NASA Langley Research Center
Hampton, Virginia

Materials

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Responsible Parties: Page Content: William H. Kinard Page Construction: Thomas H. See

In addition to the anodized aluminum and Ag/FEP, which together accounted for the large majority of the surface area on the LDEF, several selected white paints, black paints, black anodize coating, and selected highly specific specialty coatings, were flown as specimens or in-service hardware.

Z-93 white paint specimens (zinc oxide pigment, potassium silicate binder) from both leading and trailing edges were essentially unchanged by the exposure conditions. This result led to designation of the Z-93 as the baseline white thermal control paint for the International Space Station. S13G/LO used on certain experiment modules darkened under solar UV exposure. This result was expected as significant changes S13G/LO absorptance have been observed on other spacecraft and during ground-based testing.

Polyurethane-based A-276 (white) and Z-306 (black) Chemglaze paints showed significant degradation under the range of LDEF exposures: loss of binder from each paint under atomic oxygen attack, loss of pigment in the Z-306 under AO attack, and severe darkening of A276 under solar UV exposure. The white paint used for the paint buttons on the aluminum tray clamps was 1 1/2 quarts of a Dissler flattener (DX 256) for every 1/2 gallon of A-276.

Black D111 paint and SiO_x/nickel coatings performed satisfactorily. Optical properties of an aluminum leaf in epoxy binder used as a coating on the leading edge actually improved over the mission. Absorptance increased due to UV-induced darkening of the binder on trailing edge aluminum leaf coated specimens. Mechanical integrity of the leading-edge specimens was compromised but this should not be an in-service problem on spacecraft as long as no physical contact is made with the surface.

A number of panels on the Earth-facing end and an area on the McDonnell-Douglas experiment on tray F09 were coated with black chrome plate. Post-flight examination clearly showed areas of discoloration of the black chrome coating. Despite considerable effort, including optical property measurements, surface analysis, and thermal modeling, a clear and obvious mechanism to explain the discoloration pattern has not been found. Contamination has been ruled out. The tan areas were shielded by the aluminum backing from a failed aluminized Kapton blanket. The process which caused the changes is still not understood.

This summary was taken from Analysis of Materials Flown on the Long Duration Exposure Facility: Summary of Results of the Materials Special Investigation Group, NASA CR, May 1995.

The following report addresses LDEF polyurethane thermal-control materials:

J.L. Golden, Results of the Examination of the LDEF Polyurethane Thermal Control Coatings, NASA CR-4617, July 1994.

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