View source for Engineering:BeiDou Navigation Satellite System

{{Infobox navigation satellite system
|name= BeiDou Navigation Satellite System
|image= [[File:Beidou logo.png|frameless]]
|image_caption= The BeiDou system's logo
|country= China 
|type= Military, commercial
|status= Operational (regionally)<!--remove parenth. later-->
|operator= [[Organization:China National Space Administration|CNSA]]
|coverage= Global
|precision= 10 m (public)<br/>10 cm (encrypted)<ref>http://www.spacesafetymagazine.com/space-on-earth/international-relations/department-defense-reports-chinas-space-capabilities/</ref>
|satellites_nominal= 35 (2020)
|satellites_current= 23
|first_launch= 30 October 2000
|last_launch= 10 July 2018<ref>https://spaceflightnow.com/2018/07/10/chinese-navigation-satellite-deployed-by-long-march-rocket/</ref>
|launch_total= 25
|regime= [[Astronomy:Geostationary orbit|GEO]], IGSO, [[Astronomy:Medium Earth orbit|MEO]]
|cost=
}}
{{Geodesy}}

The '''BeiDou Navigation Satellite System''' ('''BDS''') is a Chinese [[Earth:Satellite navigation|satellite navigation]] system. It consists of two separate satellite constellations. The first BeiDou system, officially called the BeiDou Satellite Navigation Experimental System and also known as BeiDou-1, consists of three satellites which since 2000 has offered limited coverage and navigation services, mainly for users in China and neighboring regions. Beidou-1 was decommissioned at the end of 2012.

The second generation of the system, officially called the BeiDou Navigation Satellite System (BDS) and also known as COMPASS or BeiDou-2, became operational in China in December 2011 with a partial constellation of 10 satellites in orbit.<ref name="op_china">{{cite news|url=https://www.bbc.co.uk/news/technology-16337648|title=China GPS rival Beidou starts offering navigation data|publisher=BBC | date=2011-12-27}}</ref> Since December 2012, it has been offering services to customers in the [[Earth:Asia-Pacific|Asia-Pacific]] region.<ref name=CustomersDec2012>{{cite web|url=https://www.bbc.co.uk/news/technology-20852150|title=China's Beidou GPS-substitute opens to public in Asia|publisher=BBC|date=27 December 2012|accessdate=27 December 2012}}</ref> 

In 2015, China started the build-up of the third generation BeiDou system (BeiDou-3) in the global coverage constellation. The first BDS-3 satellite was launched on 30 March 2015.<ref name=chinanews_20150331>{{Cite web|title=中国北斗导航卫星再次进入密集发射期|url=http://www.chinanews.com/gn/2015/03-31/7170977.shtml|publisher=中国新闻社|date=March 31, 2015|access-date=June 16, 2017}}</ref> As of January 2018, nine BeiDou-3 satellites have been launched.<ref name=xinhuanet>{{Cite web|title=我国成功发射第五颗新一代北斗导航卫星|url=http://news.xinhuanet.com/tech/2016-02/01/c_1117960743.htm|publisher=新华社|date=February 1, 2016|access-date=June 16, 2017}}</ref> BeiDou-3 will eventually consist of 35 satellites and is expected to provide global services upon completion in 2020. When fully completed, BeiDou will provide an alternative global navigation satellite system to the United States owned [[Engineering:Global Positioning System|Global Positioning System]] (GPS),<ref>{{cite news|title=China's BeiDou to overtake GPS|url=http://www.ecns.cn/2017/04-07/252420.shtml|work=www.ecns.cn}}</ref><ref name=beidou-road-to-global-service>{{cite news|title=Directions 2017: BeiDou’s road to global service|url=http://gpsworld.com/directions-2017-beidous-road-to-global-service/|work=GPS World|date=6 December 2016}}</ref> and is expected to be more accurate than the GPS.<ref>{{cite news|last1=Miranda|first1=Erika|title=BeiDou Navigation Satellite System: China's More Accurate Version of GPS Nears Completion|url=http://en.yibada.com/articles/132467/20160617/beidou-navigation-satellite-system-chinas-more-accurate-version-of-gps-nears-completion.htm|work=Yibada English|date=17 June 2016}}</ref> It was claimed in 2016 that BeiDou-3 will reach millimeter-level accuracy (with post-processing), which is ten times more accurate than the finest level of GPS.<ref name=beidou-road-to-global-service />

According to China Daily, in 2015, fifteen years after the satellite system was launched, it was generating a turnover of $31.5 billion per annum for major companies such as China Aerospace Science and Industry Corp, AutoNavi Holdings Ltd, and China North Industries Group Corp.<ref>http://www.chinadaily.com.cn/bizchina/tech/2015-11/16/content_22464083.htm</ref>

==Nomenclature==
The official English name of the system is ''BeiDou Navigation Satellite System''.<ref>[http://www.beidou.gov.cn/2013/03/29/20130329622a1d8c79ee4e5d849867358c1a97bf.html English Name of BeiDou]</ref> It is named after the [[Astronomy:Big Dipper|Big Dipper]] [[Astronomy:Asterism|asterism]], which is known in Chinese as ''Běidǒu'' ({{zh|北斗}}).  The name literally means "Northern Dipper", the name given by ancient Chinese astronomers to the seven brightest stars of the Ursa Major constellation.<ref name="iTWire">{{cite web
|first=William
|last=Atkins
|url=http://www.itwire.com/science-news/space/9201-chinese-BeiDou-navigation-satellite-launched-from-long-march-3a-rocket
|title=Chinese BeiDou navigation satellite launched from Long March 3A rocket
|publisher=iTWire.com
|date=2007-02-05
|accessdate=2010-05-19}}</ref> Historically, this set of stars was used in navigation to locate the [[Astronomy:Polaris|North Star]]. As such, the name BeiDou also serves as a metaphor for the purpose of the satellite navigation system.

