At a telecon held by Air Force Space Command (AFSPC) last Friday, I asked a question regarding which GPS navigation data parameters were being modified to fix the elevation-based, excessive ranging errors that SVN 49 (PRN 01) is producing.  The answer on the telecon was not as detailed as I would have liked, so I followed up with an e-mail asking for the definitive terms that are being adjusted.  I received their reply today; here is the answer:

"Two methods are being evaluated for mitigating the effects of the SVN-49 problem.  This first method involves adjusting the AF0 and Tgd terms in the broadcast NAV message from SVN-49.  The second method involves adjusting the AF0 and Tgd terms as well as the square root of the semi-major axis and the mean motion difference terms in the broadcast NAV message.  The pros and cons of each method are still being assessed.  The satellite is currently being operated using the second mitigation method without the Tgd adjustment."

So, now we know what's being considered and tested.  I don't doubt that they would consider other parameters as well, if they think they can model the fix better, so this may not be the final answer.  I'll keep the Nog updated if I hear anything further.

More detailed analysis can be found on another blog by Tim Springer.

All comments and questions are appreciated, thanks for following!

Happy Nogging...