Beidou navigation system

Beidou Navigation System (CJKV|s=北斗导航系统|p=běidǒu dǎoháng xìtǒng) or Beidou Satellite Navigation and Positioning System (CJKV|s=北斗卫星导航定位系统|p=běidǒu wèixīng dǎoháng dìngwèi xìtǒng) is a project by China to develop an independent satellite navigation system. The current Beidou-1 system (made up of 4 satellites) is experimental and has limited coverage and application. However, China has planned to develop a truly global satellite navigation system consisting of 35 satellites (known as Compass or Beidou-2).

Name

Beidou Navigation System is named after the Big Dipper constellation, which is known in Chinese as "Běidǒu". The name literally means "Northern Dǒu",which are seven brightest stars of the constellation Ursa Major, the Great Bear. Historically, this set of stars has been used in navigation to locate the North Star Polaris. As such, Beidou also serves as a metaphor for the purpose of the satellite navigation system.

History

Beidou 1A was launched on 30 October 2000, Beidou 1B followed on 20 December 2000, and Beidou 2A was put into orbit on 24 May 2003. [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] The latest Beidou navigation satellite was successfully launched on 3 February 2007.

In September 2003, China joined the Galileo positioning system project. China will invest €230 million (USD296 million, GBP160 million) in Galileo over the next few years. [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] Galileo positioning system is currently not yet operational.

On November 2, 2006, China announced that from 2008 Beidou would offer open service with an accuracy of 10 meters. [cite news
first=Paul
last=Marks
title=China's satellite navigation plans threaten Galileo
publisher=NewScientist.com
url=http://www.newscientist.com/article/dn10472-chinas-satellite-navigation-plans-threaten-galileo.html |accessdate=2006-11-09]

atellites

* Note: all dates are based on China Standard Time

Current technology (Beidou-1)

Unlike the GPS, GLONASS, and Galileo systems, which use medium Earth orbit satellites, Beidou 1 uses satellites in 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. The area that can be serviced is from 70°E to 140°E, and from 5°N to 55°N.

The Beidou 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. [ [http://www.vectorsite.net/ttgps_2.html#m2 International Navigation Satellite Systems] ]

To calculate a position, the following procedure is utilized:
#A signal is transmitted skyward by a remote terminal.
#Each of the geostationary satellites receive the signal.
#Each satellite sends the accurate time of when each received the signal to a ground station.
#The ground station calculates the longitude and latitude of the remote terminal, and determines the altitude from a relief map.
#The ground station sends the remote terminal's 3D position to the satellites.
#The satellites broadcast the calculated position to the remote terminal.

Additionally, the terminal can communicate with the ground station via sending and receiving short messages.

Future Plans (Beidou-2 or Compass)

The two satellites (1A,1B) mentioned above were designed as experimental satellites; China has yet to build the remaining satellites to make Beidou an operational global positioning utility.

The new system will be a constellation of 35 satellites, which include 5 geostationary orbit (GEO) satellites and 30 medium Earth orbit (MEO) satellites, that will offer complete coverage of the globe. There will be two levels of service provided; free service for those in China, and licensed service for the military.

* The free service will have a 10 meter location-tracking accuracy, will synchronize clocks with an accuracy of 50 ns, and measure speeds within 0.2 m/s.
* The licensed service will be more accurate than the free service, can be used for communication, and will supply information about the system status to the users.

Two satellites for Beidou 2 have been launched in early 2007. In the next few years, China plans to continue experimentation and setup system operations.

References

External links

* [http://www.navchina.com/company-english/company-english.asp 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]
* [http://www.sinodefence.com/strategic/spacecraft/beidou1.asp BeiDou-1] - SinoDefence.com
* [http://www.sinodefence.com/strategic/spacecraft/beidou2.asp BeiDou-2] - SinoDefence.com