Explore the vast range of titles available.

Atomic oxygen radical anion (O⋅−) represents an important type of reactive centre that exists in both chemical and biological systems. Gas‐phase atomic clusters can be studied under isolated and well controlled conditions. Studies of O⋅−‐containing clusters in the gas‐phase provide a unique strategy to interpret the chemistry of O⋅− radicals at a strictly molecular level. This review summarizes the research progresses made since 2013 for the reactivity of O⋅− radicals in the atomically precise metal oxide clusters including negatively charged, nanosized, and neutral heteronuclear metal clusters benefitting from the development of advanced experimental techniques. New electronic and geometric factors to control the reactivity and product selectivity of O⋅− radicals under dark and photo‐irradiation conditions have been revealed. The detailed mechanisms of O⋅− generation have been discussed for the reaction systems of nanosized and heteroatom‐doped metal oxide clusters. The catalytic reactions mediated by the O⋅− radicals in metal clusters have also been successfully established and the microscopic mechanisms about the dynamic generation and depletion of O⋅− radicals have been clearly understood. The studies of O⋅− containing metal oxide clusters in the gas‐phase provided new insights into the chemistry of reactive oxygen species in related condensed‐phase systems. This review summarizes the novel factors to control the reactivity of oxygen‐centred radicals (O⋅−) as well as the detailed mechanisms of O⋅− generation discovered by the investigation on gas phase metal oxide clusters.

In order to expand the range of materials that can be used in outer space and in development of small spacecraft, ladder polyphenylsilsesquioxanes with different molar weights and the Nb-siloxane composites based on them were studied. The properties of the polymer films were studied, including tests in an oxygen plasma flow. Both initial and filled ladder polymers feature extremely low erosion coefficients in the region of 10–26 cm3/atom O at a high fluence of atomic oxygen of 1.0 × 1021 atom O/cm2. Ladder polyphenylsilsesquioxane films irradiated with atomic oxygen (AO) retain their integrity, do not crack, and exhibit good optical properties, in particular, a high transmittance. The latter slightly decreases during AO exposure. The Nb-siloxane filling retains the AO resistance and slight decrease in optical transmission due to diffuse scattering on the formed Nb-[(SiO)x] nanoparticles. Ladder polyphenylsilsesquioxanes demonstrate their suitability for creating protective, optically transparent coatings for small spacecraft that are resistant to the erosive effects of incoming oxygen plasma.

This paper presents a standalone predictive model for Atomic Oxygen (AO), Coronal Mass Ejections (CMEs) and other space-environment parameters. The prediction is based on the numerical method of Holt–Winter’s triple smooth exponential forecasting of atmospheric constituents. Solar cycle 25 is likely to show about the same activity as cycle 23. The corresponding AO-flux–solar-activity correlation coefficients for altitudes 100, 200, and 300 km are: 0.62, 0.53, and 0.48, respectively, while the correlation coefficients for higher altitudes are lower than 0.48, an advantage that makes them more favorable for LEOs due to the harmful corrosive effects.

The oxidation and erosion of atomic oxygen are considered to be the most dangerous environmental factors for materials exposed to the aerospace environment. In order to investigate the effect of atomic oxygen on the lubricating film and improve the tribological properties, MoS2–WS2 composite film was prepared by the sputtering technique. The film structure and mechanical behavior were characterized and their vacuum tribological properties were evaluated by a friction tester. The composite film possessed better atomic oxygen (AO) resistance than pure film because of the dense structure. The tribological performance of composite film was different under the conditions after AO-irradiation and sliding and during AO-irradiation. After AO-irradiation, the tribological properties of composite film were similar to those before AO-irradiation. However, high friction noise, wear rate, and reduced wear duration were observed for the composite film under the AO-irradiation/friction process because of the continuous damage of the lubricating film due to the AO-irradiation. The addition of 16 at.% WS2 to the MoS2-based film changed the composite film structure and improved the oxidation resistance of the film, making the composite film exhibit better tribological performance than pure MoS2.

External spacecraft materials play an important role in protecting satellites from the harsh space environment. These materials undergo changes in their physical, chemical, mechanical, and optical properties due to exposure to various forms of ionizing radiation, electrons, protons with varying energy levels, oxygen ions, micrometeoroids and orbital debris (MMOD), vacuum conditions, and wide temperature fluctuations. Understanding of how these materials evolve in these conditions is crucial for planning long-term space missions. This paper evaluates the impact of radiation in the low Earth orbit (LEO) environment on the properties of both novel and heritage polymer materials. Specifically, it examines the effects of exposure to high-energy electrons, atomic oxygen (AO), and vacuum ultraviolet (VUV) radiation on key material characteristics, including color change, surface roughness, and alterations in surface elemental composition. These materials were part of the 16th Materials International Space Station Experiment (MISSE), conducted from July 2022 to March 2023.

Effective ablative thermal protection systems are essential for ensuring the structural integrity of hypersonic vehicles subjected to extreme aerothermal loads. However, the microscopic reaction mechanisms at the gas–solid interface, particularly under non-equilibrium high-enthalpy conditions, remain poorly understood. This study employs reactive molecular dynamics (RMD) simulations with the ReaxFF-C/H/O force field to investigate the atomic-scale ablation behavior of a graphene-based knitted graphene structure impacted by atomic oxygen (AO). By systematically varying the AO incident kinetic energy (from 0.1 to 8.0 eV) and incidence angle (from 15° to 90°), we reveal the competing interplay between catalytic recombination and ablation processes. The results show that the catalytic recombination coefficient of oxygen molecules reaches a maximum at 5.0 eV, where surface-mediated O2 formation is most favorable. At higher energies, the reaction pathway shifts toward enhanced CO and CO2 production due to increased carbon atom ejection and surface degradation. Furthermore, as the AO incidence angle increases, the recombination efficiency decreases linearly, while C-C bond breakage intensifies due to stronger vertical energy components. These findings offer new insights into the anisotropic surface response of knitted graphene structures under hyperthermal oxygen exposure and provide valuable guidance for the design and optimization of next-generation thermal protection materials for hypersonic flight.

