Low Earth Orbital Atomic Oxygen Interactions with Spacecraft Materials

Acknowledgements. Introduction. Organizing Committee. Section A: AO/VUV Effects, Evaluation and Modeling. 1. Monte Carlo Computational Modeling of the Energy Dependence of Atomic Oxygen Undercutting of Protected Polymers B.A. Banks, et al. 2. Dynamics of Atomic-Oxygen-Induced Degradation of Materials T.K. Minton, et al. 3. Generalization of the Predictive Model of Erosion of Carbon-Based Materials by Atomic Oxygen J.I. Kleiman, et al. 4. Spectroscopic Ellipsometry Characterization of Polymers Modified by Atomic Oxygen and Ultraviolet Radiation C.L. Bungay, et al. 5. Effect of Atomic Oxygen Exposures on the Tribological Properties of Molybdenum Disulfide Lubricants M. Tagawa, et al. 6. Influence of Shielding Upon the Structure and Properties of Polymer Composite Materials, Exposed on the Surface of the Mir Orbital Complex O.V. Startsev, et al. 7. Cleanliness Support of Vehicle Fairings for Spacecraft V. Sitalo, V. Tikhiy. 8. In situ XPS Studies of Kapton Exposed to 5 eV Atomic Oxygen E. Grossman, et al. Section B: Instrumentation, Sensors, New Technologies. 9. A Low Cost, Lightweight Reusable Sensor for Atomic Oxygen Detection J.J. Osborne, et al. 10. Large-Scale ECR-CVD Preparation of Integrated Thin-Film Structures for Space Applications R.V. Kruzelecky, et al. 11. Non-Silicone Inorganic Polymer-Based Coatings for Atomic Oxygen Protection in LEO - Part 2 E. Poire, et al. 12. Research Aspects of Scaling Up the Implantox Technology for Protection of Polymers in Space Z.A. Iskanderova, et al. Section C: ThermalControl in LEO. 13. A Comparison of Space and Ground-Based Facility Environmental Effects for FEP Teflon S.K. Rutledge, et al. 14. Evaluation of Low Earth Orbit Environmental Effects on International Space Station Thermal Control Materials J.A. Dever, et al. 15. Some Aspects of the Degradation of FEP Teflon Material Under the Action of VUV, the Sun and Ground Test VUV Facilities A. Milintchouk, M. Van Eesbeek. 16. Evaluation of COF MDPS Chromic Acid Anodization in LEO Environment C. Acket, et al. 17. A Database for the Selection of Surfaces and Materials for Space and Ground-based Applications S.H. McCall, et al. 18. Thermal Control Materials and Coatings Currently Being Developed in France for Use in Low Earth Orbit F. Guerard, J.C. Guillaumon. 19. Modification of Thermal Control Paints by Photosil (TM) Technology J.I. Kleiman, et al. Section D: Charged Particles/Soft X-Rays/Meteoroids/Thermal Cycling. 20. Simulated Solar Flare X-Ray and Thermal Cycling Durability Evaluation of HST Thermal Control Candidate Replacement Materials K.K. de Groh, et al. 21. Radiation-Induced Effects in SiO2 Protective Coatings on Polymeric Spacecraft Materials C. Coia, et al. 22. Influence of Electron and Proton Fluxes on Optical Properties of Protective Enamel S.N. Skovorod'ko, et al. 23. Meteoroid Hazard in the LEO Space Environment Y.S. Yatskiv, et al. 24. Characterizing the Annual Meteoroid Streams M. Beech. 25. Oxidation Kinetics of VB Group Metals by Atomic and Molecular Oxygen A.G. Gusakov, et al. 26.

Atomic oxygen is formed in the low Earth orbital environment (LEO) by photo dissociation of diatomic oxygen by short wavelength (< 243 nm) solar radiation which has sufficient energy to break the 5.12 eV O2 diatomic bond in an environment where the mean free path is sufficiently long (~ 108 meters) that the probability of reassociation or the formation of ozone (O3) is small. As a consequence, between the altitudes of 180 and 650 km, atomic oxygen is the most abundant species. Spacecraft impact the atomic oxygen resident in LEO with sufficient energy to break hydrocarbon polymer bonds, causing oxidation and thinning of the polymers due to loss of volatile oxidation products. Mitigation techniques, such as the development of materials with improved durability to atomic oxygen attack, as well as atomic oxygen protective coatings, have been employed with varying degrees of success to improve durability of polymers in the LEO environment. Atomic oxygen can also oxidize silicones and silicone contamination to produce non-volatile silica deposits. Such contaminants are present on most LEO missions and can be a threat to performance of optical surfaces. The LEO atomic oxygen environment, its interactions with materials, results of space testing, computational modeling, mitigation techniques, and ground laboratory simulation procedures and issues are presented.

