Tianlian

{{Infobox spacecraft class|name=Tianlian|country=China|caption=|bus=*DFH-3 - first generation

DFH-4 - second generation|applications=Tracking and Data Relay Satellite System|orbits=Geostationary|operator=China Aerospace Science and Technology Corporation (CASC)|manufacturer=China Academy of Space Technology (CAST)|image=|mass=|lifetime=|power=|status=In service|launched=10|operational=7|first=Tianlian I-01
25 April 2008|last=Tianlian II-05
27 April 2025|retired=}}

Tianlian (Simplified Chinese: 天链, Traditional Chinese: 天鏈, English: Sky Link) also known as CTDRS, is a Chinese data relay communication satellite constellation. The constellation serves to relay data from ground stations to spacecraft and rockets, most significantly China's crewed spaceflight program. The system currently consists of ten satellites in two generations, with the first satellite being launched in 2008.

Mission

Tianlian is used to provide real-time communications between orbiting satellites and ground control stations. The Chinese tracking and data relay satellites were developed by the China Academy of Space Technology (CAST) and it is similar to the American Tracking and Data Relay Satellite System (TDRSS) in concept. The system is designed to support near-real-time communications between orbiting spacecraft and ground control, as well as complement the ground-based space tracking and telemetry stations and ships in tracking spacecraft.{{cite web|title=Display: Tianlian 2-01 2019-017A|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=2019-017A|access-date=2020-11-16|website=nssdc.gsfc.nasa.gov|publisher=NASA}} {{PD-notice}} This is necessary because ground stations can only maintain contact with a satellite while it is overhead. Positioning multiple satellites in geostationary orbit ensures that the ground station and satellite are both always in view of at least one relay satellite, allowing for constant communication between the ground station and target satellite. The system provides data relay services for crewed Shenzhou missions, from Shenzhou 7 onwards, the Tiangong space station, and interplanetary missions.{{cite web|date=24 June 2021|title=China's relay satellites facilitate clear, smooth space-ground communication|url=http://www.xinhuanet.com/english/2021-06/24/c_1310026228.htm|access-date=29 June 2021|work=Xinhua News Agency}}{{cite web|author=Stephen Clark|date=2008-04-25|title=Chinese data relay spacecraft put into orbit|url=http://www.spaceflightnow.com/news/n0804/25tianlian1/|access-date=2008-04-26|publisher=Spaceflight Now}}{{cite news|last1=Li|first1=Guoli|last2=Wang|first2=Ran|date=2020-07-21|title=我国天基测控系统团队完成多项技术状态准备静待天问一号发射|language=zh|agency=Xinhua News Agency|url=http://www.xinhuanet.com/mil/2020-07/21/c_1210712768.htm|access-date=23 June 2021}} All satellites were launched from the Xichang Satellite Launch Center and operate in geostationary orbit.{{cite web|author=David Todd|date=2012-07-26|title=Chinese data relay satellite TianLian-1C is launched successfully on a Long March 3C|url=http://www.flightglobal.com/blogs/hyperbola/2012/07/chinese-data-relay-satellite-t.html|access-date=2012-08-17|publisher=Flightglobal}}{{cite web|date=14 May 2020|title=Display: Tianlian 1-02 2011-032A|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=2011-032A|access-date=11 December 2020|publisher=NASA}} {{PD-notice}}{{cite web|date=14 May 2020|title=Display: Tianlian 1-03 2012-040A|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=2012-040A|access-date=11 December 2020|publisher=NASA}} {{PD-notice}}{{cite web|date=14 May 2020|title=Display: Tianlian 1-04 2016-072A|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=2016-072A|access-date=11 December 2020|publisher=NASA}} {{PD-notice}}

Tianlian I

Tianlian I consists of five satellites, all based on the DFH-3 satellite bus. The first satellite of the series, Tianlian I-01, was launched on the maiden flight of the Long March 3C launch vehicle on 25 April 2008.{{cite web|author=Yan Liang|date=2008-04-25|title=China blasts off first data relay satellite|url=http://news.xinhuanet.com/english/2008-04/26/content_8052455.htm|access-date=2008-04-26|publisher=Xinhua|archive-date=29 April 2008|archive-url=https://web.archive.org/web/20080429170953/http://news.xinhuanet.com/english/2008-04/26/content_8052455.htm|url-status=dead}}[http://china.rednet.cn/c/2008/04/26/1493822.htm 我国成功发射首颗数据中继卫星(组图)] With the launch of Tianlian I-03, a spacecraft could be tracked for 70% of its orbit, compared to only 15% without the constellation.{{cite web|author=Xin Dingding|date=2012-07-27|title=Satellite launch completes network|url=http://www.chinadaily.com.cn/china/2012-07/27/content_15622172.htm|access-date=2012-08-17|publisher=China Daily}}

Tianlian II

Tianlian II is the second generation of the constellation and currently consists of 5 satellites based on the DFH-4 satellite bus. The second generation system greatly improves data transmission rates and its multi-targeting ability. This in turn improves spacecraft operational safety and flexibility.{{cite web|title=中国成功发射"天链二号01星"-中新网|url=http://www.chinanews.com/gn/2019/04-01/8796135.shtml|access-date=2020-11-16|website=chinanews.com}}{{cite news|title=China successfully launches second generation data relay satellite|publisher=The Economic Times|url=https://economictimes.indiatimes.com/news/international/world-news/china-successfully-launches-second-generation-data-relay-satellite/articleshow/68665863.cms?from=mdr|access-date=2020-11-16}}

Satellites

class="wikitable"

!Satellite

!Simplified Chinese Name

!Launch (UTC){{cite web|last=McDowell|first=Jonathan|title=Launch Log|url=http://planet4589.org/space/log/launchlog.txt|access-date=11 December 2020|publisher=Jonathan's Space Report}}

!Carrier Rocket

!Launch Site

!Bus

!Longitude{{cite web|date=1 January 2021|title=Union of Concerned Scientists Satellite Database|url=http://www.ucsusa.org/satellite_database|access-date=8 July 2021|publisher=UCS}}

!Status

!COSPAR ID

!SATCAT no.

colspan="10" |First Generation

Tianlian I-01

|天链一号01星

|25 April 2008, 15:35

|Long March 3C

|XSLC LC-2

|DFH-3

|77.0° East

|Inactive