NASA/TM--1998-208828

Synchrotron VUV and Soft X-Ray Radiation

Effects on Aluminized Teflon ® FEP

Joyce A. Dever

Lewis Research Center, Cleveland, Ohio

Jacqueline A. Townsend

Goddard Space Flight Center, Greenbelt, Maryland

James R. Gaier

Lewis Research Center, Cleveland, Ohio

Alice I. Jalics

Cleveland State University, Cleveland, Ohio

Prepared for the

43rd International Symposium

sponsored by the Society for the Advancement of Materials and Process Engineering

Anaheim, California, May 31-June 4, 1998

National Aeronautics and

Space Administration

Lewis Research Center

November 1998

https://ntrs.nasa.gov/search.jsp?R=19990008861 2018-05-11T16:59:48+00:00Z
Acknowledgments

Research was carried out, in part, at the National Synchrotron Light Source, Brookhaven National Laboratory,

which is supported by the U. S. Department of Energy, Division of Materials Sciences and Division of Chemical

Sciences. The authors gratefully acknowledge the support of Michael Sagurton of SFA/Los Alamos National

Laboratory, and Steven Hulbert of the NSLS, BNL during experiments conducted at the NSLS. The authors also

acknowledge the following for their technical contributions to this paper: Bruce Banks of NASA Lewis Research

Center; Thomas Stueber, Edward Sechkar and Mark Forkapa of NYMA, Inc.; Demetrios Papadopoulos

of the University of Akron; and Elizabeth Gaier of Manchester College.

Trade names or manufacturers' names are used in this report for

identification only. This usage does not constitute an official

endorsement, either expressed or implied, by the National

Aeronautics and Space Admtlistration.

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SYNCHROTRON VUV AND SOFT X-RAY RADIATION EFFECTS ON ALUMINIZED

TEFLON _ FEP

Joyce A. Dever

National Aeronautics and Space Administration

Lewis Research Center

Cleveland, Ohio 44135

Jacqueline A. Townsend

National Aeronautics and Space Administration

Goddard Space Flight Center

Greenbelt, Maryland 20771

James R. Gaier

National Aeronautics and Space Administration

Lewis Research Center

Cleveland, Ohio 44135

Alice I. Jalics

Cleveland State University

Cleveland, Ohio 44115

ABSTRACT

Surfaces of the aluminized Teflon '_:FEP multi-layer thermal insulation on the Hubble Space Telescope (HST)

were tbund to be cracked and curled in some areas at the time of the second servicing mission in February

1997, 6.8 years after HST was deployed in low Earth orbit (LEO). As part of a test program to assess

environmental conditions which would produce embrittlement sufficient to cause cracking of Tefloff _' on HST.

samples of Teflon '_' FEP with a backside layer of vapor deposited aluminum were exposed to vacuum

ultraviolet (VUV) and soft x-ray radiation of various energies using facilities at the National Synchrotron Light

Source. Brookhaven National Laboratory. Samples were exposed to synchrotron radiation of narrow energy

bands centered on energies between 69 eV and 1900 eV. Samples were analyzed for ultimate tensile strength

and elongation. Results will be compared to those of aluminized Teflon _ FEP retrieved front HST alter 3.6

years and 6.8 years on orbit and will be referenced to estimated HST mission doses of VUV and soft x-ray

radiation.

1. INTRODUCTION

Since th_ Hubble Space Telescope (HST) was deployed in low Earth orbit (LEO) in April 1990, two servicing

missions have been conducted to upgrade its scientific capabilities. The first servicing mission (SM1) was

conducted in December 1993, 3.6 years after deployment. The second servicing mission (SM2) was conducted

in February 1997, 6.8 years after deployment. The HST servicing missions provided an opportunity for on-orbit

examination and retrieval of second-surface metalized Teflon _ FEP (fluorinated ethylene propylene) used as

the top layer of multi-layer insulation (MLI) blankets and on radiator surfaces. Minor cracking of FEP surfaces

on HST was first observed upon close examination of samples with high solar exposure retrieved during SMI

(1). During SM2, astronaut observations and photographic documentation revealed cracks in the FEP layer of

the MLI on both solar-facing and anti-solar facing surfaces of the telescope.

