Unveiling the Degradation Mechanisms of MoS ₂ Lubricating Films in Authentic Low Earth Orbit via China Space Station Exposure Experiment

Abstract The inevitable performance degradation and accelerated wear of solid lubricating materials caused by in‐orbit exposure to highly reactive chemical species underscores the urgent need to clarify the evolution mechanisms of lubricating films in space environments. Herein, for the first time, radio‐frequency‐sputtered MoS 2 ‐Au films are exposed to the authentic low Earth orbit (LEO) for 1 year via the windward‐side exposure platform aboard the China Space Station. By integrating multiscale characterization techniques, including depth‐resolved X‐ray photoelectron spectroscopy, time‐of‐flight secondary ion mass spectrometry, and mechanical and tribological testing, post‐exposure analysis reveal that MoS 2 is converted to Mo and S species through an MoS 2 O intermediate under the atomic oxygen and proton erosion. Owing to the formation of oxidized and protonated species on the surface of the MoS 2 ‐Au film, the friction coefficient increases from 0.023 to 0.035, and wear life is reduced by 77%. Beyond unraveling the synergetic degradation mechanisms of MoS 2 ‐based lubricants in LEO environments, this study establishes a mechanistic foundation for the rational design of intelligent lubrication films in next‐generation space mechanisms. Moreover, the utilization of the space station platform to probe material evolution behavior in an authentic space environment paves the way for advancing deep‐space material chemistry.