Xylophaga . Hemp laid between
10710-425: Was not possible to completely back up a cable system with satellite capacity, so it became necessary to provide sufficient terrestrial backup capability. Not all telecommunications organizations wish to take advantage of this capability, so modern cable systems may have dual landing points in some countries (where back-up capability is required) and only single landing points in other countries where back-up capability
10815-490: Was struck by a meteoroid on August 11, 1993, and eventually moved to a graveyard orbit , and in 2006 the Russian Express-AM11 communications satellite was struck by an unknown object and rendered inoperable, although its engineers had enough contact time with the satellite to send it into a graveyard orbit. In 2017, both AMC-9 and Telkom-1 broke apart from an unknown cause. A typical geostationary orbit has
10920-552: Was towed across the Channel. In 1853, more successful cables were laid, linking Great Britain with Ireland , Belgium , and the Netherlands , and crossing The Belts in Denmark . The British & Irish Magnetic Telegraph Company completed the first successful Irish link on May 23 between Portpatrick and Donaghadee using the collier William Hutt . The same ship was used for
11025-471: Was used to lay a telegraph cable from Jersey to Guernsey , on to Alderney and then to Weymouth , the cable being completed successfully in September of that year. Problems soon developed with eleven breaks occurring by 1860 due to storms, tidal and sand movements, and wear on rocks. A report to the Institution of Civil Engineers in 1860 set out the problems to assist in future cable-laying operations. In
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