Kim K. de Groh and Deborah L. Waters

Glenn Research Center, Cleveland, Ohio

Jelila S. Mohammed

Goddard Space Flight Center, Greenbelt, Maryland

Bruce A. Perry

Ohio Aerospace Institute, Brook Park, Ohio

Bruce A. Banks

Alphaport, Inc., Cleveland, Ohio

Analyses of Hubble Space Telescope

Aluminized-Tefl on Insulation Retrieved

After 19 Years of Space Exposure

NASA/TM—2012-217644

October 2012
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Kim K. de Groh and Deborah L. Waters

Glenn Research Center, Cleveland, Ohio

Jelila S. Mohammed

Goddard Space Flight Center, Greenbelt, Maryland

Bruce A. Perry

Ohio Aerospace Institute, Brook Park, Ohio

Bruce A. Banks

Alphaport, Inc., Cleveland, Ohio

Analyses of Hubble Space Telescope

Aluminized-Tefl on Insulation Retrieved

After 19 Years of Space Exposure

NASA/TM—2012-217644

October 2012

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

10th International Space Conference on Protection of Materials and Structures From the

Space Environment (ICPMSE-10J)

cosponsored by ITL, MDA, CSA, JAXA, Kobe University Graduate School of Engineering,

and the Society for Promotion of Space Science

Bankoku-Shinryokan, Okinawa, Japan, June 12–17, 2011
Acknowledgments

The authors would like to thank Ben Reed and the Hubble Space Telescope Project Offi ce at the NASA Goddard Space Flight Center 

(GSFC) for their support of this project. We greatly appreciate the opportunity to analyze this unique material and provide the results 

to the space community. We would also like to thank the following people from GSFC for their contributors to testing and analysis:

Bryan Abbamonte, Josh Abel, David Hughes, Kristin McKittrick, Aparna Boddapati, Debbie Thomas, and Mollie Powell.

Available from

NASA Center for Aerospace Information

7115 Standard Drive

Hanover, MD 21076–1320

National Technical Information Service

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Available electronically at http://www.sti.nasa.gov

Trade names and trademarks are used in this report for identifi cation 

only. Their usage does not constitute an offi cial endorsement, 

either expressed or implied, by the National Aeronautics and 

Space Administration.

Level of Review: This material has been technically reviewed by technical management. 
NASA/TM—2012-217644 1 

Analyses of Hubble Space Telescope Aluminized-Teflon Insulation 

Retrieved After 19 Years of Space Exposure 

Kim K. de Groh and Deborah L. Waters 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Jelila S. Mohammed 

National Aeronautics and Space Administration 

Goddard Space Flight Center 

Greenbelt, Maryland 20771 

Bruce A. Perry 

Ohio Aerospace Institute 

Brook Park, Ohio 44142 

Bruce A. Banks 

Alphaport, Inc. 

Cleveland, Ohio 44135 

Abstract 

Since its launch in April 1990, the Hubble Space Telescope (HST) has made many important 

observations from its vantage point in low Earth orbit (LEO). However, as seen during five servicing 

missions, the outer layer of multilayer insulation (MLI) has become successively more embrittled and has 

cracked in many areas. In May 2009, during the 5th servicing mission (called SM4), two MLI blankets 

were replaced with new insulation pieces and the space-exposed MLI blankets were retrieved for 

degradation analyses by teams at NASA Glenn Research Center (GRC) and NASA Goddard Space Flight 

Center (GSFC). The MLI blankets were from Equipment Bay 8, which received direct sunlight, and 

Equipment Bay 5, which received grazing sunlight. Each blanket contained a range of unique regions 

based on environmental exposure and/or physical appearance. The retrieved MLI blanket’s aluminizedTeflon (DuPont) fluorinated ethylene propylene (Al-FEP) outer layers have been analyzed for changes in 

optical, physical, and mechanical properties, along with space induced chemical and morphological 

changes. When compared to pristine material, the analyses have shown how the Al-FEP was severely 

affected by the space environment. This paper reviews tensile properties, solar absorptance, thermal 

emittance, x-ray photoelectron spectroscopy (XPS) data and atomic oxygen erosion values of the 

retrieved HST blankets after 19 years of space exposure. 

