Celestial navigation practices


Doug Criner

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I understand that the U.S. Navy is recently teaching a smattering of celestial navigation. (I wonder who teaches it?) But what to do when GPS shoots craps? Dead reckoning, visual bearings if near land, and, of course, as a last resort, celestial navigation. I once got a bridge tour on a cruise ship. There was a continuous GPS plot running that I peeked at. It showed that the ship had sailed straight across a island. When I asked about that, they just shrugged and said GPS wasn't perfect. Maybe it was just the chart that was imperfectly imbedded into the software.
 

Mark Baber

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About 15 (maybe more) years ago, my father-in-law navigated most of a trip from San Diego to Honolulu by the stars after rain knocked out his GPS (or whatever the system of the day was) on the second day out.
 
Nov 14, 2005
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GPS with augmentation systems has become critical in aviation during instrument flying conditions at many airports. See here: Satellite Navigation — GPS/WAAS Approaches
When I was actively flying GPS was just starting to be used by the general aviation community but none of it was certified for landings. It was really nice for navigation purposes though. It was mainly VOR for me and IFR ( I Follow the Road). But GPS is still pretty cool especially after they took out the built in error. I have a hand held GPS unit but to be honest I mostly use it now to verify the speedodmeters on the toys I rebuild. Its very accurate for that.
 
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I understand that the U.S. Navy is recently teaching a smattering of celestial navigation. (I wonder who teaches it?) But what to do when GPS shoots craps? Dead reckoning, visual bearings if near land, and, of course, as a last resort, celestial navigation. I once got a bridge tour on a cruise ship. There was a continuous GPS plot running that I peeked at. It showed that the ship had sailed straight across a island. When I asked about that, they just shrugged and said GPS wasn't perfect. Maybe it was just the chart that was imperfectly imbedded into the software.
I dont know but I think it would be a very good idea. If the big one ever breaks out GPS will be targeted and taken out. It could the weapons community. I know the Trident SLBM's use stellar compensated inertial guidance. Buts thats done by onboard computer/gyro's and optics. But thats more of a geek thing than some watch officer on the bridge. They should learn the old/different ways in case they ever needed them. I don't see a down side to them learning it.
 

Mike Spooner

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Array for modern technology of satellites for GPS. What if the satellites breaks down! Where the old technology used for hundred of years might come quite handy. I don't know if sexton are still standard equipment on ships today?
 

Jim Currie

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Russia and China (and presumably the US) are developing aircraft and electronic systems which can disable satellites. Global warming issues are changing our ideas of power production and consumption. The world as we know it is constantly changing. Beware complacency.
 
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When I was actively flying GPS was just starting to be used by the general aviation community but none of it was certified for landings. It was really nice for navigation purposes though.
The same with me. My flying club started to equip our planes with them. I always considered it as a nice to have backup, not a primary navigational device. Part of the fun of flying, at least for me, was in the flight planning, which included adding in corrections for forecasted winds aloft, and then correcting for actual winds aloft during the flight itself. I do miss those cross-country flights over NJ and PA back in the good old days, and flying up the Hudson river at 1000 ft with the NY skyline along your starboard side. That was before 9/11.
 

Jim Currie

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I started navigating using exactly the same methods as were used in 1912.
In the 80's I presided over the movement of A Sedco Semi Submersible drilling barge from Bergen out to a 20 feet single point moored buoy in the middle of the North sea. It was the first time it was done entirely by computer hooked to the Azimuth drives for propulsion and to a portable GPS system in a suitcase which was accurate to within 10 yards. We did not have differential system. We hit the target right on the money. Thereafter, we deployed 27 anchors using the "suitcase " in the control room and a VHF link to the anchor handler. Great fun!
By 2004, I had an integrated GPS and sonar that could identify fish by species on my little harbour Master's launch/ Having said all that. I can still find out where I am at sea with my sextant , my very accurate wrist watch a set of old Tables and an Almanac.
I count myself so very lucky to have lived in these times.
 
