Asteroid sample return mission MUSES-C (Hayabusa)
A candidate area for the two touch downs has been defined on November 1st 2005. The first candidate for the touch down has been identified in the area named MUSES-Sea (point A in the left figure below). The second point candidate for the touch down has been identified in the area named “Woomera Desert” (point B in the right figure below)
（These pictures are from the JAXA press release）
On November 9th Hayabusa approached within 70 meters of the asteroid, and it took closer pictures of the two prospective touch down areas. In the below pictures is shown on the left a closer view of “MUSES-Sea” area, and on the right a closer view of “Woomera Desert” area.
（These pictures are from JAXA press release, in Japanese）
From these pictures it is possible to see clearly rocks formation (boulders) of several meters in size (the red line on the right corner in the above left picture represents a distance of 10 meters). These rocks can be a major obstacles during the touch down and successive ascent phase, thus here we show the results from numerical simulations for two cases where extreme conditions have been considered.
During the development stage, experimental verifications have been conducted on the sampler horn supposing that the surface around the contact area has a 30 degrees maximum inclination. The effects of a larger inclination have been analyzed through numerical simulations, using different descending velocities and different surface coefficients of friction.
In both of the previous animations the inclination of the surface in the contact area exceeds 50 degrees, but the flexible horn worked correctly to effectively compensate for such surface inclination.
Another critical situation is represented by the possibility that some parts of Hayabusa other than the horn come in contact with the surface during the descending maneuver. This can happen if there is a significant difference in height between the surface in the contact area and the surface around it. In particular, it can be critical if a part of the left and right solar paddles, each one measuring approximately 4.2m x 1.4m, is damaged, since it will be used to generate the electric power needed by the ion engine used to take Hayabusa back to the earth.
To avoid this problem, Hayabusa is equipped with a Fan Beam Sensor (FBS). The sensor has the scope to scan the area under the two solar paddles to detect any obstacle. If an obstacle is detected, the four thrusters under the probe main body are fired, and the descending operation is aborted.
The below animation shows an example of aborted touch-down due to the FBS obstacle detection. As possible to see, such a situation can arise for example if Hayabusa ends up descending in a gorge-like surface. Even if the touch down spot is relatively smooth like in “MUSESC-Sea” area, still there is the possibility of damage caused by an high isolated rock, and the FBS will be useful.
(clicking on the picture will start the movie).
Available movies from Part 3 (November 2005)
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