Introduction 

The HST was launched on April 25, 1990 into LEO as the first mission of NASA’s Great 

Observatories program. It is a telescope capable of performing observations in the near-ultraviolet, visible 

and near-infrared wavelengths. The HST was designed to be serviced on-orbit to upgrade scientific 

capabilities. Five servicing missions (SM) have taken place, with the last mission occurring in May 2009 

after 19 years in space. During servicing mission 2 (SM2), in February 1997, severe cracking of the 5 mil 

Al-FEP outer layer of the multilayer insulation (MLI) blankets was observed on the light shield (LS), 

forward shell and equipment bays of the telescope (Refs. 1 and 2). Patches of 2 mil thick (50.8 μm) 

Al-FEP were placed over the worst cracks in MLI on Equipment Bays 8 and 10 (2 patches were attached 

to each bay). 
NASA/TM—2012-217644 2 

In May 2009 during the 5th servicing mission (called SM4), two degraded MLI blankets that were 

originally installed on the telescope were replaced with new insulation pieces, called New Outer Blanket 

Layers (NOBLs), and the space exposed MLI blankets were brought back for analysis by teams at NASA 

Glenn Research Center and NASA Goddard Space Flight Center. No other spacecraft material has been 

retrieved and analyzed after having this length of space exposure. The two blankets retrieved during SM4 

included Equipment Bay 8 MLI, which received direct sunlight, and Equipment Bay 5 MLI, which 

received grazing sunlight. Also retrieved were remnants of the two patches that were placed over cracked 

areas on Bay 8 during SM2. The retrieved MLI blankets’ Al-FEP outer layers were found to be highly 

degraded and have been analyzed for changes in optical, physical, and mechanical properties, along with 

space induced chemical and morphological changes and heat induced changes. This paper reviews the 

tensile properties, solar absorptance, thermal emittance, XPS data and atomic oxygen erosion values of 

the retrieved HST blankets after 19 years of space exposure. 

Materials and Environmental Exposure 

HST SM4 Bays 5 and 8 MLI 

The Bays 5 and 8 MLI blankets originally installed on HST (exposed to space for 19.1 years), and 

2 mil Al-FEP patches installed on Bay 8 on February 18, 1997 during SM2 (exposed to space for 

12.2 years) were retrieved by astronauts on May 18, 2009 during SM4. As can be seen in the illustration 

in Figure 1, Bay 8 is located 15° from the +V3 solar facing axis, and therefore is almost directly facing 

the sun. Bay 5 faces towards the +V2 solar array drive arm direction, and at 75° from the +V3 direction, 

receives grazing sunlight. The environmental effects that cause degradation of the MLI are primarily 

temperature cycling, solar radiation, particle radiation, and atomic oxygen. 

Environmental Exposure 

The sun exposure on each bay was determined by the science pointing profile of HST. The attitude 

profile between 1/1/00 and SM4 was analyzed to determine the “typical” attitude of HST. The results were 

then extrapolated to provide estimates of the sun exposure since launch. Equivalent hours of sun exposure 

(ESH) of the telescope from deployment to SM4 are estimated as 111,000 hr, based on time in orbit, 

average time exposed to the sun per orbit, and length of each orbit. Based on the attitude profile from 2000 

and SM4, and extrapolating over mission life, Bay 5 was exposed to ~24,300 ESH and the unpatched and 

patched areas of the Bay 8 MLI were exposed to ~89,300 and ~30,300 ESH, respectively. 

Figure 1.—Locations and orientations of Bays 5 and 8 

on HST (+V3 is the solar facing axis). 

(Sun direction) 
NASA/TM—2012-217644 3 

The HST underwent an estimated 110,000 thermal cycles overall, from deployment to SM4. The 

range of temperatures seen by Bays 5 and 8 vary greatly, because they are dependent on HST attitude and 

environmental heating variables. Thermal Desktop was used to model the Bays 5 and 8 MLI and simulate 

the general thermal cycling behavior. Bay 5 MLI temperatures were estimated to range from –175 to 0 °C 

and the Bay 8 temperatures were estimated to range from –175 to 40 °C, for the attitude and orbit 

configurations modeled. 

The x-ray fluence for solar facing surfaces was computed to be 641.1 J/m2 between 1-8 Å and 

43.1 J/m2

 between 0.5-4 Å. Data for x-ray fluence is based on x-ray flux data from the Geosynchronous 

Operational Environmental Satellites (GOES) for the time period of launch (1990) through SM2 

(February 1997) (Ref. 3). For SM2 through SM4, the x-ray fluence was estimated assuming an average 

11-year solar cycle (Ref. 3). 

