I wonder if they also asked trained officers to do regular practise? The theory behind celestial navigation is fairly trivial (I've almost forgotten it all but give me an alamnac and an hour and I'm confident I'd work it all out). The successful use of a sextant for a decent fix however requires training, practise and regular use to keep your skills sharp.
Moxie Marlinspike's documentary "Hold fast" (2010) [1] inspired me to learn how to use a sextant. Most of the sextants you can get on eBay these days are just for decoration, however.
[1] "Hold Fast: Stories of maniac sailors, anarchist castaways, and the voyage of the S/V Pestilence..." https://vimeo.com/15351476
> Most of the sextants you can get on eBay these days are just for decoration, however.
Ugh, these things are a plague. There's a factory in India pumping out most of these. They do a whole bunch of variations, boxes, antiquing, etc. Some sellers on eBay list them as genuine antique instruments, which is straight up deception.
The replicas of box sextants (small pocket instruments in the shape of a round box) are especially hard to spot if the seller is dishonest.
Its also one thing, taking a sight on land but a whole other thing doing it on the ocean when the ship is rockin' and rollin'. That takes practice, too.
RYA Yachtmaster course requires celestial navigation and some schools even require candidates to perform the navigation on the qualifying passage (couple hundred nm) without GPS.
It's the Yachtmaster Ocean, and as far as I know you're allowed to use GPS on your qualifying passage you simply have to take some sights whilst on passage to present to the examiner. I think they also allow for cloudy weather preventing any sights from being taken and allow you to present some from another trip.
There's some controversy there too as to whether it should be left in the syllabus. Personally I think it's a nice thing to do, there's something very pleasing about producing a fix especially when you do fun things like producing a running fix from sun and moon sights.
Knowing the direction of the sun to within a few degrees is unlikely to help much. For one thing, you have no other "fix", and for another, an error factor of a few degrees probably represents an error of a few hundred (nautical) miles. You should probably read a bit more about celestial navigation to understand the problem.
I wonder if, with the use of image analysis, it would be possible to create a "robo-sextant" - i.e. a system which scans the sky in certain intervals, locates the waterline, sun or other celestial bodies and performs the necessary calculations. Such a system could be used to e.g. detect GPS manipulation quickly
Trident missiles (a type of ICBM currently being carried aboard US submarines) do just that.
Once launched a Trident, using a camera, gets a fix on a single specific star. It then uses the data on that star's position to correct for any errors in its internal guidance system.
First, the system would be vulnerable to many of the same problems: hacking, sabotage, and electrical failure. Second, it would likely not be as robust under less than ideal conditions in which human beings with a sextant would still be able to function (e.g., partially cloudy conditions).
I sort-of learned celestial navigation during Navy ROTC training 40 years ago. I remember the Nautical Almanac being something of a pain to work with. It would have been so nice to have the modern-day mobile-device apps that will take the sextant data and do the table-lookup number crunching.
Even with a mobile app, it may still be worth knowing how to navigate the old fashioned way. I would imagine that books / hand calculations are more resistant to power failure than apps and GPS are.
On my boat, we still did firing solutions for torpedoes using a slide ruler.
The military is quick to embrace new technology but slow to completely rely on it to the exclusion of other methods. The great fear is that technology will let you down at a critical moment via failure or damage. That's why they teach the old methods alongside the new ones.
Agree. When I was in the USAF, we had micro-processor controlled communication systems, but also still had the 1950's Teletypes as backups. Running a war at 75 baud...
One time we bolted some backpack straps to one, painted it camo, and called it our Tactical Teletype. The joke was that it was 350 pounds of steel parts and electric motor...
I wonder if modern fighter pilots still need to learn old NDB and ADF radio beacon navigation? In a modern jet, I assume that if your computer-aided nav systems are non-functional, the plane is probably non-functional as well?