Low Earth orbit effects on indium tin oxide and polyester and comparison with laboratory simulations

Atomic oxygen and molecular nitrogen are the major constituents in the residual atmosphere at low Earth orbital altitudes, and they collide with spacecraft surfaces at relative velocities of ∼7.8 km s−1. The energy associated with these hyperthermal collisions is in excess of many bond dissociation energies and may help promote materials degradation by allowing barriers to reaction or to collision‐induced dissociation (CID) to be overcome. Spacecraft in low Earth orbit (LEO) are also exposed to high fluxes of vacuum ultraviolet (VUV) radiation, which may degrade materials through various photochemical mechanisms. Fluorinated ethylene‐propylene copolymer (FEP Teflon®) is commonly used on spacecraft. Many researchers have studied the individual and/or combined effects of atomic oxygen, VUV light, and CID on FEP Teflon®, yet the detailed degradation mechanisms of FEP Teflon® in LEO are still a subject of debate. Although not as ubiquitous as a spacecraft material, polymethylmethacrylate (PMMA) has been studied as a model and control polymer because of its well known propensity to “unzip” upon exposure to VUV radiation. A combination of beam‐surface scattering, quartz crystal microbalance (QCM), and surface‐recession experiments were conducted to study the effects of various combinations of O atoms (in the ground O(3P) state), Ar atoms, and VUV light on FEP Teflon® and PMMA. A laser‐breakdown source was used to create hyperthermal beams containing O and O2 or argon. A deuterium lamp provided a source of VUV light. O atoms with 4 eV of translational energy or less did not react with a pristine FEP Teflon® surface. Volatile O‐containing reaction products were observed when the O‐atom energy was higher than 4.5 eV, and the signal increased with O‐atom energy. Significant FEP Teflon erosion (∼20% of Kapton® H) was observed when it was exposed to the hyperthermal O/O2 beam with an average O‐atom energy of 5.4 eV. FEP Teflon® and PMMA that were exposed to VUV light alone yielded volatile products and mass loss. Similarly, CID by Ar also yielded volatile products and mass loss, when the Ar energy was higher than 8 eV. However, the erosion caused by VUV light and/or CID is not significant compared to that caused by O/O2. There were no observed synergistic effects of VUV light and O/O2 exposure.

SiO2 coatings were deposited on silver foils substrate by sol–gel method and their atomic oxygen (AO) erosion resistance was tested in a ground-based AO simulator. The surface morphologies and structures of the SiO2 coatings were investigated by Scanning Electron Microscopy (SEM) 、X-Ray Photoelectron Spectroscopy (XPS). The experimental results clearly demonstrate that this kind of coatings provided a good protection from AO attack. The erosion yield of the coatings was 2×10-26 cm3/atom, decreased by 30 times compared with that of the uncoated silver foils. This SiO2 layer significantly retarded the penetration of oxygen atoms, preventing further oxidation of the bulk silver. It was found that after AO exposure, the film structure tends to transfer from SiOH to amorphous SiO2. This implies that a more stable amorphous SiO2 structure could be formed in sol-gel SiO2 film during AO exposure. The results demonstrate that the coatings prepared by sol-gel technique can protect the silver from atomic oxygen erosion and can be used easily for practical application.

Molecular design of polyimide films for combating atomic oxygen erosion through combing experiments with simulations: A state-of-the-art review

Advances in atomic oxygen resistant polyimide composite films

The environment encountered by space vehicles in very low Earth orbit (VLEO, 180 – 350 km altitude) contains predominantly atomic oxygen (AO) and molecular nitrogen (N2), which collide with ram surfaces at relative velocities of ~7.5 km s-1. Structural, thermal-control, and coating materials containing organic polymers are particularly susceptible to AO attack at these high velocities, resulting in erosion, roughening, and degradation of function. Copolymerization or blending of a polymer with polyhedral oligomeric silsesquioxane (POSS) yields a material that can resist AO attack through the formation of a passivating silicon-oxide layer. Still, these hybrid organic/inorganic polymers become rough through AO reactions as the passivating layer is forming. Surface roughness may enhance satellite drag because it promotes energy transfer and scattering angle randomization during gas-surface collisions. As potential low-drag and AO-resistant materials, we have investigated POSS-containing films of clear and Kapton-like polyimides that have an atomically smooth AO-resistant coating of Al2O3 that is grown by atomic layer deposition (ALD). Coated and uncoated films were exposed to hyperthermal molecular beams containing atomic and molecular oxygen to investigate their AO resistance, and molecular beam-surface scattering studies were conducted to characterize the gas-surface scattering dynamics on pristine and AO-exposed surfaces to inform drag predictions. The AO erosion yield of Al2O3 ALD-coated films is essentially zero. Simulations of drag on a representative satellite structure that are based on the observed scattering dynamics suggest that the use of the Al2O3 ALD-coated POSS-polyimides on external satellite surfaces have the potential to reduce drag to less than half that predicted for diffuse scattering surfaces. These smooth and AO-resistant polymer films thus show promise for use in the extreme oxidizing and high-drag environment in VLEO.

