NavList:

Dear Jeremy,

In [NavList 12783] Re: A navigation exercise , From: Anabasis75---com, Date: 7 Apr 2010 10:43 , you wrote :

QUOTE

Kermit,

I neglected to note on my scrap paper the course and speed, but i went to the hourly logs and found the course to be 108 degrees True and speed 8.2 knots at the time of the lunar.

Jeremy

UNQUOTE

Thank you very much for getting these results and sorry for keeping you running the ladders up and down ...

*******

So, I ran again your Navigation example.

You had published your position as :

24 Mar 2010 / UT10h16m43.0s / S07�03'6-E072�07'0 / GPS Position

The closest I can come from your results - through working your Lunar to determine UT and then run the Sun and Moon heights as LOP's - was obtained with my very early assumptions : consider all observations at the very same time, and use the mean values for both Sun and Moon heights. I then got the following observed position :

24 Mar 2010 / UT10h15m23.9s / S07�05'5-E072�06'0 / Lunar Derived position

Whenever I attempt refining/fine tuning the conditions of this Lunar through entering Course and Speed, and taking into account actual delays between observations .... the end results become worse (although "not more unreliable" in one sense ...) and they diverge from GPS position by up to 40 NM.

So, and as you earlier noticed it, we certainly can consider that the first position I derived was obtained through some sort of "luckily cancelling errors" ...

Thank you anyway because this example is also very instructive.

*******

I will process your Diego Garcia Lunar when time permits. No expected spare time for the upcoming week (with still a pending study on "CelNav Bodies daily data base minimum size requirement to achieve a 1" accuracy" when I have more spare time also).

*******

Til then, Thank you again and

Best Regards

Kermit

Antoine M. "Kermit" Cou�tte

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