Array ( [0] => {{Short description|Objects intentionally placed into orbit}} [1] => {{About|human-made satellites|moons|Natural satellite|other uses|Satellite (disambiguation)}} [2] => {{Use dmy dates|date=December 2019}} [3] => {{Use American English|date=July 2022}} [4] => [[File:Two 3U CubeSats.jpg|thumb|upright=1.5|alt=Two 3U CubeSats|Two [[CubeSat]]s orbiting around [[Earth]] after being deployed from the ISS [[Kibō (ISS module)|''Kibō'' module]]'s Small Satellite Orbital Deployer]] [5] => [6] => A '''satellite''' or '''artificial satellite'''{{efn|to distinguish them from [[natural satellites]].}} is an object, typically a [[spacecraft]], placed into [[orbit]] around a [[Astronomical object|celestial body]]. Satellites 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 system|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. [7] => [8] => Except for [[passive satellite]]s, most satellites have an [[electricity generation]] system for equipment on board, such as [[solar panel]]s or [[radioisotope thermoelectric generator]]s (RTGs). Most satellites also have a method of communication to [[ground station]]s, called [[Transponder (satellite communications)|transponders]]. Many satellites use a [[Satellite bus|standardized bus]] to save cost and work, the most popular of which are small [[CubeSat]]s. Similar satellites can work together as groups, forming [[Satellite constellation|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 [[Broadcast relay station|relay stations]] in orbit and carry dozens of transponders, each with a bandwidth of tens of megahertz. [9] => [10] => Satellites are placed from the surface to the orbit by [[launch vehicle]]s, high enough to avoid [[orbital decay]] by the [[atmosphere]]. Satellites can then change or maintain the orbit by [[Spacecraft propulsion|propulsion]], usually by [[Thrusters (spacecraft)|chemical]] or [[ion thruster]]s. As of 2018, about 90% of the satellites orbiting the Earth are in [[low Earth orbit]] or [[geostationary orbit]]; geostationary means 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 [[Lunar orbit|Moon]], [[Areocentric orbit|Mars]], and the [[Heliocentric orbit|Sun]]) or many bodies at once (two for a [[halo orbit]], three for a [[Lissajous orbit]]). [11] => [12] => [[Earth observation satellite]]s gather information for [[Reconnaissance satellite|reconnaissance]], [[Satellite imagery|mapping]], [[Weather satellite|monitoring the weather]], ocean, forest, etc. [[Space telescope]]s take advantage of outer space's [[Ultra-high vacuum|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 probe]]s are satellites designed for robotic [[space exploration]] outside of Earth, and [[space station]]s are in essence crewed satellites. [13] => [14] => The first artificial satellite launched into 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.{{cite web|url=https://www.ucsusa.org/resources/satellite-database |title=UCS Satellite Database |website=Union of Concerned Scientists |date=1 May 2022 }} [15] => [16] => == History == [17] => {{See also|Timeline of first artificial satellites by country}} [18] => [19] => === Early proposals === [20] => The first published mathematical study of the possibility of an artificial satellite was [[Newton's cannonball]], a thought experiment by [[Isaac Newton]] to explain the motion of [[natural satellite]]s, 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).{{cite web [21] => |title=Rockets in Science Fiction (Late 19th Century) [22] => |url=http://history.msfc.nasa.gov/rocketry/tl4.html [23] => |publisher=[[Marshall Space Flight Center]] [24] => |url-status=dead [25] => |archive-url=https://web.archive.org/web/20000901224414/http://history.msfc.nasa.gov/rocketry/tl4.html [26] => |archive-date=1 September 2000 [27] => |access-date=21 November 2008 [28] => }}{{cite book | title=Science-fiction, the Early Years [29] => | url=https://archive.org/details/sciencefictionea0000blei [30] => | url-access=registration [31] => | first1=Everett Franklin | last1=Bleiler | first2=Richard | last2=Bleiler | page=[https://archive.org/details/sciencefictionea0000blei/page/325 325] [32] => | isbn=978-0-87338-416-2 | publisher=[[Kent State University Press]] | year=1991}} The idea surfaced again in [[Jules Verne]]'s ''[[The Begum's Fortune]]'' (1879). [33] => [34] => In 1903, [[Konstantin Tsiolkovsky]] (1857–1935) published ''Exploring Space Using Jet Propulsion Devices'', which 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 [[propellant]]s could achieve this. [35] => [36] => [[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 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.{{Cite web |date=2 September 2016 |title=Introduction to satellite |url=http://www.sasmac.cn/portal/html/fc4f335929b0df0d0129b0e348f90003/_content/10_07/09/1278668367217.html |url-status=live |archive-url=https://web.archive.org/web/20160916064537/http://www.sasmac.cn/portal/html/fc4f335929b0df0d0129b0e348f90003/_content/10_07/09/1278668367217.html |archive-date=16 September 2016 |access-date=25 May 2022 |website=www.sasmac.cn}} [37] => [38] => In a 1945 ''[[Wireless World]]'' article, English science fiction writer [[Arthur C. Clarke]] described in detail the possible use of [[communications satellite]]s for mass communications. He suggested that three geostationary satellites would provide coverage over the entire planet.{{Cite book |last1=Pratt |first1=Timothy |url= |title=Satellite Communications |last2=Allnutt |first2=Jeremy E. |year=2019 |publisher=[[John Wiley & Sons Ltd]] |isbn=978-1-119-48217-8 |edition=3rd |oclc=1098222848}}{{Rp|pages=1–2}} [39] => [40] => 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 the most potent scientific tools of the Twentieth Century."{{cite journal | url=https://www.rand.org/pubs/special_memoranda/SM11827/ | title=Preliminary Design of an Experimental World-Circling Spaceship | journal=[[RAND]] | date=July 1946 | access-date=6 March 2008 | archive-date=15 June 2010 | archive-url=https://web.archive.org/web/20100615024409/http://rand.org/pubs/special_memoranda/SM11827/ | url-status=live }} 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.{{cite book | title=Venture into Space: Early Years of Goddard Space Flight Center [41] => | first=Alfred | last=Rosenthal | publisher=NASA | year=1968 | page=15}} [42] => [43] => In 1946, American theoretical astrophysicist [[Lyman Spitzer]] proposed an orbiting [[space telescope]].{{cite web|title=Hubble Essentials: About Lyman Spitzer, Jr.