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113-397: NanoSail-D was a small satellite which was to have been used by NASA 's Ames Research Center to study the deployment of a solar sail in space. It was a three-unit CubeSat measuring 30 cm × 10 cm × 10 cm (11.8 in × 3.9 in × 3.9 in), with a mass of 4 kg (8.8 lb). The satellite was lost shortly after launch due to a problem with
226-486: A CKWS-TV re-transmitter in Brighton, Ontario , and three TVOntario sites) went digital as part of a move to a lower frequency but do not provide high-definition television , digital subchannels or any functions beyond that of the original analogue site. Like a TV station, a radio re-broadcaster may have a distinct call sign or use the call sign of the originating station followed by a numeric suffix. The numeric suffix
339-591: A Diamant A rocket launched from the CIEES site at Hammaguir , Algeria . With Astérix, France became the sixth country to have an artificial satellite. Early satellites were built to unique designs. With advancements in technology, multiple satellites began to be built on single model platforms called satellite buses . The first standardized satellite bus design was the HS-333 geosynchronous (GEO) communication satellite launched in 1972. Beginning in 1997, FreeFlyer
452-414: A catalyst . The most commonly used propellant mixtures on satellites are hydrazine -based monopropellants or monomethylhydrazine – dinitrogen tetroxide bipropellants. Ion thrusters on satellites usually are Hall-effect thrusters , which generate thrust by accelerating positive ions through a negatively-charged grid. Ion propulsion is more efficient propellant-wise than chemical propulsion but its thrust
565-813: A halo orbit , three for a Lissajous orbit ). Earth observation satellites gather information for reconnaissance , mapping , monitoring the weather , ocean, forest, etc. Space telescopes take advantage of outer space's near perfect vacuum to observe objects with the entire electromagnetic spectrum . Because satellites can see a large portion of the Earth at once, communications satellites can relay information to remote places. The signal delay from satellites and their orbit's predictability are used in satellite navigation systems, such as GPS. Space probes are satellites designed for robotic space exploration outside of Earth, and space stations are in essence crewed satellites. The first artificial satellite launched into
678-409: A single-frequency network . Analog television stations cannot have same-channel boosters unless opposite ( perpendicular ) polarization is used, due to video synchronization issues such as ghosting . In the U.S., no new on-channel UHF signal boosters have been authorized since July 11, 1975. A distributed transmission system (DTS or DTx) uses several medium-power stations (usually digital) on
791-409: 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. Many communications satellites are in geostationary orbit 22,236 miles (35,785 km) above the equator , so that the satellite appears stationary at
904-549: A $ 1,000 federal-government subsidy for a portion of the additional equipment. Many other translators went dark after the digital-transition deadline, or did not apply for new channels after UHF channels 52–69 were removed from the bandplan. Some small translators operated by directly converting a parent station's signal to another frequency for rebroadcast, without any other local signal processing or demodulation. W07BA (a 16-watt repeater for WSYR-TV in Syracuse, New York )
1017-591: A Satellite Vehicle", by R. R. Carhart. This expanded on potential scientific uses for satellite vehicles and was followed in June 1955 with "The Scientific Use of an Artificial Satellite", by H. K. Kallmann and W. W. Kellogg. The first artificial satellite was Sputnik 1 , launched by the Soviet Union on 4 October 1957 under the Sputnik program , with Sergei Korolev as chief designer. Sputnik 1 helped to identify
1130-453: A U.S. Scout rocket from Wallops Island (Virginia, United States) with an Italian launch team trained by NASA . In similar occasions, almost all further first national satellites were launched by foreign rockets. France was the third country to launch a satellite on its own rocket. On 26 November 1965, the Astérix or A-1 (initially conceptualized as FR.2 or FR-2), was put into orbit by
1243-405: A bandwidth of tens of megahertz. Satellites are placed from the surface to the orbit by launch vehicles , high enough to avoid orbital decay by the atmosphere . Satellites can then change or maintain the orbit by propulsion , usually by chemical or ion thrusters . As of 2018, about 90% of the satellites orbiting the Earth are in low Earth orbit or geostationary orbit ; geostationary means
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#17327765746551356-412: A booster. All U.S. translator and booster stations are low-power and have a class D license, making them secondary to other stations (including the parent); they must accept interference from full-power (100 watts or more on FM) stations, while not causing any of their own. Boosters must not interfere with the parent station in the community of license . Licenses are automatically renewed with that of
1469-748: A call sign consisting of three letters from anywhere in Canada's ITU -prefix range followed by three digits (such as CFU758 or VEK565). Other stations in this license class have been assigned conventional Cxxx call signs. Former re-broadcasters have occasionally been converted to originating stations, retaining their former call sign; examples include CITE-FM-1 in Sherbrooke , CBF-FM-8 in Trois-Rivières and CBAF-FM-15 in Charlottetown . In Mexico , translator and booster stations are given
1582-435: A central source for broadcast at a GPS-synchronized time. A DTS does not use broadcast repeaters in the conventional sense, since they cannot receive a signal from a main terrestrial broadcast transmitter for rebroadcast; to do so would introduce a re-transmission delay destroying the required synchronization, causing interference between transmitters. The use of virtual channels is another alternative, although this may cause
1695-716: A contract with the Quintana Roo state network . The other network, operated by the Sistema Público de Radiodifusión del Estado Mexicano (SPR), has 26 stations (16 operational); most are digital. The SPR transmitters are almost exclusively in cities where the IPN never built stations, and carry Canal Once as one of the five educational networks in the multiplex of the digital station. Twenty-six of Mexico's 32 states also own and operate television services, and 16 use more than one transmitter. The largest (by number of stations)
