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{{Short description|Human-made object put into an orbit}}
{{Short description|Objects intentionally placed into orbit}}
{{Use dmy dates|date=December 2019}}
{{Use American English|date=July 2022}}
{{other uses}}
{{other uses}}
{{Cleanup|reason=Messy layout, poor references|date=April 2022}}
{{Use dmy dates|date=December 2019}}
[[File:Sputnik asm.jpg|thumb|[[Sputnik 1]], the first artificial satellite to orbit Earth|300x300px]]


[[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]]
A '''satellite''' is an object that is intentionally placed into [[orbit]]. In order to distinguish them from [[natural satellite]]s such as Earth's [[Moon]], they are called '''artificial satellites'''


A '''satellite''' or '''artificial satellite''' is an object intentionally placed into [[orbit]] in [[outer space]]. Except for [[Passive satellite|passive satellites]], most satellites have an [[electricity generation]] system for equipment on board, such as [[Solar panel|solar panels]] or [[Radioisotope thermoelectric generator|radioisotope thermoelectric generators]] (RTGs). Most satellites also have a method of communication to [[Ground station|ground stations]], called [[Transponder (satellite communications)|transponders]]. Many satellites use a [[Satellite bus|standardized bus]] to save cost and work, the most popular of which is small [[CubeSat|CubeSats]]. Similar satellites can work together as a group, forming [[Satellite constellation|constellations]]. Because of the high [[launch cost]] to space, satellites are designed to be as lightweight and robust as possible.
On 4th October 1957, the [[Soviet Union]] launched the world's first artificial satellite, [[Sputnik 1]]. Since then, about 8,900 satellites from more than 40 countries have been launched. According to a 2018 estimate, about 5,000 remained in orbit. Of those, about 1,900 were operational, while the rest had exceeded their useful lives and become [[space debris]]. Approximately 63% of operational satellites are in [[low Earth orbit]], 6% are in [[medium-Earth orbit]] (at 20,000&nbsp;km), 29% are in [[geostationary orbit]] (at 36,000&nbsp;km) and the remaining 2% are in various [[elliptical orbits]]. In terms of countries with the most satellites, the [[United States]] has the most with 2,944 satellites, [[China]] is second with 499, and [[Russia]] third with 169.<ref name="ucsusa">{{cite web |url=https://www.ucsusa.org/resources/satellite-database/ |website=ucsusa | title =UCS Satellite Database |access-date=30 March 2021 |date=1 January 2021}}</ref>
A few large [[space station]]s, including the [[International Space Station]], have been launched in parts and assembled in orbit. Over a dozen [[space probe]]s have been placed into orbit around other bodies and become artificial satellites of the [[Moon]], [[Mercury (planet)|Mercury]], [[Venus]], [[Mars]], [[Jupiter]], [[Saturn]], a few [[asteroid]]s,<ref>{{cite web|url=http://www.nasa.gov/press/2015/march/nasa-spacecraft-becomes-first-to-orbit-a-dwarf-planet/|title=NASA Spacecraft Becomes First to Orbit a Dwarf Planet|work=NASA|date=6 March 2015}}</ref> a [[Rosetta (spacecraft)|comet]] and the [[Sun]].


Satellites are placed from the surface to orbit by [[Launch vehicle|launch vehicles]], 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|ion thrusters]]. In 2018, about 90% of satellites orbiting Earth are in [[low Earth orbit]] or [[geostationary orbit]]; geostationary means the satellites stay still at the sky. 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 collision threat are becoming 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]]).
Satellites are used for many purposes. Among several other applications, they can be used to make star maps and maps of [[planetary surface]]s, and also take pictures of planets they are launched into. Common types include military and civilian [[Earth observation satellite]]s, [[communications satellite]]s, [[navigation satellite]]s, [[weather satellite]]s, and [[space telescope]]s. [[Space station]]s and human [[spacecraft]] in orbit are also satellites.


[[Earth observation satellite|Earth observation satellites]] gather information for [[Reconnaissance satellite|reconnaissance]], [[Satellite imagery|mapping]], [[Weather satellite|monitoring the weather]], ocean, forest, etc. [[Space telescope|Space telescopes]] 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|Space probes]] are satellites designed for robotic [[space exploration]] outside of Earth, and [[Space station|space stations]] are in essence crewed satellites.
Satellites can operate by themselves or as part of a larger system, a [[satellite formation flying|satellite formation]] or [[satellite constellation]].


The first satellite to launch into orbit was the Soviet Union's [[Sputnik 1]] in 1958.{{Explain|date=July 2022|reason=Needs more research}}
Satellite orbits have a large range depending on the purpose of the satellite, and are classified in a number of ways. Well-known (overlapping) classes include low Earth orbit, [[polar orbit]], and [[geostationary orbit]].

A [[launch vehicle]] is a [[rocket]] that places a satellite into orbit. Usually, it lifts off from a [[launch pad]] on land. Some are launched at sea from a [[submarine]] or a [[Sea Launch|mobile maritime platform]], or aboard a plane (see [[air launch to orbit]]).

Satellites are usually semi-independent computer-controlled systems. Satellite subsystems attend many tasks, such as power generation, [[Spacecraft thermal control|thermal control]], telemetry, [[attitude control]], scientific instrumentation, [[telecommunication|communication]], etc.


== History ==
== History ==
{{See also|Remote sensing#History}}
{{See also|Timeline of first artificial satellites by country}}

[[File:Popular_Science_May_1949.jpg|thumb|A 1949 issue of [[Popular Science]] depicts the idea of an "artificial moon"]]
[[File:ConstellationGPS.gif|thumb|right|upright=1.1|Animation depicting the orbits of GPS satellites in [[medium Earth orbit]].]]
[[File:ESTCube-1 illustration.jpg|thumb|1U [[CubeSat]] [[ESTCube-1]], developed mainly by the students from the [[University of Tartu]], carries out a tether deployment experiment in [[low Earth orbit]].]]


=== Early proposals ===
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).<ref>{{cite web
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).<ref>{{cite web
|title=Rockets in Science Fiction (Late 19th Century)
|title=Rockets in Science Fiction (Late 19th Century)
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In 1903, [[Konstantin Tsiolkovsky]] (1857–1935) published ''Exploring Space Using Jet Propulsion Devices'', which is the first academic treatise on the use of rocketry to launch spacecraft. He calculated the [[orbital speed]] required for a minimal orbit, and that a [[multi-stage rocket]] fueled by liquid [[propellant]]s could achieve this.
In 1903, [[Konstantin Tsiolkovsky]] (1857–1935) published ''Exploring Space Using Jet Propulsion Devices'', which is the first academic treatise on the use of rocketry to launch spacecraft. He calculated the [[orbital speed]] required for a minimal orbit, and that a [[multi-stage rocket]] fueled by liquid [[propellant]]s 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 the special conditions of space could be useful for scientific experiments. The book described [[geostationary]] satellites (first put forward by [[Konstantin Tsiolkovsky]]) and discussed communication between them and the ground using radio, but fell short of the idea of using satellites for mass broadcasting and as telecommunications relays.<ref>{{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}}</ref>
In 1928, [[Herman Potočnik]] (1892–1929) published his sole book, ''The Problem of Space Travel – The Rocket Motor''. He described the use of orbiting spacecraft for observation of the ground and described how the special conditions of space could be useful for scientific experiments.


In a 1945 ''[[Wireless World]]'' article, the English science fiction writer [[Arthur C. Clarke]] described in detail the possible use of [[communications satellite]]s for mass communications.<ref>{{cite book | title=Visions of Technology
In a 1945 ''[[Wireless World]]'' article, the 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.<ref name=":0">{{Cite book |last=Pratt |first=Timothy |url= |title=Satellite Communications |last2=Allnutt |first2=Jeremy E. |date=December 16, 2019 |publisher=[[John Wiley & Sons Ltd]] |isbn=978-1-119-48217-8 |edition=3rd |oclc=1098222848}}</ref>{{Rp|pages=1–2}}
| first=Richard | last=Rhodes | page=160 | publisher=[[Simon & Schuster]] | year=2000
| isbn=978-0-684-86311-5}}</ref> 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 the most potent scientific tools of the Twentieth Century."<ref>
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."<ref>{{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 }}</ref> 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.<ref>{{cite book | title=Venture into Space: Early Years of Goddard Space Flight Center
{{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}}</ref> 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.<ref>{{cite book | title=Venture into Space: Early Years of Goddard Space Flight Center
| first=Alfred | last=Rosenthal | publisher=NASA | year=1968 | page=15}}</ref>
| first=Alfred | last=Rosenthal | publisher=NASA | year=1968 | page=15}}</ref>


In 1946, American theoretical astrophysicist [[Lyman Spitzer]] proposed an orbiting [[space telescope]].<ref>{{cite web|title=Hubble Essentials: About Lyman Spitzer, Jr.|publisher=Hubble Site|url=http://hubblesite.org/the_telescope/hubble_essentials/lyman_spitzer.php}}</ref>
In 1946, American theoretical astrophysicist [[Lyman Spitzer]] proposed an orbiting [[space telescope]].<ref>{{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}}</ref>


In February 1954, Project RAND released "Scientific Uses for a Satellite Vehicle", by R. R. Carhart.<ref>R. R. Carhart, Scientific Uses for a Satellite Vehicle, Project RAND Research Memorandum. (Rand Corporation, Santa Monica) 12 February 1954.</ref> 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.<ref>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.</ref>
In February 1954, Project RAND released "Scientific Uses for a Satellite Vehicle", by R. R. Carhart.<ref>R. R. Carhart, Scientific Uses for a Satellite Vehicle, Project RAND Research Memorandum. (Rand Corporation, Santa Monica) 12 February 1954.</ref> 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.<ref>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.</ref>


=== First satellites ===
[[File:Sputnik asm.jpg|alt=Steel ball with 4 antennas|thumb|Replica of the [[Sputnik 1]]]]
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.
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.


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]].
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]].


[[Sputnik 2]] was launched on 3 November 1957 and carried the first living passenger into orbit, a dog named [[Laika]].<ref name="nasa_animals">{{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}}</ref>
[[Sputnik 2]] was launched on 3 November 1957 and carried the first living passenger into orbit, a dog named [[Laika]].<ref name="nasa_animals">{{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 }}</ref>


In early 1955, after pressure by the [[American Rocket Society]], the [[National Science Foundation]], and the International Geophysical Year, the Army and Navy were working 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.<ref>{{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}}</ref>
In early 1955, after pressure by the [[American Rocket Society]], the [[National Science Foundation]], and the International Geophysical Year, the Army and Navy were working 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.<ref>{{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}}</ref> The information sent back from its radiation detector led to the discovery of the Earth's [[Van Allen radiation belt]]s.<ref name="Allen">{{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}}</ref> 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.<ref name="Tatem">{{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}}</ref>


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.<ref>{{cite web|first1=David S. F. |last1=Portree |first2=Joseph P. |last2=Loftus, Jr |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}}</ref>
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.<ref>{{cite web|first1=David S. F. |last1=Portree |first2=Joseph P. |last2=Loftus, Jr |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}}</ref>
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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. Begun in 1997, [[FreeFlyer]] is a commercial off-the-shelf software application for satellite mission analysis, design, and operations.
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. Begun in 1997, [[FreeFlyer]] is a commercial off-the-shelf software application for satellite mission analysis, design, and operations.


=== Later development ===
The largest artificial satellite ever is the [[International Space Station]].<ref>{{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.|date=2019-02-22|publisher=ABC-CLIO|isbn=978-1-61069-094-2|pages=126|language=en}}</ref>

[[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 communication between them and the ground using radio, but fell short of the idea of using satellites for mass broadcasting and as telecommunications relays.<ref>{{Cite web |url=http://www.sasmac.cn/portal/html/fc4f335929b0df0d0129b0e348f90003/_content/10_07/09/1278668367217.html|title=Introduction to satellite|website=www.sasmac.cn|date=2 September 2016}}</ref>

==Tracking==
{{main|Ground station}}
{{further|Orbit determination|Satellite geodesy#Satellite tracking|Satellite flare}}
{{see also|Space debris#Tracking and measurement|Satellite tracking (animal migration)}}
Satellites can be tracked from Earth stations and also from other satellites.

===Space Surveillance Network===
{{Main|United States Space Surveillance Network}}

The [[United States Space Surveillance Network]] (SSN), a division of the [[United States Strategic Command]], has been tracking objects in Earth's orbit since 1957 when the [[Soviet Union]] opened the [[Space Age]] with the launch of [[Sputnik I]]. Since then, the SSN has tracked more than 26,000 objects. The SSN currently tracks more than 8,000-artificial orbiting objects. The rest have re-entered Earth's atmosphere and disintegrated, or survived re-entry and impacted the Earth. The SSN tracks objects that are 10 centimeters in diameter or larger; those now orbiting Earth range from satellites weighing several tons to pieces of spent rocket bodies weighing only 10 pounds. About seven percent are operational satellites (i.e. ~560 satellites), the rest are [[space debris]].<ref>{{cite web|title=Orbital Debris Education Package |url=http://www.orbitaldebris.jsc.nasa.gov/library/EducationPackage.pdf |publisher=[[Lyndon B. Johnson Space Center]] |url-status=dead |archive-url=https://web.archive.org/web/20080408183946/http://www.orbitaldebris.jsc.nasa.gov/library/EducationPackage.pdf |archive-date=8 April 2008 |access-date=6 March 2008}}</ref> The United States Strategic Command is primarily interested in the active satellites, but also tracks space debris which upon reentry might otherwise be mistaken for incoming missiles.

