*** After 26 years of hard construction of Beidou No. 1, No. 2 and No. 3, China's independent national space-time infrastructure has been officially completed and put into operation.

Beidou navigation and positioning system not only has the functions of positioning, navigation and timing (pnt), but also has the functions of regional short message communication, regional precision single point positioning and regional satellite based enhanced services, as well as special service functions such as international search and rescue and global short message. The completion of Beidou global satellite navigation system marks that China has an independent global satellite navigation system, and the space-time benchmark of China's important infrastructure no longer depends on foreign satellite navigation systems.

Beidou-3 global satellite navigation system consists of 30 satellites in three different orbits. It is the infrastructure of other important national infrastructures.

The national financial system, the State Grid, the communication network and the Internet are all important national infrastructures, which need high-precision time synchronization. Otherwise, the financial system may be paralyzed, the power grid may fail, and the communication network and the Internet may have service interruption or low service efficiency; National aviation system, railway transportation and highway transportation belong to national transportation infrastructure, which all need accurate positioning, navigation and time synchronization.

Beidou satellite navigation system service module can be implanted into aviation, high-speed rail and highway systems to make air transportation safer, high-speed rail operation more efficient and highway traffic management more orderly.

Beidou system can also provide location and time information for smart city, fine agriculture and digital fishery, provide independent high-precision monitoring for the maintenance and updating of national coordinate system, and provide precise location change information for crustal deformation monitoring and landslide monitoring.

The opening and operation of Beidou satellite navigation system is only an important node in the construction and service of Beidou system. As academician sun Jiadong said, "the Beidou system should be used not only in the sky, but also on the ground". Therefore, the maintenance, operation and monitoring of the Beidou satellite navigation system is very important.

The stable operation and service of Beidou system depends on the fine stability monitoring, fine regulation and rapid troubleshooting and recovery of the monitoring system.

Although redundant backup is reserved in the process of design and construction, and there is a strict monitoring and fault early warning system, Beidou system is a complex giant system. The stable operation of the system is affected not only by the space environment and the reliability of various loads on the satellite, but also by the ground environment and various operation control elements.

Any link operation error may lead to the decline of system service quality and even service interruption. Obviously, the stable operation of Beidou still faces a very arduous task.

Firstly, we should strengthen the redundant design and redundant backup of satellites to ensure the completeness of space constellation; Secondly, strengthen the monitoring and backup of operation control system to ensure the stability and reliability of Beidou operation control system; In addition, we should constantly refine the satellite orbit determination algorithm to make it have the ability of error identification and compensation, strengthen the optimization of satellite clock error monitoring and prediction calculation software, and make it have reliable satellite clock error modeling and prediction ability.

Only in this way can the stable operation and service of Beidou system be reliably guaranteed.

We must be soberly aware that Beidou satellite navigation system, like other global navigation satellite systems, has natural vulnerability. Beidou satellite navigation signal is weak, easy to be interfered and deceived, and can not benefit indoor, underwater, underground and other sheltered areas.

In order to ensure the safety, reliability and continuity of PNT information of major national infrastructure, a comprehensive pnt system of "more ubiquitous, more integrated and more intelligent" must be established.

The integrated pnt system requires the establishment of seamless pnt information infrastructure from deep space to deep sea and even deep earth based on different physical principles and different information layers. The emphasis on "different physical principles" is because once the information based on the same principle is disturbed and obscured, no matter how many information sources are useless.

Therefore, the pnt information sources provided by pulsar X-ray navigation and positioning information sources outside the galaxy, pnt information sources based on Lagrange constellation, space pnt information sources combined with high and low orbit satellite constellation, ground 5g / 6G communication information and submarine sonar beacon will become the main information sources of the next generation national pnt system, and finally be built with Beidou system as the core Pnt information infrastructure with seamless coverage from deep space to deep sea realizes pnt services with unified space-time benchmark, multi-source service information, continuous, reliable, stable service system, anti-interference and anti deception.

Based on the integrated pnt infrastructure, we must also build an elastic pnt service system with elastic integration of multi-source information, elastic optimization of observation model and elastic adjustment of random model. Realize the integration and miniaturization of multiple pnt sensors, the "cloud" of operation control means, the "adaptation" of multi-source information fusion, and finally realize the "intelligence" of PNT service mode, so as to realize the best fusion of all kinds of PNT information.

The national comprehensive pnt infrastructure and flexible pnt service system is an important guarantee to ensure the safe, stable and reliable operation of national major infrastructure, as well as an important support for national defense construction.

In short, the completion of Beidou satellite navigation system has solved the urgent needs of national economic construction and national defense construction, but the construction of more universal, independent and comprehensive pnt system and corresponding elastic pnt system is the ultimate goal we pursue.

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