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Space tribology

From Wikipedia, the free encyclopedia

Space tribology is a discipline in the field of tribology which deals with tribological systems for spacecraft applications.[1] Research in the field aims to design reliable tribological systems that can withstand the harsh environment of space.

Challenges

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In addition to regular tribological stresses, machine elements for space applications need to withstand the harsh environment during launch and in orbit. In particular, critical tribosystem inputs are:[2]

Lubricants for space applications

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Liquid lubricants

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Liquid lubricants for space applications need to have low vapor pressure (volatility) in order to withstand the high vacuum on orbit. Suitable lubricants include perfluoropolyethers, cyclopentanes and polyalphaolefins, mostly in the form of base oils for lubricating grease.[2]

Since the rate of evaporation increases with temperature, the use of liquid lubricants is often limited to temperatures below 100 °C. On the other side of the spectrum, the viscosity of liquid lubricants increases with decreasing temperature; i.e., the lower the temperature, the more viscous the lubricant (see also viscosity index). Thus, the use of liquid lubricants is limited to temperatures of around -40 °C.[2]

Solid lubricants

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Solid lubricants are used for applications with extreme temperature or where evaporation of lubricants would cause damage to sensitive instruments.

Solid lubricants are applied in the form of coatings, or through self-lubricating materials. In the former case, sputtered molybdenum disulfide (MoS2) and ion-plated lead (Pb) are commonly used; in the latter case, polyimide composite materials based on polytetrafluoroethylene (PTFE) are often employed, as well as leaded bronze.[2]

Applications

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Space tribology ensures the reliable operation of mechanisms aboard spacecraft, which can be broadly grouped into one-shot devices (such as deployable solar panels, deployable antennas and solar sails), and continuously and intermittently operating devices (such as reaction wheels, electric motors and slip rings).[3]

References

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  1. ^ W.R. Jones Jr.; M.J. Jansen (2000). "Space Tribology" (PDF). Nasa/Tm-2000-209924.
  2. ^ a b c d e Roberts, E W (2012). "Space tribology: its role in spacecraft mechanisms". Journal of Physics D: Applied Physics. 45 (50): 503001. Bibcode:2012JPhD...45X3001R. doi:10.1088/0022-3727/45/50/503001. S2CID 120418746.
  3. ^ Aglietti, Guglielmo S. (2011). "Spacecraft Mechanisms". In Fortescue, Peter; Swinerd, Graham; Stark, John (eds.). Spacecraft Systems Engineering. John Wiley & Sons, Ltd. pp. 495–526. doi:10.1002/9781119971009.ch15. ISBN 978-1-119-97100-9.