Atomic Oxygen Erosion Research Articles

On the Utility of Coated POSS-Polyimides for Vehicles in Very Low Earth Orbit.

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 Al2O3 ALD-coated POSS-polyimides on external satellite surfaces have the potential to reduce drag to less than half of that predicted for diffuse scattering surfaces. These smooth and AO-resistant polymer films thus show promise for use in an extreme oxidizing and high-drag environment in the VLEO.

Analysis of Physical-Chemical Properties and Space Environment Adaptability of Two-Component RTV Silicone Rubber.

Silicone rubber (SR) has the properties of organic–inorganic materials and good adaptability to the space environment, which can be used as an atomic oxygen (AO)-resistant layer on the spacecraft surface. In this study, SR coatings were used to spray on the polyimide surface to prevent atomic oxygen erosion. Then, the physical, chemical, and AO-resistant properties of the SR were investigated. By means of laser diffraction scattering particle size distribution tests, energy-dispersive spectroscopy elemental mapping, and X-ray photoelectron spectroscopy, the fillers and matrix were confirmed as precipitated silica and phenyl SR, respectively. Through analysis of swelling behavior, greater cross-linking density and less swelling ratio were observed at higher temperature and humidity. Furthermore, after AO was exposed with an accumulated fluence of 1.2 × 1021 atoms/cm2, cracks appeared on the coating surface with the change of element content. In addition, it was found that the degree of reaction between AO and SR should not be determined based on mass loss measurements. Our work showed the practical application and great potential of SR protective coating in spacecraft.

Pulsed Electrophoretic Deposition of Carbon Nanotube Based Low-Reflective Coatings for Space Applications

Space observatory missions requires the development of low-reflectivity surfaces/coatings for space-borne instruments, such as seeker telescopes, optical sensors, etc., to minimize stray and reflected light across the visible and infrared wavebands for facilitating the direct exoplanet detection and characterization. All space application materials require lightweight, good thermo-structural properties, and durability when exposed to harsh environments, such as UV, atomic oxygen, vacuum, etc. The excellent mechanical, thermal, optical, and electrical properties of carbon nanotubes (CNTs) make them as ideal coating materials for obtaining low reflectivity surfaces for space applications.In this presentation, Faraday Technology Inc. will discuss an innovative electrophoretic deposition (EPD) manufacturing process, based on the use of pulsed electric fields, for controlled, reproducible, scalable application of low reflective CNT based coatings. The low-reflectivity CNT coatings have been successfully deposited on a variety of geometries: flat coupons, curved surfaces, sharp edges, and internal and external surface of square tubes using the FARADAYIC® EPD process with different anode-cathode configurations (Figure 1 A). The CNT coatings show the total hemispherical reflection of ~ 1% across visible to near infrared (NIR) wavebands, which is 5 times better than the reflectance of the typically used Z306 black paint (Figure 1 B). Most importantly, the CNT coating shows no measurably discernible spectral reflectance changes after 2500 equivalent solar hours (ESH) UV/VUV illumination (Figure 1B). As a comparison, Z306 black paint shows more than 2% reflectance increases with same ESH UV/VUV illumination. These CNT coatings also withstood simulated launch conditions vibrational tests, and demonstrated no weight loss or optical degradation. Furthermore, the CNT coatings were evaluated for atomic oxygen erosion resistance in a simulated low earth orbit (LEO) environment, and showed enhanced resilience when compared to Kapton and HOPG.In summary, a scalable manufacturing process for fabricating CNT based coatings with low reflectivity across visible to near infrared wavebands has been demonstrated and shown great potential in facilitating space observatory missions by minimizing stray and reflected light on targeted telescope and baffle materials and construction. The CNT based coatings will also be beneficial for optoelectronic fields for minimizing unwanted surface reflections for solar thermal power generation and storage, solar-driven steam generation for sanitization and water purification, and so on. Acknowledgements: The financial support of NASA SBIR program through contracts No. 80NNSC18P2062 & 80NSSC19C0177 is acknowledged. The authors acknowledge Alan Hopkins, Peter Fuqua, Amber Hennessy, Aura C Labatete-Goeppinger, Martin Ciofalo, and Lee Wizda from the Aerospace Corporation for simulated launch conditions vibration tests, optical characterization, and UV radiation effect tests. David Oakes and Alan Hoskinson from Physical Sciences Inc. are acknowledged for the atomic oxygen erosion tests on the CNT based coatings. Figure 1

