As a student of more traditional forms of navigation I can't help but have an "I told you so" moment when I read things like this. I've experienced multiple GPS

As a student of more traditional forms of navigation I can't help but have an "I told you so" moment when I read things like this. I've experienced multiple GPS failures in aircraft that necessitated breaking off an approach, as well as active jamming from the ground that interfered with GNC on spacecraft. You simply cannot expect GPS to be invulnerable to attack or to never malfunction. I know this isn't an immediate concern for 99.9% of people--worst case, you have to ask someone for directions and look outside your car instead of using your phone--but for folks with navigation duties at sea, in the air, or in space, or even just someone going out for a long hike, it is imperative to have and be proficient with another system. Fortunately the US military and the engineers who build its systems know this well. I only harp on it because it can sometimes be difficult to get students to truly appreciate the dangers of relying entirely on a single means of navigation.