China planning its own full Earth GPS system by 2015
By Rick C. Hodgin
Monday, January 19, 2009 11:45
http://www.tgdaily.com/content/view/41086/113/
Beijing (China) - China's state media announced today that it plans to introduce its own set of geostationary orbiting satellites for a Chinese GPS system by the year 2015. The Beidou Navigation System (BNS) will enable its military and civilian users to find their way anywhere in the world without relying on the U.S. Global Positioning System (GPS).


According to Zhang Xiaojin, director of astronautics at China's Aerospace Science and Technology Corp, "The system will shake off the dependence on foreign systems." China plans to launch more than 30 satellites by 2015. Ten will be launched in 2009 and 2010. These will be added to the five it already has in orbit, according to the report.

The five-satellite system allows regional navigation throughout mainland China. As the new system expands it will eventually encircle the globe creating an alternative to the U.S. dominated GPS system in use today. China also views BNS as a rival to the EU's Galileo Position System and Russia's Global Navigation Satellite System (GLONASS).

GPS systems operate by receiving signals on the Earth from geostationary satellites which broadcast their location information constantly. While it only requires three sources to be able to triangulate a position, there are distortions in space-time around the Earth's gravitational field (as well as small ones introduced by the sun, moon and other planets). As a result, more than three satellites are used to correct for this error.

Some of the highest-end, several thousand dollar professional GPS systems with land-based augmentation are accurate to within one or two millimeters. The typical GPS found in most portable devices, including Garmins and TomToms, are accurate to within about 18 feet.