Titles:

• Preliminary Analysis of Polymer Film Thermal Control and Gossamer Materials Experiments on Materials International Space Station Experiment (MISSE 1 and MISSE 2)   June 2006

• Effects of the Space Environment on Polymer Film Materials Exposed on the Materials International Space Station Experiment (MISSE 1 and MISSE 2)   June 2006

• Fast Three-Dimensional Modeling of Atomic Oxygen Undercutting of Protected Polymers  May-June 2004
  

• Cermet Coatings for Solar Stirling Space Power  April 2004
  

• Solar Selective Coatings for High Temperature Applications   February 2003
  

• Durability of Solar Selective Coatings in a Simulated Space Environment   November 2002
  

• Optical Properties of Thin Film Molecular Mixtures  September 2002

• Fast Three-Dimensional Method of Modeling Atomic Oxygen Undercutting of Protected Polymers  May 2002
   
• Retention of Sputtered Molybdenum on Ion Engine Discharge Chamber Surfaces  October 2001
   
• Modeling of Transmittance Degradation Caused by Optical Surface Contamination by Atomic Oxygen Reaction With Adsorbed Silicones  June 2001
   
• Fluoropolymer Films Deposited by Argon Ion-Beam Sputtering of Polytetrafluoroethylene  2001
   
• The Dependence of Atomic Oxygen Undercutting of Protected Kapton® H Upon Defect Size  June 2000
   
• Transparent/Conducting TiO2-Based Coatings for Space Applications  April 1998
   
• Indium Tin Oxide-Magnesium Fluoride Co-Deposited Films for Spacecraft Applications  April 1996

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),” in proceedings of the 2006 MISSE Post-Retrieval Conference sponsored by the Air Force Research Laboratory, Orlando, Florida, June 26 – 30, 2006

A total of 31 samples were included in the National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) Polymer Film Thermal Control (PFTC) and Gossamer Materials experiments, which were exposed to the low Earth orbit environment for nearly four years on the exterior of the International Space Station (ISS) as part of the Materials International Space Station Experiment (MISSE 1 and MISSE 2).  MISSE is a materials flight experiment sponsored by the Air Force Research Lab/Materials Lab and NASA.  This paper describes objectives, materials, and characterizations for the MISSE 1 and MISSE 2 GRC PFTC and Gossamer Materials samples.  Samples included films of polyimides, fluorinated polyimides, and TeflonÒ fluorinated ethylene propylene (FEP) with and without second-surface metalizing layers and/or surface coatings.  Also included were films of polyphenylene benzobisoxazole (PBO) and a polyarylene ether benzimidazole (TOR-LMTM).  Polymer film samples were examined post-flight for changes in mechanical and optical properties. The environment in which the samples were located was characterized through analysis of sapphire contamination witness samples and samples dedicated to atomic oxygen (AO) erosion measurements.  Results of the preliminary analyses of the PFTC and Gossamer Materials experiments are discussed.

Dever, J. A., Miller, S. K., Sechkar, E. A., “Effects of the Space Environment on Polymer Film Materials Exposed on the Materials International Space Station Experiment (MISSE 1 and MISSE 2),” in proceedings of the 10th International Symposium on Materials in a Space Environment & 8th International Conference on Protection of Materials and Structures in a Space Environment, Collioure, France, June 19 – 23, 2006

A total of 28 polymer film samples were included in the National Aeronautics and Space Administration (NASA) Glenn Research Center (GRC) Polymer Film Thermal Control (PFTC) and Gossamer Materials Experiments, which were exposed to the low Earth orbit environment for nearly four years on the exterior of the International Space Station (ISS) as part of the Materials International Space Station Experiment (MISSE 1 and MISSE 2).  MISSE is a materials flight experiment sponsored by the Air Force Research Lab/Materials Lab and NASA.  This paper will describe objectives, materials, and characterizations for the MISSE 1 and MISSE 2 GRC PFTC and Gossamer Materials samples.  Samples included films of polyimides, fluorinated polyimides, and TeflonÒ fluorinated ethylene propylene (FEP) with and without second-surface metalizing layers and/or surface coatings.  Also included were films of polyphenylene benzobisoxazole (PBO) and a polyarylene ether benzimidazole (TOR-LMTM).  Polymer film samples were examined post-flight for changes in mechanical and optical properties and for  atomic oxygen (AO) erosion.  Results of the preliminary analyses of the PFTC and Gossamer Materials Experiments are discussed.

