1957, 10 year 10. On 4 October, the Soviet Union launched the world's first artificial earth satellite, which opened the space age of mankind. The United States pays close attention to this. Mathematician William Gay and physicist George Weifenbach discovered a phenomenon in the Applied Physics Laboratory of Hopkins University: the frequency of this satellite launched by the Soviet Union will shift to a certain extent. After research, they finally found that this is the Doppler frequency shift effect caused by relative motion. Subsequently, two scientists conducted an experimental study and found that if multiple receivers were set on the ground, the specific position of the satellite could be calculated according to the received signals with different frequency differences. They are very happy to tell Frank Macclure, director of the laboratory, that they have realized the Doppler positioning and tracking of Soviet satellites.
At that time, Director Frank was doing a naval research on how to locate the specific position of warships in the vast sea. After listening to the reports of two scientists, his eyes lit up: since you can find out where the satellite is, if you turn the question upside down, the satellite can also find out where you are. This opened the way for him to study the positioning of naval warships at that time. The GPS system was started according to this idea.
The first problem to be solved urgently in the promotion of GPS project is what kind of orbit should the satellite adopt: low, medium and high? If low orbit is adopted: the accuracy is relatively high, but it needs 200 satellites to cover the whole world, such a huge project is really unaffordable. Then if high orbit is adopted, theoretically three satellites can cover the whole world. However, in addition to the difficulty in launching high-orbit satellites, the positioning accuracy will be much lower. Therefore, the middle orbit is a relatively compromise solution, covering only 24 to 36 satellites around the world. However, because the orbit is moving, even if the objects on the ground are not moving, its speed relative to the satellite is very large, so the Doppler frequency shift method can be fully used. Based on the above comprehensive considerations, the United States chose the medium orbit scheme of 24 satellites, the first one was launched at 1978, and the whole system was put into operation at 1995. There are now 30 satellites, which are divided into military and civilian positioning modes, of which the civilian mode is open to the whole world.
It is worth noting that the use of Doppler effect for positioning is an early practice, and now the main method is to use extremely accurate atomic clocks. By measuring the signal and the time from the satellite to the object, the distance between them can be determined. The position of an object is determined by three or more such distances. The Doppler effect is now only used as an auxiliary means.
The GPS system invested heavily by the United States can be used free of charge all over the world. This is because the free GPS system will definitely form a huge market in the world, and relying on this system will generate new international industries and form a strong national soft power. Therefore, free GPS is in the national interest of the United States.
Free GPS is the welfare of people's livelihood all over the world, but it is a challenge in the military. For hostile countries in the United States, of course, GPS systems can also be installed on their military aircraft and warships. Of course, the GPS system they installed is only a civilian system, and its accuracy is ten times worse than that of the US military. More importantly, in case this country goes to war with the United States, and the United States stops the GPS system for you, it will become blind and you will not know the direction and goal; What is even more frightening is that if the United States sends you a cheat code, then the missile you aim at the United States may fly to your body. Therefore, the armaments of other countries must not use American GPS. Once they become dependent, the consequences will be unimaginable.
Therefore, it is necessary to develop our own positioning and navigation system. Of course, developing their own positioning and navigation system is only the right of a few big countries. Because the global positioning navigation system is really too big. Small countries with weak comprehensive national strength simply cannot afford it.
In fact, since the 1970s, China has put forward the "new four-star" plan. In the early 1980s, an expert group headed by Academician Chen Fangyun, the father of two bombs and one satellite, put forward a double-star positioning scheme, which was considered as the best scheme at that time. However, due to economic conditions and other reasons, it was delayed for ten years. Until 199 1, China people were awakened by the Gulf War, and the application of GPS system in the United States was very successful. The decision-makers at that time deeply realized that future wars must rely on this technology. As a result, the double-star positioning scheme, which has been shelved for ten years, started immediately.
Since the 1990s, Beidou system has been developed, and its development strategy is based on three steps: taking the initiative first and then being passive. First it is regional, then it is global. Beidou-1, Beidou -2 and Beidou -3 systems have been built successively, and a satellite navigation system with China characteristics has been built. The three-step construction of Beidou system is a development route put forward in combination with the actual development of technology and economy in different stages in China.
