Evaluation of Ion-Sputtered Molybdenum Disulfide Bearings for Spacecraft Gimbals

Abstract

High-density, sputtered molybdenum disulfide films (MoS2) were investigated as lubricants for the next generation of spacecraft gimbal bearings where low torque signatures and long life are required. Low friction in a vacuum environment, virtually no out-gassing, insensitivity to low temperature, and radiation resistance of these lubricant films are valued in such applications. One hundred and twenty five thousand hours of accumulated bearing test time were obtained on 24 pairs of flight-quality bearings ion-sputtered with three types of advanced MoS2 films. Life tests were conducted in a vacuum over a simulated duty cycle for a space payload gimbal. Optimum retainer and ball material composition were investigated. Comparisons were made with test bearings lubricated with liquid space lubricants. Self-lubricating PTFE retainers were required for long life, i. e., >40 million gimbal cycles. Bearings with polyimide retainers, silicon nitride ceramic balls, or steel balls sputtered with MoS2 film suffered early torque failure irrespective of the type of race-sputtered MoS2 film. Failure generally resulted from excess film or retainer debris deposited in the ball track which tended to jam the bearing Both grease lubricated and the better MoS2 film lubricated bearings produced long lives, although the torque with liquid lubricants was lower and less irregular.