TopicsThe Descent Observation (DO-S01)

Now that our first touchdown, TD1-L08E1, has been completed successfully, we are considering a second touchdown at candidate site, S01. In order to examine the area of the new S01 touchdown candidate site in detail, we will perform a Descent Observation and bring Hayabusa2 closer to the asteroid surface. This will be the “DO-S01” operation (DO = Descent Observation) and the altitude of the spacecraft will drop to about 23m above the S01 area. The operation will take place from March 6 to 8, 2019. On March 6, preparation work for the descent will be begin and the descent will start on March 7, reaching he lowest planned altitude on March 8.

The S01 region is shown in Figure 1. S01 is near the equator of Ryugu and about 800m to the east of the first touchdown site (nicknamed “Tamatebako”). When candidate sites for the first touchdown were first selected (in August 2018), L08 (the region around our touchdown site) seemed the most promising and the S01 site was not chosen. This was because we were searching for areas over 100m across that were as flat as possible. Since such a wide region was not found on Ryugu’s surface, we searched out smaller flat regions. Among these, S01 seems to be the best site. However, we do not yet know is S01 is suitable for touchdown until we take a closer look. For this, we will descend in the DO-S01 operation.

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    Figure 1: Location of the region S01. This is 800m east of the first touchdown point. (Image credit: JAXA)

The DO-S01 operation schedule is shown in Figure 2. The spacecraft will begin descending on March 7 at 13:27 (JST, onboard time: times below are stated similarly) at a speed of 0.4m/s. The speed will then be reduced to 0.1 m/s around 23:47 on the same day. Continuing descent at this rate, we will reach our lowest altitude at around 12:22 on March 8 and then immediately begin to rise. The altitude of this lowest point will be about 23m. Please note that the times stated here are the planned values but the actual operation times may differ.

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    Figure 2: Schematic diagram of the DO-S01 operation. Note that the times given here may differ from the actual operation. (Image credit: JAXA).

Hayabusa2 project