GPS is one of several global navigation systems. The Soviets had GLONASS (24 satellites) and China has BeiDou (33 satellites).
The European Union has Galileo (22 satellites operational).
Our USA system is the GPS system we are all so familiar with (31 satellites). BTW it is over 40 years old, so it you struggle to imagine a non-GPS world it is understandable, as a good portion of the population is too young to have experienced a non-GPS environment unless they had traveled while young.
Several of these Global Navigation Systems “cooperate” in that Global Navigation Systems Receivers are offered that use several of the different signals at the same time.
All well and good, until it doesn’t work.
Galileo has been down since July 11th 2019, and as of July 15th it appears to still be unusable.
An article on the problems: https://www.zdnet.com/article/european-gps-satellites-have-been-down-for-four-days-in-mysterious-outage/
[EDIT 15 JULY 19 – additional information right from the EU agency – https://www.gsc-europa.eu/news/update-on-the-availability-of-some-galileo-initial-services ]
Obviously this plays havoc with all sorts of systems. From our hobby point many of our communication digital modes and transceiver external references for frequency stabilization are GPS dependent.
What happens when GPS is either unavailable/unreliable or purposefully degraded for national security reasons?
Do we lose our FT8-style time-synchronized digital modes?
Will our radios lose frequency lock and become drifty?
Will have of the Emcom orientated extra services like APS (Automatic Position [reporting] Systems) go down?
What is our collective hobby and more importantly Service Capabilities plans for a non-GPS scenario? What is that “Plan-B?”
We best also have some land navigation capabilities backups for finding our way around when our Smartphones and In-Dash navigation don’t work.
Time for some contingency planning collectively and personally.