The efforts reported in this paper were conducted as part of a test program to identify the LEO environmental

constituent(s) responsible tbr cracking and embrittlement of Teflon _: FEP on HST (2). Soft x-ray radiation

from solar flares has been investigated previously as a possible cause lor mechanical properties degradation of

Teflon _' FEP (3). This paper describes an investigation of the effects of vacuum ultraviolet (VUV) and soft xray radiation on Teflon '_' FEP. Samples of aluminized Teflon _' FEP were exposed to synchrotron radiation of

various VUV and soft x-ray wavelengths between 18 nm (69 eV) and 0.65 nm (1900 eV), and doscs and

fluences were compared to those estimated for the HST mission. Synchrotron radiation exposures were

conducted using the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory (BNL).

Tensile testing was conducted on synchrotron radiation-exposed samples to determine tensile strength and

elongation.

NASA/TM--1998-208828 I
2. X-RAY AND SOLAR EXPOSURE ENVIRONMENT ON HST

Table 1 provides infi)rmation about the x-ray and solar exposure environment on HST from deploymcnt to

SMI. SM2 and end-of-life (EOL) (4-6). Radiation in the x-ray waveiength regions 0.05-0.4 nm (3-25 keV) and

0. I-(I.8 nm (I.5-12 keV) is attributed primarily to solar flares (3). Based on the x-ray fluence data for these two

wavelength regions given in Table 1, it is evident that the majority of the solar flare x-ray fluence is in the 0.4

- 0.8 nm wavelength range, or 1.5-3 keV. The data in Table I are for thc incident x-ray fluencc and do not

necessarily indicate the radiation dose absorbed by the Teflon ¢" material.

TABLE I. X-RAY AND SOLAR EXPOSURE ENVIRONMENT ON HST

X-ray fluence, 0.05-0.4 nm or 3-25 keV (J/m 2)

X-ray lluence, 0. I-0.8 nm or 1.5-12 keV (J/m 2)

Solar exposure tor solar-facing surfaces

(cquivalent sun hours)

SMI

3.6 years

14.7

SM2

6.8 years

16

4-6)

EOL

20 years

47.15

222.6 252.4 699.6

16,670 33,638 100,000

In addition to the data shown in Table 1 lbr the two regions of x-ray radiation, Reference 7 provides spectral

flux data for VUV to soft x-ray wavelengths. From these data, HST fluences for narrow wavelength bands

centered on wavelengths between 18 nm (69 eV) and 1.77 nm (700 cV), which were included in the

synchrotron exposure experiments, were calculated and are shown in Table 2. Data for the additional

synchrotron exposure energies up to 1900 eV were not available from this reference.

TABLE 2. SOFT X-RAY AND VUV FLUENCES FOR NARROW ENERGY BANDS ON HST

Estimated Fluence on HST, Assuming

Moderate Solar Activity (J/m 2)

Energy

Range, Ave.

(eV)

68.6-69.4, 69

283-297,290

490-532,510

663-742,700

Wavelength

Range, Ave.

(nm)

17.9-18.1,

18.0

Moderate Solar

Activity Flux

(,photons/cm2s) (7)

1.10E+08

4.00E+06

SMI

(!, .6 yrs. )

515

126

SM2

(6.8 yrs.)

969

238

2.00E+06

1.00E+06

133

65

251

123

EOL

(20 yrs.)

