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NASA NTRS1993

Spectral infrared hemispherical reflectance measurements for LDEF tray clamps

Infrared hemispherical reflectance measurements that were made on 58 chromic acid anodized tray clamps from LDEF are described. The measurements were made using a hemiellipsoidal mirror reflectometer with interferometer for wavelengths between 2-15 microns. The tray clamps investigated were from locations about the entire spacecraft and provided the opportunity for comparing the effects of atomic oxygen at each location. Results indicate there was essentially no dependence on atomic oxygen fluence for the surfaces studied, but there did appear to be a slight dependence on solar radiation exposure. The reflectances of the front sides of the tray clamps consistently were slightly higher than for the protected rear tray clamp surfaces.

Cromwell, B. K.↗

NASA NTRS1993

Atomic oxygen effects on LDEF experiment AO171

The Solar Array Materials Passive Long Duration Exposure Facility (LDEF) Experiment (SAMPLE), AO171, contained in total approximately 100 materials and materials processes with a 300 specimen complement. With the exception of experiment solar cell and solar cell modules, all test specimens were weighed before flight, thus allowing an accurate determination of mass loss as a result of space exposure. Since almost all of the test specimens were thermal vacuum baked before flight, the mass loss sustained can be attributed principally to atomic oxygen attack. The atomic oxygen effects observed and measured in five classes of materials is documented. The atomic oxygen reactivity values generated for these materials are compared to those values derived for the same materials from exposures on short term shuttle flights. An assessment of the utility of predicting long term atomic oxygen effects from short term exposures is given. This experiment was located on Row 8 position A which allowed all experiment materials to be exposed to an atomic oxygen fluence of 6.93 x 10(exp 21) atoms/cm(sup 2) as a result of being positioned 38 degrees off the RAM direction.

Whitaker, Ann F.↗

NASA NTRS1988

Novel oxygen atom source for material degradation studies

Physical Sciences Inc. (PSI) has developed a high flux pulsed source of energetic (8 km/s) atomic oxygen to bombard specimens in experiments on the aging and degradation of materials in a low earth orbit environment. The proof-of-concept of the PSI approach was demonstrated in a Phase 1 effort. In Phase 2 a large O-atom testing device (FAST-2) has been developed and characterized. Quantitative erosion testing of materials, components, and even small assemblies (such as solar cell arrays) can be performed with this source to determine which materials and/or components are most vulnerable to atomic oxygen degradation. The source is conservatively rated to irradiate a 100 sq cm area sample at greater than 10(exp 17) atoms/s, at a 10 Hz pulse rate. Samples can be exposed to an atomic oxygen fluence equivalent to the on-orbit ram direction exposure levels incident on Shuttle surfaces at 250 km during a week-long mission in a few hours.

Krech, R. H.↗

NASA NTRS1993

Measured space environmental effects to LDEF during retrieval

Data gathered by the Interim Operational Contamination Monitor (IOCM) with regard to the effect of the space environment on the STS-32 Shuttle mission and on the Long Duration Exposure Facility (LDEF) are reported. IOCM measures the deposition of molecular and particulate contamination during all flight phases. It also measures the thermophysical properties of thermal control surfaces by calorimetry, the flux of the ambient atomic oxygen environment, the incident solar flux, and the absolute ambient pressure in the payload bay. The IOCM also provides a structure and sample holders for the exposure of passive material samples to the space environment. One of the more salient results from the STS-32 flight suggests that the LDEF emitted a large number of particulates after berthing into the Shuttle. The mission atomic oxygen fluence was also calculated. Although the fluence was low by normal standards, the Kapton (trademark) passive samples exhibited the onset of erosion. Orbital debris and micrometeoroid impacts also occurred during the retrieval mission. The average perforation diameter was approximately 1.25 micrometers. The largest perforation diameter was measured at 65 micrometers.

Maag, Carl R.↗

NASA NTRS1993

Anodized aluminum on LDEF

A compilation of reported analyses and results obtained for anodized aluminum flown on the Long Duration Exposure Facility (LDEF) was prepared. Chromic acid, sulfuric acid, and dyed sulfuric acid anodized surfaces were exposed to the space environment. The vast majority of the anodized surface on LDEF was chromic acid anodize because of its selection as a thermal control coating for use on the spacecraft primary structure, trays, tray clamps, and space end thermal covers. Reports indicate that the chromic acid anodize was stable in solar absorptance and thermal emittance, but that contamination effects caused increases in absorptance on surfaces exposed to low atomic oxygen fluences. There were some discrepancies, however, in that some chromic acid anodized specimens exhibited significant increases in absorptance. Sulfuric acid anodized surfaces also appeared stable, although very little surface area was available for evaluation. One type of dyed sulfuric acid anodize was assessed as an optical baffle coating and was observed to have improved infrared absorptance characteristics with exposure on LDEF.