Protection of Kapton from atomic oxygen attack by SiOx/NiCr coating

SiOx/NiCr coatings with different SiOx thicknesses were deposited by the combination of ion implantation (IIP), filter cathode vacuum arc (FCVA), and electron beam (E-beam) evaporation methods to protect flexible Kapton from atomic oxygen (AO) attack. Due to the ion stitching effect and mechanical interlocking of implanted Ni+, the ductility and supporting effect of the fcc γ (Ni-Cr) alloy layer, and the low growth stress of the SiOx, the SiOx/NiCr coatings showed high adhesion and toughness. Exposure tests indicated that the AO erosion yield of the 1 μm-thick SiOx/NiCr-coated Kapton was 5.6 × 10−26 cm3 atom−1, which was attributed to the formation of a compact and continuous thin SiO2 layer. In addition, the inherent kinetic energy and oxidation performance dissipation of AO on the thick inner walls of cracks helped to reduce the cavity cross-sectional area and maximum width in the matrix.

Prediction of erosion characteristics of polyimide with different defect shape pairs based on Monte Carlo method

Under the influence of complex environmental factors such as Atomic oxygen (AO), ultraviolet radiation, and thermal cycling in low earth orbit (LEO), operating efficiency and service life will be reduced for spacecraft. This article modified the Monte Carlo binary chains list retrieval method and adopted a so-called cell array retrieval mode to consider the reaction process, which greatly decrease the number of computing nodes and increases computing speed. Based on this method, the erosion process of Polyimide materials with different defect widths, protective layer thicknesses and defect morphologies under the impact of different AO fluxes is simulated, and the erosion morphology (including depth and width) is quantitatively analyzed. The results of this work provide theoretical support for the failure criterion of materials under AO erosion.

System modelling of very low Earth orbit satellites for Earth observation

The operation of satellites in very low Earth orbit (VLEO) has been linked to a variety of benefits to both the spacecraft platform and mission design. Critically, for Earth observation (EO) missions a reduction in altitude can enable smaller and less powerful payloads to achieve the same performance as larger instruments or sensors at higher altitude, with significant benefits to the spacecraft design. As a result, renewed interest in the exploitation of these orbits has spurred the development of new technologies that have the potential to enable sustainable operations in this lower altitude range. In this paper, system models are developed for (i) novel materials that improve aerodynamic performance enabling reduced drag or increased lift production and resistance to atomic oxygen erosion and (ii) atmosphere-breathing electric propulsion (ABEP) for sustained drag compensation or mitigation in VLEO. Attitude and orbit control methods that can take advantage of the aerodynamic forces and torques in VLEO are also discussed. These system models are integrated into a framework for concept-level satellite design and this approach is used to explore the system-level trade-offs for future EO spacecraft enabled by these new technologies. A case-study presented for an optical very-high resolution spacecraft demonstrates the significant potential of reducing orbital altitude using these technologies and indicates possible savings of up to 75% in system mass and over 50% in development and manufacturing costs in comparison to current state-of-the-art missions. For a synthetic aperture radar (SAR) satellite, the reduction in mass and cost with altitude were shown to be smaller, though it was noted that currently available cost models do not capture recent commercial advancements in this segment. These results account for the additional propulsive and power requirements needed to sustain operations in VLEO and indicate that future EO missions could benefit significantly by operating in this altitude range. Furthermore, it is shown that only modest advancements in technologies already under development may begin to enable exploitation of this lower altitude range. In addition to the upstream benefits of reduced capital expense and a faster return on investment, lower costs and increased access to high quality observational data may also be passed to the downstream EO industry, with impact across a wide range of commercial, societal, and environmental application areas.

