From late November 2018 until the end of December, the solar conjunction operation is underway for Hayabusa2. Solar conjunction refers to the situation where the direction to the spacecraft almost overlaps with that to the Sun when viewed from the Earth. This is the same “conjunction” as in astronomy, whereby planets and stars appear to line up on the sky. During this time, communication with Hayabusa2 is disrupted due to radio waves emitted from the Sun and from its surrounding plasma. We therefore do not perform operations such as descending towards Ryugu during this period.
In order not to risk a collision with Ryugu while communication is disrupted, we place the spacecraft slightly further away from the asteroid in a “conjunction transition orbit”. Figure 1 shows an animation of the trajectory of the spacecraft in the Hill coordinate system. In this coordinate system, the Sun is always to the left and outside the figure. The black dot on the right is Ryugu. From late November to the end of December, the spacecraft will travel along the blue line. The red dots are points where a trajectory control manoeuvre will be performed.