Snyder, Aaron and Banks, Bruce, ““Fast Three-Dimensional Modeling of Atomic Oxygen Undercutting of Protected Polymers”, Journal of Spacecraft and Rockets, Vol. 41, Number 3, pp. 340-344, May-June 2004

A method is presented to model atomic oxygen erosion of protected polymers in low Earth orbit.  Undercutting of protected polymers by atomic oxygen can occur due to the presence of scratch, crack or pin-window defects in the protective coatings.  As a means of providing a better understanding of undercutting processes, a fast method of modeling atomic-oxygen undercutting of protected polymers has been developed.  Current simulation methods often rely on computationally expensive ray-tracing procedures to track the surface-to-surface movement of individual “atoms”.  To reduce the burden of time consuming calculations, the method introduced in this paper replaces computationally demanding individual particle simulations by substituting a model that utilizes both a geometric configuration-factor technique, which collectively governs the diffuse transport of atoms between surfaces, and an efficient algorithm, which rapidly computes the cumulative effects stemming from the series of atomic oxygen collisions at the surfaces of an undercut cavity.  This new method facilitates the systematic study of three-dimensional undercutting by allowing rapid simulations to be made over a wide range of erosion parameters.

Jaworske, D. A., and Raack, T., “Cermet Coatings for Solar Stirling Space Power,” ICMCTF-2004, San Diego, CA, April 2004.

Cermet coatings, molecular mixtures of metal and ceramic, are being considered for the heat inlet surface of a solar Stirling space power convertor.  In this application, the role of the cermet coating is to absorb as much of the incident solar energy as possible.  Cermet coatings are made using sputter deposition, and different metal and ceramic combinations can be created.  The ability to mix metal and ceramic at the atomic level offers the opportunity to tailor the composition and the solar absorptance of these coatings.  Several candidate cermet coatings were created and their solar absorptance was characterized as-manufactured and after exposure to elevated temperatures.  Coating composition was purposely varied through the thickness of the coating.  As a consequence of changing composition, islands of metal are thought to form in the ceramic matrix.  Computer modeling indicates that diffusion of the metal atoms plays an important role in island formation while the ceramic plays an important role in locking the islands in place.  Much of the solar spectrum is absorbed as it passes through this labyrinth.  This paper will discuss the solar absorption characteristics of as-deposited cermet coatings as well as the solar absorption characteristics of the coatings after heating.  The role of diffusion and island formation, during the deposition process and during heating, will also be discussed.

Jaworske, D. A. and Shumway, D. A., “Solar Selective Coatings for High Temperature Applications,” Space Technology & Applications International Forum (STAIF-2003), Albuquerque, NM, pp. 65-70, February 2003.

Solar selective coatings are envisioned for use on minisatellites, for applications where solar energy is to be used to power heat engines or to provide thermal energy for remote regions in the interior of the spacecraft.  These coatings are designed to have the combined properties of high solar absorptance and low infrared emittance.  The coatings must be durable at elevated temperatures.  For thermal bus applications, the temperature during operation is likely to be near 100°C.  For heat engine applications, the temperature is expected to be much greater.  The objective of this work was to screen candidate solar selective coatings for their high temperature durability.  Candidate solar selective coatings were composed of molecular mixtures of metal and dielectric, including: nickel and aluminum oxide, titanium and aluminum oxide, and platinum and aluminum oxide.  To identify high temperature durability, the solar absorptance and infrared emittance of the candidate coatings were evaluated initially, and after heating to temperatures in the range of 400°C to 700°C.  The titanium and aluminum oxide molecular mixture was found to be the most durable.

Jaworske, D. A., “Durability of Solar Selective Coatings in a Simulated Space Environment,” 34th International SAMPE Technical Conference, Baltimore, MD, pp. 323-332, November, 2002.

Solar selective coatings are being considered for heat engine and thermal switching applications on minisatellites.  Such coatings must have the combined properties of high solar absorptance and low infrared emittance.  High solar absorptance is needed to collect solar energy as efficiently as possible while low infrared emittance is needed to minimize radiant energy loss at operating temperature.  These properties are achieved in sputter deposited thin films through the use of molecular mixtures of metal and dielectric.  Solar selective coatings having a solar absorptance to infrared emittance ratio of 9 have been successfully deposited using a mixture of nickel and aluminum oxide.  The space environment, however, presents some challenges for the use of materials on the exterior of spacecraft, including durability to atomic oxygen and vacuum ultraviolet radiation.  To address these concerns, several candidate solar selective coatings were exposed to atomic oxygen in a plasma asher and to ultraviolet radiation in a vacuum facility equipped with calibrated deuterium lamps.  The optical properties of the coatings were monitored as a function of time to evaluate their performance over long term exposure to the simulated space environment.  Several coatings were found to be durable to both the atomic oxygen and the vacuum ultraviolet environments.

