What is Beidou? Seven problems to understand the global navigation system of Beidou

 What is Beidou? Seven problems to understand the global navigation system of Beidou

The Beidou satellite in the sky is always convenient for our life. Turn on the mobile phone, rely on the electronic map to navigate the destination, or check where the take away kid in the software has gone. These applications in daily life use the Beidou system. At present, 70% of new mobile phones can use Beidou service.

Two and a half years, 30 satellites, the largest satellite system in China with the widest coverage and the highest performance requirements, what is it? Here are 7 questions for you to understand.

30 satellites of beidou-3 system are distributed on three orbital planes. China Satellite Navigation System Management Office


One question: what is Beidou?

Generally speaking, beidou-3 system can be regarded as Chinese version of GPS.

Beidou satellite navigation system is built and operated independently by China focusing on national security and economic and social development. It can provide all-weather, all-weather, high-precision positioning, navigation and timing services for global users, and belongs to an important national space-time infrastructure.

Beidou has experienced three generations of development. Beidou No. 1 system was built at the end of 2000. It is a test system to provide services to China. From 2007 to 2012, Beidou II system was completed to provide services to the Asia Pacific region. From 2017 to 2020, the beidou-3 system, composed of 30 stars, was built, that is, the global navigation system, which can serve the world.

Second question: what kind of net has Beidou set up?

Beidou-3 is not a satellite, but a system, including 30 satellites. These satellites form a network that envelops the earth and its neighboring space. Therefore, the construction process of beidou-3 is also known as Networking.

The 30 satellites on this network are distributed in three different altitude orbit planes, including 24 MEO satellites (earth medium circle orbit satellites), 3 IGSO satellites (tilt geosynchronous orbit satellites) and 3 geo satellites (geostationary orbit satellites).

MEO satellite is the main satellite of beidou-3, which operates in an orbit about 20000 kilometers away from the earth. It mainly provides navigation, positioning and time service, as well as global short message communication, international search and rescue and other special services. IGSO satellite mainly operates in an orbit of 36000 kilometers away from the earth. Because it is a high orbit satellite, it can effectively increase the number of satellites visible in the Asia Pacific region and provide better services for the Asia Pacific region. GEO Satellite mainly operates in the geostationary orbit 36 thousand kilometers away from the earth, providing regional short message, star based enhancement and other special services.

The constellation design of the three orbital surfaces is the original creation of the Beidou navigation system, and also has significant advantages. Compared with other navigation systems, the most prominent feature is the addition of high orbit satellites, the higher the anti occlusion ability of satellites, especially in low latitude areas. At the same time, with the use of high orbit satellites, Beidou has also added communication functions to provide global exclusive short message service.

Third, what are the features of Beidou?

Short message is a unique function of Beidou, which extends from Beidou No. 1 to Beidou No. 3 system.

Navigation satellite and communication satellite are two kinds of satellites, but Beidou navigation satellite has additional communication function. Wang Bo, deputy secretary-general of China satellite navigation and positioning Association, said that Beidou users can not only know their own location, but also tell others their own situation through short message by using the terminal.

In areas with mobile network coverage, this function seems to be a weak point, but in a large number of areas without network coverage, such as deserts, oceans, mountains, forests, etc., satellite communication must be relied on. Generally, satellite communication is more expensive, while Beidou short message is cheaper, and it is attached to the navigation terminal, which is more convenient, and it has been effectively applied in emergency rescue, pelagic fishery and other fields.

Today, the short message communication ability of beidou-3 is significantly improved, from 120 Chinese characters sent at a time to more than 1000 Chinese characters at a time, and it can also send information such as pictures, with more application scenarios.

In addition to short message, Beidou system has many special applications. Another example is international search and rescue.

The six MEO satellites of beidou-3 system are equipped with search and rescue payloads, which can provide search and rescue services for global users together with other global satellite search and rescue systems. For example, when a fishing boat is in distress in bad weather during its operation, the search and rescue terminal will automatically send the search and rescue signals to the satellite after touching the water. The satellite will transmit the information to the ground system. The ground system can quickly calculate the location of the people in distress and tell the rescue forces nearby to carry out the search and rescue work quickly. Lin Baojun, chief engineer of Beidou satellite system, previously introduced.

Xichang Satellite Launch Center will transport the long march 3B carrier rocket launched by the last networking satellite of beidou-3 to the launch area. First Academy of Aerospace Science and Technology Group

There are four global navigation systems built or under construction in the world. In addition to Beidou, there are GPS in the United States, GLONASS in Russia and Galileo in the European Union. GPS began to provide global services in the last century, and it has a large scale of application in China, but China has still made great efforts to build its own Beidou system.

Xie Jun, chief designer of beidou-3 satellite project, said that satellite navigation system is an important space infrastructure of a country, even the support and foundation of infrastructure. If we use foreign key technologies to purchase foreign core products, once they are out of stock, the system will not be able to run stably for a long time.