==History==

===Conception and initial development===
The original idea of a Chinese satellite navigation system was conceived by Chen Fangyun and his colleagues in the 1980s.<ref>[http://focus.news.163.com/10/1231/09/6P7JHOMM00011SM9.html 北斗记 ——探秘中国北斗卫星导航定位系统]</ref> According to the [[Organization:China National Space Administration|China National Space Administration]], the development of the system would be carried out in three steps:<ref name="CNSA 2010">{{cite web
|url=http://www.BeiDou.gov.cn/2010/05/19/20100519101180c595f14a6d9938a42a2d796b56.html
|title=The construction of BeiDou navigation system steps into important stage, "Three Steps" development guideline clear and certain
|date=2010-05-19
|publisher=China National Space Administration
|accessdate=2010-05-19
|language=Chinese}}</ref>
#2000–2003: experimental BeiDou navigation system consisting of 3 satellites
#by 2012: regional BeiDou navigation system covering China and neighboring regions
#by 2020: global BeiDou navigation system

The first satellite, ''BeiDou-1A'', was launched on 30 October 2000, followed by ''BeiDou-1B'' on 20 December 2000. The third satellite, ''BeiDou-1C'' (a backup satellite), was put into orbit on 25 May 2003.<ref name="CNSA 2003">{{cite web
 |url         = http://www.cnsa.gov.cn/n615708/n620172/n677078/n751578/62676.html
 |title       = Comparable with American and Russian in terms of performance, BeiDou-1 navigates for China
 |date        = 2003-05-30
 |publisher   = China National Space Administration
 |accessdate  = 2010-05-19
 |language    = Chinese
 |deadurl     = yes
 |archiveurl  = https://www.webcitation.org/65ONoktDf?url=http://www.cnsa.gov.cn/n615708/n620172/n677078/n751578/62676.html
 |archivedate = 2012-02-12
 |df          = 
}}</ref><ref>{{cite web
 |first=John 
 |last=Pike 
 |url=http://www.globalsecurity.org/space/world/china/BeiDou.htm 
 |title=BeiDou (Big Dipper) 
 |work=Space 
 |publisher=GlobalSecurity.org 
 |accessdate=2006-11-09 
 |archiveurl=https://web.archive.org/web/20061128170852/http://www.globalsecurity.org/space/world/china/beidou.htm 
 |archivedate=28 November 2006 
 |deadurl=yes 
 |df= 
}} </ref> The successful launch of ''BeiDou-1C'' also meant the establishment of the BeiDou-1 navigation system.

On 2 November 2006, China announced that from 2008 BeiDou would offer an open service with an accuracy of 10 meters, timing of 0.2 microseconds, and speed of 0.2 meters/second.<ref name="NewScientist">{{cite news
|first=Paul
|last=Marks
|title=China's satellite navigation plans threaten Galileo
|work=New Scientist
|url=https://www.newscientist.com/article/dn10472-chinas-satellite-navigation-plans-threaten-galileo.html
|date=2006-11-08
|accessdate=2006-11-09}}</ref>

In February 2007, the fourth and last satellite of the BeiDou-1 system, ''BeiDou-1D'' (sometimes called ''BeiDou-2A'', serving as a backup satellite), was launched.<ref name="gov.cn">{{cite news
 |title       = China puts new navigation satellite into orbit
 |publisher   = Gov.cn
 |url         = http://english.gov.cn/2007-02/03/content_516638.htm
 |date        = 2007-02-03
 |accessdate  = 2010-05-20
 |deadurl     = yes
 |archiveurl  = https://web.archive.org/web/20120202150518/http://english.gov.cn/2007-02/03/content_516638.htm
 |archivedate = 2012-02-02
 |df          = 
}}</ref> It was reported that the satellite had suffered from a control system malfunction but was then fully restored.<ref name="SinoDefence" /><ref>{{cite web
|url=http://news.sohu.com/20070418/n249522961.shtml
|title=60-day works in space -- Story of reparation of the BeiDou satellite
|publisher=Sohu
|date=2007-04-18
|accessdate=2010-05-23
|language=Chinese}}</ref>