|publisher=Hubble Site|url=http://hubblesite.org/the_telescope/hubble_essentials/lyman_spitzer.php|access-date=16 October 2020|archive-date=9 October 2018|archive-url=https://web.archive.org/web/20181009202238/http://hubblesite.org/the_telescope/hubble_essentials/lyman_spitzer.php|url-status=live}} [44] => [45] => In February 1954, Project RAND released "Scientific Uses for a Satellite Vehicle", by R. R. Carhart.R. R. Carhart, Scientific Uses for a Satellite Vehicle, Project RAND Research Memorandum. (Rand Corporation, Santa Monica) 12 February 1954. 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.2. H. K. Kallmann and W. W. Kellogg, Scientific Use of an Artificial Satellite, Project RAND Research Memorandum. (Rand Corporation, Santa Monica) 8 June 1955. [46] => [47] => === First satellites === [48] => [[File:Sputnik asm.jpg|alt=Steel ball with 4 antennas|thumb|Replica of the [[Sputnik 1]]]] [49] => 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 the density of high [[Earth's atmosphere#Temperature and layers|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]]. [50] => [51] => In the context of activities planned for the [[International Geophysical Year]] (1957–1958), 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. [52] => [53] => [[Sputnik 2]] was launched on 3 November 1957 and carried the first living passenger into orbit, a dog named [[Laika]].{{cite web | title=A Brief History of Animals in Space | url=https://history.nasa.gov/animals.html | first1=Tara | last1=Gray | first2=Steve | last2=Garber | publisher=[[NASA]] | date=2 August 2004 | access-date=12 July 2017 | archive-date=11 October 2004 | archive-url=https://web.archive.org/web/20041011053912/https://history.nasa.gov/animals.html | url-status=live }} [54] => [55] => In early 1955, after being pressured by 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 IRBM|Jupiter C rocket]], while the civilian–Navy program used the [[Vanguard (rocket)|Vanguard rocket]] to launch a satellite. [[Explorer 1]] became the United States' first artificial satellite, on 31 January 1958.{{cite news|title=50th anniversary of first U.S. satellite launch celebrated |url=http://www.sfgate.com/cgi-bin/article.cgi?f=/n/a/2008/01/30/state/n151715S68.DTL |agency=[[Associated Press]] |first=Alicia |last=Chang |work=San Francisco Chronicle |date=30 January 2008 |url-status=dead |archive-date=1 February 2008 |archive-url=https://web.archive.org/web/20080201193510/http://www.sfgate.com/cgi-bin/article.cgi?f=%2Fn%2Fa%2F2008%2F01%2F30%2Fstate%2Fn151715S68.DTL}} The information sent back from its radiation detector led to the discovery of the Earth's [[Van Allen radiation belt]]s.{{cite web |title=James A. Van Allen |url=http://www.nmspacemuseum.org/halloffame/detail.php?id=86 |url-status=live |archive-url=https://web.archive.org/web/20180515112204/http://www.nmspacemuseum.org/halloffame/detail.php?id=86 |archive-date=15 May 2018 |access-date=14 May 2018 |website=nmspacemuseum.org |publisher=New Mexico Museum of Space History}} 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.{{cite journal |last1=Tatem |first1=Andrew J. |last2=Goetz |first2=Scott J. |last3=Hay |first3=Simon I. |date=2008 |title=Fifty Years of Earth-observation Satellites |journal=American Scientist |volume=96 |issue=5 |pages=390–398 |doi=10.1511/2008.74.390 |pmc=2690060 |pmid=19498953}} [56] => [57] => 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.{{cite web|first1=David S. F. |last1=Portree |first2=Joseph P. Jr. |last2=Loftus |url=http://ston.jsc.nasa.gov/collections/TRS/_techrep/TP-1999-208856.pdf |title=Orbital Debris: A Chronology |page=18 |work=[[Lyndon B. Johnson Space Center]] |year=1999 |url-status=dead |archive-url=https://web.archive.org/web/20000901071135/http://ston.jsc.nasa.gov/collections/TRS/_techrep/TP-1999-208856.pdf |archive-date=1 September 2000 |access-date=21 November 2008}} [58] => [59] => Astérix or A-1 (initially conceptualized as FR.2 or FR-2) is the first French satellite. It was launched on 26 November 1965 by a Diamant A rocket from the CIEES launch site at Hammaguir, Algeria. With Astérix, France became the sixth country to have an artificial satellite and the third country to launch a satellite on its own rocket [60] => [61] => France is the third country to launch a satellite on its own rocket, the [[Astérix (satellite)|Astérix]], on 26 November 1965 by a [[Diamant]] A rocket from the CIEES launch site at [[Hammaguir]], [[Algeria]]. [62] => [63] => Early satellites were built to unique designs. With advancements in technology, multiple satellites began to be built on [[Comparison of satellite buses|single model platforms]] called [[satellite bus]]es. The first standardized satellite bus design was the [[HS-333]] [[Geosynchronous orbit|geosynchronous]] (GEO) [[communication satellite]] launched in 1972. Beginning in 1997, [[FreeFlyer]] is a commercial off-the-shelf software application for satellite mission analysis, design, and operations. [64] => [65] => === Later Satellite Development === [66] => [[File:Space capabilities - launch and satellite.png|thumb|upright=1.35| [67] => {{legend|#007F00|[[Timeline of first orbital launches by country|Orbital launch]] and satellite operation}} [68] => {{legend|#00FF00|Satellite operation, launched by foreign supplier}} [69] => {{legend|#FF8040|Satellite in development}} [70] => {{legend|#FF0000|[[Comparison of small lift launch systems|Orbital launch]] project at advanced stage or indigenous [[ballistic missile]]s deployed}}]]While Canada was the third country to build a satellite which was launched into space,{{cite book |last=Burleson |first=Daphne |title=Space Programs Outside the United States |publisher=[[McFarland & Company]] |year=2005 |isbn=978-0-7864-1852-7 |page=43}} it was launched aboard an [[United States|American]] rocket from an American spaceport. The same goes for Australia, whose launch of the first satellite involved a donated U.S. [[PGM-11 Redstone|Redstone]] rocket and American support staff as well as a joint launch facility with the United Kingdom.{{cite book |author=Mike Gruntman |title=Blazing the Trail |publisher=[[American Institute of Aeronautics and Astronautics]] |year=2004 |isbn=978-1-56347-705-8 |page=426 |author-link=Mike Gruntman}} The first Italian satellite [[San Marco 1]] was launched on 15 December 1964 on a U.S. [[Scout rocket]] from [[Wallops Island]] (Virginia, United States) with an Italian launch team trained by [[NASA]].{{cite book |last=Harvey |first=Brian |title=Europe's Space Programme |publisher=[[Springer Science+Business Media]] |year=2003 |isbn=978-1-85233-722-3 |page=114}} In similar occasions, almost all further first national satellites were launched by foreign rockets.