TopicsThe Pinpoint Touchdown – Target
Marker 1 (PPTD-TM1) operation

While the decision to perform a second touchdown has not been finalized, preparation is underway. The first operation is to separate a target marker. This operation is denoted PPTD-TM1: Pinpoint Touchdown – Target Marker 1. The original mission plan was to perform a pinpoint touchdown when touching down near the crater generated by the Small Carry-on Impactor (SCI), which gives this operation its name. In fact, we have already used the pinpoint touchdown method during the first touchdown (February 22, 2019) but we retained this operation name.

This operation will attempt to deploy the target marker in the S01 area on the assumption that the S01 area is the region for touchdown. S01 has previously been observed during descent observation operations in March and April this year. Its location is shown in Figure 1.

Figure 2 shows an enlarged image near the S01 area. The S01 area is near where the SCI impacted the surface of Ryugu, which is marked in Figure 2 as area C01. In the same figure, L14 is a newly selected area located near the SCI collision point as another candidate area for the second touchdown. All the touchdown candidate points are marked with yellow circles of size about 6 to 12m in diameter. During this operation, we choice S01 to drop the target marker.

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    Figure 2: The SCI impact area and surrounding region (captured before the impact of the SCI).
    (Figure credit: JAXA, University of Tokyo, Kochi University, Rikkyo University, Nagota University, Chiba Institute of Technology, Meiji University, University of Aizu, AIST.)

The PPTD-TM1 operation will be performed from May 14 to 16, 2019. Descent preparation will take place on May 14. From 12:31 May 15 JST (on-board time), the spacecraft will begin its descent at 0.4 m/s. The speed will be reduced to 0.1 m/s at 22:51 on the same day and the descent will continue down to an altitude of approximately 35m at 11:25 on May 16 and an altitude of approximately 10m at 11:42, the lowest point. The target marker will be separated just before reaching the lowest altitude. The spacecraft will begin to rise shortly afterwards and return to the home position on May 17. The operation schedule is shown in Figure 3. Please be aware that the actual operation time may differ from the planned values shown here.

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    Figure 3: Schematic of the PPTD-TM1 operation (figure credit: JAXA).
    Note: times listed may differ from actual operation

Figure 4 shows the sequence at low altitude. At this time, the distance measurement to the surface of Ryugu is performed using the Laser Range Finder (LRF), but the LRF data is not used to control the spacecraft. After the first touchdown, the LRF performance may have changed and this will be first checked during the operation. Instead, the distance measurement will only be performed with the laser altimeter (LIDAR). The spacecraft will make a slight zig-zag while rising in order to obtain three-dimensional information about the surface through parallax.

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