In order for this to be a global system, you'd have to be able measure muon coincidence across thousands of miles, which isn't possible, as muon showers are far

In order for this to be a global system, you'd have to be able measure muon coincidence across thousands of miles, which isn't possible, as muon showers are far more localized. Systems like Loran-C used to offer this for terrestrial, radio based navigation at sea.