{{citation needed|date=September 2023}} [71] => [72] => After the late 2010s, and especially after the advent and operational fielding of large [[satellite internet constellation]]s—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 the older satellites that reached the [[End-of-life (product)|end of life]], as a part of the [[regulatory authority|regulatory process]] of obtaining a launch license.{{citation needed|date=June 2022}} The largest artificial satellite ever is the [[International Space Station]].{{Cite book |last1=Welch |first1=Rosanne |url=https://books.google.com/books?id=aWGHDwAAQBAJ&q=largest+artificial+satellite&pg=RA2-PA126 |title=Technical Innovation in American History: An Encyclopedia of Science and Technology [3 volumes] |last2=Lamphier |first2=Peg A. |year=2019|publisher=ABC-CLIO |isbn=978-1-61069-094-2 |page=126 |language=en |access-date=4 October 2020 |archive-url=https://web.archive.org/web/20210214004816/https://books.google.com/books?id=aWGHDwAAQBAJ&q=largest+artificial+satellite&pg=RA2-PA126 |archive-date=14 February 2021 |url-status=live}} [73] => [74] => By the early 2000s, and particularly after the advent of [[CubeSat]]s and increased launches of [[Microsatellite (spaceflight)|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 the atmosphere.{{cite journal |last1=Slejko |first1=EA |last2=Gregorio |first2=A |last3=Lughi |first3=V |year=2021 |title=Material selection for a CubeSat structural bus complying with debris mitigation |url=https://www.sciencedirect.com/science/article/abs/pii/S0273117720308383 |url-status=live |journal=Advances in Space Research |volume=67 |issue=5 |pages=1468–1476 |bibcode=2021AdSpR..67.1468S |doi=10.1016/j.asr.2020.11.037 |archive-url=https://web.archive.org/web/20220603044215/https://www.sciencedirect.com/science/article/abs/pii/S0273117720308383 |archive-date=3 June 2022 |access-date=3 June 2022 |s2cid=233841294}} [75] => 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.{{cite news |last1=Garrity |first1=John |last2=Husar |first2=Arndt |date=April 2021 |title=Digital Connectivity and Low Earth Orbit Satellite Constellations: Opportunities for Asia and the Pacific |work=think-asia.org |url=https://think-asia.org/handle/11540/13626 |url-status=live |access-date=3 June 2022 |archive-url=https://web.archive.org/web/20220721104450/https://think-asia.org/handle/11540/13626 |archive-date=21 July 2022}} [76] => [77] => 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]], 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.{{cite news|last1=Buchholz|first1=Katharina|title=The Countries with the Most Satellites in Space |date=4 May 2023 |url=https://www.statista.com/chart/17107/countries-with-the-most-satellites-in-space/ |access-date=11 November 2023|publisher=statista}} [78] => [79] => 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 the space in 2021 to test the material's resilience to space conditions. [80] => {{cite news|last1=Cairns|first1=Rebecca|title=Japanese scientists want to send a wooden satellite into space |date=11 November 2023 |url=https://edition.cnn.com/2023/11/07/asia/japan-wooden-satellite-scn-spc/index.html |access-date=11 November 2023|publisher=CNN}} [81] => [82] => ==Components== [83] => === Orbit and altitude control === [84] => {{further|Spacecraft propulsion}} [85] => {{redirect-distinguish|Altitude control|Attitude control}} [86] => [[File:Ion Engine Test Firing - GPN-2000-000482.jpg|thumb|Firing of ''[[Deep Space 1]]'''s ion thruster]] [87] => [88] => Most satellites use chemical or [[ion propulsion]] to [[Orbital maneuver|adjust]] or [[Orbital station-keeping|maintain their orbit]],{{Rp|pages=|page=78}} coupled with [[reaction wheel]]s to control their [[Aircraft principal axes|three axis of rotation]] or attitude. Satellites close to Earth are affected the most by variations in the [[Earth's magnetic field|Earth's magnetic]], [[Gravity of Earth|gravitational field]] and the Sun's [[radiation pressure]]; satellites that are further away are affected more by other bodies' gravitational field by the Moon and the Sun. Satellites utilize ultra-white reflective coatings to prevent damage from UV radiation.{{cite web|url=https://www.americanelements.com/space-industry.html|title=Space - American Elements Assists NASA in Development of Ultra White Coating for Satellite Applications|publisher=American Elements|access-date=2023-04-06}} Without orbit and orientation control, satellites in orbit will not be able to communicate with [[ground station]]s on the Earth.{{Rp|pages=75–76}} [89] => [90] => Chemical thrusters on satellites usually use [[monopropellant]] (one-part) or [[bipropellant]] (two-parts) that are [[Hypergolic propellant|hypergolic]]. Hypergolic means able to combust spontaneously when in contact with each other or to a [[Catalysis|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 thruster]]s, 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 is very small (around {{Cvt|0.5|N|disp=or|sigfig=1}}), and thus requires a longer burn time. The thrusters usually use [[xenon]] because it is [[Inert gas|inert]], can be easily [[ionized]], has a high [[atomic mass]] and storable as a high-pressure liquid.{{Rp|pages=78–79}} [91] => [92] => ===Power=== [93] => {{Main|Batteries in space|Nuclear power in space|Solar panels on spacecraft}} [94] => [[File:ISS-54 ELC-1, main solar arrays and radiators seen from the Cupola.jpg|alt=see caption|thumb|The [[International Space Station]]'s black solar panels on the left and white [[radiator]]s on the right]] [95] => Most satellites use [[Solar panels on spacecraft|solar panels]] to generate power, and a few in deep space with limited sunlight use [[radioisotope thermoelectric generator]]s. [[Slip ring]]s attach solar panels to 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 in space|batteries]], because sunlight is blocked inside the launch vehicle and at night. The most common types of batteries for satellites are [[Lithium-ion battery|lithium-ion]], and in the past [[Nickel-hydrogen batteries|nickel–hydrogen]].{{Rp|pages=88–89}} [96] => [97] => ===Communications=== [98] => {{Main|Transponder (satellite communications)}} [99] => * [100] => [101] => == Applications == [102] => [103] => === Earth observation === [104] => {{Main|Earth observation satellite}} [105] => [[File:Earth Radiation Budget Satellite.jpg|thumb|Deployment of the [[Earth Radiation Budget Satellite]] on [[STS-41-G]], collecting data on Earth's weather and climate]] [106] => Earth observation satellites are designed to monitor and survey 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 [[Satellite imagery|normal camera]], [[Space-based radar|radar]], [[lidar]], [[photometer]], or atmospheric instruments. Earth observation satellite's data is most used in [[archaeology]], [[cartography]], [[environmental monitoring]], [[meteorology]], and [[reconnaissance]] applications.