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The vacuum of space can be used to fabricate functional reflective coatings in space via vacuum deposition. This approach allows for the direct deposition of reflective coatings onto mirror substrates in the vacuum environment of space. By coating mirror substrates in space, the sensitivity and reflectivity of visible, UV, FUV and X-RAY mirrors can be increased by eliminating the need to deposit oxidation protective coatings, as required on-earth. In addition, depositing mirror coatings on-orbit simplifies the handling and packaging of space mirrors and provides a low-cost capability to repair and restore mirror coatings on-orbit.
In-space vacuum deposition has been successfully performed in Space during the Wake Shield Facility (WSF) demonstration missions (STS 60, 69 and 80) achieving a TRL of 7. The WSF Program was a space R&D program to develop in-space vacuum deposition technology in order to overcome the purity constraints found in terrestrial semi-conductor production. The WSF was deployed in the wake of the Space Shuttle at an orbital altitude of over 300 kilometers (186 mi), within the thermosphere, where the atmosphere is exceedingly tenuous. The forward edge of the WSF disk redirected atmospheric and other particles around the sides, leaving an "ultra-vacuum" in its wake. The experiments resulted in fabricating the highest quality GaAs semiconductors at the time and successfully proving the vacuum wake concept.
By leveraging the WSF Program heritage, the fabrication of reflective coatings in-space can be directly applied to substrates to achieve the required performance which astrophysics requires for the next generation of space telescopes. Specifically, visible, UV and FUV mirrors coated with bare aluminum to achieve unparalleled reflectivity in space.
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