Jaworske, D. A. and Shumway, D. A., “Optical Properties of Thin Film Molecular Mixtures,” 5th Conference on Aerospace Materials, Processes, and Environmental Technology, Huntsville, AL, September 2002.

Thin films composed of molecular mixtures of metal and dielectric are being considered for use as solar selective coatings for a variety of space power applications.  By controlling the degree of molecular mixing, the solar selective coatings can be tailored to have the combined properties of high solar absorptance, , and low infrared emittance, .  On orbit, these combined properties would simultaneously maximize the amount of solar energy captured by the coating and minimize the amount of thermal energy radiated.  Minisatellites equipped with solar collectors coated with these cermet coatings may utilize the captured heat energy to power a heat engine to generate electricity, or to power a thermal bus that directs heat to remote regions of the spacecraft.

Snyder, A., Banks, B. A., “Fast Three-Dimensional Method of Modeling Atomic Oxygen Undercutting of Protected Polymers,” presented at the Sixth International Conference on Protection of Materials and Structures from the Space Environment, NASA TM-2002-211578, Toronto, Canada, May 1-3, 2002.

A method is presented to model atomic oxygen erosion of protected polymers in low Earth orbit (LEO). Undercutting of protected polymers by atomic oxygen occurs in LEO due to the presence of scratch, crack or pin-window defects in the protective coatings. As a means of providing a better understanding of undercutting processes, a fast method of modeling atomic-oxygen undercutting of protected polymers has been developed. Current simulation methods often rely on computationally expensive ray-tracing procedures to track the surface-to-surface movement of individual “atoms”. The method introduced in this paper replaces slow individual particle approaches by substituting a model that utilizes both a geometric configuration-factor technique, which governs the diffuse transport of atoms between surfaces, and an efficient telescoping series algorithm, which rapidly integrates the cumulative effects stemming from the numerous atomic oxygen events occurring at the surfaces of an undercut cavity. This new method facilitates the systematic study of three-dimensional undercutting by allowing rapid simulations to be made over a wide range of erosion parameters.

Grit-blasted anode surfaces are commonly used in ion engines to ensure adherence of sputtered coatings. Next generation ion engines will require higher power levels, longer operating times, and thus there will likely be thicker sputtered coatings on their anode surfaces than observed to date on 2.3 kW-class xenon ion engines. The thickness of coatings on the anode of a 10 kW, 40-cm diameter thruster, for example, may be 22 µm or more after extended operation. Grit-blasted wire mesh, titanium, and aluminum coupons were coated with molybdenum at accelerated rates to establish coating stability after the deposition process and after thermal cycling tests. These accelerated deposition rates are roughly three orders of magnitude more rapid than the rates at which the screen grid is sputtered in a 2.3 kW-class, 30-cm diameter ion engine. Using both RF and DC sputtering deposition raters from 1.8µm/h to 5.1µm/h. In all cases, the molybdenum coatings were stable after 20 cycles from about - 60°C to + 320°C. The stable, 130 µm molybdenum coating on wire mesh is 26 times thicker than the thickest coating found on the anode of a 2.3 kW, xenon ion engine that was tested for 8200 hours. Additionally, this coating on wire mesh coupon is estimated to be a factor of > 4 thicker than one would expect to obtain on the anode of the next generation ion engine which may have xenon throughputs as high as 550 kg.

A numerical procedure is presented to calculate transmittance degradation caused by contaminant films on spacecraft surfaces produced though the interaction of orbital atomic oxygen (AO) with volatile silicones and hydrocarbons from spacecraft component. In the model, contaminant accretion is dependent on the adsorption of species, depletion reactions due to gas-surface collisions, desorption, and surface reactions between AO and silicone producing SiOx (where x is near 2). A detailed description of the procedure used to calculate the constituents of the contaminant layer is presented, including the equations that govern the evolution of fractional coverage by specie type. As an illustrative example of film growth, calculation results using a prototype code that calculates the evolution of surface coverage by specie type is presented and discussed. An example of the transmittance degradation caused by surface interaction of AO with deposited contaminant is presented for the case of exponentially decaying contaminant flux. These examples are performed using hypothetical values for the process parameters.