In April 2007, the first satellite of BeiDou-2, namely ''Compass-M1'' (to validate frequencies for the BeiDou-2 constellation) was successfully put into its working orbit. The second BeiDou-2 constellation satellite ''Compass-G2'' was launched on 15 April 2009.<ref name="ASM">{{cite web
 |url         = http://www.asmmag.com/news/compass-due-next-year
 |title       = Compass due Next Year
 |date        = May 4, 2009
 |work        = Magazine article
 |publisher   = Asian Surveying and Mapping
 |accessdate  = 2009-05-05
 |archiveurl  = https://web.archive.org/web/20090519192644/http://www.asmmag.com/news/compass-due-next-year
 |archivedate = 19 May 2009
 |deadurl     = yes
 |df          = 
}}</ref> On 15 January 2010, the [http://www.beidou.gov.cn official website of the BeiDou Navigation Satellite System] went online,<ref name="Compass-G1">{{cite web
|url=http://news.sohu.com/20100117/n269631862.shtml
|title=China successfully launched the third BeiDou satellite
|publisher=Sohu
|date=2010-01-17
|accessdate=2010-05-19
|language=Chinese}}</ref> and the system's third satellite (''Compass-G1'') was carried into its orbit by a [[Engineering:Long March 3C|Long March 3C]] rocket on 17 January 2010.<ref name="Compass-G1" /> On 2 June 2010, the fourth satellite was launched successfully into orbit.<ref name="SpaceflightNow">{{cite web
|url=http://www.spaceflightnow.com/news/n1006/02longmarch/
|title=China sends Beidou navigation satellite to orbit
|date=2010-06-02
|publisher=Spaceflight Now
|accessdate=2010-06-04| archiveurl= https://web.archive.org/web/20100605031349/http://www.spaceflightnow.com/news/n1006/02longmarch/| archivedate= 5 June 2010 <!--DASHBot-->| deadurl= no}}</ref> The fifth orbiter was launched into space from Xichang Satellite Launch Center by an [[Engineering:Long March 3|LM-3I]] carrier rocket on 1 August 2010.<ref name="Xinhua0810">{{cite news
 |url         = http://news.xinhuanet.com/english2010/china/2010-08/01/c_13424634.htm
 |title       = China successfully launches fifth satellite for its own global navigation network
 |publisher   = Xinhua
 |date        = 2010-08-01
 |accessdate  = 2010-08-01
 |archiveurl  = https://web.archive.org/web/20100803170454/http://news.xinhuanet.com/english2010/china/2010-08/01/c_13424634.htm
 |archivedate = 3 August 2010
 |deadurl     = yes
 |df          = 
}}</ref> Three months later, on 1 November 2010, the sixth satellite was sent into orbit by LM-3C.<ref name="cngov1101">{{cite news
|url=http://english.gov.cn/2010-11/01/content_1735077.htm
|title=China launches 6th satellite for indigenous global navigation, positioning network
|publisher=GOV.cn
|date=2010-11-01
|accessdate=2010-11-21| archiveurl= https://web.archive.org/web/20101231104817/http://english.gov.cn/2010-11/01/content_1735077.htm| archivedate= 31 December 2010 <!--DASHBot-->| deadurl= no}}</ref> Another satellite, the Beidou-2/Compass IGSO-5 (fifth inclined geosynchonous orbit) satellite, was launched from the Xichang Satellite Launch Center by a Long March-3A on 1 December 2011 (UTC).<ref>{{cite news
 |url         = http://www.gpsworld.com/gnss-system/news/beidou-launch-completes-regional-nav-system-12375/
 |title       = Beidou Launch Completes Regional Nav System
 |publisher   = GPS World
 |date        = 2010-12-06
 |accessdate  = 2011-12-23
 |deadurl     = yes
 |archiveurl  = https://web.archive.org/web/20120312083255/http://www.gpsworld.com/gnss-system/news/beidou-launch-completes-regional-nav-system-12375
 |archivedate = 2012-03-12
 |df          = 
}}</ref>

===Chinese involvement in Galileo system===
In September 2003, China intended to join the European Galileo positioning system project and was to invest [[Finance:Euro|€]]230 million ({{wipe|United States dollar}}296 million, GBP160 million) in Galileo over the next few years.<ref>{{cite news
|url=http://news.bbc.co.uk/1/hi/business/3121682.stm
|title=China joins EU's satellite network
|work=Business News
|publisher=BBC News
|date=2003-09-19
|accessdate=2006-11-09}}</ref> At the time, it was believed that China's "BeiDou" navigation system would then only be used by its armed forces.<ref name="NewScientist" /> In October 2004, China officially joined the Galileo project by signing the ''Agreement on the Cooperation in the Galileo Program between the "Galileo Joint Undertaking" (GJU) and the "National Remote Sensing Centre of China" (NRSCC)''.<ref>{{cite news
 |url         = http://news.xinhuanet.com/newscenter/2005-07/29/content_3281533.htm
 |title       = First contracts of the Galileo project signed, China is to invest 200 million Euro
 |publisher   = Xinhua
 |date        = 2005-07-29
 |accessdate  = 2010-05-26
 |language    = Chinese
 |deadurl     = yes
 |archiveurl  = https://web.archive.org/web/20100211174817/http://news.xinhuanet.com/newscenter/2005-07/29/content_3281533.htm
 |archivedate = 2010-02-11
 |df          = 
}}</ref> Based on the Sino-European Cooperation Agreement on Galileo program, [https://web.archive.org/web/20140620234303/http://www.chinagi.com.cn/yw/index.asp China Galileo Industries (CGI)], the prime contractor of the China’s involvement in Galileo programs, was founded in December 2004.<ref>{{cite web
 |url         = http://www.chinagi.com.cn/yw/gsjjxx.asp
 |title       = About us
 |publisher   = China Galileo Industries
 |accessdate  = 2010-05-26
 |deadurl     = yes
 |archiveurl  = https://web.archive.org/web/20110707014516/http://www.chinagi.com.cn/yw/gsjjxx.asp
 |archivedate = 2011-07-07
 |df          = 
}}</ref>  By April 2006, eleven cooperation projects within the Galileo framework had been signed between China and EU.<ref>{{cite news
 |url         = http://news3.xinhuanet.com/politics/2006-04/13/content_4420183.htm
 |title       = Eleven projects within the China-EU Galileo project have been signed and are carrying out
 |publisher   = Xinhua
 |date        = 2006-04-13
 |accessdate  = 2010-05-26
 |language    = Chinese
 |deadurl     = yes
 |archiveurl  = https://web.archive.org/web/20110719045720/http://news3.xinhuanet.com/politics/2006-04/13/content_4420183.htm
 |archivedate = 2011-07-19
 |df          = 
}}</ref> However, the Hong Kong-based ''South China Morning Post'' reported in January 2008 that China was unsatisfied with its role in the Galileo project and was to compete with Galileo in the Asian market.<ref>{{cite news
 |url         = http://china.huanqiu.com/eyes_on_china/2008-01/42334.html
 |title       = South China Morning Post: China is not going to be the little partner of the Galileo project
 |publisher   = Global Times
 |date        = 2008-01-03
 |accessdate  = 2010-05-26
 |language    = Chinese
 |deadurl     = yes
 |archiveurl  = https://web.archive.org/web/20110712231214/http://china.huanqiu.com/eyes_on_china/2008-01/42334.html
 |archivedate = 2011-07-12
 |df          = 
}}</ref>

