2018年CRI China sends twin navigation satellites into space（在线收听）

China has launched two satellites into space on a Long March carrier rocket from the Xichang Satellite Launch Center in Sichuan Province. 

The satellites are part of the country's growing BeiDou Navigation Satellite System. 

The launch of the Long March-3B carrier rocket marks the 269th mission for the Long March rocket family.

The satellites, number 30 and 31 in the BeiDou system, entered orbit more than three hours after launch. 

After the satellites pass a series of tests, they will work together with the six BeiDou-3 satellites that have already been launched. 

The new satellites contain a new type of atomic clock that will help to improve the accuracy of the BeiDou Navigation System.

An atomic clock is the most accurate type of timing device available. Accurate timing is essential for measuring the position and velocity of the navigation satellite, which in turn, provides people using the navigation system with an accurate measurement of their location. 

Li Jing is a researcher at China's Aerospace Science and Industry Corporation. Li says that an atomic clock based on hydrogen atoms was used in these satellites, in place of the rubidium type of atomic clock used in previous satellites.

"The hydrogen atomic clock allows for more stability and accuracy compared with a rubidium atomic clock. Its frequency drift rate is also lower. The frequency can be maintained without frequent calibration. These features help improved the performance of the satellites. The U.S.'s GPS satellites use cesium and rubidium atomic clocks. The atomic clock carried by the Beidou system can achieve similar performance as GPS. And the hydrogen atomic clock is 100 percent domestically made."

China has a busy schedule of satellite launches planned for 2018, including 18 of the new type of Beidou-3 satellites. 

By around 2020, when the Beidou system goes global, it will use a network of more than 30 satellites.

Chen Lin, from the China Electronics Technology Group, said the new satellites represent a great improvement in performance.

"The newly launched satellites perform as well as we expected. Some technologies are even better than we expected. In general, we delivered an effectively functioning system. For example, the performance of the atomic clocks matches our expectations."

Named after the Chinese term for the Big Dipper, the BeiDou system started providing satellite navigation services over China in the year 2000. It is due to start serving countries along the Belt and Road by the end of 2018.