Battery-Powered Process for Coating Telescope Mirrors in Space

ZeCoat Corporation will develop a battery-powered, aluminum deposition process for making broadband reflective coatings in space (wavelength range: 30-nm to 2500-nm). The process uses an array of evaporation filaments powered by batteries contained in pressurized vessels placed in the vacuum of space. The vacuum coating process is scalable for large mirrors several meters in diameter, but is applicable to any size mirror. By simultaneously discharging batteries through individual evaporation filaments, a tremendous amount of energy may be released rapidly. By placing iridium (or a multi-layer interference coating) on the mirror initially (coated on earth), followed by a fresh coat of aluminum in space, the broadband response of the telescope could be extended down to 30-nm. Current coating technologies limit the reflectance response to 90-nm because of the absorbing fluoride coating which protects the aluminum from oxidation on earth. The ability to coat optics in space offers a tremendous potential benefit to astronomy because the 30-nm to 90-nm region is rich in spectral lines. Since molten metals such as aluminum are held onto a hot tungsten filament by surface tension, the proposed evaporation process will work in zero-gravity. A high aluminum evaporation rate has been shown to produce the least scattering and most highly reflecting aluminum coatings, particularly in the vacuum UV spectral region. To achieve future wavefront requirements over a large primary mirror, it is likely that many evaporation sources will be required. By placing the power supply (the battery) very near each evaporation filament, electrical losses are minimized. In Phase I, we will demonstrate feasibility using prototype battery-powered deposition (BPD) units previously manufactured at ZeCoat Corporation. In Phase II, miniaturized battery-powered unit will be designed and manufactured, and the coating process will be developed and tested in a simulated space environment.

The primary focus for this research is a space-based coating process for future space telescopes, however, additional commercialization potential lies in coating mirrors on the ground with a battery powered process, for use in space, or, for use on the ground. Creating a EUV-quality aluminum coating with minimal impact on WFE, over a large area, is not a trivial task (and currently the state-of-the-art is far short of requirements). ZeCoat will commercialize the new technology by offering coating services, through licensing agreements, and by selling or leasing the individual BPD sources. We will advance this coating technology for broadband, UVOIR telescopes to TRL-6 by 2019 (end of Phase II) and we expect sales to begin at the end of Phase II. It is likely that future large monolithic mirrors will require new coatings facilities to coat them. Even if the final bare aluminum coating is applied in space, either an iridium coating, a multi-layer EUV coating, or a fluoride-protected aluminum coating, will be applied prior to launch. A battery-powered coating technology offers the possibility of building a coating facility on earth to make UV-quality aluminum coatings over-coated with the traditional metal-fluorides. ZeCoat is prepared to install larger coating facilities to meet the government's needs, when these technologies are mature. The marketability of the new coating technology depends primarily on the optical performance of the coating.

ZeCoat will commercialize the battery-powered coating technology developed in this research for other ground-based applications such as large mirrors for ground-based astronomy. Large mirrors for aircraft simulators are also a candidate commercial application for the new technology. We will also market the technology to prime contractors such as Northrup Grumman for applications such as coating repair in space.

This is early/mid-stage (TRL 4) — the most realistic path in is NASA SBIR/STTR, which funds small businesses and research institutions to develop technology aligned with NASA's needs (equity-free, phased funding). Check whether a current SBIR/STTR solicitation topic overlaps with this project's technology area, or contact the project directly (above) to ask.

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