09:00 〜 10:30
[MTT37-P05] 観測ロケットMOMO7号機による高度100 kmまでのインフラサウンド計測実験および励起衝撃波の観測
キーワード：MOMO観測ロケット、インフラサウンド、衝撃波、動圧
MOMO7 sounding rocket developed by Intersteller Technologies Inc. (IST) was launched at 17:45 JST on July 3, 2021 from Taiki, Hokkaido, Japan. Kochi University of Technology installed an instrument of SAYA INF03Dv4, aboard the MOMO7 to measure acoustic/infrasonic waves in middle and upper atmosphere. The INF03Dv4 sensor consists of two sets of infrasound microphones and two sets of small buzzers that emit acoustic signal of 400 and 1100 Hz repeatedly with about 15 seconds interval to make sure the possibility of acoustic wave detection in rarefied atmospheric condition during stratosphere, mesosphere, and lower thermosphere. Moreover, we conducted to explode 11 sets of fireworks on ground in Taiki Town for making acoustic/infrasonic sound source to confirm vertical wave propagation with using the onboard infrasound sensor.
Once launched, the onboard sensor caught heavy acoustic noise disturbances generated by rocket motor during about 120 seconds after the launch, when the rocket reached about 40 km altitude, then after its engine cutoff, calm environment comes up. However, the sensor caught another type of wave like disturbance with larger period as the rocket began to rotate after becoming into no axis-control situation probably due to be affected by dynamic pressure on rocket flight and attitude, indicating rapid attenuation with decreasing background atmospheric density in stratosphere to lower thermosphere.
During the 7-minute suborbital flight of MOMO7 with its apex of 99 km, the sensor also caught a very clear N-type signal at about 98 km in the beginning of its downleg. It occured just at the timing of changing the flight vector velocity exceeded Mach 1 again, after experienced low subsonic moving condition only near the apex. Therefore, we can calculate temperature condition at the exact altitude using the obtained sound speed.
When the rocket reached maximum descending velocity at about 30 km, it generated Mach cone and effectively induced shock wave, then it propagated to the ground. We deployed 9 infrasound sensors on ground at Taiki Town, as well, so as to detect this expected impulsive infrasound signal along with the previous experimental results of MOMO3 launched on May 4, 2019. The 9 sensors on ground near the launch pad successfully detected the N-type signal, while it seems that impulsive acoustic/infrasonic waves generated by the fireworks could not be detected by the onboard sensor due to its rather low overpressure values as well as the high attenuation in upper atmosphere. For comparing to the sound propagation model in middle and upper atmosphere, we calculated propagation/attenuation condition with using a raytracing code. The ray-tracing model was previously developed and confirmed with the ground distributed infrasound sensors in Kochi area when a heavy volcanic eruption of Sinmoedake volcano in Kirishima Cluster was observed in 2018 (Saito et al., 2021).
Reference: Hiroaki Saito, Tetsuo Yamamoto, Kensuke Nakajima, Kiyoshi Kuramoto, Masa-yuki Yamamoto, Identification of the infrasound signals emitted by explosive eruption of Mt. Shinmoedake by three-dimensional ray tracing, J. Acoustic. Soc. Amer., 149, 591.
Once launched, the onboard sensor caught heavy acoustic noise disturbances generated by rocket motor during about 120 seconds after the launch, when the rocket reached about 40 km altitude, then after its engine cutoff, calm environment comes up. However, the sensor caught another type of wave like disturbance with larger period as the rocket began to rotate after becoming into no axis-control situation probably due to be affected by dynamic pressure on rocket flight and attitude, indicating rapid attenuation with decreasing background atmospheric density in stratosphere to lower thermosphere.
During the 7-minute suborbital flight of MOMO7 with its apex of 99 km, the sensor also caught a very clear N-type signal at about 98 km in the beginning of its downleg. It occured just at the timing of changing the flight vector velocity exceeded Mach 1 again, after experienced low subsonic moving condition only near the apex. Therefore, we can calculate temperature condition at the exact altitude using the obtained sound speed.
When the rocket reached maximum descending velocity at about 30 km, it generated Mach cone and effectively induced shock wave, then it propagated to the ground. We deployed 9 infrasound sensors on ground at Taiki Town, as well, so as to detect this expected impulsive infrasound signal along with the previous experimental results of MOMO3 launched on May 4, 2019. The 9 sensors on ground near the launch pad successfully detected the N-type signal, while it seems that impulsive acoustic/infrasonic waves generated by the fireworks could not be detected by the onboard sensor due to its rather low overpressure values as well as the high attenuation in upper atmosphere. For comparing to the sound propagation model in middle and upper atmosphere, we calculated propagation/attenuation condition with using a raytracing code. The ray-tracing model was previously developed and confirmed with the ground distributed infrasound sensors in Kochi area when a heavy volcanic eruption of Sinmoedake volcano in Kirishima Cluster was observed in 2018 (Saito et al., 2021).
Reference: Hiroaki Saito, Tetsuo Yamamoto, Kensuke Nakajima, Kiyoshi Kuramoto, Masa-yuki Yamamoto, Identification of the infrasound signals emitted by explosive eruption of Mt. Shinmoedake by three-dimensional ray tracing, J. Acoustic. Soc. Amer., 149, 591.