Very cool.
Back in the 1970s I owned a sextant that I kept on my sailboat but I don't remember how to use one anymore. GPS is great but old skills like celestial navigation and old fashioned dead reckoning get forgotten.
Naval Academy reinstates celestial navigation
21–30 of 38 posts
Re: Naval Academy reinstates celestial navigation
#22Earlier quoted context omitted.
The point of this training today, I would expect, is that computers might not always be there.
We might have computers, but GPS signals can be spoofed: https://en.wikipedia.org/wiki/Spoofing_attack#GPS_Spoofing
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?
Re: Naval Academy reinstates celestial navigation
#23Earlier quoted context omitted.
Not to be overly pedantic, but if you have an accurate timepiece you can get your longitude from averaging sunrise and sunset times. It's not particularly accurate, if you can't see the sun, but could be useful if you where otherwise lost at sea and under total cloud cover for a long period of time.
Do you mean latitude? I remember the days being longer in the summer when I lived at higher latitudes, but I'm having trouble seeing how you could calculate longitude by looking at sunrise/sunset.
Sunrise and sunset together will give you local noon (or local midnight). Local noon plus an accurate timepiece set to a known location will give you a time offset. Knowing your time offset is equivalent to knowing your longitude (which was the whole purpose behind the Harrison chronographs). You won't know it to a tremendous accuracy, since you can't get the exact moment of sunrise or sunset, just a vague idea, your position is likely to change between sunrise and sunset, and dead reckoning on a featureless sea under a featureless sky can only be so accurate. But it's knowing the difference between local time and a reference time that gets you longitude.
Re: Naval Academy reinstates celestial navigation
#24Earlier quoted context omitted.
Not to be overly pedantic, but if you have an accurate timepiece you can get your longitude from averaging sunrise and sunset times. It's not particularly accurate, if you can't see the sun, but could be useful if you where otherwise lost at sea and under total cloud cover for a long period of time.
Do you mean latitude? I remember the days being longer in the summer when I lived at higher latitudes, but I'm having trouble seeing how you could calculate longitude by looking at sunrise/sunset.
No, it would be the longitude. The average of sunrise and sunset will be local noon, and from that you get the longitude. To get the latitude you would need to see where the Sun rises and sets or see the stars, neither of which you could do very accurately under heavy cloud cover.
Re: Naval Academy reinstates celestial navigation
#25Earlier quoted context omitted.
Not to be overly pedantic, but if you have an accurate timepiece you can get your longitude from averaging sunrise and sunset times. It's not particularly accurate, if you can't see the sun, but could be useful if you where otherwise lost at sea and under total cloud cover for a long period of time.
Do you mean latitude? I remember the days being longer in the summer when I lived at higher latitudes, but I'm having trouble seeing how you could calculate longitude by looking at sunrise/sunset.
Thanks stan_rogers and splat, using local noon plus a clock makes total sense after you described how it works. And I just read a fun Wikipedia node on the history of longitude for good measure too.
Re: Naval Academy reinstates celestial navigation
#26Earlier quoted context omitted.
We might have computers, but GPS signals can be spoofed: https://en.wikipedia.org/wiki/Spoofing_attack#GPS_Spoofing
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?
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.
Re: Naval Academy reinstates celestial navigation
#27Earlier quoted context omitted.
We might have computers, but GPS signals can be spoofed: https://en.wikipedia.org/wiki/Spoofing_attack#GPS_Spoofing
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?
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...
Re: Naval Academy reinstates celestial navigation
#28> The same techniques guided ancient Polynesians in the open Pacific and led Sir Ernest Shackleton to remote Antarctica, then oriented astronauts when the Apollo 12 was disabled by lightning, the techniques of celestial navigation.
You'd think the proof reader would at least catch an issue in the very first sentence.
Re: Naval Academy reinstates celestial navigation
#29> The same techniques guided ancient Polynesians in the open Pacific and led Sir Ernest Shackleton to remote Antarctica, then oriented astronauts when the Apollo 12 was disabled by lightning, the techniques of celestial navigation. You'd think the proof reader would at least catch an issue in the very first sentence.
[deleted]
Re: Naval Academy reinstates celestial navigation
#30We will be seeing more of this kind of stuff as the world gets more complicated. Obviously, there are not enough people who know how to troubleshoot computer networks, debug poorly written legacy code and simply maintain the complex realtime systems that are used to automate buildings, boats and planes. I can imagine pilots will continue to be required on planes for this reason even though planes largely can fly themselves. Same thing with reading topo maps - a skill that all infantry will continue to need even though they have gps. In a sense, this is insurance needed to protect us from "the ghosts of Luddites'.