Wang Bo said that in many important industries of national economy and peoples livelihood, the space-time benchmark provided by navigation system is indispensable. Precise time and space benchmark can be said to be a countrys strategic resources. Industries such as communication, power grid and finance all need precise positioning and timing functions of navigation satellites.

5. How to use the service of Beidou?

For ordinary individual users, there is no need to choose a special way to use Beidou service. Beidou service has been built into our mobile phones, cars and other devices through chips. When we use navigation and positioning services, we have already used Beidou satellite.

Yang Changfeng, chief designer of Beidou satellite navigation system engineering, previously introduced that 70% of Chinas new smartphones have built-in Beidou chips, or Beidou and GPS dual-mode chips. The dual-mode chip can use GPS and Beidou system at the same time. This kind of use is not either or, but uses Beidou and GPS satellites at the same time. The chip will automatically select the navigation satellite signals that can be received at present, which may come from the combination of Beidou satellite and GPS satellite. Through four or more satellites, the current position can be calculated.

Beidou has also been widely used in transportation, agriculture, forestry and fishery, disaster reduction and relief and other industries. It can be realized through some terminal equipment with Beidou chip in it.

Six questions: why can the Beidou system be built at a high speed?

The construction of beidou-3 is called speed. From the launch of the first star on November 5, 2017 to the end of the official period on June 23, 2020, 30 star networks have been completed in just two years and seven months, during which, two beidou-2 satellites have been launched, improving the constellation of beidou-2.

This is the largest constellation in Chinas aerospace history, and also the most intensive satellite launch of the same type. In the field of high-risk aerospace, quality and progress, quality and quantity have always been a pair of contradictions. Xie Jun once said. At this speed, the success rate is 100%. In short, it depends on the rapid manufacturing capacity of rockets and satellites, as well as the mature launch technology.

Ran Chengqi, director of China satellite navigation system management office, said that Beidou system has fully borrowed, inherited and carried forward the unique management mode of China aerospace, and has also innovated many organizational management modes. For example, a global continuous monitoring and evaluation system has been established to monitor the operation of all satellite navigation systems, so as to improve the learning of Beidou system.

The launch rocket of Beidou satellite is a series of long triple a rockets, which are divided into three configurations: long triple A, long triple B and long triple C. Long triple a series is also the launch vehicle series with the largest number of launches and the strongest adaptability in China. At present, the number of launches is 112. Starting from the Beidou-1 system, 59 Beidou satellites have been launched 44 times by the Chang San Jia series, with a success rate of 100%.

In recent years, the long triple a series Rockets have been in the state of high-strength density launch, winning the first rocket model in the number of launches in China for five consecutive years. In order to launch 30 Beidou satellites in two-and-a-half years, the long 3A series Rockets have also been improved to meet the needs of three kinds of orbit launch.

According to China Academy of launch vehicle technology, the long triple a series of rockets also have the ability to launch large satellites from two satellites, long-time taxiing at the last stage, narrow window / multi window or even zero window launch, and the ability to delay the launch for another 24 hours after low-temperature propellant filling, which ensures that the long triple a series can meet the needs of most payloads.

What are the difficulties in the construction of Beidou?

In an interview, Yang Changfeng once told the story of keeping track frequency of beidou-2.

The premise of launching a navigation satellite into the sky is to have legal orbit position and frequency resources, which are the precious resources that all countries in the world must contend for. On April 17, 2000, China won the orbit position and frequency resources in the International Telecommunication Union. According to the regulations, it is necessary to launch the satellite and receive the signal successfully within the 7-year validity period.

In fact, beidou-2 was set up in 2004, only three years. It is necessary to develop and successfully launch the first satellite, which generally takes five years. This star is not only the first satellite of the beidou-2 system, but also has the responsibility of launching the Beidou space orbit position and radio frequency.

The Beidou team worked day and night to enter the launch phase in early April 2007. At that time, the satellite had been integrated with the rocket and stood on the launch tower waiting for launch, but suddenly found that the transponder was abnormal. The researchers reopened the rocket fairing and checked the satellite.

The researchers did not close their eyes for 72 hours, and eliminated the hidden danger in time. Finally, at 4:11 a.m. on April 14, 2007, the satellite was successfully launched. At about 8:00 p.m. on April 17, when the satellite sent back signals, it was less than four hours away from ITUs seven-year limit. The orbit frequency resources of Chinas satellite navigation system play an important role in the construction of Beidou regional navigation system.

Yang Changfeng said that foreign technology blockade has become the biggest bottleneck restricting the construction of Beidou satellite navigation system. For example, in the early stage of the development of beidou-2, it was intended to introduce the core device component, the atomic clock, from abroad, but due to foreign reasons, it failed to cooperate. But in just two years, Chinese researchers have overcome the biggest technical bottleneck of the atomic clock. Today, the accuracy of the Beidou systems atomic clock has been improved to one second less than every 3 million years.

Source: Qiao JunJing, editor in charge of Beijing News_ NBJ11279