== Services ==
There are three basic categories of (non-military) satellite services:<ref name=Grant&Meadows>{{cite book | last1=Grant | first1=A. | last2=Meadows | first2=J. | year=2004 | title=Communication Technology Update | edition=ninth | page=[https://archive.org/details/communicationtec00augu/page/284 284] | publisher=[[Focal Press]] | isbn=978-0-240-80640-2 | url-access=registration | url=https://archive.org/details/communicationtec00augu/page/284 }}</ref>

===Fixed satellite services===
[[Fixed Service Satellite|Fixed satellite services]] handle hundreds of billions of voice, data, and video transmission tasks across all countries and continents between certain points on the Earth's surface.

===Mobile satellite systems===
{{main|Mobile-satellite service}}
[[File:Couverture satellite inmarsat.svg|thumb|right|220px| MMSS [[Inmarsat|Inmarsat-3]] satellite locations]] Mobile satellite systems help connect remote regions, vehicles, ships, people and aircraft to other parts of the world and/or other mobile or stationary communications units, in addition to serving as navigation systems.

=== {{anchor|Research satellites}} Scientific research satellites (commercial and noncommercial) ===
Scientific research satellites provide meteorological information, land survey data (e.g. remote sensing), Amateur (HAM) Radio, and other different scientific research applications such as earth science, marine science, and atmospheric research.

==Classification==
* '''[[Astronomical satellite]]s''' are satellites used for observation of distant planets, galaxies, and other outer space objects.
[[File:HST-SM4.jpeg|thumb|The [[Hubble Space Telescope]]]]
* '''[[Biosatellite]]s''' are satellites designed to carry living organisms, generally for scientific experimentation.
* '''[[Communication satellite]]s''' are satellites stationed in space for the purpose of [[telecommunications]]. Modern communications satellites typically use [[geosynchronous orbit]]s, [[Molniya orbit]]s or [[Low Earth orbit]]s.
* '''Earth observation satellites''' are satellites intended for non-military uses such as [[environment (biophysical)|environmental]] monitoring, [[meteorology]], [[map making]] etc. (See especially [[Earth Observing System]].)
* '''[[Global Navigation Satellite System|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.
* '''[[Killer satellite]]s''' are satellites that are designed to destroy enemy warheads, satellites, and other space assets.
* '''Crewed [[spacecraft]] (spaceships)''' are large satellites able to put [[human]]s into (and beyond) an orbit, and return them to Earth. (The Lunar Module of the U.S. Apollo program was an exception, in that it did not have the capability of returning human occupants to Earth.) Spacecraft including [[spaceplane]]s of [[reusable launch system|reusable systems]] have major [[Spacecraft propulsion|propulsion]] or [[landing]] facilities. They can be used as transport to and from the orbital stations.
* '''[[Miniaturized satellites]]''' are satellites of unusually low masses and small sizes.<ref>{{cite web | page=6 | title=Workshop on the Use of Microsatellite Technologies | url=http://www.unoosa.org/pdf/reports/ac105/AC105_903E.pdf | publisher=[[United Nations]] | year=2008 | access-date=6 March 2008}}</ref> New classifications are used to categorize these satellites: minisatellite (500–1000&nbsp;kg), [[Microsatellite (spaceflight)|microsatellite]] (below 100&nbsp;kg), [[nanosatellite]] (below 10&nbsp;kg).{{citation needed|date=December 2012}}
* '''[[Reconnaissance satellite]]s''' are [[Earth observation satellite]] or [[communications satellite]] deployed for [[military]] or [[espionage|intelligence]] applications. Very little is known about the full power of these satellites, as governments who operate them usually keep information pertaining to their reconnaissance satellites classified.
* '''[[Recovery satellite]]s''' are satellites that provide a recovery of reconnaissance, biological, space-production and other payloads from orbit to Earth.
* '''[[Space-based solar power]] satellites''' are proposed satellites that would collect energy from sunlight and transmit it for use on Earth or other places.
* '''[[Space station]]s''' are artificial orbital structures that are designed for [[human|human beings]] to live on in [[outer space]]. A space station is distinguished from other crewed spacecraft by its lack of major propulsion or landing facilities. Space stations are designed for medium-term living in orbit, for periods of weeks, months, or even years.
[[File:International Space Station after undocking of STS-132.jpg|thumb|International Space Station]]
* '''[[Tether satellite]]s''' are satellites that are connected to another satellite by a thin cable called a [[tether]].
* '''[[Weather satellite]]s''' are primarily used to monitor Earth's weather and [[climate]].<ref>{{cite web|title=Earth Observations from Space |url=http://dels.nas.edu/dels/rpt_briefs/earth_observations_final.pdf |publisher=[[National Academy of Sciences]] |year=2007 |url-status=dead |archive-url=https://web.archive.org/web/20071112000950/http://dels.nas.edu/dels/rpt_briefs/earth_observations_final.pdf |archive-date=12 November 2007}}</ref>

==Orbits==
{{Main|List of orbits}}
{{see also|Geocentric orbit#Types}}

[[File:Orbits around earth scale diagram.svg|thumb|upright=1.6|Various earth orbits to scale; cyan represents low earth orbit, yellow represents medium earth orbit, the black dashed line represents geosynchronous orbit, the green dash-dot line the orbit of [[Global Positioning System]] (GPS) satellites, and the red dotted line the orbit of the [[International Space Station]] (ISS).]]

The first satellite, [[Sputnik 1]], was put into orbit around Earth and was therefore in [[geocentric orbit]]. This is the most common type of orbit by far, with approximately 3,372<ref name="UCS-SatDB">{{cite web|title=UCS Satellite Database|url=http://www.ucsusa.org/nuclear-weapons/space-weapons/satellite-database|publisher=Union of Concerned Scientists|access-date=15 October 2020|date=1 August 2020}}</ref> active artificial satellites orbiting the Earth. Geocentric orbits may be further classified by their altitude, [[inclination]] and [[Orbital eccentricity|eccentricity]].

The commonly used altitude classifications of geocentric orbit are [[Low Earth orbit]] (LEO), [[Medium Earth orbit]] (MEO) and [[High Earth orbit]] (HEO). Low Earth orbit is any orbit below 2,000 [[km]]. Medium Earth orbit is any orbit between 2,000 and 35,786&nbsp;km. High Earth orbit is any orbit higher than 35,786&nbsp;km.

===Centric classifications===
*'''[[galactic centre|Galactocentric orbit]]''': An orbit around the centre of a [[galaxy]]. The [[Sun]] follows this type of orbit about the [[galactic centre]] of the [[Milky Way]].
* '''[[Heliocentric orbit]]''': An orbit around the Sun. In our [[Solar System]], all planets, [[comet]]s, and [[asteroid]]s are in such orbits, as are many artificial satellites and pieces of [[space debris]]. [[Natural satellite#Natural satellites of the Solar System|Moons]] by contrast are not in a heliocentric orbit but rather orbit their parent planet.
* '''[[Geocentric orbit]]''': An orbit around the planet Earth, such as the Moon or [[artificial satellite]]s. Currently there are over 6,542<ref name="UCS-SatDB" /> active artificial satellites orbiting the Earth.
* '''[[Areocentric orbit]]''': An orbit around the planet [[Mars]], such as by [[Moons of Mars|moons]] or [[artificial satellite]]s.

===Altitude classifications===
* '''[[Low Earth orbit]] (LEO)''': Geocentric orbits ranging in altitude from 180&nbsp;km – {{convert|2000|km|mi|abbr=on}}
* '''[[Medium Earth orbit]] (MEO)''': Geocentric orbits ranging in altitude from {{convert|2000|km|mi|abbr=on}} – {{convert|35786|km|mi|abbr=on}}. Also known as an [[intermediate circular orbit]].
* '''[[Geosynchronous orbit]] (GEO)''': Geocentric circular orbit with an altitude of {{convert|35786|km|mi}}. The period of the orbit equals one [[sidereal day]], coinciding with the rotation period of the Earth. The speed is {{convert|3075|m/s|ft/s}}.
* '''[[High Earth orbit]] (HEO)''': Geocentric orbits above the altitude of [[geosynchronous orbit]] {{convert|35786|km|mi|abbr=on}}.
[[File:Orbitalaltitudes.jpg|thumb|upright=1.45|Orbital Altitudes of several significant satellites of earth.]]

===Inclination classifications===
* '''[[Inclined orbit]]''': An orbit whose inclination in reference to the [[equatorial plane]] is not zero degrees.
** '''[[Polar orbit]]''': An orbit that passes above or nearly above both poles of the planet on each revolution. Therefore, it has an inclination of (or very close to) 90 [[degree (angle)|degrees]].
** '''Polar [[sun synchronous orbit]]''': A nearly polar orbit that takes advantage of [[nodal precession]] such that a satellite in such an orbit passes the [[equator]] at the same local time on every pass. Useful for [[image]] taking satellites because [[shadow]]s will be nearly the same on every pass, and for [[Solar observation#Satellites|solar observation satellites]] because they can have a continuous view of the Sun throughout the year.

===Eccentricity classifications===
* '''[[Circular orbit]]''': An orbit that has an [[Orbital eccentricity|eccentricity]] of 0 and whose path traces a [[circle]].
** '''[[Hohmann transfer orbit]]''': An orbit that moves a spacecraft from one approximately circular orbit, usually the orbit of a planet, to another, using two engine [[Impulse (physics)|impulses]]. The [[perihelion]] of the transfer orbit is at the same distance from the Sun as the radius of one planet's orbit, and the [[aphelion]] is at the other. The two rocket burns change the spacecraft's path from one circular orbit to the transfer orbit, and later to the other circular orbit. This maneuver was named after [[Walter Hohmann]].
* '''[[Elliptic orbit]]''': An orbit with an eccentricity greater than 0 and less than 1 whose orbit traces the path of an [[ellipse]].
** '''[[Geosynchronous transfer orbit]]''': An elliptic orbit where the [[perigee]] is at the altitude of a [[Low Earth orbit]] (LEO) and the [[apogee]] at the altitude of a geosynchronous orbit. Satellites use this orbit to transfer to a [[geostationary orbit]].
** '''[[Geostationary transfer orbit]]''': A geosynchronous transfer orbit that is used to transfer to a geostationary orbit.
** '''[[Molniya orbit]]''': A highly eccentric orbit with inclination of 63.4° and [[orbital period]] of half of a [[sidereal day]] (roughly 12 hours). Such a satellite spends most of its time over two designated areas of the [[planet]] (usually Russia and North America).
** '''[[Tundra orbit]]''': A highly eccentric orbit with inclination of 63.4° and orbital period of one sidereal day (roughly 24 hours). Such a satellite spends most of its time over a single designated area of the planet.

===Synchronous classifications===
* '''[[Synchronous orbit]]''': An orbit where the satellite has an orbital period equal to the average [[rotational period]] (earth's is: 23 hours, 56 minutes, 4.091 seconds) of the body being orbited and in the same direction of rotation as that body. To a ground observer such a satellite would trace an [[analemma]] (figure 8) in the sky.
* '''[[Semi-synchronous orbit]] (SSO)''': An orbit with an altitude of approximately {{convert|20200|km|mi|abbr=on}} and an orbital period equal to one-half of the average rotational period (Earth's is approximately 12 hours) of the body being orbited
* '''[[Geosynchronous orbit]] (GSO)''': Orbits with an altitude of approximately {{convert|35786|km|mi|abbr=on}}. Such a satellite would trace an [[analemma]] (figure 8) in the sky.
**'''[[Geostationary orbit]] (GEO)''': A geosynchronous orbit with an inclination of zero. To an observer on the ground this satellite would appear as a fixed point in the sky.<ref>{{cite web | title=Pearl Harbor in Space | first=James | last=Oberg | url=http://www.jamesoberg.com/pearl.html | work=[[Omni (magazine)|Omni]] | date=July 1984 | pages=42–44 | author-link=James Oberg}}</ref>
*** '''[[Clarke orbit]]''': Another name for a geostationary orbit. Named after scientist and writer [[Arthur C. Clarke]].
** '''[[Supersynchronous orbit]]''': A disposal / storage orbit above GSO/GEO. Satellites will drift west. Also a synonym for Disposal orbit.
** '''[[Subsynchronous orbit]]''': A drift orbit close to but below GSO/GEO. Satellites will drift east.
** '''[[Graveyard orbit]]''': An orbit a few hundred kilometers above [[geosynchronous]] that satellites are moved into at the end of their operation.
***'''Disposal orbit''': A synonym for graveyard orbit.
*** '''Junk orbit''': A synonym for graveyard orbit.
* '''[[Areosynchronous orbit]]''': A synchronous orbit around the planet [[Mars]] with an orbital period equal in length to Mars' sidereal day, 24.6229 hours.
* '''[[Areostationary orbit]] (ASO)''': A circular [[areosynchronous orbit]] on the [[equatorial plane]] and about 17000&nbsp;km (10557 miles) above the surface. To an observer on the ground this satellite would appear as a fixed point in the sky.
* '''[[Heliosynchronous orbit]]''': A heliocentric orbit about the Sun where the satellite's orbital period matches the Sun's period of rotation. These orbits occur at a radius of 24,360 [[gigametre|Gm]] (0.1628 [[Astronomical unit|AU]]) around the Sun, a little less than half of the [[orbital radius]] of [[Mercury (planet)|Mercury]].

===Special classifications===
* '''[[Sun-synchronous orbit]]''': An orbit which combines altitude and inclination in such a way that the satellite passes over any given point of the planets' surface at the same local [[solar time]]. Such an orbit can place a satellite in constant sunlight and is useful for [[Satellite imagery|imaging]], [[spy satellite|spy]], and [[weather satellite]]s.
* '''[[Moon orbit]]''': The [[Orbital parameters|orbital characteristics]] of Earth's Moon. Average altitude of {{convert|384403|km|mi|sp=us}}, [[elliptical orbit|elliptical]]–inclined orbit.

