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HISTORY OF TECHNOLOGY, TECHNOLOGY, OBJECTS AROUND US
Navigation system GPS. History of invention and production
Directory / The history of technology, technology, objects around us GPS (eng. Global Positioning System - global positioning system, read by G.P. Es) is a satellite navigation system that provides distance, time and location measurements in the world coordinate system WGS 84. It allows you to anywhere on the Earth (excluding the polar regions), almost at in any weather, as well as in near-Earth space, to determine the location and speed of objects. The system was developed, implemented and operated by the US Department of Defense, and is currently available for civilian use - all you need is a navigator or other device (for example, a smartphone) with a GPS receiver. The basic principle of using the system is to determine the location by measuring the time points of receiving a synchronized signal from navigation satellites by the consumer's antenna. To determine the three-dimensional coordinates, the GPS receiver needs to have four equations: "the distance is equal to the product of the speed of light and the difference between the moments of signal reception by the consumer and the moment of its synchronous emission from satellites": |x - a_{j}| = c(t_{j} - \tau). Here: a_{j} is the location of the {j}-th satellite, t_{j} is the moment of signal reception from the {j}-th satellite according to the user's clock, \tau is the unknown time of synchronous signal emission by all satellites according to the consumer's clock, c is the speed of light, x is the unknown three-dimensional position of the consumer.
With the help of a GPS receiver, not only the location of a moving object is determined, but also the speed of its movement, the distance traveled, the distance and direction to the intended point, the time of arrival and deviations from the set course are calculated. Today it is already obvious: in the first decade of the new millennium, satellite navigation systems will become the main means of positioning for land, air and sea objects. Because with today's technology, GPS receivers are small, reliable and cheap, so they are becoming more accessible to the average consumer. First, the NAVSTAR Space Radio Navigation System (NAVSTAR) appeared. The navigation system based on time and range measurements in the United States was created primarily for the coordinate-time support of troops and military equipment. The first American navigation satellite was launched in February 1978, and the active introduction of satellite navigation methods into civilian life began later. Until 1983, the navigation system was used exclusively by the military. However, after a Boeing 747 was shot down over the Tatar Strait, the system was opened for civilian use. Then, in fact, the abbreviation GPS (Global Positioning System) appeared - Global Positioning System. The term "positioning" is broader than the term "locating". Positioning, in addition to determining the coordinates, also includes determining the velocity vector of a moving object. The US government has spent more than ten billion dollars on the creation of this system and continues to spend money on its further development and support. The satellite navigation system uses satellites emitting special signals instead of geodetic signs and radio beacons. The current location of the satellites in orbit is well known. Satellites constantly transmit information about their location. Their distance is determined by measuring the amount of time it takes for a radio signal to travel from a satellite to a radio receiver and multiplying that by the speed of the electromagnetic wave. By synchronizing the clocks of satellites using Atomic Reference Frequency Oscillators and receivers, an accurate measurement of the distances to the satellites is achieved. “To calculate the coordinates of a place on Earth,” writes V. Kuryshev in the Radio magazine, “it is necessary to know the distances to satellites and the location of each of them in outer space. GPS satellites are in high orbits (20000 km), and their coordinates can be predicted with great accuracy. The US Department of Defense tracking stations regularly determine even the smallest changes in orbits, and these data are transmitted to satellites. The measured distances to satellites are called pseudoranges, since there is some uncertainty in their determination. The fact is that the Earth's ionosphere and troposphere cause delays in satellite signals, introducing an error in the calculation of the distance.There are other sources of errors - in particular, computational errors onboard computers, electrical noise of receivers, multipath propagation of radio waves.Unfortunate relative positioning of satellites in the sky can also lead to a corresponding increase in the total position error division. To determine distances, satellites and receivers generate complex binary code sequences called pseudo-random codes. The determination of the signal propagation time is carried out by comparing the delay of the pseudo-random code of the satellite with respect to the same code of the receiver. Each satellite has its own two pseudo-random codes. In order to distinguish between ranging codes and information messages of different satellites, the corresponding codes are called up in the receiver. Pseudo-random ranging codes and information messages of satellites allow the transmission of messages from satellites simultaneously, on the same frequency, without mutual interference. The radiation power of the satellites and the mutual influence of the signals from the satellites is insignificant. Measurement accuracy can be improved by using differential measurements. A reference ground station with precisely known geodetic coordinates calculates the difference between the coordinates from its receiver and its actual coordinates. The difference in the form of a correction is transmitted to consumers via radio channels to correct the readings of the receivers. These corrections eliminate a significant part of the errors in distance and location measurements. Calculation of coordinates at the reception in the indicator is carried out automatically and it is possible to use the information in a convenient cartographic form. GPS consists of 3 segments: space segment, control segment and user segment.
The space segment consists of 24 satellites that are in 6 orbits (four each) at an altitude of approximately 20350 kilometers. There are currently 28 satellites in operation. "Extra" satellites are used for insurance and replacement of failing satellites. The control segment consists of observation stations located at several points on the globe, and the main control station. The lead station is located at the Joint Military Space Systems Control Center in Colorado Springs. The center collects and processes data from tracking stations, calculates and predicts satellite ephemeris, as well as clock parameters. Observation stations monitor the satellites, recording all information about their movement, which is transmitted to the main command station for orbit correction and navigation information. The user segment includes user equipment that allows determining coordinates, speed and time. The main consumer of GPS information is the US Department of Defense. GPS receivers have been introduced on all combat and transport aircraft and ships, as well as in the guidance systems of high-precision cruise missiles and in the guidance systems of the new US guided bombs. This means that the US military can plan to launch high-precision missile strikes from a distance of a thousand kilometers, not only against buildings and structures, but also within a certain window. Moreover, these strikes can be delivered from submarines and from the air.
