MISSE 2 PEACE Polymers Experiment Atomic Oxygen Erosion Yield Error Analysis more

NASA/TM—2010-216903 MISSE 2 PEACE Polymers Experiment Atomic Oxygen Erosion Yield Error Analysis Catherine E. McCarthy Hathaway Brown School, Shaker Heights, Ohio Bruce A. Banks Alphaport, Inc., Cleveland, Ohio Kim K. de Groh Glenn Research Center, Cleveland, Ohio November 2010 NASA STI Program . . . in Profile Since its founding, NASA has been dedicated to the advancement of aeronautics and space science. The NASA Scientific and Technical Information (STI) program plays a key part in helping NASA maintain this important role. The NASA STI Program operates under the auspices of the Agency Chief Information Officer. It collects, organizes, provides for archiving, and disseminates NASA’s STI. The NASA STI program provides access to the NASA Aeronautics and Space Database and its public interface, the NASA Technical Reports Server, thus providing one of the largest collections of aeronautical and space science STI in the world. 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Banks Alphaport, Inc., Cleveland, Ohio Kim K. de Groh Glenn Research Center, Cleveland, Ohio National Aeronautics and Space Administration Glenn Research Center Cleveland, Ohio 44135 November 2010 Acknowledgments We would like to acknowledge and thank former students Jon Gummow of Ohio Aerospace Institute, Doug Wright of Cleveland State University, and PEACE Team students for making and characterizing flight and back-up samples. We gratefully acknowledge Patty Hunt of Hathaway Brown School for making it possible for the students to be a part of this project. Finally, we would like to express our sincere appreciation to the MISSE Project Office at NASA Langley Research Center and Gary Pippin, formerly of Boeing, for providing the unique opportunity to be a part of the MISSE program. Trade names and trademarks are used in this report for identification only. Their usage does not constitute an official endorsement, either expressed or implied, by the National Aeronautics and Space Administration. Level of Review: This material has been technically reviewed by technical management. Available from NASA Center for Aerospace Information 7115 Standard Drive Hanover, MD 21076–1320 National Technical Information Service 5301 Shawnee Road Alexandria, VA 22312 Available electronically at http://gltrs.grc.nasa.gov MISSE 2 PEACE Polymers Experiment Atomic Oxygen Erosion Yield Error Analysis Catherine E. McCarthy Hathaway Brown School Shaker Heights, Ohio 44122 Bruce A. Banks Alphaport, Inc. Cleveland, Ohio 44135 Kim K. de Groh National Aeronautics and Space Administration Glenn Research Center Cleveland, Ohio 44135 ABSTRACT Atomic oxygen erosion of polymers in low Earth orbit (LEO) poses a serious threat to spacecraft performance and durability. To address this, 40 different polymer samples and a sample of pyrolytic graphite, collectively called the PEACE (Polymer Erosion and Contamination Experiment) Polymers, were exposed to the LEO space environment on the exterior of the International Space Station (ISS) for nearly four years as part of the Materials International Space Station Experiment 1 & 2 (MISSE 1 & 2). The purpose of the PEACE Polymers experiment was to obtain accurate mass loss measurements in space to combine with ground measurements in order to accurately calculate the atomic oxygen erosion yields of a wide variety of polymeric materials exposed to the LEO space environment for a long period of time. Error calculations were performed in order to determine the accuracy of the mass measurements and therefore of the erosion yield values. The standard deviation, or error, of each factor was incorporated into the fractional uncertainty of the erosion yield for each of three different situations, depending on the post-flight weighing procedure. The resulting error calculations showed the erosion yield values to be very accurate, with an average error of ±3.30 percent. 1. INTRODUCTION 1.1 MISSE 2 Polymer Erosion and Contamination Experiment (PEACE) Polymers Spacecraft in the low Earth orbit (LEO) environment (between 200 and 2000 km above the surface of the Earth) endure extremely harsh conditions, including exposure to ultraviolet, x-ray, and charged particle radiation; micrometeoroids and debris; and atomic oxygen, diatomic oxygen photodissociated by short wavelength ultraviolet radiation from the sun. Atomic oxygen erosion of polymers in LEO poses a serious threat to spacecraft performance and durability. Therefore in order to design durable high-performance spacecraft systems, it is essential to understand the atomic oxygen erosion yield (E, the volume loss per incident oxygen atom, in cm3/atom) of polymers being considered for spacecraft applications. NASA/TM—2010-216903 1 MISSE 2 Figure 1. MISSE 2 PEC 2 Tray 1, containing the PEACE Polymers experiment attached to the ISS, exposed to space from August 16, 2001 to July 30, 2005. Forty polymer samples (including two Kapton H polyimide atomic oxygen fluence witness samples) and pyrolytic graphite, collectively called the PEACE (Polymer Erosion and Contamination Experiment) Polymers, were exposed to the LEO space environment on the exterior of the ISS as part of the Materials International Space Station Experiment 1 & 2 (MISSE 1 & 2).1-3 The PEACE Polymers experiment was flown in MISSE Passive Experiment