China declared the official commissioning of the BeiDou Navigation Satellite System (BDS) on Friday, marking the formal opening of the newly completed BDS-3 system for global users.
The BDS system involves efforts of more than 400 agencies and 300,000 research personnel and technicians. The China Academy of Space Technology (CAST), developer of the satellites, has gathered leading experts and manufacturers from around the country, and integrated the most advanced technologies and high-quality materials and products for the project.
Under the mechanism, the Xi'an branch of the CAST undertook the development of rubidium atomic clocks.
Dubbed the "heart" of the navigation system, rubidium atomic clocks provide time and frequency standards for BDS satellites, and are key to the system's positioning, speed measurement and timing accuracy.
In the past two decades, the Xi'an branch has delivered more than 100 rubidium atomic clocks, including 70 high-precision rubidium clocks, to the BDS program.
China started to develop atomic clocks as early as the 1960s and 1970s. However, most of the research at that time was theoretical and ground-based.
As China decided to build its own satellite navigation system, self-developed rubidium atomic clocks proved to be of great significance to the autonomous control of the whole system.
The Xi'an branch developed the first rubidium atomic clock between 1996 and 2000, but there was still a long way to go before it could work in space as the clock had to stand the test of the vacuum environment, the impact of the launch and long-term irradiation.
In order to overcome the difficulties in developing rubidium atomic clocks for space, younger members of the research team have spent day and night in the lab and worked around the clock to carry out experiments.
"I was touched by their dedication," said Lei Wenqi, a former leader of the rubidium atomic clock project at the Xi'an branch.
China's first self-developed rubidium clock was successfully tested on a satellite in 2006. Since 2012, China's self-developed rubidium clocks have fully replaced imported rubidium clocks in some of the BDS-2 satellites. In 2016, the Xi'an branch was capable of producing up to 50 satellite rubidium clocks a year.
"In the future, our goal is to enhance the performance of rubidium clocks, and improve their daily timing accuracy from one billionth of a second to one 10-billionth of a second," Lei said.