Very Good Bob. Now how can you use that info to navigate?

Joe

If you accurately know the time and roughly where you are you can estimate
your position on the surface of the earth by measuring angles from the
horizon in a given direction to known celestial bodies and the angles
between celestial bodies. Since the earth is not a sphere, one must know
roughly where one is to include an approximation for the ellipsoid surface
of the earth. Once one has a series of these angular measurements,
calculations are made and tables are consulted. Eventually, one arrives at
an estimate of position. This method has been in use for hundreds of years.
I could break out my old Dutton's from the Naval Academy and give you a
refresher if you want. It's been years for me.

Another method, used in space craft and ICBM's, has similar geometric
calculations except that the surface of the earth is no longer used as a
reference point. In fact, the reference point may be changing constantly in
radius. Typically in these astrodynamical calculations three reference stars
are used along with inertial navigation data and other types of
radiolocation data. The results of these input are Kalman filtered (weighted
time average) and the resultant intersection of the locus of the
navigational error plots from each system yield location. Typically, the
missile is whizzing along at 17,000 mph at altitudes up to 60 miles.

Amen!



..com wrote in message
oups.com...
Very Good Bob. Now how can you use that info to navigate?

Joe