1808-649: A digital uplink. Although many translators continued analog broadcasts and a minority transitioned to digital, some rural communities expected to find all local translator signals gone as a result of the originating stations' transition. By law, full-service local broadcasters are the primary occupants of the FM broadcast band; LPFM and translators are secondary occupants, with theoretically-equal status. In practice, frequencies assigned to translators become unavailable to new LPFM stations or existing stations wishing to upgrade. Some distinctions place small, local LPFM operators at
1921-553: A limited amount of regional content; Televisa prefers to use its non-national Gala TV network and Televisa Regional stations as outlets for local production. A number of translators also serve areas with little or no signal in their defined coverage area, known as equipos complementarios de zona de sombra ('shadow channels'). Most shadow channels air the same programming as their parent station. The northern and central regional network Multimedios Televisión in Monterrey uses
2034-484: A method of communication to ground stations , called transponders . Many satellites use a standardized bus to save cost and work, the most popular of which are small CubeSats . Similar satellites can work together as groups, forming constellations . Because of the high launch cost to space, most satellites are designed to be as lightweight and robust as possible. Most communication satellites are radio relay stations in orbit and carry dozens of transponders, each with
2147-527: A newscast. There is no strict rule for the call sign of a television re-broadcaster. Some transmitters have call signs different from the parent station ( CFGC in Sudbury is a re-broadcaster of CIII ), and others use the call sign of the originating station followed by a number (such as the former CBLFT-17 in Sarnia , Ontario). The latter type officially includes the television station's -TV suffix between
2260-435: A parent station's conversion to digital television. Translators which received an analog over-the-air signal from a full-service television station for rebroadcast needed to convert their receiving equipment, like individual viewers used digital converter boxes . Although the signal transmitted by the repeater may have remained analog, the uplink had to be changed. Twenty-three percent of the 4,000 licensed translators received
2373-479: A re-broadcaster of CKSB-FM . A broadcaster is limited to two stations on one band in a market, but a possible means to obtain a third FM signal in-market is to use a re-broadcaster of the AM station to move the signal to low-power FM. In Sarnia, Blackburn Radio owns CFGX-FM (99.9) and CHKS-FM (106.3); its third Sarnia station, CHOK (1070 kHz), uses an FM repeater for city coverage as Country 103.9 FM (although
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#17327765746552486-418: A satellite's lifetime. Resource use is difficult to monitor and quantify for satellites and launch vehicles due to their commercially sensitive nature. However, aluminium is a preferred metal in satellite construction due to its lightweight and relative cheapness and typically constitutes around 40% of a satellite's mass. Through mining and refining, aluminium has numerous negative environmental impacts and
2599-619: A semi-satellite is a formerly autonomous full-service station which is programmed remotely through centralcasting or broadcast automation to avoid the cost of a local staff. CBLFT , an owned-and-operated station of the French-language network Ici Radio-Canada Télé in Toronto , is a de facto semi-satellite of its stronger Ottawa sibling CBOFT ; its programming has long been identical or differed only in local news and advertising. A financially weak privately owned broadcaster in
2712-689: A small market can become a de facto semi-satellite by gradually curtailing local production and relying on a commonly owned station in a larger city for programming; WWTI in Watertown, New York , relies on WSYR-TV in this manner. Broadcast automation allows the substitution of syndicated programming or digital subchannel content which the broadcaster was unable to obtain for both cities. Some defunct full-service stations (such as CJSS-TV in Cornwall, Ontario , now CJOH-TV-8 ) have become full satellite stations and originate nothing. If programming from
2825-491: A station's main signal. They can also be used to expand market coverage by duplicating programming on another band. Relays which broadcast within (or near) the parent station's coverage area on the same channel (or frequency) are known in the U.S. as booster stations. Signals from the stations may interfere with each other without careful antenna design. Radio interference can be avoided by using atomic time , obtained from GPS satellites , to synchronize co-channel stations in
2938-449: A thin cable called a tether . Recovery satellites are satellites that provide a recovery of reconnaissance, biological, space-production and other payloads from orbit to Earth. Biosatellites are satellites designed to carry living organisms, generally for scientific experimentation. Space-based solar power satellites are proposed satellites that would collect energy from sunlight and transmit it for use on Earth or other places. Since
3051-600: A thought experiment by Isaac Newton to explain the motion of natural satellites , in his Philosophiæ Naturalis Principia Mathematica (1687). The first fictional depiction of a satellite being launched into orbit was a short story by Edward Everett Hale , " The Brick Moon " (1869). The idea surfaced again in Jules Verne 's The Begum's Fortune (1879). In 1903, Konstantin Tsiolkovsky (1857–1935) published Exploring Space Using Jet Propulsion Devices , which
3164-454: A three-digit number (201 through 300, corresponding to 88.1 to 107.9 MHz), followed by a pair of sequentially-assigned letters. The format is similar to that used by numbered television translators, where the number refers to the permanent channel assignment. The largest terrestrial radio-translator system in the U.S. in October 2008 belonged to KUER-FM , the non-commercial radio outlet of