Facile and environment-friendly mussel-inspired surface modification of PBO fibers via dopamine/3-aminopropyltrimethoxysilane co-deposition for advanced composite

The surface of poly(p-phenylene benzobisoxazole) (PBO) fibers was modified by a hybrid coating composed of polydopamine (PDA) and the hydrolysis products of 3-aminopropyltrimethoxysilane (KH551) using a facile and environment-friendly mussel-inspired co-deposition strategy. The surface morphologies and chemical composition of the obtained hierarchical reinforcement (PBO@PDA/Si) were measured for confirming the successful deposition of the coating. Compared to untreated PBO fiber, the surface roughness and wettability of PBO@PDA/Si were increased remarkably. Importantly, PBO@PDA/Si showed a 50.2% increase in the interfacial shear strength (IFSS) of resulting composite without any decrease in its tensile strength (TS). In addition, its atomic oxygen (AO) erosion and hydrothermal aging resistances were significantly improved. The “one-step” mussel-inspired surface modification strategy starts from simple chemistry and cheap raw materials, and may provide a novel and versatile design for fabricating multifunctional hierarchical reinforcements.

Multi-faceted simulation of atomic oxygen erosion of deorbit sail for cleaning space debris

Deorbit sails are used in low earth orbit to reduce the growing amount of orbital debris by rapidly removing satellites at the end of their operational missions. However, in low earth orbit, atomic oxygen (AO) is a potential threat to long-duration exposure facilities. In this work, a multi-faceted simulation for the AO erosion of the Taurus Deorbit Sail was developed to calculate the erosion yield for the membrane material and the undercutting profile at the crease site. The disintegration and erosion detail for the deorbit sail membrane during AO impacts can be studied on an atomic scale. The ReaxFF reaction force field program is used to provide a large enough calculation speed in the size of the system to describe all the chemical reactions of the reaction. The on-orbit flight data from the Materials International Space Station Experiment 2 were used to validate the simulated erosion rate in this study. The defects on the deorbit sails were experimentally measured using a scanning electron microscope and then modeled by the Monte Carlo method. The computational predictions of AO undercutting at the defect sites were validated by experimental data from the NASA long-duration exposure facility. The disintegration of the membrane could be divided into two stages: the physical reaction stage and the chemical reaction stage, after 150 AO collisions the membrane becomes highly volatilized. The maximum undercutting depth for the deorbit drag sail within the predicted 37-month deorbit time was 5.5 μm and 7.5 μm for a defect width of 500 nm and 1 μm, respectively. The undercutting width for a deorbit sail with a width of 500 nm or 1 μm was predicted to be 1.6 μm and 2 μm, respectively, and the breaker was formed at the bottom of the undercutting profile. AO erosion has been studied by researchers in terms of evaluating the effectiveness of protective coatings. This current study, however, seeks to understand the fundamental interactions between AO and creases in the deorbit sail, which provides deeper knowledge than what has been developed so far. The multi-faceted simulation results can provide design references for engineering applications for the deorbit sail.

Atomic oxygen effect of Zr-Al-C coatings on ZrNb alloys used in space environment

The preparation of suitable coating materials is crucial for enhancing the atomic oxygen erosion of zirconium alloys. Zr-Al-C ceramics composed of MAX phase have excellent inherited properties of metal and ceramic, making them useful as spacecraft materials for atomic oxygen protection. The MAX phases are a group of layered ternary compounds with the general formula Mn+1AXn (M: early transition metal; A: group A element; X: C and/or N; n = 1–3), which combine some properties of metals, such as machinability, low hardness and damage tolerance, with those of ceramics, such as high elastic moduli, high temperature strength, oxidation and corrosion resistance. In this paper, Zr-Al-C coatings were successfully prepared by the magnetron sputtering method. The macroscopy morphology, microstructure, adhesion and the effect of atomic oxygen of Zr-Al-C coatings were all investigated. The results showed the successful deposition of Zr-Al-C coatings consisting of Zr2Al3C4, Zr3Al3C5, and ZrAl3 phases on zirconium alloy surface by adding an intermediate layer using magnetron sputtering route. The adhesion between the coating and the substrate was estimated to 18 N by scratch testing. After 30 cycles of cold and hot impact tests, the Zr-Al-C coating remained undamaged without crack or peel off. The oxidation kinetics of ZIRLO with Zr-Al-C coating followed approximatively a linear variation law. The oxidation rate of ZIRLO containing Zr-Al-C coating was lower than that of uncoated Zr alloy within 30 h of atomic oxygen exposure. In other words, Zr-Al-C coating could protect Zr alloy under certain exposure dosage of atomic oxygen. Meanwhile, further increase in exposure time of atomic oxygen led to the formation of ZrO, ZrO2, Al2O3 on Zr-Al-C coating. Also, more pores appeared on Zr-Al-C coating surface due to the oxidation of carbon elements in the coatings to form volatile oxides, such as CO and CO2. As atomic oxygen erosion continued, the existing holes became connected to form complex channel-like labyrinthine two-dimensional network structures. The latter penetrated further the atomic oxygen into the interior of Zr-Al-C coating to continue the corrosion effect of atomic oxygen. By considering the protection effect of Zr-Al-C coating on Zr alloy under a certain exposure dosage of atomic oxygen, the protection time can be calculated and experiments can be designed according to the linear law obtained as a function of the thickness of Zr-Al-C coating. In sum, these results look promising for future application of MAX or MAX-like phase in spacecraft environment.

