Brightness of HAYABUSA Spacecraft Reentry: Artificial Fireball

During reentry of the HAYABUSA spacecraft, the main body became a bright fireball of full-moon class. While the images were being taken by a team of ground-based observations, it was too bright to saturate the detectors in most of our instruments. In order to estimate the brightness quantitatively, we utilized ghost images of the main body together with the spectral data. We managed to estimate the time variation of the brightness, which had several peaks of flare ups possibly due to a rapid increase of the total cross section of the fragments. The maximum brightness obtained was $-$ 13.1 $\ \pm\ $ 0.1, the apparent magnitude at 13 $^{\rm h}$ 52 $^{\rm m}$ 19 $.\!\!\!^{\rm s}$ 8 UT, which corresponds to a height of 57.2 km above sea level. The corresponding absolute magnitude is $-$ 13.7 $\ \pm\ $ 0.1.