Beidou generation

"Beidou" satellite navigation test system (also known as "double star positioning navigation system") was listed in China during the Ninth Five-Year Plan period. Its engineering code was named "Beidou-1" and the scheme was put forward in 1983. At 0: 34 on May 25th, 2003, China successfully sent the third Beidou-1 satellite into space by the Long March 3A carrier rocket (Figure 2-3) in xichang satellite launch center. The first two satellites were launched on June 3, 2000 1,1,February 2, 20001and 65438, respectively. Since the operation, the navigation and positioning system has been stable and in good condition. This launch is the backup star of the navigation and positioning system, which together with the first two working stars of Beidou-1 form a complete satellite navigation and positioning system to ensure all-weather and all-day satellite navigation information. This indicates that China has become the third country in the world to establish and improve its satellite navigation system after GPS in the United States and GLONASS in Russia. The establishment of this system will play a positive role in China's national defense and economic construction. On February 3, 2007, the fourth satellite of Beidou-1 was successfully launched, which not only served as a backup for the earlier three satellites, but also completed the related test of satellite navigation and positioning system. At present, a complete satellite navigation and positioning system has been formed to ensure all-weather and all-day satellite navigation services.

Figure 2-3 Beidou Satellite Launch Site

Beidou-1 is an all-weather and regional satellite positioning system, which provides users with fast positioning, short digital message communication and time service by using geosynchronous satellites. The system consists of two geostationary satellites (80 E and140 E), an on-orbit backup satellite (110.50 E), a central control system, a calibration system and various user computers. Its working frequency is 249 1.75MHz, and the system can accommodate 540,000 users per hour. It has the advantages of less satellites, less investment, simple and cheap user equipment, etc., and can realize various purposes such as navigation and positioning in a certain area, and can meet the current needs of navigation and positioning of land, sea and air traffic in China.

In terms of performance, Beidou-1 is far from American GPS. First, the coverage is only a preliminary ability to locate the periphery of China, which is far from the global positioning of GPS. Second, the positioning accuracy is low, with the highest positioning accuracy of 20m, while the GPS can reach within 10m. Thirdly, due to the satellite radio measurement system, the user terminal will send out radio signals when working, which will be found by enemy radio detection equipment and is not suitable for military use. Fourthly, it cannot be used on high-speed mobile platforms, which limits its application in aviation and land transportation. But most importantly, Beidou-1 is a satellite navigation system independently established by China. Its successful development indicates that China has broken the monopoly position of the United States and Russia in this field and solved the problem of China's autonomous satellite navigation system. It is a successful, practical and low-cost initial startup system. In addition, the system does not rule out the wide application of GPS in the domestic civil market. Based on the Beidou navigation test system, China has gradually implemented the construction of Beidou satellite navigation system. First, to meet the navigation and positioning needs of China and its surrounding areas, the system will be networked and tested, and gradually expanded into a global satellite navigation and positioning system.

Second, the development process

In June 2000, 365438+1October, 365438+1October, the first navigation and positioning satellite "Beidou Navigation Test Satellite" developed by China was successfully launched in xichang satellite launch center. This satellite uses the Long March 3A carrier rocket. The satellite successfully completed its mission.

On June 65438+February 2 1 day, 2000, China's last space launch in the 20th century was a complete success. China astronauts bid farewell to the 20th century with the excellent results of 5 battles and 5 wins in the whole year.

At 0: 20 on February 265438+February 2/KLOC-0, 2000, the second Beidou navigation test satellite developed by China was launched by the Long March 3A rocket in xichang satellite launch center and entered the scheduled orbit accurately. Together with the first Beidou navigation test satellite launched on June 3, the same year, it constitutes the Beidou navigation system. This indicates that it will have the first generation satellite navigation and positioning system independently developed. The "Beidou Navigation Test Satellite" and "Long March 3A" launch vehicles were developed by the Space Technology Research Institute and the Launch Vehicle Technology Research Institute of Aerospace Science and Technology Corporation. This launch is the sixty-fourth flight of China's Long March series of launch vehicles and the 22nd consecutive successful space launch of China since1June, 1996.