There is a similar system in Russia: in response to the creation of NAVSTAR by the Americans, the USSR created its own global navigation satellite system - GLONASS. The first domestic navigation satellite Kosmos-192 was launched into orbit on November 27, 1967, and in 1979 the first-generation navigation system Cicada was created, which included 4 low-orbit satellites. Then, in 1982, the first satellites of the new GLONASS navigation system were launched. The number of GLONASS satellites was brought to the standard state in 1996. GLONASS satellites are located at an altitude of approximately 19100 kilometers. Unlike NAVSTAR satellites, GLONASS satellites are placed in three orbits, respectively, 8 satellites in each. The orbital period of the satellites is 11 hours 15 minutes. Like GPS, GLONASS is used by both military and civilian users. However, there are not so many users of the system: in fact, it has not been developed since 1998. Every year the constellation of satellites decreases. The reason is banal and, one might say, standard for most domestic developments: the state has no money, and the legal framework governing the use of satellite navigation systems in Russia does not allow the system to develop at the expense of civilian consumers. Prospects for the development of GLONASS depend on the position of the state. He will have to decide whether to open this navigation system to a wide range of consumers or not. In February 2000, Russian scientists sent an open letter to Vladimir Putin (then acting president of Russia) in which they outlined their version of the development of GLONASS: : firstly, to urgently remove unjustified regime restrictions on the use of household satellite receivers for determining coordinates; secondly, by a government decree, to decree the domestic general-terrestrial geodetic coordinate system "Parameters of the Earth in 1990" (PZ-90) and the GLONASS satellite navigation system for mass use throughout Russia and the countries of the world community..." So far, the president has not made any decision. Unlike the Russian system, GPS has constantly evolved towards being open to civilian users. Prior to May 1, 2000, GPS access was selective for them, which degraded location accuracy to hundreds of meters. At the same time, the accuracy for the military was 5-20 meters. However, on May 1, President Clinton announced an end to the decline in GPS signal accuracy for civilian users. "This will mean that civilian GPS users will be able to pinpoint 10 times more accurately than currently available," he said. Why does the US government need this and what will it give the navigation system? Judge for yourself: according to the press service of the US President, in 2000 there were more than 4 million GPS users worldwide, and by 2003 the market for this navigation system will double - from 8 to 16 billion dollars. Is it necessary to explain that with this money the system can not only be maintained, but also developed? The US is already planning to put 18 additional satellites into orbit to improve GPS performance. The standard objection to the openness of navigation systems in Russia has always been security interests. The military feared that if the navigation system was made available to everyone, it could be used by external and internal enemies against the state. However, this explanation is rather weak: the United States, by making GPS available to everyone, did not harm its own security at all, reserving the right to "regional decrease in accuracy" of the signal. In practice, this means that in the event of a conflict with a particular country, the US military will be able to degrade the accuracy of the GPS receivers used by the enemy, or turn them off altogether. So, while everything is peaceful - you can receive money from GPS users. As soon as problems arise, they can be turned off. Today it is not easy even to list all the areas of application of this navigation system. As Oleg Tatarnikov notes in the Computer-Press magazine: “GPS receivers are built into cars, cell phones and even wristwatches! Tourists use pocket receivers to plot routes and navigate them clearly. Hunters and fishermen mark the coordinates of treasured hunting and fishing places , and autotourists exchange routes indicating gas stations. Nothing will stop the victorious march of GPS. Receivers are rapidly shrinking in size and getting cheaper, a matchbox-sized device can already be bought today for less than $50; navigation chips are built into watches and mobile phones, and become an integral part of car alarms, which themselves inform the police of the location of a stolen car. Unlike radio signaling systems that have not received wide application, such a system does not require a special network of direction-finding stations - conventional mobile communications are used here. In addition, the driver can, by pressing one button, signal a robbery or an accident. Another button calls for an ambulance. In the near future, a whole "route package" is expected to appear on the auto electronics market - a full-fledged on-board navigation system with electronic maps of Russian cities and regions ... ...GPS receivers are used in solving a wide variety of problems: geologists monitor the subtle movement of areas of the earth's crust in real time, rescuers identify disaster sites, zoologists make collars with portable indicators and radio transmitters to study animal migration, the military builds homing missiles and bombs, and a US National Geographic Society expedition last year measured Everest's height to centimeter accuracy."
The magazine "Computerra" published a message about the release of one of the companies of GPS-chips designed for implantation in the human body! As often happens, the navigation system turned out to have a lot of other additional useful features. With the help of the system, it is possible, for example, to determine the ultra-precise time required, say, in scientific experiments, to measure the speed developed when walking or running, and the distance covered. GPS shows the maximum and average speed of the car and with its help, in particular, you can check the correctness of the speedometer and odometer readings. Needless to say, navigation with this system is greatly simplified. As a result, among the professional "navigators" there is a whole generation of specialists who do not know how to work with classical navigation devices. Author: Musskiy S.A.
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