Satellite navigation technologies have become a familiar convenience for the average user. Millions of devices are produced every year that support such systems. GPS, the first global system, has become synonymous with geopositioning. But there is also the domestic GLONASS, the European Galileo, as well as the mysterious Beidou from China. And also the Japanese QZSS and the Indian NavIC (IRNSS), which are regional projects, but in the future have the prospect of developing into global systems.
GPS, GLONASS and Beidou have been maturing since the middle of the second half of the last century. The European program to create a global navigation system was only approved in 1994, and many more years have passed before the first launches. The idea of satellite navigation visited the bright minds of engineers after the launch of the first satellite of the USSR. It was found that the strength of the signal from the spacecraft varied depending on the distance of the satellite due to the Doppler effect.
The first satellite of the navigation system was launched by the United States, and the project has reached our time under the name GPS. In the USSR, they also worked on their own solution – Soviet engineers called their analogue GLONASS (Global Navigation Satellite System). If the American program was developed systematically, then the development of GLONASS faced problems due to restructuring, and then due to lack of funding. Beidou has also come a long way in becoming, which is caused by crises.
Navigation spacecraft GLONASS-K
GPS and GLONASS were created primarily as military technologies with all the consequences. Later, access to them was opened to civilians. Now satellite navigation is used in various spheres of human life and allows you to determine not only the location, but also the movement parameters.
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At the same time, to improve the reliability and stability of navigation, countries are joining forces, however, they are doing it in groups. So integration with Galileo is moving forward in GPS, and GLONASS is more “friendly” with Beidou.
Briefly about the principle of work
The technology is based on measuring the signal delay from the satellite to the receiver. Signal transmission is carried out in the decimeter wave range. To accurately determine the coordinates on the plane, three satellites are needed, and the fourth satellite helps determine the height.
The main elements of the system:
a satellite in earth orbit;
The satellite navigation system determines the coordinates with an accuracy of tens or even hundreds of meters. Further, algorithms that eliminate errors and errors come into play. Calculations help to reduce the error to a few meters, and advanced solutions to a few centimeters. Since the systems were developed primarily by the defense departments, the increased accuracy in most cases is provided exclusively to the military. In Galileo – on a commercial basis.
Can GPS be disabled?
Theoretically, disabling users from specific regions or countries is possible. Disabling the civilian GPS segment by the US military took place during local conflicts. Accordingly, the repetition of such scenarios in the future is possible. It is possible that the allied Galileo may also suspend work in certain areas or increase the error to unacceptable values.
If earlier this could become a serious problem, now GLONASS and Beidou have grown strong enough to become a full-fledged alternative. Moreover, in some cases, these satellite navigation systems work better than their American and European counterparts. In addition, most modern devices are equipped with two types of receivers, so no significant changes are expected for users.
Parameters of the main satellite navigation systems
GPS GLONASS Beidou Galileo
Launch of the first navigation satellite 1960 1967 2000 2005
Number of satellites 32 25 49* 26
Orbital inclination 55° 64,8° 55° 56°
Orbit altitude (thousand km) 20,2 19,1 21.528 and 35.786 23,222
Period of circulation 11 h 58 min 11 h 15 min 44 s 12 h 53 min 24 s 14 h 4 min 45 s
* Beidou uses mixed orbital constellations: 8 satellites in geostationary orbit, 12 in inclined geosynchronous orbits, 29 in medium circular orbits.
Orbits and spectrum of GPS navigation radio signals:
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Orbits and spectrum of GLONASS navigation radio signals:
Orbits and spectrum of Beidou navigation radio signals:
Orbits and spectrum of Galileo navigation radio signals:
At the moment, GPS provides the best positioning accuracy on a global scale. At the same time, Galileo uses advanced designs and may offer higher accuracy in the future.
GLONASS is slightly inferior in accuracy to GPS, but is more reliable when operating in northern latitudes.
Some European countries from the northern regions have been using the Russian satellite navigation system for many years instead of the American and European counterpart, which says a lot.
Beidou is rapidly gaining momentum, and only in recent years has it become a leader and left behind other systems in terms of the number of satellites. In addition to global coverage, the Chinese program is also focused on its own region and improving mobile communications. In addition to improving the hardware, an important component is the development of algorithms for eliminating errors and errors.
At the moment, there are two regional projects, on the basis of which the deployment of global systems is possible in the future. These are the Japanese QZSS (Quasi-Zenith Satellite System) and the Indian NavIC.
QZSS is focused on the Pacific-Asian region and Japan. As part of the project, 4 spacecraft have already been launched, which are in quasi-zenith orbits. In Japan, the system provides positioning accuracy with an error of 2 m. It is planned to expand the orbital constellation with three more satellites.
The system is also focused on improving the quality of communication, data transmission and text messages. One of the advantages of the Japanese project is the work with the LEX signal (L6 band), which provides high-precision positioning with centimeter accuracy.
Orbits and spectrum of QZSS navigation radio signals:
NavIC is focused on Indian users, and also covers the territory of nearby countries and the Indian Ocean – up to 1500 km from the country’s border. A feature of the system is the use of single-frequency equipment, which, thanks to corrections using the parameters of the ionospheric dot grid, gives results similar to two-frequency equipment.
The orbital constellation consists of three spacecraft in geostationary orbit and four in geosynchronous orbit. In its region, NavIC is more accurate and faster than GPS.
Orbits and spectrum of NavIC navigation radio signals:
What other alternatives are there
Determining the location of an object in space is possible without satellite navigation systems. There are many alternatives, but at the moment their accuracy and reliability are insufficient. An example is Location-based service (LBS) – these technologies can be used where it is not possible to work with a satellite signal. The same services can be used to improve the accuracy of the calculation of the location of an object, working in conjunction with global navigation systems.
The Starlink project, which SpaceX is deploying, can become a serious competitor to global satellite systems. According to Ohio State University researchers, scientists were able to achieve an accuracy of calculating coordinates up to 7.7 m. With an increase in the number of satellites, the error will decrease. The researchers note that Starlink satellites are closer to the surface of the planet, and the signal from them is stronger. In particular, this can reduce the influence of interference and improve the reliability of the system.
Now many are concerned about the question of what will happen if GPS (and Galileo) are turned off. In fact, modern devices support working with all four systems at once, so there will be no problems because of this. An exception may be devices with old-style receivers that were developed for GPS – in most cases these are devices from the 2000s.