Electron and proton fluence from solar wind particles trapped in Earth’s magnetic field have been 

calculated from deployment until December 9, 1999 using NASA’s proton and electron models, AP-8 and 

AE-8, respectively (Ref. 3). The data for SM4 were extrapolated from these prior data, and indicated the 

Bays 5 and 8 MLI received an electrons fluence of 5.6×1013 particles/cm2

 for electrons 40 keV, and a

proton fluence of 5.4×1010 particles/cm2 for protons 40 keV. 

The atomic oxygen fluence was computed for the duration of the HST mission over the period of time 

from deployment to SM4. This was accomplished by adding: 1) the prediction over the period of time 

from deployment to SM1 as predicted by SAIC’s version 5.0 Environmental Work Bench, which uses 

MSIS-86 atmospheric model, to 2) a prediction based on orbital and atmospheric data from NASA 

Goddard for SM1 to SM4. The parameters used in the SM1 to SM4 fluence calculation included altitude, 

atmospheric density, and orbital velocity corrected for the Earth’s atmosphere co-rotation. Based on these 

calculations the total ram fluence was 2.61×1021 atoms/cm2

. If the surfaces of Bay 8 are 15° from solar 

facing, then the fluence would be ~25.8 percent of the ram fluence or ~6.73×1020 atoms/cm2

. But, as the 

surfaces are solar facing but randomly tipped (always with Bay 8 somewhat towards the sun), then the 

fluence is decreased an additional factor of 2/ resulting in the probable fluence of ~4.28×1020 atoms/cm2

. 

Because the Bay 5 faces towards the +V2 direction and is 75° off the solar facing axis, the fluence was 

estimated as ~28.0 percent of the ram fluence, or 7.30×1020 atoms/cm2

. As the surfaces are randomly 

tipped, the fluence would be decreased by 2/ resulting in a probable fluence of ~4.65×1020 atoms/cm2

. 

Experimental Procedures 

A DDL Inc. Model 200Q Electromechanical Test System was used to determine the loaddisplacement data from which elongation to failure (percent elongation) and ultimate tensile strength 

(UTS) were determined. The tensile samples were sectioned to the specifications defined in American 

Society for Testing and Materials (ASTM) Standard D-638 for Type V tensile specimens (Ref. 4). Care 

was taken to avoid cracks and impact sites. The initial grip distance was set at 25.4 mm and the test speed 

was 12.7 mm/min. 

Solar absorptance and thermal emittance measurements were taken at both GSFC and GRC. Both 

as-retrieved and heat-treated samples were measured at GRC. Initially, heat treatment was planned to be 

conducted at two temperatures: 120 and 200 °C (the highest temperature reached for very tightly curled 

insulation (Refs. 2 and 5)). But, finally, only the effect of moderate on-orbit heating (120 °C) was 

evaluated. Heating was conducted for 96 hr as prior data indicates a minimum of 72 hr is necessary to 

heating effects to be stabilized (Ref. 6). 

Cary 5000 spectrophotometers equipped with Spectralon integrating spheres were used to measure 

total reflectance from 250 to 2500 nm at an 8° angle of incidence at both GSFC and GRC. Absorptivity 

data were integrated with respect to the air mass zero solar spectrum to obtain solar absorptance. Samples 

at GRC were measured with an Al spacer backed by a single layer of sample of the quilted Al/Kapton/Al 

inner film (Region 8.15) replicating the on-orbit configuration. 
NASA/TM—2012-217644 4 

Emissivity measurements were obtained at GSFC using a Gier-Dünkle DB-100 InfraRed 

Reflectometer following the ASTM E408-71 standard test method. The normal emittance (εn) of the 

surface was measured from 5 to 40 m while at room temperature. Three measurements were taken for 

each sample, with the exception of Bay 8 Region 3, which was highly delaminated, hence only one 

measurement was taken. Emissivity measurements were obtained at GRC using a Surface Optics 

Corporation Model SOC 400T Reflectometer. The SOC 400T measures the directional reflectance of 

surfaces over a large spectral range, 2 to 25 m, to obtain the directional thermal emittance over a large 

temperature range. Automatic integration of reflectivity data in the infrared with respect to blackbody 

curves is used to calculate total emittance for a selectable temperature range. Data were obtained at 293, 

313, and 393 K. The samples were placed in the sample holder face-down with an aluminum spacer and 

were backed by a sample of the quilted Al/Kapton/Al MLI inner layer. 

