Special coatings are being developed and tested by the NASA Glenn Research Center in collaboration with the Cleveland State University to contend with the effects of dust on the lunar surface. These coatings potentially have wide applicability ranging from the prevention of dust buildup on solar arrays and radiator surfaces to the protection of extravehicular activity space suit fabrics and visors. They need to be durable and functional based on the application.
One particular initial focus is on transparent coatings. Conventional transparent coatings are specialized for transmission (antireflective) or are made scratch resistant. The current coating development also aims at making transparent coatings that are slightly conductive to reduce the electrostatic attraction of dust particles, in particular lunar dust particles.
Planview of two-source radiofrequency magnetron sputter system for fast prototyping of mixed or doped coatings. QCM, quartz-crystal microbalance.
We have started preparing coatings approximately 80 nm thick on room-temperature glass and polycarbonate substrates using the radiofrequency magnetron sputtering technique shown in the sketch (ref. 1). The film material consists of a mixture of titanium dioxide (TiO2) and excess titanium (Ti). The TiO2 produces a hard transparent film, whereas the Ti makes the film slightly conductive. The following photograph shows representative coated and uncoated samples. The coating produces a slightly bluish tint but provides adequate transparency. A coating with high conductivity is not desirable since it can produce electrical shorting problems. Other standard and exotic coating materials are being investigated to provide the best compromise between transparency, conductivity, and durability.
Coated and uncoated polycarbonate sample coupons.
The lunar environment includes exposure to ultraviolet solar radiation and abrasive dust that can be harsh on materials. The coatings will be checked for changes in electrical properties under prolonged ultraviolet light exposure. We have also started conducting a series of environmental tests that simulate the exposure of coated samples to dust under relevant conditions, beginning with abrasion tests using lunar stimulant materials (a close lunar dust reproduction).
A custom abrasion testing device (shown in the following photograph) was developed for this purpose. The device was designed for small sample coupons, 1-in.-square coupons in this case, and allowed for a range of frictional contact pressures, from very low contact pressures. It also provided a way to control and quantify the total amount of abrasion. Also importantly, a lunar stimulant known as JSC-1 was used to prepare an abrasive medium substrate for these tests. A series of abrasion tests at light contact pressures showed that these coatings can tolerate this degree of dust abrasion and that the coatings attracted less dust during the abrasion process than did the corresponding uncoated samples. In addition, we expect that these coatings can be commercialized for applications in harsh environments such as desert and cold weather operations.
Abrasion testing device.
Last updated: December 14, 2007
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