===Phase III===
* In November 2014, Beidou became part of the World-Wide Radionavigation System (WWRNS) at the 94th meeting of The International Maritime Organization (IMO) Maritime Safety Committee,<ref>{{cite news|title=SOLAS amendments to make IGF Code mandatory approved by Maritime Safety Committee|url=http://www.imo.org/MediaCentre/PressBriefings/Pages/40-MSC94wrap.aspx|accessdate=7 April 2015|work=Maritime Safety Committee (MSC), 94th session, 17–21 November 2014|publisher=International Maritime Organization|date=26 November 2014}}</ref> which approved the "Navigation Safety Circular" of the Beidou Navigation Satellite System (BDS).<ref>{{cite web|last1=Feng|first1=Bruce|title=A Step Forward for Beidou, China’s Satellite Navigation System|url=http://sinosphere.blogs.nytimes.com/2014/12/04/a-step-forward-for-beidou-chinas-satellite-navigation-system/|publisher={{wipe|The New York Times}}|date=4 December 2014}}</ref><ref>{{cite news|title=Chinese Beidou Navigation Satellite System officially into Global Radio Navigation System|url=http://www.beidou.gov.cn/2014/12/01/2014120161d5b9e6272547ddb9d141b4129491f4.html|publisher=BeiDou|date=1 December 2014}}</ref>
* At Beijing time 21:52, March 30, 2015, the first new-generation BeiDou Navigation satellite (and the 17th overall) was successfully set to orbit by a [[Engineering:Long March 3C|Long March 3C]] rocket.<ref>{{cite web|last1=Barbosa|first1=Rui C.|title=Long March 3C in secretive launch with new Upper Stage|url=http://www.nasaspaceflight.com/2015/03/long-march-3c-launch-new-upper-stage/|publisher=NASASpaceFlight.com|date=30 March 2015}}</ref><ref name="BeiDou-launch-17">{{cite web|title=China successfully launched the first New-Generation Beidou Navigation Satellite|url=http://www.beidou.gov.cn/2015/04/01/20150401b4b91ddc213a45129a665ea3272b5aed.html|publisher=BeiDou|date=1 April 2015}}</ref>

==Experimental system (BeiDou-1)==

===Description===
[[Image:Beidou-coverage.png|right|thumbnail|Coverage polygon of BeiDou-1.]]
<!-- Image with unknown copyright status removed: [[Image:Terminal_bd1.gif|thumb|right|85px|A terminal for BeiDou 1]] -->
BeiDou-1 is an experimental regional navigation system, which consists of four satellites (three working satellites and one backup satellite). The satellites themselves were based on the Chinese DFH-3 geostationary communications satellite and had a launch weight of 1,000 kilograms (2,200 pounds) each.<ref>{{cite web
|first=Greg
|last=Goebel
|url=http://www.vectorsite.net/ttgps_2.html#m3
|title=International Navigation Satellite Systems
|date=2008-09-01
|publisher=vectorsite.net}}</ref>

Unlike the American [[Engineering:GPS|GPS]], Russian [[Astronomy:GLONASS|GLONASS]], and European Galileo systems, which use [[Astronomy:Medium Earth orbit|medium Earth orbit]] satellites, BeiDou-1 uses satellites in [[Astronomy:Geostationary orbit|geostationary orbit]].  This means that the system does not require a large constellation of satellites, but it also limits the coverage to areas on Earth where the satellites are visible.<ref name="CNSA 2003" /> The area that can be serviced is from longitude 70°E to 140°E and from latitude 5°N to 55°N. A frequency of the system is 2491.75&nbsp;MHz.<ref name="SinoDefence">{{cite web
|url=http://www.sinodefence.com/space/spacecraft/beidou1.asp
|title=BeiDou 1 Experimental Satellite Navigation System
|date=2008-09-24
|publisher=SinoDefence.com
|accessdate=2010-05-20
|deadurl=yes
|archiveurl=https://web.archive.org/web/20100327075557/http://www.sinodefence.com/space/spacecraft/beidou1.asp
|archivedate=2010-03-27
|df=
}}</ref>

===Completion===
The first satellite, BeiDou-1A, was launched on October 31, 2000. The second satellite, BeiDou-1B, was successfully launched on December 21, 2000. The last operational satellite of the constellation, BeiDou-1C, was launched on May 25, 2003.<ref name="CNSA 2003" />

===Position calculation===
In 2007, the official Xinhua News Agency reported that the resolution of the BeiDou system was as low as 0.5 metres.<ref>{{cite web 
 |url=http://orig.news.ifeng.com/mil/2/200707/0718_340_158622.shtml 
 |title=BeiDou navigation system first goes to public, with resolution 0.5 metre 
 |date=2007-07-18 
 |publisher=Phoenix Television 
 |accessdate=2010-05-19 
 |language=Chinese 
 |deadurl=yes 
 |archiveurl=https://web.archive.org/web/20090227184508/http://orig.news.ifeng.com/mil/2/200707/0718_340_158622.shtml 
 |archivedate=2009-02-27 
 |df= 
 }}</ref> With the existing user terminals it appears that the calibrated accuracy is 20m (100m, uncalibrated).<ref>{{cite web
 |url         = http://www.navchina.com/english/productlist.asp?classid=12
 |title       = BeiDou Products
 |publisher   = BDStar Navigation
 |deadurl     = yes
 |archiveurl  = https://web.archive.org/web/20090105114653/http://www.navchina.com/english/productlist.asp?classid=12
 |archivedate = 2009-01-05
 |df          = 
}}</ref>