=== Pseudo-orbit classifications ===
* '''[[Horseshoe orbit]]''': An orbit that appears to a ground observer to be orbiting a certain planet but is actually in [[Co-orbital satellite|co-orbit]] with the planet. See asteroids [[3753 Cruithne|3753]] (Cruithne) and [[2002 AA29|2002 AA<sub>29</sub>]].
* '''[[Suborbital spaceflight]]''': A maneuver where a spacecraft approaches the height of orbit but lacks the velocity to sustain it.
* '''[[Lunar transfer orbit]] (LTO)'''
* '''[[Prograde orbit]]''': An orbit with an inclination of less than 90°. Or rather, an orbit that is in the same direction as the rotation of the primary.
* '''[[Retrograde orbit]]''': An orbit with an inclination of more than 90°. Or rather, an orbit counter to the direction of rotation of the planet. Apart from those in [[sun-synchronous orbit]], few satellites are launched into retrograde orbit because the quantity of fuel required to launch them is much greater than for a prograde orbit. This is because when the rocket starts out on the ground, it already has an eastward component of velocity equal to the rotational velocity of the planet at its launch [[latitude]].
* '''[[Halo orbit]]''' and '''[[Lissajous orbit]]''': Orbits "around" [[Lagrangian point]]s.

==Subsystems==
The satellite's functional versatility is embedded within its technical components and its operations characteristics. Looking at the "anatomy" of a typical satellite, one discovers two modules.<ref name=Grant&Meadows /> Note that some novel architectural concepts such as [[Fractionated spacecraft]] somewhat upset this taxonomy.

===Spacecraft bus or service module===
The [[Spacecraft bus|bus module]] consists of the following subsystems:

====Structure====
The structural subsystem provides the mechanical base structure with adequate stiffness to withstand stress and vibrations experienced during launch, maintain [[structural integrity]] and stability while on station in orbit, and shields the satellite from extreme temperature changes and [[micro-meteorite]] damage.

====Telemetry====
The [[telemetry]] subsystem (aka Command and Data Handling, C&DH) monitors the on-board equipment operations, transmits equipment operation data to the earth control station, and receives the earth control station's commands to perform equipment operation adjustments.

====Power====
The power subsystem may consist of solar panels to convert solar energy into electrical power, regulation and distribution functions, and batteries that store power and supply the satellite when it passes into the Earth's shadow. Nuclear power sources ([[Radioisotope thermoelectric generator]]) have also been used in several successful satellite programs including the [[Nimbus program]] (1964–1978).<ref>{{cite conference | chapter=Radioisotope-based Nuclear Power Strategy for Exploration Systems Development | volume=813 | pages=334–339 | chapter-url=http://www.lpi.usra.edu/opag/schmidtstaif06.pdf | first1=George | last1=Schmidt | first2=Mike | last2=Houts | title=AIP Conference Proceedings | conference=STAIF Nuclear Symposium | date=16 February 2006| bibcode=2006AIPC..813..334S | doi=10.1063/1.2169210 }}</ref>

====Thermal control====
{{Main|Spacecraft thermal control}}
The thermal control subsystem helps protect electronic equipment from extreme temperatures due to intense sunlight or the lack of sun exposure on different sides of the satellite's body (e.g. [[optical solar reflector]])

====Attitude and orbit control====
{{Main|Attitude control|Spacecraft propulsion}}
The attitude and orbit control subsystem consists of sensors to measure vehicle orientation, control laws embedded in the flight software, and actuators (reaction wheels, [[Spacecraft propulsion|thrusters]]). These apply the [[torque]]s and forces needed to re-orient the vehicle to the desired altitude, keep the satellite in the correct orbital position, and keep antennas pointed in the right directions.

===Communications===
The second major module is the communication payload, which is made up of transponders. A transponder is capable of :
* Receiving [[uplink]]ed radio signals from earth satellite transmission stations (antennas).
* Amplifying received radio signals
* Sorting the input signals and directing the output signals through input/output signal [[multiplexer]]s to the proper [[downlink]] antennas for retransmission to earth satellite receiving stations (antennas).

==End of life==
When satellites reach the end of their mission (this normally occurs within 3 or 4 years after launch), satellite operators have the option of de-orbiting the satellite, leaving the satellite in its current orbit or moving the satellite to a [[graveyard orbit]]. Historically, due to budgetary constraints at the beginning of satellite missions, satellites were rarely designed to be de-orbited. One example of this practice is the satellite [[Vanguard 1]]. Launched in 1958, [[Vanguard 1]], the 4th artificial satellite to be put in Geocentric orbit, was still in orbit {{as of|lc=y|2022|02}},<ref>[https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1958-002B NASA Space Science Data Coordinated Archive Header Vanguard 1], lookup 28.02.2022</ref> as well as the upper stage of its launch rocket.<ref name=ha20130921a>{{cite web |title=Vanguard 1 – Satellite Information |url=http://www.heavens-above.com/SatInfo.aspx?satid=5&lat=0&lng=0&loc=Unspecified&alt=0&tz=UCT |work=Satellite database |publisher=Heavens-Above |access-date=7 March 2015 }}</ref><ref name=ha20130921b>{{cite web |title=Vanguard 1 Rocket – Satellite Information |url=http://www.heavens-above.com/SatInfo.aspx?satid=16&lat=0&lng=0&loc=Unspecified&alt=0&tz=UCT |work=Satellite database |publisher=Heavens-Above |access-date=7 March 2015 }}</ref>

Instead of being de-orbited, most satellites in the first six decades of spaceflight were either left in their current orbit or moved to a [[graveyard orbit]].<ref>
{{cite web
| url=http://www.tethers.com/OrbitalDebris.html
| title=Conventional Disposal Method: Rockets and Graveyard Orbits
| publisher=Tethers }}</ref> As of 2002, the FCC requires all geostationary satellites to commit to moving to a graveyard orbit at the end of their operational life prior to launch.<ref>{{cite web|url=http://www.space.com/spacenews/businessmonday_040628.html |title=FCC Enters Orbital Debris Debate |publisher=Space.com |url-status=dead |archive-url=https://web.archive.org/web/20090724183455/http://www.space.com/spacenews/businessmonday_040628.html |archive-date=24 July 2009}}</ref>

In cases of uncontrolled de-orbiting, the major variable is the [[solar flux]],{{how|date=June 2022}} and minor variables are the components and form factor of the satellite itself, as well as gravitational perturbations generated by the Sun and the Moon. The nominal breakup altitude due to aerodynamic forces and temperatures is 78&nbsp;km, with a range between 72 and 84&nbsp;km. Solar panels, however, are destroyed before any other component at altitudes between 90 and 95&nbsp;km.<ref>{{cite web | url=http://www.satview.org/spacejunk.php?sat_id=34602U | title=Object SL-8 R/B – 29659U – 06060B | work=Forecast for Space Junk Reentry | publisher=Satview | date=11 March 2014}}</ref>

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 reach [[end of life]], as a part of the [[regulatory authority|regulatory process]] of obtaining a launch license.{{citation needed|date=June 2022}}

=== Satellite demisability ===
By the early 2000s, and particularly after the advent of [[CubeSat]]s and increased launches of [[microsatellite|microsats]]—frequently launched to the lower altitudes of [[low Earth orbit]] (LEO)—satellites began to more frequently be designed to demise, or breakup and burnup entirely in the atmosphere.<ref>{{cite journal |title=Material selection for a CubeSat structural bus complying with debris mitigation |first1=EA|last1=Slejko |first2=A|last2=Gregorio |first3=V|last3=Lughi |journal=Advances in Space Research |url=https://www.sciencedirect.com/science/article/abs/pii/S0273117720308383 |year=2021 |volume=67 |issue=5 |pages=1468–1476 |doi=10.1016/j.asr.2020.11.037 |bibcode=2021AdSpR..67.1468S |s2cid=233841294 }}</ref>
For example, [[SpaceX]] [[Starlink]] satellites, the first large satellite internet constellation to exceed 1000 active satellites on orbit in ~2020, are designed<!-- these are the v1.0 sats; the v0.9 sats had at least one component that was not fully demiseable --> to be 100% demisable and burn up completely on atmospheric reentry at end of life, or in the event of an early satellite failure.<ref name=tasia202104>{{cite news |title=Digital Connectivity and Low Earth Orbit Satellite Constellations: Opportunities for Asia and the Pacific |last1=Garrity|first1=John |last2=Husar|first2=Arndt |url=https://think-asia.org/handle/11540/13626 |date=April 2021 |work=think-asia.org }}</ref>

==Launch-capable countries==
{{Main|Timeline of first orbital launches by country}}

This list includes countries with an independent capability to place satellites in orbit, including production of the necessary launch vehicle. Note: many more countries have the capability to design and build satellites but are unable to launch them, instead relying on foreign launch services. This list does not consider those numerous countries, but only lists those capable of launching satellites indigenously, and the date this capability was first demonstrated. The list does not include the [[European Space Agency]], a multi-national state organization, nor private consortiums.

<br />
{| class="sortable wikitable"
|+ First launch by country
|- style="background:#efefef;"
!Order
! Country || Date of first launch || Rocket || Satellite(s)
|-
| scope="row" | 1
|align="left"| [[Soviet Union]] || 4 October 1957 || [[Sputnik (rocket)|Sputnik-PS]] || [[Sputnik 1]]
|-
| scope="row" | 2
|align="left"| [[United States]] || 1 February 1958<!--UTC--> || [[Juno I]] || [[Explorer 1]]
|-
| scope="row" | 3
|align="left"| [[France]] || 26 November 1965 || [[Diamant|Diamant-A]] || [[Astérix (satellite)|Astérix]]
|-
| scope="row" | 4
|align="left"| [[Japan]] || 11 February 1970 || [[Lambda (rocket)|Lambda-4S]] || [[Ohsumi (satellite)|Ohsumi]]
|-
| scope="row" | 5
|align="left"| [[China]] || 24 April 1970 || [[Long March 1]] || [[Dong Fang Hong I]]
|-
| scope="row" | 6
| align="left" | [[United Kingdom]]|| 28 October 1971 ||[[Black Arrow]]||[[Prospero (satellite)|Prospero]]
|-
| scope="row" | 7
| align="left" | [[India]]|| 18 July 1980 ||[[Satellite Launch Vehicle|SLV]]||[[Rohini (satellite)|Rohini RS-1]]
|-
| scope="row" | 8
| align="left" | [[Israel]]|| 19 September 1988 ||[[Shavit 2|Shavit]]||[[Ofeq|Ofeq 1]]
|-
| scope="row" | –{{Ref label|RUS-UKR|1|}}
| align="left" | [[Russia]]|| 21 January 1992 ||[[Soyuz-U]]||[[Kosmos 2175]]
|-
| scope="row" | –{{Ref label|RUS-UKR|1|}}
| align="left" | [[Ukraine]]|| 13 July 1992 ||[[Tsyklon-3]]||[[Strela (satellite)|Strela]]
|-
| scope="row" | 9
| align="left" | [[Iran]]|| 2 February 2009 ||[[Safir (rocket)|Safir-1]]||[[Omid (satellite)|Omid]]
|-
| scope="row" | 10
| align="left" | [[North Korea]]|| 12 December 2012 ||[[Unha-3]]||[[Kwangmyŏngsŏng-3 Unit 2]]
|-
| scope="row" | 11
| align="left" | [[South Korea]]|| 30 January 2013 ||[[Naro-1]]||[[STSAT-2C]]
|-
| scope="row" | 12
| align="left" | [[New Zealand]]|| 12 November 2018 ||[[Electron (rocket)|Electron]]||[[CubeSat]]
|-
|}
<!-- Please do not add Italy, Australia and Bangladesh (they used US launchers) South Korea (used modified Russian rocket), Kazakhstan (provides spaceport for Russian and Ukrainian launcher) and do not delete France, UK, Ukraine. Also, do not make changes to the orders OR do not add numbers under "Order" for Ukraine or Russia – see below, and on talk page, and article Timeline of first orbital launches by country for details. -->

