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Window contamination on Expose-R

  • R. Demets (a1), M. Bertrand (a2), A. Bolkhovitinov (a1), K. Bryson (a3) (a4), C. Colas (a5), H. Cottin (a6), J. Dettmann (a1), P. Ehrenfreund (a7), A. Elsaesser (a7), E. Jaramillo (a8), M. Lebert (a9), G. van Papendrecht (a1), C. Pereira (a8), T. Rohr (a1), K. Saiagh (a6) and M. Schuster (a9)...

Expose is a multi-user instrument for astrobiological and astrochemical experiments in space. Installed at the outer surface of the International Space Station, it enables investigators to study the impact of the open space environment on biological and biochemical test samples. Two Expose missions have been completed so far, designated as Expose-E (Rabbow et al. 2012) and Expose-R (Rabbow et al. this issue). One of the space-unique environmental factors offered by Expose is full-spectrum, ultraviolet (UV)-rich electromagnetic radiation from the Sun. This paper describes and analyses how on Expose-R, access of the test samples to Solar radiation degraded during space exposure in an unpredicted way. Several windows in front of the Sun-exposed test samples acquired a brown shade, resulting in a reduced transparency in visible light, UV and vacuum UV (VUV). Post-flight investigations revealed the discolouration to be caused by a homogenous film of cross-linked organic polymers at the inside of the windows. The chemical signature varied per sample carrier. No such films were found on windows from sealed, pressurized compartments, or on windows that had been kept out of the Sun. This suggests that volatile compounds originating from the interior of the Expose facility were cross-linked and photo-fixed by Solar irradiation at the rear side of the windows. The origin of the volatiles was not fully identified; most probably there was a variety of sources involved including the biological test samples, adhesives, plastics and printed circuit boards. The outer surface of the windows (pointing into space) was chemically impacted as well, with a probable effect on the transparency in VUV. The reported analysis of the window contamination on Expose-R is expected to help the interpretation of the scientific results and offers possibilities to mitigate this problem on future missions – in particular Expose-R2, the direct successor of Expose-R.

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Note: Several of the references below are not scientific publications but technical documents that were published to support the Expose project. They can be requested from the corresponding author.
Beuselinck, T. & Van Bavinchove, C. (2011a). Expose: Environmental history by calculation: Expose-E Simulation Results. RedShift Design and Engineering BVBA, EXP-RP-017-RS, Issue A, Rev. 2, 6 May 2011.
Beuselinck, T. & Van Bavinchove, C. (2011b). Expose: Environmental history by calculation. Expose-R simulation results. RedShift Design and Engineering BVBA, EXP-RP-020-RS, Issue A, Rev. 1, 23 December 2011.
Butenko, Y. (2012). Raman spectroscopy and optical post-flight inspection of the window Suprasil 8, Expose R. Materials Report nr. 6754. ESTEC (TEC-QTE), 20 January 2012.
Dachev, T., Horneck, G., Häder, D-P., Schuster, M. & Lebert, M. (2014). EXPOSE-R Cosmic Radiation Time Profile. Int. J. Astrobiol. (this issue), published online: 12 05 2014 , Doi:
ESA-ESTEC (2004). RTV-S 691. In Space product Assurance. Data for selection of space materials and processes. ECSS-Q-70–71A Rev. 1, p. 142. ESA Publication Division, 18 June 2004.
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Rabbow, E. et al. (2012). EXPOSE-E: an ESA Astrobiology Mission 1.5 Years in Space. Astrobiology 2(5), 374386.
Rabbow, E. et al. (2014). The Astrobiological Mission EXPOSE-R on board of the International Space Station. Int. J. Astrobiol. (this issue), published online: 28 08 2014 , doi:
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RUAG (2011a). EXPOSE-R. Post-flight De-integration and Inspection, RUAG EXR-TN-HT-017, Issue 1, 14 April 2011.
RUAG (2011b). EXPOSE-R. Post-flight Inspection of Windows, RUAG EXR-TR-HT-010, Issue 2, 21 July 2011.
Tighe, A.P., Iwanovsky, B., van Eesbeek, M. & Duzellier, S. (2009). In-orbit measurements of the Columbus lab vacuum environment using the MEDET pressure gauge. In ISMSE-11, Int. Symp. on Materials in Space Environment, Aix-en-Provence, France, September 2009.
van Papendrecht, G., Butenko, Y., Bolkhovitinov, A., Demets, R., Rohr, T. & Semprimoschnig, C. (2013). Molecular contamination effects on the sample compartments of the Expose-E and -R flight experiments (ISMSE-12). In ESTEC (TEC-QTE), Proc. 12th Int. Symp. on Materials in Space Environment, Noordwijk, The Netherlands. ESA SP-705, February 2013.
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International Journal of Astrobiology
  • ISSN: 1473-5504
  • EISSN: 1475-3006
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