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Doug Criner

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Pull out your cracker jack box compass...find north then head east or west. You'll run into land sooner or later.
Ha! If GPS satelites shoot craps or are knocked out by an enemy missile, plot radar ranges and bearings of any nearby terrestrial features. If there are no terrestrial features within radar, then go with dead reckoning from last known position.
 

Doug Criner

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Fifty years ago, I had some experience on ballistic missile submarines - but only the propulsion plant (nothing to do with the missiles). However, I picked up some info through scuttlebutt, that even if it was then correct, is probably long obsolete. This was before the advent of GPS. The ships themselves had intertial guidance systems that allowed tracking their own position without any reference to the outside world, including even GPS, if such had existed at the time. The ship's position at the time of ICBM launch was loaded into the missile - but targeting required a bit more accuracy. Supposedly, when the missile reached the stratosphere, or whatever, the missile activated a celestial sighting gadget (like a sextant?) and took enough star sights to get a very accurate fix and to fine tune the final targeting. Wonderful.

But, Yes, in the event of a real nuclear war, it might have been advisable for the submarine to remain submerged until after the war ended ;)
 
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From what I understand the SLBM's actually just sight on a single star to correct for the lessor accuracy of moving launch platform data. Thats at least for the Trident II's. Which is what the brits use also. Yes I agree about staying submerged. Head for the southern hemisphere and find a nice tropical island somewhere. Back in the day the rumor was there were subs that they called "long trigger" boats. Their job was to lay under the ice for a month or 2 after the conflict and wait for the commies to crawl out of their holes and then whack them again. The cold war was an interesting and sometimes frightening time to grow up in. But at least we knew who the bad guys were. Now...?

P.S. This being a Titanic board I dont think it would have made any differance to Titanic if they knew down to the square inch what their exact position was when they sank. It was the cold water that killed most. They didn't need all the advanced technology of today to avoid the accident. Just better command decisions would have done the job.
 
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One star sight would only give a line of position, not a fix, right?
The star sighting is coupled with the inertial guidance data so apparently it only needs one known star fix in relation to its already known position to trim for greater accuracy. But thats all I really now about it. To claim more I would just be blowing smoke. I'm sure the real nitty gritty details are classified. At least I hope so. Its always being changed and upgraded so I'm not sure whats current. And thats just for the missile. I'm not sure how the MIRV'ed warheads are navigated once they leave the missile. I worked on a lot of different missiles. Phoenix, Sparrows, Shrike and Sidewinders. But those are a different field than these. A quick commentary on this subject: I liked my job when I did it. I found the technology facinating. But I wish humanity could go a different direction. Spend the trillions of dollars on something more productive. I know thats just wishful thinking. The world is full of bad guys and must be kept at bay. Only problem is that one good slip up and its Planet of the Apes. I would rather work on Titanics engines.
 

Dave Gittins

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For the sailing I do, I'd get along fine without GPS, as I did for years. I'd use charts, steering compass and hand-bearing compass, plus drawing instruments. One thing that is making this a bit harder is the increasing lack of landmarks on the charts. On one stretch of coast in my region the chart has no landmarks in 40 miles. If my GPS quit I'd have to get home by compass course and local knowledge. In other places, I'd only have natural features, such as little islands, to help fix a position. Old time charts had many landmarks, plus little drawings of the coast along the bottom edge. At least we still have lighthouses!
 

Doug Criner

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Charts should have plenty of bearing lines defined by two visual points, that may be either landmarks or tangents. For example, a chart that I have for England - West Coast has many bearing lines - for example: "Star Castle Hotel in line with west side of Hangman's I. 157 deg". I assume that modern charts still have those? They simplify plotting a precise position and permit checking your compass.
 

Dave Gittins

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Not where I sail! My chart would have the island but not the hotel. The only bearing lines might be where there are leading lights or where they define the visible arcs on sectored lights.
 

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