{{Citation needed|date=July 2022}} As of 2021, there are over 950 Earth observation satellites, with the largest number of satellites operated with [[Planet Labs]].{{cite web |date=18 August 2021 |title=How many Earth observation satellites are orbiting the planet in 2021? |url=https://www.pixalytics.com/eo-sats-2021/ |last1=Andy |website=Pixalytics |url-status=live |archive-url=https://web.archive.org/web/20220721104450/https://www.pixalytics.com/eo-sats-2021/ |archive-date=21 July 2022 |access-date=25 May 2022}} [107] => [108] => [[Weather satellite]]s monitor [[cloud]]s, [[Street light|city lights]], [[fire]]s, effects of [[pollution]], [[auroral light|aurora]]s, [[Dust storm|sand and dust storms]], [[snow]] cover, [[ice]] mapping, boundaries of [[ocean current]]s, [[energy]] flows, etc. Environmental monitoring satellites can detect changes in 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.{{cite web |website=Earth Observatory |publisher=NASA |url=http://earthobservatory.nasa.gov/Drought/ |title=Drought and Vegetation Monitoring |archive-url=https://web.archive.org/web/20080819121047/http://earthobservatory.nasa.gov/Drought/|archive-date=19 August 2008 |access-date=4 July 2008}} {{PD-notice}} Anthropogenic emissions can be monitored by evaluating data of tropospheric NO2 and SO2.{{Citation needed|date=July 2022}} [109] => [110] => === Communication === [111] => {{Main|Communications satellite}} [112] => {{Excerpt|Communications satellite|files=no|hat=no}} [113] => [114] => ===Spy satellites=== [115] => {{Main|Reconnaissance satellite}} [116] => When an Earth observation satellite or a communications satellite is deployed for military or intelligence purposes, it is known as a spy satellite or reconnaissance satellite. [117] => [118] => Its uses include early missile warning, nuclear explosion detection, electronic reconnaissance, and optical or radar imaging surveillance. [119] => [120] => === Navigation === [121] => {{Main|Satellite navigation}} [122] => 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 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. [123] => [124] => === Telescope === [125] => {{Main|Space telescope}} [126] => [127] => [[Astronomical satellite]]s are satellites used for observation of distant planets, galaxies, and other outer space objects.{{citation needed|date=February 2024}} [128] => [[File:Hubble 01.jpg|thumb|The [[Hubble Space Telescope]]]] [129] => [130] => === Experimental === [131] => [[Tether satellite]]s are satellites that are connected to another satellite by a thin cable called a [[tether]]. [[Recovery satellite]]s are satellites that provide a recovery of reconnaissance, biological, space-production and other payloads from orbit to Earth. [[Biosatellite]]s 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.{{citation needed|date=February 2024}} [132] => [133] => === Weapon === [134] => {{Main|Space weapon|Anti-satellite weapon|Early warning satellite}} [135] => Since the mid-2000s, satellites have been hacked by militant organizations to broadcast propaganda and to pilfer classified information from military communication networks.{{cite web |last=Morrill |first=Dan |title=Hack a Satellite while it is in orbit |url=http://blogs.ittoolbox.com/security/dmorrill/archives/hack-a-satellite-while-it-is-in-orbit-15690 |url-status=dead |archive-url=https://web.archive.org/web/20080320084037/http://blogs.ittoolbox.com/security/dmorrill/archives/hack-a-satellite-while-it-is-in-orbit-15690 |archive-date=20 March 2008 |access-date=25 March 2008 |publisher=[[ITtoolbox]] Blogs |date= April 13, 2007 }}{{cite news |date=22 November 2004 |title=AsiaSat accuses Falungong of hacking satellite signals |agency=[[Press Trust of India]] |url=http://www.accessmylibrary.com/coms2/summary_0286-5205866_ITM |via=AccessMyLibrary |access-date=19 May 2008 |archive-date=19 July 2012 |archive-url=https://archive.today/20120719005250/http://www.accessmylibrary.com/coms2/summary_0286-14557996_ITM |url-status=dead }} 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.{{cite news |last1=Broad |first1=William J. |last2=Sanger |first2=David E. |date=18 January 2007 |title=China Tests Anti-Satellite Weapon, Unnerving U.S. |work=[[The New York Times]] |url=https://www.nytimes.com/2007/01/18/world/asia/18cnd-china.html |url-access=subscription |access-date=23 February 2017 |archive-date=17 April 2017 |archive-url=https://web.archive.org/web/20170417190320/http://www.nytimes.com/2007/01/18/world/asia/18cnd-china.html |url-status=live }} In 2007, the [[China|Chinese]] military shot down an aging weather satellite, followed by the [[US Navy]] shooting down a [[NRO L-21|defunct spy satellite]] in February 2008.{{cite web |date= February 21, 2008 |title=Navy Missile Successful as Spy Satellite Is Shot Down (With Video) |url=http://www.popularmechanics.com/blogs/science_news/4251430.html |access-date=25 March 2008 |work=[[Popular Mechanics]] |archive-date=1 April 2008 |archive-url=https://web.archive.org/web/20080401054054/http://www.popularmechanics.com/blogs/science_news/4251430.html |url-status=dead }} On 18 November 2015, after two failed attempts, Russia successfully carried out a flight test of an anti-satellite missile known as ''[[A-235 anti-ballistic missile system|Nudol]]''.{{citation needed|date=December 2023}} On 27 March 2019, India shot down a live test satellite at 300 km altitude in 3 minutes, becoming the fourth country to have the capability to destroy live satellites.{{Cite web |title=India successfully tests anti-satellite weapon: Modi |url=https://www.theweek.in/news/india/2019/03/27/india-test-anti-satellite-weapon-modi.html |date=March 27, 2019 |access-date=27 March 2019 |website=The Week |language=en |archive-date=12 July 2021 |archive-url=https://web.archive.org/web/20210712020749/https://www.theweek.in/news/india/2019/03/27/india-test-anti-satellite-weapon-modi.html |url-status=live }}{{Cite web |last=Vasani |first=Harsh |date=June 14, 2016 |title=India's Anti-Satellite Weapons |url=https://thediplomat.com/2016/06/indias-anti-satellite-weapons/ |access-date=27 March 2019 |website=The Diplomat |language=en-US |archive-date=1 January 2018 |archive-url=https://web.archive.org/web/20180101131652/https://thediplomat.com/2016/06/indias-anti-satellite-weapons/ |url-status=live }} [136] => [137] => == Environmental Impact == [138] => 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 a satellite's lifetime. [139] => [140] => === Resource use === [141] => Resource use is difficult to monitor and quantify for satellites and [[launch vehicle]]s 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.