Golden, Johnny L.↗

NASA NTRS1994

Results from LDEF experiment A0114: The interaction of atomic oxygen with materials surfaces at orbital altitudes

In 1975 the University of Alabama in Huntsville proposed an experiment for the Long Duration Exposure Facility (LDEF) designed to investigate the effects of the collision of the ambient orbital atmosphere, mainly consisting of atomic oxygen, with satellite surfaces travelling at about 8 km per second. In 1989, the potential for recovery of significant data from A0114 on a wide variety of materials was recognized and funding for three years of data analysis was appropriated. Some significant or unique findings from the experiment A0114 include: numerous measurements of oxidation rates of surfaces under fast O atom bombardment, including Si, Ge, GaAs, SiC, and optical quality metal films; measurement of the stable attitude of the LDEF spacecraft in orbit using the gas dynamics pinhole camera; description of the formation of thick oxide films on copper at 20 C with fast oxygen; measurement of erosion rates of Kapton and other polymers at space station lifetime atomic oxygen fluences (10(exp 22) atoms/sq cm); and measurement of the cosmogenic isotopes Be-7 on spacecraft surfaces.

Gregory, John C.↗

NASA NTRS1993

Flight- and ground-test correlation study of BMDO SDS materials: Phase 1 report

Chung, Shirley Y.↗

NASA NTRS1995

Four space application material coatings on the Long-Duration Exposure Facility (LDEF)

Four material coatings of different thicknesses were flown on the LDEF to determine their ability to perform in the harsh space environment. The coatings, located in the ram direction of the spacecraft, were exposed for 10 months to the low-Earth orbit (LEO) environments experienced by the LDEF at an orbit of 260 nautical miles. They consisted of indium oxide (In2O3), silicon oxide (SiO(x)), clear RTV silicone, and silicone with silicate-treated zinc oxide (ZnO). These coatings were flown to assess their behavior when exposed to atomic oxygen and to confirm their good radiative properties, stability, electrical conductivity, and resistance to UV exposure. The flown samples were checked and compared with the reference unflown samples using high-magnification optical inspection, ESCA analysis, weight changes, and dimensional changes. These comparisons indicated the following. The 1000 A SiO(x) coating eroded uniformly, with minor changes in its radiative properties. The 100 A In2O3 coating eroded completely down to the Kapton backing, with resultant losses of reflectance. The RTV-615 showed erosion, with carbon (C) content losses, while the Si remained constant, with a doubling of the oxygen (O) concentration. The RTV-615 silicone with K2SiO3-treated ZnO changed from flat to glossy white in appearance. It lost C, was etched, and increased its O content. The upper layers showed no remaining Zn or K. Losses of reflectance occurred within certain wavelength bands. It was not possible to evaluate the experimental oxygen reaction rate using the calculated atomic oxygen fluence of 2.6 x 10(exp 20) atoms/cm(exp 2) for the exposure of these coatings during the flight. The bakeout of the coatings was not carried out prior to the flight. Hence, the coating weight and dimensional losses included losses by outgassing products.

Scialdone, John J.↗

NASA NTRS1995

LEO degradation of graphite and carbon-based composites aboard Space Shuttle Flight STS-46

Six different types of carbon and carbon-boron nitride composites were exposed to low Earth orbit aboard Space Shuttle flight STS-46. The samples received a nominal atomic oxygen fluence of 2.2 x 10(exp 20) atoms/sq cm in 42 hours of exposure. Pyrolytic graphite and highly oriented pyrolytic graphite showed significant degradation, and the measured erosion yield was within a factor of two of published values. The erosion yield of pyrolytic boron nitride was found to be 2.6 x 10(exp 26) cu cm/atom in plasma asher exposure, over 42 times lower than that of pyrolytic graphite. This low erosion yield makes graphite plus boron nitride mixtures quite resistant to low Earth orbit exposure. Evidence suggests that the graphitic component was preferentially etched, leaving the surface boron nitride rich. Degradation resistance increases with boron nitride composition. Carbon fiber/carbon composites degraded in low Earth orbit, and the carbon pitch binder was found to etch more easily than the graphite fibers which have much higher degradation resistance.

