I have a WWII vintage octant used by my Dad to do celestial navigation
when ferrying bombers to England during the war. It was also used when
Colonial Airlines flew from NYC to Bermuda in the late 40's. Still have it.
It really is possible to navigate with the beastie. The airplane
turbulence induced jerks were not an obstacle. If fact, the motions may
have been less vexing than use of a hand held sextant on a ship.
The octant has a drum and pencil arrangement. When you take a fix, it
marks the drum. You take a series of measurements of the same object,
write down the start and finish times. It has a lighted bubble to
provide the horizon. Thus one has a horizon day and night.
Insert a new drum and do another object.
Go back to your desk and do the various lines of position, advanced for
time difference between object fixes. (Generally an eyeball average of
the various pencil lines and use of the midpoint time would suffice.)
The plotting of them results in a fix. The tables used for data
reduction were much abridged from the normal several volume
set--reflecting the less precise nature of the measurement technique. It
contained something like 50 7"x10" pages compared to the normal 5+
pounds of books.
Let's face it, if you get a fix within 5-20 miles, that's good enough if
you're trying to find England. Finding the coast of North America would
have been even easier on the return trip. However, the trip back was
via boat.
Dead reckoning using speed and direction is tough on the great circle
route due to crazy magnetic compass deviations. The celestial nav fixes
at a minimum flagged that "something was wrong" if the dead reckoning
and celestial fixes disagreed a lot.
I learned celestial navigation (on land) using this octant before
getting a sextant. You can use it on land because it has a built-in
horizon.
Neat piece of history.
Brian
On 7/1/2013 12:56, Jim Lux wrote:
I had a chance to go through the Time and Navigation exhibit at the
National Air and Space Museum last week. From a "time" standpoint,
there's probably not much there that time-nuts don't know already, but
it's kind of cool to see cleaned up examples of equipment from days gone
by. (there's an old cesium beam from NIST on display, and a Symmetricom
cesium turned on and counting, but also a lot of old GPS stuff... lots
of Rb and Cs for space)
Quite a lot of the exhibit space was devoted to the problem of air
navigation, which, now that I've seen the exhibit, I can understand what
challenge it was. Over centuries, folks had figured out how to navigate
on ships and on land, but those are inherently slow moving, so you can
do things like take multiple sextant sights and reduce them.
But planes move fast, so you don't have as much time to do it. It took
real guts to be the navigator in the little cockpit out front of the
plane, taking sights with your body out in the wind. And the poor
fellow who was sucked out of a plane when taking sights standing on his
seat and the astrodome blew out.
It was interesting to see how many different schemes were used for
(mostly radio based) nav in airplanes over a fairly short time. Low
Frequency DF, A/N Ranges, VOR, LORAN, etc. I didn't see Omega.
They have an inertial nav unit there from a sub, but not much
explanation of how inertial nav works.
They talk about the DSN (and actually have a 4 bay rack of the old
time/frequency distribution gear on display), but not much discussion
on exactly how we do navigation for deep space.
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