The principle of operation of the satellite system.
The principle of operation of the satellite system
It is believed that satellite navigation appeared on October 4, 1957 — then the first artificial Earth satellite was launched. The first satellite radio navigation system, which allows determining the coordinates of an object using radio signals coming from a satellite, was created only in the late 70s. Navigation systems are used by surveyors, rescuers, work on ballistic missiles, to ensure the safety of citizens of the state.
The principle of operation of the navigatormust meet the basic requirement — the accuracy of determining spatial and temporal coordinates and the ability to receive navigation information at any time.
The principle of operation of the satellite systemis as follows: the navigation signal receiver measures the delay in the propagation of the signal from each of the visible satellites to the receiver. The signal delay multiplied by the speed of light is the distance from the satellite at the moment of emission to the receiver at the moment of reception. From the received signal, the receiver obtains information about the position of the satellite. The principle of operation of the satellite systemis based on measuring the distance from the antenna on the object (the coordinates of which must be obtained) to the satellites, the position of which is known with great accuracy. The table of positions of all satellites is called an almanac, which any satellite receiver must have before measurements begin. Usually, the receiver stores the almanac in memory from the time of the last switch-off and, if it is not outdated, immediately uses it. Each satellite transmits the entire almanac in its signal. Thus, knowing the distances to several satellites of the system, using ordinary geometric constructions, based on the almanac, it is possible to calculate the position of the object in space.
The principle of operation of the navigatorand the entire system can be conveyed schematically: the user is at the intersection of several spheres, the centers of which are visible satellites. The radii of the spheres are equal to the distance to each of the satellites. To determine latitude and longitude, the receiver must receive signals from at least three satellites; receiving a signal from a fourth satellite allows you to determine the height of the object above the surface. These data allow you to find the user's coordinates by solving a certain system of equations. The principle of the navigatorrequires additional adjustment, since errors related to the influence of the ionosphere, air temperature, atmospheric pressure and humidity (each factor introduces an error of up to 30 m) occur when determining the coordinates of an object. The ephemeris error (the difference between the calculated and actual position of the satellite) is from 1 to 5 m; interference also makes its contribution. The total error can reach 100 m. To reduce errors, the so-called differential GPS mode is used (by the way, let's not forget about the domestic GLONASS). In this mode, the user's receiver receives corrections to its coordinates from the base station. Usually, corrections are transmitted in real time via a radio channel. As a result, the accuracy of determining coordinates reaches 15 m. A new class of relative navigation systems are systems that provide (in real time) a location accuracy of about 1 cm. The principle of operation of the satellite is as follows: the reference station and the user receiver receive signals from the satellites. The reference station then sends the results of the phase and pseudorange measurements of all visible satellites to the user receiver. As a result of processing at the receiver, the relative coordinates are determined with an accuracy of 1 cm in real time with a reliability of 0.999. When the satellite receiver is operating, its clock is synchronized with the system time and, upon further reception of signals, the delay between the emission time contained in the signal itself and the time of signal reception is calculated. With this information, the navigation receiver calculates the coordinates of the antenna. Most navigation receivers use the Doppler effect to obtain speed information. The operating principle of the navigator allows for additional accumulation and processing of this data over a certain period of time, making it possible to calculate such movement parameters as speed (current, maximum, average), distance traveled, etc.
Elements of the satellite system
Like any other system, navigation consists of components that perform practical functions within the framework of the main tasks. Elements of the satellite system can be divided into the following: An orbital grouping consisting of several (from 2 to 30) satellites emitting special radio signals; A ground-based control and monitoring system, including units for measuring the current position of satellites and transmitting the received information to them to correct information about the orbits; Receiving client equipment («satellite navigators») used to determine coordinates.