Spady, Blaine R.↗

NASA NTRS1995

Orbital atomic oxygen effects on materials: An overview of MSFC experiments on the STS-46 EOIM-3

The third Evaluation of Oxygen Interaction with Materials experiment was flown on Space Shuttle Mission STS-46 (July 31 - August 8, 1992), representing a joint effort of several NASA centers, universities, and contractors. This array of active instrumentation and material exposure sub-assemblies was integrated as a Shuttle cargo bay pallet experiment for investigating the effects of orbital atomic oxygen on candidate space materials. Marshall Space Flight Center contributed several passive exposure trays of material specimens, uniform stress and static stress material exposure fixtures, the Atomic Oxygen Resistance Monitor (AORM), and specimens of thermal coatings for the EOIM-3 variable exposure mechanisms. As a result of 42 hours of spacecraft velocity vector-oriented exposure during the later phases of the STS-46 mission in LEO, EOIM-3 materials were exposed to an atomic oxygen fluence of 2.2 x 10(exp 20) atoms/sq cm. In this paper, an overview is presented of the technical approaches and results from analyses of the MSFC flight specimens, fixtures, and the AORM. More detailed results from earlier EOIM missions, the LDEF, and from laboratory testing are included in associated papers of this conference session.

Linton, Roger C.↗

NASA NTRS1995

BMDO materials testing in the EOIM-3 experiment

The NASA Evaluation of Oxygen Interactions with Materials-3 (EOIM-3) experiment served as a testbed for a variety of materials that are candidates for Ballistic Missile Defense Organization (BMDO) space assets. The materials evaluated on this flight experiment were provided by BMDO contractors and technology laboratories. A parallel ground-based exposure evaluation was conducted using the Fast Atom Sample Tester (FAST) atomic-oxygen simulation facility at Physical Sciences, Inc. The EOIM-3 flight materials were exposed to an atomic oxygen fluence of approximately 2.3 x 10(exp 20) atoms/sq cm. The ground-based exposure fluence of 2.0 - 2.5 x 10(exp 20) atoms/sq cm permits direct comparison with that of the flight-exposed specimens. The results from the flight test conducted aboard STS-46 and the correlative ground-based exposure are summarized here. A more detailed correlation study is presented in the JPL Publication 93-31 entitled 'Flight-and Ground-Test Correlation Study of BMDO SDS Materials: Phase 1 Report'. In general, the majority of the materials survived the AO environment with their performance tolerances maintained for the duration of the exposure. Optical materials, baffles, and coatings performed extremely well as did most of the thermal coatings and tribological materials. A few of the candidate radiator, threat shielding, and structural materials showed significant degradation. Many of the coatings designed to protect against AO erosion of sensitive materials performed this function well.

Chung, Shirley Y.↗

NASA NTRS1995

Evaluation of certain material films flown on the Space Shuttle Mission 46, EOIM-3 experiment

Nine film samples were carried aboard the STS-46 Atlantis shuttle to complement the 'Evaluation of Oxygen Interaction with Materials (EOIM-III)' experiment to evaluate the effects of atomic oxygen on materials and to monitor the gaseous environment in the shuttle bay. The morphological changes of the samples produced by the atomic oxygen fluence of 2.07E-20 atoms/sq cm have been reported. The changes have been verified using X-ray Photoelectron Spectrometer (XPS) also known as Electron Spectroscopy for Chemical Analysis (ESCA), gravimetric measurements, microscopic observations and thermo-optical measurements. The samples including Kapton, Tefzel, Aclar, Polyacrylonitrile film, and Llumalloy films have been characterized by their oxygen reaction efficiency on the basis of their erosion losses and the fluence. Those efficiencies have been compared with results from other similar experiments, when available. The efficiencies of the samples are all in the range of E-24 gm/atom.

Scialdone, John↗

NASA NTRS1996

Atomic Oxygen and Space Environment Effects on Aerospace Materials Flown with EOIM-3 Experiment

