Why Seeing Stars Can Be More Cool Than GPS

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I've got this thing for cool, non-electric technology: pocket watches that run on springs and gears, slide rules, carburetors.

Maybe that's why I took a shine to Bill Castlen's recent article in IFR magazine on Celestial Navigation. In many ways the underlying math isn't that different than what goes on inside the GPS units that guide most of us from A to B without much thinking. It's just that the process is so exposed when it's a person shooting the angles to the objects in the sky, a person looking up in the tables and a person doing all the calculations. The fact that it can be so accurate blows my mind.

Castlen delves a bit into the dark side, describing how Fred Noonan and Amelia Earhart would have had to work this system to find Howland Island in 1937. With only the sun to use by morning, they could have known accurately where they were east-west, but not so well north-south. They would have (probably) intentionally flown too far north and then run the north-south line trying to pick out tiny Howland Island from the shadows of cumulus clouds. Think about that the next time you're following the magenta line to your a fuel stop.

One bit I knew about celestial navigation, but had long forgotten, was how important it was to have a pretty good idea of where you are before you took your sightings. Dead reckoning is the first step and a foundation of this system. I pulled down my tattered copy of Guy Murchie's Song of the Sky and flipped to this passage: "[The navigator] must note any change of speed, direction, or any factor of temperature, altitude, or engine adjustment that might affect the speed. If he does not, he loses a clue to accurate reckoning -- which would be like a detective overlooking a bloodstain at the scene of a murder."

This kind of navigation took relentless awareness. And if there's one thing our GPS-easy world has cost us, I think it's awareness. Not that I have any urge to go fly NDB approaches to minimums in killer crosswinds again. But when I did, I was much more aware of the winds, and the weather and the terrain, than I am flying GPS approaches to those same airports today.

And while it's true that awareness could save your hide one day when all the pretty pixels go dark, I think there's a better reason to make the extra effort at least some of the time. It's just part of being more skilled at what you do. It's like what a friend and 20-year test pilot pointed out to me once about takeoffs. He asked if I noticed how almost every tricycle-gear airplane has a slight pitch-up the moment the wheels break the ground. This happens because the center of rotation moves from the wheels to the CG and that increases the arm of the elevator. It becomes slightly more effective, and the nose pitches up. Slightly.

I never noticed until he pointed it out to me. To be honest, I'm not sure I can detect it now. But I like searching for it even if it really doesn't matter. Call me a romantic, but there's a richness in a world where you bother to keep track of the little details around you; where every once in a while you have to remember to wind your watch.

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Comments (6)

If you really want to know about celestial navigation, I'll tell you how to get the definitive bible. You'll need a periscope sextant, available off and on on ebay. Order a set of sight reduction tables and an Air Almanac from the Government Printing Office. Then, at the risk of overloading their website with all your requests, you can go to the USAF e-publications website and download "Air Navigation" AFPAM11-216, (no space between AFPAM and 11). 427 pages in pdf format. Great book and a freebie. Go to www.e-publishing.af.mil and search for AFPAM11-216. Enjoy.

Posted by: Robert Ryan | July 23, 2009 8:11 AM    Report this comment

A number of years ago, I decided to read up on and learn CelNav, albeit marine, not aviation. Fascinating stuff, lots of skill involved in the art as well as the science. Celestaire (www.celestaire.com) became a good source for books/tables/plotting materials, and for reading up on sextants. I can't say that I mastered it (the beach apartment at Wrightsville, NC mysteriously moved south to Southport on my initial computations), but I do have a working appreciation of the process and marvel at how guys like Shackleton's crew could determine position accurately in raging Antarctic seas in a lifeboat. eBay can be a great source of the Astra III sextant for those interested... mine came from a senior at the Merchant Marine Academy who had to buy it for course work but didn't intend to use it again. Glad to see mention of CelNave in IFR as well as on Avweb.

Posted by: Scott Dyer | July 23, 2009 9:05 AM    Report this comment

Given the possibility that we may be putting too many of our navigational eggs in the GPS basket, certainly it doesn't hurt to look at alternatives. If there's a possiblity of GPS service degrading, we should insist that Loran-C be kept alive.

I believe also, manufacturers of avionics should develop up-to-date automatic star trackers. Such systems could see at least some stars even in daylight, as long as they have a clear view of the sky. Combining an automatic star tracker with laser ring gyro-based INS, would result in a system which, unlike GPS satellites, cannot be sabotaged. Nor would it be hostage to the willingness of our government to replace GPS satellites as they age or otherwise become defective.

Posted by: Alex Kovnat | July 24, 2009 7:04 AM    Report this comment

I've heard the government is looking at using pulsar's for a gps backup. Same theory as gps, only a natural source of signal.

Posted by: Scott Muchow | July 27, 2009 7:28 AM    Report this comment

I never need it since my flights are usually less than 3 hours. Hard to get lost in a slow plane in just a few hours...

Posted by: Mark Fraser | August 12, 2009 1:54 PM    Report this comment

I've heard AOPA stumping for keeping Loran as a backup, but how good of a backup would it be? I've never seen a plane with Loran in person, and I'd guess less than 5% of the fleet has it installed. If it died I suspect owners would go back to using VORs rather than install a Loran receiver, and by the time people could get it installed in volume, we could launch enough satellites to fix the constellation.

The best "backup" to GPS is to install enough GPS ground stations that the system will continue functioning even after losing multiple satellites. If you co-located a GPS ground station with every VOR you could probably operate without any satellites at all.

Posted by: Guy Hutchison | August 19, 2009 11:59 AM    Report this comment

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