Samples for thickness measurements were mounted in epoxy, and then SiC paper and diamond slurry 

were used to polish the cross sections. Thickness measurements were taken at three locations along each 

sample’s cross-section, using a scanning electron microscope (SEM). 

Atomic oxygen erosion yield (Ey) of the HST samples (cm3

/atom) was calculated in two separate 

ways, by mass loss and by thickness loss measurements. The mass of 12.7 mm diameter circular samples 

were measured using a Mettler M3 balance and compared to the mass of pristine material to determine 

mass loss. The mass loss was divided by the sample area (1.366 cm2

), density and the atomic oxygen 

fluence to determine Ey. Erosion yield determined by thickness loss was computed by dividing the 

thickness loss in cm by the atomic oxygen fluence. 

Samples were analyzed for elemental composition using a M-Probe X-Ray Photoelectron 

Spectrometer. Three locations on samples from various regions were run using a general survey scan, 

with a spot size of 800 m, to determine atomic percent composition. 

Results and Discussion 

To retrieve the MLI blankets, astronaut John Grunsfeld unpeeled each blanket from its Velcro secured 

border, then folded the blankets and placed them into EVA storage bags. Although great care was taken in 

retrieval planning and execution, the retrieval process did cause cracking at fold seams, introducing 

handling cracks that were not present on-orbit prior to retrieval. 

The Bays 5 and 8 MLI blankets are shown in the on-orbit photos taken during SM4 in Figures 2(a) 

and (b), respectively. As can be seen, the Bay 5 MLI has several large cracks extending from the two 

rectangular radiator areas. The Bay 8 MLI also has several very large cracks, and one side of the largest 

crack on Bay 8 curled up into a cone-like roll, as seen in Figure 2(b). Also, the Bay 8 patches were seen to 

be highly degraded with the majority of the Al-FEP completely gone. Upon post-retrieval visual 

inspection, the Bay 8 MLI appeared significantly more degraded than the Bay 5 MLI, as the Bay 8 MLI 

was broken into many pieces after removing it from the EVA bag, unfolding it and laying it flat again. In 

fact, the Bay 8 Al-FEP outer layer needed to be reassembled post-flight like a puzzle. 

Exposure Regions 

The retrieved Bays 5 and 8 MLI blankets contained a range of unique regions which were identified 

based on environmental exposure and/or physical appearance and given assigned numbers. For example, the 

Bay 8 MLI that was not covered by patch material and was exposed to the space environment for the full 

19.1 years had areas with three distinct appearances: shiny areas, hazy-white areas and areas where the Al 

was delaminated. These regions were defined as Regions 8.1, 8.2, and 8.3, respectively. Also, as mentioned, 

one of the Bay 8 outer layer Al-FEP cracked areas (not covered by patch material) curled up into a cone-like 

roll. In the curled region, the backside Al was exposed to the space environment, therefore this material 

heated to a higher temperature on-orbit than the nominal space-facing FEP because of the low emittance of 

the aluminized surface. This “curled” area was divided into two regions: a tightly curled region (8.7) and a 

loosely curled region (8.8), as those two regions may have heated differently on-orbit. 
NASA/TM—2012-217644 5 

 (a) (b) 

Figure 2.—On-orbit photos of Equipment Bays 5 and 8 just prior to retrieval 

during SM4: (a) Bay 5, and (b) Bay 8 (composite photo of two on-orbit 

images) with large cracks circled. 

TABLE 1.—HST SM4 BAYS 5 AND 8 

REGION DEFINITIONS 

HST material 

bay region 

Description 

Pristine (P) Pristine 5 mil Al-FEP 

5.1 Nominal/Shiny 

5.4 Nominal/Al-delaminated 

8.1 Nominal/Shiny 

8.2 Nominal/White hazy 

8.3 Nominal/Al-delaminated 

8.7 Cone/Tight curl 

8.8 Cone/Loose curl 

8.11 Patched SM2-SM4 

8.13 Patched SM2-SM3B 

8.15 Protected inner layer 

(Al/Kapton/Al) 

Some areas of the patches installed during SM2 eventually degraded exposing the underlying MLI to the 

space environment once again as observed during SM3B and SM4. Therefore, the MLI under the patched 

areas are divided into two regions: region patched during SM2 and exposed by SM3B (SM2-SM3B, 

patched 5.1 years, called 8.13), and region patched during SM2 and still covered at SM4 (SM2-SM4, 

patched 12.2 years, called 8.11). 

