Junichiro Ishizawa

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.

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.

Effect of ultraviolet radiation from an oxygen plasma on the atomic oxygen-induced etching of fluorinated polymer

The contribution of extreme ultraviolet (EUV) and vacuum ultraviolet (VUV) from a laser-sustained plasma on mass loss phenomenon of fluorinated polymer in the ground-based laser-detonation atomic oxygen (AO) beam source was evaluated. The AO beam and EUV/VUV from an oxygen plasma were separated by a high-speed chopper wheel installed in the beam source. Mass changes of fluorinated polymer and polyimide were measured from the frequency shift of the quartz crystal microbalances during the beam exposures. It has been made clear that the fluorinated polymer is eroded by EUV/VUV exposure alone. In contrast, no erosion was detected for polyimide by EUV/VUV alone. The AO-induced erosion was measured for both materials even without EUV/VUV exposure. However, no strong synergistic effect was observed for the fluorinated polymer even under the simultaneous exposure condition of AO and EUV/VUV. Similar results were observed even in the simultaneous exposure condition of AO (without EUV/VUV from the laser plasma) and VUV from the 172 nm excimer lamp and D2 lamp. These experimental results suggest that the primary origin of the accelerated erosion of fluorinated polymer observed in the laser detonation AO source is not EUV/VUV from the laser-sustained plasma.

Passive Space Environment Effect Measurement on JEM/MPAC&SEED

A space materials exposure experiment was conducted on the exterior 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). The MPAC&SEED experiments were aboard both the Russian Service Module (SM/MPAC&SEED) and the exposed Facility of the Japanese Experiment Module, KIBO Exposed Facility (JEM/MPAC&SEED). The JEM/MPAC&SEED was attached to the Space Environment Data Acquisition Equipment-Attached Payload (SEDA-AP).

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...

First Evaluation of Contamination on the JEM/MPAC&SEED

JEM/MPAC&SEED were exposed to the space environment for 8.5 months and retrieved via EVA in April 2010. We subsequently analyzed the surface of JEM/MPAC&SEED to determine the state of contamination.

Contamination control for the space infrared observatory SPICA

The contamination control for the next-generation space infrared observatory SPICA is presented. The optical performance of instruments on space observatories are often degraded by particulate and/or molecular contamination. Therefore, the contamination control has a potential to produce a significant risk, and it should be investigated in the risk mitigation phase of the SPICA development. The requirements from contamination- sensitive components onborad SPICA, the telescope assembly and focal plane instruments, are summarized. Possible contamination sources inside and outside the SPICA spacecraft were investigated. Based on impact on the SPICA system design, the following contamination sources were extensively studied through simulation and measurement; (1) outgassing from the payload module surrounding the telescope mirror and focal plane instruments, (2) contamination due to the thruster plume, and (3) environmental contamination during the integration, storage and verification phases. Although the outgas from the payload module and the thruster plume were estimated to produce only a negligible influence, the environmental contamination was suggested to affect significantly the telescope and focal plane instruments. Reasonable countermeasures to reduce the environmental contamination were proposed, some of which were confirmed to be actually effective.

Evaluating the bakeout effectiveness of RTV-S691 silicone adhesive by measuring outgassing rate

Outgassing rate measurements are basically performed for fresh materials, e.g. just cured adhesives, paints, etc. and reveal a lot about how the material can behave as a contamination source. It is also important to determine the bakeout process sufficiently. In the present study, a typical silicone adhesive for use in space, RTV S-691, Wacker Chemie, was selected for the measurement. Two cured specimens, 40 × 40 mm in size, were applied for several isothermal tests under identical conditions: a specimen at 125 degrees C for 144 hours with CQCM at -193 degrees C to measure TML. Consequently, it was determined that the TML and TML rate could be reduced by bakeout as expected. It also emerged that a longer bakeout, i.e. a longer cumulative bakeout time, for the material would reduce the TML and TML rate more effectively. The results suggest that bakeout mainly affects the behavior in the “low-rate” phase, whereby the TML rate curve can be divided into two phases. The elapsed time for a specimen can also be considered the cumulative test time. Based on the cumulative elapsed time, the TML rate curve is replotted and a correlation emerges between the cumulative bakeout time and TML rate. The first measurement data of TML and the TML rate could be affected by the stored time from cure, which might result from the change in unreacted substances declining as the stored time elapsed.

Optical and re-emission behavior of silicone contaminants affected by UV irradiation with different wavelength ranges

Molecular contamination by outgassing can degrade the performance of optical components. In orbit, spacecraft are exposed to various environments. UV is one of the most critical. It may also have the potential to cut the chains of organic molecules in contaminants due to its high energy, degrading optical properties and even re-emission behavior. In the present study, using two kinds of UV sources with different wavelength ranges, we compare the effect of UV lights irradiated on an optical surface with silicone contaminants. The irradiated samples were evaluated in terms of their optical properties and re-emission behavior, i.e. transmittance, and thermal desorption.

Experimental measurement of the reflection behavior of contaminant molecules

JAXA is developing a contamination analysis tool “J-SPICE” (Japanese Spacecraft Induced Contamination analysis software). Generally speaking, contamination analysis tools predict based on various input data and mathematical models of contaminant behavior, which means prediction accuracy depends on the validity of mathematical models as well as of input data. We investigated the validity of a diffuse reflection model applied in J-SPICE by comparing the reflection flux of contaminant molecules measured by the ground experiment and the analytical result of the J-SPICE. The result showed that the diffuse reflection model of J-SPICE reasonably explains molecule distribution reflected by a flat surface.