Ask HN: What would happen if all GNSS (like GPS) satellites go down?

Essentially nobody was using GPS before the Iraq war in 1990. Now in just 30 years all of us using it, including backend systems like datacenters of Google.

I don't know how to use compass for navigation, and don't think any of my friends do either.

Are there any portable easy-to-use self-contained Inertial Navigation Systems out there? I know high-end military machines have them, like fighter jets and navy ships, but I was thinking more in terms of cell-phone sized devices that we can simply enter coordinates of where we're starting from, and they automagically keep track of our location as we're on the move by foot or by car.