Modern satellite navigation has become an integral part of our lives, providing accurate positioning for transport, surveying and personal use. The operation of any global navigation satellite system is based on a strictly calculated orbital configuration, which allows signals to cover the entire surface of the Earth. For Russian system GLONASS this configuration has its own unique features that distinguish it from the American GPS counterpart.
The key parameter that determines the availability and accuracy of the signal anywhere on the planet is the number and location of orbital planes. It is the geometry of the orbit that determines how many satellites the user’s receiver “sees” at the same time and how accurately it can calculate its coordinates. Understanding the constellation structure is important not only for engineers, but also for specialists involved in the installation and calibration of navigation equipment.
In this article we will analyze in detail how many orbital planes are involved in the GLONASS system, what are their parameters and why this particular placement scheme was chosen. This data is critical for assessing the system's potential at high latitudes, where navigation often becomes challenging.
Basic configuration of the orbital constellation
The fundamental difference between the Russian navigation system is the number of orbital planes required to provide global coverage. In normal operation, the GLONASS system uses three orbital planes. This number is strictly fixed for the basic satellite deployment configuration and is included in the architectural principles of the system.
Each of the three planes contains a certain number of spacecraft that move in circular orbits. The full constellation consists of 24 satellites, evenly distributed: 8 devices in each plane. This distribution allows for continuous navigation support 24 hours a day anywhere in the world.
It is important to note that the orbits are medium altitude. The orbital altitude is approximately 19,100 kilometers above the Earth's surface. The satellite's orbital period around the planet takes 11 hours 15 minutes 44 seconds. It is these parameters, in conjunction with three planes, that create the necessary geometric shape of the coating.
The GLONASS system is based on three orbital planes, each of which contains 8 satellites in normal mode.
Orbital parameters and inclination
One of the most remarkable characteristics of the GLONASS system is the angle of inclination of the orbital planes to the equator. For the Russian system this parameter is 64.8 degrees. The choice of this particular meaning is not accidental and has deep physical and geographical justifications.
High inclination of orbits allows satellites to better “look” into the polar regions. Unlike systems with a lower inclination, GLONASS provides a more stable signal in northern latitudes, which is critical for Russia, most of whose territory is located in these zones. This makes the system preferable for use in the Arctic.
Satellites in each plane move in the same direction, but their phases are separated. This means that they are not located at one point, but are distributed evenly throughout the orbit. This synchronization eliminates situations where the signal disappears for a short time in a certain area of the Earth due to the geometric arrangement of the devices.
When choosing navigation equipment for work in northern regions, give preference to receivers with GLONASS support, since high orbital inclination provides a better angle of elevation of satellites above the horizon.
Comparison with other global systems
To better understand the uniqueness of the GLONASS configuration, it is necessary to compare it with other leading navigation systems in the world. The main competitor and analogue is the American system GPS. Despite the similar number of satellites in the full constellation (24 units), the architecture of their placement is radically different.
The GPS system uses six orbital planes, each of which contains 4 satellites. The inclination of GPS orbits is 55 degrees, which is less than that of GLONASS. This difference in the number of planes and inclination angle results in different availability of satellites at different latitudes.
European system Galileo also uses three orbital planes, like GLONASS, but the number of satellites in the active phase is 24 (8 per plane) with a total reserve of 30 devices. Galileo's orbital inclination is 56 degrees. Chinese system BeiDou has a more complex mixed configuration using geostationary and inclined orbits.
Below is a table comparing key parameters of the main navigation systems:
| Parameter | GLONASS | GPS (USA) | Galileo (EU) | BeiDou (China) |
|---|---|---|---|---|
| Number of planes | 3 | 6 | 3 | 3 (MEO) + GEO/IGSO |
| Satellites in the plane | 8 | 4 | 8 | Miscellaneous |
| Orbital inclination | 64,8° | 55° | 56° | 55° (MEO) |
| Orbit altitude (km) | 19 100 | 20 200 | 23 222 | 21 528 |
Synchronization and access method
Another fundamental difference associated with the organization of satellite operation in planes is the method of signal separation. The GLONASS system uses frequency division of channels known as FDMA (Frequency Division Multiple Access). This means that each satellite emits a signal on its own unique frequency, but they all use the same pseudo-random code.
For comparison, the GPS system uses code division CDMA, where all satellites operate on the same frequency, but are coded with different sequences. Using FDMA in GLONASS avoids signal interference, but requires the receiver to have more complex filters to process multiple frequencies simultaneously.
It is important to understand that satellites in the same GLONASS orbital plane do not have the same frequency. The frequencies are distributed in such a way that neighboring satellites do not interfere with each other. This imposes special requirements on receiving equipment, which must be able to quickly switch between frequencies or have parallel reception channels.
⚠️ Attention: When setting up professional geodetic equipment, make sure that the receiver firmware supports the current GLONASS frequency grid, as it is periodically adjusted by Roscosmos.