===Attempted first launches===
* The [[United States]] tried in 1957 to launch the first satellite using its own launcher before successfully completing a launch in 1958.{{citation needed|date=June 2022}}
* [[Japan]] tried four times in 1966–1969 to launch a satellite with its own launcher before successfully completing a launch in 1970.
* [[China]] tried in 1969 to launch the first satellite using its own launcher before successfully completing a launch in 1970.
* [[India]], after launching its first national satellite using a foreign launcher in 1975, tried in 1979 to launch the first satellite using its own launcher before succeeding in 1980.{{citation needed|date=June 2022}}
* [[Iraq]] have claimed an orbital launch of a warhead in 1989, but this claim was later disproved.{{#tag:ref|The video tape of a partial launch attempt which was retrieved by [[United Nations Special Commission|UN weapons inspectors]] later surfaced showing that the rocket prematurely exploded 45 seconds after its launch.<ref>{{cite web | url=http://www.thespacereview.com/archive/1498.pdf | title=UNMOVIC report | publisher=United Nations Monitoring, Verification and Inspection Commission | page=434 ff}}</ref><ref>{{cite web | url=https://fas.org/nuke/guide/iraq/deception.htm| title=Deception Activities – Iraq Special Weapons | publisher=FAS | url-status=dead | archive-url=https://web.archive.org/web/19990422131634/https://fas.org/nuke/guide/iraq/deception.htm| archive-date=22 April 1999}}</ref><ref>{{cite web | url=http://www.b14643.de/Spacerockets_1/Rest_World/Al_Abid/Description/Frame.htm | title=Al-Abid LV }}</ref>}}
* [[Brazil]], after launching its first national satellite using a foreign launcher in 1985, tried to launch a satellite using its own [[VLS 1]] launcher three times in 1997, 1999, and 2003, but all attempts were unsuccessful.{{citation needed|date=June 2022}}
* [[North Korea]] claimed a launch of [[Kwangmyŏngsŏng-1]] and [[Kwangmyŏngsŏng-2]] satellites in 1998 and 2009, but U.S., Russian and other officials and weapons experts later reported that the rockets failed to send a satellite into orbit, if that was the goal. The United States, Japan and South Korea believe this was actually a [[ballistic missile]] test, which was a claim also made after North Korea's 1998 satellite launch, and later rejected.<ref>{{cite news |last1=Myers |first1=Steven Lee |title=U.S. Calls North Korean Rocket a Failed Satellite |url=https://www.nytimes.com/1998/09/15/world/us-calls-north-korean-rocket-a-failed-satellite.html |access-date=9 September 2019 |work=The New York Times |date=15 September 1998 |archive-url=https://web.archive.org/web/20181209060829/https://www.nytimes.com/1998/09/15/world/us-calls-north-korean-rocket-a-failed-satellite.html |archive-date=9 December 2018}}</ref> The first (April 2012) launch of [[Kwangmyŏngsŏng-3]] was unsuccessful, a fact publicly recognized by the DPRK. However, the December 2012 launch of the "second version" of [[Kwangmyŏngsŏng-3]] was successful, putting the DPRK's first confirmed satellite into orbit.
* [[South Korea]] ([[Korea Aerospace Research Institute]]), after launching their first national satellite by foreign launcher in 1992, unsuccessfully tried to launch its own launcher, the [[Korea Space Launch Vehicle|KSLV (Naro)-1]], (created with the assistance of Russia) in 2009 and 2010 until success was achieved in 2013 by Naro-3.
* The First European multi-national state organization [[European Launcher Development Organisation|ELDO]] tried to make the orbital launches at [[Europa (rocket)|Europa I and Europa II]] rockets in 1968–1970 and 1971 but stopped operation after failures.

===Other notes===
* {{note|RUS-UKR}} [[Russia]] and [[Ukraine]] were parts of the Soviet Union and thus inherited their launch capability without the need to develop it indigenously. Through the Soviet Union they are also on the number one position in this list of accomplishments.
* [[France]], the [[United Kingdom]], and Ukraine launched their first satellites by own launchers from foreign [[spaceport]]s.
* Some countries such as [[South Africa]], [[Spain]], [[Italy]], [[Germany]], [[Canada]], [[Australia]], [[Argentina]], [[Egypt]] and private companies such as [[OTRAG]], have developed their own launchers, but have not had a successful launch.
* Only twelve, countries from the list below (USSR, USA, France, Japan, China, UK, India, Russia, Ukraine, Israel, Iran and North Korea) and one regional organization (the [[European Space Agency]], ESA) have independently launched satellites on their own indigenously developed launch vehicles.
* Several other countries, including [[Brazil]], [[Argentina]], [[Pakistan]], [[Romania]], [[Taiwan]], [[Indonesia]], [[Australia]], [[Malaysia]], [[Turkey]] and [[Switzerland]]<!--SOAR unmanned mini-shuttle launcher from airliner--> are at various stages of development of their own small-scale launcher capabilities.

===Launch capable private entities===
{{unreferenced section|date=June 2022}}
[[Orbital Sciences Corporation]] launched a satellite into orbit on the [[Pegasus (rocket)|Pegasus]] in 1990. [[SpaceX]] launched a satellite into orbit on the [[Falcon 1]] in 2008. [[Rocket Lab]] launched three cubesats into orbit on the [[Electron (rocket)|Electron]] in 2018.

==First satellites of countries==
{{main|Timeline of first artificial satellites by country}}
[[File:Space capabilities - launch and satellite.png|thumb|upright=1.35|
[[File:Space capabilities - launch and satellite.png|thumb|upright=1.35|
{{legend|#007F00|[[Timeline of first orbital launches by country|orbital launch]] and satellite operation}}
{{legend|#007F00|[[Timeline of first orbital launches by country|orbital launch]] and satellite operation}}
{{legend|#00FF00|satellite operation, launched by foreign supplier}}
{{legend|#00FF00|satellite operation, launched by foreign supplier}}
{{legend|#FF8040|satellite in development}}
{{legend|#FF8040|satellite in development}}
{{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,<ref>{{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}}</ref> it was launched aboard an [[United States|American]] rocket from an American spaceport. The same goes for Australia, who launched 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 of Great Britain and Northern Ireland|United Kingdom]].<ref>{{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}}</ref> The first Italian satellite [[San Marco 1]] 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]].<ref>{{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}}</ref> By similar occasions, almost all further first national satellites was launched by foreign rockets.
{{legend|#FF0000|[[Comparison of small lift launch systems|orbital launch]] project at advanced stage or indigenous [[ballistic missile]]s deployed}}]]


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 reach [[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]].<ref>{{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. |date=2019-02-22 |publisher=ABC-CLIO |isbn=978-1-61069-094-2 |pages=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}}</ref>
While Canada was the third country to build a satellite which was launched into space,<ref>{{cite book |title=Space Programs Outside the United States |first=Daphne |last=Burleson | publisher=[[McFarland & Company]] |page=43 |year=2005 |isbn=978-0-7864-1852-7}}</ref> it was launched aboard an [[United States|American]] rocket from an American spaceport. The same goes for Australia, who launched 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 of Great Britain and Northern Ireland|United Kingdom]].<ref>{{cite book | title=Blazing the Trail | author=Mike Gruntman | page=426 | isbn=978-1-56347-705-8 | year=2004 | publisher=[[American Institute of Aeronautics and Astronautics]] | author-link=Mike Gruntman }}</ref> The first Italian satellite [[San Marco 1]] 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]].<ref>{{cite book | title=Europe's Space Programme |page=114 | first=Brian |last=Harvey |year=2003 |publisher=[[Springer Science+Business Media]] | isbn=978-1-85233-722-3 }}</ref> By similar occasions, almost all further first national satellites was launched by foreign rockets.


By the early 2000s, and particularly after the advent of [[CubeSat]]s and increased launches of [[microsatellite|microsats]]—frequently launched to the lower altitudes of [[low Earth orbit]] (LEO)—satellites began to more frequently be designed to demise, or breakup and burnup entirely in the atmosphere.<ref>{{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}}</ref>
===Attempted first satellites===
For example, [[SpaceX]] [[Starlink]] satellites, the first large satellite internet constellation to exceed 1000 active satellites on orbit in ~2020, are designed<!-- these are the v1.0 sats; the v0.9 sats had at least one component that was not fully demiseable --> to be 100% demisable and burn up completely on atmospheric reentry at end of life, or in the event of an early satellite failure.<ref name="tasia202104">{{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}}</ref>
* [[United States]] tried unsuccessfully to launch its first satellite in 1957; they were successful in 1958.
==Components==
* [[China]] tried unsuccessfully to launch its first satellite in 1969; they were successful in 1970.
=== Orbit and attitude control ===
* [[Chile]] tried unsuccessfully in 1995 to launch its first satellite [[FASat-Alfa]] by foreign rocket; in 1998 they were successful.†
{{Main|Spacecraft propulsion|Attitude control}}
* [[North Korea]] has tried in 1998, 2009, 2012 to launch satellites, first successful launch on 12 December 2012.<ref>{{cite news | url=http://www.nbcnews.com/id/50167891 | title=North Korea says it successfully launched controversial satellite into orbit | publisher=[[NBC News]] | date=12 December 2012 }}</ref>
[[File:Ion Engine Test Firing - GPN-2000-000482.jpg|thumb|Firing of ''[[Deep Space 1]]''<nowiki/>'s ion thruster]]
* [[Libya]] since 1996 developed its own national [[Libsat]] satellite project with the goal of providing telecommunication and remote sensing services<ref>{{cite web|url=http://www.libsat.ly/index.php|title=Libsat – Libyan Satellite Project|author=Wissam Said Idrissi|work=libsat.ly}}</ref> that was postponed after the fall of [[Gaddafi]].
Most satellites use chemical or [[ion propulsion]] to [[Orbital maneuver|adjust]] or [[Orbital station-keeping|maintain their orbit]],<ref name=":0" />{{Rp|pages=|page=78}} coupled with [[Reaction wheel|reaction wheels]] to control its [[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. Without orbit and orientation control, satellites in orbit will not be able to communicate with [[Ground station|ground stations]] on Earth.<ref name=":0" />{{Rp|pages=75–76}}
* [[Belarus]] tried unsuccessfully in 2006 to launch its first satellite [[BelKA]] by foreign rocket.†
†-note: Both Chile and Belarus used Russian companies as principal contractors to build their satellites, they used Russian-Ukrainian manufactured rockets and launched either from Russia or Kazakhstan.