{{cite journal |last1=Schulz |first1=Leonard |last2=Glassmeier |first2=Karl-Heinz |title=On the anthropogenic and natural injection of matter into Earth’s atmosphere |journal=Advances in Space Research |date=2021 |volume=67 |issue=3 |doi=10.1016/j.asr.2020.10.036|arxiv=2008.13032 }} Through mining and refining, aluminium has numerous negative environmental impacts and is one of the most carbon-intensive metals.{{cite journal |last1=Farjana |first1=Shahjadi Hisan |last2=Huda |first2=Nazmul |last3=Mahmud |first3=M.A. Parvez |title=Impacts of aluminum production: A cradle to gate investigation using life-cycle assessment |journal=Science of the Total Environment |date=2019 |volume=663 |doi=10.1016/j.scitotenv.2019.01.400}} 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.{{cite journal |last1=Gaston |first1=Kevin |last2=Anderson |first2=Karen |last3=Shutler |first3=Jamie |last4=Brewin |first4=Robert |last5=Yan |first5=Xiaoyu |title=Environmental impacts of increasing numbers of artificial space objects |journal=Frontiers in Ecology and the Environment |date=2023 |volume=21 |issue=6 |doi=10.1002/fee.2624|hdl=10871/132935 |hdl-access=free }}{{cite journal |last1=Norgate |first1=Terry |last2=Haque |first2=Nawshad |title=Using life cycle assessment to evaluate some environmental impacts of gold production |journal=Journal of Cleaner Production |date=2012 |volume=29 |doi=10.1016/j.jclepro.2012.01.042}}{{cite journal |last1=Flexer |first1=Victoria |last2=Baspineiro |first2=Celso |last3=Galli |first3=Claudia |title=Lithium recovery from brines: A vital raw material for green energies with a potential environmental impact in its mining and processing |journal=Science of the Total Environment |date=2018 |volume=639 |doi=10.1016/j.scitotenv.2018.05.223}} Launch vehicles require larger amounts of raw materials to manufacture and the [[Booster (rocketry)|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,{{cite web |title=Boosters (EAP) |url=https://www.esa.int/Enabling_Support/Space_Transportation/Launch_vehicles/Boosters_EAP |website=The European Space Agency |access-date=10 April 2024}} to give an idea of the quantity of materials that are often left in the ocean. [142] => [143] => === Launches === [144] => 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.{{cite journal |last1=Durrieu |first1=Sylvie |last2=Nelson |first2=Ross |title=Earth observation from space – The issue of environmental sustainability |journal=Space Policy |date=2013 |volume=29 |issue=4 |doi=10.1016/j.spacepol.2013.07.003|doi-access=free }} These pollutants can include [[black carbon]], [[Carbon dioxide|CO2]], [[NOx|nitrogen oxides]] (NOx), [[aluminium]] and [[water vapour]], but the mix of pollutants is dependent on rocket design and fuel type.{{cite journal |last1=Dallas |first1=J.A. |last2=Raval |first2=S. |last3=Gaitan |first3=J.P.A. |last4=Saydam |first4=S. |last5=Dempster |first5=A.G. |title=The environmental impact of emissions from space launches: A comprehensive review |journal=Journal of Cleaner Production |date=2020 |volume=255 |doi=10.1016/j.jclepro.2020.120209}} The amount of [[Greenhouse gas|green house gases]] emitted by rockets is considered trivial as it contributes significantly less, around 0.01%,{{cite journal |last1=Miraux |first1=Lois |title=Environmental limits to the space sector's growth |journal=Science of the Total Environment |date=2022 |volume=806 |issue=4 |doi=10.1016/j.scitotenv.2021.150862}} than the aviation industry yearly which itself accounts for 2-3% of the total global greenhouse gas emissions. [145] => [146] => Rocket emissions in the [[stratosphere]] and their effects are only beginning to be studied and it is likely that 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. [[Radical (chemistry)|Radicals]] such as NOx, HOx, and ClOx deplete stratospheric O3 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 the impact of regulated ozone-depleting substances.{{cite journal |last1=Ryan |first1=Robert |last2=Marais |first2=Eloise |last3=Balhatchet |first3=Chloe |last4=Eastham |first4=Sebastian |title=Impact of Rocket Launch and Space Debris Air Pollutant Emissions on Stratospheric Ozone and Global Climate |journal=Earth's Future |date=2022 |volume=10 |issue=6 |doi=10.1029/2021EF002612}}{{cite journal |last1=Ross |first1=Martin |last2=Toohey |first2=Darin |last3=Peinemann |first3=Manfred |last4=Ross |first4=Patrick |title=Limits on the Space Launch Market Related to Stratospheric Ozone Depletion |journal=Astropolitics |date=2009 |volume=7 |issue=1 |doi=10.1080/14777620902768867}} Whilst emissions of water vapour are largely deemed as inert, H2O is the source gas for HOx 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 the stratosphere.{{cite journal |last1=Maloney |first1=Christopher |last2=Portmann |first2=Robert |last3=Ross |first3=Martin |last4=Rosenlof |first4=Karen |title=The Climate and Ozone Impacts of Black Carbon Emissions From Global Rocket Launches |journal=JGR Atmospheres |date=2022 |volume=127 |issue=12 |doi=10.1029/2021JD036373}} Both warming and changes in circulation can then cause depletion of the ozone layer. [147] => [148] => === Operational lifetime === [149] => ==== LEO Satellites ==== [150] => Several pollutants are released in the upper atmospheric layers during the orbital lifetime of [[Low Earth orbit|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]] is the chemical propellant used which then releases [[ammonia]], [[hydrogen]] and [[nitrogen]] as gas into the upper atmosphere. [151] => 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 [[BoPET|Mylar]] that are used to insulate and protect the satellite which then emits gasses like CO2 and CO into the atmosphere.{{cite journal |last1=de Groh |first1=Kim |last2=Banks |first2=Bruce |last3=Miller |first3=Sharon |last4=Dever |first4=Joyce |title=Chapter 28 - Degradation of Spacecraft Materials |journal=Handbook of Environmental Degreadation |doi=10.1016/B978-0-323-52472-8.00029-0|hdl=2060/20040112017 |hdl-access=free }} [152] => [153] => ==== Night sky ==== [154] => 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.