2943

722

761

373

In order to determine the radiation dose absorbed by the Teflon @layer of the MLI, it is necessary to know how

radiation is absorbed as a function of energy in Tetlon'L

3. RADIATION ABSORPTION IN TEFLON '_:'

Figure 1 shows the attenuation length of Teflon'* modeled as C2F 4 as a function of energy (8). Attenuation

length is defined as the depth into the material where the radiatio'l intensity has fallen to l/e (0.368) of its

intensity at the surface. As shown, attenuation length is dependent on energy or wavelength. The absorption

edges at approximately 290 and 700 eV are for carbon and fluorine, respectively. Crosses shown on the curve

indicate the energies used for exposure of samples to synchrotron ra_iiation, 69-1900 eV.

In order to calculate the absorbed radiation dose in Teflon -_''.it was necessary to use the fluence data for 0.05-

0.4 nm and 0.1-0.8 nm along with the data for attenuation length The equation for photon intensity at a

specific energy as a function of depth in a material, / F , is given as lollows:

IE = I,,E exp(-(p./p)x) II1

where I,,, is the incident intensity at a specific energy, ,u is the extinction coefficient, p is the density, and x is

the depth into the material. The term/-gO is referred to as the linear absorption coefficient.

NASA/TM--1998-208828 2
E

re.-

t-.

.o

-'t

e"

a)

105

104

103

102

lO_ -

100 -

10-I _

10-2

101

I I

102 103 104

Energy, eV

Figure 1.--Attenuation length of Teflon _), modeled as C2F4 (8).

The definition of attenuation length can be stated as the value of x where

IF.=/,e/e.

Substituting Equation 2 into Equation 1 gives:

/,,e/e = I,,t exp(-(it/p)x).

Solving Equation 3 for/tip gives:

or

12]

[3]

I/x=p/p 14]

attenuation length = p/I t.

Figure 1 provided x vs. energy, so, 1/x vs. energy can be obtained from the data in Figure 1. At energies above

1.5 keV, the energies provided Jbr the HST exposure environment, the I/x vs. energy data was curve-fitted to

provide the linear absorption coefficient,/.ffp, as a function of energy, E:

,u/p = 3.46xlff JE-_L' [51

Then, this was substituted into Equation I to give:

le = l,t exp((-3.46x I0_E -3l__)x). [6]

Equation 6 provides the intensity of radiation at depth x into the material for a specific energy, /_. Thercfore.

the absorbed intensity at a specific energy, AE, is given as

Ae = I,E- le 171

or

A_,= foe( I - exp((-3.46xlO _E _12).r)). [8]

Because foe and IE represent intensity, they are expressed in units of W/m 2 or Jlm2s. Therefore, they can be

described as values of x-ray flux at a specific wavelength or energy. At: is then the absorbed x-ray flux at a

NAS A/TM-- 1998-208828 3
particularenergy.TheincidentHSTx-rayfluencevaluesindicatedinTable! arereportedin unitsof J/m:

overarangeof energiesto indicatefluxintegratedovera specificnissionduration.Thiscanberepresented

bythefollowingequation:

F, =/l,,dt 191

where F,, is the incident fluence over a specific mission duration given in J/re", /,+ is the incident flux at a

specific time, and t is time. Multiplying both sides of Equation 8 by time, we obtain the following:

E_E = F,,l:( 1 - exp((-3.46x 10_E _ 12)._)) l lOl

where FaL and F,,_: are the absorbed and incident values of fluence, respectively at a specific energy. Because

fluence values in Table 1 are for the rather broad energy/wavelength bands indicated rather than for discreet

energies/wavelengths,

FOE FO.E I E

E 2 - E l

111]

Equation 11 was then substituted into Equation 10 and the result was numerically integrated over each energy

range, 1.5-12 keV and 3-25 keV, using the HST incident fluencc data from Table 1. For example, the

numerical integration approximated the absorbed fluence for the 1.5-12 keV range given by the following

equation:

12keV

F+_t+_,_v- Fo'l'5-12keV _ (I-exp((-3.46xlff)E-3_2)x))dE. 1121

..... 12-1.5

1,5keV

The absorbed x-ray radiation fluence was thus determined tbr spetific depths, x, into the Teflon '+ material.

