Due to some errors overnight, GNC 1 has been taken off as primary and GNC 2 activated. They disabled GPS as a possible cause, but problems could occur again so that's why GNC 1 is still running in a backup config.Last night they had to hand over to the Russian segment and go over to low-data rate, but with the current config -- a repeat error on one GNC would just switch to the backup and not the Russian side.They'll troubleshoot overnight and Saturday, but if no fix by Sunday they'll need to roll back all the MDM's to the last version and go from their.Strangely - no mention in today's ISS Daily Report as it says everything is running fine. This came from what I heard during the wakeup call, and more info from the daily planning conference this afternoon.
Late today they took Greg to private conference to discuss R6 rollback options.
GNC Issue Troubleshooting: After recent intermittent anomalous behaviors of both GNC MDM (Guidance, Navigation & Control Multiplexer/Demultiplexer) computers, flight controllers uploaded a software patch to the MDMs to gather more data for diagnostic analysis. The patch will not be exercised on orbit until after the Soyuz 16S undocking.