Chapter 1524: Hard!

"At present, the most mature satellite positioning system in the world is the GPS system of the United States." Chen Fangyun said slowly: "This system originated in an experimental project called "Bus Navigation System" in the United States in 1958. The project Later, it was favored and invested by the U.S. military. In 1968, the first-generation experimental satellite navigation system led by the U.S. military was officially put into use. The name was DefenseNavigationSatelliteSystem, or DNSS for short, which was translated as "National Defense Navigation Satellite System" in Chinese. It can be seen that this system was originally developed solely for military purposes.
After a brief background introduction, Chen Fangyun paused for a while, sorted out his thoughts, and continued: "After this system was put into practical use, the United States quickly established a complete set of practical systems on it, and developed on this basis. The first generation of satellite navigation precision guided weapons established a leading advantage over the former Soviet Russia in this field. Therefore, the former Soviet Russia also quickly formulated a response strategy and proposed its own global satellite navigation system plan GLONASS, which we call "GLONASS", but because the former Soviet Union's technical level in the field of microelectronics is far behind that of the United States, GLONASS completed the pre-research and program demonstration, and the time to enter the actual development work has reached 1976, and at that time The United States has started the development of the second-generation global satellite navigation system for three years."
"In 1973, the U.S. Ministry of National Defense held an internal meeting attended by 12 principals from various military departments. After the meeting, the Pentagon formally proposed to establish a global satellite navigation system—Navstar, that is, timing and ranging. Navigation Satellite (NavigationSignalTimingandRanging), for the convenience of reference and promotion, is also called the Global Positioning System Global Positioning System, which is the GPS as we know it now. In September of the same year, the U.S. Congress passed a resolution to determine that the GPS system should be dual-use for both military and civilian use."
"From a scientific point of view, the GPS system is a great invention. It can accurately determine the position and position of any point on the earth that can receive satellite signals based on the combination of mutual data between satellites operating in a specific orbit. Time. GPS is firstly a positioning system, when determining the location of a point, it can accurately determine the longitude, latitude and altitude of a point. Secondly, it is also an accurate "timing system" that can accurately determine the instant time of the point , And this time error can reach within 1s on a civilian terminal, and the GPS itself has a timing accuracy of less than 30ns. Based on these data, the GPS system can determine the accurate longitude, latitude and altitude of things; plus accurate timing , Any point that can receive GPS satellite signals can be accurately recorded and completed almost instantly. Fixed points are almost easy to locate and find, while moving points can be found on their moving tracks. And it can also generate 3D maps in real time. With this technology, every thing on the earth has accurate contact information, so that every stationary or moving object has a way to be captured. And methods, but also to connect with other signal sources, and even share real-time data."
Having said so much in one breath, Mr. Chen inevitably has to stop and catch his breath. Tan Zhenhua consciously said: "So, what is the current state of the second-generation GPS system in the United States?"
"Now, this system has been upgraded to the second generation, and most of the work to replace the first generation system has been completed. The first satellite of the second generation GPS system was launched on February 4, 1989, that year. A total of 9 satellites have been launched, and we expect that the 24 satellites required for the entire system will be launched before the end of this year, constituting the entire GPS constellation, covering more than 98% of the world’s area, and the part that has been launched and put into use will be It played an important role in the Gulf War that broke out in 1991."
Tan Zhenhua couldn't help but nod. He was one of the people who witnessed the war, and he was more familiar with the GPS system. After all, few people knew about this thing in the early 1990s, and before he was reborn, it was already a horrible thing. Up.
"The GPS space-based system consists of 21 working stars and 3 spare stars, which are distributed in 6 orbits that form 60 degrees each other. Any place in the world can receive signals from 6 to 9 satellites, and can send signals from 6 to 9 satellites around the world. The ground provides three-dimensional position, three-dimensional speed and other information; the ground control part is composed of a main control station, a ground antenna, a monitoring station and a communication auxiliary system; the receiving end can be made very small, and can even be made into a handheld personal terminal. I know that the Mi Army distributed a large number of such personal handheld GPS receiving terminals during the Gulf War, which played a major role on the battlefield."
