Abstract.Two atmospheric trajectories have been determined by simultaneous observations with image intensifier-fitted TV cameras and conventional photographic cameras for two bright Leonid meteors (fireballs) in 1995 and 1996. Beginning heights recorded by the photographic method are lower than about 130 km, but those observed by the TV systems are closer to 160 km. The primary reason for this difference is the sensitivity of the observing systems. However, the difference in the sensitive wavelengths (up to 900 mn for the TV systems) could be another factor contributing to the large difference between the two methods. This suggests that the beginning heights of high speed bright meteors such as Leonid meteors are much higher than previously thought.
Acoustic/infrasonic/seismic waves were observed during the re-entry of the Japanese asteroid explorer "HAYABUSA" at 6 ground sites in Woomera, Australia, on 2010 June 13. Overpressure values of infrasound waves were detected at 3 ground sites in a range from 1.3 Pa, 1.0 Pa, and 0.7 Pa with each distance of 36.9 km, 54.9 km, and 67.8 km, respectively, apart from the SRC trajectory. Seismic waveforms through air-to-ground coupling processes were also detected at 6 sites, showing a one-to-one correspondence to infrasound waves at all simultaneous observation sites. Audible sound up to 1 kHz was recorded at one site with a distance of 67.8 km. The mother spacecraft was fragmented from 75 km down to 38 km with a few explosive enhancements of emissions. A persistent train of HAYABUSA re-entry was confirmed at an altitude range of between 92 km down to 82 km for about 3 minutes. Light curves of 136 fragmented parts of the spacecraft were analyzed in detail based on video observations taken at multiple ground sites, being classified into three types of fragmentations, i.e., melting, explosive, and re-fragmented types. In a comparison between infrasonic waves and video-image analyses, regarding the generation of sonicboom type shock waves by hypersonically moving artificial meteors, both the sample return capsule and fragmented parts of the mother spacecraft, at an altitude of 40 ˙1 km were confirmed with a one-to-one correspondence with each other.
HAYABUSA is the first spacecraft ever to land on and lift off from any celestial body other than the moon. The mission, which returned asteroid samples to the Earth while overcoming various technical hurdles, ended on June 13, 2010, with the planned atmospheric re-entry. In order to safely deliver the sample return capsule, the HAYABUSA spacecraft ended its 7-year journey in a brilliant "artificial fireball" over the Australian desert. Spectroscopic observation was carried out in the nearultraviolet and visible wavelengths between 3000 and 7500Å at 3 -20Å resolution. Approximately 100 atomic lines such as Fe I, Mg I, Na I, Al I, Cr I, Mn I, Ni I, Ti I, Li I, Zn I, O I, and N I were identified from the spacecraft. Exotic atoms such as Cu I, Mo I, Xe I and Hg I were also detected. A strong Li I line (6708Å) at a height of ∼55 km originated from the onboard Li-Ion batteries. The FeO molecule bands at a height of ∼63 km were probably formed in the wake of the spacecraft. The effective excitation temperature as determined from the atomic lines varied from 4500 K to 6000 K. The observed number density of Fe I was about 10 times more abundant than Mg I after the spacecraft explosion. N + 2 (1 − ) bands from a shock layer and CN violet bands from the sample return capsule's ablating heat shield were dominant molecular bands in the near-ultraviolet region of 3000 -4000Å. OH(A-X) band was likely to exist around 3092Å. A strong shock layer from the HAYABUSA spacecraft was rapidly formed at heights between 93 km and 83 km, which was confirmed by detection of N + 2 (1 − ) bands with a vibration temperature of ∼13000 K. Gray-body temperature of the capsule at a height of ∼42 km was estimated to be ∼2437 K which is matched to a theoretical prediction. The final message of the HAYABUSA spacecraft and its sample return capsule are discussed through our spectroscopy.
On 2010 June 13, the HAYABUSA asteroid explorer returned to Earth and underwent a super-orbital atmospheric reentry. In order to recover the sample return capsule and to take ground-based measurements, the Japan Aerospace Exploration Agency organized a ground-observation team and performed optical tracking of the capsule, spectroscopy of the fireball, and measurements of infrasounds and shock waves generated by the fireball. In this article, an overview of the ground-based observation is presented, and an outline of the preliminary results derived from observations is reported.
The asteroid explorer HAYABUSA reentered into the Earth's atmosphere on 2010 June 13. We made simultaneous TV (television) observations at seven ground sites in order to calculate the trajectories of HAYABUSA and its sample return capsule (SRC), which both reentered into the atmosphere. Our TV observations showed that, after HAYABUSA reentered the atmosphere, the beginning time of its light emission on video was 13:51:57.4 UT at a height of 101.0 ˙0.2 km. The end time was 13:52:42.0 UT at a height of 38.6 ˙0.2 km. The initial velocity at the beginning was 12.1 ˙0.3 km s 1 , and the entry angle was 9 ı . After identifying SRC as separated light emission independent of the mother spacecraft, we analyzed the trajectory of SRC from a height of 52.9 km to 35.7 km based on video images. The actual trajectory of the capsule, determined from the TV observations, was almost the same as the predicted trajectory in terms of the position, velocity, and time. We then calculated the fall spots of the SRC heat shields from the multisite TV observations.
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