Container 2 (PEC 2) on the ram-facing tray (Tray 1) in sample tray E5. MISSE PEC 2 (MISSE 2) was attached to the exterior of the ISS Quest Airlock, as shown in Figure 1. The one-inch-diameter samples encountered atomic oxygen and solar and charged particle radiation during a 3.95-year exposure to the LEO environment from August 16, 2001 to July 30, 2005, when the experiment was successfully retrieved via spacewalk during Discovery’s STS-114 Return to Flight mission. The purpose of the MISSE 2 PEACE Polymers experiment was to obtain accurate mass loss measurements of passive samples exposed to atomic oxygen in space to combine with ground measurements in order to accurately calculate the atomic oxygen erosion yield of a wide variety of polymeric materials exposed to the LEO space environment for a long period of time.1-3 The data obtained could then help explain the dependence of erosion yield upon polymer chemistry for predictive tool development. Figures 2 and 3 show pre-flight and post-flight photos, respectively, of the MISSE 2 PEACE Polymers experiment tray containing the 41 samples. NASA/TM—2010-216903 2 Figure 2. Pre-flight photograph of the MISSE 2 PEACE Polymers experiment. Abbreviations are defined in Table 1. Figure 3. Post-flight photograph of the MISSE 2 PEACE Polymers experiment. The 40 different materials (41 samples) tested included those commonly used for spacecraft applications, such as Teflon FEP, as well as more recently developed polymers, such as high temperature polyimide PMR-15 (polymerization of monomer reactants), and pyrolytic graphite, which was included for more diverse chemistry. The atomic oxygen fluence for the experiment tray was found to be 8.43 x 1021 atoms/cm2 based on the average of the two fluence witness samples.1-3 The total equivalent sun hours (ESH) for the E5 tray was estimated to be 6,300 ESH.1-4 The base-plate thermal cycling temperature range for MISSE 2 was nominally between +40°C and -30°C, with occasional short-term excursions to more extreme temperatures.*,4 Results of x-ray photoelectron spectroscopy (XPS) contamination analysis of two MISSE 2 sapphire witness samples in sample tray E6 (located next to tray E5) indicated the experiment had received very little contamination; the sapphire witness samples sustained only extremely thin silica contaminant layers, one 1.3 nm thick and one 1.4 nm thick.5 * Details of atomic oxygen fluence calculations, the specific polymers flown, flight sample fabrication, solar and ionizing radiation environmental exposure, and pre-flight and post-flight characterization techniques are presented in Refs. 1-3. Additional details on environmental exposure are provided by Pippin in Ref. 4. NASA/TM—2010-216903 3 In any experiment, it is critical to determine the accuracy of the data obtained. To address this, the error in each polymer’s experimental erosion yield value was calculated using equations for fractional uncertainty derived from the equation used to find erosion yield. 1.2 Erosion Yield The equation to find the erosion yield (E) of a polymer calculates the volume lost per incident atomic oxygen atom: 4·∆ · · · (1) where ΔM is mass loss (g), ρ is the polymer density (g/cm3), and D is the exposed diameter of the polymer (cm). F is the atomic oxygen fluence (atoms/cm2), which is how many atoms of atomic oxygen came into contact with the polymer during the period of exposure. Two Kapton H witness samples were used to calculate the fluence because Kapton H has a well-established erosion yield in LEO, 3.0 x 10-24 cm3/atom.6 The atomic oxygen fluence for the samples can be calculated by solving Equation 1 for F and using the Kapton H mass loss value and density. The fluence was based on the frontal exposed area of each sample.† 1.3 Fractional Uncertainty Fractional uncertainty, also called relative uncertainty or percent error, is a way of quantifying the error of a data value. In this investigation the fractional uncertainty represents the fractional standard deviation of the values and is calculated by dividing the standard deviation of the value by the value itself. The general equation for fractional uncertainty in atomic oxygen erosion yield is   1 · i · (2) where E is atomic oxygen erosion yield and xi is the ith variable in the equation for erosion yield. The complete equation derivations are explained in Section 4. 2. MATERIALS A list of the different materials exposed to atomic oxygen on the MISSE 2 PEACE polymer experiment is given in Table 1, along with the material abbreviation, trade name(s), and material thickness. † It is believed that the 45° slanted edges of the aluminum sample holders contributed to a slight increase in fluence around the perimeters of the samples, causing some to erode through only around the edge; however, since this was the case for all of the samples, no further calculations needed to be done to correct for this anomalous effect. NASA/TM—2010-216903 4 Table 1. Materials Included in the MISSE 2 PEACE Polymers Experiment. Material Acrylonitrile butadiene styrene Allyl diglycol carbonate Amorphous fluoropolymer Cellulose acetate Chlorotrifluoroethylene Crystalline polyvinylfluoride with white pigment Epoxide or epoxy Ethylene-chlorotrifluoroethylene Ethylene-tetrafluoroethylene copolymer Fluorinated ethylene propylene High temperature polyimide resin Perfluoroalkoxy copolymer resin Poly-(p-phenylene