GNSS Satellite (GIOVE-A)

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Sunday, 24 August 2014

Groundtrack of the Galileo Satellites

Purely out of interest I have made a plot of the ground track of the orbits in which the last two Galileo Satellites ended up in. The results is shown in the figure below.
The figures shows the ground track of Galileo-101 (E11), one of the older Galileo satellites, and Galileo-201, one of the two new Galileo satellites, over a period of 24 hours for August 23, 2014. A couple of interesting features can be seen from the plot. Firstly the difference in inclination, 56 vs 49 degrees, is clearly visible as the maximum latitude of the Galileo-201 satellite is clearly smaller. Secondly, the orbital revolution period is clearly significantly shorter. The normal Galileo satellites have an orbital period of around 13 hours. This means that in 24 hours, the period used for the plot, they will complete less then two orbital revolutions. The new satellite clearly completes two full revolutions within the 24 hour interval. This nicely shows that the new two satellites will not fit into the Galileo constellation in their current orbit. They will move through the constellation in a very wild way.

What I find a bit scary is that with the Perigee of these orbits at merely 20000 km these three objects, the two Galileo satellites and the Fregat, are actually moving through the orbital planes of the GPS and GLONASS constellations. This means to sooner or later they will be on a "collision" course with one of those satellites. Fortunately the satellites seems to be in good order so they can be steered but not sure about the Fregat. So GPS and GLONASS may have to do collision avoidance manoeuvres because of this mishap.

But not all is bad. GNSS scientist have actually concluded a couple of times that different orbits for the different GNSS satellites would be advantegeous for their high accuracy investigations. So at least some of the GNSS scientist might be happy with this situation!

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