In a fighter, the cockpit is too cramped and the weight/balance figures too tight to allow for backup nav systems, other than a compass. With it, they could drop down and follow a road or power-line home (at the expense of greater fuel consumption and exposure to hostile ground fire). But if they still have an operating radio, they'd probably call air traffic control or an E-3 Sentry for directions. Larger planes like the B-52 might still have their radio beacon equipment installed.
What I was asking, though, was do the pilots still have to learn it? Considering the limitations we both pointed out, I wonder if it has been removed from ground school and basic pilot instruction.
You always learn the basics. I've not been USAF but you're always taught the "hard" way or "old" way before they teach you the "new" or "easy gizmo" way.
How long you spend on the topic and whether you have to prove proficiency is a different question.
It is surreal to see this mentioned here. HN mindset is progressive, after all.
But to qualify this comment, I'd say that what is specifically tied to the Myth of Progress in US Military Doctrine is the bias against thinking that an opponent relying on low(er) tech can negate/overcome this disadvantage through the use of superior tactics. For reference see: https://en.wikipedia.org/wiki/Millennium_Challenge_2002
If the only concern was that your GPS receiver could fail, then you could rely on your backup system. Either a second receiver, or some other system. (TACAN, INS, etc.)
Their concern seems to be, "What if none of the electronic systems can be trusted?" That wasn't as much a concern when the sextant courses were dropped, but they are now, which is why it seems they're reinstating them.
Curiously, INS (inertial navigation system), which uses gyroscopes, is often turned to as a backup for when GPS can't be used, or is otherwise unavailable. (Many guided systems now can use INS as a backup if the GPS signal is jammed.) Most ships have this as well. Presumably this would be an adequate fallback.
That being said, if my ship were dead in the water with no electrical power, this seems like a no-brainer.
Should be extremely good over the short to medium term. The trouble with INS is that the error is unbounded, so you have to use some other technique to get a fix periodically to reset it.
I don't know, but I do remember reading that one characteristic issue of them is that the errors compound over time. If you're say, dropping a GPS-guided bomb, and the signal is jammed, then they'll fall back to INS for the rest of the way. The distance between signal loss and impact is pretty short, so there isn't much time for errors to compound.
If you're navigating say, a submarine however, the longer you go without a real fix, the more unreliable that INS estimate is going to be, especially if maneuvers have been undertaken.
Ring-laser INS still have a drift of a few kilometres per hour.
To keep their respective INS in-check, Tomahawk looks down and performs terrain-comparison whereas Trident looks up and does stellar nav...
The Kearfott Mk 6 that is used by Trident is the successor a line of stellar nav units they produced for the Navajo, SR-71, Hound Dog and FB-111. And probably a bunch of others I've forgotten.
The early models used a sheath of acetate star-chart sheets in a mechanical loader to perform the matching operation!
Problems with celestial navigation almost caused WW3 during the Cuban Missile crisis - a bright display of the Northern Lights caused a U2 on an air sampling mission over the Arctic Ocean to get lost and stray into Soviet territory at a rather unfortunate time.
Do commissioned officers actually do any navigation at all? I understood that this is mostly done by enlisted quartermasters (QM) an navigation electronics technicians (ET).
Commissioned officers are responsible for the boat and the crew. That doesn't mean that they do all the work, but they are responsible for making sure it's done correctly and getting it done correctly if the crew can't. They are also responsible for training the crew to the highest standards.
Source: spent two years at the Naval Academy and one tour on a nuclear submarine during the summer.
Now, if the Navy wanted their sailors to be truly hardcore navigators and be totally immune from cyber hacking, they'd have them use an abacus for calculations rather than a calculator or computer.
If an enemy has managed to fry or otherwise interfere with the electronics of calculators, you expect that the balls of mostly water will have other, more serious, issues.
Isn't the GPS signal fairly low-power, and thus, trivial for an enemy to jam?
Or would they have to get their jammer close enough to be in range of the ship's guns (and presumably its loud radio broadcasts would give away its position)?
