CRlSM Bearing Lubrication  The thermal analysis of the CRlSM motor/encoder and diaphragm bearing assemblies indicated that they  would operate at -40°C and -90°C respectively. The analysis indicated that the diaphragm bearing  assembly would be too cold for oil or grease lubrication. Our tests showed that -40°C was beyond the  acceptable temperature range for Pennzane synthesized hydrocarbon based oils and greases and -90°C  was beyond the accepted range for perfluorinated polyether based Brayco oils and greases. It was  desired to use identical lubrication in both bearing assemblies for the following reasons:  0  a To simplify bearinghubrication testing  0 To have nearly identical bearings and identical lubrication in both bearing assemblies  Once the bearings and lubrication were selected, an single qualification test could be applied to  both assemblies  The three choices of dry film lubrication that were considered were:  1. Ion plated lead  2. Sputtered MoS2 (molybdenum disulfide)  3. WS2 (tungsten disulfide)  Ion-plated lead bearings were successfully used in the Compact Remote Imaging Spectrometer (CRISP)  tracking mirror assembly on the Comet Nucleus TOUR (CONTOUR) spacecraft. The CRISP tracking  mirror assembly bearings were a Barden precision angular contact duplex pair with a bronze cage. They  were purchased through BE1 as part of their motor/encoder assembly. This was done since they were the  same bearings used in the BE1 motor/encoder and they had used an identical set previously in the  SABER3 instrument on the TIMED spacecraft. However, we were unable to procure ion-plated lead thin-  section bearings at the time. If it were possible to procure them in the future, we would definitely  recommend trying them.  There is a great deal of literature touting the benefits of sputtered MoS,. Dry film lubrication tests for MoS2  and WS2 were conducted for the CRISP cover and release mechansim3. Sputtered MoS2 is supposed to  work great in vacuum, however, moisture absorption can cause severe performance degradation. Most of  the CRISP cover and release mechanism qualification testing was conducted in ambient conditions  including a test on NASA’s Low Gravity Experiment aircraft (the “Vomit Comet”). Tests comparing  sputtered MoS2 and WS,, showed WS2 to be clearly superior to sputtered MoS, for this application.  Sputtered MoS2 seemed to exhibit tremendous stiction in tests conducted in ambient conditions where as  stiction was virtually undetectable with WS2. In fact, we believe that the cover and release mechanism  would not have worked at all using sputtered MoS, in ambient conditions. Sputtered MoS2 was also used  in the bearings for the MDlS instrument on the MESSENGER spacecraft launched in 200X. In addition to  the well known issues of sputtered MoS2, this instrument suffered two additional issues:  1. Smoothness  2. The sputtered MoS2 coating is a hard and brittle coating  The MDlS instrument was able to meet its performance requirements with the sputtered MoS2 coated  bearings. However, the initial flight assembly had to be replaced and a new assembly built up because  the sputtered coating had become cracked and resulted in large unacceptable torque spikes. Based on  our experiences, we would NOT recommend sputtered MoS2 coatings.  WS,, Dicronite, was chosen for the CRlSM motor/encoder and diaphragm thin section bearings.  However, we were unable to locate any specific examples or find any heritage on WS2-lubricated  bearings used in space applications in the available literature. However, based on our previous success  with WS2 on the CRISP instrument, we were optimistic that WS2 could also work in bearings. We also  knew that the bearing companies offered it as an option and that the WS2 coaters coated bearings. We  decided to conduct our own WS2 coated thin-section Teflon-toroid bearing test.  16