Beidou navigation system

The BeiDou Navigation System (simplified Chinese: 北斗导航系统; traditional Chinese: 北斗導航系統; pinyin: Běidǒu dǎoháng xìtǒng) or BeiDou (Compass) Navigation Satellite System (simplified Chinese: 北斗卫星导航系统; traditional Chinese: 北斗衛星導航系統; pinyin: Běidǒu wèixīng dǎoháng xìtǒng) is a project by China to develop an independent satellite navigation system. It may refer to either one or both generations of the Chinese navigation system.

The first BeiDou system, officially called BeiDou Satellite Navigation Experimental System, or known as BeiDou-1, consists of 3 satellites and has limited coverage and applications. It has been offering navigation services mainly for customers in China and from neighboring regions since 2000.

The second generation of the system, known as Compass or BeiDou-2, which will be a global satellite navigation system consisting of 35 satellites, is still under construction. It became operational with coverage of China in December 2011.[1] It is planned to offer services to customers in Asia-Pacific region by 2012 and the global system should be finished by 2020.

The chief designer of the BeiDou navigation system is Sun Jiadong.

Contents

Nomenclature

The BeiDou Navigation System is named after the Big Dipper constellation, which is known in Chinese as Běidǒu. The name literally means "Northern Dipper", the name given by Chinese astronomers to the seven brightest stars of Ursa Major or 'the Great Bear' constellation.[2] Historically, this set of stars was 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 system

Original ideas of a Chinese satellite navigation system had been conceived and worked on by Chen Fangyun and coworkers in the 1980s.[3]

According to the China National Space Administration, the development of the Chinese global navigation system would be carried out in three steps:[4]

  1. 2000 - 2003: experimental BeiDou navigation system consisting of 3 satellites
  2. by 2012: regional BeiDou navigation system covering China and neighboring regions
  3. by 2020: global BeiDou navigation system

The first two satellites, BeiDou-1A was launched on 30 October 2000, BeiDou-1B followed on 20 December 2000. The third satellite BeiDou-1C (as backup satellite), was put into orbit on 25 May 2003.[5][6] The successful launch of BeiDou-1C also meant the establishment of the BeiDou-1 navigation system.

On November 2, 2006, China announced that from 2008 BeiDou would offer an open service with an accuracy of 10 meters, timing of 0.2 nanoseconds, speed of 0.2 meter/second.[7]

It followed that in February 2007, the fourth and also the last satellite of BeiDou-1 system, the BeiDou-1D (sometimes called BeiDou-2A, serving as a backup satellite), was sent up into space.[8] It was reported that the satellite had suffered from a control system malfunction but was then fully restored.[9][10]

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.[11] The third satellite (Compass-G1) was carried into its orbit by LM-3C on January 17, 2010.[12] On the 2nd of June 2010, the fourth satellite was launched successfully into orbit.[13] The fifth orbiter was launched into space by LM-3I carrier rocket from Xichang Satellite Launch Center on August 1, 2010.[14] Three months later, on November 1, 2010, the sixth satellite was sent into orbit by LM-3C.[15] 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 December 1, 2011 (UTC). [16]

On January 15, 2010 the official website of the BeiDou Navigation Satellite System went online.[12]

Involvement in Galileo

In September 2003, China intended to join the European Galileo positioning system project and was to invest €230 million (USD296 million, GBP160 million) in Galileo over the next few years.[17] It's believed that China's "BeiDou" navigation system would then only be used by its armed forces.[7] 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).[18] Based on the Sino-European Cooperation Agreement on Galileo program, China Galileo Industries (CGI), the prime contractor of the China’s involvement in Galileo programs was founded in December 2004.[19] By April 2006, eleven cooperation projects within the Galileo framework had been signed between China and EU.[20]

The Hong Kong based South China Morning Post reported in January 2008[21] that China was unsatisfied with its role in the Galileo project and was to compete with Galileo in Asian market.

