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The Beidou (“Northern Dipper”)/Compass system is China’s indigenously developed PNT satellite system. It is intended to serve as an alternative to GPS, the Russian Glonass, and the European Galileo system. In 2000, China launched the first satellites of a first-generation PNT constellation using satellites in GEO. The system provided cover-age only over East Asia, positioning accuracy was only about 100 m, and, because the system required two-way communication between the users and a central control station, the user equipment was bulkier and required greater power than the U.S. GPS system, in which the user equipment consists of passive receivers (“Beidou/Compass Series,” 2010).
Although two of the original Beidou satellites remain operational (Beidou 1B and 1C), in 2007, China began deploying the first satel-lites of a second-generation system, called Compass or Beidou 2. This system, like GPS, will be a one-way passive system with global cover-age. Unlike GPS, however, which includes only satellites in medium earth orbit (MEO), Compass will include satellites in a combination of MEO and geosynchronous orbit (GSO).5 The system will provide commercial customers with positioning accuracy to within 10 m and timing accuracy (needed for the synchronization of automated dat-alinks) to within 10 nanosec. Greater accuracy will be available to Chinese military users (“UCS Satellite Database”; “Beidou/Compass Series,” 2010).
By August 2010, four operational Beidou 2 satellites were in orbit (one in inclined GSO, two in GEO, and one in MEO). Twelve satel-lites are planned to be in orbit by 2012, providing a regional navigation system covering China and its neighboring areas. A complete system of 35 satellites is intended to be in place by 2020. These will include five satellites in GEO, 27 in MEO, and three in inclined GSO (“UCS Satellite Database”; “Beidou/Compass Series,” 2010).
The satellites appear to be experiencing technical problems. In February 2007, one of the four first-generation Beidou satellites
GSO is an orbit in which the satellite is at an altitude (42,164.km) such that it revolves around the earth at the same angular rate as the earth’s rotation but is not necessarily in the same plane as the earth’s equator. Thus, GEO is a special type of GSO.
(Beidou 1D) experienced an explosion while transiting to GEO, then it had trouble deploying its solar panels after reaching GEO. Finally, in February 2009, its orbit was raised by 130 km in an apparent attempt to place it in a “graveyard” orbit (an orbit in which nonfunctional sat-ellites are placed, where they will not interfere with operational sat-ellites). The first of the new generation of geostationary spacecraft (Beidou 2B/Compass G2) apparently lost control after being launched in April 2009. In April 2010, an analysis was published stating that there were frequent spikes in the signal from the first MEO Compass satellite, suggesting that there is a problem on the satellite. Thus, three out of nine Beidou satellites launched so far have experienced technical problems (“Beidou/Compass Series,” 2010).
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
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