There's no reason a battery powered jammer won't fit in a bouy or "mine" or drone. If you're already declared an area a "no fly zone" or "no float zone" then jamming civilians is not going to be a serious concern.
We're coming to the end of a golden era where RF electronic reasons used to mean significant jamming was somewhat unrealistic at an analog electronics level. In the "next big war" jamming is going to be cheap and ubiquitous on the battlefield (or for that matter, in terror attacks or whatever).
There is an interesting economic warfare aspect where a jammer drone is inherently always going to be cheaper than the antiaircraft missile or antiaircraft drone that shoots it down due to certain precision flying and targeting requirements. A jammer has to keep the right side up and not hit anything, and anti-jammer has a much more complicated task of finding, reaching, and destroying a jammer. So it being cheaper to jam than to unjam means only the wealthiest aggressors with good logistics support will be able to decide when GPS will be usable on a battlefield. Also unjaming has certain risks... sure go ahead shoot down that jammer drone, the site that launches a missile or even a drone will get plastered about one minute later by what amounts to counterbattery artillery fire. Now you have GPS data but no anti-aircraft cover... hmm, probably not a good trade. This is before meta level games are played where you want to lure someone into an ambush by jamming the heck out of everything but one heavily armed and prepared "empty" mountain pass. In the future I think you can pretty much count on GPS not being available or at least not being reliable on the battlefield, and when the enemy does let you use GPS they're probably messing with you.
The concept of drones being cheaper than what it takes to shoot them down has a meta problem first discussed in anti-star-wars technology in the 80s where MIRV ICBMs had decoys... You can expect X drones of which only Y contain expensive jammer hardware, making the cost ratio of anti-jammer drones even worse compared to jammer and decoy drones.
> A jammer has to keep the right side up and not hit anything, and anti-jammer has a much more complicated task of finding, reaching, and destroying a jammer.
Is this 100% true? I don't know much about RF jamming, but isn't it sufficient to fix on the strongest source of the RF signal you're interested in and guide a cheap penetrator at it?
DARPA's Exacto bullets are doing that with optical guidance. Would it be that much harder with radio guidance?
That being said, there were also stories of anti-radar missiles being redirected by modified microwave ovens during the Bosnia-Serbia war. Can't find a solid link to that thougn
The jammer is a NASCAR, get to the track, turn left, make noise. Its remarkable how simple the psuedocode will be to write and debug.
The anti-drone missile/drone is a high speed police pursuit full of all kinds of adaptive tracking and fail safes and IFF (yeah well you hope it'll have IFF) and low latency judgment calls and 3-d interception math and classified anti-jam anti-flare and predictive algorithms in case the target has anti-interception code.
Apologies for the brevity, I'm on a tablet with an annoying keyboard.
There's two things that make GPS trickier to jam:
- it's spread spectrum with relatively hign coding gain. The signal itself is pretty much imperceptible above the noise floor until you phase lock onto the signal and despread. A really effective jammer would likely need to send out a similar but corrupted signal, not just noise.
- we know where the signal will be coming from. First that it will be coming from the sky, and once we have a copy of the almanac, we've got a pretty good idea where in the sky each SV will be. Directional antennas could further mitigate the jamming.
You're not wrong about it being jammable, but it's not trivially simple.
p.s. (because kb sucks) While the spreading codes for the civilian signal are commonly available and could be replicated in a jammer, the military spreading codes are not available. A well-funded adversary might be able to get ahold of them anyway, but it'd take some effort/treason.
I'm sure you're correct, but this account seems to contradict all the horror stories we heard about LightSquared a few years ago. Is the explanation simply that civilian GPS uses crap radios and military GPS does not? I always sort of felt sorry for LightSquared, because they were obviously victims of regulatory capture.
I just read through the LightSquared story and am pretty intrigued!
