Expensive and unsafe
Why is the renowned GPS not happy with the US military? First of all, the high cost: each new satellite costs $ 223 million. This has already led to a reduction in purchases by the Pentagon in recent years. The second, more serious problem is the vulnerability of the satellite constellation to the threat of Russia's new weapons. In April of this year, the American military accused the Russian Aerospace Forces of testing an A-235 Nudol anti-satellite missile, allegedly aimed against US space objects. The potential targets were, according to the Pentagon, individual satellites of the Keyhole / Chrystal reconnaissance group, which previously (in February) "probed" the Russian spacecraft Kosmos-2542 and Kosmos-2543. The head of the US Army's Space Command, John Raymond, commented on the situation as follows:
"Russia's DA-ASAT (direct-ascent anti-satellite weapon) test shows yet another example that the threats to US space systems and [their] allies are real, serious and growing."
All this makes it clear to the American military that in the event of a conflict with Russia, a space constellation of satellites may be under attack, and GPS devices will not be the last on the list of targets. This creates global problems for the United States' favorite remote warfare, when most of the strikes are carried out not within the line of sight, but on signals from the global positioning system. And the point here is not only in the anti-satellite weapons of Russia. Last year, the Americans allegedly already caught domestic electronic warfare equipment in violation of the GPS over the Mediterranean Sea. According to the Pentagon, this was done to cover the group of Russian troops in Syria. Some powerful sources of interference for global positioning systems were deployed in Khmeimim, which “manipulated” the signals of GPS satellites even at the airports of Ben Gurion (Israel) and Larnaca (Cyprus). The special services and the Russian army are accused by the West of at least 10 thousand registered cases of so-called spoofing of GPS users. Receivers of a satellite navigation signal receive data from a third party, which displays coordinates that do not correspond to reality to the user. A very useful competence in the era of precision weapons, I must say. In particular, information circulates in the American press that in 2018, during the inauguration of the Kerch Bridge, a convoy of trucks led by Vladimir Putin was actually in the area of Anapa airport at a distance of 65 km. At least according to the GPS system. To what extent this corresponds to reality is unknown, but one can only be glad for the impressions of Russia's potential adversaries. For the sake of fairness, we note that GPS jamming technologies have been developed to one degree or another in China and even in North Korea.
The US military has been looking for a replacement for the GPS system for several years, and navigation using an atomic clock could become one of the first alternatives. In 2012, prototypes of C-SCAN atomic clock chips were created at DARPA, which, together with an inertial navigation system, allow high accuracy to determine the location of individual soldiers, equipment and direct precision weapons. At the same time, the measurement error in the new system is much lower than in the case of satellite navigation. In principle, even now the US military uses gyroscopes and accelerometers in case of GPS malfunctions, and atomic clock chips will allow all this to be miniaturized. And no interference, no third parties in the form of the Russian special services. But until these undertakings are implemented in real devices, the Pentagon has only to dream of navigating on new principles. For example, astronomical navigation with a sextant in hand was recently returned to the training program for naval officers. These are, of course, extremes that have no relation to reality and force us to look for alternatives. For example, take into account the peculiarity of the magnetic field of the area in navigation.
With a magnet in hand
Using the Earth's surface magnetic field gradient for navigation is not American know-how. Articles on similar topics have been circulating in domestic specialized scientific publications for several decades. And the idea itself was expressed back in the 1960s by the Soviet academician A. A. Krasovsky. The technologies being developed now are based on modern magnetometers, which have very high sensitivity, accuracy and speed. Considering the high variability of the Earth's magnetic field, we can confidently speak about the possibility of orientation based on an individual signature of a terrain or region. An airplane, rocket or tank equipped with sensitive magnetometers and accurate magnetic maps of the world will be able to navigate without the involvement of a GPS system. At the same time, the positioning accuracy can reach 10 meters, which does not fundamentally differ from satellite navigation. The parameters of the magnetic field gradient do not depend on solar activity, season and weather conditions. But in theory it turns out so beautifully. If the Americans decide to create such a system (it already has a name: MAGNAV) for their army, they will face a lot of problems.
First, in order to wage war on enemy territory, it is necessary to have accurate maps of the magnetic field of the area. But how to do it? It will not work from the satellite, the height is too high, the gradient will simply not be visible. A certain way out could be the hidden installation of magnetometers and recording equipment on the planes of regular flights of foreign airlines. But if you look at any online map of air traffic, for example, Russia, you will understand the futility of this. We have vast territories over which no air routes pass. And the flight altitudes of civilian ships are still very high, which does not allow studying all the subtleties of the magnetic gradient. And the Pentagon needs magnetic maps of the terrain primarily for navigating cruise missiles that go to targets several tens of meters above the surface. In Russian publications it is mentioned that for normal navigation along the magnetic gradient, aircraft should not at all rise above 1 km. In the United States, a combined navigation system is being considered for this situation, when the vehicle moves along a magnetic gradient across the previously explored territory, and when it crosses the "front line" it turns on the inertial system. It turns out inaccurate, but there are no other options yet.
Secondly, magnetometers are constantly interfered with by parasitic fields, that is, drowning noise. Especially a lot of it is generated from the aircraft itself. What about the magnetic field created by the helicopter main rotor? The Americans are trying to solve the problem of removing noise using artificial intelligence algorithms: this topic is now being worked on at the Massachusetts Institute of Technology.
Thirdly, in the course of intense hostilities, there will inevitably be explosions, gun salvos and other harmful magnetic impulses that interfere with the operation of magnetometers. And what will happen to such navigation after a series of atomic explosions? In general, the stability of the novelty to war conditions is still questionable. For strikes against banana republics, it will do, but I think there will be nothing to jam the GPS with.
Any action will inevitably be opposed. One of the forms of such "anti-navigation" work can be powerful sources of a magnetic field, dispersed over the territory of a probable clash. The purpose of this technique should be the formation of magnetic terrain gradients that distort the real position. And then the likely adversary will have to rely on the good old inertial system, or even on the sextant.
