Navigation satellite systems of the USSR, Russia and the United States. Second story
Richard Kershner (left) is one of the founding fathers of the US global positioning system. Source: gpsworld.com
The main customer was the US Navy, which needed precise navigation tools for new submarines equipped with Polaris missiles. The need to accurately determine the location of the submarines of the type “George Washington” was extremely necessary for the then-new launch of missiles with nuclear warheads from anywhere in the oceans.
Already by 1958, the Americans were able to present the first experimental model of the satellite system Transit, and 17 September 1959, he was sent into space. Ground infrastructure was also created - by the time of launch, the complex of consumer navigation equipment was ready, as well as ground tracking stations.
Engineers at Hopkins University for assembling and testing the Transit spacecraft. Source: timeandnavigation.si.edu
The Americans were working on a complete afterburner satellite navigation project: by the year 1959 they built as many as five types of Transit satellites, which were later all launched and tested. In operating mode, the American navigation system earned 1963 in December, that is, in less than five years, it was possible to create a workable system that has good accuracy for its time - the mean square error (UPC) for a fixed object was 60 m.
Transit receiver installed in the car, used by geologist Smithsonian University Ted Maxwell in the Egyptian desert in 1987 year. The workhorse of the researcher was ...
... Soviet "Niva"! Source: gpsworld.com [/ center]
Determining the coordinates of a submarine moving in the surface position was more problematic: if you make a mistake with the speed value at 0,5 km / h, the UPC will increase to 500 m. Therefore, it was more expedient to contact the satellite for help in the fixed position of the vessel, which again was not easy. Low-orbit US Navy (1100 km altitude) Transit received four satellites in the middle of 64, bringing the orbital constellation to seven vehicles, and from 67, navigation became available and mere mortal. Currently, the Transit satellite constellation is used to study the ionosphere. The inability of the first satellite navigation system in the world was the inability to determine the height of the position of the ground user, the considerable duration of the observation and the positioning accuracy of the object, which became insufficient in time. All this has led to new searches in the US space industry.
The second satellite navigation system was Timation from the Naval Research Laboratory (NRL - Naval Research Laboratory), which was led by Roger Easton. Within the project, two satellites were assembled, equipped with ultra-accurate clocks for broadcasting time signals to ground-based consumers and accurately determining their own location.
Experimental satellite Timation NTS-3, equipped with a rubidium clock. Source: gpsworld.com
At Timation, a basic principle was formulated for the operation of future GPS systems: a transmitter operated on the satellite, emitting an encoded signal, which was fixed by the ground subscriber and measured the delay in its passage. Knowing the exact location of the satellite in orbit, the equipment easily calculated the distance to it and, based on these data, determined its own coordinates (ephemeris). Of course, this requires at least three satellites, and preferably four. The first Timations went into space in the 1967 year and carried a quartz watch at the beginning, and later an ultra-precise atomic clock - rubidium and cesium.
The United States Air Force, regardless of the Navy, operated on its own global positioning system, called the 621B System (Air Force 621B). An important innovation of this technology was the three-dimensionality - now it is possible to determine the latitude, longitude and long-awaited height of the object. The satellite signals were separated according to a new coding principle based on a pseudo-random noise-like signal. Pseudo-random code increases the signal noise immunity and resolves the issue of access restriction. Civilian users of navigation equipment have access only to open codes that can be modified from the ground control center at any time. In this case, the entire "peaceful" technique will fail, determining its own coordinates with significant error. Closed military codes will remain unchanged.
The tests were launched at 1972 at the site in New Mexico, using transmitters on balloons and airplanes as satellite simulators. The 612В system showed outstanding positioning accuracy of several meters, and it was at that time that the concept of a mid-orbit global navigation system with 16 satellites was formed. In this embodiment, a cluster of four satellites (this number is necessary for accurate navigation) provided 24-hour coverage of the whole continent. For a couple of years, the 612B System was at the rank of experimental ones and was not particularly interested in the Pentagon. At the same time, several offices in the US were working on a “hot” navigation theme: the applied physics laboratory worked on the Transit modification, the Navy doped Timation, and even the ground forces offered their own SECOR (Sequential Correlation of Range). This could not but bother the Ministry of Defense, which risked encountering unique navigation formats in each type of force. At a certain moment, one of the American warriors slapped his hand on the table and was born GPS, which absorbed all the best of its predecessors. In the middle of 70, under the auspices of the United States Department of Defense, a tripartite joint committee was created called the Navigation Satellite Executive Group (NAVSEG), which determined the important parameters of the future system — the number of satellites, their heights, signal codes, and modulation methods. When we arrived at the cost figure, we decided to immediately create two options - military and commercial, with a predetermined error in positioning accuracy. The Air Force played a leading role in this program, since its Air Force 621B was the most thoughtful model of the future navigation system, from which GPS borrowed almost unchanged pseudo-random noise technology. The signal synchronization system was taken from the Timtation project, but the orbit was lifted to 20 thousands of kilometers, which provided the 12-hour period of circulation instead of the 8-hour from its predecessor. An experienced satellite was launched into space already in 1978 and, as usual, they had previously prepared all the necessary ground infrastructure - only seven types of receiving equipment were invented. In 1995, the GPS was fully deployed - around 30 satellites are constantly in orbit, despite the fact that 24 is enough to work. Six orbital planes for satellites are allocated, which have an inclination in 550. At the moment, surveying applications GPS allow to determine the position of the consumer with an accuracy of less than one millimeter! Since 1996, the Block 2R satellites have appeared, equipped with the autonomous navigation system AutoNav, which allows the device to operate in orbit when the ground control station is destroyed for at least 180 days.
The combat use of GPS until the end of the 80-x was sporadic and unimportant: determining the coordinates of the minefields in the Persian Gulf and eliminating the imperfection of maps during the invasion of Panama. Full baptism of fire took place in the Persian Gulf in 1990-1991 during the Desert Storm. The troops were able to actively maneuver in the desert, where it is difficult to find acceptable landmarks, as well as to conduct artillery fire with high accuracy at any time of the day in conditions of sandstorms. Later, GPS was useful in a peacekeeping operation in Somalia in 1993, in the landing of Americans in Haiti in 1994, and finally in the 21st century Afghan and Iraqi campaigns.
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