One of the fascinating demonstrations of the fact that GPS is relatively interference robust is that Galileo (ESA GNSS system) runs on the same frequencies as GPS; the different spreading codes mean that receivers can choose which signal to listen to.
Reading about the LightSquared system though, they do talk about a quite real concern: overloading the receiver's frontend entirely. That's one of the concerns that would be addressed by using directional antennas (if you're receiving interference, rotate your antenna so that the source is in an antenna null). As far as I know, most civilian receivers wouldn't have a directional antenna, they'd have an omni so that they work in any orientation; it'd suck if your iPhone could only receive GPS signals if it were sitting flat. On a military vessel, it'd make a lot more sense to mount an upward-cone-looking antenna high up on a mast to avoid sources of surface interference.
I'm super curious now though! I've got a software GPS receiver set up, I'd like to try injecting noise into the (virtual) signal chain and see how much noise power is necessary to lose lock. If anyone's curious, GNSS-SDR works great with $20 RTLSDR radios: http://gnss-sdr.org/source-code
Edit: I did a bit more research, and it sounds like overloading the front-end is the most common approach to jamming. People are turning on multi-watt transmitters in their vehicles (e.g. to block fleet management GPS from detecting their location). Despite the amount of power they're putting out, they seem to be limited in range to around 50 feet.
It's also pretty satisfying to see http://www.novatel.com/assets/gajt/pdf/gajt-white-paper.pdf which indicates that the solution I came up with (directional antennas with nulls pointed at the interference sources) is a solid strategy for mitigating jamming.
One interesting side effect of learning celestial nav is you can't avoid learning some astronomy and keeping up to date on the night sky.
Another side effect is its a filter on people who can't handle math or can't handle complicated written procedures. Its unclear how important that is, but it is clear its a very good filter if you value those skills for other reasons.
With respect to situational awareness, its very easy to own a GPS while confusing that attribute of ownership with understanding where you are, but its very hard to mentally do celestial nav without understanding where you are, what are the present sea and weather conditions. Also there is a difference between merely owning a (possibly GPS accurate) clock or chronometer and understanding what time it is. "I own things that could provide accurate 4 dimensional situation, were I to actually understand the outputs" is a lot different from "I can perform extensive labor and calculations with the result of being deeply aware of my 4 dimensional situation"
I'm surprised they gave it up. It is still best practice in yachting to have at least one crew member on an ocean crossing be able to do celestial navigation. You can't count on electricity, and thus GPS, so you have to return to the basics as a backup.
Maybe not. Marine diesel engines can run without the computers attached using mechanical throttles. There has been instances where the yacht's wheelhouse is flooded with water and all the navigation computers and electronic controls are lost. The captain and mate stationed in the engine room coordinate by controlling the manual throttles on each engine. Move one throttle more to turn.
Depends on the ship of course, but this wouldn't have worked on at least one of the naval vessels I've visited. Common on newer ships are electric drives, where diesel or gas turbine engines are connected to generators instead of prop shafts.
I am presuming an even darker scenario. GPS signals would not be jammed by the enemy but rather satellites would be obliterated wholesale as a result of a limited nuclear exchange. Thus sailing the old fashion way: Sextant, watch, and maps are the only way home.
Kessler Syndrome is mainly a Low Earth orbit issue. GPS sats are at 20,000 km altitude so aren't particularly vulnerable to it. They're probably far enough away to not be vulnerable to EMP either, unless someone were to lob a nuke out pretty far.
My impression, based on very limited knowledge, has been that inertial navigation was the backup to or even replacement for GPS. Does anyone know more about it?
For anyone interested, I taught myself the basics of celestial navigation a few years back after being interested in it for years. Something just feels right and maybe a bit primal about knowing where you are relative to the heavens.
"Dutton's Navigation & Piloting, 13th Edition" http://www.amazon.com/Duttons-Navigation-Piloting-Elbert-Mal...