The Influence of the Density of CNT Arrays on Their Atomic Oxygen Erosion Effects

To investigate the characteristic of carbon nanotube (CNT) arrays with high resistance to the hazardous conditions of atomic oxygen in space environment, the erosion effects of atomic oxygen on CNT arrays with different density have been studied by atomic oxygen simulation equipment. To characterizing the change of the surface morphologies of CNT arrays before and after atomic oxygen exposition, A scanning electron microscope (SEM) analysis method have been used. The SEM images shows that the morphologies of the surface of CNT arrays after atomic oxygen experiment are quite different from those before atomic oxygen experiment. The higher density CNT arrays are etched away more uniformly. The erosion yield of the CNT arrays with higher density is much less than that with lower density, which means that the CNT materials have different atomic oxygen erosion yield. The resistance ability of CNT materials to atomic oxygen is depending on their density.

Preparation of two-component hybrid polyimide film for atomic oxygen erosion resistance

Searching for a method for simple and low-cost preparation of polyimide (PI) composite film and exploring their atomic oxygen (AO) erosion resistance properties are highly important. For the first time we studied the AO erosion resistance of SiO2–Al2O3 doped composite PI film, and the associated sol–gel method and physical blending method were compared. After exposure to AO, all the nanocomposite film shows enhanced AO erosion resistance. Especially, a loading of 7.5 wt% SiO2–2.5 wt% Al2O3 can decrease the AO induced mass loss by 81% when compared to the pure PI, i.e. the AO resistance was increased by 4–5 times. It is found that with the same doping content, the AO resistance of the two-component (SiO2–Al2O3) hybrid PI film is notably higher than that of the single component one. The mechanism could be attributed to the SiO2–Al2O3 synergistic effect which induces a more stable protective layer on the material surface. The two-component PI composite film with enhanced AO resistance shows promise in the space applications where AO erosion has to be avoided.

Thermoplastic Polymeric Materials for Spacecraft Applications: Flame Retardant Properties and UV/AtOx Aging Analysis

Space-mission development introduced the problem of human isolation in extreme environments. The integration of architectural concepts such as windows, with their technical implications into human space missions, is necessary especially for long-duration space flights. Such solutions must be subjected to close certification testing in order to establish their compliance with severe space environment conditions. Moreover, projects of long-term missions involve a renewed concern about fire safety in manned space vehicles. The supposed occupancy time of the order of decades, in fact, makes unplanned fire ignition events virtually unavoidable. An experimental test-plan performed to qualify a commercial thermoplastic material for applications as transparent element in spacecraft is reported in the present work. A flame exposure test, as well as ultraviolet radiation and atomic oxygen erosion rate measurements, was carried out on a commercial poly-sulfone material, following ASTM standard procedures. The aim of the research was to develop and put forward flame retardant structures able to withstand the harsh space environment, preventing or mitigating the degradation of their physical and chemical integrity, with particular regard to the visible-light transparency. The results obtained show that the tested poly-sulfone may be considered as a promising material for the claimed application, even if further surface optimization treatments should be conceived in order to gain a full adaptability to the operative constraints.