===Terminals===
In 2008, a BeiDou-1 ground terminal cost around {{Currency|20000|CNY}}RMB ({{Currency|2929}}), almost 10 times the price of a contemporary GPS terminal.<ref>{{cite web
|url=http://tech.163.com/08/0628/08/4FGTUVT9000915BE.html
|title=BeiDou-1 commercial controversy: 10 times the price of GPS terminal
|publisher=[[Company:NetEase|NetEase]]
|date=2008-06-28
|accessdate=2010-05-23
|language=Chinese}}</ref> The price of the terminals was explained as being due to the cost of imported microchips.<ref>{{cite web
|url=http://www.prlog.org/10112053-why-is-chinas-beidou-terminal-so-expensive.html
|title=Why is China's Beidou terminal so expensive?
|publisher=PRLog
|date=2008-08-31
|accessdate=2010-05-29}}</ref> At the China High-Tech Fair ELEXCON of November 2009 in Shenzhen, a BeiDou terminal priced at {{Currency|3000|CNY}}RMB was presented.<ref>{{cite web
 |url         = http://www.eetrend.com/news/100022852
 |title       = 3000Yuan BeiDou Satellite Positioning System terminal solution was presented at ELEXCON
 |publisher   = eetrend.com
 |date        = 2009-11-17
 |accessdate  = 2010-05-29
 |language    = Chinese
 |archiveurl  = https://web.archive.org/web/20100513015654/http://www.eetrend.com/news/100022852
 |archivedate = 13 May 2010
 |deadurl     = yes
 |df          = 
}}</ref>

===Applications===
*Over 1,000 BeiDou-1 terminals were used after the 2008 Sichuan earthquake, providing information from the disaster area.<ref>{{cite web
|url=http://news.sohu.com/20080520/n256965516.shtml
|title=Hongkong report: BeiDou-1 played an important role in rescuing, 7 nations providing free satellite data
|publisher=Sohu
|date=2008-05-20
|accessdate=2010-05-23
|language=Chinese}}</ref>
*As of October 2009, all Chinese border guards in Yunnan are equipped with BeiDou-1 devices.<ref>{{cite web
|url=http://news.sohu.com/20091014/n267346694.shtml
|title=BeiDou-1 has equipped Yunnan troops, leading to command reform
|publisher=Sohu
|date=2009-10-14
|accessdate=2010-05-23
|language=Chinese}}</ref>

According to Sun Jiadong, the chief designer of the navigation system, "Many organizations have been using our system for a while, and they like it very much."<ref>{{cite web
|url=http://www.spacedaily.com/reports/China_To_Set_Up_Independent_Satellite_Navigation_System_999.html
|title=China To Set Up Independent Satellite Navigation System
|publisher=SpaceDaily.com
|date=2010-05-24
|accessdate=2010-06-04}}</ref>

The new-generation BeiDou satellites support short message service.<ref name="BeiDou-launch-17" />

=={{anchor|BeiDou-2}}{{anchor|Global system}} Global system (BeiDou Navigation Satellite System or BeiDou-2)==

===Description===
[[File:Beidou Navigation Satellite System 2012.png|thumb|Coverage polygon of BeiDou-2 in 2012.]]
BeiDou-2 (formerly known as COMPASS)<ref>{{Cite web  | url = http://www.beidou.gov.cn/2012/12/27/20121227db0e01c98b044232875e2f85cf5bb2a3.html | title = The Logo Image of BeiDou Navigation Satellite System Issued | publisher =BeiDou.gov.cn | date = 2012-12-27 }}</ref> is not an extension to the older BeiDou-1, but rather supersedes it outright. The new system will be a constellation of 35 satellites, which include 5 geostationary orbit satellites for backward compatibility with BeiDou-1, and 30 non-geostationary satellites (27 in medium Earth orbit and 3 in inclined [[Astronomy:Geosynchronous orbit|geosynchronous orbit]]),<ref name="InsideGNSS">{{cite web
|url=http://www.insidegnss.com/node/2134
|title=China Launches Another Compass GEO Navigation Satellite
|publisher=''[[Earth:Inside GNSS|Inside GNSS]]''
|date=2010-06-02
|accessdate=2010-06-04}}</ref> that will offer complete coverage of the globe.

The ranging signals are based on the CDMA principle and have complex structure typical of Galileo or modernized [[Engineering:GPS|GPS]]. Similar to the other [[Earth:Satellite navigation|global navigation satellite system]]s (GNSSs), there will be two levels of positioning service: open (public) and restricted (military). The public service will be available globally to general users. When all the currently planned GNSSs are deployed, users of multi-constellation receivers will benefit from a total over 100 satellites, which will significantly improve all aspects of positioning, especially availability of the signals in so-called urban canyons.<ref>G. Gibbons. China GNSS 101. ''Compass in the rearview mirror''. ''[[Earth:Inside GNSS|Inside GNSS]]'', January/February 2008, p. 62-63 [http://www.insidegnss.com/auto/janfeb08-china.pdf]</ref> The general designer of the COMPASS navigation system is Sun Jiadong, who is also the general designer of its predecessor, the original BeiDou navigation system.
[[Image:gps compass galileo frequency allocation Asimsky 05 2008.jpg|thumb|left|320px|Frequency allocation of GPS, Galileo, and COMPASS; the light red color of E1 band indicates that the transmission in this band has not yet been detected.]]

