performance. A first position error occurred after 30 minutes, followed by two more 4 hours later. No  errors were seen after the third error. Short scans, while not immune to errors, seemed to have improved the performance by eliminating position errors. This scanning continued for the next week without errors.  On June 22 (after developing a new diagnosis tree), the 8° scanning was extended 20° above the limb.  The goal was to see if scans that reached top speed failed. They did not fail and after running for 24  hours, it was decided to try the May 31 scanning to verify that position errors had not disappeared again.  Unfortunately, 4 errors occurred within approximately two hours and the instrument was returned to  scanning only between the limb and space. Again, there were no position errors in this range of scanning.  To try to pin down whether the errors were position dependent or slew length dependent, the scanning  was modified on June 28 to add blackbody sequences, but to do the move to and from the blackbody in a series of 8° slews instead of one long slew. This was not successful with errors still occurring on the limb scan following the blackbody scans (although at about half the rate as earlier in June). This seemed to point to a position dependent error generating mechanism. The instrument was returned to a state where it was scanning between the limb and space, and the instrument remained free of errors.  Errors Disappear after Reduced Scanning Over the July 4 week, one blackbody per day was added to the scanning. This was inserted due to  keystoning concerns since an 8° slew does not move the balls of the output bearings by a full diameter; it was essentially just rocking them back and forth. This scanning had been performed for most of the previous two weeks and was expected to continue for at least another week over the holiday. The expectation was that one position error would be generated every day or two and if the frequency increased rapidly, instrument fault protection would cut in and stow the actuators.  No position errors occurred. This led to experimentations (over the next two weeks) where the timing and  frequency of the blackbody calibrations was varied (reaching the original 5/hour rate). None generated position errors. It seemed that scanning over a limited range for an extended period with the updated motor control parameters (higher torque, cleaner waveform), had made scanning elsewhere less prone to  errors. Or perhaps scanning over any region above the limb made scanning in that region less prone to  errors. Yet, scanning in January seemed to have contributed to the increase in error frequency. Resumption of Calibration Views In late July, a spacecraft issue led to the actuator anomaly investigation going on hiatus until early  October. During this time, scanning between limb and space with occasional blackbody scans (done in short 10° scans due to the spacecraft issue) was performed. Also, further EM testing revealed that the new motor controller parameters were causing the controller to current limit when the spacecraft bus voltage was at 32.5 V. The clipping distorted the current waveforms and had the potential to introduce a  new source of position errors. This led to the design of a new set of motor controller parameters with slightly lower peak currents that did not clip on the life test actuator in the lab, but still had a slightly higher  torque then the January tables and the cleaner waveform. Starting in October, a set of steps was performed to return to more normal scanning with the new motor  controller parameters. This was done gradually with several days between each change in configuration or slew profile. These steps included increasing the number of blackbody views back to 10 and adding in  a view of the solar target. However, the elevation actuator was never allowed to go higher then 120°.  Combined, the addition of these observations allowed the science channels to be fully calibrated.  Final Flight Testing—Returning Below the Limb With full calibration restored, a new round of careful testing was started. Given that the errors seemed to  be at least partly position dependent and could possibly be improved by repeated scanning, it was decided to slowly expand the scanning below the limb (>120°). During this process, the fault protection was set on a hair trigger to stow the instrument on the first error. This was the region where large errors had previously occurred. Since large errors seemed to be associated with increased error rates elsewhere, there was a desire to minimize the number that occurred.  284