A total of 10 different regions were identified on Bay 5 (R1-R10), and 15 different regions were 

identified on Bay 8 (R1-R15) and four regions identified on the retrieved Patches (R16-19). The regions 

selected for testing are defined in Table 1. During sectioning of samples from the blankets, care was taken 

to avoid any cracks or imperfections in the samples which would affect the tests. 

The delaminated regions of Bays 5 and 8 appear very different, and were likely caused by different 

factors. Bay 5 delaminated samples have a checkerboard-like pattern of delaminated areas on a surface 

that has predominately retained its Al backing. Bending these samples indicated that there is no tendency 

for more Al to flake off. In contrast, Bay 8 delaminated samples have small patches of Al sprinkled 

throughout a mostly delaminated surface and additional Al separates from the FEP on handling the 

samples. 
NASA/TM—2012-217644 6 

Tensile Properties 

The average UTS and percent elongation at failure of the HST and pristine Al-FEP are shown in 

Figures 3(a) and (b), respectively. Because of the degree of embrittlement of the HST samples, many 

broke while being punched out or handled prior to testing. Others were tested but failed at pre-existing 

cracks, causing a premature break. Data from premature breaks were not included in the average. Five 

samples from Region 8.7 were tested, and all broke prematurely, thus no data are reported. 

(a) 

(b) 

Figure 3.—Tensile properties of pristine and HST Al-FEP: (a) Average UTS 

and (b) Average elongation at failure. 

 
NASA/TM—2012-217644 7 

All HST material was extremely embrittled. Elongation at failure was reduced from 255 percent for 

pristine material to 8.5 percent for Bay 5 nominal/shiny material and to 1.4 percent for Bay 8 nominal/ 

shiny material. The Bay 8 Al-FEP, which had a significantly higher solar exposure and on-orbit thermal 

cycling temperature, was found to fracture very easily with handling, like thin brittle glass. All regions 

also experienced large decreases in UTS, from 22.3 MPa for pristine Al-FEP to 12.7 and 3.3 MPa for 

Bays 5 and 8 nominal/shiny material, respectively. Although the standard deviation is large compared to 

some of the absolute values, both the UTS and the elongation at failure appears to correlate with the 

amount of solar exposure a sample received. For example, the solar facing Bay 8 material is more 

embrittled than the solar grazing Bay 5 material, and the elongation at failure of Bay 8 material is 

proportional to the amount of time that it was patched. 

Heating pristine Al-FEP marginally decreased its strength, and had no effect on elongation. The 

Bay 8 MLI was too embrittled to conduct studies to assess the effect of heating, but heating Bay 5 

Region 1 material at 120 °C for 96 hr further reduced both the elongation and strength of the samples. 

This supports the mechanism proposed for degradation in which solar radiation and solar heating play 

synergistic roles. 

Optical and Thermal Properties 

The as-retrieved and 120 °C-heated solar absorptance values obtained at GSFC and GRC are shown 

in Figure 4. It should be noted that the pristine Al-FEP absorptance obtained at GRC (0.15) was slightly 

higher than the value obtained at GSFC (0.13). This is attributed to calibration differences between the 

two instruments; hence comparisons should only be made between data taken on the same instrument. 

As-retrieved samples from both GSFC and GRC experienced an increase in solar absorptance, compared 

to pristine Al-FEP, with the exception of Bay 8 Region 3 (delaminated region), which was measured at 

GSFC without the inner layer. The GSFC absorptance of Bay 5 was slightly higher (0.16) than pristine 

Al-FEP (0.13), while Bay 8 had a wide range of absorptance values, with the greatest absorptance for 

Bay 8 Region 13 (0.27). This is the region that was patched between SM2 and SM3B, and then exposed 

again to space. The data trends for absorptance changes are consistent for both GSFC and GRC, with the 

Bay 8 hazy-white region (Region 2) and the patched regions (Regions 11 and 13) having the greatest 

increases in solar absorptance. 

Figure 4.—As-retrieved and 120 C (96 hr) heated solar absortpance values. 

 
NASA/TM—2012-217644 8 

Figure 5.—As-retrieved and heated emittance values. 