3277-704: A translator may broadcast programming from the originating station's HD2 subchannel as the translator's main analogue signal. W237DE (95.3 MHz in Harrisburg, Pennsylvania ) broadcasts the format formerly carried by WTCY (1400 AM, now WHGB ), receiving the signal from a WNNK (104.1 FM) HD2 digital subchannel for analogue rebroadcast from the WNNK tower site on 95.3. It is legally an FM repeater of an FM station, although each signal would be heard with unique content by users with analogue FM radio receivers. Commercial stations may own their translators (or boosters) when
3390-467: A two-hour delay behind the originating station; there is a one-hour delay in Sonora , and Quintana Roo (one hour ahead of central Mexico in 2015) receives programs one hour later than they are broadcast to most of the rest of Mexico. Ten to 15 FM shadow channels exist, and they are required to be co-channel with the stations they re-transmit. Quintana Roo has the most FM shadow channels (seven), about half
3503-465: Is Telemax , Sonora 's state network, with 59 transmitters. Many state-network transmitters broadcast at a low effective radiated power (ERP). A few stations are owned by municipalities or translator associations. Like state networks, they transmit at very low power. Transmitters re-broadcasting Mexico City stations to Baja California and other communities along the Pacific coast normally operate on
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3616-400: Is a commercial off-the-shelf software application for satellite mission analysis, design, and operations. After the late 2010s, and especially after the advent and operational fielding of large satellite internet constellations —where on-orbit active satellites more than doubled over a period of five years—the companies building the constellations began to propose regular planned deorbiting of
3729-555: Is a re-broadcaster (also in Anzac) of Edmonton 's CITV . A station's re-broadcasters are not necessarily named in the same manner; CBLT had re-transmitters with their own call signs (some used CBLT followed by a number, and some used CH numbers). CBC and Radio-Canada owned-and-operated re-transmitters were shut down on August 1, 2012, along with most TVOntario transmitters (which often were located at Radio-Canada sites) and some Aboriginal Peoples Television Network (APTN) transmitters in
3842-522: Is a re-broadcaster of Vancouver 's CHAN . Re-broadcasters of this type are numbered sequentially in the order they were licensed by the CRTC, and their call signs are unrelated to the parent station or other re-broadcasters. Although the next number in the sequence (CH2650 in Anzac, Alberta ) is a re-broadcaster of CHAN, this is because CH2649 and CH2650 were licensed simultaneously; the following number, CH2651,
3955-465: Is always sequential. For a re-broadcaster of an FM station, the numeric suffix is appended to the FM suffix; re-broadcasters of CJBC-FM in Toronto are numbered CJBC-FM-1, CJBC-FM-2, etc. If an AM station has a re-broadcaster on the FM band, the numeric suffix falls between the four-letter call sign and the FM suffix; CKSB-1-FM is an FM re-broadcaster of the AM station CKSB , and CKSB-FM-1 would be
4068-721: Is an object, typically a spacecraft , placed into orbit around a celestial body . They have a variety of uses, including communication relay, weather forecasting , navigation ( GPS ), broadcasting , scientific research, and Earth observation. Additional military uses are reconnaissance, early warning , signals intelligence and, potentially, weapon delivery. Other satellites include the final rocket stages that place satellites in orbit and formerly useful satellites that later become defunct. Except for passive satellites , most satellites have an electricity generation system for equipment on board, such as solar panels or radioisotope thermoelectric generators (RTGs). Most satellites also have
4181-610: Is currently unclear. The visibility of man-made objects in the night sky may also impact people's linkages with the world, nature, and culture. At all points of a satellite's lifetime, its movement and processes are monitored on the ground through a network of facilities. The environmental cost of the infrastructure as well as day-to-day operations is likely to be quite high, but quantification requires further investigation. Particular threats arise from uncontrolled de-orbit. Some notable satellite failures that polluted and dispersed radioactive materials are Kosmos 954 , Kosmos 1402 and
4294-399: Is dependent on rocket design and fuel type. The amount of green house gases emitted by rockets is considered trivial as it contributes significantly less, around 0.01%, than the aviation industry yearly which itself accounts for 2-3% of the total global greenhouse gas emissions. Rocket emissions in the stratosphere and their effects are only beginning to be studied and it is likely that
4407-473: Is deployed for military or intelligence purposes, it is known as a spy satellite or reconnaissance satellite. Their uses include early missile warning, nuclear explosion detection, electronic reconnaissance, and optical or radar imaging surveillance. Navigational satellites are satellites that use radio time signals transmitted to enable mobile receivers on the ground to determine their exact location. The relatively clear line of sight between
4520-553: Is generally done only if the station originates programming. Class A television stations are assigned calls with -CA and -CD suffixes. Digital stations which use numbers receive a -D suffix, such as W42BD-D. All are despite the fact that most of the full-power digital television stations had their -DT (originally -HD) suffixes dropped by the FCC before -D and -LD were implemented. Digital LPTV stations have their digital RF channel numbers as part of their digital call sign, which may differ from
4633-517: Is most used in archaeology , cartography , environmental monitoring , meteorology , and reconnaissance applications. As of 2021, there are over 950 Earth observation satellites, with the largest number of satellites operated with Planet Labs . Weather satellites monitor clouds , city lights , fires , effects of pollution , auroras , sand and dust storms , snow cover, ice mapping, boundaries of ocean currents , energy flows, etc. Environmental monitoring satellites can detect changes in
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4746-581: Is one of the most carbon-intensive metals. Satellite manufacturing also requires rare elements such as lithium , gold , and gallium , some of which have significant environmental consequences linked to their mining and processing and/or are in limited supply. Launch vehicles require larger amounts of raw materials to manufacture and the booster stages are usually dropped into the ocean after fuel exhaustion. They are not normally recovered. Two empty boosters used for Ariane 5 , which were composed mainly of steel, weighed around 38 tons each, to give an idea of
