ISTR that the US Coast Guard never stopped teaching sextant. Something about being "real sailors"...
Sextants have been off the curriculum for naval officers in the US for over a decade, but now the swabbies have reinstituted celestial navigation classes over hacking fears. The US Navy discontinued celestial navigation courses in 1998 because GPS made the old style of navigating redundant. Working out your position the old- …
Always, always have a backup, and a backup to that backup. Mother Nature is a cruel, heartless bitch, and she will kill you without a second thought if she thinks you're not giving her the respect that she deserves. And that goes double at sea (as the crew of the El Faro, RIP, found out recently).
I'm frankly surprised that the Navy discontinued celestial navigation courses. The Army's still teaching Land Navigation with map and compass.
"...and a serious amount of math work to get your position within a couple of miles"
Nothing you can't put on a programmable scientific calculator. There are power series on the orbital elements for the positions of the Sun and Moon up to navigational accuracy for a couple of years either side of now that can be downloaded into a modest calculator along with positions of the navigational stars. Coordinate transformations are relatively routine.
Coat: Mine's the one with the Ebco emergency sextant in the (large) pocket.
Exactly that. Not only the calculations actually. Given the advanced state of current imaging, image recognition and processing, you could automate the whole thing end-to-end, with a machine that takes it's own star readings, processes them, identifies the stars based on internal maps*, does all the necessary calculations and outputs the result.
As long as it has a clear view of the sky it can continuously keep a position reading, and perhaps use some form of dead reckoning to estimate a position when it can't get a star/sun reading. Also might be possible (I'm sure someone more knowledgeable than me about these things) to use not just visible light detection but other frequencies. For example would it be possible to use some form of radio telescope to identify where the stars are even if it's cloudy?
*as you mention these need to be downloaded into the machine occasionally, the machine itself should be airgapped otherwise that negates the whole anti-hacking thing
Indeed, automated star trackers have been used on spacecraft for years.
You suggestion of using radio frequencies to pinpoint stars is an interesting one. Off the top of my head the problem would probably be that the antenna required for radio astronomy would be fairly large, but then boats can be very big. And it wouldn't just work through cloud, you can do radio astronomy all day as well.
No one's mentioned inertial guidance and dead reckoning. I've not kept up with ICBM technology, but as I recall, they used optical gyroscopes to achieve targeting accuracy to within several meters.
If we can entrust doomsday to inertial guidance, surely the Navy can trust it.
> and a serious amount of math work to get your position
As has been done by the Royal Navy since about 1750.. one of the (many) reasons why their officers couldn't buy commissions but had to pass their exam before being made lieutenants.
Not really a serious amount of maths though - if it can be done on a frigate deck, in a storm in the bay of Biscay on a slate with a bit of chalk then I suspect it doesn't qualify as a 'serious amount' (except maybe the serious bit - especially if you are relying on it to keep yourself from losing your keel to rocks..)
Yep, I can make do with log tables just as well as a slipstick. Since the nav gear was "mine" I went ahead and qualified as a helmsman, quartermaster and navigator (including underway replenishment) which made me the backup in case all the officers were dead. [Which surprised the f--- out of some trainers who thought they could pull a fast one on us.]
Mine's the one with the one foot diameter, ivory circular sliderule in the huge pocket. [Gramps gave it to me in his Will.]
One hopes they can't be hijacked by some kid on the ground messing with GPS-type signals.
Or that the inertial on-board systems are damned accurate.
Or that the smaller midshipmen can fit inside the missile while using the sextant and peering out through the 1x1cm quartz window.
But the starting point for the INS is based on GPS.
That was the original purpose of the USN forerunner to GPS - to give a sub a good known starting point without it having to surface off Murmansk and wait for enough clear weather to get a fix
The starting points for military INS systems are typically military bases with the known surveyed location coordinates painted on e.g. a nearby hanger wall. GPS can and is used to verify and adjust the INS position, but I would hope that a large discrepancy would be noted and investigated.
No, the start point is a geographical reference point. OMEGA, GPS, and other data points are mapped against our INS which was a LASER Ring Gyro. In our case, since we (probably) carried Tomahawk Land Attack Missiles (TLAM), we had two of them. We trusted them a Hell of a lot more than SatNav or GPS.
Using a sextant, tables and either MSH or Long by Chron to get your position takes comfortably less than 5 minutes with practice.
In addition military vessels and aircraft usually took a starting fix using sextant and then plotted transits using compass and stopwatch during only confirming final position with another sight based fix at the end of any series of manoeuvres Much quicker and usually accurate enough for purpose.
I can also remember back when I was a 3/0 in the Merchant Navy back in the early 80's that there were one or two companies starting to produce sextants with built in navigation calculators (stand alone versions also being the latest tech at the time) so that you took the sight, pressed the button and plotted the result.
I hope this article is not a copy of something written by a naval officer, but as it seem to be, by a guy who knows nothing about celestial navigation. If the US Navy is the first in the world to give up on celestial navigation then sigh, sigh and sigh, not that I am surprised at all.
But first of all a sextant is totally worthless without the exact time, (as mentioned), the original first problem in fact. But lets assume there is somebody with a not hacked iphone or something. Then you need the nautical almanac and why not a dead wood one if you feel the computer is hacked. A very nice book and very useful for people with insomnia who have given up on counting sheep, reading it makes wonders. Some of you will also know how that book relates to "computing" history.
