A group of Japanese developers recently unveiled a new navigation system, MuWNS, which will operate underground and underwater. The system is based on the use of cosmic rays.
The range of GPS satellite navigation is paradoxically very limited. Despite the fact that the satellites that connect us to the navigation system are 20,000 km away. Yes, they fly high above the surface. So all it takes is a thick ceiling or a descent into the basement for the system to stop working. That, however, could change by using… of cosmic rays for navigation.
Satellite navigation, as phenomenal as it is, and which often saves lives (not to mention makes them easier every day), has its limitations. The ideal conditions for such a system to work smoothly are clear skies and communications that are not obstructed by trees or, even more so, buildings. Otherwise, the signal may simply not reach our device from the satellite and vice versa.
These limitations arise because satellite navigation uses a radio signal which cannot overcome many of the obstacles that surround us on a daily basis. Just as classic radio communications have problems when we are in a lift, basement or underground garage, the satellite signal does not have enough power to penetrate many metres of obstacles. Because 20,000 km is a long enough distance for radio waves and obstacles in their path.
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However, researchers at the University of Tokyo have recently developed muon-based wireless navigation technology that can be used anywhere on Earth, even deep underground and underwater. The research was published in the journal iScience. Anyone interested can read it in more detail. We will try to explain it in simple terms.
What are muons? They are unstable charged elementary particles that have the greatest penetrating power. They can be obtained in the laboratory, but most importantly, a powerful flux of muons constantly reaches the Earth in the form of cosmic rays that penetrate nearly 2 km deep into our planet. Approximately 10,000 muons per minute hit every square metre of the Earth’s surface.
In recent years, muons have attracted increased attention from scientists. It is because of their remarkable penetrating power that muons can be used to explore the depths of volcanoes, peer into the heart of pyramids and study the inner workings of cyclones. In addition, muons remain immune to interference.
“Cosmic ray muons hit the Earth in the same way and always travel at a constant speed, regardless of the matter they penetrate, traversing even a kilometre thick layer of rock,” explained Professor Hiroyuki Tanaka of Muographix at the University of Tokyo. “Now, using muons, we have developed a new type of navigation, which we have called a muometric positioning system (muPS) that works underground, indoors and underwater.”
The proposed technology is called the muometric wireless navigation system (MuWNS), which can be translated as ‘muometric wireless navigation system’. It improves on technology developed earlier by the same researchers that used muons to analyse tectonic plate movements. Such research helped track tectonic plate movements and, based on this, provide early warning of possible earthquakes.
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However, navigation requires comparing distances from at least four points to accurately determine position in a 3D environment. Muons reach Earth in a continuous stream. But simply detecting them yields little. Therefore a communication system between the four stations and the device whose location we want to track must be established. In practice, this means that the equivalent of MuWNS satellites need not be in orbit but can be installed on the Earth’s surface. That is, they can be ground-based base stations.
The first version of the technology used to explore tectonic plates was wired, meaning that the signal to and from each transmitter was sent through physical wires. However, this completely ruled out its use for effective navigation. That’s because it’s quite bulky and expensive.
The solution to the problem turned out to be fairly simple. A precision quartz clock was used to wirelessly synchronise the detectors and receivers. The MuWNS description goes like this:
“The four parameters provided by the reference stations and the synchronised quartz clock used to measure the ‘flight time’ of the muons make it possible to determine the coordinates of the receiver.”
In one of the first experiments, the receiver located in the basement was found using a station located on the sixth floor of a building. This is unbelievable, as a GPS system would not have been able to do such a task for sure.
To test this, the researchers placed the detectors on the sixth floor of the building and the detector-receiver in the basement. Moving cautiously through the corridors of the basement, the researchers, instead of using navigation, took real-time measurements to determine the course and check the path they were following.
The experiment proved that MuWNS was accurate to between 2 and 25m, with a range of up to 100m, depending on the depth and speed at which the person was moving. This is as good, if not better, than single-point GPS positioning over the ground in urban areas. But it’s still a long way from being practical. People want accuracy down to one metre and timing is the key.
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Yes, the new navigation system, MuWNS, is still under development and experimentation. It is still in its raw state and is not yet ready to be used even in a single city.
Also, the system will be much more expensive in practice, which may limit its practical use. In addition, in order to be used globally, base stations for this type of navigation would need to be distributed throughout the world, just as telecommunication stations for mobile communications are today. In comparison, the entire GPS system relies on only 31 satellites orbiting the Earth.
The second problem is accuracy. Although we can “see” more than 1.5km into the earth with the MuWNS navigation system, using a quartz clock to synchronise time allows us to target static objects, as moving quickly would entail errors in positioning. Atomic clock chips could theoretically solve this problem, but they now cost from $2,000, so it would significantly increase the cost of every device (smartphone, smart watch, etc.) that would use this technology by at least that amount.
Improving this system, which would make real-time navigation much more accurate, takes time and money. Ideally, the team wants to use a chip-scale atomic clock (CSAC), because CSACs are already commercially available and they are better than quartz clocks. However, they are too expensive for us right now. But in time, we anticipate they will become much cheaper as global demand for CSACs for mobile phones grows.
It will be at least 5 years before this technology is finally developed and widely available. Researchers have already started work on the next version of MuWNS, called Vector muPS, which will not require a real-time atomic clock, solving one of the technology’s biggest problems.
In the future, MuWNS could be used to control unmanned vehicles underground or control underwater robots. Apart from the atomic clock, all other electronic parts of MuWNS can be miniaturised and the development team expects that it will soon be possible to integrate MuWNS into portable devices such as a phone. This could change the way rescue teams search and operate in emergency situations, such as a building collapse or rockfall in a mine.
There is no doubt that MuWNS’ unique muon-based technology will be used because in certain circumstances this navigation is incomparably better than GPS. When it is necessary to navigate underground or underwater, such as during rescue or geological expeditions, such a navigation system, even if deployed locally, would be one of the most effective locators that science allows us to use. It could have been used to rescue the passengers and crew of the Titan submersible, which recently sank in the waters of the Pacific.
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