  Hayabusa asteroid explorer successfully released the sample capsule to
Australia on June 13, 2010. Since the Earth reentry phase of sample return was
critical, many backup plans for predicting the landing location were prepared.
This paper investigates the reentry dispersion using ground based optical
observation as a backup observation for radiometric observation. Several
scenarios are calculated and compared for the reentry phase of the Hayabusa to
evaluate the navigation accuracy of the ground-based observation. The optical
observation doesn't require any active reaction from a spacecraft, thus these
results show that optical observations could be a steady backup strategy even
if a spacecraft had some trouble. We also evaluate the landing dispersion of
the Hayabusa only with the optical observation.
