Investigation of Non-Contact Flame Temperature Measurement and Radiative Heat Evaluation Method in Propulsion Systems for Small Spacecrafts

To evaluate the radiative heat impact of hybrid rocket exhaust plumes on surrounding components in small spacecraft propulsion systems, this study investigates a non-contact flame temperature estimation method using a color high-speed camera. A calibration experiment using electrically heated resistive wires was conducted to derive the relationship between RGB intensity ratios and temperature. The results confirmed that the g/r ratio increases with temperature and serves as a qualitative indicator under fixed camera settings. Subsequently, a ground combustion test of a GOX/HDPE hybrid rocket was performed. The temporal variation of the g/r ratio obtained from flame images was compared with theoretical flame temperature profiles calculated from O/F history using RocketCEA. The observed g/r ratio trends were generally in agreement with the theoretical predictions. Meanwhile, radiative heat flux measured with a heat flux sensor showed a significant increase over time, suggesting that changes in emissivity due to soot or high-temperature gas had a greater effect than temperature variation alone.