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Old 05-02-2016, 17:57   #46
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Re: A sextant for the 21st century?

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Originally Posted by hellosailor View Post
maggied-
The USN won't have to ask for funding, they can ask the USAF for the surplus units from the Blackbird. The USAF had fully operational "ball turret" starfinders, that could locate and identify stars--even in daylight--and calculate the plane's position from there. Decades ago. Rarely found on the surplus market, in pieces of one kind or another.
Great story about aviation celestial navigation some of you may enjoy-

Adventures in aviation celestial navigation
Jan 1, 2003
To the editor:

What many voyagers don't seem to appreciate about celestial navigation, besides its obvious back-up benefits, is the intellectual pleasure it gives the navigator in knowing how to plot a line from a celestial sight. I know from experience how good that feels.

I set out to sea as a cadet in the Canadian merchant marine in 1946. In between chipping and painting I spent my time in the chart room gleaning what I could about chart work and the arcane ritual of sextants and chronometers. Little was actually taught to me, as it was by tradition left to the cadet to ask and sort things out for himself.

In 1950 I changed professions and became a pilot in the Royal Canadian Air Force. I did my tour of flying fighters and instructing. In 1956, unhappy at the prospect of flying a desk, I left the air force and started with United Airlines and by 1963 was flying DC-8s on the San Francisco-to-Hawaii route.

It was a pleasant way to earn a living: once airborne only the autopilot and navigator really worked -- we pilots spent the time drinking coffee, making position reports, and looking out the window. This tended to be a bore, so once we settled down in cruise I would get out of my seat and look over the navigator's shoulder and ask questions. In time I got to sit at his table and fiddle with his navigation paraphernalia. Most of it was WW II-vintage stuff, though the periscope bubble sextant was the latest model.

And it was then that I began to appreciate the enormous differences between marine and aviation celestial work. On a boat the navigator takes an altitude, notes the time, and works the tables for a line of position. Essentially simple stuff, and even if you are slow it's very unlikely there will be more than a few miles between the sighting and the plotting.

Flying at eight nautical miles a minute is another story, and only half of the story at that, because for a lot of good reasons, to do with inertia and altitude, a marine sextant won't work in high-altitude, high-speed flight. Errors of 60 or more miles are predictable if you do try to use a marine model. To compensate, the aerial navigator uses a bubble averaging sextant. The bubble replaces the horizon, and the averaging clockwork device, usually operated over a period of two minutes, balances out the inertial errors.

Besides all that, the periscopic sextant, inserted through the overhead of the cockpit, has to be pointed in the right direction and set at the right angle to locate the celestial body, as its field of view is very small. This means that the sextant has to be pre-programmed for each shot; as each one takes about five minutes to program, two minutes to shoot, and 10 minutes to fiddle with the averaging device, calculate, and plot, it means that, by the time you put pencil to chart, the line you draw is where you were 80 or so miles behind you. The net effect is that the flight navigator spends a lot of time advancing and retarding lines of position to find out where he is from where he was. Tight, neat triangular fixes that I used to see in my merchant marine days became something of the past.

It was also about this time that Inertial Navigation Systems (INS) started coming on the scene, and United declared its intention of phasing out the professional navigator in favor of these black boxes. And it was because of this and the fact that I had no ticket to reflect on my years at sea that I challenged myself to master the art of flight navigation and get an FAA Flight Navigator's ticket before the craft and position was just aeronautical history. Using the Air Force Air Navigation Manuals and the Navy's HO 216, I set to work and eventually took the battery of written exams.

The air regulations, meteorology, weight and balance, and performance exams were three hours each, and because they were already part of my pilot curriculum presented no problem. The other three exams, each lasting five hours, where as big an intellectual challenge as I've ever experienced. To begin with, the FAA examiner presented we with the exam book and a three-by-three-foot piece of paper without as much as a speck on it. Supposing it to be a chart, I took it back to him and asked where the lat and long lines were. He told me to read the first question, and that's when I really broke into a sweat. It required me to create my own Mercator chart for latitude 35° N and longitude 180°. I was stumped, and sat for five minutes before forcing my mind to remember something I had picked up in the Air Force about each succeeding latitude line being equivalent to the next increasing angle. That part solved, the exam then got worse, as all the following navigation problems had me crisscrossing the dateline with each follow-up question dependent on the accuracy of the previous problem. To top it off, the finale required a square search for a downed aircraft with the winds, of course, being variable depending on position and altitude, so that by the end of the five hours I was thoroughly wiped out.

The next exam challenged my theoretical knowledge of grid navigation: the sort of thing used when flying over the poles where longitude lines crowd into each other and magnetic variation and dip make the magnetic compass useless and aircraft have to fly by gyroscopic compass. The next exam had me pressure pattern flying, where a correlation between a radio altimeter and pressure altitude can, so they say, give you a pretty accurate line of position. This was only theory to me, but I hacked away at it the best I could.