Fluence of absorbed x-ray radiation was converted to dose. in units t)f rads, using the tbliowing equation:

Dose, rads = FA(I/p) (l/x) (I rad/(0.01 J/kg)) [131

where absorbed fluence over a particular energy range is Fa, in units of J/m"" density, ,o, is in units of kg/m_:

and thickness, x, is in units of m. Because the outer layer of MLI or HST is comprised of 127 lam thick

Teflon " FEP, absorbed radiation dose was calculated for this thickness and is shown in Table 3.

TABLE 3. X-RAY RADIATION DOSE

X-ray dose, 0.05-0.4 nm or 3-25 keV (krads)

X-ra), dose, 0.1-0.8 nm or 1.5-12 keY (krads)

ON HST FOR 127 ].tm FEP

SM1 SM2

3.6 ),ears 6.8 years

0.99 1.08

: 9.2 44.4

EOL

20 years

3.18

123

4. SYNCHROTRON RADIATION EXPOSURE CONDITIONS

Samples of second-surface aluminized Teflon + FEP were exposed t_ synchrotron radiation of various energies

between 69 eV and 19(X) eV. Two different beamlines at the NSLS _vere used to conduct experiments. As

indicated in Table 4. Beamline U16B was used to provide radiation between 69 eV and 700 eV, and Beamline

X8A was used to provide radiation between 510 eV and 1900 eV. "Iable 4 shows the energies and wave

lengths used in these experiments including the calculated bandwidt i at full-width, half-maximum and the

estimated spot size for the beam. Also shown are attenuation length; fi_r each energy, as shown in Figurc I.

As indicated by the attenuation lengths, the majority of radiation from these synchrotron radiation exposures is

deposited within the first few micrometers of material.

NASA/TM-- ,.) !998-2088,8 4
TABLE4. SYNCHROTRONRADIATIONEXPOSURECONDITIONS

NSLS

Beamline

Name

Energy

(eV)

Wavelength

(nm)

Approx.Spot

Size,hx w

(ram)

3x5

Attenuation

Length,Bm

U16B 69+_O.I 18.00_+0.026 0.033

290+ 1.7 4.28 + 0.025 3 x 4.5 0.262

700 + 10 1.77 + 0.025 3 x 4 0.403

XSA 510_+ 2.6 2.44+0.012 10 x 4 1.06

700 _+3.5 1.77 -+ 0.0089 10 x 4 0.403

1256 _+6.3 0.99 + 0.(X)5 10 x 4.5 1.74

1489 + 7.4 0.83 + 0.004 10 x 4 2.74

1900 +_9.5 0.65 -+0.003 10 x 4 5.36

5. EXPERIMENTAL PROCEDURES

5.1 Samples Samples for synchrotron radiation exposure were fabricated from TefloW" FEP of 127 lam

thickness with approximately 100 nm of vapor deposited aluminum. Samples were exposed to the synchrotron

radiation beam such that the FEP surface faced the beam and the aluminum surface was the back surface of

each sample. Samples for tensile testing were "dog bone" shaped and were die-cut with a die manufactured

according to ASTM Standard D638-95, Type V (9). For this sample size, the width of the narrow section of

the dog bone was 3.18 ram, and the gauge length was 9.53 mm. The beam size for each synchrotron energy

used is shown in Table 4 for comparison. For experiments at both beamlines, the beam covered the width of

the narrow section of the dogbone. For experiments conducted at Beamline X8A where the beam was

approximately 10 mm in height, the full gauge length of each specimen was illuminated by the beam. For

samples exposed at Beamline U16B, the lull gauge length was not covered by the beam. Additional samples

included in the experiments which were not intended for tensile testing were nominally 3 to 5 mm maximum

width and 15 mm length.

5.2 Apparatus Figure 2 shows the sample/detector holder which was able to hold up to seven pairs of

samples as shown. When pairs of samples were exposed, each pair consisted of one tensile specimen and one

non-tensile specimen.

