The ’Target marker separation operation’ scheduled for September 5 has been postponed due to the spacecraft entering the Safe-Hold [*] state. The condition of the spacecraft is normal.
Background to the current situation:
Hayabusa2 is equipped with four reaction wheels that are used to control the posture of the spacecraft, and posture control is usually performed using three of these reaction wheels. On August 29, the back-up reaction wheel that has not been used since October last year was tested, and an abnormal value (an increased torque) as detected. The spacecraft therefore autonomously moved into the Safe-Hold state. Details of the cause of the abnormal torque value are currently under investigation. On August 30, restoration steps were taken and the spacecraft returned to normal. However, as the spacecraft moved away from the home position due to entering Safe-Hold, we are currently having to return to the home position. We will return to the home position this weekend.
The attitude of the spacecraft is controlled by three reaction wheels as before. Entering the Safe-Hold state is one of the functions employed to keep the spacecraft safe, which means that procedures have worked normally.
We will report again about the target marker separation when a new schedule has been decided.
* Safe-Hold occurs when an abnormality is detected in a spacecraft (such as an artificial satellite or Solar System astronomical probe). The solar cell panel is directed towards the Sun and the level of power generation is held constant while the spacecraft spins (rotates). This mode stabilises the posture and only the minimum necessary devices are active, such as those used for communication. The state gives the safety of the spacecraft the highest priority. In the case of Hayabusa2 which is currently in the vicinity of the asteroid, moving to Safe-Hold also accelerates the spacecraft away from the asteroid to avoid a potential collision.