Beidou (Big Dipper)
The Beidou (Big Dipper) Navigation Test Satellite 1 (BNTS-1) was launched by a Chinese Long March 3M booster on 31 October 2000, into a geostationary orbit slot at 140 degrees East Longitude, to the east of China. It was followed by "Beidou 1B" on 21 December 2000, which was placed in a geostationary slot at 80 degrees East longitude. Beidou 1C was launched into an orbit at at 110.5°E on 24 May 2003 from the Xichang Satellite Launch Center on a CZ-3A booster. With this third launch, China claimed to have completed a constellation of three navigational satellites.
The Beidou satellite navigational system provides positional information for highway, railway and marine transportation. The three satellites have formed a complete satellite navigation and positioning system, which will help to ensure all-weather navigation and positioning information. The China-made system will play an important role in economic matters, offering efficient navigation and positioning services for the sectors of transportation, meteorology, petroleum production, forest fire prevention,disaster forecast, telecommunications and public security. The navigation system, which serves as a radio beacon in outer space, can help subscribers know their location at any time and place with accurate longitude, latitude and altitude data.
China based the Bei Dou satellites on the three-axis stabilised DFH-3 satellite bus, to deliver services such as power and attitude control. China is one of the few countries in the world capable of developing such a system on its own, and has also made some innovations in the positioning property of the system. Both the satellite and carrier rocket were developed by the Chinese Research Institute of Space Technology and China Academy of Launch Vehicle Technology, which are under the China Space Science and Technology Group. New testing procedures were adopted in the launch, which not only help reduce the time needed for preparing for the launch, but also improve the quality of the carrier rocket, enabling China to be at the forefront in this field around the world, said the experts.
The precise nature of this system remains somewhat obscure, but it appears to be analogous to the Wide Area Augmentation System [WAAS] implemented in the United States to supplement the Global Positioning System. In the American WAAS, a network of precisely surveyed ground reference stations receive GPS signals, which determine if errors exist and compute corrections. These corrections are then transmitted from a geostationary communication satellite on the same frequency as GPS. This could enable China to continue to use the American GPS system, even in the face of American efforts to deny GPS to adversaries in wartime.