As stated previously, the GRC samples were measured with a piece of the inner layer embossed 

Al/Kapton/Al to best replicate the optical properties in space. As might be expected, the reflectance of the 

inner layer was found to have the biggest impact on the solar absorptance of the delaminated regions 

(5.4 and 8.3), increasing the absorptance significantly as compared to the GSFC data without the inner 

layer. Heating was found to increase the solar absorptance of the pristine Al-FEP by 0.09. The Bay 8 

Al-FEP experienced similar increases due to heating (0.09-0.11), with the regions that were covered by 

patches increasing even more (0.12-0.14). Although the Bay 5 thermal cycled to a lower maximum 

temperature on-orbit (0 °C) than Bay 8 (40 °C), the Bay 5 Al-FEP experienced very small increases in 

absorptance with heating as well. The reason for this is currently unknown. 

The as-retrieved and heated thermal emittance values obtained at GSFC and GRC are plotted in 

Figure 5. The GSFC thermal emittance values were found to decrease for all samples except Bay 5 

Region 1 and Bay 8 Region 11 (the region patched between SM2 and SM4). Emittance loss is typically 

associated with thickness loss of FEP, but for Bay 8 Regions 7 and 8, samples may have experienced 

additional emittance change due to excessive heating on-orbit or possibly from contamination. For 

example, if the emittance of silicone is lower than FEP then a thick enough layer of silicone 

contamination could decrease the emittance of the FEP. Similar to the GSFC emittance values, the GRC 

emittance was found to decrease for all samples except Bay 5 Region 1 (also Bay 5 Region 4) and Bay 8 

Region 11, the region patched between SM2 and SM4. Heating had little impact on the emittance values 

of the retrieved HST MLI. 

X-Ray Photoelectron Spectroscopy (XPS) 

The XPS analyses for pristine Al-FEP and Regions 5.1, 8.1, 8.2, and 8.11 are provided in Table 2. As 

expected, the pristine Al-FEP is comprised of C (33.4 percent) and F (66.7 percent). The Bay 8 nominal 

regions (1 and 2) were similar with an increase in C (39 percent), a decrease in F (51 percent) and the 

presence of O (6 percent), N (2 percent) and Si (0.4-1.2 percent). Bay 8 Region 11, which was patched 

from SM2-SM4 had a high concentration of C, possibly due to contamination from the Velcro patch. 

Surprisingly, Bay 5 was found to have a significant amount of Si contamination with the presence of 

20 percent Si and 36 percent O. The back of the solar arrays are coated with DC 93-500 silicone and 

because Bay 5 faces towards the +V2 solar array direction, the DC 93-500 is most likely the source of 

contamination. As only one area of Bay 5 was tested, additional tests could determine if silicone 

contamination is wide spread or localized on the blanket. This would be good to determine, particularly as 

silicone contamination could impact Ey values along with optical and thermal results. 
NASA/TM—2012-217644 9 

TABLE 2.—XPS RESULTS FOR ATOMIC PERCENT COMPOSITION 

HST SM4 

material bay 

region 

Atomic % F/C Ratio 

C N O F Si 

Pristine 33.27 0.00 0.00 66.73 0.00 2.01 

5.1 19.44 1.12 36.36 22.56 20.52 1.16 

8.1 39.19 2.31 6.35 50.87 1.29 1.30 

8.2 39.50 2.12 5.43 52.55 0.41 1.33 

8.11 59.41 4.10 18.70 15.14 2.65 0.25 

In a study by de Groh et al. (Ref. 7), samples sectioned from Al-FEP circular thermal shields covering 

the bi-stem booms on the second set of HST solar arrays (retrieved after 8.25 years of space exposure) 

were examined with scanning electron microscopy for surface morphology and with energy dispersive 

spectroscopy (EDS) for surface chemistry. Pristine Al-FEP and solar-facing and anti-solar-facing thermal 

shield surfaces did not have any evidence of contamination, with only C and F peaks observed. However, 

a crazed surface texture was observed on one of the solar-grazing samples. The EDS data indicated the 

crazed texture is due to silicone contamination. Hence, the Bay 5 silicone contamination is consistent with 

contamination found on the solar-grazing surface of the retrieved solar array thermal shields, which is 

probably caused by contamination from the DC 93-500 silicone coating on the anti-solar side of the solar 

arrays. 

