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Frank, you wrote:

"What could you do while approaching the Moon if you could see tenth
magnitude stars on it's limb?"

1. Determine an assumed geographic position.
2. Calculate height of eye with a sextant limb to limb observation.
3. Refraction is zero.
4. Observed angle above the horizon is zero (hs).
5. Derive an azimuth and intercept to get a LOP.
6. Second star observation generates a true geographic position fix.
7. Combine height of eye with GP to get a three dimensional fix.

I like observing orbiting satellites better.

Greg

On Jul 21, 1:00�am,  wrote:
> Greg, you wrote:
>
> "It seems that a 2009 PDA is sufficient to handle trajectories, 
triangulations and three dimensional cross track error with optimal thrust 
applications to rendezvous or orbit."
>
> Yes, it sure would be good enough for the calculations. I proposed a laptop 
in case anyone wanted to bring the entire Hipparcos star catalog or maybe a 
complete topographic map of the Moon at ten-meter resolution (this doesn't 
exist yet, but it will be available very soon).
>
> Some things to consider:
> There are lots of satellites orbiting the Earth. Could you use them for 
anything? By 2029, there would probably be a dozen satellites orbiting the 
Moon. Any use for them? And finally, as it seems to me, the big difference 
between terrestrial celestial navigation and this "space" navigation is that 
you can see thousands of stars 24 hours a day (unless your spacecraft is 
surrounded by clouds of ice particles, as during Apollo 13). If you think 
about it, that changes everything. What could you do while approaching the 
Moon if you could see tenth magnitude stars on its limb?
>
> -FER
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