Galileo: High-accuracy iodine watches should improve satellite navigation

The global Galileo satellite navigation system already enables high accuracy of location and accurate time information. The 22 active GPS satellites that are currently active are constantly transmitting data so that users can determine their location. This should work even better in the future: Researchers from the German Aerospace Center (DLR) on the Compasso project are working together with business partners on high-precision iodine clocks for Earth satellites and a new generation of space-powered laser measurement systems.

Atomic clocks up to nanoseconds are currently doing their work in the Galileo system. A billion of them lasts for a second. Felix Huber of the Galileo Specialized Center in Oberpfaffenhofen explains that iodine laser watches currently being developed at the DLR Institute of Quantum Technologies are “several times” more accurate than other systems. The development phase of the facility that operates the DRL office should be completed soon after about two years. she runs Compass Initiative, which were originally compact, highly stable optical clocks being tested on the International Space Station (ISS).

Laser iodine watches are currently being qualified for use in space: the participating scientists face a particular challenge here, because special watches have to be especially small, powerful and durable. The principles of quantum mechanics form the basis of laser watches. So it is about physical processes at the atomic level and thus “in a smaller world”, As DLR . writes.

Galileo satellites generally transmit non-stop data about their time on board and their career. The receiver calculates the distance to the escorts in space by determining how long the signal lasted. The position is determined by three satellites at the same time. A fourth is also required for the receiver clock to operate synchronously with the satellite clocks. The latter, in turn, should be coordinated with each other as fully as possible. This accuracy is important not only for transportation, but also for financial transactions, energy supply and agriculture.

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“An inaccuracy of time measurement by one nanosecond, for example, corresponds to an error of 30 cm in the distance measurement,” explains Huber. This does not seem like much, since the satellites orbit the Earth at an altitude of about 23,000 km. But, according to the professor, this would be unbearable, especially when it comes to navigation in moving cars: “The atomic clocks in the satellites must be matched so precisely that they allow an accuracy of the position to within a few centimeters in real time . “

For Compasso, the DLR Institute of Communications and Navigation worked with partner companies Menlo and Tesat to develop a laser station that transmits data, synchronizes satellite clocks, and determines distances with high accuracy. In addition to other tools that support experiments in space, there is a frequency comb. It transmits optical signals in the frequency band for satellite navigation. The DLR Institute of Software Technology has programmed a driver for the computer that controls the tests. DLR Space Operations supports, prepares and implements the project as a whole.

The Galileo Competence Center explores how related systems should be designed in the future in order to maximize the benefit of the project Powerful accurate timing facility (RPTF). Unlike Compasso, according to the DLR, the ground systems necessary to operate the Galileo will be developed. It is about hardware and software for “perfect time distribution” in the navigation system. The measuring instruments can be expanded on the ground as desired for this purpose. They worked as a “team” and even then provided perfect times “if some of them failed or were replaced”.

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Huber asserts that “the reference time on Earth must always remain reliable for the satellites.” The side effect of RPTF is that it can make this part of the measurement so stable that it can be used in other systems for maintenance and troubleshooting. In 2019, Galileo made headlines with its one-week failure on several jobs. It is said that a series of adverse circumstances including a software update at Oberpfaffenhofen led to this. The second control center is located in the Italian city of Fucino. The system is still in general beta operation.


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