Traditional polyimides have highly conjugated structures, causing significant coloration under visible light. Fluorinated colorless polyimides, known for their light weight and excellent optical properties, are considered ideal for future aerospace optical lenses. However, their lifespan in low Earth orbit is severely limited by high-density atomic oxygen (AO) erosion, and the degradation behavior of fluorinated polyimides under AO exposure is not well understood. This study uses reactive molecular dynamics simulations to model two fluorinated polyimides, PMDA-TFMB and 6FDA-TFMB, with different fluorine contents, to explore their degradation mechanisms under varying AO concentrations. The results indicate that 6FDA-TFMB has slightly better resistance to erosion than PMDA-TFMB, mainly due to the enhanced chemical stability from its -CF3 groups. As AO concentration increases, widespread degradation of the polyimides occurs, with AO-induced cleavage and temperature-driven pyrolysis happening simultaneously, producing CO and OH as the main degradation products. This study uncovers the molecular-level degradation mechanisms of fluorinated polyimides, offering new insights for the design of AO erosion protection systems.

The relatively poor atomic-oxygen (AO) resistance of the standard polyimide (PI) films greatly limits the wide applications in low earth orbit (LEO) environments. The introduction of polyhedral oligomeric silsesquioxane (POSS) units into the molecular structures of the PI films has been proven to be an effective procedure for enhancing the AO resistance of the PI films. In the current work, a series of POSS-substituted poly (pyromellitic anhydride-4,4′-oxydianiline) (PMDA-ODA) films (POSS-PI) with different POSS contents were synthesized via a POSS-containing diamine, N-[(heptaisobutyl-POSS)propyl]-3,5-diaminobenzamide (DABA-POSS). Subsequently, the effects of the molecular structures on the thermal, tensile, optical, and especially the AO-erosion behaviors of the POSS-PI films were investigated. The incorporation of the latent POSS substituents decreased the thermal stability and the high-temperature dimensional stability of the pristine PI-0 (PMDA-ODA) film. For instance, the PI-30 film with the DABA-POSS content of 30 wt% in the film exhibited a 5% weight loss temperature (T5%) of 512 °C and a coefficient of linear thermal expansion (CTE) of 54.6 × 10−6/K in the temperature range of 50–250 °C, respectively, which were all inferior to those of the PI-0 film (T5% = 574 °C; CTE = 28.9 × 10−6/K). In addition, the tensile properties of the POSS-containing PI films were also deteriorated, to some extent, due to the incorporation of the DABA-POSS components. The tensile strength (TS) of the POSS-PI films decreased with the order of PI-0 > PI-10 > PI-15 > PI-20 > PI-25 > PI-30, and so did the tensile modulus (TM) and the elongations at break (Eb). PI-30 showed the TS, TM, and Eb values of 75.0 MPa, 1.55 GPa, and 16.1%, respectively, which were all lower than those of the PI-0 film (TS = 131.0 MPa, TM = 1.88 GPa, Eb = 73.2%). Nevertheless, the incorporation of POSS components obviously increased the AO resistance of the PI films. All of the POSS-PI films survived from the AO exposure with the total fluence of 2.16 × 1021 atoms/cm2, while PI-0 was totally eroded under the same circumstance. The PI-30 film showed an AO erosion yield (Es) of 1.1 × 10−25 cm3/atom, which was approximately 3.67% of the PI-0 film (Es = 3.0 × 10−24 cm3/atom). Inert silica or silicate passivation layers were detected on the surface of the POSS-PI films after AO exposure, which efficiently prevented the further erosion of the under-layer materials.

