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Geared towards geospatial professionals, this is a free, in-depth online Penn St. course about satellite navigation. Thought people here might be interested. Even if you don't want to run through the entire course, it's a great reference to have handy.
https://www.e-education.psu.edu/geog862/home.html
https://www.e-education.psu.edu/geog862/home.html