Corrosion in space
Corrosion in spaceis thecorrosionof materials occurring inouter space.Instead ofmoistureandoxygenacting as the primary corrosion causes, the materials exposed to outer space are subjected tovacuum,bombardment byultravioletandX-rays,solar energetic particles(mostlyelectronsandprotonsfromsolar wind), and electromagnetic radiation.[1]In the upper layers of the atmosphere (between 90–800 km), the atmospheric atoms, ions, andfree radicals,most notablyatomic oxygen,play a major role. The concentration of atomic oxygen depends on altitude andsolar activity,as the bursts of ultraviolet radiation causephotodissociationof molecular oxygen.[2]Between 160 and 560 km, the atmosphere consists of about 90% atomic oxygen.[3]
Materials
[edit]Corrosion in space has the highest impact on spacecraft with moving parts. Early satellites tended to develop problems with seizing bearings. Now the bearings are coated with a thin layer ofgold.
Different materials resist corrosion in space differently. Electrolytes in batteries or cooling loops can cause galvanic corrosion, general corrosion, and stress corrosion.[1]Aluminiumis slowly eroded by atomic oxygen, whilegoldandplatinumare highly corrosion-resistant. Gold-coated foils and thin layers of gold on exposed surfaces are therefore used to protect the spacecraft from the harsh environment. Thin layers ofsilicon dioxidedeposited on the surfaces can also protect metals from the effects of atomic oxygen; e.g., theStarshine 3satellite aluminium front mirrors were protected that way. However, the protective layers are subject to erosion bymicrometeorites.
Silver builds up a layer of silver oxide, which tends to flake off and has no protective function; such gradual erosion of silver interconnects of solar cells was found to be the cause of some observed in-orbit failures.[4]
Manyplasticsare considerably sensitive to atomic oxygen and ionizing radiation. Coatings resistant to atomic oxygen are a common protection method, especially for plastics.Silicone-basedpaintsand coatings are frequently employed, due to their excellent resistance to radiation and atomic oxygen.[5]However, the silicone durability is somewhat limited, as the surface exposed to atomic oxygen is converted tosilicawhich is brittle and tends to crack.
Solving corrosion
[edit]The process of space corrosion is being actively investigated. One of the efforts aims to design a sensor based onzinc oxide,able to measure the amount of atomic oxygen in the vicinity of the spacecraft; the sensor relies on drop of electrical conductivity of zinc oxide as it absorbs further oxygen.[citation needed]
Other problems
[edit]Theoutgassingof volatile silicones onlow Earth orbitdevices leads to presence of a cloud of contaminants around the spacecraft. Together with atomic oxygen bombardment, this may lead to gradual deposition of thin layers of carbon-containing silicon dioxide. Their poor transparency is a concern in case of optical systems andsolar panels.Deposits of up to several micrometers were observed after 10 years of service on the solar panels of theMirspace station.[6]
Other sources of problems for structures subjected to outer space are erosion and redeposition of the materials bysputteringcaused by fast atoms andmicrometeoroids.Another major concern, though of non-corrosive kind, ismaterial fatiguecaused by cyclical heating and cooling and associated thermal expansion mechanical stresses.
References
[edit]- ^abBlockley, Richard; Shyy, Wei, eds. (2010-12-15).Encyclopedia of Aerospace Engineering(1 ed.). Wiley.doi:10.1002/9780470686652.eae242.ISBN978-0-470-75440-5.
- ^Martines, S."Analysis of LEO Radiation Environment and itsEffects on Spacecraft's Critical Electronic Dev ices".Mendeley.Embry Riddle Aeronautical University.Retrieved23 August2019.
- ^"The Use of Silicone Adhesives in Space Applications".Archivedfrom the original on 2006-03-24.Retrieved2006-06-07.
- ^Myer Kutz - Handbook of Environmental Degradation of Materials (2005, 0815515006)
- ^"Optimizing Atomic Oxygen Resistance on Coated Substrates Using TechOptimizer".Archived fromthe originalon 2006-06-24.Retrieved2006-06-07.
- ^Banks, Bruce A.; De Groh, Kim K.; Rutledge, Sharon K.; Haytas, Christy A. (1999). "Consequences of atomic oxygen interaction with silicone and silicone contamination on surfaces in low earth orbit".Proc. SPIE.3784:62.Bibcode:1999SPIE.3784...62B.CiteSeerX10.1.1.870.5957.doi:10.1117/12.366725.hdl:2060/19990047772.S2CID136474988.
External links
[edit]- The Cosmos on a Shoestring: Small Spacecraft for Space and Earth Science, Appendix B: Failure in Spacecraft SystemsPDF
- New Scientistpremium article: Space is corrosive
- NASA Long Duration Exposition Facility: surface contamination in space
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