The protection of satellites from the harsh space environment is heavily reliant on external spacecraft materials. These materials undergo continuous changes in their physical, chemical, and optical properties due to exposure to solar radiation and aggressive chemical species present in Earth's upper atmosphere. By gaining a thorough understanding of how these material properties evolve over the planned lifetime of a mission, the reliability of spacecraft can be enhanced. Additionally, the establishment of correlation factors between actual space exposure and accelerated space weather experiments performed in ground facilities allows for the precise prediction of on-orbit material performance based on laboratory-based testing. This paper presents an assessment of the radiation effects of the low Earth orbit environment, including exposure to high-energy electrons, atomic oxygen, and vacuum ultraviolet, on the material properties of a prospective spacecraft polymer, Mylar® M021. The study is part of the 16th Materials International Space Station Experiment (MISSE), which our team conducted from 08/31/22 to 02/23/23. An overview of the MISSE project is provided, including details on the materials used, results of ground experiments, and preliminary findings from the orbital phase of the study.

The structure and properties of nanocomposites based on organosoluble polyimide (PI) and branched functional metallosiloxane oligomers with different types of central metal atoms (Al, Cr, Fe, Zr, Hf and Nb) were investigated. Under the same weight content of the filler, the geometric parameters of the nanoparticles and thermal properties of the nanocomposites did not exhibit a direct relationship with the ability of the materials to withstand the incident flow of oxygen plasma. The atomic oxygenerosion resistance of the filled PI films was influenced by the composition of the hybrid fillerand the type of metal atom in the hybrid filler in the base metallosiloxane oligomer. To determine the effectiveness of the nanoparticles as protective elements of the polymer surface, the nanocomposite erosion yields pertaining to the concentration of the crosslinked organo–inorganic polymer forming the dispersed phase were determined and expressed in mmol per gram PI. The filler concentration in the polymer, expressed in these units, allows for comparison of the efficiency of different nanosize fillers for use in fabricating space survivable coatings. This can be important in the pursuit of new precursors, fillers for fabricating space survivable polymer composites.

This work aims at revealing the influences of space irradiations [including the atomic oxygen (AO) and ultraviolet (UV) irradiations] on the MoS 2 /DLC solid lubricating film. The changes on microstructure, mechanical and vacuum tribological properties of nanocomposite films after irradiations have been systematically investigated. It is found that the AO irradiation mainly induces the surface oxidation of the film, whereas some oxygen atoms can erode the bulk film along the defects highway; thus, the connectivity of carbon atoms is improved. In contrast, the UV irradiation may break the carbon bonds and functional groups, as well as induce a secondary radical formation, which accelerates the broken and recombination of the carbon chain scission. Specially, the films after irradiations exhibit much higher hardness (>19 GPa), lower friction coefficient (<0.02) and wear rate compared with the original one. The excellent tribological properties of the films after irradiations can be attributed to the synergistic effect of the high sp 3 C content and good crystallization of MoS 2 in the film, which cause the lower carbon and higher MoS 2 content in the wear debris at the contact interface.

Atomic oxygen in the low Earth orbit (LEO) environment is highly oxidizing. Due to the high flight speed of spacecraft, the relative kinetic energy of high-flux atomic oxygen bombarding the spacecraft surface can reach up to about 5 eV. Therefore, atomic oxygen is one of the most dangerous space environment factors in LEO, which seriously affects the safe operation and service life of spacecraft in orbit. In order to meet the requirements for the high reliability and long lifetime of spacecraft, effective protection measures must be taken on their sensitive surfaces. Siloxane is a coating with an organic–inorganic hybrid structure. Compared with SiO2 and other inorganic atomic oxygen protective coatings, it has better flexibility and is better at anti-atomic oxygen performance. In this paper, the plasma polymerization deposition technique was used to prepare large-area siloxane coatings on different substrates with different thicknesses for improving atomic oxygen resistance by optimizing the process parameters. The thickness of the coating was measured by different methods, and the results showed that the thickness distribution was consistent. By observing the surface morphology of the coating, it was uniform and compact without obvious defects, so the uniformity of large-area coating was also ideal. The adhesion and heat/humidity resistance of siloxane coatings were examined by pull-off testing and damp-heat testing, respectively. The results showed that the siloxane coatings with a thickness of about 400 nm exhibited better physical properties. At the same time, the ground simulation testing of atomic oxygen confirmed that siloxane coatings with a thickness of 418 nm presented the best performance of atomic oxygen resistance. The atomic oxygen erosion yield of siloxane coatings with a thickness of 418 nm was as low as 5.39 × 10−27 cm3/atoms, which was three orders of magnitude lower than that of the uncoated Kapton substrate and presented a good anti-atomic oxygen performance. Meanwhile, it has also successfully passed the damp-heat test. The coating thickness is only several hundred nanometers and does not increase the weight of the spacecraft, which makes it a relatively ideal LEO atomic oxygen protection material. Furthermore, a possible mechanism was proposed to explicate the physicochemical process of atomic oxygen attacking the coating materials.