{{cite journal |last1=Kocifaj |first1=M. |last2=Kundracik |first2=F. |last3=Barentine |first3=J.C. |last4=Bara |first4=S. |title=The proliferation of space objects is a rapidly increasing source of artificial night sky brightness |journal=Monthly Notices of the Royal Astronomical Society: Letters |date=2021 |volume=504 |issue=1 |doi=10.1093/mnrasl/slab030|arxiv=2103.17125 }} This has the potential to confuse organisms, like insects and night-migrating birds, that use celestial patterns for migration and orientation.{{cite journal |last1=Sutherland |first1=W.J. |last2=Atkinson |first2=P.W. |last3=Broad |first3=S. |last4=Brown |first4=S. |last5=Clout |first5=M. |last6=Dias |first6=M.P. |last7=Dicks |first7=L.V. |last8=Doran |first8=H. |last9=Fleishman |first9=E. |last10=Garratt |first10=E.L. |last11=Gaston |first11=K.J. |last12=Hughes |first12=A.C. |last13=Le Roux |first13=X. |last14=Lickorish |first14=F.A. |last15=Maggs |first15=L. |last16=Palardy |first16=J.E. |last17=Peck |first17=L.S. |last18=Pettorelli |first18=N. |last19=Pretty |first19=J. |last20=Spalding |first20=M.D. |last21=Tonneijck |first21=F.H. |last22=Walpole |first22=M. |last23=Watson |first23=J.E.M |last24=Wentworth |first24=J. |last25=Thornton |first25=A. |title=A 2021 Horizon Scan of Emerging Global Biological Conservation Issues |journal=Trends in Ecology & Evolution |date=2021 |volume=36 |issue=1 |doi=10.1016/j.tree.2020.10.014|hdl=10400.12/8056 |hdl-access=free }}{{cite journal |last1=Foster |first1=J. |last2=Smolka |first2=J. |last3=Nilsson |first3=D.E. |last4=Dacke |first4=M. |title=How animals follow the stars |journal=Proceedings of the Royal Society Biological Sciences |date=2018 |volume=285 |issue=1871 |doi=10.1098/rspb.2017.2322|pmc=5805938 }} The impact this might have 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.{{cite journal |last1=Hamacher |first1=Duane |last2=Barsa |first2=John |last3=Passi |first3=Segar |last4=Tapim |first4=Alo |title=Indigenous use of stellar scintillation to predict weather and seasonal change |journal=Proceedings of the Royal Society of Victoria |date=2019 |volume=131 |issue=1 |doi=10.1071/RS19003|arxiv=1903.01060 }} [155] => [156] => ==== Ground-based infrastructure ==== [157] => 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. [158] => [159] => === End of life === [160] => When 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 the further pollution of space and future issues with space debris. [161] => 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.{{cite journal |last1=Miraux |first1=Lois |last2=Willson |first2=Andrew |last3=Calabuig |first3=Guillermo |title=Environmental sustainability of future proposed space activities |journal=Acta Astronautica |date=2022 |volume=200 |issue=1 |doi=10.1016/j.actaastro.2022.07.034}} 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 the earth's climate. After deorbiting 70% of satellites end up in the ocean and are rarely recovered. [162] => [163] => ==Pollution and interference== [164] => [[File:The growth of all tracked objects in space over time (space debris and satellites).png|thumb|The growth of all tracked objects in space over time{{cite journal |last1=Lawrence |first1=Andy |last2=Rawls |first2=Meredith L. |last3=Jah |first3=Moriba |last4=Boley |first4=Aaron |last5=Di Vruno |first5=Federico |last6=Garrington |first6=Simon |last7=Kramer |first7=Michael |last8=Lawler |first8=Samantha |last9=Lowenthal |first9=James |last10=McDowell |first10=Jonathan |last11=McCaughrean |first11=Mark |date=April 2022 |title=The case for space environmentalism |journal=Nature Astronomy |language=en |volume=6 |issue=4 |pages=428–435 |arxiv=2204.10025 |bibcode=2022NatAs...6..428L |doi=10.1038/s41550-022-01655-6 |issn=2397-3366 |s2cid=248300127}}]] [165] => Issues like [[space debris]], radio and [[light pollution]] are increasing in magnitude and at the same time lack progress in national or international regulation.{{cite news |last1=Seidler |first1=Christoph |date=22 April 2017 |title=Problem Weltraumschrott: Die kosmische Müllkippe – Wissenschaft |work=Der Spiegel |url=http://www.spiegel.de/wissenschaft/weltall/weltraumschrott-esa-tagung-in-darmstadt-ohne-ergebnisse-a-1144174.html |access-date=22 April 2017 |archive-date=23 April 2017 |archive-url=https://web.archive.org/web/20170423013706/http://www.spiegel.de/wissenschaft/weltall/weltraumschrott-esa-tagung-in-darmstadt-ohne-ergebnisse-a-1144174.html |url-status=live }} Space debris pose dangers to the spacecraft{{cite web |last1=Garcia |first1=Mark |date=13 April 2015 |title=Space Debris and Human Spacecraft |url=https://www.nasa.gov/mission_pages/station/news/orbital_debris.html |access-date=22 March 2022 |website=NASA |archive-date=22 March 2022 |archive-url=https://web.archive.org/web/20220322131144/https://www.nasa.gov/mission_pages/station/news/orbital_debris.html |url-status=live }}{{cite web |last1=Williams |first1=Matt |title=What would a sustainable space environment look like? |url=https://phys.org/news/2022-03-sustainable-space-environment.html |access-date=22 March 2022 |website=phys.org |publisher=Universe Today |language=en |archive-date=22 March 2022 |archive-url=https://web.archive.org/web/20220322160515/https://phys.org/news/2022-03-sustainable-space-environment.html |url-status=live }} (including satellites){{cite news |date=10 March 2022 |title=Chinese official calls for protection of space assets, international coordination mechanisms |work=SpaceNews |url=https://spacenews.com/chinese-official-calls-for-protection-of-space-assets-international-coordination-mechanisms/ |access-date=22 March 2022 |archive-date=21 July 2022 |archive-url=https://web.archive.org/web/20220721104448/https://spacenews.com/chinese-official-calls-for-protection-of-space-assets-international-coordination-mechanisms/ |url-status=live }} in or crossing geocentric orbits and have the potential to drive a [[Kessler syndrome]]{{cite web |title=The Kessler Effect and how to stop it |url=https://www.esa.int/Enabling_Support/Space_Engineering_Technology/The_Kessler_Effect_and_how_to_stop_it |access-date=22 March 2022 |publisher=ESA |language=en |archive-date=22 March 2022 |archive-url=https://web.archive.org/web/20220322160515/https://www.esa.int/Enabling_Support/Space_Engineering_Technology/The_Kessler_Effect_and_how_to_stop_it |url-status=live }} which could potentially curtail humanity from conducting space endeavors in the future.