Developmental Bearing and Bushing Testing for Mars Gearboxes  David Suffern* and Jonathan Parker*  Abstract  As a part of NASA Jet Propulsion Laboratory’s (JPL) upcoming Mars 2020 mission, Sierra Nevada  Corporation (SNC) will be providing a number of new gearbox designs to fulfill various functions in the  rover’s robotic arms. At the time of the design reviews, SNC was unable to reference published or  heritage design data that encompassed the Mars 2020 mission requirements regarding bearing lubricant  life and bushing wear. As a result of this lack of information and the accelerated schedule, componentlevel and gearbox-level developmental testing was performed during the program’s procurement phase to  substantiate design choices in advance of qualification-level testing of deliverable flight gearboxes. These  tests successfully demonstrated that the necessary mission life could be achieved. This paper aims to  highlight the benefit of these developmental tests and provide new data in an area previously unpublished  for bearing lubricant life [1][2][3] with mean Hertzian contact stresses up to 2.18 GPa (316 ksi).  Additionally, the bushing wear test results are included, indicating that the required Mars cold operating  temperatures were particularly stressing.  Introduction  SNC was tasked with providing eight different custom planetary gearbox designs to drive mechanisms on  the new Mars 2020 rover. Gearbox size and volumetric constraints required high torque-density designs  that required pushing the envelope in terms of component stresses in the bearings and bronze alloy  bushings supporting the planet gears. The life requirements for several of these gearboxes exceeded  requirements for hardware previously delivered by SNC on the Mars Science Laboratory mission, the  Lightweight gearbox design study [4], and other published data for Perfluoropolyether (PFPE) bearing  lubricant life [1][2][3]. General industrial design standards for bushings were considered uncertain for  these applications due to the use of vacuum-rated lubricants and a non-terrestrial operating environment  [5].  Summary of Successful Developmental Test Exposures:  •Operating Temperature Range: -70ºC to +70ºC •Ball Bearing Max Mean Hertzian Stresses: o2.179 GPa (316 ksi) up to 389,501 stress cycles o1.682 GPa (244 ksi) up to 2,621,338 stress cycles o1.517 GPa (220 ksi) up to 29,077,592 stress cycles •Operating Pressures for Bronze Bushing: o8.487 MPa (1,231 psi) for 1.78 km (5,895 ft) at speeds of 40.1 mm/s (7.89 ft/min) o2.766 MPa (401 psi) for 22.97 km (75,358 ft) at speeds of 17-31 mm/s (3.35-6.10 ft/min) o1.866 MPa (274 psi) for 34.17 km (112,122 ft) at speeds of 17-31 mm/s (3.35-6.10 ft/min) o0.625 MPa (91 psi) for 51.20 km (167,981 ft) at speeds of 17-31 mm/s (3.35-6.10 ft/min) SNC worked with JPL to define developmental tests for reducing programmatic risk ahead of qualification  level testing since there was a lack of widely available data to provide confidence that these operating  parameters had a high probability of success. The scope of this developmental testing was strictly  focused on demonstrating the capability of these components for the Mars 2020 mission parameters  including temperature profile, operating speeds, and frequency of direction changes. As such, these  *Sierra Nevada Corporation, Durham, NC Proceedings of the 44th Aerospace Mechanisms Symposium, NASA Glenn Research Center, May 16-18, 2018 © 2018 Sierra Nevada Corporation  NASA/CP—2018-219887 529