Although the most recent edition is the 15th (2003), I learned with the 13th, so I know its useful. The 13th was also pre-GPS and spent only 30 or so pages on Loran, so it's mostly celestial and coastal, in addition to piloting.
My favourite is 'Self-contained Celestial Navigation with HO 208' by John Letcher. It's out of print but used copies show up on abebooks for a reasonable price at times. It's often recommended.
I also like 'The Sextant Handbook' by Bruce Bauer. Also out of print.
A very nice modern coffee-table book about the history of celestial navigation is 'Finding Longitude' by Richard Dunn e.a. : http://www.amazon.com/dp/B00HPMW95A
Finally, you could subscribe to NavList at fer3.com. There's enough in the archives to fill several books and the people there really know their stuff (well, not me so much, but others do!).
The US Power Squadron back in the pre-GPS 1980s used 'The American Practical Navigator-An Epitome of Navigation (1966)' as their primary reference book. My grandfather ran one of the courses. Amazon(US) has a reprint of the 2002 version:
This is also why non-network based communication backups are important. HF radios, NVIS and Morse Code are very efficient and effective when network packets are not flowing.
75 comments
[ 3.8 ms ] story [ 153 ms ] threadLooks like they won't even get a sextant out of its box
[1] "Hold Fast: Stories of maniac sailors, anarchist castaways, and the voyage of the S/V Pestilence..." https://vimeo.com/15351476
Ugh, these things are a plague. There's a factory in India pumping out most of these. They do a whole bunch of variations, boxes, antiquing, etc. Some sellers on eBay list them as genuine antique instruments, which is straight up deception.
The replicas of box sextants (small pocket instruments in the shape of a round box) are especially hard to spot if the seller is dishonest.
There's some controversy there too as to whether it should be left in the syllabus. Personally I think it's a nice thing to do, there's something very pleasing about producing a fix especially when you do fun things like producing a running fix from sun and moon sights.
Is there not a modern equivalent of the medieval 'sun stone'?
https://en.wikipedia.org/wiki/Sunstone_(medieval)
There even appears to be a patent on the idea: https://www.google.com/patents/US7706917
https://en.wikipedia.org/wiki/Lockheed_SR-71_Blackbird#Astro...
Once launched a Trident, using a camera, gets a fix on a single specific star. It then uses the data on that star's position to correct for any errors in its internal guidance system.
See: https://en.wikipedia.org/wiki/Trident_(missile)
https://en.wikipedia.org/wiki/Star_tracker
First, the system would be vulnerable to many of the same problems: hacking, sabotage, and electrical failure. Second, it would likely not be as robust under less than ideal conditions in which human beings with a sextant would still be able to function (e.g., partially cloudy conditions).
The military is quick to embrace new technology but slow to completely rely on it to the exclusion of other methods. The great fear is that technology will let you down at a critical moment via failure or damage. That's why they teach the old methods alongside the new ones.
One time we bolted some backpack straps to one, painted it camo, and called it our Tactical Teletype. The joke was that it was 350 pounds of steel parts and electric motor...
How long you spend on the topic and whether you have to prove proficiency is a different question.
I wonder more why it was dropped in the first place...
But to qualify this comment, I'd say that what is specifically tied to the Myth of Progress in US Military Doctrine is the bias against thinking that an opponent relying on low(er) tech can negate/overcome this disadvantage through the use of superior tactics. For reference see: https://en.wikipedia.org/wiki/Millennium_Challenge_2002
Their concern seems to be, "What if none of the electronic systems can be trusted?" That wasn't as much a concern when the sextant courses were dropped, but they are now, which is why it seems they're reinstating them.
Curiously, INS (inertial navigation system), which uses gyroscopes, is often turned to as a backup for when GPS can't be used, or is otherwise unavailable. (Many guided systems now can use INS as a backup if the GPS signal is jammed.) Most ships have this as well. Presumably this would be an adequate fallback.