terephthalamide) Poly(p-phenylene-2 6-benzobisoxazole) Polyacrylonitrile Polyamide 6 or Nylon 6 Polyamide 66 or Nylon 66 Polybenzimidazole Polybutylene terephthalate Polycarbonate Polyetheretherketone Polyetherimide Polyethylene Polyethylene oxide Polyethylene terephthalate Polyimide Polyimide (BPDA) Polyimide (PMDA), sample 1 Polyimide (PMDA), sample 2 Polyimide (PMDA) Polymethyl methacrylate Polyoxymethylene; acetal; polyformaldehyde Polyphenylene isophthalate Polypropylene Polystyrene Polysulphone Polytetrafluoroethylene Polyurethane Polyvinyl fluoride Polyvinylidene fluoride Pyrolytic graphite Abbrev. ABS ADC AF CA Cycolac CR-39, Homalite H-911 Teflon AF 1601 Clarifoil, Tenite Acetate, Dexel Trade Name(s) Thickness (mils) 5 31 2 2 5 1 88-92 3 3 2 12-14 2 2.2 1 2 2 2 2 3 10 3 10 2 Alkox E-30 Mylar A-200 LaRC CP1 (CP1-300) Upilex-S Kapton H Kapton H 29 2 3 1 5 5 5 2 10 2 20 2 2 2 2 1 3 80 CTFE Neoflon CTFE M-300, Kel-F PVF-W White Tedlar TWH10BS3 EP ETFE FEP PI PFA PBO PAN PA 6 PBI PBT PC PEEK PEI PE PEO PET PI PI PI PI Hysol EA 956 Tefzel ZM Teflon FEP (round robin) PMR-15 Teflon PFA CLP (200 CLP) Balanced biaxial film Barex 210 Akulon K, Ultramid B Celazole PBI GE Valox 357 PEEREX 61 (P61) Victrex PEEK 450 Ultem 1000 ECTFE Halar PPD-T Kevlar 29 fabric PA 66 Maranyl A, Zytel PI Kapton HN PMMA Plexiglas, Lucite, Acrylite (Impact Mod.) POM PPPA PP PS PSU PTFE PU PVF PVDF PG Delrin (natural) Nomex Aramid Paper Type 410 Polypropylene Type C28 Trycite 1000, Trycite Dew Thermolux P1700-NT11, Udel P-1700 Chemfilm DF 100 Dureflex PS 8010 Tedlar TTR10SG3 Kynar 740 NASA/TM—2010-216903 5 3. EXPERIMENTAL PROCEDURES 3.1 Mass Loss Measurements For both pre- and post-flight mass measurements, all samples were vacuum-desiccated at 60100 mtorr for a minimum of four days and then weighed with a Mettler M3 Balance. Records were kept of time under vacuum, sequence of weighing, and room temperature and humidity.1-3 The same sequence and procedures used for the pre-flight measurements were repeated postflight. 3.2 Density Measurements A material’s theoretical density, provided by the manufacturer, is not always accurate because of variation among different sheets of the polymer. To obtain the densities of the exact materials used in the experiment, a process known as density column measurement was used. A density gradient column was created in a 50-mL buret with solvents of either cesium chloride (CsCl) and water (H2O), for less dense polymers, or carbon tetrachloride (CCl4) and bromoform (CHBr3), for more dense polymers. Glass standards of known densities were placed in the column and allowed to settle, and then small pieces of various polymers were placed in the columns. A curve was fit to the positions and relative known densities of the glass standards. Plotting the positions of the test polymers on this curve yielded density values for each material.1-3 3.3 Diameter Measurements The MISSE 2 PEACE polymers were fabricated into one-inch (2.54-cm) diameter discs using a double bow punch cutter and an Arbor press. Although the intended diameter of the samples was precisely one inch, the samples were flown in a tray with a metal lid that slightly overlapped the edge of each polymer, so to account for the overlap as well as for slight variations in the size of the openings, 10 diameter measurements were taken of each sample tray opening at different positions using a digital micrometer. The average of these 10 measurements was used as the sample diameter. This provided a more exact value for the respective exposed diameter for each sample.1-3 3.4 Sample Stacking MISSE 1 & 2 was originally planned as a one-year mission, and enough layers of each polymer were stacked to last 1.5 years, based on estimated erosion yield data.1-3 This set of layers was collectively called “flight sample part A.” Retrieval of MISSE 1 & 2 was significantly delayed due to the Columbia accident; the experiments were retrieved on July 30, 2005, during Discovery’s STS-114 Return to Flight mission. Because of the delay, the PEACE Polymers received nearly four years of space exposure. Fortunately, most of the polymers survived the 47month exposure to LEO conditions because a second set of sample layers, collectively referred to as “flight sample part B,” had been placed behind flight sample part A, giving a total sample thickness that, based on estimated erosion yields, would last for three years. Flight sample part A and flight sample part B of each polymer were placed together into one stack to form the entire flight sample, as shown in Figure 4. NASA/TM—2010-216903 6 Flight Sample Part A (enough layers to survive 1.5 years) Flight Sample Part B (enough additional layers to survive a total of 3 years) Figure 4. Illustration of the flight sample setup. 