====Accuracy====
There are two levels of service provided&nbsp;— a free service to civilians and licensed service to the Chinese government and military.<ref name="SpaceflightNow" /><ref>{{cite web
|url=http://www.beidou.gov.cn/2010/03/06/20100306e4ed1ecefebb41fa933ceee48024aa00.html
|title=Introduction of the BeiDou Navigation Satellite System
|publisher=BeiDou.gov.cn
|date=2010-01-15
|accessdate=2010-06-04
|language=Chinese}}</ref> The free civilian service has a 10-meter location-tracking accuracy, synchronizes clocks with an accuracy of 10 nanoseconds, and measures speeds to within 0.2&nbsp;m/s. The restricted military service has a location accuracy of 10 centimetres,<ref>{{cite web|url=http://earth.scichina.com:8080/sciDe/EN/abstract/abstract507876.shtml|title=Precise orbit determination of Beidou Satellites with precise positioning|work=Science China|year=2012|accessdate=26 June 2013}}</ref> can be used for communication, and will supply information about the system status to the user. To date, the military service has been granted only to the People's Liberation Army and to the Pakistan Armed Forces.<ref>{{cite web|url=https://www.theregister.co.uk/2012/05/17/beidou_ready_2012_three_satellites/|title=GPS rival Beidou will cover Asia Pac by end of the year|work=The Register|date=17 May 2012|accessdate=26 June 2013}}</ref><ref>{{cite web|url=http://www.spacesafetymagazine.com/tag/beidou/|title=US Department of Defense Reports on China’s Space Capabilities|work=Space Safety Magazine|date=27 May 2013|accessdate=26 June 2013}}</ref><ref>{{cite web|url=http://www.nextbigfuture.com/2016/06/china-will-make-beidou-navigation.html|title=China will make BeiDou Navigation Satellite System available to global users by 2020|work=Next Big Future|date=28 June 2016|accessdate=3 February 2017}}</ref>

====Frequencies====
Frequencies for COMPASS are allocated in four bands: E1, E2, E5B, and E6 and overlap with Galileo. The fact of overlapping could be convenient from the point of view of the receiver design, but on the other hand raises the issues of system interference, especially within E1 and E2 bands, which are allocated for Galileo's publicly regulated service.<ref>''Galileo, Compass on collision course'', GPS World, April 2008, p. 27</ref> However, under [[Organization:International Telecommunication Union|International Telecommunication Union]] (ITU) policies, the first nation to start broadcasting in a specific frequency will have priority to that frequency, and any subsequent users will be required to obtain permission prior to using that frequency, and otherwise ensure that their broadcasts do not interfere with the original nation's broadcasts. It now appears that Chinese COMPASS satellites will start transmitting in the E1, E2, E5B, and E6 bands before Europe's Galileo satellites and thus have primary rights to these frequency ranges.<ref>{{cite web|last=Levin |first=Dan |url=https://www.nytimes.com/2009/03/23/technology/23iht-galileo23.html?_r=1&scp=1&sq=chinese%20europe%20galileo&st=cse |title='&#39;Chinese square off with Europe in space'&#39; |location=China |publisher=Nytimes.com |date=2009-03-23 |accessdate=2011-12-30}}</ref>

Although little was officially announced by Chinese authorities about the signals of the new system, the launch of the first COMPASS satellite permitted independent researchers not only to study general characteristics of the signals, but even to build a COMPASS receiver.

===Compass-M1===
Compass-M1 is an experimental satellite launched for signal testing and validation and for the frequency filing on 14 April 2007. The role of Compass-M1 for Compass is similar to the role of the [[Engineering:GIOVE|GIOVE]] satellites for the Galileo system. The orbit of Compass-M1 is nearly circular, has an altitude of 21,150&nbsp;km and an inclination of 55.5 degrees.

Compass-M1 transmits in 3 bands: E2, E5B, and E6. In each frequency band two coherent sub-signals have been detected with a phase shift of 90 degrees (in [[Quadrature amplitude modulation|quadrature]]). These signal components are further referred to as "I" and "Q". The "I" components have shorter codes and are likely to be intended for the open service. The "Q" components have much longer codes, are more interference resistive, and are probably intended for the restricted service.