Chemical thrusters on satellites usually use [[monopropellant]] (one-part) or [[bipropellant]] (two-parts) that are [[Hypergolic propellant|hypergolic]]. Hypergolic means able to combust spontaneously in contact to each other or to a [[Catalysis|catalyst]]. The most commonly used propellant mixtures on satellites are [[hydrazine]]-based monopropellant or [[monomethylhydrazine]]–[[dinitrogen tetroxide]] bipropellant. Ion thrusters on satellites usually are [[Hall-effect thruster|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 is very small (around {{Cvt|0.5|N|disp=or|sigfig=1}}), 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.<ref name=":0" />{{Rp|pages=78–79}}
===Planned first satellites===
* [[Armenia]] founded [[ArmCosmos]] in 2012<ref>{{cite web|url=http://telecom.arka.am/en/news/technique/satellite_department_to_be_set_up_in_armenia_s_national_telecommunication_center/|title=Satellite department to be set up in Armenia's national telecommunication center|work=arka.am}}</ref> and announced an intention to create and launch the countries first telecommunication satellite, named [[ArmSat]]. The investment estimate is $250&nbsp;million and potential contractors for building the satellite includes Russia, China and Canada.<ref>{{cite web|url=http://asbarez.com/112629/canadas-mda-ready-to-help-armenia-launch-first-comsat/|title=Canada's MDA Ready to Help Armenia Launch First Comsat|work=Asbarez News|date=9 August 2013}}</ref><ref>{{cite web|url=http://arka.am/en/news/technology/china_keen_on_armenian_satellite_launch_project/|title=China keen on Armenian satellite launch project|work=arka.am}}</ref>
* [[Cambodia]]'s Royal Group plans to purchase for $250–350&nbsp;million and launch in the beginning of 2013 the telecommunication satellite.<ref>{{cite web | url=http://4infos.blogspot.com/2011/04/royal-group-receives-right-to-launch.html | title=Royal Group receives right to launch first Cambodia satellite | date=19 April 2011 }}</ref>
* [[Cayman Islands]]'s [[Global IP Cayman]] private company plans to launch [[GiSAT-1]] geostationary communications satellite in 2018.
* [[Democratic Republic of Congo]] ordered at November 2012 in China ([[China Academy of Space Technology|Academy of Space Technology (CAST)]] and [[Great Wall Industry Corporation|Great Wall Industry Corporation (CGWIC)]]) the first telecommunication satellite [[CongoSat]]-1 which will be built on [[DFH-4]] [[satellite bus]] platform and will be launched in China till the end of 2015.<ref>{{cite web|url=http://usa.chinadaily.com.cn/china/2012-11/18/content_15938787.htm|title=China to launch second African satellite-Science-Tech-chinadaily.com.cn|work=China Daily}}</ref>
* [[Croatia]] has a goal to construct a satellite by 2013–2014. Launch into Earth orbit would be done by a foreign provider.<ref name="CroatianSpace">{{cite web | url=http://www.astronautika.com/vremenik | title=Vremenik | publisher=Astronautica }}</ref>
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* [[Ethiopia]]n Space Science Society<ref>{{cite web|url=http://www.ethiosss.org.et/index.php/en/ |title=ESSS |work=ethiosss.org.et |url-status=dead |archive-url=https://web.archive.org/web/20150103052723/http://www.ethiosss.org.et/index.php/en/ |archive-date=3 January 2015}}</ref> planning the QB50-family research CubeSat [[ET-SAT]] by help of Belgian [[Von Karman Institute]] till 2015<ref>{{cite web|url=http://www.ethioabay.com/2013/02/ethiopia-to-design-and-construct-first.html|title=Ethiopia to design and construct first Satellite|work=ethioabay.com}}</ref> and the small (20–25 kg) Earth observation and remote sensing satellite [[Ethosat 1]] by help of Finnish Space Technology and Science Group till 2019.<ref>{{cite web|url=http://www.spacetsg.com/index.php/news/134-space-technology-and-science-group-finland-stsg-oy-to-design-develop-and-launch-first-ethiopian-research-satellite-ethosat1 |title=Space Technology and Science Group Oy – Finland (STSG Oy) to design, develop and launch first Ethiopian research satellite – ETHOSAT1 |author=Kasia Augustyniak |work=spacetsg.com |url-status=dead |archive-url=https://web.archive.org/web/20150403115213/http://www.spacetsg.com/index.php/news/134-space-technology-and-science-group-finland-stsg-oy-to-design-develop-and-launch-first-ethiopian-research-satellite-ethosat1 |archive-date=3 April 2015}}</ref>
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* [[Ireland]]'s team of [[Dublin Institute of Technology]] intends to launch the first Irish satellite within European University program CubeSat QB50.<ref>{{cite news | url=http://www.independent.ie/irish-news/students-hope-to-launch-first-ever-irish-satellite-26838594.html | title=Students hope to launch first ever Irish satellite | first=Allison | last=Bray | work=The Independent | location=Ireland | date=1 December 2012}}</ref>
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* [[Jordan]]'s first satellite to be the private amateur [[pocketqube]] SunewnewSat.<ref>{{cite web|url=https://www.behance.net/gallery/21688567/Sunewnew%7ctitle=Behance%7cwork=behance.net|title=Behance|access-date=25 June 2015}}</ref><ref>{{cite web|url=http://www.pocketqubeshop.com/meet-the-pocketqube-team-sunewnewsat/|title=Meet the PocketQube team: Sunewnewsat|work=PocketQube Shop}}</ref><ref>[http://www.pocketqubeshop.com/blogs/news/13589310-meet-the-pocketqube-team-sunewnewsat Team Interview] {{webarchive |url=https://web.archive.org/web/20140819083716/http://www.pocketqubeshop.com/blogs/news/13589310-meet-the-pocketqube-team-sunewnewsat |date=19 August 2014}}</ref>
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* [[Latvia]]'s the 5 kg nano-satellite [[:lv:Venta-1|Venta-1]] is built in Latvia in cooperation with the German engineers. The data received from satellite will be received and processed in Irbene radioastronomical centre (Latvia); satellite will have software-defined radio capabilities. "Venta-1" will serve mainly as a means for education in Ventspils University College with additional functions, including an automatic system of identification of the ships of a sailing charter developed by OHB-System AG. The launch of the satellite was planned for the end of 2009 using the Indian carrier rocket. Due to the financial crisis, the launch has been postponed until late 2011.<ref>{{cite web | url=http://www.vatp.lv/latvijas-pirmais-satelits-venta-1 | title=SLatvijas pirmais satelīts "Venta-1" | publisher=VATP | access-date=30 April 2011}}</ref> Started preparations to produce the next satellite "Venta-2". "Venta-1" started 23 June 2017. with Indian launch vehicle [[PSLV-XL]]<ref>http://space.skyrocket.de/doc_sdat/venta-1.htm {{Bare URL inline|date=May 2022}}</ref>
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* [[Republic of Moldova]]'s first [[remote sensing]] satellite plans to start in 2013 by Space centre at national Technical University.<ref>{{cite web | url=http://www.comelpro.com/publications.html | title=Наши публикации | publisher=ComelPro }}</ref>
* [[Myanmar]] plans to purchase for $200&nbsp;million their own telecommunication satellite.<ref>{{cite web | url=http://www.mizzima.com/news/breaking-and-news-brief/5414-burma-to-launch-first-state-owned-satellite-expand-communications.html | title=Burma to launch first state-owned satellite, expand communications | work=News | publisher=Mizzima | date=14 June 2011 | url-status=dead | archive-url=https://web.archive.org/web/20110617071634/http://www.mizzima.com/news/breaking-and-news-brief/5414-burma-to-launch-first-state-owned-satellite-expand-communications.html | archive-date=17 June 2011}}</ref>
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* [[Nepal]] stated that planning to launch of own telecommunication satellite before 2015 by help of India or China.<ref>{{cite web|url=https://nabinchaudhary1.wordpress.com/2013/06/03/a-step-for-nepal-own-satellite/|title=A step for Nepal own Satellite|work=Nabin Chaudhary|date=3 June 2013}}</ref><ref>{{cite web|url=http://www.china.org.cn/world/2013-06/08/content_29071844.htm|title=Nepal: No satellite launching plan so far|author=张军棉|work=china.org.cn}}</ref><ref>{{cite news|url=http://www.thehindu.com/news/international/south-asia/nepal-may-turn-to-china-for-satellite-plan/article4686835.ece|title=Nepal may turn to China for satellite plan|author=Ananth Krishnan|newspaper=The Hindu|date=5 May 2013}}</ref>
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* [[Nicaragua]] ordered for $254&nbsp;million at November 2013 in China the first telecommunication satellite [[Nicasat]]-1 (to be built at DFH-4 satellite bus platform by CAST and CGWIC), that planning to launch in China at 2016.<ref>{{cite web|url=http://www.telecompaper.com/news/nicaragua-says-nicasat-1-satellite-still-set-for-2016-launch--978722|title=Nicaragua says Nicasat-1 satellite still set for 2016 launch|work=telecompaper.com}}</ref>
* [[Paraguay]] under new [[Agencia Espacial del Paraguay –- AEP]] airspace agency plans first Eart observation satellite.<ref>{{cite web|url=http://www.bnamericas.com/news/telecommunications/paraguay-to-vote-on-aerospace-agency-bill-in-2014|title=Paraguay to vote on aerospace agency bill in 2014|author=Zachary Volkert|work=BNamericas|date=26 December 2013}}</ref><ref>{{cite web|url=http://www.globalpost.com/dispatch/news/regions/americas/140627/paraguay-space-program-agency|title=Why a little country like Paraguay is launching a space program|work=GlobalPost}}</ref>
* <!-- need to SkCube pagehttps://en.wikipedia.org/w/index.php?title=Satellite&action=submit * [[Slovakia]]n [[Slovak Organisation for Space Activities|Organisation for Space Activities (SOSA)]]<ref>{{cite web|url=http://sosa.sk/|title=SOSA|access-date=25 June 2015}}</ref> together with [[University of Žilina]] and [[Slovak University of Technology]] developing the first national satellite [[SkCube]]<ref name="skcube">{{cite web|url=http://skcube.sk/en/|archive-url=https://web.archive.org/web/20150626131100/http://skcube.sk/en/|url-status=dead|archive-date=26 June 2015|title=skCUBE –- prvá slovenská družica " English |access-date=12 November 2016}}</ref> under European University program CubeSat QB50 since 2012 aiming to launch them in 2016.<ref>{{cite web |url= http://www.gospace.sk/gospace-portfolio/sattelite-skcube/ |title= SATELLITE skCUBE |access-date= 25 June 2015 |url-status=dead |archive-url= https://web.archive.org/web/20150626142315/http://www.gospace.sk/gospace-portfolio/sattelite-skcube/ |archive-date= 26 June 2015 }}</ref>"[[skCUBE]]" started 23 June 2017. with Indian launch vehicle PSLV-XL<ref>http://space.skyrocket.de/doc_sdat/skcube.htm {{Bare URL inline|date=May 2022}}</ref> -->[[Serbia]]'s first satellite [[Tesla-1]] was designed, developed and assembled by nongovernmental organisations in 2009 but still remains unlaunched.
* [[Sri Lanka]] has a goal to construct two satellites beside of rent the national [[SupremeSAT]] payload in Chinese satellites. Sri Lankan Telecommunications Regulatory Commission has signed an agreement with Surrey Satellite Technology Ltd to get relevant help and resources. Launch into Earth orbit would be done by a foreign provider.<ref name="SLASA1">{{cite web | url=http://www.satellitetoday.com/st/topnews/SSTL-Contracted-to-Establish-Sri-Lanka-Space-Agency_32873.html | title=SSTL Contracted to Establish Sri Lanka Space Agency | work=Satellite Today | access-date=28 November 2009}}</ref><ref name="SLASA2">{{cite web | url=http://www.adaderana.lk/news.php?nid=6132 | title=SSTL contracted to establish Sri Lanka Space Agency | publisher=Adaderana | access-date=28 November 2009 }}</ref>
* [[Syria]]n Space Research Center developing CubeSat-like small first national satellite since 2008.<ref>{{cite web|url=http://www.souria.com/ar/em/hl/article.asp?at=19371 |title=Syria on the Internet |work=souria.com |url-status=dead |archive-url=https://web.archive.org/web/20150403144451/https://www.souria.com/ar/em/hl/article.asp?at=19371 |archive-date=3 April 2015}}</ref>
* [[Tunisia]] is developing its first satellite, [[ERPSat01]]. Consisting of a CubeSat of 1&nbsp;kg mass, it will be developed by the [[University of Sfax|Sfax]] School of Engineering. ERPSat satellite is planned to be launched into orbit in 2013.<ref name="IEEE">{{cite book | work=Explore | publisher=IEEE | doi=10.1109/RAST.2009.5158292 | title=2009 4th International Conference on Recent Advances in Space Technologies | pages= 750–755| year=2009 | last1=Hamrouni | first1=C. | last2= Neji| first2= B.| last3= Alimi| first3= A. M.| last4= Schilling| first4= K.| isbn= 978-1-4244-3626-2| s2cid=34741975 }}</ref>
* [[Uzbekistan]]'s State Space Research Agency ([[UzbekCosmos]]) announced in 2001 about intention of launch in 2002 first remote sensing satellite.<ref>{{cite web | url=http://www.satnews.com/stories/3may2001-4.html | title= Uzbekistan Planning First Satellite | publisher=Sat News | date=18 May 2001 | url-status=dead | archive-url=https://web.archive.org/web/20010713173220/http://www.satnews.com/stories/3may2001-4.html | archive-date=13 July 2001}}</ref> Later in 2004 was stated that two satellites (remote sensing and telecommunication) will be built by Russia for $60–70&nbsp;million each<ref>{{cite web | url=http://www.redorbit.com/news/space/62825/uzbekistan_planning_to_launch_two_satellites_with_russian_help/ | title=Uzbekistan Planning to Launch Two Satellites With Russian Help | publisher=Red Orbit | date=8 June 2004 | url-status=dead | archive-url=https://web.archive.org/web/20120112110319/http://www.redorbit.com/news/space/62825/uzbekistan_planning_to_launch_two_satellites_with_russian_help/ | archive-date=12 January 2012}}</ref>
* [[Bangladesh]] launched [[Bangabandhu-1]], its first satellite, for geostationary communications and broadcasting. It was manufactured by [[Thales Alenia Space]] and launched on 12 May 2018 and launched by [[Falcon 9 Block 5]] of SpaceX.


==Attacks on satellites==
=== Power ===
{{Main|Batteries in space|Nuclear power in space|Solar panels on spacecraft}}
{{Further|Anti-satellite weapon}}
[[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|radiators]] on the right]]
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|radioisotope thermoelectric generators]]. [[Slip ring|Slip rings]] 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]].<ref name=":0" />{{Rp|pages=88–89}}


===Communications===
Since the mid-2000s, satellites have been hacked by militant organizations to broadcast propaganda and to pilfer classified information from military communication networks.<ref>{{cite web|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 |first=Dan |last=Morrill |publisher=[[ITtoolbox]] |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}}</ref><ref>{{cite news | title=AsiaSat accuses Falungong of hacking satellite signals | url=http://www.accessmylibrary.com/coms2/summary_0286-5205866_ITM | agency=[[Press Trust of India]] | date=22 November 2004 }}</ref>
{{Main|Transponder (satellite communications)}}
*


== Applications ==
For testing purposes, satellites in low earth orbit have been destroyed by ballistic missiles launched from earth. [[Russia]], [[United States]], [[China]] and [[India]] have demonstrated the ability to eliminate satellites.<ref name="asat">{{cite news | first1=William J. | last1=Broad | first2=David E. | last2=Sanger | title=China Tests Anti-Satellite Weapon, Unnerving U.S. | url=https://www.nytimes.com/2007/01/18/world/asia/18cnd-china.html | work=[[The New York Times]] | date=18 January 2007 }}</ref> In 2007 the [[China|Chinese]] military shot down an aging weather satellite,<ref name="asat"/> followed by the [[US Navy]] shooting down a [[NRO L-21|defunct spy satellite]] in February 2008.<ref>{{cite web | title=Navy Missile Successful as Spy Satellite Is Shot Down | url=http://www.popularmechanics.com/blogs/science_news/4251430.html | work=[[Popular Mechanics]] | year=2008 | access-date=25 March 2008}}</ref> On 27 March 2019 India shot down a live test satellite at 300&nbsp;km altitude in 3 minutes. [[India]] became the fourth country to have the capability to destroy live satellites.<ref>{{Cite web|url=https://www.theweek.in/news/india/2019/03/27/india-test-anti-satellite-weapon-modi.html|title=India successfully tests anti-satellite weapon: Modi|website=The Week|language=en|access-date=27 March 2019}}</ref><ref>{{Cite web|url=https://thediplomat.com/2016/06/indias-anti-satellite-weapons/|title=India's Anti-Satellite Weapons|last=Diplomat|first=Harsh Vasani, The|website=The Diplomat|language=en-US|access-date=27 March 2019}}</ref>


===Jamming===
=== Earth observation ===
{{Main|Earth observation satellite}}
{{See also|Radio jamming}}
[[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]]
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,<ref>{{cite web|first=Jeremy |last=Singer |title=U.S.-Led Forces Destroy GPS Jamming Systems in Iraq |url=http://www.space.com/news/gps_iraq_030325.html |publisher=[[Space.com]] |year=2003 |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}}</ref><ref>{{cite web|first=Bob |last=Brewin |title=Homemade GPS jammers raise concerns |url=http://www.computerworld.com/securitytopics/security/story/0,10801,77702,00.html |work=[[Computerworld]] |year=2003 |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}}</ref> but satellite phone and television signals have also been subjected to jamming.<ref>{{cite web | title=Iran government jamming exile satellite TV | url=http://www.iranfocus.com/modules/news/article.php?storyid=2852 | work=[[Iran Focus]] | year=2008 | access-date=25 March 2008}}</ref><ref>{{cite web|title=Libya Pinpointed as Source of Months-Long Satellite Jamming in 2006 |url=http://www.space.com/spacenews/businessmonday_070409.html |first=Peter de |last=Selding |year=2007 |publisher=[[Space.com]] |archive-url=https://web.archive.org/web/20080429193429/http://www.space.com/spacenews/businessmonday_070409.html |archive-date=29 April 2008 |url-status=live}}</ref>
Earth observation satellites is 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 satellites' data is most used in [[archaeology]], [[cartography]], [[environmental monitoring]], [[meteorology]], and [[reconnaissance]] applications.{{Cn|date=July 2022}} As of 2021, there are over 950 Earth observation satellites, with the largest number of satellites operated [[Planet Labs]].<ref>{{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/ |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}}</ref>