3.5 Mass Loss Situations As previously mentioned, each flight sample included two sets of sample layers: part A was enough material to theoretically last for 1.5 years in space, and the additional layers of part B extended the time to three years. Each flight sample also had a corresponding identical “backup” sample (including both parts A and B) that was kept on the ground as a control. Though flight sample parts A and B were not separated during flight, they were separated for pre- and postflight weighing. Due to mission time constraints, part B of each sample was not weighed preflight, and so a theoretical value for the pre-flight mass of part B was calculated: the pre-flight mass of flight sample part A, MF, and the pre-flight mass of control sample part A, MC, were used to calculate the average mass per layer, MA, which was multiplied by the number n of layers in flight sample part B to get part B’s theoretical pre-flight mass, n·MA. There were three different situations for post-flight sample weighing, so three different equations to determine mass loss were required. Mass loss (ΔM) is a factor in calculating the erosion yield E of a polymer (see Equation 1), and so it was also necessary to develop three different equations for fractional uncertainty of the erosion yield. The different mass loss equations were simply substituted into the equation for erosion yield, and then from each of the three resulting equations an equation for fractional uncertainty was derived to calculate the percent error for that situation. In the first situation (see Figure 5), referred to as Situation 1, either only one sample layer was flown, or the atomic oxygen eroded through only some of the layers in flight sample part A, and all of flight sample part B was still pristine. Because flight sample part A and flight sample part B were weighed separately pre-flight, in this situation only part A needed to be weighed post-flight and compared with its pre-flight mass, so to minimize error, the terms for pre- and post-flight mass for flight sample part B were omitted from the Situation 1 mass loss equation: ∆ (3) where MF is the pre-flight mass of flight sample part A and MF' is the post-flight mass of part A. Therefore, the Situation 1 erosion yield equation is: 4· · NASA/TM—2010-216903 7 · · (4) Pre-Flight (pristine) Flight Sample Part A Post-Flight partially eroded through Flight Sample Part B pristine Figure 5. Illustration of Situation 1 sample erosion. In Situation 2 (see Figure 6), atomic oxygen erosion occurred through all of the layers of flight sample part A and some of flight sample part B. Pre-Flight (pristine) Flight Sample Part A completely eroded through Post-Flight Flight Sample Part B partially eroded through Figure 6. Illustration of Situation 2 sample erosion. In this situation, flight sample parts A and B were able to be separated to be weighed post-flight. However, because flight sample part B was not weighed pre-flight, its theoretical pre-flight mass was used. Therefore, the Situation 2 equation for mass loss is: ∆ · (5) where, again, MF and MF' are the pre- and post-flight mass values, respectively, of flight sample part A; n·MA is the theoretical pre-flight mass of flight sample part B; and ME' is the post-flight mass of part B. The erosion yield equation for Situation 2 is: 4· · · · · (6) NASA/TM—2010-216903 8 In Situation 3 (see Figure 7), the sample layers were stuck together and fragmented and were too fragile to separate without losing particles of the material and therefore compromising the erosion yield data. Pre-Flight (pristine) Flight Sample Part A Partially eroded through Flight Sample Part B Post-Flight Figure 7. Illustration of Situation 3 sample erosion. Because of this, flight sample parts A and B were weighed together post-flight. Therefore, the Situation 3 mass loss equation is: ∆ · (7) where MF is the pre-flight mass of flight sample part A, n·MA is the theoretical pre-flight mass of flight sample part B, and MS' is the post-flight mass of the entire flight sample. The Situation 3 erosion yield equation is: 4· · · · · (8) One of the variables in the erosion yield equations is atomic oxygen fluence, F, which is itself found from an equation (the erosion yield equation (see Equation 1)) rearranged. Because this F value was also based on a series of measurements, the equation for F needed to be substituted into the erosion yield equations so that the error calculations could take into account all sources of error. The equation for the fluence of the Kapton fluence witness samples is: 4·∆ · · · (9) But the atomic oxygen fluence value used in the experiment was actually the average of the two F values of the two Kapton H witness samples that were flown. This needed to be taken into account as well; the expression for the average of the two fluence values is found as follows:   1 2 4·∆ · · · · 4·∆ · · 2 · 4 · · ∆ ∆ NASA/TM—2010-216903 9 This expression for FAVG K is then substituted into the equation for sample erosion yield: 4·∆ · · ·   4·∆ · · · 4 2 · ∆ · ∆ 2·∆ · · ∆ · · ∆ (10) Therefore, the erosion yield equations for the three situations are now: 2· · 2· · 2· · · · · ∆ · · ∆ · ∆ ∆ · (11) · ∆ · · · (12) ∆ ∆ (13) In the final equations for fractional uncertainty, 3.6 Atomic Oxygen Fluence Uncertainty ∆ is replaced by the variable R. Table 2 shows the values for mass loss, density, erosion yield, exposed diameter, and the corresponding uncertainty values for each of these variables, for the two Kapton fluence witness samples. The erosion yield for Kapton H polyimide was assumed to be 3.0 x 10-24 cm3/atom6 with a probable error of ±0.05 x 10-24 cm3/atom, which is a standard deviation error of ±7.41 x 10-26 cm3/atom (or 0.024700, a ±2.5 percent fractional uncertainty). Table 2. Kapton H Witness Sample Measurement and Uncertainty Values. Kapton H Sample # 1 2 ΔM K (g) 0.124785 0.129219 δ ΔM K (g) 0.0000513 0.0000808 ρK 3 δρ K 3 (g/cm ) (g/cm ) 1.42725 0.0077 DK (cm) 2.0986 2.1342 δD K (cm) 0.00582 0.00410 EK 3 δE K 3 (cm /atom) (cm /atom) 3.00E-24 7.41E-26 δE K /E K 0.024700 NASA/TM—2010-216903 10 4. FRACTIONAL UNCERTAINTY EQUATION DERIVATIONS AND RESULTS The equations for fractional uncertainty in erosion yield were derived from the previous three erosion yield equations using partial derivatives. In all of the following derivations, ∂x is the partial derivative of x, δx is the uncertainty of x, and is the fractional uncertainty of x. The following variable definitions apply to all of the derived equations: E = erosion yield, cm3/atom ΔM = mass loss, g ρ = density, g/cm3 D = diameter of exposed area of sample, cm F = atomic oxygen fluence, atoms/cm2 MF = pre-flight mass of flight sample part A, g MF' = post-flight mass of flight sample part A, g n·MA = theoretical pre-flight mass for flight sample part B, g ME' = post-flight mass of flight sample part B, g MS' = post-flight mass of flight sample parts A and B weighed together, g A subscript of K refers to the value corresponding to the Kapton fluence witness samples, and a subscript of S refers to the value corresponding to the flight sample in question. 4.1 Fractional Uncertainty Equation Derivations for Situation 1 Using Equation 11, the equation for Situation 1 erosion yield, the equation for fractional is derived through the following process. uncertainty in erosion yield for Situation 1 Term one: x1 = MF 1 · · · 2· · ∆ · ∆ · · · 2· · ∆ · ∆ · ∆ Term two: x2 = MF' 1 · · · 2· · ∆ · ∆ · · · · 2· ∆ · ∆ · ∆ Term three: x3 = ρS 1 · · · 2· · ∆ · ∆ · · 2· · · ∆ · ∆ · · Term four: x4 = DS 1 · · · 2· · ∆ · ∆ · · 4· · · ∆ · ∆ · · 2· NASA/TM—2010-216903 11 Term five: x5 = ρK 1 · · · 2· · ∆ · ∆ · · 2· · · ∆ · ∆ · Term six: x6 = EK 1 · · · 2· · ∆ · ∆ · · 2· · · ∆ · ∆ · Term seven: x7 = ΔMK1 1 · · ∆ · ∆ 2· · ∆ · ∆ · · · 2· · ∆ ∆ · · · · ∆ ∆ · Term eight: x8 = ΔMK2 1 · · ∆ · ∆ 2· · ∆ · ∆ · · · 2· · ∆ ∆ · · · · ∆ ∆ · Term nine: x9 = DK1 1 · · · 2· · ∆ · ∆ · · 4· · · ∆ ·∆ ∆ · · · · 2·∆ · · Term ten: x10 = DK2 1 · · · 2· · ∆ · ∆ · · 4· · · ∆ ·∆ ∆ · · · · 2·∆ · · Therefore the equation for fractional uncertainty in erosion yield for Situation 1 is: 2· ∆ ∆   2·∆ · · 2·∆ · · ∆ · ∆ · (14) Table 3 shows the mass loss, density, exposed diameter, corresponding uncertainty values, and calculated fractional uncertainty for each polymer in Situation 1. NASA/TM—2010-216903 12 Table 3. Situation 1 Fractional Uncertainty in Erosion Yield. Material Abbrev. ABS ADC AF CTFE EP FEP PAN PEO PFA PG PI (Upilex-S) PI (PMR-15) POM PP PPD-T PS PTFE PVF-W δM F (g) 0.000042 0.000036 0.000004 0.000005 0.000140 0.000002 0.000066 0.000089 0.000079 0.002890 0.000009 0.000065 0.000041 0.000020 0.000041 0.000058 0.000002 0.000022 δM F' (g) 0.000020 0.000036 0.000003 0.000012 0.000220 0.000084 0.000025 0.000022 0.000005 0.000100 0.000003 0.000034 0.000018 0.000003 0.000023 0.000001 0.000001 0.000012 ΔM (g) 0.033861 0.267295 0.012352 0.052949 0.140720 0.012479 0.047281 0.066395 0.010785 0.027730 0.038127 0.118887 0.378378 0.072357 0.026790 0.115947 0.008938 0.004714 ρ (g/cm ) 1.0500 1.3173 2.1463 2.1327 1.1150 2.1443 1.1435 1.1470 2.1383 2.2200 1.3866 1.3232 1.3984 0.9070 1.4422 1.0503 2.1503 1.6241 3 δρ (g/cm ) 0.0074 0.0040 0.0086 0.0086 0.0079 0.0086 0.0228 0.0028 0.0086 0.0074 0.0212 0.0040 0.0233 0.0007 0.0017 0.0079 0.0086 0.0518 3 D (cm) 2.1093 2.1228 2.0972 2.1246 2.1283 2.0949 2.1040 2.1288 2.0980 2.1321 2.1225 2.1187 2.1146 2.1211 2.1140 2.1123 2.1062 2.0860 δD (cm) 0.0058 0.0033 0.0034 0.0030 0.0057 0.0039 0.0054 0.0045 0.0052 0.0050 0.0049 0.0018 0.0030 0.0062 0.0061 0.0045 0.0043 0.0043 δE/E 0.027017 0.025824 0.025975 0.025927 0.027020 0.026890 0.032801 0.025948 0.027248 0.107496 0.030056 0.025696 0.030556 0.026127 0.026193 0.026884 0.026089 0.041361 4.2 Fractional Uncertainty Equation Derivations for Situation 2 Using Equation 12, the equation for Situation 2 erosion yield, the equation for fractional uncertainty in erosion yield in Situation 2 is derived through the following process. One of the variables seen above in the Situation 2 equation for erosion yield, n·MA, was found from two different measurements: MA was found by averaging the mass of each layer of that flight sample’s part A and control group over the total number of layers, N. So, as with the fluence equation, the equation for MA must be substituted into the erosion yield equation to account for all sources of error. The equation for MA is: 1 · · 1 · (15) This expression for δMA will be substituted into term 3 of the error equation for this situation. Term one: x1 = MF 1 · · · 2· · ∆ · ∆ · · · · 2· · ∆ · ∆ · ∆ NASA/TM—2010-216903 13 Term two: x2 = MF' 1 · · · 2· · ∆ · ∆ · · · · · 2· ∆ · ∆ · ∆ Term three: x3 = MA 1 · · · 2· · ∆ · ∆ · · · · 2 · · ∆ · ∆ · · ∆ Term four: x4 = ME' 1 · · · 2· · ∆ · ∆ · · · · · 2· ∆ · ∆ · ∆ Term five: x5 = ρS 1 · · · 2· · ∆ · ∆ · · · 2· · · ∆ · ∆ · · · Term six: x6 = DS 1 · · · 2· 2· · ∆ · ∆ · · · 4· · · ∆ · ∆ · · · Term seven: x7 = ρK 1 · · · 2· · ∆ · ∆ · · · 2· · · ∆ · ∆ · · Term eight: x8 = EK 1 · · · 2· · ∆ · ∆ · · · 2· · · ∆ · ∆ · · Term nine: x9 = ΔMK1 1 · · ∆ · ∆ 2· ∆ · · ∆ · ∆ · · · 2· · · ∆ · ∆ · · · · ∆ NASA/TM—2010-216903 14 Term ten: x10 = ΔMK2 1 · · ∆ · ∆ 2· ∆ · · ∆ · ∆ · · · 2· · · ∆ · ∆ · · · · ∆ Term eleven: x11 = DK1 1 · · · 2· 2·∆ · · · ∆ · ∆ · · · 4· · · ∆ · ∆ ·∆ · · · · Term twelve: x12 = DK2 1 · · · 2· 2·∆ · · · ∆ · ∆ · · · 4· · · ∆ · ∆ ·∆ · · · · Therefore