{{cite news |last1=Wattles |first1=Jackie |title=Space is becoming too crowded, Rocket Lab CEO warns |work=CNN |url=https://edition.cnn.com/2020/10/07/business/rocket-lab-debris-launch-traffic-scn/index.html |access-date=26 May 2022 |archive-date=26 May 2022 |archive-url=https://web.archive.org/web/20220526100211/https://edition.cnn.com/2020/10/07/business/rocket-lab-debris-launch-traffic-scn/index.html |url-status=live }}{{cite news |date=16 October 2020 |title=What happens if two bits of space junk actually collide? |language=en |work=The Independent |url=https://www.independent.co.uk/tech/space-junk-collision-satellite-debris-iss-nasa-b1074079.html |access-date=26 May 2022 |archive-date=26 May 2022 |archive-url=https://web.archive.org/web/20220526100210/https://www.independent.co.uk/tech/space-junk-collision-satellite-debris-iss-nasa-b1074079.html |url-status=live }} [166] => [167] => With increase in the number of [[satellite constellation]]s, like [[SpaceX]] [[Starlink]], the astronomical community, such as the [[International Astronomical Union|IAU]], report that orbital pollution is getting increased significantly.{{cite web |title=IAU's statement on satellite constellations |url=https://www.iau.org/news/announcements/detail/ann19035/ |access-date=3 June 2019 |website=International Astronomical Union |archive-date=27 May 2020 |archive-url=https://web.archive.org/web/20200527073625/https://www.iau.org/news/announcements/detail/ann19035/ |url-status=live }}{{cite web |date=14 June 2019 |title=Light pollution from satellites will get worse. But how much? |url=http://www.astronomy.com/news/2019/06/light-pollution-from-satellites-will-get-worse-but-how-much |website=astronomy.com |access-date=7 November 2019 |archive-date=28 April 2021 |archive-url=https://web.archive.org/web/20210428172415/https://astronomy.com/news/2019/06/light-pollution-from-satellites-will-get-worse-but-how-much |url-status=live }}{{cite journal |last1=Hainaut |first1=Olivier R. |last2=Williams |first2=Andrew P. |date=1 April 2020 |title=Impact of satellite constellations on astronomical observations with ESO telescopes in the visible and infrared domains |url=https://www.aanda.org/articles/aa/full_html/2020/04/aa37501-20/aa37501-20.html |journal=Astronomy & Astrophysics |language=en |volume=636 |page=A121 |arxiv=2003.01992 |bibcode=2020A&A...636A.121H |doi=10.1051/0004-6361/202037501 |issn=0004-6361 |doi-access=free |accessdate=22 November 2020 |archive-date=19 December 2020 |archive-url=https://web.archive.org/web/20201219192027/https://www.aanda.org/articles/aa/full_html/2020/04/aa37501-20/aa37501-20.html |url-status=live }}{{cite journal |last1=Mróz |first1=Przemek |last2=Otarola |first2=Angel |last3=Prince |first3=Thomas A. |last4=Dekany |first4=Richard |last5=Duev |first5=Dmitry A. |last6=Graham |first6=Matthew J. |last7=Groom |first7=Steven L. |last8=Masci |first8=Frank J. |last9=Medford |first9=Michael S. |date=1 January 2022 |title=Impact of the SpaceX Starlink Satellites on the Zwicky Transient Facility Survey Observations |journal=The Astrophysical Journal Letters |language=en |volume=924 |issue=2 |pages=L30 |arxiv=2201.05343 |bibcode=2022ApJ...924L..30M |doi=10.3847/2041-8213/ac470a |issn=2041-8205 |s2cid=245986575 |doi-access=free }}{{cite web |title=Impacts of Large Satellite Constellations on Astronomy: Live Updates {{!}} American Astronomical Society |url=https://aas.org/posts/advocacy/2021/08/impacts-large-satellite-constellations-astronomy-live-updates |access-date=22 March 2022 |work=[[American Astronomical Society]] |language=en |archive-date=19 April 2022 |archive-url=https://web.archive.org/web/20220419152431/https://aas.org/posts/advocacy/2021/08/impacts-large-satellite-constellations-astronomy-live-updates |url-status=live }} A report from the SATCON1 workshop in 2020 concluded that the effects of large satellite constellations can severely affect some astronomical research efforts and lists six ways to mitigate harm to astronomy.{{cite news |last1=Zhang |first1=Emily |title=SpaceX's Dark Satellites Are Still Too Bright for Astronomers |language=en |work=Scientific American |url=https://www.scientificamerican.com/article/spacexs-dark-satellites-are-still-too-bright-for-astronomers/ |access-date=16 September 2020 |archive-date=2 January 2021 |archive-url=https://web.archive.org/web/20210102065559/https://www.scientificamerican.com/article/spacexs-dark-satellites-are-still-too-bright-for-astronomers/ |url-status=live }}{{cite news |title=Report Offers Roadmap to Mitigate Effects of Large Satellite Constellations on Astronomy {{!}} American Astronomical Society |work=aas.org |url=https://aas.org/press/report-offers-roadmap-mitigate-effects-large-satellite-constellations-astronomy |access-date=16 September 2020 |archive-date=24 September 2020 |archive-url=https://web.archive.org/web/20200924025446/https://aas.org/press/report-offers-roadmap-mitigate-effects-large-satellite-constellations-astronomy |url-status=live }} The IAU is establishing a center (CPS) to coordinate or aggregate measures to mitigate such detrimental effects.{{cite news |date=4 February 2022 |title=Astronomers stand up to satellite mega-constellations |work=BBC News |url=https://www.bbc.com/news/science-environment-60262100 |access-date=10 March 2022 |archive-date=10 March 2022 |archive-url=https://web.archive.org/web/20220310041256/https://www.bbc.com/news/science-environment-60262100 |url-status=live }}{{cite web |title=Protection of the Dark and Quiet Sky from Satellite Constellation Interference |url=https://www.mpifr-bonn.mpg.de/announcements/2022/1 |access-date=10 March 2022 |publisher=Max Planck Institute for Radio Astronomy, Bonn |language=en |archive-date=15 March 2022 |archive-url=https://web.archive.org/web/20220315090741/https://www.mpifr-bonn.mpg.de/announcements/2022/1 |url-status=live }}{{cite web |title=International Astronomical Union {{!}} IAU |url=https://www.iau.org/science/scientific_bodies/centres/CPS/ |access-date=10 March 2022 |website=www.iau.org |archive-date=13 March 2022 |archive-url=https://web.archive.org/web/20220313084016/https://www.iau.org/science/scientific_bodies/centres/CPS/ |url-status=live }} [168] => [169] => Some notable satellite failures that polluted and dispersed radioactive materials are [[Kosmos 954]], [[Kosmos 1402]] and the [[List of nuclear power systems in space|Transit 5-BN-3]]. [170] => [171] => Generally liability has been covered by the [[Liability Convention]]. Using wood as an alternative material has been posited in order to reduce pollution and debris from satellites that reenter the atmosphere.