Next you won't get a position at all, what you get is a line, much like what you get from GPS with only one satellite, just ask Fry, or perhaps not.
Apart from the sun and stars there are also planets and the moon.
And it's even possible to do without a sextant just by timing objects when they hit the horizon (hard to get anything very exact that way though).
However, what annoys me are "and a serious amount of math work to get your position" and "by a computer, which is a blessing for anyone who's ever had to do the work by hand".
That is complete rubbish, it takes less than a minute, paper and pencil, with mathematics kids learn when 6 to 7 years old (like + and - ). Oh dear.
Coat without the sextant I gave away.
"It takes less than a minute, paper and pencil, with mathematics kids learn when 6 to 7 years..."
I don't know where YOU went to school, but in my country we never studied spherical trig when we were 7. 17 maybe.
The difference is in what kind of "cheater" tables you have, such as Blewitt's book or similar. Having a big book of "cheater" summarisation in a look-up table makes the whole process, as you say, rather simple mathematics - PROVIDED YOU HAVE THE BOOK. (or the newer calculators that have the tables in them!).
But to do it the LONG FORM way, without the aforementioned tables in a book, requires the use of spherical trigonometry, as they did it back in the olden days of wooden ships of the line - Nelson's day. It is tedious, and difficult to get right (lots of chances to mess up the sign of the calculations). I've seen it done a few times, and could not do it myself if I had to. At least not from memory. Even if my life depended upon it.
..but if you don't have the book, then you don't have the celestial body position data so you can do all the spherical trig you like, you'll be missing a third of the data you need to calculate your position line.
Since you need the almanac data somewhere, why not include the sight reduction cheat-sheets in the same volume?
I suppose you can get an approximate fix from a noon-sight of the sun provided you've got a reliable timepiece. That'd be good enough for trans-oceanic intercontinental nav, but good luck if you're aiming for a fly-turd speck of an island somewhere. You're gonna need a taller lookout mast.
I remember being taught Astro-Nav in the Navy* back at the start of the century. My abiding memory is of the instructor saying not to worry if we didn't remember too much of the lessons as if we had to use it for real there'd be plenty of time to read the instructions in the almanac while we waited to take the midday sighting, or for the stars to come out.
*The original one.
That's why you get more than one and see where they intersect - exactly just GPS works. Usually, on a ship there was not a single officer taking measurement.
Of course you need a good clock - probably something better than your cell phone, but I hope any officer didn't stop also getting a good one, and ships too.
Isn't a drugstore Timex or equivalent quartz watch as accurate as an expensive chronometer of the old days, or more accurate? One could check it daily against a trusted clock, so that it would have to keep time independently only for the length of the outage.
Also, the US Hydrographic Office (now the Navy Oceanographic Office) used to publish big books of tables for just this use. I don't know where you'd get them now, but I bet the Navy does.
Do a bit of digging to learn how our "we don't need no backup, we've got all these shiny new satellites!" geniuses dumped the partially-built eLoran enhancements to the existing Loran system, after spending million$ to upgrade the existing stations. eLoran provided an order of magnitude improvement to Loran, and is essentially proof against jamming.
Yes, ye lubbers ... JAMMING! A disgruntled teen with a pocket jammer off the internet can easily blank the extremely low-power GPS signals for miles around. It's happened several times in US port locations. GPS super-high freqs are also susceptible to physical and environmental degradation.
eLoran is very low freq and very high power, virtually impossible to jam. As for hacking, it's also relatively 'low tech' and defensible.
Backup? We don't need no steenkin' backup. We gots GPS! (Think of all the military and domestic aviation, transport, commerce, and surface transportation systems that are now locked in to total GPS dependence ... and this Navy commander sez, "We'll probably just turn it off!" Oh, my achin' head!)
Backup is RDF and they still have that, even on cruise ships.
Identify a few AM stations, take bearings and plot an estimated (within a few miles, at least) position.
It won't get you into the harbour entrance, but it might tell you which way to look for it.
I took a Celestial Navigation course at UCBerkeley in the 1960s. We didn't go out to do actual sights, though the theory was discussed, but we did plenty of sight reductions to get a position from data supplied.
As for the time issue...at that point anyone who actually going to do navigation did their level best to afford to buy an Acutron watch, as they were more accurate than the ship's chronometers at the time. So long as it was set correctly and you either knew it's drift and rate or what offset to apply for a limited amount of time, you were set for time keeping good enough to navigate with. Good quality modern watches are better. For that matter, I have a $3 RTC attached to a Raspberry Pi that is good to within about 30 seconds per year and means the time error after a year would be within 7.5 arc seconds of correct, where one arc-minute is one Nautical mile.
Operation Joint Warrior 152
Dates: The exercise will run over the period 05-16 Oct 2015.
Times: There will be continuous, opportunity and pre-planned events during the period 05 0700 Oct to 16 2359 Oct 2015.
Location: GPS jammers will be located at two sites: Feraid Head and Loch Ewe.
Type: GPS jamming (denial of service only).
As in previous exercises, Safety of Life operations will at all time take precedence over exercise activities.
There are often large areas off the coast of Florida, I think it is, where there are regular wanrnings that GPS may be unreliable due to tests and exercises. If it's jammed then you [probably] know it is not working, if it's unreliable and still rely on it then who knows where you'll end up.
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