Moments are outdated! New black technology is popular among Beidou satellites

  On March 30, 2015, the first new-generation Beidou navigation satellite (the 17th satellite of Beidou Navigation) was successfully launched at the Xichang Satellite Launch Base. Starting from this satellite, Beidou satellites will haveintersatellite linkIt allows various satellites to achieve barrier-free real-time communication in space, allowing for "space conversations" at any time.

  Beidou No. 2: "Ten years ago, I didn’t know you, you don’t belong to me.

  What is an inter-satellite link?Inter-satellite link refers to the communication link established between satellites, which can connect multiple satellites together to form a satellite network. Information sharing between satellites is achieved by means of electromagnetic waves, and wireless links with data transmission and ranging functions.The inter-satellite link of Beidou satellites is mainly used to realize information transmission and two-way measurement between Beidou satellites.

  At present, other navigation systems in the world are studying "inter-satellite link" technology, and each has its own characteristics, such as the UHF band low-speed wide-beam inter-satellite link of GPS in the United States, the S-band low-speed wide-beam inter-satellite link of the Russian GLONASS navigation system, and the Ka-band phased array medium-speed inter-satellite link in our country.

  Can’t live without you

  Through the inter-satellite link, the independent operation of the Beidou satellite global system will be realized, the accuracy of orbit determination and timing will be improved, the injection frequency will be improved, and the dependence on ground stations will be reduced, effectively reducing the operation and management costs of the system.The management and maintenance of navigation satellites requires the support and cooperation of the ground station, and the user’s positioning accuracy depends on the accurate determination of the satellite position and satellite time by the ground station, and is injected into the satellite to broadcast to the user.

  For example, the United States has military bases all over the world, and GPS ground stations can choose the best location around the world to achieve all-weather seamless coverage, high orbit determination accuracy, and high injection frequency. The main control station is located in Colorado, the mainland of the United States, with three injection stations: Ascension Island, Diego Garcia Island, Kwajalein Island, and five monitoring stations (Colorado, Ascension Island, Diego Garcia Island, Kwajalein Island, Hawaii Island).

  Compared with GPS and Galileo, China’s Beidou relies more on inter-satellite links.

  For security and other factors, our country has only carried out ground station construction in China, so when the satellite runs to the place where the ground station cannot observe, how does the Beidou navigation satellite work? The answer is that we have inter-satellite links. Each satellite can act as a "router", and it can manage overseas stars through domestic stars without building websites around the world.

  What if a war breaks out and the ground station is damaged or disturbed? It doesn’t matter, with the interstellar link, our Beidou satellites can be self-reliant and self-sufficient, enter the autonomous operation mode without ground support, and continue to provide high-precision navigation, positioning, and timing services.

  peacetimeThe high-precision inter-satellite/satellite-earth observation provided by the inter-satellite link can make up for the regional layout defects of the Beidou satellite navigation system monitoring station in our country, manage overseas satellites, improve the injection frequency, and improve the comprehensive service performance of the system.

  The results show that the orbit determination accuracy of one ground station anchoring satellite-ground link and inter-satellite link data is similar to that of six L-band monitoring stations on the ground except that the orbital plane along the track direction accuracy is slightly worse. Combined orbit determination of inter-satellite link data and L-band data can improve the L-band orbit determination accuracy.

  Special periodIn extreme cases such as ground station destruction or interference, the Beidou satellite system can operate autonomously with the help of inter-satellite links, providing high-precision navigation, positioning, and timing services within 60 days without ground support.

  The inter-satellite link provides services for the Beidou system while also providing part-time services: providing communication and measurement and control support for spacecraft, missiles and other aircraft.

  China’s intersatellite link system has entered the era of "smart phones", representing the technology trend of next-generation satellite navigation systems.

  The most outstanding features include:

  1, China’s inter-satellite link system, 70,000 km ranging accuracy to centimeter level, equivalent to seeing a hair strand dozens of kilometers away, the measurement accuracy is higher than GPS.

  2. China’s inter-satellite link system is like a "mobile phone call", which is used by several people in a house and does not interfere with each other, while the GPS inter-satellite link is a "mass broadcast", which interferes with each other. One line works, and the other lines must be silent.

  According to the Doppler effect, the electromagnetic wave frequency radiated by an object varies due to the relative motion of the wave source and the observer. The faster the object, the greater the error in the received frequency, and the Doppler shift will affect the communication performance.

  Therefore, eliminating or reducing the influence of Doppler frequency shift on wireless communication is a problem that must be solved for wireless communication in high-speed motion, and the inter-satellite link needs to complete the fast acquisition and tracking of high-dynamic signals in a very short time.

  The maximum speed of high-speed rail is 350KM/h, which is about 100m/s, while the relative speed of satellites can reach 5000m/s. The Beidou inter-satellite link can complete a series of complex signal processing such as capture and tracking at extremely high speed in 100ms, and complete the high-speed establishment and handover of the inter-satellite link.

  Take China as an example.The country farthest from China geographically is Argentina, the distance between Beijing, China and Buenos Aires, Argentina is about 22,000 kilometers, and the farthest distance between the two satellites in space is 70,000 kilometers.

  This 70,000 kilometers is the furthest distance in the world, but it is also the closest distance. Two satellites are 70,000 kilometers apart, but they always know where each other is, and the accuracy of satellite position prediction can reach the meter level. This accuracy is equivalent to accurately hitting a human-sized target in Argentina in China. This is not a hundred steps through the yang, it is a hundred steps through the needle.

  The energy of the satellite is provided by two small solar panels. As an energy-limited system, the lower the power of the transmission is required, and the distance between the two satellites is so far. After a long space walk, the electromagnetic wave signal has long been submerged in the vast noise.

  How low is the signal power that our interstellar link needs to receive? Simply put, it is equivalent to 1/1 billion of the signal power received by our mobile phones. Cunning enemies are everywhere, always playing tricks in the dark, and the interstellar link has its own countermeasures. It can still work freely when the strength of the jamming signal is 100,000 times that of the useful signal.

  The intersatellite link independently developed by our country can quickly capture satellite signals flashing 70,000 kilometers away from such a low signal power. Through the intersatellite link, China’s Beidou satellite can quickly complete a handshake when flying at high speed in the vast space. After the handshake, the information exchange between the two satellites is completed, and the distance between the satellites is accurately determined. The distance measurement accuracy of 70,000 kilometers can reach 1 cm.

  In addition to the Ka intersatellite link that has been successfully verified, we also have a laser intersatellite link, which will be an intersatellite highway. Please wait and see.

  At 7:18 on January 12, 2018, the 26th and 27th Beidou Navigation Satellites developed by the Chinese Academy of Sciences Microsatellite Innovation Research Institute were successfully launched at the Xichang Satellite Launch Center. With the "assistance" of the inter-satellite link, the Beidou-3 project’s global networking and system services are one step closer!

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