The first step is to build Beidou-1 system, also called Beidou satellite navigation test system, to realize satellite navigation from scratch. 65438-0994, the construction of Beidou-1 system was officially launched. In 2000, the Beidou-1 system, which launched two geostationary orbit satellites, was completed and put into use. In 2003, the third geostationary orbit satellite was launched to further improve the system performance. The completion of Beidou-1 system has taken an exploratory first step, which has initially met the needs of positioning, navigation and timing in China and its surrounding areas. At that time, the active positioning system was adopted, which means that users need to transmit a signal system to locate. This process depends on satellite transponder, so there is time delay and limited capacity, which can not meet the high dynamic demand.
At that time, officials claimed that Beidou-1 had unique advantages in communication and positioning, but its communication function was much worse than Inmarsat's and its positioning function was much worse than GPS's. Nevertheless, Beidou-1 has achieved the design goal and is very successful in engineering. Without Inmarsat and GPS system, Beidou-1, which can locate and communicate, is simply radiant. But the problem is that when the Beidou generation came out, these two satellite systems were quite mature. In their contrast, the experience of Beidou-1 is relatively poor, so what should we do next?
At this time, China took a fancy to the Galileo project in Europe, which is a global positioning and navigation satellite system project jointly developed by European countries. At that time, Europe had technology, but was short of money. China was worried that the Beidou-1 system was not strong enough, so naturally the two families hit it off. It is reported that when China joined the Galileo program, he generously paid the entrance fee of 200 million euros directly. However, after paying the money, China felt more and more wrong. Europe actually brought Japan and India. They pay less, but they have more power. It's no problem to spend more money. The key point is that these two countries are something we should guard against militarily. Should we use the same system as them militarily? China found something was wrong and made up his mind to quit. After resigning, I went it alone and began to develop Beidou-2.
Beidou-2 system, from active positioning to passive positioning, regional navigation serves Asia-Pacific. In 2004, the construction of Beidou-2 system was started. Beidou-2 innovatively built a hybrid constellation architecture of medium and high orbit, and by 20 12, it completed the launching network of 14 satellites. Beidou-2 system is compatible with Beidou-1 active positioning system, adding passive positioning system. That is to say, users do not need to transmit signals themselves, but only need to receive signals to locate and solve the user capacity limitation, which meets the high dynamic demand. The completion of Beidou-2 system will not only serve China, but also provide users in the Asia-Pacific region with positioning, speed measurement, time service and short message communication services.
At that time, the orbit and frequency of Beidou-2 application were consistent with Galileo in Europe. This inevitably meets the position of satellite orbit and frequency competition. Satellite orbit and space frequency are common resources of human beings. How to allocate them? International rules are neither divided by country nor by population, but whoever occupies it first counts. From June 5438 to February 2005, the first satellite planned by Galileo went into the sky, but it didn't open. It just occupies the orbit, not the frequency. The main reason for not opening the frequency is that Europe lacks money and has no money to open it. Subsequently, China's Beidou-2 satellite also went up to the sky, and it started to use frequency as soon as it went up. Now it occupies both orbit and frequency. Galileo in Europe fiddled with it slowly, and China's Beidou satellites kept launching, and then they killed two stars with one arrow. Galileo and Beidou have some overlapping frequencies, and both sides have filed with the International Telecommunication Union. Whoever takes it first takes it. The rapid development of China has attracted the attention of Europe. I want to put pressure on China through the United States, asking China to slow down and so on. China, of course, ignored the protests from Europe and America and continued to launch satellites at the established pace.
The third step is to build Beidou-3 system, establish inter-satellite links and realize global networking. In 2009, the construction of Beidou-3 system was started, and by 2020, 30 satellites will be launched, and Beidou-3 system will be built in an all-round way. The recently launched satellite is the last satellite deployed by Beidou global satellite navigation system constellation. Beidou-3 has further improved its performance and expanded its functions on the basis of Beidou-2, providing global users with services such as positioning, navigation, time service, global short message communication and international search and rescue. At the same time, it provides satellite-based enhancement, ground-based enhancement, precise single-point positioning and regional short message communication services in China and surrounding areas. At present, Beidou's services are jointly provided by Beidou-2 system and Beidou-3 system, and Beidou-3 system will be the main service after 2020.