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Completed TRL 4 (started at 3, targeting 5)
Project Objective
This project seeks to develop a surface coating for transparent windows (made of, for example, silicon glass or polycarbonate), exposed to the lunar surface, that reduces adhesion of the coated surface to lunar regolith/dust.
Project Description
The objective is to develop a high-conductivity, low-surface-energy coating for transparent windows to mitigate dust adhesion in a lunar environment. To achieve the objective, the following are being performed:
- Deposit transparent diamond-like carbon coatings using pulsed laser deposition with parameters and doping materials leading to low transparency, low surface energy, low surface roughness, high electrical conductivity, good coating adhesion to the glass/polycarbonate substrate, and high hardness; and
- Evaluate the films for transparency, surface energy, surface roughness, electrical conductivity, hardness, and resistance to solid particle erosion and three-body abrasive wear.
Project Results and Conclusions
The University of Tennessee Space Institute (UTSI), the external project lead, successfully deposited transparent continuous low-roughness diamond-like carbon (DLC) coatings on silicon glass. Attempts have been made to deposit coatings on polycarbonate, but instances of coating cracks have been identified; work continues for coatings on polycarbonate. The DLC coatings have been optimized with alumina (Al2O3) as a dopant to increase the transparency. Other dopants were tried, including silicon and magnesium fluoride (MgF2), but Al2O3 (at 25% of the whole DLC/Al2O3 composition) produced the best combination of high transparency (the most important property for a transparent substrate), high hardness (for wear resistance), relatively low roughness, and low surface energy (for low surface adhesion). The best deposition temperature is still being determined. Current specimens have deposition temperatures of 100° C, 150° C, and 200° C; specimens with coatings deposited at these temperatures are being studied.
Solid particle erosion tests have so far shown wear of the entire coating thickness for DLC coatings even at moderate particle speeds. This likely indicates that thicker coatings are required for use at the lunar surface. UTSI is looking at methods to deposit at higher thickness. Abrasive wear tests will be completed before the project end date.
New materials must be developed for the harsh conditions on the Moon, as NASA looks to a long-term presence there. Transparent surfaces must be protected against lunar dust adhesion - adherence of too much dust will degrade the ability of people to see through it. Such surfaces must also be protected from excessive abrasive wear and erosive wear caused by the abrasive dust. A coating like this could be useful for Habitat Systems and Human Landing Systems (HLS). HLS and HLS commercial partners have shown interest in dust coatings and other technologies under development.
With the prospect of dust storms on Mars, a coating like the one being developed here might also be beneficial for Mars.
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