[[Weather satellite|Weather satellites]] 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.<ref>NASA, [http://earthobservatory.nasa.gov/Drought/ Drought.] {{webarchive|url=https://web.archive.org/web/20080819121047/http://earthobservatory.nasa.gov/Drought/|date=19 August 2008}} Retrieved on 4 July 2008 {{PD-notice}}</ref> Anthropogenic emissions can be monitored by evaluating data of tropospheric NO<sub>2</sub> and SO<sub>2</sub>.{{Cn|date=July 2022}}
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 that enables them to pinpoint the source of any carrier and manage the transponder space effectively. {{Citation needed|date=September 2011}}


=== Communication ===
==Earth observation==
{{main|Earth observation satellite}}
{{Main|Communications satellite}}
{{Excerpt|Communications satellite|files=no|hat=no}}


=== Navigation ===
During the last five decades, space agencies have sent thousands of space crafts, space capsules, or satellites to the universe. In fact, weather forecasters make predictions on the weather and natural calamities based on observations from these satellites.<ref>{{Cite web|url=http://nas-sites.org/earthobservations/report/|title=Earth Observations from Space " Earth Observations from Space|website=nas-sites.org|language=en-US|access-date=28 November 2018|archive-date=29 November 2018|archive-url=https://web.archive.org/web/20181129054403/http://nas-sites.org/earthobservations/report/|url-status=dead}}</ref>
{{Main|Satellite navigation}}
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


=== Telescope ===
The National Aeronautics and Space Administration (NASA)<ref>{{Cite web|url=http://www.nationalacademies.org/|title=Home {{!}} The National Academies of Sciences, Engineering, and Medicine {{!}} National-Academies.org {{!}} Where the Nation Turns for Independent, Expert Advice|website=www.nationalacademies.org|access-date=28 November 2018}}</ref> requested the [[National_academy#United_States|National Academies]] to publish a report, "Earth Observations from Space; The First 50 Years of Scientific Achievements", in 2008. It described how the capability to view the whole globe simultaneously from satellite observations revolutionized studies about the planet Earth. This development brought about a new age of combined Earth sciences. The National Academies report concluded that continuing Earth observations from the galaxy are necessary to resolve scientific and social challenges in the future.<ref>{{Cite book|last=Council|first=National Research|date=17 December 2008|title=Earth Observations from Space|url=https://www.nap.edu/catalog/11991/earth-observations-from-space-the-first-50-years-of-scientific|language=en|doi=10.17226/11991|isbn=978-0-309-11095-2}}</ref>
{{Main|Space telescope}}
[[Astronomical satellite]]s are satellites used for observation of distant planets, galaxies, and other outer space objects


=== NASA ===
=== Experimental ===
[[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.
{{See also|Earth Observing System}}
The NASA introduced an Earth Observing System (EOS)<ref>{{Cite web|url=https://earthdata.nasa.gov/about|title=About EOSDIS {{!}} Earthdata|website=earthdata.nasa.gov|language=en|access-date=28 November 2018}}</ref> composed of several satellites, science component, and data system described as the Earth Observing System Data and Information System (EOSDIS). It disseminates numerous science data products as well as services designed for interdisciplinary education. EOSDIS data can be accessed online and accessed through File Transfer Protocol (FTP) and Hyper Text Transfer Protocol Secure (HTTPS).<ref>{{Cite web|url=https://earthdata.nasa.gov/earth-observation-data|title=Earth Observation Data {{!}} Earthdata|website=earthdata.nasa.gov|language=en|access-date=28 November 2018}}</ref> Scientists and researchers perform EOSDIS science operations within a distributed platform of multiple interconnected nodes or Science Investigator-led Processing Systems (SIPS) and discipline-specific Distributed Active Archive Centers (DACCs).<ref>{{Cite web|url=https://earthdata.nasa.gov/about/daacs|title=EOSDIS Distributed Active Archive Centers (DAACs) {{!}} Earthdata|website=earthdata.nasa.gov|language=en|access-date=28 November 2018}}</ref>


=== ESA ===
=== Weapon ===
{{Main|Space weapon|Anti-satellite weapon}}
Since the mid-2000s, satellites have been hacked by militant organizations to broadcast propaganda and to pilfer classified information from military communication networks.<ref>{{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]]}}</ref><ref>{{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 |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=live }}</ref> For testing purposes, satellites in low earth orbit have been destroyed by ballistic missiles launched from earth. [[Russia]], [[United States]], [[China]] and [[India]] have demonstrated the ability to eliminate satellites.<ref name="asat">{{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 |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 }}</ref> In 2007 the [[China|Chinese]] military shot down an aging weather satellite,<ref name="asat" /> followed by the [[US Navy]] shooting down a [[NRO L-21|defunct spy satellite]] in February 2008.<ref>{{cite web |year=2008 |title=Navy Missile Successful as Spy Satellite Is Shot Down |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=live }}</ref> On 27 March 2019 India shot down a live test satellite at 300&nbsp;km altitude in 3 minutes. [[India]] became the fourth country to have the capability to destroy live satellites.<ref>{{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 |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 }}</ref><ref>{{Cite web |last=Diplomat |first=Harsh Vasani, The |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 }}</ref>


==Pollution and interference==
The European Space Agency<ref>{{Cite web|url=https://www.esa.int/ESA|title=ESA|last=esa|publisher=European Space Agency|language=en-GB|access-date=28 November 2018}}</ref> have been operating Earth Observation satellites since the launch of Meteosat 1 in November 1977.<ref>{{Cite web|url=https://www.esa.int/About_Us/Welcome_to_ESA/ESA_history/50_years_of_Earth_Observation|title=50 years of Earth Observation|website=ESA|language=en|access-date=21 August 2019}}</ref> ESA currently has plans to launch a satellite equipped with an artificial intelligence (AI) processor that will allow the spacecraft to make decisions on images to capture and data to transmit to the Earth.<ref name="SpaceNews.com">{{Cite news|url=https://spacenews.com/esa-preps-earth-observation-satellite-with-onboard-ai-processor/|title=ESA preps Earth observation satellite with onboard AI processor |date=13 November 2018|work=SpaceNews.com|access-date=28 November 2018|language=en-US}}</ref> BrainSat will use the Intel Myriad X vision processing unit (VPU). The launching will be scheduled in 2019. ESA director for Earth Observation Programs Josef Aschbacher made the announcement during the PhiWeek in November 2018.<ref>{{Cite news|url=https://newsroom.intel.com/press-kits/movidius-myriad-x-vpu/|title=Movidius Myriad X VPU {{!}} Intel Newsroom|work=Intel Newsroom|access-date=28 November 2018|language=en-US}}</ref> This is the five-day meet that focused on the future of Earth observation. The conference was held at the ESA Center for Earth Observation in Frascati, Italy.<ref name="SpaceNews.com"/> ESA also launched the PhiLab, referring to the future-focused team that works to harness the potentials of AI and other disruptive innovations.<ref>{{Cite web|url=http://phiweek.esa.int/|title=The ESA Earth Observation Φ-week EO Open Science and FutureEO|website=phiweek.esa.int|language=en|access-date=28 November 2018}}</ref> Meanwhile, the ESA also announced that it expects to commence the qualification flight of the Space Rider space plane in 2021. This will come after several demonstration missions.<ref>{{Cite news|url=https://spacenews.com/esa-targets-2021-for-space-rider-demo-flight/|title=ESA targets 2021 for Space Rider demo flight |date=13 November 2018|work=SpaceNews.com|access-date=28 November 2018|language=en-US}}</ref> Space Rider is the sequel of the Agency's Intermediate Experimental vehicle (IXV) which was launched in 2015. It has the capacity payload of 800 kilograms for orbital missions that will last a maximum of two months.<ref>{{Cite web|url=https://www.esa.int/Our_Activities/Space_Transportation/IXV|title=IXV|last=esa|publisher=European Space Agency|language=en-GB|access-date=28 November 2018}}</ref>
[[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<ref name="10.1038/s41550-022-01655-6">{{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}}</ref>]]
Issues like [[space debris]], radio and [[light pollution]] are increasing in magnitude and at the same time lack progress in national or international regulation.<ref name="sp1">{{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 }}</ref><ref name="10.1038/s41550-022-01655-6" /> Space debris poses dangers to spacecraft<ref>{{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 }}</ref><ref name="physUT">{{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 }}</ref> (including satellites)<ref name="physUT" /><ref>{{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 }}</ref> in or crossing geocentric orbits and have the potential to drive a [[Kessler syndrome]]<ref>{{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 }}</ref> which could potentially curtail humanity from conducting space endeavors in the future by making such nearly impossible.<ref>{{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 }}</ref><ref>{{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 }}</ref>


With the increase in numbers 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.<ref name="iau">{{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 }}</ref><ref>{{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 }}</ref><ref>{{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 }}</ref><ref>{{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}}</ref><ref>{{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 }}</ref> 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.<ref>{{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 }}</ref><ref>{{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 }}</ref> The IAU is establishing<!--until 1 April 2022--> a center (CPS) to coordinate or aggregate measures to mitigate such detrimental effects.<ref>{{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 }}</ref><ref>{{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 }}</ref><ref>{{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 }}</ref>
==Pollution and regulation==
{{Further|Satellite internet constellation#Issues and criticism}}
[[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<ref name="10.1038/s41550-022-01655-6"/>]]
Issues like [[space debris]], radio and [[light pollution]] are increasing in magnitude and at the same time lack progress in national or international regulation.<ref name=sp1>{{cite news|title=Problem Weltraumschrott: Die kosmische Müllkippe – Wissenschaft|url=http://www.spiegel.de/wissenschaft/weltall/weltraumschrott-esa-tagung-in-darmstadt-ohne-ergebnisse-a-1144174.html|work=Der Spiegel|date=22 April 2017|access-date=22 April 2017|last1=Seidler|first1=Christoph}}</ref><ref name="10.1038/s41550-022-01655-6">{{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 |title=The case for space environmentalism |journal=Nature Astronomy |date=April 2022 |volume=6 |issue=4 |pages=428–435 |doi=10.1038/s41550-022-01655-6 |arxiv=2204.10025 |bibcode=2022NatAs...6..428L |s2cid=248300127 |language=en |issn=2397-3366}}</ref> Space debris poses dangers to spacecraft<ref>{{cite web |last1=Garcia |first1=Mark |title=Space Debris and Human Spacecraft |url=https://www.nasa.gov/mission_pages/station/news/orbital_debris.html |website=NASA |access-date=22 March 2022 |date=13 April 2015}}</ref><ref name="physUT">{{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 |website=phys.org |publisher=Universe Today |access-date=22 March 2022 |language=en}}</ref> (including satellites)<ref name="physUT"/><ref>{{cite news |title=Chinese official calls for protection of space assets, international coordination mechanisms |url=https://spacenews.com/chinese-official-calls-for-protection-of-space-assets-international-coordination-mechanisms/ |access-date=22 March 2022 |work=SpaceNews |date=10 March 2022}}</ref> in or crossing geocentric orbits and have the potential to drive a [[Kessler syndrome]]<ref>{{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 |publisher=ESA |access-date=22 March 2022 |language=en}}</ref> which could potentially curtail humanity from conducting space endeavors in the future by making such nearly impossible.<ref>{{cite news |last1=Wattles |first1=Jackie |title=Space is becoming too crowded, Rocket Lab CEO warns |url=https://edition.cnn.com/2020/10/07/business/rocket-lab-debris-launch-traffic-scn/index.html |access-date=26 May 2022 |work=CNN}}</ref><ref>{{cite news |title=What happens if two bits of space junk actually collide? |url=https://www.independent.co.uk/tech/space-junk-collision-satellite-debris-iss-nasa-b1074079.html |access-date=26 May 2022 |work=The Independent |date=16 October 2020 |language=en}}</ref>

With the increase in numbers 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.<ref name=iau>{{cite web |title=IAU's statement on satellite constellations |url=https://www.iau.org/news/announcements/detail/ann19035/ |website=International Astronomical Union |access-date=3 June 2019}}</ref><ref>{{cite web|url= http://www.astronomy.com/news/2019/06/light-pollution-from-satellites-will-get-worse-but-how-much|title=Light pollution from satellites will get worse. But how much?|date=14 June 2019|website=astronomy.com}}</ref><ref>{{cite journal |last1=Hainaut |first1=Olivier R. |last2=Williams |first2=Andrew P. |title=Impact of satellite constellations on astronomical observations with ESO telescopes in the visible and infrared domains |journal=Astronomy & Astrophysics |date=1 April 2020 |volume=636 |page=A121 |doi=10.1051/0004-6361/202037501|arxiv=2003.01992 |bibcode=2020A&A...636A.121H |url=https://www.aanda.org/articles/aa/full_html/2020/04/aa37501-20/aa37501-20.html |accessdate=22 November 2020 |language=en |issn=0004-6361|doi-access=free }}</ref><ref>{{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. |title=Impact of the SpaceX Starlink Satellites on the Zwicky Transient Facility Survey Observations |journal=The Astrophysical Journal Letters |date=1 January 2022 |volume=924 |issue=2 |pages=L30 |doi=10.3847/2041-8213/ac470a |arxiv=2201.05343 |bibcode=2022ApJ...924L..30M |s2cid=245986575 |language=en |issn=2041-8205}}</ref><ref>{{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 |work=[[American Astronomical Society]] |access-date=22 March 2022 |language=en}}</ref> 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.<ref>{{cite news |last1=Zhang |first1=Emily |title=SpaceX's Dark Satellites Are Still Too Bright for Astronomers |url=https://www.scientificamerican.com/article/spacexs-dark-satellites-are-still-too-bright-for-astronomers/ |access-date=16 September 2020 |work=Scientific American |language=en}}</ref><ref>{{cite news |title=Report Offers Roadmap to Mitigate Effects of Large Satellite Constellations on Astronomy {{!}} American Astronomical Society |url=https://aas.org/press/report-offers-roadmap-mitigate-effects-large-satellite-constellations-astronomy |access-date=16 September 2020 |work=aas.org}}</ref> The IAU is establishing<!--until 1 April 2022--> a center (CPS) to coordinate or aggregate measures to mitigate such detrimental effects.<ref>{{cite news |title=Astronomers stand up to satellite mega-constellations |url=https://www.bbc.com/news/science-environment-60262100 |access-date=10 March 2022 |work=BBC News |date=4 February 2022}}</ref><ref>{{cite web |title=Protection of the Dark and Quiet Sky from Satellite Constellation Interference |url=https://www.mpifr-bonn.mpg.de/announcements/2022/1 |publisher=Max Planck Institute for Radio Astronomy, Bonn |access-date=10 March 2022 |language=en}}</ref><ref>{{cite web |title=International Astronomical Union {{!}} IAU |url=https://www.iau.org/science/scientific_bodies/centres/CPS/ |website=www.iau.org |access-date=10 March 2022}}</ref>


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]].
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]].


