In vacuuo tribological investigations of metal, ceramic and hybrid interfaces for high-speed spacecraft bearing applications

Abstract

New bearing technologies are being developed for use in space systems to meet future demands including longer lifetimes, higher speeds and affordability. Specifically, improvements are necessary for high speed control momentum gyroscopes as longterm operation can lead to a fluid starved condition through evaporation and/or creep. Over the course of the bearing lifetime, the bearing will progress from elastrohydrodynamic to mixed and boundary layer regimes that result in failure. In order to understand this failure scenario, this paper discusses the development of a UHV tribometer and test methodology to simulate a fluid starved condition on a laboratory scale in vacuum. Results are shown for metal-on-metal, hybrid (metal-ceramic) and ceramic material pairs using a multialkylated cyclopentane liquid lubricant. These results show that ceramic material pairs provide approximately three orders of magnitude longer life than both of the other systems through the reduction of fluid decomposition. Three regions were noted in tests run to failure that are associated with decreasing film thickness and increasing fluid decomposition. Ranking within each system can be understood based on contact angle data which gives insight into relative film thickness.