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 the combustibility of solid materials in a microgravity environment. Aiming to verify the world’s first quantitative evaluation method1 based on started on May 19, 2022 at the Kibo Japanese Experiment Module. In addition, we will release the results of the first material combustion experiment on the ISS under high-concentration oxygen conditions on June 23, 2022 (Fig. 1). The FLARE theme contributes to ensuring fire safety inside spacecraft and living facilities, which is an extremely important issue for international space exploration (Artemis Project) on the moon, etc., in which Japan is also participating.
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) material flammability test standard (NASA-STD-6001). However, the NASA standards do not take into account the effect of gravity-dependent convection around flames on the combustibility of materials. A method for evaluating the combustibility of materials that properly considers the effects of gravity, which corresponds to the above microgravity environment, has not been established. In addition, in the Artemis project, as a pressurized environment for lunar housing facilities, low-pressure, high-concentration oxygen conditions (0.56 atm, 34% O2) different from the ISS (atmospheric pressure, 21% O2) are being considered. The NASA experimental equipment used so far on the ISS was only able to conduct 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 in evaluating the flammability of materials in a microgravity environment. We will verify this through combustion experiments on the Bo. In addition, the newly developed SCEM operated on Kibo is capable of conducting combustion experiments under low-pressure conditions and high-concentration oxygen conditions of up to 45%. Since it will be possible to obtain characteristic data, it is expected that the verification for the utilization of the new method will make great progress.
JAXA will contribute to ensuring the safety of space fires in future manned space activities through experiments at the SCEM, which has excellent technological advantages.
*In the image (a), the surface temperature increases as the color changes from blue to red.
*In the image (b), the green color of the unburned “filter paper” sample is due to the lighting LED.
*The image in (c) has been processed to emphasize the outline of the dark flame.
Fig. 1 Image taken during the on-orbit flame spread experiment of the “filter paper sample” (atmospheric oxygen concentration is 34%) and the combustion chamber
Comments from Stakeholder
Professor Osamu Fujita, Department of Mechanical and Aerospace Engineering, Graduate School of Engineering, Hokkaido University (FLARE theme representative researcher)
“We are more than happy and excited. The FLARE theme has been prepared over a period of about 10 years, and during that time, it has been realized with the cooperation of not only JAXA, but also joint researchers from domestic and overseas 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 theme, I would like to contribute to the development of combustion science and the improvement of fire safety in future manned space exploration.”
1 The world’s first method that can quantitatively evaluate the combustibility of solid materials in a microgravity environment . The oxygen index method is widely used in Japan and overseas, giving the material’s combustion limit oxygen concentration as a quantitative index. (ISO 4589-2), enabling evaluation of the oxygen index (OI_mg) in a microgravity environment. By using the oxygen index (OI) and material property values as input data, HOI obtained by the oxygen index method at high flow velocity (ISO 4589-4) established based on ground research results in the FLARE theme, Combustion limit conditions (oxygen concentration and ambient flow velocity conditions) in a microgravity environment can be predicted.
2 Solid Combustion Experimental Equipment (SCEM)
The experimental equipment installed in the combustion chamber of the SCEM (Fig. 2) is equipped with a fan and a honeycomb for rectification, and can form a flow field that circulates inside the combustion chamber (Fig. 3). In the experimental area between the rectifying honeycombs is placed a sample card that holds the solid material to be tested. This sample card is exchanged remotely from the ground. By igniting one end of the sample with a heating wire, the behavior of the flame spreading in the gas flow parallel to the sample is observed with a camera. Depending on whether the ignition line located upstream or downstream of the gas flow is used, the condition is that the flame spreads toward the gas flow (counter-flow condition) or the condition that the flame spreads in the same direction as the gas flow (co-current condition). flame spread experiments can be performed.
The first series of experiments currently underway use thin ‘filter paper’ (13 cm long x 4 cm wide x 0.0125 cm thick) samples.
Fig. 2 Solid Combustion Experimental Equipment (SCEM) ©JAXA
3 FLARE Theme (FLARE: Flammability Limits at Reduced Gravity Experiment)
In 2012, “Evaluation of Gravitational Effects on Combustion Phenomena of Solid Materials for Improving Fire Safety” was adopted as one of the priority theme categories for Kibo utilization. [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 participating in this theme.
Using SCEM, we repeatedly perform experiments on solid materials of various materials and shapes by changing conditions such as oxygen concentration and ambient flow velocity. Combustion limit conditions obtained in experiments are compared with the results predicted by the new method for verification.
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