4859-430: Is the chemical propellant used which then releases ammonia , hydrogen and nitrogen as gas into the upper atmosphere. Also, the environment of the outer atmosphere causes the degradation of exterior materials. The atomic oxygen in the upper atmosphere oxidises hydrocarbon-based polymers like Kapton , Teflon and Mylar that are used to insulate and protect the satellite which then emits gasses like CO 2 and CO into
4972-608: Is unregulated in the U.S. and widely permitted in Canada , the U.S. Federal Communications Commission (FCC) regulates radio formats to ensure diversity in programming. U.S. satellite stations may request an FCC exemption from requirements for a properly staffed broadcast studio in the city of license . The stations often cover large, sparsely populated regions or operate as statewide non-commercial educational radio and television systems. A television re-broadcaster often sells local (or regional) advertising for broadcast only on
5085-425: Is very small (around 0.5 N or 0.1 lb f ), and thus requires a longer burn time. The thrusters usually use xenon because it is inert , can be easily ionized , has a high atomic mass and storable as a high-pressure liquid. Most satellites use solar panels to generate power, and a few in deep space with limited sunlight use radioisotope thermoelectric generators . Slip rings attach solar panels to
5198-912: The American Rocket Society , the National Science Foundation , and the International Geophysical Year, the Army and Navy worked on Project Orbiter with two competing programs. The army used the Jupiter C rocket , while the civilian–Navy program used the Vanguard rocket to launch a satellite. Explorer 1 became the United States' first artificial satellite, on 31 January 1958. The information sent back from its radiation detector led to
5311-586: The Chinese military shot down an aging weather satellite, followed by the US Navy shooting down a defunct spy satellite in February 2008. On 18 November 2015, after two failed attempts, Russia successfully carried out a flight test of an anti-satellite missile known as Nudol . On 27 March 2019, India shot down a live test satellite at 300 km altitude in 3 minutes, becoming the fourth country to have
5424-627: The Netherlands , Norway , Pakistan , Poland , Russia , Saudi Arabia , South Africa , Spain , Switzerland , Thailand , Turkey , Ukraine , the United Kingdom and the United States , had some satellites in orbit. Japan's space agency (JAXA) and NASA plan to send a wooden satellite prototype called LingoSat into orbit in the summer of 2024. They have been working on this project for few years and sent first wood samples to
5537-621: The Operationally Responsive Space Office of the United States Department of Defense . The launch was conducted by SpaceX , and also carried a space burial payload (Celestis-07) for Celestis . Two minutes and forty seconds after launch, the spent first stage of the rocket was jettisoned; however, unexpected residual thrust caused it to recontact the second stage, which resulted in the rocket being thrown off course. Unable to achieve orbit,
5650-470: The Transit 5-BN-3 . When in a controlled manner satellites reach the end of life they are intentionally deorbited or moved to a graveyard orbit further away from Earth in order to reduce space debris . Physical collection or removal is not economical or even currently possible. Moving satellites out to a graveyard orbit is also unsustainable because they remain there for hundreds of years. It will lead to
5763-626: The University of Utah , with 33 translator stations ranging from Idaho to New Mexico and Arizona . Unlike FM radio, low-power television stations may operate as translators or originate their own programming. Translator stations are given call signs which begin with W (east of the Mississippi River ) or K (west of the Mississippi, like regular stations) followed by a channel number and two serial letters for each channel;
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#17327765746555876-576: The White House announced on 29 July 1955 that the U.S. intended to launch satellites by the spring of 1958. This became known as Project Vanguard . On 31 July, the Soviet Union announced its intention to launch a satellite by the fall of 1957. Sputnik 2 was launched on 3 November 1957 and carried the first living passenger into orbit, a dog named Laika . The dog was sent without possibility of return. In early 1955, after being pressured by
5989-434: The broadcast range of a television or radio station beyond the primary signal's original coverage or improves service in the original coverage area. The stations may be (but are not usually) used to create a single-frequency network . They may also be used by an AM or FM radio station to establish a presence on the other band. Relay stations are most commonly established and operated by the same organisations responsible for
6102-414: The digital transition . Although no digital television mandates were forced on existing low-power television stations, Congress passed legislation in 2008 funding low-power stations which went digital by the conversion date or shortly thereafter. Some low-power stations were forced to change frequency to accommodate full-power stations which moved to UHF or operated digital companion channels on UHF during
6215-527: The launch vehicle carrying it; however, a replacement, NanoSail-D2 , was launched in 2010 to complete its mission. NanoSail-D was to have been deployed on the third flight of the Falcon 1 launch vehicle, which was launched from Omelek Island at 03:34 UTC on 3 August 2008. One of two CubeSats aboard, along with PRESat , it was a secondary payload to the Trailblazer which was to have been operated by
6328-458: The virtual channel (the analog number). Numbered broadcast translators which are moved to another frequency are normally issued new call signs to reflect the updated channel assignment. This is not true of displaced translators using another frequency temporarily under a special technical authority. Although K55KD could retain its call sign while it was displaced temporarily to channel 57 to resolve interference to MediaFLO users, W81AA received
