The Long March-3B rocket carrying two satellites for the Beidou Navigation Satellite System blasts off from the Xichang Satellite Launch Center in Sichuan Province on Saturday. Photo: Xinhua

China has successfully launched two satellites for its homegrown satellite navigation system in a move to advance the system's global coverage, as China strives to alleviate military dependence on the US Global Positioning System (GPS) due to national security concerns.

Launched from Xichang Satellite Launch Center in Southwestern China's Sichuan Province at 8:29 pm Saturday, the two satellites are the 18th and 19th in the Beidou Navigation Satellite System (BDS), China's global navigation and positioning network.

It is the first time China has launched a medium earth orbit (MEO) new-generation Beidou navigation satellite, the main type of satellites used for BDS, said Yang Changfeng, Beidou's chief designer. 

"The successful launch marks another solid step in building Beidou into a navigation system with global coverage," the satellite launch center said.

The BDS global network will have 35 satellites, including 27 MEO satellites.

The new-generation satellites will operate with a new satellite navigation platform and provide better services, Yang said.

The two new satellites will join the 17th, which was launched in late March, to test a new type of navigation signaling and inter-satellite links.

BDS currently only covers Asia-Pacific areas but is set to cover the whole world by 2020.

The new satellites will expand coverage and improve accuracy to meet the demands of global users, a Beijing-based aerospace expert, who requested anonymity, told the Global Times.

"The inter-satellite link test will help ensure the stability of the system," he said. Currently, most global navigation systems rely heavily on ground station support. If these stations were destroyed, the system would be useless, the expert said. "Inter-satellite links will help the system maintain operations even if ground stations are experiencing trouble."

The two satellites were onboard a Yuanzheng space tug on a Long March-3B/Expedition-1 launch vehicle. This is the first time that an independent craft installed on the carrier rocket has sent two satellites directly into different orbits, according to Yang.

"Previously, satellites reached orbit after being dropped from the carrier. This launch technique saves fuel, making the process more efficient," the anonymous aerospace expert said.

China launched its first BDS satellite in 2000. The system began providing positioning, navigation, timing and short message services to civilian users in China and surrounding areas in the Asia-Pacific in December 2012.

The system has been gradually put into use in extended sectors, including transportation, weather forecasting, the fishing industry, forestry and telecommunications. It also has military applications.

It will likewise be used to help log and detect possible leaks in gas pipelines, the National Administration of Surveying, Mapping and Geoinformation announced in June.

Sensitive information

Experts note that developing BDS will be crucial to China's national security.

China's military used to rely on the US GPS and Russian GLONASS systems, which risked possible sensitive information leaks, Song Zhongping, a military commentator and former lecturer on missile technology, told the Global Times.

"When it is completed, BDS could provide a better service than GPS while safeguarding the confidentiality of sensitive information. It will help military forces to position targets or navigate and can be used for communication, which GPS cannot," Song said.

Song added that it is necessary for China to improve the system, given the rising tensions in the region. 

The anonymous aerospace expert also noted that the development of a navigation system with global coverage could also safeguard China's economic security.

"Navigation systems are widely used in financial and trading areas and a small difference in timing can threaten a country's economic foundation. A domestic system can provide better protection," the expert said.

Song agreed, saying that BDS will generate great economic benefits. The gross value of the BDS system was estimated to reach 225 billion yuan ($36.3 billion) in 2015.

"A global navigation system can generate great economic interest and global competition is intense. If China doesn't speed up, there will be rivalry and there won't be enough room in orbit," the expert said.