Figure 2._Sample holder for synchrotron radiation exposure of FEP samples.

In most cases, the tensile specimen was centered on the synchrotron beam, and the other sample received the

"tail" of the synchrotron beam, typically a small fraction of the intensity provided by the beam center. Shown

at the left of the sample holder is the silicon photodiodc used to measure the synchrotron beam intensity tot

each sample exposure. The sample/detector holder was attached to a linear positioner with a movement scale

allowing positioning accurate to + 0.01 mm. Prior to installation in the vacuum chamber, distances between

the photodiode and samples were measured with digital calipers to assure accuracy in placement of the

samples in the synchrotron beam. Measurements of synchrotron beam intensity were made before and alter

each exposure and were averaged to determine photon fluence for each sample exposed. A mask was used

over the photodiode providing a measurement area 3 mm wide by 10 mm high, comparable to the gauge size

of a tensile spccimen.

NASA/TM--1998-208828 5
5.3 Tensile Testing Tensile testing was conducted to deterrrine degradation in tensile strength and

elongation for synchrotron radiation-exposed FEP samples as compared to pristine material. Sample

dimensions were described in Section 5.1. Samples exposed at Beamline X8A were tensile tested using an

Instron 4505 load frame with Instron Series IX data acquisition software. Samples exposed at Beamline UI6B

were tensile tested using an automated bench-top tensile tester and data acquisition software. A strain rate of

0.212 mm/s was used for all tests. Because samples from each beamline were tested using different

instruments at different times, results for each set of synchrotron-exposed samples were compared to a set of

pristine samples tensile tested at the same time.

6. RESULTS AND DISCUSSION

Table 5 shows results of tensile testing of synchrotron radiation-exp_)sed second surface aluminized FEP. For

each sample the exposure energy, measured fluence, absorbed dose, and comparison to orbital doses are

provided. Samples U5T and U2T were exposed to both 290 eV and 700 eV radiation, sequentially, as shown.

The objective of these experiments was to determine whether exposure to radiation at both the carbon and

fluorine absorption edges would produce synergistic degradation.

The HST EOL 0.05-0.4 nm (I.5-25 keV) doses at the attenuation length of the exposure energy were calculated

using the data in Table 1 and equations 1-11. For 69-700 eV the narrow-band energy doses for HST EOL at the

attenuation length of the exposure energy are also shown for comparison. These narrow-band energy dose

values were calculated using the data in Table 2 and equations 2, 7, 9, and 13. As shown in Table 5, in most

cases, the sample dose significantly exceeded the HST EOL dose.

The ultimate tensile strength (UTS) and elongation were measured for each tensile specimen, and data are

provided in Table 5 with the percent changes from pristine specimens. The tensile test data for pristine

specimens are given in Table 6. The tensile test data in Table 5 can be compared to the changes in tensile

strength and elongation experienced for aluminized FEP materials retrieved from HST during the first and

second servicing missions which are provided in Table 7 (10).

For most synchrotron radiation-exposed samples, some degradatkn in tensile strength and elongation was

observed. However, the degradation in tensile strength and elongation experienced by the synchrotron

radiation-exposed samples was not comparable to that demonstrated by samples retrieved from HST after 3.6

years and 6.8 years. The worst degradation in tensile strength was 30.3%, for sample XIT, which received 256

times the HST EOL x-ray dose or an equivalent of over 5000 years in space. This result can be compared to

that of an HST specimen retrieved during SMI after 3.6 years in space. This material showed a degradation in

tensile strength of 37-42%, greater than that of the worst damaged synchrotron-exposed sample. The

synchrotron radiation-exposed sample which experienced the greatest degradation in elongation was XI4T

which showed a degradation in elongation of 83%. This sample recfived an equivalent of over 1500 times the

HST EOL x-ray dose or an equivalent of over 30,000 years in space Compare this result to the complete loss

of elongation for the material retrieved from HST after 6.8 years, t is obvious from these results that at the

energies used for these synchrotron radiation exposures, VUV radiation and soft x-ray radiation were not

sufficient to cause the degradation in mechanical properties displayed by 6.8 year HST-exposed aluminized

FEP.

