Do you know the story behind Beidou satellite?

From the successful launch of the first BeiDou-1 test satellite in October 2000 to the launch of the last BeiDou-3 global networking satellite on June 23, 2020, China has launched 4 BeiDou test satellites and 55 BeiDou-2 and -3 networking satellites into space in 44 launches over the past 20 years, ushering in an era of China's "Star Network" navigation around the world. Recently, Face to Face interviewed Xie Jun, chief designer of BeiDou-3 navigation satellite, to tell the story behind BeiDou satellites.

It took three years to overcome technical difficulties and the launch was successful with only two hours left before the deadline.

In 2004, the BeiDou-2 satellite navigation system was officially launched. Xie Jun, who has 22 years of work experience and has participated in the development of many major projects, was appointed as the chief designer of the BeiDou-2 satellite system. He recalled, "From 2004 to 2007, this was probably the most difficult period for me as the chief designer."

The BeiDou-2 satellite navigation system is based on the BeiDou-1. It has been expanded from providing services only for China to covering the Asia-Pacific region. It requires the support of 14 satellites and also needs to overcome some basic problems.

However, according to ITU regulations, the frequency resources and orbital position resources of navigation satellites are limited to 7 years from the date of application, and will not be automatically invalidated after the expiration of the period. This means that he and his team only have three years to solve the basic problems and send the satellite into space before April 17, 2007.

In the early morning of April 14, 2007, the first medium-earth orbit test satellite of the BeiDou-2 system was successfully launched into space. However, there was still one key step to fulfill the ITU regulations.

Xie Jun said that this was a risky but successful decision. "I think there was a certain element of luck. We must have the courage to take responsibility, but not be blind. We still need a lot of ground experimental data to support it."

Xie Jun: Not only do we need to launch the satellite, but we also need to transmit the radio signals carried by the satellite to the ground and receive the signals. Before the microwave components of the satellite are launched into space, they may carry some moisture on the ground. Before they are completely released, a microwave phenomenon may cause discharge, ablation of the device surface, and may affect the function of the product.

At 20:14 on April 16, 2007, Xie Jun made a decisive decision and ordered the payload products on the test satellite to be powered on. One hour and 32 minutes later, the ground system correctly received the navigation signal broadcast by the satellite. At this moment, there were only two hours left before the expiration date of the space frequency application stipulated by the ITU.

Xie Jun said that this was a risky but successful decision. "I think there was a certain element of luck. We must have the courage to take responsibility, but not be blind. We still need a lot of ground experimental data to support it."

Imported atomic clocks could not be delivered on time, so they produced China's own atomic clocks

From the project launch in 2004 to its completion in 2012, the positioning accuracy of the BeiDou-2 satellite navigation system was improved from 20 to 30 meters for BeiDou-1 to 10 meters for both horizontal and vertical directions, which was close to the civilian standard of GPS at that time. The improvement of positioning accuracy requires the support of a number of key technologies and components on the satellite, including the atomic clock, which is known as the "heart of the navigation satellite."

In 2006, the BeiDou-2 project was almost aborted due to the failure of imported atomic clocks to be delivered on time, which deeply hurt Xie Jun. He realized that as a major space power, China must have an independent time and frequency reference system, which requires overcoming the technical difficulty of atomic clocks.

Xie Jun: When the project was launched, I thought how could it be completed? Several of our units had great difficulties in making atomic clocks for BeiDou-2. Often when the atomic clocks were needed for the satellite, we had to rush and struggle to deliver them on time.

At that time, the first onboard atomic clock developed often had sudden signal jumps during operation and had very poor accuracy. Xie Jun's own major was not in atomic clock research, so he could only work on the front line, analyzing problems with the experts who developed atomic clocks and trying every possible way to overcome difficulties. Three years later, they overcame the hurdle of atomic clocks.

The atomic clock currently used by Beidou satellites has a timing accuracy equivalent to an error of only 1 second in 3 million years, reaching the world-class level.

"To contribute to the country's major projects, we must do our job well"

After completing the construction of the BeiDou-2 system, Xie Jun began to serve as the deputy chief designer of the BeiDou-3 project and the chief designer of the BeiDou-3 navigation satellite. During this period, Xie Jun worked continuously for a long time and fainted three times at the satellite launch site. Every time he woke up, he immediately rushed back to his post.

Xie Jun recalled, "One New Year's Eve, we were at work, and we were eating dumplings in the cafeteria. When we were eating, no one left, so we immediately went back to test."

Xie Jun: The process was not easy, but everyone felt that they could contribute to the country's major projects and they must do their jobs well.

On June 23, 2020, the last BeiDou-3 satellite was successfully launched, completing the BeiDou global network. The localization rate of all BeiDou-3 satellites has increased from 80% to 100%, making China the third country in the world to have a global satellite navigation system after the United States and Russia.

At the same time, Xie Jun and his team launched the demonstration of the next-generation Beidou system construction and development system and began to tackle key technologies. By 2035, they will design and build a national comprehensive timing, navigation and positioning system with the Beidou system as the core.

Xie Jun: Currently, users can get good navigation, positioning and timing services on the ground and within 1,000 kilometers above the ground. The next system will address higher space requirements. In terms of positioning accuracy, it will address centimeter-level navigation requirements such as autonomous driving, which everyone is looking forward to.