6441-501: The AM signal remains the station's official primary transmitter). Low-power radio re-broadcasters may have a call sign consisting of VF followed by four numbers; a call sign of this type may also denote a low-power station which originates its own programming. Some stations licensed under the CRTC's experimental-broadcasting guidelines, a special class of short-term license (similar to special temporary authority ) sometimes granted to newer campus and community radio operations, may have
6554-489: The Commission's rules to re-transmit all or part of the programming of a parent station that is typically commonly owned". Since most satellite stations operate in small or sparsely-populated areas with an insufficient economic base to support full-service operations, many received FCC authorization on a case-by-case basis to flash cut from analog to digital on the same channel instead of simulcasting in both formats during
6667-457: The Earth's vegetation , atmospheric trace gas content, sea state, ocean color, and ice fields. By monitoring vegetation changes over time, droughts can be monitored by comparing the current vegetation state to its long term average. Anthropogenic emissions can be monitored by evaluating data of tropospheric NO 2 and SO 2 . A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via
6780-417: The Earth's orbit was the Soviet Union 's Sputnik 1 , on October 4, 1957. As of December 31, 2022, there are 6,718 operational satellites in the Earth's orbit, of which 4,529 belong to the United States (3,996 commercial), 590 belong to China, 174 belong to Russia, and 1,425 belong to other nations. The first published mathematical study of the possibility of an artificial satellite was Newton's cannonball ,
6893-500: The Earth, called remote sensing . Most Earth observation satellites are placed in low Earth orbit for a high data resolution, though some are placed in a geostationary orbit for an uninterrupted coverage. Some satellites are placed in a Sun-synchronous orbit to have consistent lighting and obtain a total view of the Earth. Depending on the satellites' functions, they might have a normal camera , radar , lidar , photometer , or atmospheric instruments. Earth observation satellite's data
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#17327765746557006-553: The Moon and the Sun. Satellites utilize ultra-white reflective coatings to prevent damage from UV radiation. Without orbit and orientation control, satellites in orbit will not be able to communicate with ground stations on the Earth. Chemical thrusters on satellites usually use monopropellant (one-part) or bipropellant (two-parts) that are hypergolic . Hypergolic means able to combust spontaneously when in contact with each other or to
7119-587: The TV channel number of the analogue signal they replaced. TVOntario's CICO-DT-53 (digital UHF 26, Belleville ) is an example; the station was converted in 2011 to vacate an out-of-core analogue channel (UHF 53), and retains CICO-TV-53's former analogue UHF television call-sign numbering as a surviving TVO repeater. Low-power re-broadcasters may have a call sign consisting of the letters CH followed by four numbers; for example, CH2649 in Valemount , British Columbia ,
7232-455: The atmosphere. Given the current surge in satellites in the sky, soon hundreds of satellites may be clearly visible to the human eye at dark sites. It is estimated that the overall levels of diffuse brightness of the night skies has increased by up to 10% above natural levels. This has the potential to confuse organisms, like insects and night-migrating birds, that use celestial patterns for migration and orientation. The impact this might have
7345-603: The atmosphere. For example, SpaceX Starlink satellites, the first large satellite internet constellation to exceed 1000 active satellites on orbit in 2020, are designed to be 100% demisable and burn up completely on their atmospheric reentry at the end of their life, or in the event of an early satellite failure. In different periods, many countries, such as Algeria , Argentina , Australia , Austria , Brazil , Canada , Chile , China , Denmark , Egypt , Finland , France , Germany , India , Iran , Israel , Italy , Japan , Kazakhstan , South Korea , Malaysia , Mexico ,
7458-547: The basis of economic hardship, where a rural location unable to support a full-service originating station may be able to sustain a full-power re-broadcaster. Some stations (such as KVRR in Fargo, North Dakota ) are chains of as many as four full-power transmitters, each with its own call sign and license, covering a large, sparsely-populated region. LPTV stations may also choose a four-letter call sign with an -LP suffix (shared with low-power FM ) for analog or -LD for digital; this
7571-470: The call sign and the number, although it is often omitted from media directories. The numbers are usually applied sequentially, beginning with "1", and denote the chronological order in which the station's rebroadcast transmitters began operation. Some broadcasters may use a system in which the number is the transmitter's broadcast channel, such as CJOH-TV-47 in Pembroke, Ontario . A broadcaster cannot mix
7684-609: The call sign of the parent station. Most television stations in Mexico are operated as repeaters of the networks they broadcast. Translator stations in Mexico are given call signs beginning with XE and XH. Televisa and Azteca maintain two national networks apiece. Televisa's Las Estrellas network includes 128 stations (the most in Mexico), and Azteca's networks have 88 and 91 stations. The stations may insert local advertising. Azteca's stations in larger cities may include local news and
7797-447: The capability to destroy live satellites. The environmental impact of satellites is not currently well understood as they were previously assumed to be benign due to the rarity of satellite launches. However, the exponential increase and projected growth of satellite launches are bringing the issue into consideration. The main issues are resource use and the release of pollutants into the atmosphere which can happen at different stages of
7910-551: The density of high atmospheric layers through measurement of its orbital change and provided data on radio-signal distribution in the ionosphere . The unanticipated announcement of Sputnik 1's success precipitated the Sputnik crisis in the United States and ignited the so-called Space Race within the Cold War . In the context of activities planned for the International Geophysical Year (1957–1958),