All synchrotron-exposed tensile specimens were examined using optical microscopy for evidence of surface

embrittlement or cracking. This effect was described in Reference 3 The only specimens showing cvidcnce of

surface cracking after tensile testing were those samples exposed :o 290 eV synchrotron radiation, samples

UIT and U4T. Figure 3 shows a photomicrograph of sample U4T a'ter tensile testing as compared to sample

U6T, exposed to 69 eV synchrotron radiation of a higher absorbed r_ diation dose. Sample U6T was comparable

to all other synchrotron-exposed specimens in that it showed no evkence of surface cracking. It is possible that

because 290 cV is at the carbon absorption edge, more severe degradation in the radiation-absorbing layer may

Occur.

NASA/TM--1998-208828 6
Sample

Label

TABLE5.

EnergyIncident

(eV) Fluence

(J/m2)

U3T 69 5304

U6T 69 5076

U4T 290 3136

U1T 290 3099

U5T 290 1583

700 1534

TENSILETESTINGOFSYNCHROTRONRADIATION-EXPOSED FEPSAMPLES

Doseatatten,length(krads)

Sample HSTEOL HSTEOL UltimateElongation% Changec_ Change in

Dose 0.05-0.8 nm Narrow Tensile (%) at in UTS c_ Elongation

Dose Energy Strength, Break from from pristine

Band Dose UTS pristine

IMPat

4.73E+06 839 2.7E+06 19.48 214 0.2 4.4

4.52E+06 17.29 176 - I 1.0 - 14.1

3.52E+05 825 5.6E+04 15.08 107 -22.4 -47.8

3.48E+05 14.76 I 14 -24.1 -44.4

1.78E+05 825 5.6E+04 > 14.34" > 134* > -26.2* > -34.6*

I. 12E+05 816 2.1 E+04

U2T 290 1611

700 1521

X6T 510 474

X 17T 700 973

X 15T 700 3055

X 16T 700 10347

X10T 1256 17982

X3T 1489 16 I

X2T 1489 821 I

XIT 1489 16123

X8T 1489 21938

XI4T 1489 95859

X4T 1900 32

X5T 1900 3014

X 12T 1900 6632

*Due to power failure, test

1.81E+05 825 5.6E+04 14.25 87,6 -26.7 -57.3

1.! ! E+05 816 2. I E+04

1.31 E+04 777 1.6E+04 22.36 649 16.0 I 1.1

7.10E+04 816 2.1E+04 16.18 434 -16.1 -25.7

2.23E+05 17.60 489 -8.7 - 16.3

7.55E+05 16.97 484 - 12.0 - 17.2

3.04E+05 742 N/A i 6.23 406 - 15.8 -30.4

1.73E+03 695 N/A 20.34 626 5.5 7.2

8.81E+04 20.56 629 6.7 7.7

1.73E+05 13.45 194 -30.3 -66.8

2.35E+05 i4.36 322 -25.5 -44.8

1.03E+06 13.85 98 -28.2 -83.2

1.76E+02 599 N/A 17.30 516 -10.3 -I 1.6

! .65E+04 19.32 596 0.2 2.0

3.64E+04 16.58 440 - 14.0 -24.6

stopped at this point prior to sample break

TABLE 6. TENSILE TESTING OF PRISTINE ALUMINIZED FEP

Specimen Description

X7T, Unexposed witness

Pristine, Avg. for 5 specimens, comparison for

U samples

Pristine, Avg. for 3 specimens, comparison for

X samples

Ultimate Tensile

Strength (MPa)

20.48

19.43 + 1.9

Elongation (%)

600.3

205 + 28

19.28 + 3.2 584 + 126

TABLE 7.

