During the PPTD-TM1 operation between May 14〜16, the spacecraft descended to an altitude of about 50m before autonomously stopping the descent and beginning to rise. This abort by the spacecraft was due to an incorrect distance measurement by the laser altimeter (LIDAR) and meant that the target marker could not be dropped. Despite this, it was possible to image around the artificial crater at low altitude. The name of this next operation is ‘PPTD-TM1A’, denoting it as the second operation with almost the same plan as PPTD-TM1. PPTD stands for ‘Pinpoint Touchdown’ while ‘TM1’ refers to the separation of the first target marker for this touchdown.
In the previous PPTD-TM1 operation, the plan was to descend towards the region SO1 and drop the target marker. In PPTD-TM1A, the target marker will be dropped in area CO1, near area SO1. The location is shown in Figure 1.
Figure 1 is the same image as shown in previous articles, displaying the surface of the asteroid before the generation of the artificial crater. Figure 2 shows the image taken as the spacecraft rose during the PPTD-TM1 operation. The addition of Figure 2 allowed the area around the artificial crater to be understood more clearly, and the area CO1 to be investigated in more detail. The examination revealed the possibility of a touchdown in area CO1. It was therefore decided to descend towards area CO1 and this time, drop the target marker in this region.
The PPTD-TM1A operation will be performed from May 28〜30, 2019. The plan for the operation is almost the same as for PPTD-TM1. Preparation for the descent will take place on May 28 and the spacecraft will start the descent on May 29 at 12:06 JST (on-board time) at a speed of 0.4 m/s. On the same day at 22:26 JST, the spacecraft speed will be reduced to 0.1 m/s. The descent will continue to reach an altitude of about 35m on May 30 at 11:00 JST, and then to 10m at 11:23 JST, the lowest point. The target marker will be separated just before the lowest altitude is reached. The spacecraft will then soon begin to rise and return to the home position on May 31. The operation schedule is shown in Figure 3. Please be aware that the actual operation times may differ as the times listed here are the planned values.
Figure 4 shows the sequence at low altitude. This is almost the same as for the PPTD-TM1 operation.