MIR Solar Array Returned Experiment

(SARE) Archive System

NASA Langley Research Center
Hampton, Virginia

Analyses of Mir Solar Array Handrail Samples

Kim K. de Groh
NASA Lewis Research Center
Terry R. McCue
Dynacs Engineering

November 4, 1998

Two solar array samples retrieved from Mir after 10 years in space have been evaluated. One is a piece of a rigid handrail (labeled "zero-point"). This sample, which is a thermal control white paint coated aluminum rectangular hollow bar, was discolored brown on all sides of the exterior surfaces. The brown contamination or stain appears darker on one side (side A) than the other side (side B). The handrail can be seen at the top of panel 8, as seen in the Image Index under Panel 8, photos, image 98e03093 and 98e03096. The second sample is a piece of "flexible handhold tape over-wrap." This woven fabric tape was wrapped around the flexible handhold such that half of the width of the sample was shielded from space exposure, and appears white, while the exposed half is discolored brown. A section of the flexible handhold which shows the tape over-wrap can be seen in the Image Index under Photos, Panel Photos (2^nd page), image back2. Samples were evaluated using optical microscopy (OM), field emission scanning electron microscopy (FESEM) and energy dispersive spectroscopy (EDS). Solar absorptance and room temperature emittance were also obtained

The results of optical property characterization are listed in Table 1. The surface browning has increased the solar absorptance of the samples significantly. The white paint on the rigid handrails is believed to be the Russian AK-573 paint.¹ The solar absorptance of unexposed AK-573 is 0.294.¹ The solar absorptance of the darkened handrail paint is 0.54-0.56. The flexible over-wrap fabric has an increase in absorptance of 0.14 in the exposed area compared to the unexposed area.

Table 1. Optical Properties of Mir Samples

Flexible Handhold Tape Fabric

Optical microscopy examination of the exposed, brown region of the handhold tape fabric revealed micro-crazing of a contamination layer. This crazed layer is not present on the protected, unexposed region. EDS spectra for the unexposed fabric area show the presence of only C and a small amount of O, as shown in Figure 1. The exposed brown stained area of the fabric was imaged with FESEM and revealed a very thick layer of contaminant which has spalled off in some areas, as shown in Figure 2. EDS analysis of the image in Figure 3, shows very large peaks of Si and O, and a small C peak (see Figure 3). The thick contaminant layer is clearly oxidized silicon. A higher magnification image of Figure 2 revealed a near cross-section area of the contaminant layer. The thickness of the contaminant layer is approximately 1.6m m in this area. Figure 4 shows an area where the contaminant layer has spalled off while in space, and atomic oxygen has eroded the fibers. This shows that the contaminant is so thick it has become a source of particulate contaminant in space.

Figure 1. EDS spectra of an unexposed area of the flexible handhold tape over-wrap fabric.

Figure 2. FESEM image of the brown contaminant layer on the exposed flexible handhold tape fabric.

Figure 3. EDS spectra of the contaminated area of the flexible handhold tape over-wrap fabric shown in Figure 2. The contaminant is oxidized silicon.

Figure 4. FESEM image showing atomic oxygen erosion at locations where the contaminant layer has spalled off.

Handrail Paint Sample

The darker brown side (side A) of the handrail specimen was clearly crazed. A flake of paint containing the brown stain was easily removed from the handrail sample for FESEM imaging. The sample was broke into two pieces that exposed a clean white cross-section surface for analysis. The EDS spectra of the cross-sectioned paint chip is shown in Figure 5. The spectra indicates that the paint consists primarily of Zn, O and C, with small amounts of Si, Ti and Al. An image of the brown stained surface is shown in Figure 6. There appears to be a contaminant layer that is crazing and lifting off the sample in areas. Figure 7 shows the EDS spectra of the region shown in Figure 6. The following are present: O, Si, C, Ti, and Zn, with small amounts of Al and P (based on peak heights). EDS point spectra were taken on a flaked-off contaminant piece (point A) and on an area where the contaminant layer appears to be missing (point B). The contaminant layer was found to be composed primarily of oxidized silicon, similar to the handhold fabric contaminant.

Figure 5. EDS spectra of the cross-sectioned paint chip sample.

Figure 6. FESEM image of the brown stained area on the surface of the rigid handrail sample. The contaminant layer is crazed and lifting away, or spalled off in areas.

Figure 7. EDS spectra of contaminated paint chip surface image shown in Figure 6.

Summary

Analyses of two samples from the Mir solar array, a piece of flexible handhold tape over-wrap fabric and a piece of white paint coated rigid handrail, have been conducted. Optical microscopy and FESEM imaging have shown brown stained areas to have thick layers of contamination that has crazed and spalled off the surface in regions. An area where the cross-section of the handhold tape contaminant is visible shows the film to be approximately 1.6 mm thick. Energy dispersive spectroscopy revealed that the brown contaminant on both samples is composed of oxidized silicon with very little carbon content. There is no silicon present on the unexposed fabric, and very small amounts in the white paint. Therefore, the contaminant layer on both samples is due to silicone contamination from other spacecraft sources while on orbit, which has been oxidized by atomic oxygen present in the low Earth orbit environment. FESEM images of the handhold fabric also show areas where the contaminant layer has spalled off the organic fibers and atomic oxygen erosion has occurred. This implies that flakes of the thick contaminant coating have spalled off while in space and therefore have been sources of particulate contamination.

References

1. J. Visentine, et. al., MIR Solar Array Return Experiment, AIAA 99-0100, to be presented at the 37^th AIAA Aerospace Sciences Meeting, Reno, NV, January 11-14, 1999.

Note: A full report on this work is being submitted to the 34^th Intersociety Energy Conversion Engineering Conference (IECEC) being held August 1-5, 1999 in Vancouver, British Columbia, Canada.

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