Anyway, I passed this horrendous intellectual torture and took the results to the chief fight navigator. He was as surprised as I was that I had passed because it had been years since anyone had taken the test and nobody seemed to know what was on it anymore. A flight test date was scheduled, and both he and an FAA examiner came along to hover over me on my rating ride between San Francisco and Honolulu. As part of the test a fix from three celestial bodies was required, and as it was a day flight I spent the previous day pre-calculating where the sun, the vaguely visible moon, and the almost invisible Venus would be so that I would be able to set the azimuth and altitude into the sextant before each shot and not waste time scanning for them.

After we got airborne and cleared the departure corridors I took over and just about blew it, but totally. My first required action was to give the captain a card with the magnetic heading to the first waypoint with an ETA. The old-time navigators had warned me never to let go of that card till I had doubly checked the variation and deviation arithmetic, because if it was wrong it would mean an automatic failure for the whole test. The captain put out his hand to grab the slip, but for some instinctive reason I would not let him take it way from me. A potential tug of war nearly was averted when I said: let me double check it. And sure enough I had added instead of subtracted. Everyone, both pilots and examiners, breathed sighs of relief, for they had noticed the error and none of them wanted me to fail.

The three-LOP celestial fix, something I had never done in flight before, went surprisingly well, thanks to the preflight planning. I used the second shot as the master line and advanced one line and retarded the other.

There were other challenges to overcome, but I knew I had it made when we passed the halfway point and the FAA examiner cheerfully quipped, "I hope you don't miss the islands because we don't have enough fuel for China."

My navigator's ticket is now buried with a lot of my other aeronautica in a cardboard box in the garage. I never did use it professionally, but I'm more proud of my navigator's ticket than any other of my FAA licenses

I don't venture too far from land in my boat anymore, and my sextant sits on a shelf, but I have the pleasure of being a celestial navigator, and learning how to be one was the most intellectually satisfying thing I ever did.
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Old 05-02-2016, 19:19   #47
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Re: A sextant for the 21st century?

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Originally Posted by Reefmagnet View Post
It's what magician's say when they pull a rabbit out of a hat :-)
It's spelled "Voila".
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Old 05-02-2016, 19:38   #48
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Re: A sextant for the 21st century?

Delancey,

Thank you for that wonderful story. Beautifully told and deeply satisfying.

Bill
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Old 05-02-2016, 19:40   #49
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Re: A sextant for the 21st century?

+1 delancy, great story, thanks for sharing.

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Old 05-02-2016, 23:07   #50
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Re: A sextant for the 21st century?

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It's spelled "Voila".
I added a Hungarian accent.

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Old 06-02-2016, 09:12   #51
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Re: A sextant for the 21st century?

Hey everyone!

Please do understand my initial post. I don't want to start a discussion on what backup for GPS is best and why. There are way to many on those as it is. My intention is only to start a discussion on the concept of a digital sextant and to what extent it would give 'added value' over the existing (analogue) sextants. Perhaps I should have mentioned that in my initial post (my bad, sorry!)

The lightning problem is actually the only real danger to a device like I suggested. As it is for any electronics. Sometimes failures may occur months or even years after being struck. So, even if your precious (backup) GPS might seem to have survived, it well might collapse 3 months later. When you are out on the big-big-lake, approximately eight notevencloses south of the next radio contact.

I would have the same problem with the digital sextant. Although it is of course well possible to engineer it in such a fashion that it is also possible to use it in the analogue mode with the good old pen and paper. In which case it is a backup of a backup
(shouldn't lose the backup, cause I would lose its backup as well )

Anyway. Apart from anyone's favorite backup for GPS, what are your ideas on the proposed new cousin of the digital calipers?
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Old 06-02-2016, 09:29   #52
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Re: A sextant for the 21st century?

exMaggieDrum
You probably mean this:
Seeing stars again: Naval Academy reinstates celestial navigation - Capital Gazette

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Originally Posted by trifan View Post
I figured someone would have said something by now about the OP's use of a slip stick. I have compared slide rule calcs vs printed tables and my position accuracy is far better with the tables. 4 or 5 digit precision vs 2 or 3. I guess it is all relative. A few feet error with GPS, couple of miles maybe with the tables and the slide rule will show you which ocean you're in ;-)
I like to play with the slide rule. I agree that it is less accurate, but then again... also water resistant to 1000 feet (thing is made of plastic) which the book is not. Also, I usually use the tables, but every so often I want to brush up the 'skills and drills', just to keep them fresh in my mind.
When it is not fresh, there is a step-by-step instruction, plasticized, in the front of the almanac (and a spare in the sextant box) to help me in case of neurological problems (heatstroke, stroke, poisoning, trauma) in conjunction with GPS problems.
(call me what you like, I just like to have contingency plans and be save you can do whatever you like)
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Old 06-02-2016, 09:40   #53
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pirate Re: A sextant for the 21st century?

Quote:
Originally Posted by A ursae minor View Post
Hey everyone!

