Polyimide film (Kapton) is an important polymer material used for the construction of spacecrafts. The performance of Kapton can be degraded for atomic oxygen erosion in space. Commonly used atomic oxygen protective layers have issues such as poor toughness and poor adhesion with the film. In this paper, Kapton/Al₂O₃ nanocomposite films were prepared via an ion exchange method, and the optical properties, mechanical properties, and mechanisms for the change in the mass and microstructure, before and after atomic oxygen exposure, were analyzed. The results show that the deposition of the Kapton/Al₂O₃ surface nanocomposite film prepared via the ion exchange method has no obvious effects on the internal structure and optical transmittance of the Kapton film matrix. The tensile strength and elongation of the prepared film were much higher than those of the pure Kapton film, demonstrating its good flexibility. Scanning electron microscope (SEM) analysis showed that the etching pits had a carpet-like morphology on the composite film surface and were relatively small after atomic oxygen erosion. In contrast with the C–C bond rupture in the oxydianiline (ODA) benzene in Kapton films, the Kapton/Al₂O₃ nanocomposite film mainly destroyed the C=C bond in the pyromellitic dianhydride (PMDA) benzene ring. On exposure to an atomic oxygen environment for a short period, the Kapton/Al₂O₃ nanocomposite film exhibited improved atomic oxygen erosion resistance because the Al₂O₃ layer inhibited atomic oxygen diffusion. With increasing atomic oxygen exposure time, the atomic oxygen diffused into the Kapton matrix via the pores of the Al₂O₃ layer, causing damage to the substrate. This resulted in a detachment of the surface Al₂O₃ layer and exposure of the Kapton matrix, and thereby the atomic oxygen resistance was decreased. The applicability of the ion exchange mechanism of trivalent Al element on the surface modification of the polyimide is explored in this study. The behavior of the Kapton/Al₂O₃ composite film under the atomic oxygen environment of space is investigated, which provides the basis for studying the effects of atomic oxygen on the flexible protective Kapton film.

Thermal protection systems play a pivotal role in astronautical engineering fields. However, traditional rectangular fin (RF) structures exhibit low thermo-fluid properties. Inspired by the minimal surfaces in nature, this study develops three types of triply periodic minimal surface (TPMS) lattices, namely, sheet primitive (SP), network I-WP (NW), and sheet I-WP (SW) by using mathematical formulae. The TPMS lattices are fabricated by laser powder bed fusion using AlSi10Mg powder. A convective heat transfer simulation model of TPMS lattices is established and validated through experiments. The fluid flow characteristics, heat transfer characteristics, and overall heat transfer performance of the TPMS lattices are comprehensively investigated based on the simulation model. Results show that the relationship between pressure loss and flow velocity of the TPMS lattices satisfies the Darcy–Forchheimer law. Compared to traditional RF structures, the TPMS lattices exhibit a more uniform temperature distribution at the same flow rate, and the highest convective heat transfer coefficient is increased by approximately 96.62%. This is due to the complex internal structures of the TPMS lattices, which enhance the disturbance of the fluid flow and further improve the heat transfer coefficient. The overall thermal transfer index ($\alpha$) of the TPMS lattices is higher than that of traditional RF structures with an order of ${\alpha }_{SP}>{\alpha }_{SW}>{\alpha }_{NW}>{\alpha }_{RF}$, which confirms the potential applications of TPMS lattices in thermal protection systems.

To fabricate high-quality polycrystalline VO₂ thin film with a metal–insulator transition (MIT) temperature less than 50 °C, high-power impulse magnetron sputtering with different discharge currents was employed in this study. The as-deposited VO₂ films were characterized by a four-point probe resistivity measurement system, visible-near infrared (IR) transmittance spectra, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy. The resistivity results revealed that all the as-deposited films had a high resistance change in the phase transition process, and the MIT temperature decreased with the increased discharge current, where little deterioration in the phase transition properties, such as the resistance and transmittance changes, could be found. Additionally, XRD patterns at various temperatures exhibited that some reverse deformations that existed in the MIT process of the VO₂ film, with a large amount of preferred crystalline orientations. The decrease of the MIT temperature with little deterioration on phase transition properties could be attributed to the reduction of the preferred grain orientations.

In this paper, the 650 V N-channel GaN MOSFETs are chosen as the research object to study the radiation and annealing effects under 1 MeV electron irradiation. The output, transfer, and breakdown characteristics are measured before and after electron irradiation. The experimental results show the variation of the I-V curves after irradiation, which is related to the increased conductivity due to the generation of an oxide charge in the GaN MOSFETs. However, the gradual formation of the interface trapped charge offsets the effect of the oxide charge, which decreases the conductivity of the GaN MOSFETs and the drain-source current. The long-term annealing at room temperature degrades the interface trapped charges, leading to the restoration of the I-V characteristics. After room temperature annealing, the breakdown voltage is still higher than the unirradiated level, and this is because the displacement defects caused by electron irradiation cannot be recovered at room temperature.