8023-546: The discovery of the Earth's Van Allen radiation belts . The TIROS-1 spacecraft, launched on April 1, 1960, as part of NASA's Television Infrared Observation Satellite (TIROS) program, sent back the first television footage of weather patterns to be taken from space. In June 1961, three and a half years after the launch of Sputnik 1, the United States Space Surveillance Network cataloged 115 Earth-orbiting satellites. While Canada
8136-484: The earth's climate. After deorbiting 70% of satellites end up in the ocean and are rarely recovered. Using wood as an alternative material has been posited in order to reduce pollution and debris from satellites that reenter the atmosphere. Space debris pose dangers to the spacecraft (including satellites) in or crossing geocentric orbits and have the potential to drive a Kessler syndrome which could potentially curtail humanity from conducting space endeavors in
8249-420: The far north. Private commercial broadcasters operate full-power re-broadcasters to obtain "must carry" status on cable television systems. Transmitters in small markets with one (or no) originating stations were, in most cases, not required to convert to digital even if operating at full power. Transmitters broadcasting on UHF channels 52–69 were required to vacate the channels by August 31, 2011; some (such as
8362-450: The first stations on a channel are AA, AB, AC and so on). Television channels have two digits, from 02 to 36 (formerly 02 to 83; 02 to 69 and 02 to 51); FM radio channels are numbered from 200 (87.9 MHz) to 300 (107.9 MHz), one every 0.2 MHz (for example, W42BD or K263AF). An X after the number in these call signs does not indicate an experimental broadcasting license (as it may in other services), since all 26 letters are used in
8475-444: The further pollution of space and future issues with space debris. When satellites deorbit much of it is destroyed during re-entry into the atmosphere due to the heat. This introduces more material and pollutants into the atmosphere. There have been concerns expressed about the potential damage to the ozone layer and the possibility of increasing the earth's albedo , reducing warming but also resulting in accidental geoengineering of
8588-433: The future. Broadcast relay station A broadcast relay station , also known as a satellite station , relay transmitter , broadcast translator (U.S.), re-broadcaster (Canada), repeater ( two-way radio ) or complementary station (Mexico), is a broadcast transmitter which repeats (or transponds ) the signal of a radio or television station to an area not covered by the originating station. These expand
8701-412: The impact of regulated ozone-depleting substances. Whilst emissions of water vapour are largely deemed as inert, H 2 O is the source gas for HO x and can also contribute to ozone loss through the formation of ice particles. Black carbon particles emitted by rockets can absorb solar radiation in the stratosphere and cause warming in the surrounding air which can then impact the circulatory dynamics of
8814-462: The impacts will be more critical than emissions in the troposphere. The stratosphere includes the ozone layer and pollutants emitted from rockets can contribute to ozone depletion in a number of ways. Radicals such as NO x , HO x , and ClO x deplete stratospheric O 3 through intermolecular reactions and can have huge impacts in trace amounts. However, it is currently understood that launch rates would need to increase by ten times to match
8927-614: The local transmitter, and may air a limited amount of programming distinct from its parent station. Some "semi-satellites" broadcast local news or separate news segments during part of the newscast . CHEX-TV-2 in Oshawa , Ontario , aired daily late-afternoon and early-evening news and community programs separate from its parent station, CHEX-TV in Peterborough, Ontario . The FCC prohibits this on U.S. FM translator stations, only permitting it on fully licensed stations. In some cases,
9040-400: The mid-2000s, satellites have been hacked by militant organizations to broadcast propaganda and to pilfer classified information from military communication networks. For testing purposes, satellites in low earth orbit have been destroyed by ballistic missiles launched from the Earth. Russia , United States , China and India have demonstrated the ability to eliminate satellites. In 2007,
9153-725: The most potent scientific tools of the Twentieth Century." The United States had been considering launching orbital satellites since 1945 under the Bureau of Aeronautics of the United States Navy . Project RAND eventually released the report, but considered the satellite to be a tool for science, politics, and propaganda, rather than a potential military weapon. In 1946, American theoretical astrophysicist Lyman Spitzer proposed an orbiting space telescope . In February 1954, Project RAND released "Scientific Uses for
9266-571: The national Public Broadcasting Service . In Canada, "re-broadcaster" or "re-broadcasting transmitter" are the terms most commonly used by the Canadian Radio-television and Telecommunications Commission (CRTC). A television re-broadcaster may sell local or regional advertising for broadcast only on the local transmitter. Rarely, they may air limited programming distinct from their parent station. Some "semi-satellites" broadcast local newscasts or separate news segments in part of
9379-418: The national total. Three more FM shadows are authorized: XETIA-FM / XEAD-FM ( Ajijic , Jalisco ) and XHRRR-FM (Tecolula, Veracruz ). In July 2009, the basic FCC regulations concerning translators were: There is one way programming may differ between a main station and an FM translator: an HD Radio signal may contain digital subchannels with different programming from the main analogue channel, and
9492-683: The new call sign W65AM when channel 81 was deleted from the bandplan and the translator was moved to channel 65. On the rare occasion that a station moves back to its original channel, it receives its old call sign (which is not reused by another station). Low-power television stations are not required to simulcast a digital signal, nor were they required to cease analog operation in June 2009 like full-power stations. Full-power stations used for simulcasting another station were (like other full-service TV broadcasters) required to convert to digital in June 2009. The FCC defines "TV satellite stations" as "full-power broadcast stations authorized under Part 73 of
9605-472: The numbering systems under a single call sign; the transmitters are numbered sequentially or by their analogue channel. If sequential numbering reaches 99 (such as TVOntario 's former broadcast transmitters), the next transmitter is assigned a new call sign and numbered "1". Translators which share a frequency (such as CBLT 's former repeaters CBLET, CBLHT, CBLAT-2 and CH4113 on channel 12) are given distinct call signs. Digital re-broadcasters may be numbered by