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.<ref>{{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 }}</ref>
===Techniques===
{{See also|#End of life|Space debris#Dealing with debris}}
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.<ref>{{cite news |title=Japan developing wooden satellites to cut space junk |url=https://www.bbc.co.uk/news/business-55463366 |last=Harper |first=Justin |date=29 December 2020 |access-date=29 December 2020 |work=bbc.co.uk}}</ref>


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,<ref>{{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]]}}</ref><ref>{{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]]}}</ref> but satellite phone and television signals have also been subjected to jamming.<ref>{{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 }}</ref><ref>{{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]]}}</ref>
==Open source satellites==
Several [[open source]] satellites both in terms of [[open source hardware]] and [[open source software]] were flown or are in development. The satellites have usually form of a [[CubeSat]] or [[PocketQube]]. In 2013 an [[amateur radio satellite]] [[OSSI-1]] was launched and remained in orbit for about 2 months.<ref>{{Cite web|title=ossicode – Overview|url=https://github.com/ossicode|access-date=2021-02-27|website=GitHub|language=en}}</ref> In 2017 [[UPSat]] created by the Greek [[University of Patras]] and [[Libre Space Foundation]] remained in orbit for 18 months. In 2019 FossaSat-1 was launched.<ref>{{Cite web|last=Kulu|first=Erik|title=FossaSat-1 @ Nanosats Database|url=https://www.nanosats.eu/sat/fossasat.html|access-date=2021-02-27|website=Nanosats Database|language=en}}</ref><ref>{{Cite web|title=FossaSat 1, 1b|url=https://space.skyrocket.de/doc_sdat/fossasat-1.htm|access-date=2021-02-27|website=Gunter's Space Page|language=en}}</ref><ref>{{Cite web|title=FossaSat-1, an Open Source Satellite for the Internet of Things|url=https://www.hackster.io/news/fossasat-1-an-open-source-satellite-for-the-internet-of-things-7f31cab00ef5|access-date=2021-02-27|website=Hackster.io|language=en}}</ref><ref>{{Citation|title=FOSSASystems/FOSSASAT-1|date=2021-02-24|url=https://github.com/FOSSASystems/FOSSASAT-1|publisher=FOSSA Systems|access-date=2021-02-27}}</ref> As of February 2021 the Portland State Aerospace Society is developing two open source satellites called OreSat<ref>{{Cite web|title=oresat|url=https://www.oresat.org/|access-date=2021-02-27|website=www.oresat.org|language=en-US}}</ref><ref>{{Cite web|title=Oregon Small Satellite Project|url=https://github.com/oresat|access-date=2021-02-27|website=GitHub|language=en}}</ref> and the Libre Space Foundation also has ongoing satellite projects.<ref>{{Cite web|title=PocketQubes|url=https://libre.space/projects/pocketqubes/|access-date=2021-02-27|website=Libre Space Foundation|language=en-US}}</ref><ref>{{Cite web|title=QUBIK|url=https://libre.space/projects/qubik/|access-date=2021-02-27|website=Libre Space Foundation|language=en-US}}</ref><ref>{{Cite web|title=Qubik|url=https://gitlab.com/librespacefoundation/qubik|access-date=2021-02-27|website=GitLab|language=en}}</ref>


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 that enables them to pinpoint the source of any carrier and manage the transponder space effectively. {{Citation needed|date=September 2011}}
==Earth observation satellite==

[[File:A-Train w-Time2013 Web.jpg|thumb|upright=1.40|Six Earth observation satellites comprising the [[A-train (satellite constellation)|A-train]] satellite constellation as of 2014.]]

An '''Earth observation satellite''' or '''Earth remote sensing satellite''' is a satellite used or designed for [[Earth observation]] (EO) from [[orbit]], including [[spy satellite]]s and similar ones intended for non-military uses such as [[environmental monitoring]], [[meteorology]], [[cartography]] and others. The most common type are '''Earth imaging satellites''', that take [[satellite image]]s, analogous to [[aerial photograph]]s; some EO satellites may perform [[remote sensing]] without forming pictures, such as in [[GNSS radio occultation]].

The first occurrence of satellite remote sensing can be dated to the launch of the first artificial satellite, [[Sputnik 1]], by the Soviet Union on October 4, 1957.<ref name="Tatem"/> Sputnik 1 sent back radio signals, which scientists used to study the [[ionosphere]].<ref name="Kuznetsov">{{cite journal|last1=Kuznetsov|first1=V.D.|last2=Sinelnikov|first2=V.M.|last3=Alpert|first3=S.N.|title=Yakov Alpert: Sputnik-1 and the first satellite ionospheric experiment|journal=Advances in Space Research|date=June 2015|volume=55|issue=12|pages=2833–2839|doi=10.1016/j.asr.2015.02.033|bibcode=2015AdSpR..55.2833K}}</ref>
The United States Army Ballistic Missile Agency launched the first American satellite, [[Explorer 1]], for NASA’s Jet Propulsion Laboratory on January 31, 1958. The information sent back from its radiation detector led to the discovery of the Earth's [[Van Allen radiation belt]]s.<ref name="Allen">{{cite web|title=James A. Van Allen|url=http://www.nmspacemuseum.org/halloffame/detail.php?id=86|website=nmspacemuseum.org|publisher=New Mexico Museum of Space History|access-date=14 May 2018}}</ref> 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.<ref name="Tatem"/>

In 2008, more than 150 Earth observation satellites were in orbit, recording data with both passive and active sensors and acquiring more than 10 terabits of data daily.<ref name="Tatem">{{cite journal |last1=Tatem|first1=Andrew J.|last2=Goetz|first2=Scott J.|last3=Hay|first3=Simon I.|title=Fifty Years of Earth-observation Satellites|journal=American Scientist|date=2008|volume=96|issue=5|pages=390–398 |doi=10.1511/2008.74.390|pmid=19498953|pmc=2690060}}</ref> By 2021, that total had grown to over 950, with the largest number of satellites operated by US-based company [[Planet Labs]].<ref>{{cite web|title=How many Earth observation satellites are orbiting the planet in 2021?|date=18 August 2021 |url=https://www.pixalytics.com/eo-sats-2021/}}</ref>

Most [[Earth]] observation satellites carry instruments that should be operated at a relatively low altitude. Most orbit at altitudes above {{convert|500|to|600|km|mi|sp=us}}. Lower orbits have significant [[Drag (physics)|air-drag]], which makes frequent orbit [[reboost]] maneuvers necessary. The Earth observation satellites [[European Remote-Sensing Satellite|ERS-1, ERS-2]] and [[Envisat]] of [[European Space Agency]] as well as the [[MetOp]] spacecraft of [[EUMETSAT]] are all operated at altitudes of about {{cvt|800|km|mi}}. The [[PROBA|Proba-1]], [[Proba-2]] and [[Soil Moisture and Ocean Salinity satellite|SMOS]] spacecraft of European Space Agency are observing the Earth from an altitude of about {{cvt|700|km|mi}}. The Earth observation satellites of UAE, [[DubaiSat-1]] & [[DubaiSat-2]] are also placed in [[Low Earth orbit|Low Earth Orbits (LEO)]] orbits and providing [[satellite imagery]] of various parts of the Earth.<ref>{{cite web|title=DubaiSat-2, Earth Observation Satellite of UAE |url=http://mbrsc.ae/en/page/dubai-sat-2|publisher=Mohammed Bin Rashid Space Centre}}</ref><ref>{{cite web|title=DubaiSat-1, Earth Observation Satellite of UAE|url=http://mbrsc.ae/en/page/dubai-sat-1 |publisher=Mohammed Bin Rashid Space Centre}}</ref>

To get (nearly) global coverage with a low orbit, a [[polar orbit]] is used. A low orbit will have an orbital period of roughly 100 minutes and the Earth will rotate around its polar axis about 25° between successive orbits. The [[ground track]] moves towards the west 25° each orbit, allowing a different section of the globe to be scanned with each orbit. Most are in [[Sun-synchronous orbit]]s.

A [[geostationary orbit]], at {{cvt|36000|km|mi}}, allows a satellite to hover over a constant spot on the earth since the orbital period at this altitude is 24 hours. This allows uninterrupted coverage of more than 1/3 of the Earth per satellite, so three satellites, spaced 120° apart, can cover the whole Earth except the extreme polar regions. This type of orbit is mainly used for [[Weather satellite|meteorological satellites]].

== Applications ==
=== Weather ===
{{Main|Weather satellite}}
{{See also|Satellite temperature measurements}}
[[File:GOES 8 Spac0255.jpg|thumb|300px|[[GOES-8]], a [[United States]] weather satellite.]]

A weather satellite is a type of satellite that is primarily used to monitor the [[weather]] and [[climate]] of the [[Earth]].<ref name="NESDIS">NESDIS, [http://www.nesdis.noaa.gov/satellites.html Satellites.] Retrieved on 4 July 2008 {{PD-notice}}</ref> These meteorological satellites, however, see more than [[cloud]]s and cloud systems. 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., are other types of environmental information collected using weather satellites.

Weather satellite images helped in monitoring the volcanic ash cloud from [[Mount St. Helens]] and activity from other volcanoes such as [[Mount Etna]].<ref>NOAA, [http://www.spaceref.com/news/viewpr.html?pid=15216 NOAA Satellites, Scientists Monitor Mt. St. Helens for Possible Eruption.] Retrieved on 4 July 2008 {{PD-notice}}</ref> Smoke from fires in the western United States such as [[Colorado]] and [[Utah]] have also been monitored.

=== Environmental monitoring ===
[[File:Blue Marble 2002.png|thumb|upright=1.40|left|Composite satellite image of the Earth, showing its entire surface in [[equirectangular projection]]]]

Other environmental satellites can assist [[environmental monitoring]] by detecting 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.<ref>NASA, [http://earthobservatory.nasa.gov/Drought/ Drought.] {{webarchive |url=https://web.archive.org/web/20080819121047/http://earthobservatory.nasa.gov/Drought/|date=19 August 2008}} Retrieved on 4 July 2008 {{PD-notice}}</ref> For example, the 2002 oil spill off the northwest coast of [[Spain]] was watched carefully by the European [[Envisat|ENVISAT]], which, though not a weather satellite, flies an instrument (ASAR) which can see changes in the sea surface. Anthropogenic emissions can be monitored by evaluating data of tropospheric NO<sub>2</sub> and SO<sub>2</sub>.

These types of satellites are almost always in [[Sun-synchronous orbit|Sun-synchronous]] and [[Frozen orbit|"frozen"]] orbits. A sun-synchronous orbit passes over each spot on the ground at the same time of day, so that observations from each pass can be more easily compared, since the sun is in the same spot in each observation. A [[Frozen orbit|"frozen"]] orbit is the closest possible orbit to a circular orbit that is undisturbed by the [[Geopotential model|oblateness of the Earth]], gravitational attraction from the sun and moon, [[solar radiation pressure]], and [[air drag]].

=== Mapping ===
Terrain can be mapped from space with the use of satellites, such as [[Radarsat-1]]<ref>Grunsky, E.C. [http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/7969/22036/01024985.pdf?arnumber=1024985 The use of multi-beam Radarsat-1 satellite imagery for terrain mapping.] Retrieved on 4 July 2008</ref> and [[TerraSAR-X]].

==International regulations==
[[File:RapidEye Satellites Artist Impression.jpg|thumb|250px|[[RapidEye]] ''Earth exploration-satellite system'' in action around the Earth.]]

