Eiji Miyazaki

Degradation Property of Commercially Available Si-containing Polyimide in Simulated Atomic Oxygen Environments for Low Earth Orbit

Real-time measurement of the erosion rate of a commercially available Si-containing polyimide (BSF30) under hyperthermal atomic oxygen (AO) beam exposure condition, which simulates the AO environment in low Earth orbit (LEO), was performed. It was found that the erosion rate of BSF30 decreased with increasing AO fluence and it reached as low as 4% of the standard PMDA-ODA polyimide. X-ray photoelectron spectroscopy confirmed that the surface of AO-exposed BSF30 was covered by a SiO2 layer which functioned as a protective coating. In contrast, an SiO2 surface layer thick enough to protect bulk BSF30 was not formed by thermal AO, which was generated by vacuum ultraviolet exposure in an O2 atmosphere. Exposure to hyperthermal AO collision in LEO can also form an SiO2 layer which enables the surface to be self-healing and is desirable for a polyimide that would be used in LEO.

Investigations into Synergistic Effects of Atomic Oxygen and Vacuum Ultraviolet

Polymermaterials exposed to a space environment exhibit strongly degraded properties because of environmental factors, for example, atomic oxygen, vacuum ultraviolet, and radiation. In addition, the degradation of polymer materials can be accelerated because of the synergistic effects of these environmental factors. For designing highreliability spacecraft, it is important to understand precisely the polymer materials’ degradation. In this report, the synergistic effects of atomic oxygen and vacuum ultraviolet on polyimide films, Kapton H, and silver-coated fluorinated ethylene propylenefilmswere investigated through comparison of the degradation behaviors after single, sequential, and simultaneous irradiations. For both materials, there was no significant change attributed to the synergistic effects in erosion yield and thermo-optical properties. However, the surface morphology of silver-coated fluorinated ethylene propylene changed substantially depending on the irradiationmethod. Surfaces of silver-coated fluorinated ethylene propylene were eroded by atomic oxygen, but were smoothed by vacuum ultraviolet. The surface morphology after sequential irradiations differed depending on the irradiation sequence. A rougher surface with low blunt cones was produced after simultaneous irradiation because of the interaction of the erosion by atomic oxygen attacks and smoothing by vacuum ultraviolet irradiation. This report also describes the measurement methods for fluence of each beam under simultaneous irradiation.

Results of Space-Environment Exposure of the Flexible Optical Solar Reflector

This paper presents exposure results for the flexible optical solar reflector, a sample material in the International Space Station Service Module/Micro-Particles Capturer and Space Environment Exposure Device experiment mission. The flexible optical solar reflector, which has a conductive layer and a mirror layer coated on a polyetherimide base film, is a thermal controlfilmmaterial for spacecraft. It achieves low solar absorptance andhigh infrared emittance. Results indicate a mass increase: the flexible optical solar reflector was not eroded by atomic oxygen in low Earth orbit. Thermo-optical properties show no significant change. In fact, flexible optical solar reflector is confirmed to retain its initial properties after exposure on an International Space Station orbit for 46months. Transmission electronmicroscopy observation of the cross sections including the exposed surface showed that a new layer had formed over the flight sample. Qualitative analysis of the new layer indicates that the layer mainly comprises silicon and oxygen. The layer is chemically produced by deposited silicone contamination and atomic oxygen, which would be SiO2. This experiment also provides actual quantitative contamination data on the International Space Station, contributing to improvement of contamination control on the International Space Station in the future.

Passive Space-Environment-Effect Measurement on the International Space Station

The Micro-Particles Capturer and Space Environment Exposure Device is the Japan Aerospace Exploration Agency’s experiment on particle capture and space exposure of material mounted on an aluminum tray. The trays were placed on the exterior of the Russian service module of the International Space Station. All trays were retrieved and returned toEarth. This paperpresents our analysis of the effects that space exposure imparted on themonitoring samples in the firstand second-retrievedMicro-Particles Capturer and Space Environment Exposure Device trays. The monitoring samples yield space-environment data such as atomic oxygen, ultraviolet, fluence, and space radiation dose data. The exposure and monitoring samples were retrieved after 315 and 865 days of exposure.

Influence of atomic oxygen irradiation on secondary electron emission yield of polyimide films

We studied the measurement of secondary electron emission (SEE) of metal and insulating materials used for satellite thermal insulation or other such purposes. The SEE yield measurement is very important for analyzing charge accumulation on satellite surfaces in a space environment because electron emission related to irradiated electrons influences the amount of surface charge. We considered degradation phenomena of surface materials for spacecraft caused by radioactive rays. Those SEE yields might change for a nondegradation sample. We measured the SEE yields of surface materials for spacecraft that are treated using the degradation process. In preparation of the degradation sample, the samples were irradiated by atomic oxygen (AO) to simulate degradation in a space environment. We take three irradiation conditions and two irradiation methods related to a GEO orbit and operating period. This report introduces the measurement results of the reference material: polyimide films. We discuss the relationship between the SEE yields and sample degradation when irradiated by atomic oxygen. Furthermore, we consider the effect of different AO irradiation methods: the laser detonation method and the plasma asher method.