Atomic Oxygen-Resistant Polyimide Composite Films Containing Nanocaged Polyhedral Oligomeric Silsesquioxane Components in Matrix and Fillers

For the development of spacecraft with long-servicing life in low earth orbit (LEO), high-temperature resistant polymer films with long-term atomic oxygen (AO) resistant features are highly desired. The relatively poor AO resistance of standard polyimide (PI) films greatly limited their applications in LEO spacecraft. In this work, we successfully prepared a series of novel AO resistant PI composite films containing nanocaged polyhedral oligomeric silsesquioxane (POSS) components in both the PI matrix and the fillers. The POSS-containing PI matrix film was prepared from a POSS-substituted aromatic diamine, N-[(heptaisobutyl-POSS)propyl]-3,5-diaminobenzamide (DABA-POSS) and a common aromatic diamine, 4,4′-oxydianline (ODA) and the aromatic dianhydride, pyromellitic dianhydride (PMDA) by a two-step thermal imidization procedure. The POSS-containing filler, trisilanolphenyl POSS (TSP-POSS) was added with the fixed proportion of 20 wt% in the final films. Incorporation of TSP-POSS additive apparently improved the thermal stability, but decreased the high-temperature dimensional stable nature of the PI composite films. The 5% weight loss temperature (T5%) of POSS-PI-20 with 20 wt% of DABA-POSS is 564 °C, and its coefficient of linear thermal expansion (CTE) is 81.0 × 10−6/K. The former is 16 °C lower and the latter was 20.0 × 10−6/K higher than those of the POSS-PI-10 film (T5% = 580 °C, CTE = 61.0 × 10−6/K), respectively. POSS components endowed the PI composite films excellent AO resistance and self-healing characteristics in AO environments. POSS-PI-30 exhibits the lowest AO erosion yield (Es) of 1.64 × 10−26 cm3/atom under AO exposure with a flux of 2.51 × 1021 atoms/cm2, which is more than two orders of magnitude lower than the referenced PI (PMDA-ODA) film. Inert silica or silicate passivation layers were detected on the surface of the PI composite films exposed to AO.

Research on experimental method of carbon nanotubes space environment effect

Due to its unique structure and superior performance, carbon nanotubes are proposed to have great potential applications in many fields. Recently, more and more concerns have been focused on the application of carbon nanotubes in space technology. It is believed that carbon nanotubes can have a broad impact on space missions in future with benefits principally in space technology, such as lightweight structure materials, environment protection materials, energy gerneration and storage and nanoelcetronics. However, carbon nanotubes would suffer chemical and physical damage from the space environment when it was used in spacecraft, just like all the other space materials. The environment where spacecrafts operate is extremely intricate, primarily represented by electromagnetic irradiation, charged particle irradiation, high vacuum, cold and hot alternation, atomic oxygen erosion, clash from space debris, and other factors. The mostly effect in space environment is atomic oxygen and debris for grapheme. This paper is about the research on the experimental methods of carbon nanotubes space environment effect with atomic oxygen and space debris as examples, in a bid to propose the experimental scheme of carbon nanotubes space environment effect. It will be great helpful to promote the applications of carbon nanotubes in space technology.

Facile method for fabricating atomic oxygen resistant polyimide films with excellent optical homogeneity containing hyperbranched polysiloxane

Mechanically robust optical homogeneous polyimide (PI) films with desirable atomic oxygen (AO) erosion duration were fabricated by initially synthesizing amine-functionalized hyperbranched polysiloxane (NH2-HBPSi), then reinforcing the pristine polyimide skeleton with it via copolycondensation reactions. NH2-HBPSi macromolecule imparts desirable AO survivability to the resulting hybrids. The mass loss per unit area of hybrid films had a downward trend with rising NH2-HBPSi content and AO dose before the complete silica protective layer was formed. It has been proven by the experiments in an underground simulated AO environment. It decreased to 1% of that of pristine polyimide when NH2-HBPSi accounted for 30% of the solid content after 24 h AO attack. The stable thickness uniformity that can meet the Rayleigh criterion was achieved in a 30 wt% HBPSi PI film, mainly due to the selection of the best process parameters. Meanwhile, 30 wt% HBPSi PI demonstrates satisfactory mechanical properties, with a tensile strength of 228.9 MPa and elongation at break of 7.3%. The characterization of scanning electron microscopy confirmed that pristine polyimide was substantially eroded after AO exposure while the surface morphology of 30 wt% HBPSi polyimide showed no evident change. The low AO erosion yield and prominent film thickness uniformity may find extensive usage in ultra-lightweight space diffractive optical elements (DOE) working in low earth orbit (LEO).

Preparation and Properties of Intrinsically Atomic-Oxygen Resistant Polyimide Films Containing Polyhedral Oligomeric Silsesquioxane (POSS) in the Side Chains.

