NavList:

Bob,

The way you are advancing the LOPs is perfect. Your problem is in the way you are interpreting and using these LOPs.

Basically, what you have here is the usual 3-body fix. Observation 1 is of the morning sun, observation 2 is of Venus, observation 3 is of the afternoon sun. Each observation is fraught with its own observation error and corresponds to a LOP at its time. To use them all for a fix, they must be advanced to the same point in time (the time of the fix). Now you have the classical case of three LOPs forming a cocked hat. The fact that two of the LOPs are advanced ones has become irrelevant. The fix of all three is the Lemoine Point (symmedian point) within the cocked hat.

Of course, you can always obtain a preliminary fix from just any two of the three LOPs. These three "fixes" will be the corners of the cocked hat. There is nothing alarming about them being different from each other. Just like with any simultaneous 3 star fix. It simply means that your cocked hat is larger than zero because your observation errors are larger than zero and that you are a human being.

Herbert