NavList:

David, yes, jamming is a real threat. I would say that are two reasons we haven't discussed it this time around. First, we've discussed it ad nauseam in the past. I mean literally we've been discussing this possibility for over a decade. Second, despite the frequent worries over it, jamming has clearly been a minor problem. I have never encountered real GPS jamming, and I don't know anyone who has. Although it is real, and as you say, jammers are cheap and widely available, it rarely occurs in practice. The users of vast numbers of commercial devices that depend on GPS serve as insurance for the network. They complain at the drop of a hat.

Spoofing is a more interesting problem. It's new, and it raises some fascinating issues. So far, it has only been demonstrated in experiments, and other experiments have shown that it can easily be defeated. But I certainly talk about spoofing as one of the best reasons to take sextants sights in my modern celestial class. Better yet, from a security point of view, would be some form of automated celestial, like that optical system on the SR-71 and other aircraft, but of course simpler and cheaper thanks to digital camera technology. Even if we stick with manual sextant sights, if our goal is to detect spoofing then all the other baggage of celestial navigation becomes a handicap. Sights should be instantly cleared and compared with the GPS position. I've previously described my Android app (still in trials) which does just that (it's also a terrific sight-training tool).

As for electronics getting fried on your boat. Sure, that's a threat. And the solution is to provide backup GPS receivers in appropriate Faraday cage shielding. The best backup for a GPS is another GPS. And the best backup for the second GPS is a third GPS. Celestial should be at the very bottom of the list of tools if our concern is really navigation and vessel safety. I'm not saying it shouldn't be on the list of backups -- only that, as a backup, it's a last resort. 

Solar storms wiping out all the satellites? Yeah... that could happen. It's the sort of grand technology-failure scenario that captivates some of the more exuberant fans of celestial navigation. You can just hear them whispering... "Ooooh... then I'll be important!". But the probability is very low, despite doomsday talk about another Carrington event. I don't lose much sleep over that one. But a robot apocalypse... now that's something to think about! Ha.

Maybe you can help me out here: how would an eLORAN system be any less vulnerable than GPS from attack? Can't I hack that, too?? I don't really see any big advantage compared to a satellite-based system.

Frank Reed
ReedNavigation.com
Conanicut Island USA