Sample

Pristine aluminized

FEP, 3 samples

SM I-retrieved MLI,

3.6 yrs., 11,339 ESH

SM2-retrieved MLI,

16.8 yrs., 33,638 ESH

TENSILE TEST DATA OF HST-EXPOSED MATERIALS (10)

Yield

Strength

(MPa)

14.1_+0.3

14.3

14.3

N/A

N/A

Ultimate Tensile

Strength, UTS

(Mpa)

26.5+1.7

15.4

16.6

13.2

2.2

% Change in

UTS from

Pristine

-42

-37

Elongation

(%)

363±25

196

116

Change in %

Elongation from

Pristine

-46

-68

-50 0 - I(X)

-92 0 - I(X)

NASA/TM-- 1998-208828 7
Figure 3.--Photomicrographs of tensile-testec, synchrotron radiationexposed samples. (a) U6T exposed to 5076 J/m 2 at 69 eV. (b) U4T

exposed to 3136 J/m2 at 290 eV.

NAS A/TM-- 1998-208828 8
7. CONCLUSIONS

Exposure to synchrotron radiation in the VUV and soft x-ray range of energies is capable of causing

degradation in the mechanical properties of Teflon _" FEP. However, FEP samples exposed to synchrotron

radiation of doses significantly greater than HST EOL doses did not show loss of tensile strength or elongation

comparable to that of the severely embrittled aluminized FEP retrieved from HST during SM2 which

experienced 6.8 years on orbit. Some evidence of wavelength-dependence of damage was observed tbr

samples exposed to 290 eV synchrotron radiation which is at the carbon absorption edge. These samples

showed surface cracking after tensile testing. Based on these results, exposure to VUV and soft x-ray radiation

alone is not sufficient to cause the severe degradation in mechanical properties observed for FEP materials

exposed to the HST environment.

8. ACKNOWLEDGMENTS

Research was carried out, in part, at the National Synchrotron Light Source, Brookhaven National Laboratory,

which is supported by the U. S. Department of Energy, Division of Materials Sciences and Division of

Chemical Sciences. The authors gratefully acknowledge the support of Michael Sagurton of SFA/Los Alamos

National Laboratory, and Steven Hulbert of the NSLS, BNL during experiments conducted at the NSLS. The

authors also acknowledge the following for their technical contributions to this paper: Bruce Banks of NASA

Lewis Research Center: Thomas Stueber, Edward Sechkar and Mark Forkapa of NYMA, Inc.; Demetrios

Papadopoulos of the University of Akron: and Elizabeth Gaier of Manchestcr College.

9. REFERENCES

1. Zuby, T. M., de Groh, K. K, Smith, D. C., "Degradation of FEP Thermal Control Materials Returned from

the Hubble Space Telescope," NASA Technical Memorandum 104627, December 1995.

2. Townsend, J. A., Hansen, P. A., Dever, J. A., and Triolo, J. J., "Analysis of Retrieved Hubble Space

Telescope Thermal Control Materials," Sci. Adv. Matl. Proc. Eng. Set., 43, 000 (1998).

3. Milintchouk, A., Van Eesbeek, M., Levadou, F. and Harper, T. "Influence of X-ray Solar Flare Radiation

on Degradation of Teflon ':_:in Space," Journal of Spacecraft and Rockets, Vol. 34, No. 4, July-August 1997,

p. 542-8.

4. NASA Memorandum from J. Barth to P. Hansen, July 7, 1997.

5. Jackson and Tull Technical Note from T. H. Gregory to P. Hansen, May 12, 1997.

6. Jackson and Tull Technical Note from T. H. Gregory to J. Townsend, June 25, 1997.

7. Tobiska, W. K., "A Brief History of Empirical Modeling of the Solar EUV Spectral Irradiance," in

Proceedings of the Workshop on the Solar Electromagnetic Radiation Study for Solar Cycle 22, Richard F.

