GPS / GNSS signals are relatively weak, frequencies/protocols are known and anyone with a bit of knowledge and malicious intents can build a GPS jammer. I do not understand how anyone came up with the idea to use such vulnerable system as primary means of navigation for vehicles, where safety risks in case of wrongdoing are considerable. The only way is to have paralel navigation system, that does not rely on such signals and of course, with monitoring of the integrity/comparators used. Inertial systems (with enough redundancy) shall be the primary means, combined/corrected with GNSS / DME... as it currently is, but I see pressure to move entirelly to GNSS/satnav more and more. Being involved in future design of satelite navigation systems will not prevent jamming. How hard is it to understand that?