Is it really all GLONASS burned?

You could have news like “GLONASS stopped working all over the world” or terrible stories. “About half of the satellites of the operating Glonass orbital group developed a warranty period. At the same time, there are only five Glonass-M devices in the ground reserve, of which the impression could have been made that GLONASS was not completely broken, or it was breathing its last. And how are things really?
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Preparations for the launch of three satellites "Glonass-M"

A bit of history


In general, in the history of GLONASS there was a period when the system actually turned out to be practically inoperable. By the second half of the 90s, the Soviet inertia of launching new devices had ended, already launched into orbit one after another broke, and by the beginning of the zero, 6-7 satellites were functioning, according to various sources, which was completely inadequate. But in 2001, they adopted the federal program “Global Navigation System”, allocated funds, and gradually, by the end of 2011, they redeployed the grouping to the full strength of 24 vehicles, not counting the reserve ones.
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Early Transit Satellite Launch Preparation
Plunging into the story even deeper, satellite navigation systems have been an attribute of a superpower since the beginning of the space age. The Americans were the first to create the Transit system to ensure the combat duty of their ballistic-missile submarines. The first satellite went into orbit in 1960, and was officially adopted by Transit in 1964. The USSR was somewhat delayed, the Cyclone system’s satellites were launched in 1967, and adopted in 1976. But the Cyclone system provided not only navigation, but and communication. Then, at about the same time, on both sides of the ocean, they began to develop second-generation systems, and the American NAVSTAR / GPS was fully deployed in 1993, and the Russian GLONASS - in 1995. Both systems turned out to be similar. Is that GLONASS works better in high latitudes, but, despite a common mistake, not because of the height of the orbit (the GPS satellites are slightly higher), but because of its greater inclination.

In the crosshairs of spheres


When in orbit under the thirty devices of the grouping, the breakdown of the next is a normal working event. And to understand how this will affect the functioning of GLONASS, it is necessary to understand the principles of its work.
Let's start with a simplified problem on the plane. Imagine that we are in an unknown place and want to determine where we are. As luck would have it, passers-by that come across to us can only report distances to any settlements without a direction. We are armed with a map, compass and begin to draw. The first passer-by says that to Moscow in a straight line 160 km. So we can be at any point of the circle. The second - that to Smolensk 275 km. The search area is narrowed down to two points where the circles intersect. The third one says that 310 km from Kursk, and we can now say for sure that the compiler of the task left us in Kaluga.
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Figure gisgeography.com
In three-dimensional space, the principle is the same, only the intersection of two spheres is a circle, three points are two, and only the intersection of four spheres will give us the exact location. And the illustration becomes too complex to start right away from it.
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Figure gisgeography.com
Speaking quite simply, GPS or GLONASS satellites constantly broadcast the exact time and parameters of their orbit. The ground receiver cannot determine directions, but it calculates from the orbit parameters where the satellite is in space,and the delay in receiving the signal of exact time, which moves from the satellite to the receiver at the speed of light, calculates the distance to the satellite.
In theory, everything works very simply, but in practice it is necessary to take into account the arising interference.
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Atmospheric noise, illustration gisgeography.com
First of all, the signal from the satellites is distorted by the atmosphere. Therefore, ground stations make sense and are actively used - if we know its exact location, we can calculate changes in the speed and direction of propagation of a signal from a satellite and send corrections to receivers located in the same area.
Further, the mutual position of the satellites matters. For a perfect determination of the position, one satellite should be directly overhead, and the three remaining evenly distributed just above the horizon. And if all the devices in the sky next to each other, then the accuracy drops due to the geometrically inappropriate position.
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Illustration of gisgeography.com
In addition, there are interferences in the signal re-reflection from the satellite from ground objects, the accuracy problems of the atomic clocks on the satellite (even nanoseconds will introduce errors here), inaccuracies in the determination of satellite orbits and other factors.
It turns out that when one of the satellites fails, in some places, instead of him, you have to choose the signal of the other, in a worse position, which increases the error. Naturally, when one unit breaks down, it does not disable the entire system. So the news "GLONASS stopped working all over the world" should be more correctly reformulated to "in some areas of the Earth, the position accuracy is expected to deteriorate." But this, of course, does not sound so clickbate.
The GLONASS information center monitors the accuracy of the signal and displays it on its website. Now, when 24 devices are functioning, the accuracy is uniformly good on the map, but in the event of a breakdown, areas with a larger error will appear. Satellites can maneuver in orbit, so the control center positions them so that the positioning accuracy deteriorates away from the territory of Russia, somewhere in the deserted part of the Pacific Ocean.
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A separate irony is that civilian users will not notice any changes at all, because since 2011 they have been producing chips that work simultaneously with GPS and GLONASS, and now receivers are able to work also with the Chinese Beidou and European Galileo. not fully deployed.Therefore, a civilian device in 2018, even being far from an ideal place, sees two dozen satellites.
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The experiment from the balcony, to the west and south satellites obstruct the house, nevertheless the accuracy is 4 meters

Strategy issues


It is known that today there are no backup satellites in the second and third orbital planes. According to the most recent data, the next launch of the Glonass-M satellite will be in October, so it is quite possible that we will have time to read the new iteration of the creepy news.
The situation in the system can be submitted in two opposite ways:
“About half of the satellites of the existing Glonass orbital constellation have worked out a warranty period. At the same time, there are only five Glonass-M devices in the ground reserve
"The GLONASS satellites finally learned to do so that they began to work longer than the warranty period, and until the old ones broke, there is no point in launching new ones. And in case of major problems, we have as many as five spare ones in storage."
Personally, the second option is closer to me - for modern satellites, the rate exceeds the planned work time, and there is no sense in changing the devices that can be functioning for a long time.At the same time, the absence of an orbital reserve in two planes of three and the apparent inability to instantly launch a new replacement satellite means that after a crash in the second or third planes for several months, the grouping will be incomplete. From the outside, we cannot estimate the degree of risk that the operators have taken, only time will tell us the success of the chosen path.

Conclusion


Satellite navigation very quickly became an integral part of modern life. It is used not only by "serious" military, pilots and seafarers, now these are taxi services, fitness, drones, photos with geotags, and many other uses. And so far the world is unanimous that a developed country should have its own navigation system. Europe, China, India prefer to create their own constellations of satellites, rather than using ready-made GPS. GLONASS, albeit on the second attempt, has become a full-fledged and sought-after navigation system, and the next time you see a bright title, do not be in a hurry to give in to emotions.
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