The following from Space News indicate that a laser gyroscope failed and that software changes were developed and uploaded to the spacecraft bringing it back on line again recently:
I"m wondering for example if DSCOVR had three axes of gyroscopic measurement and if it had enough star cameras to provide the same functionality in principle, and how the cameras could be used in situations where the angular rate was significant. Gyros and star cameras complement each other, the former works well for instantaneous rate but sampling and noise issues make absolute attitude a problem, whereas star cameras are good for absolute attitude but may have issues if the spacecraft is rotating.
Question: How was DSCOVR fixed? What software changes were implemented to allow sufficiently dynamic attitude determination from star cameras? What kinds of algorithms were added to make this possible? Is this described in any detail somewhere?