Atomic Oxygen Erosion Yield (Ey) 

Atomic oxygen Ey values determined through mass loss for the probable AO fluence are provided in 

Table 3. Because the AO fluence for Bay 8 Regions 7, 8, 11, and 13 were not computed, Ey values were 

not determined for these regions. The Ey value of the HST SM4 Bay 8 nominal shiny FEP 

(Ey = 1.37×10–23 cm3

/atom) was found to be an order of magnitude greater than for the Bay 5 nominal 

shiny FEP (Ey = 1.43×10–24 cm3

/atom). This is attributed to the significantly higher dose of solar 

radiation, combined with the higher on-orbit temperature, for the solar facing blanket. These data provide 

evidence that solar exposure plays a significant role in the AO erosion of FEP. 

Table 3 also provides the average Al-FEP thickness, Ey values calculated based on thickness loss and 

the ratio of thickness loss Ey to mass loss Ey. The two Ey methods gave consistent results, with thickness 

loss Ey ~16 percent higher than mass loss Ey. The reason for this difference is not known. 

TABLE 3.—ATOMIC OXYGEN EROSION YIELD COMPARISON 

HST 

material bay 

region 

Description Mass loss Ey

(cm3

/atom) 

Average 

thickness 

(cm) 

Thickness lossa

Ey 

(cm3

/atom) 

Ratio of 

Ey(TL)/ 

Ey(ML) 

8.1 Shiny 1.17E-23 0.00722 1.37E-23 1.17 

8.2 White hazy 8.22E-24 0.00886 9.84E-24 1.20 

8.3 Al-delaminated 1.12E-23 0.00769 1.29E-23 1.15 

5.1 Shiny 1.27E-24 0.01241 1.43E-24 1.12 

P Pristine ----------- 0.01308 ----------- ---- a

Based on 130.1 m original thickness 

 
NASA/TM—2012-217644 10 

The Ey values of the HST SM4 FEP were found to be orders of magnitude greater than those 

determined from shuttle flight experiments such as the Evaluation of Oxygen Interaction with Materials 

III, reported from 5.0×10–26 cm3

/atom (Ref. 8) to 1.8×10–25 cm3/atom (Ref. 9), the Long Duration 

Exposure Facility, determined to be 3.37×10–25 cm3

/atom for ram facing surfaces (Ref. 10) and Materials 

International Space Station Experiments 2 (MISSE 2), determined to be 2.00×10–25 cm3

/atom for ram 

facing surfaces (Ref. 11). Again, this is thought to be attributed to the effects caused by the significantly 

higher solar exposure of the HST materials. 

Summary and Conclusions 

Two MLI blankets retrieved from the HST during SM4 after 19.1 years in space have been analyzed 

for space-induced mechanical, optical and thermal properties. In addition, atomic oxygen Ey values were 

determined. The blankets experienced different solar exposures and thermal cycling temperature ranges, 

due to their positions on the telescope and each had regions with differing types of damage. 

The mechanical properties of the blanket’s Al-FEP outer-layers were extremely degraded. The Bay 8 

Al-FEP, which had a significantly higher solar exposure and on-orbit thermal cycling temperature, was 

more embrittled than the solar-grazing Bay 5 insulation, and was found to fracture like thin brittle glass. 

Areas on Bay 8 which had been protected by a patch for a period of time on-orbit were slightly less 

embrittled than areas which had been exposed for all 19.1 years. However, even the least brittle samples 

still had only 3 percent of the elongation at failure of pristine materials. Heating pristine Al-FEP 

marginally decreased its strength, and had no effect on elongation. The Bay 8 MLI was too embrittled to 

conduct studies to assess the effect of heating, but heating Bay 5 Region 1 material reduced both the 

elongation and strength of the samples. The results of these tests support the proposed model for on-orbit 

degradation of Al-FEP, in which radiation causes chain scission of the polymers, and thermal heating to 

high temperature extremes causes the Al-FEP to become much more embrittled. 

All space exposed samples experienced an increase in solar absorptance, as compared to pristine 

Al-FEP, with the exception of Bay 8 Region 3, which is the region where the Al has delaminated from the 

FEP. The greatest increase in absorptance occurred in the patched areas, likely due to contamination from 

the patches. The thermal emittance values were found to decrease for all samples except Bay 5 Region 1 

and Bay 8 Region 11, the region patched between SM2 and SM4. 

