Makoto YOSHIKAWA

<p>More than 200 years have passed since the first discovery of an asteroid, Ceres, in 1801, and at present the number of discovered asteroids has exceeded 700,000. Spacecraft have approached about 10 asteroids, and we know various features of asteroids, which were not seen from ground based observations. Japanese spacecraft Hayabusa succeeded in sample return form an asteroid, and the sample analysis is on going. Thus, our knowledge about asteroids is increasing rapidly now. In this paper we summarize about the current situation from the point of asteroid explorations.</p>

In this paper, we propose methods to estimate positions of `HAYABUSA' during the period of the first touchdown on Itokawa in order to visualize the trajectories of `HAYABUSA'. In this period, there are no reliable ephemeris data of `HAYABUSA'. We used a variety of telemetry data and a shape model of Itokawa to estimate the trajectories. The period is divided into several sub-periods according to the availability of the data. In each sub-period, we propose suitable methods to estimate the positions. The methods are based on the policy that the trajectory should be smooth and continuous in each sub-period.