Silsesquioxane (RSiO_3/2) has been researched as a potential atomic oxygen (AO) protective coating material for spacecraft applications. To this end, the present study focuses on the development of photocurable silsesquioxane (SQ series, manufactured by Toagosei Co., Ltd.) coating on polyimide base films. Photocurable silsesquioxanes “SQ series” are a new type of organic–inorganic hybrid materials that feature photoinitiated polymerizable groups (organic units) introduced into silsesquioxane frameworks (inorganic units) as multifunctional groups at an intramolecular level. This coating has the following excellent properties for use as a protective coating for space materials: 1) high AO tolerance, 2) high adhesion to substrate material (polyimide), 3) high transparency, 4) low outgassing and low re-condensability, and 5) ease of handling. In this study, we selected two types of space-qualified polyimide films, both of which were 25 μm thick and aluminized on the rear. We adopted roll-to-roll wet coating technology for this product with a width of 1 m. The SQ-coated films thus obtained were evaluated for their resistance to space environmental factors such as AO, electron beam, and ultraviolet irradiations; thermal cycling; and high-temperature vacuum conditions. The acquired outgassing properties complied with the ASTM E 595 standard. Results indicate excellent space environmental tolerance in the prepared coatings. Thus, the present study established a facile roll-to-roll wet coating process for developing SQ coating on two types of polyimide base films.

This paper experimentally examines the heating performance brought by the chemical igniter (used in NASA-STD-6001B and ISO-TS16697) exposed in various oxygen concentrations. Final goal of this study is to discuss about the reliability of the chemical igniter for such material screening test ensuring the fire safeness in space. Prescribed mixture of nitrogen and oxygen was flowed into the test chamber and the chemical igniter is burned under the heat flux gauge. Time-sequence of heat flux brought by the chemical igniter was recorded and analyzed. It is understood that time-sequence curve of heat flux is varied under various oxygen concentration, suggesting that the thermal enthalpy accumulated in the test specimen to be burned has clear dependency on the ambient oxygen concentration. Namely, thermal status of entire test specimen is strongly depended on the environmental condition to be tested, when the chemical igniter is used as the heating source due to its inherent heating properties. Importantly, when ambient gas is strongly diluted (i.e., low oxygen concentration), complete burning of the chemical igniter tends to be prohibited, accordingly, reproducibility becomes less. Under such condition, the weak but long heating is experienced. Because such slow rate of heat supply (for ignition) shall be easily dissipated, resulting that no ignition might be induced by the chemical igniter; Hence, the chemical igniter would be insufficient to be a “universal” heating source for any screening purpose. As substitute, the electric heater (wire igniter) could work effectively to cover the disadvantages of the chemical igniter as presented in this study.