Mars Science Laboratory Rover Mobility Bushing Development  Benjamin Riggs * Abstract NASA’s Mars Science Laboratory (MSL) Project will send a six-wheeled rover to Mars in 2009. The rover  will carry a scientific payload designed to search for organic molecules on the Martian surface during its primary mission. This paper describes the development and testing of a bonded film lubricated bushing system to be used in the mobility system of the rover.  Introduction The MSL Rover Mobility System contains several pivots that are tightly constrained with respect to mass  and volume. These pivots are also exposed to relatively low temperatures (-135°C) during operation. The  combination of these constraints led the mobility team to consider the use of solid film lubricated metallic bushings and dry running polymeric bushings in several flight pivot applications. A test program was developed to mitigate the risk associated with using these materials in critical pivots  on the MSL vehicle. The program was designed to characterize bushing friction and wear performance  over the expected operational temperature range (-135°C to +70°C). Seven different bushing material / lubricant combinations were evaluated to aid in the selection of the final flight pivot bushing material /  lubricant combination.  Background The mobility team recognized during the rover preliminary design phase that the large size and mass of  the new vehicle required a fresh look at the design approach for many of its pivots. The rover required pivots that could tolerate intermittent, low speed (<2.5 rpm) dithering motion at operational temperatures that precluded the use of wet lubricants. After an extensive trade study that assessed mass, complexity  and volumetric efficiency the team decided to pursue main pivots based on primarily on flanged bushings.  Flanged bushings provided a simple, robust, mass-effective solution to the design challenges associated  with the highly loaded main mobility pivots. With the general design approach selected the team accelerated its search for viable material/lubrication  options for the bushings. A large number of material and lubrication options were considered for use in the pivots including various bronze bushing alloys, zinc aluminum, polymeric materials, and coated stainless steel. Although a number of these materials had merit the team selected coated, gall-resistant stainless steel bushings for the initial test series on the basis of compressive strength, gall resistance in the event of lubricant failure and published coated coefficient of friction information. Isolating a bushing material also allowed for a manageable set of bushing material, mating surface and lubricant combinations during testing. Three candidate bonded film lubricants with inorganic binders were selected to coat the stainless steel bushings during the initial test series. Testing The unproven combination of bonded film lubricants and bushing materials in the rover mobility pivots  required testing to enable their use on the flight vehicle. Friction and wear performance data was also  desired to enable more accurate modeling of the pivots in dynamic simulations. These factors led the design team to plan a multiphase test series to select a final bonded film lubricant and characterize the friction and wear performance of the bushings over the pivot operational temperature range. * Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA Proceedings of the 39th Aerospace Mechanisms Symposium, NASA Marshall Space Flight Center, May 7-9, 2008  83