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China's Beidou satellite navigation system (also known as COMPASS), a potential competitor to the US Global Positioning System (GPS), has been fast-tracked following the announcement of the 12th Five-Year Plan (2011-15).

Beidou satellite navigation system.[File photo]

According to the Xinhua News Agency, the Beidou-II system will involve more than 10 satellites by 2012, covering the Asia-Pacific region. The global navigation system, which consists of 35 satellites, is planned to be completed by 2020.

Beidou was conceived in the mid-1980s. Unlike GPS, which uses a large constellation of satellites, the early Beidou system adopted a dual-satellite positioning method, whereby the ground station sends inquiry signals to users via two satellites, and the user terminal sends a response that is then carried via the two satellites. The user's two-dimensional position is then derived using geometrical calculations based on the travel time of the signals and the positioning of the satellites, mapped against stored three-dimensional terrain data, and the information sent back to the user.

After years of study and experiment, the first two satellites, Beidou-1A and 1B, were successfully launched into geostationary orbit in 2000 and began offering navigation and positioning services in late 2001. The successful launch of the backup satellite in 2003, the Beidou-1C, marked the completion of the Beidou-1 project. The service became available to civilians in April 2004, making China the third country, after the US and Russia, to deploy an operational satellite navigation system. France, the EU, and Japan also have plans for regional navigation networks.

Beidou is classified as an "active system," as users have to broadcast data rather than simply receive their position. "An active system has disadvantages, because electronic support measures, such as radio location systems, can pick up the signal and derive the direction and position of users," a source inside the aerospace industry told the Global Times. "In a passive system such as GPS, the terminal receives signals from at least three to four satellites at any given places and derives its 3D position data itself by computing the distance to each satellite," he added.

The source also confirmed that the active Beidou system is not very capable at tracking velocity, explaining the signal travels for about one second during the whole positioning process. "Aerial vehicles can travel for over several hundred meters during one second, resulting in relatively high error in measurement," the source said.

In contrast, GPS terminals have been integrated in most modern military aircraft and the guidance kits of many precision guided bombs and missiles.

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