Donnelly, ed., July 1992, pp. 338-53.

8. Calculation done interactively using Lawrence Berkeley Laboratory Center tor X-Ray Optics, Internet

Website, http://www-crxo.lbl.gov.

9. ASTM D638-95, "Standard Test Method for Tensile Properties of Plastics," 1995.

10. Dever J. A., de Groh, K. K., Townsend, J. A., Wang, L. L., "Mechanical Properties Degradation of Teflon

FEP Returned from the Hubble Space Telescope," AIAA-98-0895, presented at the A1AA 36t" Aerospace

Sciences Meeting, Reno, NV, Jan. 12-16, 1998, NASA Technical Memorandum 1998-206618.

NAS A/TM-- 1998-208828 9
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i Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office of Management and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503

1. AGENCY USE ONLY (Leave blank) 2. REPORT DATE 13. REPORT TYPE AND DATES COVERED

November 1998 Technical Memorandum

4. TITLE AND SUBTITLE

Synchrotron VUV and Soft X-Ray Radiation Effects on Aluminized Teron @ FEP

6. AUTHOR(S)

Joyce A. Dever, Jacqueline A. Townsend, James R. Gaier, and Alice I. J_lics

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Lewis Research Center

Cleveland, Ohio 44135-3191

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

5. FUNDING NUMBERS

WU-632-I A-1E--O0

8. PERFORMING ORGANIZATION

REPORT NUMBER

E-II439

10. SPONSORING/MONITORING

AGENCY REPORT NUMBER

NASA TM--1998-208828

11. SUPPLEMENTARY NOTES

Prepared for the 43rd International Symposium sponsored by the Society for the Advancement of Materials and Process

Engineering, Anaheim, California, May 31-June 4, 1998. Joyce A. Dever and James R. Gaier, NASA Lewis Research

Center, Jacqueline A. Townsend, NASA Goddard Space Flight Center, _nd Alice I. Jalics, Cleveland State University,

Cleveland, Ohio 44115-2403. Responsible person, Joyce A. Dever, org_ nization code 5480, (216) 433-6294.

12a. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified - Unlimited

Subject Categories: 27 and 18 Distribution: Nonstandard

This publication is available from the NASA Center for AeroSpace Information, (301) 621-0390.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

Surfaces of the aluminized Teflon® FEP multi-layer thermal insulation m the Hubble Space Telescope (HST) were found

to be cracked and curled in some areas at the time of the second servicirg mission in February 1997, 6.8 years after HST

was deployed in low Earth orbit (LEO). As part of a test program to ass,'ss environmental conditions which would

produce embrittlement sufficient to cause cracking of Teflon® on HST, ;amples of Teflon® FEP with a backside layer of

vapor deposited aluminum were exposed to vacuum ultraviolet (VUV) and soft x-ray radiation of various energies using

facilities at the National Synchrotron Light Source, Brookhaven Nation_ I Laboratory. Samples were exposed to synchrotron radiation of narrow energy bands centered on energies between 69 rV and 1900 eV. Samples were analyzed for

ultimate tensile strength and elongation. Results will be compared to th )se or aluminized Tel]on® FEP retrieved from

HST after 3.6 years and 6.8 years on orbit and will be referenced to estifaated HST mission doses of VUV and soft x-ray

radiation.

14. SUBJECT TERMS

Synchrotron Vacuum Ultraviolet; Soft X-ray radiation; Teflon @ degradation

17. SECURITY CLASSIFICATION

OF REPORT

Unclassified

NSN 7540-01-2.80-5500

18. SECURITY CLASSIFICATION

OF THIS PAGE

Unclassified

19. SECURIT' CLASSIFICATION

OF ABST_ACT

Ur classified

15. NUMBER OF PAGES

15

!16. PRICE CODE

A03

20. LIMITATION OF ABSTRACT

Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std. Z39-18

298-102