That being said, if my ship were dead in the water with no electrical power, this seems like a no-brainer.
If you're navigating say, a submarine however, the longer you go without a real fix, the more unreliable that INS estimate is going to be, especially if maneuvers have been undertaken.
In other words I guess, "it depends". =)
To keep their respective INS in-check, Tomahawk looks down and performs terrain-comparison whereas Trident looks up and does stellar nav...
The Kearfott Mk 6 that is used by Trident is the successor a line of stellar nav units they produced for the Navajo, SR-71, Hound Dog and FB-111. And probably a bunch of others I've forgotten.
The early models used a sheath of acetate star-chart sheets in a mechanical loader to perform the matching operation!
Commissioned officers are responsible for the boat and the crew. That doesn't mean that they do all the work, but they are responsible for making sure it's done correctly and getting it done correctly if the crew can't. They are also responsible for training the crew to the highest standards.
Source: spent two years at the Naval Academy and one tour on a nuclear submarine during the summer.
Or would they have to get their jammer close enough to be in range of the ship's guns (and presumably its loud radio broadcasts would give away its position)?
We're coming to the end of a golden era where RF electronic reasons used to mean significant jamming was somewhat unrealistic at an analog electronics level. In the "next big war" jamming is going to be cheap and ubiquitous on the battlefield (or for that matter, in terror attacks or whatever).
There is an interesting economic warfare aspect where a jammer drone is inherently always going to be cheaper than the antiaircraft missile or antiaircraft drone that shoots it down due to certain precision flying and targeting requirements. A jammer has to keep the right side up and not hit anything, and anti-jammer has a much more complicated task of finding, reaching, and destroying a jammer. So it being cheaper to jam than to unjam means only the wealthiest aggressors with good logistics support will be able to decide when GPS will be usable on a battlefield. Also unjaming has certain risks... sure go ahead shoot down that jammer drone, the site that launches a missile or even a drone will get plastered about one minute later by what amounts to counterbattery artillery fire. Now you have GPS data but no anti-aircraft cover... hmm, probably not a good trade. This is before meta level games are played where you want to lure someone into an ambush by jamming the heck out of everything but one heavily armed and prepared "empty" mountain pass. In the future I think you can pretty much count on GPS not being available or at least not being reliable on the battlefield, and when the enemy does let you use GPS they're probably messing with you.
The concept of drones being cheaper than what it takes to shoot them down has a meta problem first discussed in anti-star-wars technology in the 80s where MIRV ICBMs had decoys... You can expect X drones of which only Y contain expensive jammer hardware, making the cost ratio of anti-jammer drones even worse compared to jammer and decoy drones.
Is this 100% true? I don't know much about RF jamming, but isn't it sufficient to fix on the strongest source of the RF signal you're interested in and guide a cheap penetrator at it?
DARPA's Exacto bullets are doing that with optical guidance. Would it be that much harder with radio guidance?
That being said, there were also stories of anti-radar missiles being redirected by modified microwave ovens during the Bosnia-Serbia war. Can't find a solid link to that thougn
The jammer is a NASCAR, get to the track, turn left, make noise. Its remarkable how simple the psuedocode will be to write and debug.
The anti-drone missile/drone is a high speed police pursuit full of all kinds of adaptive tracking and fail safes and IFF (yeah well you hope it'll have IFF) and low latency judgment calls and 3-d interception math and classified anti-jam anti-flare and predictive algorithms in case the target has anti-interception code.
But I don't know if that's the only solution if being economical ends up being important.
Spike strips are really good at stopping cars, especially if they're running around a track in a circle.
There's two things that make GPS trickier to jam:
- it's spread spectrum with relatively hign coding gain. The signal itself is pretty much imperceptible above the noise floor until you phase lock onto the signal and despread. A really effective jammer would likely need to send out a similar but corrupted signal, not just noise.
