There are several global satellite navigation systems in the world that harmoniously complement each other: American GPS, Russian GLONASS, European Galileo and Chinese Beidou. Global navigation systems are arranged according to one similar principle. They combine complexes of ground and space equipment for positioning in space and time, on the basis of which the location, speed, direction and other parameters of the movement of an object are determined.

The principle of operation of navigation systems is tied to measuring the distance from satellites in orbit, the location of which is reliably known with great accuracy, to the antenna of the receiving device. Each satellite emits accurate time signals using atomic clocks synchronized with the system time. In the course of receiving a signal from orbiting satellites, the delay between the time of signal emission and the time of its reception by the antenna of the terminal device is calculated. From this information, the receiver calculates the antenna coordinates. An object's displacements are calculated based on the measurement of the time it takes to move between two or more points with pre-calculated coordinates.

Accurate positioning in space is provided by receiving a signal from at least three satellites overnight.

For accurate positioning in space, the receiver antenna must receive a signal from at least three satellites overnight, and preferably from four. A trio of satellites transmit data about their location relative to the Earth and each other, the fourth - fixes the time of signal travel from the transmitter to the receiver. Since the satellites are constantly in motion, their trajectory is tracked by ground stations. Up-to-date information is sent to gadgets in almanacs - libraries with the most accurate information about the location of all available satellites. Almanacs are updated via mobile networks or via Wi-Fi, which significantly reduces the duration of the "cold start" of navigation systems.

Initially, satellite navigation systems were military developments. Many of them remain under the control of the military departments to this day. The first public navigation system was the American GPS. Actually, the words "navigation" and "GPS" have long been perceived as synonymous.

Popular travel navigators

GPS

The development of the NAVSTAR (Navigation Satellite Time and Ranging) project was undertaken by the US Department of Defense in the 70s of the last century. The first satellite of the system was launched into orbit in 1974, and over the next 20 years, all the necessary number of satellites for the correct operation of the system (24 pieces) were launched into space. The GPS (The Global Positioning System) navigation system was opened for civilian needs, however, in order to avoid its military use by opponents, the accuracy of the system was forcibly reduced by special algorithms to about 100 m. Most of the restrictions were removed only by the beginning of the third millennium.

The GPS navigation system consists of 32 satellites that revolve around the Earth in circular orbits in six different planes. All satellites are located in an orbit with a daily multiplicity of 20,200 km above sea level. As a result, at any point on the planet, at least four satellites are always observed at any given time (usually from 4 to 12 satellites are visible at the same time). Every 30 seconds, the satellite transmits radio signals at a frequency of 1575.42 MHz, which contain information about the satellite's position in space, signal quality information, satellite clock error, and ionospheric model coefficients.

Satellites of the GPS system revolve around the planet in six different planes in an orbit with a daily multiplicity of 20,200 km above sea level.

Ground stations are called upon to improve the accuracy of determining the coordinates, which transmit corrections for the differential mode: WAAS in the United States and Canada, EGNOS in European countries. Standard receivers fix the location with an accuracy of several meters, the newest ones have an accuracy of up to several centimeters.

Early versions of GPS had a long so-called "cold start" time. This was due to the need to transfer the almanac (astronomical calendar) and a whole bunch of related corrections to the receiving device. The aGPS (Assisted GPS) system solved the problem. Devices with it can receive service information from the nearest mobile operator base station, which eliminates the need for gadgets to maintain direct communication with satellites and reduces the navigation start time by several times (literally in a few seconds).

A visual principle of how aGPS technology works: 1 - GPS satellites; 2 - GPS signals; 3 - auxiliary signals; 4 - communications operator tower; 5 - mobile gadget.

Also in modern navigation modules there is Dual GPS technology. Receivers with its support do not operate on one frequency, like traditional counterparts, but on two (L1 + L5). Such a format significantly improves positioning accuracy - in some cases up to 10-20 cm. Dual GPS allows you to correctly process signals reflected from high-rise buildings in dense urban areas. Note that full support for L5 is available in the European Galileo system, in GPS such broadcasting is carried out by only half of the satellites, and in the GLONASS system it is expected not earlier than 2030 at all.

Shockproof Phones

GLONASS

The Russian radio navigation satellite system GLONASS began to be developed under the USSR in the 1970s. Flight tests of the system started in 1982 with the launch of the first satellite into orbit. A full constellation of 24 satellites was deployed closer to 1995. However, due to funding problems and the short operational life of spacecraft, by 2001 the number of operating satellites was reduced to six.

The situation was reversed in the middle of the "zero", and the completion of the creation of the GLONASS navigation system was announced at the end of 2015. It is based on 24 active satellites that rotate at an average altitude of 19,100 km above the Earth's surface in three orbital planes. There are 8 evenly spaced satellites in each orbit. The GLONASS system also provides for backup spacecraft.

The integral constellation of GLONASS satellites is formed from 24 active spacecraft.

The satellites of the system transmit radio emissions of two types: the navigation signal of the L1 band and the high-precision navigation signal in the L2 and L3 bands. Errors in determining the location are about 3-6 m, and with adjustments - up to 1 m. An important feature of GLONASS is the ability to use the navigation system at high latitudes in the northern and southern polar regions, where the GPS signal catches poorly.

Galileo

Galileo is a European satellite navigation system created as an alternative to American GPS and Russian GLONASS. It is noteworthy that it is under the control of civilian departments. With a full fleet of 24 active satellites, the system gives an accuracy of up to 1 m in public mode and up to 20 cm with the GHA service. In total, there are 30 Galileo satellites in orbit (6 spacecraft are in hot standby).

Orbits of satellites of the European navigation system Galileo.

The Galileo satellites rotate in three orbital planes at an altitude of 23,222 km above the planet's surface. In each of the orbits, when the system is fully deployed, there are 8 active and 2 standby satellites. This constellation configuration provides simultaneous visibility from anywhere in the world to at least four vehicles.

In the future, the satellites of the Galileo system will be able to transmit user alarms to regional rescue coordination centers. In this case, feedback will be provided - confirmation of receipt of notifications about alarm situations.

Interesting fact. The satellite communication function for sending emergency messages to rescue services in places with no traditional cellular coverage was introduced into the entire line of 14 iPhones from Apple.

Beidou

In 2020, the creation of global coverage was completed for the Chinese Beidou navigation system. Its satellite flotilla consists of 48 spacecraft, 35 satellites are in operation. Satellites are placed in three orbits: medium circular, geostationary, geosynchronous inclined high.

A stand with a visualization of the principles of the structure of the Beidou global navigation satellite system.

The Celestial Empire's desire to create its own satellite navigation system is due to the desire to gain independence from the United States and its GPS system. The positioning accuracy of Beidou for the civilian population is less than 10 meters, and the speed measurement accuracy reaches about 0.2 meters per second.

Other regional systems

Individual countries are developing their own navigation systems. They have not yet reached the global level, however, IRNSS (Indian Regional Navigation Satellite System) in India, as well as QZSS (Quazi-Zenith Satellite System) in Japan and the countries of the Asia-Pacific region are already operating as regional navigation systems.

Working together in synergy, different navigation systems provide more accurate location measurements, especially in densely populated areas and large metropolitan areas where the signal is repeatedly reflected from tall structures. Modern gadgets often support work with all known satellite systems, thanks to which navigation becomes more accurate literally every day.