Reservation and modernization of the group
Although the basic configuration assumes 24 satellites, the actual orbital constellation often includes more devices. This is necessary to ensure the reliability and continuity of the system. There are always reserve satellites in orbit, ready to replace those that have failed or are undergoing scheduled maintenance.
The process of launching satellites into orbit and distributing them across planes is a complex engineering process. New devices in the series Glonass-K and Glonass-M Old models are gradually being replaced. They have an increased active lifespan and improved signal characteristics.
The distribution of reserve satellites may be uneven across planes during transition periods. However, the control system strives to maintain balance so that if one of the segments fails, the load is redistributed evenly. This ensures that the user does not notice a decrease in positioning accuracy.
What happens to old GLONASS satellites?
When a satellite reaches the end of its life, it is not simply abandoned in orbit. There are two main scenarios. If the device still has fuel reserves, it can be transferred to a “disposal orbit” - a higher orbit where it will not interfere with working satellites. If there is no fuel, it burns in dense layers of the atmosphere. This process is monitored by the Coordination Scientific Information Center.
Effect of orbital structure on accuracy
The number of orbital planes directly affects the geometric accuracy reduction factor known as PDOP (Position Dilution of Precision). The better the geometric distribution of visible satellites, the higher the accuracy of coordinate determination. Three GLONASS planes provide excellent geometry, especially at mid and high latitudes.
In equatorial regions, the effectiveness of three high-inclination planes may be slightly lower than that of six GPS planes, since GLONASS satellites pass through the zenith here, but there are fewer of them horizontally. However, on a global scale, especially when used together with other systems, this effect is leveled out.
Modern receivers, as a rule, are multi-system. They simultaneously receive signals from GLONASS, GPS, and Galileo. In this mode, the number of available satellites increases significantly, and the influence of the configuration of the orbital planes of a particular system becomes less critical for the end user, giving way to general visibility statistics.
☑️ Checking the quality of the GLONASS signal
Technical features of signal reception
For engineers and developers of navigation systems, it is important to take into account the specifics of signal transmission from GLONASS satellites. Due to the characteristics of the orbit and the frequencies used, signal strength may vary. Receivers must have high sensitivity to “catch” satellites located low above the horizon.
The antenna field also plays an important role. Antennas optimized for GLONASS must have a radiation pattern that takes into account the high declination of satellites. In some cases, especially fixed solutions, an active antenna with an amplifier is used to compensate for cable losses.
When integrating navigation modules into vehicles or special equipment, signal shielding must be avoided. Metal body structures can create blind spots, especially since GLONASS satellites are often high overhead rather than near the horizon.
⚠️ Attention: When installing the antenna on the roof of a car, make sure that there are no metal protrusions or weights above it that could block the field of view, especially in the direction of the North Pole, where the concentration of GLONASS satellites is higher.
Prospects for the development of the orbital constellation
The development of the GLONASS system does not stand still. Modernization plans include not only replacing the devices with more modern ones, but also a possible change in the structure of the group. Options are being considered to increase the number of satellites to 30 or more to improve accuracy and fault tolerance.
The introduction of new types of orbits, such as highly elliptical orbits, could further improve coverage in the Arctic region. This is a strategically important direction for Russia, where the development of the Northern Sea Route requires impeccable navigation support.
However, the basic principle of three orbital planes remains the cornerstone of the GLONASS architecture. This time-tested scheme has proven its effectiveness and continues to serve as the basis for navigation support for the country and millions of users around the world.
The future of GLONASS is associated with an increase in the total number of satellites and the introduction of new generation devices, but the basis of three planes will remain unchanged.
Why are there only 3 planes in GLONASS, and 6 in GPS?
The difference is due to different approaches to building the system and historical reasons. The USSR chose a design with fewer planes, but a larger number of satellites in each (8 versus 4) and a higher inclination. This saved on the complexity of plane control, but required more complex solutions for frequency division of signals. Both schemes mathematically provide global coverage.
Can a navigator work if it sees satellites on only one plane?
Theoretically, 3-4 satellites are enough to determine coordinates (2D), even if they are in the same plane, but the accuracy will be extremely low, and the vertical component (height) may not be determined at all. For full 3D navigation and high accuracy, visibility of satellites from different parts of the sky, that is, from different planes, is necessary.
How often is information about GLONASS satellite ephemeris updated?
Information about ephemeris (orbital parameters) transmitted in the navigation message is updated every 30 minutes. However, the data itself in the almanac may be relevant longer. The receiver must periodically receive fresh data to correctly calculate the position, since the satellites are constantly moving along their orbital planes.
Does the number of planes affect the time to first start (TTFF)?
Yes, it does have an indirect effect. If the system's almanac is out of date, the receiver has to search for satellites. In a system with three planes and 8 satellites each, the likelihood of quickly acquiring a signal with a known approximate location is high. However, modern receivers use A-GPS/A-GLONASS technologies, receiving orbital data via the Internet, which reduces the influence of the number of planes on the launch time to a minimum.