Black molecular adsorber coatings for spaceflight applications

Abstract

The molecular adsorber coating is a new technology that was developed to mitigate the risk of on-orbit molecular contamination on spaceflight missions. The application of this coating would be ideal near highly sensitive, interior surfaces and instruments that are negatively impacted by outgassed molecules from materials, such as plastics, adhesives, lubricants, epoxies, and other similar compounds. This current, sprayable paint technology is comprised of inorganic white materials made from highly porous zeolite. In addition to good adhesion performance, thermal stability, and adsorptive capability, the molecular adsorber coating offers favorable thermal control characteristics. However, low reflectivity properties, which are typically offered by black thermal control coatings, are desired for some spaceflight applications. For example, black coatings are used on interior surfaces, in particular, on instrument baffles for optical stray light control. Similarly, they are also used within light paths between optical systems, such as telescopes, to absorb light.Recent efforts have been made to transform the white molecular adsorber coating into a black coating with similar adsorptive properties. This result is achieved by optimizing the current formulation with black pigments, while still maintaining its adsorption capability for outgassing control. Different binder to pigment ratios, coating thicknesses, and spray application techniques were explored to develop a black version of the molecular adsorber coating. During the development process, coating performance and adsorption characteristics were studied. The preliminary work performed on black molecular adsorber coatings thus far is very promising. Continued development and testing is necessary for its use on future contamination sensitive spaceflight missions.

Preliminary testing of NASA’s Molecular Adsorber Coating technology for future missions to Mars

“…The James Webb Space Telescope (JWST), among many other missions, have also extensively used the MAC technology as an effective contamination getter during vacuum chamber testing of critical flight and optical ground support hardware. [8][9][10][11][12][13][14] 2. APPROACH…”

“…[8][9][10][11][12][13][14] These tests were executed by saturating the coating with a known contaminant source at a specified temperature within the confines of a test apparatus in a vacuum chamber. [8][9][10][11][12][13][14] A similar test configuration is used to perform this two phase preliminary study. The samples were placed in two trays in the upper compartment of the test apparatus.…”

“…Previous experiments have studied the molecular adsorption capacity of the MAC technology using a volatile, long-chain hydrocarbon species called stearyl alcohol, and a complex, silicone-based compound called DC-704 diffusion pump oil. [8][9][10][11][12][13][14] Consequently, the contaminant source that was selected for this preliminary study was a plasticizer.…”

Using NASA’s Molecular Adsorber Coating technology during thermal vacuum testing to protect critical laser flight optics on the ATLAS instrument

“…For example, MAC plates were installed in the Far Ultraviolet (FUV) instrument of NASA's Ionospheric Connection Explorer (ICON) mission to address on-orbit material outgassing within the instrument. [10][11][12][13][14] MAC has also been extensively used in ground-based applications as a passive getter material during TVAC testing to mitigate the risk of molecular contamination on many NASA missions. For example, MAC panels were installed throughout the Chamber A test facility at NASA Johnson Space Center (JSC) during the four major cryogenic vacuum tests for the James Webb Space Telescope (JWST) from 2014 to 2017.…”

“…The experimental data shown in Figure 11 demonstrate that the vacuum molecular adsorption capacity of MAC is directly proportional to the total coating thickness. [10][11][12][13][14][15][16] The MAC samples that were used for the two TVAC tests measured a coating thickness of 6.2 mils and a coating area of 95.2 cm 2 . Therefore, from Figure 11, the molecular adsorption capacity per sample is approximately 2.4 mg/cm 2 .…”