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I acquired a copy of Space Navigation Handbook (Navpers 92988) from
Amazon.com. The book has enough differential equations to gag me,
without getting into Hamiltonians and quaternions.  Most of the math
was applied to orbital determinations.

The book concentrated on near-earth navigation, as that was where the
authors (chief of whom was Capt. P.V.H. Weems) expected most people
to be in the near future; very practical.  The basic method advanced
for fixing a position was essentially what earth-bound types use.
They advocated use of spherical coordinates with an origin at the
center of the earth.  Range to the spacecraft could be determined by
marine sextant measurement of the apparent diameter of the earth.
Altitudes of stars could be determined with reference to the earth's
edge, using the semi-diameter obtained from the range measurement to
bring the measurement to the center of the earth.  They also
discussed some other instruments and optical systems, but it was cool
to see reference to marine sextants.

I don't know that marine sextants would be too useful peering through
the thick windows of a spacecraft, but still....

One big problem earth-bound types have is that our planet is
rotating.  So one needs to know the time to locate the first point of
Aries.  That is not necessary for a spacecraft, unless it wants to
know what part of the earth it's over, which might be useful
information at re-entry or other times.

I'm still wondering what it would be like to navigate in interstellar
space.  There, position (parallactic) shifts of nearbye stars would
need to be accounted for.  I suppose until one got very far away, a
coordinate system centered on the sun could be used.  It doesn't
appear one could use a marine sextant to determine range to the sun
by diameter measurement after one was very far away.

I hope others will expand on some of these points.  Perhaps Dan Allen
could summarize more of Richard Battin's book for us poor souls too
far from research librarires.   This is all very slow going for me,
but fascinating.  I also wonder how the Apollo astronauts and
engineers actually navigated their craft.

Fred

   

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