9718-557: The older satellites that reached the end of life , as a part of the regulatory process of obtaining a launch license. The largest artificial satellite ever is the International Space Station . By the early 2000s, and particularly after the advent of CubeSats and increased launches of microsats —frequently launched to the lower altitudes of low Earth orbit (LEO)—satellites began to more frequently be designed to get destroyed, or breakup and burnup entirely in
9831-495: The originating stations they repeat. Depending on technical and regulatory restrictions, relays may also be set up by unrelated organisations. In its simplest form, a broadcast translator is a facility created to receive a terrestrial broadcast over the air on one frequency and rebroadcast the same (or substantially identical) signal on another frequency. These stations are used in television and radio to cover areas (such as valleys or rural villages) which are not adequately covered by
9944-410: The parent station and do not require separate applications, although the renewal may be challenged with a petition to deny. FM booster stations are given the full call sign (including an -FM suffix , even if there is none assigned) of the parent station plus a serial number such as WXYZ-FM 1, WXYZ-FM2, etc. FM translator stations may use sequential numbered call signs consisting of K or W followed by
10057-512: The parent station must be removed or substituted due to local sports blackouts , the modified signal is that of a semi-satellite station. Most broadcasters outside North America, portions of South America, and Japan maintain a national network, and use relay transmitters to provide service to a region (or nation). Compared with other types of relays, the transmitter network is often created and maintained by an independent authority (funded with television license fees); several major broadcasters use
10170-550: The possible use of communications satellites for mass communications. He suggested that three geostationary satellites would provide coverage over the entire planet. In May 1946, the United States Air Force 's Project RAND released the Preliminary Design of an Experimental World-Circling Spaceship , which stated "A satellite vehicle with appropriate instrumentation can be expected to be one of
10283-412: The quantity of materials that are often left in the ocean. Rocket launches release numerous pollutants into every layer of the atmosphere, especially affecting the atmosphere above the tropopause where the byproducts of combustion can reside for extended periods. These pollutants can include black carbon , CO 2 , nitrogen oxides (NO x ), aluminium and water vapour , but the mix of pollutants
10396-490: The rocket and payloads fell into the Pacific Ocean . NanoSail-D was to have been operated in a low Earth orbit with a perigee of 330 km (210 mi), an apogee of 685 km (426 mi) and 9.0° of inclination . It would have been operational for around seven days, after which time it would have been expected to run out of power. Its solar sail had an area of 10 m (110 sq ft). The satellite
10509-482: The same channel to appear several times in a receiver – once for each relay station – and require the user to tune to the best one (which may change due to propagation issues such as weather). Although boosters or DTS cause all relay stations to appear as one signal, they require careful engineering to avoid interference. Some licensed stations simulcast another station. Relay stations in name only, they are generally licensed like any other station. Although this
10622-680: The same frequency to cover a broadcast area, rather than one high-power station with repeaters on a different frequency. Although digital television stations are technically capable of sharing a channel, this is more difficult with the 8VSB modulation and unvariable guard interval used in ATSC standards than with the orthogonal frequency-division multiplexing (OFDM) used in the European and Australian DVB-T standard. A distributed transmission system would have stringent synchronization requirements, requiring each transmitter to receive its signal from
10735-495: The same manner as other full-power broadcasters. This simulcasting is generally not regulated by the FCC, except when a station owner seeks an exemption from requirements such as restrictions on owning several full-service stations in the same market, limits on overlap in coverage area between commonly-owned stations, or requirements that each full-service station have a local studio and a skeleton staff capable of originating programming locally. These exemptions are normally justified on
10848-427: The same point in the sky; therefore the satellite dish antennas of ground stations can be aimed permanently at that spot and do not have to move to track the satellite. Others form satellite constellations in low Earth orbit , where antennas on the ground have to follow the position of the satellites and switch between satellites frequently. When an Earth observation satellite or a communications satellite
10961-632: The same system to a smaller extent (its XHSAW-TDT is the shadow channel of main station XHAW-TDT in Monterrey), with regional output for local newscasts and advertising on a master schedule. There are two main national networks of non-commercial TV stations in Mexico. One is the Canal Once (or XEIPN-TDT) network, operated by the Instituto Politécnico Nacional (IPN). Operating 13 transmitters, it airs its programs under
11074-427: The same transmitters. In North America, a similar pattern of regional network broadcasting is sometimes used by state- or province-wide educational television networks. A state or province establishes an educational station and extends it with several full-power transmitters to cover the entire jurisdiction, with no capability for local-programming origination. In the U.S., such regional networks are member stations of
11187-409: The satellite; the slip rings can rotate to be perpendicular with the sunlight and generate the most power. All satellites with a solar panel must also have batteries , because sunlight is blocked inside the launch vehicle and at night. The most common types of batteries for satellites are lithium-ion , and in the past nickel–hydrogen . Earth observation satellites are designed to monitor and survey
