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  Mechanical and optical degradation of flexible optical solar reflectors during simulated low earth orbit thermal cycling

Putz, B., Wurster, S., Edwards, T. E. J., Völker, B., Milassin, G., Többens, D. M., et al. (2020). Mechanical and optical degradation of flexible optical solar reflectors during simulated low earth orbit thermal cycling. Acta Astronautica, 175, 277-289. doi:10.1016/j.actaastro.2020.05.032.

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 Creators:
Putz, Barbara1, 2, Author              
Wurster, Stefan3, Author              
Edwards, Thomas Edward James2, Author
Völker, Bernhard4, Author              
Milassin, Gabor5, Author              
Többens, Daniel Maria6, Author              
Semprimoschnig, Christopher O.A.5, Author              
Cordill, Megan Jo7, 8, Author              
Affiliations:
1Erich Schmid Institute of Materials Science, Austrian Academy of Sciences, Jahnstrasse 12, Leoben, Austria, ou_persistent22              
2Empa, Swiss Federal Laboratories for Materials Science and Technology, Thun, Switzerland, ou_persistent22              
3Erich-Schmid Institute of Materials Science, Austrian Academy of Sciences, Jahnstraße 12, 8700 Leoben, Austria, ou_persistent22              
4Structure and Nano-/ Micromechanics of Materials, Max-Planck-Institut für Eisenforschung GmbH, Max Planck Society, ou_1863398              
5European Space Research and Technology Centre (ESTEC), Noordwijk, The Netherlands, ou_persistent22              
6Helmholtz-Zentrum Berlin für Materialien und Energie, Albert-Einstein-Str. 15, 12489 Berlin, Germany, ou_persistent22              
7Erich Schmid Institute of Materials Science, Leoben, Austria, ou_persistent22              
8Department Materials Physics, Montanuniversitt Leoben, Jahnstrae 12, A-8700 Leoben, Austria, ou_persistent22              

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Free keywords: Communication satellites; Corrosion protection; Cracks; Ethylene; Expansion; Film preparation; Grain growth; Ion beams; Mechanical stability; Multilayers; Optical multilayers; Orbits; Polymers; Reflection; Scanning electron microscopy; Substrates; Thermal cycling; Thermal expansion; Thermal stress, Coefficients of thermal expansions; Flexible polymer substrates; Fluorinated ethylene propylene; Metal polymer interfaces; Optical solar reflectors; Reflection characteristics; Thermomechanical stability; Through-thickness cracks, Thermal insulation
 Abstract: Multilayer thin film systems on flexible polymer substrates are used as flexible optical solar reflectors or thermal insulation of satellites and spacecraft. During one year of operation, a satellite in low earth orbit typically encounters 6000 thermal cycles of ±100 °C. Due to the different coefficients of thermal expansion between the individual layers and the substrate it is important to investigate the thermo-mechanical stability of the multilayers as a function of the cyclic heat load. Scanning electron microscopy and focused ion beam cross-sectioning revealed that Inconel-Ag bilayers on fluorinated ethylene propylene (FEP) substrate severely degrade during thermal cycling of ±150 °C in a gaseous N2 atmosphere. After only 100 cycles through thickness cracks and subsurface voids in the Ag layer form as a result of equi-biaxial thermal stresses caused by the large difference in thermal expansion between film and substrate. Transmission Kikuchi Diffraction (TKD) before and after thermal cycling also revealed grain growth and twin widening in the Ag layer. Cracking and void formation are detrimental to application relevant material properties including corrosion protection (Inconel) and reflectivity (Ag). Reflectance measurements revealed that the amount of reflected energy as well as the reflection mode (specular vs. diffuse) significantly change during the first 100 cycles. Saturation of reflection characteristics was observed after 25 cycles, which correlates to a turning point in the evolution of Ag voids. Results of this study indicate that special focus should be directed towards thermal stress control (Δα) and tailoring of the metal-polymer interface to improve resistance of versatile metal-polymer systems against thermal cycling. © 2020 IAA

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Language(s): eng - English
 Dates: 2020-10
 Publication Status: Published in print
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: -
 Identifiers: DOI: 10.1016/j.actaastro.2020.05.032
 Degree: -

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Title: Acta Astronautica
  Abbreviation : Acta Astronaut.
Source Genre: Journal
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Affiliations:
Publ. Info: Oxford : Pergamon
Pages: - Volume / Issue: 175 Sequence Number: - Start / End Page: 277 - 289 Identifier: ISSN: 0094-5765
CoNE: https://pure.mpg.de/cone/journals/resource/954925464213