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Polyimides are polymeric materials that are widely used in spacecraft applications owing to their unique properties. However, exposure to a low-Earth-orbit environment containing atomic oxygen (AO) results in the disintegration of polymeric materials on the surface of spacecraft, thereby affecting the lifespan. Along with the development of theoretical research, the reactive force-field (ReaxFF) interatomic potential has become a robust computational method for exploring, developing and optimizing the material properties. This study employs the ReaxFF reactive-force-field molecular dynamics simulation (ReaxFF MD) program to investigate and compare the performance of two typical polyimide materials, Kapton and Upilex-S, under the impact of AO. Various aspects such as variations in the temperature, mass loss, decomposition products, and damage propagation depth were examined. Although these materials have similar elemental composition (C/H/O/N), they have different structures. Our results indicate that AO is initially adsorbed on the surfaces of both Kapton and Upilex-S. The continuous impact of AO leads to chemical reactions between AO and Kapton/Upilex-S. Erosion proceeds from the surface toward the interior of the materials. Similar to the findings of Experiment 2 conducted by the Materials International Space Station, our results also reveal that Upilex-S exhibits a lower mass loss and erosion yield than Kapton under the same AO conditions. This difference is primarily attributed to the distinct molecular structures of both Kapton and Upilex-S. Our study could provide valuable technical support for the extensive application of Upilex-S in spacecraft.

Polymer-matrixed materials are widely used in the spacecrafts' structures. However, crafts located in the LEO（Low Earth Orbit） would suffer from hazardous environment factors when orbiting in the space. It has been reported that the space environment factors’ integral effect (which represents the factual detriment in space) is not equivalent to the simple summation of each individual. Hence, atomic oxygen and thermal cycling were selected as the starting point for studying the typical LEO synergistic effects on polymer-matrixed space material. In this work, methods such as surface morphology observation, surface components analyzation and inter-laminar-shear strength test were embraced to gather the basic information for the study of degradation. As a result, focusing on the composites selected in this work, synergistic effects do exist between the two factors (AO&TC, representing for atomic oxygen and thermal cycling combined). Besides, a quantified index was proposed to represent synergistic characteristics，so as to lay the foundation for the scientific evolution of material characterization.

In this paper, we investigate the effect of thermal annealing on the degree of crystallinity, the fraction of electroactive phase (β-phase) and the dielectric properties, such as dielectric constant and loss tangent. Through control the thermal annealing conditions, dramatic improvements have been achieved. The degree of crystallinity is greatly enhanced up to 45.2%. The relative content of electro-active phase increases remarkably by 61% and the dielectric constant is improved greatly by 17.8% and reaches its maximum value of 9.9 meanwhile the dielectric loss being as low as 0.026. [ABSTRACT FROM AUTHOR]

The charging events of the International Space Station have been a focus of concern in recent years. Hollow cathode plasma contactors were applied to control the floating potential for their high emission currents of amps order. The in flight measurements showed that the floating potential was much smaller than predicted originally, and the actual emitted currents by the plasma contactors were well below amps level. In such case, a simpler method to control the floating potential may be applicable and suggested in the paper. By application of a metal sphere, which is biased at a high negative voltage relative to the structure and used as an ion current collector, the electron charging current of the structure can be effectively neutralized and the structure's floating potential can be controlled nearly to zero. The mechanism is introduced and the constraint condition for the system is investigated. Finally, a range of parameters for design are presented. Typically, for 100V high voltage array, a sphere of r=0.3-0.7m and biased at 500-200V is enough. For its simplicity, the method has obvious advantages, such as no requirement of working gas, high reliability and long life, etc. [ABSTRACT FROM AUTHOR]