Japan Aerospace Exploration Agency
National University Corporation Hokkaido University
JAXA program update
The Japan Aerospace Exploration Agency (President: Hiroshi Yamakawa, hereinafter referred to as JAXA) and Hokkaido University (President: Kiyohiro Hokin) have announced the results of ground-based tests on combustibility of solid materials in a microgravity environment. The aim is to verify the world’s first quantitative assessment method1 based on began May 19, 2022 in the Kibo Japanese Experiment Module. In addition, on June 23, 2022, we will publish the results of the first material combustion experiment on the ISS under conditions of high oxygen concentration (Fig. 1). The FLARE theme helps ensure fire safety in spacecraft and living quarters, which is an extremely important theme for international space exploration (Artemis project) on the moon, etc., in which Japan is also involved.
Until now, it has been a general rule that materials used in spacecraft should be flame retardant and have passed the National Aeronautics and Space Administration (NASA) Flammability Test Standard for Materials (NASA-STD-6001). However, NASA standards do not consider the effect of gravitational convection around flames on the combustibility of materials. A method for evaluating the combustibility of materials that properly accounts for the effects of gravity, which corresponds to the above microgravity environment, has not been developed. In addition, the Artemis project considers conditions of low pressure and high oxygen concentration (0.56 atm, 34% O2) different from those of the ISS (atmospheric pressure, 21% O2) as the pressure environment for lunar shelters. The NASA experimental equipment previously used on the ISS could only carry out material combustion experiments at atmospheric pressure and oxygen concentrations of 21% or less.
Under the FLARE theme, we have already internationally standardized the ground combustion test method used to evaluate the flammability of materials in a microgravity environment. We will verify this with combustion experiments on the Bo. In addition, the newly developed SCEM operating on Kibo is capable of conducting combustion experiments under low-pressure and high oxygen concentration conditions of up to 45%. Since characteristic data can be collected, it can be expected that the verification of the use of the new method will make great progress.
JAXA will help ensure space fire safety in future human space activities through experiments at the SCEM, which has excellent technological advantages.
*In image (a), the surface temperature increases as the color changes from blue to red.
*In image (b), the green color of the unburned “filter paper” sample is due to the lit LED.
*The image in (c) has been edited to emphasize the outline of the dark flame.
Cowardly. 1 Image of the “filter paper sample” (concentration of atmospheric oxygen is 34%) and the combustion chamber taken during the in-orbit flame propagation experiment
Professor Osamu Fujita, Department of Mechanical and Aerospace Engineering, Graduate School of Engineering, Hokkaido University (representative researcher for the FLARE topic)
“We are beyond happy and excited. The FLARE topic was prepared over a period of about 10 years and during this time it was realized not only in cooperation with JAXA, but also with researchers from domestic and foreign universities, NASA and European space agencies. We are here. I would like to take this opportunity to express my gratitude and through the results of this topic I would like to contribute to the development of combustion science and the improvement of fire safety in future human space exploration.”
1 The world’s first method that can quantitatively assess the combustibility of solid materials in a microgravity environment. The oxygen index method is widely used in Japan and overseas, and indicates the combustion limit oxygen concentration of the material as a quantitative index. (ISO 4589-2) which allows an assessment of the oxygen index (OI_mg) in a microgravity environment. Using the oxygen index (OI) and material property values as input data, HOI, obtained by the high flow rate oxygen index method (ISO 4589-4), which is based on soil research results in the FLARE topic, combustion boundary conditions (oxygen concentration and ambient flow rate conditions) in a microgravity environment can be predicted.
2 Solid Combustion Experimental Equipment (SCEM)
The test facility installed in the combustion chamber of the SCEM (Fig. 2) is equipped with a fan and honeycomb for rectification and can form a flow field that circulates inside the combustion chamber (Fig. 3). A sample card containing the solid to be tested is placed in the test area between the rectifier honeycombs. This pattern card is exchanged remotely from the ground. By igniting one end of the sample with a heating wire, the behavior of the flame propagating in the gas stream parallel to the sample is observed with a camera. Depending on whether the ignition line upstream or downstream of the gas flow is used, the condition that the flame propagates in the direction of the gas flow (counterflow condition) or the condition that the flame propagates in the same direction as the gas flow (cocurrent condition) . Flame propagation experiments can be performed.
The first series of experiments currently underway uses thin “filter paper” samples (13 cm long x 4 cm wide x 0.0125 cm thick).
Cowardly. 2 Solid Combustion Test Equipment (SCEM) ©JAXA
3 FLARE topic (FLARE: Flammability Limits at Reduced Gravity Experiment)
In 2012, “Evaluation of Gravitational Effects on Combustion Phenomena of Solid Materials for Improvement Fire Safety” was accepted as one of the priority topic categories for Kibo use. [Representative researcher: Professor Osamu Fujita (Hokkaido University)]. JAXA, NASA, the European Space Agency (ESA), the French National Center for Space Studies (CNES) and the German Aerospace Center (DLR) are involved in this topic.
With SCEM, we repeatedly conduct experiments on solid materials of different materials and shapes by changing conditions such as oxygen concentration and ambient flow speed. Combustion boundary conditions determined in experiments are compared to the results predicted by the new verification method.
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