Hayabusa - Final autonomous descent and landing based on target marker tracking

In November of 2005, Hayabusa performed descent flights to the Itokawa surface five times. The Itokawa surface is full of boulders against expectation and there are few flat areas where the spacecraft can touch down safely. With the reaction wheels lost prior to the events, it was very difficult to control translation motion accurately, since the guidance accuracy of several millimeters per second was requested. The guidance and navigation before launch assumed the autonomous guidance by identifying the illumination center aboard. However, it was not successful due to the highly irregular shape of the asteroid. On the other hand, the scenario based on the terrain recognition in quasi real time well worked. It was anticipated not useful before launch, since such process was conceived to take a lot of time and not effectively useful in real time operation. The Hayabusa project team devised and built the special tool on the ground and had tuned it before the successful three touch downs and one long landing on the surface.