The investigation of the transmitted signals started immediately after the launch of Compass -M1 on 14 April 2007. Soon after in June 2007, engineers at [[Organization:CNES|CNES]] reported the spectrum and structure of the signals.<ref>T. Grelier, J. Dantepal, A. Delatour, A. Ghion, L. Ries, ''Initial observation and analysis of Compass MEO satellite signals'', ''[[Earth:Inside GNSS|Inside GNSS]]'', May/June 2007 [http://www.insidegnss.com/auto/IG0607_CompassFinal.pdf]</ref>  A month later, researchers from [[Organization:Stanford University|Stanford University]] reported the complete decoding of the “I” signals components.<ref>G. Xingxin Gao, A. Chen, S. Lo, D. De Lorenzo, P. Enge, GNSS over China. ''The Compass MEO satellite codes''. ''[[Earth:Inside GNSS|Inside GNSS]]'', July/August 2007, pp. 36–43 [http://www.insidegnss.com/auto/IG0807_Gao-Lo_final.pdf]</ref><ref>G. Xingxin Gao, A. Chen, Sh. Lo, D. De Lorenzo and Per Enge, ''Compass-M1 broadcast codes and their application to acquisition and tracking'', Proceedings of the ION National Technical Meeting 2008, San Diego, California, January 2008.{{cite web |url=http://www.stanford.edu/~gracegao/publications/ION_NTM_08%20Compass.pdf |title=Archived copy |accessdate=2016-02-08 |deadurl=yes |archiveurl=https://web.archive.org/web/20121020031639/http://www.stanford.edu/~gracegao/publications/ION_NTM_08%20Compass.pdf |archivedate=2012-10-20 |df= }}</ref> The knowledge of the codes allowed a group of engineers at [[Company:Septentrio|Septentrio]] to build the COMPASS receiver<ref>W. De Wilde, F. Boon, J.-M. Sleewaegen, F. Wilms, ''More Compass points. Tracking China’s MEO satellite on a hardware receiver''. ''[[Earth:Inside GNSS|Inside GNSS]]'', July/August 2007, pp. 44–48. [http://www.insidegnss.com/auto/IG0807-DeWilde_etal_final.pdf]</ref>  and report tracking and multipath characteristics of the “I” signals on E2  and E5B.<ref>A. Simsky, D.  Mertens, Wim De Wilde, ''Field Experience with Compass-M1 E2 and E5B Signals''. Proceedings of ENC GNSS 2008, Toulouse, 22–25 April 2008.</ref>
{| class="wikitable" style="text-align:center; font-size:90%;"
|+ style="font-size:105%;"| Characteristics of Compass signals reported as of May 2008 compared to GPS-L1CA
|-
! Parameters !! E2-I !! E2-Q!! E5B-I !! E5B-Q !! E6-I!! E6-Q!! GPS L1-CA
|-
|style="text-align:left;"| Native notation || B1 || B1 || B2 || B2 || B3 || B3 || ---
|-
|style="text-align:left;"| Code modulation || BPSK(2) || BPSK(2) || BPSK(2) || BPSK(10)|| BPSK(10)|| BPSK (10) || BPSK (1)
|-
|style="text-align:left;"| Carrier frequency, MHz || 1561.098||  1561.098|| 1207.14 ||  1207.14 || 1268.52 || 1268.52 || 1575.42
|-
|style="text-align:left;"| Chip rate, Mchips/s || 2.046 ||2.046 ||2.046 ||10.230||10.230||10.230||1.023
|-
|style="text-align:left;"| Code period, chips || 2046 ||  ??  ||2046||  ?? || 10230|| ??  ||1023
|-
|style="text-align:left;"| Code period, ms || 1.0 ||>400 ||1.0||>160||1.0||>160|| 1.0
|-
|style="text-align:left;"| Symbols/s || 50 || ?? || 50 || ?? || 50 || ?? || 50
|-
|style="text-align:left;"| Navigation frames, s || 6 || ?? || 6 || ?? || ?? || ??||6
|-
|style="text-align:left;"| Navigation sub-frames, s || 30 || ?? || 30 || ?? || ?? || ??||30
|-
|style="text-align:left;"| Navigation period, min || 12.0 || ?? || 12.0 || ?? || ?? || ??||12.5
|}
Characteristics of the "I" signals on E2 and E5B are generally similar to the civilian codes of GPS (L1-CA and L2C), but Compass signals have somewhat greater power. The notation of Compass signals used in this page follows the naming of the frequency bands and agrees with the notation used in the American literature on the subject, but the notation used by the Chinese seems to be different and is quoted in the first row of the table.

===Operation===
[[File:Ground track beidou-m2 satellite.jpg|thumb|right|[[Astronomy:Ground track|Ground track]] of BeiDou-M5 (2012-050A)]]
In December 2011, the system went into operation on a trial basis.<ref name="CD69">{{cite news |url=http://europe.chinadaily.com.cn/business/2011-12/28/content_14343656.htm |title=Satellite navigation system launched |work=China Daily |date=28 December 2010 |accessdate=29 December 2011}}</ref> It has started providing navigation, positioning and timing data to China and the neighbouring area for free from 27 December. During this trial run, Compass will offer positioning accuracy to within 25 meters, but the precision will improve as more satellites are launched. Upon the system's official launch, it pledged to offer general users positioning information accurate to the nearest 10&nbsp;m, measure speeds within 0.2&nbsp;m per second, and provide signals for clock synchronisation accurate to 0.02 microseconds.<ref name="BBC8">{{cite news |url=https://www.bbc.co.uk/news/technology-16337648 |title=China GPS rival Beidou starts offering navigation data |publisher=BBC  |date=27 December 2010 |accessdate=29 December 2011}}</ref>

The BeiDou-2 system began offering services for the Asia-Pacific region in December 2012.<ref name=CustomersDec2012/> At this time, the system could provide positioning data between longitude 55°E to 180°E and from latitude 55°S to 55°N.<ref>{{Cite web | url =http://www.beidou.gov.cn/2012/12/26/20121226bac9c0de3e6b430d997368b19ff2c6b5.html | script-title=zh:"5+5+4"这样的星座结构有什么特点？  | publisher =WWW.BEIDOU.GOV.CN  | date = 2012-12-26 | accessdate = 2013-01-03|language=Chinese}}</ref>

====Completion====
In December 2011, Xinhua stated that "[t]he basic structure of the Beidou system has now been established, and engineers are now conducting comprehensive system test and evaluation. The system will provide test-run services of positioning, navigation and time for China and the neighboring areas before the end of this year, according to the authorities."<ref>{{cite web
|url=http://news.xinhuanet.com/english2010/sci/2011-12/02/c_131283096.htm
|title=China launches 10th satellite for independent navigation system
|date=2011-12-02
|publisher=Xinhua
|accessdate=2011-12-23}}</ref>  
The system became operational in the China region that same month.<ref name="op_china" /> The global navigation system should be finished by 2020.<ref>{{cite web
|url=http://news.xinhuanet.com/mil/2010-03/03/content_13087844.htm
|title=BeiDou navigation system covers Asia-Pacific region till 2012
|date=2010-03-03
|publisher=Xinhua News Agency
|accessdate=2010-05-19
|language=Chinese}}</ref> As of December 2012, 16 satellites for BeiDou-2 have been launched, 14 of them are in service. And as of December 2017, 150m Chinese smartphones (20% of the market) were equipped to utilize Beidou. <ref>{{Cite news|url=http://www.theworldin.com/article/14433/edition2018digital-silk-road|title=A digital Silk Road|access-date=2017-12-03|language=en}}</ref>