Forty-one different polymers are being exposed to the low Earth orbit (LEO) environment on the exterior of the International Space Station (ISS) for one year as part of MISSE (Materials International Space Station Experiment). MISSE is a materials flight experiment sponsored by the Air Force Research Lab/Materials Lab and the National Aeronautics and Space Administration (NASA). A second set of the same polymers is planned to be flown as part of PEACE (Polymer Erosion And Contamination Experiment), a short duration shuttle flight experiment, and therefore these forty-one polymers on ISS are collectively called the MISSE PEACE Polymers. The objective of the MISSE PEACE Polymers experiment is to accurately determine the atomic oxygen (AO) erosion yield of a wide variety of polymeric materials. The polymers range from those commonly used for spacecraft applications, such as Teflon FEP, to more recently developed polymers, such as high temperature polyimide PMR (polymerization of monomer reactants). Additional polymers were included to explore erosion yield dependence upon chemical composition. Details on the specific polymers being flown, flight sample fabrication, and pre-flight characterization techniques will be discussed. The MISSE PEACE Polymers experiment was placed on the exterior of ISS during a spacewalk on August 16, 2001 and is planned to be retrieved in the fall of 2002. The erosion yield data obtained from this experiment will be compared with data from the future short duration experiment PEACE and with predicted results from models developed by a Canadian group that predicts the AO erosion yield of organic materials based on their chemical structure. Having flight data, and comparing flight data with the predictive model results, will be valuable for spacecraft design purposes.

Irradiation effects of 12 eV oxygen ions on polyimide and fluorinated ethylene propylene

ABSTRACTThe application of graphene (Gr) to enhance atomic oxygen (AO) erosion resistance and mechanical properties was demonstrated in this study. Gr‐reinforced cellulose acetate (CA) composite films were obtained by flattening with a glass rod, and the AO erosion resistance was investigated in a plasma‐type, ground‐based AO effect simulation facility. Significant improvements in the mechanical properties and AO erosion resistance were achieved at relatively low Gr contents. A 59 ± 7% decrease in the mass loss and a 12 ± 3% increase in the tensile strength were achieved by the addition of only 1 wt % Gr. Moreover, the layered structure of the fractured surfaces and the excellent mechanical properties illustrated the homogeneous dispersion of Gr in the CA matrix and the strong interactions between Gr and CA. Furthermore, Gr flakes served as shields to defend the underside of CA from AO erosion because of the specific two‐dimensional structure and outstanding AO erosion resistance. Therefore, this research provides a new and effective strategy for improving the mechanical strength and AO erosion resistance of polymer materials. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40292.

Polyimides are widely used for the external surfaces of spacecraft. In low Earth orbit (LEO), they are exposed to atomic oxygen (AO) and to problems of electrostatic discharge (ESD). This work demonstrates that liquid-phase deposition (LPD) of titania creates a protective coating on Kapton polyimide that is effective in reducing AO-induced surface erosion and in preventing ESD. Adherent titania coatings, 100−300 nm thick, were deposited on Kapton at near-ambient conditions by LPD using an aqueous solution of a metal-fluoride complex and boric acid. Characterization of the oxide-coated Kapton included atomic force microscopy (AFM) in tapping and nanoindentation modes, electrostatic force microscopy (EFM), scanning electron microscopy (SEM), Rutherford back-scattering (RBS) and X-ray photoelectron spectroscopy (XPS). The as-deposited titania-coated Kapton can be prepared without significant changes in the original thermo-optical properties of the polymer, while preventing ESD and improving the surface hardness. The durability of the oxide coating under AO attack was studied using an oxygen RF plasma. Surface erosion was measured both gravimetrically and by in situ quartz crystal microbalance (QCM) measurements. The AO exposure caused some changes in the thermo-optical properties and surface morphology. The erosion yield of titania-coated Kapton was only 2% of that observed for uncoated Kapton after exposure to 4 × 1020 O-atoms cm−2 of LEO equivalent AO fluence.

There have been five Materials International Space Station Experiment (MISSE) passive experiment carriers (PECs) (MISSE 1–5) to date which have been launched, exposed in space on the exterior of International Space Station (ISS) and then returned to Earth for analysis. An additional four MISSE PECs (MISSE 6A, 6B, 7A & 7B) are in various stages of completion. The PECs are two‐sided suitcase size sample carriers that are intended to provide information on the effects of the low Earth orbital environment on a wide variety of materials and components. As a result of post retrieval analyses of the retrieved MISSE 2 experiments and numerous prior space experiments, there have been valuable lessons learned and needs identified that are worthy of being documented so that planning, design, and analysis of future space environment experiments can benefit from the experience in order to maximize the knowledge gained. Some of the lessons learned involve the techniques, concepts, and issues associated with measuring atomic oxygen erosion yields. These are presented along with several issues to be considered when designing experiments, such as the uncertainty in mission duration, scattering and contamination effects on results, and the accuracy of measuring atomic oxygen erosion.