According to the [[International Telecommunication Union]] (ITU), '''Earth exploration-satellite service''' (also: '''Earth exploration-satellite radiocommunication service''') is – according to ''Article 1.51'' of the [[ITU Radio Regulations]] (RR)<ref>ITU Radio Regulations, Section IV. Radio Stations and Systems – Article 1.51, definition: ''earth exploration-satellite service / earth exploration-satellite radiocommunication service''</ref> – defined as:
<blockquote>A [[radiocommunication service]] between [[earth station]]s and one or more [[radio space station|space station]]s, which may include links between space stations, in which:
*information relating to the characteristics of the Earth and its natural phenomena, including data relating to the state of the environment, is obtained from passive or [[Radar|active sensors]] on [[satellites]];
*similar information is collected from airborne or Earth-based platforms;
*such information may be distributed to earth stations within the system concerned;
*platform interrogation may be included.
This service may also include feeder links necessary for its operation.</blockquote>

===Classification===
This ''radiocommunication service'' is classified in accordance with ''ITU Radio Regulations'' (article 1) as follows: <br />
[[Fixed service]] (article 1.20)
*[[Fixed-satellite service]] (article 1.21)
*[[Inter-satellite service]] (article 1.22)
*<span style="color:#060;">'''Earth exploration-satellite service'''</span>
**[[Meteorological-satellite service]] (article 1.52)

===Frequency allocation===
The allocation of radio frequencies is provided according to ''Article 5'' of the ITU Radio Regulations (edition 2012).<ref>''ITU Radio Regulations, CHAPTER II – Frequencies, ARTICLE 5 Frequency allocations, Section IV – Table of Frequency Allocations''</ref>

In order to improve harmonisation in spectrum utilisation, the majority of service-allocations stipulated in this document were incorporated in national Tables of Frequency Allocations and Utilisations which is with-in the responsibility of the appropriate national administration. The allocation might be primary, secondary, exclusive, and shared.
*primary allocation: is indicated by writing in capital letters (see example below)
*secondary allocation: is indicated by small letters
*exclusive or shared utilization: is within the responsibility of administrations
However, military usage, in bands where there is civil usage, will be in accordance with the ITU Radio Regulations.

; Example of [[frequency allocation]]:
{| class=wikitable
|- bgcolor="#CCCCCC" align="center"
|align="center" colspan="3"| '''Allocation to services'''
|- align="center"
| [[International Telecommunication Union region|Region 1]] || Region 2 || Region 3
|-
|colspan="3"|401–402&nbsp;MHz &nbsp;&nbsp; &nbsp;&nbsp; METEOROLOGICAL AIDS<br />
::::: SPACE OPERATION (space-to-Earth) <br />EARTH EXPLORATION-SATELLITE (Earth-to-space) <br />METEOROLOGICAL-SATELLITE (Earth-to-space)<br />Fixed <br />Mobile except aeronautical mobile
|-
|colspan="3"|13.4–13.75&nbsp;GHz &nbsp;&nbsp;'''EARTH EXPLORATION-SATELLITE (active)'''<br />
::::: RADIOLOCATION<br />SPACE RESEARCH<br />Standard frequency and time signal-satellite (Earth-to-space)
|-
|}

==Satellite services==
{{Div col|colwidth=30em}}
* [[Satellite crop monitoring]]
* [[Satellite Internet access]]
* [[Satellite navigation]]
* [[Satellite phone]]
* [[Satellite radio]]
* [[Satellite television]]
{{Div col end}}

==See also==
{{Portal| Spaceflight}}{{Spaceflight sidebar}}{{Div col|colwidth=22em}}
* [[2009 satellite collision]]
* [[Artificial moon]]
* [[Artificial satellites in retrograde orbit]]
* [[Atmospheric satellite]]
*[[Crowdfunded satellites]]
* [[Cubesat]]
* [[Fractionated spacecraft]]
* [[Ground track]]
* [[Imagery intelligence]]
* [[International Designator]]
* [[List of communications satellite firsts]]
* [[List of Earth observation satellites]]
* [[List of passive satellites]]
* [[Rocket engine test facility]]
* [[Satellite Catalog Number]]
* [[Satellite formation flying]]
* [[Satellite geolocation]]
* [[Satellite watching]]
* [[Space exploration]]
* {{annotated link|Research station}}
* {{annotated link|Space observatory}}
* [[Space station]]
* [[Space probe]]
* [[Spaceport]] (including list of spaceports)
* [[U.S. space exploration history on U.S. stamps|Satellites on stamps]]
* [[USA-193]] (2008 American anti-satellite missile test)
*[[Sputnik-1]]
{{Div col end}}
* [[Committee on Earth Observation Satellites]]
* [[Data collection satellite]]
* [[Earth observation]]
* [[Earth observation satellites transmission frequencies]]
* [[Earth Observing System]] – a NASA program comprising a series of satellite missions
* [[First images of Earth from space]]
* [[Satellite imagery#Imaging satellites|Imaging satellites]]
* [[List of Earth observation satellites]]
* [[Space telescope]]
* [[Satellite imagery]]
*[[GNSS radio occultation]]
*[[Microwave radiometer#Spaceborne]]
*[[Radar earth observation satellite]]
**[[Radar imaging]]
**[[Synthetic-aperture radar]]
***[[Interferometric synthetic-aperture radar]]
*[[Satellite altimetry]]


== References ==
== References ==
{{Reflist}}
{{Reflist}}

==Further reading==
* [[Ann Finkbeiner]], "Orbital Aggression: How do we prevent war in space?", ''[[Scientific American]]'', vol. 323, no. 5 (November 2020), pp.&nbsp;50–57.


==External links==
==External links==
Line 545: Line 136:
{{commons category|Satellites}}
{{commons category|Satellites}}
* {{curlie|Business/Telecommunications/Services/Wireless/Satellite/|Satellite}}
* {{curlie|Business/Telecommunications/Services/Wireless/Satellite/|Satellite}}
* [http://www.vega.org.uk/video/programme/12 ''Eyes in the Sky'' Free video by the Vega Science Trust and the BBC/OU] Satellites and their implications over the last 50 years.
* [https://directory.eoportal.org/web/eoportal/satellite-missions EO Portal directory]
* [https://directory.eoportal.org/web/eoportal/satellite-missions EO Portal directory]
* [https://web.archive.org/web/20160406191132/http://www.campevans.org/_CE/html/tiros1-2.html The TIROS I and II Ground Control Station where the first Earth Observing Satellite (TIROS I) sent it first photos]


{{Space-based meteorological observation}}
{{Space-based meteorological observation}}
{{Spaceflight}}
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Revision as of 06:32, 25 July 2022

For other uses, see Satellite (disambiguation).
Two 3U CubeSats
Two CubeSats orbiting around Earth after being deployed from the ISS Kibō module's Small Satellite Orbital Deployer

A satellite or artificial satellite is an object intentionally placed into orbit in outer space. 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 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 is small CubeSats. Similar satellites can work together as a group, forming constellations. Because of the high launch cost to space, satellites are designed to be as lightweight and robust as possible.

Satellites are placed from the surface to 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. In 2018, about 90% of satellites orbiting Earth are in low Earth orbit or geostationary orbit; geostationary means the satellites stay still at the sky. 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 collision threat are becoming 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 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 satellite to launch into orbit was the Soviet Union's Sputnik 1 in 1958.[further explanation needed]

History

See also: Timeline of first artificial satellites by country

Early proposals

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 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).[1][2] 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 is the first academic treatise on the use of rocketry to launch spacecraft. He calculated the orbital speed required for a minimal orbit, and 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 the special conditions of space could be useful for scientific experiments. The book described geostationary satellites (first put forward by Konstantin Tsiolkovsky) and discussed communication between them and the ground using radio, but fell short of the idea of using satellites for mass broadcasting and as telecommunications relays.[3]

In a 1945 Wireless World article, the English science fiction writer Arthur C. Clarke described in detail the possible use of communications satellites for mass communications. He suggested that three geostationary satellites would provide coverage over the entire planet.[4]: 1–2 

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."[5] 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.[6]

In 1946, American theoretical astrophysicist Lyman Spitzer proposed an orbiting space telescope.[7]

In February 1954, Project RAND released "Scientific Uses for a Satellite Vehicle", by R. R. Carhart.[8] 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.[9]

First satellites

Steel ball with 4 antennas
Replica of the Sputnik 1

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.

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 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.

Sputnik 2 was launched on 3 November 1957 and carried the first living passenger into orbit, a dog named Laika.[10]

In early 1955, after pressure by the American Rocket Society, the National Science Foundation, and the International Geophysical Year, the Army and Navy were working 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.[11] The information sent back from its radiation detector led to the discovery of the Earth's Van Allen radiation belts.[12] 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.[13]

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.[14]

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. Begun in 1997, FreeFlyer is a commercial off-the-shelf software application for satellite mission analysis, design, and operations.

Later development

  orbital launch and satellite operation
  satellite operation, launched by foreign supplier
  satellite in development
  orbital launch project at advanced stage or indigenous ballistic missiles deployed

While Canada was the third country to build a satellite which was launched into space,[15] it was launched aboard an American rocket from an American spaceport. The same goes for Australia, who launched first satellite involved a donated U.S. Redstone rocket and American support staff as well as a joint launch facility with the United Kingdom.[16] The first Italian satellite San Marco 1 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.[17] By similar occasions, almost all further first national satellites was launched by foreign rockets.

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 the older satellites that reach end of life, as a part of the regulatory process of obtaining a launch license.[citation needed] The largest artificial satellite ever is the International Space Station.[18]

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 demise, or breakup and burnup entirely in the atmosphere.[19] 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 atmospheric reentry at end of life, or in the event of an early satellite failure.[20]

Components

Orbit and attitude control

Main articles: Spacecraft propulsion and Attitude control
Firing of Deep Space 1's ion thruster

Most satellites use chemical or ion propulsion to adjust or maintain their orbit,[4]: 78  coupled with reaction wheels to control its 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 the Moon and the Sun. Without orbit and orientation control, satellites in orbit will not be able to communicate with ground stations on Earth.[4]: 75–76 

Chemical thrusters on satellites usually use monopropellant (one-part) or bipropellant (two-parts) that are hypergolic. Hypergolic means able to combust spontaneously in contact to each other or to a catalyst. The most commonly used propellant mixtures on satellites are hydrazine-based monopropellant or monomethylhydrazine–dinitrogen tetroxide bipropellant. 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 is very small (around 0.5 N or 0.1 lbf), 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.[4]: 78–79 

Power

Main articles: Batteries in space, Nuclear power in space, and Solar panels on spacecraft
see caption
The International Space Station's black solar panels on the left and white radiators on the right

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 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.[4]: 88–89 

Communications

Main article: Transponder (satellite communications)

Applications

Earth observation

Main article: Earth observation satellite
Deployment of the Earth Radiation Budget Satellite on STS-41-G, collecting data on Earth's weather and climate

Earth observation satellites is 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 normal camera, radar, lidar, photometer, or atmospheric instruments. Earth observation satellites' data is most used in archaeology, cartography, environmental monitoring, meteorology, and reconnaissance applications.[citation needed] As of 2021, there are over 950 Earth observation satellites, with the largest number of satellites operated Planet Labs.[21]

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 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.[22] Anthropogenic emissions can be monitored by evaluating data of tropospheric NO2 and SO2.[citation needed]

Communication

Main article: Communications satellite

A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. Communications satellites are used for television, telephone, radio, internet, and military applications.[23] Many communications satellites are in geostationary orbit 22,236 miles (35,785 km) above the equator, so that the satellite appears stationary at 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.

The radio waves used for telecommunications links travel by line of sight and so are obstructed by the curve of the Earth. The purpose of communications satellites is to relay the signal around the curve of the Earth allowing communication between widely separated geographical points.[24] Communications satellites use a wide range of radio and microwave frequencies. To avoid signal interference, international organizations have regulations for which frequency ranges or "bands" certain organizations are allowed to use. This allocation of bands minimizes the risk of signal interference.[25]
Main article: Satellite navigation

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

Telescope

Main article: Space telescope

Astronomical satellites are satellites used for observation of distant planets, galaxies, and other outer space objects

Experimental

Tether satellites are satellites that are connected to another satellite by 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.

Weapon

Main articles: Space weapon and Anti-satellite weapon

Since the mid-2000s, satellites have been hacked by militant organizations to broadcast propaganda and to pilfer classified information from military communication networks.[26][27] For testing purposes, satellites in low earth orbit have been destroyed by ballistic missiles launched from earth. Russia, United States, China and India have demonstrated the ability to eliminate satellites.[28] In 2007 the Chinese military shot down an aging weather satellite,[28] followed by the US Navy shooting down a defunct spy satellite in February 2008.[29] On 27 March 2019 India shot down a live test satellite at 300 km altitude in 3 minutes. India became the fourth country to have the capability to destroy live satellites.[30][31]

Pollution and interference

The growth of all tracked objects in space over time[32]

Issues like space debris, radio and light pollution are increasing in magnitude and at the same time lack progress in national or international regulation.[33][32] Space debris poses dangers to spacecraft[34][35] (including satellites)[35][36] in or crossing geocentric orbits and have the potential to drive a Kessler syndrome[37] which could potentially curtail humanity from conducting space endeavors in the future by making such nearly impossible.[38][39]

With the increase in numbers of satellite constellations, like SpaceX Starlink, the astronomical community, such as the IAU, report that orbital pollution is getting increased significantly.[40][41][42][43][44] 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.[45][46] The IAU is establishing a center (CPS) to coordinate or aggregate measures to mitigate such detrimental effects.[47][48][49]

Some notable satellite failures that polluted and dispersed radioactive materials are Kosmos 954, Kosmos 1402 and the Transit 5-BN-3.

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.[50]

Due to the low received signal strength of satellite transmissions, they are prone to 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,[51][52] but satellite phone and television signals have also been subjected to jamming.[53][54]

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 that enables them to pinpoint the source of any carrier and manage the transponder space effectively. [citation needed]

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