Polymer materials samples mounted on a passive carrier tray were flown aboard the STS-46 Atlantis shuttle as complement to the EOIM-3 (Evaluation of Oxygen Interaction with Materials) experiment to evaluate the effects of atomic oxygen on the materials and to measure the gaseous shuttle bay environment. The morphological changes of the samples produced by the atomic oxygen fluence of 2.07 x 10(exp 20) atoms/cm(exp 2) are being reported. The changes have been verified using Electron Spectroscopy for Chemical Analysis (ESCA), gravimetric measurement, microscopic observations and thermo-optical measurements. The samples, including Kapton, Delrin, epoxies, Beta Cloth, Chemglaze Z306, silver Teflon, silicone coatings, 3M tape and Uralane and Ultem, PEEK, Victrex (PES), Polyethersulfone and Polymethylpentene thermoplastic, have been characterized by their oxygen reaction efficiency on the basis of their erosion losses and the oxygen fluence. Those efficiencies have been compared to results from other experiments, when available. The efficiencies of the samples are all in the range of E-24 g/atom. The results indicate that the reaction efficiencies of the reported materials can be grouped in about three ranges of values. The least affected materials which have efficiencies varying from 1 to 10(exp 25) g/atom, include silicones, epoxies, Uralane and Teflon. A second group with efficiency from 10 to 45(exp 25) g/atom includes additional silicone coatings, the Chemglaze Z306 paint and Kapton. The third range from 50 to 75(exp 25) includes organic compound such as Pentene, Peek, Ultem, Sulfone and a 3M tape. A Delrin sample had the highest reaction efficiency of 179(exp 25) g/atom. Two samples, the aluminum Beta cloth X389-7 and the epoxy fiberglass G-11 nonflame retardant, showed a slight mass increase.

Scialdone, John J.↗

NASA NTRS2000

The Spacecraft Materials Selector: An Artificial Intelligence System for Preliminary Design Trade Studies, Materials Assessments, and Estimates of Environments Present

Institutions need ways to retain valuable information even as experienced individuals leave an organization. Modern electronic systems have enough capacity to retain large quantities of information that can mitigate the loss of experience. Performance information for long-term space applications is relatively scarce and specific information (typically held by a few individuals within a single project) is often rather narrowly distributed. Spacecraft operate under severe conditions and the consequences of hardware and/or system failures, in terms of cost, loss of information, and time required to replace the loss, are extreme. These risk factors place a premium on appropriate choice of materials and components for space applications. An expert system is a very cost-effective method for sharing valuable and scarce information about spacecraft performance. Boeing has an artificial intelligence software package, called the Boeing Expert System Tool (BEST), to construct and operate knowledge bases to selectively recall and distribute information about specific subjects. A specific knowledge base to evaluate the on-orbit performance of selected materials on spacecraft has been developed under contract to the NASA SEE program. The performance capabilities of the Spacecraft Materials Selector (SMS) knowledge base are described. The knowledge base is a backward-chaining, rule-based system. The user answers a sequence of questions, and the expert system provides estimates of optical and mechanical performance of selected materials under specific environmental conditions. The initial operating capability of the system will include data for Kapton, silverized Teflon, selected paints, silicone-based materials, and certain metals. For situations where a mission profile (launch date, orbital parameters, mission duration, spacecraft orientation) is not precisely defined, the knowledge base still attempts to provide qualitative observations about materials performance and likely exposures. Prior to the NASA contract, a knowledge base, the Spacecraft Environments Assistant (SEA,) was initially developed by Boeing to estimate the environmental factors important for a specific spacecraft mission profile. The NASA SEE program has funded specific enhancements to the capability of this knowledge base. The SEA qualitatively identifies over 25 environmental factors that may influence the performance of a spacecraft during its operational lifetime. For cases where sufficiently detailed answers are provided to questions asked by the knowledge base, atomic oxygen fluence levels, proton and/or electron fluence and dose levels, and solar exposure hours are calculated. The SMS knowledge base incorporates the previously developed SEA knowledge base. A case history for previous flight experiment will be shown as an example, and capabilities and limitations of the system will be discussed.

Pippin, H. G.↗

NASA NTRS2001

The Development of Surface Roughness and Implications for Cellular Attachment in Biomedical Applications

The application of a microscopic surface texture produced by ion beam sputter texturing to the surfaces of polymer implants has been shown to result in significant increases in cellular attachment compared to smooth surface implants in animal studies. A collaborative program between NASA Glenn Research Center and the Cleveland Clinic Foundation has been established to evaluate the potential for improving osteoblast attachment to surfaces that have been microscopically roughened by atomic oxygen texturing. The range of surface textures that are feasible depends upon both the texturing process and the duration of treatment. To determine whether surface texture saturates or continues to increase with treatment duration, an effort was conducted to examine the development of surface textures produced by various physical and chemical erosion processes. Both experimental tests and computational modeling were performed to explore the growth of surface texture with treatment time. Surface texturing by means of abrasive grit blasting of glass, stainless steel, and polymethylmethacry I ate surfaces was examined to measure the growth in roughness with grit blasting duration by surface profilometry measurements. Laboratory tests and computational modeling was also conducted to examine the development of texture on Aclar(R) (chlorotfifluoroethylene) and Kapton(R) polyimide, respectively. For the atomic oxygen texturing tests of Aclar(R), atomic force microscopy was used to measure the development of texture with atomic oxygen fluence. The results of all the testing and computational modeling support the premise that development of surface roughness obeys Poisson statistics. The results indicate that surface roughness does not saturate but increases as the square root of the treatment time.