Space Environment Effects on Materials at Different Positions and Operational Periods of ISS

A space materials exposure experiment was condcuted on the exterior of the Russian Service Module (SM) of the International Space Station (ISS) using the Micro‐Particles Capturer and Space Environment Exposure Device (MPAC&SEED) of the Japan Aerospace Exploration Agency (JAXA). Results reveal artificial environment effects such as sample contamination, attitude change effects on AO fluence, and shading effects of UV on ISS. The sample contamination was coming from ISS components. The particles attributed to micrometeoroids and/or debris captured by MPAC might originate from the ISS solar array. Another MPAC&SEED will be aboard the Exposure Facility of the Japanese Experiment Module, KIBO Exposure Facility (EF) on ISS. The JEM/MPAC&SEED is attached to the Space Environment Data Acquisition Equipment‐Attached Payload (SEDA‐AP) and is exposed to space. Actually, SEDA‐AP is a payload on EF to be launched by Space Shuttle flight 2J/A. In fact, SEDA‐AP has space environment monitors such as a high‐energy partic...

Decomposition of dioctyl phthalate (DOP) using titanium dioxide photocatalyst in a vacuum

We have focused on photocatalytic materials to solve contamination problem for spacecraft. We have fabricated TiO2 thin films and measured decomposition rates of methyl orange (MO) and dioctyl phthalate (DOP) in vacuum by TiO2 thin films as a photocatalyst. From XRD results, fabricated TiO2 thin films have anatase-type crystal structure, which is known to have stronger decomposition activities than rutile-type TiO2. The TiO2 thin films we made were shown to decompose methylene blue (MB) solution, which means that the TiO2 thin films have general photocatalystic activity in atmosphere. In decomposition of MO in atmosphere and vacuum, TiO2 shows photocatalytic activity even in vacuum although the decomposition rate in vacuum is slower than that in atmosphere. In decomposition of DOP in vacuum, DOP was effused from an effusion cell in vacuum chamber and was deposited on a TiO2 thin film using the in-situ measurement apparatus at Tsukuba Space Center, JAXA. Transmission spectra of DOP on TiO2 thin films after UV irradiation were measured to estimate decomposition rate from absorbance of DOP. The results show that TiO2 thin films can decompose DOP even in vacuum. Moreover, H2O can promote the decomposition of DOP. In order to use photocatalyst materials in vacuum for long time, the studies on the durability of photocatalystic activity of TiO2 in vacuum and the effects of O2 and H2O are necessary in the future.

Flight Experiment Results of the Polysiloxane-Block-Polyimide “BSF-30” on the JEM/MPAC&SEED Mission on the ISS

Atomic oxygen (AO) in low Earth orbit (LEO) is one of the most dangerous environmental factors leading to erosion of the external materials of a spacecraft. As one of the methods to improve AO tolerance, the use of silicon-containing materials has been proposed. On such materials, an SiO2 layer is formed from the reaction of the silicon contained in the material and the AO existing in orbit, which can therefore be called a “self-organized” layer. In the present study, polysiloxane-block-polyimide “BSF-30”, which is a silicon-containing polyimide, was investigated by ground testing and in a flight experiment. BSF-30 was exposed to the LEO space environment on the Japanese Experimental Module/Micro Particles Capturer & Space Environment Exposure Device (JEM/MPAC&SEED) mission on the ISS for 8.5 months. As a result, a mass loss of 0.011 mg was measured, which is about 1/500 times smaller than that of a common polyimide. From a cross sectional transmission electron microscopy analysis the formation of a layer about ~50 nm thick was observed on the exposed surface, within which high fractions of Si and O were also detected. In conclusion, it is verified that BSF-30 has sufficient AO tolerance in a LEO environment by the JEM/MPAC&SEED.

Effects of vacuum on photocatalytic activity of TiO2

Contamination outgassed from spacecrafts materials can degrade optical devices in orbit. Therefore, solving the contamination problem is important because it in uences the success of spacecraft missions. In this study, methyl red (MR) and oleamide were decomposed in vacuum by TiO2 photocatalyst. Absorbance spectra, mass decrease and GC/MS were measured after and before decomposition. In vacuum, TiO2 could decompose MR to intermediate products, whereas it could not decompose the intermediate products to volatile substances because TiO2 cannot open benzene rings of the intermediate products. On the other hand, TiO2 could decompose oleamide to volatile substances even in vacuum. However, decomposition by TiO2 stopped after a certain period of time in vacuum. The decrease in mass for oleamide by photocatalytic reaction in vacuum was enough compared to standard molecular contamination levels.

A new experimental procedure of outgassing rate measurement to obtain more precise deposition properties of materials

Outgassing rate measurement, or dynamic outgassing test, is used to obtain outgassing properties of materials, i.e., Total Mass Loss, “TML,” and Collected Volatile Condensed Mass, “CVCM.” The properties are used as input parameters for executing contamination analysis, e.g., calculating a prediction of deposition mass on a surface in a spacecraft caused by outgassed substances from contaminant sources onboard. It is likely that results obtained by such calculations are affected by the input parameters. Thus, it is important to get a sufficient experimental data set of outgassing rate measurements for extract good outgassing parameters of materials for calculation. As specified in the standard, ASTM E 1559, TML is measured by a QCM sensor kept at cryogenic temperature; CVCMs are measured at certain temperatures. In the present work, the authors propose a new experimental procedure to obtain more precise VCMs from one run of the current test time with the present equipment. That is, two of four CQCMs in the equipment control the temperature to cool step-by-step during the test run. It is expected that the deposition rate, that is sticking coefficient, with respect to temperature could be discovered. As a result, the sticking coefficient can be obtained directly between -50 and 50 degrees C with 5 degrees C step. It looks like the method could be used as an improved procedure for outgassing rate measurement. The present experiment also specified some issues of the new procedure. It will be considered in future work.