Conclusions  Based on the test results discussed above, the chosen bearing arrangement with the use of a Braycote  micronic 601EF grease-plate with a 10 vol% grease slurry fill (50/50 wt% Braycote micronic 601EF grease and Brayco 815Z oil) meets the SRT grinding bit shaft 3x life requirement (~6 x 10 7 revs or 1.73 x  108 stress cycles). This arrangement showed minimal signs of degradation over the course of the life test.  In contrast, the purely grease-plated bearing does not meet the requirement. The purely grease-plated bearing ran at a consistently higher torque and showed signs of failure beginning at ~2.2 x 10 7 revs (~6.3  x 107 stress-cycles) with a torque over-limit failure at ~4.5 x 107 revs (~1.3 x 108 stress-cycles). Barring  cold-start torque margin limitations, it is recommended that any long-life bearing application include some vol% grease-pack in addition to a standard grease-plate to reduce parasitic torque and increase bearing  life.   

PFPE lubricants, such as Brayco 815Z oil, can be used in the high stress, high stress-cycle regime  depending on the application. In the  case of mechanisms that have sufficient torque margin, PFPE  lubricants can be pushed beyond the currently documented allowable stress conditions. More research is  necessary in the field of PFPE lubrication for space and planetary exploration applications where  mechanisms tend to be less about precision and more about ruggedness. Data does exist; however test conditions and geometry are not always well documented and many test results are applicable only to  Hertzian stress levels below 0.69 GPa. There exist many possibilities to further the abilities of PFPE  lubricants and bearing life in general, including the use of hybrid bearings or specialty steels. Carefully documented research will be paramount to future exploration missions that require long life for tools such  as abraders, drills and other rugged mechanisms that may operate continuously under high loads.    Acknowledgements  The authors would like to thank all of the SRT program technicians, machinists, designers, engineers and  managers at Honeybee Robotics and JPL for their commitment to developing this device. Specifically, the  authors would like to thank Mark Balzer of JPL and Jeff Lince of the Aerospace Corporation for their time  and technical insights.   This work was performed under a contract with Jet Propulsion Laboratory, California Institute of  Technology, for the National Aeronautics and Space Administration. References herein to any specific  commercial product, process or service by trade name, trademark, manufacturer, or otherwise does not  constitute or imply its endorsement by the United St ates Government or the Jet Propulsion Laboratory.  References  [1] NASA’s Mars Exploration Program . 09 Oct. 2007. NASA. 09 Oct. 2007 <http://mars.jpl.nasa.gov/>  

[2] Lince, Jeff. Aerospace Corp. Teleconference. March 2007.    [3] Conley, P. L. and J. J. Bohner, “Experience With Synthetic Fluorinated Fluid Lubricants”, Proc. 24 th Aerospace Mechanisms Symp. , NASA CP-3062, 1990.  

[4] Jones, W. R., and M. J. Jansen, “Lubrication for Space Applications”, NASA Glenn Research Center,  NASA CR-2005-213424, 2005.  

[5] Tribology for Aerospace Applications . Ed. E. V. Zaretsky, Illinois: STLE, 1997.    [6] Fleischauer, P. D., “Tribology in the Space En vironment”, Aerospace Corp., El Segundo, CA, Report  No. TR-97(8570)-2, 1997.  

[7] Suzuki, M. and M. Nishimura, “Tribological characteristics of ball bearings lubricated with a sputtered  molybdenum disulphide film in a vacuum und er a high thrust load”, Proc. 5th European Space  81