Please do understand my initial post. I don't want to start a discussion on what backup for GPS is best and why. There are way to many on those as it is. My intention is only to start a discussion on the concept of a digital sextant and to what extent it would give 'added value' over the existing (analogue) sextants. Perhaps I should have mentioned that in my initial post (my bad, sorry!)

The lightning problem is actually the only real danger to a device like I suggested. As it is for any electronics. Sometimes failures may occur months or even years after being struck. So, even if your precious (backup) GPS might seem to have survived, it well might collapse 3 months later. When you are out on the big-big-lake, approximately eight notevencloses south of the next radio contact.

I would have the same problem with the digital sextant. Although it is of course well possible to engineer it in such a fashion that it is also possible to use it in the analogue mode with the good old pen and paper. In which case it is a backup of a backup
(shouldn't lose the backup, cause I would lose its backup as well )

Anyway. Apart from anyone's favorite backup for GPS, what are your ideas on the proposed new cousin of the digital calipers?
To late mate... its got its own life now..
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Old 06-02-2016, 09:59   #54
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Re: A sextant for the 21st century?

A Ursae Minor

I'm in neither of these 2 categories. I have a sextant on board - because I have to- but never bothered to learn how to use it, even if feeling slightly guilty about it ;-)

But , I love your idea! If you could come up with a sextant as easy to use as you describe, I would be happy to be your first customer :-)
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Old 06-02-2016, 10:40   #55
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Re: A sextant for the 21st century?

On my South Atlantic crossing last fall the owner had a very nice sextant that he had been given. He was not using it.

While wondering through the mall at the Albert and Victoria Waterfront I saw Sextant: A Voyage Guided by the Stars and the Men Who Mapped the World's Oceans by David Barrie and bought it.

To while away the hours I decided to renew my celestial skills - I had copy an almanac and sight reduction tables on my tablet as well as a worksheet and plotting chart. so I printed off some the forms.

I quite liked the mental challenge I faced each day.

As I was finishing Barrie's book, one line made the whole read worthwhile.

Quote:
"It is time to rediscover the joys of celestial navigation, not merely as a safety net, but because using a sextant to find our way puts us in the closest possible touch with the natural world at its most sublime. "

We use the universe to find our place in it.

The sextant helped be get in touch with universe that exists off the boat.

You can add that to reasons for using a sextant.
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Old 06-02-2016, 10:57   #56
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Re: A sextant for the 21st century?

Boaty is right.

Dump the sextant.

What's your backup?

Learn emergency navigation the right way. Just say no to being a sissy.

Emergency Navigation

Navigation Quick Sheet

Weather Quick Sheet
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Old 06-02-2016, 11:26   #57
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Re: A sextant for the 21st century?

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A Ursae Minor

I'm in neither of these 2 categories. I have a sextant on board - because I have to- but never bothered to learn how to use it, even if feeling slightly guilty about it ;-)

But , I love your idea! If you could come up with a sextant as easy to use as you describe, I would be happy to be your first customer :-)
I have one on my phone. It only uses Polaris, not much good in the Southern hemisphere.
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Old 06-02-2016, 13:52   #58
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Re: A sextant for the 21st century?

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Originally Posted by jackdale View Post
We use the universe to find our place in it.

The sextant helped be get in touch with universe that exists off the boat.

You can add that to reasons for using a sextant.
When I crossed the Atlantic, I stood a long watch every night. Never in my life had I been so familiar with the night sky and the moon. The moon truly became my friend, and when it did not appear for a few nights, as it does each month, I really missed "my friend". I had never known true darkness until then. And when I saw Venus, the morning star, I knew my watch was almost done. But so low and bright, I had to check every day to be sure it was not another boat. And then the skipper would turn on the light in the head, totally blinding me.

IMHO, living in cities full of light pollution, staring at screens, and not the heavens above, we have lost our knowledge and appreciation of the night sky.
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Old 06-02-2016, 14:27   #59
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Re: A sextant for the 21st century?

Well, it seems there already are a bunch of apps for this purpose: 25+ Top Apps for Celestial Navigation (iPhone/iPad) and http://appcrawlr.com/app/search?go=g...device=android
Now load one of them in a waterproof phone, like the Xperia m4 aqua, and it's done...
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Old 06-02-2016, 14:39   #60

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Re: A sextant for the 21st century?

Yah, hoosier, you missed the entire point. As I said, you can WORK BACKWARDS using optical pattern recognition of the sky to figure out what you are looking at, and where you might be, without the GPS. Of course, you'll need a lot more memory than the 16k found in most of the cheap phones, and it will take a while for the slow processor in the phone, but any "equation" can be solved in either direction. Given a picture and the time (and the phones keep time pretty well without the GPS or network) you can work backwards and figure out where it was taken.
Not to mention, as I said, the accelerometers in the phone are capable of better inertial navigation than the classified (and rather bulky) ring accelerometers that used to do the same job on the early nuclear submarines. Without any skyview at all.
The equipment is all there, I wouldn't be surprised if you could hire some enterprising Chinese or Indian programmer to write the code for under fifty grand.
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