Abstract
The result of scale analysis showed that the thermal-regime, in which the flame became most robust, located in low ambient flow condition. This predicted that the robust flame could exist in microgravity with a mild flow even if the oxygen concentration was below the limiting oxygen index (LOT). The result of the flight experiment agreed with the prediction; the flame spread in mild flow environment was observed even at 15.3% oxygen level in microgravity whereas the downward spread was not observed at the same oxygen level.
