[usrusr]

Three hours of training? Either celestial navigation is much easier than i think it is or this is exactly the sort of compromise mothers should warn their children about. I'd rather sail into a GPS outage with a one in ten chance of having a navigator trained 30 hours on board than with a 100% chance of having one trained three. And it gets better when you consider crews larger than one. Sure, we all know that decision making isn't easy, but that should not be an excuse to get away with a compromise like that.

[SamReidHughes]

Celestial navigation is way easier than you think it is. We have accurate clocks now, and you can just take the measurements and feed it into the computer.

[toyg]

The point of this training today, I would expect, is that computers might not always be there.

[superuser2]

GPS depends on satellites to stay in the right place, intact, and powered, as well as the ability to receive authentic RF signals from those satellites.

Celestial navigation requires (the computational equivalent of) a graphing calculator.

[knodi123]

If the people on a modern naval ship don't have access to some kind of basic computer, then they have bigger problems than navigation.

[showerst]

A total blackout has happened to a US Navy Ship in recent memory: https://en.wikipedia.org/wiki/USS_Yorktown_(CG-48)#Smart_shi...

[knodi123]

And when that happened, they had a bigger problem than navigation.

[gavazzy]

We might have computers, but GPS signals can be spoofed:

https://en.wikipedia.org/wiki/Spoofing_attack#GPS_Spoofing

[gruez]

Is there a reason why the signals aren't digitally signed? I understand that GPS and GLONASS was deployed over 30 years ago, but surely Galileo, with its first satellite launched 4 years ago can have this?

[Nrsolis]

Spoofing of GPS signals isn't generally the problem the US military is most concerned about. It's availability.

The assumption is that in any significant event, US space assets will be unavailable either momentarily or for some extended period. Chinese Anti-SAT weapons are one indicator that this is a likely avenue of attack for any weaker actor seeking to degrade our capabilities.

So, celestial navigation is a crude but workable substitute for GPS but it has the distinct advantage of being ancient and nearly impossible to impede unless you can change the weather or the positions of the heavenly objects.

[kevinchen]

Here's a paper that proposes GPS authentication based on signing and statistics about the signals (lots of math): http://radionavlab.ae.utexas.edu/images/stories/files/papers...

Paper from Los Alamos with a receiver-only implementation that would use:

- abnormally high signal strength

- abnormally regular transmissions

- a secondary time source to double-check time (e.g. NTP on a smartphone)

- dead-reckoning based on accelerometers/gyroscopes/compass to double-check position

http://lewisperdue.com/DieByWire/GPS-Vulnerability-LosAlamos...

[maaku]

GPS signals are weak. You simply jam them.

[sfall]

the problem persists because like any skill use it or lose it