==Constellation==

{|class="wikitable" style="float:right; margin: 0 0 1em 1em"
|+ Summary of satellites
! rowspan="2" | Block || rowspan="2" | Launch <br />Period || colspan="3" | Satellite launches || rowspan="2" | Currently in orbit<br /> and healthy
|-
! Success || Failure || Planned
|-
! 1
| 2000-2007 || 4 || 0 || 0 || 0
|-
! 2
| From 2007 || 19 || 0 || 1 || 16
|-
! 3
| From 2015 || 19 || 0 || 21 || 19
|-
! colspan="2" | Total
| 42 || 0 || 22 || 35
|-
| colspan="7" style="font-size: smaller;" | (Last update: September 21, 2018)<br />
For a more complete list, see ''list of BeiDou satellites''
|}

The regional Beidou-1 system was decommissioned at the end of 2012.

The first satellite of the second-generation system, Compass-M1 was launched in 2007. It was followed by further nine satellites during 2009-2011, achieving functional regional coverage. A total of 16 satellites were launched during this phase.

In 2015, the system began its transition towards global coverage with the first launch of a new-generation of satellites,<ref name="BeiDou-launch-17"/> and the 17th one within the new system. On July 25, 2015, the 18th and 19th satellites were successfully launched from the Xichang Satellite Launch Center, marking the first time for China to launch two satellites at once on top of a [[Engineering:Long March 3B|Long March 3B]]/Expedition-1 [[Engineering:Launch vehicle|carrier rocket]]. The Expedition-1 is an independent [[Astronomy:Multistage rocket|upper stage]] capable of delivering one or more spacecraft into different orbits. On September 29, 2015, the 20th satellite was launched, carrying a [[Physics:Hydrogen maser|hydrogen maser]] for the first time within the system.<ref>{{cite web|url=http://www.beidou.gov.cn/2015/09/30/201509303994d237a4c8419e925c86df8f5e1c32.html|title=我国成功发射第四颗新一代北斗导航卫星|publisher=beidou.gov.cn|date=2015-09-30}}</ref>

In 2016, the 21st, 22nd and 23rd satellites were launched from Xichang Satellite Launch Center,<ref>{{cite web|url=http://www.beidou.gov.cn/2016/02/01/20160201acefeef4af98428dad6b46b83a72b179.html|title=我国成功发射第五颗新一代北斗导航卫星|publisher=beidou.gov.cn|date=2016-02-01}}</ref> the last two of which entered into service on August 5 and November 30, respectively.<ref>{{cite web|url=http://www.beidou.gov.cn/2016/08/05/20160805be35373a002d45788fc4b8e4b798750c.html|title=第22颗北斗导航卫星正式入网提供服务|publisher=beidou.gov.cn|date=2016-08-05}}</ref><ref>{{cite web|url=http://www.beidou.gov.cn/2016/11/30/201611304b14b49a9cca4afa99b25abb519a9cee.html|title=第23颗北斗导航卫星入网工作|publisher=beidou.gov.cn|date=2016-11-30}}</ref>

==See also==
* [[Engineering:Global Positioning System|Global Positioning System]]
* Galileo
* [[Astronomy:GLONASS|GLONASS]]
* [[Astronomy:Indian Regional Navigation Satellite System|NAVIC]]
* [[Earth:Restrictions on geographic data in China#Coordinate systems|Chinese coordinate systems]]

==References==
{{Reflist|35em}}

==External links==
* [http://en.beidou.gov.cn/ Official website of BeiDou Navigation Satellite System]
* [https://web.archive.org/web/20160303223248/http://www.navchina.com/english/ BDstar Navigation]
* [http://www.globalsecurity.org/space/world/china/beidou.htm BeiDou (Big Dipper)] - GlobalSecurity.org
* [http://www.ainonline.com/Issues/03_07/03_07_china_62.htm Aviation International News]
* [https://web.archive.org/web/20160219103537/http://earth.scichina.com:8080/sciDe/EN/abstract/abstract513011.shtml Preliminary assessment of the navigation and positioning performance of BeiDou regional navigation satellite system]
* [http://earth.scichina.com:8080/sciDe/EN/abstract/abstract507876.shtml Precise orbit determination of Beidou Satellites with precise positioning]
* [https://web.archive.org/web/20100327075557/http://www.sinodefence.com/space/spacecraft/beidou1.asp BeiDou-1] - SinoDefence.com
* [https://web.archive.org/web/20110209094629/http://www.sinodefence.com/space/spacecraft/beidou2.asp BeiDou-2] - SinoDefence.com
* [https://web.archive.org/web/20130801105341/http://www.dragoninspace.com/navigation/compass-beidou2.aspx <!-- http://www.sinodefence.com/satellites/compass-beidou.asp is dead --> Compass on the Chinese Defence Today website]
* [http://www.space-track.org Compass-M1 orbit details can be found in the Space-Track catalogue with a name "Beidou M1"]
* [http://www.navipedia.org/index.php/Category:BEIDOU Navipedia information on BeiDou]—Wiki initiated by the European Space Agency

{{CNSA space program}}
{{Satellite navigation systems}}

{{DEFAULTSORT:Beidou Navigation System}}
[[Category:Satellite constellations]]

{{Sourceattribution|BeiDou Navigation Satellite System|1}}