the equation for fractional uncertainty in erosion yield for Situation 2 is: · ∆ ∆ ∆ · ∆ ∆ · ∆ 2· (16) 2·∆ · · 2·∆ · · Table 4 shows the mass loss, density, exposed diameter, corresponding uncertainty values, and calculated fractional uncertainty for each polymer in Situation 2. NASA/TM—2010-216903 15 Table 4. Situation 2 Fractional Uncertainty in Erosion Yield. Material Abbrev. CA ETFE PA 66 PBI PBO PC PE PEEK PEI PI (Kapton HN) PPPA PSU PVDF PVF δM F (g) 0.000790 0.000003 0.000088 0.000156 0.000062 0.000020 0.000018 0.000117 0.000018 0.000052 0.000162 0.000035 0.000005 0.000011 δM C (g) 0.000433 0.000002 0.000034 0.000141 0.000000 0.000110 0.000004 0.000026 0.000018 n N 6 1 3 2 5 1 2 3 1 14 2 8 4 13 2 8 6 2 δM F ' (g) 0.000098 0.000003 0.000007 0.000040 0.000001 0.000002 0.000010 0.000001 0.000003 δM E ' (g) 0.000069 0.000005 0.000019 0.000029 0.000004 0.000012 0.000013 0.000013 0.000009 ΔM (g) 0.191482 0.049108 0.065562 0.082708 0.056778 0.142287 0.102760 0.107764 0.126853 ρ (g/cm ) 1.2911 1.7397 1.2252 1.2758 1.3976 1.1231 0.9180 1.2259 1.2873 1.4345 0.7200 1.2199 1.7623 1.3792 3 δρ (g/cm ) 0.0025 0.0029 0.1509 0.0036 0.0752 0.0079 0.0007 0.0457 0.0036 3 D (cm) 2.1059 2.1066 2.1185 2.1038 2.1268 2.1113 2.1257 2.1056 2.1216 δD (cm) 0.0060 0.0022 0.0051 0.0056 0.0031 0.0028 0.0029 0.0054 0.0053 δE /E 0.026573 0.025598 0.125851 0.026275 0.059587 0.026545 0.025620 0.045436 0.026088 0.000035 1 4 0.000010 0.000012 0.121315 0.000188 0.000032 0.000007 0.000011 3 3 1 6 6 6 2 13 0.000060 0.000012 0.000006 0.000013 0.000102 0.000015 0.000001 0.000010 0.030549 0.105948 0.066860 0.132537 0.0020 2.1313 0.0038 0.025748 0.0074 0.0221 0.0086 0.0013 2.1298 2.1113 2.1108 2.1331 0.0055 0.0054 0.0061 0.0028 0.028987 0.031645 0.026549 0.025612 4.3 Fractional Uncertainty Equation Derivations for Situation 3 Using Equation 13, the equation for Situation 3 erosion yield, the equation for fractional uncertainty in erosion yield for Situation 3 is derived through the following process. Equation 15 will be used to substitute for δMA in term 2 of the final equation. Term one: x1 = MF 1 · · · 2· · · ∆ ∆ · · · · 2· · ∆ · ∆ · ∆ Term two: x2 = MA 1 · · · 2· · · ∆ ∆ · · · · 2 · · ∆ · ∆ · · ∆ Term three: x3 = MS’ 1 · · · 2· · · ∆ ∆ · · · · 2· · ∆ · ∆ · ∆ Term four: x4 = ρS 1 · · · 2· · · ∆ ∆ · · · 2· · · · ∆ ∆ · · · NASA/TM—2010-216903 16 Term five: x5 = DS 1 · · · 2· · · ∆ ∆ · · · 4· · · · ∆ ∆ · · · 2· Term six: x6 = ρK 1 · · · 2· · · ∆ ∆ · · · 2· · · · ∆ ∆ · · Term seven: x7 = EK 1 · · · 2· · · ∆ ∆ · · · 2· · · · ∆ ∆ · · Term eight: x8 = ΔMK1 1 · · ∆ · ∆ 2· · · ∆ ∆ · · · 2· · · ∆ · ∆ · · · · ∆ ∆ · Term nine: x9 = ΔMK2 1 · · ∆ · ∆ 2· · · ∆ ∆ · · · 2· · · ∆ · ∆ · · · · ∆ ∆ · Term ten: x10 = DK1 1 · · · 2· 2·∆ · · · · ∆ ∆ · · · 4· · · · ∆ ∆ ·∆ · · · ·   Term eleven: x11 = DK2 1 · · · 2· 2·∆ · · · · ∆ ∆ · · · 4· · · · ∆ ∆ ·∆ · · · · Therefore the equation for fractional uncertainty in erosion yield for Situation 3 is: · ∆ ∆ ∆ 2· (17) ∆ · ∆ · 2·∆ · · 2·∆ · · NASA/TM—2010-216903 17 Table 5 shows the mass loss, density, exposed diameter, corresponding uncertainty values, and calculated fractional uncertainty for each polymer in Situation 3. Table 5. Situation 3 Fractional Uncertainty in Erosion Yield. Material Abbrev. ECTFE PA 6 PBT PET PI (CP1) PMMA PU δM F (g) 0.000008 0.000088 0.000027 0.000160 0.000038 0.000495 0.000051 δM C (g) 0.000004 0.000112 0.000017 0.000010 0.000038 0.000126 0.000040 n (g) 1 4 0.000012 4 8 0.000055 2 6 0.000049 4 8 0.000033 2 4 0.000025 5 10 0.000017 4 10 0.000042 N δM S' ΔM (g) 0.088869 0.118376 0.036429 0.125187 0.080648 0.194588 0.057227 ρ (g/cm ) 1.6761 1.1233 1.3318 1.3925 1.4193 1.1628 1.2345 3 D (g/cm ) (cm) 0.0059 2.1141 0.0079 2.1304 0.0040 2.1296 0.0029 2.1240 0.0167 2.1205 0.0028 2.1247 0.0174 2.1165 3 δρ δD (cm) 0.0027 0.0033 0.0026 0.0058 0.0030 0.0034 0.0039 δE /E 0.025821 0.026617 0.025798 0.026157 0.028199 0.025932 0.029353 5. RESULTS AND DISCUSSION The MISSE 2 PEACE Polymers LEO atomic oxygen erosion yield data are given in Table 6.1-3 These results represent the widest variety of extremely accurately measured high atomic oxygen fluence data to date. Including enough material in each flight sample to theoretically last for three years was crucial to the experiment’s success, because although the experiment received nearly four years of atomic oxygen exposure, only one polymer (PBI) was completely eroded away. However, for five other samples (PE, ADC, PMMA, PEI, and PMR-15) the atomic oxygen did in some places erode through all layers of the flight sample. For these six samples, therefore, the calculated erosion yields are less than the actual erosion yields, because if there had been more material the mass loss would have been greater. These six erosion yield values are highlighted in Table 6. Since the samples in these cases appeared to have eroded partially or completely through at a fluence level close to the full mission fluence, the measured erosion yields of these samples were still included in the data set as estimates to develop a predictive erosion yield equation.7 These samples have been re-flown in LEO for actual erosion yield determination as part of the Stressed PEACE Polymers experiment on MISSE 6.8 Table 6 also includes the uncertainty and fractional uncertainty in erosion yield for each of the MISSE 2 PEACE Polymers samples. The highest fractional uncertainty was for PA 66, ±12.59 