85 Once the wear mechanism was understood, the effort was turned into one of developing a mitigation that  could be implemented on- orbit with minimal impact to the science provided by the instrument . With the  experience in hand of another program that used the Teflon toroids successfully, it was suggested that a modified scan pattern be implemented to allow for the re- orientation of the toroids . We looked long and  hard at new permutations of the instrument scan profile . Eventually, this lead to the suggestion of doing  some limited number of reversals at a point in the spacecraft orbit that would have negligible impact to science . The SNPP science team came to rescue by suggesting that  the instrument science would not be  significantly impacted if a limited number of reversals were implemented at a high latitude point in the orbit .  Eventually, we settled on doing the reversals above 74 degrees  North latitude.  

Northrop Grumman was tasked to develop and test a command sequence to have the scanner go in a  reverse direction. They came back wi th an elegant and simple process of uploading a new scan profile  table that would perform the desired operation. Once loaded, this new t able would be en abled by command  at a time desired and then another command would be issued to go back to a normal scan table. Northrop  Grumman tested this process on their simulator and also on the sensor Engineering Development Unit .  Also, after a number discussions and some test information from the still running bearing test stations, we  settled on doing six  contiguous scans  in reverse direction once per day above 74 degrees  North latitude.  

The six reversals per day were tested on two running bearing test stations  at different times . At this period  of time, both stations were down because both stalled in late 2014 due to high torque and were shut down pending new engineering direction. The reversal testing was started on test station 3 in April 2015 while  test station 1 was restarted in March of 2015 running the normal scan profile without reversals . While test  station 3 was being used for reversal testing, test station 1 stalled in early August of 2015. At this point in  time we needed to develop mor e experience with reversals, so we decided to restart station 1 doing daily  reversals . At first, test station #1 was reluctant to re- start, but eventually did in mid -August 2015. Test station  #1 was run with the daily reversal s for about  a month before its disassembly . At the time of its test  terminati on, test station #1 was past it s 2X mission  life. Test station #3 continues to run with good results  and is almost at its 2X life point as t his is being written. Figure 11 shows the motor current data for test   station #3 as of December 8, 2015 and Figure 12 show s the motor current for test station #1.    It is anticipated that the toroids in the test station #3 bearings are compromised to some extent, but no definitive statement can be made as to their actual state. It would be logical to expect that the station 3  toroid condition is somewhere between the states of the disassembled test stations 1 and 2.    The reversals on test stations 1 and 3 were successful in giving these bearings new life. However due to the debris generated by the failure of the toroids, some torque spikes are expected to occur. The toroid debris is being ground up by the action of the balls against the races. It is thought that the reversals arrest the further degradation of intact toroids as  contact surfaces are being re- wetted with remaining lubricant.  

The on- orbit scanner bearing condition is not thought to be in as dire a condition as the test set #2 and  certainly not like test station #1 bearings at past its 2X mission life, but it is conceivable that a number of  toroids are missing in the flight bearings. So far the scanner on- orbit is still performing within pointing limits  and the bearing torque has returned to near mission -start levels after reversal implementation so our  expectation is that toroid damage is not too severe.