Hydrodynamic Bearings for Space Mechanisms Considering Surface Roughness and Elastic Deformation

The Space Tribology Handbook makes only a brief mention of hydrodynamic bearings, stating that “hydrodynamic bearings are not considered, as such bearings are generally either impractical for space applications or do not involve tribological behavior.” While this assessment holds true for most space mechanisms, certain specialized applications do employ hydrodynamic bearings. One notable example is pumps used in spacecraft thermal fluid loops, where such bearings enable complete rotor encapsulation and eliminate the need for dynamic seals between the rotor and stator. Some heritage designs of space-qualified pumps exist and are discussed as background in this paper. However, the existing literature lacks comprehensive guidelines for the sizing and design of mechanisms incorporating hydrodynamic bearings. The work conducted by nano SPACE and ESTL aims to address this gap through dedicated activities in bearing design, modeling, and experimental validation. In space mechanisms, hydrodynamic bearings are vital for ensuring precise, low-friction, and long-life rotational motion under microgravity and vacuum conditions. This study investigates the influence of surface roughness and structural deformation (elastic or thermoelastic) on the performance characteristics of hydrodynamic bearings operating in space environments. The analysis incorporates the modified Reynolds equation, accounting for roughness parameters, film thickness variations, and bearing elastic compliance. Results indicate that micro-level roughness significantly alters pressure distribution and load capacity, while elastic deformation plays a key role in maintaining film stability under varying thermal and dynamic loads. The findings are crucial for designing reliable, lightweight, and durable bearings for satellites, gyroscopes, reaction wheels, and robotic joints.