Image: Seven of about 1,700 Starlink satellites make up the skies over Georgia. Because they are at a much lower altitude than standard GPS satellites, they give a stronger signal.
Almost everyone regularly uses a GPS or GPS in one way or another. The apps on your smartphone use it to give advice about restaurants and in the car, extensive discussions about maps like those of your parents are no longer necessary, to give just two examples.
The system – which operates thanks to about thirty satellites orbiting the Earth – is very old. It’s been used by the US military since the early 1980s, and although newer satellites provide upgrades, the Global Positioning System (GPS) has remained essentially the same in the early years.
That can sometimes be a problem, according to three engineers at Ohio State University in the US. “Scientists and developers now know so much about GPS signals that you can actually compare the system to open source software,” says Zach Casas, president of the Carmen Mobility Institute at Ohio State University. This knowledge is useful for companies that design GPS receivers, but it also makes the system vulnerable to attacks. Additionally, GPS satellites are farther from the Earth’s orbiting constellations in low orbit. This makes their signals weaker and easier to disable.
According to some circles, “jamming” or blocking GPS signals is a growing problem. Just like diverting drones. Scientists think it’s time to look for an alternative.
Can direct alternatives to GPS provide any consolation? There are several of them, such as the Russian Glonass, the European Galileo, and the Chinese BeiDou. But global navigation satellite systems, or GNSSs, are often created for political reasons. Furthermore, they pretty much use the same GPS recipe. Sometimes with improvements, but often with only partial coverage. For example, the Indian NavIC system only allows its users to locate in South Asia and the Indian Ocean.
This means that Glonass and Galileo are more GPS complements than complete alternatives. Therefore, many mobile devices determine their position on the basis of satellites from several GNSS systems, based on the idea that accuracy increases if you include as many satellite signals as possible in the positioning. With an app like GPSTest (Android), you can see for yourself what signals your smartphone is receiving at a particular location.
There is also such a thing as satellite-based augmentation systems (SBAS). These are additional satellites that are in a higher but geostationary orbit around the Earth. They stay over a certain area and thus act as a kind of fixed beacon. This increases accuracy, so that GPS can still be used, for example, for air traffic around airports. You will find EGNOS satellites over Europe.
If the GPS satellites provide a weak signal, the solution is to look closer to home. That’s what scientists have found in the StarLink constellation, SpaceX’s satellites you may have seen in a row in recent months like a train in the sky.
About 1,700 Starlink satellites are now active. Remarkably, it is designed for Internet distribution, and not as a navigation system. That is why it is also suspended at an altitude of about 1,200 km, so that it can provide a strong signal. This is well below the orbit of at least 20,000 km that typical GNSS satellites reside in.
The bottleneck with this idea: SpaceX does not give third parties access to Starlink’s signals. This is difficult, but the engineers managed to adapt the sleeves. In an article that appeared in the magazine IEEE Transactions on Space and Electronic Systems They explain that an algorithm can be used to extract the location and movement of satellites from Starlink signals. This allows you to specify the location.
“All of this is happening without us being able to see the data sent via Starlink,” the researchers assert. In a test on an Ohio campus, engineers were able to pinpoint their positions with an accuracy of 7.7 metres. This is inferior to what GPS currently offers: the accuracy of this system is from 5 to 0.3 meters, depending on the type of receiver.
But the scientists believe that their algorithm will become more accurate. Elon Musk will launch more Starlink satellites with SpaceX. 1700 may seem like a lot, but the company has already indicated that it wants to put a total of forty thousand satellites into orbit around the Earth.
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