Throughout history, communication and navigation have been at the heart of military maneuver, in order to coordinate the action and movement of distant units. From summary maps, smoke signals and flags used since antiquity, armies have evolved towards increasingly efficient and precise systems, capable of bringing about the expected effect at the desired moment, and thus multiplying its effectiveness.
In the field of navigation, the invention of the Global Positioning System or GPS in the early 1970s, based on a position signal triangulated from at least 4 satellites moving 20,000 km above the earth, and on the precision of the new atomic clocks, represented a considerable revolution in the conduct of military actions initially, then in the emergence of precision weapons also using this signal to reach their target with metric precision.
As GPS positioning has become a key component for armies, it was predictable that other countries, or groups of countries, would also develop similar solutions. This was the case of the Russian GLONASS system which entered service in the mid-1990s, the Chinese BeiDou system from the early 2000s, as well as the European Galileo system from the mid-2010s.
Indeed, controlling all technology, and in particular the satellites themselves, allows countries, and therefore their armies, to restrict its use or precision for other operators, or even to use variations that are more precise and more resistant to jamming, as is the case with the GPS signal used by the American armed forces and their 5 Eyes allies.
Above all, many of these countries undertook to develop capabilities aimed at depriving the adversary of the use of their own systems. China, but more so Russia, have thus developed several technologies to make a given space opaque to the signal through the use of intense electromagnetic jamming, but also to reduce its precision, by using parasitic signals causing receiver drift, this can be counted in kilometers. This is called spoofing.
If, as previously mentioned, the United States has developed variations of the GPS signal that are more resistant to jamming and spoofing, secondary users are, as a general rule, not equipped with them. This explains in particular the reports indicating a certain lack of effectiveness of the Ground-Launched Small Diameter Bombs or GLSDB rockets used by the Ukrainians in recent months.
In fact, although satellite positioning systems are now found in the vast majority of modern weapon systems, the world's major armies have also undertaken to develop alternative positioning solutions to GPS, beyond inertial navigation. , allowing them to operate with precision above or in a space for which the signal would be inaccessible, or incoherent, without returning to the famous 3C triptych: Map, compass and chronometer, effective, but otherwise complex and difficult to implement .
There are currently 4 of these technologies: celestial navigation, visually assisted navigation, navigation by signals of opportunity and magnetic navigation.
1- Celestial Navigation versus GPS
The stars, whose trajectory is known and predictable, have been used to navigate since the dawn of humanity, when the first humans understood that the sun rose in the same place, and set in the same place every day, all at least in the perception of the time.
During antiquity, the stars were frequently used to find their way and navigate, particularly on the seas, using basic instruments which gave birth to the Astolab then, many centuries later, to the sextant.
This technology, which may seem archaic and imprecise at first glance, is nevertheless used today intensively and very precisely for space navigation, whether satellites, probes or space vehicles. Above all, it is implemented by most strategic ballistic missiles to ensure the transit and precision of strikes.
Basically, using a sky map, a stopwatch and a tool to calculate the elevation of the stars, it is possible to obtain a very precise position on the entire planet, and even beyond. However, it is not without certain limitations, the first and most obvious of them being its dependence on cloudiness to be able to target the stars used to establish the position.
If, once combined with modern technologies, it proves effective for devices operating at high altitude, for which the weather is very rarely a factor, it quickly degrades as soon as the altitude decreases, making it a secondary tool. effective, for example to validate the data received by the GPS, but whose effectiveness cannot be guaranteed over time.
A solution to this problem has been developed in recent years, based on the detection of X-rays emitted by known Pulsars in the sky. If, theoretically, this technology should make it possible to overcome the problems of cloudiness, its precision, today, is still insufficient, of the order of 5 km, for operational military use, outside of space navigation.
2- Assisted visual navigation or odometry
Until recently, fighter pilots carrying out low-altitude penetration missions used, as previously mentioned, a method based on a precise map, a compass and a stopwatch, as well as a good dose of mental arithmetic.
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