Tan Zhenhua nodded again. He was also familiar with this kind of handheld terminal. When he was in Riyadh that year, he even bought a few metric military-grade GPS receivers from some underground channels at a high price for Xie Li and them. When marching in the desert where it is difficult to discern the direction, he can accurately find his position.
"I have just introduced that the GPS system is divided into civilian and military versions," Mr. Chen breathed a sigh and continued: "The civilian version uses C/A code, also known as "rough code", with a frequency of 1.023MHz, repeat The cycle is one millisecond, the code interval is 1 microsecond, and the positioning accuracy is 14 meters; the military uses P code, also called "fine code", with a frequency of 10.23MHz, a repetition period of 266.4 nanoseconds, a code spacing of 0.1 microseconds, and positioning accuracy At the meter level, it is reported that the GPS system is upgrading from P code to Y code. The Y code is formed on the basis of P code, which has better security performance and higher positioning accuracy. According to its principle calculation, the accuracy can reach the level of 0.3 meters. , The Americans are called the centimeter level."
"Then what research has our country done most in this aspect?" Tan Zhenhua asked in due course.
"Our country started much later than the two big countries like Missu." Chen Fangyun sighed: "In 1983, at that time, I had not retired and served as the director of the "Tracking and Communication Technology Institute" in Beijing. After a period of tracking research on the development of GPS technology, together with my colleagues, I put forward a proposal for the development of China’s "satellite positioning system". Due to the constraints of the objective conditions at the time, my proposal was to first establish a "dual satellite positioning communication system." That is, a positioning method that uses two geostationary satellites to achieve regional rapid navigation and positioning and also has a communication function."
"and after?"
"Later, the country approved this pre-research project, and our institute also began to make technical reserves in this area. On April 15, 1985, a seminar on the international application of GPS global positioning system was held in Washington, United States. A meeting was held to promote its system in the civilian area. China Huaxia was also invited to participate in the meeting. It was Bu Qingjun who went to the meeting. He came back and told me that the Americans made it clear at the meeting: In the GPS system of the civilian part, The Americans joined the SA jamming signal, which artificially reduced the positioning accuracy. At the same time, in special circumstances, in order to ensure national security, the U.S. military will take three measures to deal with emergency situations: first, reduce the other party’s navigation accuracy; second, Change coding at any time; third, carry out regional management."
Tan Zhenhua nodded. He was not surprised by this American practice. Americans have always been like this. It is impossible to give you a free lunch, and even if it is charged, various restrictions will be added. In short, you If you want to use his things, you must accept his jurisdiction!
Take this GPS as an example. The statement of the American shows that he has absolute control over the GPS system and can decide to turn off the GPS signal of a specific area, a specific country, or a specific user when necessary, or change the code of these specific users. Differentiated and selective management, preventing them from using GPS. At the same time, a more complex password protection is added for GPS signals for personal use, making it difficult for specific groups of people to interfere and attack GPS.
"After communicating with Bu Qingjun, we reached two consensuses." The old man continued: "First, we must track, research, and apply GPS; second, we must set up our own satellite positioning system. So, I was in the research institute. A five-person team was formed, led by Liu Zhikui, a researcher from our institute, to demonstrate whether the dual-satellite positioning and communication system could be feasible and developed into a satellite navigation system. In February of the second year, Bu Qingjun submitted a report entitled "Recommended Research Use Two "Stars Solve the Positioning Problem" report, the recommendations were finally adopted by the superior and included in the "863" plan."
"Since it has been included in the 863 plan, shouldn't it be ushered in a major development?" Tan Zhenhua asked knowingly.
After hearing what he said, Chen Fangyun let out a bitter smile and sighed:
"Dr. Tan, it's difficult!"