{{cite news |last=Harper |first=Justin |date=29 December 2020 |title=Japan developing wooden satellites to cut space junk |work=bbc.co.uk |url=https://www.bbc.co.uk/news/business-55463366 |access-date=29 December 2020 |archive-date=29 December 2020 |archive-url=https://web.archive.org/web/20201229014751/https://www.bbc.co.uk/news/business-55463366 |url-status=live }} [172] => [173] => Due to the low received signal strength of satellite transmissions, they are prone to [[Radio jamming|jamming]] by land-based transmitters. Such jamming is limited to the geographical area within the transmitter's range. GPS satellites are potential targets for jamming,{{cite web |last=Singer |first=Jeremy |year=2003 |title=U.S.-Led Forces Destroy GPS Jamming Systems in Iraq |url=http://www.space.com/news/gps_iraq_030325.html |url-status=dead |archive-url=https://web.archive.org/web/20080526204956/http://www.space.com/news/gps_iraq_030325.html |archive-date=26 May 2008 |access-date=25 March 2008 |publisher=[[Space.com]]}}{{cite web |last=Brewin |first=Bob |year=2003 |title=Homemade GPS jammers raise concerns |url=http://www.computerworld.com/securitytopics/security/story/0,10801,77702,00.html |url-status=dead |archive-url=https://web.archive.org/web/20080422164053/http://computerworld.com/securitytopics/security/story/0%2C10801%2C77702%2C00.html |archive-date=22 April 2008 |access-date=25 March 2008 |work=[[Computerworld]]}} but satellite phone and television signals have also been subjected to jamming.{{cite web |year=2008 |title=Iran government jamming exile satellite TV |url=http://www.iranfocus.com/modules/news/article.php?storyid=2852 |access-date=25 March 2008 |work=[[Iran Focus]] |archive-date=14 January 2006 |archive-url=https://web.archive.org/web/20060114173408/http://www.iranfocus.com/modules/news/article.php?storyid=2852 |url-status=live }}{{cite web |last=Selding |first=Peter de |year=2007 |title=Libya Pinpointed as Source of Months-Long Satellite Jamming in 2006 |url=http://www.space.com/spacenews/businessmonday_070409.html |url-status=live |archive-url=https://web.archive.org/web/20080429193429/http://www.space.com/spacenews/businessmonday_070409.html |archive-date=29 April 2008 |publisher=[[Space.com]]}} [174] => [175] => Also, it is very easy to transmit a carrier radio signal to a geostationary satellite and thus interfere with the legitimate uses of the satellite's transponder. It is common for Earth stations to transmit at the wrong time or on the wrong frequency in commercial satellite space, and dual-illuminate the transponder, rendering the frequency unusable. Satellite operators now have sophisticated monitoring tools and methods that enable them to pinpoint the source of any carrier and manage the transponder space effectively. {{Citation needed|date=September 2011}} [176] => [177] => ==See also== [178] => * [[High-altitude platform station]] [179] => * [[Solar aircraft]] [180] => * [[Satellite refuelling]] [181] => [182] => ==Notes== [183] => [184] => {{notelist}} [185] => [186] => == References == [187] => {{Reflist}} [188] => [189] => ==External links== [190] => {{wikiquote}} [191] => {{commons category|Satellites}} [192] => * {{curlie|Business/Telecommunications/Services/Wireless/Satellite/|Satellite}} [193] => * [https://directory.eoportal.org/web/eoportal/satellite-missions EO Portal directory] {{Webarchive|url=https://web.archive.org/web/20130923090413/https://directory.eoportal.org/web/eoportal/satellite-missions |date=23 September 2013 }} [194] => [195] => {{Spaceflight}} [196] => {{Portal bar|Spaceflight|Outer space}} [197] => {{Authority control}} [198] => [199] => {{DEFAULTSORT:Earth Observation Satellite}} [200] => [[Category:Satellites| ]] [201] => [[Category:Articles containing video clips]] [202] => [[Category:Spacecraft]] [203] => [[Category:Soviet inventions]] [] => )
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Satellite

A satellite is an object that orbits another object in space. They can be either natural, such as moons, or artificial, such as spacecraft launched by humans.

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They can be either natural, such as moons, or artificial, such as spacecraft launched by humans. Satellites are used for a variety of purposes, including communication, weather observation, navigation, research, and military surveillance. They also play a crucial role in gathering data about space and celestial bodies. The concept of satellites dates back centuries, with the understanding that celestial bodies orbit around each other. However, the first artificial satellite, Sputnik 1, was launched by the Soviet Union in 1957, marking the beginning of the space age. Since then, numerous countries and organizations have sent satellites into orbit, contributing to advancements in technology and scientific knowledge. Satellites are typically placed into different types of orbits depending on their intended purpose. Geostationary satellites, for example, remain fixed above a specific location on Earth, enabling continuous communication coverage for broadcast services and telecommunication. Polar orbiting satellites, on the other hand, travel over Earth's poles and provide valuable data for weather forecasting and climate monitoring. Satellites work by receiving signals from ground stations, performing various tasks or experiments, and transmitting the collected data back to Earth. They are equipped with different instruments and sensors, depending on their specific mission objectives. For communication purposes, satellites feature transponders to receive, amplify, and retransmit signals between different locations on Earth. Weather satellites, on the other hand, use sensors to gather information about atmospheric conditions, cloud cover, and other meteorological data. In recent years, satellite technology has become increasingly important for global connectivity, with networks of satellites being deployed to provide internet access to remote areas. Companies like SpaceX and OneWeb are leading the way in this endeavor, launching thousands of small satellites into low Earth orbit. Satellites have revolutionized various fields, from telecommunication and broadcasting, to weather forecasting, navigation, and scientific research. They have provided crucial insights into Earth's climate, natural disasters, and geological processes. Moreover, satellites have allowed for the exploration of other celestial bodies, such as the Moon, Mars, and beyond. As technology continues to advance, satellites will likely play an even greater role in expanding human knowledge and presence in space.

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