11300-404: The satellites and receivers on the ground, combined with ever-improving electronics, allows satellite navigation systems to measure location to accuracies on the order of a few meters in real time. Astronomical satellites are satellites used for observation of distant planets, galaxies, and other outer space objects. Tether satellites are satellites that are connected to another satellite by
11413-538: The satellites stay still in the sky (relative to a fixed point on the ground). Some imaging satellites chose a Sun-synchronous orbit because they can scan the entire globe with similar lighting. As the number of satellites and space debris around Earth increases, the threat of collision has become more severe. A small number of satellites orbit other bodies (such as the Moon , Mars , and the Sun ) or many bodies at once (two for
11526-589: The sequence. When the sequence is exhausted, another letter is added. This has already happened for translator on channels 7 and 13 in K territory; what is now KMNF-LD was assigned callsign K13AAR-D in September 2018 and K07AAH-D in May 2019. Numbered translator stations (a format such as W70ZZ) are typically low-power repeaters – often 100 watts (or less) on FM and 1,000 watts (or less) on television. The former translator band, UHF television channels 70 through 83 ,
11639-599: The signal. They may not transmit in the FM reserved band from 88 to 92 MHz , where only non-commercial stations are allowed. Non-commercial stations may broadcast in the commercial portion of the band. Unlike commercial stations, they can relay programming to translators via satellite if the translators are in the reserved band. Translators in the commercial band may only be fed by a direct on-air signal from another FM station (or translator). Non-fill-in commercial-band translators may not be fed by satellite, according to FCC rule 74.1231(b). All stations may use any means to feed
11752-540: The space in 2021 to test the material's resilience to space conditions. Most satellites use chemical or ion propulsion to adjust or maintain their orbit , coupled with reaction wheels to control their three axis of rotation or attitude. Satellites close to Earth are affected the most by variations in the Earth's magnetic , gravitational field and the Sun's radiation pressure ; satellites that are further away are affected more by other bodies' gravitational field by
11865-458: The special conditions of space could be useful for scientific experiments. The book described geostationary satellites (first put forward by Konstantin Tsiolkovsky ) and discussed the communication between them and the ground using radio, but fell short with the idea of using satellites for mass broadcasting and as telecommunications relays. In a 1945 Wireless World article, English science fiction writer Arthur C. Clarke described in detail
11978-459: The stratosphere. Both warming and changes in circulation can then cause depletion of the ozone layer. Several pollutants are released in the upper atmospheric layers during the orbital lifetime of LEO satellites. Orbital decay is caused by atmospheric drag and to keep the satellite in the correct orbit the platform occasionally needs repositioning. To do this nozzle-based systems use a chemical propellant to create thrust. In most cases hydrazine
12091-507: The transition period. By 2008, low- and full-power channel 55 licensees were encouraged to relocate early to free spectrum for Qualcomm 's MediaFLO transmitters. By 2011, remaining LPTV broadcasters on UHF channels 52 through 69 were forced onto lower channels. Many transmitters on the original UHF 70–83 translator band had to move twice; channels 70–83 were lost to mobile phones in 1983, followed by channels 52–69 between 2009 and 2011. Many low-power translators were also directly affected by
12204-460: The translator (or booster) is in the parent station's primary service contour; they can only fill in where terrain blocks the signal. Boosters may only be owned by the primary station; translators outside a primary station's service contour cannot be owned by (or receive financial support from) the primary station. Most translators operate by receiving the main station's on-air signal with a directional antenna and sensitive receiver and re-transmitting
12317-542: Was a simple piece of broadcast apparatus, shifting the main station's signal from channel nine to channel seven to cover a small valley in DeWitt . Syracuse became a UHF island , WSYR-TV's main ABC signal became a 100 kW digital broadcast on channel 17, and there is no longer a channel 9 signal to feed the repeater. Translators in remote locations with no commercial power were expected to have problems deploying equipment for
12430-651: Was developed and tested in four months. NanoSail-D2 was built as a ground spare for NanoSail-D. Following the launch failure of NanoSail-D in August 2008, NanoSail-D2 was launched on a Minotaur IV launch vehicle in November 2010, and deployed from the FASTSAT satellite. Solar sail CubeSats This article about one or more spacecraft of the United States is a stub . You can help Misplaced Pages by expanding it . Satellite A satellite or artificial satellite
12543-511: Was originally occupied primarily by low-powered translators. The combination of low power and high frequency limited broadcast range. The band was reallocated to cellular telephone services during the 1980s, with the handful of remaining transmitters moved to lower frequencies. Full-power repeaters such as WPBS-TV 's identical-twin transmitter, WNPI-TV , are normally assigned TV call signs like other full-power stations. These "satellite stations" do not have numbered call signs, and must operate in
12656-426: Was the first academic treatise on the use of rocketry to launch spacecraft. He calculated the orbital speed required for a minimal orbit, and inferred that a multi-stage rocket fueled by liquid propellants could achieve this. Herman Potočnik explored the idea of using orbiting spacecraft for detailed peaceful and military observation of the ground in his 1928 book, The Problem of Space Travel . He described how
12769-483: Was the third country to build a satellite which was launched into space, it was launched aboard an American rocket from an American spaceport. The same goes for Australia, whose launch of the first satellite involved a donated U.S. Redstone rocket and American support staff as well as a joint launch facility with the United Kingdom. The first Italian satellite San Marco 1 was launched on 15 December 1964 on
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