percent, and the lowest fractional uncertainty was for Tefzel ZM, ±2.56 percent. The average fractional uncertainty in erosion yield was very small, ±3.30 percent. NASA/TM—2010-216903 18 Table 6. MISSE 2 PEACE Polymers Experiment Fractional Uncertainty Data Summary. Material Acrylonitrile butadiene styrene Allyl diglycol carbonate Amorphous fluoropolymer Cellulose acetate Chlorotrifluoroethylene Crystalline polyvinylfluoride with white pigment Epoxide or epoxy Ethylenechlorotrifluoroethylene Ethylene-tetrafluoroethylene copolymer Fluorinated ethylene propylene High temperature polyimide resin Perfluoroalkoxy copolymer resin Poly-(p-phenylene terephthalamide) Poly(p-phenylene-2 6benzobisoxazole) Polyacrylonitrile Polyamide 6 or Nylon 6 Polyamide 66 or Nylon 66 Polybenzimidazole Polybutylene terephthalate Polycarbonate Polyetheretherketone Polyetherimide Polyethylene Polyethylene oxide Polyethylene terephthalate Polyimide Polyimide (BPDA) Polyimide (PMDA) Polyimide (PMDA) Polyimide (PMDA) Abbrev. ABS ADC AF CA CTFE PVF-W EP Trade Name(s) Cycolac CR-39, Homalite H-911 Teflon AF 1601 Clarifoil, Tenite Acetate, Dexel Neoflon CTFE M-300, Kel-F White Tedlar TWH10BS3 Hysol EA 956 Fractional Uncertainty Erosion Yield Uncertainty in in Erosion 3 (cm /atom) Yield Erosion Yield 0.027017 2.96E-26 1.09 ± 0.03 E-24 0.025824 0.025975 0.026573 0.025927 0.041361 0.027020 0.025821 0.025598 0.026890 0.025696 0.027248 0.026193 0.059587 0.032801 0.026617 0.125851 0.026275 0.025798 0.026545 0.045436 0.026088 0.025620 Alkox E-30 Mylar A-200 LaRC CP1 (CP1-300) Upilex-S Kapton H Kapton H Kapton HN 0.025948 0.026157 0.028199 0.030056 0.024700 0.024700 0.025748 1.76E-25 5.13E-27 1.34E-25 2.15E-26 4.17E-27 1.14E-25 4.63E-26 2.46E-26 5.39E-27 7.77E-26 4.72E-27 1.64E-26 8.08E-26 4.63E-26 9.33E-26 2.27E-25 5.81E-26 2.35E-26 1.14E-25 1.36E-25 8.63E-26 9.59E-26 5.01E-26 7.87E-26 5.38E-26 2.77E-26 7.41E-26 7.41E-26 7.24E-26 >6.80 E-24 1.98 ± 0.05 E-25 5.05 ± 0.13 E-24 8.31 ± 0.22 E-25 1.01 ± 0.04 E-25 4.21 ± 0.11 E-24 1.79 ± 0.05 E-24 9.61 ± 0.25 E-25 2.00 ± 0.05 E-25 >3.02 E-24 1.73 ± 0.05 E-25 6.28 ± 0.16 E-25 1.36 ± 0.08 E-24 1.41 ± 0.05 E-24 3.51 ± 0.09 E-24 1.80 ± 0.23 E-24 >2.21 E-24 9.11 ± 0.24 E-25 4.29 ± 0.11 E-24 2.99 ± 0.14 E-24 >3.31 E-24 >3.74 E-24 1.93 ± 0.05 E-24 3.01 ± 0.08 E-24 1.91 ± 0.05 E-24 9.22 ± 0.28 E-25 3.00 ± 0.07 E-24 3.00 ± 0.07 E-24 2.81 ± 0.07 E-24 ECTFE Halar ETFE Tefzel ZM FEP PI PFA Teflon FEP (round robin) PMR-15 Teflon PFA CLP (200 CLP) PPD-T Kevlar 29 fabric PBO PAN PA 6 PBI PBT PC PEI PE PEO PET PI PI PI PI PI (balanced biaxial film) Barex 210 Akulon K, Ultramid B Celazole PBI GE Valox 357 PEEREX 61 (P61) Ultem 1000 PA 66 Maranyl A, Zytel PEEK Victrex PEEK 450 NASA/TM—2010-216903 19 Table 6. cont. MISSE 2 PEACE Polymers Experiment Fractional Uncertainty Data Summary. Material Polymethyl methacrylate Polyoxymethylene; acetal; polyformaldehyde Polyphenylene isophthalate Polypropylene Polystyrene Polysulphone Polytetrafluoroethylene Polyurethane Polyvinyl fluoride Polyvinylidene fluoride Pyrolytic graphite Abbrev. PMMA POM PPPA PP PS PSU Trade Name(s) Plexiglas, Lucite, Acrylite (Impact Mod.) Delrin (natural) Nomex Aramid Paper Type 410 C28 Trycite 1000, Trycite Dew Thermolux P1700-NT11, Udel P-1700 Dureflex PS 8010 Tedlar TTR10SG3 Fractional Uncertainty Uncertainty in in Erosion Yield Erosion Yield 0.025932 0.030556 0.028987 0.026127 0.026884 0.031645 0.026089 0.029353 0.025612 0.026549 0.107496 1.45E-25 2.79E-25 4.10E-26 7.00E-26 1.00E-25 9.31E-26 3.69E-27 4.59E-26 8.17E-26 3.41E-26 4.46E-26 Erosion Yield (cm /atom) >5.60 E-24 9.14 ± 0.28 E-24 1.41 ± 0.04 E-24 2.68 ± 0.07 E-24 3.74 ± 0.10 E-24 2.94 ± 0.09 E-24 1.42 ± 0.04 E-25 1.56 ± 0.05 E-24 3.19 ± 0.08 E-24 1.29 ± 0.03 E-24 4.15 ± 0.45 E-25 3 PTFE Chemfilm DF 100 PU PVF PG PVDF Kynar 740 6. SUMMARY The purpose of the MISSE 2 PEACE Polymers experiment was to obtain the atomic oxygen erosion yields of a wide variety of polymeric materials exposed to the LEO space environment for a long period of time.1-3 The MISSE 2 PEACE Polymers experiment is unique in that it included the widest variety of polymers exposed to identical LEO conditions and received a high fluence of atomic oxygen exposure (8.43 x 1021 atoms/cm2). Because of this, the experiment provides very valuable erosion yield data for spacecraft design purposes.1-3 It is therefore extremely important to know how accurate the atomic oxygen erosion yield data are. To address this, the error in each polymer’s experimental erosion yield value was calculated using equations for fractional uncertainty derived from the equation used to find erosion yield. Because three different situations were required for post-flight sample weighing, a factor in calculating the erosion yield E of a polymer, three different equations were derived for determining the fractional uncertainty of the erosion yield values. The uncertainty and fractional uncertainty in erosion yield for each of the MISSE 2 PEACE Polymers samples have been determined. The highest fractional uncertainty was for PA 66, ±12.59 percent, and the lowest fractional uncertainty was for Tefzel ZM, ±2.56 percent. The average fractional uncertainty in erosion yield was very small, ±3.30 percent. The results listed in Table 6 represent the widest variety of extremely accurately measured high atomic oxygen fluence data to date. NASA/TM—2010-216903 20 References 1. de Groh, K. K., Banks, B. A., McCarthy, C. E., Rucker, R. N., Roberts, L. M., and Berger, L. A., “MISSE 2 PEACE Polymers Atomic Oxygen Erosion Experiment on the International Space Station,” High Performance Polymers, Vol. 20, no. 4/5, pp. 388-409, Aug. 2008. 