Banks, Bruce↗

NASA NTRS2002

Measurements of Optically Transparent and Mirrored Specimens from the POSA and EOIM III Space Flight Experiments

A selected set of optically transparent specimens and first surface mirror specimens have been examined subsequent to on-orbit exposure. Certain specimens were from the Passive Optical Sample Assembly I and II experiments flown on the MIR Space Station. Other specimens were from the Energetic Oxygen Interaction with materials III experiment flown on the STS in August 1992. A comparison of pre- and post-flight transmission of reflectance measurements, as appropriate, has been carried out. Data from different specimens includes results of measurements for IR, optical, UV and/or vacuum UV wavelength intervals. Results of these measurements clearly show the effects of molecular contamination deposits on the surfaces during the on-orbit exposures. Surface analysis on a attracted set of specimens provides and estimate of contaminant thickness and composition and provides an insight into on-orbit deposition rates and surface oxidation reactions. For both the EOIM III and POSA I & II experiments, the primary source of contamination were outgassed silicones. Both experiments received approximately the same fluence of atomic oxygen (approx. 1-2 x 1020 atoms per square centimeter). ROSA specimens received between approx. 400 and 580 equivalent sun hours (ESH) of solar radiation over an 18 month period in orbit. The EOIM specimens were on an STS flight of about 1 week duration and received only approx. 5-10 ESH of solar radiation.

Pippin, Gary↗

NASA NTRS2004

Atomic Oxygen Durability Evaluation of a UV Curable Ceramer Protective Coating

The exposure of most silicones to atomic oxygen in low Earth orbit (LEO) results in the oxidative loss of methyl groups with a gradual conversion to oxides of silicon. Typically there is surface shrinkage of oxidized silicone protective coatings which leads to cracking of the partially oxidized brittle surface. Such cracks widen and branch crack with continued atomic oxygen exposure ultimately allowing atomic oxygen to reach any hydrocarbon polymers under the silicone coating. A need exists for a paintable silicone coating that is free from such surface cracking and can be effectively used for protection of polymers and composites in LEO. A new type of silicone based protective coating holding such potential was evaluated for atomic oxygen durability in an RF atomic oxygen plasma exposure facility. The coating consisted of a UV curable inorganic/organic hybrid coating, known as a ceramer, which was fabricated using a methyl substituted polysiloxane binder and nanophase silicon-oxo-clusters derived from sol-gel precursors. The polysiloxane was functionalized with a cycloaliphatic epoxide in order to be cured at ambient temperature via a cationic UV induced curing mechanism. Alkoxy silane groups were also grafted onto the polysiloxane chain, through hydrosilation, in order to form a network with the incorporated silicon-oxo-clusters. The prepared polymer was characterized by H-1 and Si-29 NMR, FT-IR, and electrospray ionization mass spectroscopy. The paper will present the results of atomic oxygen protection ability of thin ceramer coatings on Kapton H as evaluated over a range of atomic oxygen fluence levels.

Banks, Bruce A.↗

NASA NTRS2007

Effect of LEO Exposure on Aromatic Polymers Containing Phenylphosphine Oxide Groups

As part of the Materials on The International Space Station Experiment (MISSE), aromatic polymers containing phenylphosphine oxide groups were exposed to low Earth orbit (LEO) for approximately 4 years. All of the aromatic polymers containing phenylphosphine oxide groups survived the exposure despite the high fluence of atomic oxygen that completely eroded other polymer films such as Kapton and Mylar of comparable or greater thickness. The samples consisted of a colorless polyimide film and a poly(arylene ether benzimidazole) film and thread. The samples were characterized for changes in physical properties, thermal/optical properties (i.e. solar absorptivity and thermal emissivity), surface chemistry (X-ray photoelectron spectroscopy), and surface topography (atomic force microscopy). The data from the polymer samples on MISSE were compared to samples from the same batch of material stored under ambient conditions on Earth. In addition, comparisons were made between the MISSE samples and those subjected to shorter term space flight exposures. The results of these analyses will be presented.

Watson, K. A.↗