On September 29 (UTC), 2015, Chinese conducted successful launch of Long March 3B launch vehicle carrying another BeiDou navigation satellite from Xichang Satellite Launch Center in southwest China's Sichuan Province.
According to Xinhua News, it was for the first time when BeiDou satellite featured hydrogen atomic clock. In order to prove new technologies, a series of tests related to the clock and a new navigation-signal system will be undertaken. The satellite, designated as BeiDou I2-S, was likely launched into an inclined geosynchronous orbit.
It is believed that BeiDou I2-S, built by Shanghai Small Satellite Center of the Chinese Academy of Sciences (CAS), weighs about 800-850 kg and has operational lifespan of 10 years. It represents another step to complete Phase-III of BeiDou Navigation Satellite System (BDS), which is a collective name for three generations of 'sub-systems'.
The first was BeiDou Satellite Navigation Experimental System that consisted only of three satellites and offered limited navigation services, mainly for customers in China and neighboring regions, since 2000. BeiDou second generation system, also known as COMPASS, was developed since 2007 to provide positioning, navigation, timing and short message services to civilian users in the Asia-Pacific with 10 orbiting satellites.
Construction of the global network (Phase-III) officially began in 2015. It is planned that BeiDou satellite constellation will consist by 2020, or even earlier, of 35 spacecraft – 5 at geostationary orbit, 27 at MEO, and the remaining 3 at an inclined geosynchronous orbit. As a comparison, US GPS and Russian Glonass navigation satellites are only MEO-orbiting.
The launch has become the 212th orbital mission for Long March family of rockets, and third mission to orbit a Chinese navigation satellite in 2015, after March 30 and July 25 launches. It was the 20th satellite for BeiDou Navigation Satellite System.