2. de Groh, K. K., Banks, B. A., McCarthy, C. E., Berger, L. A., and Roberts, L. M., “Analysis of the MISSE PEACE Polymers International Space Station Environmental Exposure Experiment,” Proceedings of the 10th International Symposium on Materials in a Space Environment and the 8th International Conference on Protection of Materials and Structures in a Space Environment (ISMSE-10 & ICMPSE-8), Collioure, France, June 19-23, 2006ESA SP-616, September 2006). 3. de Groh, K. K., Banks, B. A., McCarthy, C. E., Rucker, R. N., Roberts, L. M., and Berger, L. A., “MISSE PEACE Polymers Atomic Oxygen Erosion Results,” Proceedings of the 2006 National Space & Missile Materials Symposium (2006 NSMMS) in conjunction with the 2006 MISSE Post-Retrieval Conference, Orlando, Florida, June 26-30, 2006; also NASA TM-2006-214482, November 2006. 4. Pippin, G. and Normand, E., “Estimated Environmental Exposures for MISSE-1 & MISSE-2,” proceedings of the 2006 MISSE Post-Retrieval Conference, Jun. 26-30, 2006, Orlando, FL. 5. Dever, J. A., Miller, S. K., Sechkar, E. A., and Wittberg, T. N., “Preliminary Analysis of Polymer Film Thermal Control and Gossamer Materials Experiments on Materials International Space Station Experiment (MISSE 1 and MISSE 2),” Proceedings of the 2006 MISSE Post-Retrieval Conference, Jun. 26-30, 2006, Orlando, FL. 6. ASTM E 2089-00, “Standard Practices for Ground Laboratory Atomic Oxygen Interaction Evaluation of Materials for Space Applications, June 2000. 7. Banks, B. A., Backus, J. A., Manno, M. V., Waters, D. L., Cameron, K. C. and de Groh, K. K., “Atomic Oxygen Erosion Yield Prediction for Spacecraft Polymers in Low Earth Orbit,” Proceedings of the International Symposium on Materials in a Space Environment (ISMSE11), September 15-18, 2009, Aix-en-Provence, France, 2009; also NASA TM-2009-215812, September 2009. 8. de Groh, K. K., Banks, B. A., Dever, J. A., Jaworske, D. J., Miller, S. K., Sechkar E. A. and Panko, S. R., “NASA Glenn Research Center’s Materials International Space Station Experiments (MISSE 1-7),” Proceedings of the International Symposium on “SM/MPAC&SEED Experiment,” Tsukuba, Japan, March 10-11, 2008, JAXA-SP-08-015E, March 2009, pp. 91–119; also NASA TM-2008-215482, December 2008. NASA/TM—2010-216903 21 REPORT DOCUMENTATION PAGE Form Approved OMB No. 0704-0188 The public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE (DD-MM-YYYY) 01-11-2010 2. REPORT TYPE Technical Memorandum 3. DATES COVERED (From - To) 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 4. TITLE AND SUBTITLE MISSE 2 PEACE Polymers Experiment Atomic Oxygen Erosion Yield Error Analysis 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER McCarthy, Catherine, E.; Banks, Bruce, A.; de Groh, Kim, K. WBS 825080.04.02.30.17 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) National Aeronautics and Space Administration John H. Glenn Research Center at Lewis Field Cleveland, Ohio 44135-3191 8. PERFORMING ORGANIZATION REPORT NUMBER E-17481 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) National Aeronautics and Space Administration Washington, DC 20546-0001 10. SPONSORING/MONITOR'S ACRONYM(S) NASA 11. SPONSORING/MONITORING REPORT NUMBER NASA/TM-2010-216903 12. DISTRIBUTION/AVAILABILITY STATEMENT Unclassified-Unlimited Subject Category: 25 Available electronically at http://gltrs.grc.nasa.gov This publication is available from the NASA Center for AeroSpace Information, 443-757-5802 13. SUPPLEMENTARY NOTES 14. ABSTRACT Atomic oxygen erosion of polymers in low Earth orbit (LEO) poses a serious threat to spacecraft performance and durability. To address this, 40 different polymer samples and a sample of pyrolytic graphite, collectively called the PEACE (Polymer Erosion and Contamination Experiment) Polymers, were exposed to the LEO space environment on the exterior of the International Space Station (ISS) for nearly 4 years as part of the Materials International Space Station Experiment 1 & 2 (MISSE 1 & 2). The purpose of the PEACE Polymers experiment was to obtain accurate mass loss measurements in space to combine with ground measurements in order to accurately calculate the atomic oxygen erosion yields of a wide variety of polymeric materials exposed to the LEO space environment for a long period of time. Error calculations were performed in order to determine the accuracy of the mass measurements and therefore of the erosion yield values. The standard deviation, or error, of each factor was incorporated into the fractional uncertainty of the erosion yield for each of three different situations, depending on the post-flight weighing procedure. The resulting error calculations showed the erosion yield values to be very accurate, with an average error of ±3.30 percent. 15. SUBJECT TERMS Atomic oxygen; low Earth orbit (LEO); Polymers 16. SECURITY CLASSIFICATION OF: a. REPORT b. ABSTRACT c. THIS PAGE 17. LIMITATION OF ABSTRACT 18. NUMBER OF PAGES 19a. NAME OF RESPONSIBLE PERSON STI Help Desk (email:help@sti.nasa.gov) 19b. TELEPHONE NUMBER (include area code) U U U UU 27 443-757-5802 Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39-18