Golub, M. A., Banks, B. A., Rutledge, S. K., and Kitral, M. C., “Fluoropolymer Films Deposited by Argon Ion-Beam Sputtering of Polytetrafluoroethylene,” America Chemical Society, Ch 16, pp 213-221, 2001.

The FT-IR, XPS and UV spectra of fluoropolymer films (SPTFE-I) deposited by argon ion-beam sputtering of polytetrafluoroethylene (PTFE) were obtained and compared with prior corresponding spectra of fluoropolymer films (SPTFE-P). Although the F/C ratios for SPTFE-I and –P (1.63 and 1.51) were similar, the SPTFE-I structure had a much higher concentration of CF2 groups than the SPTFE-P structure: ca. 61 and 33% of the total carbon contents, respectively. Reflecting the difference, the FT-IR spectra of SPTFE-I showed a distinct doublet at 1210 and 1150 cm-1 whereas SPTFE-P presented a broad, featureless band at ca. 1250 cm-1. The absorbance of the 1210-cm-1 band in SPTFE-I was proportional to film thickness in the range of 50-400 nm. SPTFE-I was more transparent in the UV than SPTFE-P at comparable thickness. The mechanism for SPTFE-I formation likely involves “chopping off” of oligomeric segments of PTFE as an accompaniment to “plasma” polymerization of TFE monomer generated in situ from PTFE on impact with energetic Ar ions. Data are given for SPTFE-I deposits and the associated Ar+--bombarded PTFE targets where a fresh target was used for each run or a single target was used for a sequence of runs.

Understanding the behavior of polymeric materials when exposed to the low-Earth-orbit (LEO) environment is important in predicting performance characteristics such as in-space durability. Atomic oxygen (AO) present in LEO is known to be the principle agent in causing undercutting erosion of SiOx protected polyimide Kapton® H film, which serves as a mechanically stable blanket material in solar arrays. The rate of undercutting is dependent on the rate of arrival, directionality and energy of the AO with respect to the film surface. The erosion rate also depends on the distribution of the size of defects existing in the protective coating. This paper presents results of experimental ground testing using low energy, isotropic AO flux together with numerical modeling to determine the dependence of undercutting erosion upon defect size.

Gajdos, S. M., Adorjan, A. J., Jalics, A. I., Hambourger, P. D., Dever, J. A., Lippens, P., Lievens, H., Taylor, A., and Dievens, D., "Transparent/Conducting TiO2-Based Coatings for Space Applications", Proceedings of Society of Vacuum Coaters, 41st Annual Technical Conference, Boston, Mass., April, 1998.

Highly transparent, slightly conductive thin films of oxygen-deficient TiO2 (TiOx) may have applications for static charge elimination on spacecraft surfaces such as solar panels. These films are considerably easier to prepare than the co-deposited ITO/insulator materials currently under consideration. TiOx films 10-35 nm thick were prepared by DC magnetron sputtering on a PET web. They had sheet resistivity (R ) 105-1010 ohms/square with visible transmittance ~85% (not corrected for substrate absorption. R increased by 1-3 orders of magnitude in the first 250 days after deposition, with much of the increase occurring in the first 90 days. The temperature dependence of R before and after aging suggests this instability arises from changes in carrier concentration or crystallographic disorder rather than macroscopic cracking or grain growth. Previous experience with ITO/insulator films suggests that stability of TiOx can be improved by increasing film thickness.

Highly transparent coatings with a maximum sheet resistivity between 108 and 109 ohms/square are desired to prevent charging of solar arrays for low Earth polar orbit and geosynchronous orbit missions. Indium tin oxide (ITO) and magnesium fluoride (MgF2) were ion beam sputter co-deposited onto fused silica substrates and were evaluated for transmittance, sheet resistivity and the effects of simulated space environments including atomic oxygen (AO) and vacuum ultraviolet (VUV) radiation. Optical properties and sheet resistivity as a function of MgF2 content in the films will be presented. Films containing 8.4 wt.% MgF2 were found to be highly transparent and provided sheet resistivity in the required range. These films maintained a high transmittance upon exposure to AO and to VUV radiation, although exposure to AO in the presence of charged species and intense electromagnetic radiation cause significant degradation in film transmittance. Sheet resistivity of the as-fabricated films increased with time in ambient conditions. Vacuum heat treatment following film deposition caused a reduction in sheet resistivity. However, following heat resistivity values remained stable during storage in ambient conditions.

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Last Updated:06/30/2008