The Ey value of the HST SM4 Bay 8 nominal shiny FEP (1.37×10–23 cm3

/atom) was found to be an 

order of magnitude greater than for the Bay 5 nominal shiny FEP (1.43×10–24 cm3

/atom). This is 

attributed to the significantly higher dose of solar radiation, combined with the higher on-orbit 

temperature, for the solar facing blanket. The silicone contamination on Bay 5 may have decreased the Ey 

somewhat, but further studies are needed to assess this. The Ey values of the HST SM4 FEP were found 

to be orders of magnitude greater than those determined from prior flight missions, such as shuttle 

experiments (0.5-1.8×10–25 cm3

/atom), LDEF (3.37×10–25 cm3/atom) and MISSE 2 experiments 

(2.00×10–25 cm3

/atom). These results support the belief that the effects of solar exposure play a significant 

role in the AO erosion of FEP. 

References 

1. Hansen, P.A., Townsend, J.A., Yoshikawa, Y., Castro, D.J., Triolo, J.J. and Peters, W.C., SAMPE 

International Symposium, 43, 570, (1998). 

2. Townsend, J.A., Hansen, P.A., Dever, J.A., de Groh, K.K., Banks, B.A., Wang L. and He, C., High 

Perform. Polym. 11, 81-99 (1999). 

3. Dever, J.A., de Groh, K.K., Banks, B.A., Townsend, J.A., Barth, J.L., Thomson, S., Gregory, T. and 

Savage, W., High Performance Polymers, 12, 125-139 (2000). 

4. American Society for Testing and Materials ASTM D 638-95, “Standard Test Method for Tensile 

Properties of Plastics,” 1995. 

5. de Groh, K.K. and Martin, M.J. Spacecraft & Rockets, 41 (3), 366-372 (2004). 
NASA/TM—2012-217644 11 

6. de Groh, K.K., Gaier, J.R., Hall, R.L., Espe, M.P., Cato, D.R., Sutter, J.K. and Scheiman, D.A., 

High Performance Polymers 12, 83-104 (2000). 

7. de Groh, K.K., Finlay, K.A. and Snyder, A., High Performance Polymers, 20 (2008) 410-428. 

8. Koontz, S.L., Leger, L.J., Visentine, J.T., Hunton, D.E., Cross, J.B. and Hakes, C.L., J. Spacecraft 

and Rockets, 32 (3), 483-495 (1995). 

9. Rutledge, S.K., Banks, B.A. and Cales, M., NASA TM 106622; also AIAA-94-2628 (1994). 

10. Banks, B.A., Chapter 4 in Modern Fluoropolymers: High Performance Polymers for Diverse 

Applications, edited by J. Scheirs, John Wiley & Sons Ltd, 1997. 

11. de Groh, K.K., Banks, B.A., McCarthy, C.E., Rucker, R.N., Roberts, L.M. and Berger, L.A., High 

Perform. Polymers, 20, 388-409 (2008). 
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Analyses of Hubble Space Telescope Aluminized-Teflon Insulation Retrieved After 19 Years 

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14. ABSTRACT

Since its launch in April 1990, the Hubble Space Telescope (HST) has made many important observations from its vantage point in low 

Earth orbit (LEO). However, as seen during five servicing missions, the outer layer of multilayer insulation (MLI) has become successively 

more embrittled and has cracked in many areas. In May 2009, during the 5th servicing mission (called SM4), two MLI blankets were 

replaced with new insulation pieces and the space-exposed MLI blankets were retrieved for degradation analyses by teams at NASA Glenn 

Research Center (GRC) and NASA Goddard Space Flight Center (GSFC). The MLI blankets were from Equipment Bay 8, which received 

direct sunlight, and Equipment Bay 5, which received grazing sunlight. Each blanket contained a range of unique regions based on 

environmental exposure and/or physical appearance. The retrieved MLI blanket’s aluminized-Teflon (DuPont) fluorinated ethylene 

propylene (Al-FEP) outer layers have been analyzed for changes in optical, physical, and mechanical properties, along with space induced 

chemical and morphological changes. When compared to pristine material, the analyses have shown how the Al-FEP was severely affected 

by the space environment. This paper reviews tensile properties, solar absorptance, thermal emittance, x-ray photoelectron spectroscopy 

(XPS) data and atomic oxygen erosion values of the retrieved HST blankets after 19 years of space exposure. 

15. SUBJECT TERMS

Hubble Space Telescope (HST); Thermal control insulation; Space environment; Extraterrestrial radiation; Environmental 

degradation; Polymer; Embrittlement; Absorptance; Emittance; Tensile properties 

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