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.

A reactive molecular dynamics study of hyperthermal atomic oxygen erosion mechanisms for graphene sheets

Carbon-based composite materials are widely used in the aerospace field due to their light weight and excellent physical/chemical properties. The mechanisms of the erosion process, e.g., surface catalysis and ablation, during the impact of oxygen atoms, however, remain unclear. In this study, the surface catalysis and ablation behavior during the erosion process of hyperthermal atomic oxygens were achieved through the molecular dynamics method with the reactive force field potential. The concomitant impacts of energy flux density of energetic oxygen atoms, the presence of multiple layers beneath the graphene sheet, and the morphology of graphite surfaces, i.e., graphite basal plane, armchair (AC) edge surface, and zigzag edge surface, respectively, were discussed. The results show that the adsorption of oxygen atoms dominates at the beginning by generating O2 molecules, suggesting the importance of surface catalytic for any ablation study. A unique “layer-by-layer” ablation phenomenon by hyperthermal atomic oxygen is observed for multi-layered graphite slab, and the ablation rate reduces as the number of graphene layers increases. The morphology/structure of the surface shows significant effects on the ablation rate, with AC surfaces showing the largest etching rate and the basal one showing the lowest. The low binding energies of the AC edge are responsible for the difficulty in the formation of stable functional group structures to resist the etching of high-enthalpy oxygen atoms. Such revelation of the detailed surface catalysis and ablation mechanism at the atomistic scale provides insight into design of future materials for the augmentation of the thermal protection effect.

Transparent metamaterial absorber with broadband radar cross‐section (RCS) reduction for solar arrays

Solar arrays are the primary energy source of the satellite. In this study, a metamaterial absorber for solar arrays with simultaneous high optical transparency and broadband microwave absorption is presented. By tailoring the reflection response of meta-atoms, 87% absorption performance from 6.8 to 18 GHz is obtained. In the meantime, by employing transparent substrates, including indium tin oxide film and anti-reflection glass, a maximum of 87% light transmittance is achieved. The absorptivity of the proposed metamaterial absorber is simulated and measured experimentally. Optical transmittance and the effect of transparent metamaterial absorber on the conversion efficiency of the solar array have also been measured. These results fully demonstrate the reliability of the authors’ design for solar arrays, which also meet the actual requirements of structural strength, atomic oxygen erosion resistance, weight limitation etc.

Janus polyimide films with outstanding AO resistance, good optical transparency and high mechanical strength

Polyimide films are required onboard spacecrafts withstanding atomic oxygen (AO) erosion in low earth orbit environment. We report a janus polyimide composite film consisting of HBPSi enriched and scanty surfaces/sides. This unique structure ensures both outstanding AO resistance—with relative mass loss merely 8.34% that of standard Kapton H—and admirable mechanical performance with ultimate tensile strength as high as ca. 89 MPa and fracture toughness up to 5.22 MJ·m−3. Besides, janus polyimide composite films are good at maintaining its surface morphology and integrity upon AO attack, showing a higher transmittance after AO exposure (ca. 82% at 600 nm) and lower root mean square roughness (RMS) value (5.14 nm vs. 6.62 nm) in comparison to its monolayered counterpart. These janus polyimide films demonstrate exceptional performance and thus show great potential for making surface protective blanket for spacecrafts functioning in space environment.

First-principles insights into atomic oxygen diffusion inside polyhedral oligomeric silsesquioxane cages

Atomic oxygen erosion is a significant threat to exterior spacecraft polymers. Polyhedral oligomeric silsesquioxane (POSS) is a potential kind of material in resisting AO diffusion erosion, but lack of mechanism studies for application supports. In this research, we used the first-principles calculations to investigate the mechanism based on two types of nominally hydrated POSS named T8 (Si8O12H8) and T10 (Si10O15H10). According to the results, we found that the minimum energy path (MEP) of AO diffusing inside POSS is the adjacent-edge-path rather than the center-path. We also found the energy barriers that hinder the diffusion motion of AO inside POSS are originated from the structural distortion of POSS, which are negatively correlated to Si-O bond length and positively correlated to structural compactness. Thus, compacter POSS structures with shorter Si-O bond length are expected to give better AO diffusion resistance properties.