On May 25th, 2003, China successfully sent the third Beidou navigation and positioning satellite into space by the Long March 3A carrier rocket in xichang satellite launch center. This indicates that China has independently established a perfect satellite navigation system, which will play a positive role in China's national economic construction.

At 0: 28 on February 3, 2007, China successfully sent the Beidou navigation test satellite into space by the Long March 3A carrier rocket in xichang satellite launch center. After the Beidou navigation test satellite was launched in xichang satellite launch center, the satellite could not operate normally due to the failure of the solar panel.

On April 1 1 day, 2007, after 60 days of hard work by space researchers, the failure of the Beidou navigation test satellite launched on February 3 has been eliminated, the satellite runs well, and the on-board instruments work normally, and it has been transferred to on-orbit long-term management.

Third, its own characteristics.

(A) the basic characteristics

1) "Beidou" has dual functions of positioning and communication, and has short message communication function that GPS does not have.

2) The positioning accuracy of Beidou is about 20m.

3) At present, the price of Beidou terminal has tended to the price of GPS terminal.

4) The receiving terminal is adopted, and the ground base station is not laid.

5) Ships in the disaster center can send messages within one second.

(2) Introduction of advantages

1) coverage: Beidou satellite navigation system is a regional navigation system covering China. The coverage is about 70 ~ 140 east longitude and 5 ~ 55 north latitude. GPS is an all-weather navigation system covering the whole world. It can be guaranteed that 6 ~ 9 satellites can be observed anywhere on the earth at any time (in fact, at most 1 1 satellite can be observed).

2) Satellite number and orbit characteristics: Beidou satellite navigation system has two geosynchronous satellites on the equatorial plane of the earth, and the equatorial angular distance between the two satellites is about 60. GPS will set 24 satellites on six orbital planes, with an equatorial inclination of 55 and an equatorial angular distance of 60. The navigation satellite is in quasi-synchronous orbit, circling the earth once 1 1 hour for 58 minutes.

3) Positioning accuracy: The three-dimensional positioning accuracy of Beidou satellite navigation system is about tens of meters, and the timing accuracy is about 100ns. The accuracy of GPS three-dimensional positioning is improved from 16m to 6m, the accuracy of C/A code is improved from 25 ~ 100m to 12m, and the timing accuracy is about 20ns.

4) User capacity: Beidou satellite navigation system is an inquiry and answer system with active two-way ranging. User equipment and geosynchronous satellite not only need to receive the inquiry signal from the ground center control system, but also need to send the reply signal to the geosynchronous satellite. In this way, the user capacity of the system depends on the channel blocking rate allowed by the user, the interrogation signal rate and the user's response frequency. Therefore, the user equipment capacity of Beidou satellite navigation system is limited. GPS is a one-way ranging system. As long as the user equipment receives the navigation message from the navigation satellite, it can perform ranging and positioning, so the capacity of GPS user equipment is unlimited.

5) Survivability: Like all navigation and positioning satellite systems, "Beidou-1" is based on the central control system and satellites, but "Beidou-1" obviously relies much more on the central control system because the positioning solution is not completed by the user equipment. In order to make up for the fragility of this system, GPS is developing the technology of interstellar transverse data link, so that GPS satellites can operate independently when the main control station is destroyed. Beidou-1 system ruled out this possibility in principle. Once the central control system is damaged, the system cannot continue to work.

6) Real-time performance: The positioning application of Beidou-1 user should be transmitted back to the central control system, which will calculate the user's three-dimensional position data and then transmit it back to the user, during which it will go back and forth through the geostationary satellite, plus satellite forwarding, the processing delay of the central control system will be longer, so the positioning error will be increased for high-speed moving objects.