- we know where the signal will be coming from. First that it will be coming from the sky, and once we have a copy of the almanac, we've got a pretty good idea where in the sky each SV will be. Directional antennas could further mitigate the jamming.
You're not wrong about it being jammable, but it's not trivially simple.
p.s. (because kb sucks) While the spreading codes for the civilian signal are commonly available and could be replicated in a jammer, the military spreading codes are not available. A well-funded adversary might be able to get ahold of them anyway, but it'd take some effort/treason.
One of the fascinating demonstrations of the fact that GPS is relatively interference robust is that Galileo (ESA GNSS system) runs on the same frequencies as GPS; the different spreading codes mean that receivers can choose which signal to listen to.
Reading about the LightSquared system though, they do talk about a quite real concern: overloading the receiver's frontend entirely. That's one of the concerns that would be addressed by using directional antennas (if you're receiving interference, rotate your antenna so that the source is in an antenna null). As far as I know, most civilian receivers wouldn't have a directional antenna, they'd have an omni so that they work in any orientation; it'd suck if your iPhone could only receive GPS signals if it were sitting flat. On a military vessel, it'd make a lot more sense to mount an upward-cone-looking antenna high up on a mast to avoid sources of surface interference.
I'm super curious now though! I've got a software GPS receiver set up, I'd like to try injecting noise into the (virtual) signal chain and see how much noise power is necessary to lose lock. If anyone's curious, GNSS-SDR works great with $20 RTLSDR radios: http://gnss-sdr.org/source-code
Edit: I did a bit more research, and it sounds like overloading the front-end is the most common approach to jamming. People are turning on multi-watt transmitters in their vehicles (e.g. to block fleet management GPS from detecting their location). Despite the amount of power they're putting out, they seem to be limited in range to around 50 feet.
It's also pretty satisfying to see http://www.novatel.com/assets/gajt/pdf/gajt-white-paper.pdf which indicates that the solution I came up with (directional antennas with nulls pointed at the interference sources) is a solid strategy for mitigating jamming.
Another side effect is its a filter on people who can't handle math or can't handle complicated written procedures. Its unclear how important that is, but it is clear its a very good filter if you value those skills for other reasons.
With respect to situational awareness, its very easy to own a GPS while confusing that attribute of ownership with understanding where you are, but its very hard to mentally do celestial nav without understanding where you are, what are the present sea and weather conditions. Also there is a difference between merely owning a (possibly GPS accurate) clock or chronometer and understanding what time it is. "I own things that could provide accurate 4 dimensional situation, were I to actually understand the outputs" is a lot different from "I can perform extensive labor and calculations with the result of being deeply aware of my 4 dimensional situation"
Do you think that the USNA admissions process and or the Academy's graduation requirements do not provide an equivalent filter?
I agree its a much more useful discriminator for civilians than naval officers or professional sailors.
Still it seems smart to keep the skill around as the GPS system can be locally jammed and in WWIII could be completely knocked out.
I used the book http://smile.amazon.com/Celestial-Navigation-GPS-John-Karl/d... and really enjoyed it. Fun to do with kids too.
Edit: And the http://smile.amazon.com/Davis-Mark-3-Marine-Sextant/dp/B0014... makes a fine sextant to start with.
My favourite is 'Self-contained Celestial Navigation with HO 208' by John Letcher. It's out of print but used copies show up on abebooks for a reasonable price at times. It's often recommended.
I also like 'The Sextant Handbook' by Bruce Bauer. Also out of print.
A very nice modern coffee-table book about the history of celestial navigation is 'Finding Longitude' by Richard Dunn e.a. : http://www.amazon.com/dp/B00HPMW95A
Finally, you could subscribe to NavList at fer3.com. There's enough in the archives to fill several books and the people there really know their stuff (well, not me so much, but others do!).
http://www.amazon.com/The-American-Practical-Navigator-Bowdi...
But you can study it online gratis at:
https://en.wikisource.org/wiki/The_American_Practical_Naviga...