Investigation into tolerance of polysiloxane-block-polyimide film against atomic oxygen

doi:10.1016/j.actaastro.2009.09.002

Acta Astronautica

Volume 66, Issues 5–6, March–April 2010, Pages 922-928

https://doi.org/10.1016/j.actaastro.2009.09.002 Get rights and content

Abstract

Silicon containing polyimide is proposed as an atomic-oxygen (AO)-tolerant material for Low Earth Orbit flight. For this study, commercially available polysiloxane-block-polyimide film is selected for investigation. An AO beam is irradiated on the polysiloxane-block-polyimide film at the Combined Space Effects Test Facility of JAXA in Tsukuba, Japan. To investigate the AO tolerance, mass change measurement, cross-sectional transmission electron microscopic (TEM) observation, and X-ray photoelectron spectroscopic (XPS) analysis are performed. Results show that the mass loss of polysiloxane-block-polyimide is one one-hundredth or less than that of Kapton^® H: Cross-sectional TEM observation and XPS analysis reveals that the AO protective SiO₂ layer is self-organized by AO irradiation. Furthermore, the self-organized SiO₂ layer is intentionally damaged to investigate reorganization of a new layer on it. Further AO irradiation of the damaged surface revealed that the new layer is built with a 500-nm-deep eroded region. The result verifies the “self-healing” ability of polysiloxane-block-polyimide. These results suggest that polysiloxane-block-polyimide film has high potential to provide many advantages of a space-use material, especially for LEO spacecraft.

Introduction

In low earth orbit (LEO), atomic oxygen (AO) is one of the severe environmental factor degrading the outboard materials of spacecraft [1], [2]. Originating from Earth's atmosphere, oxygen molecules are dissociated into neutral atoms by ultraviolet rays. The resultant AO remains at LEO altitude. Spacecraft fly on LEO at ca. 8 km/s, colliding with AO at a high relative velocity that imparts the equivalent of ca. 5 eV of translational energy, thereby causing erosion called AO Attack. Polyimide is a well-known AO-attack material. Its AO-attacked surface shows a distinctive shape with micrometer-sized asperity: a so-called carpet shape or needle-like shape. The AO attack degrades the material properties. Improving space materials’ tolerance against AO necessitates study of AO tolerance-improvement techniques. Coating is a standard method: inorganic thin coatings such as ITO and silicone resin are used [3], [4], [5]. However, such a coating must have high reliability to maintain its performance during missions and very low defect during production because coating degradation engenders severe erosion of the base film. Furthermore, a hard inorganic coating is very fragile, necessitating special care in handling during assembly, thereby raising production costs. A method to achieve AO tolerance other than coating should be considered. One method is the use of silicon-containing materials. The AO tolerance of such materials has been investigated [6], [7].

A SiO₂ layer is made from reaction of silicon contained in the material and AO existing on orbit; it can therefore be called a “self-organized” layer. The layer functions as an AO-protective layer. In addition, such a self-organized layer presents advantages over films with manufactured AO-tolerant layers because a self-organized layer has a self-healing function when the layer is damaged: such a film is expected to enable easier handling on the ground and high reliability on orbit.

The polysiloxane-block-polyimide film, a commercially available silicon containing polyimide film, is proposed herein as one silicon-containing film. It was developed for ground use, not for space use. If a thermal control film made of polysiloxane-block-polyimide were applicable to space use, especially for LEO spacecraft, it would improve cost effectiveness, reliability, and design flexibility.

In this study, the polysiloxane-block-polyimide film is evaluated for space application, especially in terms of its tolerance against AO. The tolerance is expected to be achieved through self-organization of the SiO₂ layer—the AO protective layer—by AO irradiation. First, the AO tolerance and self-organization of protective layer are investigated using AO irradiation tests. Then, the self-healing ability of the AO protective layer—the advantageous feature of this type AO tolerant film—is investigated using additional AO irradiation tests.

Section snippets

Sample preparation

A commercially available material, polysiloxane-block-polyimide is manufactured by Nippon Steel Chemical Co., Ltd. for ground use, mainly in the electronic industry. For this study, polysiloxane-block-polyimide is prepared as a 25-μm-thick film. For evaluation, 25-mm-diameter pieces are cut from the whole film. The initial mass of each piece is ca. 15.6 mg. The sample is used as received for irradiation tests #1–#3. For irradiation test #4, an AO-irradiated sample obtained by irradiation test #3

Mass change measurement

The measured mass change is shown in Fig. 2. The mass loss by AO irradiation was 0.02–0.04 mg. Compared to the mass loss of Kapton^® H used for the AO fluence monitor at the irradiation, as depicted in Fig. 3, the mass loss of polysiloxane-block-polyimide was one-hundredth or less than to that of Kapton^® H. Between AO irradiation tests #1 and #2, the mass loss of polysiloxane-block-polyimide is not proportional to the AO fluence: the mass loss at #2 is 1.5 times greater than that at #1, although

Future plans

In the future, polysiloxane-block-polyimide will be evaluated on the International Space Station (ISS) in the next space environment exposure experiment mission of JAXA, named “Japanese Experimental Module/Micro-particles capturer and Space Environment Exposure Device” (JEM/MPAC&SEED). JEM/MPAC&SEED will be launched by the Space Shuttle STS-127, ISS flight 2J/A in 2009. It will provide much more data related to polysiloxane-block-polyimide in terms of its tolerance against the real space

Conclusion

Polysiloxane-block-polyimide film, which is commercially available for ground use, was evaluated for its tolerance against AO. For this study, AO irradiation tests were performed at the Combined Space Effects Test Facility at JAXA's Tsukuba Space Center. Results demonstrate that the polysiloxane-block-polyimide mass loss is one-hundredth or less than that of Kapton^®. Cross-sectional TEM observation and XPS analysis reveals that the AO protective SiO₂ layer is self-organized by AO irradiation.

Acknowledgments

The authors thank Mr. Koji Nakamura, Mr. Masatoshi Yuasa, Mr. Kiwamu Tokuhisa, Mr. Akira Mori, and Mr. Yukihiro Wada, Nippon Steel Chemical Co., Ltd., for their cooperation in supplying the polysiloxane-block-polyimide film for our evaluation. The authors would also like to thank Mr. Susumu Baba, Advanced Engineering Services Co., Ltd., for his kind support on XPS analysis.

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