System Description

Experimental System (BeiDou-1)

Description

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.[22]

Unlike the American GPS, Russian GLONASS, and European 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.[5] The area that can be serviced is from longitude 70°E to 140°E and from latitude 5°N to 55°N.[9]

Completion

The first satellite, BeiDou-1A was sent into its orbit on October 31, 2000. The second satellite, BeiDou-1B was successfully launched on December 21, 2000. The last satellite of the constellation, BeiDou-1C was carried into its orbit position on May 25, 2003, this launch also completed the construction of the experimental system.[5]

Position calculation

To calculate a position, the following procedure is used:[5]

  1. A signal is transmitted skyward by a remote terminal.
  2. Each of the geostationary satellites receive the signal.
  3. Each satellite sends the accurate time of when each received the signal to a ground station.
  4. The ground station calculates the longitude and latitude of the remote terminal, and determines the altitude from a relief map.
  5. The ground station sends the remote terminal's 3D position to the satellites.
  6. The satellites broadcast the calculated position to the remote terminal.

In 2007, the official Xinhua News Agency reported that the resolution of the BeiDou system was as high as 0.5 metres, considerably better than unaided GPS.[23] With the existing user terminals appears that the calibrated accuracy is 20m (100m, uncalibrated).[24]

Terminal

The terminal can communicate with the ground station by sending and receiving short messages.

As of 2008, one BeiDou-1 terminal costs about ¥20,000RMB (US$2,929), almost 10 times the price of GPS counterpart.[25] It's said that the reason why is the terminal so expensive is due to "using expensive imported Chips"，but China seemed to have found replacement and the price could lower to less than ¥1,000RMB.[26] By the China High-Tech Fair ELEXCON 2009 (November 16–21, 2009) in Shenzhen, China, a terminal solution costing no more than ¥3,000RMB was presented.[27]

Applications

According to Sun Jiadong, chief designer of the navigation system, "Many organizations have been using our system for a while, and they like it very much."[30]

Advantages and drawbacks

Global System (BeiDou-2 or Compass navigation system)

Main article: Compass navigation system

Description

BeiDou-2 is not an extension to the existing BeiDou-1. 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 geostationary orbit),[31] that will offer complete coverage of the globe. There will be two levels of service provided; free service to civilians and licensed service to Chinese government and military users:[13][32]

Completion

It is planned that BeiDou-2 system will have more than 10 satellites by 2012 and may offer services for the Asia-Pacific region; The global navigation system should be finished by 2020.[33]

As of December 2011, ten satellites for BeiDou-2 have been launched. According to a Xinhua news report,[34] "[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." The system became operational in the China region in December 2011.[1]

List of Satellites (as of December 23, 2011)

Date Launcher Satellite Orbit Usable System
10/31/2000 LM-3A BeiDou-1A GEO 59°E  ? BeiDou-1
12/21/2000 LM-3A BeiDou-1B GEO 80°E Yes
5/25/2003 LM-3A BeiDou-1C GEO 110.5°E Yes
2/3/2007 LM-3A BeiDou-1D supersync orbit[35] No
4/14/2007 LM-3A Compass-M1 MEO ~21,500 km Testing only BeiDou-2 (Compass)
4/15/2009 LM-3C Compass-G2 Drifting No
1/17/2010 LM-3C Compass-G1 GEO 144.5°E [12] Yes
6/2/2010 LM-3C Compass-G3[36] GEO 84°E Yes
8/1/2010 LM-3A Compass-IGSO1 118°E incl 55°[37] Yes
11/1/2010 LM-3C Compass-G4 GEO 160°E Yes
12/18/2010 LM-3A Compass-IGSO2[38] 118°E incl 55° Yes
04/10/2011 LM-3A Compass-IGSO3[39] 118°E incl 55°, 200~35,991 km Yes
07/26/2011 LM-3A Compass-IGSO4[40] 35695 x 35865 km incl 55.2 deg long: 80 to 112 deg E[41]
12/02/2011 LM-3A Compass-IGSO5 35712 x 35873 km incl 55.2 deg long: 79 to 110 deg E[42]  ?

References

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